Effect of heat treatment on properties of plasma-sprayed BSAS environmental barrier coating

Abstract

Using BSAS powder prepared by solid-state sintering method, Si/Mullite+BSAS/BSAS three-layer environmental barrier coatings were fabricated on SiC substrate by atmospheric plasma spraying process. The phase composition and microstructure evolution behaviour of the environmental barrier coating subjected to various heat treatment temperatures were studied by scanning electron microscope, energy dispersive spectrometer and X-ray diffraction analyzer, etc. The results indicate that as-sprayed BSAS coating is mainly composed of monoclinic BAS phase and amorphous phase; After heat treatment at 1100 ℃, the amorphous phase inside the coating is transformed to hexagonal BAS phase. With the temperature increases to 1200 ℃, the hexagonal BAS phase gradually changes to the monoclinic BAS phase. The fraction of the monoclinic BAS phase reaches the maximum at 1300 ℃ heat-treated; With further increase of the heat treatment temperature, tridymite SiO2, Ba3SiO5 and paracelsian BAS phase appear. Moreover, silicon droplets exude is detected during heat treatment at 1400 ℃.

Keywords

• environmental barrier coating
• plasma spraying
• silicon carbide ceramic matrix composite
• bsas