Influence of Al Composition Thickness on Critical Current Density in Transformation-Processed Nb3Al Superconductors

The influence of the Al layer thickness on the critical current density J(c) of transformation-processed Nb3Al superconductors was investigated. The Al layer thickness in the jerry-roll filaments of precursor wires was varied from 120 to 250 nm; the Nb layer thickness is proportional to the Al thickness, keeping the Nb-Al composition ratio to 3. The rapid heating and quenching (RHQ) operation condition was varied within a range of the conditions to form the ductile body-centered cubic (BCC) Nb-Al phase. The RHQ wires were also followed by an areal reduction process prior to the Nb3Al phase transformation. Thinner Al thickness wires show a steeper increase in J(c) with reduction in the area, whereas thicker Al thickness wires show a slower increase. The best J(c) performance was obtained for the thinnest Al thickness sample. Without areal reduction, there was not much difference in the optimum J(c) with respect to the Al thickness.