Pressure-free reactive-sintered SiC/Si₃N₄ composites under switching Ar and N₂: Preparation, microstructure, and properties

SiC/Si₃N₄ composites, renowned for their excellent overall performance, are widely used in various applications. This work focuses on enhancing their preparation process. By employing a coat-mix technique for raw materials to coat Si particles with phenolic resin, pressure-free reactive sintered SiC/Si₃N₄ composites (PFRSSCSN) were successfully obtained through stepwise low-temperature carbonization and high-temperature nitridation of Si under switching between Ar and N₂. This approach effectively resolved issues of residual carbon and silicon, as well as the uneven dispersion of SiC. The resulting composites exhibited low thermal conductivity. With 5 wt% to 20 wt% SiC, the microstructure was refined, and both mechanical properties and thermal conductivity were improved. The synergy between sintering additives (Y₂O₃ and Al₂O₃) and catalyst (Ni(NO₃)₂·6H₂O) promoted efficient sintering and phase synthesis, enhancing flexural strength and fracture toughness by 289.37 % and 621.87 %. Toughening mechanisms, including particle dispersion enabling fiber pull-out, bridging, and crack deflection, work synergistically to enhance toughness. This study opens new pathways for fabrication and expands the research on ceramic toughening.