CuNb Composite Research Articles

Thermo-kinetic orientation study on interface behavior of polycrystalline Cu-Nb composite by crystal plasticity finite element method

In this work, a 3-dimensional (3D) crystal plastic finite element method (CPFEM) combined with the qualitative analysis of slip thermodynamics and kinetics is applied to study the co-deformation behavior of heterophase interface and its relationships with the initial grain orientation or misorientation upon compression of FCC/BCC Cu-Nb polycrystalline metal matrix composites (MMCs). The present simulations well predict the interface instability of the 5-layered polycrystalline Cu-Nb composites arising from the onset and aggregation of the non-crystallographic bandlike concentrated strain. Meanwhile, by changing the grain orientation, the suppression or promotion of plastic shear localization can be realized, where the occurrence of interface instability depends not only on inhomogeneous stress fields, i.e., a single thermodynamic factor, but also on an implicit kinetic factor, i.e., misorientation. On this basis, a so-called artificial “coding” strategy by translating orientation-inhibited strain localization into implicit thermodynamic and kinetic information is presented to tailor the Cu-Nb MMCs, i.e., triggering as much plastic slip as possible from a thermodynamic perspective, while narrowing the misorientation as much as possible from a kinetic selection.

First performance test of a 25 T cryogen-free superconducting magnet

A 25 T cryogen-free superconducting magnet (25T-CSM) was developed and installed at the High Field Laboratory for Superconducting Materials (HFLSM), IMR, Tohoku University. The 25T-CSM consists of a high-temperature superconducting (HTS) coil and a low-temperature superconducting (LTS) coil. A high-strength CuNb/Nb3Sn Rutherford cable with a reinforcing stabilizer CuNb composite is adopted for the middle LTS section coil. All the coils were impregnated using an epoxy resin for conduction cooling. Initially, a GdBa2Cu3Oy (Gd123) coil was designed as the HTS insert coil, and then a Bi2Sr2Ca2Cu3Oy (Bi2223) coil was also developed. The HTS insert and the LTS (CuNb/Nb3Sn and NbTi) outsert coils are cooled by two 4K GM and two GM/JT cryocoolers, respectively. The LTS coils successfully generated a central magnetic field of 14 T at an operating current of 854 A without any training quench. The Gd123 coil generated 10.15 T at an operating current of 132.6 A in the absence of a background field. Subsequently, the operating current of the Gd123 insert was increased in a step-by-step manner under a background field of 14 T. The Gd123 coil could be operated up to 124.0 A stably, which corresponds to 23.55 T, but quenched at around 124.6 A (23.61 T). The Bi2223 insert coil using a Ni-alloy reinforced Bi2223 tape successfully generated 11.48 T at an operation current of 204.7A in a stand-alone test and 24.57 T in a background field of 14 T. The differences between the calculated and the measured values of the central magnetic fields are about 0.4 T for the Gd123 insert and 0.1 T for the Bi2223 insert around 24 T.

Construction of a 25-T cryogen-free superconducting magnet

The construction of a 25-T cryogen-free superconducting magnet (25T-CSM) has started in 2013 at the High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. The 25T-CSM consists of a low-T superconducting (LTS) coil and a high-Tc superconducting (HTS) coil. A high-strength CuNb/Nb3Sn Rutherford cable with the reinforcing stabilizer CuNb composite is adopted for the middle LTS section coil. The characteristic feature of the new technology using a CuNb/Nb3Sn Rutherford cable is a react-and-wind method for the coil-winding process. The LTS coil of 300-mm winding inner diameter is fabricated, and a central magnetic field of 14 T is generated at an operation current of 851 A. The HTS insert coil wound with GdBa2Cu3Oy (Gd123) tape has a 52-mm experimental room temperature bore, and a central magnetic field of 25.5 T will be generated at an operation current of 150 A in a background field of 14 T.

