Phase and volume changes during reaction heat treatment of Nb3Sn wires
Résumé
Nb3Sn magnet coils are wound of multifilament wires that contain the ductile precursors Nb and Sn. During the subsequent Nb3Sn formation heat treatment, the volume of the pre-cursor wire changes. We compare the diameter changes of different Nb3Sn wire types (Internal Tin, Restacked Rod Process, Powder in Tube) with the phase transformations and associated void volume evolution, all measured in situ during the reaction heat treatment. Wire diameter changes were measured by dilatometry, and phase changes were monitored by differential scanning calometry and by high energy synchrotron X-ray diffraction. Unlike the Nb3Sn wire length changes, the wire diameter evolution is characteristic for each Nb3Sn wire type, and the wire diameter changes are closely related to the void space evolution monitored by high energy synchrotron micro-tomography.