Lectures on Superconductivity: Materials I

Nb₃Sn is often used in superconducting magnets operating at above 10 T, for which NbTi is unsuitable. Nb₃Sn is very brittle, so wires are made from niobium and tin-containing components, and Nb₃Sn itself is formed by heat treatment only after all the deformation processing is complete. Heat treatments have to be chosen carefully to maximise the proportion of Nb₃Sn whilst keeping grain sizes small enough for strong flux pinning.

Wires can be produced by the bronze, internal tin or power-in-tube routes. In the bronze process, tin is carried in Cu-Sn (tin bronze): this work hardens severely, so several stages of annealing are necessary during wire drawing. The internal tin process avoids this, and allows a larger proportion of tin, at the expense of longer heat treatment durations and greater complexity.