Prebending Effect for Mechanical and Superconducting Properties of Nb-Rod-Processed Cu–Nb Internal-Reinforced $\hbox{Nb}_{3} \hbox{Sn}$ Wires

We are planning to develop three large superconducting magnets, using CuNb-reinforced Nb3Sn Rutherford cables with the prebending treatment. CuNb-reinforced Nb3Sn wires using a new Nb-rod-processed CuNb composite were developed for the Rutherford cables. In this study, the prebending effects for the mechanical and the superconducting properties of the Nb-rod-processed CuNb/Nb3Sn wire were investigated. We found that the CuNb/Nb3Sn wire with 0.8% prebending treatment had largely enhanced critical current at 4.2 K. The reduction of the n-value was observed around 0.8% prebending strain. The mechanical properties of the prebent wires were enhanced. Young's modulus and 0.2% proof stress of the wire with prebending treatment at 4.2 K are 180 GPa and 270 MPa, respectively. The residual strain was released from 0.30% to 0.15% by 0.8% prebending treatment.

Microstructure and Properties of Cu-Nb Wire Composites

Abstract Nowadays, there is much activity all over the world in development of Cu-Nb composites for their potential use as conductors in high field magnets. This study was aimed at investigation of microstructure, mechanical and electrical properties of Cu-Nb composite wires. The investigated materials have been processed by vacuum furnace melting and casting, and then hot forging and cold drawing. Initial results of research into Cu-Nb composite material obtained using repeated iterative drawing of niobium wires compacted into copper tube, have been also presented in this article. The ultimate tensile strength versus cold deformation degree has been presented. These changes have been discussed in relation to microstructure evolution. It was assumed that repeated drawing of compacted wires is a promising method for fibrous composite production (more than 823,000 Nb fibres of nanometric diameter) characterized by high mechanical properties and electrical conductivity. Original SPD technique applied for Cu-Nb composite deformation result in initial microstructure refinement and improves effectiveness of wire production process.

High-Strength Nb<sub>3</sub>Sn Wire Development for Compact Superconducting Magnets

A superconducting magnet with a magnetic energy of E = B2/2μo [J/m3] has to overcome a magnetic force of P = B2/2μo [Pa] in the same expression. This means that a high-field 20 T superconducting magnet produces an electromagnetic force of 160 MPa. In order to stand such a large force, Nb3Sn superconducting wires are usually reinforced by the hard-copper housing as an external reinforcement method or the stainless steel winding as a mechanical backup of an outermost Nb3Sn coil. If we focus on a compact superconducting magnet like a cryocooled superconducting magnet, a high-strength superconducting wire with a small diameter size of 1- 2 mm is required. The High-Field Laboratory for Superconducting Materials, IMR, Tohoku University has developed Nb3Sn wires internally reinforced with CuNb or CuNbTi composite. These high-strength Nb3Sn wires were successfully employed to construct the unique compact cryocooled 28 T hybrid magnet and the cryocooled 18 T high-temperature superconducting magnet. In addition, we found that the prebending effect for high-strength Nb3Sn wires outstandingly improves the Tc, Bc2 and Ic properties. As a next step, we intend to develop new Nb3Sn strand cables with the strong mechanical property of 500 MPa, applying the prebending effect for a future 22 T-φ400 mm room temperature bore superconducting magnet of a 50 T-class hybrid magnet.

Spheroidization Effects on the Electrical and Magnetic Properties of Cu-Nb Composites

We report on the microstructure evolution in Cu-15% Nb multifilamentary wires upon annealing and the corresponding effects on their electrical and magnetic properties. During annealing at temperatures higher than 800 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ C$</tex> thermal instability mechanisms take place in the microstructure of the Cu-15%Nb composite, leading to spheroidization, followed by coarsening of niobium filaments. Such microstructural changes exert considerable influence on the magnitude of the normal electrical resistivity for the Cu-Nb composite. In addition, the annealing process leads to a double-peak structure in the isothermal DC magnetization curves of the composite, which is strongly dependent on the annealing time. This behavior suggests that the spheroidization kinetics can be obtained from M(H) curves.

Annealing effects on the electrical and superconducting properties of a Cu-15vol%Nb composite conductor

In this paper, annealing effects on the electrical and superconducting properties of a multifilamentary Cu-Nb composite were investigated. During annealing, noticeable changes in the microstructure take place, in special those related to recovery and recrystallization of copper and niobium followed by spheroidization and further coarsening of the Nb-filaments. Results show that spheroidization becomes significant only above 800/spl deg/C and, even after annealing at severe conditions, e.g., 1050/spl deg/C for 32 h, the continuity of the niobium-conducting path is partially preserved. The influence of these microstructural changes on the superconducting and normal properties of the multifilamentary Cu-15vol%Nb composite conductor is discussed.

