Effect of hot-pressing temperature on the properties of Si3N4 ceramics with a low content of eutectic CaO–Al2O3 sintering additive

This study investigates the influence of hot-pressing temperature on the phase composition, microstructure, mechanical and thermophysical properties of silicon nitride (Si 3 N 4 ) ceramics containing 1.5 wt% of the CaO–Al 2 O 3 low-temperature eutectic sintering additive. The ceramics were obtained by hot pressing at 1600–1750 °C in a nitrogen atmosphere. Complete α→β phase transformation was achieved at 1650 °C, and further temperature increases led to progressive grain coarsening and elongation, accompanied by improved densification. As a result, the Vickers hardness, fracture toughness, flexural strength, and Young's modulus reached their peak values at 1750 °C. Thermal conductivity increased from 17.5 to 22.6 W m −1 K −1 , correlating with grain growth and elastic modulus enhancement. These findings confirm that dense, high-performance Si 3 N 4 ceramics can be obtained using a minimal amount of additive through optimized hot pressing.