A Method for Measuring Interface Roughness from Cross-Sectional Micrographs

Uniform co-deformation of Nb, Ta, and their alloys in a Cu matrix is vital for performance yield for most internal-Sn Nb3Sn conductors, however, multiple factors can result in instabilities during extrusion and drawing. A better understanding of the variability can be attained by quantifying the interface roughness, however, there has been no consistent method developed to do this. Here we present a method to derive traditional stylus-based roughness measurements, including root-mean-square and average roughness values from micrographs of curved interfaces by image and signal processing analysis. Deformation creates interface roughness with different wavelengths. The longer wavelength or waviness and shorter wavelength or roughness are separated in this method. We apply the technique to 12 different commercial Nb filaments drawn in a Cu matrix. We find good correspondence between the roughness and initial Nb grain size of the rods. The procedure developed has been made available with the open-source code made available to the community. The procedure developed could be used to optimize the wire architecture for next-generation high-field magnets that use Nb alloys.

Automated summary

Uniform co-deformation of Nb, Ta, and their alloys in a Cu matrix is crucial for the performance yield of Nb3Sn conductors. However, there are instabilities during extrusion and drawing due to multiple factors. This study presents a method to quantify interface roughness, which can provide a better understanding of variability. The procedure developed can optimize the wire architecture for next-generation high-field magnets.