Bronze-processed Nb3Sn Wires Research Articles

Investigation of the Cu based binary alloys and the internal matrix reinforcement bronze processed Nb3Sn wires

Mechanical strength improvement on Nb3Sn wire is the most important research subject to realize high field magnet applications operated under higher electromagnetic force environment. Recently, we approached to the internal matrix reinforcement technique due to the solid solution mechanism using ternary bronze alloy matrix on the bronze processed Nb3Sn wire. In this study, the effect of the solute element on the mechanical property of the matrix after Nb3Sn synthesis heat treatment was evaluated. Several Cu based binary alloys were casted, and these alloys were sintered in order to demonstrate the matrix after Nb3Sn synthesis. We confirmed that the both 0.2% proof stress and ultimate tensile stress of the Cu-In alloy was higher than those of the pure Cu and Cu-Zn alloy. The mechanical strength improvement due to the internal matrix reinforcement using Cu-Sn-In ternary alloy matrix was caused by (Cu, In) solid solution formation. The comparisons of mechanical property between several Cu alloys were also investigated for the further mechanical strength improvement.

Development of the internal matrix reinforcement bronze processed Nb3Sn multicore wires using Cu-Sn-In ternary alloy matrix for fusion magnet application

We approached the solid solution strength process for the high mechanical strength bronze processed Nb3Sn wires by the internal matrix reinforcement. Previously, we already reported the mechanical strength improvement of the Nb3Sn wire by the increasing of the amount of Zn element composition of the Cu-Sn-Zn ternary alloy matrix. However, there was also a trade-off relationship between the Sn and Zn compositions of the ternary matrix on the mechanical strength and superconducting properties. A Cu-Sn system ternary alloy containing Indium (In) element as a solute element (Cu-Sn-In), which is thought to be more effective solute element compared with Zn, was casted in order to improve mechanical strength beyond Cu-Sn-Zn ternary alloy matrix samples on the solid solution strength process. We fabricated various Cu-Sn-In-(Ti)/Nb precursor wires having 19 Nb multicores. The In element remained in the matrix after the Nb3Sn synthesis through the diffusion reaction, and then the Vickers hardness of the Cu-Sn-In matrices after the Nb3Sn synthesis heat treatment was higher than that of the conventional bronze and Cu-Sn-Zn matrices. We also confirmed that critical current density (Jc) property of the Nb3Sn wires using Cu-Sn-In-(Ti) was drastically increased at low and middle magnetic field below 15 T. These suggested that the In solute element in the matrix contributed the solid solution strengthening of the matrix after Nb3Sn synthesis and also improve Jc -B performance.

Performance of Polyvinyl Formal Insulated Cu–Nb/Nb3Sn Wires for React-and-Wind Process

In this study, polyvinyl formal (PVF) insulated Cu-Nb/Nb 3 Sn wires were successfully developed for react-and-wind (R&W) process. The bronze-processed Nb 3 Sn wires, composed of the Nb-rod-method Cu-Nb reinforcing stabilizer around the Nb 3 Sn filament bundle, have superior mechanical strength against tensile and bending stress, not only at low temperature but also at room temperature. The Cu-Nb/Nb 3 Sn wires of 0.8- or 1.3-mm bare-diameter were heat-treated at 670 °C for 96 h on the stainless bobbins of predetermined diameter. Then, prebending strains were applied to the reacted wires under individual conditions. After that, the PVF insulation was applied with a thickness of 20 or 40 μm. Enhancement of the critical currents occurred by applying the appropriate prebending treatments and controlling the strain under PVF insulation processing to ±0.5% or less. This paper presents the performance of the PVF-insulated Cu-Nb/Nb 3 Sn wires applicable to R&W coils.

