Direct formation of A15 phase through RHQ treatment in RIT processed Nb/Al-Cu precursor wire
In Nb/sub 3/Al wire with 2.5at% added copper, the Nb/sub 3/Al filaments form directly during a RHQ (rapid heating and quenching) treatment and show excellent superconducting properties. The Nb/sub 3/Al filaments appear to form rapidly during the quenching, because many stacking faults are observed. We found that two different transformation conditions yielded excellent superconducting properties. At high temperature, the Cu-added Nb/sub 3/Al wire showed T/sub c/ of 18.3 K, B/sub irr/ (4.2 K) of 29.3 T, and J/sub c/ (4.2 K, 20 T) of 800 A/mm/sup 2/, while at lower temperature these values were 18.2 K, 29.4 T, and 710 A/mm/sup 2/. Although the resultant properties are similar, the latter processing conditions produced a significant quantity of /spl sigma/-phase particles. The net J/sub c/ (4.2 K) of Nb/sub 3/Al phase in this latter wire is very high, e.g., 1760, 1180, and 700 A/mm/sup 2/ at 18, 20 and 22 T respectively.