Evading the strength-ductility trade-off dilemma in steel through gradient hierarchical nanotwins

It is a long-standing goal in metallurgy to enhance the strength of materials without sacrificing ductility. In a recent article in Nature Communications, we reported an effective way to evade the strength-ductility trade-off dilemma in twin-induced plasticity steel. By applying pre-torsion to axisymmetrical twin induced plasticity steel, we produced gradient twin structures in the steel: The core is essentially twin free, and twin boundary density increases along the radial direction and maximizes at the surface. The material with such microstructure exhibits substantial increase in strength at no ductility trade-off. More importantly, such a method can process materials with no limitations on sample dimensions. The latter will be essential in enabling practical applications of the method developed to enhancing any axially symmetric structural components, including axles in machines, engines and transmission systems in mechanical, civil, aerospace, transportation, oil, automotive, and energy industries. We also revealed 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. Theoretical analyses are also supplied 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. The interested colleagues may download the open access paper from the website of  Nature Communications. Thank you!