材料期刊网

Low-amplitude constant plastic cyclic deformation of copper single crystals oriented for single slip [(1) over bar 23] was carried out at room temperature in air. The plastic shear strain amplitude was 1 x 10(-3). The observation of dislocation structure evolution in the early stages of fatigue and the investigation of the formation of persistent slip bands (PSBs) in the latter stage were conducted using the scanning electron microscopy electron channelling contrast technique. Inspecting the variations in shape and distribution of matrix walls for different numbers of cycles, dislocation evolution in the early cyclic deformation was roughly divided into two stages. During the evolution process, the primary edge dislocations on the primary slip planes and the screw segments between matrix walls may play a key role in the two successive stages respectively. From the observation of PSB initiation and of its morphology and dislocation structure, a possible mechanism for PSB formation was proposed. It was suggested that, once the spacing between matrix walls and the width of the matrix walls reached critical values, the collapse of a matrix wall which was caused by the unbalance of the forces exerted by crew segments could induce collapse of an adjacent matrix wall. Therefore a persistent slip line (PSL) was formed consequently. Along the PSL, the neighbour screw segments would strongly activate and finally induce the formation of the ladder structure of a PSB.