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 ButlereVolmer 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. (c) 2019 Elsevier Ltd. All rights reserved.