Effects of Temperature on Thermal and Mechanical Properties of Spark Plasma Sintered Silicon Nitride Ceramics

The effects of sintering temperature on mechanical and thermal properties of the SPSed silicon nitride ceramics were investigated. In the present work, silicon nitride ceramics were prepared by spark plasma sintering process at different temperatures (1600, 1700 and 1800 degrees C) with the addition of 6 wt% Lu2O3 and 2 wt% MgO. The silicon nitride ceramics obtained at all sintering temperatures are almost fully dense with both alpha and beta phases existing for the one prepared at 1600 C while all alpha phases are completely transferred to beta phases for the ceramics sintered at 1700 and 1800 degrees C. The thermal conductivity of the silicon nitride ceramics increases with temperature, while the hardness decreases. It may be owe to the larger grain size and less a phase. However, no obvious temperature effects can be found for the fracture toughness. The results show that the sample sintered at 1800 degrees C owns a good combination of thermal property and mechanical properties with thermal conductivity of 45.4 W/(m.K), hardness of (18.10 +/- 0.20) GPa and fracture toughness of (7.32 +/- 0.14) MPa.m(1/2).