Fabrication and characterization of the joining of Bi-Pb-Sr-Ca-Cu-O superconductor tape

We evaluated the effects of the joining process on the electrical and mecha nical properties of Bi-2223 superconductor tape fabricated by the powder-in -tube technique. The joining of tapes was carried out by a lap-joint method . In the process, tapes were masked and etched to expose the superconductor cores in windows located near or at the end of the tape. The exposed cores of the two tapes were brought into contact, uniaxially pressed in the rang e 140-4000 MPa and sintered. The current carrying capacity of the jointed t ape was evaluated as a function of uniaxial pressure and the shape of windo ws. It was observed that the current carrying capacity was reduced in the t ransition region of the jointed tape because of the non-uniform microstruct ure during the pressing. In addition, the current carrying capacity was sig nificantly dependent on the uniaxial pressure. The highest current carrying capacity was obtained to be similar to 90% for the jointed tape to the tap e itself by optimizing the window shape and pressure. It is believed that t he highest value of current carrying capacity results from improvements in interface uniformity, core density, contacting area and grain alignment. Th e strain tolerance of the jointed tape was also evaluated, and the irrevers ible strain was measured to be 0.1%, which is lower than that of the unjoin ted tape. The decrease in the strain tolerance for jointed tape is believed to be due to the irregular interface and Ag intrusion in the transition re gion which acts as a stress concentration.