Phase field model for diffusion-reaction stress field in the thermal barrier coatings corroded by the molten CMAS

Abstract

Thermal barrier coatings (TBCs) are prone to attacking by molten calcium-magnesium-alumino-silicates (CMAS) in service. Reactions of molten CMAS and the ceramic coating are solution-reprecipitation ones that generate a new phase, ZrSiO4. Swelling caused by these reactions result in accumulation of localized stresses in the ceramic coating, which subsequently contributes to the premature failure of TBCs. In this work, the CMAS diffusion-reaction with TBCs is investigated based on the phase field theory. A two-dimensional phase field model is developed, which fully couples the Cahn-Hilliard equation for the diffusion of CMAS and the constitutive equation for the prediction of the chemical reaction-induced stresses. The results indicate that very high compressive stresses emerged in the coating, which may lead to the spallation failure of the coating. Furthermore, it is found that the presence of mechanical action accelerates the corrosion kinetics in TBCs and the evolution of CMAS concentration in the coating is consistent with previous reports. Finally, approximately 3.4% volume strain caused by CMAS corrosion reaction is predicted.