Effect-of-SI-Content-on-Microstructure-and-Mechani

2981068-1302/15/0506-02982015SpringerScience+BusinessMediaNewYorkPowderMetallurgyandMetalCeramics,Vol.54,Nos.5-6,September,2015(RussianOriginalVol.54,Nos.5-6,May-June,2015)REFRACTORYANDCERAMICMATERIALSEFFECTOFSICONTENTONMICROSTRUCTUREANDMECHANICALPROPERTIESOFTHESPRAY-FORMEDSiCP/Al–SiCOMPOSITESWeiLi,1,2,3YunfeiNing,1JianChen,1YouPingSun,2andCongLi1UDC669.782TheeffectofthesiliconcontentonthemicrostructureandmechanicalpropertiesoftheSiCp/(1–x)Al–xSi(x=7,13,and20wt.%)composites,producedbyspraydeposition,areinvestigated.TheaveragesizeoftheeutecticSiandprimarySiinthecompositecontaining20%Si(3.44and7.85m)ishigherthanthatinthecompositescontaining13%Si(2.51and5.85m)or7%Si(1.95and0m).WithincreasinginSicontent,compositesdemonstrateanincreaseinthevolumefractionoftheprimarySiandeutecticSiphases,andadecreaseintheaveragedistancebetweenSiandSi-phaseparticle.Duringtensiletests,theas-sprayedcompositewithahigherSicontentshowsanincreaseinelasticmodulus,yieldstrength,andultimatetensilestrength,butadecreaseinelongation.BothSiCparticle/matrixdebondingandSidecohesionareobservedinallthreecomposites,whiletheprimarySiparticlecrackingisdominantinthecompositescontaining13and20%Si.ThefracturerevealsanincreaseinbrittlenessandinthetendencyfortheprimarySiparticlestocrack,astheSicontentincreases.Keywords:composites,microstructure,spraydeposition;fracture.INTRODUCTIONDuetotheirlowweight,goodcorrosionresistance,andlowthermalexpansioncoefficient,theSiC-reinforcedAl–Sialloycompositeshaveawiderangeofuseinautomotiveandaerospaceindustries[1–2].However,conventionalingotmetallurgymethods,suchasstircasting,leadtocoarseprimarySiphaseandceramicparticleagglomeration,whichlimitthefurtherimprovementoftheproperties.Spraydeposition(anapproachthatcombinesrapidsolidificationandnear-net-shapefabrication)canbeaneffectivewaytoproducepreformsinasingle-stepoperationdirectlyfromamoltenalloy[3].1KeyLaboratoryofReliabilityControlofMechanicalManufacturingTechnolgySystem,EducationDepartmentofGuangxiProvince,GuangxiUniversityofScienceandTechnology,Liuzhou,Guangxi,China.2SchoolofEnergyandPowerEngineering,ChangshaUniversityofScience&Technology,Changsha,Hunan,China.3Towhomcorrespondenceshouldbeaddressed;e-mail:[e-mail]etallurgiya,Vol.54,Nos.5–6(503),pp.60–67,2015.OriginalarticlesubmittedDecember1,2014.DOI10.1007/s11106-015-9713-8299Theremaybeanumberofphasesinspray-formedSiC-reinforcedAl–Sialloycomposites:SiCparticles,-Al,primaryandeutecticsilicon,andinter-metallicconstituents(dependingonthealloycomposition).Siliconhasaprofoundeffectonthemicrostructure,mechanicalproperties,andwearresistanceofthesecomposites[4].Chenetal.[5]foundthatthewearresistance(andalsothehardness)ofspray-depositedAl–Si/SiCpcompositesincreasedwithincreasingthesiliconcontent.Theeffectofthesiliconcontentonthelong-crackfatiguebehaviorofaluminum–siliconpistonalloyswasinvestigatedbyMoffatetal.[6].TheyfoundthatthehighSicontentalloyhadworsefatigueresistanceathigherKlevels,butshowedsomeimprovement(overthelowerSicontentalloys)innear-thresholdcrack-growthbehavior.Inaword,theroleofSiiscomplex.Intheabsenceofpores,cracksinitiatedinSiparticlesfracturedorde-boundtheinterfacesoftheSiparticles[7].Siparticlesprovideasiteforinitiation,whichmeansthatSireducesthetimeforinitiationand,therefore,reducesthefatiguelife.However,theeffectoftheSicontentonthemicrostructureandmechanicalbehaviorofthecomposites,producedbyspraydeposition,wasnotevaluatedindetails.Therefore,weconductedasystematicinvestigationoftheSiCp/Al–SicompositeswithdifferentSicontentpreparedbyspraydeposition.TheinfluenceoftheSicontentonthemicrostructureandtensilebehaviorwasexamined.abcdefFig.1.Microstructuresofcomposites:aandb)SiCp/Al-7Si(hypoeutectic);candd)SiCp/Al-13Si(eutectic);eandf)SiCp/Al-20Si(hypereutectic)300EXPERIMENTALPROCEDURESamplesofAl–Sialloy(nominalcompositionAl–(7,13,20)Si–0.3Mg–0.01Mn–0.01Cu(wt.%),reinforcedwith15vol.%SiCparticles,werepreparedbymultilayerspraydepositiontechnology,whosedetailsarementionedin[12].TheaveragesizeofSiCparticleswas4.5m.ThecompositesamplespreparedfromtheAl–SialloyswiththreeSicontents(7,13,and20wt.%)aredenotedinthispaperasSiCp/Al–7Si,SiCp/Al–13Si,andSiCp/Al–20Si,respectively.Thesamplesof160mmindiameterand300–400mminheightweremachinedfromthecenterofthesprayedpiece.Theywerethensubjectedtohotextrusionina1250tonhorizontalextrusionpressat450C.Theingotswereextrudedintoa120mmwide,10mmthickplateatanextrusionratioof17.3:1.Opticalmicroscopywasusedtoanalyzethemicrostructureofthecomposite.TensiletestswerecarriedoutonanInstronMachine(Instronmodel8871);sampleshadagaugelengthof25mmanddiametersof5mm,correspondingtotheASTMstandard(E-8).Samplesweremachinedparalleltotheextrusionaxis.Alltestswerecarriedoutonaprecisionalignedservo-hydraulicloadframe,atambienttemperature,instraincontrolatstrainratesof10–4–(0.510–2)sec–1.Thefracturesurfaceswereexaminedbyscanningelectronmicroscopy(SEM).RESULTSANDDISCUSSIONMicrostructureCharacterization.Figure1showsopticalmicrographsofthecomposites.Despitesomeclusteringofthe