CONTROL AND CHARACTERIZATION OF ABNORMALLY GROWN GRAINS IN SILICON-NITRIDE CERAMICS

The intrinsic grain growth behavior of beta-Si3N4 was investigated by annealing fine-grained beta-Si3N4 ceramics with 0-30 wt% beta-nuclei. The development of bimodal microstructures was observed in annealed ma terials with 0.1-10 wt% nuclei, caused by the abnormal grain growth of nuclei due to the large driving force. This driving force was related to the difference in nuclei and matrix grain solubility in the liquid phase. The driving force for abnormal grain growth was also related t o the stable morphology of beta-grains of about 4 in aspect ratio. The fact that the driving force was constant in materials with 0.1-3 wt% nuclei is explained by the constant diffusion space for nuclei. Nuclei addition exceeding 10 wt% decreased the driving for ce because of nuc lei interaction. A unimodal microstructure was developed with 30 wt% n uclei addition. (C) 1997 Elsevier Science Limited.