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.
Highlights
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
The strength-ductility synergy of NTed materials is controlled by the deformation mechanisms, involving dislocation pile-up at the twin boundary (TB), partial dislocation slip along the TB, and TB migration, or detwinning[5,6,7,8,9,10]
We investigate the λ-dependent effect on the deformation transitions of NTed steels
Summary
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. The strength-ductility synergy of NTed materials is controlled by the deformation mechanisms, involving dislocation pile-up at the twin boundary (TB), partial dislocation slip along the TB, and TB migration, or detwinning[5,6,7,8,9,10]. As the second generation of advanced high strength steels, metastable austenitic steels such as austenitic stainless steel (SS) and high manganese steel are widely used in the chemical, transportation, and aerospace industries These steels with NTed structure exhibit ultrahigh strength, good ductility, and high work hardening[23,24,25,26,27,28]. We generated a deformation map of NTs as a function of λ, which may aid in the design of advanced steels with superior strength-ductility synergy
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