The electromechanical properties of (0.3 υm thick) yttrium-barium-copper-oxide (YBCO) coatings on buffered pure-nickel rolling-assisted-biaxially-textured substrates (RABiTS) were measured at 76 K and self magnetic field. YBCO coatings on buffered substrates both 50 υm 125 υm thick were tested. Significant degradation of transport critical-current density (Jc) can occur from transverse compressive stress unless the inplane yielding of the substrate is prevented by providing friction support to the sample or by using substrate materials of high yield-strength. Scanning electron microscopy was used to investigate the microstructure of the samples after electromechanical testing. Isolated defective regions were found with a mixed pattern of cracks, both longitudinal and transverse to the direction of electrical-current flow. the more the degradation of (Jc) from electromechanical testing, the greater the density of the observed cracked regions. Also, it was found that the use of magnetic substrates in the fabrication of the YBCO coated-conductor tapes produces a significant reduction in (Jc) when the tapes are arranged in a stack of two or more layers. This effect is reversible upon unstacking the tapes.
Citation: Advances in Cryogenic Engineering
Pub Type: Journals
critical current density, fatigue, high Tc superconductors, transverse compressive stress, YBaCuI, yield strength