Design aspects of dual Nb-Ta sheet diffusion barriers for Nb3Sn conductors

Tantalum (Ta) diffusion barriers used in Nb3Sn superconductors deform nonuniformly during wire drawing. A strategy sometimes used to mitigate this problem is to place a sacrificial layer of niobium (Nb) next to the Ta to act as a mechanical transition zone between the softer Cu-Nb composite and the harder Ta. This approach can promote more uniform co-deformation of the Ta layer enabling thinner Ta layers and a reduced chance of layer rupture, and has the added benefit of providing additional Nb for conversion to Nb3Sn. A thinner Ta layer translates to less Ta volume and less cost. In the current work the authors find that a layer of Nb adjacent to a Ta layer embedded in Cu significantly increases the composite wire strain to fracture, and appears to decrease the Ta layer interface roughness. © 2011 IEEE