Incorporation of vacancy generation/annihilation into reactive diffusion concept – Prediction of possible Kirkendall porosity

Abstract

The reactive diffusion concept represents an approved handy tool for simulation of diffusive phase transformations in binary systems. The local value of the site fraction of a particular component, obtained by solution of diffusion equation, determines its affiliation to a phase or to an interface, to which the respective chemical potentials and kinetic coefficients, used in diffusion equation, can be assigned. The reactive diffusion concept is now generalized to account for intensity of non-ideal sources and sinks for vacancies, which allows the treatment of the Kirkendall effect and an according prediction of formation of pores. The new concept is demonstrated on an instructive example showing the kinetics of phase transformation, shift of the Kirkendall plane and evolution of site fraction profiles. Local supersaturation by vacancies indicates the possible formation of pores.