Corrosion Behavior and Degradation Mechanism of Novel Environmental Barrier Coatings (Yb1/5Y1/5Lu1/5Er1/5Ho1/5)2Si2O7 in High-Temperature Water-Oxygen Environments

To address the performance degradation of conventional rare-earth silicate environmental barrier coatings (EBCs) in high-temperature water-oxygen environments, this study developed a novel high-entropy EBC system. The coating with a composition of (Yb1/5Y1/5Lu1/5Er1/5Ho1/5)2Si2O7/Si/SiC was prepared via atmospheric plasma spraying. Thermal cycling corrosion tests were conducted at 1400 °C under a 90% H2O–10% O2 atmosphere. Results show that after heat treatment, the monosilicate phase content decreased, and the structure stabilized. The coating surface exhibited a ridge-like morphology with pits and microcracks after corrosion. A porous corrosion layer formed at the edges, and the SiO2 layer thickness increased parabolically from 2.75 μm after 100 cycles to 5.65 μm after 300 cycles. The coating demonstrated excellent corrosion resistance, with degradation initiated by surface thermochemical corrosion, leading to corrosion layer formation and SiO2 accumulation. This study provides important insights for developing long-life EBCs for aero-engine applications.