Low‐temperature synthesis of high‐entropy (Hf0.2Ti0.2Mo0.2Ta0.2Nb0.2)B2 powders combined with theoretical forecast of its elastic and thermal properties

A theoretical calculation combined with experiment was used to study high‐entropy (Hf0.2Ti0.2Mo0.2Ta0.2Nb0.2)B2 (HEB‐HfTiMoTaNb). The theoretical calculation suggested HEB‐HfTiMoTaNb could be stable over a wide temperature range. Then, a novel solvothermal/molten salt‐assisted borothermal reduction method was proposed to efficiently pre‐disperse transitional metal atoms in a precursor and synthesize (Hf0.2Ti0.2Mo0.2Ta0.2Nb0.2)B2 nanoscale powders at 1573 K for 6 h, which is nearly 300 K lower than previous reports. The characterization results indicated that the as‐synthesized nanoscale HEB‐HfTiMoTaNb powder was hexagonal single‐phase with homogeneous elements distribution and uniform size, and the oxygen content of the particles is 0.97 wt%. Simultaneously, the mechanical properties, anisotropic nature, and thermal properties of HEB‐HfTiMoTaNb were investigated by density functional theory (DFT) calculations. The Cannikin's law was adopted to explain the improvement of comprehensive mechanical properties. In addition, a significant reduction of thermal conductivity was observed for HEB‐HfTiMoTaNb and it only was 1/15 of the value of HfB2. This work suggests a reliable technique for synthesis of nanosized HEB powders and discovery of high‐entropy materials under the guidance of first‐principle theory. The solvothermal treatment enables a molecular scale uniform distribution of transition metal in precursors and the molten salt liquid media can accelerate the diffusion rate of the reactants and reduce the average diffusion distance. Attributed to the above beneficial features, the (Hf0.2Ti0.2Mo0.2Ta0.2Nb0.2)B2 powders size was minimized and the synthesis temperature was reduced by 300 K, significantly lower than 1873 K when the traditional method was used. The theoretical predictions based on density function theory (DFT) calculations indicated the high entropy can significantly improve the comprehensive mechanical properties, anisotropic nature and thermal properties of (Hf0.2Ti0.2Mo0.2Ta0.2Nb0.2)B2. This work provides a new perspective toward the realization of synthesizing nanosized high entropy materials with high compositional uniformity under relatively mild conditions and the theoretical guidance for screening and developing various high entropy materials.