Atomic self-diffusion in TiNi

Abstract

The projector augmented wave method was applied to investigate the energetics of point defect formation at finite temperatures and the Ni-vacancy jumps in the intermetallic B2-TiNi alloy. It was shown that the effective formation energy of the Ni-vacancy (1.14 eV) is significantly lower than that of Ti-vacancy (1.74 eV); however, the antistructural atoms are dominant defects irrespective of alloy composition. The obtained results reveal that the migration barrier of the Ni-vacancy to the nearest-neighbor site is less (0.19 eV) than that for the Ni-vacancy jump to the next-nearest-neighbor site (1.64 eV). The Ni-vacancy implements two sequential nearest-neighbor jumps with short-lived intermediate configuration and some of such jumps initiate six-jump cycles of the Ni-vacancy along [0 0 1] and [1 1 0] directions with [0 0 1] bent mechanism as preferential one. In the latter case the calculated migration barrier of 0.82 eV is found to be in good agreement with experiment. The energy barrier for four-jump cycle flat mechanism is calculated by 0.27 eV higher. It is shown that the Ni-vacancy diffusion in B2-TiNi is strongly dominated by both six-jump cycle [0 0 1] bent and flat mechanisms at low temperatures but the contribution of the next-nearest-neighbor jumps become important with temperature increase.