Molecular dynamics simulations of grain boundary migration in bicrystals had suggested that, in pure materials, grain boundary diffusion and grain boundary migration involved distinct mechanisms and hence different activation barriers. Here simulations were made of grain growth in an impurity-free model nanocrystalline palladium microstructure containing only high-energy grain boundaries. In contrast to the bicrystal simulations, virtually identical activation energies were observed for grain growth and grain boundary diffusion. Several mechanisms were considered that might be responsible for this difference between the bicrystal and polycrystal results, including accommodation of the curvature-driven grain boundary migration by the elimination of grain boundary area and grain boundary excess free volume and a possible finite mobility of the triple junctions. The qualitative agreement of these observations with general experimental findings was remarkable given the absence of any impurities in the model system. This suggested that a fundamental intrinsic process might be responsible for the similar activation energies for grain boundary migration and grain boundary diffusion in polycrystals. In the model system this process seemed to involve accommodation of the curvature-driven grain boundary migration by grain boundary diffusion to eliminate the grain boundary area and related grain boundary free volume at the triple junctions.

Relation between Grain Growth and Grain-Boundary Diffusion in a Pure Material by Molecular Dynamics Simulations. Yamakov, V., Moldovan, D., Rastogi, K., Wolf, D.: Acta Materialia, 2006, 54[15], 4053-61