EFFECT OF PRESSURE ON GRAIN-BOUNDARY MIGRATION IN ALUMINUM BICRYSTALS

The temperature and pressure dependencies of [100], [110], and [111] t ilt grain boundaries in bicrystals of pure aluminum were measured, and the corresponding activation enthalpies and activation volumes were d etermined. While the activation enthalpy strongly depended on orientat ion. in particular close to low SIGMA coincidence orientation relation ships. the activation volume was found independent of orientation exce pt for [110] tilt boundaries. The absolute values of the activation vo lume for [100] and [111] tilt boundaries were about the same as for bu lk self-diffusion. which agrees with previous measurements on polycrys tals. The activation volume for migration of [110] tilt boundaries sub stantially exceeded the activation volume for bulk self-diffusion. It is concluded that at least [110] tilt boundaries migrate by a group me chanism rather than by diffusive jumps of single atoms.