Influence of Nb alloying on Nb recrystallization and the upper critical field of Nb3Sn

IF 3.1 3区 材料科学 Q2 MATERIALS SCIENCE, MULTIDISCIPLINARY
Nawaraj Paudel, Chiara Tarantini, Shreyas Balachandran, William L. Starch, Peter J. Lee, David C. Larbalestier
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State-of-the-art Ta- and Ti-doped strands exhibit upper critical field, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>H</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub></math>, values of ∼24–26.5 T (4.2 K) and do not reach the Future Circular Collider target <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>J</mi><mi>c</mi></msub></math>, which serves as the present stretch target for <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi mathvariant=\"normal\">Nb</mi><mn>3</mn></msub><mi>Sn</mi></mrow></math> development. As recently demonstrated, to meet this goal requires enhanced vortex pinning but an independent and supplementary approach is to significantly enhance <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>H</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub></math>. In this study, we have arc melted multiple Nb alloys with added Hf, Zr, Ta, and Ti and drawn them successfully into monofilament wires to investigate the possibilities of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>H</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub></math> enhancement through alloying. <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>H</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub><mo>(</mo><mi>T</mi><mo>)</mo></math> was measured for all samples in fields up to 16 T and some up to 31 T. We have found that all alloys show good agreement with the standard Werthamer, Helfand, and Hohenberg fitting procedure without the need to adjust the paramagnetic limitation parameter (<i>α</i>) and spin-orbit scattering parameter <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mo>(</mo><msub><mi>λ</mi><mi>so</mi></msub><mo>)</mo></math>. The evaluation of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>d</mi><msub><mi>H</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub><mo>/</mo><mi>d</mi><mi>T</mi></mrow></math> near <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>T</mi><mi>c</mi></msub></math>, which is proportional to the electronic specific heat coefficient <i>γ</i> and the normal state resistivity <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>ρ</mi><mi mathvariant=\"normal\">n</mi></msub></math>, allows a better understanding of the induced disorder introduced by alloying in the A15 phase. 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引用次数: 0

Abstract

Nb3Sn conductors are important candidates for high-field magnets for particle accelerators, and they continue to be widely used for many laboratory and nuclear magnetic resonance magnets. However, the critical current density, Jc, of present Nb3Sn conductors declines swiftly above 12–15 T. State-of-the-art Ta- and Ti-doped strands exhibit upper critical field, Hc2, values of ∼24–26.5 T (4.2 K) and do not reach the Future Circular Collider target Jc, which serves as the present stretch target for Nb3Sn development. As recently demonstrated, to meet this goal requires enhanced vortex pinning but an independent and supplementary approach is to significantly enhance Hc2. In this study, we have arc melted multiple Nb alloys with added Hf, Zr, Ta, and Ti and drawn them successfully into monofilament wires to investigate the possibilities of Hc2 enhancement through alloying. Hc2(T) was measured for all samples in fields up to 16 T and some up to 31 T. We have found that all alloys show good agreement with the standard Werthamer, Helfand, and Hohenberg fitting procedure without the need to adjust the paramagnetic limitation parameter (α) and spin-orbit scattering parameter (λso). The evaluation of dHc2/dT near Tc, which is proportional to the electronic specific heat coefficient γ and the normal state resistivity ρn, allows a better understanding of the induced disorder introduced by alloying in the A15 phase. So far, we have observed that Hf alloying of pure Nb can enhance Hc2(0) by 3–4 T to ∼28 T, while adding just 1at.% Hf or Zr into a Nb-4 at. % Ta base alloy can raise Hc2(0) to ∼31 T. Very importantly we find that Hf and Zr raise the alloy recrystallization temperature above the usual A15 reaction temperature range of 650C750C, thus ensuring denser A15 phase nucleation in the Nb alloy grain boundaries, possibly leading to a more homogeneous A15 phase Sn content and refined A15 grain size. The potential for further advancements in Nb3Sn properties is explored in relation to the recrystallization of the Nb alloy and the factors controlling the upper critical field.

Abstract Image

铌合金化对铌再结晶和 Nb3Sn 上临界场的影响
Nb3Sn 导体是粒子加速器高磁场磁体的重要候选材料,目前仍被广泛用于许多实验室和核磁共振磁体。然而,目前 Nb3Sn 导体的临界电流密度 Jc 在 12-15 T 以上迅速下降。最先进的掺钽和掺钛股显示出的上临界磁场 Hc2 值为 24-26.5 T(4.2 K),达不到未来环形对撞机的目标 Jc,而这正是目前 Nb3Sn 发展的延伸目标。正如最近证明的那样,要达到这一目标,需要增强涡旋引脚,但一个独立的补充方法是显著增强 Hc2。在这项研究中,我们用电弧熔化了多种添加了 Hf、Zr、Ta 和 Ti 的 Nb 合金,并成功地将它们拉制成单丝,以研究通过合金化提高 Hc2 的可能性。我们发现所有合金都与标准的 Werthamer、Helfand 和 Hohenberg 拟合程序显示出良好的一致性,无需调整顺磁限制参数 (α) 和自旋轨道散射参数 (λso)。dHc2/dT 与电子比热系数 γ 和正常态电阻率 ρn 成正比,评估 Tc 附近的 dHc2/dT 可以更好地理解合金化在 A15 相中引入的诱导无序。到目前为止,我们已经观察到纯 Nb 的 Hf 合金可将 Hc2(0) 提高 3-4 T 至 ∼28 T,而在 Nb-4 at.非常重要的是,我们发现 Hf 和 Zr 能将合金的再结晶温度提高到通常的 A15 反应温度范围(650∘C-750∘C)以上,从而确保在 Nb 合金晶界中形成更致密的 A15 相核,并可能导致更均匀的 A15 相 Sn 含量和细化的 A15 晶粒大小。我们结合铌合金的再结晶和控制上临界场的因素,探讨了进一步提高 Nb3Sn 性能的潜力。
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来源期刊
Physical Review Materials
Physical Review Materials Physics and Astronomy-Physics and Astronomy (miscellaneous)
CiteScore
5.80
自引率
5.90%
发文量
611
期刊介绍: Physical Review Materials is a new broad-scope international journal for the multidisciplinary community engaged in research on materials. It is intended to fill a gap in the family of existing Physical Review journals that publish materials research. This field has grown rapidly in recent years and is increasingly being carried out in a way that transcends conventional subject boundaries. The journal was created to provide a common publication and reference source to the expanding community of physicists, materials scientists, chemists, engineers, and researchers in related disciplines that carry out high-quality original research in materials. It will share the same commitment to the high quality expected of all APS publications.
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