Oxidation resistance and diffusion behavior of MoSi₂/WSi₂/(Nb,X)Si₂ compound coating at 1400 °C

MoSi₂/WSi₂/(Nb,X)Si₂ compound coating showed outstanding oxidation resistance at 1400 °C. After oxidation for 100 h, the specimen kept good integrality and the parabolic rate constant of the scale growth was about 1.497 µm² h⁻¹. NbSi₂ layer could improve the bonding of MoSi₂/WSi₂ layers to the substrate, postpone their degradation into porous sub-silicide layer and provide adequate Si for oxidation. The intense interdiffusion between MoSi₂ and WSi₂ layers would result in formation of pores in WSi₂ layer and then weaken its barrier effect. In addition, a small amount of alloying elements Ti, Cr and Al from the substrate could diffuse through the MoSi₂/WSi₂ layers along the grain boundaries during oxidation. As a result, there are TiO₂ formed in the scale. After oxidation for 100 h, a gradient compound layer of (Mo,W)Si₂/(W,X)Si₂/(Ti,Nb)₅Si₄ formed eventually.