titanium welding procedures

* NASA TECHNICAL N ,SA TM X- 53432

MEMORANDUM October 1965

I , -s

WELDING PROCEDURES FOR TITANIUM AND TITANIUM ALLOYS

By J. J. Vagi, R. E. Monroe, R. M. Evans, and D. C. Martin

Prepared Under the Supervision of theResearch Branch, Redstone Scientific Information CenterDirectorate of Research and DevelopmentU. S. Army Missile CommandRedstone Arsenal, Alaboma

NASACLEARINGHOUSE

FOR FEDERAL SC',r!-TIFIC ANDGeorge C. Marshall TEC,,NICAL 1,,TO•I ,oNH a'4 o -p J M i ero -fich -1 -Space Flight Center, .oo 1$. A5+2

Huntsville, Alabama • 1II7 •i . 7

TECHNICAL MEMORANDUXMI X - 53432

WELDING PROCEDURES FOR TITANIUM ANDTITANIUM ALLOYS

By

J. J. Vagi, R. E. Monroe, R. M. Evans, and D. C. Martin-*

ABSTRACT

This report covers the state of the art of welding procedures fortitanium and its alloys.:'- Methods employed in the past and presentare described. Many of the conventional welding and brazing processesare used for joining titanium and its alloys. Information on the use ofthese processes, when available, was condensed or extracted and in-cluded in this report. Necessary additional processing such as pre-weld cleaning, joint preparation, postweld cleaning, and postweldoperations are also included since they form an integral part of thewelding processes without which successful welding cannot be accom-plished. Joining processes that have been tsed only experimentallyalso are described briefly.

The need for proper preweld cleaning operations and propershielding to prevent contamination of titanium welds is emphasizedthroughout.

This report does not exhaustively cover the selection of titaniumalloys for specific applications or mechanical properties obtained fromjoints. These areas were not included in the scope of this program.The reader is reminded of the importance of these areas in obtainingdesired service performance in structures fabricated from titanium.

":Principal Investigators, Battelle Memorial Institute,

Contract No. DA-01-0ZI-AMC-l1651(Z)::'Adhesive bonding and mechanical joining are covered in other

reports.

NASA - GEORGE C. MARSHALL SPACE FLIGHT CENTER

- .-

PAGESARE

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ORIGINALDOCUMENT

**TACA elD "q' k ).AADCLTAT T C10AfV V'T Tr'-Trr /fI'•TT

TECHNICAL MEMORANDUM X - 53432


By

J. J. Vagi, R. E. Monroe, R. M. Evans, and D. C. Martia

Prepared for

Manufacturing Engineering Laboratory

In Cooperation with

r Technology Utilization Office

Under the Supervision of

Redstone Scientific Information CenterU. S. Army Missile CommandRedstone Arsenal, Alabama

MSFC Order No. H-76715Report No. RSIC-470

Subcontmacted to

Battelle Memorial Institute505 King AvenueColumbus, Ohio

Contract No. DA-01 -021 -AMC-1 1651(Z)

j

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PREFACE

This report is one of a series of state-of-the-art reports beingprepared by Battelle Memorial Institute under C"ontract No. DA-01 -

2Z1-AMC-l1651(Z) in the general field of materials fabrication.

This report describes practices for welding titanium and titaniumalloys. It is intended to provide information useful to designers andmanufacturing engineers. The information in this report has been se-lected primarily as a guide for selecting conditions, equipment, andfabricating techniques for welding titanium. Common problems en-countered in welding and brazing titanium and its alloys are identified,and precautions for avoiding the problems are described.

The report summarizes information obtained from equipmentmanufacturers, titanium producers, technical publications, reports onGovernment contracts, and from interviews with engineers employedby major titanium fabricators. A total of 133 references, most ofthem covering the period from 195.7 to the present, are cited. In addi-tion, much detailed data covered by reports and memoranda issued bythe Defense Metals Information Center are used. A recent AircraftDesigners Handbook on Titanium and Titanium Alloys prepared for theFederal Aviation Agency by Battelle also provided much backgroundinformation. The assistance afforded by these previous programs hashelped in the preparation of this report.

In accumulating the information necessary to prepare this report,the following sources within Battelle were searched for publicationsfrom 1957 to the present: Defense Metals Information Center, MainLibrary, Slavic Library. Information was obtained also from informa-tion centers outside Battelle, viz., the Redstone Scientific InformationCenter and the Defense Documentation Center. Descriptors employedfor recovering information from these information centers are given inAppendix A.

Personal contacts also were made by visit or telephone with thefollowing individuals and organizations:

Durwood G. Anderson Howard CaryAirite Division Hobart Technical CenterElectrada Corporation Troy, OhioLos Angeles, California

ii

.. Mitchel

John Rudy Titanium Metal0 Corporation ofThe Martin Company AmericaDenver, Colorado New York, New York

Melvin C. Clapp F. L. MurphyColumbus Division Pratt & Whitney Aircraft DivisionNorth American Aviation, Inc. United Aircraft CorporationColumbus, Ohio East Hartford, Connecticut

R. S. Emlong V. H. PaganoE. R. Funk Materials LaboratoryAstro Metallurgical Corporation U. S. Army Tank-AutomotiveWooster, Ohio Center

Warren, MichiganJ. L. FlemingAluminum Company of America J. Gordon ParksPittsburgh, Pennsylvania Methods Research and Develop-

ment BranchG. Garfield Manufacturing EngineeringAerojet-General Corporation DivisionDowney, California George C. Marshall Space Flight

CenterGrumma~i Aircraft Engineering National Aeronautics and Space

Corporation AdministrationBethpage, Long Island Huntsville, AlabamaNew York

Reactive Metals, Inc.A. M. Krainess Niles, OhioSpace and Information Systems

Division William S. RudinNorth American Aviation, Inc. Sciaky Brothers, Inc.Downey, California Chicago, Illinois

K. C. Linepensel A. SchoeniLinde Division Ling-Temco Vought, Inc.Union Carbide Corporation Dallas, TexasNewark, New Jersey

Howard SiegelJ. Manfre McDonnell Aircraft CorporationCrucible Steel Company of St. Louis, Missouri

Ame ric aPittsburgh, Pennsylvania

iii ••

Sumner Smith Fred W. VogelSMenasco Manufacturing Company Modern Machine Shop

Burbank, California Watertown ArsenalWatertown, Massachusetts

W. 0. SunafrankGeneral Dynamics/Fort Worth

Fort Worth, Texas

The authors wish to thank each of these individuals and their or-ganizations for contributions. They also wish to thank Vernon W.Ellzey and Albert G. Imgram, of Battelle, Project Technical Coordi-

nators, and Walter H. Veazie, Battelle Information Specialist, fortheir assistance during this program.

i

iv

TkBLE OF CONTENTS

Page

SUMMARY .................... ............... 1

INTRODUCTION ................... ... ......... 2

WELDING FUNDAMENTALS ........... ............ 3

Materials ............ . . .... ............... 3Component Materials ......... . .. ......... 3Process Materials ........ . .......... . 8

Process Selection ........... . . ........... 12Joint Design ............... ............. 13Cleaning ............... . . ............... 21

Grease and Oil ......... . ............ 22Scale Removal .......... .............. 24Handling and Storage ....... .......... 25Evaluating Cleanliness ........ . ......... 25

Shielding .................. ............. 26Tooling ................. . . ........ .... 40

Heat Input .............. . .............. .. 41Shrinkage - Distortion . ............. .. 42

Residual Stress ............. .............. 43Stress Distribution ............ ......... 44Stress Effects .......... . ............. 46Stress Relieving ........... . ........... 49

Specifications ............. . .............. 51Defects ................ ................ 52

Porosity .............. . .............. 54

REPAIRS ... ....... ...................... 55

WELDING PROCESSES .......... ............. 56

TIG Welding ........................ .... 57Equipment ............. ............... 57Materials ............. . .............. 57Welding Conditions ......... ............ 60Tack Welding ........... .............. 63Properties ............ . .............. 64Applications for TIG Welding Titanium Alloys . . . 64

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I NP

TABLE OF CONTENTS(Continued)

Page

MIG Welding ................ ....... . .. 84

Equipment ............... ........ . .. 84

Materials ................... . ..... . 92Tooling and Fixtures ............ . ..... 93Welding Conditions ......... . .... . .... 94

Properties .................. ...... .. 95Applications for MIG Welding Titanium Alloys . 101

Arc Spot Welding ........... ........... . .. 103

Equipment . ... . .. ....... ..... 104

Materials ........... . . .... ........ 104Welding Conditions ....... . . .... ...... 104

Electron-Beam Welding ........... ........ 104Ecuipment ................. ....... . .. 105

Materials ............... . ...... . . .. 105Welding Conditions ............. . ..... 105

Properties ............... . . ........ . 107Applications for Electron-Beam Welding

Titanium Alloys ............ ........ . 107

Plasma-Arc Welding ........... . .. .. ........ . 110Keyhole Action ........... ........... . .113

Equipment ............. . . ............ I113

Welding Conditions ......... . . ......... . 115Applications ............. . . ......... 116

Resistance Spot Welding . . .. . ................ 117

Equipment ............... .......... .. . 118Joint Design Considerations ...... . .. . .. 121

Welding Conditions ......... . . ..... . .. 122

Properties ............. . ........... .. 126Applications ............. . . ...... ... 133

Roll Spot Welding .............. ........... 135Seam Welding ............. .............. 139

Applications ........... . .. ........... .. 140

Flash Welding ............... . . ........ . 143

Equipment ............... ........... 144Joint Design and Joint Preparation ... . . . . . 144

Inert-Gas Shielding ......... . . ......... 144

Conditions ............. . . ...... .... . 144

vi

B.

TABLE OF CONTENTS(Continued)

Page

PropertieE ............... . . ..... . 147

High-Frequency Welding ......... . ...... .. 154

Brazing . ....................... .. 154Filler Metals .............. . . ..... . 154

Brazing Methods ......... . . ..... . .. 157

Properties ............. . . ...... . .. 157

Appiications ........... . ..... . ...... 160

Solid-State Weldcng ............. . . ...... 163Diffusion Welding ........... . ........ 164

Deformation Welding ........... . . . ... 169

DISSIMILAR METAL JOINTS..... . ............ 177

MIG Spot Welding Aluminum to Titanium . .......... 178

TIG Plug Welding ............ . . . . ...... 180

Resistance Spot Welding ... . . ..... ...... 181

Capacitor Discharge Welding ... ....... ...... 182

CONCLUSIONS AND RECCMMENDAT!ONS. . .......... 182

Welding Metallurgy ............. . ....... 183

Cleanliness ................ . . ......... 183

Filler Metals ................. . . .. ... 183Welding Conditions ............... ....... 184

Tack Welding ............... ........... 184

Contamination and Porosity ......... ...... 184

Cracking ................ . ............. . 185

Thick Titanium Plate ........... .. ...... . 185

Stress Relief ................... . ..... . 185

Repair Welding ........... . . ...... .... 185

APPENDIX A

DESCRIPTORS FOR LITERATURE ON FABRICATION OF

TITANIUM AND TITANIUM ALLO'S BY WELDING . . . 187

vii

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(Continued)

Page

APPENDIX B

DESIGNATIONS, PROPERTIES, AND TREATMENTS OFTITANIUM AND TITANIUM ALLOYS ..... ........ 193

REFERENCES............. . . . .. 203

viii

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LiST OF ILLUS'I RATIONS

Figure Title Page

I. Surface Area to Volume Ratio for Welding FillerWires ............. .............. . 9

2. Welding-Wire Defects . . . . ............ 9

3. Typical Joints in Titanium and Titanium Alloys. . . 14

4. Stiffened-Skin Component ....... ........ 15

5. Flow Sheet Showing Possible Relation of Weldingto Other Operations ........ ............ 15

6. Typical Fusion- Weld-Joint Designs ...... ....... 17

7. Joint Designs for Special Applications of MIGWelding of Titanium Alloys . ... ...... .. 20

8. Consumable-Land Joint Design ..... ....... o. 21

9. Back-Up-Ring Joint Design ... ....... o. 21

10. Flow Chart of Cleaning Procedure for TitaniumAlloys ............. ................ 22

11. Tank-Type Controlled-Atmosphere Welding Chamberfor Manual or Machine, TIG or MIG Welding TitaniumAlloys and Other Reactive Metals ...... ....... 27

12. Controlled-Atmosphere Chambers for TIG WeldingSmall Subassemblies ....... ........... .28

13. Adaptation of a Small Size Chamber for TIG Weldingan Oversize Part .......... ............ 29

14, Flexible -Plastic Controlled-Atmosphere WeldingChamber ........ ............ ... 29

15. Inert-Gas-Shielding Arrangements for ConventionalMaterials Compared with Titanium Alloys . . . 31

16. Torch-Trailing-Shield Arrangements ...... ..... 32

ix

iL- T~T T' T1 T TTQ4 A' C ~

(Continued)

Figure Title Page

17. Detachable Torch-Trailing-Shield Assembly. . . . 33

18. Modified Manual TIG Welding Torch-ShieldingNozzle ............. .............. .. 34

19. TIG-MIG Torch-Trailing -Shield Assembly withLeading Shield Baffle for Welding Titanium Alloys. . 34

20. External Shielding Baffles Used to Protect ButtWelds in Titanium Tubing and Pipe ... ...... 35

21. Shielding Baffles for an Outside-Corner Weld . . 36

22. Backing Shield .............. ........ 36

23. Shielding Devices for Protecting Root Sides of ButtWelds in Tubing, Pipe, and Cylinders ....... 37

24. Shielding Arrangements for Protecting the Root Sidesof Flange-to-Tubing Welds .......... ... .... 38

25. Cross Section of Original Coil Designed for WeldedSpacers and Supports ....... ........... 39

26. Tack-Welded Mechanical Fastener for the CoilSpacers Shown in Figure 25 ..... ......... 39

27. Coils in Various Stages of Completion ShowingMechanical Supports and Tack-Welded Nuts . . . . 39

28. Types of Weld-Joint Distortion ..... ....... 42

29. Distribution of Residual Stresses in a Butt Weld 45

30. Distribution of Residual Stresses Around Spot Weld 47

31. Fusion-Weld Defects .... ...... ........ 53

32. A Combination Torch-Trailing-Shield Arrangement 58

x

I *a17' 7

LIST OF ILLUSTRATIONS(Continued)

Figure Title Page

33. The Use of Starting and Runoff Tabs .. ...... 63

34. Calcium Hypochlorite Plant Heat-Exchanger CoilsMade From Commercially Pure Titanium . . . . 67

35. Out-of-Position Butt Weld Being Made in the OpenAtmosphere Using Torch Shielding Combined WithSupplementary Shielding Equipment ... ....... 67

36. Heat-Exchanger Subassemblies Welded in aControlled Atmosphere Chamber .... ...... 68

37. Detail of the Mechanical Support Showing That theNuts Are Tack Welded ......... .......... 68

38. Photograph Taken Through a Borescope of aTypical Weld Root ......... .......... .. 70

39. Inspection of the Root Pass of the Butt Weld Shownin Figure 38 ............... ......... 70

40. Segmented Welding Fixture With Solid Copper Back-UpShoes Mounted on Positioner ..... .... .... 71

41. Mercury Space Capsule ........ ......... 73

42. Fixture Holds First Two Panels of Outer ConicalSkin for TIG Welding .......... .......... 73

43. Rotating Fixture Moves the Work Past Stationary TIGTorch at 7 ipm to Join Two Sections of SphericalBulkhead. Segmented Fingers Hold Edges of Jointin Alignment ............. ............ 74

44. Vigilante Wing Leading Edge ..... ........ 75

45. Typical Cross Section of Welded Titanium LeadingEdge ............... ................ 75

46. Wing Leading-Edge Joint Designs .. .. .... ..... 76

xi

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Figure Title Page

47. Arc-Seam Tee Weld-Joint Design ... .... .. 76

48. General View of the Sine-Wave Welding Machine 78

49. Welding of Thin Corrugated Titanium Sheet . . 78

50. Sine-Wave Welding Station Area ... ...... .. 79

51. Completed Rib for the American RS-70 Aircraft 79

52. MIG Welding-Equipment Arrangement for Welding inthe Open Atmosphere ....... ......... .. 86

53. MIG Welding Arrangement in a Controlled-Atmosphere Welding Chamber ... ...... .. 86

54. Typical Wire-Drive System for MIG Welding . . 87

55. Wire-Straightening Rolls ....... ....... .. 87

56. Entry of Wire into Wire-Feed Cable .. .... .. 88

57. Wire Entry into Drive Rolls ... ........ .. 88

58. Wire Distortion From Excessive Drive-RollPressure ........... .............. .. 89

59. Cleanliness Factor as Applied to the Wire-FeedCable ................ ............ .. 89

ou6 MIG Welding Setup Shows Sharp Bends in Wire-FeedCable ................ ............. .. 91

61. Hose-and-Cable Support Arrangement Employed toEliminate Wire Whip During MIG Welding . . . . 91

62. Illustration of Tank-Cupola Components FabricatedUsing the MIG Welding Process ... ....... .. 102

xli


Figure Title Page

63. Typical Joint Dimensions for Welds in 2-Inch-Thick Ti-13V-IlCr-3A1 Titanium Alloy Plate . . . 103

64. Schematic Diagram of an Electron-Beam WeldingMachine ............ ................ 106

65. Electron-Beam Welded Titanitumn Pressure -VesselSphere ..... ............... .. 110

66. Examples of Electron-Beam Welding for Salvage ofCostly, Precision Parts ..... .......... III

67. Schematic Representation of Plasma-Arc WeldingOperation ............. ............... .113

68. Mechanized Plasma-Arc Welding Torch ..... 114

69. Tungsten and Copper Electrodes Used for Str-aightand Reverse Polarity Operation, Respectively . . . 114

70. Conventional Resistance-Spot- Welding Equipment . . 119

71. Spot-Weld Strength Versus Welding Current forSpherical-Faced and Truncated-Cone Electrodes . . 120

72. The Effect of Minimum Contacting Overlap on theType of Resulting Failure for Tension-ShearSpecimens ............. ............... 121

73. The Effect of Spot Spacing on Weld Geometry . . . 122

74. Inference of Spot-Welding Current on Strength andTension/Shear Ratio for 0.035-f 0. 062-, and0. 070-Inch-Thick Ti-6AI-4V Alloy ......... 125

75. Tension-Shear Spot-Welded Specimen Before andAfter Strength Testing ....... ........... 131

76. Cross-Tension Spot-Welded Specimen Before andAfter Strength Testing ........... . 131

xiii

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(Continued)

Figure Title Page

77. Jig for Cross-Tension Test ..... ......... 131

78. Spot Welding Attaches Stiffeners to Sidewall SkinAssembly of the Mercury Capsule ... ...... 133

79. Typical Resistance -Welding Applications in VariousSpacecraft Sections ........... .......... 134

80. Typical Rib Subassembly With Hour-Glass-ShapedDoubler Spot Welded to Rib ..... ........ 136

81. Typical Rib Subassembly With Short-Angle StiffenersSpot Welded to the Rib ........... ....... 136

82. Typical Rib Subassembly With Long-Angle StiffenersWelded to the Rib .......... .......... 136

83. Panel Ready for Resistance Spot Welding ofStiffeners ......... .......... ...... 137

84. A Spot-Welding Operation on the Upper SkinSubassembly ....... . ............. .... 138

85. Project Mercury Spacecraft, Built of Titanium,Required 20,500 Inches of Spot Weld Per Capsule . . 139

86. Schematic of Seam Welds Used in Mercury Capsule . 142

87. Inner and Outer Mercury Capsule Skins Are SeamWelded ......... ............ . . . . 142

88. Three-Phase, 200 Kva, Seam-Welding MachineJoining Titanium Panels 0.002 Inch Thick to BaseSheet 0.020 Inch Thick .... ......... .... 143

89. Transformer Capacity Versus Weld Area . . 145

90. Maximum Machine Upset-Pressure RequirementsVersus Weld Area ..... .......... .... 145

xiv


Figure Title Page

91. Total Metal Allowance Versus Stock Thickness . . . 146

92. Production Yoke With Stabilizer Panels Attached . . 150

93. Flash-Welded Foil Stabilizer Yoke Assembly . . . 150

94. A Yoke Subassembly in Position to Be Flash Welded 151

95. Welded Yoke Subassembly Prior to Removal ofFlash ................ ............... 152

96. Typical Examples of the Economy of Flash-WeldedRing Products .......... ............. .. 153

97. High-Frequency Welding Methods for ManufacturingTitanium Tubing ......... ............ .. 155

98. Double-Wall Retort System for Brazing TitaniumAlloys Sandwich Panels ...... .......... .. 161

99. Approximate Locations of Elevon Surface Panel,Nacelle Panel, and Elevon Traiiing Wedge . . . . 165

100. Exploded View of Roll-Welded Pack Prior to HotRolling ............ ............... .. 170

101. Typical Applications of Roll-Welded CorrugatedSandwich Construction ..... ........ .... 171

102. Apparatus for Pressure-Gas Welding . . . . . . 173

103. Close-Up View of the Pressure-Gas Welding Station . 174

104. Cross Section of Gas Metal-Arc Spot Weld Joining0. 025-Inch Aluminized Steel and 0. 064-Inch 3003Aluminum With 4043 Aluminum Alloy Filler Metal,No Pilot Hole ........... .............. 180

xv 4

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Table Title Page

I. Dimensions of Typical Joint Designs for TitaniumAlloys ................ ........ 18

II. Single-U-Groove Joint-Design Details ........ 19

ImI. Chemical Composition of Electrode Materialsfor TIG Welding ......... ............. 59

IV. Conditions for Manual TIG Welding Titanium andTitanium Alloys ......... ............. 61

V. Conditions for Machine TIG Welding Titanium andTitanium Alloys ............. ............ 62

VI. TIG Weld Property Data Sources .. ....... 65

VII. Variations of a Modified Double-Vee-J oint DesignUsed for Experimental TIG Weldments and for a2 x 30 x 30-Inch Final Plate Weldment on 2-Inch-Thick Commercially Pure Titanium Plate . . .. 81

VIII. Welding Conditions Used in Conjunction WithVariations in Weld Design for the Various Experi-mental TIG Weldments and the Final 2 x 30 x 30-Inch Plate TIG Weldment on 2-Inch-ThickCommercially Pure Titanium Plate Welded WithCommercially Pure Titanium Filler Wire . . . . 82

IX. Base Metal and Weld Metal Tensile and CompressionTest Results on Commercially Pure 2-Inch-ThickPlate TIG Weldments - Welded Ylith CommerciallyPure Titanium Filler Wire ..... ......... 83

X. MIG Welding Conditions for Various Titanium Alloys . 96

XI. Gas Metal-Arc Welding Conditions for Fabricationof Ti-4A1-4V Titanium Tank Cupola .. ...... 97

XII. Tensile Properties of MIG Weld Metals inTitanium Alloys ...... ....... .. .... 98

Xvi

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LIST OF TABLES(Continued)

Table Title Page

XIII. Transverse Tensile Properties of MIG Weldmentsin Titanium and Titanium Alloys. . . . . . . . 99

XIV. MIG Weld Property Data Sources .... ....... 100

XV. lectron-Beam Welding Conditions . . . . . . 108

XVI. Electron-Beam Weld Property Data Sources . . . 109

XVII. Plasma-Arc Welding Conditions for Square ButtJoints in Titanium ......... ........... .115

XVIII. Recommended Practices for Spot Welding StainlessSteels ........ ............ .. 124

XIX. Resistance Spot Welding Conditions for SeveralTitanium-Base Alloys ....... ........... 127

XX. Room Temperature Properties of Spot Welds inSeveral Titanium-Base Alloys ..... ...... 128

XXI. Spot-Weld Property Data Sources ......... .. 129

XXII. Seam-Welding Conditions and Room-TemperatureProperties of Resistance Seam-Welded Joints inTitanium .............. ............... 141

XXIII. Flash-Welding Conditions . . . . . . . . . . 147

XXIV. Room-Temperature Tensile Properties of Flash-Welded Joints............. . . . . . . . 148

XXV. Behd Ductility and Fatigue Strength of Flash-WeldedJoints ....................... . . 149

XXVI. Titanium Brazing and Soldering Patents From the"Titanium Abstracts" of the Industrial ChemicalIndustries Ltd. (ICI) ........ ............ 158

xvii

LIST OF TABLES(Continued)

Table Title Page

XXVII. Shear Strengths of Titanium Brazed Joint. ....... 159

XXVIII. Summary of Diffusion Welding Processes forTitanium Alloys ......... ............ .. 168

XXIX. Tensile, Notched Tensile, and Impact Properties ofPressure Welds in Ti-6A1-4V Tubing .. ...... 176

XXX. Welding Parameters and Typical Tensile ShearStrengths of Gas Metal-Arc Spot Welds in VariousMetal Combinations .............. ......... 179

XXXI. Strength of Joints Between Commercially PureTitanium and 0. 255-Inch-Thick Low-Carbon SteelUsing a Vanadium Intermediate .. ...... .... 181

B-1. Physical Properties of Titanium Alloys and Some

Commonly Welded Metals ......... ....... 213

S~xviiiAI

• • • m m II II I I II I I II ll I ! I ii ii i III I • III II III I I IXVI I II

TECHNICAL MEMORANDUM X-53432


SUMMARY

Titanium and titanium alloys can be welded by a variety ofmethods. Most welding processes used in the past for joining morecommon metals have been used to successfully join titanium. Manynew metals-joining processes also have been used with success in pro-duction and experimental applications. It i-s expected that the olderestablished joining processes will continue to be used successfully, andthat applications of the newer joining processes will gai.n wider use fortitanium as more experience and knowledge is developed.

Difficulties in welding titanium and titanium alloys originate fromseveral basic sources. The high reactivity of titanium with other ma-terials, poor cleaning of parts before joining, and inadequate protec-tion during joining can lrad to contamination, porosity, and embrittle-ment of the completed joints. There are many fabricators currentlyjoining titanium, however, by various processes. The successfuljoining of various titanium-alloy products has been accomplishedthrough the use of good welding practices and a knowledge o, the fac-tors that affect titanium-weld-joint quality.

Many of the difficulties experienced in joining titanium and titaniumalloys can be minimized or eliminated by following the procedures de--scribed in this report. When proper techniques are employed, weldingof titanium is not an unusually difficult operation. An awareness of thecleanliness needed to successfully weld titanium is essential, and goodcleaning practices must be followed throughout the welding fabrication.Brazing of titanium is still limited by difficulties encountered in se-lecting suitable filler alloys that satisfy performance criteria.

I

INTRODUCTION

Titanium and titanium alloys have a number of desirable proper-ties and, when suitably combined, these properties make the metal thebest material for a variety of service applications. These propertiesinclude:

(I) Excellent fatigue resistance

(2) Good notch toughness

(3) Stability over wide temperature range

(4) Low coefficient of thermal expansion

(5) Low thermal conductivity

(6) Outstanding corrosion characteristics for some of themost troublesome industrial chemicals

(7) Excellent resistance to erosion and cavitation from high-velocity fluid flow

(8) No scaling below 800 F, although discolorati, n of themetal may occur

(9) Inert in electrochemical operations, when charged as ananode in electrochemical circuit.

These properties are important in a variety of applications includingairframes, jet engines, aerospace equipment, chemical or processingequipment, and electroplating equipment. Whether manufactured frombar, plate, sheet, or forgings, some type of joining operation often isrequired to assemble components or subassemblies as a step in com-pleting the final product.

The joining of titanium oy welding and brazing processes is de-scribed in this report. Previous reports in this 'series have describedadhesive bonding and mechanical fastening of titanium. Emphasis isbting placed in these reports on the details of joining procedures.This report is organized into three major sections: (1) Joining funda-mentals that cover those aspects of titanium joining that are commonto several joining methods, (2) Joining processes that cover equipmentprocedurps, typical joining conditions, and applications, and (3) Dis-similar metal joining in which titanium is one of the materials beingjoined.

2

2ZI____________

WELDING FUNDAMENTALS.

Successful titanium welding involves a careful consideration ofmany factors related to the actual joining operation. These factorsare common to most joining processes and include such items as ma-terial selection, process solution, cleaning, tooling residual stresses,repairs, etc. Collectively these factors constitute the fundamentalbasis of a successful joining procedure. The following sections dis-cuss these basic considerations, particularly as they relate totitanium joining.

MATERIALS

Joining operations involve two types of materials: (1) those thatmake up the component being joined and (2) those used or supplied inthe joining operation.

Component Materials. Component materials are selected toobtain desirable combinations of mechanical and physical propertiesunder the imposed service conditions. ' Consideration of all the fac-tors involved in the selection of component materials is important but,in this report, only those factors related to joining operations will bediscussed.

Important features of titanium alloys that must be considered tosuccessfully join this highly reactive material are:

(1) The extreme sensitivity of titanium to embrittlement bysmall amounts of some impurities

(2) The very high reactivity of titanium, not only at weldingtemperatures but at temperatures as low as 1200 F

(3) The effects of the heating and cooling cycles involved injoining operations on the mechanical properties of the alloys

(4) The inherently brittle structures, which are almost alwaysformed when titanium is joined to other metals

(5) The specific titanium alloy composition to be used.

The sensitivity of titanium and titanium alloys to embrittlementimposes limitations on the joining processes that may be used. Small

amounts of carbon, oxygen, nitrogen, or hydrogen impair ductility

"Appendix B (DMIC Memorandum 171. July 15, 1963) tabulates the physical and mechanical propertiesof many titanium alloys. Information on titanium-alloy producers also is included.

3

TO-N W

and toughness of titanium joints. As little as 5000 parts per million ofthese elements will embrittle a weld beyond the point of usefulness.Titanium has a high affinity for these elements at elevated tempera-tures and must be shielded from normal air atmospheres during join-ing. Consequently, joining processcs and procedures that minimizejoint contamination must be used. Dust, dirt, grease, fingerprints,and a wide variety of other contaminants also can lead to embrittle-ment and porosity when the titanium or filler metal is not properlycleaned prior to joining. Contamination that arises either from theopen atmosphere or from dirt on the filler metal or surfaces to bejoined must be strictly avoided for the successful joining of titaniumand titanium alloys.

Recognition of several metallurgical characteristics of titaniumis im.portant if we are to understand the reasons for using the specificjoining methods discussed later. These characteristics, (1) chemicalactivity, (2) interstitial alloying, (3) substitutional alloying, and(4) strengthening mechanisms, are discussed in the following sections.

Chemical Activity. When heated to joining temperatures,titanium and titanium alloys react with air and most elements andcompounds, including most refractories. Therefore, gas-fusion andarc-welding processes where active gases and fluxes are in contactwith hot metal are not used. The reaction products cause brittlewelds. Titanium can, however, be wel.ded by inert-gas-shielded orelectron-beam fusion welding and spot, seam, flash, induction-pressure, gas-pressure, and other welding and joining processes.With the inert-gas-shielded arc-welding processes, argon or heliumshields the welds from air and prevents weld contamination. Electron-beam welding takes place in a vacuum. In spot and seam welding, themolten titanium in the weld is surrounded by the titanium-base metalso *he welds are protected from contamination. In flash and pressurewelding, air mray be in contact %vLth the weld, but most of the contami-nated metal is pushed out of the weld area and any remaining impuri-ties diffuse iWto the metal away from the weld interface. Inactive fluxbackups have been developed for use in combination with inert-gasshielding for welding titanium.

Brazing and solid-state-welding processes for titanium generallyare limited to those techniques that involve vacuum or inert-gasatmospheres.

- Interstitial Alloying. Of the few elements that can forminterstitial solid solutions in titanium, only carbon, oxygen, nitrogen,and hydrogen are of specific interest in the joining of titanium.

4

I-lo

Carbon, n'trogen, and oxygen all behave in about the same way in ti-tanium. Small amounts of these elements cause significant embrittle-ment of titanium welds. The effects of these elements on weld duc-tility and toughness are both progressive and additive (Ref. 1)'%.Because of this, it is difficult to establish a definite amount of anysingle interstitial element that causes a distinct change from good tobad properties. During joining of titanium, contamination by carbon,oxygen, hydrogen, and nitrogen must constantly be guarded against;when these elements are found in titanium joints it is because:

(1) They are deliberate alloying additions to some forms oftitanium

(2) They may be present as residual impurities

(3) They may be picked up as contaminants from variousprocessing steps.

Hydrogen behaves somewhat differently in titarlium; nevertheless, itspresence in titanium welds can be extremely harmful. Hydrogen isnever deliberately added to titanium and should be kept at as low aconcentration as possible in all processing operations.

Interstitial elements have potent effects on properties of titaniumalloys. Consequently, caution is necessary when comparing titaniumalloys or different heats of the same alloy. Variations in impuritycontent, or interstitial content, can cause significant changes intoughness. Therefore, it is important to consider the effects of allimpurity content and alloying elements when selecting welding pro-cedures, processing procedures, and other parameters..

The interstitial level that can be tolerated in welded joints dependson the use to which the welds will be put and the alloy that is beingwelded. Weld toughness is decreased by lower interstitial levels thanthose that will affect ductility. Therefore, greater care should betaken to insure against weld contamination in fabricating assembliesthat are subjected to impact loading. Also, welds in some alloys aremore ductile, and have a higher toughness than welds in other alloys.Welds with a high basic ductility or toughness can tolerate higher in-terstitial levels. Unalloyed or lower alloy or extra-low interstitial(ELI) filler wire is often used to improve weld ductility.

The interstitial level that can be tolerated in welds is lower thanthe corresponding tolerance level in base material. Interstitials that

*References are given on page 182.

5

•u ~ ~ . AuAn rn um • m

are present in the base metals prior to welding or are introduced dur-ing welding may cause weld embrittlement.

Substitutional Alloying. The most generally recognizedeffects of substitutional-alloy additions in titanium relate to the type ofalloy formed by the specific addition or additions. Titanium alloys areclassified as pure titanium, alpha alloys, alpha-beta alloys, or betaalloys, depending on their metallurgical structures. Each titaniumalloy behaves according to the characteristics of its alloy type duringjoining. The initial base-material condition (cold worked or heattreated in some manner) is equally as important as alloy content, aswill be shown in the next section.

a'0

Commerciall- Pure and Alpha Alloys. All commer-cially pure titanium and alpha alloys are weldable. The mechanicalproperties of joints in either commercially pure titanium or alphaalloys are not affected by welding operations or brazing thermal cycleson annealed sheet material. Alloys of this type that have beenstrengthened by cold working will exhibit a loss of strength in weldheat-affected zones or brazements. Very little use is made, however,of cold working to increase the strength of either commercially pure oralpha-type alloys. Welded joints in annealed alpha-titanium materialare ductile and exhibit strengths that are equal to those of the basemetal. Alpha alloys with a maximum of usable strength are obtainedby using a level of substitutional-alloy addition that is close to themaximum solubility. The 7AI-l2Zr titanium alloy is of this type andis the highest strength all-alpha alloy currently available that exhibitsgood weldability.

Alpha-Beta Alloys. The mechanical properties andductility of alpha-beta alloys can be affected greatly by heat treatment.The response of these alloys to heat treatment depends upon the exactalloy content. Therefore, very few generalized statements aboutweldability of alpha-beta alloys can be made. Welding or brazingthese alloys may significantly change the strength, ductility, andtoughness as the result of the thermal-cycle exposure during joining.The selection of an alpha-beta alloy for use in an application requiringjoining should be based on the known effects of the alloy content and thcintended application. Alloys that contain about 3 per cent of eitherchromium, iron, manganese, or molybdenum, and more than 5 per centof vanadium either singly or in combination with each other are seldomused in fusion-welding applications because of the resulting low weldductility. When welding alloys contain percentages of these ele-ments in excess of the amounts given above, it is sometimes possibleto improve weld ductility by a postweld heat treatment. However, the

4 6

7,. ;-

use of heat treatment is not always effective in improving ductility.The thermal stability of welded alpha-beta alloys is another area ofconcern if the intended application involves prolonged service at ele-vated temperatures.

Alpha-beta alloys are sometimes welded with either commerciallypure or alpha-alloy filler metals. This is done to lower the alloy con-tent of the weld fusion zone. The use -of filler metals of this typelowers the beta-phase content of the fusion zone and generally resultsin improved weld ductility and toughness. The composition of theheat-affected zone, however, remains unchanged. In alpha-beta alloysthat are subject to heat-affected-zone embrittlement, special fillermetal alloys are ineffective in obtaining an overall improvement inweldment properties.

Beta Alloys. The all-beta alloy, l3Cr-llV-3A1, de-pends very strongly on either cold work or heat treatment to obtaindesirable strength properties. In these conditions, welded joints arereadily made, but the resulting weld strength is considerably lowerthan that of the base plate. Postwelding operations designed to raisethe weld-strength level either are not practical or result in severeembrittlement of the beta alloy. The reasons for this are not wellknown, but are apparently related to different aging responses ofstructures that differ in grain size, grain structure, or orientation.All-beta alloys are also susceptible to thermal instability. Their usein a fully annealed condition is generally not warranted because of thelow strengths available.

Strengthening Mechanisms. Titanium alloys can bestrengthened by cold working (strain hardening) and by heat treatments.The strengthening mechanisms used for titanium alloys are importantbecause of their effects on weldability of alloys as based on mechanicalproperties. Some alloys are considered to be weldable if the weldsare not given any postweld heat treatment. However, quite often weldsin such alloys are much lower in strength than the heat-treated basemetals. Attempting to increase the strength by a postweld heat treat-ment may be successful, but quite often some other property (such asductility) is degraded.

