Etch Pit Studies of Dislocations in Copper Crystals Deformed by Bending: I. Annealed Crystals; II. Irradiated Crystals

Abstract

Annealed and irradiated copper crystals of low initial dislocation density were deformed by bending, and dislocation multiplication and motion were studied using an etch pit technique for observing the dislocations. For the annealed crystals there was dislocation motion and multiplication prior to macroscopic yielding, and the percentage of grown-in dislocations moved by the stress increased with the stress. The dislocations were hindered in the motion by subboundaries and by interaction with other dislocations. Relaxation effects were observed and were much greater for stresses less than the yield stress than for higher stresses. For the neutron-irradiated crystals there was no motion or multiplication of dislocations prior to yielding. The slip traces were long, with dislocations closely spaced in the trace. Although not conclusive, the evidence apparently was best interpreted in terms of source hardening. A cube-root dependance of the yield stress on neutron dose was observed. No hardening resulted from irradiation with 1018/cm2 cobalt γ rays.