Development of a niobium-tin multifilamentary wire with artificial tantalum inclusions

A multifilament Nb/sub 3/Sn conductor containing Nb/Ta composite filaments was manufactured using bronze route processing. The Ta inclusions deformed uniformly during the fabrication process with little ductility problems. Ta to Ta spacings of less than 60 nm were obtained at final wire sizes. Samples were reacted using various heat treatment conditions and compared to a multifilament Nb(Ti)/sub 3/Sn conductor processed from a Nb 1.5 Ti alloy. The Ta inclusions reduce the grain growth of the A15 phase during the final reaction heat treatment and were responsible for a 15-20% increase in J/sub c/ (9 T, 4.2 K) as compared to the Nb(Ti)/sub 3/Sn wire. In addition, Ta dissolved in the A15 phase resulted in an enhanced upper critical field. Improvement of the filament uniformity through the use of fine-grained sheets was confirmed by magnetization and image analysis.>