Damage resistance in gum metal through cold work-induced microstructural heterogeneity - 图文

JMaterSci(2015)50:5694–5708DOI10.1007/s10853-015-9105-y

抗破坏性Damageresistanceingummetalthroughcoldwork-inducedmicrostructuralheterogeneity

异质性 不均匀性 不同质J.-L.Zhang1?C.C.Tasan1?M.L.Lai1?J.Zhang1?D.Raabe1Received:2March2015/Accepted:14May2015/Publishedonline:3June2015óSpringerScience+BusinessMediaNewYork2015

AbstractCold-workedalloysexhibithighstrength,butmechanisms[1–14].Itexhibitssigni?cantlyextended

遭受sufferfromlimitedductility.Incontrast,Ti-basedgumelasticregime(withalowelasticmodulusof*40GPa)

metalwasreportedtoexhibithighstrengthcombinedwithandplasticdeformationregime(withverylowstrain

hardeningrate).Thesepropertieswerereportedtobepre-预应变goodductilityuponseverepre-straining.Motivatedbythis

anomaly,wesystematicallystudiedtheevolutionofgumsentonlyinspeci?ccompositionsthathavethreeelectronic演变metalmicrostructureduringseverecoldworking(swagingparameters:(i)acompositionalaveragevalenceelectronandrolling)andtheresultingdeformationanddamagenumberof*4.24;(ii)abondorderofabout2.87anda‘‘d’’micro-mechanicalmechanismsduringfollow-uptensileelectron-orbitalenergylevelof*2.45eV[1].Thesepe-deformation.Tothisend,variousexperimentalinsituandculiaritiestriggeredthreemainresearchdirectionsfocusing

事后剖析post-mortemmethodologiesareemployed,includingontheroleofchemicalcompositionvariations(e.g.of事后研究scanningelectronmicroscopyimaging,high-resolutionoxygen[5,10,15]),non-linearelasticbehaviour[2–4]andelectronbackscatterdiffractionmappingandtransmissionplasticdeformationmechanisms[6–9,16].Wefocushere,

强烈的electronmicroscopy.Theseobservationsrevealthatintenseontheotherhand,mainlyontheunderlyingmicrostructural

grainre?nementtakesplacethroughdislocationplasticity-causesofanothermechanicalanomaly:thismaterialex-dominateddeformationbandinguponcoldworking.Thehibitshighstrengthandductilityevenupon90%coldobservedenhancementincrackbluntingandfailureresis-swaging[1].Focusingontheeffectsofthepre-straining

tancewhichprolongsthepost-neckingductilityofgumalsoenablesustoinvestigate:(i)themicro-mechanicalrolemetalduringfollow-uptensilestrainingcanbeattributedtoofthemedium-straincoldworking(e&1.5–4)inducedthedeformation-induceddevelopmentoflocalhetero-deformationbands(e.g.microbands(MBs),shearbands)

geneitiesintextureandgrainsize.andgrainre?nementtherein[17]inthefollow-uptensile

deformation,sincetheformerwasinvestigatedpreviouslymainlywithinlow-straincoldworkingregime(e\\1.5)[18]andthelatterwithinthesevereplasticdeformationIntroduction

regime(e[4)[19–21];(ii)therelativeactivityofdifferentdeformationmechanismsingummetal(dislocation-freeInthepastdecade,Ti–Nb-basedgummetalhasdrawn

bulkshearing[1,6–8,13,14],stress-inducedxanda00signi?cantattentionduetoitssuperiormechanicalprop-ertiesandthecomplexityofthereporteddeformationphasetransformations[2,3,10]anddislocationplasticity[5,9,11,22]);(iii)theroleofthecrystallographictexturedevelopment[23–25]ingum-typebody-centredcubic(bcc)alloysand,morespeci?cally,therelevanceoftex-turesoncrackblunting.

&C.C.TasanHere,thesedifferentaspectsareinvestigatedfollowingac.tasan@mpie.de

multi-scaleexperimentalapproach,inanefforttoprovide

1additionalguidelinesforimprovingthealloydesigncon-¨rEisenforschung,Max-Planck-Stra?eMax-PlanckInstitutfu

ceptsforb-Tialloys.¨sseldorf,Germany1,40237Du

123

JMaterSci(2015)50:5694–5708Experimentalmethodology

Alloyprocessing

AnalloywithcompositionTi–35.7Nb–1.56Ta–2.83Zr–0.438O(wt%)wasproducedviaarc-meltingunderargonatmosphereandcastintoacylindricalcoppermould(in-ternaldiameter:15mm)forensuingswaging.Forthecoldrollingprocess,anothercastsamplewiththesamecom-positionwasproducedinthesamefurnace.Thesamplesolidi?edinarectangularcoppermouldwithinternaldi-mensionof109509150mm3.Bothingotsweresub-sequentlyannealedfor4hat1200°Cforhomogenizationandthenfurnacecooled.Thechemicalcompositionwastestedbyinductivelycoupledplasmaopticalemissionspectrometryandinfraredabsorptionmeasurements.

