Effect of β-Si3N4 starting powder size on elongated grain growth in β-Si3N4 ceramics

The microstructural evolution of pressureless sintered silicon nitride ceramics prepared from different particle sizes of β-Si3N4 as starting powders, has been investigated. When the specimen prepared from as-received β-powder of 0.66 μm in average size, was sintered at 1850°C, equiaxed β-Si3N4 grains were observed. As the size of the initial β-powder went down to 0.26 μm, however, the growth of elongated grains was enhanced, which resulted in a whisker-like microstructure similar to that made from α-starting powder. When the sintering temperature was increased to 2000°C, the elongated grains were also developed even in the specimen made from 0.66 μm β-powder. The observed results were discussed with relation to the two dimensional nucleation and growth theory for faceted crystals. In addition, fracture toughness of the specimen consisting of elongated grains, which was prepared from finer powders, increased.