Development of bronze processed Nb3Sn wires using various Cu-Sn-In ternary alloy matrices

The degradation of transport current caused by high mechanical strain on practical Nb3Sn wire is a serious problem for future fusion magnets whose conductor is subjected to high electromagnetic forces. Therefore the increase of mechanical strength of Nb3Sn wire is an important research subject for fusion applications. We applied "internal matrix strengthening" using a solid solution strengthening mechanism to strengthen Nb3Sn wire and also fabricated bronze processed Nb3Sn wires using various ternary bronze alloys containing Indium (In) as the third solute element (Cu-Sn-In). Indium remained in the matrices of these wires after the Nb3Sn synthesis. The Vickers hardness of the Cu-Sn-In ternary matrices after the Nb3Sn synthesis was then higher than those of the conventional bronze and Cu-Sn-Zn ternary matrices. It is suggested that In acts more effectively as the third solute element for the solid solution strength process compared to Zn and that this may contribute to the further mechanical strengthening of Nb3Sn wire. In this study the effect of In as the solute element on microstructure and superconducting properties of bronze processed Nb3Sn wires using various Cu-Sn-In matrices was investigated.

Performance Boost in Industrial Multifilamentary Nb3Sn Wires due to Radiation Induced Pinning Centers.

We report non-Cu critical current densities of 4 . 09 ⋅ 109 A/m2 at 12 T and 2.27 ⋅ 109 A/m2 at 15 T obtained from transport measurements on a Ti-alloyed RRP Nb3Sn wire after irradiation to a fast neutron fluence of 8.9 ⋅ 1021 m−2. These values are to our knowledge unprecedented in multifilamentary Nb3Sn, and they correspond to a Jc enhancement of approximately 60% relative to the unirradiated state. Our magnetometry data obtained on short wire samples irradiated to fast neutron fluences of up to 2.5 ⋅ 1022 m−2 indicate the possibility of an even better performance, whereas earlier irradiation studies on bronze-processed Nb3Sn wires with a Sn content further from stoichiometry attested a decline of the critical current density at such high fluences. We show that radiation induced point-pinning centers rather than an increase of the upper critical field are responsible for this Jc enhancement, and argue that these results call for further research on pinning landscape engineering.

Fabrication and Superconducting Properties of the Bronze-Processed $\mbox{Nb}_{3}\mbox{Sn} $ Multifilamentary Wire Using Cu–Sn–Zn Alloy Matrix

We developed several new Cu-Sn-Zn-(Ti) alloys, which are so-called “CSZ alloy,” for practical bronze-processed Nb 3 Sn wires. Several CSZ alloys were fabricated via the Mizuta method. The Zn was uniformly dissolved in the α phase of the Cu-Sn alloy, and the Zn-Ti compounds were not found in the CSZ alloy. Various 19 Nb-filament CSZ Nb 3 Sn precursor wires were fabricated using CSZ matrices with different Sn and Zn nominal compositions. We also found that the CSZ/Nb composites showed excellent workability at room temperature. In this paper, changes in microstructure and superconducting properties of Nb 3 Sn wires with different CSZ matrices as a function of the heat treatment condition were investigated. We clearly observed that the amount of Zn in the matrix remained constant after the Nb 3 Sn formation. Thicker Nb 3 Sn layers were formed by the Zn addition. T c transitions of about 18 K have been obtained. Finally, we have succeeded in fabricating multifilamentary wires using CSZ matrices through the restacking method. The number of Nb filaments is 7771 with a diameter of 3.4 μm. The effect of the Zn addition on microstructures and superconducting property of the CSZ wires are also reported.

Influence of Wire Parameters on Critical Current Versus Strain Characteristics of Bronze Processed ${\hbox {Nb}}_{3}{\hbox {Sn}}$ Superconducting Wires

In order to develop bronze processed Nb3Sn wire for the ITER CS coil operating under higher compressive strain, the influence of various parameters of wires such as filament diameter, barrier materials, barrier thickness, heat treatment pattern and Ti addition on critical current (Ic) versus intrinsic strain eν(-1.0% <; eν <; +0.1%) characteristics was investigated. The change of these parameters brought significant changes to superconducting properties such as Ic and n-value. In spite of different wire parameters, the strain dependency of normalized Ic was almost the same, except that a Ti addition affects the upper critical field Bc2. This result suggests that assuming the same Ti-addition level, Nb3Sn wire with higher performance at a certain eν would exhibit higher performance at any eν in the compressive regime. Based on the result, bronze processed Nb3Sn wires with non-Cu critical current density more than 1100 A/mm2 at 12 T, 4.2 K, zero applied strain have been successfully developed for the CS coil.

