THERMOMECHANICAL PROCESSING OF REACTIVELY SINTERED AG-CLAD (BI, PB)2SR2CA2CU3O(X) TAPES

Ag-clad tapes of Bi1.8Pb0.4Sr2Ca2Cu3Ox, annotated as 2223, were fabricated from polyphase powders which reactively sinter in situ to form 2223, and from completely reacted 2223. Annealing temperatures, as well as mechanical processing schemes involving intermittent cold uniaxial pressing, were investigated to arrive at a thermomechanical regimen that would promote increased critical current density (J(c)). Reactive sintering of polyphase tapes is very sensitive to annealing temperature and must be optimized to allow maximum transformation to, and prevent decomposition of, the 2223 phase. Continued intermittent pressing, after initial grain-growth annealing, is necessary to advance the reaction and allow consumption of alkaline earth cuprate second phases, as well as to promote grain texturing. The highest J(c) values (9000 A/cm2 at 77 K and 0 T field) were obtained in tapes containing a polyphase starting powder composed of nearly equal fractions of 2212 and 2201 annealed for 350 h at 845-degrees-C with three intermittent pressings. Similarly treated tapes containing completely reacted starting powders attained J(c) values of only 3000 A/cm2.