Processing and characterization of Nb-16%Ta-12%W (wt%) alloy for superconductivity applications

The present investigation aims to carry out a preliminary evaluation of the Nb-16%Ta-12%W (wt%) alloy as a potential artificial pinning center material (APC) for Nb-Ti superconductors. An ingot of the ternary alloy was produced by aluminothermic reduction (ATR) of a Nb2O5 + Ta2O5 + WO3 mixture and electron beam melting (EBM). The oxygen and nitrogen content of the ingot after triple EBM steps were 16 wt-ppm and 19 wt-ppm, respectively. The metallic yield (Nb + Ta + W) in each of the melting steps were: 75% (1st); 94% (2nd) and 96% (3rd). A rod from the ingot was then cold swaged and drawn down to a true strain (epsilon) of approximately epsilon = 7.7. At the true strain of epsilon = 2.8 a piece of the rod was taken and annealed at 1300 degrees C for 2 h in vacuum. The annealed material was also cold swaged and drawn to a true strain of epsilon = 4.9. The slope of the microhardness versus true strain deformation curves for the as-cast and annealed materials were 9.4 and 14.3, respectively. The alloy presented a critical temperature (T-c) of T-c = 7.1 K and a normal residual resistivity (rho(N)) of 605 mu Ohm m. In an additional work the Nb-16Ta-12W alloy will be introduced in a Nb-Ti matrix for the production of a Nb-Ti superconductor wire. (C) 1999 Elsevier Science Ltd. All rights reserved.