EFFECT OF MECHANICAL DEFORMATION ON THE MASS DENSITY OF AG-CLAD (BI,PB)(2)SR2CA2CU3O10 WIRE AND TAPE

The mass densities of Ag-clad (Bi,Pb)(2)Sr2Ca2Cu3O10 wire and tape var ies during the mechanical deformation process, which is one of the ste ps of the oxide-powder-in-tube technique used to fabricate the composi te superconductor. Results show that the rolling has a more significan t effect on densifying the tape core, whereas the drawing process can only densify the core to about 75% of the theoretical density. SEM obs ervations of the rolled samples also reveal very dense morphology, con sistent with the mass density calculations. SEM observation also shows that with increasing the deformation extent, the average grain size i s reduced. It is proposed that although the rolling densifies the tape core significantly, it also destroys the crystallinity of the superco nducting phases and results in the formation of an amorphous phase. Si nce the textured Bi-2223 phase forms by the epitaxial growth on the te xtured Bi-2212 seed crystals, the deformation induced texture is criti cal. Appropriate deformation extent is necessary, since too high an ex tent of deformation may change the well-aligned grains into amorphous phase. The formation of the amorphous phase is harmful to the texturin g formation of the Bi-2223 phase, which finally leads to critical curr ent degrading.