Electron microscopy studies of point defect clusters in metals

Abstract

Transmission electron microscopy (TEM) has been widely used to study point defect clusters in metals following quenching and irradiation. As a result of this work considerable progress has been made in our understanding of the nucleation, morphology, and growth of clusters and this paper reviews the current state of this understanding. The cubic metals (fcc and bcc) have been studied most widely. Cluster geometry, and how it is affected by a wide range of variables such as the temperature at which clustering occurs has been well characterized. Detailed quantitative studies have been made of cluster nucleation and growth kinetics and a self-consistent picture has been developed of the physical processes involved which describes the behaviour of quenched-in and radiation - induced defects. It has been shown that fundamental differences exist between fcc and bcc metals particularly with regard to the formation of vacancy clusters. In contrast, comparatively little work has been carried out on hcp metals and a clear picture has not yet emerged of the factors influencing cluster geometry. The results indicate that considerable differences exist between one metal and another within the general class of hexagonal metals. Moreover, virtually no quantitative results have been reported on the nucleation and growth of clusters in hcp metals.