Defect accumulation in fcc and bcc metals and alloys under cascade damage conditions – Towards a generalisation of the production bias model

Abstract

In recent years, it has been shown that the problem of defect accumulation under cascade damage conditions can be properly addressed within the framework of production bias model (PBM) based on intracascade clustering of point defects, differences in the thermal stability of the resulting clusters and one-dimensional (1-D) diffusion of interstitial clusters. Within this framework, different aspects of defect accumulation such as the high swelling rate at low dislocation densities, enhanced swelling near grain boundaries, effects of grain size, irradiation dose and recoil energy on void swelling have been treated quantitatively. In the present work we have attempted to address the problem of differences in the defect accumulation behaviour between fcc and bcc metals under cascade damage conditions. In this analysis we have chosen copper and molybdenum to represent fcc and bcc metals, respectively. This choice was suggested by the fact (a) that a large amount of experimental information exists on these metals and (b) that the damage accumulation behaviour in copper can be fully accounted for in terms of the PBM. An analysis of the existing experimental observations in terms of the PBM raises the question about differences between the reaction kinetics of the one-dimensionally diffusing interstitial clusters with sinks in fcc and bcc metals. In the present paper, the impact of different frequencies of changes in the 1-D diffusion direction of such clusters on their reaction kinetics is discussed. The present considerations provide an appropriate framework for generalising the PBM in order to describe damage accumulation behaviour in metals and alloys in general, including the formation of void superlattices.