Enhancement of thermal shock resistance in β-Si3N4 coating with in situ synthesized β-Si3N4 nanowires/nanobelts on porous Si3N4 ceramics

Abstract

A dense β-Si3N4 coating toughened by β-Si3N4 nanowires/nanobelts was prepared by a combined technique involving chemical vapor deposition and reactive melt infiltration to protect porous Si3N4 ceramics in this work. A porous β-Si3N4 nanowires/nanobelts layer was synthesized in situ on porous Si3N4 ceramics by chemical vapor deposition, and then Y–Si–Al–O–N silicate liquid was infiltrated into the porous layer by reactive melt infiltration to form a dense composite coating. The coating consisted of well-dispersion β-Si3N4 nanowires/nanobelts, fine β-Si3N4 particles and small amount of silicate glass. The testing results revealed that as-prepared coating displayed a relatively high fracture toughness, which was up to 7.9 ± 0.05 MPa m1/2, and it is of great significance to improve thermal shock resistance of the coating. After thermal cycling for 15 times at ΔT = 1200 °C, the coated porous Si3N4 ceramics still had a high residual strength ratio of 82.2%, and its water absorption increased only to 6.21% from 3.47%. The results will be a solid foundation for the application of the coating in long-period extreme high temperature environment.