碳纤维复合材料英文文献

TEMstudyofcarbon®brereinforcedaluminiummatrixcomposites:in¯uenceofbrittlephasesandinterfaceonmechanicalpropertiesM.Lancin*,C.MarhicPhysiqueCristalline,InstitutdesMateÂriauxJeanRouxel,BP32229Nantescedex3,FranceReceived13May1999;receivedinrevisedform4November1999;accepted8November2000AbstractThemicrostructureofA357aluminiumalloy(7wt%Si+0.6wt%Mg)reinforcedby1D-M40Jcarbon®bresischaracterisedusingdi€erenttechniquesoftransmissionelectronmicroscopy(di€raction,HRTEM,EDX,EELS).ThemicrostructureofthehighmodulusPANbased®breandofthepyrolyticcarboncoating(Cp)isfullycharacterised.SiliconandMg2Sigrainswhichdeterminematrix-reinforcementadhesionareinvestigated.Onthebasisofthemicrostructuralfeatures,themechanicalpropertiesofthecompositesarediscussed.ThemechanicalbehaviourofcompositespreparedwithandwithoutCpinterphasescorrespondstoabrittlematrixreinforcedbybrittle®bres.InthecaseofthecompositewithoutCpinterphase,themostin¯uentparameteristhehighresistancetoslidingattheinterfacebetweensiliconand®breswhichleadstoastrong®bre-matrix``bonding''andthus,toaweakandbrittlematerial.TheinterfacialresistancetodecohesionandtoslidingislowerinthecompositewithCpinterphaseresultinginhigherstrengthandlimitedpullout.Thislowerinterfacialresistanceisduetothesuccessivemicroporousandlayeredmicro-structuresofthepyrolyticcarboncoating.#2000ElsevierScienceLtd.Allrightsreserved.Keywords:Alalloy;Al4C3;Carbon®bre;Composites;Electronmicroscopy;Interphase;Mechanicalproperties1.IntroductionCarbon®bresareusedtoincreasestrengthandsti€-nessofaluminiumalloyswhilekeepinglowweightandgoodthermalandelectricalconductivity.However,brittlephaseswhichformorprecipitateduringthepro-cessingmayhaveadeleteriousin¯uenceonthemechanicalpropertiesofthecomposites.1ÿ11Studiesarebeingperformedtoimprovetheprocessingandtoobtaintherequiredproperties.C/Alcompositespre-paredatONERA-Chatillonforaerospaceapplicationscontainahighvolumefractionof®bres(70%).12,13Inoneofthese,anA357aluminiumalloyisreinforcedwithhighmodulusM40Jcarbon®bres,sometimescoatedwithapyrolyticcarboninterphase(Cp).TheM40J/A357compositewithouttheCpinterphaseisbrittleandweak(700MPa).13TheM40J/Cp/A357compositewiththeCpinterphaseisstronger(1360MPa)butlesssothanexpectedfromthelawofmixturesand,moreover,itisratherbrittle(limitedpseudo-plasticdeformation,lowworkoffracture),despitesome®bredebonding.14Scanningelectronmicroscopy(SEM)didnotrevealanyreactionlayerineithertypeofcomposite.13Atransmissionelectronmicroscopy(TEM)studywasthusperformedtoreachafullknowledgeofthemicrostructuralfeaturesofthematerialsandabetterunderstandingoftheirmechanicalbehaviour.Themechanicaltestsandpropertiesarefullydescribedinapaperpreviouslypublished.14Inthispaper,themicrostuctureofthehighmoduluscarbon®breandofthecarboncoatingischaracterised.Theamountsandlocationsofthebrittlephases,alumi-niumcarbidesandsilicon,aredetermined.Interdi€u-sion,whichisknowntoin¯uencethefailureresistanceattheinterfaces,isalsostudied.Thediscussionofthemicrostructuralfeaturesrevealsimportantparametersandshowsthatthemechanicalbehaviourofthecompo-sitesdoesnotdependonthemetalmatrix.Modelsdevel-opedforceramic±ceramiccompositesaresuccessfullyusedtoanalysethemechanicalproperties.2.Materialsandexperimentalprocedure1D-compositeswerefabricatedwithA357alloy(alloyingelements:Si=7wt%,Mg=0.6wt%)andM40J®bres(r=4400MPa,E=377GPa)-byliquidmetalin®ltration(LMI),undermoderatepressure0955-2219/00/$-seefrontmatter#2000ElsevierScienceLtd.Allrightsreserved.PII:S0955-2219(00)00021-2JournaloftheEuropeanCeramicSociety20(2000)1493±1503*Correspondingauthornowat:TECSENLaboratory,case231,13397MarseilleCedex20,France.E-mailaddress:[e-mail](M.Lancin).(15MPa),during1min,at918K.13Twocompositeswereobtainedusingrespectivelybare®bresor®brescoatedbypyrolyticcarbon(Cp),bothcontainingahighvolumefractionof®bres(70%).Longitudinalandcrosssectionswerepreparedbymechanicalgrindingandionthinning.Duringgrindingandpolishing,thecohesionofthesampleswasmain-tainedbyusinganappropriateglueandaTiring(Bal-zers).Thesenecessaryprecautionsandtheoccurrenceofcrackssometimesobservedbetween®bresandmatrix(Fig.1a)revealtheweakadhesionbetween®bresandmatrixinbothcomposites.IonthinningiscarriedoutinaBalzersionthinnerusingalowbeamdensityandasampleholdercooledwithliquidnitrogen.Thecompositemicro-structureisnotmodi®edbysuchionthinningconditions.Phaseidenti®cationandlocalisationwereperformedbyelectrondi€ractionpatterns(EDP)andnanodi€raction,highresolutiontransmissionelectronmicroscopy(HRTEM),energydispersiveX-raysspectroscopy(EDX)andelectronenergylossspectroscopy(EELS).Experi-mentswerecarriedoutusinga®eldemissiongun(FEG)HF2000Hitachimicroscope(200KV,Scherzerresolu-tion=2.6AÊ)equippedwithaCCDcamera(MSCGatan),aSi-Lidetector(KevexSuperQuantek)andaPEELS(Gatan).Analyseswereperformedusingacoolingholder(Gatan),a4±10nmprobesizeanda12tiltangleforEDXspectroscopy.3.ResultsManymicrostructuralfeaturesaresharedbythetwocomposites.Wethusdescribethemandunderlinethedi€erenceswheretheyoccur.Fig.1.Microstructureofacross-sectionoftheM40J/A357composite.B