Abstract
Most experiments on neutron or heavy-ion cascade-produced irradiation of pure metals and metallic alloys demonstrate continuous unlimited void growth as well as development of the dislocation structure. In contrast, the theory of radiation damage predicts saturation of void swelling at sufficiently high irradiation doses and according termination of accumulation of interstitial-type defects. It is shown in the present paper that, in the conditions of steady production of one-dimensionally (1-D) mobile clusters of self-interstitial atoms (SIAs) in displacement cascades, three reasons can be behind these observations. First, if the fraction of SIAs generated in the clustered form is smaller than some finite value of the order of the dislocation bias factor. Second, if solute, impurity or transmuted atoms segregate to voids and repel the SIA clusters. Third, if spatial correlations between voids and other defects, such as second-phase precipitates and dislocations, establish that provide shadowing of voids from the SIA clusters. The driving force for the development of such correlations is the same as for the void lattice formation and is argued to be always present under cascade-damage conditions. It is emphasized that the mean-free path of 1-D migrating SIA clusters is typically at least an order of magnitude longer than the average distance between microstructural defects; hence spatial correlations on the same scale should be taken into consideration. A way of developing a predictive theory is discussed. An interpretation of the universal steady-state swelling rate of ~1%/dpa observed in austenitic steels is proposed for the first time.
