In the present work multifilamentary Tube type and distributed barrier Rod-in-Tube (RIT) type Nb3Sn composites were studied in detail. Tube type composites consisting of subelements of Nb-7.5 wt% Ta alloys with simple Cu/Sn binary metal inserts were studied in an attempt to enhance the performance boundaries of these conductors. We focused on correlating the composition and morphology of the intermetallic A15 to the transport and magnetic properties for varying heat treatments. In particular, lower temperature HTs were studied, specifically 625°C and 635°C as a function of time. The extent of A15 formation, the ratio of the coarse/fine grain areas, and the amount of untransformed 6:5 phase were then observed as a function of time –temperature.
A15 stoichiometry was investigated and compared for two different Nb3Sn strand designs, specifically Tube type and high performance RIT type strands. Transport measurements were performed on both categories of conductors for various conditions. The objective of the study was to investigate the limits of tube type conductor performance and to compare this to that of RIT conductors. Specifically, the Sn stoichiometry and A15 grain size for RIT and Tube type conductors were compared and to correlated with the transport properties of the two strand types. Tube type conductors were compared to RIT conductors, each after the application of single step and two-step HTs with plateaus ranging from 615°C to 675°C for various times. The influence of strand geometry and reaction route was related to the resulting A15 stoichiometries. Fractography was performed to investigate the effect of a two-step reaction on the morphology, the ratio of coarse/fine grain area and grain size of fine grain A15. The effect of Ti doping on superconducting properties of RIT type Nb3Sn strands was also studied.