The importance of strengthening mechanisms as a consideration inthe weidability of titanium alloys can be illustrated in another way byconsidering the following statements.

7

-3______---____,-._,_ _ .__ I_ __.. .. _ __ _

i

"I • hi Jne properties of titanLu-ZU-uase alluys are ,A ... t £ eCA

alloy content and a controlled-mechanical and thermal-processing history.

(2) Welding imposes variable thermal cycles on material inthe joint area that are unlike any other exposure conditionsnormally used on titanium alloys.

(3) The effect of welding thermal cycles on the properties oftitanium alloys may be insignificant or very significant.

(4) The apparent weldability of any given titanium alloy canbe altered considerably by either the initial base-material condition or postweld thermal or mechanicaltreatments.

Strengthening mechanisms also are important items to consider inplanning brazing operations for titanium.

Process Materials. The principal materials used in joiningoperations are filler metals, protective shielding gases, and, on rareoccasions, protective fluxes.

Filler Metals. Some fusion-welding processes involvethe addition of metal from sources other than the base metal. Wire isgenerally used and added at a controlled rate. Wire added during TIGwelding is called "filler wire" or "cold wire". Wire used in MIGwelding also is called filler wire, or it may be called "electrode wire".

Titanium wire for welding must meet high-quality standards. Thesame is true for most welding wire. This requirement results fromthe high surface area to volume ratios characteristic of the commonwire sizes used in welding (see Figure 1). Obviously, any wire-surface-layer contamination represents a sizable addition to a weld.Also, it is much more difficult to process titanium to wire withoutcontamination than is the case with other products. For example,wire cannot be processed by any method comparable to the pack-rolling procedures used for thin sheet.

Wire products sometimes contain defects. The terminology usedto describe various wire defects is illustrated in Figure 2. None ofthese defects can be tolerated in titanium wire intended for weldingstructural components of high-performance airframes.

8

S. . . . 1 i a i I I iu i m i l l I Iw m- . . .. . .. . . .. .. .. . ..

150E

> C \ Range of wore sizes

S S0

0 005 010 0S 020

Wire Diameter, in.

FIGURE 1. SURFACE AREA TO VOLUME RATIO FOR WELDING FILLER WIRES

Defect Drawing Stock Wire

Seam 0GLop 0)

Center burst (

CrOck

FIGURE 2, WELDING-WIRE DEFECTS

Any of the surface defects may contain foreign .,matter (drawing compound, oxide, etc.)

9

RWAý rq OF WMP_____-TZPW

The availability of good-quality titanium welding wire in the pastand today has been debated extensively. Some welding engineers feelthat high-quality titanium wire just does not exist. Others do not thinkthere is a "welding wire problem". The real answer probably liessomewhere between these two extremes.

The "titanium welding wire problem", if there is one, must be re-solved before some fusion-welding processes can be used for certainapplications. Titanium-welding-wire development has suffered fromthe lack of a sizable market. Unalloyed titanium commercially purewire has been the major marketable item. Experience with the varioustitanium alloys has been limited. The required quality level and relia-bility in titanium-alloy wire probably can be developed once a marketis evident.

Filler wires for welding titanium are produced by the major ti-tanium fabricators and by a number of specialty-wire manufacturers.

Filler metals also are used in brazing and some solid-state-welding processes. Requirements pertinent to these applications arediscussed in the appropriate process sections.

Protective Shielding Gases. When molten, or even justcherry red, titanium acts like a blotter for gases containing carbon,hydrogun. nitrogen, oxygen, and water vapor. Small amounts of thesegases can embrittle titanium alloys beyond the point of usefulness.Even trace amounts of these gases can have large effects on propertiesof titanium alloys. Extensive tests have shown that argon used to pro-tect the weld zone had to contain less than 500 ppm of air by volumewhen welding Ti-5A1-2. 5Sn (Ref. 2). Bend tests showed a 50 per centreduction in ductility when air contamination was increased from100 ppm or less to 500 ppm. Consequently, when joining titanium andits alloys, any melted or heated metal must be protected from cominginto contact with air and other atmospheres containing these potentiallyharmful elements.

Air around a titanium joint must be replaced by an inert gas dnd itmust be replaced whether the joint is fully penetrated or not. In actualpractice, inert gases, argon and helium, or mixtures of argon andhelium are used for shielding titanium with all fusion-welding pro-cesses. Electron-beam fusion welding normally is done in a vacuumat pressures low enough to preclude air contamination. Brazing andsolid-state joining are usually done in inert-gas atmospheres orvacuum. Inert-gas shields help blanket all of the heated metal withinert gas. The inert gases do not react with titanium whether the

10

metal is hot or cold and there is no embrittling effect from thesegases. If the normal surrounding air contacts the heated metal it willreact with it to promote porosity, embrittlement, cracking, or otherserious effects. In addition to shielding, the inert gases argon andhelium are used to provide distinct welding arc characteristics andweld features. Arc voltage in helium is about 30 to 50 greater than inargon for a given welding current. The heat energy liberated inhelium is about twice the heat given off in argon. This means thatfaster welding speeds can be obtained with helium shieldin6. Heliumalso provides greater weld penetration and permits welding of thickergages more readily. Argon is used for welding thinner gages wherelesser heat may be desirable. Arc length can be changed in argonwithout appreciably changing the heat input to the work. This is animportant factor when the electrode cannot be brought close to thework or when arc length may vary as in manual welding operations.Mixtures of shielding gases also are used to obtain characteristics thatare intermediate between those of the pure gases. Selection of theparticular shielding gas, therefore, is made to provide desired weld-ing arc characteristics in addition to preventing contamination. Also,gases such as hydrogen, carbon dioxide, and oxyacetylene mixturesthat are normally used in joining other metals cause severe embrittlingeffets when used in joining titanium; consequently, they are not used.Special grades of inert gas containing additives, such as oxygen, thatare used in some welding should not be used in welding titanium.

High-purity inert gases are needed for joining titanium. Specialwelding grades of inert gases are available commercially. The majorconcern with inert gas is insuring that the basic-gas quality is not de-graded during flow through the joining equipment. The number of dis-connectable fittings used in the gas- system should be minimized. Allsuch fittings must be kept in good condition and must be tight to preventaspirating air and moisture into the shielding gas stream. Damaged orloose fittings can allow air or water leaks to contaminate the inert-gasshield and the joint.

Protective Fluxes. Titanium and titanium alloys havebeen welded using a proprietary-flux back-up, conventional MIG-welding technique. In feasibility studies, 3/4-inch-thick commerciallypure titanium and 7/16-inch-thick ELI Ti-5AI-2. 5Sn plates werewelded in the flat position (Ref. 3). Torch-trailing-shield arrange-ments were used to protect the access side of the welds while theunderbead side was protected with the proprietary flux. The flux wasplaced in the separation between two back-up bars. The fused fluxforms a cocoon on the back sides of the welded plates and affords good

11

iN .

protection from the atmosphere. The fused flux was removed byscraping or wire brush"ing and ...... in w.t..r R.f. 41.

Similar techniques have been used for manual and mechanized TIGwelding titanium and there are indications that the flux ma~erial alsomay be useful for submerged-arc-welding applications (R,- 3).

On the basis of preliminary results, it appears that fluxes forwelding titanium have merit although there are no known commercialuses as yet.

PROCESS SELECTION

Titanium has been joined by many common welding and brazingprocesses. Widespread use has been made of the following processes:

(1) TIG welding (tungsten inert gas)(2) MIG welding (metal inert gas)(3) Electron-beam welding(4) Resistance spot-, roll spot-, seam welding.

Limited use has been made of many other joining processes including:

(1) Arc spot welding(2) Plasma-arc welding(3) Brazing(4) Diffusion welding(5) Roll welding(6) Pressure-gas welding(7) Flash welding(8) High-frequency resistance welding.

Processes such as oxygen-gas fusion welding, submerged-arc welding,coated-electrode welding, and arc welding with active gases are notused for joining titanium because of the resulting embrittlement of thejoint area.

As with many other metals, selection of a joining process for ti-tanium often is influenced by the physical characteristics of the part tobe joined. Fortunately, the varied characteristics of joining processes

lead to a very broad range of possible applications. Most titaniumjoints can be made by any one of a number of joining processes. How-ever, welding finds major usage in subassembly fabrication and a fewlarge structural compco:ents. Cost, available equipment, maintenance,

12

--* ..i a a • "' -- -.'- -

k.

reliability, accessibility, thickness, and overall component size alsoare important factors in assessing the proper usage of welding andalternative joining methods.

Joint design also can influence the selection of the joining process.Design can limit the number of potentially usable processes and ex-clude those processes that are either not usable or would be very dif-ficult to adapt for the particular application. Figure 3 illustratesseveral joint designs and lists the processes that normally would orwould not be used for joining; it is apparent that several processes canbe selected for making e ich joint when considered from a purely capa-bility viewpoint. Other factors reviewed earlier may reduce the num-ber of potentially useful processes to a fewer number than thoseindicated.

The relationship of joining to other fabrication operations is animportant aspect in process selection. A simplified subassembly-process flow chart follows to show some of the possibilities. The partused as an example is a contoured stiffened skin too large to makefrom a single titanium sheet. The materials involved are skin sheetsand formed stiffeners as sketched in Figure 4. The flow chart, Fig-ure 5, shows that many possible approaches might be used to fabricatethis single part. The important point here is to remember that thefabrication operations immediate" ', before and after joining are closelyrelated to successful part fabrication. Good joint fitups are neededand all titanium parts must be properly cleaned before joining. Stressrelieving of complex (and perhaps any) weldments immediately afterwelding is sometimes essential.

JOINT DESIGN

Suitable joint designs must be selected for all types of joining op-erations, but they are particularly important in welding. Joints withsquare abutting edges for arc or electron-beam welding for the thinnergages of titanium normally require machining to provide a good fit-up.Thicker gages require a more complex joint preparation. Typically,such preparation involves machining bevels or contours on the abuttingedges. Part tolerances also are an important consideration in e--*ab-lishing good joint designs. Close tolerances are always preferred, butthey cannot always be planned for in production parts. With titanium itis also essential that the joint design selected be one that can beproperly shielded from contamination if welding is to be done in air.

Joints designed for TIG, MIG, or electron-beam welding titaniumalloys normally are prepared by machining so as to provide a good

13- ~ ,~ --.-. ~.w-*- -. w--~-- -- -

a. Butt Joint

Select: TIG, M!G, electron beam,flash, pressure gas b. Fabricated Tee

Exclude: resistance spot and seam Select: TIG, MIG, electron beamConsider: plasma, high frequency Exclude: flash, resistance spot and seam

Consider: plasma, high frequency, solid state

c. Sheet-Stringer Lop

Select: resistance spot or seam d. Multilayer Lap

arc spot, solid state Select: resistance or arc spot or seam,solid state

ExClude, flash, pressure Exclude: flash, pressure gasConsider: electron beam, plasma Considerr electron beam, plasma

e Sheet Splice With Doubler f. Cop or Tee

Select: resistance or arc Select: electron beam, TIG, MIG,spot or seam, solid state high frequency

Exclude: flash, pressure gas Exclude: flosh, orc and resistance spot

Consider: electron beam, plosmo Consider: solid st6te, resistance seam

FIGURE 3. TYPICAL JOINTS IN TITANIU'J AND TITANIUM ALI.OYS

14

.-

FIGURE 4. STIFFENED-SKCIN COMPONENT

I lk.- Sbect

van 3 a V.3.3w sw lk ýT

P~c~low Ice.

pwdb V.34

* ~.~ ts,. us~c. in.

L9-aft w

1tsall sofa woi p . **gf(Mb ft.UIOW.M

FIGURE 5. FLOW SHEET sirIoWiNG POSSIBLE RELATION OF WELDING TO OTHER OPERATIONS

15

joint fit-up. Unless the parts are well fitted together, burnthrough orexcessive deposits that may crark can result. The joints are ma-chined by milling, shaping, and grinding. Draw files often are usedto remove burrs and to help clean the surfaces before welding. Al-though many f-.bricators regularly use draw filing as part of theirnormal joint-preparation procedures, some fabricators believe thatdraw filing produces burrs that contribute to porosity; consequently,the latter hesitate to use draw files for titanium-joint preparation.

Preparation of edges to be welded is performed by conventionalmethods such as machining and grinding. Oxyacetylene-flame cuttingfollowed by light manual grinding also has been used to prepare weldgrooves in the 6A1-4V titanium alloy (Refs. 5, 6). The edges can bedye-penetrant inspected to assure the absence of surface defects.Cracks can occur in the flame-cut edge during cutting. Also, delayedcracks can form so grinding should be done immediately following theflame-cutting operation (Ref. 7).

Typical weld-joint designs for fusion welding titanium alloys areshown in Figure 6 (Ref. 8). Information available regarding joint di-mensions is given in Table I. Dimensional details of U-joints aregiven in Table II. Other special joint-design details for MIG weldingare shown in Figure 7 (Refs. 5, 9). A consumable-land joint designshown in Figure 8 also has been used for welding titanium (Ref. 9);the thickened portion of the joint is melted during welding and servesas the filler metal. This joint design is useful when satisfactory fillermetals are not available. However, the joint must be prepared fromthicker parent metal sheet or plate or the edge must be upset to per-mit machining. The joint design shown in Figure 9 incorporating aback-up ring also has been used for welding titanium (Ref. 9). Theback-up ring is used to help hold the molten metal in place and to helpcontrol the underbead-weld geometry. Since the back-up ring is fusedduring welding, it becomes an integral part of the weldment. In theonly known application of this joint design for welding titanium, theback-up ring was not machined away. For other applications, theback-up ring probably can be machined away. In most applications,however, welding is performed without back-up rings.

Resistance welding usually involves joints that consist of overlap-ping layers of material. Multiple layers may be included in a singlejoint. In resistance welding such factors as edge distances and inter-spot spacings are an important consideration in the selection of a suit-able joint design. Another important factor is the initial sheet separa-tion. Sheet separation must not be so great that unusually high forcesare required to bring the surfaces into contact.

16

"'4-., .4• A• •..m.w .~ .amm m m .m m •• .mm mml m ww m . mw . . W. •m I 7 U.• ;

i-IL

VERTICA VE.OH0ZONAL"LT•

EDGE WGLD

FLAT SWNGLELLE? WEL

ZLAP WILD- PLUG -,--..

