Displacement collision cascade damage in hcp metals

Abstract

This paper will briefly review our understanding of loop geometry and the factors that control vacancy loop formation in the hcp system. In particular, reference will be made to a study of heavy ion irradiated ruthenium, a high melting point hcp metal with c/a ratio similar to zirconium but with non of the associated sample preparation problems. In this study the vacancy loops formed as a result of cascade collapse were analysed using transmission electron microscopy (TEM) techniques, with emphasis on determining not only loop geometry but also the efficiency of the collapse process. The results from the ruthenium study have revealed that vacancy loops nucleate on both the prism and basal planes. This latter type of loop with large c component is not the predicted loop geometry and raises several key questions. The implications of these observations are therefore discussed and in particular the problem of irradiation growth in zirconium is considered.