Electron microscope observations on the dislocation arrangement in deformed copper single crystals in the stress-applied state

The dislocation arrangement in the stress-applied condition of copper single crystals deformed in tension at 78°K was pinned by irradiating with a dose of 1018 n/cm2 fast neutrons at 4·2°K or 20°K. Transmission electron microscope studies of the primary glide plane showed that significant differences exist between the dislocation arrangements in the stress-applied and in the stress-removed state of the crystals, indicating considerable dislocation rearrangement during unloading. In particular, dislocation groups and pile-ups consisting of 10–20 dislocations of the same sign were observed in stage II in the stress-applied state.