2024年5月3日发(作者：)

MaterialsandDesign34(2012)509–515

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MaterialsandDesign

journalhomepage:/locate/matdes

Effectofelectronbeamweldingonthemicrostructuresandmechanical

propertiesofthickTC4-DTalloy

WeiLu

⇑

,YaowuShi,YongpingLei,XiaoyanLi

CollegeofMaterialsScienceandEngineering,BeijingUniversityofTechnology,Number100,PingleyuanDistrict,Beijing100124,PRChina

articleinfo

abstract

Electronbeamwelding(EBW)wasappliedto50mmthickdamage-tolerantTi–6Al–4V(TC4-DT)alloy,

andmicrostructure,microhardnessandtensilepropertiesofthedefect-freeweldedjointswereexam-

ultsindicatedthatthemicrostructureofthebasemetaliscomposedofprimary

a

phases

andthelamellar(

a

+b)EBWjoint,martensitebasketweavemicrostructure

isformedinfusionzone(FZ).Moreover,theheataffectedzone(HAZ)nearFZconsistsofacicularmar-

tensiteandasmallportionofprimary

a

nearbasemetalconsistsofprimary

a

phase

andtransformedbcontainingaciculate

a

.ItisfoundthattheboundaryofthetwoportionsoftheHAZ

ardnessvaluesforFZ

andHAZarehigherthanthatofbasemetal,andtherearethepeakvaluesfortheHAZneartheweld

cturelocationsofalltheEBWtensilespecimensareinbasemetal,andtheultimatetensile

strengthofthejointsmayreachabout95%tion,withthedepthincreasingalong

theweldthickdirection,thegrainsizeoftheFZdecreasesandmicrohardnessincreases.

Óhtsreserved.

Articlehistory:

Received5July2011

Accepted2September2011

Availableonline7September2011

Keywords:

Non-ferrousmetalsandalloys

Welding

Metallography

uction

Titaniumanditsalloyshavebeenwidelyemployedinthefieldof

aerospaceindustryduetotheirsgoodproperties,suchashighspe-

cificstrength,lowspecificgravity,andhighcorrosiveresistance

especiallyunderhightemperatureandhighstress[1].Withthe

increasingdemandoflonglifeandwellreliabilityfortheaircraft,

thetitaniumalloyswithwelldamage-tolerantpropertiesforexam-

plehighfracturetoughnessandfatiguecrackpropagationresistance

areneeded[2].Theductility,fracturetoughness,stress-corrosion

resistanceandresistanceagainstcrackgrowthofthematerialcan

beimprovedwhenthecontentofinterstitialelementssuchasoxy-

genandnitrogendecreases[3].Moreover,the

a

–bphaseTi–6Al–4V

alloysispresentlythemostwidelyusedtitaniumalloyduetothe

highstrength,andthepossibilityofvaryingmechanicalandphysical

propertieswhichcanbeofferedbycontrolofthemicrostructural

developmentduringthermomechanicalprocessing[4,5].Therefore,

thetitaniumalloyswithwelldamage-tolerantpropertieshavebeen

widelydevelopedbydecreasingthecontentofinterstitialelements

ofTi–6Al–4Valloy[6].

Thedamage-tolerantTi–6Al–4V(TC4-DT)alloyisanewalpha–

betatitaniumalloydevelopedinChinabydecreasingtheintersti-

tialelementcontentoftheTi–6Al–4Valloyandadoptingspecial

loyhasmediumstrength,highfracture

⇑

.:+86;fax:+86.

E-mailaddresses:luwei870808@,luwei87@().

0261-3069/$-seefrontmatterÓhtsreserved.

doi:10.1016/.2011.09.004

toughnessandresistanceagainstfatiguecrackgrowth,thus,theal-

loywiththicknessmorethan45mmiswidelyappliedintheload

umalloysmaybejoinedbya

tion,

itisknownthattitaniumisveryeasilyreactivetowardsmost

atmosphericgasincludingoxygen,nitrogen,andhydrogen,attem-

peraturesabove350°C[3].Therefore,electronbeamwelding

(EBW)isconsideredasthemostsuitableweldingmethodforjoin-

ingthethicktitaniumalloys,duetothehighvacuumenvironment,

whichcanprotectthehotmetalfromgaseouscontaminationin

theconditionofthelargewelddepth/widthratioofelectron

weldedmetal[7–9].

