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.

[http://dx.doi.org/10.1038/ncomms4580]

Y.Wei acknowledges the support from MOST 973 of China (2012CB937500), Chinese Academy of Sciences, and National Natural Science Foundation of China (NSFC)(11021262, 11272327). G. W. thanks the supports from Shanghai Pujiang Program (no.11PJ1403900) and the Eastern Scholar Program at Shanghai Institutions of Higher Learning. Z. M. thanks the support from MOST 863 of China (2012AA03A508). H. W. and J. L. acknowledge the supports from NSFC (11002124, 11202183). H. G. acknowledges financial support from the National Science Foundation through grant CMMI-1161749 and the Center for Mechanics and Materials at Tsinghua University. We also thank Zhiwei Ma for assistance to EBSD observations.

The article was published as:
Wei YJ,Li YQ,Zhu LC,et al. Evading The Strength- Ductility Trade-off Dilemma In Steel Through Gradient Hierarchical Nanotwins.Nature Communications,2014,5:3580.