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 silicon (Si)–hafnium (Hf)–nitrogen (N) precursor. The synthesis of the γ-Si3N4/Hf3N4 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-Si3N4/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-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.

We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association of German Research Centres (HGF), for the provision of experimental facilities. Part of this research was carried out at PETRA III LVP at beamline P61B (beamtime I-20200434) and P02.1. Shrikant Bhat and Robert Farla acknowedge the support from the Federal Ministry of Education and Research, Germany (BMBF; Nos. 05K16WC2 and 05K13WC2). Wei Li and Leonore Wiehl also acknowledge the travel support from DESY. Zhaoju Yu thanks the National Natural Science Foundation of China (Nos. 51872246 and 52061135102) for financial support. Marc Widenmeyer and Anke Weidenkaff are grateful for the financial support by the German Ministry of Education and Research (No. 03SF0618B). Wei Li acknowledges the financial support from China Scholarship Council (No. 201907040060).