A systematic microscopic approach to diffusion and diffusion-limited processes in Ni3Al was presented. These processes were identified as controlling the deformation of the material under specific circumstances. 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 agreement with available experiments was good. It was found that, at temperatures 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 setting in a temperatures below about 1300K. It was shown that the structure arose from the composition dependence of both the vacancy formation energy and the pre-exponential of the diffusivity. The mobility of an antiphase boundary perpendicular to its plane was also computed, and it was concluded that vacancy-assistance was very plausible. It was deduced that the kMC+Dimer method worked well for these problems above 700K, but less well below, due to the presence of short-range low-energy hops 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. Harris, C., Tedstrom, R., Daw, M.S., Mills, M.J.: Computational Materials Science, 2006, 37[4], 462-9