Room-temperature tensile behaviour of bronze-processed multi-filamentary Nb3Sn superconducting materials

Abstract

Structure and its relation to fracture behaviour of multi-filamentary Nb3Sn superconducting composite materials prepared by the bronze method were studied by tensile testing at room temperature. There were two types of fracture mode. Type I showed high elongation, accompanied by apparent plastic deformation of composites as a whole and the Nb3Sn layer exhibited multiple fracture. Type II showed no apparent plastic deformation and the composites fractured in a brittle manner. Type I occurred when the fraction of the Nb3Sn layer was small and the drop of load-bearing capacity due to fracture of Nb3Sn layer could be compensated mainly by strain hardening of ductile constituents of Nb, Cu-Sn and Cu. On the other hand, Type II occurred when the fraction of Nb3Sn layer was large and the fracture of the Nb3Sn layer caused fracture of composites as a whole. To describe the tensile strength of composites for both types, a model was proposed, which explained well the experimental results. It was found that the strength of the Nb3Sn layer decreases with increasing diameter of composites and with increasing annealing temperature and time.