Abstract

The effects of the beta-Si_3N_4 starting particle size and alpha/beta phase transformation during sintering process on the microstructure evolution of Yttrium alpha-Sialon ceramics were investigated. As-received beta-Si_3N_4 powder (mean particle size: 0.54mum) and classified beta-Si_3N_4 powder(mean particle size: 0.26mum) were used as starting powders. With decreasing the starting particle size, the growth of elongated grains was enhanced, which resulted in the whisker -like microstructure with elongated grains. These results were discussed in relation to the two-dimensional nucleation and growth theory. In the specimen heat treated at 1600°C for 10h before sintering at 1950°Cfor 1h under 40atm(2-step sintering), the grain size was smaller than of the 1-step sintering at 1950°C for 1h. However, bimodal microstructure evolution were not not remarkable in both sample, which is ascribed to the alpha-phase contents existing in beta-Si_3N_4 starting powder.