Investigation of Yb2SiO5/BSAS/Si coating on Cf/SiC composites: processing and steam corrosion behavior

Environmental Barrier Coatings (EBCs) are used to protect silicon carbide-based composites in the high-temperature steam combustion environment of the latest generation of high-efficiency gas turbine aero-engines. The Yb2SiO5/BSAS/Si coatings with gradient coefficient of thermal expansion were prepared using atmospheric plasma spraying (APS) method on the carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC) composites surface. The coating preparation process parameters were optimized by evaluating the influence of spraying power on the bonding strength, deposition efficiency, and porosity. The corrosion behaviors and mechanism of the optimized Yb2SiO5/BSAS/Si coating was investigated at 1200 ℃ by thermal cycle test in steam conditions. The results indicated that the decomposition of Yb2SiO5 and the conversion of SiO2 to Si(OH)4 were the main corrosion reactions of Yb2SiO5 top coating. Noticeably, the SiO2 component acted as an obvious sign of the reaction front diffusing, forming the clear SiO2-gradient layers. The gradient Yb2SiO5/BSAS/Si coating remained intact after thermal cycles for 500 h at 1200 ℃ in steam conditions which effectively enhanced the resistance of Cf/SiC composites to high temperature steam corrosion.