ブロンズ法Nb&lt;sub&gt;3&lt;/sub&gt;Sn 線材の高性能化

Characteristics such as the critical current density (Jc) and mechanical property of bronze-processed Nb 3 Sn superconducting wires have improved with the progress on high-field superconducting magnets such as nuclear magnetic resonance (NMR) magnets. On the other hand, for Nb 3 Sn wiresused in intermediate magnetic-field applications such as fusion and particle accelerator magnets, the wire parameters have been optimized to realize high Jc around 12 T. In this article, improvements in the Jc and mechanical property of bronze-processed Nb 3Sn wires based on the activities of Japan Superconductor Technology, Inc. (JASTEC) and Kobe Steel, Ltd. are described.

Development of Nb 3Sn superconducting wires for high field magnets at Kobe Steel and JASTEC

Research and development activities and some recent results related to Nb 3Sn superconducting wires in Kobe Steel, Ltd. (KSL) and Japan Superconductor Technology Inc. (JASTEC) are introduced. First, an outline of the activities is described briefly from a historical point of view. Following that, improvements in the characteristics (i.e., critical current density ( J c), n-value and mechanical properties) of bronze-processed Nb 3Sn wires are reviewed. Finally, the status of development for the Ta–Sn powder-in-tube (TS-PIT) process is briefly discussed.

Investigations of bronze processed Nb3Sn wires with enhanced characteristics

The bronze processed Nb3Sn strands differed by specific layouts and the matrix and filament composition were investigated. Two ways of alloying were used: artificial alloyed filaments by Ti and use of alloyed bronze. By means of optical and electron microscopy the features of wire microstructure were explored. The dependences of critical current density from magnetic field and temperature have been determined. It is established that in explored alloyed wires the critical current density (Jc) is higher than 800 A/mm2(non-copper, diameter 0.82mm, 4.2K, 12T).

強化ブロンズ法Ｎｂ３Ｓｎ線材の機械的性質と臨界電流の応力／ひずみ特性

This paper reviews the stress/strain characteristics of some typical highly strengthened bronze-processed practical Nb3Sn superconducting wires examined in the HFLSM, IMR of Tohoku University up to the magnetic field of 14.5 T at a temperature of 4.2 K. Internal reinforcement of the superconducting composite wires using the materials with high strength and high electrical conductivity such as in situ processed or jelly rolled Cu-Nb microcomposite, Ta, and recently developed Cu-Nb-Ti compound was proved to be promising, although the stability of the wire is decreased to some extent. Although the intrinsic axial tensile strain sensitivity of Ic was not markedly changed, the reinforcements changed not only mechanical properties such as the 0.2% proof stress but also the parameters relevant to the tensile strain characteristics of Ic, the strain corresponding to the Ic peak, em, and reversible strain limit, eirr, where permanent damage such as cracking starts to take place in the Nb3Sn filaments. Furthermore, the transverse compressive stress sensitivity of Ic decreased and the reversible stress limit increased. The effect of parameters on the Cu-Nb composite reinforced bronze-processed Nb3Sn wires and the strain characteristics are intensively discussed.

高磁場マグネット用Nb&lt;sub&gt;3&lt;/sub&gt;Sn超電導線材の開発

Research and development activities and some recent results related to Nb3Sn superconducting wires produced by Kobe Steel, Ltd. and Japan Superconductor Technology Inc. (JASTEC) are introduced. An outline of the activities is described from a historical point of view. Improvements in the characteristics (i.e., critical current density (Jc), n-value and mechanical properties) of bronze-processed Nb3Sn wires are reviewed. Finally, the status of development for the Ta-Sn powder-in-tube (TS-PIT) process newly proposed by Tachikawa is described.

ＩＴＥＲ用Ｔａ添加型ブロンズ法Ｎｂ３Ｓｎ素線の開発と量産

Development work to produce a high-performance Nb3Sn superconducting wire for the center solenoid coil of the ITER was carried out. The effects of concurrently adding Ti and Ta to bronze-processed Nb3Sn wires were examined. In addition, a high-Sn-concentration bronze matrix was applied. Then, the relation between hysteresis loss and filament diameter was examined. Moreover, the cause of wire breakage during processing was elucidated. As a result, a reliable manufacturing process for high-performance Nb3Sn superconducting wire was established.

