Center of Electron Microscopy and State Key Laboratory of Silicon Materials, Department of Materials Science and Engineering, Zhejiang University, Hangzhou, China.
Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
Nature. 2019 Oct;574(7777):223-227. doi: 10.1038/s41586-019-1617-1. Epub 2019 Oct 9.
High-entropy alloys are a class of materials that contain five or more elements in near-equiatomic proportions. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical properties. Rational design of such alloys hinges on an understanding of the composition-structure-property relationships in a near-infinite compositional space. Here we use atomic-resolution chemical mapping to reveal the element distribution of the widely studied face-centred cubic CrMnFeCoNi Cantor alloy and of a new face-centred cubic alloy, CrFeCoNiPd. In the Cantor alloy, the distribution of the five constituent elements is relatively random and uniform. By contrast, in the CrFeCoNiPd alloy, in which the palladium atoms have a markedly different atomic size and electronegativity from the other elements, the homogeneity decreases considerably; all five elements tend to show greater aggregation, with a wavelength of incipient concentration waves as small as 1 to 3 nanometres. The resulting nanoscale alternating tensile and compressive strain fields lead to considerable resistance to dislocation glide. In situ transmission electron microscopy during straining experiments reveals massive dislocation cross-slip from the early stage of plastic deformation, resulting in strong dislocation interactions between multiple slip systems. These deformation mechanisms in the CrFeCoNiPd alloy, which differ markedly from those in the Cantor alloy and other face-centred cubic high-entropy alloys, are promoted by pronounced fluctuations in composition and an increase in stacking-fault energy, leading to higher yield strength without compromising strain hardening and tensile ductility. Mapping atomic-scale element distributions opens opportunities for understanding chemical structures and thus providing a basis for tuning composition and atomic configurations to obtain outstanding mechanical properties.
高熵合金是一类含有五种或更多等原子比例元素的材料。它们非常规的组成和化学结构有望实现前所未有的机械性能组合。这种合金的合理设计取决于对近无限组成空间中组成-结构-性能关系的理解。在这里，我们使用原子分辨率化学映射来揭示广泛研究的面心立方 CrMnFeCoNi Cantor 合金和一种新的面心立方合金 CrFeCoNiPd 的元素分布。在 Cantor 合金中，五种组成元素的分布相对随机且均匀。相比之下，在 CrFeCoNiPd 合金中，钯原子的原子尺寸和电负性与其他元素明显不同，均匀性大大降低；所有五种元素都倾向于更大的聚集，初生浓度波的波长小至 1 到 3 纳米。由此产生的纳米级交替拉伸和压缩应变场导致位错滑移的阻力相当大。在应变实验中的原位透射电子显微镜揭示了在塑性变形的早期阶段大量位错交叉滑移，导致多个滑移系统之间的位错相互作用强烈。CrFeCoNiPd 合金中的这些变形机制与 Cantor 合金和其他面心立方高熵合金中的机制明显不同，这是由组成和堆垛层错能的明显波动促进的，从而在不损害应变硬化和拉伸延展性的情况下提高屈服强度。原子尺度元素分布的映射为理解化学结构提供了机会，并为调整成分和原子构型以获得优异的机械性能提供了依据。
