Phase Transformations during the Reaction Heat Treatment

The evolution of Nb containing phases during the diffusion heat treatment of three different high critical current Nb$_{3}$Sn strand types is compared, based on synchrotron X-ray diffraction results that have been obtained at the ID15 beam line of the European Synchrotron Radiation Facility (ESRF). In all strands studied, Nb$_{3}$Sn formation is preceded by the formation of a Cu-Nb-Sn ternary phase, NbSn2 and Nb6Sn5. As compared to the PIT and Tube Type strand, the amount of these phases formed in the RRP strand is relatively small. In the RRP strand subelements with a fine filament structure Nb$_{3}$Sn grows more quickly, thereby preventing to a large extent the formation of the other higher tin phases.