The formation of high pressure precipitation phases during the implantation of inert gas and other insoluble atom species in metals

Abstract

Recent work on the precipitation of heavier inert gas atoms implanted into metals at ambient temperatures has demonstrated that the inert gas trapped within matrix cavities can be present in the solid phase. This result provides excellent evidence for these precipitates being under very high pressures, of the order of a few GPa. The present paper examines the cavity growth mechanisms relevant to the inert gas atom implants, where normally a very high concentration of precipitates is found and in particular compares the growth rate expected from bias-driven cavity swelling with that due to pressure-driven processes. This comparison shows that the latter will dominate up to temperatures at which thermal vacancies become available, even when displacement damage rates are high. The presence of the specimen surface is also considered. Although it can be an important sink in the near-surface regions for vacancies, self-interstitials and the mobile gas atoms, in normal circumstances it can be shown that this does not materially alter the above result. These conclusions fit the observations on the heavier inert gas atoms but in addition they should be applicable to other insoluble atoms implanted into metals. Provided precipitate densities are high, it is predicted that high pressure phases might often be found.