Aftertheheattreatment,thealloyswerecoldswaged(CS)orcoldrolled(CR),respectively,tovariousstrainlevels.Theswagingprocesswascarriedoutatroomtem-peratureinseveralpasseswitharound0.5-mmdiameterdecreaseperpass(initialdiameterD0=15mm).Threestates,whichwereCSto*30%cross-sectionalareare-duction(Df=12.2mm,e&0.41),*60%areareduc-tion(Df=9.2mm,e&0.98)and*90%areareduction(Df=5.05mm,e&2.20),wereselectedfordetailedanalysis.Forcoldrolling,two10910920mm3rect-angularblockswererolledatroomtemperatureto*30%thicknessreduction(t0=10mmtotf=7mm,e&0.36)and*90%thicknessreduction(tf=1.03mm,e&2.30),respectively.Thetruestrainswerecalculatedusingln(A0/Af)andln(t0/tf)forswagingandrolling,re-spectively,whereAisthecross-sectionalareaandtisthethickness.Allcold-workedmaterialswerethencharacter-izedandmechanicallytestedtostudythein?uenceofthespeci?ctypeofcoldworkingonmicrostructuralevolutionandmechanicalproperties.AsthereisagradualchangeofthemicrostructurefromtheoutsideshelltotheinsidecoreoftheCSbarandfromtheroll-contactsurfacestowardsthecentreoftheCRsheet,allmicrostructuralandmechanicalspecimensweretakenfromthecoreoftheCSbarandthemiddlelayeroftheCRsheet,respectively,exceptthoseusedtostudytextureevolution.Mechanicaltesting

Dog-bone-shapedtensilesamples(gaugegeometry:49291mm3)werecutbysparkerosionfromthecentreoftheCSrodandtheCRsheetwiththegaugelengthparalleltotheswagingorrollingdirection,respectively.TensiletestswerecarriedoutusingaKammrath&Weisstensilestageinconjunctionwithinsituimagingusinganopticalmicroscopeoracamera.Thesamplesurfacewas

5695

polishedfortheformertestsandpaintedwithaspecklepatternforthelatter.Thelatterdatawereusedfordigitalimagecorrelation(DIC)analysiscarriedoutemployingthe

ARAMISsoftware(GOM-Gesellschaftfu

¨rOptischeMesstechnikmbH,38103Braunschweig,Germany).Inthisway,thelocalstraindistributionoverthegaugelengthofthetensilesamplescouldbemapped.Microstructuralcharacterization

Allsamplesprobedbyscanningelectronmicroscopy(SEM)werewet-grindedandpolished.Finalpolishingwascarriedoutusingasolutionof75%colloidalsilicaand25%H2O2.Themicrostructurewascharacterizedsystematicallyintheas-cold-workedstateandwithincreasingfurther(tensile)deformationinaZeiss-CrossbeamXB1540FIB-SEMin-strument(CarlZeissSMTAG,Germany).TheEDAX/TSLsystem(EDAX/TSL,Draper,UT,USA)equippedwithaHikaricamera(Draper,UT,USA)wasusedforenergy-dispersiveX-rayspectroscopy(EDX)andelectronbackscatterdiffraction(EBSD)measurementsformicro-scalechemicaldistributionandorientationmapping,respectively.Backscatteredelectron(BSE)imagingwasalsoconductedforvisualizingthedeformationfeaturesatdifferentlocalstrainstatesusingvariableacceleratingvoltagesbetween15and30kV.Thedamageareafractionswerecalculatedfromfourto?veSEimagestakenatdifferentstrainlevels.ThelocalstrainforeachindividualimageistakenastheDIC-basedstrainvalueofthecentralpoint.

Transmissionelectronmicroscopy(TEM)lamellapreparationwasperformedusingadual-beamfocusedionbeam(FIB)(FEIHeliosNanolab600),usingthemethodpresentedbyGiannuzzietal.[26].TEMobservationswereperformedinJEOLJEM-2200FSatanaccelerationvolt-ageof200kV,throughwhichbright-?eldimage(BFI),dark-?eldimage(DFI)andselectedareadiffractionpattern(SADP)wererecordedbyGatanCCDCamera.

Results

Inthecurrentwork,experimentsonbothcoldswagingandcoldrollingweresystematicallycarriedout.Sincethe90%CSstatewasoriginallyproposedtoexhibittheme-chanicalanomaly,themainfocuswasplacedhereontheanalysisofthecoldswagingcaseandonlywhererelevant,comparisonstothecoldrollingcaseweremade.MicrostructureevolutionduringcoldworkingInFig.1a–c,three-dimensional(3D)BSEimagesshowthemicrostructureoftheas-solutiontreated90%CSand

123

5696Fig.13Dbackscatteredelectrons(BSE)imagesoftheaas-solutiontreated,b90%CSandc90%CRstatesofgummetalareshown.Theimagequalityunderlaidphasemapsofthedas-solutiontreated,e90%CSandf90%CRstatesshowsinglebccb-Tiphase

90%CRgummetal.Intheas-solutiontreatedstate,equiaxedgrainswithhomogeneouslydistributedelementsandanaveragegrainsizeof*80lm(Fig.1a)arepresent.Themicrostructureobservedafter30%CSandCRbothshowstrongdeformationcontrastinthegraininterior(notshownhere).Afterfurtherdeformationto90%(Fig.1c,e),grainsareelongatedalongthecoldworkingdirection.Themicrostructuresinthetransversedirectionobtainedfromthetwoprocessingroutesarequitedifferent.LaminatedzonesthatlayalmostfullyparallelontopofeachotherareobservedfortheCRmaterial(Fig.1c),whileintheCScasethelaminatedzonesarefurthertwistedaroundeachother(Fig.1b),resultingincurlingwhichisgenerallyobservedinswagedandwire-drawnmaterials[27,28].Imagequality(IQ)underlaidphasemaps(Fig.1d–f),corresponding,respectively,tothetransversedirectionsofFig.1a–e,allshowsinglebccb-Tiphase.Oneshouldnote,however,theuncertaintyinlocalEBSDphase

123

JMaterSci(2015)50:5694–5708

detectionwhichisduetothe(expected)increaseinthefractionofunindexedpointsincreasesatlargerstrains.Followingthisoverviewonthemicrostructuralmor-phology,wenextfocusonthedeformationmechanismsduringcoldworkingusingFigs.2,3,4,5,6.Thecrystal-lographictextureevolutionprovidesanindicationoftheactiveunderlyingdeformationmechanismsandtheirindi-vidualshearcontributionsduringdeformation[29].Theevolutionofthecrystallographictextureduringcoldrollingandswagingisplottedasorientationdistributionfunction(ODF)mapsatu2=45°fortheformerandash110ipole?gures(PF)forthelatterinFig.2.Theformer(rolling)revealsthatbothabcc-andcbcc-?bres(boththe?bresandtheirmostimportantcomponentsareshownschematicallyinFig.2)becomestrongerduringcoldrolling,andthelatter(swaging)revealstheformationofh110i?bretexturewithmaximumdeviationofaround15°at90%CSstate.Allofthesetypicalbcc?bretextures[23,25]indicatepredominantdislocationplasticityingummetal.

