The Study of Strengthening and the Electrical Resistivity of Deformation Processed Cu/Cu-16%Nb and Cu/Cu-7.7%Nb Microcomposites

The extremely high level of tensile strength values (1000-1700 MPa) combining with the high electrical conductivity of 55-75% IACS are attained for industrially produced new class of microcomposite Cu-Nb wires. For the real industrial application of such wires the optimal combination of physical properties must be supplemented with the reasonable cost. One of the ways to reduce the price of Cu-Nb microcomposite wires can be attained by reducing of content of expensive Nb. In the present study, we compare two composites with a standard niobium content Cu/Cu-16%Nb and with a significantly lower one. The effects of deformation of these wires on physical properties are studied. The low Nb fraction allows to achieve the higher level of cold deformation up to 12 in comparison with 8.6 for Cu/Cu-16%Nb wire. The upper limits of tensile strength were 1200 MPa and 1500 MPa for Cu/Cu-7.7%Nb and Cu/Cu-16%Nb accordingly, however the level of electrical resistance for maximum deformation was approximately the same for both wires. For both wires, a stepwise dependence of the electrical resistivity on the deformation was observed at a cryogenic temperature (10 K). This is speculated as an evidence for non-monotonic evolution of the Cu/Nb interface. These composites demonstrate a phase transition to the superconducting state and temperature of the phase transition decreases with increasing deformation. However, at extremely high deformations for the composite with reduced niobium content, an unexpected effect of increasing the critical temperature is found. The reasons for this behavior are discussed in relation to microstructure features of Cu/Cu-7%Nb wire.