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The Cu-Sn phase diagram. This phase diagram will be very relevant for the rest of this chapter and in chapters to come. 

The Cu-Sn phase diagram. This phase diagram will be very relevant for the rest of this chapter and in chapters to come. 

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... During heat treatment of certain types of conductor wires to produce the superconducting Nb 3 Sn, nausite forms during the intermediate heattreatment stages and decomposes at higher temperatures before Nb 3 Sn formation takes place [6][7][8][9][10][11][12][13]. This leads to disconnected and large-grain Nb 3 Sn, which degrades its superconducting properties [14][15][16][17]. Still, nausite already formed can also promote Cu diffusion to the Sn source, which decreases the amount of unwanted melt developing during further heat-treatment steps [14,17,18]. ...
... This leads to disconnected and large-grain Nb 3 Sn, which degrades its superconducting properties [14][15][16][17]. Still, nausite already formed can also promote Cu diffusion to the Sn source, which decreases the amount of unwanted melt developing during further heat-treatment steps [14,17,18]. Hence, availability of a thermodynamic description of the Cu-Nb-Sn system including the nausite phase is highly desirable for planning of heat-treatments of such superconducting Nb 3 Sn wires. ...
... It is known from heat-treated superconducting Nb 3 Sn wires that nausite shows local phase equilibria with NbSn 2 , Cu 6 Sn 5 , Cu 3 Sn, and Sn [9,[14][15][16][17][18]. As mentioned above, the CuMg 2 -type NbSn 2 and NiMg 2 -type nausite both share a MSn 2 formula (M = Cu, Nb) with nausite being present at a significant substitution of Nb by Cu [7]. ...
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Currently available Cu–Nb–Sn phase diagrams lack the recently discovered nausite phase (Cu,Nb)Sn2, which is an important intermediate in the course of thermal processing of superconducting Nb3Sn wires. Processing decisively determines the resulting microstructure of Nb3Sn and, thus, its superconducting properties. Lack of suitable and complete phase diagrams, however, obstructs rational design of such thermal processing procedures. To close this gap and to obtain valid knowledge of homogeneity and stability range of nausite, various Cu–Nb–Sn samples, which are heat-treated between 300 °C and 500 °C, are investigated. By means of energy-dispersive X-ray spectroscopy (EDX), a temperature-dependent homogeneity range of nausite is observed, which covers average mole fractions of Cu between 0.09 and 0.15. This is correlated with a change in the mean atomic volume and can be seen in the lattice parameters determined by X-ray diffraction (XRD). Additionally performed first-principles calculations on different CuSn2 and NbSn2 model structures confirm this trend. Furthermore, the peritectic decomposition of nausite to NbSn2 and liquid at 586 °C is determined by means of in situ XRD and differential scanning calorimetry (DSC). By using the CALPHAD (CALculation of PHase Diagrams) approach, all these findings are used to extend a previous thermodynamic description of the Cu–Nb–Sn system by including the nausite as an additional phase. With this noteworthy integration, the updated modelling of the Cu–Nb–Sn system can be used for optimizing the multistage heat-treatment steps during processing superconducting Nb3Sn wires.
... An important recent contribution was the reassessment of heat treatment design for Restacked Rod Process (RRP ® ) wires (Bruker OST) undertaken by Sanabria et al. [2], [3]. Conventional heat treatments include steps at around 210 °C and 400 °C, followed by the reaction step that forms Nb3Sn at 650-665 °C (Fig. 1), but the low temperature steps were not well understood. ...
... Digital Object Identifier will be inserted here upon acceptance. treatment step at ~370 °C could increase Jc, avoiding the reduction often found in wires with small sub-elements [2], [3]. Nausite is a Sn-rich Cu-Nb-Sn phase, which was first identified surprisingly recently. ...
... The inclusion or omission of this step had no impact on the microstructure after the 400 °C step. During the 400 °C step, a nausite 'membrane' forms at the interface between the core and the Nb filament region, which progressively thickens, retaining Sn in the core but permitting the inward diffusion of Cu, resulting in a decreasing η content in the core [2], [3]. ...
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In recent years, the phase formation sequence during heat treatment of Nb<sub>3</sub>Sn wires, and the influence of the microstructure and compositional homogeneity of Nb<sub>3</sub>Sn on in-field critical current ( I<sub>c</sub> ), have received increasing attention. For RRP<sup></sup> wires, the importance of understanding and managing the formation of the ternary phase nausite has been demonstrated. However, a published CuNbSn phase diagram including this phase is still not available; and conductor development for the Future Circular Collider (FCC) study has introduced a variety of less-studied internal tin wire layouts. In this article, a study of phase transformations in the ternary CuNbSn system is summarized, and selected isothermal sections of the re-evaluated phase diagram are presented. The phase transformations during low-temperature heat treatment steps of wires developed for the FCC study are also presented and analyzed in comparison to established RRP<sup></sup> conductors.
... In the sub-element, the Cu content between the Nb filaments is much lower than that of ITERgrade Nb 3 Sn strand, causing them to be in close proximity with each other. This Nb filament proximity, combined with the significant expansion of Nb in the Nb 3 Sn reaction, produces bonding of the filaments and in many cases a monolithic column of Nb 3 Sn and an increased D eff [5]. The bonding of filaments in the sub-elements causes some issues such as high hysteresis loss and thermo-magnetic instability, but the most critical issue of high-J c Nb 3 Sn strand for the conductor operating under the huge electromagnetic (EM) force is the sensitivity to the bending strain [6], which could cause irreversible degradation of conductor performance with EM cycling. ...
