Phase transformations in Ti-Zr-Ni compositions by mechanical alloying and annealing

Formation of quasicrystalline phase in Ti45Zr38Ni17 and Ti41.5Zr41.5Ni17 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 Ti2Ni-type phase with fcc structure. Increase of temperature up to 525 degrees C resulted in formation of bcc crystalline approximant of quasicrystalline phase Ti11Zr10N4. Differential scanning calorimetry (DSC) showed extended exothermal effect starting from 300 degrees 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.