DEFECT ACCUMULATION IN PURE FCC METALS IN THE TRANSIENT REGIME - A REVIEW

Over the years, a considerable amount of experimental results have been reported on defect accumulation in low-dose neutron irradiated pure fcc metals. In an effort to further the understanding of the processes involved in the defect accumulation in the transient regime, the experimental results are compiled and the salient features of these results are pointed out. Experimental results in pure aluminium, copper and nickel are chosen for this review. The dose dependence of the experimentally measured parameters makes it abundantly clear that the rate of build-up of cluster density, cavity density and the void swelling reaches a maximum at very low doses (less-than-or-equal-to 0.1 dpa). There is no experimental evidence for the formation of a well defined dislocation network during irradiation of pure metals at temperatures in the void swelling regime up to a dose level of approximately 1 dpa. The experimental results allow us to identify three significant aspects of the defect accumulation behaviour under cascade damage conditions: (a) evolution of cavity microstructure in a spatially heterogeneous and segregated fashion, (b) high swelling rates at very low doses when the dislocation density is negligibly low and (c) enhanced vacancy accumulation in the vicinity of grain or subgrain boundaries. It is pointed out that these features cannot be rationalized in terms of conventional mean-field approach using chemical rate equations and dislocation bias as the only driving force. These features can be explained, however, by taking into considerations the specific nature of the cascade damage, namely, the intracascade recombination and clustering of interstitials and vacancies during the cooling down phase of a multidisplacement cascade.