Improvement of small to large grain A15 ratio in Nb<sub>3</sub>Sn PIT wires by inverted multistage heat treatments

Segal, Christopher; Tarantini, C.; Lee, Peter J.; Larbalestier, D. C.

doi:10.1088/1757-899x/279/1/012019

Cited by 12 publications

(10 citation statements)

References 11 publications

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“…From the images it can be calculated that the average FG area fractions in filaments are ~33% and ~22% for APC-A and APC-B, respectively, and the residual Nb area fractions are 36% and 45%, respectively. The calculated coarse-grain (CG) fractions for APC-A and APC-B are ~13%, similar to those of TT [25] and PIT [29] wires. In comparison, the residual Nb fractions for present PIT conductors are typically below 25% [29].…”

Section: Resultsmentioning

confidence: 59%

“…The calculated coarse-grain (CG) fractions for APC-A and APC-B are ~13%, similar to those of TT [25] and PIT [29] wires. In comparison, the residual Nb fractions for present PIT conductors are typically below 25% [29]. This means that the above APC conductors can form more FG by converting more Nb via properly tweaking the recipe design (e.g., Nb/Sn ratio) and optimizing reaction so that no Sn remains in the core.…”

Section: Resultsmentioning

confidence: 59%

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Ternary Nb₃Sn superconductors with artificial pinning centers and high upper critical fields

Rochester

Peng

et al. 2019

Supercond. Sci. Technol.

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In this letter we demonstrate the development of ternary Nb3Sn multifilamentary conductors with artificial pinning centers (APC) which achieve high critical fields. These recently-developed conductors were tested in a 31 T magnet, and the results showed that their upper critical field (Bc2) values at 4.2 K are 27-28 T, and irreversible field (Birr) values are above 26 T, values similar to or higher than those of best RRP conductors. The non-Cu Jc has been brought to nearly 1200 A/mm 2 at 16 T and 4.2 K, comparable to RRP, in spite of the fact that the fine-grain Nb3Sn fractions in filaments are still low (20-30%) and the grain sizes are still not fully refined (70-80 nm) due to conductor designs and heat treatments that are not yet optimized. The Nb3Sn layer Jc at 4.2 K, 16 T is 4710 A/mm 2 for the APC wire with 1%Zr, about 2.5 times higher than RRP conductors, in spite of the fact that its grain size is not yet fully refined due to insufficient oxygen and unoptimized heat treatment. An analysis is presented about the non-Cu Jc that can be achieved by further optimizing the APC conductors and their heat treatments.

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Section: Resultsmentioning

confidence: 59%

Section: Resultsmentioning

confidence: 59%

Ternary Nb₃Sn superconductors with artificial pinning centers and high upper critical fields

Rochester

Peng

et al. 2019

Supercond. Sci. Technol.

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“…Moreover, the Nb1Ta4Hf alloy could also be beneficial for PIT conductors presently made with Nb4Ta tubes. Detailed studies of the A15 reaction in present PIT conductors by Segal et al show that Jc is in fact limited by the fact that about one quarter of the ~55% A15 (formed by decomposition of large grain Nb6Sn5) is >1 m in size [12,13,34]. This large grain A15 does not contribute to current transport, thus degrading the overall Jc of PIT conductors with respect to RRP® conductors.…”

Section: Discussionmentioning

confidence: 93%

Beneficial influence of Hf and Zr additions to Nb4at%Ta on the vortex pinning of Nb₃Sn with and without an O source

Balachandran

Tarantini

Lee

et al. 2019

Supercond. Sci. Technol.

