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.

Synergetic strengthening far beyond rule of mixtures in gradient structured aluminum rod

“…Gradient structures can be defined as microstructures with macroscopic gradients in one or a combination of the several types of microstructural features including, but not limited to, grain size [1][2][3][4][5][7][8][9], texture [4], dislocation density, twin density [6], precipitates, etc. The most common and well studied gradient structure is grain size gradient structure [1][2][3][4][5], which often consist of nanocrystalline or ultrafine grains at the surface of a tensile sample, which gradually transition to coarse grains in the interior over distances of~50 μm or longer.…”

Special Rolling Techniques for Improvement of Mechanical Properties of Ultrafine‐Grained Metal Sheets: a Review

“…Recently, gradient microstructures, in which the UFG/NG grains gradually change into coarse grains from sample surface to sample core, are revealed to possess improved ductility and strength. [99][100][101][102][103] For nanogradient Cu, both hardening and softening occur concurrently in the gradient microstructure, and the dominant deformation mechanism changes gradually from dislocation slip to grain boundary migration as the grains become smaller. [99,100] The strain hardening caused by a change in stress states and a macroscopic strain gradient was also considered as a mechanism to improve the ductility and strength of IF steel.…”

Ductility Sensitivity to Stacking Fault Energy and Grain Size in Cu–Al Alloys

“…In fact, efforts on ductility improvement were made and intriguing results have been reported. [5][6][7][8] The ductility (especially UE) is governed by the strain-hardening rate and true stress according to the Considére criterion. [9] It is frequently observed that *Corresponding author.…”

“…[1,10] In parallel, recent studies show that the face-centered cubic (FCC) alloys with low stacking fault energy (SFE) draw good balance of strength and ductility. [6,[11][12][13] In FCC materials, it is known that SFE can affect the deformation mechanisms significantly. [14][15][16] When the SFE is high, dislocation slip in the wavy mode dominates the plastic deformation.…”

“…Though tensile strength and ductility are readily improved in FCC metallic materials with decreasing the SFE, [6,[11][12][13]] the ductility cannot be enhanced monotonically as shown in Figure 1(e). Thus the ductility sensitivity to the SFE and grain size was summarized and shown in Figure 4 in both the fine-grained regime and the coarse-grained regime.…”