Gradient tri-layered TGOs in MoSi ₂/HfO ₂ duplex EBCs for effective protection of SiC substrate against steam corrosion at 1500 °C for 200 h

The protective effectiveness of environmental barrier coatings (EBCs) for SiC-based composites is challenged by the thickening and phase transformation of the SiO₂ scale, known as thermally grown oxide (TGO). In this study, a tri-layered TGOs scale, comprising cristobalite, Hf-doped SiO₂ glass, and particle-reinforced Hf-Si-O glass, was formed during the oxidation of MoSi₂/HfO₂ duplex EBCs. The incorporation of the gradient Hf-doping and HfO₂/HfSiO₄ particle-reinforcement were demonstrated to effectively suppress the crystallization and phase transition of the SiO₂ and mitigate internal stress within the EBCs, generating a crack-blocking effect. This effect prevented the TGOs scale from further channel crack propagation, enabled the SiC substrate with no detectable corrosion after 200 hours of exposure at 1500 °C in steam, even when the TGOs thickness reached 24.5 μm. This work presents a novel strategy to simultaneously extend the service lifetime and enhance the high-temperature capability of EBCs through the tailored design of TGOs composition and structure.