Oxidation behavior of plasma-sprayed MoSi₂-Yb₂O₃ composite coating at 1700 °C

Rare earths with unique electronic structure and properties have incomparable advantages for modifying the comprehensive performance of silicide materials. In this study, MoSi₂-based composite coatings with different rare-earth Yb₂O₃ contents were prepared using supersonic atmospheric plasma spraying, and their microstructural features and oxidation behavior at 1700 °C were investigated systematically. Results showed that the sprayed MoSi₂-Yb₂O₃ composite coating possessed the dense structure without visible defects and tightly adhered to the SiC transition layer. During oxidation at 1700 °C, all the samples exhibited an explicit linear oxidation mode, in which the MoSi₂-10 wt%Yb₂O₃ coating qualified the optimal oxidation resistance with the lowest specific mass loss relative to other coatings. It was natural to consider that the Yb₂O₃ dopant changed the microstructural aspects of the formed oxide scale upon oxidation, and then affecting the oxidation behavior of the applied coating. Moderate doping of Yb₂O₃ stabilized the Si–O covalent bonds in SiO₂ network, leading to the enhanced viscosity of oxide glass scale, thereby delaying the effective delivery of oxygen molecules as well as the oxidation degradation of the coating.