The primary damage state in fcc, bcc and hcp metals as seen in molecular dynamics simulations

Recent progress in the use of molecular dynamics (MD) to investigate the primary state of damage due to displacement cascades in metals is reviewed, with particular emphasis on the influence of crystal structure. Topics considered include the effect on defect formation in pure metals and alloys of primary knock-on atom (PKA) energy and irradiation temperature. An earlier empirical relationship between the production efficiency of Frenkel pairs and cascade energy is seen to have wide validity, and the reduction in efficiency with increasing irradiation temperature is small. Crystal structure has little effect on the defect number. In terms of the development of models to describe the evolution of radiation damage and its role in irradiation-induced changes in material properties, the important parameters are not only the total number of Frenkel defects per cascade but also the distribution of their population in clusters and the form and mobility of these clusters. Self-interstitial atoms form clusters in the cascade process in all metals, and the extent of this clustering does appear to vary from metal to metal. Vacancy clustering is also variable. The mobility of all clusters depends on their dislocation character and thus on the crystal structure and stacking fault energy. It is shown that computer simulation can provide detailed information on the properties of these defects.