Low-amplitude constant plastic cyclic deformation of single crystals, oriented for [123] single slip, was carried out at room temperature in air. The plastic shear strain amplitude was 0.001. Observations of dislocation structure evolution in the early stages of fatigue, and investigations of the formation of persistent slip bands in the latter stages, were performed by using scanning electron microscopy electron channelling contrast techniques. By inspecting variations in the shape and distribution of matrix walls for various numbers of cycles, dislocation evolution during early cyclic deformation could be roughly divided into 2 stages. During the evolution process, primary edge dislocations on the primary slip planes and screw segments between matrix walls, could play a key role in the 2 successive stages. From observations of persistent slip band initiation and its morphology and dislocation structure, a possible mechanism for persistent slip band formation was deduced. It was suggested that, once the spacing between matrix walls and the width of the matrix walls reached critical values, collapse of a matrix wall which was caused by an imbalance of the forces exerted by screw segments could induce the collapse of an adjacent matrix wall. A persistent slip line was thereby formed. Along the persistent slip line, the neighbouring screw segments were strongly activated and finally led to the formation of the ladder structure of a persistent slip band.

The Early Stages of Fatigue and Evolution of Persistent Slip Bands in a Copper Single Crystal. S.X.Li, Y.Li, G.Y.Li, J.H.Yang, Z.G.Wang: Philosophical Magazine A, 2002, 82[5], 867-83