Preparation of porous Si3N4 ceramics with excellent mechanical properties:effect of the grain growth mechanism on microstructure evolution

In recent years, porous Si 3 N 4 ceramics have been recognized as the most promising materials for radomes. In this study, porous Si 3 N 4 ceramics with excellent mechanical properties have been successfully prepared by adding 2 wt% Lu 2 O 3 , of which the effect of sintering temperature on the grain growth mechanism is investigated for microstructure tailoring. When sintered at 1720 °C, the lower liquid viscosity allows the grain growth rate to match with dissolution-precipitation process. Through this process, the grains further grew together to form a more homogeneous rod-like structure, resulting in a more concentrated aspect ratio and particle size distribution . In addition, the grains along the c-axis grew faster due to the Lu 3+ ions, resulting in a higher aspect ratio. However, when further increased to 1750 °C, the viscosity of the liquid decreases significantly, leading to the precipitation of a large number of β-Si 3 N 4 nuclei. Due to the combined effect of the steric hindrance and the liquid phase mainly distributed at the ends of the grains, a short and thick morphology with a thick center and fine ends is formed, which is unfavorable to the bending strength . Therefore, when the porosity of the sample at 1720 °C is 64.5 %, the bending strength can still reach 162 MPa with a structure factor of 2.82.