Numerical Modeling of Localized Corrosion Using Phase-Field and Smoothed Boundary Methods

A modeling framework is presented for localized corrosion of metals. This model employs the phase-field and smoothed boundary method to track the moving metal/electrolyte interface and to couple it to mass transport within the electrolyte and Butler-Volmer electrochemical kinetics. A microscopic expression of the maximum current is derived that smoothly captures the transition from activation-to IR- and transport-controlled kinetics. Simulations of pitting corrosion are performed to highlight the capabilities of this framework. One-dimensional simulations are conducted to predict corrosion-pit depth as a function of time for multiple fixed applied potentials. The results indicate a transition from activation-controlled kinetics to first IR-controlled and then transport-controlled kinetics with increasing applied potentials. Two-dimensional simulations are also performed with and without a protective surface layer. Without the inert surface layer, the pit spreads as the sides of the pit corrode faster due to facile mass transport to the bulk electrolyte. With a protective surface layer, simulation results predict semi-circular pit growth at a slower rate due to limited mass transport. Both results agree with experimental observations. Finally, simulations are conducted to illustrate the model's capability to study polycrystalline and precipitate microstructures. (C) The Author(s) 2018. Published by ECS.