Durable dual-state duplex Si–HfO <sub>2</sub> with excellent oxidation and cracking resistance
Lin Chen, Jing-Chuan Luo, Yang Wen-qi, Chang‐Jiu Li, Guan‐Jun Yang
Abstract
The lifetime of Si bond coatings in environmental barrier coatings is constrained by phase-transition-induced cracking of the SiO<sub>2</sub> scale. In this study, Si-HfO<sub>2</sub> dual-state duplex composite materials are proposed to address this issue by partially forming HfSiO<sub>4</sub> and minimizing the SiO<sub>2</sub> content. The as-prepared composite exhibited a structure comprising discrete HfO<sub>2</sub> "bricks" embedded in a continuous Si "mortar", while the oxidized state transformed into discrete HfSiO<sub>4</sub> "bricks" within continuous thin SiO<sub>2</sub> "mortars". The results indicate that continuous thin SiO<sub>2</sub> contributes to reducing the oxidation rate to a level comparable to that of pure Si, and discrete HfSiO<sub>4</sub> 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<sub>2</sub> 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 lifetimes.