In order to determine the mechanism of grain boundary sliding, stress-change tests were carried out on various types of high-angle grain boundary by using controlled-orientation bicrystals. Tests were performed at 773K, using grain boundary shear stresses of between 0.3 and 0.7MPa. Grain boundary hardening was always observed. It was found that stress changes caused marked alterations in the grain boundary sliding rate. The extent to which sliding was accelerated by the stress increments depended upon the sliding rate which existed just before the stress change, and upon the grain boundary type. After stress reduction, the sliding rates became extremely low. Re-loading after a stress reduction caused a grain boundary sliding that was faster than that which existed immediately before the stress reduction. It was concluded that grain boundary hardening during sliding had the nature of a recovery process. Overall, the results suggested that the elementary process of grain boundary sliding was the motion of dislocations in the grain boundaries.

H.Fukutomi, K.Nonomura, Y.Takada, T.Yamamoto: Materials Science Forum, 1997, 233-234, 399-404