TEM INSITU DEFORMATION STUDY OF THE INTERACTION OF LATTICE DISLOCATIONS WITH GRAIN-BOUNDARIES IN METALS

The passage of dislocations across grain boundaries in metals has been studied by using the in situ TEM deformation technique. A detailed analysis of the interaction of glissile matrix dislocations with grain-boundary dislocations has been performed. The results show that the dislocations piled-up at the grain boundary can: (1) be transferred directly through the grain boundary into the adjoining grain; (2) be absorbed and transformed into extrinsic grain-boundary dislocations; (3) be accommodated in the grain boundary, followed by the emission from the grain boundary of a matrix dislocation; and (4) be ejected back into their original grain. To predict which slip system is favourable for slip transfer, three criteria have been considered, namely: (1) the angle between the lines of intersection of the incoming and outgoing slip planes with the grain boundary, this should be as small as possible; (2) the resolved shear stress acting on the possible slip systems in the adjoining grain, this should be large and (3) the magnitude of the Burgers vector of the extrinsic dislocations left at the grain boundary following emission of dislocations, this should be a minimum. The Burgers vector of the generated dislocation is dictated primarily by condition (3). © 1990 Taylor & Francis Group, LLC.