Effects of pre-service heat treatments on microstructure and properties of atmospheric-plasma-sprayed Yb2SiO5 environmental barrier coating

Abstract

In this work, Yb₂SiO₅ coating was plasma sprayed, and the phase evolutions (such as recrystallization and isostructural monosilicate transformation) as well as the microstructural modification in this as-sprayed amorphous coating has been explored during thermal aging process. Results show that a pre-service heat treatment at temperatures ≥1200 °C is necessary to complete the transformations and to recover the mechanical and thermophysical properties of Yb₂SiO₅ coating. Furthermore, the water vapor corrosion behaviors of as-sprayed and heat-treated Yb₂SiO₅ coatings were evaluated at 1300 °C for 50–200 h. The Yb₂O₃ phase in coating preferably volatilizes, leaving a relatively dense reacted layer composed of Yb₂SiO₅ on the surface of all corroded Yb₂SiO₅ coatings. However, it is found although promoting crystallization and performance recovery of Yb₂SiO₅ coating, heat treatment exacerbates the steam corrosion to some extent by facilitating water vapor penetration along the enlarged and widened vertical microcracks.