Critical shear stress for onset of plasticity in a nanocrystalline Cu determined by using nanoindentation

The plastic deformation behavior was investigated by using nanoindentation in a magneto-sputtered nanocrystalline (nc) Cu film with an average grain size of 14 mn. The determined critical shear stress to initiate plasticity in the nc-Cu sample (about 8.3 GPa) is identical to that for nucleation of lattice dislocations in an annealed coarse-grained Cu (8.5 GPa), and both values are close to the theoretical shear strength in the dislocation-free single crystal. This observation, in agreement with the atomistic simulation results, supports the argument that the onset of plasticity of the nc-Cu is associated with initiation of dislocation activities at grain boundaries. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.