Durable dual-state duplex Si-HfO₂with 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 °C 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.