Effect of CMAS concentration on the failure mode of Yb₂Si₂O₇-based environmental barrier coatings in water vapor environments

A single-phase Yb₂Si₂O₇ coating was deposited on SiC_f/SiC composites with a silicon bond coat using air plasma spraying. The hot corrosion behavior of Yb₂Si₂O₇-coated SiC_f/SiC was investigated in a coupling environment consisting of water vapor and calcium–magnesium–aluminum–silicate (CMAS) with static oxidation at 1350 °C. The evolution of the phase and cross-sectional morphology of the samples was characterized using X-ray diffraction and scanning electron microscopy. The results indicate that thermal stress generated by the growth of the thermally grown oxide (TGO) layer leads to the fractures at the TGO–Yb₂Si₂O₇ interface in samples loaded with low CMAS concentration. In samples with high CMAS concentration, excess CMAS reacts with the TGO layer, destroying its structure and accelerating the oxidation of the Si bond coat. Cracks bifurcate within the TGO layer, extend along the TGO interface, and ultimately penetrate the interior of the TGO layer. The concentration of CMAS influences the crack propagation mode within the TGO layer and alters the failure behavior of the coating.