BUTT WILD OVEBNI4A, WILD

LIGHT GAUGE WELD L

~~~0 COMMIGL ILE W

SINGLE "V** GROOVE WELD

DOUBLE 'V' GROOVE WELD WILD BEAD

"Ull GROOVE WELD DOUBLE FILLMT WELD

DOUBLE "U" GROOVE SINGLE "r GROOVE DOUBLE ",r GROOVE

FIGURE 6. TYPICAL FUSION-WELD-JOINT DESIGNS (REF. 24)

17

- l7|• nall m~w • •• Ban •a •nw • • • n wn •• a mm aa~m mw• i----------- •

'Io

a. 00 0c "--0 -

C. . .. .Al .l$ .. j . .'.

%J -J, 4 , N J 4 4 4 4 4

0 3 , 0

Is 3.3 0. 4. Is 3.3. 13

o 0 .) 0 3 3 3 a 0 C.

# .SS

a' o3 -Z 0, 033 1,3l

ig a. ... _; 2 2 2 2 _: ".: • o

.- It

'I "-

18

o-A - " -J "' - - .. . -. . . ."-"

0 0

C; ~ ~ 0 0C 0 0 i

c2400

, .4 - f 4'- A .0 n

0 42 0

C!-C5 ~ ~ ~ ~ 0 ; 0 ;

.0 40 0

0 0 a O : 0 I4- -. -. -; o C; 0 0 a -

S . 0 0 0 400' 0 ' 0 ' 0 ' 0 ~~0 0

o; Ct 0 ; 0 0 0 0; 0 C

4w

JD 0 a C

tf - 0 4 . 0 0 0A 0 .

Z ~~ Ij 0 041..

00~~ ~ ~ 0;C ; C o S 0 0do 0 0% e d o ft 0c o

0 ' .~0 0 00 0 f*

0 0 0 0 0 : c; 0; 06 0 0 0

6 0 d o o 05 0 d d 19

hel

40450 \~

r455

a. Several Special Joint Designs for Welding Titanium Al loys (Ref.9)

SN1 -9= tube 2

20

01

.011 C 3T 60

FIGURE 8. CONSUMABLE-LAND JOINT DESIGN (REF. 15)

a. Before Welding b. After Welding

FIGURE 9. BACK-UP-RING JOINT DESIGN (REF. 15)

Many of the joint designs used for resistance welding are not in-tended to transmit transverse tensile loads. Joints of this type aresometimes referred to as scab or attachment joints.

All joints designed for resistance welding must normally be ac-cessible from both sides of the parts being joined. Sufficient clear-ance must be maintained to allow for the extension of the electrodesand electrode holders to properly contact the sheets.

CLEANING

Careful preweld cleaning is essential to the successful joining oftitanium alloys. Proper surface preparation is important to (1) re-move scale, dirt, and foreign material that can contaminate the joint,(Z) help control weld porosity in arc-welding operations, and (3) in-sure uniform surface conditions and thereby improve weld consistencyin resistance-spot- and seam-welding operations. A flow chart of asuccessful cleaning operation is shown in Figure 10 (Ref. 16).

Prior to resistance welding the cleaning of the surfaces of sheetsas received from the mill with any of the commercial solvents thatleave no residue often is satisfactory. However, if elevated-temperature forming has been performed, the light oxide scale shouldbe removed. Otherwise the oxide skin on the adjacent surfaces beingjoined will be fused into the weld nugget, which can lead to a drastic-reduction in the ductility of the welded joint. Poor or variable clean-ing can have another bad effect in resistance welding. Much of the

21

S-,..'., -l: . --• ___.__________ ___ __ __r

IIScale Formied Scale Formed

Below 1000 F J Above 10=01!

Nitric -Hydrofluoric

FIGUREE 10 FLWCAToFCENIGPO eDRFO

Pickling Can Be

Repeated Providing tofTotal Immerf on Back to Cau s cc-Time Does Nan Sodium Dichromate

Exceed 10 Mportes ant d Repea n Cycleif Necessary

FIGURE 10. FLOW" CHART OF CLEANING PROCEDURE FORTITANIUM ALLOYS (REF. 16)

initial heat generated during the early stages of resistance welding islocalized at the joint interface. This happens because the electricalresistance through the interfaces is generally higher than the resis-tance of the bulk material. Thus, the surface resistance of the matingsurfaces is an important factor controlling the heat generated duringthe weld cycle, and it is important that this resistance not i'luctuate

widely. The surface resistance of any metal is controlled largely bythe surface preparation of cleaning techniques that are used infrior towelding.

Grease and Oil. Grease and oil accumulated on titaniumparts during machining and other operations must be removed prior tojoining to avoid contamination. Scale-free titanium often is degreasedonly; titanium having an oxide scale is degreased prior to descalingoperations. Degreasing may be accomplished in any of the following

ways:

(1) Steam clean

(2) Alkaline wash or dip in a dilute solution of sodiumhydroxide

(3) Solvent wash methyl ethyl ketone, methyl alcohol, toluene,acetone, or other chlorine-free solvents

If

22

9 VR

(4) Hand wipe with solvent-dampened. clean- lint-free clothsimmediately before welding. Plastic gloves are recom-mended for this type of operation. Reactions betweensolvents and some of the compounds in rubber gloves canleave deposits on the joint that cause porosity.

The steps followed in a typical cleaning procedure for machined partsprior to joining are as follows (Ref. 17):

(1) Degrease with toluene, alkaline-steam cleaners, or com-mercial degreasing equipment. (Residues from silicatedor chlorinated solvents have been blamed for cracking ofsome titanium weldments. Consequently, this use forcleaning titanium is prohibited by many fabricators.)

(2) Force air dry with clean, dry air

(3) Alkaline clean (commercial cleaners)

(4) Water rinse with running water or a spray rinse at ambienttemperature until a pH of 6 to 8 is reached. pH paper isused for this determination

(5) Water rinse for 4 to 6 minutes with deionized water atambient temperature

(6) Alcohol rinse for 15 to 30 seconds with alcohol at ambienttemperature. Alcohol rinse is optional

(7) Dry by blowing with hot dry air or nitrogen gas.

Parts showing evidence of surface contamination immediately prior toassembly should be rejected and must be recleaned. If the surfacecontamination is light dust settled out of the atmosphere, the parts arewiped with solvent-dampened cloths and dried just prior to the joiningoperation.

Chlorinated solvents, such as trichloroethylene and silicated sol-vents, should not be used to degrease titanium. * Stress-corrosioncracking in weld areas during subsequent processing has been attrib-uted to the use of chlorinated solvents (Ref. 1). Cleaning of parts con-taining crevices should be analyzed carefully to avoid trapping solu-tions that can cause porosity. Good rinsing and drying procedures areimportant in these operations. Residue from the degreasing treatmentmust not be allowed to remain in the joint area.

*Some solutions used in dye -penetrant testing may contain chlorinated solvents. Use of these materialsshould be carefully checked out prior to approving their use on titanium.

23

Temperature-sensitive crayon and paint markings and pencil andink markings also should be removed from. areas fM arheate d,-a, r -

ing joining operations. These materials can contaminate either theunderlying metal or the weld metal and result in embrittlement orporosity.

Scale Removal. Light scales are formed on titanium at tem-peratures up to about I100 F., This scale is generally thin and can beremoved by chemical pickling. Chemical pickling is often the mostefficient and economical process for scale removal compared withmechanical techniques (Ref. 18). The most commonly used picklingbaths are solutions of hydrofluoric acid, nitric acid, and water, Thesebaths contain from 2 to 5 per cent HF and 30 to 40 per cent HNOQ. Apickling bath used by many fabricators contains 5 per cent HF, 35 percent HNO 3 , balance water, and a 30-second immersion time. Afterpickling, the parts are rinsed in water and dried. Pickling treatmentsalso are used to prepare scale-free material for spot- and seam-welding cperations. Pickling should be avoided when possible on as-semblies that contain crevices that may entrap the acid solution.

The steps followed by one fabricator in removing light scale areas follows:

(1) Degrease to remove oil or grease

(2) Alkaline clean

(3) Rinse

(4) Immerse in scale. conditioner

(5) Rinse

(6) Immerse in HF-HNO 3 pickle. Stains resulting from theIIF-HNO3 pickle can be removed by a 30-second im-rmersion in a 45 to 55 per cent HNO 3 pickling solution.

Prolonged immersion can remove too much material, so pickling pro-cedures must be developed and controlled carefully.

When heated to temperatures above 1100 F the scale formed ontitanium ii thicker than the scale formed below 1100 F. Removal ofthe heavier scale requires a more complex treatment than is requiredfor removal of light scale. Chemical or salt-bath treatments, me-chanical treatments, or combinations of these treatments are used.Molten-salt baths, which are basically sodium hydroxide to whichoxidizing agents or hydrogen have been added to form sodium hydride,

24

I • s• •m •m • ms •m m • • • s mm • • • m n • u • •m • • • m • • • m

are commonly used to remove this scale in preparation for welding.Caution is needed in using these molten-salt baths. Bath compositionsand temperatures must be carefully controlled to prevent the introduc-tion of excessive amounts of hydrogen into the titanium.

Both the molten-salt-bath treatments and mechanical scale-removal operations are followed by a pickling operation to insure com-plete scale removal and to remove subsurface contaminated metal ifnecessary. Removal of scale can be aided by scrubbing with a brushand reimmersing (Ref. 16). Caution is necessary when pickling tita-nium. Titanium can absorb hydrogen readily when improper picklingprocedures are used. During subsequent welding operations, porositycan occur from hydrogen absorbed during pickling operations. Picklingbaths that contain HF with little or no HNO3 acid cause hydrogen ab-sorption. HNO 3 inhibits hydrogen pickup during the reaction betweentitanium and HF. At least a 7 to I HNO 3 to HF weight ratio normallyis recommended.

Handling and Storage. All part handling after cleaning andbefore joining must be controlled. So-called "white glove" operationsare often used to prevent contamination after careful cleaning. Cleanedmaterial should be joined within a few hours or wrapped with iint-freeand oil-free wrapping for storage until needed. Some recleaning ofmaterial that has been in storage may be recuired before certain join-ing operations.

Between cleaning and joining operations, the parts maybe exposedto the open atmosphere. During such exposure, dust and fine dirt par-ticles may settle out on the joint surfaces and adjacent areas. The"fallout" dirt also can contaminate titanium joints. In many instances,these dust particles are removed by carefully wiping the joint areawith lint-free cloths dampened with a solvent such as methyl ethylketone.

Fabricated parts that are to be hot formed or stress relieved mustbe clean. In view of the problems in cleaning complex parts, it maybe simpler to keep such parts from becoming dirty during joining op-erations. This will require careful handling and storage throughoutall operations associated with the actual joining.

Evaluating Cleanliness. The effectiveness of cleaninf meth-ods is evaluated by variou_" methods. The most unpopular mnethod isdiscovering porosity, cracks, or other evidence of contamination in acompleted weldment.

Z,

, - i- .- . - - -,t •

A common method for evaluating the cleanliness of a part emerg-ing from descaling and pickling operations is to observe water breaksduring the water rinse. No water break indicates a clean surfacewhile the presence of a water break indicates some foreign materialremaining on the surface.

Limited contact-resistance measurements have been made tocompare the effectiveness of several cleaning methods prior toresistance-spot welding Ti-3A1-13V-ilCr alloy in the solution treated

condition (Ref. 19). Average contact-resistance values obtained forthree cleaning methods were as foilows:

Belt sanding Ill microhms

2. 5% HF, 30% HNO 3 , bal H2 0 158 microhms(2. 5 minutes)

Proprietary solvent (5 minutes) 160 microhms

Measurements of contact resistance can p'ovide useful information onthe effectiveness and consistency of cleaning operations.

SHIELDING

Protection of titanium from contamination during joining opera-tions can be accomplished in several ways.

(1) Perform the operation inside an inert-gas-filled chamber

(2) Perform the operation with flowing inert gases throughthe welding .-,rch, back-ups, fixtures, and auxiliarytooling

(3) Perform the operation in a good vacuum "i a closedchamber.

A wide variety of tooling has been designed to contain and/or supplyinert gases for shielding titanium welds. Although these shieldingdevices vary in constructional detail, they all serve the same basicpurpose, i. e., protecting the weldrnent from gases that can contami-nate the hot metal.

Several types of shielding and controlled-atmosphere chambershave been used to weld titanium and other reactive metals. Suchchambers are designed to contain the entire component to be welded,or in some cases, merely the weld-joint area. The air in the chamberis replaced with inert gas by (1) evacuation and backfilling, (2) flow

26

IS: TZ •.• z .. g g g .. g- -7 - - ,- . m i si • •Pm i n •'.a• • . .. ..

purging, or (3) collapsing the chamber and refilling it with inert gas.Welding chambers are particularly useful in the welding of complexcomponents that would be difficult to fixture and protect properly inthe air. Use of a welding chamber, however, is not a cure-all. Theinert gas in many welding chambers is of much poorer quality than theinert gas contained in the conventional flowing shields. Leakage of airor water vapor into a chamber atmosphere must be avoided to do agood job in welding titanium. Monitor devices that will disclose con-tamination o0 a chamber atmosphere are available.

A tank-type controlled-atmosphere welding chamber for manualand machine, TI,3 and MiG welding of titanium alloys is shown in Fig-ure 11 (Ref. 20). Many small chambers are made from plastic domesand steel or stainless steel spheres; stainless steel is preferred be-cause it does not rust and is easy to clcan. Several small-sizechambers for welding small subassemblies are shown in Figure 12(Refs. 21, 22). The adaptation of a small-size chamber to welding anoversize part is shown in Figure 13 (Ref. 22); only the localized areathat is heated needs to be inert-gas shielded.. Flexible-plastic cham-bers are illustrated in Figure 14 (Ref. 23).

N73600

FIGURE 11. TANK-TYPE CON'TROLLED-ATMOSPHERE WELDINGCHAMBER FOR MANUAL OR MACHINE, TIG OR MIGWELDING TITANIUM ALLOYS AND OTHERREACTIVE METALS (REF. 20)

27

pomwa= vi

a. Welding of Subassemblies in a Controlled -Atmosphere-Box -Type Chamber (Ref. 21)

b. Close-Up of Transparent -Plastic -Dome-Type Welding Chamber

(Ref. 22)

FIGURE 12. CONTROLLED-ATMOSPHERE CHAMBERS FOR :IG WELDIING SMALL SUBASSENIBUES

28

40-*~

S•.... ~ -... .. • ,, _ ,_m_

ItI-

FIGURE 13. ADAPTATION OF A SMALL SIZE CHAMBER FOR TIG WELDING ANOvERSIZE PART (REF. 22)

The welding chamber has two pairs of glove ports. In this operation.

one glove port is used for insertion of a titanium part too large to fitinside the chamber,

FIGURE 14. FLEXIBLE-PLASTIC CONTROLLED-ATMOSPHERE WELDING

CHAMBER (REF. 23)

29

A -WP

Shielding gas used in these chambers may or may not flowthrough the torch, depending on the fabricator. Also, the shieldinggas can be recirculated through a purifying train to remove undesir-able gases that are evolved from the alloy being welded or from thechamber walls and tooling as these become heated.

For in-air welding with the TIG and MIG processes, shielding isprovided in several ways.

(1) Flowing inert-gas shield through the torch to shield themolten weld pool and adjacent surfaces

(2) Flowing inert-gas shield through a trailing shield to pro-tect the weldment as it cools (usually to below 1200 F)

(3) Flowing inert-gas shield through hold-down and back-upbars. Shielding gases flowing through the hold-downbars provides additional shielding for the face side ofthe weld. The back-up gas flow protects the root sideof the weld during welding and during cooling of theweld metal.

A variety of inert-gas-shielding devices have been developed forin-air welding of titanium alloys. However, all are designed primarilyfor blanketing the hot titanium metal from the surrounding air atmo-sphere. Figure 15a illustrates shielding methods for aluminum andstainless steels, as compared with the hold-down and back-up shield-ing parts used with titanium alloys, Figure 15b.

Examples of torch-trailing-shield arrangements for TIG and MIGwelding are shown in Figures 16a and 16b (Ref. 6), respectively. Thetrailing shield shown in Figure 16b is detachable as shown in Figure 17(Ref. 5). The detachable-trailing-shield concept provides for inter-changeable trailing-shield units for use with other joint designs ordegrees of accessibility.

Phenolic-plastic nozzles in TIG-welding electrode holders havebeen blamed for carbon pickup (Ref. 10). This effect can be over-come by replacing the phenolic nozzles with ceramic or metal nozzles.As titanium needs good shielding, the torch nozzle should be largerthan for other metals. A torch nozzle can be modified as shown inFigure 18 (Ref. 8). The copper shavings act as a diffuser so the inertgas will flow down over the weld in a soft cloud. For manual welding,this device generally gives better results than a trailing shield and itis easier to manipulate. Porous-metal diffusers are often used in the

30

CZ. -- -. ~

-. . . --.- , -n l I l

a~~_ WO o~ rAWW% W tooft

.In*"

T 1* Swewa Taof~q vT.aufl ( Siep~u

FIGURE 15. INERT-GAS-SHIELDING ARRANGEMENTS FORCONVENTIONAL MATERIALS COMPAREDWITH TITANIUM ALLOYS

trailing shields to help obtain better coverage of the hot metal by inertgas at lower flow rates. For machine MIG welding, a flat metalbaffle as shown in Figure 19 (Ref. 8), attached to the leading side ofthe torch is advisable; otherwise, small metal globules (spatter) wouldleave the protective gas atmosphere, become oxidized, and drop downon the joint line where they would be drawn into the weld and causeweld contamination and porosity. Studies of the effects of air currentsand blasts were made ior a typical TIG-welding arrangement (Ref. 24).As was expected, inert gases flowing from 1/2- and 5/8-inch nozzlesin still air gave satisfactory coverage, but in some instances provedexcessive and wasteful. When cross currents of 40 to 300 fpm wereintroduced, the picture changed drastically. Air currents greaterthan 60 fpm had detrimental effects on titanium welds, greater than180 fpm was harmful to aluminum welds, and at 330 fpm stainlesssteel welds were harmed if the nozzle was not kept as close to thework as possible. Side shielding also can be provided through thehold-down bars shown in Figure 15b or by means of baffles as shownin Figures 20 (Ref. 21) and 21 (Ref. 8). The baffles help to retain theinert-gas ;hield in desired areas and help prevent stray drafts fromdisturbLag and deflecting the shield-gas-flow pattern.

31

AI g rTorch. I Troilong -gas shield

Porous diffusionsheet

m. Tog- Welding Torch-Troiling- Shield Combination

b. Mg- Welding Torch- Troifing-gued Awrangment

• "FIGURE 16. TORCH-TRAILING SHIELD ARRANGEMENTS

32

r. --A

Pp'

IP""

FIGURE 17. DETACHALE TORCH - TRAILING- SHIELDASSEMBLY (REF. 5)

Top left - wide shield for wide joint open-ii, and capping passes; bottom left -narrow shield for root passes and narrowjwmM openiugs.

Similar, concepts are used to protect the nonaccess (root) side of awele joint. figures 22, 2Z3, and 24 (Refs. U1, S, 6,8) illustrate sev-eral methods of preventing root _ontamination.

Advantage also is taken 0f the fact that argon tend" to seftle anddisplace air. Conversely, helium is best suited for die#Larcing airwhen a rising gas flow is desir-9ble. For in-air wel&ng, fta-ilingshields designed for MMG welding are usually considerably longer thanthose used in TIG welding. This is .c insure good provection for thelarger volurmes of mate-rial that are heated during MIG welding and asa result cool more slowly.

Inert-gas-shielding considerations also are important in designingjoints for weLding. Figure 25 (Ref. ZI1) shows the orig.. 1 design of acoil cross section with welded spacers or supports. Adequate externalshielding would be extremely difficult if not impossible to achieve dueto the gap at the root of the fillet weld out away from the contact painitof the spacer. Furthermore, if the ends oL the spacer bars were ma-chined to fit the curvature of the pipe ait could be trapped and er -

brittle the root side of the fillet weld. Figures 26 and 27 (Ref. 21)show the design modifications to elimiaate welding required in theoriginal design and a compieted assembly, respectively. The chaigewas to a mechanical support.

33

" "W"Pri

Copper shavings

SElectrode

• • Copper shield

,,.Copper shavings

V

Gas. fGos

"Tungsten electrode

FIGURE 16. MODIFIED MIANUTAL TiG WELDING TORCII-SIHELDING NOZZLE (REF. 6)

Electrode woe

Torch Coohlng-water Cooling-watr7Gzle inlet rioutlet

Ooffle for MIG

Ga

welding only ,

Dffuse inert goS,Stainless steel

,,_ _ .... ._w ire s c re e n

Direction -of - motion

FIGURE 19. TIG-MIG TORCIH-TRAILING-SFHELD ASSEMBLY WITH LEADING SIIlELD BAFFLE

FOR WELDING TITANIUM Al LOYS (REF. 8)

34

40

u CL

-4 c

~z

0~

ar

co:

U 35

%lorOW'CoPW tube

PAWunde adrside --f WO

FIGURE 21. SHIELDING BAFFLE. FOR AN OUTSIDE-CORNER WELD) (REF. 8)

8•k•Naor-cooe

shield copper backing

FIGURE 22. BACKING SHIELD (REFS. 5,6)

At right is complete backing-shield oevicefor Army first-pass crack-susceptibility test

plates and for li-plate cross bars.

36

;4. Av.,-

7'I

- -- - - I

a Root Shielding of Tubing JoAnt

b. Two Interr'al Purging Devices (Ref 21)

Top fixture is for straight runs lower fixture is designed foruse around bend and curves

Sp�'t ring with proosctewe

c� IiiterraI and External Shielding �)evices (Ref. �)

FIGURE 23. SHIELDING DEVICES FOR PROTECTING ROOT SIDES OF BUTT WELDS

IN TUBING* PIPE. AND CYLINDERS

37

-�

GasbleedOrýTio umai tube

a. Fixture for Fillcý Welding Flange to Tubing

Gas bleeder

\''Collapsible fing

Gas PqWrnshield Thoni~Yf ýtubei

Titaniuvm f lange

b. Fixhav for Flrsb Welding Flawje IG Tubing

c. s Fixture for glasEn Welduki

FIGURE 24. SHIELDING ARRA ielETdO RTCTN OTSDE FFAG-O

TUBING~~ WEDS(RF.s

38Gs_

- La .-

pial/ toteV

T ube

UbO

FIGURE 25. CROSS-SECTION OF ORIGINAL COIL FIGURE 26. TACK-WELDED MECHANICALDESIGNED FOP, WELDED SPACERS ANID FASTENERS FOR THE COIL SPACERSSUPPORTS (REF. 21) SHOWN IN FIGURE 25 (REF. 21)

FIGURE 27. COILS IN VARIOUS STAGES OF COMPLETIONT SHOWING MECHANICAL SUPPORTS ANDTACK-WELDED NUTS (REF. 21)

39

TOOLING

The tooliag used in joining titanium may differ markedly fromtooli.ý; normrally used in joining other materials. Contamination,porosity, distortion, and penetration can be affected by tooling; specialtechniques have been developed to help minimize or eliminate these ef-fects. Tooling per se may range from simple clamps to hold parts inposition to more elaborate holding devices designed for specific par-ts.Simple tooling is adequate for welding titanium when other means areused to insure adequate shielding, for example, electron-beam or arcwelding in an enclosed chamber. However, for fusion-welding opera-tions conducted outside of chambers, tooling can provide a much moreeffective safeguard against weld contamination than other shielding de-vices. Tooling often is used to cool the weld area rapidly so that e.x-posure in the temperature range of high chemical reactivity is mini-mized. Such tooling is referred to as "chill" type.

Welding and stress-relief fixtures must never come in contactwith trichloroethylene for degreasing purposes, because of the stress-corrosion problem. Rigid tools are a necessity. For example, theTi-5AI-Z. 5Sn -iloy has a 1,-ield strength of I10 ksi at room tempera-tare, and every weld is going to -develop t-at voiount of nuli in at leastone and perhaps several directions. A weak tool wil be pulled out rifshape allowing the weldment, in turn, to distort.

Materials that come in contact with titanium on both root and facesides of welds include copper, aluminum, stainless steel, carbonsteel, and other common materials. Often, these materials are usedin the form of bar-type inserts or sheet- or plate-type facing platesfor fixtures. Top-side hold-down bars extend the full length of theweld and often contain inert-gas passages for weld face and rootshielding.

Considerable trouble wil.U welding operations is inevitable unlessweld-joint preparations are accurately machined, and the joints areheld properly in the welding fixtures.

The tooling used in resistance welding titanium is general.ly simi-lar to tooling used in resistance welding other materials. Resistance-vwelding tooling consists of suitable fixtures or jigs to hold the parts in

proper position for welding. Sometimes tooling is also designed toindex the part through the welding equipment to insure that welds aremade at the proper positions. The same general rules followed in de-signing any resistance-welding tooiing should be followed in designingtooling for use with titanium. Generally, this means that nonmetallic

40

Tf - -7--- A

or nonmagnetic components should be used exclusively, and the toolingshould not contaminate the titanium.

HEAT INPUT

The term "heat input" is widely used in the welding industry tocharacterize many of the conditions typical of arc welding. Limitingheat inputs are defined by:

(1) The rninimun energy required to melt sufficient metal to

form a weld

(2) The maximum usable energy level that will produce an

acceptable weld

(3) A maximum level Ihat will not degrade properties of aparticular material.

With titanium, it is best to use heat inputs just above the minimumrequired to form the weld. Greater heat inputs expose the titaniumwelds to conditions that promote contamination distortion and otherbad effects. An exact measure of heat input is not :-eadily made, butgood empirical formulae are known for each welding process. Intra-process comparis,,ns -of heat inputs are not always valid and should beviewed with caution.

Lowest heat inputs are obtained with electron-beam welding.Then, as a gener 11 ruie, heat inputs typical of normal welding condi-tions increase as follows:

(1) Single-pass TIG - no filler(2) Single-pass TIG - with filler(3) Multipass TIG - with filler

(4) Single-pass MIG(5) Multipass MIG.

Other general trends useful in estimating heat input are-

(1) Welds made with helium shielding gas have a lower heatinput than similar welds madewith argon shielding.

(2) Higher welding speeds result in lower heat inputs.

(3) High currents or voltages result in high heat inputs (atany given speed).

(4) Snall melted zones are characteristic of low heat inputs.

41

----- ....

SHRINKAGE - DISTORTON

Fusion-weld processes are characterized by thier:'na1 cycles thatcause localized shrinkage. This shrinkage often causes -:Jistor, Ion ofl

the parts being joined. Figure 28 illustrates the changes n shape that

occur as the result of wielding just a s-imple butt Joint. More cotpicpkcweidments obviously involve much more comple.-x shrinkage1 and distor-

tion patterns.

A=~ LOngitudiroi bowngB Transver-se towingC Tros rs st-einkogeLLTT

FIGILURE 28. TYPES OF WELD-jOINT DISTORTION

Shrinkage and d-strartion are mruch less tro,ýublesomre in brazingand solid-state welding because usually heating iS unifo~rmn.

Weld shrinkage must be planned fo, since there is no absolutewaytoaxol A Tus aknov.dedge of expected shrinkage valuces for

typical1 weld configurations isneeded befere production wcelding a-.ppi-

cations. Also, a logical -sequence of welding components inv~olvingseveral welds mnust be established -with shrinkage in mind. With theproper w.elding sequence, shrinkage can be 'turned to good use to

minimize distortion. This is accompl.shed by. properly balancing thevarious shrinkage forces developed.

Shrinkage also can be controlled to sonmc extent by the restraintimposed by tooling. Use of this technique is sometirnes helpful in

preventing serious part distortion. (Caution: Freedom from

42

;!1 I t:

distortion does not mean that a weldrnent is not highly stressed' Quite

often the coL'verse is true. )

Shrinkage and distortion are minimized by using low he:,t inputs.Thus, the listing given earlier also .s valid for showing the relativetendencies of fusion-welding piocesses to produce these changes. Un-necessary welc, reinforcement also is undesirable from the standpointof keeping shrinkage and distortion as low as possible.

Thermal cycles employed in resistance welding a!so result inhighly localized shrinkage. This shrinkage may cause some distortionof the part being joined, but generally distortion is not as noticeable inresistance-welded components as it would be in fusion-welded parts.

The effects of weld shrinkage and subsequent distortion aje gen-erally minimized in resistance welding by starting the welding near thecenter of any component and following a welding sequence that involvesmoving progressively toward the edges of the component. Sequencesof this type are not readily used during seam welding or roll-spot

welding, and consequently distortion may be more of a problem whenthese processes are used. Selection of improper welding sequencescan also introduce various problems with sheet separation prior towelding. For example, if three welds are being made in a.row and thetwo outside rows are welded first, then there is a good chance that thecenter row will be welded under conditions where excessive sheetseparation is likely. In a case such as this, the center row should bewelde-. first followed by the outside welds.

RESIDUAL STRESS

Shrinkage inevitably leaves residual stresses in fusion weldments.Residual stresses are defined as those which zexist in a body withoutany external force acting. The residual strefses in a welded joint arecaused by the contraction of the weld metal and the plastic deformationproduced in the base metal near the weld during welding. Residualstresses in a welded joint are classified intc: (1) "residual weldingstress", which occurs in a joint free from any external constraint and(2) "reaction stress" or "locked-in stress", which are induced by anexternal constraint.

Residual stresses generally are not a problem in brazed or solid-state-welded joints.

43$

Stress Distribution. The distribution of residual stresses isdetermined largely by joint geomnetry. Therefore, similar stress dis-tributions are found in joints of similar geometry, regardless of how

the joint was made. (For example, resistance-seam welding and TIGwelding will result in a similar stress distribution in a long straight

joint. )

A typical distribution of residual stresses in a butt weld is shownin Figure 29. The stress components concerned are those parallel tothe weld direction, designated ox and those transverse to the weld,designated oy. The distribution of the Ox residual stress along a linetransverse to the weld, YY, is shown in the Figure 29b. Tensilestresses of high magnitude are produced in the region of the weld;these taper off rapidly and become compressive after a distance ofseveral times the width of the weld, then gradually approach zero asthe distance from the weld increases.

The maximum residual stress in the weld is determined by:

(1) Expansion and contraction characteristics of the base metaland the weld metal during the welding thermal cycle

(2) Temperature versus yield strength relationships of thebase metal and the weld metal.

Much research in mild-steel weldments has shown that the maximum

stress is as high as the yield stress of the weld metal. However, in arecent investigation (Ref. 25), the maximum stresses in weldments

made with heat-treated SAE 4340 steel were around 50, 000 to80, 000 psi, considerably less than the yield strengths of the weldmetal (around 150, 000 psi) and the base metal (Z24, 000 psi). Inlimited investigation on titanium-alloy weldments, maximum residualstresses ranging from 35, 000 to 85, 000 psi have been observed, de-pending upon the type of base metal and welding processes (Refs. 26-28).However, the effects of base metal and weld metal properties andwelding processes on the magnitude of residual stresses on titanium-

alloy weldments have not been established.

Out-of-flat base plate also can contribute to restraint problems inwelding (Ref. 5). As-received materials that are wavy and out of flatlead to a condition of misalignment when placed in the welding fixture.

Where this condition creates fabrication difficulties it is necessary toflatten the plates. This working when added t. the already high levelof restraint can increase susceptibility to cracking, or cracking canoccur during the flattening operation.

44

yV

Y

acx

0. Butt Weld

Compression Tension

b Distribution of ax AloN YY

-' Curve 2

•"Reoctiol".X- str CTurve "'-

Compressicxj

c. Distribution of crv Along XX

FIGURE 29. DISTRIBUTION OF RESIDUAL STRESSES IN A BUTT WELD

45

The residual stress distribution in a spot-welded joint is very dc-pendent on the joint pattern or weld pattern used. The simplest caseto consider is the residual stress due to a single spot weld. Figure 30is a schematic representation of the distribution of residual strcssesin the area near a single spot weld. The components of stress of mostconcern are those in the radial direction and those in the circumfer-ential direction. The relation between the distance from the weldcenter and the radial-residual stress is shown by Curve I in the figure.Tensile stresses as high as the yield strength of the material mayexist in the weld zone. Outside the actual weld zone the tensile re-

sidual stress decreases as the distance frz..n the weld area is in-crepsed. Curve Z shows the distribution of the circumferential stress.Again, very high tensile stresses exist within the weld zone; however,outside the weld these stresses are compressive and again fall off asthe distance from the weld is increased. From Curve 2 it is apparentthat there is an extremely sharp stress gradient around the circum-ference of any spot weld where the stresses undergo a complete re-versal from very high tensile values to high compressive values.

The actual stress distributions in a spot weld in an area veryclose to the weld are not nearly as simple as shown in Figure 30.Very concentrated .st-:esses often exist in the heat-affected zone close"• the original interface of the sheets.

When several spot welds are considered instead of .just a singlespot, the resulting residual stress patterns are even more complex.An approximate distribution of the residual stress pattern produced bya series of spot welds can be obtained by the saperposition of the re-sidual stress distributions produced by e-ach weld as shown in thefigure. The interaction between the residual stresses accompanyingeach individual weld becomes significant when the distance betweenthe welds is short - probably at any distance less than four times thediameter of the weld.

The residual stresses left in resistanc-c spot welds can be alteredby changes in the welding schedule. Changes in heat input, heat pat-tern, or possible forging action that may be applied through the elec -

trodes are effective. Some information on the effect of such changes

in welding parameters on residual stresses has been obtained butthere are many corflicting aspects to this data.

Stress Effects. For many years there was a trend among en-gineers to discount the effect of residual stress, since it had beenprcven that the effect of residual stress is almost negligible when a

welded structure fails ir. a ductile manner. During the last several

46

a. Stress Components

1 ° I °

g ~I €

I C urve 1: c orCuv

.2 I

I

I r

r0

r

CI /**Curve 2: crgE

I,'

b. Relationships Between Radius From the Weld Center rand Stresses

FIGURE 30. DISTRIBUTION OF RESIDUAL STRESSES AROUND SPOT WELD

47

P

_____________________________________ 4;

years much information has been obtained on the effect of residualstress on brittle fracture in steel weldments. It has been found thatresidual stresses decrease the fracture strength of weldments onlywhen certain conditions are satisfied, but that the loss of strength canbe drastic when these conditions are satisfied. No systematic investi-gation has been made on the effects of residual stresses on fracturesin titanium-alloy weldments. The following discussions are based oninformation on steel weldments and the limited data on titanium-alloyweldments.

In general, the effect of residual stress is significant on fracturesthat take place at low applied stresses. Observations that have beenmade on various types of fracture are as follows:

(1) Dut.tite fracture. Ductile fracture occurs at high stressesafter general yielding. The effect of residual stress onfracture strength is negligible.

(2) B:ittle fracture. W-hen a notcn is located in areas wherehigh residual tensile stresses exist, brittle fracture caninitiate from the notch at a low applied stress and thenpropagate through the weldment. Extensive research hasbeen conducted during the last several years on the low-stress brittle fracture of steel weldments. No systematicinvestigations have been Ynade on the low-stress brittlefracture of titanium-alloy weldments. Some failures havebeen observed which ndicate that residual stresses mayhave caused premature failures in titanium-alloy weldments.

(3) Stress-corrosion cracking and hydrogen-induced cracking.Stress corrosion of titanium or titanium alloys can causecracking or degradation of properties under some combi-nations of time, temperature, stress, and environment.Stress-corr:sion cracking and hydrogen-induced crackingcan occur under low, applied stresses, even under no ap-plied stress. Residual welding tensile stresses promotethe cracking, while, residual compressive stresses sup-press the cracking.

(4) Fatigue fracture. The effect of residual stress on fatiguefracture is still a controversial subject. Many investi-gators have reported fatigue-test results which they claimwere affected by residual stresses. However, others be-lieve that the effect of residual stress on fatigue is notsignificant.

48

(5) Buckling failure. It is known that residual compressivestresses in the base-metal regions around welds may

decrease tie buckling strength of welded columns andplates.

Stress Relieving. There a number of reasons for reducing orrelieving residual stresses associated with welded joints. It is proba-

bly necessary to relieve residual stresses whenever a welded struc-ture is: (1) manufactured to close dimensional tolerances, (2) com-3lex and contains many stress risers, (3) subjected to dynamic leading,(4) subjected to low-temperature service, or (5) subjected to serviceconditions that might promote stress corrosion. The decision ofwhether or not to 't-'"a -.... •. c. anent andprevious experience.

Residual stresses can be relieved in two ways: (1) mechanicalstress-relieving treatments, or (2) thermal stress-relieving treat-ment. Stress relieving can be performed on a finished part or duringvarious stages of processing when dimensional control is a problem.

Occasionally, both treatments are used.

Mechanical stress-relieving treatments take a variety of forms.These include tensile . .: etching, roll planishing, and peening. With

any mechanical stress-relieving treatment, control of the process isdifficult. in addition, the complete removal of residual stresses bymechanical techniques is difficult to accomplish. Mechanical stress-relieving techniques are most effective in accomplishing a redistribu-tion of residual stresses in a single direction. Effective stress re-lieving by operations such as roil planishing requires that the weld

geometry be very consistent prior to the planishing operation.

Thermal stress-relieving treatments are commonly employed formany materials, including a number of titanium alloys. These treat-ments can be combined quite effectively with hot-sizing operations to

control both the existing residual stresses and to produce parts toclose dimensional tolerances. Thermal stress -relieving treatmentsproduce much more uniform changes in the residual stress patternsthan do mechanical stress-relieving treatments. For most titanium

alloys, a treatment between 1000 and 1450 F for a period of timeranging from one-half to several hours is required for stress reliev-ing. Possible interactions between a thermal stress-relieving treat-ment and other changes in a material that may affect its propertiesmust be anticipated. For example, age hardening will occur in the6A1-4V titanium alloy within the weld zone over a certain temperaturerange. If this age hardening is allowed to occur, it may reduce the

49

_ _ _ _ _ _

I

beneficial effects of stress relieving. A similar effect is noted vith

the Ti-13V-IlCr-3Al alloy, although for different reason.s. With this

alloy exposure to the normal stress-relieving temperature range will

result in a drastic loss of bend duc:tility in the weld zone; thus, it is

necessary to find other methods of relieving the residual stresses.

This has been done by combining mechanical and thermal treatments

to alter the residual stress patterns in the circumferential joints of

rocket motor cases (Ref. 1).

Residual stresses in resistance welds can be altered and to some

extent elinminated by either mechanical or thermal stress-relieving

treatments. The application of mechanical stress-relieving methods

to spot welds is difficult because of the complexity of the residual

stress patterns and the limitations generally imposed by joint con-

figurations. At best, mechanical techniques can probably only result

in a redistribution of the residual stress pattern and not the comrplete

elimination of residual stress. On the other hand, thermal stress re-

lieving can be used effectively to eliminate all residual stresses re-

sulting from resistance welding. It is difficult to see how such treat-

ments can be employed effectively though, unless the treatments are

conducted in vacuum furnaces. The major problem with methods of

thermal stress relief is that it would be almost impossible to prevent

some contamination of the surfaces of titanium components in the

overlap area characteristic of resistance -welded structures. Clean-

ing -fdter such a thermal stress-relief treatment would impose equally

severe probltxns.

P,_rhaps the most fruitful method of controlling residual stresses

in r'ýsisla.cce -,v'lded joints will be by the selection of suitable process

paraatr.:.,: rs.

INSPEC TIC,-

tMes-. joined components are inspected for two reasons. First, it

