An EFTEM study of compositional variations in Mg–Ni–Nd bulk metallic glasses

AbstractArangeofMg–Ni–Ndbulkmetallicglasseshasbeencast.AroundthecompositionMg 65 Ni 20 Nd 15 (at.%),butnotatneighbouringcompositions,energy-filteredtransmissionelectronmicroscopyprovidesevidenceforstrongcomposi-tionalinhomogeneitiesintheas-castglass.Inthisfullyglassymaterial,anapparenttwo-phasecellularmicrostructureisseen;onephaseisrichinNi,theotherinMgandNd.Annealingatatemperaturejustabovetheglasstransition,orevenholdingatroomtemperatureforseveralmonthscaneliminatetheinhomogeneities.Thediffusivityvaluesderivedfromthehomogenizationkineticsareingoodagreementwiththoseknownforotherbulkmetallicglasses.Thepresentresultssuggesttheexistenceofaclosed-loopmiscibilitygapintheglass-formingliquid. 2003ElsevierScienceB.V.Allrightsreserved. PACS:81.05.Kf;81.40.Ef;66.30. h;64.75.þg 1.IntroductionThestabilityofbulkmetallicglasseshasfacili-tatedfundamentalstudiesoftheglassyandsu-percooled-liquid states. Phase separation hasreceivedsomeattentioninexplainingthenano-metrescaleofdevitrificationseenparticularlyinZr-basedbulkglasses[1].Inconventionaltrans-missionelectronmicroscopy(TEM),thecontrastfrom glassy thin foils has contributions fromvariationsinboththicknessandcomposition,andtheevidenceforphaseseparationcanbeambigu-ous.Inthepresentworkenergy-filtered(EF)TEMisusedtoprovideclearevidenceforcompositionalvariationsinMg-basedbulkglassesinwhichphaseseparationhasnotsofarseenmuchattention.Theinhomogeneitiesinas-castglassescanbeannealedoutbothneartheglasstransitionandatroomtemperature;thenatureofthemiscibilitygapisconsidered.2.ExperimentalmethodsTheAlloyAMg