Modelling atomic scale radiation damage processes and effects in metals

Primary knock-on atoms (PKAs) that recoil under collision from energetic atomic particles such as neutrons or ions are the principal source of radiation damage effects in metals. At high enough recoil energy (greater than ∼ 1 keV), a PKA creates a cascade of atomic displacements, which are the origin of the self-interstitial and vacancy defects that give rise to property changes. The time and length scales of the cascade process are of picosecond and nanometre order, respectively, and are ideally suited to atomic scale computer simulations such as molecular dynamics. This method has been used extensively to investigate displacement cascades in metals. The paper reviews recent progress in this field. It includes results dealing with the effect of PKA energy on defect formation in various metals. It is shown that in addition to data on the number of defects produced, computer simulation can provide quantitative information on the distribution of defects created in clusters. This was not available from earlier models and so the nature of the primary damage state is now much clearer. Molecular dynamics is also being used to reveal the nature of the motion and interaction of defects and their clusters, and to simulate dislocation-obstacle interactions. This detailed atomic level information about the stability, motion, and interaction of defects will lead to the successful development of multiscale models to describe the evolution of radiation damage microstructure and its impact on material performance. The place of atomic scale modelling in the multiscale problem of radiation damage is discussed.