Published online by Cambridge University Press: 15 February 2011
Conventional Nb-Ti superconductors are optimized by thermal and mechanical treatments which ultimately produce a nanostructure consisting of 1-2nm thick ribbons of α-Ti dispersed in a matrix of β-Nb-Ti. Several groups are now investigating artificial dispersions of second phase in Nb-Ti which may develop stronger flux pinning nanostructures. However, these new methods generally require true strains of 30 or more. We avoid these large strains (and their associated problems) by forming our composites from a mixture ∼ -50¼m size Nb and Nb-Ti powders, thus permitting the desired nanostructure to be produced with strains of order 12. Nb pinning particles were found to develop an irregular shape, tending to nanometer thick ribbons at large strains. The final size nanostructure resembles conventional Nb-Ti, except that the “second” phase is Nb rather than α-Ti. The critical current density (Jc) was found to increase by over two orders of magnitude to peak values of 5490 and 1980A/mm2 at 2 and 5T as the particle thickness was reduced.