Size-dependent deformation mechanisms and strain-rate sensitivity in nanostructured Cu/X (X = Cr, Zr) multilayer films
Size-dependent deformation mechanisms and strain-rate sensitivity in nanostructured Cu/X (X = Cr, Zr) multilayer films
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纳米结构 Cu/X (X = Cr, Zr) 多层薄膜中尺寸相关的变形机制和应变率敏感性
DOI：
10.1016/j.actamat.2012.03.052
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发表时间：
2012-05
期刊：
影响因子：
9.4
通讯作者：
Sun, J.
中科院分区：
文献类型：
--
作者：
Niu, J. J.;Zhang, J. Y.;Liu, G.;Zhang, P.;Lei, S. Y.;Zhang, G. J.;Sun, J.
Cu/Cr（面心立方 (fcc)/体心立方）和 Cu/Zr（fcc/六方密排）纳米结构多层膜的硬度、活化体积和应变率灵敏度分别作为调制周期 (L) 和调制比 (η) 的函数进行了系统测量。所有三种塑性变形特征均发现显着的尺寸效应，即随着尺寸长度 L 的减小，硬度和活化体积增加，但应变率敏感性降低。对微观结构演变进行了统计检查，以合理化这些尺寸依赖性。至关重要的是，我们观察到，铜晶粒中存在丰富的纳米孪晶，尽管纳米孪晶的形成因 L 较小而受到抑制。这种与尺寸相反的纳米孪晶形成是导致应变率敏感性降低的原因，因为纳米孪晶减少引起的负面影响超过了来自凸起界面/边界的正面影响。修改机械模型以考虑界面效应和纳米孪晶效应，当 L 大于约 20 nm 时，应变率灵敏度的计算结果与实验结果基本一致。低于这个临界长度尺寸，由于变形机制从约束层中的位错成核/滑移到位错穿越界面的变化，计算结果与实验结果之间存在差异。还通过考虑纳米孪晶强化来修改约束层滑移模型，以定量描述与 L 相关的硬度。此外，还讨论了组成相及其相对含量对 NMF 的活化体积和应变率敏感性的影响，以及 η 的变化。
Hardness, activation volume and strain-rate sensitivity of Cu/Cr (face-centered cubic (fcc)/body-centered cubic) and Cu/Zr (fcc/hexagonal close-packed) nanostructured multilayer films have been systematically measured as a function of modulation period (L) and modulation ratio (η), respectively. Significant size effects were found for all the three plastic deformation characteristics, i.e. enhanced hardness and activation volume but reduced strain-rate sensitivity with decreasing the dimension length L. Microstructure evolution was statistically examined to rationalize these size dependences. It was crucially observed that abundant nanotwins existed in the Cu grains, though nanotwin formation was depressed with smaller L. This inverse size-dependent nanotwin formation is responsible for the reduction in strain-rate sensitivity, because the negative effect induced by the decreased nanotwins predominates over the positive effect coming from the raised interfaces/boundaries. A mechanistic model is modified to account for the interface effect as well as the nanotwin effect, which yields calculations of strain-rate sensitivity in broad agreement with the experimental results when L is larger than about 20nm. Below this critical length size, there are discrepancies between the calculations and the experimental results, due to the change in deformation mechanism from dislocation nucleation/slip in confined layers to dislocation crossing interfaces. A confined layer slip model is also modified by considering the nanotwin strengthening to quantitatively describe the L-dependent hardness. In addition, the effects of constituent phases and their relative content on the activation volume and strain-rate sensitivity of NMFs are discussed with regard to variation in η.
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影响因子：
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作者：
Zhang, J. Y.;Liu, G.;Zhang, X.;Zhang, G. J.;Sun, J.;Ma, E.
通讯作者：
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DOI：
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