Size dependence of rate-controlling deformation mechanisms in nanotwinned copper

Nanotwinned metals exhibit an unusual combination of ultrahigh strength, considerable ductility and enhanced rate sensitivity. We find that a Hall-Petch-type relationship closely fits the experiment data of activation volume as a function of twin spacing. The results suggest a transition of the rate-controlling mechanism from intra-twin- to twin-boundary-mediated processes with decreasing twin lamellar thickness. These findings provide insights into the possible routes for optimizing the strength and ductility of nanostructured metals by tailoring internal interfaces. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.