RELATIONSHIPS BETWEEN PROCESSING, MICROSTRUCTURE AND PROPERTIES OF DENSE AND REACTION-BONDED SILICON-NITRIDE

Some aspects of processing, microstructure and properties of the various types of silicon nitride are discussed. Special emphasis is placed on the relationships between powder properties, process conditions, densification and microstructure, as well as the inter-dependence between microstructure and properties. After summarizing the areas of crystal structure and thermodynamic properties, and processing of the different types of Si//3N//4, the state-of-the-art of dense and reaction-bonded silicon nitride is given. For both types the formation mechanisms and microstructure, relationships between powder properties, additives (in the case of dense Si//3N//4), process conditions, and densification and microstructure, as well as data and microstructural effects of various mechanical, thermal and thermo-mechanical properties, are outlined. Advanced processing techniques, such as sintering, gas-pressure sintering, post-sintering, and the different routes of hot-isostatic pressing (starting with powder compacts, reaction-bonded Si//3N//4 or pre-sintered Si//3N//4), and the resulting properties, are discussed.