In-situ resistance measurements of RHQT processed Nb/sub 3/Al superconductors

The bcc supersaturated solid solution, Nb(Al)/sub ss/ obtained by rapid heating and quenching of a multifilamentary Nb/Al composite wire has shown a change from a disordered to an ordered structure before finally transforming to the A15 Nb/sub 3/Al phase. It is believed that such ordering is responsible for suppressing the critical temperature, T/sub c/, the upper critical magnetic field, B/sub c2/, and the critical current density, J/sub c/. The ordering of the bcc phase can be suppressed by increasing the heating rate, and therefore this should improve the superconducting properties of the resulting Nb/sub 3/Al wires. Enhancement of J/sub c/ can also be achieved if the Nb(Al)/sub ss/ phase is mechanically deformed before transformation. The transformation process was studied in as-quenched and mechanically deformed Nb/Nb(Al)/sub ss/ wires by in-situ resistance measurement under heating at two different rates, 200/spl deg/C/h and 800/spl deg/C/h. The electrical resistivities of the wires decrease abruptly during the transformation from bcc to A15 phases and the process is much faster for mechanically deformed wires. Also, the heating rate affects the onset temperature of the A15 transformation. The results also show that the J/sub c/ of the transformed Nb/sub 3/Al wires increases with increasing reduction in area.