title: Evading the strength-ductility trade-off dilemma in steel through gradient hierarchical nanotwins.
abstract: The strength-ductility trade-off has been a long-standing dilemma in materials science. This has limited the potential of many structural materials, steels in particular. Here we report a way of enhancing the strength of twinning-induced plasticity steel at no ductility trade-off. After applying torsion to cylindrical twinning-induced plasticity steel samples to generate a gradient nanotwinned structure along the radial direction, we find that the yielding strength of the material can be doubled at no reduction in ductility. It is shown that this evasion of strength-ductility trade-off is due to the formation of a gradient hierarchical nanotwinned structure during pre-torsion and subsequent tensile deformation. A series of finite element simulations based on crystal plasticity are performed to understand why the gradient twin structure can cause strengthening and ductility retention, and how sequential torsion and tension lead to the observed hierarchical nanotwinned structure through activation of different twinning systems.
authors.affiliation: LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Yujie
authors.initials: Y
authors.lastname: Wei
authors.affiliation: LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Yongqiang
authors.initials: Y
authors.lastname: Li
authors.affiliation: LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Lianchun
authors.initials: L
authors.lastname: Zhu
authors.affiliation: LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Liu
authors.affiliation: LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Xianqi
authors.initials: X
authors.lastname: Lei
authors.affiliation: Laboratory for Microstructures, Shanghai University, Shanghai 200444, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Wang
authors.affiliation: National Engineering Research Center for Advanced Rolling Technology, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Yanxin
authors.initials: Y
authors.lastname: Wu
authors.affiliation: National Engineering Research Center for Advanced Rolling Technology, University of Science and Technology Beijing, Beijing 100083, China.
authors.forename: Zhenli
authors.initials: Z
authors.lastname: Mi
authors.affiliation: Institute of Applied Mechanics, Zhejiang University, Hangzhou, Zhejiang 310027, China.
authors.forename: Jiabin
authors.initials: J
authors.lastname: Liu
authors.affiliation: Institute of Applied Mechanics, Zhejiang University, Hangzhou, Zhejiang 310027, China.
authors.forename: Hongtao
authors.initials: H
authors.lastname: Wang
authors.affiliation: School of Engineering, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: Huajian
authors.initials: H
authors.lastname: Gao