Hardness and strain rate sensitivity of nanocrystalline Cu

The measured hardness of nanocrystalline Cu with grain sizes (d) as small as 10 nm still follows the Hall–Petch relation. A rate sensitivity of 0.06 ± 0.01 and a flow stress activation volume of 8b3 were determined at d = 10 nm, suggesting grain boundary activities are enhanced but not yet dominant in the plastic deformation.