The influence of annealing on the microstructure and electrical resistivity of jelly-rolled Cu-Nb composite wires

In this paper, the annealing effects on the microstructure and electrical resistivity of jelly-rolled Cu-x% vol. Nb (x=25, 33, 50, and 63) composite wires were investigated. During annealing, noticeable changes take place in the microstructure, including recovery and recrystallization of copper and niobium, followed by spheroidization and further coalescence of niobium filaments. With increasing annealing temperature, the diffusion-controlled coalescence of niobium filaments is enhanced due to their proximity. The behavior of the electrical resistivity in the normal state of the Cu-Nb composite shows a noticeable change at a specific value of temperature in the range between 50K and 70 K. This temperature varies with the niobium volume fraction. Such a behavior is discussed in terms of the decrease of the amount of Cu-Nb interfaces promoted by coarsening and by electron scattering effects at these interfaces.