Cheng Guangming, Yin Sheng, Chang Tzu-Hsuan, Richter Gunther, Gao Huajian, Zhu Yong
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA.
School of Engineering, Brown University, Providence, Rhode Island 02912, USA.
Phys Rev Lett. 2017 Dec 22;119(25):256101. doi: 10.1103/PhysRevLett.119.256101. Epub 2017 Dec 21.
In spite of numerous studies on mechanical behaviors of nanowires (NWs) focusing on the surface effect, there is still a general lack of understanding on how the internal microstructure of NWs influences their deformation mechanisms. Here, using quantitative in situ transmission electron microscopy based nanomechanical testing and molecular dynamics simulations, we report a transition of the deformation mechanism from localized dislocation slip to delocalized plasticity via an anomalous tensile detwinning mechanism in bitwinned metallic NWs with a single twin boundary (TB) running parallel to the NW length. The anomalous tensile detwinning starts with the detwinning of a segment of the preexisting TB under no resolved shear stress, followed by the propagation of a pair of newly formed TB and grain boundary leading to a large plastic deformation. An energy-based criterion is proposed to describe this transition of the deformation mechanism, which depends on the volume ratio between the two twin variants and the cross-sectional aspect ratio.
尽管针对纳米线（NWs）力学行为的众多研究聚焦于表面效应，但对于NWs的内部微观结构如何影响其变形机制，仍普遍缺乏了解。在此，我们通过基于定量原位透射电子显微镜的纳米力学测试和分子动力学模拟，报告了在具有平行于NW长度的单个孪晶界（TB）的双晶金属NWs中，变形机制从局部位错滑移转变为通过异常拉伸孪生机制的非局部塑性。异常拉伸孪生始于在无分解剪应力的情况下，对预先存在的TB的一段进行孪生，随后一对新形成的TB和晶界传播，导致大的塑性变形。提出了一个基于能量的准则来描述这种变形机制的转变，该准则取决于两个孪晶变体之间的体积比和横截面长宽比。
