Molten Salt Corrosion Behaviors and Mechanisms of Ytterbium Silicate Environmental Barrier Coating

Environmental barrier coating (EBC) is essential for protection of ceramic matrix composite hot-sections in future gas turbine engines with high thrust-to-weight ratio. Rare-earth silicates, such as Yb2SiO5 and Yb2Si2O7, have been developed for potential application as EBC. However, the corrosion behaviors and mechanisms of EBC in molten salt environment such as Na2SO4 at high temperature are not clear. In this work, the Yb2SiO5/Yb2Si2O7/Si coating was prepared by vacuum plasma spraying (VPS). The molten salt (Na2SO4+25% NaCl, in mass) corrosion behaviors and mechanisms of the coating at 900 degrees C for 60-240 h were investigated. Results showed that the Yb2SiO5/Yb2Si2O7/Si coating exhibited dense structure with good bonding between the triple ceramic layers. The molten salt of Na2SO4+25% NaCl penetrated the Yb2SiO5 top layer and enriched in the Yb2Si2O7 interlayer, while the interfacial bonding between the coating and substrate still remained good after corrosion for 240 h. The Yb2SiO5 phase in the top layer exhibited good stability, while the second phase of the Yb2O3 reacted with molten salt. The content of the Yb2O3 decreased with the increase of corrosion time. The Yb2Si2O7 phase in the interlayer reacted with molten salt to form apatite phase of NaYb9Si6O26 and sodium silicate as well as volatile species such as Cl-2 and SO2, which might shorten the service life of the coating. Moreover, there was almost no molten salt in the silicon bond layer, which remained intact. The Yb2SiO5/Yb2Si2O7/Si coating exhibited good resistance to molten salt corrosion.