The development of microstructures under cascade-damage conditions, in volumes which were far away from any major sink, was considered. It was noted that, in the mean-field theory, an homogeneous distribution of point defects and their clusters was a pre-imposed artificial constraint on the kinetic system. A resultant excessive recombination of vacancies and interstitials at a high density of accumulated point-defect clusters imposed a low rate of void growth. By progressing beyond the mean-field theory, and taking account of concentration fluctuations in both the point defects and their clusters, it was possible to relax the restriction of an homogeneous distribution. In the present case, a system was considered which did not have any pre-existing sinks (apart from void nuclei) and in which vacancies, interstitials and their clusters were continuously produced. By taking account of the mobility of small clusters and stochastic fluctuations in the point-defect fluxes, an ab initio kinetic theory could be formulated. It was shown that, due to stochastic fluctuations and to the positive feedback effect of the mobility of small clusters upon the interstitial concentration, the homogeneous interstitial distribution was unstable at temperatures above stage-V. This led to the formation of a spatially heterogeneous microstructure in pure metals at low irradiation doses. The characteristics of microstructural evolution and void swelling, as predicted by the theory, were found to be in good agreement with experimental results.

The Stability of Homogeneous Microstructure Development under Cascade-Damage Conditions. A.A.Semenov, C.H.Woo: Applied Physics A, 2001, 73[3], 371-85