Tofurtherunderstandthemicrostructuralevolutionduringcoldswaging,Figs.3and4showtheEBSDmapsandmisorientationpro?lesofthe30and90%CSmi-crostructures,respectively.Comparativeanalysisofthekernelaveragemisorientation(KAM)mapandtheinversepole?guremapswithrespecttotheswagingdirection(SD-IPF)inFig.3a,brevealsthatthegrainsubdivisionpro-ceedsinahighlyheterogeneousandcrystallographicori-entation-dependentmanner.Thisismostobviousfortwospeci?csubdivisionprocesses,namely,for(i)theforma-tionofcellsorsubgrains,i.e.thedevelopmentofequiaxedvolumesboundedbydislocationboundariesand(ii)de-formationbanding,i.e.thedevelopmentofaband-likestructureofapproximatelyconstantorientation,thatissigni?cantlydifferentfromtheorientationpresentelse-whereinthegrain,forwhichdeformationgradientorevenlow-angleboundariesarenormallypresentwithinthebands.Thesetwosubdivisionprocessesaretypicalforlow-andmedium-straindeformationsofbccmetals[17,18].Examplesoftheorientationdependenceofthesemechan-ismsarerevealedinfourselectedgrains(i–ivmarkedwithblackarrows),whicharere-plottedasuniquegraincolour(UGC)mapsinFig.3c,basedonagrainboundarytoler-anceangleof5°.UGCmapsaresuitedasavisualizationvehicletohighlightgrainsthataredividedbyboundarieswithananglelargerthanaspeci?ctolerancevalue.Grain(i)showninFig.3c,whichiscloselyorientedtoh110idirection,deformsinarelativelyhomogeneousmannerwithoutthedevelopmentofanyinternalboundaries.Ontheotherhand,grains(ii,iii,iv)whichareorientedclosetoh100i-orh111i-orientations,tendtoheavilysubdivide[17,30].Figure3dshowstheenlargedIQunderlaidSD-IPFmapoftheareaindicatedbyredrectangleinFig.3a,b.Figure3eshowsthemisorientationpro?lealongthearrow

JMaterSci(2015)50:5694–57085697

Fig.2Textureevolutionofgummetalduringcoldrollingandswagingprocessestogetherwiththeschematicinstructionofthemain?bresandcomponentsofbccrollingtexture

Fig.3Orientationdependenceofgrainre?nementin30%CSgummetalisrevealedbyathekernelaveragemisorientation(KAM)map,andbtheinversepole?guremapwithrespecttoswagingdirection(SD-IPF).cTheuniquegraincolour(UGC)mapsofblackarrowmarkedgrainsareshownbasedongrainboundarytoleranceangleof5°.5°ratherthan2°isde?nedheretofullyexcludethepossibleerrorthatcouldbeinducedbyunindexedpointswithcon?denceindex\\0.1.dTwosetsofmicrobandsareshownintheenlargedIPFmapoftheareamarkedwiththeredrectangle.Themisorientationpro?lealongthearrowdirectionispresentedin(e)(Color?gureonline)

directioninFig.3d.Deformationbandsareherecharac-terizedasthoseband-likestructuresthatassumeabound-arymisorientationrangebetween15°to30°.Acrosstheremainingbulkofthesegrains,onlyminor(\\5°)misori-entationsareobserved.

Atthe90%CS,nearlyallofthegrainsareh110iori-entedwithrespecttotheSD(Fig.4a),withahighdensityofcurvedshearbandsandboundaries.Shearbands(markedbywhitearrows)correspondtonarrowregionsofintenseshear(showingblackcolouredlowimagequalityinEBSD)thatoccurindependentofthegrainstructure.Fig-ure4b,cshowtheIQunderlaidSD-IPFmapandSD-IPFmapoftheareasmarkedbyorange(Fig.4a)andred(Fig.4b)rectangles,respectively.Misorientationpro?les1and2inFig.4dshowmisorientationsalongthearrowdi-rectionsinFig.4b,c.Densesetsofhigh-angleboundariesareshowninpro?le1,indicatingthattheseh110itexturedgrainscarrystrongin-grainlatticerotationswithrespectto

123

5698JMaterSci(2015)50:5694–5708

Fig.4aImagequality(IQ)underlaidinversepole?guremapwithrespecttoswagingdirection(SD-IPF)of90%CSgummetalisshown.b,chighermagni?cationviewsoftheareasmarkedbytheorangeandredrectangles,respectively.Misorientationpro?les1and2indarealongthearrowdirectionsinb,c.InetheTEMbright-?eldFig.5Grainsizeevolutionduringswagingprocessisshown.Insetsaretheuniquegraincolourmapsoftheaas-solutiontreated,b30%CS,c60%CSandd90%CSstates(Color?gureonline)

imageandtheSADPrevealthepresenceofsubmicroncrystalswithintheshearbands.TheshearbandsaremarkedwithyellowdottedlinesintheBSEimagesoff90%CSandg90%CRgummetal(Color?gureonline)

123

5704deformationbanding.Suchkinkbandsareoftenobservedinhexagonalmaterialsintheabsenceofeasyglidesystems[42].Theobservationspresentedhereinthiswork,how-ever,suggestthatthecharacteristicsanddevelopmentofdeformationbandsinbccgummetalhavemoreincommonwithMBs.MBsareplate-likezonesboundedbycrystalrotationboundaries[43],thedevelopmentofwhicharerationalizedintermsoftheTaylormodel[30,44].Ingrainsinwhichdifferentcombinationsofslipsystemsareacti-vatedtoachievestraincompatibilitywiththeneighbouringgrains,thedensedislocationwalls(DDW)developbe-tweenthesedifferentregionsexperiencingdifferentlatticerotations.Inordertocomplywiththeincreasingstrainoftheneighbouringregions,MBsareformedatacertainpointbysplittingtheDDWsintotwoormoreroughlyparallelwalls.IntheregionbetweenthesesplitDDWs,newsetsofslipsystemswouldoperate[43].

