Abstract The microstructures and room temperature tensile properties of as-cast and directionally solidified AlCoCrFeNi2.1 eutectic high-entropy alloy were investigated using OM, SEM, EDS, TEM and tensile tests. The microstructure of as-cast alloy, including the well-aligned lamellar structures, the radial emanating lamellar structure and mesh-like structure, consists of NiAl-rich (B2) and CoCrFeNi-rich (L12) phases. From the longitudinal section of directionally solidified alloy, when the withdrawal rate is 6 μm/s, the solid-liquid interface morphology is planar, and the well-aligned lamellar structure is observed. The three-dimensional morphologies of well-aligned lamellar structures are well characterized by deep etching. With increasing the withdrawal rate to 15 μm/s, the solid-liquid interface morphology change from planar to cellular, and the microstructure changes from planar eutectic to cellular eutectic, even the dendritic eutectic at local region occurs at 60 and 120 μm/s. From the transverse section, the well-aligned lamellar structures occur in the cell interior, and the interlamellar spacing decreases gradually with increasing the withdrawal rates. The TEM result indicates that NiAl-rich phase has an orientation relationship with CoCrFeNi-rich phase of [ 1 ¯ 11] NiAl-rich//[ 1 ¯ 22]CoCrFeNi-rich and (211)NiAl-rich//(02 2 ¯ )CoCrFeNi-rich. The nano-precipitates occur in NiAl-rich (B2) and CoCrFeNi-rich (L12) phases. The directionally solidified alloy possesses a good combination of strength and ductility at 60 μm/s. In particular, using the directional solidification technology is a good way to improve the ductility of the alloy (∼37%). The strengthening and plasticizing mechanisms are discussed by analyzing the fracture and side surfaces.

中文翻译：

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铸态定向凝固AlCoCrFeNi2.1共晶高熵合金的显微组织和室温拉伸性能

摘要 采用OM、SEM、EDS、TEM和拉伸试验研究了铸态和定向凝固AlCoCrFeNi2.1共晶高熵合金的显微组织和室温拉伸性能。铸态合金的微观结构，包括排列良好的层状结构、放射状的层状结构和网状结构，由富 NiAl (B2) 和富 CoCrFeNi (L12) 相组成。从定向凝固合金的纵截面看，当拔出速率为6 μm/s时，固液界面形貌为平面状，观察到排列良好的层状结构。良好排列的层状结构的三维形态通过深度蚀刻得到了很好的表征。随着提取速率增加到 15 μm/s，固液界面形态从平面变为蜂窝状，微观结构由平面共晶转变为胞状共晶，甚至局部区域的树枝状共晶在60和120μm/s时发生。从横切面看，细胞内部出现排列整齐的层状结构，层间距随着提取率的增加而逐渐减小。TEM 结果表明富 NiAl 相与富 CoCrFeNi 相的取向关系为 [ 1 ¯ 11] NiAl-rich//[ 1 ¯ 22]CoCrFeNi-rich and (211)NiAl-rich//(02 2 ¯ )CoCrFeNi 富集。纳米沉淀出现在富含 NiAl (B2) 和富含 CoCrFeNi (L12) 的相中。定向凝固合金在 60 μm/s 时具有良好的强度和延展性组合。特别是，使用定向凝固技术是提高合金延展性（~37%）的好方法。