Size-dependent deformation behavior of dual-phase, nanostructured CrCoNi medium-entropy alloy



The mechanical size effect of nanostructured, dual-phase CrCoNi medium-entropy alloy (MEA) was investigated by combining in-situ micro-compression testing with post-mortem electron microscopy analysis. The alloy possesses a superior yield strength up to ∼4 GPa, primarily due to its hierarchical microstructure including column nanograins, preferred orientation, a high density of planar defects and the presence of the hexagonal close packed (HCP) phase. While the yield strength of the alloy has shown size-independency, the deformation behaviour was strongly dependent on the sample size. Specifically, with decreasing the pillar diameters, the dominant deformation mode changed from highly localized and catastrophic shear banding to apparently homogeneous deformation with appreciable plasticity. This transition is believed to be governed by the size-dependent critical stress required for a shear band traversing the pillar and mediated by the competition between shear-induced softening and subsequent hardening mechanisms. In addition, an unexpected phase transformation from HCP to face-centered cubic (FCC) was observed in the highly localized deformation zones, leading to strain softening that contributed to accommodating plasticity. These findings provide insights into the criticality of sample dimensions in influencing mechanical behaviors of nanostructured metallic materials used for nanoelectromechanical systems.


本文结合原位扫描电子显微镜微柱压缩与透射电子显微镜技术, 研究了具有双相多级纳米结构的CrCoNi中熵合金变形行为的尺寸效应. 研究表明, 该合金的屈服强度高达~4 GPa, 这主要归因于其多级微观结构特征, 包括柱状纳米尺寸晶粒、 织构、高密度的层错、 孪晶界、 晶界和相界. 在变形过程中, 该合金的屈服强度基本与微米尺度样品的尺寸无关, 但其变形行为却强烈依赖于样品大小. 具体来说, 随着微柱直径减小, 材料主要的变形模式从突发的局部剪切带变为具有明显塑性的均匀变形. 这种转变是由剪切带穿过微柱所需的临界应力与样品尺寸紧密相关所决定的, 剪切诱导的软化和随后的硬化机制之间的竞争也起了重要作用. 此外, 变形引起了六方密排结构到面心立方结构的相变, 该相变导致的应变软化对材料变形中的塑性有重要贡献. 这些发现揭示了样品尺寸对可用于微纳机电系统的纳米结构金属材料的力学行为有着重要影响.


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This work was supported by the Australian Research Council Discovery Projects Grant, and partly supported by the Fundamental Research Funds for the Central Universities (SWU118105). An X acknowledges the financial support from Australia Research Council (DE170100053) and the Robinson Fellowship Scheme of the University of Sydney (G200726). The authors acknowledge the facilities and the scientific and technical assistance of the Australian Microscopy and Microanalysis Research Facility ( node at the University of Adelaide: Adelaide Microscopy. In particular, the authors thank Dr Animesh Basak and Dr Ashley Slattery of Adelaide Microscopy for their support and expertise.

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Author contributions Chen Y, Xie Z, An X and Zhang S conceived the project. Chen Y conducted the FIB, microcompression and TEM experiments. Zhou Z fabricated the samples. Chen Y, An X, Liao X and Xie Z interpreted the results and wrote the manuscript. All authors contributed to the discussion of the results, and comments on the manuscript.

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Correspondence to Xianghai An 安祥海 or Sam Zhang 张善勇.

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Conflict of interest The authors declare that they have no conflict of interest.

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Yujie Chen obtained her BEng degree (first-class honors) in 2011 and PhD degree in materials science in 2016 from The University of Sydney. Upon completion of her PhD, she was employed as a postdoc in the School of Mechanical Engineering in the University of Adelaide in Australia. She is currently a research fellow in the Southwest University in China. Her current research involves microstructure optimization and mechanical properties enhancement of alloys, and calcified tissues.

Xianghai An received his PhD degree from the Institute of Metal Research, Chinese Academy of Sciences in 2012. After receiving his PhD degree, he commenced to work as a research fellow at The University of Sydney. He is currently a Lecture/Robinson Fellow at The University of Sydney. His research mainly focuses on materials design, mechanical behavior, and structure-property relationship of advanced metallic materials, nanomechanics and nanoplasticity, metallic additive manufacturing and advanced materials processing.

Sam Zhang received his PhD degree (1991) in ceramic materials at the University of Wisconsin-Madison, USA. He joined Nanyang Technological University as an associate professor and was promoted to full professor in 2006. He is currently a professor and head of the Center for Advanced Thin Films and Devices in the Southwest University in China. He is also Fellow of the Institute of Materials, Minerals and Mining, Fellow of the Royal Society of Chemistry and Fellow of the Thin Films Society. His research interests include preparation and characterization of hard yet tough ceramic nanocomposite coatings, and functional thin films.

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Chen, Y., An, X., Zhou, Z. et al. Size-dependent deformation behavior of dual-phase, nanostructured CrCoNi medium-entropy alloy. Sci. China Mater. 64, 209–222 (2021).

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  • medium-entropy alloy
  • size effect
  • shear banding
  • phase transformation
  • nanostructure