Mechanical deformation of high-purity sputter-deposited nano-twinned copper

Near classical yield points were reproducibly observed at room and liquid nitrogen temperatures during tensile deformation of 170 gm thick, high-purity copper foils synthesized by magnetron sputter deposition. Uniformly distributed mobile dislocations introduced by rolling to similar to 20% reduction in thickness eliminated the yield point at both temperatures. The experimental observations clearly demonstrate that the observed yield-point behavior is a direct result of the very low initial dislocation density in these sputtered films as expected for "ideal" nanoscale microstructural materials. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.