Electromechanical properties and microstructural evolution of REBCO coated conductor tapes under fatigue loading

Various types of fatigue loading conditions, including exposure to periodic electromagnetic forces and repeated thermal cycles, are unavoidable in applications utilizing Rare-Earth-Barium-Copper-Oxide (REBCO) coated conductor (CC) tapes. Fatigue loadings might irreversibly degrade the superconducting properties of REBCO CC tapes and significantly influence the long-term reliability of superconducting magnets winded by the REBCO CC tapes, warranting extensive analysis. However, most studies in literature use quasi-static tensile tests to evaluate the electromechanical characteristics of REBCO CC tapes. Detailed analysis of the electromechanical behavior and microstructural evolution of REBCO CC tapes subjected to fatigue loadings are scarce and the relationship between the microstructural changes and macro-multi-field responses for REBCO CC tapes subjected to fatigue loading conditions remain unclear. Elucidating the microstructural changes and macro-behavior of REBCO CC tapes subjected to fatigue loadings is critical to assess the reliability of superconducting magnets. In this study, the electromechanical fatigue properties of EuBCO CC tapes manufactured by Shanghai Superconductor Technology Co., Ltd. were investigated under different values of maximum stress (σ_max), number of fatigue cycles (N) and stress ratio (R). The effects of σ_max and R on the superconducting properties for EuBCO CC tapes were compared. At the microscopic level, scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to observe microcracks formations and analyze the local plastic strain and the misorientation angles in the superconducting film during fatigue loading. Based on experimental results, the deterioration in the superconducting properties of EuBCO CC tapes on fatigue loading was ascribed to the increased misorientation angles and the local plastic strain, which led to the destruction of the original texture of the superconducting layer in the system. The findings of this study are expected to assist manufacturers in improving the electromechanical properties of commercial REBCO tape, facilitating their application in advanced technologies.