Ma Mengdong, Yang Xinyu, Meng Hong, Zhao Zhisheng, He Julong, Chu Yanhui
School of Materials Science and Engineering, South China University of Technology, Guangzhou 510641, China.
Center for High Pressure Science (CHiPS), State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
Fundam Res. 2022 Apr 26;3(6):979-987. doi: 10.1016/j.fmre.2022.04.010. eCollection 2023 Nov.
The development of high-entropy borides with combined structural and functional performance holds untold scientific and technological potential, yet relevant studies have been rarely reported. In this work, we report nanocrystalline (LaCeNdEu)B high-entropy rare-earth hexaboride (HEReB-1) ceramics fabricated through the high-pressure sintering of self-synthesized nanopowders for the first time. The as-fabricated samples exhibited a highly dense (96.3%) nanocrystalline (94 nm) microstructure with major (001) fiber textures and good grain boundaries without any impurities, resulting in a remarkable mechanical, electrical, and thermionic emission performance. The results showed that the samples possessed outstanding comprehensive mechanical properties and a high electrical resistivity from room temperature to high temperatures; these were greater than the average values of corresponding binary rare-earth hexaborides, such as a Vickers hardness of 23.4 ± 0.6 GPa and a fracture toughness of 3.0 ± 0.4 MPa•m at room temperature. More importantly, they showed high emission current densities at elevated temperatures, which were higher than the average values of the corresponding binary rare-earth hexaborides. For instance, the maximum emission current density reached 48.3 A•cm at 1873 K. Such superior performance makes the nanocrystalline HEReB-1 ceramics highly suitable for potential applications in thermionic emission cathodes.
具有结构和功能综合性能的高熵硼化物的发展具有巨大的科技潜力，但相关研究报道很少。在这项工作中，我们首次报道了通过自合成纳米粉末的高压烧结制备的纳米晶（LaCeNdEu）B高熵稀土六硼化物（HEReB-1）陶瓷。制备的样品呈现出高密度（96.3%）的纳米晶（94nm）微观结构，具有主要的（001）纤维织构且晶界良好，无任何杂质，从而具有卓越的机械、电学和热电子发射性能。结果表明，样品具有优异的综合机械性能以及从室温到高温的高电阻率；这些性能优于相应二元稀土六硼化物的平均值，例如室温下维氏硬度为23.4±0.6GPa，断裂韧性为3.0±0.4MPa•m。更重要的是，它们在高温下表现出高发射电流密度，高于相应二元稀土六硼化物的平均值。例如，在1873K时最大发射电流密度达到48.3A•cm。如此优异的性能使得纳米晶HEReB-1陶瓷非常适合热电子发射阴极的潜在应用。