TheenlargedSD-IPFmap(Fig.3d)canprovideprooffortheformationmechanismofsuchMBsasdescribedabove.InFig.3e,besidesthehigh-anglemisorientationpresentacrosstheMBboundaries,therearealsocon-tinuousmisorientationspresentinsidethebands,develop-ingduetodislocationactivitywithinthebands.ThecontinuousrotationofthecrystallatticeacrosstheMBboundariestowardstheh112iorientation(see1-2-3inFig.3d)indicatespossiblytheoperationof{112}h111islipsystemstherein.AnotherindicationofplasticitywithintheMBsisprovidedbytheshearoffsetsinthelow-anglegrainboundaries(LAGB)(misorientation:3.5°)oftheoriginalmatrixcreatedbytheparallelsetofMBslyinginclinedfromthelowerlefttoupperrightinFig.3d(seetheredarrowsalongthereddottedline).Similarly,theMBsde-velopingfromtheupperlefttothelowerrightalsocreateshearoffsetsonthe?rstgenerationMBs(seebluearrowsinFig.3d).

Wefocusnextontheshearbandswhichstarttoformate*1anddeveloptremendouslywithinthemedium-straincoldworkingregime(e&1.5–4).Thedensityofshearbandsislowat60%CS(1–2pergrain)andtheymostlyformclosetothegrainboundaries(Fig.5c).Inthiscase,itisobservedthatmostoftheshearbandsstarttoforminthevicinityofthehigh-anglegrainboundaries(HAGB)wheredislocationplasticitycouldnotfullyaccommodatethestrainlocalization[45].Inaddition,giventhesimilarityinthemorphology,andevolutionofdefectdensities,itcanbeproposedthatsomeoftheshearbandsobservedat90%CSstatedevelopfromtheMBsobservedinthe30%CSstate.At90%CS,boththeirdensityandsize(averagewidth4lm)haveincreasedwhencomparedtothatatthe60%CSstate(seeFig.5dvs.c).Whatisworthtoem-phasizearethe?negrains(\\5lm)withintheshearbands(Fig.4c,e).Itiswellknownthatsubmicron-sizedornano-sizedcrystalscouldeasilyformwithintheshearbands

123

JMaterSci(2015)50:5694–5708

[17].However,themicron-andsubmicron-sizedgrainsshowninFig.4c,emarkthe?rsttimethatsuch?negrainsareobservedexperimentallyingummetal.TheHAGBs,indicatedbythemisorientationpro?lesinFig.4d,revealthepresenceofrecrystallizationintheshearbands[46].ThemuchlargeraveragesizeofshearbandsintheCScase(4lm)thanintheCRcase(700nm)isprobablyrelatedtotheshearstrainateachswagingpass.Atthesametime,temperatureincrease(*300°C,[47])duringswagingcouldpromotethemicronandsubmicroncrystalformationwithintheshearbands.

Insummary,medium-straincoldworkingrendersthehomogeneousmicrostructureofthismetastableb-Tialloyseverelyheterogeneousatmultiplescales,i.e.bygrainsubdivision,MBandshearbandformationandevenre-crystallizationwithintheshearbands[46].Coldwork-induceddamageresistance

Consideringtheknownlowductilityofb-typeTialloys[48],gummetalcanbesurprisinglycoldworkedto90%withoutintermediateannealing.Thisobservationalreadyimpliesitsexcellentcoldworkability.Thetensilebe-haviourofthe90%CSgummetalrevealsinadditionanumberofparticularlyinterestingfeatures.AsshowninFig.7a,thestrengthof*1.2GPaisachievedwith*9%totalelongation,althoughmostisinthepost-neckingregime.Theextendedpost-neckingductility2isoftenob-servedinthenanostructuredalloys,whichmainlydeformbygrainboundary-dominatedmechanisms[50,51],andattributedtostrongstrainratesensitivity[51].Giventhegrainre?nementduetodevelopmentofdeformationbands(seeFigs.4and9),andtheobserveddouble-strainlocal-ization3phenomenon(Fig.8c2),strainratesensitivityisplausiblyplayingaroleforthedeformationofthecold-workedgummetal.However,themainfocuspointofthisstudyisthesecondpositivecontributionthatarisesfromthecoldwork-inducedformationofalaminatedandtex-turedmicrostructurewithmicronandsubmicroncrystalzones.AsobservedinFigs.8d2,d3,10and11,micro-cracksaslargeas*100lminsizecouldbebluntedsuchthattheircoalescencetoformmacro-crackscouldbede-layed.EmployingBSEandEBSD,twotypesofmechan-ismsareobservedatthecracktips,whichareinvolvedwiththeseprocesses:Fig.11b1,b2showthepieslice-like

2Itisnottheresultoftheartefactofsmallgaugegeometrybecause(i)thestrainwasmeasuredusingDIC;(ii)thegaugelengthtothicknessratio(4)wasfollowingtheASTMstandard;(iii)decreasingthegaugelengthto4mmwasreportedtohaveminorin?uenceonthemechanicalpropertiesofthematerial[49].3Theincreaseinstrainratesensitivitymaydelaythestrainlocalization,transforminglocalizedneckingtodiffuseneckingorcausingdoublenecking[39].

