JPS6262003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a Nb ₃ Sn-based superconducting wire.

As is well known, Nb ₃ Sn-based superconducting materials, which are intermetallic compounds, have superior superconducting properties compared to other intermetallic compound-based superconducting materials and alloy-based superconducting materials, so they are the most popular superconducting materials used in nuclear fusion reactors. It is seen as promising as a superconducting wire for magnets, etc. however
Nb ₃ Sn is extremely brittle in the state of an intermetallic compound;
Because of poor workability, especially ductility and malleability, it is difficult to process Nb ₃ Sn rods into wire rods of a desired diameter by general plastic working. Therefore, several proposals have been made as practical methods for manufacturing Nb ₃ Sn-based superconducting wires, one of which is a method called the bronze method. This bronze method
A large number of Nb core materials are embedded in a base of Sn alloy (bronze), and after being subjected to diameter reduction processing before the intermetallic compound Nb ₃ Sn is formed, heat treatment is performed to mutually combine Nb and Sn. It diffuses and generates Nb ₃ Sn. In this method, Cu acts as a carrier for Sn diffusion, so the heat treatment time required to generate Nb ₃ Sn is relatively short;
-Sn alloys can be industrially reduced in diameter and can be practically applied from these points of view. However, although this method allows diameter reduction as mentioned above, if a Cu-Sn alloy with a relatively high Sn concentration is used to efficiently generate Nb ₃ Sn, work hardening is likely to occur. There is a problem that the number of intermediate annealing operations during the diameter reduction process increases significantly, resulting in a significant decrease in work efficiency and a significant increase in manufacturing costs.

Therefore, the inventors of the present invention have already proposed an improved method of the bronze method in order to solve the above-mentioned problems. This method uses a Cu-Sn alloy with a low Sn concentration of less than 10% Sn as the Cu-Sn alloy.
After reducing the diameter of a composite wire made by embedding a large number of Nb core materials in a Sn alloy base in the same manner as described above, the surface of the composite wire (i.e., the Cu-Sn alloy surface) is Sn-plated, and then heat-treated. was applied to perform Sn diffusion and Nb ₃ Sn generation.
In this method, the Cu-Sn alloy base has a low Sn concentration, so it has good workability and the number of intermediate annealing can be reduced, and the outer Sn plating layer compensates for the lack of Sn in the Cu-Sn alloy. High Sn
This method has advantages such as being able to obtain Nb ₃ Sn production efficiency comparable to that of the bronze method using a Cu-Sn alloy with a high concentration.

By the way, the above-mentioned improved bronze method (bronze-
In the Sn plating method), Sn is diffused and Nb ₃ Sn
It is considered that heat treatment for producing Nb ₃ Sn is performed on the composite wire after diameter reduction and Sn plating at a temperature of 700 to 800°C for several tens to 100 hours. . There is no particular problem with this heat treatment method when the thickness of the Sn plating layer is thin, but in order to obtain good superconducting properties, a large amount of Nb ₃ Sn
When the thickness of the Sn plating layer is increased in order to produce , the problem with the above-mentioned heat treatment method is that extremely brittle parts that appear black appear on the wire surface after treatment. This black part is thought to be Nb ₃ Sn ₂ , which is another intermetallic compound that does not have superconducting properties, and this Nb ₃ Sn ₂ layer is formed by the Sn on the surface during the heat treatment mentioned above.
The diffusion of Sn from the plating layer into the Cu-Sn alloy base and the diffusion of Sn from the Cu-Sn alloy base to the Nb core material do not occur simultaneously, and the diffusion of Sn from the surface Sn plating layer is delayed. This seems to be because an Nb ₃ Sn ₂ layer, which has a faster formation rate than Nb ₃ Sn, is formed on the surface layer. This kind of black Nb ₃ Sn ₂
As mentioned above, this layer is extremely brittle and does not have superconducting properties, so if this layer is generated, it will deteriorate the mechanical properties of the superconducting wire, and the amount of Nb ₃ Sn layer produced will decrease, causing the superconducting properties of the superconducting wire to deteriorate. The problem of deterioration arises. On the other hand, after diameter reduction and Sn plating as described above, the Nb 3 Sn is not directly heat treated at the Nb ₃ Sn formation temperature, but is heat treated at around 400°C for several hours to several tens of hours before forming the Nb ₃ Sn. A method of applying heat treatment for several tens to 100 hours at the formation temperature (700 to 800 degrees Celsius) has also been attempted, but even with this method, a black Nb ₃ Sn ₂ layer is generated in the thick part of the Sn plating layer. The reality is that it is impossible to reliably prevent this from happening.

