Strain scaling law for flux pinning in practical superconductors. Part 1: Basic relationship and application to Nb3Sn conductors

Cu‐Nb wire composites with 0.105, 0.148, and 0.182 volume fraction of Nb filaments were produced in situ and their mechanical properties measured as a function of filament size and interfilament spacing. The yield stress and the ultimate tensile strength increased with both niobium volume fraction and overall composite reduction. At room temperature, the ultimate tensile strength of the Cu–18.2 vol% Nb composite reduced by 99.999% in cross‐sectional area (100–200 A filament thickness) reached the value of 2230 MN/m2 (323 ksi) and further increased to 2850 MN/m2 (413 ksi) when measured at 77 °K. These values are higher by a factor of 4 than the values predicted by the rule of mixtures based on the highest reported strength of both niobium and copper. The composite strength is as high as that of the best copper whiskers and is shown to closely approach the theoretical strength of the material. The anomalous increase in strength despite the low volume fraction of reinforcing filaments suggests that the filam...

Anomalous increase in strength of in situ formed Cu‐Nb multifilamentary composites

Characterization of the strength and microstructure of heavily cold worked CuNb composites

A combined resistivity transmission electron microscopy (TEM) study has been done on heavily drawn Cu‐20 vol % Nb alloys (so‐called in situ alloys). The results show that electron scattering at Cu‐Nb interfaces makes the major contribution to resistivity in heavily drawn wire. The dislocation contribution is small and constant at deformation strains greater than around 4, apparently as a result of dynamic recovery/recrystallization of the Cu matrix which occurs during room‐temperature drawing. Results of this study and other recent TEM dislocation studies indicate that the dislocation density in heavily drawn Cu‐20 vol % Nb material does not exceed 1011 cm−2. It is demonstrated here that the 1013‐ cm−2 dislocation density predicted by the resistivity study of Karasek and Bevk [J. Appl. Phys. 52, 1370 (1981)] is high because the interface scattering contribution is more strongly reduced by coarsening than they assumed. It is shown that resistivity measurements provide a means of evaluating an average Cu ch...

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1123&context=mse_pubs

The resistivity and microstructure of heavily drawn Cu‐Nb alloys

A wide range of surface modification processes has been developed over the past decades. Beside the well-established processes such as shot peening, there are other emerging surface modification processes such as machine hammer peening with a potential of applications that still needs to be evaluated. Therefore, all surface modification processes using guided tools with periodic or continuous contact to the workpiece are compared in this paper. After a classification of the processes, the paper presents a systematic description by comparing the different technologies and it explains the proposed standardized nomenclature. It identifies the relevant physical mechanisms of the surface modifications processes and it compares the influences on surface roughness, residual stresses, work hardening and microstructure. One section is dedicated to the need of an accompanying quality assurance. Furthermore, the capabilities of different process simulation approaches are analyzed with respect to process mechanisms and the resulting surface layer characteristics. The service performance such as fatigue life, corrosion resistance, friction and wear are discussed based on best practice results. Finally, the paper discusses the actual and potential applications of surface modification processes: surface strengthening, post welding treatments, smoothing of tools and molds as well as surface structuring and embedding of coating materials.

Surface modification by machine hammer peening and burnishing

A method and apparatus for automatically sensing the configuration of a damaged surface area and wherein the apparatus is provided with an arc gouging tool, a welding tool, and a grinding tool to gouge damaged areas and fill them with weld material to at least the surface profile of the surface in the working environment and to grind the filled areas flush with the surface of the working environment. A track is bent to a profile enabling the apparatus to work without any collision with its environment while keeping full access to the work area. The geometry of the track is generally unknown to the control circuit of the robot. A motor-actuated robot member is connected to the track and is displaceable on the track by a motorized element. A working arm is displaceably coupled to the robot member and has one or more working tools connected thereto. A control circuit displaces the robot and operates the working arm and tool. The working arm has a sensor connected thereto with a probe to sense parameters and to feed information data of the X, Y and Z coordinates to the control circuit to determine the geometry of the surface of the working environment and contour of areas in the working environment requiring a work procedure to be effected by the one or more working tools.

Method and apparatus for automatically sensing the configuration of a surface area and effecting a work function thereon

High‐field properties of improved in situ Cu‐Sn‐Nb alloys are presented. Values of critical current densities of 104 A/cm2 and a resistivity of less than 2×10−13 Ω cm are observed at 12 T. Critical current densities for various in situ alloys are presented for fields to 18 T.

High‐field critical current in in situ multifilamentary Cu‐Sn‐Nb alloys

Superconductivity in copper‐rich niobium alloys has been investigated. A controlled cooling technique was developed to provide homogeneous distributions of niobium in the copper. Two distinct microstructures were observed depending on the cooling rate. For low cooling rates (<700 °C/sec) and low niobium concentrations a subgrain structure of niobium is evident. These samples are superconducting with low critical current density (<10 A/cm2). For faster cooling rates (≳1000 °C/sec) the subgrain structure is eliminated and a critical concentration for the observation of superconductivity is observed experimentally at 10–12 wt% Nb (7–9 at.% Nb). The experimentally determined critical concentration is explained by a model based on site percolation theory modified for the shape of the precipitate. The model suggests that continuous niobium chains in the copper matrix lead to the observed superconducting properties. The proximity effect, previously suggested as the basis for superconductivity in these alloys, ap...

Origin of superconductivity in copper niobium alloys

’’In situ’’ multifilamentary Nb3Sn wires with improved high‐field properties are reported. An overall critical current density greater than 104 A/cm3 is achieved at 14 T for a Cu–36 wt%–Nb–20 wt% Sn material. The results are comparable to the best reported commercial multifilamentary Nb3Sn materials.

Improvements of ’’insitu’’ multifilamentary Nb3Sn superconducting wires

The mechanical properties of in situ Cu–36 wt% Nb–x wt% Sn superconducting wires are presented where 5<x<20 wt% Sn. For high x, no degradation of critical current Jc is observed for stresses σ up to 700 MPa (∼100 ksi) and a maximum Jc occurs at σ≃450 MPa. Strains of ∼0.6–0.9% are measured at 300 and 77 K for 450 MPa, and ∼1.5–2% for 700 MPa. Cyclic stress data are consistent with a prestress model for composite materials.

J. L. Fihey

Papers

Method and apparatus for automatically sensing the configuration of a surface area and effecting a work function thereon

High‐field critical current in in situ multifilamentary Cu‐Sn‐Nb alloys

Origin of superconductivity in copper niobium alloys

Improvements of ’’insitu’’ multifilamentary Nb3Sn superconducting wires

Mechanical properties of in situ multifilamentary Nb3Sn superconducting wires