Tailoring Microstructure of High‐Thermal‐Conductivity Si ₃ N ₄ Ceramics Through β‐Si ₃ N ₄ Incorporation

Silicon nitride (Si 3 N 4 ) ceramics are widely applied in electronic packaging due to their excellent mechanical properties and high thermal conductivity. This study systematically investigated the effects of β‐Si 3 N 4 size and content on the sintered reaction‐bonded silicon nitride (SRBSN) ceramics, with particular focus on nitridation behavior, microstructure development, and resultant properties. Results show that fine β‐Si 3 N 4 (1 µm) enhances α→β phase transition rate during nitridation, promoting a bimodal microstructure after sintering. Coarse β‐Si 3 N 4 (3 µm, 10 µm) reduces nucleation sites but accelerates Ostwald ripening during sintering, resulting in pronounced grain coarsening. A moderate amount of β‐Si 3 N 4 promotes grain growth and increases the aspect ratio, whereas excessive coarse β‐Si 3 N 4 forms a rigid particle skeleton, impairing densification. Thermal conductivity increased with grain coarsening due to reduced grain boundary, reaching a maximum of 124.7 W·m −1 ·K −1 for the sample with 30 wt% 10 µm β‐Si 3 N 4 . The flexural strength was strongly influenced by grain size and aspect ratio, and peaked at 903 ± 17 MPa for the sample with 20 wt% of 1 µm β‐Si 3 N 4 . A sample with 10 wt% of 3 µm β‐Si 3 N 4 demonstrated the excellent comprehensive properties, achieving a flexural strength of 758 ± 27 MPa and a thermal conductivity of 111.8 W·m −1 ·K −1 .