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

Cubic silicon nitride (gamma-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 gamma-Si3N4/Hf3N4 ceramic nanocomposite derived from single-phase amorphous silicon (Si)-hafnium (Hf)-nitrogen (N) precursor. The synthesis of the gamma-Si3N4/Hf3N4 nanocomposite is performed at similar to 20 GPa and ca. 1500 degrees C in a large volume multi anvil press. The structural evolution of the amorphous precursor and its crystallization to gamma-Si3N4/Hf3N4 nanocomposites under high pressures is assessed by the in situ synchrotron energy-dispersive X-ray diffraction (ED-XRD) measurements at similar to 19.5 GPa in the temperature range of ca. 1000-1900.. The fracture toughness (KIC) of the two-phase nanocomposite amounts similar to 6/6.9 MPa center dot m1/2 and is about 2 times that of single-phase gamma-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 gamma-Si3N4-based nanocomposites with excellent thermal stabililty.