Evidence for a deformation-induced supersaturation of vacancies at grain boundaries was deduced from data on alloy samples which had been quenched, under load, from superplastic deformation temperatures. The excess vacancies coalesced into nm-sized cavities that were visible along most of the grain boundaries following deformation under conditions where grain boundary sliding predominated. Re-heating samples  in situ  in a transmission electron microscope showed that the nano-cavities first coalesced and coarsened, and then disappeared as the temperature increased. Localized changes in the Mg concentration also resulted from near-boundary vacancy motion.

J.S.Vetrano, E.P.Simonen, S.M.Brümmer: Materials Science Forum, 1997, 243-245, 493-8