JPH0317332B2 - - Google Patents

Description

Detailed Description of the Invention The present invention improves workability and strong magnetic field characteristics by adding one or more selected from group a elements titanium, zirconium, and hafnium.
This invention relates to a method for manufacturing Nb ₃ Sn superconducting wire. Superconducting wires are used as winding materials for electromagnets for generating strong magnetic fields because they allow large currents to flow without consuming power and maintain their superconducting state even in strong magnetic fields. Currently, the most widely used wire rod is Nb-Ti alloy wire rod, but the magnetic field generated by this alloy wire rod is limited to 9 Tesla (90,000 Gauss), and if a stronger magnetic field than this is required. For this purpose, it is necessary to use a compound-based superconductor with a high critical magnetic field. However, compound superconductors lack plasticity, which has been a major obstacle to their practical application. In recent years, methods using diffusion such as surface diffusion method and composite processing method have been invented, and Nb ₃ Sn (critical temperature: approx. 18K, critical magnetic field: approx. 21
Tesla) and V ₃ Ga (critical temperature: approximately 15 K, critical magnetic field: approximately 22 Tesla) compound superconducting wires have come into practical use. In the surface diffusion method, for example, in the case of a Nb ₃ Sn compound wire, after the base niobium tape is passed continuously through a molten tin bath, niobium and tin are caused to undergo a diffusion reaction through heat treatment to form Nb ₃ Sn on the base tape surface. This is a method of generating a compound layer. For example, the composite processing method is
In the case of Nb ₃ Sn compounds, a niobium base and a copper-tin alloy base are compositely integrated and processed into a wire, tape, or tube shape, and then the tin and niobium base in the copper-alloy base are selectively separated by heat treatment. In this method, a Nb ₃ Sn compound layer is formed around a niobium substrate by a diffusion reaction. Using this composite processing method, it is possible to manufacture an ultrafine multifilamentary wire in which a large number of thin niobium cores are embedded in a copper-tin alloy substrate, and stable superconducting properties can be obtained against rapid magnetic field changes. In addition,
A V ₃ Ga ultrafine multifilamentary wire can also be produced in a similar manner. Nb ₃ Sn or V ₃ Ga compound wires produced by such surface diffusion methods and composite processing methods are already being used as small-sized strong magnetic field magnets for research on physical properties. On the other hand, the development of large-scale strong magnetic field magnets for use in nuclear fusion reactors, high-energy accelerators, superconducting generators, etc. is actively progressing, and the superconducting wire used in these has a large criticality in the strong magnetic field region of 15 Tesla or more. There is an urgent need to commercialize compound-based ultrafine multifilamentary wires that carry current and are stable against rapid changes in magnetic fields. However, the critical current of the conventional Nb ₃ Sn compound wire made from a composite of a niobium base and a copper-tin alloy base decreases rapidly in a magnetic field of about 12 Tesla or more; It has been difficult to create superconducting magnets that can generate a magnetic field. On the other hand, V ₃ Ga compound wire has superior strong magnetic field characteristics compared to Nb ₃ Sn compound wire, but the material is more expensive than Nb ₃ Sn, so it is not advantageous for large equipment that uses a large amount of wire. I can't say that.
Therefore, it is better to use a Nb ₃ Sn compound wire with improved strong magnetic field characteristics by adding a small amount of alloying elements. From this point of view, a method of adding titanium, zirconium, or hafnium, which are Group A elements, to a niobium substrate or a copper-tin alloy substrate is attracting attention. A method for manufacturing Nb ₃ Sn compound wires with significantly improved superconducting properties in strong magnetic fields has been proposed. (Special application No. 128551, 1983,
(Special Application No. 121479/1983). In these methods, group a elements added to the niobium substrate or copper-tin alloy substrate promote the generation of nuclear dispersion of Nb ₃ Sn compounds, and some of them are
It forms a solid solution within the Nb ₃ Sn compound layer and has the effect of enhancing superconducting properties in strong magnetic fields. However, in the production of these, group A elements are added to the niobium base or copper-tin alloy base, so the plastic workability is not good, and the
Intermediate annealing is required for every % cross-sectional reduction ratio, and the number of annealing steps is extremely large in order to produce a practical long wire, which has the disadvantage of significantly increasing manufacturing costs. Furthermore, in the copper-tin alloy substrate used in conventional composite processing methods, the amount of solid solution of tin is limited in order to maintain plastic workability, and as a result, the amount of Nb ₃ Sn compounds that diffuse and form is small per the total cross-sectional area of the wire, which reduces the critical current capacity. There was a difficulty in making large wire rods. Nb ₃ Sn produced by a composite processing method of a copper alloy base, a tin base, and a niobium base in which Group A elements are added to pure copper.
The method for manufacturing compound wire (Patent Application No. 57-25981) is
Each substrate has relatively good plastic workability, and since it contains group a elements, it has excellent strong magnetic field critical current characteristics, which solves the above-mentioned problems to some extent. However, when producing practical-scale ultra-fine multifilamentary wires that require high-strength processing using this manufacturing method, in order to uniformly draw the wire to the final wire diameter without intermediate annealing, it is necessary to reduce the content of group A elements in terms of workability. It is necessary to use an extremely small amount of copper alloy. As a result, the content of group a elements in the Nb ₃ Sn compound produced also decreases, resulting in an unfavorable result of deterioration of the strong magnetic field critical current characteristics. The present invention improves superconducting properties in a strong magnetic field by adding titanium, zirconium, or hafnium, which are Group A elements, to a tin substrate, which has extremely excellent workability, instead of a copper substrate.
