Transverse compressive stress effect in Y-Ba-Cu-O coatings on biaxially textured Ni and Ni-W substrates

Electromechanical properties of yttrium-barium-copper-oxide (YBCO) coatings on both pure Ni and Ni-5at.%W alloy rolling-assisted, biaxially-textured substrates (RABiTS) were investigated. The effect of transverse compressive stress on transport critical-current densities (J(c)) was measured on samples at 76 K and self magnetic field. Transverse compressive stress can significantly degrade J(c) in YBCO deposited on pure Ni RABiTS unless sufficient frictional support is provided to the sample or the substrate is given a work-hardening treatment. On the other hand, results obtained for YBCO on Ni-5at.%W alloy RABiTS show that the tolerance to transverse stress of these conductors is significantly improved. These electromechanical properties are interpreted with scanning-electron micrographs of the microstructure of the samples after electromechanical testing, as well as stress-strain characteristics measured on RABiTS substrates at 76 K. The tensile yield strength, Young's modulus, and proportional limit of elasticity of candidate RABiTS substrate materials are tabulated and compared.