EFFECTS OF INITIAL Sn∕Cu RATIO AND HEAT TREATMENT ON THE MICROSTRUCTURE AND MICROCHEMISTRY OF Cu-Nb-Sn-Ta TUBE TYPE COMPOSITES (original) (raw)

Multifilamentary tube-type composites consisting of subelements of Nb-7.5wt%Ta tubes with a simple Cu/Sn binary metal insert were studied in an attempt to improve the performance limits of these conductors. Transport J c values for these multifilamentary strands were found to be in excess of 2200A/mm 2 at 12 T, 4.2 K. In order to further improve these values we performed a study of the reaction systematics, focusing initially on correlating the composition of the A15, the coarse/fine grain ratio, and the transport properties to the original Sn/Cu ratio and heat treatment temperature with the aid of an analytical model. Samples were heat treated at five different temperatures between 650°C-800°C for 250 hours. The extent of A15 growth, the coarse/fine grain area ratios, and the levels of residual phases were then observed as a function of temperature. In addition the temperature variation of the grain size, B c2 , and microchemistry across the A15 were determined.