Cu-Nb Composite Wires Research Articles

Influence of Nb Morphology on the Structure and Properties of High Strength and High Conductivity Cu-Nb Composite Wires

Influence of Nb Morphology on the Structure and Properties of High Strength and High Conductivity Cu-Nb Composite Wires

Multiscale modeling of the elasto-plastic behavior of architectured and nanostructured Cu-Nb composite wires and comparison with neutron diffraction experiments

Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (∼100T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu-Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured, and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shape along the wire axis. This paper presents a comprehensive study of the effective elasto-plastic behavior of this composite material by using two different approaches to model the microstructural features: full-field finite elements and mean-field modeling. As the material exhibits several characteristic scales, an original hierarchical strategy is proposed based on iterative scale transition steps from the nanometric grain scale to the millimetric macro-scale. The best modeling strategy is selected to estimate reliably the effective elasto-plastic behavior of Cu-Nb wires with minimum computational time. Finally, for the first time, the models are confronted to tensile tests and in-situ neutron diffraction experimental data with a good agreement.

Multiscale modeling of the anisotropic electrical conductivity of architectured and nanostructured Cu-Nb composite wires and experimental comparison

Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (> 90T) as they combine both high electrical conductivity and high strength. Multi-scaled Cu-Nb wires can be fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured and nanostructured microstructure providing a unique set of properties. This work presents a comprehensive multiscale study to predict the anisotropic effective electrical conductivity based on material nanostructure and architecture. Two homogenization methods are applied: a mean-field theory and a full-field approach. The size effect associated with the microstructure refinement is taken into account in the definition of the conductivity of each component in the composites. The multiscale character of the material is then accounted for through an iterative process. Both methods show excellent agreement with each other. The results are further compared, for the first time, with experimental data obtained by the four-point probe technique, and also show excellent agreement. Finally, the qualitative and quantitative understanding provided by these models demonstrates that the microstructure of Cu-Nb wires has a significant effect on the electrical conductivity.

Evolution of Radial Texture and Microhardness of Cu-Nb Composite Wires

Evolution of Radial Texture and Microhardness of Cu-Nb Composite Wires

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.

The Influence of Annealing on the Microstructure and Electrical Resistivity of Jelly-Rolled Cu-Nb Composite Wires

In this paper, the annealing effects on the microstructure and electrical resistivity of jelly-rolled Cu-x% vol. Nb (x=25, 33, 50, and 63) composite wires were investigated. During annealing, noticeable changes take place in the microstructure, including recovery and recrystallization of copper and niobium, followed by spheroidization and further coalescence of niobium filaments. With increasing annealing temperature, the diffusion-controlled coalescence of niobium filaments is enhanced due to their proximity. The behavior of the electrical resistivity in the normal state of the Cu-Nb composite shows a noticeable change at a specific value of temperature in the range between 50K and 70 K. This temperature varies with the niobium volume fraction. Such a behavior is discussed in terms of the decrease of the amount of Cu-Nb interfaces promoted by coarsening and by electron scattering effects at these interfaces.

The influence of annealing on the microstructure and electrical resistivity of jelly-rolled Cu-Nb composite wires

In this paper, the annealing effects on the microstructure and electrical resistivity of jelly-rolled Cu-x% vol. Nb (x=25, 33, 50, and 63) composite wires were investigated. During annealing, noticeable changes take place in the microstructure, including recovery and recrystallization of copper and niobium, followed by spheroidization and further coalescence of niobium filaments. With increasing annealing temperature, the diffusion-controlled coalescence of niobium filaments is enhanced due to their proximity. The behavior of the electrical resistivity in the normal state of the Cu-Nb composite shows a noticeable change at a specific value of temperature in the range between 50K and 70 K. This temperature varies with the niobium volume fraction. Such a behavior is discussed in terms of the decrease of the amount of Cu-Nb interfaces promoted by coarsening and by electron scattering effects at these interfaces.

512 in-situ 法 Cu-Nb 複合線材の極低温疲労強度

512 in-situ 法 Cu-Nb 複合線材の極低温疲労強度

304 in-situ 法 Cu-Nb 複合線材の疲労特性

304 in-situ 法 Cu-Nb 複合線材の疲労特性

Some studies on Zr- and Ti-doped multifilamentary Cu-Nb composite wires prepared by in situ techniques

Abstract Multifilamentary superconducting wires of Cu70Nb30 and Cu70Nb29X1 (where X = Zr and Ti) have been fabricated using the in situ technique. A small decrease in the transition temperature and an increase in both the critical current density and the upper critical field is observed for both dopants. For Zr-doped wires of diameter 0.20 mm, the critical current density is almost independent of field up to 1.5 T, after which there is a sharp drop around μ0 H c2. The change in the magnitude and the position of the maximum pinning force have been studied for Zr-doped wires of different diameters.

Flux pinning and superconductivity in in situ prepared Al- and Zn-doped Cu-Nb composite wires

The effects of Al and Zn on the critical current density, upper critical field and pinning force of in situ prepared Cu-Nb wires have been studied. Doping this system by 1 wt% of these impurities results in a change in critical current density and pinning force. The critical current density increases at lower fields for both additives but decreases at high fields. The upper critical field HC2 shows a decrease for both additives. We have modified the Kramer flux pinning law for these two additives. It is found that the value of n, which is a constant in the scaling law of Fietz and Webb with a value of 2.5, varies in the case of these additives and does not remain constant.

Reinforcing stabilizers for large scale and/or high field superconducting magnets

It is desired to develop a high-strength high-conductivity material for reinforcing composite superconductors which will be employed in large-scale and/or high-field superconducting magnets in emerging large-scale projects such as fusion magnets, SMES magnets, hybrid magnets, and so on. A review of our decade long study of reinforcing stabilizers, and recent results on CuNb composite wires and high-purity Ta wires are reported. Mechanical and electrical properties are reported for CaO crucible melted and drawn CuNb composite wires and for heavily cold worked high-purity Ta wires. Tensile tests at room temperature show a yield stress of about 556 MPa even after annealing at 750°C for 1 h for CuNb composite wires and 0.2% proof stress of about 666 MPa for the Ta wires. Resistivity at 4.2 K is about 0.25 μ ω cm for CuNb wires and about 0.40 μω cm for the Ta wires, respectively at a field of 15 T. It is concluded that the CuNb composite wires, the high-purity Ta wires and the Al 2O 3 dispersion-strengthened copper are suitable as a reinforcing stabilizer for conductors of large-scale and/or high-field superconducting magnets.

高強度・超伝導率Ｃｕ‐Ｎｂ複合線材

Cu-Nb composite wires prepared in the first step of the in-situ process for the Nb3Sn superconducting wires are considered as composite materials for the conductor of water-cooled coils and for reinforcing stabilizer of high field superconductor. Mechanical and electrical properties are studied for several samples prepared by induction melting in a CaO crucible and drawing. These composites have large yield stress above 50kg/mm2 even after annealing at 750°C for 1 hour. Moreover annealed wires show magnetoresistance of about 0.25μΩcm at high field of 15T, comparable with that of Al2O3 dispersion strengthened copper (K. Noto et al.: Proc. MT-9 (1986) 700). Therefore, it is found that Cu-Nb composite wires are applicable not only to normal conductors in high field, but also to reinforcing stabilizers for large-scale and/or high-field superconducting wires.

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.