Significant differences in defect accumulation behaviour between fcc and bcc crystals under cascade damage conditions

Various aspects of irradiation-induced damage production and accumulation in fcc and bcc metals and alloys are examined. Results on the evolution of defect morphology in individual cascades, the global evolution of planar (clusters/loops) and three-dimensional defect agglomerates (voids) and the temperature dependence of defect accumulation in the form of loops and voids in fcc and bcc metals are compiled and compared. The comparison demonstrates that the damage accumulation in the form of clusters/loops and voids and their dependence on irradiation temperature are dramatically different in fcc and bcc metals. These differences may arise because of significant differences in the number of surviving defects (in cascades) and intracascade clustering of vacancies and self-interstitial atoms (SIAs) that get established already during the thermal spike phase of cascades. The implications of these differences are discussed. It is suggested that theoretical treatments of the damage accumulation in fcc and bcc metals must explicitly include the details of intracascade clustering of vacancies and SIAs, for example, the ratio of clustered to non-clustered vacancies and SIAs.