Effect of hexagonal BN on the microstructure and mechanical properties of Si3N4 ceramics

Silicon nitride materials containing various amounts of hexagonal boron nitride were prepared by hot-pressing at 1800 °C for 1 h. Effect of h-BN on microstructure and mechanical properties of h-BN/Si3N4 ceramics was investigated. Analysis of microstructure and properties of the specimens showed that the growth of the elongated β-Si3N4 were hindered by h-BN, which results in the decrease of fracture toughness of silicon nitride with addition of h-BN. However the effect of h-BN on the α → β Si3N4 transformation of the h-BN/Si3N4 composites was negligible. Fiber-like morphology of h-BN was observed in the plane perpendicular to the hot press direction.