Hard and tough novel high-pressure γ-Si 3N 4/Hf 3N 4 ceramic nanocomposites

Cubic silicon nitride (γ-Si₃N₄) is superhard and one of the hardest materials after diamond and cubic boron nitride (cBN), but has higher thermal stability in an oxidizing environment than diamond, making it a competitive candidate for technological applications in harsh conditions (e.g., drill head and abrasives). Here, we report the high-pressure synthesis and characterization of the structural and mechanical properties of a γ-Si₃N₄/Hf₃N₄ ceramic nanocomposite derived from single-phase amorphous Si-Hf-N precursor. The synthesis of the γ-Si₃N₄/Hf₃N₄ nanocomposite is performed at ~20 GPa and  ca. 1500 °C in a large volume multi anvil press. The structural evolution of the amorphous precursor and its crystallization to γ-Si₃N₄/Hf₃N₄ nanocomposites under high pressure is assessed by in situ synchrotron energy-dispersive X-ray diffraction measurements at ~19.5 GPa in the temperature range from ca. 1000-1900 °C. The fracture toughness of the two-phase nanocomposite amounts ~6/6.9 MPa·m^1/2 and is about 2 times that of single-phase γ-Si₃N₄, while its hardness of ca. 30 GPa remains high. This work provides a reliable and feasible route for the synthesis of advanced hard and tough γ-Si₃N₄-based nanocomposites with excellent thermal stabililty.