Hafnium carbonitride

Hafnium carbonitride (HfCN) is an ultra-high temperature ceramic (UHTC) mixed anion compound composed of hafnium (Hf), carbon (C) and nitrogen (N).

Ab initio molecular dynamics calculations have predicted the HfCN (specifically the HfC0.75N0.22 phase) to have a melting point of 4,110 ± 62 °C (4048-4172 C), highest known for any material. Another approach based on the artificial neural network machine learning pointed towards a similar composition — HfC0.76N0.24. Experimental testing conducted in 2020 has confirmed a melting point above 4000 C, substantiating earlier predictions made with atomistic simulations in 2015.

Properties
The HfCxN1−x has been assessed to possess the following properties:
 * Thermal conductivity:
 * 19–24 W·m−1·K−1 at room temperature,
 * 32–39 W·m−1·K−1 at high temperature and with increased nitrogen content.
 * Electrical conductivity: (149×104)–(213×104) Ω−1 m−1
 * Plasticity limit: 2000 C
 * Fusion enthalpy: 150 kJ/mol
 * Flexural strength:
 * 638 ± 28 MPa at room temperature,
 * 324 MPa at 1000 C,
 * 139 MPa at 1600 C,
 * 100 MPa at 2000 C.
 * Fracture toughness: 6.73 ± 0.07 MPa·m1/2, 4.7 ± 0.3 MPa·m1/2
 * Vickers hardness: 19.08 GPa, 21.3 ± 0.55 GPa (21.3 GPa)