美国加州大学Miao, Jianwei研究团队报道了中、高熵纳米合金的三维原子结构和局部化学有序化。相关研究成果发表在2023年12月20日出版的《自然》。

中、高熵合金（M/HEAs）混合了几种成分接近等原子的主要元素，代表了在冶金，催化和其他领域中设计以前未知材料的模型转换策略。M/HEAs的核心假设之一是晶格畸变，这已经通过不同的数值和实验技术进行了研究。然而，确定M/HEA中的三维（3D）晶格畸变仍然是一个挑战。

此外，X射线和中子研究、原子模拟、能量色散光谱和电子衍射对M/HEAs中假定的随机元素混合提出了质疑，这表明M/HEAs存在局部化学序。然而，3D局部化学有序的直接实验观察一直是困难的，因为能量色散光谱整合了沿带轴的原子柱的组成，并且扩散电子反射可能源于平面缺陷而不是局部化学有序。

该文中，研究人员使用原子电子断层摄影确定M/HEA纳米颗粒的3D原子位置，并定量表征局部晶格畸变、应变张量、孪晶边界、位错核和化学短程有序（CSRO）。研究发现，高熵合金比中熵合金具有更大的局部晶格畸变和更多的非均匀应变，并且该应变与CSRO相关。研究人员还在中熵合金中观察到CSRO介导的孪晶，即孪晶发生在能量不利的CSRO区域，但不发生在能量有利的CSRO区，这代表了首次在任何材料中将局部化学顺序与结构缺陷相关联的实验观察结果。

该项工作不仅能扩展人们对这类重要材料的基本理解，还能为通过工程晶格畸变和局部化学秩序来定制M/HEA特性提供基础。

附：英文原文

Title: Three-dimensional atomic structure and local chemical order of medium- and high-entropy nanoalloys

Author: Moniri, Saman, Yang, Yao, Ding, Jun, Yuan, Yakun, Zhou, Jihan, Yang, Long, Zhu, Fan, Liao, Yuxuan, Yao, Yonggang, Hu, Liangbing, Ercius, Peter, Miao, Jianwei

Issue&Volume: 2023-12-20

Abstract: Medium- and high-entropy alloys (M/HEAs) mix several principal elements with near-equiatomic composition and represent a model-shift strategy for designing previously unknown materials in metallurgy1,2,3,4,5,6,7,8, catalysis9,10,11,12,13,14 and other fields15,16,17,18. One of the core hypotheses of M/HEAs is lattice distortion5,19,20, which has been investigated by different numerical and experimental techniques21,22,23,24,25,26. However, determining the three-dimensional (3D) lattice distortion in M/HEAs remains a challenge. Moreover, the presumed random elemental mixing in M/HEAs has been questioned by X-ray and neutron studies27, atomistic simulations28,29,30, energy dispersive spectroscopy31,32 and electron diffraction33,34, which suggest the existence of local chemical order in M/HEAs. However, direct experimental observation of the 3D local chemical order has been difficult because energy dispersive spectroscopy integrates the composition of atomic columns along the zone axes7,32,34 and diffuse electron reflections may originate from planar defects instead of local chemical order35. Here we determine the 3D atomic positions of M/HEA nanoparticles using atomic electron tomography36 and quantitatively characterize the local lattice distortion, strain tensor, twin boundaries, dislocation cores and chemical short-range order (CSRO). We find that the high-entropy alloys have larger local lattice distortion and more heterogeneous strain than the medium-entropy alloys and that strain is correlated to CSRO. We also observe CSRO-mediated twinning in the medium-entropy alloys, that is, twinning occurs in energetically unfavoured CSRO regions but not in energetically favoured CSRO ones, which represents, to our knowledge, the first experimental observation of correlating local chemical order with structural defects in any material. We expect that this work will not only expand our fundamental understanding of this important class of materials but also provide the foundation for tailoring M/HEA properties through engineering lattice distortion and local chemical order.

DOI: 10.1038/s41586-023-06785-z

Source: https://www.nature.com/articles/s41586-023-06785-z