Superconducting performance of production NbTi alloys

A producer of multifilamentary NbTi superconducting composites must depend on specified and uniformly reproduced production quantities of NbTi. Characterization of commercial NbTi starting diameter rod has sug-tested that impurity content, nonmetallic inclusion content and mechanical properties of the NbTi may also affect superconducting performance of multifilamentary wire. This paper describes the superconducting performance, i.e. critical current density at field of commercial NbTi containing 45 to 46.5 wt. pct. Ti and analyzes the influence of NbTi mechanical properties on superconducting performance. Production billets with Cu/NbTi ratios of 1.25:1 to 5.5:1 which contain as many as 2046 NbTi filaments are included in this survey. All billets were extruded and drawn to final size with constant major heat treatment and 90-97% reduction after major heat treatment. Superconducting critical current density is shown to be a function of total reduction of NbTi under these conditions, with values of 2.4 × 10⁵A/cm²(4T), 2.0 × 10⁵A/cm²(5T), and 1.6 × 10⁵A/cm²achieved reduction ratios from starting rod size to final filament size of 10⁵or better. Superconducting performance of NbTi heats with tensile reductions in area of 65.5% to 80.5% do not support the suggestion that more ductile NbTi produces higher current density filaments. Mechanical properties appear to be too simple a parameter to predict superconducting performance of NbTi.