Effects of additional elements to Nb/sub 3/Al multifilamentary wire fabricated by rapid-heating/quenching process

We have developed an RHQT process (Rapid-Heat, Quench, and Transformation), for fabricating Nb/sub 3/Al multifilamentary wires, which showed 2 to 5 times larger J/sub c/ (4.2 K) than those of commercially available Nb/sub 3/Sn multifilamentary superconducting wires. We studied the effects of Mg and Ge additions to the RHQT-processed Nb/sub 3/Al 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 Nb/sub 3/Al multifilamentary wire, respectively. The Mg addition reduced T/sub c/ of the Nb/sub 3/Al multifilamentary wire a little from 17.6-17.9 K to 17.1-17.4 K, but had no apparent influence on H/sub c2/ (4.2 K) of 25-27 T. The large J/sub c/ (4.2 K, 20 T) of 200-450 A/mm/sup 2/ were obtained for the Nb/sub 3/Al multifilamentary wire independently of the Mg addition. On the other hand the Ge addition increased not only T/sub c/ of Nb/sub 3/Al multifilamentary wire from 17.6 K to 19.4 K, but also H/sub c2/ (4.2 K) from 25.4-27.2 T to 34.0-39.4 T. The Ge addition improved drastically the J/sub c/ (4.2 K) in fields above 22 T, but reduced the J/sub c/ (4.2 K) in low fields.