Grain Growth During Gas‐Pressure Sintering of β‐Silicon Nitride

The microstructures of gas‐pressure‐sintered materials from β‐Si 3 N 4 powder were characterized in terms of the diameter and aspect ratio of the grains. The size distributions of diameters in materials fabricated by heating for 1 h at 1850° to 2000°C were nearly constant when they were normalized by average diameters because of normal grain growth. The rate‐determining step in the densification and grain growth was expected to be the diffusion of materials through the liquid phase. The activation energy for grain growth was 372 kJ/mol. The average aspect ratio of the grains was 3 to 4, whereas that of large grains was smaller because of shape accommodation. The fracture toughness was about the same as that of material from α‐Si 3 N 4 powder despite the smaller aspect ratio of the grains