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WELDING TITANIUMA DESIGNERS AND USERS HANDBOOK

£ 25.00

TIGTHE

T I T A N I U M

INFO RMATIO NG R O U P

WORL D CENTRE FOR

MATERIALS JOINING

TECHNOLOGY

Electronic copyright in this document as follows: Copyright TWI and the Titanium Information Group,

- Guide to best practice -

1999



TITANIUM INFORM ATION GROUP

The TITANIUM INFORMATION G ROUP, (TIG) is an a ss ocia tio n o f Europ ea n sup pliers, d es ign en gineers, a nd

fabricators of titanium formed with the intention of promoting the use of titanium.

The a im o f the G roup is to influence t he initial select ion o f ma terials so tha t titanium is given the c onsiderat ion

merited by its uniq ue combination of physica l and m echa nica l properties, outsta nding resista nce to co rrosion andcost effectiveness in a wide range o f dem anding applications.

Regular publications and literature available from the Group present detailed and up-to-date technical and

com mercial information to m at erials engineers, plant a nd eq uipment des igners and buyers, and provide t he answ ers

to everyday questions about cost, availability, fabrication and use of titanium and its alloys.

Membe rs of the Group a re available to give presenta tions abo ut titanium o n either general or specific to pics to

com pa nies o r at sem inars. A list o f mem ber comp anies of TIG appe ars on pa ges 32 a nd 33 Cop ies o f the TIG

vide o, ‘Titanium Tod ay’ and the da ta diskett e ‘Titanium a nd Its Alloys’ are ava ilable fo r use in ed ucat iona l and

training establishments to provide an introduction to the metal its applications and properties.

Further informat ion o n TIG publica tions ca n be fo und o n the we b: w ww. titaniuminfogroup.co. uk

TWI

TWI is ba sed at Abingto n, nea r Cambridg e, UK and is o ne of Europe ’s largest indepe ndent contra ct resea rch and

techno logy o rganisations. O ver 400 staff, w ith a uniq ue blend of te chnica l bac kgrounds, international experience

and language skills, work with industry world-wide to apply joining technology effectively. Some 2500 member

co mp anies in over 50 co untries be nefit from TWI service s.

TWI’s know ho w a nd expertise co vers:

Engineering - des ign, st ructura l integ rity, fract ure, NDT.

Mat erials - stee ls, no n-ferrous a lloys including titanium, plas tics, co mpo sites, ce ramics.

Welding a nd joining- arc, e lectron bea m, las er, resistanc e a nd friction w elding, braz ing, so lde ring, a dhes ive

bond ing, fast ening.

Surfacing - arc cladding, friction, high velocity oxyfuel, laser, arc spraying.

Cutting - flam e, plasm a, wa ter jet, las er.

Manufac turing - project m ana gem ent, production/ma nufacturing e ngineering, d ecision support, ma nufacturing

systems, health and safety, q uality assurance.

Indust ry’s o bjec tives a re TWI’s o bject ives

Reduce cos ts.

Ma rket effe ctively.

Continuously improve quality and reliability.

Innovate.

TWI, Gran ta Pa rk, G reat Abingto n, Ca mbridge , CB1 6AL, UK

Tel: + 44 (0)1223 891162 Fax: + 44 (0)1223 892588Web: htt p: //w w w.tw i.co. uk em a il: tw i@t w i.co. uk

The da ta and othe r informat ion co nta ined he rein are de rived from a variety o f

so urces w hich TIG a nd TWI believe a re reliable. Be ca use it is not po ssible to

ant icipate spec ific uses a nd op erating co nditions TIG a nd TWI urge you t o

consult with the sales or technical service personnel as appropriate of the

individua l com pa nies.

M ay 1999

Written b y: Lee S Smith, Philip Threa dg ill and Micha el Gitt os TWI

Editor: Da vid Pea co ck Titanium Meta ls Corporation

Dat a ava ilab le in literature a vailab le from TWI, TIMETa nd o ther m emb ers o f TIG a nd

TWI is inco rpora te d in this publica tion .



INTRODUCTION

The high strength, low w eight and o utsta nding corrosion resista nce po sses sed by tita nium and titanium a lloys ha ve

led to a wide and diversified range of successful applications in aerospace, chemical plant, power generation, oil

and ga s extrac tion, med ical, spo rts, and othe r industries. There is a com mo n q uestion w hich links a ll of the se

app licat ions, a nd tha t is how be st to join titanium pa rts toget her, or to other ma terials to prod uce the final compo nent

or structure. The variety o f titanium a lloys, and the va stly greater number o f engineering me ta ls a nd m at erials

requires that there should be a versatile selection of joining processes for titanium if the metal is to be capable of

use in the w ide st range o f applica tions. Although me chanical fastening, ad hesives, a nd o ther techniq ues have their

place, we lding cont inues to be the mo st impo rtant p rocess for joining titanium. Welding of t ita nium by various

processes is widely practised, and service performance of welds is proven with an extensive and continuously

extending record of achievements. Newer methods adaptable for titanium are further advancing the science,

tec hnology and ec ono mics of we lding. Applica tion of this techno logy to the de sign, manufact ure and app lica tion of

titanium is as relevant to first time use rs as to com mitted custo mers. For ma ny applica tions, choo sing the welding

process is as important a step in design as the specification of the alloy.

This ha ndb oo k, t he s ixth in a se ries, is prod uced jointly by t he Titanium Info rma tion G roup a nd TWI World

Centre fo r Mat erials Joining Techno logy. The a im of this ed ition rema ins a s w ith its p redece sso rs, to bring t oge ther

key elements of w ide ly dispersed d at a into a single source boo k. Use o f this hand boo k w ill ena ble tho se respo nsible

to select welding processes that will be appropriate to the titanium alloy, the component, and the application. Inthis way the most demanding goals for reliability, maintainability and safety can be achieved, together with the

lowest overall cost for components and systems of the highest performance and integrity.

1

CONTENTS

Introduction 1

Why use Tita nium 2

Prop erties of Titanium a nd its Alloys 3

Joining Tita nium a nd its a lloys 4

TIG w eld ing 5MIG w elding 6

Plasma and fluxed welding 7

Las er and EB w elding 8

Resistance welding 9

Frictio n we lding proc ess es 10

Diffusion bonding 13

Forge we lding proce sses 14

Brazing and soldering 15

Adhes ive bond ing a nd m echa nica l fast ening 16

Joining titanium to ot her meta ls 17

Workshop prac tice 18

Ope n air welding 19

Preparat ion of the joint for w elding 20

Welding te chnique s 21

Evaluat ion o f w eld q uality 25

Visua l inspe ct ion 26

Repair of defects 28

Distortion a nd stress relief 29

The do ’s a nd d on’ts of w elding 30

Standa rds a nd specifications 31

For furthe r help 32

TIG me mb ers 33

Titanium a l loy (grad e 5) fa br ica ted structure for high

specification military application

Keyhole plasm a w elding



WHY USE TITANIUM

In all fields of engineering, designers, fabricators and

end users are ready to consider titanium for an ever

wide ning range o f ap plications. The m eta l and its a lloys

are no longer seen a s ‘exotic’. Outd ated and misguided

notions a bout c ost , a vailability, a nd fa brica tion are less

likely than ever to prejudice engineers who can see for

themselves all the excellent benefits which titanium

offers. This brochure has be en co mpiled to show how

the m eta l’ s reputat ion for being difficult to we ld, is bot h

mislead ing and inap prop ria te . Titanium alloy s joined by

any one of a wide range of welding processes are

routinely at work in applications as widely differing as

aero engines, offshore platform pipework, implants for

the human body and ultra lightweight roofing. Practical

and competitive welding processes ensure there are

t o d a y f e w o t h e r m a t e r i a l s t h a t c a n a p p r o a c h ,eco nom ica lly or te chnica lly, t he pe rforma nce p rovide d

by tita nium.

Titanium is as st rong as st ee l, yet 45%light er. Titanium

alloys will work continuously at temperatures up to

600°C, resisting creep and oxida tion, and d ow n to liq uid

ni trogen temperatures wi thout loss of toughness .

Titanium w ill survive ind efinitely w ithout co rros ion in

sea wa ter, a nd m os t ch lor ide env ironments . The

metallurgical characteristics which give titanium its

favourable properties can be reproduced, by selection

of an appropriate practice, in welded joints for mosttita nium alloys . The o xide film, w hich is the ba sis of the

metal’s corrosion resistance forms equally over welds

and heat a ffected z ones as over parent metal, and other

than in a few very harsh environments, weldments

perform identically to parent metal in corrosion resistant

service.

The w ide range of ava ilable tita nium a lloys ena bles

de signers to s elect ma terials and forms closely tailored

to the nee ds of the ap plica tion. The versatility o f tw o

basic compositions is such however that they continue

to satisfy the majority of applications, and this level of

com mo n use rema ins a ma jor facto r in the cost effective

production, procurement and application of titanium.

The tw o c om pos itions a re com mercially pure titanium,

(ASTM G rade 2), selected for ba sic corrosion resistance

with strength in the range 350 - 450MPa, and high

st reng th tita nium a llo y Ti-6Al-4V, (900 - 11 00MPa ).

Welding cons uma bles are rea dily ava ila ble for these

grades . Although there are other weldable a l loys ,

consumables for these may need to be obtained from

spe cialist so urces . The full range of titanium a lloys

reaches from high d uctility com mercially pure titanium

used where ex t reme formab i l i ty i s essent i a l , in

2

a p p l i c a t i o n s s u c h a s p l a t e h e a t e x c h a n g e r s a n d

architectural cladd ing and roofing, to fully heat treat able

alloys w ith strength a bove 1500MPa . Corrosion resistant

alloys are capable of withstanding attack in the most

ag gressive sour oil and g as e nvironments o r geo therma l

brines at temperatures above 250°C. High strength

oxidation and creep resistant alloys see service in aero

engines at temperatures up to 600°C. Suitable welding

p r o c e s s e s a r e e s s e n t i a l f o r t h e a p p l i c a t i o n a n d

performa nce of titanium to be op timised in most o f these

uses.

Improving the understand ing o f w elding titanium and

the p reservat ion of its properties a fter joining a re de sign

step s t ow ards increase d flexibility in ma terials selection

and use, resulting in improved q uality and performanceof products and processes. In this way, the technical

superiority o f titanium w ill be co nfirmed for even m ore

engineering applications than at present, to the mutual

benefit of the titanium industry and its customers.

What is the cost? This q uestion freq uently come s

first. The price pe r kilo o f titanium is no guide to the c os t

o f a p r o p e r l y d e s i g n e d c o m p o n e n t , o r p i e c e o f

eq uipme nt. First cost is in any event o nly one p art o f the

f u l l c o s t e q u a t i o n . M a i n t e n a n c e , d o w n t i m e a n d

replacement costs which may be a very significant

element in plant designed for long and reliable servicelife a re ano ther. In this area , w elding plays a significa nt

role , ensuring that the performance of a t i tanium

fabrica tion mat ches tha t of the m eta l overall. Add itional

costs of e nergy a ssociated with operating unnecessarily

hea vy or thermally inefficient eq uipme nt m ay be a third

penalty o n life cycle costs. Titanium is freq uently spe cified

for its ability to cut costs through reliable and efficient

performance . Tita nium w elded tube is fo r example

installed in steam turbine condensers and welded pipe

in nuclear power plant service water applications with

40 year performance gua rantees a ga inst co rrosion failure.

One ma nufact urer offers a 100 year wa rranty o n its me tal

supplied for a rchitec tural applica tions.

It is not possible in this guide to give an absolute

cost or an a ccurate compa rison o f cost for the different

we lding process es d escribed. The eq uipme nt ca pa bilities

and cost s tructures of equal ly competent welding

cont racto rs freq uently results in a range o f prices being

offered for the same basic job. Some processes are,

how ever, intrinsically m ore expensive tha n o thers. Alwa ys

seek advice from an appropriate welding specialist or

contractor before attempting to develop a budget or

notional cost for a welding project.

Light, strong titanium should be considered for applications wherever weight or space are factors or corrosion/erosion is a problem.



PROPERTIES OF TITANIUM AND ITS ALLOYS

3

A convenient and widely used system for specif ic

identifica tion of t he various g rade s o f com mercially pure

titanium and titanium alloys used for engineering and

co rrosion resist ing app lica tions is provide d by ASTM

which cover all the forms supplied in titanium and its

alloys:-

B 265 - Strip Sheet and Plate

B 337 - Sea mless a nd Welded Pipe

B 33 8 - Sea mless an d Welde d Tube

B 348 - Bars a nd B illets

B 363 - Sea mless a nd Welde d Fittings

B 367 - Castings

B 381 - Forgings

B 861 - Seamless Pipe (to replace B337)

B 862 - Welde d Pipe

B 863 -Wire

F 67 - Una lloyed Tita nium for Surgica l App lica tions

F 136 - Ti-6Al-4V fo r Surg ica l App lica tio ns

Grades 1 ,2 ,3 ,4 a re commerc ia l l y pure ( a lpha)

titanium, used prima rily for co rros ion resista nce. Strength

and hardness increase , a nd d uctility reduces w ith grade

number. Grade 2 is the most widely used specification

in all product forms. G rade 1 is specified w hen superior

formability is required. Grades 3 and 4 are used where

higher levels of s trength a re neces sary.

Grades 7, 11, 16, 17, also alpha alloys, contain

palladium (Pd) and provide superior corrosion resistance

in pa rticular to reducing ac id chloride s. Grad es 26 and

27 are similarly also alpha alloys, and contain .1%

ruthenium (Ru) to provide enha nced co rros ion resista nce

in red ucing e nvironments . The m echa nica l prope rties of

grades 7, 16 and 26 are identical to those of Grade 2.

The mecha nica l properties of grad es 11, 17 and 27 are

similarly ide ntical to tho se o f Grad e 1.

Grade 12 (alpha) also offers superior corrosion

resista nce t o c om mercially pure titanium, but is stronge r

and retains useful levels of strength up to 300°C.

Grade 5 is the ‘workhorse’ alpha-beta alloy of the

titanium range. It is also spec ified with red uced o xygen

content (ELI) for enhanced toughness (Grade 23), and

with addition of .05%palladium for added corrosion

resistance, (Grade 24) and with palladium and nickel

(Grade 25). Current interest in this alloy for marineappl icat ions is focused upon Grade 23 with .05%

pallad ium or Gra de 29 w ith .1 %ruthenium. Restrictions

on fabricability may limit availability in certain products.

Grade 9, (near alpha) has good fabricability and

med ium levels of strength. Grade 18 (Grad e 9 + .05%

Pd) and Grade 28, (Grad e 9 + .1%Ru) offer enhanced

corrosion resistance.

Bet a -C a nd TIMETAL® 21S are high st rength highly

co rros ion resista nt be ta alloys in the ASTM rang e. They

are respe c t ive ly Grad e 19, and Grad e 21. (Thecounterpart of Grade 19 with .05%Pd is Grade 20).

