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History-independent cyclic response of nanotwinned metals

机译：纳米孪晶金属的历史独立循环响应

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摘要

Nearly 90 per cent of service failures of metallic components and structures are caused by fatigue at cyclic stress amplitudes much lower than the tensile strength of the materials involved(1). Metals typically suffer from large amounts of cumulative, irreversible damage to microstructure during cyclic deformation, leading to cyclic responses that are unstable (hardening or softening)(2-4) and history-dependent(5-8). Existing rules for fatigue life prediction, such as the linear cumulative damage rule(1,9), cannot account for the effect of loading history, and engineering components are often loaded by complex cyclic stresses with variable amplitudes, mean values and frequencies(10,11), such as aircraft wings in turbulent air. It is therefore usually extremely challenging to predict cyclic behaviour and fatigue life under a realistic load spectrum(1,11). Here, through both atomistic simulations and variable-strain-amplitude cyclic loading experiments at stress amplitudes lower than the tensile strength of the metal, we report a history-independent and stable cyclic response in bulk copper samples that contain highly oriented nanoscale twins. We demonstrate that this unusual cyclic behaviour is governed by a type of correlated 'necklace' dislocation consisting of multiple short component dislocations in adjacent twins, connected like the links of a necklace. Such dislocations are formed in the highly oriented nanotwinned structure under cyclic loading and help to maintain the stability of twin boundaries and the reversible damage, provided that the nanotwins are tilted within about 15 degrees of the loading axis. This cyclic deformation mechanism is distinct from the conventional strain localizing mechanisms associated with irreversible microstructural damage in single-crystal(12,13), coarsegrained(1,14), ultrafine-grained and nanograined metals(4,15,16).
机译：金属部件和结构近90％的服务失效是由循环应力振幅下的疲劳引起的，该应力远低于所涉及材料的抗张强度（1）。金属通常在循环变形过程中遭受大量的累积的，不可逆的微观结构破坏，导致循环响应不稳定（硬化或软化）（2-4）并取决于历史（5-8）。现有的疲劳寿命预测规则（例如线性累积损伤规则（1,9））无法说明加载历史的影响，工程组件通常由振幅，平均值和频率可变的复杂循环应力加载（10， 11），例如飞机机翼在湍流的空气中。因此，在实际载荷谱下预测循环行为和疲劳寿命通常极具挑战性（1,11）。在这里，通过在小于金属拉伸强度的应力振幅下进行的原子模拟和可变应变振幅循环加载实验，我们报告了包含高度取向的纳米级孪晶的块状铜样品的历史独立且稳定的循环响应。我们证明了这种异常的循环行为是由一种相关的“项链”位错控制的，该位错由相邻双胞胎中的多个短组分位错组成，它们像一条项链的链节一样连接。如果纳米孪晶在加载轴的约15度范围内倾斜，则这种位错会在周期性载荷作用下形成于高度定向的纳米孪晶结构中，并有助于维持孪晶边界的稳定性和可逆损伤。这种循环变形机制不同于传统的应变局部化机制，后者与单晶（12,13），粗晶粒（1,14），超细晶粒和纳米晶粒金属（4,15,16）中不可逆的微结构损伤有关。

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  • 来源
    《Nature》 |2017年第7679期|214-217|共4页
  • 作者

    Pan Qingsong; Zhou Haofei; Lu Qiuhong; Gao Huajian; Lu Lei;

  • 作者单位

    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Liaoning, Peoples R China;

    Brown Univ, Sch Engn, Providence, RI 02912 USA;

    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Liaoning, Peoples R China;

    Brown Univ, Sch Engn, Providence, RI 02912 USA;

    Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Liaoning, Peoples R China;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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