weldability of tungsten and its alloys - american...
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Weldability of Tungsten and Its Alloys
Tungsten and its alloys can be successfully joined by gas tungsten-arc welding, gas tungsten-arc braze welding, electron beam welding and by chemical vapor deposition
BY N. C. C O L E , R. G. G I L L I L A N D A N D G. M. S L A U G H T E R
ABSTRACT. The weldability of tungsten and a number of its alloys consolidated by arc casting, powder metallurgy, or chemical-vapor deposition (CVD) techniques was evaluated. Most of the materials used were nominally 0.060 in. thick sheet. The joining processes employed were (1) gas tungsten-arc welding, (2) gas tungsten-arc braze welding, (3) electron beam welding and (4) joining by CVD.
Tungsten was successfully welded by all of these methods but the soundness of the welds was greatly influenced by the types of base and filler metals (i.e. powder or arc-cast products). For example, welds in arc-cast material were comparatively free of porosity whereas welds in powder metallurgy products were usually porous, particularly along the fusion line. For gas tungsten-arc (GTA) welds in V ] 0 in. unalloyed tungsten sheet, a minimum preheat of 150° C (which was found to be the ductile-to-brittle transition temperature of the base metal) produced welds free of cracks. As base metals, tungsten-rhenium alloys were weldable without preheat, but porosity was also a problem with tungsten alloy powder products. Preheating appeared not to affect weld porosity which was primarily a function of the type of base metal.
The ductile-to-brittle transition temperatures (DBTT) for gas tungsten-arc welds in different types of powder metallurgy tungsten were 325 to 475° C, as compared to 150° C for the base metal and that of 425° C for electron beam-welded arc-cast tungsten.
Braze welding of tungsten with dissimilar filler metals apparently did not produce better joint properties than did other joining methods. We used Nb, Ta, W-26% Re, Mo and Re as filler metals in the braze welds. The Nb and Mo caused severe cracking.
Joining by CVD at 510 to 560° C
N. C. COLE and G. M. SLAUGHTER are with Metals and Ceramics Div., Oak Ridge National Laboratory, Oak Ridge, Tenn.: R. G. GILLILAND is with the University of Wisconsin. Milwaukee.
Paper presented at the American Welding Society 49th Annual Meeting, Chicago, April 1-5. 1968.
eliminated all but a small amount of porosity and also eliminated the problems associated with the high temperatures necessary for welding (such as large grains in the weld and heat-affected zones).
Introduction Tungsten and tungsten-base alloys
are being considered for a number of advanced nuclear and space applications including thermionic conversion devices, reentry vehicles, high temperature fuel elements and other reactor components. Advantages of these materials are their combinations of very high melting temperatures, good strengths at elevated temperatures, high thermal and electrical conductivities and adequate resistance to corrosion in certain environments. Since brittleness limits their fabricability, the usefulness of these materials in structural components under rigorous service conditions depends greatly upon the development of welding procedures to provide joints that are comparable in properties to the base metal. Therefore, the objectives of these studies were to (1) determine the mechanical properties of joints produced by different joining methods in several types of unalloyed and alloyed tungsten; (2) evaluate the effects of various modifications in heat treatments and joining technique; and (3) demonstrate the feasibility of fabricating test components suitable for specific applications.
Materials Unalloyed tungsten in 1 / 3 6 in.
thick sheets was the material of most interest. The unalloyed tungsten in this study was produced by powder metallurgy, arc casting and chemical-vapor deposition techniques. Table 1 shows the impurity levels of the powder metallurgy, CVD and arc-cast tungsten products as received. Most fall within the ranges nominally found in tungsten
but it should be noted that the CVD material contained more than the normal amounts of fluorine.
Various sizes and shapes of tungsten and tungsten alloys were joined for comparison. Most of them were powder metallurgy products although some arc-cast materials were also welded. Specific configurations were used to determine the feasibility of building structures and components. All materials were received in a fully cold worked condition with the exception of the CVD tungsten, which was received as-deposited. Because of the increased brittleness of recrystallized and large-grained tungsten the material was welded in the worked condition to minimize grain growth in the heat-affected zone. B e c a u s e of t h e high cost of the material and the relatively small amounts available, we designed test specimens that used the minimum amount of material consistent with obtaining the desired information.
