Abstract
Si3N4 ceramics were sintered at 1873-2023 K (1600-1750°C) with additives from the SiO2-MgO-Y2O3 system. The degree of densification, α-β transformation, mass loss and microstructure were measured as a function of additives composition, sintering temperature, nitrogen gas pressure, and with/without packing powder. Specimen prepared from 3 mass% SiO2, 3 mass% MgO, and 5 mass% Y2O3 as the sintering additive could be sintered to almost full density at relatively low temperature as 1923 K for 2 h under ambient pressure of nitrogen atmosphere without using packing powder. The α-β transformation was not completed at this condition. The mass loss was relatively high due to the evaporation of SiO2 and MgO. However, the resulted materials have high bending strength as 980 MPa, with fracture toughness of 6.6 MPa•m1/2, Vickers hardness of 18.4 GPa, and thermal conductivity of 34 Wm-1K-1.
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