Mechanism of stress evolution in environmental barrier coatings considering the presence of crack channels

Abstract

The roles of crack channel transitions and thermally grown oxides (TGO) in the failure of environmental barrier coatings (EBCs) should be clarified. Hence, in this study, the laws of penetration and delamination crack evolution were investigated using a virtual crack extension method for multilayer materials to gain insights into the transformation conditions with a framework for a coupled thermal/mechanical/chemical numerical model of TGO containing channel cracks developed based on this law. The framework integrates diffusion, TGO growth, and phase transformation of the oxides. A theoretical model for high-temperature gas corrosion of EBCs coupled with deformation, mass diffusion, and chemical reactions was proposed, with the results indicating that the cracks transitioned from vertical to exfoliation cracks in the ytterbium dibasic silicate (YbDS) layer. The coupling effect of cracks and stresses led to non-uniform growth of the TGO by affecting the oxygen diffusion and inflow rates. The y-direction stresses at the YbDS/TGO interface near the crack channel changed from compressive to tensile stresses after cooling, making the first location to undergo delamination failure. The proposed model can provide better guidance for designing EBCs systems and supporting the life prediction of EBCs in service environments.