Silicon nitride, Si₃N₄, ceramics were produced using either silicon or silicon nitride powder. The silicon was reaction bonded in nitrogen atmosphere to form reaction bonded Si₃N₄,which was then sintered between 1700°C and 1800°C to form a dense Si₃N₄ ceramic. The silicon nitride powder compacts were also sintered between 1700°C and 1800°C. In order to achieve densification Y₂O₃-A1₂O₃ additive combination was used in both processing routes. The physical and mechanical properties of the Si₃N₄ materials was found to be dependent on the processing conditions. The post sintered reaction bonded Si₃N₄ materials had the highest densities and hardness values, while the sintered Si3N4 materials had the highest strength and toughness values. The microstructure was also influenced to a great extent by the processing conditions, and this in tum influenced the mechanical properties of the ceramics.

Bibliography: pages 129-139.