Procedure Since the ductile-to-brittle transition
temperature (DBTT) of tungsten is above room temperature, special care must be used in handling and machining to avoid cracking1. Shearing causes edge cracking and we have found that grinding and electrodis-charge machining leave heat checks on the surface. Unless they are removed by lapping, these cracks may propagate during welding and subsequent use.
Tungsten, like all refractory metals, must be welded in a very pure atmosphere of either inert gas (gas tungsten-arc process) or vacuum (electron beam process)2 to avoid contamination of the weld by interstitials. Since tungsten has the highest melting point of all metals (3410° C) , welding equipment must be capable of withstanding the high service temperatures.
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420-S i S E P T E M B E R 1 9 7 1
["CARTRIDGE HEATER
.-THERMOCOUPLE
CARTRIDGE HEATER
Fig. 1—Automatic welding apparatus. A (left)—apparatus incontrolled atmosphere chamber (arrow points to preheating fixture; B (right)—schematic of preheating fixture
Results for Unalloyed Tungsten
General Weldability
Gas Tungsten-A rc Welding — In gas tungsten-arc welding of V 1 6 in. thick unalloyed sheet, the work must be substantially preheated to prevent brittle failure under stress induced by thermal shock. Figure 2 shows a typical fracture produced by welding without proper preheating. The large grain size and shape of the weld and heat-affected zone are evident in the fracture. Investigation of preheating temperatures from room temperature to 540° C showed that preheating to a minimum of 150° C was necessary for consistent production of one-pass butt welds that were free of cracks. This temperature corresponds to the DBTT of the base metal. Preheating to higher temperatures did not appear to be necessary in these tests but material with a higher DBTT, or configurations that involve more severe stress concentrations or more massive parts, may require preheating to higher temperatures.
The quality of a weldment depends greatly upon the procedures used in fabricating the base metals. Autogenous welds in arc-cast tungsten are essentially free from porosity, Fig. 3A, but welds in powder metallurgy tungsten are characterized by gross porosity, Fig. 3(b) , particularly along the fusion line. The amount of this porosity, Fig. 3B, particularly along 3C, in welds made in a proprietary, low porosity product (GE-15 produced by General Electric Co., Cleveland).
Gas tungsten-arc welds in CVD tungsten have unusual heat-affected zones due to the grain structure of the base metal7. Figure 4 shows the face and corresponding cross section of such a gas tungsten-arc butt weld. Note that the fine grains at the substrate surface have grown due to the heat of welding. Also evident is the lack of growth of the large columnar
grains. The columnar grains have gas bubbles at grain boundaries caused by fluorine impurities8. Consequently, if the fine grain substrate surface is removed before welding, the weldment does not contain a metallographically detectable heat-affected zone. Of course, in worked CVD material (such as extruded or drawn tubing) the heat-affected zone of the weld has the normal recrystallized grain structure.
Cracks were found in the columnar grain boundaries in the HAZ of several welds in CVD tungsten. This cracking, shown in Fig. 5, was caused by rapid formation and growth of bubbles in the grain boundaries at high-temperatures". At the high temperatures involved in welding, the bubbles were able to consume much of the grain boundary area; this, combined with the stress produced during cooling, pulled the grain boundaries apart to form a crack. A study of bubble formation in tungsten and other metal deposits during heat treatment shows that bubbles occur in metals deposited below 0.3 Tm (the homologous melting temperature). This observation suggests that gas bubbles form by coalescence of entrapped vacancies and gases during annealing. In the case of CVD tungsten, the gas is probably fluorine or a fluoride compound10.
Electron Beam Welding — Unalloyed tungsten was electron beam welded with and without preheating. The need for preheat varied with the thickness, length and shape of the
specimen. To ensure a weld free of cracks, preheating at least to the DBTT of the base metal is recommended. Electron beam welds in powder metallurgy products also have the weld porosity mentioned previously.
