Yan Jingyuan, Yin Sheng, Asta Mark, Ritchie Robert O, Ding Jun, Yu Qian
Center of Electron Microscopy and State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, 310027, Hangzhou, China.
Institute of Engineering Innovation, The University of Tokyo, Tokyo, 113-8656, Japan.
Nat Commun. 2022 May 19;13(1):2789. doi: 10.1038/s41467-022-30524-z.
High-entropy alloys (HEAs), although often presumed to be random solid solutions, have recently been shown to display nanometer-scale variations in the arrangements of their multiple chemical elements. Here, we study the effects of this compositional heterogeneity in HEAs on their mechanical properties using in situ compression testing in the transmission electron microscope (TEM), combined with molecular dynamics simulations. We report an anomalous size effect on the yield strength in HEAs, arising from such compositional heterogeneity. By progressively reducing the sample size, HEAs initially display the classical "smaller-is-stronger" phenomenon, similar to pure metals and conventional alloys. However, as the sample size is decreased below a critical characteristic length (~180 nm), influenced by the size-scale of compositional heterogeneity, a transition from homogeneous deformation to a heterogeneous distribution of planar slip is observed, coupled with an anomalous "smaller-is-weaker" size effect. Atomic-scale computational modeling shows these observations arise due to compositional fluctuations over a few nanometers. These results demonstrate the efficacy of influencing mechanical properties in HEAs through control of local compositional variations at the nanoscale.
高熵合金（HEAs）尽管通常被认为是随机固溶体，但最近已被证明在其多种化学元素的排列上呈现出纳米尺度的变化。在此，我们使用透射电子显微镜（TEM）中的原位压缩测试，并结合分子动力学模拟，研究了高熵合金中这种成分不均匀性对其力学性能的影响。我们报告了高熵合金屈服强度上的一种反常尺寸效应，这种效应源于这种成分不均匀性。通过逐步减小样品尺寸，高熵合金最初表现出经典的“越小越强”现象，类似于纯金属和传统合金。然而，当样品尺寸减小到低于临界特征长度（约180纳米）时，受成分不均匀性尺寸尺度的影响，观察到从均匀变形到平面滑移的不均匀分布的转变，同时伴随着反常的“越小越弱”尺寸效应。原子尺度的计算模型表明，这些观察结果是由于几纳米范围内的成分波动引起的。这些结果证明了通过控制纳米尺度的局部成分变化来影响高熵合金力学性能的有效性。