Grade 32 (Navy alloy) has go od we lda bility to gether w ith

high toughness and resis tance to s tress corrosion

c r a c k i n g i n m a r i n e e n v i r o n m e n t s . G r a d e 21 ,

(TIMETAL® 21S) and G rade 32 , (TIMETAL® 5111) a re a lso

ava ilable w ith the ad dition of .05%pallad ium.

Weldm ent s in ASTM gra d e 2 a re no rma lly

characterised by increase d strength, a ccompa nied by a

reduction of ductil i ty and fracture toughness. Any

strengthening induced by cold work will be lost in the

joint region . Weldme nts in Ti-6Al-4V typica lly exhibit near-

matching strengths to the base metal, but have lower

ductility. The t oughnes s o f the we ld zo ne is superior to

alpha-beta processed material, showing similar values

to a lpha-beta processed parent alloys. Som e examples

of actua l we ld properties are given for process es

de scribed in the text, but you are strongly ad vised t o

consult with your we lding specialist in cases whe re weld

performance is critical in your design.

Designation Commerically Medium High HighestPure Titanium Strength Strength StrengthAlloys Alloys

Alloy Type Alpha Alpha-Beta Alpha-Beta Beta

0.2% Proof Stress MPa 345 - 480 480 - 550 725 - 1000 1100 - 1400

Tensile Strength MPa 480 - 620 600 - 650 830 - 1100 1200 - 1500

Elongation % 20 - 25 15 -20 8 - 15 6 - 12

Tensile Modulus GPa 103 104 110 - 120 69 - 110

Torosion Modulus GPa 45 43 40 - 48 38 - 45

Hardness HV 160 - 220 200 - 280 300 - 400 360 - 450

Density kg/1 4.51 4.48 - 4.51 4.43 - 4.60 4.81 - 4.93

Thermal Expansion 10-6/ºC 8.9 8.3 8.9 7.2 - 9.5

Conductivity W/mK 22 8.0 6.7 6.3 - 7.6

Specific Heat J/kg/ºC 525 544 565 490 - 524

Typical mecha nical prope rties a nd phys ical prope rties o f titanium and titanium a lloys (100MPa = ap prox. 15 ksi)



WELDABILITYMost titanium a lloys ca n be fusion w elded a nd a ll alloys

can be joined by solid state processes (see table).

Indeed , Welds in titanium a re substa ntially immune to

ma ny of the w eld cracking problems that ca use trouble

with ferrous alloy fabrications. Despite this and other

beneficial characteristics, some engineers still believe

that titanium is difficult to weld, possibly due to its

pa rticular requireme nts w ith rega rd to ga s shielding, or

beca use it has no rmally been ha ndled o nly by specialist

fabrica to rs. Tita nium is act ually ea sy to we ld by m ost

processes, as are most of its more common alloys.

Embrittlement through contamination with air and

carbonaceous materials poses the biggest threat to

successful fusion welding titanium, so the area to be

welded must be clean and protected by inert ga s w hile

hot. The mea ns to protect the weldment with inert ga s

are commercially available and easy to implement.

4

JOIN ING TITANIUM AND ITS ALLOYS

Welding cons uma bles are read ily a vailable fo r the

comm on t itanium grades and specifications for w elding

wire a re provided in AWS Spe cifica tion A5.16. Permissible

filler meta l, no rmally identical to the pa rent met al, ma y

be s pec ified a s in ASTM B 8 62.

The w elda bility of tita nium a lloy s is usually as se sse d

on the ba sis o f the toughness a nd d uctility of the weld

metal. Commercially pure grades are considered very

eas y to fa bricate and are ordinarily used in the as -welded

cond ition. Titanium a lloys show reduced we ld met al

ductility a nd toughnes s. The t able below highlights the

we lda bility of the c om mo n ASTM titanium grad es a nd

ot her alloys . Tec hnical consulta tion sho uld be s oug ht

prior to de signing o r fabrica ting any o f the t ita nium a lloys,

if there is any likelihood of problems arising from

unfamiliarity w ith the ma terials co ncerned.

ASTM Grades Weldability Comments

1,2,3,4,7,11,12,13 Excellent Commercially pure and low alloy grades

14,15,16,17,26,27 w ith minor additions of Pd, Ru, Mo etc

9,18,28 Excellent Ti-3A1-2.5V grades

5,23,24,29 Fair-good Ti-6A1-4V grades

21 Excellent Beta alloy

6,6ELI Good-excellent Ti-5A1-2.5Sn

Welda bility of the c om mo n ASTM grad es

Alloy Weldability Comments

Ti-6A1-2Sn-4Zr-2Mo Fair-good C ommon aerospace alpha

&beta grade

Ti-6A1-2Sn-4Z r-6Mo Limit ed Aero space alpha &bet a grade

Beta III Excellent Beta alloy

Ti-15V-3A1-3Sn-3Cr Excellent Beta alloy

Welda bility of se lect ed no n-ASTM Ti alloys

Welding of a titanium fuel ta nk for the reco rd breaking

Breitling O rbiter III balloon (Bunting Titan ium)Fab rica tion of a large titanium pressure vesse l

(Bunt ing Tita nium)



5

TUNGSTEN INERT GAS (TIG) WELDINGTungsten inert ga s w elding is a lso know n a s t ungsten

a rc we lding and g a s-tungs te n arc w elding (GTAW) a nd

is currently the mo st c om mo nly ap plied joining proce ss

for titanium and its alloys. Titanium is o ne o f the ea siestof me ta ls to w eld by the TIG process; the w eld poo l is

fluid a nd its com bination of low density and high surface

tension ena bles go od cont rol of the w eld surface p rofile

and penetrat ion, even when unsupported. An arc

between the tungsten alloy electrode and workpiece

obt ains fusion o f the joint region, w hile a n inert ga s (the

torch gas) sustains the arc and protects the tungsten

e l e c t r o d e a n d m o l t e n m e t a l f r o m a t m o s p h e r i c

cont am ination. The inert g as is t ypica lly a rgon, but a

mixture of helium and argon can be used to increase

penetration o r speed. Welds can be mad e a utogenously

( i .e . wi thout f i l ler addi t ion) or wi th addi t ion of a

co nsuma ble wire into t he a rc. The TIG proc es s is fullycapable of operating in all welding positions and is the

only process that is routinely used for orbital welding.

Specialist orbital welding equipment is commercially

available for a wide range o f compo nent diameters and

often has the a dd ed a dvanta ge of incorporating the inert

ga s tra iling shield nece ssa ry for tita nium fa brica tion.

ARC WELDING PROCESSES

Higher prod uctivity variants o f the TIG proce ss ha ve

been a pplied to t ita nium. Ho t w ire TIG enables a g reate r

fil l rate to be achieved, improving productivity on

multipa ss w elds req uired for heavier sec tion thickness es.Act ivate d TIG (A-TIG) ac hieves d ee pe r pe net rat ion

through the use o f a sp ecial flux sprayed onto the joint

surface s prior to we lding. The latte r proce ss ha s ha d

particular success for welding stainless steels, but its

pot ential applica tion to titanium joints ha s yet to be fully

exploited.

TIG (GTAW)

Advantages

• Manua l or mechanised process

• All posit ion capabilty• Capable of producing high quality welds

• Significant industrial experience

• No w eld spa tter

Disadvantages

• Lo w p ro d uc tivit y

• Tungsten inclusions if electrode touches

weld pool

Example welding paramet ers (1mm = .04inch) Manua l TIG w elding of a titanium vesse l (Bunting Titanium)

Tensile Strength Proof Stress Elongation (%)Alloy (MPa) (MPa)

Parent Weld Parent Weld Parent WeldGrade 2 460 510 325 380 26 18

Ti-6A1-4V 1000 1020 900 880 14 8

Ti-3A1-2.5V 705 745 670 625 15 12

Typica l tensile prop erties o f TIG w eldm ent s

v



PLASMA ARC (PAW) WELDINGPlasma arc welding retains the high quality associated

w ith TIG we lding whilst ha ving significa nt pe net ration

and speed ad vantag es. Similar to TIG, heat is transferred

by an arc generate d betw een a tungsten electrode a nd

the w orkpiece ; but, in the PAW proce ss t he a rc is

constricted by a copper alloy orifice to form a highly

collimated arc column (see figure). In addition to a

surrounding shielding gas , a ‘plasm a ga s’ flow s through

the copper orif ice and a portion of this is ionised

p r o d u c i n g t h e c h a r a c t e r i s t i c p l a s m a j e t . I n t h e

conduction-limited mode a weld pool similar to that

produce d during TIG w elding is gene rated , w hilst in the

keyhole mo de , the p las ma jet fully penet rates t he joint.

Molten metal flows around the keyhole and solidifies

behind the plasma jet as the torch traverses along the

joint line. In many w ays t he keyhole plasm a a rc proce ss

is akin to a slower version of one of the power beam

processes (electron beam and laser welding). A thirdproces s variat ion exists, referred t o a s microplasm a a rc

w elding. This is simply a low current va ria nt (typica lly

0.1-15A) of the conduction-limited mode, suitable for

prod ucing sma ll co ntrolled w eld bea ds . Welding is

generally performed w ith co ntinuous d irect current w ith

the e lectrod e neg at ive (DCEN), but a pulsed current c an

be used to broaden the tolerance window of welding

parame ters which prod uce accepta ble we lds.

Plasma arc w elding offers significa nt prod uctivity ga ins

over both TIG and MIG, espec ially whe n ope rated in the

keyhole mode. Although welds are only typically madein the 1G o r 2G positions, single pa ss w elds can be m ad e

in ma te rial up to 18 mm thick. Furthermo re, the keyho le

PAW process ap pea rs to o ffer grea ter imm unity to we ld

metal porosity than any other fusion welding process.

Because introduction of filler into the arc can cause

insta bilities in the ga s pla sm a, keyho le PAW is norma lly

performed auto geno usly, thus a sm all am ount o f underfill

is typical. Completing a second pass, adding filler with

the same torch operated in the conduction-limited

mo de , o r alternatively using TIG w elding, ca n co rrect

this. Pipe circumferential welding (e.g. pipe joints) is

certainly pos sible, but req uires a co ntrolled slope -dow n

of the plasm a ga s flow rate and a rc pow er to a void a ny

porosity defects a t the sto p position.

FLUXED WELDING PROCESSESThe a pplica tion of fluxed we lding proce sses such a s

submerged arc, electroslag and flux cored arc welding

have been investigated and reportedly used in the formerSoviet U nion fo r we lding t hick sec tion t itanium a lloy. The

main difficulty is the selection of an appropriate flux;

oxides ca nnot be used these w ould co ntaminate the we ld

metal and, for similar reasons, fluxes should not be

hygroscopic (i.e. adsorb moisture). Most of the fluxes

have be en rare ea rth and /or alka line meta l-base d

h a l o g e n s a n d h a v e b e e n r e p o r t e d t o p r o d u c e

contam inant-free we lds. Some tests carried out in the

UK on commercially pure titanium showed mechanical

properties in conforma nce w ith ANSI stand ards. Work

performed at the Pato n Institute, Kiev has sho wn that

j o i n t s c a n b e p r o d u c e d i n t i t a n i u m a l l o y s w i t hperforma nce co mpa rable to those of TIG welds. In

practice, how ever, the q uality o f w elds ma de using fluxes

is suspect , since the oppo rtunities for conta mination a nd

slag inclusions a re significa nt. Due t o thes e intrinsic risks,

f l u x e d w e l d i n g p r o c e s s e s c a n n o t c u r r e n t l y b e

reco mm end ed for joining tita nium. Further rese arch into

these we lding methods is need ed but the improvements

to be gained, over conventional arc welding, are

considerable and could present ma jor cost savings for

thick sect ion titanium alloy fabrica tion.

PAW

Advantages

• Fas ter than TIG

• Single pass welds possible in material up to

18mm thick

• Greater immunity to weld metal porosity

than any other fusion process

Disadvantages

• Lmited posit ional capability

ˇKeyho le PAW is used exte nsively in the fa bricat ion of the Ti-6Al-4V VSEL light w eig ht field g un.

MIG welding has found application for a ppliqué armour plate such as for the General Dynamics M1 Abrams tank.

7



8

LASER WELDINGLaser welding is f inding increasing application for

titanium, for example in the production of welded tube

and pipe. The proces s, w hich offers low distortion and

go od prod uctivity, is po te ntially mo re flexible t ha n TIG

or electron bea m for auto ma ted we lding. Applica tion is

not restricted by a requirement to evacuate the joint

region. Furthermo re, las er beam s ca n be d irected ,

enabling a large range of component configurations to

be joined using different welding positions. CO2 lasers

offer the greate st po we r range, with single pa ss w elds

possible in 20mm thick titanium using 25kW systems.

Nd-YAG las er weld ing offe rs supe rior flexibility due to

the p os sibility o f fibre opt ic beam de livery syste ms, but

penetration is restricted by a lower power capability.Laser welds can suffer from weld spatter, which may

pose a problem on the root surface, particularly if

postw eld a ccess is restricted.

POWER BEAM WELDING PROCESSES

La se r we ld 10m m (.4 ” ) thick Gr 2 joined to Ti-6Al-4V

ELECTRON BEAM WELDINGElect ron bea m (EB) welding has trad itiona lly been t he

preferred process for making critical joints in titanium

alloys. High quality welds can be produced with low

distortion and with high reliability. Productivity can also

be good, especially for thick sections which can be

welded readily in a single pass. Conventional electron

beam we lding is performed in a vacuum o f abo ut 10 -4

mba r, requiring a se aled cha mber and pumping system.

This a dd s to the ca pital cost of the eq uipment, especially

for large components. A further drawback for large

compo nents is the extended time it takes to a chieve a

vacuum in the chamber, decreasing product iv i ty .

How ever, electron beam guns have been d esigned w hich

can operate a t lower vacuum or near a tmosphericpressure. So called ‘reduced pressure’ electron beam

(RPEB) welding show s great promise for dec reasing cost s

and increasing productivity beyond that achievable using

conventional EB welding. Simple seals can be used to

isolate the joint region of a large component, which is

evacuated to a pressure of around 10 -1mba r (achievable

using inexpens ive m echa nical vacuum p umps ). An RPEB

ste el pipe J-laying syst em is currently unde r developm ent

at TWI. High q uality w elds ha ve a lso been produce d in

titanium a lloy pipe a nd plate .

