A phase field model for simulating the pitting corrosion

• New phase field model for simulating the evolution of corrosion pits is proposed.
• Accuracy of the model is verified versus analytical and other numerical results.
• The model is able to simulate activation-, diffusion- and mixed-controlled pitting.
• Several examples with complex pit morphologies are provided.

This manuscript presents the formulation and implementation of a phase field model for simulating the activation- and diffusion-controlled pitting corrosion phenomena in metallic materials. Introducing an auxiliary phase field variable to represent the physical state of each material point, the free energy of the corroding metal–electrolyte system can be expressed as a function of field variables and their gradients. The governing equations for the evolution of each field variable are then derived such that the system free energy is decreased during the mass transfer and metal dissolution processes. The propagation of the diffuse interface is tracked implicitly by solving the phase field variable over the entire system, which allows the accurate approximation of complex morphological evolutions. A comprehensive study is presented to verify the accuracy of the proposed model. We show that by calibrating the interface kinetics parameter with the exchange current density, the proposed model can reproduce different portions of the polarization curve associated with the activation-controlled, diffusion-controlled, and mixed-controlled corrosion kinetics. We also demonstrate the application of this model for simulating the electropolishing process, interactions between multiple growing pits, and pitting corrosion in a metal matrix composite and a polycrystalline stainless steel.