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Severe plastic deformation-produced gradient nanostructured copper with a strengthening-softening transition

机译：具有强化软化转变的严重塑性变形制备的梯度纳米结构铜

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摘要

Low-excess energy twin boundary can effectively stabilize the conventional grain boundary. It has been reported that deformation-activated nanotwins in nanograined metals produced by severe plastic deformation techniques can significantly enhance mechanical-thermal stability. However, fabrication, structural evolution, and the effect of grain size and twin thickness on the mechanical stability of nanograined-nanotwinned metals, where both the grain size and twin thickness reach the nanometer scale (especially grain size is lower than 40 nm), remain unclear. In this study, a gradient nanostructured layer containing a nanograined-nanotwinned sub-layer region and an extremely refined twin-free nanograined top surface layer with grain size as small as ～10 nm is achieved on copper by using an ultrahigh-strain rate single point diamond turning technique. High-resolution transmission electron microscope observations, atomistic molecular dynamic simulations, and nanoindetation tests were performed to reveal the size-dependent mechanisms of grain refinement and hardness along the gradient direction. The propensity of deformation multifold twinning is increased firstly in large-size nanograins and then decreased once grain size is below ～48 nm, finally replaced by detwinning to form extremely fine twin-free nanograins at the topmost surface layer. In other words, both the zero-macrostrain-induced deformation multifold twinning and symmetry-breaking-based detwinning processes can continuously refine nanograins along the gradient direction. Critical grain sizes for deformation multifold twinning and detwinning are discussed. Interestingly, a Hall-Petch strengthening-softening transition is discovered at a critical grain size of ～30 nm in the gradient nanostructured layer. The softening mechanisms are elucidated to be attributed to the twin thickness effect on deformation mode in nanograined-nanotwinned structures and the pure grain boundary-mediated plasticity in extremely fine twin-free nanograins. A series of critical twin thicknesses for softening in nanograins with different grain sizes are discussed; that is, the smaller the grain size is, the smaller the critical twin thickness will be. This study offers the potential for understanding and developing stable nanostructured metals.
机译：低过量的能量双边界可以有效地稳定传统的晶界。据报道，由严重塑性变形技术产生的纳米金属中的变形活化的纳米管道可以显着提高机械热稳定性。然而，制造，结构演化和晶粒尺寸和双厚度对纳米纳米丝金属的机械稳定性的影响，其中晶粒尺寸和双厚度达到纳米尺度（特别是粒度低于40nm）不清楚。在该研究中，通过使用超高应变速率单点在铜中达到含有纳米纳米型亚层区域和具有小于〜10nm小至约10nm的极小精细的双无纳米纳米表面层的梯度纳米结构层金刚石转动技术。进行高分辨率透射电子显微镜观察，原子分子动态模拟和纳米茚处理测试，以揭示沿梯度方向的晶粒细化和硬度的尺寸依赖性机制。第一颗粒颗粒的变形多聚孪晶的倾向增加，然后在大型纳米中增加，然后一旦粒径低于〜48nm，最终取代以在最顶部的表面层处形成极细的双无纳米预料。换句话说，零型宏型诱导的变形多滤脉孪晶和基于对称性的基于脱扣过程可以沿着梯度方向连续地细化纳米纳米。讨论了变形多层孪晶和纠正的临界粒度。有趣的是，在梯度纳米结构层中以〜30nm的临界晶粒尺寸发现霍尔 - 铺设强化软化转变。阐明软化机构归因于纳米纳米型结构中的变形模式的双厚度效应，以及极细无双纳米的纯晶界介导的塑性。讨论了一种用于用不同粒度的纳米粗糙化软化的一系列关键双厚度;也就是说，晶粒尺寸越小，临界双厚度越小。本研究提供了理解和开发稳定的纳米结构金属的潜力。

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  • 来源
    《Materials Science and Engineering》 |2021年第5期|141495.1-141495.12|共12页
  • 作者

    Bo Wu; Hui Fu; Xiaoye Zhou; Lei Qian; Jiasi Luo; Jiaming Zhu; Wing Bun Lee; Xu-Sheng Yang;

  • 作者单位

    State Key Laboratory of Ultra-precision Machining Technology Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hung Horn Kowloon Hong Kong China;

    State Key Laboratory of Ultra-precision Machining Technology Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hung Horn Kowloon Hong Kong China;

    Guangdong Province Key Laboratory of Durability for Marine Civil Engineering School of Civil Engineering Shenzhen University Shenzhen Guangdong 518060 PR China;

    State Key Laboratory of Ultra-precision Machining Technology Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hung Horn Kowloon Hong Kong China;

    State Key Laboratory of Ultra-precision Machining Technology Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hung Horn Kowloon Hong Kong China;

    School of Civil Engineering Shandong University Jinan 250061 China;

    State Key Laboratory of Ultra-precision Machining Technology Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hung Horn Kowloon Hong Kong China;

    State Key Laboratory of Ultra-precision Machining Technology Department of Industrial and Systems Engineering The Hong Kong Polytechnic University Hung Horn Kowloon Hong Kong China Hong Kong Polytechnic University Shenzhen Research Institute Shenzhen China;

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  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    Nanograined-nanotwinned Cu; Ultra-precision machining technique; Multifold twinning; Strengthening-softening transition; High-resolution transmission electron; microscopy;

    机译：纳米纳米型铜;超精密加工技术;多丁孪生;加强软化过渡;高分辨率传输电子;显微镜;

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