Intergrown columnar clusters toughening silicon nitride ceramics

Silicon nitride (Si₃N₄) is an excellent candidate for engineering ceramics; however, its toughness and hardness remain fundamentally constrained by the inherent limitations arising from the incompatible α-phase (characterized by high hardness) and β-phase (characterized by high toughness). Herein, we report the exploration of advanced Si₃N₄ ceramics enabled by an intergrown cluster microstructure, which achieves a synergistic enhancement in both toughness (10.2±0.3 MPa·m^1/2) and Vickers hardness (20.1±0.3 GPa). These synergistic properties represent the state-of-the-art among Si₃N₄ ceramics fabricated via liquid-phase sintering reported to date. The formation of columnar clusters is driven by a high-pressure-induced coarsening process. The established metastable growth mechanism may open an avenue for fabricating new-generation Si₃N₄ ceramics with superb performance.