The influence of Ti doping methods on the high field performance of (Nb, Ta, Ti)3Sn multifilamentary wires using Osprey bronze

We have analyzed the influence of the two different Ti doping methods on the superconducting properties of bronze processed (Nb,Ta,Ti)3Sn multifilamentary wires with identical configuration, consisting of a Nb7.5wt.%Ta alloy processed to 14641 filaments of 4.5 micrometer size embedded in an Osprey bronze and externally stabilized by Cu. The first doping method introduces NbTi rods into NbTa filaments in a Cu15.4Sn Osprey bronze and has been applied to two wires containing 1 and 2 wt.%Ti in the filaments, respectively. The second method uses a Ti added Cu15.5Sn0.25Ti Osprey bronze, while the filaments of two thereby fabricated wires contain 0 and 0.5wt.%Ti, respectively. A reference wire containing no Ti addition was also prepared. All five wires were manufactured by three hot extrusion steps, cold drawing and several intermediate anneals. Wire samples with round cross section have been prepared and reacted between 600 and 730°C. The residual Sn content in the bronze after reaction and the residual niobium ratio of the filaments were determined by means of EDX and SEM analysis, respectively. The grain size of the A15 layer has been compared by FE-SEM and the local composition profile has been observed by systematic quantitative EDX measurements made on a TEM. Non-Cu Jc values up to 300 Amm-2 and n values up to 50 at 17 T and 4.2 K reveal clearly the Ti added bronze as more performing.