Influence of phase transformation on densification behavior and grain growth of fine silicon nitride powder

Fine and uniform silicon nitride powders having different or-content were prepared from commercial submicron powders by centrifugal sedimentation, The densified pre-sintered materials were fabricated from these powders by hot-pressing. The fine powders with similar particle size distribution showed the same densification behavior during hot-pressing. The microstructures of pre-sintered materials of the fine powders showed the fine and homogeneous microstructures, and the similar one irrespective of alpha content, The pre-sintered materials were annealed at 1800 degrees C for 1h under 1 MPa nitrogen atmosphere. The annealed material from the fine beta powder showed the fine and homogeneous microstructure. On the other hand, the material from the fine alpha powder developed ''in-situ composite'' microstructure consisting of large grains and fine matrix grains by annealing, Because, the abnormal grain growth was caused by the alpha- to beta- phase transformation during annealing. While, these results of the fine powders were compared with those of the commercial submicron powders.