PREPARATION, MICROSTRUCTURE, AND MECHANICAL PROPERTY RELATIONSHIPS IN SILICON-NITRIDE BASED CERAMICS

Two commercial Si3N4 powders and several sintering aid systems (AIN + Y2O3; Al2O3 + Y2O3; La2O3 + Y2O3) were chosen to produce fully dense materials to investigate the relationships between the preparation methods, microstructure, and mechanical properties of some silicon nitride ceramics. Correlations between the aspect ratio and gi cain size, grain boundary phrase characteristics and Young's modulus, hardness, strength, and fracture toughness are discussed. The study was focused on crack propagation and grain boundary toughness in order to contribute to the understanding of the fracture resistance of silicon nitride based ceramics. (C) 1995 The Institute of Materials.