Migration of Vacancies and the Formation of Surface Vacancy Pits

Abstract

The formation of vacancy pits on the surface of electropolished aluminum on heating and subsequent cooling has been observed by several workers. The observations indicate that the formation of pits is a nucleation and growth process, and a minimum temperature drop ΔT is required in order to observe the pits. In the present work, a new technique has been developed to study this phenomenon. From a consideration of nucleation and growth of the pits, a relationship has been derived between ΔT and T_h the holding temperature. The relationship shows that ΔT depends on T_h and p, the rate of cooling. ΔT and T_h have been measured experimentally and a value of E_m, the energy of migration of vacancies, has been evaluated on the basis of the relationship derived here. A value for E_m of 0.6 eV is obtained for pure aluminium, which is in good agreement with the previously determined values of E_m in aluminium by other methods.