Dislocations and persistent slip bands in fatigued copper

Persistent slip bands in fatigued OFHC copper single crystals have been examined using both replica and transmission electron microscopy techniques. In general, the dislocation structure below persistent slip bands is found to consist of rows of elongated cells within a region extending at least 170 microns below the specimen surface. It is suggested that there is a one-to-one correspondence between these cells and intrusions and extrusions observed on the persistent slip bands. The longer cell walls are nearly pure twist boundaries lying in the primary slip plane, indicating that slip occurs in at least two directions in the primary plane. The cell structure at persistent slip bands is stable at an annealing temperature which causes the matrix structure to disappear.