DISLOCATION BEHAVIOR IN THE VICINITY OF GRAIN BOUNDARIES IN FCC METALS AND ALLOYS.

Abstract

Dislocation behavior has been investigated by in situ deformation with a 3 mv electron microscope in bicrystals of aluminum, copper and copper-aluminum alloys. The dislocations in a Cu-5 wt%Al alloy can move through the boundary with a misfit angle of 5 degree at places where the dislocations pile up two-dimensionally when the tensile axis is perpendicular to the tilt boundary. When the stacking fault energy and the misfit angle increase, the dislocations cannot move through the boundary. Three-dimensional pile-ups occur against the boundary in a crystal whose Schmid factor is large, when the tensile axis is perpendicular to the boundary. Many slip systems operate in the vicinity of the boundary and dislocation tangles are formed when the tensile axis is parallel to the boundary. Recrystallization occurs in regions near the boundary when the specimen is stretched along the boundary.