Effect of initial phase composition on the phase composition, microstructure, and mechanical properties of Si₃N₄ ceramics

Abstract

Silicon nitride (Si3N4) ceramics with initial β‐Si3N4 content from 3% to 88% were prepared by spark plasma sintering from 1450 to 1700°C. The effect of initial β‐Si3N4 content on the phase transition, microstructure evolution, and mechanical properties of the Si3N4 ceramics was studied. The existence of initial β‐Si3N4 accelerated the α–β phase transition. When the initial β‐Si3N4 content was 12% and 46%, the aspect ratio of the grains was increased. When the initial β‐Si3N4 content was 88%, the grains were mainly composed of short rod‐like grains. As the initial β‐Si3N4 content increased, the densification process was slowed down. The hardness and fracture toughness of samples reached about 18 GPa and 6 MPa·m1/2. It is proposed that the mechanical properties of samples are connected with the densification process and β‐Si3N4 content.