Silicon nitride polyphase systems: fabrication, microstructure, and properties

Abstract

Known interrelationships between fabrication, phase equilibrium, microstructure, and properties are reviewed for dense, polyphase silicon nitride materials fabricated with densification aids. In the first and second sections the raw materials, the manufacture of silicon nitride powder, impurities in these powders, and the two Si₃N₄ crystal structures are reviewed. In the third section the densification process, phase relationships of known systems, volatilization phenomena, and development of microstructure are dealt with. The final section is concerned with properties, Le. fracture toughness, strength, creep, and oxidation phenomena, and how these properties are related to the secondary phases and microstructure of the materials.