The influence of processing parameters and tensile stresses on the properties of Bi-2223 tapes with Ag and AgMn sheaths

In order to investigate the degradation of critical current (I c ) in the Ag alloy sheathed Bi-2223 tapes due to a transverse compressive stress introduced during manufacturing and operation of the HTS systems, a sample holder consisting of the upper block made of Ti alloy and the lower support plate made of glass fibre reinforced plastic was prepared. A shorter spacing of voltage taps caused large degradation of critical current with respect to compressive stress. It was found that the extent of the I c degradation is proportional to the initial critical current density of the tapes. Through the experiment optimizing the shape of voltage terminals and the pressing load for the continuous contact type 4-probe I c measurement system, it was found that the conical shape tip with large curvature radius was effective in suppressing the I c degradation in Bi-2223 tapes during the I c measurement. A hard alloy sheath of Ag-0.6wt%Mn was found to be quite tolerant to the I c degradation against the pressing load of voltage terminals.

Section: Resultssupporting

confidence: 92%

Influence of transverse compressive stress onI_cdegradation of Ag alloy sheathed Bi-2223 tapes

et al. 2003

“…The microhardness of the specimen increases uniformly with increasing deformation up to 80%. Fischer et al [4,5] reported an increase of microhardness of AgMn x (x = 0.06-0.4) when heat treated at 817-820 • C in an oxidized atmosphere. An H V = 115-150 increase was attributed to the formation of submicron Mn oxide or Mn-O clusters with a stable size and structure as a result of lengthy annealing times.…”

Section: Resultsmentioning

confidence: 99%

Electromechanical properties of Ag/Bi2223 flat wire in a short thermocycle

Adam¹,

Osamura²

2006

An independently oxidized AgMn alloy is used to gauge the overall tensile strength of technical Ag/Bi2223 composite flat wire through the contributions of individual constituent strengthenings. Theoretical analysis based on the rule of mixtures shows similarity between measured and calculated curves of the composite at room temperature (RT) and 77 K. The elastic modulus of the composite wire, deduced from initial and loading/unloading curves, is found to be around 95-98 GPa, while for Bi2223 filaments, the modulus of elasticity was estimated to be 129 GPa. The effect of thermal cycling between RT and 77 K on the electromechanical properties of the wire is also examined. The critical current is significantly reduced by tensile strain above 0.4% but not affected by the short thermocycle when measured across different specimens. Finally, the relation between the fracture strain and the strain span of the Bi2223 filaments is found to accommodate an intrinsic filament fracture strain of about 0.04-0.11% in the wire.

“…Until now, developments in this direction have been restricted to the use of hardened Ag alloys [10]. Although resulting in interesting improvements [11][12][13][14][15][16], this solution is not satisfactory if the tapes are used for applications resulting in significant mechanical stresses. Therefore, corrosion resistant metals should be considered as possible alternatives to Ag alloys.…”

Section: Introductionmentioning

confidence: 99%

Composite metallic sheathes: the key to low-cost, high strength (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀-based tapes?

Grivel¹

2007

(Bi,Pb)2Sr2Ca2Cu3O10-based superconducting tapes were prepared by the powder-in-tube process, using a bimetallic sheath consisting of Ag and Ni. Ag was in contact with the superconducting ceramic core and acted as a protective layer against reaction between the external Ni sheath and the core. (Bi,Pb)2Sr2Ca2Cu3O10 phase formation was possible if a path for oxygen diffusion was opened in the Ni sheath. This was achieved by removing Ni on one edge of the tape edges by polishing. Transport critical current densities as high as 35 000 A cm−2 (77 K, self-field), corresponding to a je of about 11 000 A cm−2, were achieved in a single heat-treatment. The efficient protection offered by the Ag layer against Ni diffusion into the ceramic core suggests that Ag layers as thin as 5 µm may be applied, thus reducing the production costs. The superior stiffness of Ni provides a stronger sheath, greatly improving the mechanical stability of the composite, and may be responsible for the high ceramic densities and critical current densities obtained without intermediate densification.