Materials that can withstand extreme conditions, such as very high temperatures, thermal shocks or corrosive environments are increasingly being studied in order to enable innovative technologies (next generation space vehicles, high temperature turbines, nuclear reactors…). Ultra-High-Temperature Ceramics (UHTC) are interesting candidates as they can maintain their structural stability at temperatures exceeding 3000 K. Among all materials, tantalum carbide (TaC) and hafnium carbide (HfC) have the highest melting temperature (>3500 K) [1]. Recently, hafnium carbo-nitride HfC0.56N0.38 was reported in a modelling work as the compound with the highest melting temperature (>4000 K) [2]. Based on this result and the development of novel experimental techniques, both for the synthesis and the characterisation of UHTC, we studied the hafnium and tantalum carbo-nitride systems. One of the goals is to investigate experimentally compounds close to the composition HfC0.56N0.38. The synthesis of UHTC was done by spark plasma sintering which allows densification of these materials at temperature below 2273 K. Chemical and structural properties of the samples were analysed by several techniques, such as X-ray diffraction, scanning electron microscope or light element analysing. These characterisations allowed finding the optimum sintering parameters. Mechanical properties of selected samples were determined by mechanical experiments like nano-indentation. Finally, thermophysical properties, such as the melting point of the UHTC, were obtained by using a non-contact laser heating method [3].

[1] W. G. Fahrenholtz and G. E. Hilmas, ‘Ultra-high temperature ceramics: Materials for extreme environments’, Scr. Mater., vol. 129, pp. 94–99, Mar. 2017.

[2] Q.-J. Hong and A. van de Walle, ‘Prediction of the material with highest known melting point from ab initio molecular dynamics calculations’, Phys. Rev. B, vol. 92, no. 2, p. 020104, Jul. 2015.

[3] D. Manara, M. Sheindlin, W. Heinz, and C. Ronchi, ‘New techniques for high-temperature melting measurements in volatile refractory materials via laser surface heating’, Rev. Sci. Instrum., vol. 79, no. 11, p. 113901, Nov. 2008.