The dependence of Jc on bending strain in round multifilament Bi2Sr2CaC2Ox wires sheathed in Ag and Ag alloys

High strength dispersion strengthened (DS) Ag/Al alloys with various Al content are studied as candidates for sheathing Bi 2 Sr 2 CaCu 2 O 8+x (Bi2212) wire. The Ag/Al alloys are fabricated by powder metallurgy and internally oxidized in pure oxygen. The time and temperature of the internal oxidation heat treatment is varied to maximize the strength after undergoing the Bi2212 partial melt process (PMP). Vickers micro-hardness number (HVN), room temperature tensile behavior, optical and scanning electron microscopy, ion channeling contrast imaging using a focused ion beam and electrical resistivity measurements are used to characterize the alloys. An Ag/0.2wt%Mg (Ag/Mg) alloy is used for comparison. Results show that internal oxidation at 650-700 • C for 4 h produces the highest HVN for the DS Ag/Al alloy; when oxidized at 675 • C for 4 h the HVN, yield strength and tensile strength of the DS Ag/Al are 50% higher than the corresponding values of Ag/Mg. Microstructural observations show that Al 2 O 3 precipitates play the main role in strengthening the DS Ag/Al alloy. The alloy retains its fine grain structure and strength after PMP heat treatment.

Section: Introductionmentioning

confidence: 99%

High strength oxide dispersion strengthened silver aluminum alloys optimized for Bi₂Sr₂CaCu₂O_8+xround wire

Kajbafvala¹,

Nachtrab²,

Kumar³

et al. 2013

“…Even though the Ag/0.20 wt%Mg alloy shows relatively good strength after PMP in oxygen, the Mg reactivity limits its use to the outer sheath where it is separated from direct contact with Bi2212 filaments by the pure Ag. To enhance the mechanical properties of Bi2212, stronger sheath materials are required [13][14][15][16][17][18][19].…”

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confidence: 99%

“…There have been attempts to enhance the electromechanical properties of Bi2212 wires and tapes through alternative sheath materials [16][17][18][19][20][21][22][23]. Wesche et al [19] studied the axial and bending strain effects in Ag and AgNiMg/ Bi2212 wires.…”

mentioning

confidence: 99%

“…The reduction of J c due to axial strains was found to be irreversible, though the yield strength (YS) of AgNiMg/Bi2212 wire was much larger than that of Ag sheathed wires. Motowidlo et al fabricated Bi2212 RW with less porosity and more uniform filaments using various dispersion-strengthened (DS) Ag alloy sheaths, including Ag/Al and Ag/Zr [16][17][18]. Guo et al investigated the effects of sheath composition and rolling conditions on the microstructural development and superconducting properties of Bi2212 powder-in-tube tapes [20].…”

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confidence: 99%

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Bi₂Sr₂CaCu₂O_{8 + x}round wires with Ag/Al oxide dispersion strengthened sheaths: microstructure–properties relationships, enhanced mechanical behavior and reduced Cu depletion

Kajbafvala¹,

Nachtrab²,

Wong³

et al. 2014

Ag/Al alloys with various Al content (0.50 wt%, 0.75 wt%, 1.00 wt%, and 1.25 wt%) are made by powder metallurgy and used as the outer sheath material for Bi 2 Sr 2 CaCu 2 O 8 + x (Bi2212)/Ag/ AgAl multifilamentary round wires (RW). Bi2212/Ag/AgAl RW microstructural, mechanical and electrical properties are studied in various conditions, including as-drawn, after internal oxidation, and after partial melt processing (PMP). The results are compared with the behavior of a Bi2212/Ag/Ag0.20Mg wire of the same geometry. The grains in as-drawn Ag/Al alloys are found to be ∼25% smaller than those in the corresponding Ag/0.20 wt%Mg, but after PMP, the Ag/Al and Ag/0.20 wt%Mg grain sizes are comparable. Tensile tests show that Bi2212/Ag/AgAl green wires have yield strength (YS) of ∼115 MPa, nearly 65% higher than that of Bi2212/Ag/ Ag0.20Mg. After PMP, the Bi2212/Ag/AgAl YS is about 35% greater than that of Bi2212/Ag/ Ag0.20Mg. Furthermore, Bi2212/Ag/AgAl wires exhibit higher ultimate tensile strength and modulus and twice the elongation-to-failure. Atomic resolution high-angle annular dark-field scanning transmission electron microscopy, high resolution transmission electron microscopy and energy dispersive spectroscopy demonstrate the formation of nanosize MgO and Al 2 O 3 precipitates via internal oxidation. Large spherical MgO precipitates are observed on the Ag grain boundaries of Ag/0.20 wt%Mg alloy, whereas the Al 2 O 3 precipitates are distributed homogenously in the dispersion-strengthened (DS) Ag/Al alloy. Furthermore, it is found that less Cu diffused from the Bi2212 filaments in the Bi2212/Ag/Ag0.75Al wire during PMP than from the filaments in the Bi2212/Ag/Ag0.20Mg wire. These results show that DS Ag/Al alloy is a strong candidate for improved Bi2212 wire.

“…Much work has been reported on the strain tolerance of silver-sheathed Bi-2223 tapes [10][11][12][13][14][15][16]. Generally, the best strain tolerance is found for multifilamentary PIT material [14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Bending strain tolerance of critical current values in Tl-based superconducting tapes

Naylor¹,

Fox²,

Moore³

et al. 1997

Mono-and multifilamentary silver-sheathed Tl-1223 powder-in-tube (PIT) tapes have been strained by bending at 77 K. The changes in the critical current of the samples due to the bending strain have been related to the tape microstructure. The shapes of the curves are similar to those found in the literature for Bi-2223 PIT samples. In situ reacted samples show a significant improvement in bending strain tolerance compared to samples prepared using pre-reacted powder.