Gradient tri-layered TGOs in MoSi <sub>2</sub>/HfO <sub>2</sub> duplex EBCs for effective protection of SiC substrate against steam corrosion at 1500 °C for 200 h
Kexue Peng, Ying Qiao, Qian Li, Xinxin Cao, Long Wang, Guifang Han, Jianzhang Li, Jingyu Qin, Jingde Zhang
Abstract
The protective effectiveness of environmental barrier coatings (EBCs) for SiC-based composites is challenged by the thickening and phase transformation of the SiO<sub>2</sub> scale, known as thermally grown oxide (TGO). In this study, a tri-layered TGOs scale, comprising cristobalite, Hf-doped SiO<sub>2</sub> glass, and particle-reinforced Hf-Si-O glass, was formed during the oxidation of MoSi<sub>2</sub>/HfO<sub>2</sub> duplex EBCs. The incorporation of the gradient Hf-doping and HfO<sub>2</sub>/HfSiO<sub>4</sub> particle-reinforcement were demonstrated to effectively suppress the crystallization and phase transition of the SiO<sub>2</sub> 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.