Characterization of Ti and Ta Influence on Grain Shape and Size, as well as Transport Properties of Conductors Fabricated by the Internal‐Sn Process

Several different Nb3Sn strand types have been investigated with a focus on relating their microstructure and superconducting properties. Two types of strand were studied: (1) a standard internal‐Sn‐type rod‐in‐tube (RIT) conductor and (2) a so‐called “tube‐type” conductor comparable in structure to the above except that the annulus of Cu‐clad Nb rods was replaced by a Cu‐lined Nb tube. One member of each type was doped with Ti, initially present either in the filamentary array or in the Sn core. After full reaction, the Nb3Sn filaments and their grain structure were observed using high resolution scanning electron microscopy (SEM), and their grain sizes characterized. Subsequently, Energy Dispersive Spectroscopy (EDS) was used to obtain the composition of the filaments. Superconducting properties, with a focus on Jc, were measured and correlated to these factors. The effect of Ta and Ti on the composition distribution and grain morphology, and the relationship between the local composition and morphology...