Electromechanical properties of superconducting MgB₂ wire

The current-carrying capability of superconducting wires is degraded by stress. Therefore electromechanical properties are one of the key feedback parameters needed for progress in conductor applications. In this work, uniaxial tensile stresses and bending stresses were applied to Fe /MgB₂ wires at room temperature, followed by measurement of critical current using a transport method at 4.2 K. Basic mechanical properties were calculated from the measured stress-strain characteristics. The irreversible tensile strain at which the critical current density of MgB₂ wire starts to degrade was found to be 0.5%. In addition, the degradation of I_c with decreasing bending diameters was found to be very rapid for wires that were deformed after the heat treatment that forms the MgB₂ compound, while not much degradation of I_c was found for wires that were bent before being annealed. SEM observations confirmed that cracks could be healed by post-annealing.