The effect of a surface oxide film on the lifetime of vacancies in quenched specimens

Abstract

Previous workers have found that, on heating thin foils made from quenched samples of a dilute aluminium alloy in the electron microscope, vacancy loops can grow at temperatures as high as 385°c. It is demonstrated that this cannot be due, as was supposed, to the release of vacancies from vacancy-solute aggregates. It is suggested that the enhanced vacancy lifetime within the foils is a consequence of an impervious oxide film which prevents the escape of vacancies at the surfaces of the foils. A similar explanation was used to account for the present authors' observations of the growth of vacancy loops in foils prepared from quenched specimens of pure magnesium and zinc. The implications of this oxide film effect are discussed in relation to other physical processes, in particular to the low temperature ageing of dilute aluminium alloys.