EFFECT OF PRESSURE ON GRAIN-BOUNDARY MIGRATION IN ALUMINUM BICRYSTALS

The temperature and pressure dependencies of [100], [110], and [111] tilt grain boundaries in bicrystals of pure aluminum were measured, and the corresponding activation enthalpies and activation volumes were determined. While the activation enthalpy strongly depended on orientation. in particular close to low SIGMA coincidence orientation relationships. the activation volume was found independent of orientation except for [110] tilt boundaries. The absolute values of the activation volume for [100] and [111] tilt boundaries were about the same as for bulk self-diffusion. which agrees with previous measurements on polycrystals. The activation volume for migration of [110] tilt boundaries substantially exceeded the activation volume for bulk self-diffusion. It is concluded that at least [110] tilt boundaries migrate by a group mechanism rather than by diffusive jumps of single atoms.