Properties of high strength Cu-Nb conductor for pulsed magnet applications

Various tests have been undertaken to study the effects of annealing, testing temperatures and volume fraction of the Cu cladding on the properties of Cu-Nb conductors being developed for pulsed magnet applications. The results demonstrate that short time annealing used for insulation had no significant effect on the tensile property of Cu-Nb conductors. The cryogenic temperatures are beneficial to both the conductivity and mechanical properties of the conductors, especially the tensile strength of the Cu cladding. The wire-drawing fabrications showed that wires of 4 mm/spl times/6 mm cross-section-area with a significant volume fraction of Cu cladding could be obtained, leading to final tensile strengths of up to 1100 MPa at room temperature. The strength is increased by about 20% at 77 K. The 77 K-conductivity is about 4.5 times of the room temperature one. The strengthening mechanisms and resistivity variation of the Cu-Nb composite are discussed and it is argued that the distance between the Nb ribbons plays an important role in the variation of these properties.

Advanced (Nb,Ti)&lt;sub&gt;3&lt;/sub&gt;Sn Superconducting Wire with Highly Strengthened and Good Conductive CuNb Composite Stabilizer

We developed advanced (Nb,Ti) 3 Sn multifilamentary superconducting wires with I mm in diameter and 3 km in length, which were reinforced and stabilized with Cu-20wt.%Nb composite, CuNb/(Nb,Ti) 3 Sn. In comparison with practical (Nb,Ti) 3 Sn wires with conventional Cu stabilizer, Cu/(Nb,Ti) 3 Sn, it is found that a 0.2 % proof stress of 240 MPa for CuNb/(Nb,Ti) 3 Sn after heat-treatment at 670 °C for 200 h is twice as strong as that for Cu/(Nb,Ti) 3 Sn. CuNb composite has good thermal conductivity of 200 W/m/K at 4.2 K and low resistivity of 0.16 μΩ.cm at 4.2 K and 15 T. The minimum quench energy of 2.7 mJ at 80 % of the critical current at 14 T for CuNb/(Nb,Ti) 3 Sn is a factor of two smaller than for Cu/(Nb,Ti) 3 Sn, while the normal zone propagation velocity of 2 m/s remains the same.

Development of high strength Nb/sub 3/Sn conductors for high magnetic field applications

Multifilamentary (Nb,Ti)/sub 3/Sn superconducting wires with reinforcing stabilizer of CuNb composite, CuNb/(Nb/sub 1/Ti)/sub 3/Sn, were developed. Previously, we researched on the effect of reinforcement of CuNb composite as a CuNb/(Nb, Ti)/sub 3/ wire and its stability by investigating the MQE(minimum quench energy). A test coil was was fabricated using this reinforced wire without extra reinforcing material. The coil was produced by the "react and wind method", then electromagnetic force for the wire was applied by charging electric current in the coil up to 11T. The coil was energized successfully and the generated electromagnetic force for the wire reached 224 MPa at 136 A and 9 T without any degradation of test coil. These results proved that the bronze processed multifilamentary CuNb/(Nb,Ti)/sub 3/Sn wires have an excellent mechanical property, and a possibility to realize compact design of future superconducting magnet was confirmed.

Residual strain estimation in multifilamentary Nb/sub 3/Sn wires with CuNb reinforcement

The bronze processed multifilamentary Nb/sub 3/Sn superconducting wires with Cu-20 wt.% Nb composite reinforcement, which exhibited the high yield stress even after a typical heat treatment of about 700/spl deg/C for 8 days, have been fabricated. The strain effects on the critical current of the Nb/sub 3/Sn wires reinforced with CuNb composite were measured, and the estimation of residual strain was performed using a rule of mixtures. Good agreement is obtained between measured and calculated residual strain values. >

Highly strengthened multifilamentary (Nb,Ti)/sub 3/Sn wires stabilized with CuNb composite