In view of the above circumstances, the inventors of the present invention developed a heat treatment method that prevents the formation of a black Nb ₃ Sn ₂ layer even when the Sn plating layer is thick in the aforementioned improved bronze method (bronze-Sn plating method). In other words, in order to obtain good superconducting properties
In order to develop a heat treatment method that can actually obtain good superconducting properties without compromising mechanical strength, even if the Sn plating layer is thickened in order to generate a large amount of Nb ₃ Sn, we conducted extensive experiments and experiments. After repeated research, they found the optimal heat treatment conditions and came up with this invention.

In other words, the method of this invention has low
A composite wire with a large number of Nb core materials embedded in a Cu-Sn alloy base with a Sn concentration is subjected to diameter reduction processing to form a Sn plating layer on the surface. First heat treatment is performed at a temperature of 100℃ or higher,
Next, a secondary heat treatment is performed at a temperature higher than the melting point of Sn and lower than the formation temperature of Nb ₃ Sn, and then
It is characterized by performing tertiary heat treatment at 700 to 800°C, which is the Nb ₃ Sn generation temperature.

The method of this invention will be explained in more detail below.

In the manufacturing method of this invention, first, as in the previously proposed method, a pure metal is added to the base of the Cu-Sn alloy.
A composite wire is made by embedding a large number of core materials made of Nb,
The composite wire is subjected to diameter reduction processing to obtain the desired wire diameter, and then Sn plating is applied to the surface. To explain the process up to this Sn plating, first, in order to make the above-mentioned composite wire, for example, as shown in Figure 1A, a hollow tube material 1 made of Cu-Sn alloy is injected with Nb powder, wire rod or rod. Insert the Nb core material 2 made of Nb alloy, etc., and then assemble multiple tubes and insert them into the tube material 3 made of Cu-Sn alloy as shown in Figure 1B. As shown in FIG. Diameter reduction processing such as processing, swaging processing, wire drawing/pulling processing, etc. may be performed. If the composite wire obtained in this way is subjected to diameter reduction processing until it finally reaches the desired wire diameter, an ultrafine wire-shaped Nb core is formed in the Cu-Sn alloy base 5 as shown in FIG. 1D. Since an ultrafine multifilamentary structure wire in which a large number of materials 2 are embedded is obtained, a Sn plating layer 6 of a desired thickness is then formed on its surface, that is, on the surface of the Cu-Sn alloy base 5, as shown in FIG. 1E. It may be formed by electroplating or the like. Furthermore, here
For Cu-Sn alloys, if the Sn content is 10% by weight or more, the workability deteriorates and work hardening tends to occur during diameter reduction processing, so the effect of reducing the number of intermediate annealing cannot be obtained. It is desirable that the Sn content be less than 10%, and if the Sn content is too low, even if Sn is replenished from the outer Sn plating layer, there will be no sufficient amount of Sn.
Since it becomes impossible to generate Nb ₃ Sn, it is desirable that the Sn content be at least 2% by weight.Furthermore, in order to improve processability and generate a sufficient amount of Nb ₃ Sn, the optimum range is 5 to 6%. It is about % by weight.

The ultrafine multifilamentary structural wire on which the Sn plating layer was formed as described above was subjected to heat treatment in three stages. The first primary heat treatment is carried out at the melting point of Sn, which is approximately
The primary heat treatment may be carried out at a temperature lower than 232°C and above 100°C, preferably between 150°C and 200°C, for 25 hours to 200 hours, and this primary heat treatment may be carried out in vacuum or in an inert gas atmosphere. Through this primary heat treatment, the Sn of the surface Sn plating layer and the Cu-Sn of the inner layer are separated.
Cu in the alloy matrix diffuses into each other, thereby forming a Cu--Sn alloy layer with a high Sn concentration on the surface. Next, the melting point of Sn (approximately 232℃) and Nb ₃ Sn
Secondary heat treatment is performed at a temperature lower than the production temperature (700 to 800°C), preferably about 350 to 500°C, more preferably about 400°C, for about 10 to 100 hours in the same atmosphere as described above. This secondary heat treatment improves the surface
Sn in the Cu-Sn alloy layer with a high Sn concentration diffuses into the internal base where the Sn concentration is not very high. Subsequently
At Nb ₃ Sn formation temperature, i.e. temperature of 700-800℃
Tertiary heat treatment for about 50 to 150 hours is performed in the same atmosphere as above. Through this tertiary heat treatment, Sn diffuses into the Nb core material and Nb ₃ Sn is generated.

