The evolution of Nb recrystallization in a Cu matrix: morphology of Nb and modulation ofits critical fields in a wire configuration

Abstract

We report on the microstructural evolution in Cu15%Nb multifilamentary wires upon annealing andthe corresponding effects on their magnetic properties. During annealing at temperatures higher than800 °C thermal instability mechanisms take place in the microstructure of the Cu15%Nbcomposite, leading to the spheroidization of niobium filaments. Anotherimportant consequence of annealing is the recrystallization of Nb, that has astraightforward influence on the magnetization data. When compared to the as-drawncomposite, in the annealed Cu15%Nb samples the bulk upper critical fieldHc 2(T) is reduced significantly, while the lower critical fieldHc 1(T) is increased as a function of the annealing temperature and time. Thisindicates that we may employ this process as an efficient method to modifythe basic superconducting parameters of Nb, namely the coherence lengthξ(T) and thepenetration depth λ(T).