i:; often desirable or necessary to check changes in dimensions that

may have resulhed from welding. The visual and measurement-type

inspections perfcrmed for this purpcse may also include checks ofweld-joint pr)file, and measurements of the weld thickness. Second, t

various inspection procedures are used to insure that the joints pro-

duced are of satisfact,:ry quality. The most commonly used techniquesin this area include vi'ual, dye penetrant, and X-ray techniques.

Various tyles of leak tests are also used on components designed to

S- contain gas¢s ur fluids. • 7nfortunately, no suitable nondestructive in-

spection tecl anquc exista At r deýecti.g weld conta-mination of titanium

weldn-ents.

50

I

Use is being made of indications based on surface discoloration

during welding. However, the presence or absence of a discolored

surface is not a reliable method of detecting contamination of titaniumwelds with interstitial elements. Surface discoloration, when obtained

in welding titanium, is extremely important. Surface colors indicate

that the welding atmosphere was contaminated. On the other hand a

clean-weld and heat-affected-zone area does not necessarily indicate

clean welds. Titanium is so reactive that contaminants can penetrateto below the surface without discoloring the surface.

The ease with which inspection can be accomplished varies withdifferent joint geometries. Butt joints, T-joints, and corner joints

are generally much easier to inspect than joints involving overlapping

layers of material.

Inspection of resistance welds to insure adequate quality is diffi-

cult. X-ray techniques appear to be the only suitable nondestructiveinspection method. Even this method is subject to limitations in its

usefulness. Because of the difficulties associated with inspecting re-sistance welds, the economic necessity of not allowing a large numberof defective welds to get through processing, and the difficulty of re-pairing defective resistance welds considerable emphasis is being

placed on supplementing or supplanting postweld inspection procedureswith in-process controls.

SPECIFICATIONS

Most of the materials and processes used in titanium joining are

covered by some type of specification. The basic specifications are

generally MIL standards (Refs. 29, 30) or other applicable FederalGovernment specifications. However, the most pertinent and impor-tant facets of titanium-joining techrnology are often not covered bythese specifications. Therefore, most titanium fabricators have de-veloped company specifications, which are used in lieu of, or in the

absence of suitable Federal specifications (Refs. 31-33). These com-pany specifications a-e almost always more restrictive and definitive

than any comparable Government-type specification. This is probably

because the company specifications are generally written with a more

lirmned coverage in mind than is the case with many Government

specifications.

The available company specifications are not entirely adequate to

control the fabrication of all titanium products. However, existing

51

specifications form a firm foundation for the preparation of suitable

specifications for new applications.

The lack of an adequate inspection method for determining weldcontamination makes it necessary to place a high degree of relianceon process specifications for fusion-welding processes. Such speci-fications should spell out in some detail the requirements for preweldcleaning, and operations to prevent contamination.

Almost all resistance--welding specifications require certificationof the welding machine that will be used and establishment of a suitablewelding schedule prior to the actual start of welding operations. Mostspecifications then require that various types of test coupons be weldedprior to, during, and after any production welding run. Such proce-dures, while not foolproof, are the best available for use with existingtypeý of equipment and process control.

Applicable military specifications (Ref. 29) allow the weiding ofany titanium alloy that has satisfactorily passed tests designed to es-tablish that resistance welding does not harden the weld zone or reduce

weld ductility. The requirements state that the direct tension strengthof a spot weld must not be less than 25 per cent of the minimum shearstrength required when tested in an as-weided condition. It is alsorequired that any spot welds subjected to subsequent thermal eu:posureshall exhibit a sirr-ijar minimum tension strength after such thermal

exposure.

DEFECTS

The definition of joint defects is arbitrary, Although many yearsof experience have been gained with welding codes and specificationsthat either prohibit or allow certain features characterized as defects,very little of this experience is based on statistically bound engineer-ing data. As a result, features recognized as defects are generallylimited in accordance with very conservative practices. This ap-proach to defects has been quite successful in the past, but is of some

concern when dealing with many of the newer materials being used invarious types of fabrication. This concern is based on the belief thatthe removal of certain types of features classified a- nonallowable de-fects often results in more da.mage to the service;,bility of a structurethan the damage that potentially might have been done by allowing the

feature to remain. The reluctance of many welding tngineers to re-pair certain features is based on this feeling, not on a desire to make"the welding job easier.

52

~~-44. _ __ _

Typical arc-weld features that are sometimes classilied as defectsare shown in Figure 31.

FIGURE 31. FUSION-WELD DEFECTS

Not shown: (1) Arc strike,

(2) Discoloration, and

(3) Contamination.

The fabrication of defect-free welds is highly dependent on thequality requirements of applicable specifications and on the inspectionmethods that are used. For example, few welding codes or specifica-tions allow cracks in a weld. However, cracked welds can and do getinto service if inspection methods that will insure detecting all crackspresent in a weld are not required.

Characteristics described as defects in resistance welds are diffi-cult to assess. Defects in resistance welds are generally subdividedinto external and internal defects. With the exception of cracks thatare exposed to the exterior of the sheets and which are obviously unde-sirable, the remaining external defects are probably considered as

such because they are indicative that the wvelding conditions may nothave been exactly right. External defects in this category are sheetpreparation, surface pits. metal expulsion, tip pickup, and excessive

5_ _ 3-

indentation. With internal defects, cracks are obviously undesirali»e,

but there is very little evidence that porosity in minor amounts is

harmful to properties. The same is true of either insufficient o-" ex--

cessive penetration.

The only reliable way to determine what weld features are truly

defects is to evaluate the effects of such features in a test. program.

Such an evaluation must include tests that are representative of the

service conditions. Many defect-like weld features have no effect on

the static-tension properties of the weld. However, these same fea-

tures may be found to seriously degrade performance in a fatigue test.

With the knowledge currently available about the performance of

titaniun n-fusion weldments, a conservative engineering approach to de-

fects should be followed. Because of the prevalence of porosity in

titanium-fusion weldments, it would be desirable to determine more

realistically the extent to which porosity can be allowed, or develop

simpler means of minimizing porosity than those currentl% available.

Porosity. The prevalence of porosity problems in titanium

welding warrants special mention. A special report on this subject is

available (Ref. 34). The Summary from this report is repeated below:

"Porosity in fusion welds in titanium has been encountered to

some extent in all programs using this joining method. While mea-

sures to control cleanliness and to employ good welding techniqueshave successfully reduced the occurrence of porosity, specific identi-

fication of the various causes of porosity is still lacking.

"Some factors suspected of causing porosity in titanium welds are:

(1) Hydrogen. Many of the things, which when eliminatedreduced porosity, are sources of hydrogen.

(2) Cleanliness of Joint Area. Mechanical cleaning of edges

to be welded and adjacent surfaces reduces porosity and

improves uniformity of welds. Two factors shown to

increase porosity are fingerprints and handling with

dirty rags or lint-bearing gloves. Plasticizers dissolved

from rubber gloves by solvents, especially alcohol, have

been identified as a cause of porosity. 'Soapy' residue in

cloths used for wiping cleaned jo-int areas also has beenidentified as a cause of porosity.

54

(3) Contamination in Filler Wire. Surface inclusions workedinto the filler wire duiring drawing have been ident),ied asa major cause of porosity.

(4) Welding Procedures and Techniques. There is evidencethat some of the parameters associated with weldingprocedures also affect porosity. Many of these areinterrelated and the offending parameters are not wellidentified; however, improper technique in tack welding,nd wide joint gaps in fusion welding have been idi:.tifiedas causes of porosity. Other parameters that play a partin causing porosity are rates of heat input, rates of cool-ing, welding speeds, arc voltages, and rates of gas flow. "

Anyone encountering porosity problems should obtain this report as itcontains a good summary of published information on the subject.

Unpublished data (Ref. 35) generally confirm this summary andin addition, data showing the effects of edge preparation, pickling,preheat, and welding variables on porosity formation are available.

Porosity in titanium welds can be controlled if the procedures thathave been developed by the many investigations in the area arefollowed.

REPAIRS

Repair of weldrnents is not desirable. However, it is an almostinevitable occurrence in production operations. An important aspectof repair welding is determining what cý.used the defect which must berepaired. With titanium, this is important, not only for its feedbackvalue to minimize the need for subsequent repairs, but also to deter-mine a suitable repair-welding procedure.

Cracks, which occur rarely in titanium-fusion weldments, aregenerally the result of contaminati. i. from some external source. Forexample, copper from back-ups, hold-downs, and wire guide tubesmay get ir.to a weld if the equipment malfunctions during welding. Inorder to effect a successful repair, the material contaminating the ti-tanium must be removed first. Fusion welds that are contaminated asa result of poor shielding may require complete removal of the firstweld made and its replacement.

55

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Whe-nevter_ it ;.s th S"'MI sa1VCfxtre A-oes

used on the original weld should be used for the repair. When this isnot possible, it is common practice to use manual TIG welding for re-

pair operations. The same shielding precautions used in the originalwelding procedure should be followed for all exposed surfaces.

TIG fusion welds in thin sheet and electron-beam welds have beenrepaired simply by remelting the defecti% e zone of the original weld.

The same process and conditions were used for making the repairs.

Very little information is availabhz concerning the repair of de-fective spot welds. A number of the defects classified as external de-

fects can be repaired by very light machining of the external weld sur-faces. The repair of cracked resistance welds must be accomplishedby either a fusion-weld process or through use of a mechanical

fastener.

WELDING PROCESSES

Many welding processes can be used successfully on titanium

comnponents. These processes are described in the following sections.Included are discussions of the following processes:

(1) TIG welding

(Z) MIG welding

(3) Arc spot welding

(4) Electron-beam welding(5) Plasma-arc welding(6) Resistance sDot welding

(7) Roll spot welding(8) Seam welding

(9) Flash welding(10) High-frequency welding

(11) Brazing(12) Solid-state welding.

Not included are discussions of adhesive bonding, mechanical fasten-ing, and various other specific welding processes. Adhesive bonding

and mechanical fastening of titanium are being covered in other re-ports in this series being prepared for publication. Welding pro-

cesses omitted from this report are either not suitable for use ontitanium or are seldom used.

56

A listing of titaniuni alioys that are often considered for use inwelded structures and a relative weldability rating for these alloys

appears in Appendix B.

TIG WELDING

The T"G welding process is used extensively for joining titaniumalloys and many other high-quality materials. It is particularly suitedfor the joining of very thin materials, and is adaptable to manual,semiautomatic, or fully automatic operation. It can be used on almostan- thickness, but as the thickness increases above 0. 1 inch, otherfusion-welding processes offer important advantages.

In TIG welding, all of the heat required to melt the joint edges issupplied by an arc between a tungsten electrode in the welding torchand the workpiece. The arc and surrounding area are kept free of airby a flow of inert gas around the tungsten electrode. TIG welds can bemade with or without filler metal additions. For many applicationsonly the edges of the parts to be joined are melted. Sometimes addi-tional metal is added to the weld by using a filler wire. Filler wire isalways added when the joint is open or contains a specially preparedgroove. The addition of filler wire to closed, square butt joints in-

creases the tolerance of TIG welding for slight variations in the jointfitup. This can be quite important in welding titanium, since the metalis very fluid when melted.

Most TIG welding of titanium has been done in the flat welding po-sition. Other welding positions have been used to a limited extent.WVhen welding titanium in other positions, the changes in shielding-gas

behavior should be anticipated. Welds made in the horizontal positionwould be expected to be slightly more prone to porosity entrapmentthan welds made in other positions.

Equipment. Conventional TIG welding power supplies,torches, and control systems are used effectively in welding titanium.No significant changes in welding characteristics or -'\eld propertiesthat can be attributed to the use of any specific type of welding equip-ment have been reported. Most fabricators use conventional powersupplies having drooping volt-ampere characteristics. High-frequency

arc starting is used to avoid tungsten inclusions that are often foundwith touch starting techniques. The conventional TIG welding equip-

mnent selected for use must be supplemented with auxiliary shieldingdevices of the types described in earlier sections of this report.

57

-~ - ~ =

The• shielding chambers u f.r 11' tiianium can be ofseveral basic designs. Inert gases replace the air in the chbamber byevacuating and backfilling, by flow purging, or by collapsing thechamber and backfilling. Shielding chambers are used when weldingtitanium parts that cann-bt be protected satisfactorily in the open atrno-sphere. Precautions need to be taken to prevent leakage of air, water

vapor, and water into the chambers.

Titanium alloys also can be welded very successfully in air withthe right supplemental equipment. The inert gas flowing from a con-ventional TIG welding torch is generally not sufficient to protect ti-tanium during welding. Auxiliary trailing shields attached to the weld-ing torch, or auxiliary shielding devices built into the weld toolit-gafford the required protection. The importance of tooling to assist inweld shielding was discussed earlier in this report in the section"Shielding". Figure 32 shows one of the commonly used combinedtorch-trailing-shield arrangements. Such shitids are designed tosupply a uniform nonturbulent flow of inert gas over the weld as itcools behind the torch. It is much easier to insure good shieldingduring mechanized TIG welding than in marual op-rations: thereforemechanized welding operations are recommnended anc used whereverpossible in welding titanium assemblies.

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FIGURE 32. A COMBINAT'ON TORCH-TRAILING-SHIELDARRANGEMENT

58

Electrodes for TIG welding titanium and titanium alloys normallyare operated on straight-polarity direct current. The electrodes arealways ground ei+her lo a conical shape having a sharp point or to arounded point. A cone height of 1. 5 to 2. 0 times the electrode diame-ter has been used by one fabricator (Ref. 36). Thoriated-tungstenelectrodes are used by many fabricators (Refs. 21, 12, 36, 37). Tung-sten electrodes also are used, but experience shows that weld-metalcontamination by tungsten is less with the thoriaced-tungsten elec-trodes. Tungsten inclusions are of two kinds - globular tungstendrops and tungsten oxide flakes. These inclusions are minimized byusing proper welding current for the electrode size and by providinginert-gas shielding for the electrode until it cools to temperatures atwhich oxidation cannot occur. Chemical compositions of conventionalTIG welding electrodes are given in Table Ill (Ref. 38). The gap be-tween the rod ard metal is critical in gages less than 0. 006 inch; on0. 001 -inch-thick metal a gap of 0. 010 inch has been used (Ref. 39).

TABLE WI. CHEMICAL COMPOSITION OF ELECTRODE MATERIALS

FOR TIG WELDING (REF. 38)

Tungsten. Total Other Elements.AWS-ASTM Minimum. Thorium. Zircomum. Maximum.

Classification per cent per cent per cent per cent

EWT 99.5 .... 0.5

EWTh-1 98.5 0.8 to 1.2 -- 0.5

EWTh-2 97.5 1.7 to 2.2 -- 0.5

EWZr 99.1 -- 0.3 to 0.5 0.5

The equipment used to drive titanium welding wire in the TIG pro-cess should receive special attention. Filler-metal feed rates shouldbe as uniform as possible with both manual and machine wire feedingto prevent localized irregularities that may contribute to cracking(Ref. 10). Even the best quality welding wire can be contaninated inthis equipment if periodic checks are not made to be sure that oil isnot present in the drive system or guide components.

Materials. Commercially pure titarium arn many of its al-loys can be TIG welded readily. Commercially pure titanium is themost popular filler wire, although titanium-alloy filler metals areused for some applications. Titanium and titanium-alloy filler wires

I4- I.- - - -~ ~ -. 59

I

are available in continuous coils. However, cut and straightene,4 lengths of filler wire may be used instead of -ontinuous coils. Cut

lengths are easier to clean immediately prior to welding than coiledproducts. In manual TIG welding, sheared strips of a base-metalsheet are sometimes used as filler wire. On rare occasions, a simi-lar procedure is used in mechanized welding when a preplaced strip ofsheet or wire is inserted in the joint to serv-e as a filler metal. Careis recommended when using this procedure because potential contami-nation problems involved.

Porosity, contamination, and embrittlement have been experi-enced with all of the commonly used joint designs. These problems,however, normally are eliminated by following procedures that willensure cleanliness of the material, fille r wire, and welding fixturesand protection of the parts from contamination during welding. Pre-weld cleaning is essential to the successful welding of titanium alloys.

WELDING CONDITIONS

Welding conditions are dependent on material thickness, joint de-sign, the type of weld tooling being used, and whether manual or ma-chine welds are made. Also, for any given thickness and joint designvarious combinations of amperage, voltage, welding speed, and filler-wire input speed are satisfactory. As a result, no hard-and-fast rulescan be specified for welding conditions. Tables IV and V illustratetypical weldling conditions that have been used in the TIG welding oftitanium.

Welding conditions generally do not have to be adjusted radicallyto accommodate the various titanium alloys but are often adjusted as ameans of controlling weld porosity. Almost any change in a weldingcondition that will decrease the freezing rate of the we'd will producea decrease in porosity.

As in welding other materials, starting and runoff tabs are usedby Come fabricators (Refs. 12, 36). The starting and runoff tabs usu-ally are of the same material as the parent metal being welded and areplaced against the parent part at each end of the weld as shown in Fig-ure 33. The purpose of these tabs may be one or more of the following:

Starting tabs

(1) Initiate the arc(2) Establish a steady arc

(3) Allow time to adjust welding conditions(4) Observe irregularities in material or arc behavior

60

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Runoff tabs

(1) Extinguish the arc(2) Avoid crater formation within the part(3) Avoid the formation of crater cracks within the part

(4) Eliminate weld stops and resultant craters from theweldment.

Difficulties have been experienced with starting and runoff tabs. Un-less a good fit of the tabs to the plates to be welded is maintained,burnthrough can occur at the junction. To overcome this difficulty thearc is operated at a very low current on the starting tab and increasedto weld amperage as soon as the arc crosses the part (Ref. 40). Thissequence is reversed at the end of a weld.

Tack Welding. Tack welding is used to pre-position detailparts or subassemblies for final welding operations. Elaborate fix-turing often can be eliminated when tack v4elds are used to their fulladvantage. Various tack-welding procedures are used by titanium

fabricators but good cleaning practices and adequate shielding are pro-vided to prevent contamination of the welds. Contamination or cracksdeveloped in tack welds can be transferred to the finish weld. Oneprocedure is to perform tack welding in such a way that the finishedweld never crosses over a previous tack weld. To accomplish this,

63

J sufficient filler metal is used in tack welding to completely fill the jointat a particular location. The final weld beads are blended into each

end of the tack welds (Ref. 9).

Properties. A large number of joint properties have been de-

termined for TIG welds in titanium alloys of interest. The properties

measured by static tension, notch tension, bend and crack suscepti-

bility tests compare very favorably with parent-metal properties.

Axial-tension fatigue tests generally show a significant decrease in

properties wnen compared with similar parent-metal specimens.

Fracture-toughness test results on fusion weldments are not easily in-

terpreted. Depending on the evaluation criteria selected, the data

from these tests are indicative of fair to good performance. Weldment

thermal-stability trends in the 6AI-4V and 8A1-lMo- 1V alloys appear

to parallel parent-metal trends.

"TIG weldments have been used in several structural test compo-

nents. The behavior of weldments in such tests is by tar the best

evaluation of joint properties. Reported behavior to date is encourag-

ing with few exceptions. Delayed cracking of weldments has been ob-

served in some instances. In some cases, the reasons have been ap-

parent and solutions obvious. Where the cause of such cracking is not

known, a strong effort to find the cause is indicated.

Sources of detailed information on properties of TIG welded ti-

tanium and titanium alloys are given in Table VI.

Applications for TIG Welding Titanium Alloys. TIG welding

is among the most widely used joining processes for titanium and ti-

tanium alloys. Some of the typical products manufactured by TIG

welding are described below.

Chemical Processing Equipment. Commercially pure ti-

tanium was the preferred material for several large heat-exchanger

coils for use in a calcium hypochiorite plant (Ref. 21). The coil sub-assemblies required the butt-welding of titanium tubing and pipe into

lengths necessary for each complete coil as shown in Figure 34

(Ref. 21). Inlet, outlet, and dummy connections, angle supports, and

othe:. attachments also were made. All welded connections were made

using manual TIG welding techniques. Since numerous joint designs

and part cwrifigurations had to be welded, it was necessary to use sev-

eral inert-gas-shielding techniques to make the required welds suc-

cessfully. Features of the fabricating and shielding methods aredesc ribed below.

64

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The iabrication procedure KAs desgned;% to_ perit th axinumber of welds to be visually inspected, both inside and out. To per-mit internal inspection of the weld root, strz ight lengths of pipe werewelded. Full root penetration was mandatory to avoid internal stressraisers and no undercut was permitted on either side of the joint.Weld-face reinforcement was kept to a minimum so that welds couldpass through bending rolls. (The first coil bent revealed that even veryslight reinforcement on the outside had to be dressed down to below amaximum height of 1/32 inch to avoid buckling of the pipe wall adjacentto the weld and to avoid damage to the bending rolls. )

Figure 35 shows such a butt wveld being made in pipe out of posi-tion in the open atmosphere (Ref. 21). N"one of the welds failed duringbending to a 2-1/2-foot radius. This radius was very near the bendradius of the un'velded pipe. B,.nding was done cold and the tube wasnot fi_led. After bcnding, welds were air leak tested and hydrostati-cally tested at 225-pounds pressure. Figure 36 shows some compo-nents that were welded in a controlled atmosphere box (Ref. 21). Theelbows were fabricated to the maximum bend that permitted goedvisual inspection of the root side of the butt weld connecting the elbv¢to the coil. Angles also were fabricated from 1/4-inch by 2-1/2-inch-

thick titanium bars by inside-fillet and outside-corner welding. Bothwelds were continuous. This welding resulted in considerable distor-tion but the angles were cold strightened after welding. Figure 37 il-lustrates the welded angle and attachment to the pipe coil.

Leak tests and visual inspection were selected in preference toX-ray, magnetic -particle, and ultrasonic examination for severalreasons. These processes were considered more costly and would notprovide useful information conc-rnina root-side contami.zation or em-brittlement. The back-side of welds was inspected visually using thebore inspection instrumnent to determine the physical condition of theweld root after making the root pass and again after making the coverpass. Penetration, undercut, weld concavity, and adequate back-sideshielding were inspected. Only two of approximately 275 welds were

cut out because of the loss of the back-side shielding when a workmantripped over the supply host and when a welder inadvertently ran out of

cgas from his purging bot.se.

Figure 38 shows the underbead side of a typical butt weld in pipeas seen through the bore-inspection instrument (Ref. 21). The great-est difficulty in using the bore-inspection instrument was to determinewhether the bead was concave or convex. The difficulty was entirely

one of depth perception through the optics and determining whether theweld surfaces were projecting inward or outward.

66

IFIGURPE 34. CALCIUM. HYPOCHLORITE PLANT HEAT-EXCHAN'GER COILS MADE FROMCOMIMERCIALLY PURE TITAINIUM. (REF. 21)

FIGURE 35. OUT-OF-IOSITION BUTT WELD BEING MADE IN' THE OPE2; ATMOSPHERE USIN-GTORCH SHIELDING COMBINED) WITH SUPPLEMENTARY SHIELDIN-G EQUIPMENT(REF. 2 1)

67

FiGURE 36. HEAT-EXCHANGER SUBASSEMBLIES WELDED 1N A CONTROLLEDATMOSPHERE CHAMBER (RFF. 21)

- .

FIGURE 37. DETAIL OF THE MECHANICAL SUPPORT SHOWLNG THAT THE NU'SARE TACK WELDED (REF. 21)

This is a view of the intermediate point in the coil.

68

After bending, two major areas of cracks originating from discon-tinuities on the inside of the pipe wall in the first coil were found visu-ally. The cracls were not related to welding since the nearest weldwas about 25 feet away. Air testj were used instead of water to detect

leaks.

Butt welds were inspected differently from the other welds. Theprocedure was to make the root pass leaving approximately 1 inch ofthe root on the 9 to 10 o'clock side open, the side that would not be intension when passing through the pipe bending rolls. The inside of theroot pass was inspected using a small inspection instrument as shownin Figure 39 (Ref. 21). Next, the cover pass was made except at theclosure area and a second bore inspection was made. The second in-spection was primarily to ensure that there had been no inside purge_aLure when making the cover pass. Following this last bore inspec-tion. the root side purge gas pressure was dropped and the open lengthof weld was closed. There were no failures in this area from bending.

Rings. In work aimed at developing high-strength, light-weight pressure vessels, the Ti-3Ai-13V-IlGr alloy was studied ex-tensively because of its inlerent high strength and potential of exceed-ing 1, 000, 000 inches strength-to-density ratio and possibly i eaching11 200, 000 inches (Ref. 50). The main problems involved the develop-ment of fabricating techniques to achieve consistently high strengthlevels along with the most economical use of material. Welding de-velopment was aimed primarily at obtaining good weld quality andfracture toughness. During development work 40-inch-diameter rings

were prepared from 0. 250-inch-thick plate, by TIG welding (Ref. 13).The weld joint developed for welding 1/4 by 8 by 10-inch panels was adouble vee-grcove jo ', ccn-,pleted in three-passes. The first passwas a fusion pass, followed by a filler pass from the outside, and thena filler pass from the inside. Welding conditions were not reported,but radiographic weld quality appeared satisfactory.

Roll-forged rings of Ti-6A1-6V-2Sn alloy also have been evaluatedfor weldability using the TIG process, by making single-pass circum-ferential machine butt welds, using commercially pure titanium ;illermetal. A segmented, expanding internal copper back-up of the typeshown in Figure 40 together with external stainless steel hold-downbands were used tRef. 13). Sound welds were obtained using normalwelding conditions. A small amount of porosity was the only observedweld defect. In other work, higher mechanical properties were devel-oped by the 6AI-6V-ZSn alloy welded with commercially pure titaniumwelding filler than compar.-ble welds in the 6A1-4V alloy using thesame filler metal (Ref. 51). A wider range oi aging temperatures for

69

_____ ____ ____ ____ _ _617

FIGURE 38. PHOTOGRAPH TAKEN' THRO)UGH A BOR ES-COPE OF A TYPICALWELD ROOT (REF. 21)

FIGURE 39. i1SP&..TION OF THE ROOT PASS OF THE BUTT WELDSHOWN IN FIGURE 38 (REF. 21)

70

FIGURE 40. SEGMEMTED WELDING FIXTURE WITH SOLID COPPER BAC K-UP SHOESIMOUNTED ON POSITIONER (REF. 13)

71

6A1-6V-ZSn alloy weldments has been shown to develop parent-metalyield strength of 130, 000 or better. Welding techniques used onMinuteman were designed to produce a weld with lower strength, butgreater ductility than the parent metal. The lower strength is com-pensated by thickened material at the weld so as to place the weld atlower stress than the parent metal. A stress-relief heat treatment isperformed after welding.

No significant improvement in quality or fracture toughness wasobserved with electron-beam welds as compared with TIG welds(Ref. 13).

Space Vehicles. The inner shell of the Mercury capsuleshown in Figure 41 is basically a pressure %essel consisting of a cone-shaped side wall with a large spherical pressure bulkheae )n one endand a small pressure bulkhead on the other (Ref. 52). The side walland the large bulkhead are both made of two thicknesses of 0. 010-inchcommercially pure titanium. The inner thickness is smooth, and theouter one is stamped with a pattern of strengthening beads.

Because of size limitations on the available titanium sheet, it wasnecessary to make each layer of the large bulkhead from three pieceswelded together, and each of the sidewall cones from eight pieces.Each ef the sidewall cones was fitted one inside the other so that themating surfaces were in intimate contact all over. Further, wrinklesthat might interfere with resistancc-seam welding were prohibited sothe forming operation is critical. A special machine trims the partsto size with a Z-1/2-inch high-speed steel saw blade. Speed was210 rpm, and feed wa3 8 ipm. This combinatiorn produced a smoothedge that did not require draw filing or hand fitting for welding.

Welding the Mercury capsule starts by joining the eight segmentsof the smooth inner conical skins by TIG welding without filler metal.To make a good joint with this technique, the 0. 0-10-inch titaniumsheets must be spaced with a maximum gap of 0. 004 inch. The lengthof each weld on the inner skin is about 4 feet: on the outer skin about

6 feet. The fixturing fer this operation as shown in Figure 42, in-cludes a conical support for the parts and a row of segmented clampson each side'of the joint (Ref. 52). The clamps hold the parts in pre-cise adignment and also serve as a chil' bar. To hold the propershape, the panels are strapped down against the conical supportingfixture during each weld. Then, as additional panels are added to theassembly, each one in turn occupies the same relative area on thecontour of the tool. The spherical skin assemblies are welded inmuch tht: same manner, but their shape causes an added complication.

72

L- .~

at A

FIGURE 41. MERCURY SPACE CAPSULE (REF. 52)

Astronauts were checked out on instruments in thisspace capsule at the fabricator's plant. Outer shell

is made of Rene 41 shingles. Inside is fiberglass in-sulation and the double-wall inner shell is made of

0. 010-inch titanium.

FIGURE 42. FIXTURE HOLDS FIRST TWOPANELS OF OUTER CONICAL

SKIN FOR TIG WELDING

(REF. 52)

Straps keep part tight against

contour of fixture.

73

They are made in three sections, a center piece and two pieces, sothat the joint forms a curved path about 6 feet long. The fixture for

X• this operation as shown in Figure 43, rotates the whole part so thatthe joint to be welded moves past a stationary torch, just the oppositeof the setup for welding the cones. In both operations, however, thewelding speed is 7 ipm.

•PP

FIGURE 43. ROTATING FIXTURE MOVES THE WORK PASTSTATIONARY TIG TORCH AT 7 IPM TO JOINTWO SECTIONS OF SPHERICAL BULKHEAD(REF. 52). SEGMENTED FINGERS HOLDEDGES OF JOINT iN ALIGNMENT

Aircraft Wing Leading Edge. The Ti-5,I-Z. 5Sn alloy isreadily weldable if atmospheric contamination is avoided. The A-5Vigilante wing leading edge shown in Figure 44 is fabricated from thisalloy using manual .hd mechanized -'rG welding techniques (Ref. 53).Commcr,.ially pure titr.n'un filler metal is used.

Figure 43 shows the ieating-edge section and illustrates severaltypes of weld-joint deaigns established to permit fabrication of thinparts. rhese joint designs include a simple square-butt joint,

-74

-- I . . . . . . . . . i l l l l l l l I l l l I I I I 1 l . .] [ ] •] . . - -• . . .

Becam

Lower skin

L e skin Sp(

Closeout

FIGURE 44. VIGiLANTE WING LEADING EDGE (REF. 5ý3)

Several welds are needed to assemble zhe boundary layercontrol wing section. Subsequent stress relieving is carriedout in vacuum to prevent contamination of the structure byhalogeps.

H--

1 to

FIGURE 45. TYPICAL CROSS SECTION OF WELDED TITANIUM

LEADING EDGE (REF. 53)

75

4

Fiatire 4(a a qniiare-hbitt joint having an inteisral back-up- Figure 46b;

and an arc-seam lap joint, Figure 46c (Ref. 2).

a. Simple Butt Weld b Lap Butt Weld Fillet

TSArc -Seam Lap

"FIGURE 46. WING LEADING-EDGE JOINT DESIGNS (REF. 21

The arc-seam lap joint originally involved melting completely

through the skin member with the arc and fusing it to the edge of tile

rib, as shown in Figure 47 (Refs. 2, 53). Early assemblies were suc-

cessfully welded in this manner, but the joint carried the constantdanger of being ruined if the welding electrode was misaligned with thehidden web. Because of the alignment problem, the sheet metal webwas redesigned into a flanged I-beam. The wide flange provided con-

siderable latitude for aligning the electrode. Initial welding tests in-dicated that arc-seam lap welds could be made without undue difficulty.

Water-cooled copper chill bars were used to control the width of thetop bead and enough curreA,t was fed into thie arc to melt completelythrough the top skin and into the I-beam flange. It was an engineering

requirement that the fusion zone between the skin and the flange be at

least 0. 18 inch wide. Trouble was encountered when the welding cur-

rent was increased to obtain the 0. 18-inch width. Good arc behavior

at

FIGURE 47. ARC-SEAM TEE WELD-JOINT DESIGN

(REFS. 2, 53)

76

east l evcrdi inches of weld, and then the arc-voltage-

controlled welding head would suddenly drive the welding electrodedown into the puddle. Careful observation of this runaway welding-head action revealed that just as the electrode dove into the puddle,the puddle itself seemed to get much wider and the bottom of it seemedto drop. A groove was machined on the top side of the skin to reducethe current.input necessary to get the proper width of fusion at theinterface. This change did make it easier to melt through the skin,but did not reduce the arc problems. Additional tests were made todetermine the gap that could be tolerated between the skin and theI-beam flange and still get an acceptable weld. It was found that thecurrent neeaed to melt through the skin into the flange was actuallymuch lhss when the skin was off the flange than when it was down tight.It was also found that the amount of gap present between the skin andthe flange could vary considerably, once a few thousandths of an inchgap existed, without changing the current requirements significantly.Next, tests were made with the skin thickness reduced by means of agroove on the bottom side of the skin, against the I-beam flange. Thisprovided a built-in gap of about one-half the thickness of the skin. Thegroove was made 0. 18 inch wide to match the fusion-zone width re-qui:'ement. The arc readily melted away the half thickness of the skinand actually formed a hole through the skin. The arc then went ondown and impinged on the flange, melting its surface. As the weldingoperation proceeded along the joint, the arc melted the skin ahead ofit, the molten metal flowed around the sides of the hole, and cametogether again at the back where it joined with metal from the flangethat had been melted as the arc passed along the seam.

in production operations, holes are drilled completely through theskin from the groove bottom at about 10-inch intervals. These holesprovide lineup cues on the top, visible portion of the skin during fitupin the weld tool. Tests have shown that the welding elect-rode can varyas much as 0. 030 inch from the centerline of the groove without losingfusion on the sidewall farther away. After the parts are fitted up,manual tack welds are made through the holes to anchor the skin tothe flange and keep it from creeping and crawling during the mainwelding operation. The machine weld is then made and proceeds rightover the tack welds. A second pass is made to add filler wire and fillup the concavity left from the first pass.

Structural Shapes. The equipment shown in Figures 48through 51 is used for accurate sine welding of aircraft ribs at highspeeds (Ref. 54). The ribs require the welding of thin titanium cor-rugated sheets at right angles to rib stiffeners on both ends. Becauseof the difficulty in following the long continuous series of ridges and

77VIEW

FIGURE 45. GE.NEAL VITEW OF THE SINE-W'AVE WELDING MACHINE (REF. 54)

FIGURE 49. WELDING OF THiN COR-

RUGATED T'I rANIUM

SHEET (REF. 54)

*78

_ __

i I I-- - - . -- - i - - -

FIGURE 50. SINE-WAVE WELDIN'G STATION AREA (REF. 54)

Adjustments aze being made to the argon shieldingbox whihc follows the welding head.

FIGURE 5L. COMIPLETED RIB FOR THE AMERICAN RS-770 AIRCRAFT (REF. 54)

79

grooves in extremely thin members, manual control of the weld torchS;° •.... cc ,l-q,,-;nI rne•irhnu c have hpen developed to make sine-

Swave shaped welds. The sine-wave welding machine can deal with20-foot lengths and can weld at the rate Jf 30 in. !min. Titanium inthicknesses from 0. 008 to 0. 125 inch has been welded on the machine.

This welding sciup is operated with two tables so that fixturingcan be carried out on one while the ribs and beams are being weldedon the other. Since each weld fixture has provisions for tracingtemplate, the concept eliminates the need for indexing the entirelength.

A trace mechanism works off a template guide to follow the sine-

wave weld pattern. The welding torch is led through its path by amagnetic tracing system (Refs. 54, 55). The system includes a stylusthat clings to the template by magnetic-flux attraction. Only rollingaction exists between the stylus and the template. Since no pressureis applied on the stylus, hardened templates are not needed. Con-struction of the beam and carriage assf .nbly is such that the torch tipcenter can track the seam center within ±0. 002 inch. This accuracycan be maintained over the full weld length in any direction.

By means of jog buttons that act on X and Y motions the operatorbrings the tracer to its starting point on the template. The tracer isthen set for automatic operation. The welding torch is positioned overits starting point on the weld seam by means of micrometer adjust-ment. Then the wire feeder is positioned properly. A small movingboxlike shield measuring 3-1/2 by 7 in. is linked to the welding headand moves close behind it to shield the weld. The end result of thesystem combines high production rates with higher than normal use of

both the machine and the weld tec-hnician's time (Ref. 55). Each tablefixture has provisions for a tracing template. For this reason, thereis no need to index the entire length of a weld path.

