Effect of the ratio of Y2O3 and MgSiN2 sintering additives on the microstructure, thermal and mechanical properties of Si3N4 ceramics

To investigate the mechanism of the influence of the sintering additive ratio on the microstructure evolution of silicon nitride (Si3N4) ceramics, Si3N4 ceramics were prepared by gas pressure sintering using different ratios of Y2O3/MgSiN2 as additives. Varying the ratio of Y2O3/MgSiN2 changed the composition of the liquid phase, thereby affecting the densification process and phase transformation rate of Si3N4 ceramics, and ultimately changing their microstructure. The reduction in the Y2O3/MgSiN2 ratio raised the N/O and Si/O ratios in the system, which increased the liquid phase viscosity. The Si3N4 grain distribution varied from "normal to bimodal". In the case of increasing the proportion of MgSiN2 and prolonging the sintering time, more of the glass phase evaporated, which reduced the content of the low thermal conductivity phase and increased the continuity of Si3N4/Si3N4. Therefore, Si3N4 ceramics with 1 wt% Y2O3 and 5 wt% MgSiN2 exhibited excellent properties after sintering at 1900 degrees C for 12 h, with thermal conductivity, bending strength, and fracture toughness of 106.7 Wm- 1K-1, 776 MPa, and 11.66 MPa m1/2, respectively.