Severe plastic deformation of bulk Nb for Nb3Sn superconductors

Cast pure Nb with very large grains was processed by multipass equal channel angular extrusion (ECAE) to refine the microstructure. Extrusions were performed on 25 and 50 mm square cross section bars in a right angle die at room temperature following different extrusion routes to strains above nine. The hardness of Nb reaches a saturation level after eight extrusion passes where it is ∼20% above that of fully worked Cu. Recrystallization bands appear to be absent in material processed by a new multipass route (E) which imparts shear on three intersecting planes and gives high processing yields. Hardness and optical microscopy measurements on recrystallized specimens are similar for 25 and 50 mm square bars which indicates a favorable scale-up response. Comparisons to commercially processed Nb and a cost estimate indicate that ECAE may be a viable method for manufacturing fine-grained, homogenous Nb for Nb₃Sn multifilamentary superconductor applications.