Oxidation behavior and mechanism of MoSi₂-Y₂O₃ composite coating fabricated by supersonic atmospheric plasma spraying

MoSi₂-based coatings with different Y₂O₃ additive contents were fabricated using supersonic atmospheric plasma spraying, its microstructural features and oxidation behavior as well as protective mechanism at 1500 °C were diligently studied. Experimental results revealed that the sprayed MoSi₂-Y₂O₃ (MY) composite coatings exhibited the dense microstructure and adhered well to SiC transition layer without obvious defects at their interfaces. Moreover, the composite coating with 20 wt% Y₂O₃ possessed the best oxidation resistance with a lowest mass loss percentage at 1500 °C among all sprayed MY coatings. The incorporation of rare earth Y₂O₃ accelerated the formation of multiple yttrium silicates containing Y₂SiO₅, Y₂Si₂O₇ and Y₄Si₃O₁₂ with high melting point and matching thermophysical property to SiO₂, which could occupy the open spaces and enhance the viscosity of glassy SiO₂-rich Si-O-Y compound scale. The increased viscosity of Si-O-Y multicomponent scale could delay the permeation of reactive oxygen species inwardly, enhancing the oxidation resistance of sprayed composite coating effectively.