Tailored grain growth strategy for Si3N4 ceramics with enhanced thermal and mechanical performance

To achieve high-performance Si₃N₄ ceramics for advanced thermal management, this study proposes a synergistic strategy that integrates initial particle gradation with Y 2 O 3 /MgO additive ratio to guide grain growth and microstructure evolution. A bimodal powder blend enhances green body densification and promotes the development of elongated β-Si₃N₄ grains through localized dissolution–precipitation. Simultaneously, an intermediate Y 2 O 3 /MgO ratio effectively modulates the liquid-phase viscosity and interfacial wetting, enabling controlled anisotropic grain growth while suppressing amorphous boundary phases and oxygen impurity. The optimized sample exhibits a refined bimodal microstructure with 20.8 % of grains > 8 μm and a maximum mean aspect ratio of ∼2. This tailored microstructure underpins its outstanding thermal conductivity (124 W·m⁻¹·K⁻¹), flexural strength (708 ± 10 MPa), and fracture toughness (9.0 ± 0.5 MPa·m 1/2 ). These results highlight the effectiveness of co-optimizing powder characteristics and additive chemistry to engineer grain architecture and achieve simultaneous enhancement of thermal and mechanical properties in Si₃N₄ ceramics.