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It is well-known that the total dislocation density that evolves in irradiated metals is a strong function of irradiation temperature. The dislocation density comprises two components, however, and only one of these (Frank loops) retains it temperature dependence at high fluence. The network dislocation density approaches a saturation level which is relatively insensitive to starting microstructure, stress, irradiation temperature, displacement rate and helium level. The latter statement is supported in this paper by a review of published microstructural data. It is shown that the influence of surface proximity can obscure the independence of temperature and displacement rate however.
A model has been developed to explain the insensitivity to many variables of the saturation network dislocation density. This model does not assume random motion of dislocations by climb and glide but takes into account the correlated nature of dislocation components in a dense array. The model also explains how the rate of approach to saturation can be sensitive to displacement rate and temperature while the saturation level itself is not very dependent on these variables. It is predicted that the insensitivity of ρ*d to temperature will persist until thermal emission of vacancies from network dislocations becomes important. At higher displacement rates typical of charged particle simulation experiments, the temperature at which thermally-induced climb of dislocations becomes important is increased as both the point defect and microstructural densities undergo an upward shift with displacement rate.
Frank loops, dislocations, irradiated metals, charged particles, neutrons, displacement rate, temperature, stress
Fellow scientist, Westinghouse Hanford Company, Richland, WA
Professor, University of Wisconsin, Madison, WI