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