A thermo-chemo-mechanical coupled local gradient damage model for thermal barrier coating undergoing high temperature CMAS corrosion

The attack of molten silicate, (simulated by CaO-MgO-Al₂O₃-SiO₂ (CMAS) melt) is a primary driver of channel cracking and multi-level delamination in thermal barrier coatings (TBCs). Yet existing models cannot capture the fully coupled thermo–chemo–mechanical processes governing fracture evolution. Here, we develop a thermo-chemo-mechanical local gradient damage model within a micromorphic framework which is capable of simulating 1) CMAS penetration, 2) reaction-induced phase transformations, 3) thermal mismatch, and 4) crack initiation and propagation in yttria-stabilized zirconia coatings. The model incorporates damage-dependent CMAS diffusivity, phase-transition-induced strain, and crack-controlled thermal insulation, enabling the explicit prediction of channel cracks and horizontal delamination. Our simulations reveal that CMAS concentration is the dominant factor controlling fracture mode: low concentrations generate solely vertical channel cracks, whereas high concentrations trigger multi-level delamination as reaction-induced expansion accumulates. The impact of temperature increase is primarily to accelerate diffusion and crack growth kinetics. Channel cracks act as pathways for relatively rapid transport, whereas delamination creates local high-temperature regions and catastrophic coating separation. The proposed framework reveals the coupled mechanisms driving CMAS-assisted cracking and provides quantitative guidance for designing CMAS-resistant coating systems.