... The progression of technology from discovery to multi-filamentary wire was very rapid for Nb 3 Sn. The history of Nb 3 Sn and the need for finely divided filaments is very nicely summarized in two recent theses 1,2 . The brittle nature of Nb 3 Sn required the clever invention of creating the multifilamentary structure first and then converting ductile niobium into Nb 3 Sn by solid state diffusion of tin through a copper matrix. ...
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... Les [Dresner, 1995]. (a) Câble Rutherford ouvert à une extrémité pour mettre en évidence le pas de transposition des brins [Sanabria, 2017]. ...
... FIGURE I.27 -Représentation de : (a) un monofilament et (b) la billette multifilamentaires du brin PIT [Sanabria, 2017]. ...
... Le brin RRP est basé sur la méthode de l'étain interne (IT Ce brin présente une structure assez complexe. Plusieurs études sont disponibles par rapport à la structure de ce brin et à l'influence du traitement thermique [Jewell, 2008], [Sanabria, 2017]. . ...
Thesis
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Les câbles supraconducteurs sont largement utilisés dans le domaine des aimants à haut champ et sont en plein développement pour le transport de l’énergie. Un câble est un assemblage complexe de fils composites, euxmêmes constitués de filaments supraconducteurs torsadés dans une matrice métallique et entourés d’une couronne. La dépendance des brins supraconducteurs à la déformation est connue pour être responsable de la dégradation des performances électriques des câbles. La compréhension et la prédiction du comportement mécanique des brins est donc nécessaire afin de prédire les propriétés électriques des câbles dans le but d’optimiser leur mise en forme pour augmenter leurs performances (champ magnétique et capacité de transport).Une caractérisation mécanique multi-échelle de brins Nb3Sn et MgB2 a été réalisée au travers d’essais sur brins complets et sur brins dont la couronne a été dissoute. Un dispositif d’essais a été développé dans le cadre d’essais uniaxiaux sur fil fragile de faible diamètre. Des essais de nano-indentation ont permis d’accéder aux propriétés locales des matériaux constituants les brins. Une stratégie de modélisation et d’identification du comportement mécanique des brins a été développée. La modélisation repose sur une représentation simplifiée de la structure construite à partir des fractions volumiques et des essais de nano-indentation. L’identification des paramètres des lois de comportement est réalisée en utilisant la base de données expérimentales construite préalablement. Les modèles ainsi identifiés vont nourrir les futures simulations mécanique et électrique couplées de câbles.Une discussion sur l’endommagement des brins est menée au travers de l’étude de la localisation de la déformation observée dans certains brins, d’observations après des essais de traction interrompus et d’essais de traction in situ à un tomographe à rayons X.
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The safe and reliable operation of the China Fusion Engineering Test Reactor (CFETR) Central Solenoid Model Coil (CSMC) heat treatment system is the basis for the establishment of the CFETR central solenoid, Nb₃Sn superconducting coil. The purpose of safety analysis of a heat treatment system is to find out the unreliable factors of the system, analyze the weaknesses of the system, predict the possibility and severity of system failure, and then improve the reliability of the system. The method of combining risk priority number (RPN) with Hazard and operability study (HAZOP) can make up for the deficiency of quantitative information in traditional HAZOP analysis. It is concluded that the fan subsystem is the weakest part of the heat treatment system by means of RPN-HAZOP. The deviation caused by temperature, cleanliness, and impurity gas content will greatly affect the performance of the superconducting coil. The author tries to put forward scientific and reasonable measures according to the principle of giving priority to solving the principal contradiction. Guided by the measures and suggestions, the heat treatment system runs normally, safely, and reliably. The results of the experiment show that all the process indexes meet the requirements of coil heat treatment technology.
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Sn-based lithium-ion battery (LIB) anodes have a lower risk of lithium dendrite formation and a higher storage capacity of 993 mAh g⁻¹ vs. 372 mAh g⁻¹ compared to carbon-based anodes. Alloying Sn with Cu can reduce the reaction stresses in the anode, and Cu6Sn5 is therefore a promising candidate material to replace carbon-based anodes. However, the separation of Cu during the second stage of the lithiation reaction results in slow kinetics and degrades the cyclability of the anodes. This study proposes an effective method to inhibit the separation of Cu via the addition of Ni. Ni occupies the Cu positions in the Cu6Sn5 crystal structures to form (Cu, Ni)6Sn5, and therefore alters the crystal structure of the anode, leading to the formation of superstructures. As a result, Ni partially blocks the diffusion pathways of Li and therefore inhibits the Cu separation reaction, while the superstructure provides additional Li storage sites to increase the capacity of the anodes. Ni also refines the grain size of Cu6Sn5, leading to faster kinetics. The reaction mechanisms of the modified anodes are confirmed by in-situ synchrotron X-ray powder diffraction and ex-situ high voltage transmission electron microscopy.
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In the context of the Future Circular Collider (FCC) Study, industrial and academic partners are developing novel Nb3Sn superconducting wires with a wide variety of layouts, production methods and compositions, with the aim of achieving challenging performance targets including a non-copper critical current density of 1500 A $mm^{-2}$ at 16 T and 4.2 K. There is a clear need for a systematic and quantitative approach to analyzing these conductors, identifying correlations between performance, micro-structure and wire design, in order to optimize designs and heat treatments, and to identify the most promising directions for future trials. Image analysis methods have been developed to provide a quantitative description of key geometrical characteristics of a wire with an impact on $Nb_{3}Sn$ phase formation and superconducting performance. In this article, these methods are introduced, examples are presented of their application to prototype conductors produced for the FCC study, and opportunities for improving the performance of these prototype conductors are identified. Finally, initial steps towards models of diffusion and phase transformations are reported, and the potential for establishing a quantitative, analytical approach to wire design will be evaluated, identifying topics requiring further research.