Effect of different fillers on the microstructural evolution and high temperature oxidation resistance of Mo-Si-B coatings prepared by pack cementation

Mo-Si-B coatings were prepared on molybdenum by a pack cementation process. The effects of Al2O3, SiO2, and SiC fillers on the microstructural evolution and high temperature oxidation kinetic of Mo-Si-B coatings were studied. All the three Mo-Si-B coatings were composed of a MoSi2 layer and a MoB transitional layer. The thickness of the transitional layers showed no discernable differences in different coatings, but the coating prepared with the SiC filler showed the thickest MoSi2 outer layer owing to the additional silicon source supplied by the SiC pack agent. After oxidation at 1250 °C for 100 h, the oxidized coatings exhibited a three-layer structure consisting of an outer SiO2 film, a middle Mo5Si3 layer and an inner MoSi2 layer. The coating prepared with the SiO2 filler showed the smallest weight gain and consumption of the MoSi2 layer, which may be due to the residual SiO2 pack agent favoring the rapid formation of a dense SiO2 film.