Special Products. Weldments designed specifically fortesting purposes also often provide useful information on welding pro-cedures and properties. The Navy t-xplosive Bulge Test Specimenmay be included in this classification. During work to develop finalwelding conditions for fabricating bulge test specimens, it variety of

joint designs and welding conditions were investigated (Ref. 56); theseare illustrated in Tables VII and VIII. Properties obtained are re-ported in Table IX.

80

k

TABLE VII. VARIATIONS OF A MODIFIED DOUBLE-VEE-JOINT DESIGN USED FOR EXPERIMENTAL

TIG WELDMENTS AND FOR A 2 x 30 x 30-IN7H FINAL PLATE WELDMENT ON 2-INCH-

THICK COMMERCIALLY PURE TITANIUM PLATE (REF. 56)

--f,~ ' "hick •)

Weldment Indicated Angle or Dimension IIdentification Land (x). in. (y). in. Angle (a), deg- Angle (b), deg Gap (s), in.-

1 (1:xperimental) 0.100 1/4 45 20 Butt

2 (Experimental) 0. 100 1/4 45 20 Butt

3 (Experin. ntal) 5/16 1/4 45 15 Butt

4 (Experimental) 1/2 1/4 30 15 0.060"

5 (Expcrimental) 1/2 1/4 45 15 0.070"

Final weldnient 3/1 3/16 30 15 Butt

(2 x 30 x 30 in.)

81

- ' 0

QD to .f) a; V

C.) C-3 V.)ON 4i C-)

Cl)D

14 ~ ~ OD to 'I

ILC4 U. 0. _4C).4 '15 C.)

0D to CDD Q

030

La 0

,4 CD CDcl1 - -4 1 0 Lo 0. D C

.* m2

-03 0 o0

z ~ L C ~ C. .

- 1 4 C3 d5 CD

z. V ) 0C 4 C'.)

00

C- t- In C; C - 1

- .4 0 -LO

- 0a

-, D)) 03 CIA 1)85

F -0

0~ C D 9cz

CL 00 0

CCI

0 En3u. 'D

OD C> 4 r

Slk-

C2 -0 ct-C

-> .. 1 -

82

I

TABLE IX. BASE METAL AND WELD METAL TENSILE AND COMPRESSION TEST RESULTS ONCOMMERCIALLY PURE 2-INCII-TIIICK PLATE TIG WELDMENTS - WELDED WITH

CC.MMERCIALLY PURE TITANIUM FILLER WIRE(REF. 4-4)

YS. Elongat:on.Sample 0. 21o Offset. TS. RA. per c•'t ILucaitiuo ksi ksi "o 2 ii J

Tensil Tests

Base Metal 77.3 9c 8 45 24

(Weldment 1)Weld 1 69.3 16.5.0Weld 2 73.3 90.7 37 7

Wcld 3 -1G. (; 4-1.S S 3

Weld 4 64.C 101.8 14 7WLid 73.3 9,2.1 37 17

Spnec. Mm. 70.0 80.0

(RS-70 Grade)

Compression Tests

Base Metal 64. 2(Weldnment 1)

Weld 1 73.2

W-.1d 2 u!..5

Weld 3 G9.5

Weld 4 82.5

Wold 5 79.2

I8IV

I

MIG WPvELDING

MIG w,-d:' - is a process that can provide high deposition ratesand ease in ,welaing in the "out-of-fiat position". The process is being

A deveioped for joining titanium alloys and has been used to a somewhatlesser degree than TIG welding for actual production and prototypecomponents. MIG welding can be manual, semiautomatic, or fullyautomatic. MIG welding is particularly well suited for the joining ofthicker sections of titanium. The process is very economical for thistype of work because high weld finishing rates are obtainable. How-ever, MIG welding also can be used on light gage thicknesses.

In MIG welding, the heat required to melt the joint edges is sup-plied by an arc between the filler wire and the workpiece. The fillerwire replaces the tangsten electrode used in TIG welding. The fillerwire, there.fare, is designated as the electrode in MIG welding as wasthe tungsten electrode in TIG welding. The MIG welding filler wirealso is called "electrode wire". "consumable electrode", "consumableeIectrode wire", "filler metal", and "filter wire". For welding of ti-

1: .ium, the consumable electrode is either commercially pure titaniumwire or a titanium-alloy wire. The arc and surrounding area is keptfree of air by a flow of inert gas around the electrode, as is the case inTIG welding. All of the metal added to the weld joint is supplied by theconsumable electrode. This mete-I is transferred from the electrode tothe workpiece as fine droplets, a metal spray, or by short-circuittransfer. The metal being transferred across the arc may be exposedto much higher temperatures than if it were just being melted. Thecombination of very high temperatures and fine particle sizes repre-sents a set of coz.ditions ideal for the contamination of titanium.Therefore, in MIG welding, it. is extremely important that the arc areabe completely protected from exposure to any gases other than theinert gases.

MIG welding of titanium is normally done in the flat wr'ding posi-tion. However, when required other -'-elding positions ca -e used.For exampie, the Navy has developed suitable out-of-posi.. 'I weldingtechniques that could be applied to the fabrication of titanium hullstructures. A chcck should always be made before MIG welding 'ita-nium in any position to insure that adequate gas shielding is being ob-tained. In general, good shielding is more difficult to provide whenwelding in positions other than the flat position.

Equipment. Conv:ýntir.-al MIG welding power supplies,torches, and control systems a; e used effectively in welding titanium.The nature of MIG welding makes this process zo-newhat more

84

sensitive to changes in welding equipment characteri-tics than is thecase for TIG welding. The limited published information on MIGwelding (Refs. 1,6,57-59) indicates that constant potential powersources are being used with various types of constant wire feeders.Conventional MIG welding water-cooled torches are modified to providethe necessary supplemental gas shielding needed for titanium. Al-though MIG welding has been conducted in vacuum-purged weld cham-bers and in the open atmosphere, it is likely that most applications ofthis process will be set up in dir. Typical MIG welding equipment ar-rangements are shown in Figures 52 and 53 (Refs. 7, 20).

For in-air welding with the MIG process, supplemental shieldingdevices described earlier should be employed. Trailing shields de-signed for MIG welding are usually considerably longe: than those usedin TIG welding. This is to insure good protection for the larger vol-umes of material that are heated during MIG welding and as a resultcool more slowly.

Direct-current reverse polarity is normally used in MIG weldingof titanium.

Wire-Feeding Equipment. For economic reasons MIGwelding equipmn--t should be kept in proper operating condition at alltimes. The most common causes of downtime are found in the wire-feed system. A typical wire-drive unit for constant-potential weldingis shown in Figure 54. For feeding filler wire, a spool of wire isplaced on a spindle threaded through a straightening device and into thegrip of wire-feed rolls. From the rolls the wire is pushed through aflexible wire-feed cable through the gun and into the arc. Hoses andplumbing to supply the gun with shieldiA.g gas and cooling water, ifused, are included.

The only function of thc wire feeder is to move wire and shieldinggas to the arc in such a manner as to provide a sound porosity-freeweld deposit. It is up to the operator to move the gun and the arcalong the seam to distribute the weld metal properly.

In a correctly designed wire-drive system, the wire is confinedlaterally so that it can move only in tie desired direction. If the drivemotor has sufficient power, the wire will move smoothly from spool togun.

Often there are signals of pending wire-feeding failures. An alertoperator becomes aware that the wire speed is varying, which is usu-ally the signal that something is going to happen. Before a complete

85

sto1

f eec__ - ~60):

FIGURE 5'2. MIG WELDING-EQUIPMENT ARRANGEMENT FOR WELDING IN TH~E OPENATMOSPHERE (REF. 7)

Fronm clamping bars are removed.

FIGURE .53. MIC. WELDING ARRLANGE-

MEENT IN A CONTROLLEDATMOSPHERE WELDING

CHiA: IBER (REF. 20)

86

speed

Wire food cable andpower hoses

FIGURE 54. (REF. 60)

stoppage occurs, a quick step-by-step inspection of the equipment willusually locate the trouble. Precautions that should be taken with wire-feeding apparatus are well known and are reviewed below (Refs. 5-7,60):

(1) Check the wire on the spool or coil. If it is not wrappedsnugly and if loops have slipped down over the wire as itis drawn off the spool, the effect is the same as pullingthe wire through a knot. This situation can occur if thespool is mounted horizontally and the friction device al-lows it to coast when the arc is stopped. When wire isfed from a barrel, rolling the barrel will also cause thewire to tangle. The effect of an entanglement is usuailygradual, but it can eventually stop the movement of wireentirely.

(2) Check the adjustment of the wire-straightening rolls.Very little bending is required to remove the "cast"from the wire, and excessive bending as shown in Figure 55will give At an opposite cast. This increases the load on thedrive motor and causes overheating.

W~nsP• ,rolls!

WWirejollsspool

Cwedc"No Cost' "Cast in ReverseDiection"


87

-mIS~

(3) Check the distance from the point where the wire leavesthe feed rolls to where it enters the wire-feed cable, see"Figure 56. This is possibly the most critical link in thewhole system because the wire is unsupported and is alsosubjected to maximum thrust. If this distance is adjust-able make sure the unsupported wire is as short as possible.If it ,is not adjustabl1e, make sure the various parts re inperfect condition; parts showing any wear should be replaced.

( length of wire


(4) Make sure the wire enters at the proper location on thedrive rolls. If it approaches the rolls at an angle, ittends to climb out of the groove. Then the rolls tend toseparate, loosening traction on the wire and allowing itto slip, Figure 57.

M X


(5) Make sure the drive-roll clamping pressure is as recom-mended by the manufacturer. Too light a pressure willallow slippage; and too heavy will flatten the wire to the

point where it will not go through the contact tube in thegun, Figure 58.

88

t-'


(6) Make sure the wire-feed cable is clean and free of kinks.Steel welding wires are usually copper stained, and thecopper tends to flake as it passes through the drive rolls,especially knurled drive rolls. Some ol the flakes arethen scraped off inside the wire-feed cable, Figure 59.

Dirt flakes and ChipsExterior wrop pocked in tight

( weliqwr

C#*1Ioterior wrapLongitudinal layer


If the wire-feed cable is not cleaned out often enough,dirt, copper flakes, or other foreign material can ac-cumulate and jam the wire so tight that it cannot be movedeither way, even with tools. However, the gun and cablecan usually be cleaned out (with the wire removed) byplacing an air-hose nozzle on the exit end of the contacttube and blowing the chips out. When the wire-feed cableis not free of kinks, a condition known as "wire whip" canoccur (Ref. 57). This tervn describes a condition whenthe electrode wire upon emerging from the contact tube,surges erraticaily teward the joiat faces. An analysis ofone equipment setup revealed that the wire, after leavingthe straighteners, had passed through one 90-deg turnand two 180-deg turns before entry into the welding gun.This series of turns induced -i irregular curvature inthe wire that eventually resulted in wire whip. Theproblem was alleviated by mechanically supporting the

89

_ _ _ _ . 4 tE

I

wire-carrying cable from an overhead roller device.Figures 60 and 61 illusirate hlu -hange -ma•de to ovcr,come the wire-whip problem. It is a good general ruleto clean the cable every time a new spool of wire is in-stalled, at least until a cleaning program based on ex-perience is established.

(7) Make sure the correct wire-feed cable and/or liner forthe job is used. A cable with too small a bore willcause excess friction when bent, and too large a borewill let the wire deflect laterally and possibly collapse.

The first and final test for a wire-feed system is the ease of wiremovement. With drive-roll clamping pressure removed, and with thehoses and cables relatively straight, the wire should be free to movein either direction without too much effort.

MIG Gun. Although the gun or torch is the last link in thewire-feed chain, it usually does not cause gradual failure of wire feedas the others do. Instead, its function and its possible failings aremore concerned with electric power and shielding gas.

One of its functions is to transfer the welding power to the wire,preferably at the exit end of the contact tube. Its other major functionis to direct a gas shield over the weld zone so as to exclude the adja-cent atmosphere, which would otherwise cause porosity in the com-pleted weld.

The gun is without question the most abused part of the system,and yet, it absolutely must be kept in good condition to produce goodwelds. Bent. worn, or broken parts should be replaced.

Contact Tube. Particular attention should be givento the contact tube. These tubes are usually made of copper or somespecial copper alloy, and they are subject to a number of ills. Theybecome spattered, they wear out. and they are occasionally meltedwhen the wire burns back to the tip as a result of wire-feed failure.

Burn backs are generally caused by arcing in the contact tube."This makes the wire stick, and then the open-circuit voltage burnsthe wire back to the tube.

Worn contact tubes contribute to burn backs because, as the boresize increases, the transfer of electric power to the wire becomes

90

9- 1

-. -. 7- -~ Z

FIGURE 60O. LUG WELDING SETUP SHOWS SHARP BEN;DS IN WIRE-FEED CABLE (REF. 5,6)

F"IGURE 61. HOSE-AND -CABLE SUPPORT ARRAIKGEMENT EMPLOYED TO ELMINATEWIRE WHIP DURING MIG WELDING (REF. 5, 6),

914

erratic. For this reason, reaming out the bores with'l ta-t-orch tipcleaners is not recommended.

Burn backs are not too much of a problem with CO 2 shielding gas

used with steel because of the short arc length per volt. When welding

titanium, inert gases can amplify the burn-back problem. In arc-spotwelding applications where argon or argon mixtures are necessary,

the burn-back problem can be handled very well with burn-back timers.

Shielding. Gas coverage, the second function of the

gun, is controlled by its nozzle, which is designed to produce a satis-factory gas-flow pattern. When weld spatter builds up, the shape of

the gas pattern may change, and if not corrected soon enough will

cause poor welds. The proper rate of gas flow will normally produce

a laminar flow at the nozzle tip. The flow rate is not critical but too

low a rate will not supply enough gas to do the job and too high a ratewill cause turbulence, which brings air into the gas shield and con-

taminates it.

Gas leaks or cooiing- .%ater leaks can also cause porosity in tita-nium welds. Bending, plugging or mis-installation of parts should be

corrected.

Materials. A limited number of titanium alloys have been

welded with the MIG process. The alloys that have been MIG weldedto date include:

* Commercially pure titanium (Ref. 5)

* Ti-5A1-2. 5Sn (Ref. 5)

* Ti-3A1-13V-1lCr

* Ti-4A1-4V (CP titanium filler wire) (Ref. 9)

* Ti-6AI-4V (CP titanium and Ti-6AI-4V filler wire)

(R'-fs. 5, 6)* Ti-7AI-ZC'O-lTa (similar or lower aluminum content

filler wire).

It is expected that the MIG process will be adapted for welding other

a titanium alloys in the not-too-distant future.

The most important material in MIG welding is the welding elec-

trode or filler wire Commercially pure titanium or titanium alloy

filler wires that match the base-metals composition are normallyused. MIG welding makes use of wire provided in coil form. Other

methods of supplying wire are impractical for MIG welding. The

quality requirements for MIG welding wire are perhaps even more

92

-emu

stringent than comparable requirements for TIG wire. One reason forthis is that welding current must be transferred frorm. t+he contact or

guide tube to the wire. Alsc, the wire-feed speeds employed in MIGwelding are much higher than those employed in TIG welding. There-fore, any wire characteristic that tends to impede the flow of wfrethrough the welding torch may cause undesirable variations in weldingconditions or even an equipment malfunction. Such undesirable char-acteristics as kinks, soft spots, and rough surfaces are not tolerable

in MIG welding wire.

Cleanliness of the welding filler wire is extremely important, andgood cleaning practices must be used to minimize contamination.Fabricators have experienced unacceptable variations ix. weld qualitythat have been attributed to inadequate control of filler-wirepreparation.

One fabricator found a "waxlike' surface coating at regular inter-vals aiong the length of Ti-6A1-4V filler wires (Ref. 6). The nature ofthis coating could not be identified. Since cleanliness is extremelyimportant in welding titanium, it is believed that coatings of this typecan contribute to porosity. Attempts to remove the surface coating bypassing the wire through a tube filled with abrasive fibers were nottotally effective. However, periodic inspections showed definite evi-dence of residues on the abrasive fibers.

Electrochemical surface finishing techniques have been developedfor inspection of incoming filler-wire ntialityr (Ref 6l-). Th chem-

milling technique discloses seams, laps, and some other defects thatare difficult to find by other means.

Titanium welding wire is supplied by all of the major titanium

companies and by several companies specializing in processing high-quality metals and alloys. Filler metals that are cleaned and packagedin sealed containers are available.

Gases for shielding the weld pool, underbead side of the weld, andhot weld metal include the welding grades of argon, helium, andargon-helium mixtures. Inert gases containing oxygen additionsshouid not be used.

Tooling and Fixtures. Backing for MIG welding titanium al-loys has been varied depending on joint design, quality requirements,and fabricator. Backing bars are used to provide root-side shieldingand to facilitate control of the weld puddle, root reinforcement, andheat effects of welding. Backing bars also are used to minimize I

93 . .

IZf~

distortion by promoting more rapid solidification and cooling of weld"metal. In some instances, the more rapid solidification of weld metalis reflected in higher ductility an .t "ug... s (Ref.

Copper is the most popular material for back-up bars used forMIG welding. So)id-copper back-up bars were used for fabricatingtank-cupola prototypes (Ref. 41) while water-cooled copper back-upscombined with inert-gas shielding devices were used in developmentwork on thick-plate cross sections (Refs. 5, 6). Contamination of ti-tanium welds by the back-up materials can occur and precautions mustbe taken to avoid excessive heating or puddling.

Welding Conditions. The welding conditions employed in MIGwelding are dependent on two separate groups of factors. Thesegroups include those that affect (I) welding arc characteristics and(2) welding conditions.

First, a suitable combination of curreat, voltage, heat inputrates, and other parameters that will produce the desired arc charac-teristics must be selected. The arc stability and metal transfer oc-curring in MIG welding are very dependent on these electrical vari-ables and the composition of the shielding gas used. With low currentdensities, metal transfer is erratic and consists of large metalglobules. Large globules often contact the workpiece before theyseparate from the end of the filler wire. This behavior interrupts thearc due to the short circuit formed by the large globules. Currentfl-ow continues, however, until the globule melts sufficiently to sepa-rate from the end of the filler wire. -When separation occurs, the arcreignites and the transfer process continues as before. Low-current-density MIG welding has been used for welding titanium. One impor-tant advantage is that the lower currents and heat-input rates can beused with spray-type metal transfer. As the current density is in-creased, arc stability is improved and metal transfer changes to acharacteristic spray-type transfer. High-current-density weldingconditions are generally preferred in the MIG welding of mostmaterials.

The second group of factors affecting the welding conditions arethe materiai thickness, joint design, weld tooling, and whether manualor machine welding techniques are being used. The first group offactors affecting welding conditions usually sets minimum limits on theusable current and voltage. Variation above these minimums corn-bined with the possible variations introduced by the second group offactors makes it possible to produce welds of very similar appearancewith many possible combinations of welding conditions.

94

*

Table X illustrates some of the combinations that have been usedU Y V 4 L 4L il W LA4,.J- ira LAAC; ±V1xJ VV%1.A AL J IL&AL JoantsL &i

and its alloys. Table X! illustrates welding conditions used for othertypes of weld joints. Insufficient work has been reported on MIGwelding to allow any comment on the most suitable conditions of thosethat have been investigated. Because of difficulties with crater crack-

ing and control of penetration, starting and runoff tabs are recom-mended (Ref. 9).

PROPERTIES

Information on properties of MIG welds in titanium and titaniumalloys is scarce due to the limited use of MIG welding for titaniumalloys.

The inechanical properties of the weld metal are related to itscompositions. Weld-metal composition, in turn, depends on the com-position of the filler metal that is used to deposit the weld, the coinpo-sition of the base metal, and the welding conditions that affect the ratiobetween the amount of filler wire and base metal melted in ma. :ing thewd.1d. Therefore, weld-metal properties can be varied through filler-metal selection and to a lesser extent through changes in welding con-ditions. Weld-metal properties for typical material combinations aregiven in Table XII. Weldment properties are given in Table XIII.

Only unnotched and notched tension and Charpy vee-notch impactdata are available. Satisfactory properties are generally obtained inalpha or alpha-beta alloys. Very low impact properties are obtainedin the beta alloy. Low impact values may result from foreign mate-rial or deposits (Ref. 9) on the welding wire.

Weld-cracking problems have been encountered at locations whereweld passes cross one another and in multipass welds. Accordingly,procedures have been devised by one fabricator to use single-passwelding as much as possible and to minimize the number of locationsat which two different welds come into contact (Ref. 9). In particular,crossover welding, which permitted one weld deposit to cross another,was avoided. Cracking was detected in 2-inch-thick Ti-6A1-4V weld-ments made with ten passes of Ti-6A1-4V filler wire when no preheatwas used. A similar specimen made using 125 F preheat for the firstand second passes, and a 175 F interpass temperature for the -emain-ing passes showed no radiographic evidence of cracks (Ref. 5). Theseweidments also contai,_ed porosity that tended to concentrate at theends of the joints. Sources of additional properties information arelisted in Table XIV.

95

I2

I -J

_ - K-x

C, 0

0 0 '-d C O> C00c-C

Ei ~ ~~ c'- cr, *m r-: c

> Lt

jzj

rjIC

C) 0 M.. C0 0 0 0 -Q J: 0.

gif 0 0z0

TABLE XI. GAS METAL-ARC WELDING CONDITIONS FOP. FABRICATION OF Ti-4AI-4V

TITANIUM TANK CUPOLA (REF. 9)

(1) 1/4*Fi1gt (2) l14'x4V I

- n - (7) 3/8" Fillet (8) 3/8" i45'V..

(3) I/4"Coumn Weld 4) I/4X Fillet

INPo 1(9)1/2 x45* Voe

(5) 3/8" x 450 Voo (6) I/4Fillet

CP Titanium

Filler Wire

Plate Metal FeedTiiickness. Diam. Rate.

Type of Joint in. in. Volts Amp ipm

1 1/4 1/32 38 250 1470

2 1/4 1/3-2 38 2,50 14701/16 39 400 350

3 1/4 1/32 38 250 1470

4 1/4 plate 1/32 38 250 1470

1/4 diarn

round

5 1/2 1/16 40 400 350

1/ /Ic 39 3307 1/2 1/16 40 400 350

8I 1 1/16i 40 400 350

9 !/2 1/16 40 4o00 350

97

______________ i.r

TABLE XIlI. TENSILE PROPERTIES OF MIG WELD METALS IN TITANIUM ALLOYS

Filler Metal 0. 2 Per Cent Ultimate Elongation, Reduction

Nominal Size, Offset Yield St.ength. pe: cent ip in Area,

Composition in. Strength. ksi ksi 2 in. per cent Reference

Ti 6Al-4V Parent Metal

Parent metal -- 115 132 11 21 63

CP titanium 0.062 83 93 16 39 63

CP titanium 0.062 85 100 31 25 63

5AI-2.5Sn 0.062 123 133 25 2.5 63

5AM-2. 5Sn 0.062 131 139 11 19 63

6AI-4V 0. 062 128 144 6 9 53

6AI-4V 0.062 129 143 15 13 63

6AI-4V o. 062 139 151 8 8 63

6AI-4V 0. 062 143 151 4 5. 35C? titanium 0.062 57 72 24 49 5

Parent metal -- 115 132 11 21 65

6AI-4V 0.062 -- 135 -- --

Ti -5A1-2. SSn Parent Metal

Parent metal -- 12 135 13 25 43

CP titanium 0.062 77 87 21 34 13

5AI-2.5Sn 0. 062 125 138 8 12 63

06 -2.25Sn 0. o -- 137 -- -- 64

6AI-4V -- 127 141 1 !6 63

98

W=......

iP' i

TABLE Xl1i. TRANSVEgS T1NSILE PROPERTIES OF MIG WELDMENTS IN TITANIUMAND TiT.ANIV.M ALLOYS

UltimateFiller Metal Offset yield Teasile Elongation. Reduction Location

Nominal Size, StreIQO(A). Strength. per cent in of Area. ofComposition in. kzz i a in. per cent Failure(b) Reference

Comrinercially Pure Ti

CP titanium 91(0,1) 107 22.0 49.2 -- 9

(parent metal)

C CPtitanwm(c) 0.62 99(0'1) 110 15.0 .53. HAZ 9

Ti-4AI-4V Alloy

4A1-4V I1E 12- 14 44 -- 62

(parent metal)4A1-4V@') 0.62 113 Il 5 12.9 52.5 HAZ 62CP titanium 112 12-2 -25 W

T.!l-2.5Sn Alloy

.5A-2.5Sn 13: 13i 20 43 -- 62(parent metal)

5AI-2. 5Sn -- 132 142 -- 38 -- 62C? tit3nium 12,1 130 -- 34 - 62

Ti..-6AI-4 V Alloy

6AI-4V 13.5 148 16 42 -- 62(parent metal)

6AI--" 138 152 -- 44 -- 62CP titanium -- 126 134 o- 30 -- 62

(a) 0. 2 per cent unless othcrw!5e poted.(b) HAZ = heat-affccted zonie; W -- weld metal.(c) Filler metal deposited at 365 amp arad 45 v; side-bend samples bent 180 deg without cracking.(d) Fj!lcr metal deposited az 400 al4p ani 46 v, side-bend tests fractured at 5.5 and 80 deg.

99

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IwE t- c - ha

ap

IPAf aI

twt

r5. bil--

00 0 30 W--

+ +o 192 1 *S S Ut it

S : -,

L-i

S. < < __> •.' I --

V

0 Mc~ ~ z' ' Irc

Z %)>' t a

I I su

I de

I el

Sr

.? _ .~hc

IM-

I> U towth

Z,7

1;10__ _ _ _ _ _ _ _ _ _ til

Al~J It r XATI3 ILT ,,1"~;tuA 5 Z ~

has been used to nmanulacture z variety of complex shapes from tita-nium and for welding thick titanium plates. Some good examples ofapplic~tions for the process are described in the following.

Armored Vehicles. Armored tank cupola componentsfabricated frorn Ti-4A1-4V alloy are shown in Figure 62 (Ref. 9). MIGwelding was used extensively throughout to demonstrate the fabrica-bility of complex titanium shapes by MIG welding.

Thick Titarnum Plates. Independent and Governmentfacilities have been welding thick plates of titaniumn alloys since about1952. In one program (Ref. 6) ihe objective was tu develop and estab-lish procedures for welding 2-inch and 5/8-inch annealed Ti-6AI-4Vtitanium alloy H-plates and corner joints with comnmercially pure tita-nium and Ti-6AI-4V filler metals. The procedures for welding weredeveloped using the inert -gas -shielded metal-arc consumable-electrode process using crack-susceptibility plates and I-plates.Fabrication of the joints with unalloyed filler metal was accomplishedreadily; however, with the alloyed filler metal it was necessary to usea 175 F preheat and a 170 F interpass temperature for crack-susceptibility test plates, and a 1i5 F preheat and a 200 F interpasstemperature for iabricating H-piates. Two-inch-thick plates ofli-8Mn alloy also have been welded in early titanium alloy armor-welding development progranms (Ref. 62). Due to weid-metal crackingand the development of newer, more readily weldable alloys, weldingdevelopment work with the Ti-84n alloy was terminated.

For welding 2-inch-n.hick titanium plates, automatic consumable-electrode equipment was set up in a chamber for welding 2-inch-thickplate (Ref. 20). The piates were clamped in a welding fixture thatcould be rotated inside the chamber for weld passes on either side ofthe double-vee joint. This -velding fixture was attached to a traversingmechanism that moved the plates under the welding torch mounted on ahorizontal plate a, the top of the welding chamber. The torch cotild beadjusted vertically or horizontally to position it with respect to theioint. Adjustments in wire-feed speed and welding travel speed weremade from outside the welding chamber. Water cooling was suppliedto the welding torch and to the entire shell of the welding chamber.Water cooling the chamber will be advantageous in removing some ofthe heat generated during welding. A constant-potential welding gen-erator was used in welding tests.

A typical -cint design and a back-up bar for welding thick-platetitanium alloys are shown in Figure 63.

101

S. .. ... .o . .... .. _ ... .

a* CornLeted Welded Titariwn Cupolas

a~ e~e )~tn at Hat h . e-n~~ i c. Na e-?iect- Sulmussemnbly in Position.Poccssfor weldil:g" to t:e Cradle

F&UE2. !LLUSTIRATION OF TANK -CUPFCLA COXIPNPN-1- --- IRC-TED USIG-* Mi1 - WZ1l IN* RROCESS ,

IRF 9)

T . ~ ~A

. '

RI

Titanium plate Copper back - up bar

FIGURE 63. TYPICAL JOINT DIMENSfONS FOR WELDS INZ-INCH--THICK Ti-13V-llCr-3A1 TITANIUMALýLOY PLATE (RFF. ?,U)

ARC SPOT WELDING

Arc spot welding is being developed for joining titanium alloys --napplications where resistance spot welding cannot be used or as an al-ternate to the resistance -spat -welding process. Arc spot welding c-;a-,employ either the basic Tlf3 or MIG welding Rroczss and is a semi-automatic or fully autormatic technique. Arc zinot welding can be asedto join thickness combinations which are not suitable for resistancespot welding an-c in joints that are accessible fromr ::ne side only.

The mnajor difference b-etween arc spot wel',ding and either comnven-tional TIG ~-MIG welding is thar them? is nr, relati~ve lateral rnov-e~mentbetwe en the wending torch and thc- parts being Joined. Star-tiý andstopping cycles 4.or the welding process are exct~erely imporsant -,narc spot welding- The total welding time generally is qurze sho~rt sothat it is necessary to automatically program welding paraxneut-rs toinsure a smnooth start and stop of the proco-ss. The shieldxing of arcspot welfs is somnewhat simpier than for conven-ional TiG or MIGwelds. Simple cylindrical auxiliary shieids placed around the weidingtorch are suffic L-ent to p~revent contamination from the top surface ofthe weld. Shielding o.; the underside of the joint also may be r~equLred.

103

#~;ARM

Equipment. The equipment required for arc spot welding is

ever, the arc-spot-welding nozzle is a complete down-to-the-surfaceshield and it is a locater for arc length or contact-tube-to-work dis-tance. Also, some means of programming appropriate weldingparameters to obtain desired starting and stopping cycles is used.

Materials. The materials used in arc spot welding usuallyare the same as those used in either TIG or MIG welding. Earliersections should be consulted for comments on materials.

Welding Conditions. 71he welding conditions enmployed in arc

spot welding are generally similar to the TIG or MIG welding condi-tions used in joining comparable thicknesses of the outer materials.Arc *spot welding can be used for joining similar and dissimilar metal

thickness combinations. The arc spot is always made through a rela-

tively thin member of the part being fabricated. The backing membermay be thin or thick. There are indications that the top layer that canbe penietrated by TIG spot welding is limited to 0. 060 to 0. 070-inch-thick titanium. However, detailed welding conditions for arc spot

welding of titanium have not been reported.

ELECTRON-BEAM WELDING

Electron-beam welding is an extremely attractive process for usein joining titanium and other highly reactive materials. The processis applicable to a wide range of thicknesses from about 0. 0015 inch toover 2 inches. One major advantage of the process is that all weldingis performed in a high-vacuum chambez. Contamination of the weld-ment from external sources is essentially nonexistent. All electron-beamr welding is done using mechanized equipment. Electron-bcamwelds made with high-power-density type equipment exhibit a charac-teristic high depth-to-width ratio of the weld metal and heat-affectedzone. This characteristic is advantageous from the standpoint ofminimizing the distortion that normally accompanies welding. It mayalso result in welds whose properties are not altered significantlyfrom those of the base material.

The electron beam can concentrate a large amount of energy in aspot diameter of about 0. 010 inch or less (Ref. 60). Energy densitiesrange from about 5, 000 to 40, 000 kw per square inch, compared withabout 100 kw per square inch fcr tungsten-arc welding.

In electron-beam welding, the heat required to melt the jointedges is supplied by a focused electron beam generated in an e-ectron

104

gun. This beam is focused and accelerated so that it strikes the jointline parallel to the existing interface. Electron-beam welds are usu-

ally made without the addition of any filler wire.

Equipment. Electron-beam welding equipment is classifiedin two divisions. High-voltage welding is performed in the 75, 000 to

150, 000-volt range while low-veltage welding is performed ýn the15, 000 to 30, 000-volt range. Normally, the high-voltage equipmentproduces much narrower heat-affected zones than low-voltage equip-

ment.(Ref. 66). Low-voltage equip: ent provides a wider weld and is

used very effectively in special can-sealing operations. Acceptable

welds can be made with either type of equipment. A schematic dia-gram of an electron-beam weiding machine is shown in Figure 64

(Refs. 67, 68). Special electron-beam units using either clamp-on-type chambers of special electron-gun assemblies designed to allow

the electron beam to be projected into the air have not seen much use

on titanium. Clamp-on-type chambers may be quite useful in thejoining of long lengths of special shapes fabricated from titanium.

Fixturing is needed to hold the parts in position, but the fixturing

need not be as heavy as for other welding methods (Ref. 69). Copper

chill bars can be used to restrict the width of the heat-affected zoneand to confine and control the fusion-zone geometry (Ref. 66).

Materials. No special material requirements are involved in

electron-bean welding. However, because of the very high solidifica-tion rates aszociated with most electron-beam welding, it is impera-tive that the weld area of the parts to be joined be very clean prior towelding. The high freezing rates associated with electron-beam weld-

ing allow very little time for the escape of any gaseous impuriti,-3 dur-

ing weIding. Thus, it might be anticipated that electron-beam weldscould be somewhat more prone to porosity formation than other typesof fusion welds. To date, there is very little evidence to either sub-

stantiate or refute this supposition.

There are no known applications where filler metal is used for

electron-beam welding of titanium alloys.

Welding Conditions. Welding conditions used in electron-

beam welding are dependent on material thickness and the type of

electron gun being used. For a given thickness of material, various

combinations of accelerating voltage, beam current, and travel speedare satisfactory. In electron-beam welding, the electrical parameters

do not adequately describe the heat-input characteristics of the beamsince these characteristics are affected significantly by the focus of

105

• ".. . . . . . . .. . . . .. . . .. . . . . . .. .. . f ... . Ai

[• Air-inletvalve

- -- Filament

Anode

Bypass valve

Column valve • o\

Diaphragm---- ; -

Opticalviewing - - 'system

Magnetic tensassembly

Weldingchamber -4chamberDeflection coil

t=II

ii~i

I:A

I,,;I,:'

t~l!

To voctium

Workpiece -system

FIGURE 64. SCHEMATIC DIAGRAM OF AN ELECTRON-BEAM WELDI•NG MAC'IINE (REF GS)

106

.-!--

the beam. Measurements o1 beam diameter are difficult to makeunder production conditions so that the transfer of weldin2 pararetersbetween different equipment units is very difficult. Fortunately, suit-able welding parameters can generally he developed on a given pieceof equipment with only a very few trials.

In very thick material, the first pass made to completely pene-trate the joint sometimes is undercut along both edges of the weldmetal. This undercutting car. Le eliminated by a second weld passmade at somewhat lower energy levels with a slightly defocused beam.However, undercutting has been largely reduced by making minor ad-justments in travel rate (Ref. 66). The underside of electron-beamwelds also may exhibit an undesirable contour. Some type of metal-removal operation is generally required to produce an acceptable

underside contour.

The flat welding position is used in electron-beam welding. Thewelding positions that can be used are limited by the versatility of theavailable welding equipment. Table XV shows some of the weldingconditions that have been used in the electron-beam welding of tita-nium and its alloys.

Properties. Sources of property data on electron-beam weldsare shown in Table XVI. In general, the properties obtained inelectron-beam welds are similar to those obtained in TIG welds.Strrngths up to 140, 000 psi can be obtained depending on the weldingconditions used (Ref. 70). Postweld aging of electron-beam welds in1-inch-thick Ti-6A1-4V. alloy increaseu the tensile properties 2 to 3per cent (Ref. 71).

Applications for Electron-Beam Welding Titanium Alloys.

Normally used for the production welding of precision assemblies,electron-beam welding has been used for fabricating pressure vesselspheres as shown in Figure 65 (Ref. 72). Electron-beam repair weld-ing has saved tens of thousands of dollars by its ability to make re-pairs on close-tolerance parts that might otherwise have to bescrapped. Electron-beam welding enabled one fabricator (Ref. 65) tosalvage many parts that formerly codld not be repaired because oftolerance, configuration and/or material problems. Repairs con-

sisted essentially of patching, plugginý,, joining, and similar welding-type operations. Typical applications included: adding a block ofmaterial to an area where too much stock had been machined off;plugging unwanted holes; adding tabs, bosses, and other fittings to amachined part; filling porosity or voids in machined castings; and

107

A .

I

TABLE XV. ELECTRON-BEAM WELDING CONDITIONS

Acc. Beam Travel BeamVoltage, Current, Speed. Diameter,

Base Alloy Thickness, in. kv ma ipm in. Referent2

SAI-4V 0.05 85 4 60 0.006 42Ditto 0.2 125 8 18 0.01 42

"- 0.191 28.2 170 98 .... .

Sevexal 0.084/0.125 14 250 8 to 10 66alloys

5A1-2.5Sn 0.09 90 4.8 IE -- 6913V-llCr-3A1 0.125 135 6.5 28 - 69

Ditto 0.125 20 95 30 --

"" 0.03 30 26 89 -- 40

8AI-1Mo-IV 0.05 110 2 45 0.005 40

CP titanium 0.05 95 1.8 30 ....Ditto 0.125 125 6 30 ....

"0.250 138 10 25 ...."" 0.340 150 15 60 .

108

a63

U

00UC

V) o

U3 CS -% = 0

0 -

0.. 0

U c -

U3 ca) w Sz S

~fn U 3

&e -j .. :0 - a

73 a an -4 ca .,

La 10 a a

C; C;C C

U 0 7j Z)

oo - 4

- > >

- 10109

I

FIGURE 65. ELECTRON-BEAM WELDED TITANIUMPRESSURE-VESSEL SPHERE

patching cracks in precision fixtures. Examples of electron-bearr.weld repairs are shown in Figure 66 (Ref. 65).

PLASMA-ARC WELDING (Refs. 74, 75)

Plasma-arc welding is an inert-gas welding method utilizing atransferred constricted arc. The process is now used as an alterna--tive process for TIG welding for a limited number of industrial appli-cations where greater welding speeds, better weld quality, %nd lesssensitivity to process v7ýriables are obtained.

The general characteristics and electrical circuit used forplasma-arc welding are shown schematically in Figure 67. The arcplasma or orifice gas indicated in Figure 67 is supplied through thetorch at a flow rate of 1 to 15 cfh. Suitabre gases are argon, andmixtures of argon and helium. Argon-hydrogen mixtures also areused for some materials, depending on the application. The gas flow-ing through the arc-constricting nozzle protects the electrode fromcontamination and provides the desired composition in the plasma jet.

Relatively low plasma-gas flow rates are used to avoid turbulence"and undesirable displacement of the molten metal in the weld puddle.Since the low gas-flow rates are not adequate for shielding the puddle,

110

a. boss Added b.

Precisely-machined AMS 5616 control-spider housings were saved from Elecren-lbiram welding s;the scrap pile when an engineering change called for the addition of a An unwanted hole w'as filled b'we Age-shaped boss (in circle). The critical nature of the part dictated a directing the beam parallel tcmexximum distortion of 0. 00025 inch at the weld area. The boss was welded minimurn heat requirements aat a speed of 27 ipm. Welding time was about I second. Small spot size. pair not only saved the costlyfast tavel, and precisc- beam control perr.itted concentrating the heat at fabricating a replacement.the vertical interface between the boss and hoursjg. Inspection of the weldedparns could detect no measurable distortion.

FIGURE 66. EXAMPLES OF ELECTRON-BEAM WE!

A-77,ý 1-1 -

;32

ýTI

S*

SkS

SI ll

Locc'ion

b. Hole Plugged

"b. were saved fmm Electron-beam welding salvaged this machined titanium housing. Houtings were savi

ddition of a An unwanted hole was filled by welding a titadurn plug in place. By interior slot from whichg S; -)art dictated a directing the beam parallel to the hole axis, the weld was made with away. A small block o1t" bos was welded minimum heat requirements and w;thout distortion or crackirg. The re- the slot wall to prowdo

I tc . Small spot size, pair nct only saved the costly part. but also avoided a 3-month delay for area was then renmach'

tz a -i ng the heat at fabricating a replacement. for the applicatiol.. L

Sction of the welded seort eg of 125 kv apr i

in less than 1 secnd ofi

FIGURE 66. EXAMPLES OF ELECTRON-BEAM WELDLNG FOR SALVAGE OF COSTLY, PRECISION PARTS (REF. 65)

WE!

' -- *~'*-* - -.- ~ *4*sT

WFi

5. im Mrged %M E. er o

ggea. c.iq Slot Naroe

this achied tianiu housng. ousins wee savd byusingelecron Ream i weldin ocreta

axlis, tahiewed twaniumad withg Housingsml wer kofte saved byoy usin el21r4-ea welin tod corretoadistortion or cracking. The re- the slot wall to p.id an additional thickness of metal. The built-up

L also avoided a 3-month delay for area was then remachhined to bring the slot back to the required width5 for the application. The tab was welded at 27 ipm, using a power

0- setting of 125 kv andl 5 ma. The full-penetration welds were m.adeirs less than 1 secor.J of actual welding time.

SALVAGE OF COSTLY. RiECISION PARITS (REF. 65)

4 i111

ý_ Wo

• ! ••..ELECT cog1

•-OI- y •A

EIT|G1 AS

SHIELDING

S~FIGURE 67. SCHEMATIC REPRESENTATION OF PLASMVA-AARC WELDING OPERATION (REF. 74)

