Atomistic simulation of grain boundary diffusion mechanisms in B2 NiAl

We present the results of molecular dynamics simulations of grain boundary diffusion mechanisms in B2 NiAl. The studies use embedded atom method interatomic potentials to simulate the diffusion process along a special Σ=5 symmetrical tilt boundary in a direct manner, starting with vacancies located in different sites in the grain boundary region. The simulations show a variety of diffusion jumps, all introducing disorder in the grain boundary. This is in contrast to diffusion in bulk NiAl, where cyclic mechanisms, restore order. Several series of correlated jumps were identified in the grain boundary region. The most common of these result in the vacancy remaining in the same structural unit. The rate controlling jump sequences that result in vacancy migration to a neighboring structural unit were also observed and are reported in detail.