This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Structural metals used in engineering projects are expected to have both high strength and high ductility: the ability to withstand heavy loads and deform before failure. Achieving both of these properties at the same time, however, is challenging.
An important measure of ductility is uniform elongation, or the amount of deformation a metal can sustain before that deformation concentrates in one small area, resulting in a fracture. Some metals become stronger as they are deformed—a phenomenon known as strain hardening—so if a material can continue to harden sufficiently during deformation, uniform stretching can theoretically be maintained. However, the effectiveness of strain hardening usually decreases as deformation continues.
While some advanced metals obtain additional strain hardening from deformation twinning and martensitic transformation, these processes tend to compete with each other, so metals are commonly designed to rely predominantly on just one or the other. A team of researchers at Kyoto University wondered if both mechanisms could be activated in the same material at different stages of deformation and hypothesized that this could allow the mechanisms to provide strain hardening sequentially rather than compete with each other. They proposed a strategy in which different deformation mechanisms are activated in sequence, with each providing additional strain hardening as the previous step becomes less effective.
The paper is published in the journal Materials Today. "In the field of high-strength metals, durable materials are no longer unusual, yet the elongation of metallic materials has generally remained below about 60% to 70%," says corresponding author Si Gao. "I wanted to know whether metals could be pushed beyond this apparent limit." The team experimented with this concept in an actual sample of Fe-Ni-C steel, carefully controlling the alloy composition.
In particular, the researchers increased the carbon content to delay the onset of martensitic transformation, which allowed deformation twinning to activate first at intermediate strains while postponing martensitic transformation until higher strains. This enabled the two mechanisms to operate sequentially rather than compete from the beginning. Ultimately, the researchers succeeded in developing an Fe-4Ni-0.6C steel with a uniform elongation of nearly 140%.
This exceptional ductility is a result of the mechanisms continuously providing strain hardening, which delays strain localization over a large strain range. This study suggests that metallic materials have a much greater intrinsic potential for uniform deformation than previously believed and provides a new strategy for overcoming the long-standing trade-off between strength and ductility. Future applications are likely to include buildings, vehicles, aircraft and other load-bearing structures that require both strength and ductility.
Extract — continue reading at the source.
