Preparation and Oxidation Resistance Mechanism of Silicide Coating on MoNbTaTiW Refractory High-Entropy Alloy

Solving the oxidation resistance problem of refractory high-entropy alloy at high temperature is the premise of application in engineering.The preparation of anti-oxidation coating on the surface of refractory metal is an effective way to improve its oxidation resistance.A complex silicide anti-oxidation coating(Si-20Cr-20Fe)was prepared on the surface of MoNbTaTiW refractory high-entropy alloy by slurry fusion sintering method.The microstructure, phase and composition of the initial silicide coating and the coating after oxidation at 1 300 ℃ were studied by SEM, EDS and XRD.The diffusion law of Si, Fe and Cr in the coating and the anti-oxidant mechanism of the coating were explored.Results showed that the initial silicide coating after melting was composed of disilicide, 5/3 silicide and ternary silicide Cr4Nb2Si5 formed by the reaction between metal and silicon.A good diffusion reaction interface was formed between the silicide coating and the substrate.After oxidation at 1 300 ℃, Si, Fe and Cr diffused to the substrate, and the diffusion reaction interface layer moved to the substrate, consequently the coating thickness was increased.The microstructure and composition of the diffusion reaction interface layer were almost the same as the diffusion layer of the complex initial silicide coating.After oxidation, a crack-free, dense oxide layer was formed on the surface of the coating.The layer was composed of CrNbO4, SiO2, WO3 and Fe2SiO4, and it could prevent the further diffusion of oxygen to the inside of substrate.Si, Fe and Cr had different diffusion rates in MoNbTaTiW refractory high-entropy alloy.The diffusion rate of Si was the fastest, Fe was the second, and Cr was the slowest.Therefore, Fe and Cr were enriched in the low silicon content diffusion layer and silicide layer.The complex silicide coating prepared by slurry fusion sintering could provide good anti-oxidation protection for MoNbTaTiW refractory high-entropy alloy at high temperatures.