Microstructural study of bronze-processed commercial multifilamentary superconducting Nb3Sn wires

The thickness, morphology, grain size and grain morphology of A-15 diffusion layers in bronze-processed commercial multifilamentary superconducting Nb3Sn wire have been investigated using optical microscopy and transmission electron microscopy. The layer growth appears to be controlled by the availability of tin in the matrix, and the remanent tin concentration in the matrix depends on the reaction temperature. While there is some elongation of grains in the inner parts of the annular layers grown at lower temperatures, at high temperatures all the grains are equiaxed.