Grain boundary kinetics—I. In situ observations of coupled grain boundary dislocation motion, crystal translation and boundary displacement

Abstract

Extensive stress-induced climb-glide motion of secondary grain boundary dislocations (SGBDs) in nearΣ 5 grain boundaries in gold was directly observed and video recorded by means of hot-stage in situ transmission electron microscopy. The passage of appreciable numbers of SGBDs along the boundary ( N) caused a translation of the abutting crystals with respect to one another ( T) and a lateral displacement of the boundary with respect to each crystal ( D i ). Quantitative measurements of N, T, and D i , for a number of boundaries provided unambiguous evidence that these three processes were coupled. The observed T's and D i 's were in agreement with a geometrical model involving the N's, the Burgers vectors of the moving SGBDs, and the heights of the steps which the SGBDs were expected to produce in the boundary plane. Most of the SGBDs whose motion produced the measured translations and displacements were intrinsic in nature; a minor fraction appeared to be extrinsic. The deduced SGBD-step configurations tended to be those associated with the smaller step heights possible within the framework of the Σ5 CSL. Operating sources and sinks for moving SGBDs were directly observed in some of the boundaries.