SIGNIFICANT DIFFERENCES IN DEFECT ACCUMULATION BEHAVIOR BETWEEN FCC AND BCC CRYSTALS UNDER CASCADE DAMAGE CONDITIONS

Various aspects of irradiation-induced damage production and accumulat ion in fee and bcc metals and alloys are examined. Results on the evol ution of defect morphology in individual cascades, the global evolutio n 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 fee and bcc metals are compiled and compare d. The comparison demonstrates that the damage accumulation in the for m of clusters/loops and voids and their dependence on irradiation temp erature are dramatically different in fee and bcc metals. These differ ences may arise because of significant differences in the number of su rviving defects (in cascades) and intracascade clustering of vacancies and self-interstitial atoms (SIAs) that get established already durin g the thermal spike phase of cascades. The implications of these diffe rences are discussed. It is suggested that theoretical treatments of t he damage accumulation in fee and bcc metals must explicitly include t he details of intracascade clustering of vacancies and SIAs, for examp le, the ratio of clustered to non-clustered vacancies and SIAs.