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.