DEFORMATION STATE EFFECTS ON THE J(C) OF BSCCO TAPES

Developing long-length, high-J(c) superconducting tapes has been a maj or world-wide effort in recent years because of their potential applic ations in power-transmission lines, motors, and other devices. The sup erconducting tape is usually produced by co-deforming a ductile silver sheath containing a superconducting oxide. Since the conventional the rmomechanical process has failed to yield sufficient J(c) values for m ost liquid-nitrogen temperature applications, new approaches are neede d to improve the critical current density, J(c). This study investigat ed the feasibility of improving J(c) by increasing the shear and compr essive stresses in the silver-sheathed Bi2Sr2Ca2Cu3O10+x (BSCCO-2223) tapes during the rolling. To investigate the effects on the J(c) of th e stress state during rolling, specific stress states were imposed by rolling the BSCCO tapes embedded at different locations within thick s teel blocks. mire compression loading was achieved in the center plane of the blocks, while a combined compression-shear loading state was p roduced away from the center plane. Higher compressive hydrostatic str ess at the tape edge was obtained by confining the tape width. Tapes d eformed with a shear stress component exhibited higher J(c) values tha n tapes subjected to pure compression. In addition, the compressive hy drostatic stress reduced the porosity in the oxide near the tape edge and, as a consequence, increased the J(c) value.