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

Abstract

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.