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

Abstract Silicon nitride (Si 3 N 4 ) ceramics with initial β‐Si 3 N 4 content from 3% to 88% were prepared by spark plasma sintering from 1450 to 1700°C. The effect of initial β‐Si 3 N 4 content on the phase transition, microstructure evolution, and mechanical properties of the Si 3 N 4 ceramics was studied. The existence of initial β‐Si 3 N 4 accelerated the α–β phase transition. When the initial β‐Si 3 N 4 content was 12% and 46%, the aspect ratio of the grains was increased. When the initial β‐Si 3 N 4 content was 88%, the grains were mainly composed of short rod‐like grains. As the initial β‐Si 3 N 4 content increased, the densification process was slowed down. The hardness and fracture toughness of samples reached about 18 GPa and 6 MPa·m 1/2 . It is proposed that the mechanical properties of samples are connected with the densification process and β‐Si 3 N 4 content.