RPEB w eld in 13m m t hick Ti-6Al-4V

Laser Welding

Advantages

• Aut om a te d p ro ce ss

• H ig h w e ld ing sp ee d

• Fibre o ptic bea m d elivery with Nd-YAG

Disadvantages

• Exp ens ive e q uip m ent

• Thickness limited w ith Nd-YAG• We ld Spa tt er

Electron Beam Welding

Advantages


• Single pass welding of thick sect ions

• No filler or gas shield required

• Significant industrial experience

Disadvantages

• Exp ens ive e q u ip me nt

• Component s ize limited by vacuum

cham ber (not a pplica ble fo r RPEB)



9

INTRODUCTIONResistance welding of titanium is quite straightforward

and is aided by the metal’s high resistivity and low

therma l conductivity. The a sso ciated process es rely on

the hea t generat ed by the resista nce to electrical current

flowing through the workpiece to fuse the metal with

the joint. Shaped electrodes apply the current and

pressure req uired to m ake a localised w eld. As with othe r

joining proce sses , cleanliness of t he a butting joint fac es

is ess ential for a succ ess ful we ld. Experience ga ined with

sta inless s teels is relevant for resis tance welding

com mercially pure titanium grad es, since the resistivity

and therma l cond uctivity of the t w o m eta ls are similar.

Titanium alloys , how ever, have q uite d ifferent t herma l

and electrical characteristics and should not be welded

using parameters established for stainless steel.

SPOT WELDINGSpot welding is performed using copper a l loy

electrodes with a spherical face, a current of 5-10kA

(increasing with shee t thickness) and an e lectrod e force

of s everal kiloNew to ns. Inert ga s shielding is not req uired

for spo t w elding since the therma l cycle resulting from

the brief electrical pulse is extremely rapid, minimising

loc al oxida tion.

SEAM WELDINGContinuous or intermittent seam welds are made

using rotating disc electrodes, again with a spherical

contact profile, and the repeated application of brief

electrica l pulses. During w elding, the e lectrod e is rot at ed ,

traversing the cont ac t po sition a long the joint line. Inert

gas shielding or flood water cooling may be desirable

for seam welds since the repeated thermal cycles can

result in the accumulation of heat and subsequent

oxidation.

TITANIUM RESISTA- CLADTM PLATEThis p at ented process is p rincipally used to supply

r e q u i r e m e n t s f o r v e s s e l c l a d d i n g a n d f l u e g a s

desulphurisation (FGD) duct and flue linings. Electrical

resistance heating is used to bond titanium to a less

expensive ste el backing, using an intermed iat e s ta inless

steel mesh. The bond is a sea m 12.7m m (0.5 inch) wide,having typical shear and peel strengths of 303MPa and

15kg/m respectively. The se am s ca n be spa ced to mee t

the application requirements of stresses imposed in

service by gravity, vibration, thermal expansion and

pressure cycling.

Pre-bonded sheets are supplied for installation with

the titanium offset o n tw o s ides to permit o verlap and

fillet sea l welding o f a djoining s heet s. For retrofit

insta llat ions, the thicknesses of t itanium a nd the backing

ste el wo uld e ac h be 1. 6m m, (1/16 inch). For new build,

the titanium sheet can be recessed on all sides to allow butt w elding of the ste el backer, follow ed by sea l w elding

of a titanium batten strip. Here, the thickness of the

titanium is 1.6mm , but the st eel backer ma y be hea vier

up to 25 .4mm (1 inch), or as req uired by the o perating

cond itions of t he vesse l or structure.

RESISTANCE WELDING

Resista-Clad TM plate. Methods of application

A sp ot w eld in ASTM gra de 2 she et

Resistance Welding

Advantages


• Lo w dis to rt io n

• Spot welds do not require gas shielding

Disadvantages

• Po o r fa t ig ue st re ng th

• Limited to sheet materia l

Typical pa tte rn of st eel

w a l l a t t a c h m e n t a n d

ove rla p o f Ti Res ista -Clad

plates for retofit linings.

Typica l Ti at ta chm ent a nd

Resista-Clad plate

contruction for new or tota l

duct /vesse l wa ll cons truction.



10

INTRODUCTIONThere a re app roxima te ly 20 variants o f friction we lding,

mos t of w hich could be a pplied to titanium and its a lloys.

In practice only a few of these are used industrially to

join titanium. An important feature of friction welding is

its ability to join titanium to other materials, which,

although often requiring an intermediate material, is

virtually impo ssible t o do by a ny proce ss involving fusion.

The a dvant ag es o f friction w elding include no need for

s h i e l d i n g g a s e s f o r m o s t p r o c e s s e s , v e r y r a p i d

comp letion rate s, and goo d me chanical properties. Most

we lds result in flas h forma tion, w hich typically must be

removed . The ma in process va riants are d escribed be low :

ROTARY FRICTION WELDINGThere are t wo ma in varia nts o f rot ary friction w elding;

the continuous drive and inertia processes. In the

continuous drive rotary friction welding process, a

com ponent in bar or tube form is rota ted under pressure

ag ainst a similar com pone nt, or one of larger dimensions,

FRICTION WELDING PROCESSES

Schemat ic diagrams of the tw o rota ry friction welding variants

Rot ary frict ion w eld in 13m m thick Ti-6Al-4V pipe

Prop erties of a rota ry frictio n w eld in Ti-6Al-4V

Tensile Strength Proof Stress Elongation

Region (MPa) (MPa) (%)

Base Metal 949 834 15

Weld Zone 994 854 11

Friction Welding - general comments

Advantages

• Ra p id o ne sho t pro c es se s• Fully a ut o ma t ed

• Can join dissimilar Ti alloys

• Potential to join Ti to some other materials

Disadvantages

• Exquipment may be expensive

• Inspect ion can be dif ficult

Rotary Friction Welding

Advantages

• Extensive industrial experience

• No shielding gas or f iller

Disadvantages

• Ro ta t iona l symmetry required

unde r an a pplied pressure. Frictiona l hea t de velops,causing the material close to the rubbing surfaces to

softe n and flow. After a certain displac eme nt distance

(called burn-off) has been reached, the rotation is

stopped rapidly, and the contact force increased to

provide a forging action to consolidate the joint. Any

interfacial conta mination is expelled w ith the flas h tha t

is extruded from t he joint.

Inertia friction welding has o ne com pone nt att ac hed

to a flywheel, and spun to a predetermined rotation

speed before being pushed aga inst the other component

unde r pressure. The bra king ac tion res ults in the

generation of frictional heating, and the formation of aweld. Inertia friction welding delivers energy at a

decreas ing ra te through the weld cyc le , whereas

continuous drive friction welding delivers energy at a

constant rate. Inertia welding is more commonly used

in the USA, and less so in Europe, where continuous

drive we lding is pred om inant.



11

RADIAL FRICTION WELDINGOne d rawba ck of rota ry friction we lding is the nec essity

to rota te o ne of the co mpo nents. With sma ll pa rts this

is not normally a problem, but for example with long

lengths of pipe there are obvious potential difficulties.

One solution t o this is t o use rad ial friction w elding, in

which the pipes a re held s ta tionary, a nd a V sect ion ring

of narrowe r angle than the ed ge prepa ration in the pipe

is rotated between them using a continuous drivemechanism, and simultaneously compressed radially to

force t he ring into t he joint. The e q uipme nt req uired fo r

this proce ss is more com plex than tha t req uired for rot ary

friction w elding, a s it req uires a radial com pression unit,

and also a n internal mand rel to resist the high radial loa ds.

One a dvanta ge o f the internal ma ndrel is that the internal

flash is eliminated, although there is generally a small

reduction of internal diameter which may need to be

removed.

Schemat ic d iagram of rad ial friction w elding process LINEAR FRICTION WELDINGThis proce ss variant wa s d esigned t o e liminate the

need for rota tional symmetry in one o r both of the p arts

being joined, a nd a s a result the process c an succe ssfully

join pa rts of d iffering se ctio n. As its nam e implies, linear

friction welding uses a reciprocating linear motion to

provide the friction. The freq uency is t ypically 25 to

100Hz, w ith an a mplitude of + /- 2mm.

The proc ess w ill be used extensively in the ae ro-

engine industry, in particular for joining compressor

blades to disks, but has not been taken up by other

industrial secto rs for joining a ny me ta l. Ho we ver, a close

variant of the process , v ibrat ion welding, is used

ex tens ive ly in severa l indus t r ies for jo in ing

thermoplastics.

Stolt Comex’s radial friction welding pipe laying barge

FRICTION STUD WELDINGFriction stud w elding eq uipment is porta ble and ca n be

used in-situ in remote and ad verse environments. Like other

friction w elding processes the a dd ed ad vantages of friction

stud we lding are its rapidity a t co mpleting the joint and itsability to join to dissimilar metals. Current applications

include s tud a tta chment t o a rchitectural tita nium pa nels.

Radial Friction Welding

Advantages

• No sh ie ld ing gas required

• Neither component is rota ted duringwelding

• No bo re fla sh

Disadvantages

• Expens ive equipment

• Internal bore support required

Linear Friction Welding

Advantages

• Shie ld ing gas no t required

• Very good posit ional accuracy

• Rotat ional symmetry not required

Disadvantages

• Exp ens ive e q uip m ent

Pro pe rties o f rad ial friction w eld in Ti-6Al-4V-0.1Ru

Tensile Proof Elongation

Region Strength Stress (%)

(MPa) (MPa)

Base Metal 910 840 14

Ring (as-received) 885 795 11

Ring (as-welded) 1055 925 9

Cross-weld 900 820 9



12

In this process, one component is moved against the

ot her in an o rbita l mo tion. This remo ves the req uirement

for symmetry in both of t he com ponents.

FRICTION STIR WELDING

This no vel proce ss ha s bee n w el l de ve lope d foraluminium al loys . Progress is being made for i ts

application to titanium alloys, although it will be some

time before it ca n be co nsidered a compe titive process.

A n u m b e r o f a d v a n t a g e s h a v e a l r e a d y b e e n

demonstrated for aluminium that may also apply to

tita nium. Friction stir we lding involves m oving a sm a ll

ro ta t ing too l be tween c lose but ted components .

Frictional heating ca uses the ma terial to so ften, a nd the

forwa rd mot ion of the t oo l forces ma terial from the front

of the to ol to the ba ck, w here it consolida tes to form a

solid sta te we ld. The p rocess com bines the flexibility o f

me chanised a rc welding with the excellent cha racte risticsof a friction we ld. P rogress has be en sw ift in developing

the tec hnology for titanium and development w elds ha ve

bee n co mp leted succ ess fully at TWI.

THIRD BODY FRICTION WELDINGThird bo dy friction w elding is a useful techniq ue for

joining dissimilar materials which cannot normally be

joined by co nventiona l friction w elding. In this proce ss,

one component is rotated and plunged into a hole in

the seco nd co mponent, into w hich a t hird mat erial has

ORBITAL FRICTION WELDING

Schematic diagrams of the above welding processes

Friction Stir Welding

Advantages

• No filler

• Lo w dist ort io n• Fully mechanised

• Increasing industrial usage for non-ferrous

alloys

Disadvantages

• Still under development for titanium

• G a s s hie ld re q uire d

been place d. This third m at erial can be a met al which

softens at a lower temperature than either of the twocom pone nts being joined, o r it ca n be a brazing alloy.

FRICTION TAPER PLUG WELDINGIn this proce ss a t ape red plug is rot at ed a nd plunged

into a pre-machined hole. It was developed for weld

repair of alloys that are d ifficult to fusion w eld or a re in

a ha za rdous environm ent. By placing overlap ping friction

taper plugs into the material, linear features (such as

crac ks) ca n a lso be rep aired. This is know n a s Friction

Tape r Stitc h we lding.



13

DIFFUSION BONDING

CONVENTIONAL DIFFUSION BONDINGTitanium is the ea siest o f all co mm on e ngineering

ma terials to join by diffusion bond ing, d ue to its a bility

to dissolve its own oxide at bonding temperatures.

Conventional diffusion bonding is a slow process, andrequires careful control of temperature, and joint face

alignme nt. The proce ss a lso need s to be unde rtaken in

a vacuum. Under ideal conditions a bond of very high

q uality ca n be m ad e w ith no flash fo rma tion. Ho wever,

the p rocess is slow, a nd req uires considerable precision,

ma king it unattrac tive for field use , a lthough it has been

widely used in the aerospace industry, in particular in

co njunction w ith superplast ic forming. The proc ess ,

including superplastic forming, is also used in the

successful development of t i tanium compact heat

exchangers.

Rolls Laval’s diffusion bo nded comp act heat exchanger

ELECTRON BEAM DIFFUSION BONDINGThis proc ess is a va ria nt o f diffusion bo nding in which

only the interface region is heated, resulting in a

co nside rable e nergy saving. The hea ting source is an

electron beam which is swept over the area of the joint

at such a speed that fusion of the titanium alloy is

prevented. A force is applied across the joint. As the

heated area is very limited, higher forces can be used

without the risk of plastic collapse of the components

being welded, resulting in a significant reduction of

we lding time, t ypically by a n orde r of m ag nitude . The

proces s ha s bee n investigat ed for joining several titanium

aluminide a lloys t o the mse lves and ot her tita nium alloys,

and for joining titanium a lloys. Very go od results ha ve

been reported from these trials, but to d ate the process

has not been used commercially.

Diffusion Bonding

Advantages

• Limited microstructural changes

• Can join dissimilar Ti alloys

• No fille r required

• Can fabricate very complex shapes ,

especially using superplastic forming

Disadvantages

• Slow

• H ig h va c uum re q uire d

• Expens ive equipment

Rolls Royce ’s SP FDB front fa n blad e fo r the Trent 800



14

FORGE WELDING PROCESSES

FLASH BUTT WELDINGFlash welding is a forge welding process in which

heat is generated by resistance when a large current is

pas sed across the surfaces t o be joined. During the initial

flashing stage points of contact resistance heat, meltand blow out of the joint as the faces are progressively

mo ved to gether at a predete rmined rate. When a critical

metal displacement has been reached the faces are

forged to gether rapidly to consolida te the weld.

The proces s has be en used for many yea rs for the

product ion o f aeroeng ine sta to r rings, a nd w ith suita ble

eq uipme nt is capa ble o f joining pipe and othe r extruded

sections of any configuration. Properties close to those

of the parent meta l are o btained from substantially de fect

free joints.

HOMOPOLAR WELDINGHom opo lar we lding is a new met hod c urrently under

development in the USA, where it has been developed

primarily for welding pipes. Kinetic energy stored in a

flywhe el is rapidly converted to a high d irect current low

voltage e lect rica l pulse using a hom op olar generat or, and

this high current pulse is pa ssed ac ross a closely butted

we ld joint, ca using a resistance we ld to be ma de . A high

axial load is also applied, causing softened material to

be expelled. Neither of the components has to be

rota ted , a nd no shielding ga s is required . Trials have be en

undertaken on titanium, apparently successfully, but

results ha ve yet to be published .