Effects of the germanium addition to the matrix of bronze-processed Nb 3Sn wires

The simultaneous addition of 0.5 at%Ge to the matrix and 1 at%Ta to the coreenhances the Jc of Nb 3Sn at 12T by more than one order of magnitude. The increase in the Jc seems to be attributed to the grain refinement of Nb 3Sn by the Ge addition. The formation of thin layer richer in Ge is observed at the interface between the Nb 3Sn and matrix, which may be effective for reducing the proximity effect among Nb 3Sn filaments in the AC use. Ultrafine filamentary Nb 3Sn wires with Ge addition to the matrix have been successfully fabricated. The addition of 0.25 at%Ge to the matrix and 1 at%Ta to the core improves the Qh/Jc ratio at 0.5 T by a factor of nearly four.

Anisotropy and angular dependence of critical currents in rectangular Nb3Sn superconductors made by the bronze method

An experimental study of the critical current angular dependence in flat mono- and multifilament bronze-processed Nb3Sn wires, oriented in different directions in a transverse magnetic field, is presented. The influence of various parameters, such as the shape aspect ratio and the heat treatment time and temperature, is examined. It is shown that in monofilament wires, the critical current anisotropy, defined as the ratio of the currents in the parallel and perpendicular orientations of the flat face to the magnetic field, is greater than one at low heat-treatment conditions and changes to less than one with more intensive heat treatment. The multifilament wires behave in the same manner, except that the effects of the gentle and intensive heat treatments are related to the filament size. The mechanical deformation of the niobium core determines the character of the anisotropy at relatively low heat-treatment conditions, while the morphology of the grown Nb3Sn layer is decisive at more intensive heat treatment. The critical current anisotropy of flattened conductors is very important from the theoretical (pinning) as well as from the technical (magnet winding) point of view.

A study of the H c2 enhancement due to the addition of Ti to the matrix of bronze-processed Nb3Sn superconductors

The measurements of ρn (the normal state resistivity), Tc, Hc2, and (dHc2/dt)T=Tc have been made for bronze-processed Nb3Sn wires with addition of Ti to the Cu-Sn matrix in order to study the mechanism of Hc2 enhancement due to the addition of Ti. The coefficient of electron specific heat, γ, has been derived by two independent methods: one using the Ginzburg–Landau–Abrikosov–Gor’kov (GLAG) theory and the measured values of ρn, Tc, and (dHc2/dT)T=Tc, and the other using the Kramer pinning theory and the gradient of J1/2cH1/4 -H curves. The ratios of γ/γ0 which have been derived by these two methods are in good agreement with each other. (γ0 is the value of γ for the specimen to which Ti is not added.) The upper critical fields given by the GLAG theory, H*c2 and Hc2, at 0 K increase rapidly with Ti concentration in the Nb3Sn layer up to 2 at. % and decrease slightly above 2 at. %. The rapid increase in ρnγTc caused by the addition of Ti is sufficient to explain the enhancement in Hc2, and among ρn, γ and Tc, only ρn shows a significant increase with increasing amounts of additional Ti, indicating that the main reason for the Hc2 enhancement is the increase in ρn.

Superconducting and metallurgical properties of bronze processed Nb3Sn wires with Ni and Zn additions and comparison with Ta and Ti additions

Abstract Critical current density measurements up to 23 T of nineteen core Nb 3 Sn wires with simultaneous addition of Ni to the core and Zn to the Cu-Sn bronze matrix have revealed a considerable increase of J c at fields above 11 T. For a wire with the composition Nb-0.6 wt% Ni/Cu-10 wt% Sn-3 wt% Zn, reacted at 750°C for 64 h, J c in the layer was determined to 1.3 × 10 5 A cm −2 at 14 T and to 4 × 10 4 A cm −2 at 19 T. Comparison with Ta and Ti core-alloyed Nb 3 Sn wires, also performed in the present study, shows very similar results in J c and J c vs. e up to the highest fields. Composition profiles for Sn and for Ni, Ta and Ti additives in the A15 layers were studied by Auger spectroscopy. For Sn a concentration gradient across the layer ( from ≈ 25 at % to ≈ 22 at % Sn ) was observed, with the highest Sn content occurring at the interface with the bronze. The presence of the additives in the layer was detected as well by Auger analysis as by X-ray diffractometry.