A microstructure-sensitive electro-chemo-mechanical phase-field model of pitting and stress corrosion cracking

TL;DR

This work develops the first electro-chemo-mechanical phase-field framework for pitting and stress corrosion cracking in polycrystalline materials, incorporating orientation-dependent mechanical properties and corrosion potentials. It introduces a general boundary condition for the solution potential to model electric double layer charging, enabling transient electrodiffusive and electrochemical dynamics to influence interface kinetics. Calibrated against stainless steel experiments, the model reproduces pit depth and current trajectories and reveals that microstructural features drive more extensive defect growth and irregular pit-to-crack morphologies than homogeneous materials. The approach provides a pathway to predict long-term corrosion resistance and guides microstructure design, with future work focusing on grain-boundary effects, surface roughness, interfacial-energy anisotropy, and crystal plasticity integration.

Abstract

An electro-chemo-mechanical phase-field formulation is developed to simulate pitting and stress corrosion in polycrystalline materials. The formulation incorporates dependencies of mechanical properties and corrosion potential on crystallographic orientation. The model considers the formation and charging dynamics of an electric double layer through a new general boundary condition for the solution potential. The potential of the model is demonstrated by simulating corrosion in polycrystalline materials with various grain morphology distributions. The results show that incorporating the underlying microstructure yields more extensive defects, faster defect kinetics, and irregular pit and crack shapes relative to a microstructurally-insensitive homogeneous material scenario.

Figures (20)

• Figure 1: Polycrystalline material in contact with corrosive environment and diffuse interface description of the liquid (electrolyte $\phi$ = 0) and solid (electrode $\phi = 1$) phases.
• Figure 2: Schematics of an electric double layer (EDL) and its electrode-electrolyte interface model with a resistor-capacitor equivalent circuit diagram.
• Figure 3: Dependence of corrosion potential on crystallographic orientation. (a) Experimental measurements of pit depth in stainless steel as a function of grain orientation Lindell2015. (b) Directional variation in equilibrium corrosion potential determined based on the experimental measurements in (a). $E_{eq}$ stands for the macroscopic equilibrium corrosion potential. The polarisation variation map in (b) is derived by solving three Tafel equations, one for each corner, subjected to a known applied potential and a zero net polarisation variation upon the summation. (the polycrystalline value).
• Figure 4: Schematic disposition of the experimental setup used in Ref. ERNST2002a (left) and the corresponding computational domain (right) for the 304 stainless steel (SS) wire immersed in 1 M NaCl solution.
• Figure 5: Comparison between experimental measurements ERNST2002a and phase-field predictions of (a) the evolution of the pit depth and (b) current density as a function of immersion time in 1 M NaCl solution.