EXPLOSIVE BONDINGEx p l o s i v e b o n d i n g s h o u l d b e c o n s i d e r e d f o r

applications when a thin uniform lining of titanium is

req uired o n a ba se m eta l. The te chnique is regularly used

for the prod uction of high pressure tubeplate s for tube

and shell heat exchangers, reaction vessels, chlorine

generators, and for lined plant and ductwork subject to

nega tive pressure. In the proces s, thin tita nium shee t is

placed at a closely controlled distance on top of a backing

plate. Explosive spread uniformly o n to p o f the titaniumis detonated from a single point, the explosion driving

the titanium down across the air gap to impact on the

bac king m eta l. A jet o f surface o xide s is expresse d from

the a pex of the co llapse angle formed, and this removes

any residual contamination from the mating surfaces,

producing a meta llurgical bond o f wa ve-like form and

guarante ed shea r strength. The co ntinuity of the bond

can be confirmed ultrasonically. All low to medium

strength t itanium g rade s, (ASTM 1, 2, 7, 11, 12 , 16, 17,

26, 27), can be bonded typically down to 2mm (.08

inch) thick ont o a variety of ferrous o r non ferrous backing

plates , no minally 12.7m m (.5 inch) or thicker. Plate s ha vebeen produced up to 3.5 me tres (137 inch) diam eter or

15 sq . metres area (160 sq. ft.).

Cross-section of an explosively bonded steel to titanium joint.The e xplos ive b ond ing proces s

Flash Butt Welding

Advantages

• Very rap id weld t ime

• S ing le s ho t p ro c es s

Disadvantages

• Flash remova l required

• Inspect ion may be dif ficult



15

BRAZING

CONVENTIONAL BRAZINGTitanium a lloys ha ve bee n braze d s ucce ssfully using

silver, aluminium and ti tanium alloy braze metals.

Although there a re ma ny variants , o nly vacuum braz ing

has significant application for ti tanium due to the

requirement to protect the bas e me tal from oxida tion.

Ho we ver, de velopm ent w ork has bee n performed in the

use o f sliver chlo rid e-lithium fluo ride fluxes a nd TIG

brazing has proven succes sful in so me ap plica tions. Silver

alloy braze s we re the first to be a pplied t o titanium and

commercially pure silver, silver alloys with copper and

manganese, and silver–copper alloys with zinc and tin

have all shown some success. Although joints tend to

have good duct i l i ty , s trength is poor a t elevated

temperatures and corrosion resis tance is poor in

chloride-containing environments. However, the silver

alloy braze met als have liq uidus te mpe ratures below the

bet a trans us o f a lloys s uch a s Ti-6Al-4V, t hus t he braz ingcycle will have little or no effect on the base metal

microstructure and properties. The use of aluminium-

silicon fillers also ena bles low tem perat ure braz ing to be

performed, w ith the ad ded benefit of de creased w eight.

It is crucial, how ever, to ma inta in as short a braze c ycle

as poss ib le to min imise the format ion o f b r i t t l e

intermetallics.

Titanium a lloy bra zing a lloys are by fa r the mo st

common for joining t i tanium, the most avai lab le

commercial alloys being titanium-copper-nickel alloys.

These offer high strength a nd g oo d corrosion resistance,

but t he m os t rea d ily ava ila ble alloy (Ti-15Cu-15 Ni)

requires braz ing a t te mpe ratures over 1000°C (1830° F).

A Ti-20Cu-20Ni a lloy a nd a mo rpho us Ti-Zr-Cu-Ni braz e

f o i l h a v e b e e n d e v e l o p e d f o r b r a z i n g a t l o w e r

tempera tures (850 and 950°C , (1560 - 1740°F)

respect ively). These ha ve ad vanta ges fo r applica tion with

Ti-6Al-4V. For t he highes t t em pe rature joint a pplica tions ,

pa llad ium bas ed a lloys ha ve been used a lthough brazing

must a lso be performed at high tempe ratures.

The braz ing proc ess offe rs the ca pa bility o f dissimila r

metal joining, using a silver alloy braze metal. Dissimilarti tanium alloy and ti tanium to ferrous, nickel and

Brazing

Advantages• Complex geometry ’s can be joined

• Dissimilar metal joints are possible

Disadvantages

• Slow, unless batch processing is possible

• Mus t be performed in a vacuum

• Galvanic corrosion may limit application

r e f r a c t o r y m e t a l j o i n t s a r e p o s s i b l e . C o m p l e x

configurat ions can be joined, limited only by the neces sity

to ma inta in closely abutting joint face s.

Titanium braze d w ith a silver braze met al.

TRANSIENT LIQUID PHASE BONDINGThis proces s has been d escribed as a dif fusion

bonding proce ss, but trans ient liquid pha se (TLP) bond ing

has m ore in commo n with braz ing tha n diffusion bo nding.

An interlayer, or melting point suppressant, is placed

between the joint faces prior to heating in a vacuum.

The interlaye r mat erial is cho sen t o rea ct w ith the bas e

m e t a l , f o r m i n g a e u t e c t i c l i q u i d a t t h e j o i n i n g

tem perat ure. The rea ction prog resses until the liq uid

meta l reso l id i f ies i so thermal ly , l eav ing a jo in t

microst ructurally similar to the bas e m eta l. P ure nickel

and copper, and copper-nickel alloy interlayers haveshown good performance for joining titanium alloys. A

further benefit of t he proce ss o ver conventiona l braz ing

is the reduce d w eight of the st ructures, since only a very

thin interlayer is required. However, a signif icant

perpendicular loa d m ust be a pplied to the com ponents

to maintain good surface contact during the bonding

process.

SOLDERINGTitanium is extreme ly difficult to so lde r beca use o f

the same properties that confer its superb corrosion

resista nce - the tena city and sta bility o f its surface oxide.Conventional soldering methods depend on aggressive

fluxes to allow the so lde r alloy to w et the surfac e o f the

bas e me ta l. None of the conventiona l fluxes is effective

for titanium and so the surface is typically precoated

with a m ore com pa tible me ta l, such as c opp er, by PVD

or sputte r coat ing. It is a lso p oss ible to ‘tin’ the s urface

of the titanium by extended immersion in a molten tin

bath at 600°C (1110°F); the titanium oxide is adsorbed

by the base met al, allow ing the tin to we t a no n-oxidised

surface. Some success has also been reported in the

use o f mo lten silver or tin halide s, w hich reac t w ith the

oxide surface to produce a tin or silver coating; and in

the use of conventional fluxes whilst disrupting the

surfac e o xide with a n ultraso nic s oldering iron.



16

ADHESIVE BONDING

Adhes ive bo nding provide s a n a lternative to we lding,

particularly for joining sheet material and for joints

between titanium and non-metals such as polymer

co mpo sites. The use o f ad hesives is ofte n a viable

alternative or companion process (i.e. hybrid bonding)to res i s t ance spo t weld ing in jo in ts des igned to

experience predominantly shear stresses in service.

Fac to rs such as t he service e nvironment d om inat e the

selection of a dhes ive, but this subject is too co mplex to

discus s in det a il in this publica tion. The high streng th o f

modern structural adhesives is entirely appropriate to

the use of bonded titanium in structural applications,

although careful pre-treatment of the bond surfaces is

critical for achieving maximum properties. It is strongly

recommende d that t echnical consultation is sought for

ad vice o n all aspec ts o f the bond ing process.

Adhesively bo nded carbon fibre com posite/titanium w ishbone

of a Willia ms fo rmula one rac ing ca r.

MECHANICAL FASTENING

Mecha nica l joining proc esse s fo r titanium include all

t y p e s o f f a s t e n e r , m a n y o f w h i c h a r e r o u t i n e l y

manufactured in t i tanium and widely used in the

ae rospa ce industry. Non-titanium fa stene rs in ma terials

of low er corrosion resistance co mpa red to titanium ma y

be used w here no da nger of galvanic corros ion is present,

or where the fastening is totally isolated from the

corrosive e nvironment. In environment s w hich po se a risk

Adhesive Bonding

Advantages

• Rapid

• Titanium to polymer/compo site joints arepossible

Disadvantages

• Po o r p erfo rm a nc e in pe e l

• Application is limited for most corrosive

environment

of ga lvanic co rrosion, non titanium fast eners can be used

provide d they are insulat ed from the titanium using

suitable gaskets.

Other mechanical jointing methods such as lock

seaming (e.g. in automotive exhaust box manufacture)

and overlap joints, (used for architectural panels) are

limited to the mo re ductile grad es o f the me tal and its

alloys.

Selection of titanium bolts, fast eners and capt ive nuts

Close up of joint

Both lock seaming and welding are used in the manufacture

of titanium exhaust system s



17

JOIN ING TITANIUM TO OTHER

M ATERIALS

Titanium is incom pa tible w ith m ost othe r meta ls a nd

w ill form brittle co mpo unds if fusion we lde d directly to

them. Indeed the only commercial alloys that can be

directly fusion welded to titanium are those based onzirconium, niobium and certain other refractory alloys.

More common structural materials, such as all ferrous

a nd a luminium a lloys , a re invariably unsuitab le fo r direct

fusion welding to t i tanium. Several novel joining

techniques have been adopted for making dissimilar

joints, but the range o f possibilities is to o va st to ad dress

here in any detail . Many of the welding processes

discussed in the preceding sect ions c an be applied to

dissimilar material joints between titanium and other

metals. Indeed, explosively bonded titanium clad steel

and Res i s t a-C lad TM p l a te a re pr ime examples o f

successful dissimilar bonding technologies. Explosive

bonding has also been used to form transition joints

betw een t ita nium a nd ferrous alloys, for exam ple titanium

pipe to s ta inless stee l flange joints.

The fo llow ing tab le is intend ed to highlight ge neric

processes that may be capable of fabricating joints

betw een titanium a nd othe r ma terials. These will normally

require particular practices to be adopted to achieve a

sa tisfac to ry joint. The suitability of the va rious p roces ses

will depend on the components to be joined and the

properties req uired and it is strongly reco mm ende d tha t

technical consultation be sought prior to finalising a

com pone nt d esign incorpo rating dissimilar joints.

EB Laser Friction1 Adhesives Explosive Resistance Brazing

bonding welding

Steel

Stainless Steel

Nickel alloy

Refractory

metals

Copper

Aluminium

Cobalt alloy

Ceramics

Polymer composites

Joining processes t hat m ay be capa ble of forming sound joints betw een titanium a nd o ther materials.

Notes 1 Does not indicate that all friction processes are appropriate for a given dissimilar joint.

SELECTION OF A WELDING

PROCESS The fo regoing sect ions have p rovide d a br ief

summary of the characteristics of the various joining

processe s that ca n be used to we ld titanium structures.

Most fabrica tion is performed by TIG we lding and this

is unlikely to change, however it is crucial to the

production o f low cost titanium co mponents that higher

produc t iv i ty , more cos t e f f ec t ive processes beco nside red w here po ssible. For exam ple, PAW oft en

enables significant productivity gains for a low capital

investme nt, while achieving similar o r greate r q uality t o

tha t a chievable using TIG w elding. More ‘exot ic ’

processes such as power beam and friction welding

should also be considered, since even if no in-house

capability exists, work can often be subcontracted to

experienced fa brica tors.

CAUTION:GALVANIC CORROSIO N Titanium is highly co rros ion resista nt, a nd c an a cce lerate t he co rros ion of d issimilar

meta ls w hen coupled to a less noble meta l. In add ition to accelerated co rrosion, w hen such a ga lvanic couple exists,

hydroge n can be t aken up by the titanium, lead ing in som e circumst anc es to hydride c racking and failure. Alloys w hich

occupy a similar position in the galvanic series as titanium may be safely coupled to titanium in environments which

w ould not o rdinarily lead t o co rrosion o f the uncoupled ba se me ta l. For example duplex and supe r-auste nitic sta inless

steel, a nd Ni-Cr-Mo alloys ca n often be sa fely coupled to titanium. Ho wever, it is recommend ed that specific tec hnical

ad vice is so ught fo r any given ope rating environm ent a nd d issimilar joint. Further de ta ils o n simple me chanical co uplings

ca n be found in TIG Dat a Shee t No 6.

17



OPEN AIR WELDINGThe req uirement for ad ditiona l gas s hielding o f bot h

the back-face and cap regions during open-air welding

is the only significa nt fac to r w hich differentiate s titanium

from mo st s ta inless s tee l fabricat ions . There a re,

how ever, ma ny com mercial so lutions fo r the prote ction

o f t i t a n i u m w e l d m e n t s , m a k i n g b o t h l i n e a r a n d

circumferential welds quite straightforward. Greaterexperience is necess a ry for mo re difficult configurat ions,

but many commercial fabricators weld more or less

complex shapes on a regular basis.

Conventional back purging techniques, as used for

high quality stainless steel welding, are commonly

adopted for titanium. Straight runs employ a grooved

backing bar which is purged with a moderate gas flow.

For m ore c om plex configurat ions aluminium o r cop per

foil ca n be tape d to the underside fo rming the necess ary

channe l for the ga s purge. In this instance, ca re must be

taken to prevent the foil coming into contact with thehot titanium. Purging dams or bladders are used to

protec t the underside o f circumferential welds, o r difficult

to access regions. It is important that sufficient time is

allow ed during ba ck purging to reduce the air content in

the purged region to very low levels. No hard and fast

rule exists for purge time, since this d epend s largely on

the purged volume, its complexity and the flow rate of

Purging blad de rs (Hunt ingdo n Fusion Tec hniq ues )

argon. Use of an oxygen meter is advised in most

instances to ensure that oxygen content of the purgegas i s lower than approx imate ly 20ppm pr ior to

com menc ing we lding. The cos t of so lid stat e oxygen

meters capable of reading to these low levels has

dropped in recent years and the capital investment can

be quickly recouped by a reduced use of argon, rework

and scrapped comp onents. If possible w elding should

be performed with touching root faces , since a root ga p

makes purging of the underside significantly more

difficult. If a roo t ga p is unavoida ble the n, w here there is

acce ss to the underside, a root side ga s shield’ similar

to that used for protecting the weld cap (discussed

below), is the best solution. If access is limited, then

aluminium or coppe r foil can be t ap ed o ver the to p face

and remo ved ahea d o f the torch during the com pletion

of the root weld pass.

Protection of the weld cap is routinely achieved by

the use o f a t r a i l ing sh ie ld , however in cer ta in

circumsta nces, such as a TIG roo t pa ss in a dee p groove,

the use of a n appropriate gas lens on the welding torch

can a chieve sa tisfacto ry results. Whilst no hard a nd fa st

rule ca n be s ta ted , the ceram ic no zz le is suita ble fo r TIG

welding currents up to about 35 amps and the annularga s lens for currents up to abo ut 90 am ps. It is stressed

that this depend s on a favourable joint geo met ry, a llow ing

the torch shielding gas to flood the joint and provide

ga s protec tion aw ay from t he to rch. Welding at higher

currents or anything other than slow traverse speeds,

should be carried out with a trailing shield attached to

the t orch. The a rgon supply to t his shield is via a s epa rate

supply rat her than by d iverting a propo rtion o f the to rch

argon. The bod y of the shield ca n be ma de from copper

or aluminium if l ightness is important and should

incorporate a stainless steel woven mesh gauze for

diffusing the gas stream. The d esign of a successful

t r a i l i n g s h i e l d r e q u i r e s e x p e r i e n c e , b u t p r o v e n

commercial products are available for circumferential,

fillet and straight w elding. Their length and w idth de pend s

on the we lding process: MIG and auto ma tic TIG we lding

req uire long er tra iling shields tha n for m a nual TIG since

traverse speed s a re greate r. Hea t resistant glass ma y be

employed instead of metal for shields where better

visibility is req uired .

