Hard and tough novel high-pressure <i>γ</i>-Si <sub>3</sub>N <sub>4</sub>/Hf <sub>3</sub>N <sub>4</sub> ceramic nanocomposites
Wei Li, Zhaoju Yu, L. Wiehl, Tianshu Jiang, Ying Zhan, Emmanuel Ricohermoso, Martin Etter, Emanuel Ionescu, Qingbo Wen, C. Lathe, Robert Farla, Dharma Teppala Teja, Sebastian Bruns, Marc Widenmeyer, Anke Weidenkaff, Leopoldo Molina‐Luna, Ralf Riedel, Shrikant Bhat
Abstract
Cubic silicon nitride (γ-Si<sub>3</sub>N<sub>4</sub>) 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-Si<sub>3</sub>N<sub>4</sub>/Hf<sub>3</sub>N<sub>4</sub> ceramic nanocomposite derived from single-phase amorphous Si-Hf-N precursor. The synthesis of the γ-Si<sub>3</sub>N<sub>4</sub>/Hf<sub>3</sub>N<sub>4</sub><sub> </sub>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-Si<sub>3</sub>N<sub>4</sub>/Hf<sub>3</sub>N<sub>4</sub> nanocomposites under high pressure is assessed by <em>in situ</em> 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<sup>1/2</sup> and is about 2 times that of single-phase γ-Si<sub>3</sub>N<sub>4</sub>, 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-Si<sub>3</sub>N<sub>4</sub>-based nanocomposites with excellent thermal stabililty.