Tillnow,manyinvestigationshavebeendonewiththebasic

characteristicsoftheTi–6Al–4Vtitaniumalloy,suchastheequi-

libriumphasediagram,physicalandmetallurgicalproperties,heat

useful

tion,theresearchesonthe

microstructureandmechanicalpropertiesofEBWjointarecon-

ductedfortheTi–6Al–4Valloy[9–14].Thesestudiesshowthe

microstructuretransformationinEBWTi–6Al–r,

verylimitedstudiesabouttheEBWjointhavebeenreportedfor

theTC4-DTalloy,

primaryobjectiveofthepresentworkistostudytheeffectof

theelectronbeamweldingonthemicrostructureandmechanical

propertiesforthickTC4-DTalloy,andclarifytherelations

betweenmicrostructureandmechanicalpropertiesofthewelded

joint.

510

Table1

ChemicalcompositionsofTC4-DTalloy.

Al

5.90

V

4.20

Fe

<0.25

C

0.028

./MaterialsandDesign34(2012)509–515

N

0.0042

H

0.0011

O

0.0395

Y

0.005

Si

<0.026

Ti

Balance

Table2

Electronbeamweldingparameters.

Beamcurrent

I

b

/mA

132

Voltage

U/kV

150

Focuscurrent

I

f

/mA

2139

Velocityv/

(mms

À1

)

800

HeatinputE/

(kJm

À1

)

24.75

(a)

(b)

47

21

Φ

3

R3

ticofspecimen:(a)weldingdirection,samplingorientationand(b)

geometryoftensilespecimen.

mentalprocedure

ThethickTC4-DTplateinduplexannealingconditionwasused

micalcompositionofthisalloyisgivenin

teswiththesizeof400mmÂ200mmÂ50mm

weregroundwithmiller,cleanedwithacidsolution,andthen

ctronbeamwelding

M

6

×

1

11

wascarriedoutalongthetransversedirectionoftheplateinahigh

pressurevacuumEBWmachineZD150-15A,andthewelding

processparametersarelistedinTable2.

ThespecimensofEBWjointsforobservingthemetallography

werecutperpendiculartotheweldbead,andcrosssectionswere

preparedformetallographicanalysisbygrindingandpolishing

ngwasaccomplishedusingaseriesofSiCsand

polishingwasperformedusing2.5

l

mand0.5

l

msiliconcarbide

lishingwasperformedusing0.05

l

malumina

fiedetchantwith1%hydrofluoricacidand12%nitric

acidin50%distilledwaterwasusedtorealthemicrostructure.

Then,themicrostructureoftheweldedjointswasobservedby

anOLYMPUSBX51Mopticalmicroscope(OM)andaFEIQUANTA

200Fscanningelectronmicroscope(SEM).Grainsizewasmea-

suredinthemicrographsobtainedatthedifferentpositionofthe

weldbeadusingImageJsoftware,andtheresultsareobtained

bytheaverageofthemeasurementsforabouttenpicturesatthe

relativeposition.

Microhardnessmeasurementofweldedjointswasconducted

onahardnesstester(HXD1000)atroomtemperaturebyholding

ssvaluesweredirectlyobtained

surementintervalinFZandBM

wasfixedat0.4mm,whileinHAZthedistancewas0.2mm.

Tensilespecimensofthebasemetalalongthetransverseand

longitudinalweremadeandthespecimensofweldedjointsper-

pendiculartoweldsweremachinedatthedifferentpositionalong

ticconfigurationoftheweldingdirection,

samplingorientation,andtensilespecimendimensionisshown

silespecimendimensionischosenonabasisof

thesmallsizegeometryoftheASTME8M-04specification[15],

andthedimensionofthetensilespecimensisthesameforthebase

etestswerecarriedoutatroom

temperatureusingaMTSsystemwithadisplacementextensome-

ferentdisplace-

mentrateswereemployedduringthetensiletest:3mm/min

beforereachingtheyieldpointand5mm/minbeyondtheyield

testingresultswereaverageofthreespecimens.

-sectionalmacrographofthejoint:(a)overallviewand(b)magnifiedimageoftheboxin(a).