Effects of hot rolling on powder-in-tube BSCCO tapes

High critical currents have been obtained in Bi-Sr-Ca-Cu-O (BSCCO) by the powder-in-tube approach. Because of the inherent structural anisotropy of the Bi-based high-Tc superconducting materials, high-(Jc) is obtained only when the wires are subsequently rolled into rectangularly cross-sectioned tapes. Previously, intermediate annealing was employed to maintain ductility in the silver, with a high-temperature sintering just before the final rolling in order to form the high-Tc superconducting phase. Here, the authors report on the effects of hot rolling at various temperatures for the final rolling of powder-in-tube BSCCO-2212 tapes. Hot rolling was accomplished by preheating the rolls with infrared heaters and rolling the tapes directly from the furnace. The highest current densities were obtained by a final hot rolling of the 2212 tapes at 420 degrees C, with the furnace temperature at 750 degrees C (the highest temperature studied). Results showed that the enhancement of (Jc) was due to the improvement of grain alignment, as well as to the reduction of the size and fraction of Bi-free phases during the final heat treatment. Furthermore, an analytical model of the hot-rolling process that has been developed illustrates the importance of preheating the tapes and heating the rolls