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Watching the Nanograins Roll

Nanocrystalline metals with grain diameter less than 30 nanometers may exhibit a range of new and interesting deformation mechanisms. In his Perspective,
 Ma
 discusses the results reported in the same issue by
 Shan
 et al., who recorded motion of the nanograins during deformation of nickel samples using an in situ transmission electron microscopy technique. Unlike the normal plastic deformation governed by dislocation movement, significant grain rotation and grain boundary sliding were observed in the nanocrystalline nickel at room temperature. The Perspective gives a brief overview of the transition from dislocation-based to grain boundary-mediated plasticity in nanocrystalline grains.