Gas Tungsten-Arc Braze Welding— In an effort to establish whether braze welding could be used to advantage, we experimented with the gas tungsten-arc process for making braze welds on powder metallurgy tungsten sheet. The braze welds were made by pre-placing the filler metal along the butt joint before welding. Braze welds were produced with unalloyed Nb, Ta, Mo, Re, and W—26% Re as filler metals. As expected, there was porosity at the fusion line in metallographic sections of all joints (Fig. 6) since the base metals were powder metallurgy products. Welds made with niobium and molybdenum filler metals cracked.
The hardnesses of welds and braze welds were compared by means of a study of bead-on-plate welds made with unalloyed tungsten and W—26% Re as filler metals. The gas tungsten-arc welds and braze welds were made manually on unalloyed tungsten powder metallurgy products (the low porosity, proprietary (GE-15) grade and a typical commercial grade). Welds and braze welds in each material were aged at 900, 1200, 1600 and 2000° C for 1, 10, 100 and 1000 hr. The specimens were examined metallographically, and hardness traverses were taken across the weld, heat-affected zone, and base metal both as-welded and after heat treatment.
Table 2—Typical Analyses of Interstitials
Type of tungsten
Typical powder metallurgy Proprietary powder metal
lurgy, low porosity Chemically vapor deposited Arc cast
F
14.7
7.9 9.3 1
in Una lloyed Tungsten After Welding
Interstitial Weld metal
N2 O, C
4
1 1 1
56
120 72 10
<20
<20 <20
14
content,
F
2.9
<2 10.5-23 1
ppm Base
N2
5
1 1 1
meta l — 0 ,
41
140 52
7
C
<20
<20 <20
14
WELDING RESEARCH SUPPLEMENT | 421-s
..- 7\77 -;:,.„,... . 1 , - . - ' , . ' ::*;.. .
• _ ,
WmmMtZjwms,''.
Fig. 2—Gas tungsten-arc weld in unalloyed tungsten. A (top)—fracture which occurred while welding without a preheat; B (bottom)—end view of the fracture. Note the contrasting intergranular failure of weld and heat-affected zone versus the cleavage type failure of the base metal
Since the materials used in this study were powder metallurgy products, varying amounts of porosity were present in the weld and braze weld deposits. Again, the joints made with typical powder metallurgy tungsten base metal had more porosity than those made with the low porosity, proprietary tungsten. The braze welds made with W—26% Re filler metal had less porosity than the welds made with the unalloyed tungsten filler metal.
No effect of time or temperature was discerned on the hardness of the welds made with unalloyed tungsten as filler metal. As welded, the hardness measurements of the weld and base metals were essentially constant and did not change after aging. However, the braze welds made with W—26% Re filler metal were considerably harder as produced than the base metal (Fig. 7 ) . Probably the higher hardness of the W-Re braze weld deposit was due to solid solution hardening and/or the presence of o-phase finely distributed in the solidified s t r u c t u r e . The tungsten-rhenium phase diagram11 shows that localized areas of high rhenium content could occur during rapid cooling and result in the formation of the hard, brittle o- phase in the highly segregated substructure. Possibly the o-phase was finely dispersed in the grains or grain boundaries, although none was large enough to be identified by either metallographic examination or X-ray diffraction.
Hardness is plotted as a function of distance from the braze-weld center line for different aging temperatures in Fig. 7A. Note the abrupt change
Fig. 3—Centogenous gas tungsten-arc welds in tungsten. A (top)—arc-cast tungsten, B (middle)—typical powder metallurgy tungsten, C (bottom)—proprietary, low porosity powder metallurgy tungsten. Etchant: 25% H20», 25% NH..OH, 50% H.0 (reduced 50% in reproduction.
in hardness at the fusion line. With increasing aging temperature, the hardness of the braze weld decreased until, after 100 hr at 1600° C, the hardness was the same as that of the unalloyed tungsten base metal. This trend of decreasing hardness with increasing temperature held true for all aging times. Increasing time at a constant temperature also caused a similar decrease in hardness, as shown for an aging temperature of 1200° C in Fig. 7B.
Joining by Chemical Vapor Deposition—Joining of tungsten by CVD techniques was investigated as a method for producing welds in various specimen designs. By use of appropriate fixtures and masks to limit deposition to the desired areas, CVD and powder metallurgy tungsten sheets were joined and end closures on tubing were produced. Deposition into a bevel with an included angle of about 90 deg produced cracking, Fig. 8A, at the intersections of columnar grains growing from one face of the bevel and the substrate (which was etched away). However, high integrity joints without cracking or gross buildup of impurities were obtained, Fig. 8B, when the joint configuration was changed by grinding the face of the base metal to a radius of V 2 in. tangent to the root of the weld.