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Here we show that addition of Hf to Nb4Ta can significantly improve the high field performance of Nb3Sn, making it suitable for dipole magnets for a machine like the 100 TeV future circular collider (FCC). A big challenge of the FCC is that the desired non-Cu critical current density (Jc) target of 1500 A/mm 2 (16 T, 4.2 K) is substantially above the best present Nb3Sn conductors doped with Ti or Ta (~1300 A/mm 2 in the very best sample of the very best commercial wire). Recent success with internal oxidation of Nb-Zr precursor has shown significant improvement in the layer Jc of Nb3Sn wires, albeit with the complication of providing an internal oxygen diffusion pathway and avoiding degradation of the irreversibility field HIrr. We here extend the Nb1Zr oxidation approach by comparing Zr and Hf additions to the standard Nb4Ta alloy of maximum Hc2 and Hirr. Nb4Ta rods with 1Zr or 1Hf were made into monofilament wires with and without SnO2 and their properties measured over the entire superconducting range at fields up to 31 T. We found that group IV alloying of Nb4Ta does raise HIrr, though adding O2 still degrades this slightly. As noted in earlier Nb1Zr work with an O source, the pinning force density Fp is strongly enhanced and its peak value shifted to higher field by internal oxidation. A surprising result of this work is that we found better properties in Nb4Ta1Hf without SnO2, FpMax achieving 2.35 Times that of the standard Nb4Ta alloy, while the oxidized Nb4Ta1Zr alloy achieved 1.54 times that of the Nb4Ta alloy. The highest layer Jc(16 T, 4.2 K) of 3700 A/mm 2 was found in the SnO2free wire made with Nb4Ta1Hf alloy. Using a standard A15 cross-section fraction of 60% for modern PIT and RRP wires, we estimated that a non-Cu Jc of 2200 A/mm 2 is obtainable in modern conductors, well above the 1500 A/mm 2 FCC specification. Moreover, since the best properties were obtained without SnO2, the Nb4Ta1Hf alloy appears to open a straightforward route to enhanced properties in Nb3Sn wires manufactured by virtually all the presently used commercial routes employed today.

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“…However, the FCC requirements in terms of non-Cu critical current density (non-Cu J c > 1500 A/mm 2 at 16 T and 4.2 K), residual resistivity ratio of the Cu stabilized (conductor RRR > 150 to maintain > 100 after cabling and winding) and filament diameter (d eff < 20 µm) are very challenging and beyond the performance of presently available commercial Nb 3 Sn wires 3 , 4 . For this reason in the last few years there has been an increasing effort to improve the J c performance of internal-tin (IT) and powder-in-tube (PIT) wires by investigating the phase evolution and by heat treatment optimizations 5 – 9 . Although a 36% J c increase ( J c (4.2 K,16 T) ~ 1300 A/mm 2 ) was achieved in small filament diameter RRP (Restacked Rod Process) wires 8 , other approaches have also been pursued.…”

Section: Introductionmentioning

confidence: 99%

Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping

Tarantini

Kametani

Balachandran

et al. 2021

Sci Rep

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In recent years there has been an increasing effort in improving the performance of Nb3Sn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields (HIrr and Hc2, respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties. Electron microscopy, Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and Atom Probe Tomography (APT) characterization clearly show that, in presence of oxygen, both fine Nb3Sn grains and HfO2 nanoparticles form. Although EXAFS is unable to detect significant amounts of Hf in the A15 structure, APT does indeed reveal some residual intragrain metallic Hf. To investigate the layer properties in more detail, we created a microbridge from a thin lamella extracted by Focused Ion Beam (FIB) and measured the transport properties of Ta-Hf-doped Nb3Sn. Hc2(0) is enhanced to 30.8 T by the introduction of Hf, ~ 1 T higher than those of only Ta-doped Nb3Sn, and, even more importantly the position of the pinning force maximum exceeds 6 T, against the typical ~ 4.5–4.7 T of the only Ta-doped material. These results show that the improvements generated by Hf addition can significantly enhance the high-field performance, bringing Nb3Sn closer to the requirements necessary for FCC realization.

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Improvement of small to large grain A15 ratio in Nb₃Sn PIT wires by inverted multistage heat treatments

Cited by 12 publications

References 11 publications

Ternary Nb₃Sn superconductors with artificial pinning centers and high upper critical fields

Ternary Nb₃Sn superconductors with artificial pinning centers and high upper critical fields

Beneficial influence of Hf and Zr additions to Nb4at%Ta on the vortex pinning of Nb₃Sn with and without an O source

Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping

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Improvement of small to large grain A15 ratio in Nb3Sn PIT wires by inverted multistage heat treatments

Cited by 12 publications

References 11 publications

Ternary Nb3Sn superconductors with artificial pinning centers and high upper critical fields

Ternary Nb3Sn superconductors with artificial pinning centers and high upper critical fields

Beneficial influence of Hf and Zr additions to Nb4at%Ta on the vortex pinning of Nb3Sn with and without an O source

Origin of the enhanced Nb3Sn performance by combined Hf and Ta doping

Contact Info

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Improvement of small to large grain A15 ratio in Nb₃Sn PIT wires by inverted multistage heat treatments

Ternary Nb₃Sn superconductors with artificial pinning centers and high upper critical fields

Ternary Nb₃Sn superconductors with artificial pinning centers and high upper critical fields

Beneficial influence of Hf and Zr additions to Nb4at%Ta on the vortex pinning of Nb₃Sn with and without an O source