Effect of filler on the oxidation protective ability of MoSi₂ coating for Mo substrate by halide activated pack cementation

To protect molybdenum against oxidation, MoSi₂ coatings were prepared by halide activated pack cementation, and the effect of filler cases, Al₂O₃, SiO₂ and SiC, on the microstructure and oxidation resistance of MoSi₂ coating was studied. The deposited coatings using Al₂O₃ and SiO₂ filler presented a double-layer microstructure of the outer MoSi₂ and the inner Mo₅Si₃ layer. Whereas, the coating deposited in SiC-filler case displayed only one MoSi₂ layer. Lower inert ability of SiC filler in the pack and the possible reaction with molybdenum are responsible for the mono-layer structure. The coating prepared with SiO₂ filler presented rough morphologies and more residual SiO₂ fillers embedded on the coating surface than the Al₂O₃ or SiC filler cases. Attributed to the residual embedded fillers, all three kinds of deposited coatings exhibited perfect anti-oxidation property at 773K and could effectively protect molybdenum substrate against pest oxidation. As for high temperature oxidation of 1473K in air, the coating corresponding to SiO₂ filler displayed the best oxidation protective ability with only 0.05% mass change after 110h oxidation. The protective SiO₂ layer formed on the surface of MoSi₂ coating at high temperature is responsible for the good oxidation resistance of the coating.