Microstructural characterization and mechanical properties of self-reinforced Si₃N₄ ceramics containing high oxynitride glass

Self-reinforced Si₃N₄ ceramics containing high oxynitride glass have been fabricated by the control of microstructure evolution and β-Si₃N₄ grain growth. The effects of the size distribution of the elongated β-Si₃N₄ grains, and the β-Si₃N₄ grain growth as well as the oxynitride glass chemical characteristic on the microstructure and mechanical properties were investigated. The experimental results show that the β-Si₃N₄ grains in high oxynitride glass grow to elongated rod-like crystals and form the stereo-network structure. Under the sintering conditions of 1800°C and 60 min, a quite uniform microstructure with an average aspect ratio of 6.5 and an average of 1 μm can be obtained. A large amount of oxynitride glass phase with high nitrogen content enhances the elevated temperature fracture toughness because of its high softening temperature and high viscosity. In the present material, the crack deflection and pullout of the elongated rod-like β-Si₃N₄ grains are the primary toughening mechanisms.