Nb3Al and Nb3(Al,Ge) composite tapes fabricated by CO2laser beam irradiation

Nb3Al and Nb3(Al,Ge) tapes with excellent superconducting properties were fabricated by the laser beam irradiation method. Nb-25 at %Al and Nb-20 at % Al-5 at % Ge tapes were prepared by the powder metallurgy process. Continuous CO2laser beam irradiation was carried out on the tape surface in an argon gas atmosphere at 1-13m/min, velocities. Beam power was 0.3-4kW and beam diameter at the tape surface was 0.5-3mm. As the power density was high and irradiation time was short, the tape could be heated and cooled much faster than a tape that was heat treated by the conventional method. The results were fine grain structure and large Jcvalues at high magnetic fields. Tcfor an as-irradiated tape was 16-18K. This Tcincreased by ∼2K by the subsequent annealings at 700°C for 100 hours. The maximum Tc(onset) values obtained were 18.6K for the Nb3Al tape and 20.1K for the Nb3(Al,Ge) tape, which indicated that stoichiometric compounds could be formed by laser beam irradiation. Annealed tapes, after the irradiation, showed excellent Jcvalues, especially at high magnetic fields. Jcvalues over 2×104A/cm²at 23 Tesla were obtained for both Nb3Al and Nb3(Al,Ge) tapes. These values are much larger than those obtained by conventional heat treatment. Jcvalues of as-irradiated tapes at high fields were smaller than those for annealed tapes, due to the lower Tcand, hence, lower Hc2. The large Jcvalues, as well as easy scale-up procedure, indicate that the laser irradiation method is promising for the fabrication of advanced superconductors, e.g. Nb3Al and Nb3(Al,Ge) capable of generating fields over 20 Tesla.