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Deformation mechanisms in nanotwinned metal nanopillars

Nature Nanotechnology volume 7, pages 594–601 (2012)Cite this article

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Abstract

Nanotwinned metals are attractive in many applications because they simultaneously demonstrate high strength and high ductility, characteristics that are usually thought to be mutually exclusive. However, most nanotwinned metals are produced in polycrystalline forms and therefore contain randomly oriented twin and grain boundaries making it difficult to determine the origins of their useful mechanical properties. Here, we report the fabrication of arrays of vertically aligned copper nanopillars that contain a very high density of periodic twin boundaries and no grain boundaries or other microstructural features. We use tension experiments, transmission electron microscopy and atomistic simulations to investigate the influence of diameter, twin-boundary spacing and twin-boundary orientation on the mechanical responses of individual nanopillars. We observe a brittle-to-ductile transition in samples with orthogonally oriented twin boundaries as the twin-boundary spacing decreases below a critical value (∼3–4 nm for copper). We also find that nanopillars with slanted twin boundaries deform via shear offsets and significant detwinning. The ability to decouple nanotwins from other microstructural features should lead to an improved understanding of the mechanical properties of nanotwinned metals.

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Figure 1: Characterization of fabricated nanotwinned copper pillars.
Figure 2: Stress–strain curves and failure behaviours of nanotwinned pillars.
Figure 3: Comparison of deformation mechanisms of nanotwinned pillars with orthogonal and 18° slanted twin boundaries.
Figure 4: Typical deformation characteristics of the simulated samples (diameter, 50 nm; twin-boundary spacing, 1.05 nm) with orthogonal and slanted twin boundaries.
Figure 5: Molecular dynamics simulations of nanotwinned copper pillars under uniaxial tension.

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Acknowledgements

D.J. and J.R.G. acknowledge financial support from the NSF CAREER Grant (DMR-0748267) and the Office of Naval Research (N00014-09-1-0883). X.L. and H.G. also acknowledge financial support from the NSF-sponsored MRSEC Center at Brown University (DMR-0520651) and grant no. CMMI-0758535. The authors acknowledge critical support and infrastructure provided by the Kavli Nanoscience Institute at Caltech. The simulations were performed on the NICS Kraken Cray XT5 system (MS090046).

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Author notes

  1. Dongchan Jang and Xiaoyan Li: These authors contributed equally to this work

Authors and Affiliations

  1. Division of Engineering and Applied Sciences, California Institute of Technology, 1200 E. California Blvd, MC 309-81, Pasadena, 91125, California, USA

    Dongchan Jang & Julia R. Greer

  2. School of Engineering, Brown University, 610 Barus and Holley, 182 Hope Street, Providence, Rhode Island, 02912, USA

    Xiaoyan Li & Huajian Gao

  3. The Kavli Nanoscience Institute at Caltech, California Institute of Technology, Pasadena, 91125, California, USA

    Julia R. Greer

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  1. Dongchan Jang
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Contributions

D.J. conducted experiments, including synthesis and in situ testing of samples. X.L. performed atomistic simulations. J.R.G. and H.G. conceived the research and provided guidance. All authors analysed the data, discussed the results and wrote the manuscript.

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Correspondence to Dongchan Jang or Huajian Gao.

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The authors declare no competing financial interests.

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Jang, D., Li, X., Gao, H. et al. Deformation mechanisms in nanotwinned metal nanopillars. Nature Nanotech 7, 594–601 (2012). https://doi.org/10.1038/nnano.2012.116

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