The influence of magnesium addition to the bronze on the critical current of bronze-processed multifilamentary Nb₃Sn

Abstract

Results show that Mg may be used to improve J/sub c/ in multifilamentary wire, and that the increase is large (60 to 100%). Chemical analysis reveals that the Mg segregates to the reacted layer, and resides principally in the bulk Nb/sub 3/Sn. The microstructural analyses suggest that its principal effect is to suppress coarsening of the Nb/sub 3/Sn grains and establish a uniformly grained layer. Preliminary data also suggests that Mg decreases the minimum Nb/sub 3/Sn grainsize and improves the overall stoichiometry of the reacted layer. The samples used had very high bronze to Nb ratios (R). Since the increase in J/sub c/ apparently depends on the concentration of Mg in the reacted layer, and since virtually all the Mg accumulates there, it may prove difficult to achieve comparable results at lower R values without substantially raising the Mg content of the bronze, or changing to an external bronze process. 6 figures.