Effect of Cu doping on properties of RHQT processed powder in tube Nb3Al wires

Powder-in-tube (PIT) Nb-3(Al1-xCux)(x = 0-0.04) superconducting wires were fabricated by rapid heating, quenching and transformation (RHQT) process. With the addition of Cu, disordered Nb3Al A15 phase with stoichiometric composition was formed in the quenched wires and atomic long range ordering occurred during the low temperature annealing process, resulting in improvement of T-c, J(c) and B-irr performance compared to the pure Nb3Al sample. The highest T-c of 18.0 K, narrowest Delta T-c of 0.6 K and best layer J(c) of about 30481 A/cm(2) @12 K, 4T was found in the Nb-3(Al0.97Cu0.03) wire, which is nearly four times of pure Nb3Al sample. The Nb-3(Al0.97Cu0.03) wire also shows the highest B-irr value of 25.7T at 8 K and 12.9T at 12 K, respectively. The formed A15 phase exhibit uniform microstructure and composition. Flux pinning of the Nb-3(Al1-xCux) wires follows the surface pinning mechanism, where grain boundary and stacking faults were considered as pinning centers.