Diffusion Mechanisms in Grain Boundaries in Conventional and Nanostructured Materials

摘要

We present an overview of atomistic theory of grain boundary diffusion with emphasis on the recent progress in the understanding of diffusion mechanisms. The interaction of vacancies and interstitials with grain boundaries is more complex than it was thought earlier. Point defects can alter the local grain boundary structure, delocalize in it, or be mechanically unstable. Vacancies and interstitials are equally important in grain boundaries. They can move in the boundary core by single-atom jumps or by collective transitions involving several atoms. The calculated diffusion coefficients in Cu and Al grain boundaries reproduce many features observed experimentally, such as diffusion anisotropy and the correlation between grain boundary diffusion and grain boundary energy. It is proposed that internal stresses and especially their gradients that always exist in grain boundaries are responsible for the unusual behavior of point defects and for the multiplicity of diffusion mechanisms. The impact of these findings on the understanding of diffusion in nanocrystalline materials is discussed.