Durable dual-state duplex Si–HfO2 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 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.

Keywords

• environmental barrier coatings (ebcs)
• bond coatings
• oxidation
• phase transition
• cracking