Microstructure in silicon nitride containing β-phase seeding:: Part I

A proper powder preparation technique was used to develop elongated beta-Si3N4, particles as seeds from raw materials. The phase transformation and development of microstructure in Si3N4 ceramics containing beta-Si3N4 seeds were investigated. The specimens of seeded silicon nitride had higher phase transformation rates than the specimens without seed. A core/shell structure was observed by transmission electron microscopy in seeded specimens owing to the difference in aluminum concentration in Si3N4 grains. The misfit between the core and the shell was accommodated by interfacial dislocation that has a rotation character. The growth mode was epitaxial, although there was some compositional difference between the core and the shell. A relatively larger grain size and wider,grain size distribution in seeded Si3N4 specimens was due to the amount of beta-phase seeds that could act as the nuclei, and the final modification of the microstructure was due to the coalescence process. The crack wake process characterized the mechanism of toughening.