Atom probe to mography was used to cluu'acterize the A 15 phase in a bronze-route Nb3Sn supercond ucting wire wi th a bronze matrix compos itio n of Cu-8 nO. Ti (in a t.%). We observed dep le ti o n of ni obium and segregati on of Cu and Ti atoms at b3 'n grai n boundaries. Whil e the Nb dep letio n is abo ut 15% relative to the grain interior. the average ra ti o between u and Ti excess va lu es is 9 to 2. Segregation extend s to a distance d '" 9 ' A. from the point of

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Six practical composite wires of Nb3Sn (Furukawa Electric Co, Ltd) with different architectures (design and reinforcement) were compared from the normal state resistance R, critical temperatures Tconset, Tcoffset and ΔTc, upper critical field Bc2 (at 4.2 K) and critical current density Jc points of view. Wires were as follows: three of near-the-edge reinforcement design with Nb reinforcement of 0, 21, 50 vol% in the CuNb region, and two of central reinforcement design with Nb of 21 and 50 vol%. One wire with near the edge 50% vol Nb reinforcement had a different reinforcement/superconductor ratio. As-reacted wires show very different patterns of R, Tconset, Tcoffset, ΔTc, Bc2 and Jc. For the superconducting parameters this is probably due to different 3D thermal residual strains. Data suggest that the architecture of the as-reacted wire can control residual strain values and distribution. During multiple bending of the wires at room temperature (named pre-bending), introduction of the reinforcement improves relaxation of the 3D residual strain and especially of the lateral components. As a consequence, Bc2 and Jc versus pre-bending strain, εpb, are enhanced to values closer to those of the Nb3Sn in the stress-free state. Relative enhancement of these critical parameters for the reinforced wires is higher than for the reinforcement-free wire. Evolution during pre-bending and maximum attained absolute values of the superconducting parameters can be grouped roughly as a function of near-the-edge or central reinforcement design. Variation of the superconducting parameters suggests that the pre-bent state may depend on the as-reacted one (which is a function of wire architecture and processing history); when Jc was low as in the case of as-reacted wires with central reinforcement, during pre-bending, despite a relatively high Jc enhancement, this parameter attained lower absolute maximum values than for the other wires. Depending on the wire, when pre-bending strain εpb = 0.8–1%, the enhancement of non-Cu Jc at 4.2 K in the pre-bent wire is by up to 43.5% at 15 T compared to the as-reacted case. The maximum absolute value of Jc is obtained for the near-the-edge reinforcement pre-bent wires with 21 and 50% vol Nb. Bc2 of these wires was lower than for the other reinforced wires and higher than for the reinforcement-free wire. Pre-bent wires with near-the-edge reinforcement are identified as new and promising candidates for fabrication of react-and-wind coils with improved performance.

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