Effect of mechanical deformation on the mass density of Ag-clad (Bi,Pb)2Sr2Ca2Cu3O10 wire and tape

Abstract

The mass densities of Ag-clad (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10 wire and tape varies during the mechanical deformation process, which is one of the steps of the oxide-powder-in-tube technique used to fabricate the composite superconductor. Results show that the rolling has a more significant effect on densifying the tape core, whereas the drawing process can only densify the core to about 75% of the theoretical density. SEM observations of the rolled samples also reveal very dense morphology, consistent with the mass density calculations. SEM observation also shows that with increasing the deformation extent, the average grain size is reduced. It is proposed that although the rolling densifies the tape core significantly, it also destroys the crystallinity of the superconducting phases and results in the formation of an amorphous phase. Since the textured Bi-2223 phase forms by the epitaxial growth on the textured Bi-2212 seed crystals, the deformation induced texture is critical. Appropriate deformation extent is necessary, since too high an extent of deformation may change the well-aligned grains into amorphous phase. The formation of the amorphous phase is harmful to the texturing formation of the Bi-2223 phase, which finally leads to critical current degrading.