Phase formation and microstructure development in silver-clad Bi-2223 multifilament composite conductors

Abstract

Phase evolution and microstructure development in silver-clad Bi-2223 composite conductors have been investigated as a function of filament count (mono, 19, 85 and 361), precursor powder type (metallic powder or oxide powder), oxygen partial pressure (<10-3 to 0.13 atm), temperature (790-855 °C) and time (0-6000 min). Favourable conditions for rapid Bi-2223 phase formation and stability were achieved with an oxygen partial pressure around 0.08 atm, regardless of precursor type or filament count. In general, the rate of the Bi-2223 formation reaction increased and the width of the temperature window for rapid kinetics became broader as the filament count increased. The most rapid kinetics and the broadest heat treatment window were observed for the 361-filament metallic powder composite. These trends in Bi-2223 formation rate and stability are believed to be associated with the increased proximity of powder to silver as the filament count increases and the filament transverse dimensions become smaller. For each conductor type (in terms of precursor form and filament type) there was an optimum processing temperature in ca 0.08 atm O2 that produced a well-developed Bi-2223 grain colony microstructure with the least amount of second-phase. This optimum temperature was near the peak of the reaction rate versus temperature profile.

Microstructure and J/sub c/ improvements in overpressure processed Ag-sheathed Bi-2223 tapes

“…For the 1 atm GT samples, decreases with increasing pO , with the highest for 0.075 atm. This is consistent with reported results that the optimum pO for 2223 formation is around 0.075 atm [7], [8]. Fig.…”

Heating rate effect on the evolution of texture in (Bi,Pb)2Sr2Ca2Cu3O10Ag-sheathed tapes

“…Our experiments were performed for a fixed sintering temperature of 830 • C, a standard value for tapes processed in low oxygen partial pressure [33,34]. The effect is however likely to be temperature dependent.…”

Effect of various mechanical deformation techniques on pinning force densities in Ag/Bi-2223 tapes

“…Ag/Bi-2223 multi-filamentary tapes with the nominal stoichiometry of Bi1.83Pbo,34SrI.91 Caz.03Cu3.0S0y were fabricated by the powder-in-tube method, involving two last sintering processes with an intermediate deformation [4,8,11]. For comparison of experimental results, all samples used here were cut from the same green tape with an identical length before two last sintering processes.…”

“…SR processing also shows its advantages on Birr. 4.4 J e depending on relative core density Figure 4 shows self-field J e dependence on relative core density of tapes fabricated by SR, P and NR, respectively. The relationship between J e and core density for each defonnation technique is approximately linear and the slope of the linearity varies with defonnation techniques.…”

“…Techniques of normal rolling (NR), pressing (P) and sandwich rolling (SR) were used ill; this experiment as intermediate deformations. NR was a traditional processing of the intermediate deformation [1][2][3][4][5]. P often used in laboratories was the second method to improve the tape properties, especially to increase the core density of tapes [6,7].…”