Improved Jcin mechanically fabricated Nb3Al wires and ribbons

Nb3Al wire which is essentially all A15 may be fabricated by powder or rod composite techniques, with subsequent reaction and ordering anneals. Several of the previously existing problems, including aluminum loss and Kirkendall porosity, have been identified and solved, and transverse-field critical current densities well into the 10⁵amp/cm²range can be produced. However, reproducibility of the critical current density seems to depend on reproducible control of grain size, which we have not as yet achieved. The internal oxidation techniques which succeed for Nb3Sn do not appear to work for Nb3Al, for several reasons. A possible solution to the grain size problem, and to the problem of manufacture of Nb3Al in stabilized form, is to lower the initial reaction temperature. To achieve the latter we have reduced the scale of the elemental composite to a required diffusion distance of about 3000 Å. before reaction. We were thus able to produce substantial quantities of A15 at 1100°C, but for several reasons (see text) we believe finer composites will be necessary.