JMaterSci(2015)50:5694–57085705

Table1Three(110)-oriented(withrespecttoswagingdirection)latticesareshownasexamplestogetherwithstereographicprojectionsandprimaryslipsystemsOrientation(00-1)[110]

Lattice

Stereographicprojection

Primaryslipsystems(01-1)[-1-1-1](-10-1)[11-1](0-1-1)[11-1](10-1)[-1-1-1](-1-1-2)[11-1](11-2)[-1-1-1]

Schmidfactor0.4080.4080.4080.4080.4710.471

Angle45°45°45°45°90°90°

(-1-1-1)[110](01-1)[-1-1-1](-10-1)[11-1](0-1-1)[11-1](10-1)[-1-1-1](-1-1-2)[11-1](11-2)[-1-1-1]

0.4080.4080.4080.4080.4710.471

30°30°60°60°40°40°

(1-10)[110](01-1)[-1-1-1](-10-1)[11-1](0-1-1)[11-1](10-1)[-1-1-1](-1-1-2)[11-1](11-2)[-1-1-1]

0.4080.4080.4080.4080.4710.471

35°35°35°35°35°35°

TheSchmidfactorswithtensilestressalong[110]directionandtheangleofslipplanetraces(greenorreddottedlinesfor{110}or{112}planesonthestereographicprojections)withrespecttoSDoftheseprimaryslipsystemsarealsoshown

deformationzonemarkedbywhitedashedlines,whichsuggestslocalizedhardeningtoblunttheuppertipofcrack3(typeA).Figure11c1,c2showthelowertipofcrack2,whichisblunted(asinthefracturesurfaceexampleofFig.10c)uponintersectingthekinkedgrain-re?nedzonemarkedbywhitedashedlines(typeB).Owingtothe*31%shearbandedareafractioninthe90%CSmi-crostructure,itcanbeproposedthatthecrackshave*30%chanceofbeingtypeB.Next,wediscussthesetwomechanismsindetail.

Dislocationemissionfromthecracktipandfromthenearcracktipsourcesiscriticalforlocalizedhardeningandcracktipbroadening.Theeffectivenessofthisprocessisenhancedwhentherearetwoslipsystemssymmetricallyplacedatthetwosidesoftheadvancingcrack.Whenah110i?bretexturedbccmetaldeformsunderuniaxialtensileloadalongh110idirection,eachoneofits{110}h111iand{112}h111islipsystemshasitscorre-spondingtransversedirectionsymmetricalslipsystems,anditproducessliptracessimilartothoseinFig.8d1,d2.

Thiscanbeshownbythreelattices(Table1)frombcclatticesrotatingaroundthe[110]orientationat90°.4Forthesethreelattices,stereographicprojections,primaryslipsystems(andtheirrespectiveSchmidfactors)andtheangleoftheslipplanetraces(i.e.greenorreddottedlinesfor{110}or{112}planesonthestereographicprojections)withrespecttoSDarealsoshown.TheseSchmidfactorsrevealanequalshearstresstoactivatethetransversedi-rectionsymmetricalpairof{110}h111ior{112}h111islipsystems.Thetwosymmetricalslipsystemsatthetwosidesofthecracktipwouldpreventthestresstobeconcentrated,whicheffectivelybroadenthecrackanddelayitspropagation.Thecaseofcrack3(Fig.11b)correspondstothe(1-10)[110]-orientedlatticeinTable1.Atthecracktip,dislocationsliptracesareclearlyobservedinFig.11b1,b24Basedonthecrystallographicsymmetryofthebcclattice,allotherh110i-?bretexturedlatticeseithercorrespondtooneofthesethreestatesortheyareonthewayofrotating(aroundtheirtexturedh110idirection)towardsoneofthem.

123

5706(markedbywhitedottedlines),incliningat35°withre-specttotensiledirectionandcorrespondingtoboth{110}and{112}slipplanetraces.Thecrackbluntingshouldbeinitiallyaccomplishedbydislocationemissionon{112}h111islipsystems,sincetheSchmidfactorsshowninTable1revealhighervaluesforapairofprimary{112}h111islipsystemsthanfortheprimary{110}h111islipsystems.Thistypeofcrack-arrestingmechanismwasalsoreportedexperimentallyinbccsinglecrystal[52]andtheoreticallybymoleculardynamicssimulation[53].Be-sidesturningtothemaximumsheardirection(45°toten-siledirection),theincliningdirectionsofthecracksarealsoin?uencedbythe?rstlyactivatedslipsystems,be-causeoftheorientationdeviationfromthetexturedh110iorientation(max.15°deducedfromthetexturecalcula-tion).Thekinkedcrack(arrow4)revealedinFig.11aisanexampleforthisin?uence.

ThebluntingmechanismisdifferentforcracktypeB(Fig.11c).Fractographyanalysisrevealssubmicrondim-ples(Fig.10c)indicatinginteractionofmicro-crackswithmicron-andsubmicron-sizedgrainscontainingshearbands.BSEandEBSDinvestigationsdemonstratethattheadvanceofthecracktypeBisindeedblunteduponimpingingthemicronandsubmicroncrystalzones,andthekinkingrevealstheslidingofmicronandsubmicrongrainboundaries.Thein?uenceofgrainsizeinthebelow-micronregimeoncrack-relatedpropertieswasalreadyreviewed[54].Numerousmodellingworkshavebeendoneonthecrackinteractionswithnanocrystals.TwoveryrecentlymodelledmechanismscanbeproposedforexplainingthephenomenonshowninFig.11c:cooperativegrainbound-aryslidinginconjunctionwithstress-drivengrainbound-arymigrationmechanismontheonehand[55,56]andaspecialrotationaldeformationmechanismontheotherhand[57,58].Thesetwomechanismswereproposedtoincreasethecriticalstressintensityfactorforcrackgrowthinnanocrystallinematerialsbyafactorofthree[55]or10–15%[58].

