Microstructural characterization and anti-oxidation properties of molybdenum disilicide coating on niobium by spent MoSi${}_2$-based materials

MoSi${}_2$ coatings are prepared using spent and commercial MoSi${}_2$ powders as raw materials to protect niobium (Nb) substrate by spark plasma sintering (SPS) technique, and the microstructure and oxidation resistance of the coatings at 1500 °C are investigated. Results showed that obvious pores are found in MoSi${}_2$ coating using commercial MoSi${}_2$ (MC coating) after SPS while MoSi${}_2$ coating using spent MoSi${}_2$ (MS coating) is dense with low porosity. (Mo,Nb)${}_5$Si${}_3$ diffusion layer is generated between MS coating and the substrate with no gap or cracks, showing excellent metallurgical bonding. After long-term oxidation at elevated temperature, pores and exposed Mo${}_5$Si${}_3$ can be observed in the oxide scale of MC coating, while dense and complete oxide scale is obtained by MS coating. Lowest mass gain (2.78 mg cm${}^{-2}$) is acquired by MS coating after oxidation at 1500 °C for 40 h because SiO${}_2$ oxide scale is completely formed on the dense and bentonite-containing coating, blocking the diffusion of oxygen at high temperature. Compared with MC coating, no further oxidation occurs inside the MS coating or substrate, exhibiting better high-temperature oxidation resistance. (© 2020 Wiley-VCH GmbH)