Effects of Gd2O3 and MgSiN2 Sintering Additives on the Thermal Conductivity and Mechanical Properties of Si3N4 Ceramics

Si3N4 ceramics were prepared by gas pressure sintering at 1900 degrees C for 12 h under a nitrogen pressure of 1 MPa using Gd2O3 and MgSiN2 as sintering additives. The effects of the Gd2O3/MgSiN2 ratio on the densification, microstructure, mechanical properties, and thermal conductivity of Si3N4 ceramics were systematically investigated. It was found that a low Gd2O3/MgSiN2 ratio facilitated the thermal diffusivity of Si3N4 ceramics while a high Gd2O3/MgSiN2 ratio benefited the densification and mechanical properties. When the Gd2O3/MgSiN2 ratio was 1:1, Si3N4 ceramics obtained an obvious exaggerated bimodal microstructure and the optimal properties. The thermal conductivity, flexural strength, and fracture toughness were 124 W center dot m(-1)center dot k(-1), 648 MPa, and 9.12 MPa center dot m(1/2), respectively. Comparing with the results in the literature, it was shown that Gd2O3-MgSiN2 was an effective additives system for obtaining Si3N4 ceramics with high thermal conductivity and superior mechanical properties.