Phase field study of mechanico-electrochemical corrosion

A phase field (PF)model was proposed to investigate corrosion in a stressed metal. The Allen–Cahn equation, associated with the Nernst–Planck, Poisson's, and mechanical equilibrium equations, was established to govern phase transformation, ion diffusion, electric potential distribution, and mechanical deformation, respectively. The electrochemical reaction rate was expressed as a function of the electrochemical potentials of reactants and products based on a detailed balance of reactions, which conforms to a generalized Butler–Volmer relationship. The numerical results reveal that the stress concentration at the tip of a corrosion pit promote a higher corrosion rate, which leads to a sharpened tip and the accelerated failure of a metallic structure. To consider a more complicated scenario, a metal matrix composite (MMC)reinforced with inert fibers/particles was investigated. If a fixed displacement boundary condition is applied, the corrosion resistance of the MMC would benefit from the decrease in reinforcement stiffness; whereas when the MMC is under a constant load, a stiffer reinforcement would result in an increase in corrosion resistance.