Influences of Different ECAE Routes on Filament Deformation in Cu Clad Nb Composite Wires

Abstract

A strategy to obtain higher critical current density (Jc) in Nb3Sn conductors is to increase the Nb fraction. This can be achieved by improving the deformation behavior of the Nb filaments so less Cu is needed between filaments enabling smaller diameter filaments and more filaments in the subelement region. The objective of this project is to better understand the influence of different pre-processing strain path (texture) on the deformation of a Nb filament in a Cu-matrix. Initial severe plastic deformation by equal channel angular extrusion (ECAE) was used to obtain a uniform fine grain size with slightly different textures in starting Nb rods. Cu-Nb composite bars were warm extruded and wire drawn to evaluate the performance of different starting Nb fine grained microstructures on Nb filament deformation behavior. The initial textures in the various Nb samples were different but quite weak; little difference is seen in the final Nb filament circularities. However, this study indicates the Cu-Nb interface roughness is influenced somewhat by non-uniformity in the Nb microstructure. The evidence suggests that to obtain better deformation characteristics in Nb filaments, one should start with fine-grain weak or untextured Nb with a globally uniform microstructure. This should enable finer as-drawn Nb filaments with better concentricity, composite wires with a higher Nb loading fraction, and conductors with higher Jc.