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

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 degrees 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 degrees 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.