Pressureless sintering of high performance silicon nitride ceramics at 1620 °C

Abstract

MgO-LiF is used as a sintering aid for the pressureless sintering of silicon nitride (Si3N4) ceramics at 1620 °C. The effects of different LiF contents on the mechanical and thermal properties of Si3N4 ceramics were studied in detail. Si3N4 ceramics with a relative density of 92.08 % were obtained with the addition of 7 wt% MgO + 3 wt% LiF. These ceramics were sintered at 1620 °C. The bending strength, hardness, fracture toughness, and thermal conductivity were 556.73 (± 10.18) MPa, 9.07 (± 0.07) GPa, 6.02 (± 0.29) MPa/m1/2 and 47.59 (± 0.03) W/(m·K), respectively. Si3N4 ceramics with different LiF contents were characterized using XRD and SEM. The introduction of LiF was found to have a positive effect on the transition from the α phase to the β phase in Si3N4 ceramics. The results demonstrate that MgO-LiF is an effective sintering aid for pressureless sintering of silicon nitride ceramics.