Novel insights into the water vapor accelerated degradation mechanism of zirconium-based TBCs for hydrogen gas turbines

Abstract

Thermal barrier coatings (TBCs) applied in hydrogen gas turbines encounter a critical challenge of water vapor corrosion at higher operating temperatures. However, the degradation mechanism of ceramic top coats exposed directly to high-temperature water vapor environments is still unclear. In this study, the degradation of YSZ coatings with feather-like structures was found to have depth and temperature dependence and could be accelerated by water vapor. The non-uniform phase transformation in the through-thickness direction driven by oxygen vacancy gradient was characterized utilizing the difference in detection depths between neutron and X-ray diffraction. Meanwhile, accelerated sintering was observed throughout the whole depth due to the diffusion and reaction of hydroxyl groups dissociated from water vapor, which was elucidated by computational analysis. Furthermore, direct proofs of transition in diffusion mechanisms were obtained, which were responsible for the severe degradation of YSZ coatings at elevated temperatures. In comparison, the excellent phase/chemical stability and enhanced sintering resistance of the (Gd_0.9Yb_0.1)₂Zr₂O₇ (GYbZ) and the novel high-entropy (Gd_0.2Dy_0.2Ho_0.2Tm_0.2Yb_0.2)₂Zr₂O₇ (GDHTY) coatings were evaluated, which demonstrated the potential as alternatives to YSZ applied in hydrogen gas turbines.