Effect of metallurgical history on ´Jc(5T)´ in surface diffused multifilamentary Nb3Sn

Data are presented of critical current density ´Jc(5T)´ in a 5 T perpendicular magnetic field (and 10 T as well for selected samples) for multifilamentary Nb3Sn formed by Sn diffusion from a Cu-Nb composite´s outer surface. The parameters varied are: composite diameter and Cu/Nb ratio; Sn percentage; filament diameter; reaction temperature and time; and different combinations of the above parameters. The composite diameter varied from 0.254 to 0.08 mm; Cu/Nb volume ratio from 1.7 to 3; volume percentage of Sn from 2% to 13.8%; average filament diameter from 2 microns to 7 microns. The reaction temperature was varied between 550° C to 795° C for different lengths of time, one to several thousand hours. A three-stage heat treatment was selected to formulate the basis for the reaction heat treatment map. The Jc(5T) varied from 10³to > 3 × 10⁵A/cm²over the entire composite cross section (Cu-Sn, Nb3Sn, Nb). The optimum performances were 38.8 A in 0.127 mm diam 1.9/1 Cu/(Nb + Nb3Sn) composite at 5 T and 78 A in a 0.18 mm diam 3/1 CU/(Nb + Nb3Sn) at 5 T.