Nb3Al Multifilamentary Wires Continuously Fabricated by Rapid-Quenching
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 Jc 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 Jc 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.
KeywordsSigma Phase Post Annealing Composite Wire High Critical Current Density Metastable Solid Solution
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