To demonstrate a typical application of this process in fabrication of fuel elements, a few end closures were made in tungsten tubes. These joints were leak-tight when tested with a helium mass spectrometer leak detector.
422-s I S E P T E M B E R 1 9 7 1
: • ' • •
-:•:-;..7: ~, ... -A Fig. 4—Gas tungsten-arc butt weld in chemically vapor deposited tungsten; top view and cross section. Etchant: H20a NHXIH, H20
V
J
Fig. 5—Cracking and bubble formation in heat-affected zone of weld in chemically vapor-deposited tungsten. Same general area is shown at increasing magnifications. Etchant: H202, NH,OH, H20
Mechanical Properties Bend Tests of Fusion Welds—
Ductile-to-brittle transition curves were determined for various joints in unalloyed tungsten. The curves in Fig. 9 shows that the DBTT of two powder metallurgy base metals was about 150° C. Typically, the DBTT (the lowest temperature at which a 90 to 105 deg bend could be made) of both materials increased greatly after welding. The transition temperatures increased about 175° C to a value of 325° C for typical powder metallurgy tungsten and increased about 235° C to a value of 385° C for the low porosity, proprietary material. The difference in the DBTTs of welded and unwelded material was attributed to the large grain size and possible redistribution of impurities of the welds and heat-affected zones. The test results show that the DBTT of typical powder metallurgy tungsten welds was lower than that of the proprietary material, even though the latter had less porosity. The higher DBTT of the weld in the low porosity tungsten may have been due to its slightly larger grain size, Fig. 3A and 3C.
The results of investigations to determine DBTTs for a number of joints in unalloyed tungsten are summarized in Table 3. The bend tests were quite sensitive to changes in testing procedure. Root bends appeared to be more ductile than face bends. A properly selected stress relief after welding appeared to lower the DBTT substantially. The CVD tung-
Fig. 6—Braze welds on powder metallurgy tungsten sheet. The various fille metals used are columbium, tantalum, W—26% Re, molybdenum, and rhe nium. As-polished
WELDING RESEARCH SUPPLEMENT | 423-s
TYPICAL POWDER METALLURGY o BASE METAL -4 WELDS
PROPRIETARY LOW POROSITY POWDER METALLURGY • BASE METAL * WELDS
^ - A S W L M o
""^r fe0"
!
— — WELO MET
7
. '. TEMPERATURE-
wm
200* C
DISTANCE FROM WELD CENTE!
Fig. 7—Effect of aging on hardness of powder metallurgy tungsten welded with W—26<% Re fil ler metal. A (top)— effect of varying temperature at constant 100-hr aging time. B (bottom)— effect of varying time at constant 1200° C aging temperature. Diamond pyramid hardness tested at 1-kg load
sten had, as welded, the highest DBTT (560° C) ; yet when it was given a 1 hr stress relief of 1000° C after welding, its DBTT dropped to 350° C. Stress relief of arc welded powder metallurgy tungsten for 1 hr at 1800° C reduced the DBTT of this material by about 100° C from the value determined for it as-welded. A stress relief of 1 hr at 1000° C on a joint made by CVD methods produced the lowest DBTT (200° C) . It should be noted that, while this transition temperature was considerably lower than any other transition temperature determined in this study, the improvement was probably influenced by the lower strain rate (0.1 vs 0.5 ipm) used in tests on CVD joints.
Fig. 8—Joints made by chemical vapor deposition process between powder metallurgy tungsten sheets. A (top)— crack in joint at intersections of columnar grains. Bevel was 90 deg included angle. B (bottom)—joint free of cracks. Bevel was ground to a radius of y2 in. tangent to the root of the weld. Etchant: H202, NH,OH, H20 (reduced 57% in reproduction)
Bend Tests of Braze Welds—Gas tungsten-arc braze welds made with Nb, Ta, Mo, Re, and W—26% Re as filler metals were also bend tested and the results are summarized in Table 4. The most ductility (a 90 deg bend angle at 525° C) was obtained with a rhenium braze weld. (This amount of bending is probably borderline since the specimen was cracked when removed from the testing rig.)
