The Effect of Al2O3 addition on the Characteristics of Sintering Behavior, Phase Transformation and Mechanical Properties of Spark Plasma Sintered Si3N4 Ceramics

Silicon nitride(Si3N4) is one of the most widely used structural ceramic materials. However silicon nitride is difficult to sinter because of its strong covalent bonding characteristics. In this study, Si3N4 ceramics were fabricated by spark plasma sintering process with Y2O3 and Al2O3 addition to improve the sinterability and the mechanical properties and their phase transformation behavior, microstructure and mechanical properties were evaluated. Fully densified Si3N4 ceramics could be obtained by spark plasma sintering process at a lower temperature than conventional sintering method. The formation of network microstructure was affected by the addition of Al2O3 because it could accelerate alpha to beta phase transformation of Si3N4. As a result, the mechanical properties depended on amounts of Al2O3 addition. The hardness value increased with increasing beta-phase fraction, but fracture toughness value increase with increasing beta-phase fraction.