Microstructure superconducting property relationships in a fermilab Nb-46.5w/o Ti filamentary superconducting composite

A transmission electron microscopy study has been performed on a production Fermilab Energy Saver composite from an intermediate stage in the manufacturing process. Studies of the dynamics of sub-band growth and α-Ti precipitation show that sub-band growth is quite rapid and occurs to a significant extent before α-Ti precipitation starts. Following analysis at intermediate size, the behavior of heat-treated samples was compared to that of samples drawn to final size without heat-treatment. Heat-treated samples were found to have smaller final sub-band diameters, in spite of the initial increase caused by heat-treatment and their critical current densities were also greater. The microstructural evidence points to the crucial role played by α-Ti precipitation in developing high Jcvalues in this Nb46.5w/oTi alloy.