Ablation-resistant yttrium-modified high-entropy refractory metal silicide (NbMoTaW)Si2 coating for oxidizing environments up to 2100 °C

Abstract

Refractory high-entropy alloys (RHEAs) are pivotal in ultra-high temperature applications, such as rocket nozzles, aerospace engines, and leading edges of hypersonic vehicles due to their exceptional mechanical ability to withstand severe thermal environments (in excess of 2000 °C). However, the selection of materials that satisfy the stringent criteria required for effective ablation resistance remains notably restricted. Here, a novel yttrium-modified high-entropy refractory metal silicide (Y-HERMS) coated on a refractory high-entropy NbMoTaW alloy is developed via pack cementation process. The developed Y-HERMS coating with sluggish diffusion effect demonstrates extraordinary ablation resistance, maintaining near-zero damage at sustained temperatures up to 2100 °C for a duration of 180 s, surpassing state-of-the-art high-performance silicide coatings. Such exceptional ultra-high ablation performance is primarily ascribed to the in-situ development of a high viscosity Si-Y-O oxide layer with increased thermal stability and the presence of high-melting Y(Nb_0.5Ta_0.5)O₄ oxides as skeleton structure. Theoretical results elucidate that the Y-HERMS promotes the formation of SiO₂, which impedes the diffusion of O into metal silicide layer, synergistically contributing to the superior ablation resistance. These findings highlight the potential of utilizing high-entropy materials with excellent ablation resistance in extreme thermal environments.