The effects of the mixing medium,
ultrasonic dispersing, the content of different sintering additives and nano-Ti(C_7N_3) on the mechanical properties and
microstructure are investigated. The results show that the optimum composition is 5%Y_2O_3+5%La_2O_3+5%CeO_2+85%Si_3N_4 through ultrasonic dispersing at the aqueous medium, and composites exhibit the excellent mechanical properties under the condition of sintering temperature 1700～1800℃, soaking for 40min and pressure 30MPa. The
flexural strength,
fracture toughness and
hardness are respectively up to 1002.1MPa, 8.2 MPa·m~ 1/2 and 13.56GPa. The SEM experiments indicate that the microstructure of material is homogenous and the elongated grain ofβ-Si_3N_4 is interlaced. In the Si_3N_4 ceramic
composite with the inclusion of nano-TiC_7N_3, the aspect ratio of grain is decreased remarkably and the second-phase particles is embedded among the interface. As a result, the flexural strength is reduced while the fracture toughness and hardness are improved.