An Extended Finite Element Model of Crevice and Pitting Corrosion

A sharp interface model formulation is developed for simulating the electrochemical environment in crevices/pits due to galvanic corrosion in aqueous media. The concentration of ionic species and the electrical potential in the crevice is established using the non-dimensionalized Nernst-Planck equations along with the assumption of local electro-neutrality. The crevice/pit interface fluxes are defined in terms of the cathodic and anodic current densities using Butler-Volmer kinetics. The extended finite element method is used to discretize the governing equations and the level set function to describe the interface morphology independent of the underlying finite element mesh. The advantage of this formulation is that it eliminates the need for cumbersome mesh generation and remeshing when the interface morphology changes. Numerical investigations of steady-state intergranular crevice corrosion in idealized Al-Mg alloy microstructures in two-dimensions are conducted to establish the viability of the formulation. Simulation results predict large pH and chloride concentration within the crevice environment, which leads us to the conclusion that chemical reactions and precipitation play a prominent role during crevice corrosion.