Improvement of the microstructure and critical current densities of Bi-2212 round wires with a precisely controlled heat treatment

Abstract

We succeeded in obtaining excellent Jc values of Bi2212 multifilamentary round wire with a precisely controlled heat treatment. The heat treatment, which consisted of melt solidification and a subsequent slow-cooling process, was applied to Bi-2212 superconductors. The Ic values of Bi-2212 wires heat treated with a maximum processing temperature Tmax below the optimum Tmax of Bi-2212 were zero, while high Ic values of 450 A, Jc = 280 kA cm−2 at 4.2 K and 10 T magnetic field, were obtained in a very narrow temperature range of the optimum Tmax. When the wires were heat treated with Tmax over the optimum Tmax, however, the Ic values were almost one-half of the highest Ic values. We found that the optimum Tmax window was very narrow for our multifilamentary wires. The well controlled heat treatment resulted in uniform filaments with few outgrowths from multifilaments and, hence, high Ic values for the wires.

The influence of the maximum heat treatment temperature on the performance of thin reinforced multifilament Bi-2212 wires for cables

“…This is extremely important for a reproducible, homogeneous production of wires in large lengths. A dramatically increased critical current (peak effect) within a few tenth of a degree at the beginning of melting the 2212 phase as was found by Matsumoto et al [3] is only weakly pronounced. Rikel et al [13] confirmed this behavior but, however, it is in contrast to earlier papers in which a pronounced peak effect was shown [2,3].…”

“…A dramatically increased critical current (peak effect) within a few tenth of a degree at the beginning of melting the 2212 phase as was found by Matsumoto et al [3] is only weakly pronounced. Rikel et al [13] confirmed this behavior but, however, it is in contrast to earlier papers in which a pronounced peak effect was shown [2,3]. For a better comparison with literature data and to see the influence of different wire diameters, the critical current density is shown via T max in figure 2.…”

“…Such degradation is caused by the reaction between the Mg and the filaments, which induces the contamination and/or the formation of impurity phases in the filaments. An additional reason for the J c reduction may be the reduced amount of intergrowths (figure 4) compared to [3,14]. …”

“…In the past, several groups investigated Bi-2212 mono and multifilament tapes and wires [1][2][3][4] but all of them used pure Ag sheath without mechanical reinforcement. For large magnets as for instance in fusion facilities we need a high current conductor with extraordinary mechanical strength.…”

Inert Gas Buffered Milling and Particle Size Separation of μm-Scale Superconducting Precursor Powders

“…The powder-in-tube (PIT) process is used to fabricate high-performance multi-filament superconducting wires of Nb 3 Sn [1], Bi-2212 [2], and MbB 2 [3,4]. While the specific powders, the synthesis routes, the sheath metal, and the PIT processing after powder filling are different in each case and indeed among the several practitioners of each superconductor, there is a common element that paces the ability to fabricate drawn multifilamentary composites of these materials.…”