·34· 第41卷第1期2013年1月 硅酸盐学报 硅酸盐学报 JOURNALOFTHECHINESECERAMICSOCIETY 2013年 Vol.41，No.1January，2013 原位反应法制备Cr2AlC-Fe复合材料 陈新华，翟洪祥，王文娟，黄振莺 (北京交通大学，北京100044) 摘要：采用原位反应法制备了Cr2AlC-Fe系复合材料，并采用热分析、X射线衍射、扫描电子显微镜和三点弯曲实验，研究了原位反应的烧结工艺对产物和显微结构的影响，以及对原料中Cr2AlC的含量对复合材料性能的影响。
结果表明：通过高温原位反应，原料中Cr2AlC发生了分解，形成了网络状陶瓷增强结构，所制备的复合材料具有较好的强度和韧性，且随着Cr2AlC含量的增加，复合材料的强度也在增加，但断裂韧性逐渐下降。
当Cr2AlC的体积分数达到30%时，复合材料的抗弯强度达1417MPa。
关键词：复合材料；原位反应；烧结；弯曲行为中图分类号：TB333文献标志码：A文章编号：0454–5648(2013)01–网络出版时间：网络出版地址： FabricationofCr2AlCFe-basedCompositesbyin-situReactionMethod CHENXinhua，ZHAIHongxiang，WANGWenjuan，HUANGZhenying(CenterofMaterialsScienceandEngineering,SchoolofMechanicalandElectronicControlEngineering, BeijingJiaotongUniversity,Beijing100044) Abstract:Aposite,whichcouldhavepotentialapplicationsinnuclearenergyindustryasengineeringmaterials,wassynthesizedbyanin-situreactionmethod.Thein-situreactionsbetweenCr2AlCandFeatdifferenttemperaturesandratioswereanalyzedbythermogravimetricanalysis-differentialthermalanalysis,X-raydiffractionandscanningelectronmicroscopy,respectively.TheeffectofsCr2AlCcontentonthebendingbehaviorswasinvestigated.TheresultsshowthatCr2AlCcanin-situreactwithFe,andposetoformchromiumcarbide.Thepositeexhibitsahigherflexuralstrengthandagreaterfracturetoughnessatroomtemperature. Keywords:posites;insitureaction;sintering;bendingbehaviors 1Introduction Combinewiththeuniquedesirablepropertiesofasinglemetalorceramicmaterialandoffsettingeachother'sdeficiencies,positescanbeusedastheengineeringmaterialsforextremeenvironmentofnuclearenergyindustry,miningindustry,chemicalandmetallurgicalindustryandsoon.[1–3]ThereinforcingceramicparticulatesincludeAl2O3,TiC,Si3N4,WC,etc..[4–8]Althoughthosetraditionalceramicreinforcementsownhighstrength,theyhavelowfracturetoughness,poorwetting,inconsistencyoflinearexpansioncoefficientwithiron,andarehardtobemachinedbyusingnormaltools. Recently,Cr2AlCandpositeshaveattractedincreasingattention,[9–13]whichbelongtoanew 收稿日期：2012–04–23。
修订日期：2012–09–25。
基金项目：国家“863”项目(2006AA03Z527)。
第一作者：陈新华(1983—)，男，博士研究生。
typeofternarystructuresadvanceceramicssocalledMAXphase.Comparedwithtraditionalceramicreinforcingagents,thesekindsofceramicspossessuniquecrystallaminatedstructureasgraphite.IntheCr2AlCcrystalstructure,theCratomsandCatomsformmonedgesCr6CtetrahedronwithstrongionicbondareseparatedbyAlatomicplanes,[14]andthelinkbetweenAlatomicplanesandCr6CtetrahedronareweakCr–Almetallicbond.[15–16]ThisstructureleadtheCr2AlCbinationalpropertiesofbothmetalsandceramics,suchaslowdensity,highmodulus,easymachinability,goodelectricalandthermalconductivity,excellentthermalshockandhigh-temperatureoxidationresistance,butalsocanreactwithFebythetechniqueofinsitureactionmethod,[17–19]whichisaprocesswhere Receiveddate:2012–04–23.Reviseddate:2012–09–25.Firstauthor:CHENXinhua(1983–),male,Ph.D.,Candidate.E-mail:07116311@ 第41卷第1期 陈新华等：原位反应法制备Cr2AlC-Fe复合材料 ·35· reinforcementsaresynthesizedinmetallicmatrixbychemicalreactions,andensuredtheintroductionofchemicalbondingforceintheinterfaceofthereinforcementsandthemetalmatrix,andthehighperformancebondingwillmaketheexternalappliedstresstransferredfromthematrixtothereinforcements.Zhangetal.