Relationship between Microstructure and Mechanical Performance of a 70% Silicon Nitride–30% Barium Aluminum Silicate Self-Reinforced Ceramic Composite

The abnormal grain growth of β-Si₃N₄ was observed in a 70% Si₃N₄–30% barium aluminum silicate (70%-Si₃N₄–30%-BAS) self-reinforced composite that was pressureless-sintered at 1930°C; Si₃N₄ starting powders with a wide particle-size distribution were used. The addition of coarse Si₃N₄ powder encouraged the abnormal growth of β-Si₃N₄ grains, which allowed microstructural modification through control of the content and size distribution of β-Si₃N₄ nuclei. The mechanical response of different microstructures was characterized in terms of flexural strength, as well as indentation fracture resistance, at room temperature. The presence of even a small amount of abnormally grown β-Si₃N₄ grains improved the fracture toughness and minimized the variability in flexural strength.