High aspect ratio β-Si3N4 grain growth

It has been shown by others that high aspect ratio beta-Si3N4 grains formed in-situ on sintering lead to high fracture toughness in Si3N4 ceramics. In this work beta-Si3N4 powder was sintered at 1750 degrees C for varying times with Y2O3, La2O3, SiO2, and CaO additives. The microstructure of the materials was examined by electron microscopy and microanalysis. The beta-Si3N4 grain growth rate was controlled by diffusion through the liquid phase. A maximum aspect ratio of about 20 was observed for beta-Si3N4 grains heated for 6 h and was dependent on the chemistry of the liquid phase present. The formation of high aspect ratio Si3N4 at a relatively low temperature and short sintering times is discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.