[20]nosedoutthatthereactionbetweenCuandTi3AlC2formTiCxandCu(Al)above950℃.Ourpreviouswork[21–24]showsthattheincorporationofTi3SiC2orTi3AlC2withCuincreasethestrengthandmodulusaswellaswearresistancewithoutthelossofconductivityandmeettherequirementsofapplicationsinelectricalslidingcontactsinhigh-speedrailway.Infact,similarreactionsalsoexistbetweentheCr2AlCwithFematrix. Hence,thispaperintendstoreportonprocessingandpropertyofFe-basedMetalMatrixComposites(MMCs)usingtheCr2AlC,whichisatypememberoftheMAXphaseceramics,asprecursorintherawmaterial.Byusingthisin-situreactionmethod,theCr2AlCceramicparticlesmightposetofinechromiumcarbidereinforcingagents.Differentfromthetraditionaldirectsynthesismethods,thismethodhasseveraladvantages,suchasthebetterlinkbetweenthereinforcingagentswiththematrix,andtheeasierdistributedevenlyofthereinforcingagents,andsoon. 2Experimental Reducedironpowders(purity99.5%,size<74μm,BeijingChemicalReagentCompany)andCr2AlCpowders(purity>97%,averagesize5.197μm,thedetailscanbefoundelsewhere[10])aremixedfor10hinplasticcanstoensurehomogeneousreactantmixtures.TheCr2AlCparticlepowderssizemeasurementwasperformedonlaserdiffractionparticlesizeanalyzer(Mastersizer2000,Malvern,Britain).Then,themixedpowderswerehotpressed(HP)at1300℃under30MPafor30mininflowingargongas.Theflexuralstrengthofpositeswastestedbythree-pointbendingmethodbyGB/T6569–1986,andthefracturetoughnesswastestedbysingleedgenotchedandthree-pointbendingmethod(SENB).Thefinalsampleswerecutintoblockswithdimensionsof3mm×4mm×36mmforbendingtests,of4mm×6mm×36mmforSENBtests,thebothtestswereperformedonauniversaltestingmachine(ZWICK,Z005)ataloadingspeedof0.5mm/min.ordingtothestandardforceanddisplacementfromtheuniversaltestingmachine,thebendingstrengthandfracturetoughnessofpositesarecalculatedfromfollowingequationsrespectively: R=3FL
(1) tr2bh2 K=3FL×a(1.93−3.07a+ IC2bh2h
(2) 14.53a2−25.07a3+25.80a4) h2 h3 h4 whereRtrandKICaretheflexuralstrengthandfracturetoughnessofpositesrespectively,Fistheforcerequiredtothefracture,Listhedistancebetweenthefulcrums,bandharethewidthandthicknessofthesamplesrespectively,aisthecracklengthofposites,hereis2.8mm. Afterthebendingtests,thespecimenswereanalyzedbyascanningelectronmicroscopy(SEM)(JSM–6460). 