Improving the thermal conductivity and mechanical properties of Si ₃ N ₄ ceramic by regulating bimodal microstructure

Abstract The preparation of silicon nitride (Si 3 N 4 ) ceramics with high thermal conductivity and excellent mechanical properties has been a challenge, which limits their application in high‐power devices. In this work, a two‐step sintering process was designed to regulate the content of in situ‐generated β‐Si 3 N 4 seeds, which enables fine control of the bimodal microstructure and the successful fabrication of Si 3 N 4 ceramics with excellent properties. Remarkably, the mechanism of bimodal microstructure evolution of two‐step sintered Si 3 N 4 ceramics is elucidated, and the effect of the difference in the degree of bimodal microstructure on thermal conductivity and mechanical properties is also explained. After pre‐sintering at 1390°C for 2 h and second‐step sintering at 1900°C for 12 h, the thermal conductivity, bending strength, and fracture toughness of Si 3 N 4 ceramics were 104.6 ± 0.36 W·m −1 ·K −1 , 725 ± 14.5 MPa, and 9.9 ± 0.65 MPa·m 1/2 , respectively. Overall, this study provides a strategy to enhance the thermal and mechanical properties of Si 3 N 4 ceramics by optimizing the bimodal microstructure.