Growth of elongated grains in α-SiAlON ceramics

Abstract

The microstructural evolution of pressureless sintered α-SiAlON, which was made from different particle sizes of α-Si 3N 4 as starting powders have been investigated. The microstructure of the specimens prepared from as-received powder of 0.55 μm in average size, which was sintered at 1850°C, consisted of equiaxed α-SiAlON grains. However, by decreasing the initial α-powder size to 0.27 μm, the growth of elongated grains was enhanced, resulting in a microstructure with elongated grains of a high aspect ratio. In addition, when the specimen prepared from as-received α-Si 3N 4 powder of 0.55 μm in average size was heat treated at 1600°C for 10 h, and then sintered at 1950°C for 1 h, elongated grains were also formed, probably due to the nuclei size reduction by the dissolution of remaining α-Si 3N 4 during intermediate heat treatment. The specimen prepared from finer powders showed increased values of hardness and fracture toughness as a result of the microstructure containing elongated grains.