Conclusions

Wesystematicallyinvestigatedthecoldworking-inducedmicrostructuredevelopmentingummetalanditseffectsonthefollowinguniaxialtensiledeformation.Themainob-servationandresultsofthisstudyareasfollows:1.

Coldworking-inducedmicrostructuralprocesses(e.g.grainsubdivision,MBsandshearbandsformation,在…之内recrystallizationwithinshearbands)developami-crostructureingummetalthathasaheterogeneousnatureindifferentscales.BCCdislocationplasticitycanexplainthemainfeaturesofthedevelopmentofthismicrostructuralheterogeneity.

123

JMaterSci(2015)50:5694–5708

2.

Gummetal,whenexposedbothtoseverecoldrollingandswaging,exhibitsahighstrengthof*1.2GPaincombinationwith*9%overallductility.Theincreaseinpost-neckingductilityisnotonlyduetostrainratesensitivitybutalsoowingtothepresenceofcrackbluntingmechanisms,effectiveevenatseverepre-strainedstate.Thisenhanceddamageresistancearisesfromthedevelopedmicrostructuralheterogeneitymentionedabovewhichhaszonesofidealtextureandre?nedgrainsize,thatplaythemostcriticalroleinbluntingnucleatedcracks.

3.

Severeplasticdeformationprocessestypicallyaimforprovidinghomogeneousnanostructuredalloys.Theresultspresentedhererevealthatheterogeneityinseverelydeformedmicrostructureshasclearbene?tsindamageresistance.Inthisaspect,traditionalcoldworkingtechniquesstillhavethepotential,asshownhereinthecaseofgummetal.

AcknowledgementsFundingfromtheEuropeanResearchCouncilundertheEU’sseventhFrameworkProgram(FP7/2007-2013)/ERCgrantagreement290998‘‘SmartMet’’isalsogratefullyacknowl-edged.M.LaiexpresseshisgratitudetoChinaScholarshipCouncilforthescholarshipgrantedtosupportthiswork.TheauthorsthankDr.HaukeSpringerandDr.HanZhangforprovidingsupportonmaterialprocessingandeffectivediscussions.Con?ictofinterestTheauthorsdeclarethattheyhavenocon?ict

ofinterest.

References

1.SaitoT,FurutaT,HwangJH,KuramotoS,NishinoK,SuzukiN,ChenR,YamadaA,ItoK,SenoY,NonakaT,IkehataH,Na-gasakoN,IwamotoC,IkuharaY,SakumaT(2003)Multifunc-tionalalloysobtainedviaadislocation-freeplasticdeformationmechanism.Science300(5618):464–467.doi:10.1126/science.1081957

2.TallingRJ,DashwoodRJ,JacksonM,DyeD(2009)Onthemechanismofsuperelasticityingummetal.ActaMater57(4):1188–1198.doi:10.1016/j.actamat.2008.11.013

3.MorrisJW,HanlumyuangY,SherburneM,WitheyE,ChrzanDC,KuramotoS,HayashiY,HaraM(2010)Anomaloustrans-formation-induceddeformationinh110itexturedgummetal.ActaMater58(9):3271–3280.doi:10.1016/j.actamat.2010.02.0014.TaneM,AkitaS,NakanoT,HagiharaK,UmakoshiY,NiinomiM,MoriH,NakajimaH(2010)LowYoung’smodulusofTi–Nb–Ta–Zralloyscausedbysofteninginshearmodulic0andc(44)nearlowerlimitofbody-centeredcubicphasestability.ActaMater58(20):6790–6798.doi:10.1016/j.actamat.2010.09.007

5.TaneM,NakanoT,KuramotoS,HaraM,NiinomiM,TakesueN,YanoT,NakajimaH(2011)LowYoung’smodulusinTi–Nb–Ta–Zr–Oalloys:coldworkingandoxygeneffects.ActaMater59(18):6975–6988.doi:10.1016/j.actamat.2011.07.050

6.KuramotoS,FurutaT,HwangJH,NishinoK,SaitoT(2006)PlasticdeformationinamultifunctionalTi–Nb–Ta–Zr–Oalloy.MetallurgMaterTransA37A(3):657–662.doi:10.1007/s11661-006-0037-7

JMaterSci(2015)50:5694–5708

7.GutkinMY,IshizakiT,KuramotoS,Ovid’koIA(2006)Nan-odisturbancesindeformedgummetal.ActaMater54(9):2489–2499.doi:10.1016/j.actamat.2006.01

8.GutkinMY,IshizakiT,KuramotoS,Ovid’koIA,SkibaNV(2008)Giantfaultsindeformedgummetal.IntJPlast24(8):1333–1359.doi:10.1016/j.ijplas.2007.09.009

9.GuoW,QuadirMZ,MoriccaS,EddowsT,FerryM(2013)Microstructuralevolutionand?nalpropertiesofacold-swagedmultifunctionalTi–Nb–Ta–Zr–Oalloyproducedbyapowdermetallurgyroute.MaterSciEngA575:206–216.doi:10.1016/j.msea.2013.03.029

10.TaneM,NakanoT,KuramotoS,NiinomiM,TakesueN,

NakajimaH(2013)Omegatransformationincold-workedTi–Nb–Ta–Zr–Oalloyswithlowbody-centeredcubicphasestabilityanditscorrelationwiththeirelasticproperties.ActaMater61(1):139–150.doi:10.1016/j.actamat.2012.09.041

11.DannoA,WongCC,TongS,JarforsA,NishinoK,FurutaT

(2010)EffectofcoldseveredeformationbymultidirectionalforgingonelasticmodulusofmultifunctionalTi?25mol%(Ta,Nb,V)plus(Zr,Hr,O)alloy.MaterDes31:S61–S65.doi:10.1016/j.matdes.2009.11.007

