Deformation-resistant Ta_0.2Hf_0.8C solid-solution ceramic with superior flexural strength at 2000°C

In this study, we explored the consolidation, solid-solution formation and high-temperature properties of tantalum hafnium carbide with the 1 TaC:4 HfC ratio, that is, Ta_0.2Hf_0.8C. Tantalum hafnium carbide bulks can be consolidated using spark-plasma sintering only at temperatures exceeding 2200°C. The bulks prepared using a 40-min dwell at 2200°C had the lattice parameter a = 4.571(9) Å. Based on the three-point flexural tests, it was observed that the toughness and strength of Ta_0.2Hf_0.8C remained high at 2000°C (3.4 ± 0.4 MPa m^1/2, 500 ± 20 MPa). At 2000°C, majority of carbides show a plastic behavior, but the strain-stress curves of the SPSed Ta_0.2Hf_0.8C ceramic were linear. Using the shrinkage rate data during the SPS and the strain-stress data from the high-temperature flexure, we estimated the activation energies for the densification and flexure as 820 ± 20 kJ/mol and 1180 ± 120 kJ/mol, respectively.