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 metallurgy^{1,2,3,4,5,6,7,8}, catalysis^{9,10,11,12,13,14} and other fields^15,16,17,18. One of the core hypotheses of M/HEAs is lattice distortion^5,19,20, which has been investigated by different numerical and experimental techniques^{21,22,23,24,25,26}. 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 simulations^28,29,30, energy dispersive spectroscopy^31,32 and electron diffraction^33,34, 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 axes^7,32,34 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.

中熵合金和高熵合金 (M/HEA) 混合了多种具有接近等原子组成的主要元素，代表了设计冶金中以前未知的材料的模型转换策略^{1,2,3,4,5,6,7,8} 、催化^{9、10、11、12、13、14}等领域^{15、16、17、18} 。 M/HEA 的核心假设之一是晶格畸变^5,19,20 ，已通过不同的数值和实验技术对其进行了研究^{21,22,23,24,25,26} 。然而，确定 M/HEA 中的三维 (3D) 晶格畸变仍然是一个挑战。此外，M/HEAs 中假定的随机元素混合受到 X 射线和中子研究²⁷ 、原子模拟^28,29,30 、能量色散谱^31,32和电子衍射^33,34的质疑，这表明局部存在M/HEA 中的化学顺序。然而，3D局部化学有序的直接实验观察是困难的，因为能量色散光谱沿着区域轴^7,32,34整合原子柱的组成，并且漫电子反射可能源自平面缺陷而不是局部化学有序³⁵ 。在这里，我们使用原子电子断层扫描³⁶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)。我们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异质应变，并且该应变与 CSRO 相关。 我们还在中熵合金中观察到 CSRO 介导的孪生，即孪生发生在能量不利的 CSRO 区域，但不会发生在能量有利的 CSRO 区域，据我们所知，这代表了将局部化学顺序与结构相关联的第一个实验观察结果。任何材料的缺陷。我们期望这项工作不仅能扩展我们对这一类重要材料的基本理解，还能为通过设计晶格畸变和局部化学有序来定制 M/HEA 性能奠定基础。