Thermochemical Stability of Yb₂Si₂O₇ Environmental Barrier Coatings During Thermal Cycling and Water Vapor Corrosion at 1350 °C

In this study, Si/mullite/Yb₂Si₂O₇ trilayer environmental barrier coatings (EBCs) were prepared by atmospheric plasma spraying. The thermochemical stability of trilayer EBCs was assessed by thermal cycling and water vapor corrosion tests at 1350 °C. The results show that the current EBCs remain intact throughout the cycling and corrosion processes at 1350 °C, indicating full protection to the SiC substrate. Because the mullite coating effectively inhibited crack propagation and the SiO₂ phase transition, the Si/mullite/Yb₂Si₂O₇ trilayer EBCs provided more protection to the SiC substrate than the Si/Yb₂Si₂O₇ bilayer EBCs. In addition, the as-sprayed Yb₂SiO₅ phase caused the generation of penetrated vertical cracks during thermal cycling at 1350 °C, and the microcracks coalesced to form corrosion channels during water vapor corrosion. These results indicate that the durability of the current EBCs can be further improved by eliminating microcracks and optimizing the Yb₂SiO₅ phase within the as-sprayed Yb₂Si₂O₇ coating.