In-situ resistance measurements of RHQT processed Nb3Al superconductors

The bee supersaturated solid solution, Nb(Al)(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 Nb3Al phase. It is believed that such ordering is responsible for suppressing the critical temperature, T-c, the upper critical magnetic field, B,2, and the critical current density, J(c). The ordering of the bee phase can be suppressed by increasing the heating rate. and therefore this should improve the superconducting properties of the resulting Nb3Al wires. Enhancement of J(c), can also be achieved if the Nb(Al)(ss) phase is mechanically deformed before transformation. The transformation process was studied in as-quenched and mechanically deformed Nb/Nb(Al)(ss) wires by in-situ resistance measurement under heating at two different rates, 200 degrees C/h and 800 degrees C/h. The electrical resistivities of the wires decrease abruptly during the transformation from bee to A15 phases and the process is much faster for mechanically deformed wires. Also, the heating rate affects the onset temperature of the A 15; transformation. The results also show that the J(c), of the transformed Nb3Al wires increases with increasing reduction in area.