Etch pit studies of dislocation arrangements resulting from the deformation of single crystals of copper 7.5 at.% aluminium alloys

Abstract

Single crystals of copper 7.5 at.% aluminium alloys, oriented for single slip, have been deformed in tension at room temperature. Narrow bands of deformation are introduced. The densities and distributions of dislocations within the bands have been determined by the etching method. Primary dislocations of opposite sign are generated at opposite surfaces and migrate across the crystals in near-edge orientations on adjacent clusters of glide planes. This provides the first clear example of a moving forest of edge dislocations of the type envisaged by Taylor in 1934. A fraction of these dislocations are retained within the crystals in the form of extended sequences of pile-ups. Forest dislocations, generated by the activation of internal sources, are revealed by etching sections parallel to the primary planes. They occur within thin disc-shaped volumes with irregular contours. All the secondary systems may be activated within these volumes and the resulting distributions introduce effective obstacles to the further propagation of primary dislocations. The yield stress is the stress required for the activation of surface sources. The activation of internal sources requires the superposition of internal stresses, due to dislocation configurations, on the resolved component of the applied stress.