Multi-Phase-Field Model of Intergranular Corrosion Kinetics in Sensitized Metallic Materials

Improperly heat-Treated metals exhibit preferential corrosion along sensitized grain boundaries when exposed to a corrosive electrolyte. This localized corrosion process is commonly known as Intergranular Corrosion (IGC). A multi-phase-field (MPF) model is presented to quantitatively predict IGC kinetics in metallic materials. The total free energy of the system is defined in terms of chemical, gradient and electromigration energy. The system is defined by a set of phase field variables which evolve due to the minimization of Gibbs free energy of the system. The simulation results show that IGC predicted by two-dimensional MPF model agrees well with the experimental results. The model also predicts plane-direction-dependent IGC in rolled sheets, commonly observed in the experimental studies. It is also observed that the corrosion process becomes transport controlled even at lower values of applied potentials due to the saturation of the metal ions in the corroded grain boundaries region. A three-dimensional study is also presented to show the practical applications of using this MPF model for complex three-dimensional geometries.