Microstructure, phase composition and superconductivity of Cu-Nb-Sn alloys

Investigated were the peculiarities of structure formation and the transition to superconductive state of Cu-Nb-Sn alloys containing up to 30 atomic % Nb and up to 6 atomic % Sn as a function of the condition of crystallization and heat treatment. The microstructure of cast alloys consists of niobium-based solid solution dendrites, a bronze matrix and a thin interlayer of Nb3Sn between them. It is suggested that the interlayer is formed in solid state. The character of the transition of cast alloys into superconductive state depends on the content of tin. Annealing at 750 deg C promotes the growth of the Nb3Sn layer, thickness, reduces the content of Sn in the matrix and varies the parameters of the Nb3Sn lattice. The temperature of the start of the transition Tsub(H) increases with the annealing time, whereas the width of the transition decreases