Synergistic improvement of flexural strength and fracture toughness in Si ₃ N ₄ ceramics featuring high-entropy grain boundary phase

Developing silicon nitride (Si3N4) ceramics with concurrently enhanced flexural strength and fracture toughness presents significant challenges due to the critical dependence of these macroscopic properties on microstructure. This study produced high-performance Si3N4 ceramics by employing multiple rare earth oxides (RE2O3) as sintering additives to construct a multi-component rare earth ion liquid phase via hot pressing sintering (HPS). The designed multi-component RE-ion liquid phase reduces shrinkage onset temperature while facilitating densification and α→β phase transformation. Synergistic effects among the multi-component RE-ion liquid phase foster a distinct bimodal microstructure characterized by an optimized spatial distribution of refined matrix grains interlocked with elongated rod-like β-Si3N4 grains exhibiting elevated aspect ratios. Concurrently, the multi-component RE-ion liquid phase crystallizes into a high-entropy (Gd0.2Y0.2Yb0.2Lu0.2Sc0.2)2Si2O7, enabling high crystallinity of grain boundary phase in Si3N4 ceramics. Through concurrent optimization of microstructure and grain boundary phase properties in Si3N4 ceramics, synergistic enhancement in flexural strength (1322 MPa) and fracture toughness (10.88 MPa·m1/2) is achieved. Collectively, this high-entropy approach establishes a highly promising transformative strategy for developing high-performance structural ceramics.