Recent results of atomistic computer simulations of grain boundary diffusion in metals were analyzed. At temperatures well below the bulk melting point, Tm, grain boundary diffusion occurred by the random walk of individual vacancies and self-interstitials. Both defects were equal participants in the diffusion process and could move by a wide variety of mechanisms; many of which were collective transitions. Grain boundary diffusion coefficients could be computed using kinetic Monte Carlo simulations. At high temperatures, the presence of large concentrations of point defects was likely to alter the diffusion mechanisms. Molecular dynamics simulations of grain boundary structure and diffusion in Cu revealed a continuous grain boundary pre-melting in the close vicinity of Tm. However, diffusion in high-energy grain boundaries became almost independent of the grain boundary structure at temperatures well below Tm. This behavior could be tentatively explained in terms of heterophase fluctuations from the solid to the liquid phase. The exact diffusion mechanisms in the presence of heterophase fluctuations were not established.

Atomic Mechanisms of Grain Boundary Diffusion - Low versus High Temperatures. A.Suzuki, Y.Mishin: Journal of Materials Science, 2005, 40[12], 3155-61