A finite difference calculation of vacancy migration under non-steady state conditions

The hydrogenation of metals, often a rapid process, may lead to the production of high vacancy concentrations in the solid when equilibrium is reached. The achievement of equilibrium in this "upquenching" process depends, at least in part, upon the migration of vacancies from the surface into the interior of the solid. Because individual vacancy jump frequencies may depend on position within the vacancy density gradient, particularly when the solid is under an applied stress, analytical solutions of Fick's second law are not appropriate. A finite difference method has been developed to treat such vacancy diffusion problems and applied to vacancy migration in nickel. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.