"supplementary shielding gas is provided through an outer gas cup. Thetype and flow rate of supplemental shielding gas are determined by thewelding application. Typical arc and shielding gas flow rates are 4 and35 cfn, respectively.

Keyhole Action. In plasma-arc welding, the term "keyhole"has been applied to a hole that is produced at the leading edge of theweld puddle where the plasma jet displaces the molten metal, allowingthe arc to pass completely through the workpiece. As the weld pro-gresses, surface tension causes the molten metal to flow in behind thekeyhole to form the weld bead.

Keyholing can be obtained on most metals in the thickness range of3/32 inch to 1/4 inch, and is one of the chief differernces between theplasma-arc and gas tungsten-arc processes. Presence of the keyhole,which can be observed during welding, gives a positive indication ofcomplete penetration.

Equipment. A mechanized plasma-arc welding torch is shownin Figure 68. This torch can be operated with either straight or re-verse polarity connections at arc currents up to 450 amp. Water-cooled power cables are connected at the top of the torch to supplypower and cooling water to the electrode. Fittings are provided on thelower torch body for the plasma-gas hose, the shielding-gas hose, andthe cooling water for the nozzle.

The two types of electrodes used in the plasma-arc torch areshown in Figure 69. The tungsten electrode shown on the left is usedfor straight-polarity operation and is available in 1/16-, 3/32-, and1/8-inch diameters, depending on the current to be used. A

i4113

I

II

FIGURE 68. MECHANIZED PLASMA-ARC WELDING TORCH (REF. 74)

Straight ;loaritypo!o •- Iy elecI -ode

electrode

SFIGURE 69. TUNGSTEN AND COPPER ELECTRODES USED FOR STRAIGHT AND

REVERSE POLARITY OPERATION, RESPECTIVELY (REF. 75)

- i114

It __.

x

water-cooled copper electrode shown on the right side of Figure 69 isused for reverse-polarity operation.

A variety of multiport nozzle designs are available for differentwelding applications. The diameter of the central port of the nozzledepends on the welding current and gas-flow rate. The spacing be-tween the side gas ports is inlfuenced by the thickness of theworkpiece.

Welding Conditions. Typical welding conditions for squarebutt joints in titanium arc shown in Table XVII. Often, conditions de-termined for joining various thicknesses of stainless steel can be usedas starting-polnt conditions for welding the same thicknesses of othermateriais. The data in Table XVII were obtained with the electrodeset back 1/8 inch from the face of the torch nozzle. Electrode setbackis accomplished by rotating a collar on the upper torch body, and thedistance is gaged with a probe on a setback tool. Nominal torch-to-work distance is 3/16 inch.

TABLE XVII. PLASMA-ARC WELDING CONDITIONS FOR SQUARE BUTTJOINTS IN TTANIUM

Plate Welding '11c ArcThickness, Speed, -urtient. Voltage. Gas Flow Rate. cfh

in. ipm amp ',dc-sp) v Nozzle Shielding

1/8 20 185 21 8 30

3/16 15 190 26 12 45

Pure argon is used to weld reactive materials that have a strongaffinity for hydrogen, such as zirconium and titanium. Use of Vrgonas the nozzle gas and CO? as the auxiliary shicld has increased speedson certain miid-siede welding applications but CO0 is not to be used forwelding titanium cr its alloys. When making the second or cap pass ona joint requiring two passes, helium can be used for the plasma andshielding gases. The helium effluent does not have the momentum re-quired to produce a keyhole, but this is not necessary on the cap pass.

There is no information on properties of plasma-welded titaniumalloys available in the- published literature at this time. However,since several organizations are using the process in developmentwork, properties data probably will be available in the near future.

1115

~-.,- J

Applications. Plasma-arc welding has proven commerciallyimportant advantages in several specific areas of application. Theseinciude the welding of stainless steel tubing, making circumferentialjoints on copper-nickel and stainless steel pipe, and the welding ofreactive-metal compacts to form furnace electrodes. Developmentactivities are under way on other promising applications incluA.ingmissile cases.

Aerospace Applications. Development work is in prog-ress on the plasma-arc welding of missile casings of titanium, 18 percent nickel maraging steel, D6AC steel, Type 410 stainless steel, and4130 steel. The plasma-arc welds on thicknesses where keyholing isobtained, have strength, elongation, and notch-toughness propertiesequivalent to thzse of TIG welded joints. In addition, welding speed isincreased and greater uniformity is obtained. For example, lo-c-.-tudinal and circumferential joints in 3/16-inch-thick titanium t: nkageare welded in one-fourth the time required for the TIG process- Theoverall time saving is even greater, because the plasma-arc welds aremade on square butt joints while prepared joint designs were requiredfor TIG welding.

Titanium Sponge. Production of ingots of reactive metalssuch as titanium and zirconium starts with the pressing of small chipsof the metal and alloying elements into a mold to form a sponge com-pact or briquette. The compacts are then welded together to form aprimary electrode which in turn is melted into ingot form in a vacuumelectric furnace. The wLIding of the metal compacts is another com-mercial application for plasma-arc welding.

Use of TIC welding is not permitted in the production of reactor-grade zirconiun. L;ecause of the possibility of tungsten inclusions in thebase metal. Since TIG welding is ruled out, MIG welding (or consum-able electrode welding) was generally used to join the compacts. How-ever, MIG is an expensive process for this application because of theprice of zirconium welding wire (about $17.00 per lb). Occasionalburn backs of the guide tubes in MIG torches resulted in excessivecopper deposits in the primary melt ele'ctrodes which sometimescaused the copper content of the finished ingot to exceed the specifica-tion. Similar difficulties would be expected with titanium made by thismethod.

In plasma-arc welding of titanium and zirconium sponge, the torch"- uses a nonconsumable water-cooled electrode operating on reverse po-

larity without filler-wire addition. There is no tungsten present whicheliminates the possibility of tungsten inclusions. The cost of the

i

116i t

", _

welding wire is also eliminated. Plasma-arc welding of sponge com-pacts is performed both in the atmosphere and in inert-gas chambers.When the compacts are loaded into a chamber, the air is evacuated andthe space is back filled with argon. The plasma-argon issuing throughthe torch nozzle keeps the chamber under positive pressure. Whencompacts are being welded in the open atmosphere, a trailing shield isattached to the torch to blanket the weld puddle with inert gas to pre-vent contamination.

Laboratory tests and production experience indicate that transferof copper from the water-cooled copper electrodes used in this pro-cess is essentially zero. In one plant, the plasma torch is taken outof service after each 60 hours arc time to clean accumulated spatterfrom the electrode and nozzle. In another plant, downtime per torchvaries from 5 to 7 hours per month, with production time scheduledfor 550 hours per torch.

In one installation, the savings realized by eliminating the use ofwelding wire paid back the investment in plasma-arc welding equipmentin fifteen 8-hour shifts.

RESISTANCE SPOT WELDING

Resistance s-;-z welding has been used more than any otherresistance-welding process for joining titanium and its alloys. Spotwelding has been used to join titanium in thicknesses ranging from alittle under 0. 01 inch up to pile-up thicknesses totaling 2-1/2 inches.The thickness that can be welded in any given application is limitedonly by the power and force capacity of the available equipment.

In resistance spot welding, all the he•.t required to accomplishjoining is supplied by the passage of an el.'ctric current between twoopposed electrode tips that contact the surfaces of the parts to bcjoined. The electrode tips are held against the workpieces with con-.,iderable force, so that good electrical contact is maintained through-

out the assembly. Resistance-spot-welding techniques can also beused to make joints in which no melting is involved. Such joints canbe called diffusion welded, diffusion bonded, yield-point diffusionbonded, or solid-state bonded. Joints of this type are very similar toconventional resistance welds with the exception that no molten metal

"*is formed during the joining process. Titanium normally is weldedusing the conventional technique involving melting. The diffusion-bonding technique has been used only experimentally. Even conven-tional spot welds in titanium contain an area around the molten nugget

1171

that is diffusion bonded. The bond in this area is generally strongenough to make a significant contribution to the load-carrying abilityof the spot weld.

v Titanium is spot welded in much the same manner as other metals."In many respects, titanium is an easy material to resistance spotweld (Ref. 11). The configurations involved in spot welding and therelatively short time periods used with the process tend to precludeany contamination from the atmosphere. As a result, there appearsto be little need to consider auxiliary shielding of titaniurn during re-sistance spot welding. The relatively low thermal and electrical con-ductivities of titanium are definite advantages for the spot-weldingprocess. As a result, titanium is often considered to be more readilyspot welded than aluminum and many of the carbon and low-alloy steels.Titanium and stainless steel alloys are similar in thermal and electri-cal conductivity and strength at elevated temperatures. These simi-larities have simplified the spot welding of titanium. A titanium alloyof a given thickness can be spot welded with the settings that are satis-factory for a similar gage of stainless steel. The recommended spot-welding machine settings developed for titanium by various investi-gators substantiate this to a degree which is generally as accurate asthe ability to incorporate any recommended data into the settings fromone production machine to another. In fact, the differences of control-panel settings from machine to machine probably exceed the differencesin recommended settings between titanium and stainless steel (Ref. 11).

EQUIPMENT

Titanium has been successfully welded on almost all types ofavailable conventional resistance -spot -welding equipment.

Figure 70 "¶Ref. 11) illustrates a conventional spot-welding opera-tion. Spot-welding machines used for welding titanium should provideaccurate control over the four basic spot-welding parameters: weldingcurrent, duration of welding current, force applied to the welding elec-trodes, and electrode geometry. Various data indicate that each ofthese parameters may vary to a certain degree without appreciably re-ducing weld quality. But once the optimum settings are obtained for agiven application,, it is desirable to have enough control over theparameters to obtain reproducible results. Light gage sheet (less than0. 040 inch) can be welded with most of the 30 kva, 6 0-cycle, single-phase, rocker-arm-type machines. Because of the higher currents andelectrode forces required for heavier gage sheet, the larger press-type"machines are more suitable for gages above about 0. 040 inch.

118

£r

FIGUJRE 70. CONVENTIONAL RESISTANCE -SPOT -WELDING

EQUIPMENT

Press-type, 600 kva, 60-cycle single-phase

spot-welding machine with control unit, forwelding sheets in thicknesses oi 0. 062,0.070, and 0. 093 inch (Ref. 11).

Various auxiliary controls such as up slope or down slope, orpostweld heat controls have not demonstrated any advantages whenused in welding titanium.

No significant changes in welding characteristics or static weldproperties have been reported that cý n be attributed to the use of anyspecific type of resistance--welding equipment. Future developmentsmay show such a preference when weld properties are evaluated morethoroughly on the basis of properties, such as fatigue, or the reductionin residual-welding stresses.

Electrode Types. The most satisfactory electrodes arethe spherical-faced, copper-alloy types. They allow a wide range ofcurrent settings from the point of no weld up to the point of metal ex-pulsion. Also, higher weld strengths can be obtained with larger weld

nuggets, better control of penetration, less electrode indentation, and

119

less sheet separation for a given set of welding conditions in compari-son with other types of electrodes. The truncated-cone electrodeshave been satisfactory for some cases but often produce nonuniformsheet separation and excessive electrode indentation. A comparisonbetween weld strengths obtained when using spherical-faced andtruncated-cone electrodes for spot welding 0. 093-inch Ti-6A1-4V isshown in Figure 71 (Ref. 11). The figure indicates that higherstrengths for a given set of weld conditions can be obtained withspherical-faced electrodes. Also, metal expulsion occurs at signifi-cantly higher current settings. Resistance Welder Manufacturers As-sociation Class 2 copper alloy was used for both electrode configura-tions. RWIN.A Class 3 copper alloy electrodes may also be used andwill result in a longer tip life where production rates are high. Elec-trodes for resistance spot and seam welding may be water cooled ex-ternally. Wez,-einc- conditions and weld properties obtained with externalwater cooling are not available.

14 07S0114rvcoI-faCed electrode(3 in. top redhs. 5/8 *n-ieo)Tensin shseer

12 06 0 Cfress tension

- Tisicod-cone electrode ODttmum M eapu l

0minr 05 -. Cur:on! I ITrulncet~ll O - s ,n. meeor i 13 o radius) 11 cone

• U- Cress tnsione

Mil 8lis T-S43 Wredii)

U0C 03 T-S I

4- 02 (Trion cr *)( rediuns)

2 Os W *C-T(3-,oiius)

0 C-T

Welding Current. 103 amip

FIGURE 7i. SPOT-WELD STRENGTH VERSUS WELDING CURRENTFOR SPHERICAL-FACED AND TRUNCATED-CONEELECTRODES (REF. 11)

As welded with 2400 lb electrode force, 16 cycles weldtime. Class 2 electrodes.

120

I

Joint Design Considerations.

Minimum Joint Overlap. When spot welding overlappedsheet joints, it is important to maintain a minimum jcint overlap greatenough to avoid end tearing of the sheet in tension-shear loading. In-sufficient overlap will result in metal expulsion and a very weak spotusing the weld settings ordinarily considered to be optimum withproper joint overlap. An illustration of the type of tension-shearfailures cbtained with varying overlaps at the optimum weld settingsis shown in Figure 71 (Ref. 11). For the 0.062-inch sheet, an overlapof 1/4 inch resulted in metal expulsion and end tearing; end tearing isevident with the 1/2-inch overlap, while at overlaps of 3/4 inch andabove the tension-shear failures occurred by nugget pullout which istypical of the strongest tension-shear ruptures in titanium. For this0. 062-inch sheet, a minimum overlap of 5/8 inch was selected as theoptimum. The 0. 070-inch specimen in Figure 72 (Ref. 11) illustratesthe occurrence of metal expulsion caused by too little overlap. Here,overlap was only 3/8 inch, while the optimum for this gage was fixedat 5/8 inch.

FIGURE 72. THE EFFECT OF MINIMUM CONTACTING OVERLAPON THE TYPE OF RESULTING FAILURE FORTENSION-SHEAR SPECIMENS (REF. 11)

The specimen at the left is 0. 070-in. sheet with3/8-in. overlap. Overlap distances for 0. 06Z-in.specimens from left to right are: 1/4, 1/2, 3/4. 1,and 1-1/2 inches, respectively. A decrease in over-lap changes failure from button pullout to end tearing.

i

121

Minimum Spot-Weld Spacing. In most materials, 'spot welds are placed too close together, a portion of the current re-quired for the second weld is shunted through the preceding weld.This, of course, means that the actual weld current is somewhat belowthe optimum and the resultant weld may be weak because of low heat.even though the machine is set at the optimum weld current.

Current shunting is not as critical a factor as with most other ma-terials due to the high electrical resistance of titanium and weldstrengths are not appreciably reduced until spacings are small enoughto produce spot overlap. Figure 73 shows that the weld nugget sizeremains about the same with various spacings up to the point of spotoverlap.

FIGURE 73. THE EFFECT OF SPOT SPACING ON WELDGEOMETRY (REF. 11)

Welding Conditions. Resistance spot welding conditions areprimarily controlled by the total thickness of the assembly being

¶ welded, and to a rather large degree, by the welding machine beingused. Similar welding conditions may be perfectly suitable for makingwelds in the same total thickness where the number of layers differssignificantly. However, for any given thickness, or total pile up,various combinations of welding current, time, and applied force may

. - produce similar welds. Other variables such as electrode size and

122

I

shape are important in controlling such characteristics ?s metal ex-pulsion, sheet indenta'ion, and sheet separation. The use of slopecontrols such as preheat, postheat, and additional weld forging cycleshave not been found necessary in the early welding of titanium alloys.

Establishing Machine Settings. It is recommended thatfor each sheet thickness of titanium alloy the initial values for elec-trode force and weld time be obtained from the Resistance WeldingManual (Ref. 76) for comparable thicknesses of stainless steel(Ref. 11). Then optimum settings for welding current for titaniumalloys caýn be determined.

In a recent investigation to check the spot-welding settings listedin the Resistance Welding Manual, many tests were conducted onTi-6A1-4V using electrode forces and weld times recommended forstainless steel. The RWMA recommended conditions for spot weldingstainless steels are given in Table XVIII. These settings were foundto produce good spot welds with no advantage gained by varying any ofthe settings. When using electrode forces lower than those recom-mended, the welds were weaker in both tension and shear. Higherelectrode forces than those recommended produced higher shearstrengths but lower cross-tension strengths, the result being muchlower cross -tension/tension -shear ratios. Higher electrode forcesalso caused metal extrusion to occur at lower current settings, thusincreasing the per cent of sheet separation at the optimum currentsetting.

Establishing Welding Current. After selecting the rec-ommended electrode force and welding time for a given sheet thick-ness, the optimum weld current must be established. This is the mostimporta.it spot-welding variable and determination of the optimum cur-rent setting is best accomplished by welding some test specimens andchoosing the weld current on the basis of weld strength, sheet separa-tion, electrode indentation, weld dia.meter, and per cent penetration.Figure 74 (Ref. 11) illustrates the variation in some of the weld-quality parameters obtained by a.sing welding currents below and abovethose selected as optimuin for .he various gages. If some of the pa-rameters such as sheet separation, etc., are of no concern higherweld currents (up to the point of metal expulsion) may be used to obtainstronger welds. There ;_s a definite decrease in weld strength andsheet separation at the point of metal expulsion.

Establishing Squeeze Time and Hold Time. Electrodeforce is applied to the sheets being welded for a period longer than thetime that welding current flows. The total time that electrode force is

123

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30 - 012 -X Rotio-CT/TS

25 - n00-a. 0. 035-Inch Ti-6AI-4V

2.0 - 08 -As welded with 600-lb

Metal electrode force,1.5 6 e~s~n7 cycles weld time,

CC x 3 -in. spherical radius,1.0- 04- Class 2 electrodes.

05[ 02V -

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5 - -050 - Ror-TT:. 045 -einn Weld diomn b. 0. 062-inch Tj-6A1-4V

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- 0 0li3 =5 030- electrode force.

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1 010 - 0-CT Z

0 2 4 6 a iO 12 14 16 M8 20

7- 07 o Tension sheer -o Cross tension

6- 06 -A Weld diomneete* Nugget diameter

5- E 05 -X Ratio-CU~TS OtmmWeld diaomCurren. 0. 070-Inch Ti-6A1-4V

41 A- 04uge dr991ain0 cCurorent As welded with 1700-lb

- 0.3 -xRatioa, electrode force,UO cyle weldtie

x CL 3 -in. spherical radius,

2 - 02 -T * Class Z electrodes.

I0 01

0 2 4 6 8 10 121416 22 9 24Welding Current. 103 amp

FIGURE 74. INFLUENCE OF SPO T-WELDING CURRENT ON STRENGTH AND TENSION /SHEAR RATIOFOR 0. 035-. 0.062-. AND 0. 070-INCH-THICK Ti-6AI-4V ALLOY (REF. 11)

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applied consists of squeeze time, weld time, and hold time. Squeezetime is the time that the electrodes hold the material together at therequired force before the weld current is actuated. Weld time is thetime of actual zurrent flow. Hold time is the interval during whichthe electrodes are in contact with the material after the current flowhas o4,'-rped. Solidification of the weld nugget takes place during thehold time. Both the squeeze and hold times are generally set at aboutZO cycles duration, but can be varied according to the sheet gage. Inlight gage sheet, the weld nugget is solidified in less than 20 cycleshold time and adjustments in these machine settings can be made inaccordance with production requirements.

Spot-welding conditions used in industry for titanium alloys aregiven in Table XIX.

Properties. The quality of spot welds is determined by sev-eral testing methods. In addition to cross-tension and tension-shearstrengths, many specifications, such as the military specificationMIL-W-6858B (Ref. 8), place certain restrictions on weld penetration,sheet separation, electrode indentation, and weld diameter. Theselimits were originally set for stainless steel spot welds, but becauseof the similarity bet .veen the spot-welding characteristics of stainlesssteel and titanium, most of the quality parameters for stainless areapplied to titanium.

Many of the properties and characteristics of resistance spotwelds in titanium alloys have been determined. The properties usu-ally determined for various titanium alloy .pot weldmcnts are givenin Table XX. In many instances, complex testing procedures are re-quired to determine the behavior of titanium spot welds under specialconditions. Sources for additional information obtained from thesespecial tests are given in Table XXI. Some of the conventional spot-weld evaluation meihods are described in the following.

Tension-Shear and Cross-Tension Strength. A tension-shear test on a spot-welded specimen gives some indication of ductilitysince stress gradients and concentrations are set up by the nonaxialityof the specimen, the attendant bending stresses, and the stress con-centration at the end of the spot weld.

A cross-tension specimen undergoes even more severe loadingand, therefore, is a still better evaluation of ductility. I-Kwever, spotwelds in service are practically never subjected to this type of loading.Presumably, if extr-emely brittle zones exist in the region of a spotweld, the specimen will have low resistance to the cross-tension type

126

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TABLE XXI. SPOT-WELD PROPERTY DATA SOURCES

Total ThicknessBase Alloy of Test Plate, in. Type of Tests and Test Temperature, F Reference

6AI-4V 0.04-0.180 Tensile shear (RT). penetration, an..d 41nugget diameter

SAI-1Mo-1 0.04-0.175 Ditto 416AI-4V. " 0.1 Tensile shear(a), cross tension(a), and 12

8AI-lMo-IV fracture toughness (-110. 75. 400,650); thermal stability, and multispotshear (IT)

6AI-4V, 0.180 Tensile shear(a). and cross tension(a), 128AI1IMo-1V (-110. 75, 400. 650); multispot shear

(rT)SAI-1Mo-IV 0.044. 0.078. 0.124 Tensile shear, cross tension, and multi- 77

spot fatigue (RT); tensile shear (200,400, 600. 800, 1000, and 1200);

thermal stability (RT)6AI-4V 0.070-0.186 Tensile shear (RT. 600. 800. and 10GO); 78

cross tension, thermal stability., andthermal-stress stability

6AI-4V 0.05, 0.1 Tensile shear, cross tension, and 79fatigue (RT)

CP :itanium,6AI-4V

CP titanium.6A1-4V. 0.05 Tensile shear, cross tension, and 805A!-2.5Sn fatigue (RT)

6AI-4V,5A I-2.5Sn

8AI-lMo-!V 0.04. 0.08 Tensile shear, cross tension, and 47thermal stability (RT. 600. 800t 1600)

13V-1IC'-3Al 0.128 Fatigue (RT and ET) 8113V-1lCr-3A1 -- Airframe structures - static and 82

rc-peated load (RT)CP titanium 0.08 Tensile shear, cross tension, and 83

fatigue (RT)Pre-1960 data summarized 1

5A1-2.5Sn 0.05. 0.064, 0.08 Tensile shear (RT. 200. 40(,. 600. 800. 841000); fatigue (RT)

8AI-lMo-1V 0. 0.04-1.5 Various (RT to 650) including all simple --

tests plus thermal stabiiity. thermal-stres stability, and structures evaluation

5AI-2.5Sn 0.02. 0.040, 0.063. Effects of peel loading 850.100. 0.125

2.5AI-16V 0.040. 0.063, 0.090 Tensile shear 86

(a) About one-half of these tests made after exposure to 1300 F for 10 hours, all ozhers as welded.

129

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of loading, cross-tension strength will be low, and the commonly used

"ratio of cross-tension strength/tension-shear strength will be low.

The properties measured by tension-shear tests are excellent.

Cross-tension values also are good. Cross -tension/tension-shear

ratios are somewhat low (0.20 to 0.35) except in the Ti-13V-IlCr-3AI

alloy. Examples of tension-shear and cross-tension specimens are

shown in Figures 75 and 76 (Ref. 11). The tension-shear specimens

are pulled in a tensile testing machine employing grip jaws. A com-

monly used jig for pulling cross-tension specimens is shown schemati-

cally in Fioure 77 (Ref. 11). In both cases, the maximum load prior

to failure is recorded in pounds.

Fatigue and Fracture Toughness. The fatigue properties

of spot welds are low, but this behavior is characteristic more of the

joint type than of titanium alloys. Spot-weld thermal stability stuaies

indicate some loss in room-temperature properties from exposure at

050, 1000, and 1200 '. Similar exposure at 800 F did not lower the

room-temperature properties. A reason for this apparent inconsis-

tency is not apparent. Fracture toughness tests of spot weldments

exhibit properties inferior to comparable TIG fusion weldments. Spotwelding ha-s been used in a number of structural test comnponents. Such

tests provide the best evidence of expected weldment performance.Data from such tests have not been available for review.

Penetration. Spot-weld penetration is a measure of the

distance that the weld nugget extends through the thickness of the

sheets that were spot welded. It is normally expressed as a percent-

age of the sheet thickness with equal penetration in each of two similar

sheet thicknesses.

dt dbPt = 1= - x 100 - x 100

tt tb

Penetration is a function of weld current but can be affected, or con-

trolled, by such factors as the cooling effect of the electrodes, the

material thicknesses and thermal and electrical conductivity. When

dissimilar sheet thicknesses, electrodes, materials, or welding con-" d ition s o n th e tw o sid e s of th e sh e et ex ist, p en etratio n of th e w e ld nug -

get in each of two sheets can be quite different values. When proper

welding conditions are used, spot-weld penetration usually is less than

100 per cent. Most specifications limit weld penetration to a minimum

of 20 per cent and a maximum of 90 per cent for high quality spot, roll

spot, and seam welds (Ref. 87).

130i

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teetdSheet Separation. Sheet separation occurs as a result of

the electrode force tending to extrude the plastic phase of the weldnugget out between the adjacent surfaces of the weld joint. This sepa-ration in actual practice is generally measured away from the edge ofthe weld at a distance equal to half the diameter of the electrode in-dentation. It is common practice to sp.-ecify a maiximum acceptableseparation of 10 per cent of the sheet thickness joined, or 0. 006 inch,whichever is larger (Ref. 87).

One should be careful about sacrificing weld strength for low sheetseparation. It is possible to have very low separation with lower thanoptimum weld current. Higher than optimum weld currents also pro-duce low sheet separation, but at the expense of excessive weld-metalexpulsion. In either case, the weld strength would be somewhat lessthan optimum, and it would be more advisable to select an electrodewith a larger spherical tip radius, it is also possible to reduce sheetseparation through proper selection and control of the weldingvariables.

Electrode Indentation. Electrode indentation is a mea-sure of the depth of the indentations produced in the outer sheet sur-faces contacted by the electrodes. It is caused by a combination ofelectrode force, weld current,, weld time, and upsetting and shrinkageof the heated metal. Most specifications restrict electrode indentationto 10 per cent of the sheet thickness.

Weld Diameter and Weld-Nugget Diameter. The welddiameter includes the weld nugget and heat-affected zone (assuming ncmetal expulsion). This can be controlled, for the most part, by theradii of the electrode tips. Weld-nugget diameter is a measure of thediameter of the fused or cast metal. These diameters are expressedin inches or in terms of sheet thickness. It was shown in Figure 73cthat as the weld current increases, the weld nugget diameter and theoverall weld diameter approach each other.

Extrusion. The only apparent difficulty with the actualmaking of titanium resistance spot we'ds is a problem with metal ex-trusion between the faying surfaces of the overlapping sheets. Withthinner gages of material, extrusion does not appear to be a significantproblem. However, as the gage thickness is increased there appearsto be - much greater tendency for extrusion to occur. Proper weldingconditio-n-s and close control of welding variables are required to mini-mize or eliminate extrusion.

132

-u ill.

^-':--*---o Alpplications requiring the use of resistance

spot welding range from small aircraft components to spacecraft.Representative examples of the use of spot welding for fabricating ti-tanium alloys are given in the following.

Spacecraft. Spot welding has been used for many jointsin Mercury and Gemini spacecraft. Many combinations of materialthicknesses are encountered in resistance welding stiffeners todoublers and to skins. Spot welds have been made through as manyas seven layers and more than 300 thickness combinations have beenwelded successfully. Gemini spacecraft involved over 25, 000 spotwelds.

Figure 78 shows the arrangement of the parts and equipment forspot welding stiffeners to the side wall of a Mercury capsule (Ref. 52).Spot welding fixtures are moved manually but the path of travel is es-tablished by the fixture. Typical applications of resistance spot weld-ing to the fabrication of various spacecraft sections are shown inFigure 79 (Ref. 88).

Seam" • welds

FIGURE 78. SPOT WELDING ATTACHES STIFFENERS TOSIDEWALL SKIN ASSEMBLY OF THEMERCURY CAPSULE (REF. 52)

Stiffened Titanium Sheet Panels. A statically strong,

spot-welded titanium skin structure is highly practical for use in high-speed transport, according to tests conducted by one aircraft manufac-turer (Ref. 87). Tests have been made on Z -stiffened sheet panels forapplication in the empennage section of the transport. Three panels,

133

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134

18 bv 18 inches. were made from Ti-8AI-IMo-lV with five equallyspaced Z-stiffeners. All material was 0.060 inch thick, and weldswere spacc-d at 1.05, 2. 10, and 3. 15 inches. Equipment used was a100-kva, single-phase spot-welding machine. Spacing at 2. 10 inches,center to center, was found to be best for resisting inter-spot-\veld

kMing, yet wide enough to avoid residual-stress interaction between.,pots. An average lap-shear strength of 4500 pounds was produced onindividual spots, along with an average normal tensile strength of1000 pounds.

Aircraft Structures. Several steps in the fabrication ofa left-hand horizontal -stabilizer test component from Ti-4A1-3Mo-IVusing spot welding to establish fabricability are shown in Figures 79 to83 (Ref. 90). The subassembly fabrication consisted of spot weldingdoublers and angles to flanged ribs, Figures 80, 81, and 82; these de-tails then were welded to the upper external skin, Figure 83. Thespot-welding machine and fixture used for spot welding are shown inFigure 84.

ROLL SPOT WELDING

Roll spot welding is very similar in most respects to standard spotwelding. The major difference between the two processes is that inroll spot welding, wheel-shaped electrodes are used instead of thecylindrical type of electrode used in conventional spot welding. Theuse of the wheel electrodes in roll spot welding provides a convenientmeans of indexing the parts between each individual spot weld. Rota-tion of the wheels is intermittent; the wheel electrodes are in a fixedposition riuring the actual welding cycle. Electrode wear is more uni-formly distributed with a wheel-type electrode than it is with a conven-tional cylindrical electrode, thus it is possible to make many" morewelds without dressing of the electrodes when using roll spot welding.Con-ersely, roll spot welding techniques are less flexible than thoseused in conventional spot welding.

Equipment for roll spot welding differs from conventional spot-welding equipment primarily in that provision must be made to accom-mrdate the wheel-shaped electrodes. Also, a suitable drive and index-ing mechanism must be provided.

Roll spot welding of titanium alloys has been performed by at leastone aircraft manufacturer. Welding conditions for roll spot welding oftitanium have not been found in the literature, but they are expected tobe very similar to conventional spot-weldinxg conditions. Equipment

135

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F!GURE C-4. A SPOT -WELDING OPERATION ON THE UPPER SKIN SUB ASSEMBLY (RE. 90J)

- Skin is clanmoed m: tile contoured ýoot-welded asse~nbly jig.

138

for roll spot welding is essentially the same as equipment for resis-tance seam welding as shown in Figure 85 (Ref. 91).

7 iý

'FIGURE 85. PROJECT MERCURY SPACECRAFT, BUILT OFTITANIUM, REQUIRED 20, 500 INCHES OF

SPOT WELD PER CAPSULE (REF. 91)

SEAM WELDING

Seam welding also is similar to spot and roll spot welding. In

seam welding wheels are used in place of spot-welding electrodes.Individual overlapping spots are created by coordinating the welding

current flow, time, and wheel rotation. Seam welds often are madewith conventional spot-welding techniques. However, it is much more

common to use equipment designed specifically for seam welding andavailable comm-nercially. The principal advantage of seam welding isthat it can be used to produce leaktight joints. The principal disadvan-

tage is that there is much more distortion with sea-m welding than with

other types of resistance welding. In seam welding, the wheel- usu-ally can be rot.ated continually or intermittently.

139

The use of continuous scam welding imposes additional limitationson the weld-cycle variations that can be used. For example, a forgepressure cycle is not possible during continuous seam welding becauseof the continuous rotation of the electrodes.

Selected data on seam-welding conditions and properties of seam-welded joints are given in Table XXiI. Theze data include room-Lemperature static tensile strength. Static tensile propert~es arecomparable in efficiency to the parent metal for r.-iost of the titaniumalloys for which seam-welding data are available.

Applications. Resistance seam welding is of interest formany applications where titanium i..lRoys are used in sheet form. Rep-resentative applications of the process fcr fabricating various productsare described in the following.

Aircraft and Spacecraft. For the Mercury capsule skinassemblies the inner and outer skins of each section are joined to-gether by an intricate pattern of resistance seam welds, as shown inFigure 86 (Ref. 91). The size of the two cones is extremely important.Because of the seam-welding operation, they must fit together in inti-mate contact. In the cone section, the total length of these circurmwfer-

ential and longitudinal seam welds is about 22, 000 inches. The resultis hundreds of small, separately sealed pockets, which means that acrack anywhere will stop instantly. Special handling fixtures at thewelding machines move the work radially or longitudinally, dependingon the machine, with the electrode providing the driving force. Thecarriage-mounted fixture for seam welding is shown in Figure 87(Ref. 91). Several additional applications of seam welding for space-craft fabrication were shown earlier in Figure 78.

The use of seam welding to apply fuel-cell insulation for theF4B/C aircraft is shown in Fieure 88 (Ref. 11).

Commercially pure titanium in the form of rigidized sheet alsohas been resistance seam welded successfully for an engine-coolingshroud assembly (Ref. 93). The original thickness of the embossedsheets was 0. 012 inch. The ridges in the embossed sheets offered nodifficulty to seam "welding and lap joints had 100 per cent joint effi-ciency in static tension-shear tests.

140

wm

E E E

10 -D -

0~1

S.10' : :

; -b~E

uu~ u~ u

1A

FIGURE Z46. SCHEM\ATIC OF SEAM WELDSUSED IN MERCURY CAPSULE (REF. 91)

\ Detail shows offset rows of reinforcing beads\ and intricate pattern of lonmitudinal and

~ circumnferential seam welds that hold the twoU. 01 u-inch -thick mercury capsule titanium

kL skinS topether.

FIGURE 87. INNER AND MI2TER MERCURY CAPSULE SKINS ARE SEAM WELDED

(REF. 91)

(:iriave-.rncuw~ed fixture hVlds worhS% for hiitermittent seams.

142

FIGURE 88. THREE-PHASE, 200 KVA, SEAM-WELDINGMACHINE JOINING TITANIUM PANELS0. 002 INCH THICK TO BASE SHEET0. 020 INCH THICK (REF. 11)

End unit is for fuel-cell insulation in F4B/Caircraft.

FLASH WELDING

Flash welding is used almost exclusively to weld titznium rings for

jet engines. In addition, it has been used to weld many prototype andexperimental assemblies, including propeller blades and other complexassemblies.

In two respects, flash welding is better adapted to the high-strength, heat-treatable alloys than are arc, spot, or seam welding.First, molen metal is not retained in the joint, so cast structures arenot present. Second, the hot mnetal in the joint is upset, and this up-

setting operation may improve the ductility of the heat-affected zone.

Flash welding has several important advantages. Welding speeds

are very rapid, heavy sections can be joined, and high production ratescan be achieved. Filler metal is not added. Weight saving can berealized because there is no need for overlapping bolting, riveting, or

welding flanges. Extruded shapes can be flash welded and with suitabledesigns machining costs can be reduced. Good quality welds can be

obtained with the process.

143

.... L -%i Le% LOJ VveU LiLa jIIUl1

and titanium alloys does not differ greatly from that required for steel.This is especially true for transformer capacity. The upset-pressurecapacity for making titanium (Ref. 94) weldments is not so high as thatrequired for steel. Figures 89 and 90 (Ref. 94) show the transformerand upset capacity required for welds of different cross-sectional area.Also of importance, however, is the fact that transformer-capacityrequirements vary from one machine to another, depending upon thecoupling between the parts and transformer.

Joint Design and Joint Preparation. Joint designs for flashwelds also are similar to those used for other metals. Flat edges aresatisfactory for wrelding sheet and plate up to about 1/4 inch thick. Forthicker sections, the edges axe sometimes beveled slightly. Figure 91(Ref. 94) shows the metal allowances used in making titanium flashwelds. The allowances include the metal lost in the flashing and uset-ting operations.

Inert-Gas Shielding. For joints witn solid cross sections,inert-gas shielding is not necessary (Ref. 95) but may be used. Whenused, Fiberglas enclosures are placed around the joints, and inert gasis introduced into the enclosure. For joints in tubing or assemblieswith hollow cross sections, inert gas is introduced into the assemblies.

Conditions. The flash-welding conditions that are of greatestimportance are flashing current, speed and time, and upset pressureand distance. With proper control of these variables, molten metal,which may be contaminated, is not retained in the joint, ane the metalat the joint interface is at the proper temperature for welding.

Generally, fast flashing speeds and short flashing times are usedto weld titanium and titanium alloys. These conditions are desirablefor minimizing weld contamination and arc possiLble because of the lowelectrical and thermal conductivities of these metals. Also, the useof a parabolic flashing curve is more desirable than the use of a linearflashing curve because maximum joint efficiency can be obtained with aminimum of metal loss. Low-to-intermediate (7, 000 to Z0, 000 psi)upset pressures are used (Ref. 94).

Although flash-welding variables vary from machine to machineand application to application, -some conditions that proved satisfactoryfor two titanium alloys are listed in Table XXII (Ref. 96). Weldingcurrent is not given, but welding current and arc voltage depend on thetransformer tap that is used.

144

2200 I__

o 18001 1400 ~ ~~Steel '.,// /

~-1400 __

~1000__

0

C 800inessel ,•nlttnr

0 5 t0 15 20 25 30 35 40 45 50

Weld Area, square inches

FIGURE 89. TRANSFORMER CAPACITY VERSUS WELD AREA (REF. 94)

00

o 800

8 600 Stainless steei-inconel- I o e__20)0 -7to 301 0p 0 sS

Z 500 0

8400

200 0

Weld AreaMsquare inches A--ttn

FIGURE. 90. MAXIMUM MACHINE UPSET-PRSURE REQUIREMENTS VERSUS WELD AREA

145

7

1.200 Add 0.030-0.120 for

hand-feed allowance

Constant feed, accelerated• '/ /.,- , burnof f, upset0.600

Steel Envelopeashownd 0.400• . n.coel-- Upper port ion of

Stainle - envelope

/l tont feed

| - accelerated burnoff,

0-40I ------ Extrapolated0.0 - Test data

00.200, ,

