Simulation of Bulk and Grain Boundary Diffusion in B2 NiAl

Abstract

Molecular dynamics simulations of the diffusion process in ordered B2 compounds at high temperature were performed using an embedded atom interatomic potential developed to fit NiAl properties. Diffusion in the bulk occurs through a variety of cyclic mechanisms that accomplish the motion of the vacancy through nearest neighbor jumps restoring order to the alloy at the end of the cycle. The traditionally postulated six-jump cycle is only one of the various cycles observed and some of these are quite complex. Diffusion at the grain boundary mainly takes place through sequences of coordinated nearest neighbor jumps yielding to a rearrangement of the grain boundary structure. Two distinct mechanisms resulting in a structural unit migration of the vacancy are also identified. The results are analyzed in terms of the activation and configuration energies calculated using molecular statics simulations.