Thermophysical and mechanical properties of novel high‐entropy metal nitride‐carbides

Abstract In this work, a novel (Hf 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )(N 0.5 C 0.5 ) high‐entropy nitride‐carbide (HENC‐1) with multi‐cationic and ‐anionic sublattice structure was reported and their thermophysical and mechanical properties were studied for the first time. The results of the first‐principles calculations showed that HENC‐1 had the highest mixing entropy of 1.151R, which resulted in the lowest Gibbs free energy above 600 K among HENC‐1, (Hf 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )N high‐entropy nitrides (HEN‐1), and (Hf 0.2 Zr 0.2 Ta 0.2 Nb 0.2 Ti 0.2 )C high‐entropy carbides (HEC‐1). In this case, HENC‐1 samples were successfully fabricated by hot‐pressing sintering technique at the lowest temperature (1773 K) among HENC‐1, HEN‐1 and HEC‐1 samples. The as‐fabricated HENC‐1 samples showed a single rock‐salt structure of metal nitride‐carbides and high compositional uniformity. Meanwhile, they exhibited high microhardness of 19.5 ± 0.3 GPa at an applied load of 9.8 N and nanohardness of 33.4 ± 0.5 GPa and simultaneously possessed a high bulk modulus of 258 GPa, Young's modulus of 429 GPa, shear modulus of 176 GPa, and elastic modulus of 572 ± 7 GPa. Their hardness and modulus are the highest among HENC‐1, HEN‐1 and HEC‐1 samples, which could be attributed to the presence of mass disorder and lattice distortion from the multi‐anionic sublattice structure and small grain in HENC‐1 samples. In addition, the thermal conductivity of HENC‐1 samples was significantly lower than the average value from the “rule of mixture” between HEC‐1 and HEN‐1 samples in the range of 300‐800 K, which was due to the presence of lattice distortion from the multi‐anionic sublattice structure in HENC‐1 samples.