12.PremkumarM,HimabinduVS,BanumathyS,BhattacharjeeA,

SinghAK(2012)Effectofmodeofdeformationbyrollingontextureevolutionandyieldlocusanisotropyinamultifunctionalbetatitaniumalloy.MaterSciEngA552:15–23.doi:10.1016/j.msea.2012.04.077

13.FurutaT,HaraM,HoritaZ,KuramotoS(2009)Severeplastic

deformationingummetalwithcompositionatthestructuralstabilitylimit.IntJMaterRes100(9):1217–1221.doi:10.3139/146.110184

14.FurutaT,KuramotoS,HwangJ,NishinoK,SaitoT(2005)Elastic

deformationbehaviorofmulti-functionalTi–Nb–Ta–Zr–Oalloys.MaterTrans46(12):3001–3007.doi:10.2320/matertrans.46.300115.BesseM,CastanyP,GloriantT(2011)Mechanismsofdefor-mationingummetalTNTZ-OandTNTZtitaniumalloys:acomparativestudyontheoxygenin?uence.ActaMater59(15):5982–5988.doi:10.1016/j.actamat.2011.06.006

16.CastanyP,BesseM,GloriantT(2011)Dislocationmobilityin

gummetalbeta-titaniumalloystudiedviainsitutransmissionelectronmicroscopy.PhysRevB84(2):020201.doi:10.1103/PhysRevB.84.020201

17.HumphreysFJ,HatherlyM(2004)Recrystallizationandrelated

annealingphenomena.Elsevier,Oxford

18.HughesDA,HansenN(1997)Highangleboundariesformedby

grainsubdivisionmechanisms.ActaMater45(9):3871–3886.doi:10.1016/s1359-6454(97)00027-x

19.WangYM,ChenMW,ShengHW,MaE(2002)Nanocrystalline

grainstructuresdevelopedincommercialpurityCubylow-temperaturecoldrolling.JMaterRes17(12):3004–3007.doi:10.1557/jmr.2002.0436

20.ValievR(2004)Nanostructuringofmetalsbysevereplastic

deformationforadvancedproperties.NatMater3(8):511–516.doi:10.1038/nmat1180

21.ValievRZ,IslamgalievRK,AlexandrovIV(2000)Bulknanos-tructuredmaterialsfromsevereplasticdeformation.ProgMaterSci45(2):103–189.doi:10.1016/s0079-6425(99)00007-9

22.YangY,WuSQ,LiGP,LiYL,LuYF,YangK,GeP(2010)

EvolutionofdeformationmechanismsofTi–22.4Nb–0.73Ta–2Zr–1.34Oalloyduringstraining.ActaMater58(7):2778–2787.doi:10.1016/j.actamat.2010.01.015

23.RaabeD,Lu

¨ckeK(1994)RollingandannealingtexturesofBCCmetals.In:BungeHJ(ed)Proceedingsofthe10thinternationalconferenceontexturesofmaterials,Pts1and2—Icotom-10,vol157.,MatersciforumTranstecPublicationsLtd,Zurich-Uetikon,pp597–610

5707

24.RaabeD(1995)Simulationofrollingtexturesofb.c.c.metals

consideringgraininteractionsandcrystallographicslipon{110},{112}and{123}planes.MaterSciEng,A197(1):31–37.doi:10.1016/0921-5093(94)09770-4

25.SanderB,RaabeD(2008)TextureinhomogeneityinaTi-Nb-basedbeta-titaniumalloyafterwarmrollingandrecrystallization.MaterSciEngA479(1–2):236–247.doi:10.1016/j.msea.2007.06.077

26.GiannuzziLA,StevieFA(eds)(2005)Introductiontofocusedion

beams:instrumentation,theory,techniquesandpractice.Springer,NewYork

27.RaabeD,OhsakiS,HonoK(2009)Mechanicalalloyingand

amorphizationinCu–Nb–Aginsitucompositewiresstudiedbytransmissionelectronmicroscopyandatomprobetomography.ActaMater57(17):5254–5263.doi:10.1016/j.actamat.2009.07.028

28.ZelinM(2002)Microstructureevolutioninpearliticsteelsduring

wiredrawing.ActaMater50(17):4431–4447.doi:10.1016/s1359-6454(02)00281-1

29.RotersF,EisenlohrP,HantcherliL,TjahjantoDD,BielerTR,

RaabeD(2010)Overviewofconstitutivelaws,kinematics,ho-mogenizationandmultiscalemethodsincrystalplasticity?nite-elementmodeling:theory,experiments,applications.ActaMater58(4):1152–1211.doi:10.1016/j.actamat.2009.10.058

30.RaabeD,ZhaoZ,ParkSJ,RotersF(2002)Theoryoforientation

gradientsinplasticallystrainedcrystals.ActaMater50(2):421–440.doi:10.1016/s1359-6454(01)00323-8

31.BanerjeeS,TewariR,DeyGK(2006)Omegaphasetransfor-mation—morphologiesandmechanisms.IntJMaterRes97(7):963–977

32.YangY,LiGP,ChengGM,LiYL,YangK(2009)Multiple

deformationmechanismsofTi–22.4Nb–0.73Ta–2.0Zr–1.34Oalloy.ApplPhysLett94(6):3.doi:10.1063/1.3078521

33.YanoT,MurakamiY,ShindoD,HayasakaY,KuramotoS

(2010)Transmissionelectronmicroscopystudiesonnanometer-sizedomegaphaseproducedingummetal.ScrMater63(5):536–539.doi:10.1016/j.scriptamat.2010.05.025

34.RaabeD,SanderB,Fria

′kM,MaD,NeugebauerJ(2007)Theory-guidedbottom-updesignofb-titaniumalloysasbiomaterialsbasedon?rstprinciplescalculations:theoryandexperiments.ActaMater55(13):4475–4487.doi:10.1016/j.actamat.2007.04.024

35.PlancherE,TasanCC,SandloebesS,RaabeD(2013)Ondis-locationinvolvementinTi–Nbgummetalplasticity.ScrMater68(10):805–808.doi:10.1016/j.scriptamat.2013.01.034

