Continuum and atomistic scale computational mechanics for structures with small length scales. With on-demand call to molecular dynamics simulations and scale up to continuum level constitute models, where predictions can be made for laboratory accessible time and length scales.

Material systems including: crystal plasticity in singly/poly crystalline metals, interfacial/grain-boundary mechanics in nanostructured materials, amorphous solids, nanowires, soft materials.

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PNAS报道力学所等突破材料强-韧对立的纳米析出相设计

       工程材料通常需要经过一定的处理流程以提升其抵抗变形的能力,尤其是抵抗位错的运动导致的初始塑性变形或者屈服,材料在这一点的应力值对应于其强度。和我们熟知的弹性变形不同,塑性变形是不可恢复的。与此同时,金属材料的塑性变形量,或者韧性,是衡量其应用的另一个关键指标。如果位错在运动中受到阻碍或者非连续的界面时,我们需要施加更高的应力以驱动它们,也即材料获得了强化。 

  在诸多的强化途径中,析出强化具有非常悠久的历史,今天被广泛应用于工程中的铝合金,镍基超级合金,马氏体钢,以及高熵合金等都采用了这一强化机制。然而这种基于传统析出相强化的方法面临巨大挑战:析出相的强化同样可导致位错的局部塞积,由此形成应力集中而降低材料韧性,导致我们熟知的强度-韧性两种之间的鱼和熊掌效应。 

  中国科学院的科研团队和南洋理工学院/布朗大学的科研人员发现在具有高密度纳米析出相的金属材料中,纳米析出相在作为可持续的位错源(如图所示),可提升高应力状态下的材料的变形能力,实现这类材料的强-韧协同优化。该工作近期在Proc. Nat. Acad. Sci上发表(Doi:10.1073/pnas.1914615117)。  

  论文中,该小组揭示高应力下的纳米析出相作为位错源这一新机制(见图)。结合析出相的传统硬化功能,这一机制强度和韧性的双重机制可以实现高密度析出相合金在强度和韧性上的综合优异性能。同时他们也给出了纳米析出形成位错源的影响因素,它依赖于析出相和基底材料的晶格失配。 

  综合考虑纳米析出相的硬化效应和它作为位错源的机制,该团队提出可通过析出相材料中的两个关键尺度,析出相大小及析出相之间的距离(或者析出相密度),来实现材料强度-韧性的最优化匹配设计。通过理论分析,他们给出了材料设计过程中这两个尺度的相互关系。这一方面的研究将有助于形成高密度析出相合金材料的强韧化优化设计基础。 

  该科研工作获得了国家基金委 (基金号 11988102,11425211),中国科学院先导专项以及卓越中心的支持。论文的第一作者为来自力学研究所的彭神佑博士,他目前在湖南大学担任助理教授。

图:纳米析出相诱导的位错源机制:(a) 析出相(蓝色)所代表的原子结构示意图. (b)-(f) 原子速度场显示在定常临界应变控制下,位错从析出相和基底界面上不断萌生的过程。通过图(b) 和(c)中下方的方框区域放大图,可以看到螺位错的基本原子结构。图中所给出的标尺为8 nm

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