Pressureless Sintering Of High Performance Silicon Nitride Ceramics At 1620 Degrees C

MgO-LiF is used as a sintering aid for the pressureless sintering of silicon nitride (Si3N4) ceramics at 1620 degrees 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 degrees 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/m(1/2) 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 alpha phase to the beta phase in Si3N4 ceramics. The results demonstrate that MgO-LiF is an effective sintering aid for pressureless sintering of silicon nitride ceramics.