Trailing shields (Hunt ingd on Fusio n Tec hniq ues

Desp ite t he high rea ctivity of t ita nium, shielding ga sesare no t no rmally req uired fo r friction w elding. Ma terial

conta minated by exposure to a ir is pushed into the flash,

and can be remo ved. There wi ll be som e surface

discolorat ion c lose to the weld, but the depth of

cont am inat ion is very sm all. If the ap plica tion is critical,

it m ay be ad visable to remove this mat erial after w elding.

An exception to the lack of requirement for shielding

gases occurs when processes are used which develop

little or no fla sh. Friction stir we lding of t itanium req uires

a high q uality ga s shield.

19



The need for care a nd planning at t he ma terials

p r e p a r a t i o n s t a g e c a n n o t b e o v e r e m p h a s i s e d .

Frequent ly, w here problems ha ve been repo rted w ith

titanium fabrications, all or part of the cause can be

traced to t his sta ge. The correct preparat ion o f the we ld

joints is essential for arc welding, diffusion bonding,resistance welding and brazing, although friction welds

are typically more forgiving.

GEOMETRY OF WELD PREPARATIONS:For TIG we lding, a sq uare-cut ed ge ca n be used for

all butt or corner welds in thin gauge sheet and tube

where the thickness do es not exceed 1mm. Rough edge s

with burrs are difficult to set up and can result in high

levels o f we ld poro sity. Thicker shee t a nd t ube sho uld

be p rovide d with a V-prepa ration w ith the 90º included

angle V terminating in a 0. 6mm root fa ce. By t his me ans

it is possible to achieve consistent penetration duringt h e f i r s t w e l d r u n . Ex p e r i e n c e h a s s h o w n t h a t

co mm ercially pure titanium gives low er weld pene tration

tha n Ti-6Al-4V a lloy. Thus, a lthough t he d ifferenc e is no t

as extreme as is commonly found between different

cas ts o f sta inless steels, joint de signs sho uld be q ualified

for the titanium grad e to be w elded . For plat e w elding at

more than 6mm thickness, a simple open V can give

rise to unacceptable distortion due to thermal stresses.

In this case a machined J-preparation is used in which

the a ngle of t he sides is as steep a s pos sible co nsistent

with achieving complete side-wall fusion. As a guide,

the total included angle should be not greater than 65º

and not less tha n 45º. A do uble V-prepa ration is an

acceptable alternative to the J-preparation when there

is acce ss to bot h sides o f the weld.

Prepa rations tha t a re suita ble for TIG we lding are a lso

generally a ppropriate for MIG and plasm a when o perated

in the co nduct ion-limited mo de . Keyhole plasma we lding

requires only a simple square butt penetration for

thicknesse s up to ap proxima tely 18mm (.7”). Thicker

ma terial can be prepared as for TIG we lding, but w ith a

root fac e up to 15m m, and filled by PAW or TIG. Elect ron

bea m, laser and mo st friction we lds req uire simple butt

geometry.

CUTTINGA n y t h i c k n e s s o f t i t a n i u m c a n b e c u t w i t h

conventional flam e cutt ing eq uipment. How ever, it must

be remembered that contamination of the metal with

oxygen w ill result in harde ning o f the m eta l adjacent of

the cut edges. Thus a size to lerance of + 6mm, (.25”)

should be allowed for subsequent cleaning up. Plasma

arc cutting or the use of lasers are possible alternative

techniques to the oxyacet ylene proce ss. As-cut surface s

should not be w elded be fore the joint faces a re finished

using a machining technique capable of giving a non-cont am inate d goo d q uality surface. As-guillotined joint

20

faces sho uld not be w elded . Experience has shown t hat

this cutting tec hniq ue which produces a smea red ed ge

leads to excessive weld metal porosity.

MACHININGThe follow ing technique s a re suita ble for the prepa ration

of titanium joints:

(a) Turning, milling a nd planing: The surfac e ob ta ined by

conventional machining processes such a lathe-

turning, milling and planing are suitable for welding

w ith no ad ditional clea ning other than de greasing to

remove cutt ing lubrica nts. Ca re is need ed to ensure

that the me tal is not overhea ted during the m achining

operation and that other (non machined) surfaces

to be w elded are not oxidised.

(b) Grinding: This techn ique is w idely used for prepa ring

the ed ges o f med ium and thick ma terial for we lding.The aim should be to prod uce the smo othest, most

regular profile po ssible with the s crat ch lines running

along the line of the weld and never across it. If

overheat ing o f the ma terial occ urs it w ill be evide nt

from discoloration. Whenever practicable, grinding

should be followed by draw fil ing, or any other

technique which improves the smoothness and

profile of the weld and ensures that any grinding

particles are removed.

(c) Linishing: Belt or disc finishers are suitable for edge

preparation o f med ium gauge compo nents. A 100

grit grade o f paper can be used for most purposes.

Linishing is a relat ively slow ope ration w hich p roduces

fine d ust a nd is expensive on consuma bles. How ever,

it is very flexible and can give excellent results.

(d) Draw filing: Preparations made by grinding can be

improved by draw filing. A fine toothed flat file is

drawn repea tedly a long the meta l sur f ace , an

op erat ion w hich remo ves minor irregularities. Filing

requires skill and the use of a clean file or it can

worsen rather than improve the surface

(e) Scratch brushing: Surfaces can be scratch brushed

to remove a ny residua l conta mination. With st ainless

ste el brushes th ere is a slight risk of iron pick up a nd

t i t a n i u m b r u s h e s s h o u l d b e u s e d f o r c r i t i c a lapplications.

It is usual to ma chine the abut ting surfac e o f a friction

weld before w elding. It is not necessary to have great

accuracy in the finish, although a good square set up is

usually needed. Since there is always a loss of length

due to burn-off into the flash, there is little point in

ma chining o verall lengths t o a ny precision. This should

be done after welding, when the flash must also be

removed . Much grea ter precision is required for diffusion

bonding and, to a lesser extent, brazing since good fit-

up of the joint faces is essential to the success of thesejoining me thod s.

PREPARATION OF THE JOINT FOR WELDING



Mac hined joint face s a nd m at erial likely to be fused

(i.e. nearby ma terial on the joint underside and top face),

should be cleaned and degreased prior to welding to

remove a ny cutting fluids or grease .

PICKLINGAcid p ickling ca n be used to remove oxygen

contaminated metal from the surface of titanium. It is

also useful for removing any surface iron conta mination

tha t m ay be prese nt from ma chining. Pickling so lutions

are typically aqueous solutions of hydrofluoric (48%

co nce ntrat ion) a nd nitric ac id (70%conc ent ration). The

acid ratio s hould always be maintained betw een 1:5 a nd

1:9 (5%HF/35%HNO3 has bee n found to be an effective

solut ion) . P ickl ing should be carr ied out a t room

tem perature, for 1-5 minutes d epe nding on the act ivity

of the bath. If the surface of the metal is dirty or oily,

de greasing or aq uablasting must preced e pickling or theac id dissolution w ill be non-uniform prod ucing a pitted

effect.

PREWELD CLEANINGThe surface o f the w eld preparat ion a nd a djoining

met al is critical to the q uality of t he joint and should be

scrupulously clea n prior to w elding. The surfa ce s ho uld

be inspected to see whether a f inal hand f inishing

operat ion is necessary , e .g . to smooth out rough

ma chining ma rks a nd rem ove s livers of m eta l. The

smoothness of abutting edges is particularly important

for reduced porosity in arc welds and diffusion bonds.Vapo ur and liq uid deg reasing metho ds are a pplica ble fo r

titanium alloys.

(a) Vap our: Imm ersion ta nks ba sed on trichlorethylene

vapour a re e f fec t ive in removing grease , o i l ,

fingermarks and general dirt from the surface of

titanium co mponents. It should be ensured that the

tanks are not located too near to the welding area

nor that components are transferred immediately

from the tank to the welding booth because of the

risk of pho sge ne fo rma tion. Trichlorethylene sho uldregularly be checked for HCl acidity.

(b) Liquid: Small components can be degreased by

immersion in, for example, acetone or isopropyl

alcoho l. Larger item s ca n be cleaned by wiping w ith

lint free cloths o r tissues so aked in the so lvent. Under

no circumstances should m ethanol be employed a s

a de greasing agent.

Once com ponents have been degreased, t he surfaces

must be handled only with clean gloves and preferably

not a t a ll: ba re hands, even ostensibly clean ones, depo sit

a surprising amount of grease and salt.

CLAMPING AND FIXTURESClamps and f ixtures for arc welding should be

designed to minimise distortion and, where necessary,

incorporate the purging system required to protect the

underside of the w eldme nt.

For co nventiona l rota ry friction w elds, the rota ting

part is norma lly held in a t hree jaw chuck, a lthough special

too ling ma y be req uired fo r the non-rotat ing pa rt if it is

not axially symme trical. For linear frict ion we lding, spe cial

tooling specific to the component is always required.

The to oling for the reciproca ting comp onent must be

de signed w ith ca re in order to m inimise the w eight and

hence inertia of the system, which will have to change

direction typically 100 times every seco nd.

ARC WELDING TECHN IQUE

POWER SOURCES AND TORCHESTitanium and its a lloys c an be we lded with mo st

conventiona l we lding pow er sources and torches. For

TIG welding a po we r source eq uipped with a non-cont ac t

arc strike facili ty is essential to prevent tungsten

conta mination of the w eld, which occurs if a touch do wn

technique is employed . The po we r source must also be

capable of breaking the arc on completion of a weld

run, without stopping the inert gas flow, or weld metal

conta mination by air may o ccur at the w eld st op p osition.

TUNGSTEN ELECTRODEThe choice o f electrod e c ompo sition a nd d iam eter

is no different t han fo r TIG w elding sta inless stee ls a nd

is influence d by t he req uirement s fo r elect rode long evity,

ease of arc initiation and stability. A simple 60º conegives sa tisfacto ry results for mo st ma nual TIG w elding.

With angles less t han 4 0º the re is a g reate r risk of

tungsten loss while above 80º arc initiation is difficult

and the arc has a t endency to w ande r. Should the

electrode touch the weld bo th must be ca refully examined

before restarting. Any tungsten in the weld, no matter

how sma ll must be excavated.

SELECTION OF WELDING PARAM ETERSTIG, PAW and MIG w elds c an be ma de using a va riet y

of current/spee d com binat ions, the d ifferences being the

result of operator preference. However, i t is worth

remembering that the aim should be to a chieve a go od

bead shape with minimum heat input. In that way,

disto rtion a nd a rgon shielding problems w ill be minimised.

TIG and plasma we lding are best ac hieved with direct

current electrode nega tive (DCEN) polarity and , fo r MIG

welding , pu lsed opera t ion i s genera l ly pre fer red .

Suggested welding parameters are given in the table,

although these should be used as a guideline only.

21



SHIELDING GASESFor most purpose s, the co mme rcial grad e of argon

ma y be used for welding tita nium, a lthough prod uctivity

can be enhanced through the use of argon-helium

mixtures or pure he lium. The use of he lium-co nta ining

gases has particular advantages for MIG welding since

spatter can be reduced considerably. Commercially

available cylinders of welding grade argon and helium

are o f sufficient purity for a ll welding o perat ions, how ever

ca re should be ta ken to ensure that non-permea ble hose s

are used for all attachme nts to ensure tha t m oisture is

not incorporat ed into the shielding gas . If cylinders a re

used it is inevita ble t hat they w ill conta in a sma ll amo unt

of m oisture. This level is extreme ly low w hen the ga s

cylind er is full, but as t he pres sure in the c ylinde r drops ,

so t he mo isture co ntent rises . There is some justifica tion

for using gas from a cylinder for welding titanium only

until the pressure has fa llen to ~ 25ba r, a fter which it

should be used to supply gas for w elding less s ensitive

met als. Bulk supplies o f argon ha ve much low er moisture

contents. Where an on-site gas tank is used to supply

several welding stations gas purifiers, moisture and

oxygen met ers can be co nnected to the ma in feed line

to provide overall q uality a ssurance.

Inad eq uate shielding of the w eld cap can o ccur when

argon flow from the to rch is either too low so tha t all the

air is not d isplaced , or too high so tha t turbulence o ccurs.

Some experimentation on off-cuts of material may be

needed to estab l ish the most sui tab le condi t ions .

Keeping a record o f values used on p revious w ork

eventually helps to reduce the time spe nt in setting up.

It is ad vised that a gas lens be used to m aintain a lamellar

ga s flow. This a pplies e q ually to the ga s flow rate fo r

trailing shields, although the minimum flow rate willdepend on the size of the shield.

22

Dia meter Flow

in. mm in. mm cfh l/min ipm mm/s ipm mm/s

0.008 0.20 Melt-in 0.030 0.76 0.5 2.3 Ar 5 - 5 2.1 - -

0.015 0.38 Melt-in 0.030 0.76 0.5 2.3 Ar 6 - 5 2.1 - -

0.125 3.18 Keyho le 0.136 3.45 9 42 Ar 150 24 15 6.3 40 16.90.188 4.78 Keyho le 0.136 3.45 10-12 47-57 Ar 175 30 15 6.3 42 17.8

0.250 6.35 Keyho le 0.136 3.45 16 76 Ar 160 30 12 5.1 45 19

0.313 7.95 Keyho le 0.136 3.45 15 71 Ar 172 30 12 5.1 48 20.3

0.390 9.92 Keyhole 0.136 3.45 32 151 He+ 25Ar 225 38 10 4.2 - -

0.500 12.7 Keyhole 0.136 3.45 27 127 He+ 50Ar 270 36 10 4.2 - -

Notes: * Direct current electrode negative** 0.062inch (1.6mm) diameter wire

Suggest ed Welding pa rame ters fo r PAW w elding titanium

ThicknessWelding

techniq ue Nozzle OrificeOrifice and

shielding gas

Welding

current, A*

Arc

vo lt a ge , V Tra ve l s pe ed Fille r w ire fe ed **

Suggested w elding param eters for automa tic TIG and MIG welding titanium (1/16” = 1.6mm)

TIG (GTA) w ithout filler TIG (GTA) w ith filler MIG (GMA)

Ga uge, in 0.030 0.060 0.090 0.060 0.090 0.125 0.125 0.250 0.500 0.625

Electrode diam ete r, in 1/16

1/16

1/16

-3/32

1/16

1/16

-3/32

3/32

-1/8

1/16

1/16

1/16

1/16

Filler w ire d ia meter, in - - - 1/16

1/16

1/16

- - - -Wire feed ra te, ipm - - - 22 22 20 200-225 300-320 375-400 400-425

Voltage, V 10 10 12 10 12 12 20 30 40 45

Amps, A 25-30 90-100 190-200 120-130 200-210 220-230 250-260 300-320 340-360 350-370

No zzle ID, in ¾ ¾ ¾ ¾ ¾ ¾ ¾ -1 ¾ -1 ¾ -1 ¾ -1

To rch shield , cfh 15Ar 15Ar 20Ar 15Ar 20Ar 20Ar 50Ar+ 50Ar+ 50Ar+ 50Ar+15He 15He 15He 15He

Tra iling shield , cfh 20Ar 30Ar 50Ar 40Ar 50Ar 50Ar 50Ar 50Ar 60Ar 60Ar

Ba cking ga s, cfh 4Ar 4Ar 5Ar 5Ar 6Ar 6Ar 30Ar 50Ar 60Ar 60Ar

Tra vel speed, ipm 10 10 10 12 12 10 15 15 15 15Pow er supply DCEN DCEN DCEN DCEN DCEN DCEN DCEP DCEP DCEP DCEP



Bac king ga s flow rates d epend largely on the volume

being filled. Flow rates for backing bars will normally be

lowe r than tho se fo r the to rch. Simila rly, ba cking ga s flow

rates for a d amm ed pipe a re limited by the ma gnitude

of the pos itive p ressure m aintained inside the pipe. The

pressure must not be too great or the weld root ma y be

‘pushe d’ in, giving a conc ave p rofile. Sufficient t ime must

be allowed for the argon to sweep all air out of thebac king volume, and this will vary a cco rding to the exac t

volume a nd flow ra te s used . Typically, a g reat er flow rate

is used whe n purging a da mm ed a rea. Where a bac king

bar is used , localised oxida tion can result from either an

inadequate purge time or excessive argon flow rate. A

similar effect can be caused by a badly fitting jig or by

impure a rgon.

