The obstacles responsible for the hardening of neutron irradiated copper crystals

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Abstract
A critical analysis has been made of both the experimental evidence on the deformation characteristics of neutron irradiated copper crystals and the hardening models which have been proposed. It is shown that the observed behaviour is explicable only in terms of the presence in as-irradiated crystals of a spectrum of thermally activated obstacles with values of F max of μb 2 and greater. During annealing the obstacles with the smallest values of F max are removed first, resulting in the formation of a low temperature ‘athermal’region in the flow stress–temperature curve with deformation characteristics similar to those observed in crystals containing very hard second-phase particles. The conclusion of Koppenaal and Arsenault (1965) that only a single type of thermally activated obstacle exists in irradiated copper is shown to be incorrect. Fleischer's (1962 b) theory, as applied to irradiation hardening, is criticized.