Although the results of this cursory study indicate that a dissimilar filler metal may produce joints with mechanical properties inferior to those of homogeneous welds in tungsten, some of these filler metals may be useful in practice.
Results for Tungsten Alloys
General Weldability
Gas Tungsten-Arc Welding—In
80
60
20
•
BASE METAL
1 i
J
r n ' rn / 1 WFI ns E&
/
JZ 2 0 0 3 0 0 4 0 0
TEMPERATURE (°C1
F ig . 9—Ductile-to-brittle t r a n s i t i o n curves for powder metallurgy tungsten base metal and welds
contrast to unalloyed tungsten, W— 26% Re tubing and sheet were autog-enously welded without the need for preheat. Powder metallurgy W—26% Re, like the unalloyed powder metallurgy tungsten, also exhibited weld porosity, Fig. 10A. The absence of porosity in arc cast W—26% Re, Fig. 10B, again illustrates the influence of the process history of the base metal upon weldability.
Tungsten-rhenium-molybdenum material can also be welded without preheating. However, a high temperature stress relief near the recrystallization temperature is needed before welding. Without a sufficient stress relief, severe centerline cracking may be encountered at the centerline, as shown in Fig. 11. A stress relief of 1300° C for 1 hr eliminated the problem. Powder products again exhibited large amounts of porosity.
Electron Beam Welding—Electron beam welds in tungsten alloys are illustrated in Fig. 12. End caps were welded to several test capsules with a defocused electron beam. Both the cap and the capsule shown in Fig. 12A were made of powder metallurgy W—25% Re. Note the gross porosity at the fusion lines. The specimen shown in Fig. 12B had an arc cast cap and a powder metallurgy capsule. No porosity was present near the fu-
Table 3—Ductile-to-Brittle
Jo in ing techn ique
Gas tungsten-arc
Electron-beam CVD
Transition Temperatures of Joints in Una
Type of tungs ten
Powder meta l lurgy
Powder meta l lurgy ( low porosi ty)
CVD CVD Arc cast Powder meta l lu rgy CVD
Type bend
Longi tud ina l Longi tud ina l Transverse Longi tud ina l
Longi tud ina l
Longi tud ina l Longi tud ina l Longi tud ina l Longi tud ina l Long i tud ina l
lloyed Tungsten
Surface in tens ion
Faceb
Root Face Face
Root
Face Face Face Face Face
Joint cond i t ion
As welded As welded As welded Stress re l ieved, 1800°C Stress re l ieved, 2800°C As welded
As welded Stress re l ieved, 1000°C As welded Stress re l ieved, 1000°C Stress re l ieved, 1000°C
Approx imate DBTT" (°C)
450 325 475
<350 >500
385
560 350 425 235b
200"
a Ductile-to-brittle transit ion temperature, defined as lowest temperature at which specimen bent ful ly (90 to 105 deg without cracking. b Bend test strain rate changed to 0.1 ipm (all others tested at 0.5 i pm).
424-s | S E P T E M B E R 1971
Table 4—Results of Longitudinal Bend Tests at 525° C of Gas Tungsten-Arc Braze Welds in Powder Metallurgy Tungsten
Filler metal
Niobium Tantalum
W-26% Re Molybdenum Rhenium
Bend angle at which first crack occurred (deg)
14 53
17 44 90
Visual observations of tested specimens
Fractured across entire width Cracks in weld, heat-affected zone, and base
metal Cracks in weld and heat-affected zone Fractured across entire width Very slight crack in weld
sion line with the arc cast cap. Figure 12(c) shows both an arc cast cap and capsule of W—5% Mo, which contains no porosity at either interface. This type of evidence is found frequently with both unalloyed tungsten and tungsten alloys.
