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 mechanical 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 range 140-4000 MPa and sintered. The current carrying capacity of the jointed tape was evaluated as a function of uniaxial pressure and the shape of windows. It was observed that the current carrying capacity was reduced in the transition region of the jointed tape because of the non-uniform microstructure during the pressing. In addition, the current carrying capacity was significantly dependent on the uniaxial pressure. The highest current carrying capacity was obtained to be approximately 90% for the jointed tape to the tape itself by optimizing the window shape and pressure. It is believed that the highest value of current carrying capacity results from improvements in interface uniformity, core density, contacting area and grain alignment. The strain tolerance of the jointed tape was also evaluated, and the irreversible strain was measured to be 0.1%, which is lower than that of the unjointed 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 region which acts as a stress concentration.