测定超细晶粒金属的机械强度
Summary
本文介绍的方案描述了高压径向金刚石-铁砧-细胞实验并分析了相关数据，这对于获得纳米材料的机械强度至关重要，并且对传统方法有重大突破。
Abstract
金属的机械强化是工业界和学术界材料科学的长期挑战和热门话题。纳米金属强度的大小依赖性已经引起了很多人们的兴趣。然而，在较低的纳米尺度上表征材料的强度一直是一个很大的挑战，因为传统技术变得不再有效和可靠，例如纳米压痕，微孔压缩，拉伸等。目前的协议采用径向金刚石砧电池（rDAC）X射线衍射（XRD）技术来跟踪差分应力变化并确定超细金属的强度。结果表明，超细镍颗粒比粗颗粒具有更显著的屈服强度，镍的尺寸增强持续到3 nm。这一重要发现在很大程度上取决于有效和可靠的表征技术。rDAC XRD方法有望在研究和探索纳米材料力学方面发挥重要作用。
Introduction
抗塑性变形性决定了材料的强度。金属的强度通常随着晶粒尺寸的减小而增加。这种尺寸增强现象可以通过传统的霍尔-佩奇关系理论很好地说明，从毫米到亚微米状态1，2，该理论基于块状尺寸金属的位错介导的变形机制，即位错堆积在晶界（GB）并阻碍其运动，导致金属3，4中的机械强化。
相比之下，机械软化，通常被称为逆霍尔 – 佩奇关系，在过去二十年中已经报道了精细纳米金属的5，6，7，8，9，10。因此，纳米金属的强度仍然令人费解，因为检测到粒径低至~10 nm11，12的连续硬化，而低于10 nm状态的尺寸软化情况也报告了7，8，9，10。这个有争议的主题的主要困难或挑战是对超细纳米金属的机械性能进行统计上可重复的测量，并在纳米金属的强度和晶粒尺寸之间建立可靠的相关性。另一部分困难来自纳米金属塑性变形机理的模糊性。纳米尺度上的各种缺陷或工艺已有报道，包括位错13、14、变形孪生15、16、17、堆垛断层15、18、国标迁移19、国标滑动5、6、20、21、晶粒旋转22、23、24、原子键参数25、26、27、28 等然而，哪一个主导塑性变形，从而决定纳米金属的强度尚不清楚。
对于上述这些问题，传统的机械强度检验方法，如拉伸试验29、维氏硬度试验30、31、纳米压痕试验32、微孔压缩33、34、35等，效果较差，因为高质量的大片纳米结构材料很难制造，而常规压头比单纳米颗粒材料大得多（对于 单粒子力学）。在本研究中，我们将径向DAC XRD技术36，37，38 引入材料科学 ，以原位 跟踪各种晶粒尺寸纳米镍的屈服应力和变形变形纹理，这些材料在以前的研究中用于地球科学领域。已经发现，机械强化可以扩展到3纳米，比以前报道的最大尺寸的纳米金属小得多，这扩大了传统的霍尔 – 佩奇关系的制度，暗示了rDAC XRD技术对材料科学的重要性。
Protocol
1. 样品制备 从商业来源获得3 nm，20 nm，40 nm，70 nm，100 nm，200 nm和500 nm镍粉（参见 材料表）。形态表征如图 1所示。 通过使用反应釜加热3nm镍颗粒来制备8nm镍颗粒（参见 材料表）。 将〜20mL无水乙醇和〜50mg 3nm镍粉放入反应釜中。注意：整个溶液不应达到水壶体积的约70%。 将反应釜在80°C下加热24小时。 …
Representative Results
在静水压缩下，展开的X射线衍射线应该是直的，而不是弯曲的。然而，在非静水压力下，曲率（XRD环的椭圆度，转化为沿方位角绘制的线的非线性）在相似的压力下显着增加超细晶粒镍（图4）。在类似的压力下，3nm尺寸的镍的差应变是最高的。机械强度结果（应力-应变曲线）如图 5所示。强度从较粗的晶粒不断增加到较细的晶粒，这与传统知识<sup cla…
Discussion
计算模拟已被广泛用于研究纳米金属5，6，16，17，27，42的晶粒尺寸对强度的影响。完美位错、部分位错和GB变形已被提出在纳米材料的变形机理中起决定性作用。在分子动力学模拟中，Yamakov等人42提出了一个变形机理图，包括完全…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
我们感谢国家自然科学基金（NSFC）的支持，资助编号为11621062，11772294，U1530402和11811530001。本研究还得到了中国博士后科学基金（2021M690044）的部分支持。这项研究使用了先进光源的资源，这是美国能源部科学用户设施办公室，合同编号为DE-AC02-05CH11231和上海同步辐射设施。这项研究得到了COMPRES的部分支持，COMPRES是NSF合作协议EAR 1606856下的地球科学材料特性研究联盟。
Materials
| 20 nm Ni | Nanomaterialstore | SN1601 | Flammable |
| 3 nm Ni | nanoComposix | Flammable | |
| 40, 70, 100, 200, 500 nm Ni | US nano | US1120 | Flammable |
| Absolute ethanol | as the solution to make 8 nm Ni | ||
| Absolute isopropanol | as the solution to make 12 nm Ni | ||
| Amorphous boron powder | alfa asear | ||
| Copper mesh | Beijing Zhongjingkeyi Technology Co., Ltd. | TEM grid | |
| Epoxy glue | |||
| Ethanol | clean experimental setup | ||
| Focused ion beam | FEI | ||
| Glass slide | |||
| Glue tape | Scotch | ||
| Kapton | DuPont | Polyimide film material | |
| Laser drilling machine | located in high pressure lab of ALS | ||
| Monochromatic synchrotron X-ray | Beamline 12.2.2, Advanced Light Source (ALS), Lawrence Berkeley National Laboratory | X-ray energy: 25-30 keV | |
| Optical microscope | Leica | to mount the gasket and load samples | |
| Pt powder | thermofisher | 38374 | |
| Reaction kettle | Xian Yichuang Co.,Ltd. | 50 mL | |
| Sand paper | from 400 mesh to 1000 mesh | ||
| Transmission Electron Microscopy | FEI | Titan G2 60-300 | |
| Two-dimension image plate | ALS, BL 12.2.2 | mar 345 |
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Citazione di questo articolo
Xu, J., Wang, Y., Yan, J., Chen, B. Determining the Mechanical Strength of Ultra-Fine-Grained Metals. J. Vis. Exp. (177), e61819, doi:10.3791/61819 (2021).