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 degrees 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 degrees 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.