The equiatomic Cr-Co-Fe-Ni medium-entropy alloy has the face-centered cubic structure. Single crystals of this alloy were tested by in-situ micropillar compression along different loading axes under scanning electron microscope. The transmission electron microscopy characterization and molecular dynamics simulation were incorporated for quantitative analysis of the effects of different crystal orientations on the deformation mechanisms. The <001>-oriented pillar not only exhibited extensive deformation-induced nano twinning, but also has been identified for the first time to undergo the FCCHCP phase transformation at room temperature. The strain localization tendency of <011>-oriented samples was confirmed through uniaxial tests to interpret the significant serration on stress-strain curves. The prominent strain hardening of <111>-oriented pillars was attributed to intense intersection between slip planes as evidenced by the extra density of Lomer-Cottrell locks. Such a high hardening rate has caused subsequent kinking of pillars. Functional division of different regions of kink band was conducted based on Orowan model. In principle, multi-principal element alloys can theoretically be designed and developed to combine a variety of excellent properties, which is an important class of candidate structural materials for advanced engineering systems. These findings provide promising guidance for understanding the mechanical anisotropy and application of these alloys.

中文翻译：

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揭示CoCrFeNi中熵合金机械各向异性的变形微观机制


等原子Cr-Co-Fe-Ni中熵合金具有面心立方结构。在扫描电子显微镜下沿不同加载轴对这种合金的单晶进行了原位微柱压缩测试。结合透射电子显微镜表征和分子动力学模拟，定量分析不同晶体取向对变形机制的影响。 <001>取向的柱不仅表现出广泛的变形诱导的纳米孪晶，而且还首次被鉴定出在室温下经历FCCHCP相变。通过单轴试验证实了<011>取向样品的应变局部化趋势，以解释应力-应变曲线上的显着锯齿。 <111> 取向柱的显着应变硬化归因于滑移面之间的强烈相交，洛默-科特雷尔锁的额外密度证明了这一点。如此高的硬化率导致了随后的支柱扭结。基于Orowan模型对扭结带不同区域进行功能划分。原则上，多主元合金理论上可以设计和开发以结合多种优良性能，是先进工程系统的一类重要的候选结构材料。这些发现为理解这些合金的机械各向异性和应用提供了有希望的指导。