Effects of additional elements to Nb3Al multifilamentary wire fabricated by Rapid-Heating/Quenching process

We have developed an RHQT process (Rapid-Heat, Quench, and Transformation), for fabricating Nb3Al multifilamentary wires, which showed 2 to 5 times larger J(c)(4.2 K) than those of commercially available Nb,Sn multifilamentary superconducting wires. We studied the effects of Mg and Ge additions to the RHQT-processed Nb3Al multifilamentary wire. In order to add Mg and Ge, Al-5at% Mg alloy and Al-20at%Ge alloy were used instead of pure,Al for making the precursors of Nb3Al multifilamentary wire, respectively The Mg addition reduced T-c of the Nb3Al multifilamentary wire a little from 17.6-17.9 K to 17.1-17.4 K, but had not apparent influence on H-c2(4.2 K) of 25-27 T. The large J(c)(4.2 K, 20T) of 200-450 A/mm(2) were obtained for the Nb,AI multifilamentary wire independently on the Mg addition. On the other hand the Ge addition increased not only T-c of Nb3Al multifilamentary wire from 17.6 K to 19.4 K, but also H-c2(4.2 K) from 25.4-27.2 T to 34.0-39.4 T. The Ge addition improved drastically the 5,(4.2 Ii) in fields above 22 T, but reduced the J(c)(4.2 K) in low fields.