Electron Microscope Studies of Irradiation Damage in Metals and Alloys

Abstract

Irradiation of crystalline solids with energetic particles results in the generation of lattice point defects and of transmutation products. At practically relevant temperature, i.e. > 20°C, a majority of the point defects are lost by recombination or migration to fixed sinks. However, a significant fraction may survive to aggregate into clusters and it is these surviving clustered point defects that form an evolving damage structure. Both the morphology of the clusters and their distribution are generally influenced by the presence of solute atoms and particularly important here are hydrogen and helium atoms generated by transmutation reactions during neutron irradiation. It is emphasised that the clustered point defects can cause large changes in physical and mechanical properties. Such changes can result in problems of considerable importance in nuclear (fission or fusion) reactor components. We shall discuss the contribution made by transmission electron microscopy (TEM) to the study of irradiation damage structures. As an introduction we shall summarise briefly the main factors involved in defect production and initial defect distributions during irradiation. This will be followed by a description of image contrast from point defect clusters observed in the electron microscope and the methods used to analyse the properties of such defects. Finally, we will highlight the principle results from electron microscope studies of irradiation damage in metals and alloys.