Transverse compressive stress, fatigue, and magnetic substrate effects on the critical current density of Y-Ba-Cu-O coated RABiTS tapes

Abstract

The electrochemical properties of (0.3 μm 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 μm and 125 μm thick were tested. Significant degradation of transport critical-current density (Jc) can occur from transverse compressive stress unless the in-plane yielding of the substrate is prevented by providing frictional 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.