2020 Volume 30 Issue 3 Pages 210-215
Transparent nanopolycrystalline cubic silicon nitride (γ-Si3N4) was fabricated under high pressure and temperature using Kawai-type apparatus. Vickers indentation tests were carried out and the hardness value of 35 GPa was obtained. Fracture toughness was estimated based on length of crack generated from the Vickers indentation prints and the estimated value is 3.5 MPa m1/2, which is similar to that of polycrystalline alumina. Elastic moduli of this material were measured by Brillouin spectroscopy. These results show that cubic silicon nitride is one of the third hardest materials. We confirmed excellent thermal metastability of this material in air at temperatures up to 1,460℃. Low-temperature heat capacities of β- and γ-Si3N4 were measured and the equilibrium phase boundary between these two phases were calculated.
