Isothermal oxidation and interdiffusion behavior of MoSi₂/WSi₂ compound coating on Nb-Ti-Si based alloy

The oxidation and diffusion behaviors of MoSi₂/WSi₂ compound coating on the Nb-Ti-Si based alloy at 800, 1250 and 1350 °C have been investigated. The coating exhibited excellent oxidation resistance at 800 °C and 1250 °C, and the scale growth rates were about 0.335 μm² h⁻¹ and 0.939 μm² h⁻¹, respectively. At 800 ^oC, pesting oxidation was successfully suppressed and formation of Mo₅Si₃ was mainly resulted from the slow diffusion rate of Si atoms. Therefore, there was no Mo₅Si₃ at the scale/MoSi₂ interface when oxidized at 1250 and 1350 °C. At 1250 °C, WSi₂ layer showed strong restriction against outward diffusion of alloying element atoms. Thus, a pure SiO₂-Al₂O₃ scale about 9.5 μm thick was obtained after oxidation for 100 h. At 1350 °C, the WSi₂ layer degraded into porous W₅Si₃ in situ within a short duration and the outward diffusion was increased. As a result, oxides like Nb₂O₅, YNbO₄ and AlNbO₄ formed in the thick scale.