INFLUENCE OF SPREAD ROLLING ON PROPERTIES OF BISMUTH-BASED OXIDE SUPERCONDUCTING TAPES SHEATHED IN SILVER

Spread rolling methods are applied to a fabrication process of silver- sheathed superconductor (Bi, Pb)2Sr2Ca2Cu3Ox tapes. Two spread rolling methods are adopted. One method is the satellite-mill rolling which h as been developed by the authors. The method is applied to the forming process of tapes. And the other method is a cross rolling, in which t he tapes are rolled in the transverse directions. The cross rolling is applied as an intermediate rolling during the final sintering process , that is, the thin tape is pre-sintered, rolled and re-sintered. The deformation characteristics of tapes, the microstructure and the textu re of the oxides are investigated. And the critical current densities J(C) are measured at 77 K, 0 T. In order to make clear the effect of t he spread rollings, these results are compared with those by the conve ntional longitudinal rolling method. Main results are as follows. (1) The high lateral spread rolling is realized by the satellite-mill roll ing. In the tapes produced by the satellite-mill rolling, however, the silver sheath/oxide core interface is slightly inhomogeneous, and cri tical current density is little lower. (2) The critical current densit ies of the tapes deformed by the intermediate cross rolling is several times higher than those by the conventional rolling. (3) The sintered oxide grains are elongated in the direction of intermediate rolling. The texture is the c axis//N.D. fiber texture, and the c axes are disp ersed in the direction of the intermediate rolling.