The thermal and electrical properties were measured for a high entropy carbide ceramic, consisting of (Hf, Ta, Zr, Nb)C. The ceramic was produced by spark plasma sintering a mixture of the monocarbides and had a relative density of more than 97.6%. The resulting ceramic was chemically homogeneous as a single‐phase solid solution formed from the constituent carbides. The thermal diffusivity (0.045–0.087 cm2/s) and heat capacity (0.23–0.44 J/g•K) were measured from room temperature up to 2000°C. The thermal conductivity increased from 10.7 W/m•K at room temperature to 39.9 W/m•K at 2000°C. The phonon and electron contributions to the thermal conductivity were investigated, which showed that the increase in thermal conductivity was predominantly due to the electron contribution, while the phonon contribution was independent of temperature. The electrical resistivity increased from 80.9 μΩ•cm at room temperature to 114.1 μΩ•cm at 800°C.

Thermal and elastic properties were measured for ceramics that contained as much as 96 wt% zeta phase tantalum carbide (ζ‐Ta4C3−x). The ceramics were produced from tantalum hydride that was milled to reduce particle size and then blended with carbon. Powders were reaction hot‐pressed at 1800°C for 2 hours under a flowing He environment, which resulted in ζ‐Ta4C3−x that was about 99% dense. The main secondary phases present in the reacted ceramic were TaC and Ta2O5. ζ‐Ta4C3−x had a thermal conductivity of 9.6 W/m·K and an electrical resistivity of 160 ± 4.2 μΩ‐cm, which are lower and higher than those of TaC, respectively. The Young's modulus was 379 ± 5 GPa and the hardness was 5.1 ± 0.7 GPa, which are also both lower than TaC. This study is the first to report the thermal properties and elastic moduli of high‐purity ζ‐Ta4C3−x.

Tantalum carbide ceramics containing at least 75-wt% ζ-Ta 4 C 3−x were synthesized and densified to ∼99% of the theoretical density. Flexural strength in four-point bending was measured from room temperature up to 1600 • C, achieving strengths of 710 ± 36.5 MPa at room temperature and decreasing to 180 ± 19.7 MPa at 1600 • C. Fracture toughness was measured via the chevron notch method from room temperature up to 1600 • C, with a toughness of 10.2 ± 0.4 MPa m 1/2 at room temperature and decreasing to 4.7 ± 0.1 MPa m 1/2 at 1600 • C. At 1600 • C, ductile behavior was observed during testing, and mixed mode fracture was observed on all fracture surfaces. Vickers indentations were used at room temperature to damage the surface of specimens and shed some light on damage mechanisms in the material. Kinking and delamination were observed around the indentations. At elevated temperatures, these deformation mechanisms may activate more often, causing a decrease in strength and resulting in ductility between 1400 and 1600 • C. The Griffith analysis was also used to identify critical flaws. The long axis of high aspect ratio grains appears to be the critical flaw from room temperature up to 1400 • C, prior to any ductile behavior.Overall, the nanolaminate microstructures, and the kinking and delamination deformation mechanisms that result from it, are reminiscent of MAX phase and kinking nonlinear elastic materials.