The purpose is to manufacture Nb ₃ Sn superconducting wire with a large critical current capacity. The present invention provides one or two selected from group a elements titanium, zirconium, and hafnium.
At least one of a tin alloy base, a copper base, and a niobium base containing at least one of the following substances is charged with another base powder, or either of the tin alloy base and the niobium base The method is characterized in that another base powder is charged into one tube, processed into a predetermined shape, and then subjected to diffusion heat treatment to generate a Nb ₃ Sn compound containing group a elements around the niobium base. Further, the tin alloy substrate may contain a small amount of copper in addition to the above group a elements. The amount of titanium, zirconium, or hafnium to be added to the tin substrate is 0.1 atomic % or more in total of one or more types in order to obtain excellent superconducting properties, and to maintain good workability of the tin alloy substrate. It must be within the range of 15 atomic percent or less. Preferably it is in the range of 1 to 10 atom%. Copper contained in the copper substrate or the tin alloy substrate assists in the diffusion of tin and group a elements during diffusion heat treatment, and is effective in obtaining excellent superconducting properties. The amount of copper added to the tin alloy base is set to be 2 atomic % or more, which is effective for increasing the diffusion rate of tin, and 30 atomic % or less, in order to maintain good workability of the tin alloy base. The heat treatment performed after processing into the specified shape is
The temperature must be above 400°C to generate Nb ₃ Sn, and below 950°C to obtain excellent superconducting properties. Part or all of each substrate may be in the form of powder, and the same substrate may be used as a tube at the same time. In the present invention, a composite of powder and tube is used, which is composed of a tin alloy base with extremely excellent workability and a niobium base (and copper base) with good workability. Compared to the manufacturing method in which it is contained in the base material, wire drawing becomes much easier.
Even practical-scale ultra-fine multifilamentary wires that require high-strength processing can be processed into thin wires without intermediate annealing, and the cost of wire production is significantly reduced. Group A elements such as titanium, zirconium, or hafnium added to the tin alloy substrate promote the formation of Nb ₃ Sn compounds, and some of the added elements dissolve in the Nb ₃ Sn compounds, thereby increasing the superconducting critical magnetic field. It also significantly increases the critical current in strong magnetic fields above 15 Tesla. On the other hand, in the heat treatment process, a sufficient amount of tin can be supplied by diffusion from inside the composite, so a wire rod with a large critical current capacity can be produced due to effects such as obtaining a large amount of Nb ₃ Sn compound phase. As a result, it is possible to improve the performance of various superconductor-based devices and reduce manufacturing and cooling costs through miniaturization. In addition, since the wire produced by the present invention is in the form of an ultra-fine multicore wire, its superconductivity is stably maintained even in the face of rapid magnetic field changes, which is an excellent feature that significantly improves the safety and reliability of equipment used in strong magnetic fields. It has a good effect. Next, the present invention will be specifically demonstrated by showing examples. Examples 1-2 As shown in Figure 1, copper powder (3), niobium powder (2) and tin-5 were placed in a niobium tube (2) with an outer diameter of 8 mm and an inner diameter of 6 mm.
A composite was prepared in which atomic % titanium powder (1) or tin-5 atomic % hafnium powder (1) was filled in a ratio of 5:3:1. The powders used were each approximately 100 μm in size. This composite was processed into a long length of 0.4 mgφ by swaging and wire drawing without intermediate annealing. Next, after being sealed in a quartz tube in an argon atmosphere, diffusion heat treatment was performed at 650°C for 50 hours.
Table 1 shows the measurement results of the critical current (Ic) and critical temperature (Tc) of the superconducting properties of the sample prepared in this way. Table 1 also shows the measurement results of a wire rod (Comparative Example 1) produced in a similar manner to tin in which group a elements were not added. As is clear from the measurement results, compared to Comparative Example 1, the wire of this example has significantly improved superconducting characteristics Ic and Tc. 【table】

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the cross-sectional shape of the composite shown in the example. In the figure, 1 indicates a tin alloy containing a group A element or a tin alloy substrate containing a group A element and copper, 2 indicates a niobium substrate, and 3 indicates a copper substrate.

Claims (1)

[Claims] 1. One or more selected from titanium, zirconium, and hafnium in total of 0.1 to 15
atomic percent of the tin alloy base, the copper base, and the niobium base. After charging other base powder into the tube and processing it into a wire, tape, or tube, a Nb ₃ Sn compound containing titanium, zirconium, or hafnium is formed around the niobium base by diffusion heat treatment at 400 to 950℃. A method for producing a Nb ₃ Sn superconducting wire characterized by generating a phase. 2. A tin alloy containing a total of 0.1 to 15 atomic % of one or more selected from titanium, zirconium, and hafnium as a tin alloy substrate, and further containing 2 to 30 atomic % of copper is used. The manufacturing method according to claim 1.