Simulation and analysis of the migration mechanism of (sigma)5 tilt grain boundaries in an fcc metal

The atomistic mechanism by which grain boundaries migrate is important for understanding the relationship between their structures and dynamical properties. We perform a series of three-dimensional molecular dynamic simulations of the migration of (sigma)5 tilt grain boundaries of different inclinations in nickel. We identify the migration mechanism through frequent quenches and analysis of the atomic displacements, local and global excess volume, and stress. The migration mechanism has the following components: local volume fluctuations precede the displacements of 3-4 linear atomic clusters in the direction parallel to the tilt axis which, in turn, are followed by individual atomic hops that are primarily perpendicular to the boundary plane. Excess volume is key to both the volume fluctuations and the atomic hops perpendicular to the boundary plane. The linear, or string-like, atomic motion parallel to the tilt axis also gives rise to a strong anisotropy in the grain boundary selfdiffusivity.