原位合成碳化钛增强铝合金复合材料
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JournalofMaterialsProcessingTechnology171(2006)
411–416
Insitureactedtitaniumcarbide-reinforcedaluminumalloyscomposite
R.F.Shyua,∗,C.T.HobaDepartmentofMechanicalManufacturingEngineering,EducationandTrainingDivisionofComputerCenter,NationalFormosaUniversity,1Sec.3,ChungHsiaoE.Road,Taipei106,TaiwanbDepartmentofMechanicalDesignEngineering,NationalFormosaUniversity,Yunlin632,TaiwanReceived6October2001;receivedinrevisedform23June2004;accepted17August2004
AbstractAnaluminummatrixcontainingtitaniumcarbideparticleswasfabricatedbyinsituprocessinwhichacarbonaceousgasreactswithtitaniuminaliquidmelttoformTiC.Thetensileandyieldstrengthincreasedbyupto18%aftertheformationofTiCintheAlalloymatrix.Thehardnessincreasedbyupto20%.TheabrasiveandslidingwearresistanceincreasedwiththeinsituformationofTiCparticles.©2005ElsevierB.V.Allrightsreserved.Keywords:Insituprocess;Titaniumcarbide;Aluminumalloys;Composite
1.Introduction
Leaded-tinbronzeshavebeenusedinmanytribologicalapplications,includingplainbearings,and,evennow,theyareamongtheuniversallyacceptedmaterialsforsuchapplica-tions.However,thehighdensityofbronzes,associatedwithproblemssuchashealthhazardscausedbythetoxicproper-tiesofleadeffectiveduringmeltingandtheuseofthecostlyandscarceelementtinhasledtothesearchingforalternativematerialsforpossibleapplications.Inmanytribologicalapplications,aluminumalloysaredesirablebecauseoftheirlowdensities,buttheyarenotusedbecauseoftheirextremelypoorwearresistance.Thereforethedevelopmentofaluminummatrixcompositesisreceiv-ingconsiderableemphasisinmeetingtherequirementsofvariousindustries.Inpreviouswork,itwasshownthattheincorporationofbothhardceramicparticles(e.g.alumina[1–3],siliconcarbide[4–6],silica[7]orzircon[8,9])andasoftsolidlubricant(e.g.graphite[10–12]ormica[13])intoanaluminumalloyincreasedthewearresistance.
∗Correspondingauthor.Tel.:+88656315059;fax:+88656315310.E-mailaddress:rfshyu@nfu.edu.tw(R.F.Shyu).Considerableprogresshasbeenmadeintheapplicationofparticle-reinforcedmetals,mostnotablyforenginecompo-nents.Aluminaparticle-reinforcedaluminumalloypistonsperformedwell.Poweroutputincreasedwitharemarkablylowwearrateofthecompositepiston[14].TheuseofanAl–Si–graphiteparticlecompositepistonresultedina9%reductioninthefrictionalhorsepowerlossesoftheengineandupto3%reductioninthespecificfuelconsumption[10].AnAl–Si–graphitepistoncylin-derusedinaFerrariFormulaOneworldchampionshipwinningengineprovidedincreasedandconsistentoutputandreducedfuelconsumption[15,16].Particle-reinforcedmetalsaresopromisingthatmetal–matrixcompositesmaybegraduallyreplacingmostunreinforcedmetals[17].Transitionmetalcarbides(groupsIV–VI)arecommer-ciallyimportantbecauseoftheirextremehardness.ThesecarbidesarethebasisforcementedcarbidetoolsandwearresistantpartswherealloyswithlargevolumefractionsofWCandTiCareutilized.Theirexcellenthigh-temperaturestrengthandgoodcorrosionresistancemakesthemusefulashigh-temperaturestructuralmaterials.Muchbinarycarbidehasmicrohardnessvaluesbetween2000and3000kg/mm2
0924-0136/$–seefrontmatter©2005ElsevierB.V.Allrightsreserved.doi:10.1016/j.jmatprotec.2004.08.034412R.F.Shyu,C.T.Ho/JournalofMaterialsProcessingTechnology171(2006)411–416andliebetweenAl2O3anddiamondintermsofhardnessandmodulus[18].Carbidesareincreasinglybeingusedinmetal–matrixcomposites(MMC)asareinforcingconstituent.Thesecar-bidesintheformofwhiskers,monofilaments,fiberandparticulatesarebeingdevelopedandcommercialized[19].AnotableexampleisthedieselenginepistondevelopedbyToyotausingafiberreinforcedaluminummatrixcomposite[19].Anotherrecentapplicationofcarbide-reinforcedMMCistheflightqualifiedproductionofa6061aluminummatrixreinforcedwith25vol.%ofSiCparticulate[3].ThepresentstudywillutilizeaninsituprocessinwhichacarbonaceousgasreactswithtitaniumintheliquidmelttoformTiC,Al–M(liquid)+C=MC(solid)+Al(liquid)[20].Fromaprocessingviewpoint,theadvantagesoftheinsituprocessvisconventionalpowdermetallurgyorcastingpartic-ulateapproachinclude:(i)asinglestep,cost-effectivereac-tionandcastingapproach;(ii)finerparticulates(0.1–2m)withamorehomogeneousdistribution;(iii)improvedwetta-bilitybetweentheparticulateandthematrixand(iv)elimina-tionofdeleteriousaluminumcarbideformation.Oneofthelimitationsofthecurrenttechniqueistherelativelyhightem-perature(1300–1600K)necessaryforprocessingthemate-rial.Asecondarylimitisthehighapparentviscosityofthemelt,whichprecludeshighpercentage’sfractionsoftherein-forcement[20].Inthispaper,thewearbehaviorofaninsituTiCparticle-reinforcedaluminumalloyisinvestigated,andcomparedwithaconventionallyusedcopper-basedbearingalloy.
2.Experimentalprocedure
Al–5.1Cu–6.2Tiwasusedasthematrixmaterial.Theinsitureactionwascarriedoutinavacuuminductionfurnace.MeltingofAl–5.1Cu–6.2Tiwasachievedundervacuumandsubsequentlythechamberwasback-filledwithpurifiedargongas,whichwasalsobethecarriergas.Uponreachingtheappropriateprocessingtemperature,thecarboncarryinggaswasintroducedintothemeltviaagasdiffusersystem.Thereactionwascarriedoutataconstanttemperature1400Kforanappropriatelengthoftimeof4htoensurecompletecon-versionoftitaniumcarbide.ThevolumefractionofTiCwasabout6%,whichwasdeterminedfromthetheoreticalden-sitiesofphases.Aftercompletionofreactionthemeltwassolidifiedinamouldcavityof6cmlengthand1.3cmwidthfortensiletestingsamplesoramouldcavityof14mmdiam-eterforweartestingsamples.ThemouldmaterialisSKD4.Afterpouringtheliquidsamplesintothemould,apressure,rangingfrom30to50MPawasappliedimmediatelythroughapistonatthetopofthemould.Thepressurewasmaintainedfor20min,thenthesampleswerecooledtoroomtemperature[20].Thecompositeswereexaminedbyopticalmicroscopyandscanningelectronmicroscopy(SEM)withlinkelectronenergydispersiveanalysis(EDX)afterpolishing.
