Durable dual-state duplex Si–HfO₂ with excellent oxidation and cracking resistance

The lifetime of Si bond coatings in environmental barrier coatings is constrained by phase-transition-induced cracking of the SiO₂ scale. In this study, Si–HfO₂ dual-state duplex composite materials are proposed to address this issue by partially forming HfSiO₄ and minimizing the SiO₂ content. The as-prepared composite exhibited a structure comprising discrete HfO₂ “bricks” embedded in a continuous Si “mortar”, while the oxidized state transformed into discrete HfSiO₄ “bricks” within continuous thin SiO₂ “mortars”. The results indicate that continuous thin SiO₂ contributes to reducing the oxidation rate to a level comparable to that of pure Si, and discrete HfSiO₄ 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% HfO₂ 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.