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

A proper powder preparation technique was used to develop elongated β–Si₃N₄ particles as seeds from raw materials. The phase transformation and development of microstructure in Si₃N₄ ceramics containing β–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 β-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.