Scale law of complex deformation transitions of nanotwins in stainless steel

Abstract

Understanding the deformation behavior of metallic materials containing nanotwins (NTs), which can enhance both strength and ductility, is useful for tailoring microstructures at the micro- and nano- scale to enhance mechanical properties. Here, we construct a clear deformation pattern of NTs in austenitic stainless steel by combining in situ tensile tests with a dislocation-based theoretical model and molecular dynamics simulations. Deformation NTs are observed in situ using a transmission electron microscope in different sample regions containing NTs with twin-lamella-spacing ( λ ) varying from a few nanometers to hundreds of nanometers. Two deformation transitions are found experimentally: from coactivated twinning/detwinning ( λ < 5 nm) to secondary twinning (5 nm < λ < 129 nm), and then to the dislocation glide ( λ > 129 nm). The simulation results are highly consistent with the observed strong λ -effect, and reveal the intrinsic transition mechanisms induced by partial dislocation slip.

Hierarchical twinning governed by defective twin boundary in metallic materials

“…3 and fig. S6), as well as in some other metals and alloys reported in literature ( 22 – 24 , 44 , 45 ). With the activation of these built-in twinning sites, defective TBs can frequently stimulate the development of secondary or even hierarchical twins, as demonstrated by the geometric extreme of fivefold twin ( Fig.…”

“…In principle, both secondary and multifold twins can provide additional plastic deformation dynamics to accommodate the accumulating strain and dense barriers against multiple dislocation slip systems inside the grain ( 22 , 47 ). Consequently, an improved strain hardening capability is expected for hierarchically twinned materials, which has received increasing attention in the community ( 20 , 23 , 43 , 44 ).…”

Microstructure Evolution and Mechanical Properties of Austenite Stainless Steel with Gradient Twinned Structure by Surface Mechanical Attrition Treatment

“…The gradient structure is caused by the attenuated strain rate of SMAT [ 21 , 27 ]. During impacting deformation, three competitive mechanisms control the microstructure of the austenitic SS, basically, slip, twinning, and transformation [ 30 , 31 ], which are all relative to the impacting strain rate. Two impacting velocities are used in this experiment.…”

“…Notably, the NC/UFG surface also exhibits an increased hardness during the tensile deformation, which means the strengthening still operates. During the deformation process, the multiple-scale twins strengthen by secondary twinning and intersected twinning, and change the orientation of the subgrains to transfer the deformation to the adjacent grains or subcrystals [ 31 , 33 , 34 ]. Through relieving the stress concentration by the graded structure, the extension of deformation is achieved, which endows the SMATed samples high plasticity ( Figure 2 a and Figure 3 a).…”

Full-annealing and its effect on the Mechanical Properties of Alloy 304H Stainless Steel

“…It has an excellent corrosion resistance and good ductility [1][2]. Austenitic stainless steels, including AISI 316L and 304, are widely used as structural materials in industries such as petrochemistry, transportation, ultra-supercritical power and nuclear power plants, mostly due to their high specific strength, ductility, fracture toughness and excellent corrosion resistance [3][4][5][6][7]. However, hydrogen embrittlement sensitization and formation of different carbides and sigma phase can also affect the mechanical properties.…”