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1、ARTICLESPUBLISHEDONLINE:7AUGUST2011
2、DOI:10.1038/NMAT3077Highlymonodispersecore–shellparticlescreatedbysolid-statereactionsV.Radmilovic1,2*1,E.A.Marquis3,M.D.Rossell1,4,A.Tolley1,5,A.Gautam1,M.Asta1,6,C.OphusandU.Dahmen1Thesizedistributionofparticles,whichisess
3、entialformanypropertiesofnanomaterials,isequallyimportantforthemechanicalbehaviouroftheclassofalloyswhosestrengthderivesfromadispersionofnanoscaleprecipitates.However,particlesizedistributionsformedbysolid-stateprecipitationaregenerallynotwellcontrolled.Herewe
4、demonstrate,throughtheexampleofcore–shellprecipitatesinAl–Sc–Lialloys,anapproachtoforminghighlymonodisperseparticlesizedistributionsbysimplesolid-statereactions.Theapproachinvolvestheuseofatwo-stepheattreatment,wherebythecoreformedathightemperatureprovidesatem
5、plateforgrowthoftheshellatlowertemperature.Ifthecoreisallowedtogrowtoasufficientsize,theshelldevelopsina‘sizefocusing’regime,wheresmallerparticlesgrowfasterthanlargerones.Theseresultssuggeststrategiesformanipulatingprecipitatesizedistributionsinsimilarsystemsth
6、roughsimplevariationsinthermaltreatments.incetheinventionofdispersion-hardenedAlalloysmorethanAtwo-stageageingtreatmentusedtoinducesolid-stateacenturyago1,theformationofsecond-phaseparticlesbyprecipitationleadstothedistributionofAl(Li;Sc)precipitates3Ssolid-st
7、ateprecipitationreactionshasbeenusedasama-illustratedinFig.1a.TheparticlesconsistofacoreoftheAl3Scjorstrengtheningmechanismforstructuralmaterials.Thestrongphase,whichformsduringahigh-temperatureannealingstep(18heffectsonmechanicalpropertiesarisingfromtheformat
8、ionofat450C),surroundedbyashellofAlLi,whichformsduring3second-phaseparticlesarewellknown,andexploitedinapplica-asubsequentlower-temperatureheattreatment(4hat190C).tionsrangingfromenergygenerationtoaerospacestructures2.ToFrommicrographssuchasthatshowninFig.1a
9、wemeasuredfullyoptimizethepropertiesofprecipitation-strengthenedalloysthesizedistributionsplottedinFig.1b.Themeancoreradius,requiresadetailedunderstandingofthefactorscontrollingpre
