High-temperature oxidation resistance of spent MoSi2 modified ZrB2-SiC-MoSi2 coatings prepared by spark plasma sintering

The spent MoSi2 modified ZrB2-SiC-MoSi2 coatings were prepared on carbon matrixes by spark plasma sintering. A continuous metallurgical bonding was formed at the interface between the coating and matrix, and no obvious defects such as pores and cracks were observed inside. The effects of spent MoSi2 content and trace doping in the spent powder on the oxidation behavior of the coatings in air at 1700 degrees C were investigated. During the active oxidation stage, the spent MoSi2 promoted the densification of the coating and enhanced the structural oxygen barrier properties. With the increase of service time, during the inert oxidation stage, doping an appropriate amount of spent MoSi2 helped to increase the fluidity of the rich-SiO2 protective layer so that the Zr oxides fully dispersed in the generated Zr-B-Si-O-Al multiphase glass layer, which could impede the penetration of oxygen and enhance the oxidation protection efficiency. However, excessive spent MoSi2 exacerbated the volatilization of gas by-products, forming pores and cracks in the glass layer and rising the oxidation loss. When the content of spent MoSi2 was 20 vol%, the glass layer is dense and uniform, with few defects and the best oxygen resistance property. Moreover, compared with commercial powders, spent MoSi2 contained Al2O3 and SiO2. Al2O3 had an excellent modification effect, while SiO2 glass can promote liquid phase sintering and seal the defects in the coatings. By adding spent MoSi2, the modified ZrB2-SiC-MoSi2 composite coatings could inhibit the formation of defects and improve the dynamic stability of the coatings effectively.