Effects of two-step sintering on microstructure and properties of self-reinforced Si₃N₄ containing La₂O₃-Y₂O₃

To improve high temperature properties of ceramics in aero-engine, one-step sintering was replaced with two-step sintering. Experiment shows that the growth of β-Si₃N₄ grains in two-step sintering is quite different from that in one-step sintering. This is because that: (1) In one-step sintering, phase transformation occurs first and then grain growth occurs, both at the same temperature; (2) In two-step sintering, phase transformation occurs first at one temperature (1700°C in the experiments) and then grain growth occurs at a higher temperature (1800°C in the experiments). The fracture toughness measured at room temperature is 12.3MPa √m for two-step sintering as against 11.2MPa √m for one-step sintering.