Effects of sintering additives on mechanical properties and microstructure of Si3N4 ceramics by microwave sintering

Si3N4 ceramics with excellent mechanical properties and microstructure were fabricated by microwave sintering. The effects of sintering additives on the densification, phase transformation and grain growth of Si3N4 ceramics were investigated. The results showed that Y2O3 can promote the phase transformation, MgO can decrease the sintering temperature, Al2O3 can increase the Vickers hardness of the samples and the combination of Y2O3 and MgO was more effective in enhancing the densification and phase transformation in the microwave sintering. The samples with 5 wt%Y2O3, 5 wt%MgO and 2 wt%Al2O3 sintering additives had the optimum mechanical properties when sintered at 1700 ℃ for 10 min. Its relative density, fracture toughness and Vickers hardness were 98.52±0.13%, 6.44±0.02 MPa m1/2 and 14.92±0.20 GPa, respectively. Compared to other microwave sintered Si3N4, the hardness and fracture toughness were enhanced by 6.6-24.3% and 5.6-11%, respectively, while the sintering holding time was reduced by 33.3-83.3%.