In the above three-stage heat treatment process, the Sn plating layer on the surface is alloyed during the first heat treatment, so the surface does not melt and flow during the second heat treatment, and the Cu-Sn alloy base and the outer alloy layer (Sn The Sn concentration in the hot plating layer is made uniform, and the Sn concentration increases to the inside. Therefore, during the tertiary heat treatment at the Nb ₃ Sn formation temperature, Nb ₃ Sn is quickly generated, and at this time, not only Sn is diffused into the Nb core material but also Nb is diffused into the Cu-Sn alloy layer. At the time of diffusion, the Sn plating layer (Sn alone layer) on the surface with a high Sn concentration has already almost disappeared, so the formation of a Nb ₃ Sn ₂ layer on the surface is prevented.

As described above, Nb _{3 Sn is efficiently generated without forming a black brittle Nb 3 Sn 2} layer on the surface.

Next, examples and comparative examples of the present invention will be described.

Comparative Example 1 In a Cu-Sn alloy matrix containing 6% by weight of Sn,
Embedded with 1045 Nb core materials, outer diameter 0.2mmφ, one side
A composite wire is made by reducing the diameter of the Nb core material until it becomes approximately 2.8 μm, and a 3.0 μm
After forming the following plating layer, directly heat the plate at 740℃ for 100℃.
When subjected to heat treatment for a period of time, an Nb ₃ Sn-based superconducting wire could be obtained without forming a black phase of Nb ₃ Sn ₂ , and when its superconducting properties were measured,
Good characteristics were obtained with a critical current value I _C of 50 A in a magnetic field of 4.2 K and 4 T.

Comparative Example 2 When a 3.5 μm Sn plating layer was formed on the same composite wire as in Comparative Example 1 and directly heat treated at 740°C for 100 hours, a black and brittle Nb ₃ Sn ₂ layer was formed on the surface. was confirmed. Also, please set the temperature to 180℃ in advance.
When heat-treated for ×72 hours and then heat-treated at 740°C for 100 hours, and when heat-treated at 740°C for 100 hours after previously heat-treated at 400°C for 10 hours, the same black brittle Nb ₃ Sn ₂ layer has been generated.

Example After forming a 3.5 μm Sn plating layer on the same composite wire as in Comparative Example 1, it was heat treated at 180°C for 72 hours as a primary heat treatment, and then at 400°C for 8 hours as a secondary heat treatment.
740℃×100 as a third heat treatment.
After time heat treatment, a Nb ₃ Sn based superconducting wire was obtained without any black brittle parts appearing on the surface of the wire, and when its superconducting properties were measured, the critical current value in a magnetic field of 4.2 K and 4 T was obtained. but
70A, and it was confirmed that it has high characteristics.

As is clear from the above explanation, according to the manufacturing method of the present invention, even if the thickness of the Sn plating layer on the surface is increased in _the bronze _- Sn plating method, Nb _3Sn , and therefore, by thickening the Sn plating layer on the surface to generate a large amount of _Nb3Sn , it is possible to practically and stably manufacture superconducting wires with high superconducting properties. Moreover, various effects can be obtained, such as not deteriorating mechanical properties.

[Brief explanation of the drawing]

FIGS. 1A to 1E are schematic illustrations for step-by-step explanation of an example of the bronze-Cu plating method that is the premise of this invention. 2...Nb core material, 5...Cu-Sn alloy base, 6...
...Sn metal layer.

Claims (1)

[Claims] 1 A composite wire is made by embedding a large number of Nb core materials in a Cu-Sn alloy base, and after the composite wire is subjected to diameter reduction processing, Sn plating is applied to the surface of the Cu-Sn alloy base. administer,
After that, Sn is diffused to produce Nb ₃ Sn _.
In the method for manufacturing a superconducting wire, after the Sn plating, the temperature is lower than the melting point of Sn and 100%
First heat treatment is performed at a temperature of ℃ or higher, then second heat treatment is performed at a temperature higher than the melting point of Sn and lower than the Nb ₃ Sn formation temperature, and further heat treatment is performed at the Nb ₃ Sn formation temperature to generate Nb ₃ Sn. A method for manufacturing a Nb ₃ Sn-based superconducting wire, characterized by: