Durable dual-state duplex Si–HfO ₂ with excellent oxidation and cracking resistance

Abstract

The lifetime of Si bond coatings in environmental barrier coatings is constrained by phase-transition-induced cracking of the SiO 2 scale. In this study, Si-HfO 2 dual-state duplex composite materials are proposed to address this issue by partially forming HfSiO 4 and minimizing the SiO 2 content. The as-prepared composite exhibited a structure comprising discrete HfO 2 "bricks" embedded in a continuous Si "mortar", while the oxidized state transformed into discrete HfSiO 4 "bricks" within continuous thin SiO 2 "mortars". The results indicate that continuous thin SiO 2 contributes to reducing the oxidation rate to a level comparable to that of pure Si, and discrete HfSiO 4 particles aid in relieving phase transition-induced stress and inhibiting crack propagation, thereby enhancing oxidation and cracking resistance simultaneously. Consequently, the composite with 20 mol% HfO 2 and a mean particle size of ~500 nm at 1370 ℃ exhibited a service lifetime 10 times greater than that of pure Si. This research provides valuable insights for designing Si-based bond coatings with improved service lifetime.