A systematic microscopic approach was made to diffusion and diffusion-limited processes in Ni3Al. These processes were identified as controlling the deformation of the material under specific circumstances. The embedded atom method calculations were performed using kinetic Monte Carlo combined with the Dimer method of finding saddle-points. The tracer diffusivities were computed as functions of composition and temperature. The comparison with available experiments was good. It was found that, at below about 1000K, the diffusivity was a sharp function of composition, showing a pronounced dip on the Ni-rich side at 76at%Ni. This agreed well with experiment, except that the experiments showed this structure appearing below about 1300K. It was shown that the structure arose from the composition dependence of both the vacancy formation energy and pre-exponential of the diffusivity. The mobility of an antiphase boundary perpendicular to its plane was also compute and it was concluded that vacancy-assistance was very plausible. It was concluded that the kMC+Dimer method worked well for these problems above 700K but less effectively below, due to the presence of short-range low-energy hopping that tended to localize the vacancy and lower the efficiency of the calculation.

Calculations of Diffusion and Diffusion-Limited Processes in Ni3Al using Accelerated Molecular Dynamics. C.Harris, R.Tedstrom, M.S.Daw, M.J.Mills: Computational Materials Science, 2006, 37[4], 462-9