Fabrication and thermal shock resistance of multilayer γ-Y₂Si₂O₇ environmental barrier coating on porous Si₃N₄ ceramic

A dense multilayer γ-Y₂Si₂O₇ environmental barrier coating was in-situ fabricated by the liquid infiltration and filling method on porous Si₃N₄ ceramic for water resistance. When the sintering temperature was 1350°C, as-prepared coating consisted of the top glass layer, the γ-Y₂Si₂O₇ interlayer and the bottom bond layer. With increasing sintering temperature from 1350 to 1450°C, the microstructure of the coating transformed from three layers into two layers including the γ-Y₂Si₂O₇ layer and the bond layer. The γ-Y₂Si₂O₇ layer in the coating consisted of γ-Y₂Si₂O₇ and Y-Si-Al-O glass, and the γ-Y₂Si₂O₇ content increased with the increase of sintering temperature. Thermal shock resistance of the coatings was tested. The results showed that the coating prepared at 1450°C displayed the better thermal shock resistance. After thermal shock for 15 times from 1000°C to room temperature, the microstructure of the coating showed little change, and water absorption increased slightly from 4.8% to 5.3%.