Alloying effect on kinetics of formation of superconducting layers and thin structure of Nb/Cu-Sn composites

The methods of transmission and scanning electron microscopy, electron probe microanalysis and optical metallography were applied to investigate the kinetics of formation of Nb3Sn superconducting layers and fine structure of single and multicore composites with the bronze matrix alloyed by Zr, Zn, Mg. It is revealed that these elements each promote an increase of growth rate of superconducting layer and its thickness. The growth rate is shown to be determined by grain boundary diffusion of tin. Its increase occurs due to oxygen binding into oxides of alloying elements and grain boundary refining. Zirconium segregations at grain boundaries are considered as the reason for grain refinement in the layer Nb3Sn. 24 refs., 5 figs., 2 tabs