Nb₃Al Multifilamentary Wires Continuously Fabricated by Rapid-Quenching

Abstract

The Nb tube process has recently been developed at NRIM(Japan) for fabricating Nb₃Al multifilamentary superconductors,^1–3 which are characterized by the heat treatment at low temperature (<1000°C) and hence extremely high critical current density J_c in fields less than 10 T. However, high field properties were essentially inferior to those of commercial multifilamentary (Nb,Ti)₃Sn conductors, due to the depression of Tc probably caused by the deviation from stoichiometry. Since stoichiometric Nb₃A1 with high Tc is only stable at high temperatures (>1700°C), many attempts were made to form Nb₃A1 by heat treating Nb/AI composite at high temperatures.^4–6 However, rapid grain growth decreased the density of pinning center (grain boundary) in Nb₃A1 and thereby degraded J_c in particular at low magnetic fields. To overcome this problem, Nb₃A1 conductors fabricated through a rapid-quenching process have been studied. In this process the A15 Nb₃A1 phase with fine grain structure can be precipitated from the supersaturated Nb-Al bcc phase by aging at ~800°C. However, no attempt was made to fabricate a practical-structure conductor such as a long multifilamentary wire through continuous rapid-quenching and subsequent annealing (post annealing) process.