Comparative study of radiation damage accumulation in Cu and Fe

Bcc and fee metals exhibit significant differences in behavior when exposed to neutron or heavy ion irradiation. Transmission electron microscopy (TEM ) observations reveal that damage in the form of stacking fault tetrahedra (SFT) is visible in copper irradiated to very low doses, but that no damage is visible in iron irradiated to the same total dose. In order to understa nd and quantify this difference in behavior, we have simulated damage produ ction and accumulation in fee Cu and bcc Fe. We use 20 keV primary knock-on atoms (PKAs) at a homologous temperature of 0.25 of the melting point. The primary damage state was calculated using molecular dynamics (MD) with emp irical, embedded-atom interatomic potentials. Damage accumulation was model ed using a kinetic Monte Carlo (kMC) algorithm to follow the evolution of a ll defects produced in the cascades. The diffusivities and binding energies of defects are input data for this simulation and were either extracted fr om experiments, the literature, or calculated using MD. MD simulations reve al that vacancy clusters are produced within the cascade core in the case o f copper. In iron, most of the vacancies do not cluster during cooling of t he cascade core and are available for diffusion. In addition, self-intersti tial atom (SIA) clusters are produced in copper cascades but those observed in iron are smaller in number and size. The combined MD/kMC simulations re veal that the visible cluster densities obtained as a function of dose are at least one order of magnitude lower in Fe than in Cu. We compare the resu lts with experimental measurements of cluster density and find excellent ag reement between the simulations and experiments when small interstitial clu sters are considered to be mobile as suggested by recent MD simulations. (C ) 2000 Published by Elsevier Science B.V. All rights reserved.