0 00200 0.400 0.600 0.800 1.00

Stock Thickness, in.

S~FIGURE 91. TOTAL METAL ALLOWANCE VEP.SU•S STOCK THICKNESS (REF. 94)

1.00

146

V

0.8W

TABLE XXIII. FLASH-WELDING CONDITIONS (REF. 1)

Material ConfigcUradon Ti -4A I-4Mn. Ti -8A-4V. Ti-6A I-4V.3-1/2-Inch Round 3-1/2-Inch Round 1/4-Inch Plate

Flashing Voltage. volts 5.0 5. 0 4.5

Total Metal Allowance. inch 0.617-0.940 0.617-0.940 0.700-0.800

Upset. inch 0.200-0.500 0.200-0.500 0.225-0.275

Current Cutoff. inch 0.150-0.400 0.150-0.400 0.205-0. 255

Upset Pressure. ksi 15 15 18

Sheet Height. inch 1. 10 1.10 0.63Atmosphere Argon Argon Argon

Properties. Flash welds that have mechanical properties ap-proaching those of the base metals are being regularly produced in

conventional machines.

The static-tension-test properties of flash-welded joints are sum-

marized in Table XXIV (Refs. 94, 95, 96). The bend ductility and

fatigue strengths of the flash-welded joints are summarized in

Table XXV (Refs. 95, 96).

The static and fatigue properties of flash-welded joints are good.

Most tension specimens fail away from the weld center line with

strengths that are almost equal to or exceed those of the base metals.in fatigue tests, more failures at the weld center line a-re observed

than in tension tests, but the incidence of center-line failures is not

high.

Application. Flash welding has been used for fabricating

components ranging from light sections such as jet-engine rings to

heavy sections such as aircraft landing gear. Steps in the fabrication

of several components illustrating the use of flash welding are de-scribed in the following.

Airframe Structural Components. In a program to de-

velop new methods and techniques for titanium airframe structural

components, an aluminum stabilizer yoke for the FlIF-1 supersonicfighter airplane was redesigned and manufactured from Ti-5A1-2. 5Sn

(Ref. 98). The original yoke was made from numerous aluminum alloypieces bolted and riveted together as shown in Figure 92. The titanium

yoke for flash welding, Figure 93, consisted of three box-type sub-

assemblies and two end-fitting subassemblies. One of the subassem-

blies is shown before and after flash welding in Figures 94 and 95,respectively.

147

A

I

TABLE XXIV. ROOM-TEMPERATURE TENSILE PROPERTIES OF FLASH-WELDED JOINTS (REF. 1)

UltimateNominaP Tensile Elongation

Composition. Condition of Strength, in 2 Inches,weight per cenit Base Metal Postweld Heat Treatment ksi per cent

Commercially pure Annealed Not welded 117 21-23titanium Annealed 1000 F. 1 hour, air cool 114-118 19-23

5AI-2.5Sn Annealed Not welded 133-134 14-31Annealed 1200 F. 2 hours, air cool 127-136 11-28

Ti-4Mn-4AI Annealed Not welded(a) 130-141 15-19Annealed 1400 F. 2-3 hours, furnace cool 127-138 11-17

Ti-4Mn-4A1 1450 F. 3 hours. Not welded lb5-160 10-12water nuerch; 1450 F, 3 hours, water quench; 153-162 1(b)_ 1 0

100 F. 8 hours, 1000 F. 8 hours, air coolair cool

Ti-3Cr-3AI Annealed Not welded 142 15Annealed -- 142 12

Ti-6AI-4V Annealed Not welded 133-137 12-19Annealed 1300 F. 2 hours, air cool 13C-145 10-15

Ti-6AI-4V 1550 F. 1 hour, Not welded 144-148 9-10

water quench; 100 F. 1 hour, water quench; 142-143 8-10

950 F, 24 hours 1000 F. 24 hours, air coolair cool

(a) Some specimens furnace cooled to 1000 F and then air cooled.(b) Failed on weld center iine.

148

-pc

- •

TABLE XXV. BEND DUCTILITY AND FATIGUE STRENGTHOF FLASH-WELDED JOINTS (REF. '75)

NominalComposition. Minimum Fatigue

weight Condition of Postweld Heat Bend Radius, Strength(a),per cent Base Metal Treatment T ksi

Ti-5A1-2.5Sn Annealed Not welded 2-4 --

Annealed Annealed 4 --

Ti-4AI-4Mn Annealed Not welded 3 56-72Annealed 1400 F. 2 hours, furnace 3-4 35-79

cool to 1000 F. air cool

Ti-4AI-4Mn 1450 F. 3 hours, water Not welded 3-4 70-89quench; 1000 F. 1450 F. 3 hours, water8 hours, air cool quench; 1000 F.

8 hours, air cool 5->5 53-87

Ti-5Cr-3AI Annealed Not welded 2-3 84Annealed 2-3 70

Ti-6A1-4V Annealed(b) Not welded 3 80-911300 F, 2 hours, air cool 4 44-87

(a) Rotary beam specimens. Prot method used. Most specimens failed away from the weldcenter line but some failed on the weld center line.

(b) Fatigue data on another heat obtained, but was very low because of impurities.

1i

149

I

'U A

FIGURE 92. PRODUCTION YO' .F WITH STABILIZER PANELS ATTAC'iED ("EF. 98)

. . -. , .. , STAGE 2--Il

STAGE 3

FIGURE 93. FLASH-WELDED FOIL STABILIZER YOKE ASSEMBLY (REF. 53)

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Clamping during flash welding had to be clean, secure, and uni-form in order to insure low contact resistance and avoid die burns.Flash was removed by chip hammering, grinding, and polishing.

Rings. Titanium rings used primarily as inlet guideflanges and as front compressor flanges in aircraft jet engines alsohave been fabricated by flash welding (Ref. 95). Cross-section areasthat have beea welded range from 0. 26 to 5. 39 square inches for com-mercially pure titanium and from 0. 66 to 3. 84 square inches for sometitanium alloys. However, 12-square-inch sections of titanium areweldable with commercial flash-welding machines. The rings usuallyare rolled to near the final size, allowing for material that will beflashed away. The open ends of the rolled rings then are flash weldedtogether to form the completed rings. Substantial cost savings can berealized using this fabricating technique (Ref. 99). Examples of theeconomy of flash-welded ring products are illustrated in Figure 96(Ref. 100).

C:igualca•-430 lb

•.ri' Ww 2,"r•WeA - DD N PRde U I T S. (REF. 1

ora 931I ua*. 71 It,

k f~r~d Vav"Vadde

IIIC_ #"N1NrJ-b Voe"m la"pd Sct.Sx

FIGURE 96. TYPICAL EXAMPLES OF TH ECONOMY OFFLASH- WELDED RING PRODUCTS (REF. 100)

153

..... ...

"HIGH- FR EQUENC .WELDP.G

Titanium tubing has been made using the high-frequency weldingprocesses illustrated in Figure 97 (Ref. 101). Althoaigh used for de-velopment quantities, speeds up to 105 fpm have been used.

At trcsent, only one fabricator has referred to production of high-frequency welded tubing (Ref. 102). The tubing has a 0. 025-i:ich-thickwall and is used in manufacturing a heat-exchanger bundle. The tubing

features a 12 per cent cost reduction. Because of high tube mill andmaterial costs, it is unlikely that high-frequency wel,:ed titanium ortitanium-alloy tubing will become available as a standard product untilquantity requirements increase. High-frequency welding, however,does have long-range potential for making titanium tubing economical.

High-frequency welding also has capabilities for manufacturingfabricated structural shapes from titanium. Titanium tees have beenfabricated experimentally and indications are that the process can beadapted to fabricate I-beams, stiffened-skin sections, and other struc-tural shapes.

BRAZING

Brazing has attractive advantages over other joining processes inthe fabrication of titanium sandwich structure, and in the completion ofdissimilar metal joints. Despite the great potential for these twoareas, most of the programs that have been conducted to complete re-quired development have not produced universally acceptable proce-dures for completing such joints.

Most of the problems encountered in attempting to braze titaniumare related in one way or another to the characteristics of titaniummetal. The high affinity of titanium for other elements leads to a re-quirement that brazing must be conducted under conditions that preventcontamination or degradation of the material being joined. Also, be-cause of its high reactivity, it is difficult to find suitable braze fillermetals that do not react excessively with the titanium base materialproducing subsequent embrittlement or serious erosion of the base

metal. The final problem area has been one of finding brazing fillermetals suitable for use with brazing thermal cycles that are compati-ble with the limited thermal heat-treatment cycles that can be used ontitanium alloys.

Filler Metals. To be useful as a brazing filler metal, analloy must melt within a desired tempel ature range, it must wet the

154

Source of high-frequency currentSeam guide

Bulk current flowand heat pattern

-Insulation

Small circumferential

current flow (mirnimizedS--" " by impeder )

4 _W Squeeze rolls

eld

Ferrite impeder

a. Mechod of operation of contact-resistance tube-welding head

Seam guideWork coil- I

Earthf" •

Current concentrato Source of high-

- ~frequency currentCenter of closure ofsqueeze rolls(rot ic niot shown '

//• .a pattern

ýFerrite flux concentrator eld

b. Meth•od of operation of induction rube-welding head

FIGURE 97. HIGH-FREQUENCY WELDING METHODS FOR \L-ANUFACTURING TITANIUMTUBING (REF. 101)

155

I

base ratpria! :nvolverd. and it should flow to some extent while moltenon the base metal. Of all the various metals and alloys that meet oneor more of these criteria, only the silver-base alloys have been usedwith much success for the brazing of titanium. Not all of the silver-base brazing alloys are suitable for use with titanium, but at least sev-eral have been found that appear to exhibit many of the desirable prop-erties of a brazing filler metal. The most promising allo 3 are eithersilver-lithium, silver -aluminum. -manganese, or silver-copper-lithium allols. The most common problem encountered with otherbrazing alloys, which on the surface appear usable, is that they reactreadily with titanium. Only through the use of very short brazingtimes is it possible to prevent excessive alloying between the fillermetal and the titanium-base material.

The most promising alloys at present are those containing alumi-num and manganese in a silver base. Although alloys of this type ap-pear to be somewhat better than the silver-lithium alloys with respectto oxidation resistance and salt-spray corrosion resistance, there isstill some reluctance to use the materials where exposure to theseconditions can be expected. The brazing temperature for the silver-aluminum-manganese alloys ranges between about 1450 to 1650 F.

The silver-lithium alloys are used in a composition ranging from0. 5 to 3 per cent lithium. However, joints made with these alloys donot have good oxidation resistance in air at temperatures of about800 F and the joint strength is seriously degraded by exposure to theseconditions. Joints made with the silver-lithium alloys also appear tohave poor corrosion resistance in salU-spray environments.

The silver-cachnium-zinc brazing filler metals al~o have been de-veloped and have been used for oxyacetylene torch-brazing applica-tions. Consistent joint tensile strengths in the range of from 40, 000 to50,000 psi and single-lap-joint sheai-strength values in excess of30, 000 psi are reported. Silver-cadmium-zinc brazing filler alloyscontaining 20 per cent silver have been patented for combining excep-tional mechanical properties (Ref. 104). These alloys were developedfor use in joining titanium to itself, steel, stainless steel, and silveralloys. Fluxes for use with these alloys have also been developed.

The experimental palladium-base alloy, Pd-14. 3Ag-4. CSi, hassome very desirable characteristics (Ref. 103). It has excellent flowcharacteristics in the temperature range of 1395 to 1450 F (below thebeta-transition temperature of pure titanium). The alloy forms ametallurgical-bond, with alloy interfacial penetration of 0. 0015 inchinto titanium and 0. 003 inch into stainless steel. Ultimate tensile

156

strengths of joints as high as 75, 000 psi have been achieved. Connec-tions brazed with the alloy are inert to nitric acid and, -inder vacuum,helium leakage is less than 0. 63 cubic centimeters per year.

A wide variety of brazing alloys has been investigated and someare available commercially. A partial listing of patents issued onbrazing filler metals and fluxes is given in Table XXVI (Ref. 104).Many additional alloys and properties of brazed joints are described inpublished literature. Obviously, brazing alloys for titanium alloysmust be selected with care, depending on the alloy being joined, thick-ness, mass, penetration tolerance, and service requirements.

Brazing Methods. The methods that have been used to brazetitanium are similar to those used for other materials such as stain-less steel. With titanium, however, particular care must be taken toinsure against contamination of the base metal during the brazingcycle. This has necessitated the careful use of either inert gas orvacuum environments during the brazing cycle. Heating for bra-.ingis generally accomplished in retorts placed in furnaces or by sometype of radiant heating device such as quartz lamp panel. Ceramicblanket brazing also has been used (Ret. 105). Some success has beenreported with a conventional oxyacetylene -torch brazing technique(Ref. 104). Brazing methods used on titanium demand careful controlthroughout all steps to insure that the titanium-base material is notdegraded or contaminated from any source.

Properties. .The lap-shear btrength of brazed joints is listedin Table XXVI. These data were obtained from specimens brazedusing inert-gas-filled retorts and conventional furnaces. The brazingcycle for most of the joints consists of heating the retort to a temper-ature of 1450 ±L0 F, holding for 5 minutes, and air cooling to roomtemperature. The joints made with the silver-aluminum-manganesealloy were brazed at a temperature of 1600 F. The joints preparedwith the silver-aluminum alloys have better elevated-temperaturestrength and better resistance to salt-spray corrosion and elevated-temperature oxidation than the joints made with the silver-lithiumalloys even when the brazing alloys 're plated.

Effects of Brazing Cycles on Base-Metal Properties. Animportant factor in selecting brazing filler metals for titanium alloysis the effect of the brazing cycle on base-metal properties. This fac-tor is especially important in brazing heat-treatable titanium alloys.Several general rules may be outlined.

157

F__S

TABLE XXVI. TITANIUM Bgq-ZING AND SOLDERING PAI ENTS FROM THE "TITANIUM ABSTRACTS-.-iL THE t2' IST'PTALCHETCA!C A!!iNDSTRIIý LTD- (!C!I !REF. 1041

Patents Authors Annotations

British

741.735 Industrial Chemical Industries. Ltd. Ti:anium flux containing KKF2 KCI741.736 Ditto Joining titanium articles with aluminum

base - 2 to T7 magnesium filler metal741. "737 Titanium brazing aluminum base 5 to 1I

silicon filler metal

750.928 Lundin. H. Flux for coating titanium 25 to 70t AIF3

45 to 6.* NaF, bal. KF752,117 Long. R. A. Ni-Ti-Cu brazing compounds768.126 Nat. Res. Dev. Corp. Titanium flux containing Cu Cl. Ag CI788.589 Kaisha. S. K. K. Titanium brazing to stainless steel, silver.

Ag-Mn, Ag-Cd alloys used

824.256 Thompsen-Houston Co. Titanium brazing with chromium carbides

German (Applications)

1003012 Titanium soldering with A!-12% silicon

alloys1003013 Titanium soft solder Al-5.•' Mg alloy.

KHF2 -KCI flux

10036017 Like U. S. 2.666.7725

German

859.249 Degussa Co. Ag-Cd-Zn alloy silver up to 2056

United States2.666. 725 Chemer. E. S. LiF. KCI. KHF 2 brazing flux2. 781. 04-7 Meredith. H. L. Joining titanium to aluminum2. 76,.. 27 1 Meredith. H. I.. Brazing titanium with gas tungsten-arc

process and silver filler metal2.798.1843 Slovin. G. W. Plating and bWazing titanium

2.82-2.269 Long, I. H. Bonding titanium to base metals by aTi-Ni eutectic composition

2.834. 101 Boam. W. M. and Friedman. I. Plating method for braziisg titanium2.844.867 Wernz. D. E. and Swartz. M. M. Titanium dip-brazing method2.847.302 Long. R. A. Titanium bonding ceramics by Ti-Ni eutectic

with additions of copper, cobalt.manganese. etc.

2.882.593 Sobel. M. %'. and'Weigert. K. M. KHF 2 . KC1. BaCh2. LiF brazing flux2.914. 848 Ph-llips. E. and Blum. S. Titanium brazing alloy with 2 to .V tin.

2 to 5ý, aluminum. balancr. silver

2.919. 984 Eutectic Welding Co. Silver 51. cadmium, zinc alley

S18

!New

r -* -

TABLE XXVII. SHEAR STRENGTHS OF TITANIUM BRAZED JOINTS (REF. 106)

TestTemperature. Shear Strength. ksi

Condition F Low High Average

Ti-.WAI-2.75Cr-1.25Fe Base MetalsNickel-Plated 97Ag-2Li Filler Metals

As brazed RT 12 !6 14As brazed 800 3 5 4

Ti-5AI-2.75Cr-I.25Fe Base MetalsPlatinum-Plated 97Ag-2Li Filler Metals

As brazed RT 17 23 19

As brazed 800 2 4 3

Ti-5AI-2.75Cr-1.2SFe Base MetalsAg-Al-Mn Filler Metals

As brazed RT 22 26 24As brazed 800 14 17 16

The brazing temperature shculd be 100 to 150 Fbelowthebetatran-

sus for the alloy. If the brazing temperature exceeds the beta transus,

the base-metal ductility may be impaired, especially in the alpha-beta

aiioys. In beta-type alloys, the beta transus may be exceeded without

impairing base-metal properties but if the temperature is too high, the

ductility of the alloy after heat treatment may be impaired.

In brazing heat-treatable alloys, the brazing temperature may af-

fect the ultimate and yield strengths of the alloy after final heat treat-

ment unless it is possible to fully heat treat the assembly after braz-

ing. For example, full heat treatments for most of the heat-treatable

alpha-beta alloys consist of two operations: solution treatments to

adjust the ratio of aipha and beta phases (thereby adjusting the compo-

sition of the beta phase) for optimum heat-treatment response, and

age-&hardening treatments. If the brazing operation is part of the heat-

treatment cycle, it is desirable to braze at either the solution-treating

or age-hardening temperatures. However, the age-hardening tem-

peratures are low (800 to 1100 F) and satisfactory alloys that rrvelt and

flow at these temperatures are not available.

If the brazing operation is pF•rformed near the solution-treating

temperature as part of the heat-treating operation, then, the cooling

rate from brazing temperature may affect the final properties of the

base metals. This is especially true for alloys, such as Ti-6A1-4V,

159

Z"P V0 0_' " zA

that have low beta content and require rapid cooling f.rom solution-

treating temperature to obtain good heat-treatment response. Someof the all-beta alloys retailn g0d r ---,-ponse- ---..furnace-cooling operations.

Applications. Brazing has been used for joining titanium ex-perimentally for about 20 years, and in production applications for

about 10 years; the widest use has been in fabricating honeycomb sand-wich panels. This application has been studied by many organizations(Refs. 103, 105, 107-109). Representative applications of titaniumbrazing techniques are described in the following.

Honeycomb Sandwich Structures. In furnace and retortbrazing operations, titanium can be contaminated by leakage of airinto the brazing atmosphere. To insure agz.inst such leakage, onefabricator has devloped a double-layer inert-gas shroud retort forbrazing titanium (Ref. 110). ' he shroud retort has been used mainlyfor fabricating brazed honeycr.mb panels from titanium and from stain-less steel. In addition to providing good protection against contami-nants, the process provides ior lo-..wer argon consumption and shorterbrazing cycles than were obtained with conventional retorts. Thetechnique permits the use of gas or electric furnaces and eliminatesthe need for a secondary argon-filled retort around the brazing retort.

The technique isolates the titanium from contamination both dy-namically and mechanically. Protection is afforded by two separateatmosphere zones and a pressure differential that insures more effec-tive protection. This system, shown in Figure 98, is similar to a

conventional retort, except that it is larger and is divided into twopressure zones. The outer zone is maintained at a reduced pressure

while the inner zone is filled with argon gas. Air entering through aleak in the retort is removed between the retort and the barrier Zndexhausted through the vacuum tube. The pressure differential helpshold the parts in intimate contact duriing the brazing cycle. A typicalbrazing sequence of operations is described below.

Thin contoured skins are cold stretch formed. Only the close-tolerance sheet-metal edge members are hot formed to obtain correctdimensions and contour. After the titanium parts are produced, theyare checked for fit, dimensions, and tolerances in a prefit operation,or trial assembly. Then they are cleaned as follows:

(1) V-por degrease thoroughly(Z) Soak 10 to 15 minutes in caustic cleaner (180 to 190 F)

(3) Rinse in tap water (120 to 140 F)

160

Tf

Atmosphere

Vacuum diaphragm rBarrier sheet

Vacuum _N N_/PnlArgon gasOrf ice 2supply

I L

1'= OrificeI

Brazing retort Graphite Barrier sheet

Pressure inside barrierPressure outside barrier

a. Honeycomb Panel Shielded by Two Pressure Zones to Keep Contaminants Out

Pressure outside barrierPressure inside bl.rrier

4 - Brazing retorf

G r-raphite

Barrier

Leak in retort

b. When Retort Leaks, Contoainonts Are Exhausted Through EvacuationTube

FIGURE 98. DOUBLE-WALL RETORT SYSTEM FOR BRAZING TITANIUM ALLOYS SANDWICH

PANELS (REF. 110)

I

161

(4) Acid clean 15 to 30 seconds (3% Hf-15% HNO 3 )

(5) Rinse in tap water (RT)

(6) Soak 2 minutes in caustic cleaner (180 to 190 F)

(7) Rinse in tap water (120 to 140 F)

(8) Rinse in distilled or demineralized water (RT)

(9) Dry in hot air.

Brazing alloy foil, Ag-Al-Mn, is cleaned by vapor df-greasing, soaking2 to 5 minutes in caustic cleaner, rinsing in hot tap water (120 to 140 F),and wiping with soft cheesecloth. From this point on, extreme caremust be taken to keep the parts clean. Operators must wear clcangloves and perform the following operations as rapidly as possible tominimize the formation of oxides on the clean metal surfaces.

First the panel is assembled and checked in a lay-up fixture thathas copper chill bars for tack brazing. Here the parts are fastened inposition with light tack-braze spots. Then the panel is placed insidethe stainless steel brazing retort and thu atmosphere barrier tool.Slip sheets that prevent the skins from bonding to the diaphragm andfillers are added. Next, antibraze "stop-off" material is painted onsurfaces where adhesion is not desired. After this, the vacuum dia-phragm, or cover sheet, is welded in position on the retort, and theunit is checked for leaks. If leaks are not eliminated, air cannot bepurged from the retort satisfactorily. Purging consists of alternatelydrawing a vacuum on the retort and then supplying it with argon gas;the number of repeat cycles depends on retort capacity and vacuumpressure. Pressures of 25 to 50 microns are desirable, but effectivepurging can be done with pressures as high as 1.92 inch Hg (absolute).

Next, thermocouples are attached to the vacuum diaphragm di-rectly over the panel, and the diaphragm is covered with insulatingmaterial to offset the effect of the graphite reference tool - one layerof 0. 080-inch aluminum silicate paper for each inch of graphite thick-ness. This b.1ances the heat input to the panel from both sides. Thenthe automatic vacuum control is set to maintain the desired pressure.This setting is critical, because insufficient vacuum fails to provideenough contact pressure for a good quality braze- but too much vacuumcan crush the honeycomb core, which becomes extremely weak atbrazing temperatures. The rate of heating to brazing temperature(1625 F) dues nct appear to be critical. However, to reduce the risk"of contamination, it is desirable to complete the hot cycle as quicklyas possible.

162

€,wVi

The retort is then removed from the furnace and air cooled. With

sone titanium alloys the retort rnmv he in'zprted into An naing furnace,

although additional cooling will do no harm.

Residual antibraze material is removed by scrubbing wth alumi-

nun oxidf powder and a stiff-fiber brush. Then a light coating (-"

silicone oll is applied to prevent surface contamination in subsequent

handling. All panels are inspected radiographically to verify the quai-ity of internal brazed joints, but visual examination determines the ex-

tent of possible external defects. The basic retort is re-useable. Theparts are cleaned and straightened after each brazing operation for re-use. The vacuum diaphragm and slip sheets, however, are expendable.

Three titanium-5Al-l. Z5Fe-2. 75Cr sandwich panels ased on the

B-58 aircraft, as illustrated in Figure 99, have been made by brazing

using the system described above. The panels included an elevon sur-face panel, a nacelle panel, and an elevon training wedge.

Brazing Stainless Steel to Titanium. Commercially pure

titanium and stainless steel tubes, 1 -inch OD by 0. 035-i. ch wall havebeen brazed (Ref. 111). The titanium tube was inserted in the ex-

panded end of a stainless tube, with various amounts of 98Ag-2Li alloy

foil and wire. The assembly was placed in a Vycor glass tube with aflowing argon gas atmo.,-phere. An induction coil with five turns was

placed around the joint. A 10-kw (450-kc) induction generator wasused as the heating source. The brazing cycle consisted of argon

purge for 5 to 10 minutes and heating to the brazing temperature of1450 to 1500 F in Z to 4 minutes. Up to 75 per cent of the circumfer-

ence of the tubing joint was brazed. No benefits were obtained from

either silver plating the titanium tubing or nickel plating the stainlesssteel tubing. All the sections of the brazed joints that were exposed to

salt spray failed within 100 hours.

SOLID-STATE WELDING

In solid-state welding, joints are formed with all components ofthe joining system being maintained as solids. Welds can be made

under these conditions if two metallic surfaces, which have been pre-

pared properly, are brought together under an applied pressure at asuitable temperature for a sufficient length of time. Deformation and

diffusion are important mechanisms of solid-state welding. It is con-venicnt to subdivide this type of welding on the basis of whether de-

formation or diffusion is the predominant mechanism contributing toweld formation. Actually, both mechanisms always operate to some

163

- C .. 1 --. -• .-

extent during the formation of a joint, but there are significant differ-ences in the extent to which these two mechanist-as control a givenwelding process. Deformation may be limited to very smnall surfaceareas during welding that is controlled primarily by diffusion mecha-nisms. When considerable deformation is used during the welding op-eration, diffusion can be quite linnited. Both deformation and diffusionwelding have been applied successfully to titanium.

Solid-state welding consists of ma.iy joining urocesses that haveoeen referred to by a numbe" of di;ferent names. As used in this re-port, the term solid-state welding is intended to cover all joiningprocesses in which either diffusion or deformation plays a major rolein the formation of the joint and in which a liquid phase is absent dur-ing welding.

Diffusion Welding. Solid-state diffusion welding is a joiningmethod in which metals are welded through the application of pressureand heat. Pressure is limited to an amount that will bring the sur-faces to be joined into intimate contact. Very little deformation of theparts takes place. Solid-state diffusion welding does not permit rnelt-ing of the surfaces to be joined. Once the suriaces are inl intimate

contact, the joint is formed by diffusion of some element or elementsacross the original interfaces.

Some of the merits that make this process attractive as a methodof fabrication are as follows:

(1) Multiple welds can be made simultaneously.

(2) Welds can be -nade that have essentially the same mechani-cal, physical, and chemical properties as the base metal.

(3) Welding can be done below the recrystallization temperatureof most materials.

(4) The formation of brittle compounds can be avoided providedthat proper materials and welding conditions are selected.

(5) For each material combination, the:-e are several con.bina-

tions of parameters which will produce v ;!ds.

Diffusion welding is primarily a time- and temperature-controlledprocess. The time required for welding can be shortened considerably

by using a high welding pressure or temperature because diffusion ismuch more rapid at high temperatures than at low temperatures. Boththe weiding time and temperature often can be reduced by using an

164

r°

N,,

i ",, a J" ~

FIGURE 99. APPROXIMATE LOCATIONS OF ELEVON SURFACE PANEL, NACELLE PANEL AND

ELEVON TRAILING WEDGE

165

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I

intermediate material of different comrosition to promote diffusion.This procedure reflects the increase in diffusion rate that is obtainedby the introduction of a dissimilar metal.

The steps involved in diffusion welding are as follows:

(1) Preparation of the surfaces to be welded by cleaning orother special treatments

(2) Assembly of the components to be welded

(3) Application of the required welding pressure and tempera-ture in the selected welding environment

(4) Holding under the conditions prescribed in Step 3 for therequired welding time

(5) Removal from the welding equipment for inspection and/ortest.

The peparation step involved in diffusion welding usually includesa chemical etching and other cleaning steps similar to those employedduring fusion welding or brazing. In addition, the surfaces to bewelded may be coated with some other material by plating or vapordeposition to provide surfaces which will weld more readily. Coatings,such as ceramics, are sometimes applied to prevent welding in certainareas of the interface. The methods used to apply pressure includesimple presses containing a fixed and movable die, evacuation ofsealed assemblies so that the pressure differential applies a givenload, and placing the assembly in autoclaves so that high gas pres-sures can be applied. A variety of heating methods also can be usedin diffusion welding, but generally, the temperature is raised by heat-ing with some type of radiation heater. As suggested above, the en-vironme:At during welding is another important factor during this typeof joining. With titanium, a vacuum environment is desirable, al-though it is possible to bond in an inert gas.

Diffusion-welded joints have been made in titanium and several ofits alloys at selected conditions including 'he foilowing ranges:

Temperature 1500 to 1900 FTime 30 minutes to 6 hoursPressure 57 000 to 107 000 psi.

Welding conditions reported in the published literature are given inTable XXVII!. In all cases, the environment during welding was avacuum. Some zuccess has been reported with the diffusion welding

167

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168

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of titanium employing an intermediate material to either decrease thewelding temperature or the required time. The usefulness of thismethod with titanium is limited by the difficulty in finding an inter-mediate material which will not re- t excessively with the titanium toform either brittle intermetallic compounds or other undesirablephases.

Deformation Welding. Deformation welding differs from dif-fusion welding primarily in that a measurable reduction in the thick-ness of 4he parts being joined occurs during deformation welding. Thelarge amount of deformation involved makes it possible to produce aweld in much shorter times and frequently at lower temperatures thanare possible during diffusion welding. The major application of defor-mation welding of titanium to date has been in the fabrication of roll-welded sandwich structures. Unidirectional structural panels witheither a corrugated or ribbed structure have been produced with thisprocess. In addition, the process shows promise for the fabricationof structural shapes such as tees or I-beams.

The steps involved in deformation welding are very similar tothose used in diffusion welding. The major difference between thesetwo solid-state-joining methods is the amount of deformation used.Diffusion welding uses only that deformation required to bring the fay-ing surfaces, with commonly encountered roughnesses, into intimatecontact. The deformation is confined to a narrow region on either sideof the interface. In deformation welding, however, the restrictionsgiven above do not apply. Welding deformations as great as 95 percent may be used, for example. The use of high deformations, appliedrapidly, can substantially reduce the time required for welding; e.g.,I second or less.

Roll Welding. Roll welding is a solid-state deformation-welding process that has been used for the fabrication of titaniumsandwich panels and other structural shapes (Refs. 119, 120). Truss-core panels., with the structural members supported by a matrix ma-terial of mild steel, are fabricated using a hot-plate rolling-mill re-duction sequence. The cleaned and assembled pack, Figure 1010. issealed by welding, evacuated, and outgassed at 1600 F for about'I hours. For .most titanium alloys, the rolling temperature is in therange of 1400 and 1800 F. Subsequent to rolling, the composite can beformed, with conventitnal equipment in the same mannr as a solidplate. After forming, the mild-steel supporting structure can be re-moved by leaching with a nitric-acid solution.

i69

--..

Pock cover

•/1 Sandwich face

YokeCore . " /

Filler bars -

Hole fre, Sc/ faceevacuation tube • Sandw.ch face",--Pock cover

FIGURE 100. EXPLODED VIEW OF ROLL-WELDED PACK

PRIOP. TO HOT ROLLING (REr. 119)

Materials which have been investigated and found to be suitable for

this method of fabrication include:

(1) Aluminum alloys, 2024 and 5052

(2) 1iitaniu,-n, alpha and alpha-beta alloy

(3) 300 series stainless steels

(4) PH 15-7 Mo precipitation hardening stainless steel

(5) Nickel-base alloys, Rene 41 and Inconel

(6) Ref:actory metais, tantalum, columbium, mnolybdenum,

and tungsz:n.

Roll weids between columbiurn andc molybdenum. B66 columbiumr-base

alloy c.,nd TZM molybdenum bast- alioy, tantalum and tungsten, tungstenind Te-I0W, copper and titanium, stainless steel and :itanium, and

stainles steel a-.,d tantalum have recently been reported (Ref. 121).

!70

jL________________________________________________ ______________________

trated in Figure 301.

Heated or coo~ed Cylinders predominantlylooding edge axial lood and bending

Pred~minantly pressure L~oor conductivity saridifich

FIGURE 101. T YPICAL APPLICATIONS OF ROLL- WELDEDCORRUG AT ED SAND WICH CONSTR UC TIOiR(R EF - 1l1'4)

Pressu~re -Gias Welding. Pres sure -gas welding faefs. 122,123, 124), is a welding ?,rocess in which the joint is prod.,,-ed ssirul-taneousiy over the e-ntire area of abutt-ing surfaces, by he--ting wi~th gasflam-ies and by the application of pressure, without the use of fl~metal- Pressure-gas wvelding may or may not be a solid -stase-%velringprocess, depending on the actual welding procedure used. The twqo

modifications of the process in commri.o use are the closed-joint amdthe open-iciints method-s. in the- clos~e-iPýoinr method, the cle~an fac-es ofthe parts Ito be joined are abutted tog~ether under pressure and heate-dby gas f~larmes until a predeterminied upsetting of tZhe -*imt OCCUTS- Th imethod off pressure-gas welding has been used for wektlng severa ta-taniurn alloys for tubing andi prressure vessel. applkcatio-is. in theopen-joint mmethod the faces to bejoined are individual'I heated by -igas f'lames to the melting temnperatu~e and then brought into contactfor upsett~ng. The open-Joint method has not been used for weldingtitanium or titanium alloys. The process in both modifications isideally adapated to a mechanized ope~ratiorz, and practically all cor-mmercial applicatio-ns are either partially or fully mechansized- 7heprocess is 4,adaptable aisc. zo the welding of low- and high-carbon sleells,low- and hig-.-allov steels, and several nonferrous metal alloys.

Since the metal along the interface in the closed-joint method doesnot reach the melting point, the ode •f we•Idi•g is different from thatof fusion-type welding. Generally speaking, welding takes place by theaction of grain growth, diffusion, and grain coalescence across theinterface under the impetus of high temperature and upsetting or pres-

sure. It has been demonstrated in several research programs thatthese forces are capable of creating a high grade weld. Pressure-gaswelds are characterized by a smooth-surfaced bulge or upset at theweld and by the general absence of fused metal in the weld zone.

In the open-joint method, welding takes place in the molten statebut most of the molten metal is squeezed from the interface by impactpressure. The welds made by the open-joint technique resemble flashwelds in general appearance.

Pressure-gas welding has been successfully applied to the fabri-cation of titanium alloys for liquified-gas container tanks, tubing andpipe, and stabilizer arms for B58 aircraft escape capsules. A widerange of thicknesses and sizes have b.!en welded by this method. Tobe acceptable, for these applications weld strength must equal or ex-ceed 95 per cent of the average base-metal strength.

Pressure-gas welding equipment used for joining titanium is thesame as for pressure-gas welding other materials. The process pro-duces a forged butt weld by upsetting the faying surfaces under heatand pressure. The heating system consists of a multi-orifice circularoxyacetylene torch equipped with suitable pressure regulators andflowmeters to provide a controlled heating rate at the joint. in oneapplication for joining titanium the circular to,-ch is oscillated so theindividual pinpoint flames are oscillated back and forth around thejoint to avoid local overheating. The welding pressure is supplied bya hydraulic system of a size sufficient to produce the requirea forgingpressures. Pressures may vary from 3,000 to 15, 000 psi of weldarea. Ar' overall view of a pressure-gas welding machine is shown inFigure 102. A close-up view of the welding station showing the torch,gas flames, and joint being welded are shown in Figure 103. Althoughthe equipment used for pressure-gas -.velding is a conventional machinefor heating and applying pressure, details of the equipment such as thecircular -heating -torch design are considered proprietary. Pressure-gas welding has been successfully applied to the welding of the follow-ing alloys: Ti-5A1-2. 5Sn, Ti-6AI-4V. Ti-6Al-6V-ZSn, andTi-7AI-4Mo. Prior to welding, all of these materials are in the an-nealed or solution-treated condition. ýWhether the process can beapplied to other titanium alloys remains to be determined. Size

172

now_

031

I.L

173

4 -- -

-~r-- -

I

ranges that are pressure-gas welded include thicknesses ranging from

1.!8 to 1-1/4 inches.; diameter_ u i_,p to . 2.6. n h,-• .s .•e• gths up to arbout60 inches.

A typical pressure-gas-wel. :g cycle is as follows:

(1) The parts to be welded are aligned in the machine.

(2) A controlled welding force is applied.

(3) The torch is ignited.

(4) Heating is continued until sufficient forging has been pro-duced to upset the joint a predetermined amount to completethe joint.

(5) The gas flame is extinguished.

(6) Hydraulic welding force is released.

(7) The part is removed from the machine after cooling to apredetermined temperature.

After welding, the completed weidments are heat treated as required.

It should be noted that there is no shielding gas used to protect

either the inside or outside of the titanium vessels during pressure-gas welding. Argon gas is used to help protect the inside of the tanks,jr containers during heat-treating operations.

ii-6A1-4V is the only alloy for which information is available onpressure-gas-weld properties. The tensile, notch-tensile, and impactproperties of pressure welds are listed ia Table XXIX. These dataseen' to indicate that the pressure welds have lower strength than thebase metal; this is true for some welds but not others. Usually the

joints have strengths eqaivalert to or exceeding those of the basemetals.

Experience has indicated that forgings and extrusions are supe-rior to plate or spun sections for high-strength light-weight pressure-vessel assemblies. Heat treating after welding is employed to providemaximum tensile strength both in steel and titanium-ailoy pressure

vessels currently in production.

Although not directly concerned with welding, pressure-gas-

welding equipment has another interesting applica•ion. This applica-tion is called upsetting and may be compared with the process knownas resistance-metal gathering. During fabrication of cylindrical

175

S3 - -AL

TABLE XXIX. TENSILE. NOTCHED TENSI.V. AND IMPACT PROPERTIES OF PRESSUREWELDS IN Ti-6AI-4V TUBING

UltimateTesting Tensile Tensile Yield Elongation. Reduction Impact Energy(a).

Temperature, Strength. Strength, per cent in Area, ft-lbSpecimen F ksi ks;. in 41) per cent -65 F 80 F

Unnotched, 8s 172 2 36 10 28 12-13 12-17bas-e metal

Unnorzhed. so 166 146 8 33 9-11 10-12pressure weld

Notched, 80 221 -- -- -- -- --

base metal

Notched, 80 2114pressure weld

SNOtcned. -, 20 -- 230base metal

- Notched. -65 220 --

pr'!ssuze Weld

(a) Vee-notch Charpy specimens.

2i

176

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sections, inside or outside shoulders are often required. Normallywhen additional material is required for such shoulders, it is neces-sary to start with stock or forgings of sufficient size so that these canbe machined. By using the upsetting method, the wall thickness canbe increased locally, and the design located for either external or in-ternal shoulder. This has the double advantage of requiring lessweight initially plus the fact that less machining is required to makethe final part. More detailed information on solid-state welding maybe found in the literature (Ref. 125).

DISSIMILAR METAL JOLNTS

Occasionally, it is desirable to join titanium-base alloys to othermetals for various applications. Titanium is difficult to weld to steels,aluminum, nickel, and copper alloys because brittle structures resultwhen it is highly alloyed with these metals. Highly alloyed structuresare formed in the fusion zones of welds that are made with processesthat result in melting of both base metzls. These highly alloyed zonescontain intermetallic compounds and are extremely brittle. Colum-bium, molybdenum, tantalum, and zirconium are more compatible forwelding to titanium than are steel, nickel, and copper. When titaniumis highly alloyed with columbium, molybdenum, tantalum, or zir-conium, brittle intermetallic compounds are not formed. The result-ing solid solutions usually have low ductility.

