THE BULK PROCESSING OF 2223-BSCCO POWDERS .1. DENSIFICATION AND MECHANICAL RESPONSE

The anisotropic mechanical properties of densified BSCCO (Bi-Sr-Ca-Cu- O) powders are of paramount importance during thermo-mechanical proces sing of superconducting tapes and wires. Maximum current transport req uires both high relative density and a high degree of alignment of the single crystal superconducting planes parallel to the plane of the ta pe. This is also a configuration that causes high stresses during comp ressive (i.e. densifying) processing modes. These high stresses can le ad to cracking, and thus degrade the density, and eventually the condu ctive properties of the tape. The current work develops a micromechani cally based material model for such densified powders. The deformation mechanisms of interest are crystallographic glide and porosity evolut ion; thus the model takes the form of a porous, elastic-viscoplastic p olycrystal material theory. This has been achieved by coupling the mod ified Taylor type polycrystal model of Schoenfeld, Ahzi and Asaro in a generic way to yield surface type flow theories. The porosity model o f Fleck, Kuhn and McMeeing is used to describe the evolution of porosi ty with deformation. Compaction experiments on 2223 BSCCO (Bi2Cr2Ca2Cu 3Ox) powder is done in a confined channel die environment so as to sim ulate the plane strain tape rolling environment. The model is calibrat ed and compared to these experimental results, and then employed to re solve the effects of initial texture and confinement pressure on the d ensification and ultimate formability of the powder. In Part II of thi s work, the current model will be applied in order to resolve states o f stress and textural alignment in the BSCCO conductor during tape rol ling, and hence improve the current state of the art in tape manufactu ring.