Strong a ir currents ca n reduce t he efficiency o f even

we ll de signed argon shields a nd sho uld thus be a voided .

Screens ma y be used indoo rs to minimise the effect of

draughts while for on-site work, a polythene sheet tent

or other draught proof enclosure may be necessary.

SELECTION OF FILLER WIREFiller wires are p roduced for a wide range o f titanium

a lloys , a nd tho se for gra de s 2 (CP) and 5 (Ti-6Al-4V) are

read ily available t o AWS spe cifica tions in st raight lengths

and spo ols. The expedient o f cutting strips from s heet

to provide filler ma terial is one w hich may pro ve far from

sa tisfacto ry. Wire for welding is ma de to a s pecifica tion

which includes com position, dimensions, surface q uality

a nd c lea nlines s. Edge s littings are unlikely to c onfo rm in

all these a spects a nd their use without great care ma y

prove troublesome.

Unde r normal circumsta nces, the gra de of filler wire

will be identical with tha t o f the pa rent ma terial. Thus,

when two grade 2 components are to be welded, a grade

2 filler wire should be used. Where some atmospheric

contaminat ion can be ant ic ipated, for example on

positional welds in pipework, or where specifications

impose low hardness differences between weld bead

and pa rent meta l, a s ofter grad e of w ire such as grade 1can be e mployed. How ever, on no acco unt should the

use of a softer filler be used as a substitute for good

shielding pract ice. Welds bet we en d ifferent grade s o f

com mercially pure titanium ca n be ma de using filler of

either comp os ition. The cho ice will depe nd o n w hich is

the most important property of the weld, strength or

ductility.

For we lds in Ti-6A1-4V, TIG w eld ing w ith a ma tc hing

filler met al ca n lea d t o a reduction in ductility in the w eld-

because of metallurgical changes within the structure.

This ca n be o vercome to som e extent by the use o f Ti-

6Al-4V ELI, extra low interstitial grade wire. Joints

betw een low and higher alloy titanium g rade s (e.g. Ti-

6Al-4V to CP) sho uld be conside red c arefully, pa rticula rly

w h e r e p o s t w e l d h e a t t r e a t m e n t i s e m p l o y e d , a s

hydrogen embrittlement can be more likely.

When t he a rc is extinguished the tip of t he filler w ire

should remain, with the weld, in the argon stream from

the t orch until bot h a re sufficiently co ol not to oxidise. If

f i l ler wire does accidentally become oxidised, the

contam inated end m ust be removed before w elding is

recommenced.

23

Titanium we lding electrod e co mpo sitionsAWS WireCla ssifica tio n ASTM G ra de Co mpo sitio n, w t. %

C O H N Al V Fe Other TiERTi-1* 1 0.03 0.10 0.008 0.012 - - 0.10 - Rem.ERTi-2 1 0.05 0.10 0.008 0.020 - - 0.20 - RemERTi-3 2 0.05 0.10-0.15 0.008 0.020 - - 0.20 - RemERTi-4 2,3,4 0.05 0.15-0.25 0.008 0.020 - - 0.30 - RemERTi-0.2Pd 7,16,17,11 0.05 0.15 0.008 0.020 - - 0.20 Pd 0.12-0.25 RemERTi-3Al-2.5V 9 0.05 0.12 0.008 0.020 2.5-3.5 2.0-3.0 0.25 - RemERTi-3Al-2.5V-ELI* 9 0.04 0.10 0.005 0.012 2.5-3.5 2.0-3.0 0.15 - RemERTi-6Al-4V 5 0.05 0.15 0.008 0.020 5.5-6.75 3.5-4.5 0.25 - RemERTi-6 Al-4V-ELI* 5,23 0.04 0.10 0.005 0.012 5.5-6.75 3.5-4.5 0.15 - RemERTi-12 12 0.03 0.25 0.008 0.020 - - 0.30 Mo 0.2-0.4

Ni 0.6-0.9 RemNotes: * This clas sifica tion of filler met al restricts t he allowa ble interstitial content to a low level so tha t the high toughne ss req uired fo r cryo -genic applications a nd other special uses ca n be obta ined in the deposited w eld metal.



TACK WELDINGTac k w elds a re used to fix parts into t he co rrect

relative position before welding. Since the tack is

eventually incorporat ed into the w eld, it must be shielde d

to t he sa me high sta nda rd as t he w eld itself. Tac ks ma y

be used in conjunction with a root gap i.e. where the

edges of the weld are deliberately set slightly apart to

as sist in achieving uniform penet ration. A tapering roo tgap, wider at the finish end, can be set to counteract

the scissor effect ca used by w eld co ntraction.

MULTIPASS WELDINGThe initial pa ss o f a m ultipa ss w eld w ill genera lly be

autogenous with only minor filler additions to correct

for small variations. It is advisable to X-ray the weld at

this stage if work is being carried out to radiographic

stand ards since porosity and lack of fusion d efects a re

more often associated with this first pass than with

subsequent runs.

Bright silvery coloured welds which have been

correctly shielded do not require any attention before

laying subsequent pa sses onto them.

Heat build up from previous weld runs can lead to

surface co ntamination on subsequent pa sses. In extreme

cases, the only solution may be to leave the work to

cool before further welding is carried out. Another

ap proac h is to m ake any long w elds in shorter sections.

In addition to helping with cooling, sequence welding

can also be effective in reducing distortion. Interpass

tempe ratures up to 500oC, depe nding on circumstances ,

ca n be us ed for co mm ercial purity t itanium a nd Ti-6Al-

4V. This ensures tha t he a t build up o f the w ork piec e

does not reduce the effectiveness of the shielding

arrangements, which are typically based on single pass

welds.

RESISTANCE WELDING TECHNIQUE

24

Equipment and technique are very similar to those

required for austenitic stainless steels. As with fusion

welding techniques, the quality of the joints depends

largely on the cleanliness of the joint surfaces, which

should be free of grease oil and other contaminants.

Similarly, an oxidised surface, even one which is only

lightly discoloured, should be ground o r scratch brushedwith a titanium o r stainless stee l brush, prior to we lding.

Pickling achieves the lowest contact resistance, but

mechanical cleaning methods are more than adequate

for the production of sound joints. Gas shielding is not

typically necessary, since contamination is minor as a

resul t of the very rapid thermal cycle . However ,

met allographic and m echa nical testing should a lwa ys be

used to determine if shielding is required for a given

com bination of pa ramete rs, materials, req uirements and

machine.

The face of resistance w elding electrode s should havea domed profile, rather than the truncated cone profile

favoured for som e ot her mate rials, to prevent excessive

indentation of the titanium.

Guideline spot welding parameters are given in the

Ta ble fo r Ti-6Al-4V, a lthough t he re q uired pa ram et ers for

a given job d epends o n ma ny factors and the values in

the table should only be regarded as a starting point

when esta blishing proced ures. For sea m we lding, an

ap preciably grea ter welding loa d sho uld be a pplied t han

is necessary for spot welding (3 times the spot welding

loa d is typically a goo d sta rting po int for w elding trials).

Current and on/off cycle ratios sho uld be d ete rmined by

trial and error. Ca re must be ta ken w hen evaluating the

welds to ensure that goo d o verlap is achieved betw een

succes sive w eld nugget s. Weld pene tration is norma lly

high but t he grain coa rsened H AZ can ea sily be m ista ken

for the nugget z one.

Paramete rs for spot welding (1 inch = 25.4mm; 1lb = 0.454 kg)

Sheet thickness (inches) 0.035 0.062 0.070 0.093

Jo int overla p (inches) ½ 5/8

5/8

¾

Sq ueeze time (ms) 60 60 60 60Weld time, cycles 7 10 12 16

Hold time (ms) 60 60 60 60

Electrode force (lbs) 600 1500 1700 2400

Weld current (A) 5500 10600 11500 12500

Cross tensile strength (lbs) 600 1000 1850 2100

Tensile shea r strength (lbs) 1720 5000 6350 8400

Ra tio C-T/T-S 0.35 0.20 0.29 0.25

Weld d ia meter (inches) 0.255 0.359 0.391 0.431

Nugget d iameter (inches) - 0.331 - -

Weld penetra tion (%) - 87.3 - -

Electrode indenta tion (%) - 3.1 - -

Sheet separa tion (inches) 0.0047 0.0087 0.0079 0.0091Notes : Electrode type : 3“ (75mm) spherical radius, 5/8” (15.9mm ) dia, class 2 cop per

Guide line pa ramet ers fo r spo t w elding Ti-6Al-4V.



LIKELY DEFECTSTitan ium, like a ll me ta ls, is sus ce pt ible to ce rta in

we lding defects . How ever, the range o f possible defec tsis m uch less extensive t han, sa y, fo r ferrous fabrica tions.Solidificat ion crac king, a c om mo n de fect in stainless s tee l

and a luminium we ldments , is not fo und in Ti-6Al-4V. orCP. Likew ise, liq uat ion and rehea t cra cking a re notencountered in titanium fabricat ions. Contam ination d ueto inadeq uate ga s shielding is one o f the more comm ondefects responsible for rework or scrap and applies toall welding processes with the exception of frictionw elding. Tiny po res, irreleva nt to ma ny app lications , ca nbe formed in titanium weld metal but careful surfacepreparat ion w ill substantially reduce their presenc e.

Most of the defects commonly encountered intitanium TIG weldme nts ca n be traced to a de viat ionfrom ideal welding parameters. Molten titanium metalis fluid and its combination of low density and high

surface te nsion ena bles go od control of the weld surfaceprofile a nd pe net ration. Thus, tita nium is mo re forgivingin this respe ct tha n many othe r met als, but defects suchas lack of fusion, incomplete penetration and underfillare still possible. Porosity can also be encountered intitanium weld metal, typically at the fusion boundary.Pores a re spherica l and be tw een 50 -300µm in diame ter.MIG welds are susceptible to similar defects, but arealso prone to spa tte r. For critica l applica tions, it isimportant that the parent material be protected usingm e t a l f o i l o r h e a t r e s i s t a n t f a b r i c . Hy d r o g e nconta mination in the we ld o r pa rent mate rial can lea d tohydride cracking (typically in positions of maximumresidual stress), but this is typically encountered only

when Ar-H shielding ga ses, used com mo nly for sta inlesssteels, are used for titanium fabrication.

Plasm a a rc welds a re susceptible to the sam e rangeof defe cts a s TIG welds. Incomplete penet ration whenope rated in the keyhole mod e typically results in grosstunnel porosity. Autoge nous keyhole plasm a we lds inthick ma teria l typica lly exhibit a m inor amo unt o f unde rfill,but this can be read ily ad dresse d by a pplying a PAW orTIG final pa ss. One of t he m ajor benefits of keyholeplasm a welds is their seeming immunity to weld m eta lporos ity. Elect ron bea m a nd lase r welds a re suscept ibleto poros ity, voids, und erfill, incomplete penet ration andmissed seams. Again, the likelihood of these defects is

no grea ter than fo r most o ther meta ls. A lac k of bo ndingis the m ost co mmo n defect in diffusion bond s, brazedjoints, ad hesive bonds and resistance w elds.

The mo st likely defec t in a friction w eld, a nd t he mo stdifficult to detect non-destructively, is the so called“ kissing bond” , which is a region where intimate co ntac tis made between the two parts of the weld, but whereeither the joint is w ea k or no m eta llurgical bond exists.If insufficient flas h is ge nera te d d uring w elding, the jointcan be seriously embrittled, but this can typically beas sess ed visually. Po rosity is no t e ncountered in friction

welds.

25

RADIOGRAPHY.Rad iograp hy is one o f the mo re useful we ld inspection

techniq ues for titanium a nd its a pplication d oes not d iffersubstantially from the radiography of o ther meta ls, e itherin execution o r interpretat ion. Allow ance must be m ad e

for the low er abso rption o f X-rays than is found withiron or copper. One minor difficulty is that a titaniumimage qual i ty indicator ( IQI) is not avai lab le : thealuminium IQI is probably the best choice rather thaniron or copper.

Radiography will reveal:-• tungsten inclusions as sha rp white spots• porosity which shows up a s da rk spots that usually appearcircular• lack of root o r sidew all fusion indicat ed a s a da rk line orarea, often w ith asso ciated porosity• cracking, which is evident a s a da rk line, so metimes a ngular

and sha rp

DESTRUCTIVE TESTSThe principles used in approva l a nd q ualification

test ing of ot her meta ls ap ply eq ually to titanium but someprovision is necessary for assessing contamination.Colour should certainly be noted, but is an inadequateindicat or on its ow n. Transverse t ens ile te sts no rma llywill not show contamination, since the weld is usuallystronger than the p arent me tal . For plat es tha t a resufficiently thick, results of side bend tests will give aguide. For thinner plate or shee t, the long itudinal bendtest is preferable to the transverse, since this gives adirect co mparison w ith base m eta l performance. So me

care is needed, because the weld zone will usually beless ductile even in the absence of contamination,particularly with some alloys. Comparison should bemad e betw een the we ld and HAZ (rather than p arent),so as to account for hardening that occurs during thew eld the rmal cycle. Finally, the oxygen a nd nitroge nconte nt of the welds ma y be analysed to provide a directmea sure of a ny contamination.

