Nucleation of surface pits by the condensation of vacancies

Abstract

Small surface pits were observed to form on electropolished (111) surfaces of aluminium single crystals during cooling from elevated temperatures. The formation of these pits was attributed to the condensation of vacancies from the supersaturation produced during cooling at the points of intersection of dislocations with the surface. A finite temperature drop, δT, which was a function of the holding temperature, T _h, was required to nucleate the pits. The principles of statistical mechanics when applied to vacancy clustering led to an equation which quantitatively predicted δT as a function of T _h. The temperature dependence of the nucleation phenomenon was experimentally measured and found to be consistent with the theoretical predictions. The experimental results led to a corrected value of 1·8 × 10⁻⁵ ergs/cm (0·3 ev/plane) for the average dislocation core energy per unit length in aluminium.