Comment on "Grain Boundary-Mediated Plasticity in Nanocrystalline Nickel"

by Mingwei Chen & Xiaoqin Yan Science, 15 Apr 2005 Nanograin rotation via grain boundary sliding has been predicted as an important deformation mode in nanocrystalline materials as grain sizes approach less than 10 nm. However, definite experimental evidence beyond molecular dynamics simulations has been long sought. Recently, Shan et al. reported in situ straining dark-field transmission electron microscope observations of grain rotation in nanocrystalline Ni and claimed that the plastic deformation of nano-Ni is mediated by this grain boundary behavior. Although the experimental results reported by Shan et al. are interesting, their assessment and analysis of the TEM images are problematic. Using the images presented we have quantitatively measured the relative displacements and grain sizes. Both results suggest that the grain rotation and associated contrast change reported by Shan et al. more likely come from low-temperature nanograin growth, caused by electron-beam irradiation and applied stresses, than from plastic deformation. Read the article