Typical bend radii for a s-we lde d titanium

ASTMGrades

1, (11, 17, 27)

2, (16, 7 26)

3, 4

5, (24)

23, (29)

12

-

Alloy type

CP (+ Pd/Ru)

CP (+ Pd/Ru)

CP

Ti-6A1-4V (+ Pd)

Ti-6A1-4V ELI (+ Ru)

Ti-0.7Ni-0.3Mo

Ti-6A1-6V-6Sn

Minimum

bend radius

2t

3t

4t

10-12t

8-10t

5t

16-18t

EVALUATION OF WELD QUALITY



ALTERNATIVES TO THE COLOUR CRITERIAHardness te sting and edd y current inspection ca n be

used to provide supporting evidence for contamination

i n c o m m e r c i a l l y p u r e g r a d e s o f t i t a n i u m , s i n c e

contaminated welds will exhibit greater hardness and

resistivity. Porta ble ha rdness te sting proced ures t hat can

be a pplied in-situ are c urrent ly being d evelope d a t TWIfor grade 2 a nd 5 titanium. The succe ssful app lica tion of

these techniques will allow rejects to be minimised a nd

the highest quality to be achieved.

Cont am ination of TIG electrode s from a ir entrainment (from

left to right 0%, 0 .5%, 1%, 1. 5%a ir in the Ar to rch s hielding ga s)

.

DYE PENETRANT INSPECTIONUnder normal circumstances, weld cracking is very

rare with tita nium. Ho we ver, problems c an so met imes

arise where several weld seams intersect or where

contam ination has occurred. In these ca ses, the d efects

can be detected by dye penetrant inspect ion, the

technique also being suitable for locating porosity in

partly mac hined w elds. It should be no ted , how ever, thatthe d ye penetrant m ust be completely removed prior to

at tem pting weld repa ir.

NOTES FOR FRICTION WELDSFriction w elded com pone nts a re by d efinition very

difficult to inspec t. As the process is o nly eco nom ic for

mass produced items, individual inspection of each

component can seldom be justified. Experience has

shown that, as the process is fully mechanised, and

therefore repeatable, reliance on statistical processcontrol is normally satisfactory. In this approach, the

tolerance of the process to key w elding pa rameters is

first determined, and much tighter tolerances are then

imposed on the production process. Providing the

process is kept within these tolerance levels, the

probability of getting a poor weld should be very small

indeed . If a pa rameter is recorded to be just outside the

tolerance range, t he we ld sho uld st ill be ac cept able, but

this issues a wa rning tha t so me intervention is required

to return the pa rameter to its intended set ting, and to

investigate the cause fo r the change.

27

TIG welds in comm ercially pure titanium shee t ma de w ith successively great er air cont am ination of the shielding ga s.



REPAIR OF DEFECTS

LOCALISED MINOR REPAIRSDefects in titanium welds such as isolated tungsten

inclusions a nd poro sity are q uite ea sy to repair. The

affected area is removed by drilling or grinding and

cleaned prior to filling the hole or depression with theappropriate filler material, taking care that any metal

added is properly fused into the existing weld metal.

SEAM REPLACEMENTWhere a line of pores is found by radiography, the

weld ca n be re-melted up to a maximum o f, say, 3 times

subject t o a satisfactory contam ination check after each

sta ge . This re-m elt w ill req uire a higher current tha n tha t

used o n the o riginal we ld but ca n pote ntially remove a ll

or most of the porosity. Should this fail, however, or if

the defect is of a more serious nature, the entire weld

bead must be removed by machining or grinding and

then rewe lde d. These t ypes o f ma jor we ld repa irs are

usually slow and cos tly and conside ration should be g iven

to p atching or even complete replacem ent of the items.

REPAIR OF LARGE AREASAny substant ial area s ca n be repaired by cutting out

and replacing with new material or by welding a patch

over the e ntire a rea. G enera lly, replacem ent is preferable

to patching except for the repair of thick sheet with

access to only one side, a nd for the repair of titanium/

stee l explosively clad p lat e. Electron be am we lding has

proven particularly successful for replacement repair

welding, allow ing sections to be w elded into co mponents

w ith minima l dist ortion a nd high ac curac y. For exam ple,

fla p t racks fo r the Torna do fighter/bo mbe r aircraft ha ve

been repa ired using this technique.

TIG w eld repair and H VOF surfac ing wa s used to repa ir slat

tra cks on t he Trist ar a ircraft

REPAIR OF DETAILSDetails on components that are damaged either in

service or during fabrication are routinely repaired by

the build up o f we ld be ad s using, for exam ple, TIG

we lding. Fine d eta ils c an be repa ired using microplas ma

we lding, allow ing the precise pos itioning o f sma ll weld

beads prior to machining to the required geometry.

FURTHER NOTES ON POROSITY Weld me ta l po rosity occurs com mo nly in mo st

materials, including for example nickel alloys and

sta inless ste el. Tita nium fusion w eldment s ca n also

exhibit pores, but under most circumstances they do

not have a ny pa rticular d etriment al effects. For examp le,

pores a re typica lly isolate d a nd less than 0.3m m (.012”)

diameter, and have no discernible consequence for

tens ile prop erties or to ughnes s. Similarly, if the w eld ca p

and root profile a re left intact (i.e. not ground flush w ith

the p arent m eta l), fatigue life is typically de termined by

the severity of the stress concentration a t the w eld to e

and will not be influenced by the presenc e o r otherwise

of small pores.

For so me ap plica tions, ho w ever, a ll geom etry-specific

stress-raisers, such a s w eld t oes, are removed in order

to m aximise the fat igue performance o f the joints. Under

these circumstances fatigue strength can be lowered

significantly by the presence of weld metal pores,

espe cially tho se ne ar the surfac e. This is true of m ost

ma terials, but the de grad at ion in fatigue life is typically

greate r for titanium, than, sa y, s tee l. Und uly restrictive

maximum specified pore sizes in welding codes maynot ha ve any profound effect on fa tigue performa nce.

Indeed, the removal of such defects and subsequent

weld repa i r may be more de t r imenta l to f a t igue

performance than the original defect. It is stressed,

however, that if the weld cap and root are left intact,

then weld metal porosity becomes irrelevant, and

allow able stresses ca n be calculat ed s olely on the bas is

of the severity of the profile of the weld toe.

Porosity in titanium fusion welds can be formed for

a va riety o f rea sons , but the m ost profound influence is

the condition of the joint surfaces. In principle, final

machining of the joint surfaces wi thout aqueous

lubrica nts a nd w elding in the sa me 24h period is advised,

although a cid pickling ma y be used successfully o n ‘o ld’

joint surfaces, provided welding is performed shortly

a fter the p ickling treat me nt. The joint surfac es sh ould

always be ca refully d egreased.

The prese nce o f a hyd rate d s ca le a nd/or surface

cont am inants ca n be ide ntified during ta ck w elding. If a

discoloured ring has formed within the protection of

the ga s shielded area a nd surrounds silver weld me tal

then, if porosity is to be minimised, the joint surfaces

should be re-prepared . Not a ll we lding proce sses sho w

the sam e s usceptibility to we ld met al po rosity. AlthoughTIG, MIG, EB a nd lase r welds o ften exhibit we ld met al

28



pores, keyhole plasma welds are typically pore-free,

show ing tha t this lat ter process ha s significa ntly greate r

to lerance to the c ond ition of the joint surfac es. Weld

meta l porosity can o f course be com pletely avoided by

using a solid state welding process.

DISTORTION Beca use w elding involves highly localised hea ting of

joint edges to fuse the material, non-uniform stresses

are set up in the component. Initially, compressive

stresses a re creat ed in the surrounding co ld parent meta l

when the weld pool is formed due to the thermal

expansion of the hot m eta l (heat a ffected z one) adjacent

to the weld pool. However, tensile stresses arise on

coo ling when the c ontraction o f the we ld m etal and the

immed iate heat affected zone is resisted by the bulk of

the cold parent metal. If the stresses generated from

therma l expa nsion/cont raction exceed ed the yield

s t r e n g t h o f t h e p a r e n t m e t a l , l o c a l i s e d p l a s t i cdeformation of the metal occurs. Plastic deformation

causes a permanent distortion in the structure.

The ma in facto rs affecting the type and de gree of

distortion, are parent material properties, amount of

restraint, joint de sign, part fit-up and w elding proce dure.

PARENT MATERIAL PROPERTIESParent material properties which influence distortion

are coefficient of thermal expansion (greater values

increase distortion) and specific heat per unit volume

(lower values increase distortion). As distortion is

de termined by expans ion and cont rac t ion o f thematerial, the coefficient of thermal expansion of the

material plays a significant role in determining the

stresses generated during welding and, hence, the

degree of distortion. Simple calculations and practical

experience shows that the level of distortion expected

in a titanium co mponent lies betw een thos e o bserved

for stee l and s ta inless stee l (i.e. distortion w ill be greate r

that for steel, but lower that observed in many austenitic

sta inless stee ls).

RESTRAINT

I f a component is welded wi thout any externalrestraint, it distorts to relieve the welding stresses. So

met hods of restraint such as ‘strong ba cks’ in butt welds

ca n prevent mo vement a nd reduce disto rtion. It should

be no ted , how ever, tha t restraint produces higher levels

of residual stress in the m at erial.

JOINT DESIGNBoth butt and fillet joints are prone to distortion. It

ca n be m inimised in butt joints by ad opt ing a joint type

which balances the thermal stresses through the plate

thickness. For exam ple, a do uble-sided in preference to

a single-sided weld. Double-sided fillet welds shouldeliminate angular distortion of the upsta nding mem ber,

STRESS RELIEF As for welds in any other metal , postweld heat-

treatme nts are performed to reduce the residual stresses

encountered in the weld zone and improve fatigue

performance. Residual stresses in ferrous fabrications

can e q ual the yield stress o f the a lloy, but residual stresse s

in tita nium are t ypica lly low er. For exam ple a m a ximum

residual stress of approximately 85%of yield can beenc ounte red in Ti-6Al-4V in highly rest rained me ta l, such

as t ypical for repair welds. Postwe ld hea t treatm ents of

different durations are required for stress relief of the

various titanium alloy grad es. Hea t-trea tme nt sched ules

for weldable higher s trength a l loys are commonly

combined so that postweld heat-treatment relieves

residual stresses a nd a ges t he pa rent ma terial.

Postweld heat-treatment may be performed in a

vacuum o r argon atmo sphere to prevent the fo rma tion

of co nta minated laye rs. Ads orbed o xygen forms a brittle

surface, or ‘a lpha case’ , and is best avoided. Heat

treatment in air is possible provided that the oxidised

surface is removed by pickling, grinding or blasting and

descaling.

Welde d fa brica tions in com me rcia lly pure titanium,

including pipe and fittings, w ill not norma lly req uire stress

relief. Alloy fabrications, however, typically do require

stress relief. One to t wo hours at 60 0°C (1110°F) max is

usua lly ad eq uat e fo r bot h CP a nd Ti-6Al-4V, t o reduc e

residual stress to manageable levels whilst avoiding

excess ive therma l oxida tion. Indeed , higher temp eratures

should be avoided, since microstructural ageing can

reduce toughness and ductility. Suppliers should be

consulted for a suita ble hea t treatm ent cycle for welded

alloys req uiring post we ld so lution trea tme nt and ag eing.

29

especially it the two welds are deposited at the same

time.

PART FIT-UPFit-up should be uniform to produce predictable a nd

consistent shrinkag e. Excess ive joint ga p ca n a lso increase

the de gree of distortion by increasing the a mount o f weldme ta l neede d to fill the joint. The joints s hould be

ad eq uately tacked to prevent relative mo vement betwe en

the pa rts during w elding.

WELDING PROCEDUREThis influence s the d egree of d istortion mainly through

its effect on the heat input. As welding procedure is

usually selected for reaso ns of q uality a nd p roductivity,

the w elder has limited sco pe fo r red ucing d isto rtion. As

a g eneral rule, w eld volume sho uld be kept t o a minimum.

Also the w elding seq uence a nd tec hniq ue should a im to

balance the therma lly induced stresse s around the neutralaxis of the co mponent.



Design Cost Control: The prac tical points o f succes sful de sign cos t co ntrol are principally tho se o f value eng ineering

using a light, strong, corrosion-resista nt m at erial.

Surface Treatment: The practical points of succes sful surfac e treat ment s are the t hose of know ing the problem to

be so lved a nd de ciding the appropriate treatment.

Do: Check ava ilable stand ard prod ucts and s pecificat ions

to obtain best availability and lowest cost.

Use de sign strate gies based o n using minimum ma terialthickness.

Exploit corrosion resistant characteristics to the full.

Consider the use o f liners and cladd ers in preference t o

solid design where heavy sections are unavoidable.

Consult suppliers and fa brica tors at t he ea rliest st ag e of

design.

Do not: Simp ly substitute titan ium into existing designs.

Budget for titanium project costs by weight, especiallynot by the weight of steel or other alloys.

Specify little-used alloys or fo rms.

Machining: The pra ctical points o f succe ssful machining a re principally tho se of o bserving the different mec hanical

and surfac e cha racteristics o f titanium. Fire safet y proced ures m ust be app lied for handling a nd co ntrol of t ita nium

fines and turnings.

Do: Use rigid set ups, correct speed s, feed s and too ling.

Use floo d lubrication.Use roller stea dies a nd running ce ntres.

Regularly remove turnings from machines.

Employ sp ecial closea ble cont ainers for titanium turnings.

Do not: Allow titanium t o rub on blunt to oling o r smea r

on the o ther metals.Mix co mbus tible rubbish with tita nium fines o r turnings.

Allow ope n flam es o r we lding nea r tita nium fines.

Fabrication: The pract ica l points o f success ful fabrica tion are principally thos e o f goo d ho usekeep ing a nd clean

practice in the workshop.

Do: Use the correct weld preparation and remove all

burrs.

Remove all grease, oil, paint and dirt before welding or

heat treatment.

Clea n we ld a reas w ith ace tone o n a lint-free cloth or use

sta inless ste el or tita nium w ire brushes.Dry tita nium surfaces before w elding.

Use clean d ry tita nium filler wire o f the c orrect grad e.

Ensure that the top and back face of the w eld a nd w eld

areas a re adeq uately shielded with argon gas.

Do not: Hea t treat t ita nium in a reducing atmo sphere, it

will absorb hydrogen and become embrittled.

Use methyl alcohol (methanol) as a cleaning fluid, dry

methanol can cause stress cracking.

Use sulpho -chlorinat ed or s ulphurised cleaning fluids.

Apply cleaning fluid with tissue paper, wool or rags.Wire brush with mild steel brushes.

Use hydorgen containing shielding gases.

Do not: At t e m p t t o a p p ly c o a t in g s t o s o i le d o r

contam inated s urfaces.

Exceed recommended inspection and maintenance

intervals.

Re-use components showing excessive wear or surfacedamage.

