Intermetallics21(2012)97e104

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Intermetallics

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Effectofpackrollingonmicrostructuresandtensilepropertiesofas-forgedTi-44Al-6V-3Nb-0.3Yalloy

H.Z.Niu*,F.T.Kong,S.L.Xiao*,Y.Y.Chen,F.Yang

NationalKeyLaboratoryforPrecisionHotProcessingofMetals,HarbinInstituteofTechnology,Harbin150001,PRChina

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Articlehistory:

Received25June2011Receivedinrevisedform16September2011

Accepted5October2011

Availableonline4November2011Keywords:

A.Titaniumaluminides,basedonTiAlC.Rolling

D.Microstructure

B.Mechanicalpropertiesatambienttemperature

abstract

ThemicrostructuresandtensilepropertiesofTi-44Al-6V-3Nb-0.3Y(at.%)alloybeforeandafterhotrollingwereinvestigatedsystematically.SEMresultsindicatedthattheas-rolledTiAlsheetwaschar-acterizedbycompletelydynamicallyrecrystallizatedmicrostructures,exceptsomere nedlamellarcoloniesinthebackend,whichareprimarilycausedbythetemperaturedropduringcannedforgingandsubsequentpackrolling.ByTEManalysis,thecoarseningofglamellaebyalathdecompositionduringhotrollingarefound.Meanwhile,byEBSDmeasurements,thephasecompositionandgrainfeaturesoftheas-forgedandtheas-rolledconditionswerecharacterizedandcompared.Additionally,thetensilepropertiesweretestedto ndthattheroomtemperaturetensilestrengthdecreasedobviouslyafterhotrolling,withyieldstrengthdecreasingfrom620MPato520MPaalongtransversedirection(TD)andto485MPainrollingdirection(RD),andtheUTSfrom680MPato598MPaand556MParespectively.Thereasonforthedegradationofthetensilestrengthisinterpreteddetailedly.Afterbeingheat-treatedinsingleaphase eld,betaphasewaseliminatedfromcurrentdeformedTiAlalloyandthetensileprop-ertieswereenhancedobviously.

CrownCopyrightÓ2011PublishedbyElsevierLtd.Allrightsreserved.

1.Introduction

TiAlbasedalloysarehighlypromisingforhightemperaturestructuralapplicationsinaerospaceandautomotiveindustries,duetotheirattractiveproperties,suchaslowdensity,goodelevatedtemperaturestrength,highresistancetooxidation,excellentcreepproperties[1,2].However,thelowroomtemperatureductilityandpoordeformabilitylimittheirextensiveapplications[2e4].Toovercometheseproblems,tremendouseffortshavebeendevotedtopreparingTiAlalloyswithre nedandhomogeneousmicro-structures,suchasalloying[5],heattreatment[6],thermo-mechanicaltreatment(TMT)[7e10],includingisothermalforging,packforging,hotextrusionandrollingetc.

GammaTiAlsheetshaveextremelypromisingaerospaceapplications,includingnozzletilesforgasturbineengines,nozzlesforhelicopters,backstructuresforscramjets,andthermalprotec-tionsystemsforreusablelaunchvehicles(RLV)etc.[11].g-TiAlsheetsaregenerallyfabricatedbyingot-metallurgical(IM)andpowder-metallurgical(PM)processingroutes[11,12].Uptonow,onlytheadvancedsheetrollingprocess(ASRP)developedby

*Correspondingauthors.P.O.Box434,SchoolofMaterialsScienceandEngi-neering,HarbinInstituteofTechnology,Harbin150001,PRChina.Tel./fax:þ8645186418802.

E-mailaddresses:hzniu@126.com(H.Z.Niu),xiaoshulong@hit.edu.cn(S.L.

Xiao).PlanseeAG(Austria),reachesproductionscale[13].AstoIMprocess,packrollingusuallyproceedsaftercannedforgingstepstoensurethere nedmicrostructureandexcellenthotdeformability.However,itisgenerallydif culttoproduceTiAlpancakeorsheetwithhomogeneousand neequiaxedmicrostructures.Becausethecoarselamellarmicrostructureofingotcanhardlybebrokendowncompletelybydynamicrecrystallizationduringdeformation,duetotheinhomogeneousplastic owcausedbytemperaturedropandfriction.Additionally,afterforgingandrolling,themicrostructurecompositionbecomesmorecomplexandsomesubstructures(i.e.subgrains,twins,andsubboundariesetc.)readilygenerate[14],andthemechanicalpropertiesarecloselyrelatedtomicrostructurefeatures.Itisdif culttoevaluatetheeffectofprocessinghistoryonthe nalproductproperties.However,understandingthecorrela-tionsofprocessingconditionswiththeresultingmicrostructuresandcorrespondingmechanicalpropertiesisofprimeimportancetoobtainTiAlalloyswithexpectedserviceperformance.Meanwhile,processde cienciescanbefedbackbymicrostructuralstudyandfurtherbeimproved.Bynow,thecomparativestudyofmicro-structuresandpropertiesbetweenas-forgedandsubsequentas-rolledTiAlalloyshasbeenrarelyreported,especiallynearlynorelevantreportsonbetagammaTiAlalloysheetshavebeenmade.

Inthisstudy,onebetagammaTiAlalloysheetfabricatedbyIMroutewasintroduced.Themicrostructuresandtensilepropertiesofas-forgedandas-rolledTi-44Al-6V-3Nb-0.3Y(at.%)alloywere

0966-9795/$eseefrontmatterCrownCopyrightÓ2011PublishedbyElsevierLtd.Allrightsreserved.doi:10.1016/j.intermet.2011.10.003