Hard and tough novel high-pressure γ-Si3N4/Hf3N4 ceramic nanocomposites

Cubic silicon nitride (γ-Si3 N4) 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-Si3 N4 /Hf3 N4 ceramic nanocomposite derived from single-phase amorphous silicon (Si)-hafnium (Hf)–nitrogen (N) precursor. The synthesis of the γ-Si3 N4 /Hf3 N4 nanocomposite is performed at ~20 GPa and ca. 1500 ℃ in a large volume multi anvil press. The structural evolution of the amorphous precursor and its crystallization to γ-Si3 N4/Hf3N4 nanocomposites under high pressures is assessed by the in situ synchrotron energy-dispersive X-ray diffraction (ED-XRD) measurements at ~19.5 GPa in the temperature range of ca. 1000-1900 ℃. The fracture toughness (KIC) of the two-phase nanocomposite amounts ~6/6.9 MPa·m1/2 and is about 2 times that of single-phase γ-Si3 N4, 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.