Hardening of Irradiated Alloys due to the Simultaneous Formation of Vacancy and Interstitial Loops

Abstract

A model is presented for the simultaneous nucleation and growth of vacancy and interstitial loops in irradiated metals. The model is based on the homogeneous time-dependent rate theory. Conservation equations are developed for single defects as well as defect clusters. Defect-conservation equations include production by irradiation and thermal sources; and destruction by mutual recombination, migration to sinks as well as clustering into loops. Interstitial clustering is assumed to occur by diffusion of interstitial atoms. Vacancy loops, on the other hand, are assumed to form by an athermal cascade-collapse process. The density of such loops is determined as a result of the production of cascades and the finite loop lifetime. Cascade overlap and coalescence are also included in the model. The calculations are extended to the analysis of the radiation-induced changes in tensile properties due to formation of interstitial and vacancy loops. A simpe hardening model relates the microstructural calculations to predictions of changes in tensile strength. The results of this study show good agreement with hardening data for copper irradiated in RTNS-II at room temperature. The results also provide insight on differences in microstructural results observed in various experimental studies on copper. 7 figures.