Environmental Protection Coating System for Refractory Metal Alloys in Extreme Environments

The refractory multi-principal elements alloys (RMPEAs) are promising structural materials to help increase power efficiency in high-temperature oxidation environments, while the intrinsic poor oxidation resistance of the refractory elements limits their application. The oxidation behavior of a refractory high entropy alloy WMoTaNbV is investigated at 1300°C. By using an innovative two-step coating strategy with Mo-precoat followed by Si-B pack cementation, a multilayer Mo-Si-B coating with strong oxidation resistance and compatibility as well as a diffusion barrier is developed. The coating can protect the substrate at 1300°C for more than 750 h of thermal cycles. An RMPEA boride phase develops at the alloy/coating interface after longtime service and acts as an additional diffusion barrier to maintain the coating integrity. The oxidation test results demonstrated that this two-step coating system provides robust oxidation protection at high temperatures and can be widely applied in RMPEAs.