Phase Transformations in Ti-Zr-Ni Compositions by Mechanical Alloying and Annealing

摘要

Formation of quasicrystalline phase in Ti_(45)Zr_(38)Ni_(17) and Ti_(41.5)Zr_(41.5)Ni_(17) systems both directly by mechanical alloying (MA) and after subsequent annealing was studied. Presence of icosahedral quasicrystalline phase together with initial metallic components was found in as-milled samples. Further MA processing resulted in almost complete amorphisation of the samples. Low temperature annealing of MA samples brought to increase of quasicrystalline phase content; beside the quasicrystalline phase the powders contained a Ti_2Ni-type phase with fcc structure. Increase of temperature up to 525°C resulted in formation of bcc crystalline approximant of quasicrystalline phase Ti_(11)Zr_(10)Ni_4. Differential scanning calorimetry (DSC) showed extended exothermal effect starting from 300°C, which corresponds to crystallization of the powders. Specific area measurements of the as-milled samples showed rather small specific surface (0.16-0.42 m~2/g), which well agrees with the results of SEM study.