Effect of Si addition on the mechanical and thermal properties of sintered reaction bonded silicon nitride

Advanced silicon nitride (Si3N4) ceramics were fabricated using a mixture of Si3N4 and silicon (Si) powders via conventional processing and sintering method. These Si3N4 ceramics with sintering additives of ZrO2 + Gd2O3 + MgO were sintered at 1800 °C and 0.1 MPa in N2 atmosphere for 2 h. The effects of added Si content on density, phases, microstructure, flexural strength, and thermal conductivity of the sintered Si3N4 samples were investigated in this study. The results showed that with the increase of Si content added, the density of the samples decreased from 3.39 g/cm3 to 2.92 g/cm3 except for the sample without initial Si3N4 powder addition, while the thermal diffusivity of the samples decreased slightly. This study suggested that addition of Si powder, which varied from 0 to 100%, in the starting materials might provide a promising route to fabricate cost-effective Si3N4 ceramics with a good combination of mechanical and thermal properties.