Do: Confirm that any side effects are a ccounted for in

the d esign and application.

Ensure that surface preparation is appropriate to the

coa ting selected .

Provide the sp ecified grad e o f lubrica tion.

Installation: The prac tical points o f succes sful installat ion a re principally tho se o f obs erving the d ifferent me cha nica l

properties, corrosion resistance and surface characteristics of titanium.

Do: Allow for the lower modulus of titanium in struts

and support spans.

Provide surface treatment for titanium parts in sliding

conta ct, o r on bearing surfaces.

Coa t external surfac es o f exposed titanium st ructures in

areas where dynamically induced sparking is a defined

hazard.

Do not: C o n n e c t t i t a n i u m w i t h o u t i s o l a t i o n t o

immediately adjoining less corrosion resistant metals,

(to red uce t he likelihoo d of ga lvanic corrosion).

PRACTICAL POINTS..... THE DO’S AND DON ’TS OF TITANIUM

CO MPREHENSIVE GU IDES ON MACH INING AND FABRICATION ARE AVAILABLE FROM TIG

30



STANDARDS AND

SPECIFICATIONS ASME provides the only international non-aerospace

sta nda rd for we ldm ent q ualifica tion in titanium. For

pressure vessel construction, the ASME Boiler and

Pressure Vesse l Cod e de ta ils proced ure and performa nce

tests w hich must be met for coded grades 1, 2, 3, 7, 9,and 12. Tensile a nd bend tests on trial welds m ad e under

conditions intended fo r prod uction a re the acce ptance

criteria. Impact or notch tensile tests may also be

required , pa rticularly for low tem perature a pplica tions.

Once good procedures are established, as evidenced

by tensile a nd bend tes ts, the y should be strictly follow ed

in subsequent production welding. Although weld colour

should ce rtainly be included in a ny w elding q ualifica tion

testing, ASME Code suggests that , if titanium we ld m eta l

hardness is more than 40 BHN (50VPN) greater than

base meta l hardness , excess ive contamina t ion i s

possible. A substantially greater hardness differential

necessitates removal of the affected weld-metal area.The Co de further spe cifies tha t a ll tita nium w elds be

examined by liq uid penet rant. In a dd ition, full rad iograp hy

of many titanium joints is required by the Code.

A Europe an s ta nda rd is currently being discussed for

we lde r approval for tita nium fabricat ion, but a s yet (May

’99) the final content of this document has not been

ratified.

HEALTH AND SAFETY Welding fume g eneration from the co mm on t ita nium

a lloys during TIG w elding is minima l a nd t here a re no

extract ion req uirements beyond those necess ary for TIG

w elding ot her struct ural ma te rials. Titanium w ill not

com bust d uring w elding. Instances in w hich titanium has

caught fire are associated with finely divided material

and ignition from co mbustible fluids or ma terials.

GLOSSARY TIG: tungsten inert gas or gas tungsten arc welding

(G TAW)

MIG: met al inert ga s o r gas met al arc w elding (GMAW)

PAW: plasm a arc w elding

DCEN: Direct current e lectrod e neg at ive

DCEP: Direct current electrode pos itive

EB: electron bea m

RPEB: reduced pressure electron beam

Nd-YAG (las er) Neo dym ium-yttrium-aga te -garnet

ASME American Society of Mechanical Engineers

Welding positions fo r plat e a nd c ircumferent ial welds.

31



FOR FURTHER INFORMATION The list o f TIG Mem bers over includes fabrica tors w ho w ill be pleased to as sist w ith further informa tion a nd a dvice.

In ad dition, there a re ma ny industrial membe rs of TWI that have conside rable e xperience in fabricating titanium.

Informa tion on these com pa nies c an be o bta ined from TWI. Those loo king for US fa brica tors sho uld visit the

following web sites: http://www.welding-services.com. The me mbe rship o f TIG a nd the internat iona l Titanium

Asso ciation includes m any international specialist fabrica to rs and t hese c an be fo und on http://www.titanium.net.

Titanium International LtdKeys Ho useGra nby Avenue

Garretts GreenBirmingham B33 0SP, U KTel: + 44(0)121 789 8030Fax: + 44(0)121 784 7694

Huntingdon Fusion Techniques LtdStukeley MeadowsHutingdonCambridgeshire PE18 6EJ, UKTel:+ 44(0)1480 412432Fax: : + 44(0)1480 412841

FOR BRAZING CONSUM ABLES

WESGOGTE Prod ucts Corpo ration477 Harbor BoulevardBelmont, CA 94002, USATel: + 01 (415) 592 9440

32

FOR FURTHER READING There is a va st bo dy o f literat ure c overing the joining o f titanium a nd its a lloys, far mo re than ca n be highlighted in

this brochure. Req uest for informa tion o n spe cific w elding issues should be directe d to TWI.

L S Smith and M F Gi t tos : “Highproduct ivity p ipe w eld ing o f Ti-6Al-4Va lloys” . TWI mem bers repo rt 660,November 1998.

M F Gitto s: “ Welding of t itanium”.Titanium World, Sept em ber 1 996.

P L Threa dgill: “ The p ot ent ial for so lidsta te welding of t i t an ium pipe inof f shore industr ies” . P resented a t‘Right use of titanium III’, StavangerNorwa y, 4-5 November 1997.

D Howse, R Wiktorowicz and M F

Gi t tos : “Using shielding gases forimproved productivity arc welding oftita nium”. TWI Bulletin,

“AWS Welding H an db oo k, Ma te ria lsand Applica tions Part 2” , 8th e dition ,Ame rica n Welding So ciet y, Miam i.

M J H u ss i on : “ P r ac t i c a l u se o f aco lla psible purge cha mbe r for titaniumw elding” . Welding Journa l 66, July1997.

Ti tanium: Des ign and Fa br ica t ionHandbook for Industrial Applications,TIMET, Tita nium M et a ls Co rpo rat ion1997

B.Ha nson, “ The Selection and Us e of

Titanium - Des igners Guide ” , Instituteof Materials, 1995

TIMET UK LTDP.O. Bo x 704,Witton,

Birmingham B6 7UR UKTel : + 44(0)121-356-1155Fax: + 44(0)121-356-5413

RMI Titanium CompanyRiverside Esta teFa ze ley Ta mw orth

Sta ffordshire S78 3RWTel : + 44(0)1827 262266Fax: + 44(0)1827 262267

FOR SHIELDING AND WELDING EQU IPM ENT

FOR WELDING CONSUM ABLES

Vacuum Brazing Consultants LtdThe Ho b Hill, Chap el Roa dSteetonKeighley BD20 6NUTel: + 44(0)1535 653598Fax:+ 44( 0)1535 656707

FOR HELP FROM TWI

TWI,Grant a Park, Grea t Abingto n, Cam bridge , CB1 6ALTel: + 44(0)1223 891 162Fax: + 44(0)1223 892588Ema il: tw i@ tw i.co.uk

L S Smith a nd M F Gitto s: “A review ofwe l d m eta l p or os i t y an d h ydr i decracking in titanium and its alloys”.TWI Memb ers Report 658 , Nove mbe r1998.

M B D Ellis a nd M F Gitto s: “ Tungst eninert gas welding of titanium and itsalloys” . Welding & Met a l Fa brica tion,Janua ry 1995.

M H Scott: “Arc welding titanium”.Welding Inst itute Resea rch B ulletin,20, June 1979.



M EM BER COM PANIES OF TIG

33

Time t UK Limite dPO Box 704WittonBirmingham B6 7URTel: 012 1 356 1155Fax: 0121 356 54 13

Manufacturers and stockists of titaniummill products

Doncasters Plc28-30 Derby RoadMelbourneDerby DE7 1FETel: 0 133 2 86 490 0Fax: 01332 864888Manufacture titanium forgings andcastings - specialist fabricator includingsuper-plastic forming/diffusion bonding

Wyma n Go rdon LtdHouston RoadLivingston

West Lo thian EH54 5 BZTel: 015 06 446200Fax: 01506 446330Manufacturer of large titanium forgingsincluding large diameter extruded tube

Bunting Tita nium Ltd34 Middlemore Industrial EstateSme thw ick Wa rleyWest Midland s B66 2 EETel: 012 1 558 5814Fax: 0121 558 80 72Titanium fabricator specialising in pipespools - manufacturer of a range of titanium valves

Aero spa ce Forgings LtdChurchbridgeOldburyWa rleyWest Midland s B6 9 2AUTel: 012 1 552 2921Fax: 0121 544 57 31Manufacturer of closed die and handforged titanium forgings

TWIAbington HallAbingtonCambridge CB1 6ALTel: 0 122 3 89 116 2Fax: 01223 892588Research, development and consultancy

on joining techniques for materialsincluding titanium

Meta l Improvement Co IncNavigation H ouseHam bridge LaneNewburyBe rks RG14 5 TUTel: 0 163 5 3 107 1Fax: 01635 31474Surface treatment of titaniumcomponents to improve mechanicalproperties and to prolong service life

RMI Titan ium Com pa nyRiverside Esta teFa ze ley Ta mw ort hStaffordshire B78 3RWTel: 01 827 262 266Fax: 0 1827 26 2267

Manufacturer and stockist of a full rangeof titanium mill products including pipingand OCTG tubulars

Ore me t Titan iumKeys HouseGra nby AvenueGarretts GreenBirmingham B33 0SPTel: 012 1 789 8030Fax: 0 121 784 8054Manufacturer and stockist of titaniummill products and castings

Aurora Forgings LtdPa rkga te St ee l WorksPO Box 16 RotherhamSo uth Yorkshire S62 6EBTel: 01 14 2 61 5 000Fax: 0 114 261 5025Open and closed die forgings, extrusionsand rolled rings

Euro-Tita n Ha nde ls AG/Ha nse a tischeWaren Ha nde lsgesellscha ft mbH & Co Kgc/o Interne t Agencies18 Cofton Church LaneBirmingham B45 8PTTel: 01 21 4 47 7 492Fax: 0 121 447 7493Stockist of titanium ingot, bar, plate,sheet, profile, tube and wire products

Rolls LavalPO Box 100Wolverha mp to n WV4 6JYTel: 01 902 353 353Fax: 0 1902 40 3334Manufacturers of compact heatexchangers

Super Alloys International Ltd5 Ga ramond e DriveClarendon Industrial EstateWymbushMilton Keynes MK8 8DFTel: 01 908 260 707Fax: 0 1908 26 0494Stockist of titanium wrought products

Scomark Engineering LtdHartshorne RoadWoo dville Sw ad lincot eDerbyshire DE11 7JFTel: 01 283 218 222Fax: 0 1283 22 6468Fabricator of high performance materialsincluding titanium

DERAGriffith Building A7Structural Materials CentreDERA Fa rnbo roughHampshire GU14 0LXTel: 01 252 392 540

Fax: 0 1252 39 4135Research and development on materialsincluding titanium

Tec va c Limite dBuckingway Business ParkSwaveseyCambridge CB4 5UGTel: 0 195 4 23 370 0Fax: 01954 233733

Surface treatment of titaniumparticularly nitriding

Titan ium Mill Prod ucts LtdLöwe House1 Ranmoo r CrescentSheffield S10 3GUTel: 0 114 2 30 8 85 5Fax: 01142 302 83 2Stockists of titanium wrought products

Alba ASLilleakerveien 23N-0283 OsloNorwayTel: 4 7 2 2 50 00 20

Fax: 4 7 22 50 01 11Titanium castings

Deutsc he Titan G mbHAltendorfer Strasse 10445143 EssenGermanyTel: 00 4 9 020 1 188 2 593Fax: 49 0201 18 8 3520Manufacturer of a wide range of titaniummill products

Rolls Royce PlcP.O. Box 200 0Derby DE21 7XXTel: 0 133 2 66 146 1Fax: 01332 622948Fabrication and design of components formarine power systems

Aerom et Inte rnationa l PlcWat chmea dWelwyn G arde n CityHert ford shire AL7 1LTTel: 0 179 5 41 500 0Fax: 01795 415050Fabricator specialising in super plasticforming and diffusion bonding

Azko NobelPermascand ABBox 42S-840 10 Ljungaverk

SwedenTel: 069 1 3 550 0Fax: 0691 33040Titanium fabricators

Euro -Tita n Ha nd els AGKatternberger Strasse 155-159Solingen 42655GermanyTel: 0 2 12 248 16-0Fax: 02 12 248 1 6-16Stockist of titanium mill products



TITANIUM

TITANIUM is the fourth m os t a bunda nt st ructural meta l in the e a rth’s crust, a nd t he ninth industrial meta l. No

othe r engineering met al has risen so sw iftly to p re-eminence in such a w ide range o f critical and d ema nding

applications.

TITANIUM AND ITS ALLOYS OFFER:Availa bility in a ll forms

Comparable cost to other high performance engineering materials

Weight sa ving - as strong a s st eel but half the w eight

Outstanding corrosion resistance in a wide range of aggressive media

Resistance to erosion a nd ca vitation

Fire a nd s hoc k resista nce

Fa vourable cryog enic prop erties

Biocom pat ibility and non t oxicity

TITANIUM AND ITS ALLOYS DELIVER:High performance co mponents a nd systems

• Aerospace engine and airframe parts

• Automot ive compo nents including valves, springs, connecting rods

• Orthopaed ic implants surgical instruments, medical centrifuges

• Lightweight vehicle and body armour

• Offshore oil and g as e q uipment, stress joints, risers, flow lines, valves

• Seawa ter pipework systems for ballast, coo ling and f ire protection

• 100 million metres of stea m conde nser tubing in power plant wo rldw ide

• High pressure compact heat exchangers

• Process plant eq uipment, vessels, heat exchangers, pumps, mixers

• High strength corrosion resistant fasteners

• Strong co rrosion resistant a lloys for high pressure high temperature processe s• Naval ball valves up to 600mm diameter

• Equipment for safe handling of food, beverage a nd pharmaceuticals

• Erosion resistant com poments for high velocity wa ter duties

• Computer hard drive substra tes

• Flue gas d esulphurisation plant d uct and flue linings

• Lightweight steam turbine blading

• Safe long term storage of nuclear waste

• Corrosion resistant wet air oxidation process plant

Sports, leisure and fashion goods

• Rac ing and mounta in bicyc les

• Go lf clubs

• Ya c ht fit ting s

• Watches and personal jewellery

• Ultra lightweight spectac le frames

Attract ive a nd d urable a rchitect ural finishes and ornam ents

• Curta in walling and roof ing

• Elec tro pa in ted p ic tures

• Sculp tures , plaques and monuments

• Corrosion resistant cladd ing for marine structures

In the ma jority of the se a nd o the r applications TITANIUM has rep la ced hea vier, less se rvicea ble and les s

co st e ffect ive m at erials. D esigning with TITANIUM and ta king all fac to rs including selection o f the a pprop ria te

surface trea tme nt into a ccount has resulted in reliable, econo mic and mo re durable systems a nd com ponent s

twi (welding titanium)

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