Microstructure and high-temperature oxidation behavior of plasma-sprayed Si/Yb2SiO5 environmental barrier coatings

An environmental barrier coating (EBC) consisting of a silicon bond coat and an Yb₂SiO₅ top-coat was sprayed on a carbon fibers reinforced SiC ceramic matrix composite (CMC) by atmospheric plasma spray (APS). The microstructure of the coating annealed at 1300 °C and its high-temperature oxidation behavior at 1350 °C were investigated. The significant mass loss of silica during the plasma spray process led to the formation of Yb₂SiO₅ and Yb₂O₃ binary phases in the top-coat. Eutectics of Yb₂SiO₅ and Yb₂O₃ were precipitated in the top-coat, and channel cracks were formed in the top-coat after 20 h annealing because of the mismatch between the coefficients of thermal expansion (CTEs) of Yb₂SiO₅ and the SiC substrate. The EBC effectively improved the oxidation resistance of the CMC substrate. The channel cracks in the Yb₂SiO₅ top-coat provided inward diffusion channels for oxygen and led to the formation of oxidation delamination cracks in the bond coat, finally resulting in spallation failure of the coating after 80 h oxidation.