Nano-fabrication is not new to the manufacturers of superconducting wires, in fact the dominant commercial superconductor, Nb-Ti, relies on a mechanically induced nano-structure for its remarkable properties. In this paper we show how these wires are manufactured so that their microstructure achieves the same scale as the superconducting vortex spacing. Recent attention on superconductors has emphasized the importance of the critical temperature, that being the temperature below which a material is superconduct

Niobium-Titanium Superconducting Wires: Nanostructures by Extrusion and Wire Drawing

The most widely used superconducting materials are based on Nb-Ti alloys with Ti contents ranging from 46-50 weight % Ti. These alloys of Nb and Ti have both high strength and ductility and can be processed to achieve high critical current densities that make them ideal candidates for magnet and applications. Nb-Ti based superconductors are commercially produced in long uniform lengths and cost significantly less to produce than other superconductors. The main drawbacks of this material are a low critical temperature, typically requiring cooling by liquid helium, and a low upper critical field which limits the applied field at which they can be used to below 12 T.

Abridged metallurgy of ductile alloy superconductors

A development program was initiated in order to develop strand with improved current density at 10.5 T and 1.9 K over existing SSCL designs. The two successful strand designs reported on here both utilized high Fe content Nb-47 wt%Ti alloys to improve the critical current density at high field by 7 %. At 10.5 T and 1.9 K, critical current densities exceeding 1450 A/mm/sup 2/ were obtained. In this paper we report detailed quantification of the macro- and micro-structures of these strands and correlate these with critical current density measurements at 1.9 K and 4.2 K. The high Fe content significantly reduced the /spl alpha/-Ti precipitate size. The linear relationship between critical current density and precipitate volume found is in agreement with earlier studies. High resolution FESEM electron backscatter contrast suggests a thin layer of high atomic number at grain boundaries.

/pdf/development-of-high-performance-nb-ti-fe-multifilamentary-3n9x0u2mq4.pdf

Development of high performance Nb-Ti(Fe) multifilamentary superconductor for the LHC insertion quadrupoles

Superconducting wires and cables are employed in many application fields, from NMR and MRI magnets, to high field magnets for test equipments, for nuclear fusion devices or for accelerators, where the low temperature superconductors Nb–Ti and Nb 3 Sn are typically used. The possibility to use liquid nitrogen or cryo-free cooling technologies for high temperature superconductors, such as Bi-2223 or REBCO tapes, is driving important developments in applications such as power transmission lines. Promising for very high field applications at low temperature are the properties of Bi-2212 round wires, still to reach a well assessed industrialization, and of REBCO tapes, that would require further cost reduction. MgB2 offers the potential of a low-cost superconductor that could be operated at reduced refrigeration costs due to its high T c . Interesting J c values have also been achieved in the novel Fe-based materials. The main requirements for superconducting wires and cables are summarized in the paper; the type of processing and the current development status is reported for each material.

Superconducting Wires and Cables: Materials and Processing

The sections in this article are


1
The Nb–Ti Alloy System

2
The Conventional Process

3
The APC Process

4
2 K Operation

Superconductors, Metallurgy of Ductile Alloys

The effect of iron addition on the ductility and superconducting properties of Niobium Titanium alloys has been explored. The conclusion of this study is that iron up to 2000 parts per million by weight is not deleterious to the fabricability of multifilamentary composites. The hardening rate of the iron rich alloy as filaments in a copper matrix was observed to be the same as for low iron versions of the same nominal composition. The development of the pinning microstructure was monitored and compared to the critical current properties of the wire. The results for multifilamentary wires are compared for heats with and without high iron contents. The results were reproduced in the production environment from a full scale ingot. The critical current density for the iron enriched material is elevated relative to the low iron material at high fields. The beneficial influence of iron on the superconducting properties is discussed in light of the microstructure. A designed experiment was conducted to explore the range over which the chemistry can be varied without affecting the behavior. The goal is to broaden the range of iron allowed in Niobium Titanium alloys for superconducting applications.

https://www.jstage.jst.go.jp/article/matertrans1989/37/3/37_3_519/_pdf

Improved Niobium 47 Weight % Titanium Composition by Iron Addition

Teledyne Wah Chang (TWC) has been a supplier of Nb based superconductors since 1960. An original producer of Nb50Zr, TWC switched to the production of Nb47Ti because of its superior ductility and the demand from customers. The material specified for all superconducting accelerator magnet projects since Fermilab’s Energy Doubler project and the Isabelle project at Brookhaven National Laboratory (BNL) has been High Homogeneity Nb 47wt.% Ti (HiHo NbTi). HiHo NbTi was developed at TWC as a response to customer demand after difficulties experienced in the development of wire for Fermilab and Isabelle. The presence of freckles in the alloy interfered with uniform alpha titanium precipitation and resulted in highly variable, low critical current density product1. Other methods of consolidation were attempted with good results but these had other problems such as niobium inclusions and chemical variation along the ingot length2. The process of consolidating niobium and Titanium to produce homogeneous Nb47Ti was refined at TWC in the early 1980’s to produce product with minimal freckling and consistent properties. Our HiHo NbTi has normal compositional variation from the dendritic structure formed as the material is cast and little or no evidence of the high titanium regions, commonly called freckles. The titanium has normal compositional fluctuations on the order of 1 weight percent. Freckles are small regions in which titanium content is 5 to 10 weight percent higher than the surrounding matrix. Freckles can be easily seen in radiographs of billet slices or seen in rod samples after proper polishing and etching. Verification of the HiHo grade is made by radiographic examination and comparison to standards of acceptability, but it is guaranteed by control of the process3.

Production and Quality Control of High Homogeneity Niobium 47 Weight Percent Titanium for Accelerator Applications

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Improved Niobium 47 Weight % Titanium Composition by Iron Addition

Production and Quality Control of High Homogeneity Niobium 47 Weight Percent Titanium for Accelerator Applications