36.JinM,MinorAM,StachEA,MorrisJW(2004)Directobser-vationofdeformation-inducedgraingrowthduringthenanoin-dentationofultra?ne-grainedAlatroomtemperature.ActaMater52(18):5381–5387.doi:10.1016/j.actamat.2004.07.044

37.SoerWA,DeHossonJTM,MinorAM,MorrisJW,StachEA

(2004)EffectsofsoluteMgongrainboundaryanddislocationdynamicsduringnanoindentationofAl–Mgthin?lms.ActaMater52(20):5783–5790.doi:10.1016/j.actamat.2004.08.03238.ZhangF,BowerAF,MishraRK,BoyleKP(2009)Numerical

simulationsofneckingduringtensiledeformationofaluminumsinglecrystals.IntJPlast25(1):49–69.doi:10.1016/j.ijplas.2007.12.006

39.HutchinsonJW,NealeKW(1977)In?uenceofstrain-ratesen-sitivityonneckingunderuniaxialtension.ActaMetall25(8):839–846.doi:10.1016/0001-6160(77)90168-7

40.JoshiVA(2006)Titaniumalloys—anatlasofstructuresand

fracturefeatures.Taylor&FrancisGroup,BocaRaton

41.SandimHRZ,PadilhaAF,RandleV,BlumW(1999)Grain

subdivisionandrecrystallizationinoligocrystallinetantalumduringcoldswagingandsubsequentannealing.IntJRefractMetHardMater17(6):431–435.doi:10.1016/S0263-4368(99)00035-9

123

5708

42.Kuhlmann-WilsdorfD(1999)Overviewno.131—’’Regular’’

deformationbands(DBs)andtheLEDShypothesis.ActaMater47(6):1697–1712.doi:10.1016/s1359-6454(98)00413-3

43.BayB,HansenN,HughesDA,Kuhlmann-WilsdorfD(1992)

Overviewno.96evolutionoff.c.c.deformationstructuresinpolyslip.ActaMetallMater40(2):205–219.doi:10.1016/0956-7151(92)90296-Q

44.GottsteinG(2004)Physicalfoundationsofmaterialsscience.

Springer,Heidelberg

45.JiaN,RotersF,EisenlohrP,RaabeD,ZhaoX(2013)Simulation

ofshearbandinginheterophaseco-deformation:exampleofplanestraincompressedCu–AgandCu–Nbmetalmatrixcom-posites.ActaMater61(12):4591–4606.doi:10.1016/j.actamat.2013.04.029

46.LinsJFC,SandimHRZ,KestenbachH,RaabeD,VecchioKS

(2007)Amicrostructuralinvestigationofadiabaticshearbandsinaninterstitialfreesteel.MaterSciEngA457(1–2):205–218.doi:10.1016/j.msea.2006.12.019

47.HaoYL,ZhangZB,LiSJ,YangR(2012)Microstructureand

mechanicalbehaviorofaTi–24Nb–4Zr–8Snalloyprocessedbywarmswagingandwarmrolling.ActaMater60(5):2169–2177.doi:10.1016/j.actamat.2012.01.003

48.Lu

¨tjeringG,WilliamsJC(2007)Titanium,2ndedn.Springer,Heidelberg

49.ZhaoYH,GuoYZ,WeiQ,ToppingTD,DangelewiczAM,Zhu

YT,LangdonTG,LaverniaEJ(2009)In?uenceofspecimendimensionsandstrainmeasurementmethodsontensilestress-straincurves.MaterSciEngA525(1–2):68–77.doi:10.1016/j.msea.2009.06.031

123

JMaterSci(2015)50:5694–5708

50.ValievR(2002)Materialsscience—nanomaterialadvantage.

Nature419(6910):887–889.doi:10.1038/419887a

51.ValievRZ,AlexandrovIV,ZhuYT,LoweTC(2002)Paradoxof

strengthandductilityinmetalsprocessedbysevereplasticde-formation.JMaterRes17(1):5–8.doi:10.1557/jmr.2002.0002

52.Spielmannova

′A,LandaM,Machova′A,HausˇildP,LejcˇekP(2007)In?uenceofcrackorientationontheductile–brittlebe-haviorinFe–3wt%Sisinglecrystals.MaterCharact58(10):892–900.doi:10.1016/j.matchar.2006.09.001

53.Uhna

′kova′A,Machova′A,HoraP(2011)3Datomisticsimulationoffatiguebehaviorofaductilecrackinbcciron.IntJFatigue33(9):1182–1188.doi:10.1016/j.ijfatigue.2011.02.011

54.AntolovichSD,ArmstrongRW(2014)Plasticstrainlocalization

inmetals:originsandconsequences.ProgMaterSci59:1–160.doi:10.1016/j.pmatsci.2013.06.001

55.BobylevSV,MorozovNF,Ovid’koIA(2010)Cooperativegrain

boundaryslidingandmigrationprocessinnanocrystallinesolids.PhysRevLett105(5):4.doi:10.1103/PhysRevLett.105.05550456.LiJ,SohAK(2013)Tougheningofnanocrystallinematerials

throughshear-coupledmigrationofgrainboundaries.ScrMater69(4):283–286.doi:10.1016/j.scriptamat.2013.04.014

57.MorozovNF,Ovid’koIA,SheinermanAG,AifantisEC(2010)

Specialrotationaldeformationasatougheningmechanisminnanocrystallinesolids.JMechPhysSolids58(8):1088–1099.doi:10.1016/j.jmps.2010.04.003

58.LiuY,ZhouJ,ShenTD,HuiD(2011)Grainrotationdependent

fracturetoughnessofnanocrystallinematerials.MaterSciEngA528(25–26):7684–7687.doi:10.1016/j.msea.2011.06.035

本文来源：https://www.bwwdw.com/article/xc4h.html