Electropolishing of Ni–5at.%W substrates for YBCO coated conductors

The application of NiW substrates for YBCO coated conductor is hindered due to their roughness of surfaces. It was demonstrated that the smooth NiW substrate surfaces can be obtained through electropolishing in a sulfuric acid electrolyte. In this paper, the parameters in the electropolishing process, such as electrolyte temperature, current density and time, are optimized so as to attain the best surface brightness measured by an atomic force microscopy. The e1ectropolishing mechanism was discussed on the film generated during the electropolishing process. The results suggest that the electropolishing behavior of NiW alloy is under mass-transfer control and H2WO4 is the governing factor for the film formation mechanism during anodic dissolution.

► Electropolishing was used to obtain smooth surfaces on Ni5W substrates for the preparation of YBCO coated conductors without obvious change of the textures of these Ni5 W substrates.
► Combining the phenomena observed during experiments and electropolishing theories, the electropolishing mechanism in this system has been studied, which is different with that on Ni metals due to the additional tungsten.
► In our theory, H2WO4, functioning as the viscous film, plays more important role during the electropolishing than NiO in the selective dissolution.