Effect of metallurgical history on 'J<inf>c</inf>(5T)' in surface diffused multifilamentary Nb<inf>3</inf>Sn

Abstract

Data are presented of critical current density 'J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (5T)' in a 5 T perpendicular magnetic field (and 10 T as well for selected samples) for multifilamentary Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn 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 J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (5T) varied from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to > 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> over the entire composite cross section (Cu-Sn, Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn, Nb). The optimum performances were 38.8 A in 0.127 mm diam 1.9/1 Cu/(Nb + Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn) composite at 5 T and 78 A in a 0.18 mm diam 3/1 CU/(Nb + Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn) at 5 T.