The effect of seeds on the microstructure and mechanical properties of self-reinforced Si₃N₄ with La₂O ₃-Y₂O₃

The effect of seeds on the microstructure and mechanical properties of self-reinforced Si₃N₄ with La₂O ₃-Y₂O₃ was investigated. The results show that with the adding of seeds, large elongated β-Si₃N₄ grains increased. The higher the seeds content, the larger the area ratio of large elongated grains, the coarser the microstructure. The fracture toughness of self-reinforced Si₃N₄ could be improved without affecting the strength, producing a microstructure having coarse elongated β- Si₃N₄ grains distributed without contact each other by adjusting the content of seeds. It is also shown that, the bridging caused by coarse columnar grains is the predominant mechanism. The improvement of fracture toughness could be related quantitatively with diameter and area ratio of columnar β-Si₃N₄ grains.