A computational modeling framework for reaction and failure of environmental barrier coatings under silicate deposits

Environmental barrier coatings (EBCs) for use with SiC-based composites in gas turbine engines may fail following reaction with molten silicate deposits. The processes involved may include dissolution of the EBC material into the deposit, reactions that produce new phases, and cracking or spallation upon cooling, the latter driven by thermal expansion mismatch between the reaction products and the underlying EBC and substrate. Here, we describe an integrated computational framework to simulate the processes and to predict the conditions leading to coating loss through reactive consumption and/or spallation. The framework integrates distinct models to determine: (a) the nature and quantity of phases resulting from dissolution and chemical reactions; (b) thermo-physical properties of those phases; and (c) energy release rates for penetration cracking and spallation upon cooling. We demonstrate the use of the framework by computing critical deposit thicknesses for one specific EBC material (Y₂Si₂O₇) as a function of deposit composition. In this system, the critical deposit thickness for typical coating thicknesses is dictated mainly by spallation, not by consumption, and may vary by orders of magnitude, depending on deposit composition and coating thickness and toughness. With respect to deposit composition, the key parameter governing coating failure is the Ca:Si ratio.