Mechanical properties of Si3N4 ceramics from an in-situ synthesized a-Si3N4/β-Si3N4 composite powder

Sintered Si3N4 ceramics were prepared from an ɑ-Si3N4/β-Si3N4 whiskers composite powder in-situ synthesized via carbothermal reduction at 1400-1550 °C in a nitrogen atmosphere from SiO2, C, Ni, and NaCl mixture. Reaction temperatures and holding time for the composite powder, and mechanical properties of sintered Si3N4 were investigated. In the synthesized composite powder, the in-situ β-Si3N4 whiskers displayed an aspect ratio of 20-40 and a diameter of 60-150 nm, which was mainly dependent on the synthesis temperature and holding time. The flexural strength, fracture toughness and hardness of the sintered Si3N4 material reached 794±136 MPa, 8.60±1.33 MPa m1/2 and 19.00±0.87 GPa, respectively. The in-situ synthesized β-Si3N4 whiskers played a role in toughening and strengthening by whiskers pulling out and crack deflection.