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1、MaterialsScienceandEngineeringA383(2004)1420EvolutionofmicrostructureinsprayformedAl18%SialloyV.C.Srivastavaa,∗,R.K.Mandalb,S.N.OjhabaMaterialsProcessingDivision,NationalMetallurgicalLaboratory,Jamshedpur831007,IndiabDepartmentofMetallurgicalEngineering,Ban
2、arasHinduUniversity,Varanasi221005,IndiaReceived27January2004AbstractSprayatomizationanddepositionprocesshasemergedasanalternativetoingotandpowdermetallurgyroutes.Inthepresentinvestigation,westudythemicrostructuralcontrolduringspraydepositionofhypereutectic
3、AlSialloy,employingdifferentnozzletosubstratedistances.Spraydepositioniscarriedoutusingconvergentdivergentclose-couplednozzledesignatdepositiondistancesof200,300,450,and550mm.Microstructuralcharacterizationofoversprayedpowdersaswellassprayformeddepositswasp
4、erformed.Microstructuralfeaturesobtainedatsmallerdepositiondistanceconsistofco-existingprimarySiphaseandneedlelikeeutecticSi.Dendritesof-Alphaseareobservedindicatingalargeundercoolingoftheliquidpoolpriortosolidification.Alargenumberofpre-solidifiedparticlesw
5、ithveryfinemicrostructure,embeddedinarelativelycoarseregion,typicallycharacterizethoseevolvedatlargedepositiondistances.However,atintermediatedepositiondistances,uniformandrefinedprimarySiphases,38msize,areobserved.Anundercoolingeffectismanifestedinboththesp
6、raydepositsaswellaspowderparticles.Thesemicrostructuralfeatureshavebeendiscussedinlightofaproposedmodel,whichdescribesthepresenceoftwolayers(1)solidificationlayerand(2)interactionlayerintheliquidpool.©2004ElsevierB.V.Allrightsreserved.Keywords:Spraydepositio
7、n;Microstructure;Phase;HypereutecticAlSi;Undercooling1.Introductionoftheconstituentphaseswithinherenthomogeneityofthemicrostructure[35].However,powderparticlesrequireAluminiumSiliconalloyspossesshighstrengthtoconsolidationbyhotextrusionorhotisostaticpressin
8、g.weightratio,lowthermalexpansioncoefficient,andhighConsequently,thenumberofprocessingstepsareincreased.wearresistance.ThesealloysalsoshowimprovedstrengthSomeoftheproblemsofRSProuteofmaterialsprocess-an