Multifilamentary (Nb,Ti)/sub 3/Sn superconducting wires with reinforcing stabilizer of CuNb composite, CuNb/(Nb,Ti)/sub 3/Sn, were developed. The outstanding point is that the 0.2% proof stress at 4.2 K in CuNb/(Nb,Ti)/sub 3/Sn was extremely improved to 320 MPa even after the heat treatment at 670/spl deg/C for 192 hours, which is 1.8 times higher than that in ordinary Cu/(Nb,Ti)/sub 3/Sn. The overall J/sub c/ value in CuNb/(Nb,Ti)/sub 3/Sn was obtained to be 110 A/mm/sup 2/ at 16 T and 4.2 K. These results show that the bronze processed multifilamentary (Nb,Ti)/sub 3/Sn superconducting wire with CuNb reinforcing stabilizer is actually employable for a high field superconducting magnet.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electrical sliding friction and wear behavior of Cu-Nb in situ composites

The sliding friction and wear behavior of Cu-Nb in situ composites was studied in the presence of electrical load. Electrical sliding was performed between a Cu-Nb composite pin and a flat surface of a hardened tool steel disk in ambient atmosphere. The effects of Nb proportion, electrical current density, sliding speed, and Nb-filament orientation on the friction and wear behavior were investigated. It was found that the coefficient of friction decreased with increasing Nb proportion and Cu-20 vol.%Nb has the best wear resistance. Both the coefficient of friction and wear rate increased as a small electrical current was applied and then decreased as the current density increased. With increase in sliding speed, the coefficient of friction and wear on the Cu-Nb composite decreased. The composite with Nb-filaments perpendicular to sliding direction was found to have higher wear resistance than that of parallel orientation. The deformation layer and oxide film of the composite are much thicker at electrical sliding than nonelectrical sliding. The surface oxide played a key role in governing the sliding friction and wear behavior of the Cu-Nb composites under electrical current. >

Cold hydrostatic extrusion of powder metallurgy processed superconducting materials

Hydrostatically extruded multifilamentary composites of Cu-Nb, Cu-Nb with a central tin core and Nb-Al were directly drawn to fine wires without intermediate annealing. Uniform deformation was observed throughout the process. Cu-Nb composite wires were Sn plated for external diffusion. Overall critical current densities of better than 104 A/cm2 at 16 T were achieved for Nb3Sn-Cu composite wires with nominal areal reductions of 2000.

Superconducting Cu-Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Sn composites produced by cold extrusion of fine powders

Multifilamentary Cu-Nb composites were produced by cold P/M processing. Elementary powders of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\leq 40 \mu</tex> m diameter were first cold extruded and subsequently drawn to wires or ribbons. Cu-Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn composites were produced by electrochemical Sn plating of the Cu-Nb composite, followed by a reaction annealing at temperatures between 650 and 850°C. After cross-sectional reduction by a factor R = 500, a sample of the composition Cu-30%Nb (20 at%Sn) had a J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> value of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 12 T, which is comparable to the values obtained by other techniques. This cold P/M technique is adaptable to a wide range of superconducting systems and appears to be promising for industrial applications.

Effect of metallurgical history on 'J&amp;lt;inf&amp;gt;c&amp;lt;/inf&amp;gt;(5T)' in surface diffused multifilamentary Nb&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;Sn

Data are presented of critical current density 'J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (5T)' in a 5 T perpendicular magnetic field (and 10 T as well for selected samples) for multifilamentary Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn formed by Sn diffusion from a Cu-Nb composite's outer surface. The parameters varied are: composite diameter and Cu/Nb ratio; Sn percentage; filament diameter; reaction temperature and time; and different combinations of the above parameters. The composite diameter varied from 0.254 to 0.08 mm; Cu/Nb volume ratio from 1.7 to 3; volume percentage of Sn from 2% to 13.8%; average filament diameter from 2 microns to 7 microns. The reaction temperature was varied between 550° C to 795° C for different lengths of time, one to several thousand hours. A three-stage heat treatment was selected to formulate the basis for the reaction heat treatment map. The J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> (5T) varied from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to > 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> over the entire composite cross section (Cu-Sn, Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn, Nb). The optimum performances were 38.8 A in 0.127 mm diam 1.9/1 Cu/(Nb + Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn) composite at 5 T and 78 A in a 0.18 mm diam 3/1 CU/(Nb + Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn) at 5 T.