The bulk processing of 2223 BSCCO powders II. Tape rolling

Abstract

Abstract The anisotropic mechanical properties of densified BSCCO (Bi-Sr-Ca-Cu-O) powders are of paramount importance during thermo-mechanical processing of superconducting tapes and wires. Maximum current carrying capacity requires both high relative density and a high degree of alignment of the BSCCO single crystal's superconducting planes parallel to the plane of the tape. This is also a configuration that causes high stresses during compressive (ix. powder compaction) deformation processing. These high stresses can lead to cracking and thus degrade the conductive properties of the tape. In Part I of this work, we outlined some of the basic phenomenology of such powders under confined channel die compression. In this part we report results from a detailed finite element analysis of the tape rolling environment. We calculate both pressures and shear strains in the core of oxide powder-in-tube (OPIT) processed tapes. Rod-in-tube processing is investigated, as well as rolling with extra packing material. The calculated deformations were then applied as boundary conditions to the detailed micromechanical model developed in Part I. The goal here was to understand the deformation environment in the core of a rolled OPIT workpiece and how this environment affects the microstructural evolution of the BSCCO powder. Such microstructures, in turn, have significant effects on the macroscopic phenomenology of the core, and thus on the success of the processing. Our calculated results are used in order to help interpret a set of prototypical rolling experiments which have been designed specifically for the purpose of investigating core morphologies as a result of various rolling environments.