Abstract The mechanical properties of high-entropy alloys (HEAs) strongly depend on their microstructural features. In this work, the phase formation and morphologies of Fe26.7Co26.7Ni26.7Si8.9B11.0 HEAs fabricated under different undercooling levels by the drop tube technique together with subsequent quenching were investigated in detail. It was found when the droplet size decreases (i.e. the increase of the undercooling level), the grain refinement is easily achieved without any phase transformation for the present hypoeutectic HEA which is composed of the fcc dendrites and eutectic structure. After quenching under large undercooling levels, the liquid should be deeply undercooled into an asymmetric couple zone, leading to the primary formation of eutectic structure and the subsequent precipitation of the fcc dendrites. The direct product of rapid solidification after deep undercooling and subsequent recalescence may induce the decoupled eutectic growth, resulting in a transition from the regular into anomalous eutectic structures. Furthermore, the volume fractions of the eutectic structures and the fcc dendrites increase and decrease with decreasing droplet size, respectively. As a result, the Vickers hardness gradually increases with decreasing droplet size, which exhibits a linear relationship with the volume fraction of eutectic matrix. The present study may provide a simple way to tailor microstructures and mechanical properties of HEAs.

中文翻译：

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高熵 Fe-Co-Ni-Si-B 合金无容器凝固引起的显微组织细化和异常共晶组织

摘要 高熵合金（HEAs）的力学性能很大程度上取决于其微观结构特征。在这项工作中，详细研究了在不同过冷度下通过落管技术以及随后的淬火制造的 Fe26.7Co26.7Ni26.7Si8.9B11.0 HEA 的相形成和形貌。发现当液滴尺寸减小（即过冷度增加）时，对于目前由fcc枝晶和共晶结构组成的亚共晶HEA，无需任何相变即可实现晶粒细化。在大过冷度下淬火后，液体应深度过冷进入不对称耦合区，导致共晶组织的初步形成和随后的 fcc 枝晶析出。深度过冷和随后的再发光后快速凝固的直接产物可能会导致解耦共晶生长，导致从常规共晶结构转变为异常共晶结构。此外，共晶结构和 fcc 枝晶的体积分数分别随着液滴尺寸的减小而增加和减少。结果，维氏硬度随着液滴尺寸的减小而逐渐增加，这与共晶基体的体积分数呈线性关系。本研究可能提供一种简单的方法来定制 HEAs 的微观结构和机械性能。共晶结构和 fcc 枝晶的体积分数分别随着液滴尺寸的减小而增加和减少。结果，维氏硬度随着液滴尺寸的减小而逐渐增加，这与共晶基体的体积分数呈线性关系。本研究可能提供一种简单的方法来定制 HEA 的微观结构和机械性能。共晶结构和 fcc 枝晶的体积分数分别随着液滴尺寸的减小而增加和减少。结果，维氏硬度随着液滴尺寸的减小而逐渐增加，这与共晶基体的体积分数呈线性关系。本研究可能提供一种简单的方法来定制 HEAs 的微观结构和机械性能。