Component Fabrication Another part of our program con
cerns determining the feasibility of fabricating test components from tungsten and tungsten alloys. A demonstration assembly simulating a corrosion loop was successfully tungsten arc, braze welded, Fig. 13A. Nondestructive inspection revealed the welds to be helium leak-tight and crack-free. It was constructed from 0.275-in. OD by 0.035-in. wall CVD tungsten tubing. It was welded manually in a chamber with a controlled atmosphere of very pure argon. In an effort to reduce the required heat input, W—26% Re was chosen as the filler metal.
In general, problems increase in making manual welds as the temperature increases (glove deterioration, welder inconvenience). Also, in building complex components, the lower heat required for braze welding is a definite advantage in decreasing weld stresses and reducing the size of the heat-affected zone. In the case of a small thin tube welded to a large component, a filler metal with a lower melting point increases the ease and
Fig. 11—Effect of stress relief on welds in W—25% Re—30% Mo. A (top)—stress relieved 1 hr at 950° C. B (bottom)— stress relieved 1 hr at 1300° C
assurance of making the joint without melting through the thin tube.
Metallographic e x a m i n a t i o n of these prototype welds revealed that they had complete penetration, no cracks and only a small amount of fine porosity. Figure 13B shows the difference in grain growth exhibited by the two tungsten tubes. In the bottom tube, the grains grew very little as compared to the rapid grain growth in the vertical tube. Since the porosity shown was along the interface between the braze weld deposit and the fine grained tungsten tube, a higher concentration of impurities may be present in the grain boundaries of the fine grained tube, which may have slowed the grain growth.
Upon closer examination the o-phase of the tungsten-rhenium system was discovered near the edge of the braze weld, Fig. 13C. It was positively identified by microprobe analysis and by the use of special etching techniques (0.5 N NaOH solution preferentially attacks o- phase in tungsten-rhenium). Sigma phase, since it is hard and brittle, is an undesired microcon-stituent. Microsegregation during solidification of the weld metal probably produced areas high enough in rhenium content to form the o- phase.
Fig. 10—Autogenous gas tungsten-arc welds in W—26% Re. A (top)—weld in powder metallurgy base metal. B (bottom)—weld in arc-cast base metal. Etchant: H202, NH.OH (reduced 62% in reproduction)
Conclusions Tungsten and many of its alloys can
be successfully joined by welding, braze welding, and chemical vapor deposition, provided certain techniques are used. Special machining processes must be employed, the material must be handled with care, and equipment must be capable of producing and handling the extreme heat needed for welding tungsten. For single-pass welds in unalloyed tungsten, the workpiece must be heated to at least the DBTT of the base metal before welding to avoid transverse cracking. Neither W—26% Re nor W—25% Re—30% Mo required this preheat because the transition temperatures of the base metals are below room temperature. However, a preheat may be desirable for large or complex structures, which may require multipass welds.
Possibly because of solid solution hardening and the presence of o-phase, W—26% Re weld metal is
W-25% Re W-25%Re W-3%Mo
Fig. 12—Electron beam welds in tungsten alloy capsules. Porosity is located only at the interface of weld metal and powder metallurgy product. A (left)—powder metallurgy tungsten cap and tube, B (center)—arc-cast tungsten cap and powder metallurgy tungsten tube, and C (right)—arc-cast tungsten cap and tube (reduced 25% in reproduction)
W E L D I N G R E S E A R C H S U P P L E M E N T | 425-s
Fig. 13—Simulated corrosion loop braze welded with W—26% Re filler metal. A (left)—completed loop, B (middle)— cross section of one of the braze-welds; C (right)—higher magnification (X100) of the root of the weld. Note the a
phase along the edge of the root. Etchant: 25% NH4OH, 25% H202, and 50% H»0.
harder than unalloyed tungsten (480 vs 400 dph). Aging for increasing times and temperatures up to 1600° C and 1000 hr decreases the hardness of the W—26% Re weld metal to that of unalloyed tungsten.
Powder products, whether unalloyed tungsten or tungsten alloys, have porosity in the weld zone, particularly along the fusion line. The amount of porosity depends on the process history of the base metal as well as of its composition.
As expected, the DBTT of all grades of tungsten was greatly increased by welding. Stress relief before welding reduced the cracking susceptibility of the welds and heat treatments after welding appeared to improve the ductility of the welds. The DBTT for unalloyed tungsten welds ranged from 325 to 560° C, depending on the type of base metal and testing conditions. Use of a dissimilar filler metal (braze weld technique) did not improve the properties of the resulting joint but appeared to cause further embrittlement.