Titanium can be joined to some other metals by the use of specialtechniques. The problem usually is to join titanium to aluminum,copper, stainless steels or carbon steels while providing a leak-proof,reliable joint or a good electrical contact. There are many differentapproaches geared to suit the individual problem. Some of these ap-proaches are listed in the literature as follows (Ref. 8):

(1) Welding, using pure vanadium rod as a filler material

(Z) Welding, using ultrasonic or electron-beam techniquesto avoid formation of high-temperature phases

(3) Brazing, by furnace, torch, induction, or resistancebrazing. Techniques are most advanced for silver-basebrazing alloys, however, these have some limitation incorrosion applications.

(4) Titanium-lined steel. Heavy walled pressure vesselshave been lined successfully by expanding a light-gagetitanium cylinder into a steel shell. Successful joining

177

4V

techniques have been developed to prevent contamination ofthe titanium liner with the steel shell.

(5) Titaniun-,-clad steel. Special welding techniques have beendeveloped for joining either brazed or rolled clad titanium.

Examples of titanium-dissimilar metal applications are describedin the following.

MIG SPOT WELDING ALUMINUM TO TITANIUM

MIG welding has been adapted for attaching titanitun to aluminumalloys (Ref. 126). With this process, a lap joint is welded with alumi-num filler metal through the titanium into the aluminum to produce a"fused rivet"t . The shear strength of the assembly depends on theproduct of the shear strength of the deposited filler metal and itscross-section area.

It is well known that direct fusion welds between aluminum andmost other metals produce brittle intermetallic compounds that seri-oushv limit st.Length and ductility. In gas metal-arc spot welds, how-ever, the brittle int,.rmetallic c,,:.r1 ou•nds formed at the periphery ofthe welds do not extend across the s:-_ear piane and have little effect onstrength and ductility in shear loading. This joint geometry permitsmetal-arc spot welding of metal combinations that cannot be resistanceseamn weldea without the use of special techniques.

The equipment is the same type used for gas metal-arc spot weld-ing all-aluminum joints. Good spot timing controls should be ccmbinedwith a reliable wire feeder and a constant potential (and preferablyvariable slope) power supply. Argon shielding is used.

Welded lap joints between aluminum and titanium are made byMIG arc spot welds fused through one sheet into the bottom sheet.When the titanium is thin, the weld can be made simply by meltingthrough it with the arc. The in-rushing filler metal and arc forcepush the other metal away from the center of the weld so that the coreand head are composed of relatively ductile aluminum. Another tech-nique that is used involves drilling a hole through the top sheet andfilling the hole with filler metal. This technique helps minimize dilu-tion and resulting ermbrittlement. An illustration of a dissimilarmetal arc spot weld is shown in Figure 104 (Ref. 126). These fused-rivet joints are about as strong as gas metal-arc spot welded allaluminum joints. Typical tensile-shear strengths and welding pa-rar-neters for a variety of titanium-to-aluminum joint thicknesscombinations are shown in Table XXX.

178

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FIGURE 104. CROSS SECTION OF GAS METAL-ARC SPOT WELDJOINING 0. 025-INCH ALUMINIZED STEEL AND0. 064-INCH 3003 ALUMINUM WITH 4043 ALUMI-NUM ALLOY FILLER METAL, NO PILOT HOLE

(REF. 126)

TIG PLUG WELDING

TIG plug welding has been used to join titanium to steel (Ref. 127).In development work, two procedures were used to weld 0. 040-inch-thick commercially pure titanium to 1/4-inch-thick low-carbon steel.Both were modifications of plug welding using a standard gas tungsten-arc torch. Vanadium and "olybdenum were investigated as the inter-mediate filler metals. Aluminum and silver were not considered be-cause of the considerable uifference between their melting temperatureand those of titanium and steel.

The first method of fabrication, which was used only with thevanadium, was to bottom drill 1/16 inch deep, a 9/16-inch-diameterhole in the steel. A standard counterboring tool with a replaceablepilot drill was used for this purpose. This hole was filled by deposit-ing two layers of vanadium using 1/16-inch-diameter filler wire. A1/4-inch-diameter hole was drilled through the titanium, aligned con-centrically with the vanadium, and welded to it using commerciallypure titanium filler wire.

The second procedure was similar to the first. Instead of surfac-ing the mild steel, however, a solid disk of the intermediate materialwas inserted in the steel, flush with the top, and welded around itsperiphery. Both 0. 062-inch-thick vanadium and 0. 032-inch-thickmolybdenum were used. As in the first procedure, the titanium waswelded to the intermediate material. Results were more promising

180

with vanadium than with molybdenum. Process equipment has beenfabrIcated asing these methods.

RESISTANCE SPOT WELDING

Limited development work has been done on resistance spot weld-ing of titanium to Gther metals (Refs. 127, 128). Process equipmentutilizing titanium-to-steel joints made by resistance spot welding hasbeen fabricated and is being evaluated (Ref. 127). Titanium can bespot welded to steel if an intermediate layer of vanadium is sandwichedin the joint. Both conventional and series-spot-welding arrangementshave been used successfully. Properties of series-welded titanium-to-steel joints are given in Table XXXI.

TABLE XXXI. STRENGTH OF JOINTS(a) BETWEEN COMMERCIALLY PURE TITANIUM AND0.255-IN.-THICK LOW-CARBON STEEL USING A VANADIUO(b)INTERMEDIATE (REF. 127)

Electrode Tension-TI=:,ium Electrode Separation. Welding Welding Shear

Thickness, in. Force, lb in. Current. amp Time. cycles Strength. lb

0.025 450 3-3/4 6,900 15 14900.025 450 3-3/4 6,900 15 13200. 025 450 3-3/4 6,900 15 14330.025 450 2-1/2 6.900 15 1r250.025 450 2-1/2 6.900 15 1508

e 0.025 110 2-1/2 6,100 15 6250.025 i10 2-1/2 6,100 15 13250.025 110 2-1/2 6,100 15 13420.062 675 2-1/2 10.300 1= 27300.062 675 2-1/2 10,300 15 27850. 062 375 2-1/2 10,300 15 20300.062 375 2-1/2 10,300 15 31200.062 375 2-1/2 !0.300 15 31100.062 375 2-1/2 10,3•0 15 3122

(a) Scrics-type resistance spot wcld.(b) Vanadium was 0.010 in. thick.

Resistance spot welding of commercially pure titanium to .ISI 301and 446 stainless steel, iron, nickel, chromium, zirconium, aluminum,and magnesium alloys also has been surveyed (Ref. 128). Titanium-zirconium spot welds had the highest strength of any combination; duc-dlity was poor, and the tension-shear strength was about 1100 pounds.

181

Magnesium and aluminum produced braze-type joints having tension-shear strength of 525 pounds. The maximum tension-shear strengthof titanium-stainless steel spot welds, 640 pounds, was obtained withsolid-state bonds. Increasing welding heat caused cracking and rapiddecrease in tension-shear strength accompanied by the formation ofintermetallic compounds.

CAPACITOR DISCHARGE WELDING

Capacitor discharge welding of titanium to aluminum for miniaturemissile a-:•d electronic components has been reported (ref. 129), butno details are available.

CONCLUSIONS AND RECOMMENDATIONS

Titanium and titanium alloys normally are considered to be diffi-cult-to-weld materials. This is because titanium will react readilywith most other materials when heated to elevated temperatures suchas those encountered with most welding processes. These reactionscan reduce the ductility and toughness of titanium, and in addition, cancause porosity, cracking, and embrittled welds. Titanium is welded,however, on a day-to-day basis by many fabricators and the" techniquesthat were considered "special" or higbly sophisticated are now oftenconsidered conmnonplace.

Experience has shown that good-quality welds can be prepared witha variety of joining processes, provided the heated metals are pro-tected from contamination by foreign materials. Processes and proce-dures that minimize joint contamination must be used. Dust, dirt,grease, fingerprints, and a wide variety of foreign materialc can leadto embrittlement and porosity when the base metals or filler metalsare not properly cleaned prior to joining. Contamination that ariseseither from the open atmosphere or from foreign material on the fillermetal or surfaces to be joined must be strictly avoided for the suc-cessful joining of titanium.

Although titanium and many titanium alloys can be joined readilywith conventional processes combined with special techniques to pre-vent contamination, a significant number cannot be welded satisfac-torily and additional information on joining these materials is stillneeded. The needed information is concerned with nearly all phases

1 82

I

of joining - cleaning and preparation of the base metals and fillermetals, welding processes, posfweld heat treatments and inspections.Particular areas in which additional information would be helpful forjoining titanium and titanium alloys are described in the following.

WELDING METALLURGY

Although titanium and titanium alloys have been fabricated exten-sively by various welding processeýs during recent years, a betterunderstanding of the welding metallurgy of these alioys is needed in

e order to develop successful joining processes and procedures. Studiesof the metallurgical changes that occur in these alloys during w,'eldingand related processing are recommended. These studies should beaimed at establishing the effects of potentially important processingvariables such as prior working history, heating and cooling rates,postweld heat treatments, intermetallic reaction, dilution when addingfiller metals, and microstructure on weld-joint properties. Existinginformation should be evaluated and additional needed informationdeveloped.

CLEANLINESS

Limits need to be established for the cleanliness requirements fortitanium-base metals and filler metals, welding atmospheres, andfluxes; also, more reliable and simpler methods for establishingcleanliness wouLd be helpful. Instruments and monitoring devices areavailable for detecting surface contact resistance and the presence ofsome contaminants in the welding atmosphere, while chemical anal-ytical methods can be used for analysis of flux compositions. How-ever, these methods often cannot be used and may be cumbersome orexpensive. Since extensive cleaning procedures are employed forcleaning titanidm, it appears that studies aimed at developing improvedcleanliness standards and methods of evaluation would be helpful totitanium-welding fabricators.

r FILLER METALS

Filler-metal development programs probably will be needed tofulfill future needs for preparing higher strength, high-quality jointsbetween similar and dissimilar metals and titanium alloys. Filler-metal development has been slow due to the lack of suitable marketsand funds. In this area of development, a thorough knowledge of thewelding metallurgy of titanium alloys will be required. Filler-metal

183i163

I

quality requirements and inspections methods also need further devel-

opment and wi.l be worthy of study.

WELDING CONDITIONS

Conditions for joining and related processing need to be establishedfor the older and often infrequently used joining processes and for newjoining processes that are promising for titanium and titanium alloys.Examples of such processes include pressure-gas and other solid-state joining processes, flash, seaLI, MIG, electron-beam, andplasma-arc welding.

TACK WELDING

Tack welding is often used to help position and maintain alignmentof weld joints in preparation for final welding. Unless tack welding isperformed properly, the weld joint may become contaminated and ruinthe joint. Studies to establish satisfactory tack-welding proceduresand quality requirements are recommended to supplement the meagerinformation that is now available. One result of such a study could bethe eliminatiarn of cumbc-rsome and expensive tooling that might other-wise be required for large-size weldments in addition to improved-quality tack welds.

CONTAMINATION AND POROSITY

Embrittled welds and porosity in titanium are attributed to variouskinds of foreign materials that react with titanium. However, thereare no known nondestructive techniques for detecting contaminationwhen present in a titanium or titanium-alloy weld. Detection of con-tamination requires destructive inspections such as hardness tests,metallographic examinations, or chemical analyses that often renderthe part useless. Studies are recommended, therefore, to developreliable nondestructive methods of detecting contamination in titaniumwelds. In addition, specific identification of the causes of the porosityin titanium welds is needed. Porosity is a troublesome and recurrentproblem in titanium welds; probably every welding fabricator who is

"*4k inexperienced with titanium alloys will encounter porosity early whenattempting to weld these alloys. Less complex, less expensive, morereliable solutions to the porosity and contamination problems areneeded, however, by all titanium welding fabricators.

184

CRACKING

Specific identification of the mechanisms and causes of stress-corrosion cracking, hydrogen-induced cracking, and delayed crackingof welded joints in titanium and titanium alloys is needed. There ap-

.ed pears to be no easy solution to these problems. However, studies ofthe welding metallurgy of these alloys and the metallurgical change-,that take place during welding and related processing will provide in-formation that will be useful in overcoming these problems.

THICK TITANIUM PLATE

The future needs for joining of thick titanium or titanium-alloyplate should be evaluated. Present information on the joining of tita-

it nium alloys over I/Z inch in thickness is limited to relatively fewS alloys. Studies aimed at developing welding and related joining proce-fl dures for thick plates of titanium alloys not yet welded in thick-plate

form can provide useful information. Oxygen-fuel-gas cutting of thicktitanium plates, for example, has been performed for armored-tankwelding development. Gas cutting methods may be useful for thick-plate joint preparation prior to welding.

STRESS RELIEF

Stress-relieving requirements Fnd procedures need to be estab-lished for various titanium alloys. Although thermal and mechanical

us stress-relieving procedures are used by current titanium fabricators,the question of when and how to stress relieve titanium weldments stillrequires more definitive answers. Studies need to be undertaken toestablish proper techniques for determining residual-welding-stressmagnitudes and their effects, and ways to prevent or eliminate them.

REPAIR WELDINGnty Information available on repair welding of titanium alloys is

limited. Studies are needed, therefore, to provide information onmaking satisfactory weld-joint repairs in alloys and weld seamswhere they may be anticipated. Information available should be eval-uated and new information developed to fulfill expected future needs.

I185

777 .

6-1

APPENDIX A

I DESCRIPTORS FOR LITERATURE ONFABRICATION OF TITANIUM ANDTITANIUM ALLOYS BY WELDING

187

4P

- 4< - ~ -A m

DESCRIPTORS FOR LITERATURE

on

FABRICATION OF TITANIUM AND TITANIUM ALLOYS BY WELDING

Descriptors for titanium welding and joining fabrication are re-

viewed below.

GENERAL AREA OF INTEREST

Fabrication of titanium and titanium alloys by welding and

joining.(1 )

DESCRIPTORS FROM THE "THESAURUS OF ASTIADESCRIPTORS, SECOND EDITION"

IZa - 96 Metals Joining, p. 39

Arc welding Silver solders Spot weldsArc welds Soldered joints Thermal joiningBrazing Soldering WeldingFlash welds Soldering alloys Welding fluxesFluxes (fusion) Soldering fluxes Welding rodsResistance welding Spot welding Welds

DESCRIPTORS FOR RELATED AREAS SELECTEDFROM THE "THESAURUS OF ASTIA DESCRIPTORS,SECOND EDITION"

1-7 - Aircraft Structures, p. 12

Air frames Fuselages*k Airplane pan-els Wings

1-150 Spacecraft, p. 55

Space tools

(1) Adhesive bonding and mechanical joining excluded.

188

11-8 - Alloys, p. 13

Titanium alloys

MetalsTitanium

11-38 - Containers & Packaging, p. 23

Propellant Tanks

Storage tanksTank linersTanks (containers)

13-153 - Structural Engineering, p. 55

Angle barsBeams (structural)Filament wound constructionHoneycomb coYesMonocoquesPipe bendsPipeSandwich construction

17-114 - Ordnance, p. 45

Armor

Armor plateBody armorTanks

20-141 - Rockets, p. 53

Rocket cases

22-104 - Mvodels, p. 41

Rocket modelsShip modelsSubmarine models

I

189 J

-moor="=VA

23-145 - Ship Structures & Marine Equipment, p. 53

Hulls

Hydrofoil boatsHydrofoilsSubmarine hulls

25-163 - Vehicle Parts, p. 57

Tank turretsVehicle tracksVehicle wheels

25-164 - Vehicles, p. 58

Armored vehicles

RELATED KEY WORDS AND PHRASES

Key words and phrases listed below also may be helpful in isolat-ing the information desired.

B razingFabricationPostweld operations

Preweld operationsRecommendations for welding titaniumSoldering

Tack weldingTitanium and titanium alloysWelding

Arc

Electron-beamFrictionPlasma

Pressure

Diffusion bonding

Roil welding

190

I

54

Resistance

ButtFlashProjectionSeamSpotUpsetUpset butt

Ultrasonic welding

Welding equipmentWelding problems & solutionsWelding proceduresWelding techniques

1i19i1j

n • •- - -i~

I4

APPENDIX B

DESIGNATIONS, PROPERTIES, AND TREATMENTSOF TITANIUM AND TITANIUM ALLOYS

193 *

SjI

I ___________ Pfoduzcers Nomenclatim ________

Copgti rciblie Steel f Hanecy P eactivt Republic Stce-l Titanium

(3.Alancc Ti). ICo.. Tit&anium jA 2WT~nL.m Metals Co.. Special Metals

P" cent I Division ritaniurn Division Ptoducts hicfls, Divineon Cotporatiot

99.5 MA _________ f1930 16ST-30 RS-25 _________

99.2 1 A-40 - I A- 1940 %Ws -40 RS -40 _________

99.0 -I A-55 HA -' 950 MST-65___ Rs-55 Ti-65A99________0 __ A__70__________% ST-?O RS-70 T-5

0. 15 t 0.20Pd A___40Pd__ ____________ MST-Ti-0.2?d Ti-O. 15Pd

______________ ___________ ALPPA ALLODY GRADES______

_______________ A-IIOAT MA -5137 %IST-SAI-2.Snt i RS-IlOC - Ti-SAI-2-56n

WA-2.Wri (owv0) A-9-ET IHA -5137ELI M.STI-SAl-2.5SnE11l RS-lIOC-L T I- 5A -2.-%n ELI5AI-5Sn-5Zr Tj-AI-5Sna5r

7IA -127-i __________________fNIST-7.A1-127t Ti-?IA I- I2Zr

jA l-2Cb-lITa (b) I________________MST-72i _______ Ti-7A1-:Cb-lTa

aAl-L'4o-lV f HA-81l6 16ST-821 R-SliX Ti-gAI-Lo-IV

_______________ ___________ ALPHA-BETA ALL40Y GRADES _______ ______

SWi C- 11M j________MST-aln RS-110.A Ti-BMn2ft-2r-alo ________j________ITi-140A

2.5&1l-16V _______ _______ ST-16V-2.5&M1 _______

3A1-2.5V I ___________ -4AI-4M.n C-13DAM WA -414 5 MST-4A11-4ln RS-130 1

4A1-3%1o-iV %I_______ _______ ST--kAI-3VMo-IV RS-115 Ti-4AI-3M.-WV

SAI-i.251'e- I _______ ________ IS-140 jTi-5AI-4FeCr5Al--1.Fe-I.4Cr- _______________ _______-i-15xss.,

EA 1-4V j C-l2O0AV IHA -650 MSTI-G&I-4V. RS-!20.A Ti-6A1-4V

&A 1-4V (lowO0) _ _____ HA-6510EI. PS_____ 5- 120A -L Ti-6A1k1-4V ELI6Al-6V-2Sn- I _____ HA-51ISS =S-6AI-G-V-2S13 ______ TF8&-6-

jA 1-411o jC-135A~o HA-714E jMST ~I-4Mo j 11-135 T--IAI-4Mo J________________ __________BETA ALLOY GP4LDES ______

2AI-8V- SNe ST-1Al-EV-61 Fe

3A1-13V-IlCr -20C MST1- ISV-i Ict-3A1 11-120B Ti- 3-iiCr-3A1

(a)Oth crnb= -}117~ xW WAt-6~l pl o allg-au andal ptoduct 7-14W7~. T-i4568. T-9046C. and T-9041C

appy i al rads:and T-SSS4ASG) applies to vanoias grades.

194

mm- aut NX-

4 9

Fonmability. NominlOthet Designanons Minimum Melting Compolston

.hiS Military Forms ?.nd Radi,,. Weldability Temperatue. (Balance Ti).No. No. I Available(c) T l(emauls F pet cent

B. b.P.S.s.T.W. E I to 2 All ualloyed 3038 99.5

"4902 1 grades I _I4941 T-90473-1 B. b.P.S.s.T.W.E I ao3 ae 13000-3100 99.2

[4951 c.ompletely4S•OA T-7993B B.b.P.S.s.T.W.E I to3 weldable (W) 3000-3100 99.0

f49018 B. b.P.S.s.T.W.E 2 to3 3020 99.0a.2_ B~b. WE I -- 3025 98.9B.b.P.S.s.T.W.E •-I Lo, Completely W 3000-3100 0. 15 to.2Pd

149104926 aB.b.P.S.s. W.E 3 to 5 Weldable 2820-3000 6AI-2.56n4953

B__. b. P.rS.as. W.E 3 to 5 Weldable 2820-3000 5A 1-2. 56n (low 0)

in pmpatica B. b.PS.s _3 to ,5 Weldable ,3000 lA1-56=-5ZT

In preparation B.b.P.S.s 3-1/2 r 5 Weldable -3000 IAI-l2Zr

IQ I preparation B.b.P S. W.E 4 to 6 Weldable 3005-3115 7A1-2Cb-1TarO)In p.-ep- In preparation S. b.r. -,s. W.E 3 to 5 Weldable 8AI-lMo-1Vaa~tton

4908a. I_ _ _ __ .__ _ 2-1/2 %D 4 W not recommcdeJd 2730-2970 $Mn4923 _B. b. S.s 3 to 5 W not reconmiended I _2Fe-2Ct-2Mo

ST-b,.4i) B.b.P.S.s. W 2 W not recomnmended 2. 5Al-36V

_.1 _2so 3 3A1-2.5V

492A B. b.P. W -- W not reconmmended 2820-3000 4AI-4Mn

4912. P.S.s 2-1/2 to 4 Special coendtios -3000 4A1-3Mo-1V4913 permt same w

3._b.P.S 3-1/2 to 5 Special conditions _,_-_.25Fe-2.'_Cr

I ~Permit ionic Wf4929 ID._b.P -- W not recommended -3100 5A-i.3:e-I.4Cr-

4969 1 1.2340

4911l492MA 0S-10737 B.b.P.S.s. W.E 3to5 Weldable ,-3000 6A!-4V

T,4-935 OS - 0740 B. b.P.S.s.T.W.E 3 to 5 Weldable -2000 6A1-4V (3ott0)

T-46035 B.b.P. W.E -- Special co-dios ,31LI0 6AI-6V-2Sn-

T-41638 _ _ _nit som _ _l(Fe.Cu)

DB.b.P. W.E Special conidtci"s -3000 7AI-4Mo

P. b.P - W not rewonmended 2 f AI-8V-SFe

4917 B.kP.S.s. W 2 to 4 Weldablej 3I-13V-ICr

(b) Formrzly 8AI-2Cb-ITa. All data given are Jo: The 3-2-1 composMion.(c) B. bilict b. bar P. plate: S. sheet: s. strip. T. tubing; W. wire. E. extrui.OOL

195

I

Al

"Nominal Betz

Compositioc Recommended Forguog Transus . . Recommended Ilcar Treat-(Ealance Ti. Tem rrature Range. F Temp.

"per cent Sart Finisit F i 5 5F Sirris-Rclici Annealing Annealing Treatment

99.s 1500-1100 120G-1500 1630 1000 toOO I 1-0/0F r. AC 1250 to 1300 F, 2 h,. AC

1500-1700 1200-1500 1675 1000 to 1100 F. 112 hi. AC 1260 to 1300 F. 2 hr. AC

49 n 1600-1700 1200-1600 690 1000 tvi 1W00 F. 1/2 hi. AC ' 1253 m 1300 F. 2 hr. AC

99-0 1700-1750 1300-1600 140 ________ ."qa 4 1750 1550 1760 1000 to 1i1%F. 1 J.hr. AC 12.50 t 1300 F. 2hr. AC

0.15 zo 0.20 Pd 1200 1650 1675 10 OW 110. F '.112h., A(' 1250 o '300 F. 2hL. AC

ALPHA ALLOY GkADES

fs•1-2sn 1 1600-1950 1400-1750 190o 1000 to 120- F. 1/4 to 2 hr. AC 132i to C F. IC r,- -o_ 0%_ _ AC

5AI-2.5Sn (low 0) 1600-1900 1400-1150 1910 1000 to 1200 F. 1/4 to 2 hr. AC Dr.to

5Al-,Sn-SZr 180C-1900 1600 1515 110C F. 1/2 hr. AC 1650 C. 4 hr AC7AI-12Zt 182--1925 1800 182.5 I000 F. 1/2 ht. AC to)( ) 600-!650F.1/2to-hr. A

[(2) 1300 F., 1 hr, AC?A'n-.Chi 1950 1656 1920 1100 to 1200 ý. 1/2. AC 1650 F. 1 hr. AC

8AI-lMo-IV 1950 1850 1900 1100 to 1200 F. I hr. AC (1) 1450F. 8 hr. FC (Co-ult

""_ _ _ _"__Fo: sheet_2) 1450F. 8hr. FC+ 1455 F.

_ _and plate • 3).1450 F. 8 hr. PC + le5o .

S1'For forzins 1(4) 1550 F, 1hr. AC + o00oF.ALPHA-BETA ALLOY GRADES

Wmn : ... iý ucc reco'nreded 1475 9 to 1100 F. 1/2 to 2 hr. AC 1250rt 1300F. lhr.FCtc1000F

2Fe-2Ct-2Mo .101,001 1300 900 to 1000 F. 1/2 to 1 hr. AC 1200F. 1/2hr. AC

2.5AI-1V 1400 (max) 1350 (i.,) Solution treating is rtcommended for both anneali.

and stress relieving3A 1-2. SV Forgin2 not rr ernmended _____I_____________1 13C0 F. 1It& AC4A1-416n 41600-1150 1300-1600 1200 41300 F, 2 h:. FC 1300 F. . to 4 hr. FC

S-450 1650 15.5 . 1000 to I100. 1 hr. AC Ij2F4 hr.SCtol O05F. A4 Forein2 rnot reconamended I

5AI-1.25Feý-2•.5Cr 1400-1759 1400-1500 IM25 1100 F. I hr. AC *450F. AIr.SCtoIl0S.F

5AI-.5Fe-'I.4Cr- 1650-1750 1650 1755 .. 1200F. 2h;. AC !SOO F, 4

to24 h. AC

^AI.-4V 11450-1900 1400-11750 1820 900 to 1200 F, I to 4 hr, AeC slto 15OF, I to 8hr, SC

1250 (max)t (Usual: I hr. 1100 F. AC) to 1050 F. AC6%1-4V flow 0) IIS0-1900 14010-1750 IM20 Ditto Ditto6Al- -- 1 "426 15-0 0 1735 1100F, 2 hr Af, 100lo140F. lt02hr'AC

7fI-Wf o 1C00-u0 150-16u 1846 900 to 1300 F, I to 8 hr, AC 1450 F. 1 to B hr, SC to

I IM _ A105, CL I- - - " -BETA AU.OY GRAIDES

AIM-8V-SFe 1500 1450 1.525 1 00 IOto 1 1006F. I1hr. AC 12506 F,*1hr, FCto 90_0_F.ACI

--3(I3V-blCr )1500150 1400-1800_e i11325 Solution treating is snoonomo with a•wea•ing for this alloy.

(a) Abbreviatiom AC = air cool. SC = slow cool. FC = furnace cool. WQ = water q".eoch. CR = cold rolled.(b) %umbers in paremb-es refer to beat a'eatments used to generate the data give.-I inlater tables. See Condhtioa te-m,.'s.

.II--

I 196

Tvpic..xs Tensic PropertiesRoom Extreme

Tern "atmc 600 F _ Temprta rcs Nominal

men (a E E. Test Comproston

Solution Tr,-atment 106 Us. YS.. US. YS. ETep. US. -. (Balance Ti).

(Aging Treatment) Form Condzu psi kI kss , psi W ks M kt i per cent

Not heat treatable S- Ann 14,9 3 273 011. 20- 94 5

Not heat treatable 5 Ann 14.9 60 45 28 12-31 28 13 45 -423115 99.2.

--- -

Not heat treaable S A^nn 15.0 1,56o 25 12.5 33. 19 -321 .165 99.05 I ! 15.1 90 25 2312.5 43121 28 -3411 .... 99,0INot teal treatable S Ann 15.5 100 85 17 12.6 4 30 259

Not beat treatable S Ann 14.9 62 46 27 12.328 1330, 0.15 to 0.20 Pd

Not heat treatable S Ann 16.0 1251117 18.13.4 82165 19 1000 75 56 18 5AI-2.5Snb Ann 16.0 115 1O 20 I

Not heat treatxble 5 [Arn 16.0 110 95 20.13.4 78 60 20 -423 M 06 15 5AI-2.Sn~hnv 0Not beat treauble S Ann 15.0 125 120 IS 1.4.2 94 "34 20 1000 84 E-7 21 5Al-5Sn-*?r

Not heat treatable S (1) Ann 16.0 135 130 1514.3 '09 86 21 1000 93 25 23 "2A1-22zrb () Ann -- 165 159 14 130 119 18b Ann 17.7 126 120 11115.1 100 81 _25_ _ AI-2Cb-ITa

producers for other zmatme*vs) S (1) Ann 18.b 160 150 181 1000 85 70 20 SAI-1Mo-1V ,1/4 it, AC(Dupk - S ) 18.0 145 138 15I

5min AC. 1375F. 1/4hr. AC S (3) Ann -- 150 142 13;

8hr. AC - (4)Ann -- 41301S-- -n17 -519_1000 88 71 20

Solution treat ont recommended S Ann 16.4 132 125 15 14.4 8 75 13, 001400 to 1480 F. 1 hr- WO or AC b Ann 16.7 137 125 30 .f900 to 950 F. 2 to 8 hr. AC) b 4Aid -- 179 171 13 -- 136 112.161360 to 1400 F, 20 to 30 min. WO S | $ -- 10( 4516 2.1A1-1/'

(960to990F, 4hr, AC) S ]AM . 15.0 180 165 6 3.5 155 1401 8 800 140 25 !0Solefion treat not recommended S . Ann 15.5 100 6. 0 1j -3 0 - _ 50-_25__________1400 to 1500 F, 1/2 to 2 hr. WO b Arn 16.4 148 135,1.5 3.9 110 90 12 800 100 521 4AI-4Mm

t OO to 10O F- Rt 124 hr- AC) M h A IL... -- ' 1-3lh-1tn 1950F 1/41-r W - j 16.5 L4120 ____-___._- __S(925 F 8 to 12 hr. AC) S-q ! .-- 195 1" - 1m M A SOO I I .R1tc-rILSOF 2l-X b I An. I§- n155 14-5 15 L5Al-_.Fe2.75r

(900 to 950 F. 5 to 6 s.t. AC) h.. A2ed 17.,6 190 1l. § 62-1600 to 1625 F. 1 hr. WO b _Ann_ 16.5 154 145 16 15. 0 00 B U SAI-2.SWe-1.4C0-(i000F. 24hr, AC) b Aga n17..0 195 184 14.6 1.M151o

15•0 t. 1-750?. 5 mn to I hr, WO S. b Ann 16.5 13 i2 5 2 - c an . IR I 5 AI-4V(900to l000F, 4to 8., AC) S Aged . - _10 1p, v2n nn a

Solution treat no recommended S Anm 1.. 122= "n" /3 21 1 AA 12 -4ty .1600 to 1625 F. I hr WO Anb 1A5 151 = Poo W C h, SAI-6V-2sn-

(900to 1100 F. 4to8hr, AC) _ h_ And 16-5 11. 10 (2jFie- C.1 6 5 0 to 1 7; 5 0 F , 1/ 2 to 1 - 1 /2 hr . b I A nn 1 6 .2 16 0 1 5 0 iq42 1 2 A I A I - 4 16o

WC(900to1200F. 4o16h.AC) b Aged 16.9 185 125 10 13 0 Ki -______

1375 to 1425 F. 1/hr. W O b Ann I 6.5 177 17.0 i 4 -4 1 0 Boo 5 132 IA I- 4-,oe

(92,5 to 1000F. 2 5? . AC) b Aged 16.5 221 15 10 I-..5 140 123 12 SO0 120 _00 130

1400to ISOfF. 1/4tolbr. WQo;;A. SJ Ann 14.2 1351130 16 13.2 Boo800 I15 OO M_ 3AI-13V-1IQC

(900F. 2 to 96hz. AC)1450 F. S e 14.8 185 175 8 3.8 125 145 8 800 160 20 :12I/ 3 h,. A C . C R. S ~o F . 2 4h !. ., Z s - -~g d . 2 6 z o 45 i 4 !

197

iI

Xaac V) S, - - - - - ------ -

o .ninti C~ee, Di ____ - St, c.P.u otue Data -

[arm STress. Time. ?lstic Temp. Strcss. Time. Ktper cent ,:tio F ki i ht Df. . Form C -:__ttl__ F Imi ht Factor

I9 -- _h AU)__n AM - - -

• 9 9 . 0 • A n n R -s 0 a 8 15 0 0. 1 ,5 b A n n 8 0 0 i I / 4 3 0 1

lo - _5 2 0 E ,d.

Ann•_s R • soo 4P zoo m.! s Ann so 62 IoDo IA" 1000 150 0.15 S Ar 1 1 1

5A' -2-6SD iw 0_ -i

SA I-fSin-57r s .-- A=- 3..- 150 q A.i 1000 60 99 1""AI-12zf S (1) Ann 1000 30 150 0.15 S (1) Ann 1000 60 330 1

h A1 0),12h low0 20 cl. 0.1t0"IAl-2Cb-Ta Is 1000 I i 1-, 0 0S , A- 10:Q 32 1000 18AI-IMo-lV S (1) Am 1000 18 4 150 0.15

S __ Ann - I.--SO - - -

S 4) Ann 0 25 10 040, (4) Anm 1000 60 40 1

____ A LPJ, A-BETA.. - __

_S A__ 900 5 100 0.50 S Ann 400 100 1000 121e!2Ct°2Up

_ SA1-16V- - -___v_ - s Aged 600 90 100 1

,_-4Mn b Ann 400 99 800 4.50 b0nn SOO 47 1.00 1

b A-a-- I oo L o2 100 1

______S__,___ 200 44 200 0 S SOed 00 72 500 1

. - b Ann 800 46 1000 0.20 b Ann 800 is 100 1

1.2!J ________o________

- b Ann 600 70 1000 0. i0 b A=- 850 68 100 1

b Aged 850 -2 100 1

L~t-AV Mgstr'• . .lAI-'V-2Sn b Arn 6S0 100 150 0.20 I

I (Fe- CC) b Aged 600 100 191 0.2.?AI-41M6_ b Ann 1000 14 150 0.20 b Arm 800 11.'7 153 1

b Aged 1000 50 3 1

N, 'A I--V-SF, b Ann 600 120 310 0 .b Aged 80o 45 212 6.60

- - s Anm 600 107 500 0.20 b Ann 600 107 S00 1

198

- ____ Fatigue DAta RT ~r~stress. Kt Factor Charpy i Nomoiiona

Tcnp, 0 (Stress Impact. H ard-. (Balance Ti).Fo-mCodiioF Tye = yc fne)4 t-b ej)Usagee Remarks Per cent

Ann ft_ 1209 Highest formability Wrde "1____5 _

b Ann 2_.5-40 .200 8 AerOsPace. ___9-___

_________22_ _____ Q miciij and ________

Ann___ -0J ____ fll .. efw 0.15 toO0.20 Pd

S .AL. ~'R- DiCI ax1ialh 93- f1A=2 36 RC -A &--~- bezfr ghi qU 9A12 Wit

b A' T P t. b a 27 3.2 -_ _

1b 36 -k - __ Coeic grade 5AI-2.5SO (low 0);

_____ ______ - High creep strenot grade SAl-~-I2zr

_____ __ ____ __ __ ____High strength Plas laon time l-hnI

Ann ~ ~ ~ ~M creesittstance ______

b±i(4) Ann j____ __- ________

SIAnn RT Direct axial 9C 1(A=WC ___[1n or-Ahi~ ih.mdra tc~I

fl Ann 600 Reverve bend 14~.6 221 - Z___________ e-2r-2jao

b_ Aged __LQ __ __ _ __ _ _ _ _ _ _ _

S Ann - _____ - - __ xee11ent fabrlita!y as annealed 2_ SAl-IbVS ilged RT Ei-ect axial 32 ICA - 21 M__ __Hat treatable to bugh UM20s~

T.. .A.n -. la - __ 3A1-Z.5V

b Aan RT Rot, beam 90 1 NG-15 HUME" .1s tr arrf 4A1-4Mn

.L I.g -ka. -incledint famstemr

... L t.. -, -oo - lnability. Heat Vimtable 4Al- d-IV

S i r D..ect axial 124 I A= -61 tobg Zeo T~R An P I IL.Ir NL.. asOJ I_ Atrframe RRMn22ORes 5At--i2Mec

b Aged RZT IRot, beams 105 1 _ ___________ 2.75Cr

b Ann RT Rot. beam 100 1 !0 ___ Airframe and ordnance corr~coents ZAl-i. S'e-2.4Czb A ed RT Rom. beamn 110 1 1____________ _ 2Mo

b Ann FRT Foot. beam 75 1 1020 9R1 C Wide vetsarillryr grade.. Heat 6JA1-4V~b A ed RT Rot, beam 92 1 - trazable to hig s ______

b Ann ____10 3 R :mnic jade 6AM-4V flow 0

Iaircraft componentrs I MFe- Calb Ain RT IROt. beam 10 1 is ___ ngaean arframe 7A1-4Mo

b gd10 ___ applications _____

b Aged ST IDirect axial F0 IThreaded___________ _ _

I--'______I Ex_ j 1 ~tC£cellent formability and beat 3AI-13v-!ICr

(a) A Altetrnating garcus/Ztsca stress. (b) Brinelli(8) or Rockwell (RC).

199

7 ---.. . ..- --.-- -- -- -'"----- - - -'• " -

Ther-Tmal ExpauLoa tsia"J Nalaal Mean Coeffia 7amal Con- Zmutanemw ElecatrlCal IlasUc

campoaldsw w F (10") dc€t•ity. st/he SpsClc H"t. Re."viy. Modu,.

(BUaaCe TO L L T R ft2/f /ft DW/lff microbm-en. 106 md

perceCt b/iLt. 3 200 F t000!t w1000 rT 800? IT 80? ItT g00?F I G

._ 0.10_ 4.8 5,2 _ 9 1o. -- S7 -- 14.9 6.5

1 --.2 - 0.103 4.8 5.2 5.5 9.5 -- 0.125 56 -- 14.9 6.5

W.0 0.163 4.8 5.2 5.5 9.5 to 11.5 10.5 0.125 0.155 48 to57 117.7 15.0 6.599.0 0.164 4.8 5.2 5.5 9.8to10.1 10.0 0.129 0.15 t5o5o60 122... 15.1 6.596.9 0.164 4.S 5.2 5.5 9.8 -- 0.129 -- 58 1- 15.5 6.5

0.5wo0.20 IN 0.163 4.8 5.1 I 5.4 19.5 0.m5 -- 1 56 -- 14.9 6.5

ALHA ALLOYS___ ___ - - - - __ - - I - 1

_______ 015. 3 5.3 4.W 5 7.2 0.125 0.15 157 180 16.0 17.0to .1_

ZA,-2.SSa(low0) 0.161 5.2 5.3 3.4 4.5 -- 0.125 -- 157 -- 16.0 --

~0. ic-. .. -- -- -- -- -- I.o --

-7AL-12Z 0.16.5 ... ... .. .. .. 16.5 --

7AX-2Cb-ITa 0.159 .. .. .. .... -.. .. . .. 17.7sA1-lMo-lV 0.158 4.7 ;.0 5.6 .... .. .. 199 203 18.5

ALWA-EA ALLOYS Asun 0.171 4.8 5.4 6.0 6.3 9.0 0.118 0.152 92 140 16.4 7.0

-=--_r-2Mo 0.171 - 16.7 --

2.15AI-16Y, 0.165 .. ..

3Al-.6V15.0 M kEMO

AI-2.5V 0.163 15.5 --4*,l-4We 0.113 4.9 5.1 5.4 4.2 7.4 0.126 0.159 153 172 16.4 7.3

4A1-JmO-IV 0.163 5.0 5.3 5.5 3.9 6.8 0.132 0.142 165 - 16.5 7.0

Ml-1.2*e- 0.162 5.2 5.3 5.5 -- -- -- 16.8 3 -2.7'5Cr to . 1_ _ 17.6 (AsJ}

.:-1.-1.4Cr- 0.162 5.2 5.5 5.7 4.7 7.0 - -- 163 180 M6. 6.3I.Xwl to -15317.0 IAe

6AI-4V 0.160 4.9 5.1 5.3 4.2 6.8 0.135 -- 171 187 Is.S 6.1

-4V(Ma O) o0.160 5.3 5.3 5.3 -- .. 0.13 -- 171 -- 16.5 6.1rFaw-- 10.164 5.0 5.2 5.3 4.2 - 0.155 -- is.5 -- 15.0 -

i,,rt. Cu) ______ ____157 j17o 16.5 Xm

Al-Wo 0.2162 5.0 5.2 5.6 .7 7.0 0.123 0.151 175 183 16.2 6.5

TA AlLO16_____

::-0V-lC 0.175 5.2 5.6 5. .0 " 90.= o.19 153 14.2 6.2

Mza p ~tmc Pameabilzy at IT fEm sbov a•U• 1.00005 At 20 Oemeds.

200

KSL416p otI 11.0 ft-lb metallaqlcal metal pez caMs

________ 201 15.5 30 60 13 f 3 dCOW 101-A TU.....C........

_______ 217 1553 90 70 10 F- WC 10 2-A 2L2M~217 15-1 W0 70 10 - W C103 0__15_to_0_20_P

________ 321 16.0 140 10 11 a COdC 166-A A-.s

________ 321 127.0 145 1IN 2 63-A .... I.......LA4_____ 311 17.0 147 130 10 17 ouc 26612

201

S 0.

0 00 . .- •.S •

0::,. .... .0 ~ W

I . 0*

33

1 .4

REFERENCES

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S- . . .. : .

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i2

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209

~~RM JW -'

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21I 2(

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211

(90) Myers, P. E., "DOD High Strength Titanium Alloy Sheet Re-search Program", North American Aviation, Inc., ColumbusDivision, Columbus, Ohio, Report No. NA57H-527-11, FileNo. NA-9510, Contract No. NOas 57-785d (April 29, 1960)(RSIC 0787).

(91) "Construction of the Mercury Spacecraft", Welding and MetalFabrication, 30, pp 116-18 (March 1962) (RSIC 0639).

(92) Koelling, H. A., "Roll-Seam Welded Titanium", McDonnell Air-craft Corporation, St. Louis, Missouri, Contract No.AF 33(657)-11215, 7 p (September 10, 1963) (RSIC 0638).

(93) Stier, H. H., Bergstedt, P. W., and Turner, H. C.. "EmbossedTitanium Welding Analysis", General Dynamics/Convair, SanDiego, California, Report 57-980, Contract No. AF 33(600)-30169 (June 16, 1958) (RSIC 0768).

(94) "Processing and Materials Review for Aircraft Design Manual",A. 0. Smith Corporation, Report No. ARDC-TR-56-7-Pt. I, onContract No. AF 18(600)-1513 (RSIC 0512).

(95) Foster, R. N., "Flash Butt-Weld Procedures for F-Extruded Ti-tanium Parts", Welding Engr., 43 (2) 29-30 (February 1958)(RSIC 0637).

(96) "Evaluation of Titanium Flash and Fusion Welds for AircraftDesign Manual", A. 0. Smith Corporation, Aeronautical Divi-sion, Milwaukee, Wisconsin, Report No. ARDC-TR-56-7-Pt. IVon Contract No. AF 18(600)-1513 (June 30, 1958) (RSIC 0514).

(97) "Typical Flash Weld Properties", Unpublished data from Ameri-can Welding & Manufacturing Company (January 18, 1956)(RSIC 0869).

(98) Conover, J. E., and Cyphers, R. J., "Developnent of RollForging and Flash Welding Techniques for Production of Tita-nium Aircraft Parts", Grumman Aircraft Engineering Corpo>ra-

* tion, Bethpage, Long Island, New York, Interim Engineering

Report No. rAB No. AD-200143, Report No. GAEC-RD57-1-3,.Contract AF 33(600)-34257 (January 3, 1957, March 29, 1958,April i5, 1958) (RSIC 0636).

(99) "Rings for Exacting Requirements", American Welding Com-pany, Warren, Ohio (RSIC 0677).

212

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(100) Savage, W. F., "Flash Welding - The Process and Applica-tions", Welding Jour..al, 41 (3) 227-37 (March 1962)

(RSIC 0635).

(101) Wollaston, K. H., "High-Frequency Welding of Titanium Tube",Institute of Metals Journal, 90 (2) 33-37 (October 1961)(RSIC 0506).

(102) Brochure, Astro Metallurgical Corporation, Wooster, Ohio

(RSIC 0030).

(103) "Design Concepts for Minimum Weight, High Perfor~manceSupersonic Aircraft Structures", Douglas Aircraft Company,Inc., Aircraft Div.sion, Long Beach. California, ReportNo. 31237, Contract No. AF 33(657)-8541 (April 1, J363)(RSIC 0857).

(104) Weigert, K. M., "High-Strength Titanium Bonding by TorchHeating", Welding Journal, 41 (2) 84s-88s (February 1962)(RSIC 0690).

(105) "Titanium Honeycomb Panels Being Produced Experimentally",Industrial Heating, 30 (7) 1250-54 (July 1963) (RSIC 0634).

(106) Faulkner, G. E., and Lewis, W. J., "Recent Developments inTitanium Brazing", DMIC Memorandum 45, Defense Metals In-formation Center, Battelle Memorial Institute, Columbus, Ohio(RSIC 0692).

(107) Johnson, W. E., Sunafrank, W. 0., Kaarlela, W. T.YKastrop, C. J., and Slifer, W. M., 'Titanium Sandwich PanelResearch and Development", General Dynamics Corporation,Convair Division, Fort Worth, Texas, Final Report, ReportNo. AMC TR 59-7-618, Contract No. AF 33(600)-343922 2(November 1959) (RSIC 0633).

(108) Elsner. N. B., Mack, E. B., Metcalfe, A. G., and Troy,

W. C., "Development of Low-Temperature Brazing Alloys for

Titanium Honeycomb Sandwich Panels", Solar Aircraft Company,ASD Technical Report 61-313, Contract No. AF 33(616)-7249,Task No. 735102 (December 1961) (RSIC 0632).

(109) Sliney, J. L., "Feasibility of Brazing High-Strength Sheet Tita-nium", Watertown Arsenal, Watertown, Massachusetts, Tech-nical Report No. WAL TR 401.54/1 (November 1960) (RSIC 0631).

213II

(110) Cochran, J. F., and Torgenson, D. R., "Double-Wrap ShroudWards Off Brazing Contaminants", Metalworking Production,106, pp 56-58 (January 3, 1962) (RSIC 0691).

(111) Levy, V., "Process-Brazing Stainless Steel to Titanium Evalua-"tion", General Dynamics Corporation, Fort Worth, Texas, Re-port No. FTDM-7123, Contract No. AF 33(657)-7248 (January 16,1962) (RSIC 0846).

(112) Albom, M. J., "Solid-State Bonding", Welding Journal, 43 (6)491-504 (1964) (RSIC 0871).

(113) Irving, R. R., "Pressure Bonding Contains Powders", Iron Age,192 (16) 85-87 (October 1963) (RSIC 0507).

(114) "Bonding, Cladding and Densification by Pressure Bonding".Battelle Memorial Lnstitute, Columbus, Ohio (RSIC 0515).

(115) Afanas'ev, I. V., Kosichkin, N. V., Khudyshev, A. F., andEibakidze, V. G., "Vacuum Diffusion Welding and DiffusionWelding in a Controlled Atmosphere", Welding Production, 4,pp 28-29 (1963). British Welding Research Association Transla-ticn, pages 49-52 (RSIC 0499).

(116) Clark, E. J., "Vauuum Diffusion Joining of Titanium", WeldingJournal, 38 (6) 251s-58s (1959) (RSIC 0749).

(117) Kazakov, M. F., Shiskova, A. P., and Charukhina, K. E.,"Vacuum Diffusion Bonding Titanium", Automatic Welding, 10,pp 82-86 (1963), British Welding Research Association Transla-tion, pages 71-74 (RSIC 0498).

(118) McGowan, P. R.J. Williams, N. R., and Allen, J. I., "DiffusionBonded Titanium Alloy Honeycomb Panels", Interim EngineeringProgress Report from Douglas Aircraft Company, to Air Force

Systems Command, Contract No. AF 33(615)-1399 (July-October, 1964) (RSIC 0856).

(119) U. S. Patent 3, 044, 160 "Method of Producing Ribbed-MetalSandwich Structures" (March 3, 1958) (RSIC 0500).

(120) Leach, J. E., Jr., "Diffusion Bonding of Structures by HotRolling Plate Mill Techniques", Douglas Missile and Space Sys-tems Division, Presented at the SAE National Aeronautic and

214

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0"T

Space Engineering and Manufacturing Meeting, Los Angeles,California (October 5-9, 1964) (RSIC 0678).

(121) Bianchi, L. M., "Fabricating Under an Inert Atmosphere',

Metal Progress, 87 (3) 127-31 (March 1965) (RSIC 0750).

(122) Lage, A. P., "Pressure-Vessel Fabrication", DMIC AccessionNo. 58137, Paper presented at SAE Aerospace ManufacturingForum, Los Angeles, California (October 5, 1964)(RSIC 0763).

(123) Pressure Gas Welding, Welding Handbook, Section 2, Fifth Edi-tion, American Welding Society, New York, New York (1963),pp 22. 2-22. 22 (RSIC 0870).

(124) Lage, A. P.., "Application of Pressure Welding to the AircraftIndustry", Revision of a paper presented at the 1956 AmericanWelding Society National Spring Meeting in Buffalo, New York,May 7-11, 1956 (Revised February 1959) (RSIC 0178).

(125) Hauser, D., Kammer, P. A., and Martin, D. C., "Fundamen-tals of Solid-State Welding and Their Application to Beryllium,Aluminum, and Stainless Steels", Contract No. DA-01-0I-AMC-11706(Z), Unpublished Report from Battelle MemorialInstitute, Redstone Scientific Information Center, RedstoneArsenal, Alabama (RSIC 0872).

(126) Stoehr, R. A., and Collins, F. R., "Gas Metal-Arc Spot Weld-ing Joins Aluminum to Other Metals", Welding Journal, 42 (4)302-308 (April 1963) (RSIC 0679).

(127) Mitchell, D. R., and Kessler, H. D., "The Welding of Titaniumto Steel", Welding Journal, 40 (12) 546s-52s (December 1961)(RSIC 0630).

(128) McBee, F. W\., Hensen, J., and Benson, L. R., "ProblemsInvolved in Spot Welding Titanium to Other Metals", WeldingJournal, 35 (i0) 481s-87s (October 1956) (RSIC 0785).

']Z9) "Capacitor Discharge Process Welds Dissimilar Metals", ironAge. 184 (14) 78-79 (October 1, 1959) (RSIC 0748).

I -

(130) Wood, R. A., "A Tabulation of Designations, Properties andTreatments of Titanium and Titanium. Alloys", DMIC Memoran-dum 171, Defense Metals Information Center, Battelle MemorialInstitute, Columbus, Ohio, 8 pp (July 15, 1963) (RSIC 0293).

215

jl'

(131) Alcoa Aluminum Handbook, Aluminum Company of America,Pittsburgh, Pennsylvania (1956) (RSIC 0760).

(132) "Properties and Selection of Metals", Metals Handbook, Vol. 1,8th Edition, Published by American Society for Metals, MetalsPark, Novelty, Ohio, p 44-62 (RSIC 0339).

(133) "Stainless Steel Fabrication", Table 1-2, Allegheny LudlumSteel Corporation, Pittsburgh, Pennsylvania, pp 5-10 (1957)(RSIC 0759).

216

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APPROVAL NASA TM X-53432

WELDING PROCEDURES FOR TITANIUMAND TITANIUM ALLOYS

By J. J. Vagi, R. E. Monroe, R. M. Evans, and D. C. Martin

The information in this report has been reviewed for securityclassification. Review of any information concerning Department ofDefense or Atomic Energy Commission programs has been made bythe MSFC Security Classification Officer. This report, in itsentirety, has been determined to be unclassified.

This document has also been reviewed and approved for tecnmi-cal accuracy.

W. A. WJLSONChief, Methods Development Branch

J. pZ

C , Manufacturing Research ande7chnology Division

WERNER R. KUERSDirector, Manufacturing EngineeringLaboratory

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titanium welding procedures

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