3Resultsanddiscussion Figure1showstheTG–DTAcurveof30%Cr2AlC/70%FesystemandtheDTAcurvesofpureFe.IntheTG–DTAcurveof30%Cr2AlC/70%Fesystem,therearenoobviouschangesintheweightduringthereactionbetweenCr2AlCandFe,whichindicatesthatthereisnoobviouschangeintheweightduringthereactionbetweenCr2AlCandFe.IntheDTAcurve30%Cr2AlC/70%Fesystem,twoendothermicpeakssat763.5℃and914.5℃canbeobserved.Fortheendothermicpeaks,paretotheDTAcurvesofpureFe,onecannoticethatalmostsameendothermicpeaksat770.21and915.24℃areobservedintheDTAcurvesofFe.Hence,itcanbeconcludedthattwoendothermicpeaksat763.1℃and913℃areprobablyascribedtothephasetransitionofFe.Indeed,ordingtotheFe–Alphasediagrams,[25]itcanbeseentheictransitiontemperature(Tc)ofFeat770℃andthetransformationofα-Fetoγ-Feat912℃areingoodagreementwithourresultshere.Above914.5℃,theendothermicreactionispredominantandtherewasnonewobviouspeak.ThedifferentphasecopositionsatdifferenttemperaturesweremadecertainbytheanalyzingofXRD. Fig.1TG–DTAcurvesfor30%Cr2AlC/70%FeandDTAcurvesforpureFepowderinargonatmosphere Figure2showstheXRDpatternsofsamplesof30%Cr2AlC/70%positessinteringatthetemperaturesfrom1000℃to1400℃under30MPafor30min.Theresultsshowthat,whenthesinteringtemperatureisbetween1000to1300℃,thepeaksfromCr2AlCdisap- ·36· 硅酸盐学报 2013年 Fig.2 XRDpatternsofCr2AlCpowdersandsamplesof 30%Cr2AlC/70%positessinteredat1000to1400℃ pearedandthemainphaseswerestabilityof(Cr,Fe)7C3andFe(Al).Asthesinteringtemperaturecontinuedriseto1400℃,theintensityofthediffractionpeaksfromFe(Al)wasgrowingsubstantially,andgreatcontractiondeformationhasemergedinthesamplesaftersinteringat1400℃,thisphenomenonindicatingthattheceramicsegregationhadurredatthishightemperature.Sothetemperaturefrom1000to1300℃istheappropriatesinteringtemperaturerange. Figure3showstheXRDpatternsofsamplesofCr2AlC-FemixtureswithdifferentCr2AlCcontentsaftersinteredat1300℃under30MPafor30min.WhentheCr2AlCcontentsinthemixturesbelow30%,nonewphasescanbedetectedbesidesFe(Al)and(Cr,Fe)7C3.AstheCr2AlCcontentsincreasingto50%,thediffractionpeaksfromCr7C3becamehigher.Themainreasonofthereactionscanbecontributedtothein-situreactionbetweenCr2AlCandFe.Thisin-situreactioncanbedescribedasthis:Athighsinteringtemperature,AlatomscanstripfromCr2AlCduetotheweakCr–AlmetallicbondinCr2AlC,anddissolveinthemetalmatrix,formingCr7C3grainsandFe(Al)solidsolution.Atthesametime,FewillthroughintotheceramicsparticlesbytheAlvacancies.WhentheCr2AlCcontentsincreasingto50%,theliquidFeareinsufficientandresultsinsomeCr7C3phaseremaining.Thereactioncanbedescribedasfollowing: Cr2AlC+Fe→Cr7C3+Fe(Al)
(1) Cr7C3+Fe→(Cr,Fe)7C3
(2) Figure4showsthemicrostructureofsamplesof30% Fig.3 XRDpatternsofsamplesofCr2AlC-FemixtureswithdifferentCr2AlCcontentsaftersinteredat1300℃for 30min Fig.4Microstructureofsamplesof30%Cr2AlC/70%Fesinteredat1300℃under30MPafor30min Cr2AlC/70%Fesinteredat1300℃under30MPafor30min.Chooseanotableceramicsareainabulk30%Cr2·AlC/70%posites’polishedsurface,anditsSEM 第41卷第1期 陈新华等：原位反应法制备Cr2AlC-Fe复合材料 ·37· imageshowsasFig.4(a).Inposites,theceramicparticulatesareuniformlydistributedinthematrix,andtheceramicparticulateswithshapesofneedle,spindle,andflake.Figure4(b)isarepresentativeSEMimageofthebulk30%Cr2AlC/70%Feposites’polishedsurfacewhichwasetchedinnital.Thistypicalmicrographexhibitsthatpositeswithpacttexture,andtheceramicparticulatesareuniformlydistributedintheFematrixwiththeaveragethicknesssizeof1.3μm,formahardcontinuousskeleton.ThisstructurecanbecontributetothemicrostructureiceffectsfromthesuperimposedshapeoftheplateletmicrocrystallineCr2AlCintheofCr2AlCpolycrystallinegrains. Thesampleof30%Cr2AlC/70%Fesinteredat1300℃for30mininargonatmosphere,anditsflatwell-polishedsurfaceanalyzedbyEDSareshowninFig.5.ItclearlyshowsthattheCr2AlCparticlesalmostturnedintoCr7C3.WecanalsoobservethatFehaddiffusedintotheCr2AlCparticles,Al,CrandCcanbedetectedintheFematrix. Fig.6 Relationshipbetweentheflexuralstrength,fracture toughnessandthevolumecontentofCr2AlCforCr2AlC-positessinteredat1300℃for30min alsomuchstrongerthanthestrengthsofCr2AlCbulk(whichflexuralstrengthsisabout378MPa).Thisphenomenoncanbecontributedtothehardcontinuousskeletonmicrostructureandstronginterfacebondingbetweenthereinforceparticulatesandthemetalmatrixinposites. Figure7showsthetypicalbendingsitespecimenphotographof30%Cr2AlC/70%Fesamplesinteredat1300℃for30minafterthebendingtests.Alotofslipbandsareformedinthematrixatabout45°withrespecttodrawaxis.Thisresultindicatesthattheinterfacialbondbetweentheceramicreinforcementsandmetalmatrixarestrong.Afterinsitureaction,thechemicalbondisformedintheinterfacebetweenthechromiumcarbideparticulatesandmatrix.Duringdeformation,theceramicparticlesnotonlycanresistthepassingdislocations,butalsocaninducedragforcetothegrainboundariesofthematrix.Asaresult,theexternalappliedstresswillbetransferredfromthematrixtochromiumcarbideparticulates,andundoubtedly,theloadbearingcapacityofpositeswith Fig.5EDXofsamplesof30%Cr2AlC/70%Fesinteredat1300℃under30MPafor30min Figure6showstherelationshipbetweentheflexuralstrength,fracturetoughnessandthevolumecontentofCr2AlCforpositessinteredat1300℃for30min.Theflexuralstrengthofthesamplewasincreasedgreatly,butthefracturetoughnesswasdecreasedwhileraisingCr2AlCcontent.WhentheCr2AlCcontentwas50%inthestartingmaterials,theflexuralstrengthsof50%Cr2AlC/50%Fecanreach1417.05MPa,however,itsfracturetoughnessdropto18MPa·m1/2.AmostremarkablefeatureisthestrengthsofpositesnotonlymuchstrongerthanthestrengthsofpureFebulk,but Fig.7 Typicalbendingsitespecimenphotographof30%Cr2·AlC/70%Fesamplesinteredat1300℃for30minafter bendingtests ·38· 硅酸盐学报 2013年 moreceramicreinforcementwillbegreaterduringtheperiodofelasticdeformation. 4Conclusions ThechromiumcarbidereinforcesFe(Al)positescanbepreparedbyin-situreactionmethodusingCr2AlCpowdersasprecursor.Thein-situreactionbetweenCr2AlCandpletedabove1000℃,andtheproductsmainphaseskeepstableinthe1000–1300℃sinteringtemperaturerange.AstheCr2AlCcontentincreasing,theflexuralstrengthofthesampleisincreasedgreatly,butthetoughnessisdecreased. References: [1]ABENOJARJ,VELASCOF,TORRALBAJM,etal.Reinforcing316Lstainlesssteelwithintermetallicandcarbideparticles[J].MaterSciEngA-struct.2002,335(1–2):1–
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