摘要
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 sizeindependency,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 sizedependent critical stress required for a shear band traversing the pillar and mediated by the competition between shearinduced 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.
作者
Yujie Chen
Xianghai An
Zhifeng Zhou
Paul Munroe
Sam Zhang
Xiaozhou Liao
Zonghan Xie
陈玉洁;安祥海;周志烽;Paul Munroe;张善勇;廖晓舟;谢宗翰(Centre for Advanced Thin Films and Devices,School of Materials and Energy,Southwest University,Chongqing,400715,China;School of Mechanical Engineering,The University of Adelaide,Adelaide,SA,5005,Australia;School of Aerospace,Mechanical and Mechatronic Engineering,The University of Sydney,Sydney,NSW,2006,Australia;Department of Mechanical Engineering,City University of Hong Kong,Kowloon,Hong Kong,China;School of Materials Science and Engineering,The University of New South Wales,Sydney,NSW,2052,Australia;School of Engineering,Edith Cowan University,Perth,WA,6027,Australia)
基金
supported by the Australian Research Council Discovery Projects Grant
partly supported by the Fundamental Research Funds for the Central Universities(SWU118105)
the financial support from Australia Research Council(DE170100053)
the Robinson Fellowship Scheme of the University of Sydney(G200726)。
