Size-induced enhanced mechanical properties of nanocomposite copper/niobium wires: nanoindentation study

The effect of microstructure dimension delta on plasticity of high strength multi filamentary nanocomposite copper/niobium, wires was studied by nanoindentation. Two structures were tested: a Cu matrix containing Nb filaments and a Cu matrix containing Nb tubes filled with Cu. For delta > 10 mum, no size effect on the composite hardness is observed. In the 1-10 mum range, a strong increase in hardness indicates a change in plasticity mechanism, attributed to the classical Hall-Petch grain size strengthening. In the nanometre range, the hardness of the nanocomposite Cu/Nb regions exceeds that of nanocrystalline Cu or Nb, reaching 5.8 GPa for the finest conductors. The observed size effect on the plasticity of Cu/Nb nanostructures added to the dislocation barrier role of Cu/Nb interfaces confirms previous analyses based on the occurrence of a single dislocation regime at nanometre scale associated with impenetrable Cu/Nb interfaces. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.