GRAIN-BOUNDARY STRUCTURE IN Al//2O//3.

The factors affecting the structure of grain boundaries in Al//2O//3 polycrystalline materials are discussed. Illustrations are presented on the basal twin ( SIGMA equals 3), the rhombohedral twin ( SIGMA equals 8), and two different SIGMA equals 13 grain boundaries. The CSL/O lattice models are helpful in understanding the predominant grain-boundary plane, but it is suggested that kinetic rather than energetic factors may cause other facets to lie parallel to densely packed planes in the oxygen sublattice rather than parallel to planes containing either a high density of coincident lattice sites or O points. The DSC lattice can be used to predict the allowed grain-boundary dislocation Burgers vectors. The structures of the boundaries examined are shown to influence segregation to, diffusion along, and migration of the boundary. (Edited author abstract. )