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The dilute Cu-Nb-Sn alloys containing small amounts of Nb and Sn less than 1 at % exhibited superconductivity after quenching from the liquid state and ageing. The best superconducting properties (\(T_{{\text{c}}_2 } \) andJc=130 A cm−2) in a Cu-0.30 at % Nb 0.15 at % Sn alloy were obtained when the sample was aged at 550° C for 384 h. This sample exhibited a structure of fine Nb3Sn precipitates of 200 to 500A diameter distributed homogeneously in the Cu matrix, and therefore it was concluded that superconductivity in these alloys resulted from the proximity effect of Nb3Sn particles. In spite of the similar structure obtained by ageing at 800° C, the Cu-Nb-Sn alloys showed inferior superconducting properties compared to the Cu-0.4 at % Nb alloy and this would be explained qualitatively by the difference in the mean free path in the two alloys.

Microstructures in a commercial Nb-Ti alloy heat-treated or repeatedly aged and cold worked have been investigated by transmission electron microscopy. In the aged samples after solution treatment,ω-phase forms at ageing temperatures below 673 K andα-phase precipitates at 773 K. Cold work after solution treatment or heavy cold work without prior solution treatment results in accelerated precipitation ofω-phase on ageing at 623 K and ofα-phase on ageing at 773 K, while it givesα-precipitation instead ofω on ageing at 673 K. Repeated ageing and cold work make the microstructures very fine. The refinement is due to formation of dislocation cell structures and subgrains and precipitation ofω- andα-phases.