Chemical vapor deposition is a feasible and promising process for joining tungsten. Of all the joints studied, those made by CVD methods followed by a stress relief of 1000° C had the lowest DBTT (200° C) .
However, more development must be done before this process can be applied.
A cknowledgements
The authors gratefully thank J. D. Hudson for preparing, welding and testing specimens, G. E. Moore of the Welding and Brazing Facility, Plant and Equipment Division, for manually welding the bead-on-plate specimens. We thank R. L. Heestand (now at BMI), R. G. Donnelly, A. C. Schaffhauser, R. E. McDonald, W. C. Robinson (now with Union Carbide, Greenville, S.C.) and J. I. Federer for their invaluable assistance in material procurement and consultation. The work of the following groups of the Metals and Ceramics Division is also appreciated: the Mechanical Properties Group for testing the bend specimens, the Metallography Group for preparing the photomicrographs and metallographic samples, and the Reports Office for preparing the manuscript.
References 1. Barth, V. D.. Physical and Mechani
cal Properties of Tungsten-Base Alloys, DMIC-127, pp. 6-10 (March 1960).
2. Lessman, G. G, and Gold, R. E., "The Weldability of Tungsten Base Alloys," WELDING JOURNAL, 48(12), Research
Suppl., 528-s to 542-s (1969). 3. "Vapors Create Tungsten Joints,"
Iron Age 19(21). p. 76-77 (May 1963). 4. Heestand, R. L., Federer, J. I., and
Leitten, C. F., Jr., Preparation and Evaluation of Vapor Deposited Tungsten, ORNL-3662 (August 1964).
5. Schaffhauser, A. C., "Low-Temperature Ductility and Strength of Thermo-chemically Deposited Tungsten and Effects of Heat Treatment," pp. 261-276, Summary of the 11th Refractory Composites Working Group Meeting, AFML-TR-66-179 (July 1966).
6. Evaluation Test Methods for Refractory Metal Sheet Materials, Materials Advisory Board Refractory Metal Sheet Rolling Panel, MAB176-M (Sept. 6, 1961). Revised.
7. Lundin, C. D., and Farrell, K., "Distribution and Effects of Gas Porosity in Welds in CVD Tungsten," WELDING JOURNAL, 49(10). Research Suppl., 461-s to 464-s (1970).
8. Schaffhauser, A. C., and Heestand, R. L., "Effect of Fluorine Impurities on Grain Stability of Thermochemically Deposited Tungsten." pp. 204-211, 1966 IEEE Conference Record of the Thermionic Conversion Specialist Conference, Nov. 3 and If, 1966, Houston, Texas, Institute of Electrical and Electronics Engineers, New York,
9. Farrell. K., Houston, J. T., and Chumley, J. W., "Hot Cracking in Fusion Welds in Tungsten," WELDING JOURNAL, 49(3), Research Suppl., 132-s to 137-s (1970).
10. Farrell, K., Federer, J. I., Schaffhauser, A. C, and Robinson, W. C., Jr., "Gas Bubble Formation in Metal Deposits," pp. 263-267, Chemical Vapor Deposition 2nd Intern. Conf., ed. by J. M. Blo-cher, Jr., and J. C. Withers, The Electrochemical Society, New York, 1970.
11. English, J. J., Binary and Ternary Phase Diagrams of Columbium, Molybdenum, Tantalum and Tungsten, DMIC-152, p. 92 (April 28, 1961).
NEW WELDING RESEARCH COUNCIL BULLETINS
WRC BULLETIN 160:
WRC BULLETIN 161:
"High-Frequency Resistance Welding" by D. C. Martin
"The Fabrication and Welding of High-Strength Line-Pipe Steel" by H. Thomasson
The price of either WRC Bulletin 160 or 161 is $1.50 per copy. Orders for single copies should be sent to the American Welding Society, 345 East 47th St., New York, N.Y. 10017. Orders for bulk lots, 10 or more copies, should be sent to the Welding Research Council, 345 East 47th St., New York, N.Y. 10017.
426-s I S E P T E M B E R 1971