Enhanced Critical Current Densities in Nb3Sn Superconducting Strands Prepared by Bronze Process

In the development of Nb3Sn superconducting strands, the improvement of the non-Cu critical current density (J(c)) has been greatly emphasized. Different Nb3Sn strands were manufactured by the bronze route artificially doped with titanium in bronze. The influences of bronze on Nb volume ratio, filament material, filament diameter, and heat treatment were studied. In this paper, bronze-to-Nb volume ratio affected J(c) slightly due to the formation of the Sn shortage and similar Nb3Sn volume after heat treatment. The study of filament diameter indicates that J(c) increases largely as the filament diameter reduces for the full reaction. Different heat treatment times at 575 degrees C, 650 degrees C, and 675 degrees C will result in various performances. According to microstructure images, residual Nb core can be seen in each filament. Bigger average grain size will lead to lower J(c).