Effect of post-annealing at extensively varied temperature on phase formation and superconductive properties in Bi-2223/Ag tapes

摘要

The phase formation and superconductive properties of the high T_c superconductive Bi-2223/Ag tapes were studied by different post-annealing conditions. Monocore tapes were prepared for the thermo-mechanical process in air, in which a final heat treatment with isothermal post-annealing was performed. After an isotherm at 836 deg C for 48 h in this process, successive isotherms were applied at extensively varied temperatures in a range of 820400 deg C at a fixed time of 12 h. Two peaks were observed in the critical current density (J_c) as well as in the critical temperature (T_c) against this temperature. The phase formation behaviour and microstructure development were identified from XRD and SEM-EDS. The results could be correlated with each other, and a qualitative understanding was obtained with the aid of the reported equilibrium phase relationships. Furthermore, a stepwise post-annealing process was developed and applied to the same tapes. Post-annealing of two sequential isotherms was designed by adopting the two peak temperatures found above. The J_c was enhanced relative to that by normal post-annealing.