Cooperative phenomena at grain boundaries during superplastic flow

Abstract

In situ observations in a scanning electron microscope (SEM) performed on different microstructural scales in Pb—62%Sn specimens, superplastically deformed in single shear and in simple tension, showed sliding of grain groups [cooperative grain boundary sliding (CGBS)], rotation of grain groups (cooperative grain rotation) and cooperative grain boundary migration (correlated migration of sliding grain boundaries). The observed macroscopic pattern of the CGBS surfaces is consistent with predictions of slip-lines field theory. The progress of the sliding of grain blocks at the scale of grain groups can be modeled in terms of cellular dislocations. The micromechanism for such sliding and the migration of sliding grain boundaries at the scale of the individual interface might be interpreted from the viewpoint of grain boundary dislocations.