ThetransformationbehaviourofbulknanostructuredNiTialloys

摘要

ThephasetransformationbehaviourofbulknanostructuredNiTishapememoryalloys,producedbyaninnovativeapproachcalledMARES(mechanicallyactivatedreactiveextrusionsynthesis),wasinvestigatedusinginsitux-raydiffractionanddifferentialscanningcalorimetrymeasurements.Fortheexperimentalconditionsused,asuitableadjustmentoftheNiTimatrixcompositionwasachievedafterageingat500-Cfor7h.TheagedmaterialsshowedahomogeneousdispersionofNi4Ti3precipitatesembeddedinaB2-NiTimatrix.UnderthisconditiontheB2-NiTimatrixhasundergoneaB2-R-B19 two-stagephasetransformation.ThiswasattributedtothecomplexmicrostructuralevolutionduringMARESprocessing,i.e.formationoflarge-scaleandsmall-scaleheterogeneities.Transmissionelectronmicroscopyinvestigationsofthesolution-treatedmaterialsshowedtheexistenceofequiaxednanocrystalsinthenanocrystallineNiTimatrix.