VOID SWELLING AND SPATIAL HETEROGENEITY IN MICROSTRUCTURE EVOLUTION IN PURE METALS AT VERY-LOW IRRADIATION DOSES

The effect of stochastic fluctuations in the point-defect concentrations on the microstructure development in a fully annealed metal at low irradiation doses is investigated. It is found that the appearance of an order structure consists of segregated vacancy-rich and interstitial-rich regions may be understood as a noise-induced transition. This occurs through the nonlinear coupling between the microstructure evolution at low dose and the fluctuations in the point-defect concentrations resulting from the random nature of cascade initiation and the point-defect migratory jumps. Unlike in the conventional mean field rate theory where concentrations of point defects are taken to be homogeneous, the appearance of an ordered structure in the form of vacancy-rich and interstitial-rich regions does not require the actual long-range transport of point defects in the present investigation. The swelling rate in the void growth regions and the sizes of these regions are calculated and found to be in agreement with experimental results.