It was recalled that radiation-induced microstructural and compositional changes were governed by interactions between the material and the fraction of defects that escaped their nascent cascades. A combination of molecular dynamics and kinetic Monte Carlo simulations was used to calculate the damage production efficiency and the fraction of freely migrating defects in the a-phase at 600K. The molecular dynamics simulations provided information on the nature of the primary damage state as a function of recoil energy, and on the kinetics and energetics of point defects and small defect clusters. The kinetic Monte Carlo simulations used the molecular dynamics results as input and provided a description of defect diffusion and interaction over long times and length scales. The Johnson-Oh analytical embedded-atom potential was used for the molecular dynamics simulations, and included a modification of the short-range repulsive interaction. Molecular dynamics were used to calculate the diffusivities of point defects and small defect clusters and the binding energy of small vacancy and interstitial clusters. It was shown that, at temperatures below about 600K, small interstitial clusters formed prismatic dislocation loops which migrated in one dimension with an activation energy of 0.1eV. The results of molecular dynamics simulations of displacement cascades at energies of up to 20keV were also presented. The results showed that, for recoil energies above 5keV, interstitials were very likely to be produced in the form of small prismatic loops, but vacancies were not. The molecular dynamics results were then combined with a kinetic Monte Carlo simulation of defect interaction and diffusion, which included the 1-dimensional glide of small interstitial loops. The results provided a clear picture of damage-annealing and showed that, for 20keV cascades, the escape probability for both vacancies and interstitials was about 65%. This resulted in a freely migrating defect production efficiency of 20% of the total defect production which was predicted by the modified Kinchin-Pease model. The capability of the hybrid molecular dynamics and kinetic Monte Carlo method for carrying out long distance and long-term simulations of damage evolution in irradiated materials was emphasized.

Defect Production, Annealing Kinetics and Damage Evolution in a-Fe: an Atomic-Scale Computer Simulation. N.Soneda, T.Diaz de la Rubia: Philosophical Magazine A, 1998, 78[5], 995-1019