Computer simulation on the void formation in neutron-irradiated Cu and Ni at high temperature

Atomistic processes of evolution of damage structure in neutron-irradiated Cu and Ni at high temperature are investigated on the linkage of experimental results and computer-simulation. Interstitials and their clusters move to form a grouping of interstitial clusters which subsequently evolve to dislocation at high temperature. Vacancies aggregate to stacking fault tetrahedron (SFT) and void. At high temperature gas atoms do not make a significant contribution to the nucleation of voids at low fluence of neutron irradiation such as 10(18) n/cm(2). SFT relax at a high temperature to a string of vacancy clusters, in which vacancies are connected one-dimensionally. The break-up of SFT occurs by jumping of an atom into a SFT. A loosely bound vacancy cluster of a string shape moves with low activation energy of 0.2 eV. Voids are formed by the coalescence of moving vacancy clusters of string shape at high temperature. This is due to low Helmholtz free energy of void-containing crystal than that of SFT-containing crystal. The role of gas atoms in the formation of voids is to degrade the mobility of movable vacancy clusters when captured by the clusters. (C) 1999 Elsevier Science B.V. All rights reserved.