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

Niobium-aluminum precursor strands were fabricated using the conventional jelly roll method with two Nb:Al volume ratios, 3:1, and 5:1. These mono-elements 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 were resistively heated under high vacuum to temperatures as high as 2200 degrees C for various times, and either allowed to cool by radiation plus lead conduction or quenched into liquid gallium. Vacuum cooling led to a disordered A15 phase, which was then ordered by annealing at 800 degrees C; gallium quenching tended to produce the bcc phase, which could be transformed into A15 also by annealing for various times at 800 degrees C. The superconducting properties of the final wires were examined by vibrating-sample magnetometry (chi(dc) and T-c) as well as transport J(c) measurement. Best results so far are for a 5:1 Nb:Al volume ratio sample Ga quenched from 2000 degrees 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.