Atomistics of helium bubble formation in a face-centered-cubic metal

Atomistic calculations of helium interstitial clustering in the absence of a vacancy and helium clustering about vacancies have been performed for up to ten helium atoms in up to four associated vacancies in copper. It is found that clusters of six helium atoms in a vacancy (He6 V) are bound by 0.86 eV relative to dissociation by loss of helium. Using this and other information, a system of 42 coupled, stiff, rate equations are solved to determine the kinetics of defect formation and migration under irradiation conditions. Complexes of from five to eight helium atoms in a vacancy are shown to form rapidly at room temperature. Monte Carlo calculations are presented to quantify the concept of interconnection of these defects as a function of the range of their interaction. The calculations suggest that helium-bubble formation may occur because of the fourth-neighbor site-percolation of Hen V complexes.