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Science 30 July 2004:
Vol. 305. no. 5684, pp. 654 - 657
DOI: 10.1126/science.1098741
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Reports

Grain Boundary-Mediated Plasticity in Nanocrystalline Nickel

Zhiwei Shan,1 E. A. Stach,2 J. M. K. Wiezorek,3 J. A. Knapp,4 D. M. Follstaedt,4 S. X. Mao1*

The plastic behavior of crystalline materials is mainly controlled by the nucleation and motion of lattice dislocations. We report in situ dynamic transmission electron microscope observations of nanocrystalline nickel films with an average grain size of about 10 nanometers, which show that grain boundary–mediated processes have become a prominent deformation mode. Additionally, trapped lattice dislocations are observed in individual grains following deformation. This change in the deformation mode arises from the grain size–dependent competition between the deformation controlled by nucleation and motion of dislocations and the deformation controlled by diffusion-assisted grain boundary processes.

1 Department of Mechanical Engineering, University of Pittsburgh, 648 Benedum Hall, Pittsburgh, PA 15261, USA.
2 National Center for Electron Microscopy (NCEM), Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA 94720, USA.
3 Department of Materials Science and Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA.
4 Physical and Chemical Science Center, Sandia National Laboratories (SNL), Albuquerque, NM 87185, USA.

* To whom correspondence should be addressed. E-mail: smao{at}engr.pitt.edu

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