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.