Fabrication and thermal shock resistance of β-Si₃N₄-based environmental barrier coating on porous Si₃N₄ ceramic

A dense β-Si₃N₄-based waterproof environmental barrier coating was fabricated using the liquid infiltration and filling method on porous Si₃N₄ ceramic. Microstructure and thermal shock resistance of the coating were investigated. The results showed that the coating consisted of β-Si₃N₄, Y₁₀Al₂Si₃O₁₈N₄ and Y-Si-Al-O glass. As-prepared coating exhibited excellent thermal shock resistance. During thermal shock at ∆T=1200 °C, cracks were formed within the coating, but they did not penetrate through the whole coating due to the toughening mechanisms of the coating, including β-Si₃N₄ particle bridging and crack branching. In addition, the coating had a good crack self-sealing ability during thermal cycling, which is mainly attributed to glass flow and oxidation of β-Si₃N₄ particles within the crack. After thermal cycling for 25 times, the coating still had a good waterproof ability, and the water absorption of the coated porous Si₃N₄ sample increased slightly from 4.5% to 9.3%.