Correlation between microstructure and toughness of hot pressed Si3N4 ceramics seeded with β-Si3N4 particles

Silicon nitride materials with distinct microstructures have been prepared by hot-pressing mixtures of α-Si3N4 powders plus oxide additives and β-Si3N4 seeds. These seeds were β crystals obtained by the SHS technology. The presence of these β-Si3N4 particles retarded the densification rate. The influence of the holding time at the sintering temperature on the microstructure and mechanical properties has been analysed in the β-seeded Si3N4 materials, in comparison with the non-seeded materials. These β-seeds were effective in enhancing α→β transformation and the general coarsening of the microstructure. The toughness has been discussed as a function of microstructural parameters, such as average grain size, average aspect ratio and area fraction of elongated grains.