Microstructure evolution under thermal cycling and water-oxygen corrosion behavior of Yb2Si2O7-Yb2SiO5 gradient structural environmental barrier coating

Abstract

Si/Yb₂Si₂O₇/Yb₂Si₂O₇-Yb₂SiO₅ gradient structural environmental barrier coating (EBC) was designed and fabricated with stoichiometric Yb₂Si₂O₇ as the intermediate transition coat to mitigate the thermal expansion mismatch between the layers and thus improve the service life. Subsequently, the thermal cycling and water-oxygen corrosion behavior of this gradient structural EBC and a traditional Si/Mullite/Yb₂SiO₅ EBC were comparatively investigated at 1350 °C. The results showed that the plasma-sprayed 0.5Yb₂Si₂O₇-0.5Yb₂SiO₅ coating exhibited a dense microstructure composed of 52.96 mol% Yb₂SiO₅ and 47.04 mol% Yb₂Si₂O₇. The thermal cycling life of gradient structural EBC reached 672 times at 1350 °C, approximately 160 % higher than that of traditional EBC. The overall structure of the gradient structural coating remained stable during the thermal cycling. However, with an increasing number of cycles, the Si bond coat underwent continuous oxidation, leading to the thickening and cracking of the thermally grown SiO₂ layer, ultimately resulting in the spalling failure of the Yb₂Si₂O₇/Yb₂Si₂O₇-Yb₂SiO₅ coating. The water-oxygen corrosion resistance of the gradient structural EBC at 1350 °C was comparable to that of the traditional EBC. After 200 h of water-oxygen corrosion, the content of the Yb₂Si₂O₇ phase in the topcoat decreased due to its reaction with high-temperature water vapor. Nevertheless, the coating structure remained stable and dense, without peeling. Furthermore, the failure mechanism after thermal cycling and kinetics of water-oxygen corrosion were also discussed in detail.