High Strength Cu-Nb Research Articles

Concept Design of 100-T Pulsed Magnet at the Wuhan National High Magnetic Field Center

A 100-T pulsed magnet with a bore size of 12 mm has been designed at the Wuhan National High Magnetic Field Center (WHMFC). This magnet consists of three coils. The inner coil will be wound from high-strength CuNb wire. The middle and the outer coils will be wound from copper wire. All the three coils will be reinforced with Zylon/epoxy composite. In order to increase the efficiency of the inner and the middle coils and reduce the coupling between them and the outer coil, the inner and the middle coils have a height of 400 mm, which is shorter than the 500-mm height of the outer coil. The inner and the middle coils are driven by 1.6- and 11-MJ capacitor banks, and the outer coil is driven by the combination of a 100-MJ/100-MW pulse generator and the 1000-V lead-acid battery system. At the peak field, the three coils contribute 47, 37, and 16 T, respectively.

Peculiarities of Structure and Texture of High-Strength Cu-Nb Composites

The evolution of structure of high-strength heavily deformed Cu-Nb composites processed by two different methods (melt-and-deform and bundle-and-deform) is briefly reviewed based on the authors’ (with their coauthors) original studies and the available publications. Specific features of their texture are considered. In particular, it is demonstrated that the ribbon-like Nb filaments possess not only the sharp fiber texture but the limited texture with components characteristic of cold-drawn Nb. The semi-coherent and amorphous state of Cu/Nb interfaces is discussed. The thermal stability of single-core and multi-core wires is considered. The effect of Zr and Ti doping on the structure and mechanical properties is demonstrated.

High Strength, High Conductivity Microcomposite Cu-Nb Wires with Cross Sections in the Range of 0.01–100 ${\hbox{mm}}^{2}$

Effect of anomalous increase of strength in fine heavily deformed Cu-Nb microcomposites is associated with nano-scaled microstructure. For these wires with cross sections in the range of 0.01-0.5 mm2 the high level of ultimate tensile strength (UTS) can be attained by straight deformation of initial in situ composite Cu-Nb ingot with logarithmic strain up to 11. For fabrication of high strength Cu-Nb wires with much larger cross sections up to 100 mm2 the ldquobundle-and-deformrdquo method should be used. In this case the final wire consists of bulk soft copper matrix with embedded high strength Cu-Nb microcomposite cores. The design features of high strength high conductivity Cu-Nb winding wires with extremely wide range of cross sections have been analyzed. Some peculiar features of deformation of non-uniform composites containing the nanostructured elements have been presented. Mechanical properties and conductivity of these wires have been reviewed. It was shown that UTS values from 900 MPa up to 1500 MPa and conductivity values in the wide range from 55% IACS to 85% IACS could be attained for Cu-Nb wires with different designs. The analysis has been done on the correlation of the mechanical and conducting properties with microstructure.

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.

Investigation on the CuNb "in-situ" microcomposites conductivity during the process of tensile testing

Resistivity of the high strength CuNb microcomposites have been investigated just in the process of tensile testing at the temperatures of 293 K and 77 K. Two processes determine the character resistivity-strain dependencies in microcomposites during elongation: the increase of the lattice defects concentration in copper which leads to the increase of resistivity; the decrease of compression of Cu lattice along the conductor axis which leads to decrease of resistivity. It was shown that the deformation of microcomposite wires at 77 K with following relaxation at 293 K led to the increase of ultimate tensile strength at room temperature. This increase could be as large as 3-6% depending on the level of strain applied at cryogenic temperature.

Electrical conductivity of high-strength Cu-Nb microcomposites

The conductivity of Cu-Nb microcomposites was studied as a function of the composition and the parameters of the microstructure varying with the degree of deformation. The effect of heat treatment on conductivity of Cu and composites is also considered. The conductivity of Cu-Nb composites with the reduction in area lnA/sub 0//A<4.9 is well described by the Landauer formula allowing for conductivity and the volume fraction of the components. The influence of the principal scattering mechanisms on conductivity of Cu in the composite is treated on the grounds of the experimental results obtained in this work and the analysis of the literary data. The linear correlation between strength and conductivity is obtained for the specimens heat treated at temperatures up to 600/spl deg/C. This correlation is violated, however, for the specimens subjected to heat treatment at temperatures above 600/spl deg/C.

Fibre composites combined with matched high strength Cu-Nb microfilament conductors for high performance pulsed magnets

High performance pulsed magnets for fields in excess of 70 T at a pulse duration of 15 ms are made by combining strong fibre composites with different types of conductor materials. These solenoids are optimized for constant stress throughout the volume. The best results are obtained when the modulus of elasticity of the conductor is matched to that of the fibre composite. To this end, a high strength Cu-Nb microfilament wire has been developed that matches the modulus of all S-glass fibre composite. >

Investigations of electrophysical and mechanical properties of high-strength Cu-Nb composites for pulse magnetic system winding wires

Melting by consumable electrode vacuum arc melting and casting processes for ingots of pseudo-alloy Cu-Nb with Nb content of up to 20% have been investigated. The effect of the degree of deformation of composites with different Nb content in the initial alloy on strength properties has been investigated. The process for manufacturing long-length composite conductors of rectangular cross-section 3 mm/spl times/2 mm of various designs has been developed. The application of the method of repeat assembling has been shown to allow the variation over a sufficiently wide range of the electrical and mechanical parameters of conductors with large cross section area. Thus, for wires with 6 mm in cross section, relative elongation values of 3-8%, ultimate tensile strength values of 0.7-1.1 GPa (at room temperature) and electroconductivity of 50-80% of IACS are achievable. The results of wire testing in high-field pulsed magnet windings are given.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>