Short-sample quenching of Nb3Al precursor strand in support of reel-to-reel process development

Niobium-aluminum precursor strands were fabricated using the conventional j elly roll method with two Nb:Al volume ratios, 3:1, and 5:1. These mono-ele ments were restacked in 7-, 19- and 36-core arrangements and drawn down to wires approximately 0.8 mm and 0.4 mm in diameter. Short lengths of wire we re resistively heated under high vacuum to temperatures as high as 2200 deg rees C for various times, and either allowed to cool by radiation plus lead conduction or quenched into liquid gallium. Vacuum cooling led to a disord ered A15 phase, which was then ordered by annealing at 800 degrees C; galli um quenching tended to produce the bcc phase, which could be transformed in to A15 also by annealing for various times at 800 degrees C. The supercondu cting properties of the final wires were examined by vibrating-sample magne tometry (chi(dc) and T-c) as well as transport J(c) measurement. Best resul ts so far are for a 5:1 Nb:Al volume ratio sample Ga quenched from 2000 deg rees C with a secondary reaction of 800 degrees C/3 h, giving J(c) = 4.5 x 10(8) A/m(2) at 12 T, with a T-c = 18-18.5 K.