Preparation of nickel substrates for coated conductors

Polycrystalline Ni has been used as a substrate for high-current, coated YBa₂Cu₃O_x superconductors. For many conductors, Ni is rolled to large deformation and annealed to produce a cube texture. In this study, Ni was rolled to >95% reduction and annealed in 5% H₂/95% He at 300-1000 °C for various times. The resulting substrates were examined by scanning electron microscopy, X-ray and electron diffraction, and surface interferometry. Key determinations for the Ni were extent of in-plane and out-of-plane texture, surface smoothness, and grain size. The extent of texture was approximately independent of annealing temperature and increased slightly with annealing time. Annealing at temperatures >600 °C increased surface roughness, primarily due to grain-boundary grooving. Grain growth was fastest at 1000 °C and was proportional to time to the 0.1 power.