JPS6152226B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a simple and economical method for manufacturing a Nb ₃ Sn-based superconducting material that has both excellent flexibility and a high critical current value. In recent years, superconducting magnets have been applied to nuclear fusion devices and large accelerators for nuclear research, and as they are required to be used in high magnetic fields, they generally have higher critical current values than alloy systems. Compound-based superconducting materials that exhibit The bottleneck in the practical use of compound-based superconducting materials is firstly that manufacturing is complicated, and various manufacturing methods such as surface diffusion method, gas phase reduction method, plasma spray method, and composite processing method have been proposed. Although attempts have been made, they have all been complicated and cumbersome. Furthermore, the second bottleneck is that they have poor flexibility, which is a characteristic characteristic of compounds. In view of the above-mentioned circumstances, the inventors have previously proposed a method for manufacturing a highly flexible Nb ₃ Sn-based superelectric material in an extremely simple and economical manner, and an application has already been filed for this method as Japanese Patent Application No. 10537/1983. The present invention relates to an improvement on the above-mentioned invention, and aims to provide a method for producing a Nb ₃ Sn-based superconducting material in which the critical current value Jc can be further increased by adding Ga as a third element. The present invention will be explained in detail below. First, a Cu-Nb-Ga alloy consisting of 15 to 70% by weight of Nb and 0.2 to 8% by weight of Ga is melted and cast. This results in
Finely crystallized Nb dendrites in the Cu matrix. In this case, in order to obtain a high critical current value Jc, it is desirable to perform homogeneous and fine crystallization so that the average distance between the crystallized Nb is 6 μm or less. However, if the amount of Nb is less than 15%, it is too dilute and does not effectively improve the Jc value, so it is excluded. Moreover, if it exceeds 70%, the melting point will rise rapidly, and it will be extremely difficult to obtain the homogeneous and fine casting structure necessary to improve Jc properties.The volume ratio of copper, which will form the upper matrix, will be too small, resulting in the so-called stabilizing effect. is excluded because it is not retained.
It is thought that some of Ga is dissolved in Cu and some in Nb, but the amount is 0.2%.
If it is less than that, it will not contribute to the increase in Jc characteristics. Furthermore, if the amount is 8% or more, the workability deteriorates rapidly, and it becomes extremely difficult to process the Nb phase into a filament phase, which will be described later, so it is excluded. The composition range of the present invention is Nb15-70%Ga0.2
A Cu--Nb--Ga alloy consisting of ~8% can be conventionally melted in a conventional arc melting furnace or beam melting furnace. In this case, in order to obtain the Nb dendrite phase having an average separation distance of 6 μ or less as described above, it can be achieved by rapid cooling or by adding a small amount of a certain element. The material melted and cast as described above is subjected to drawing processing, and the crystallized Nb phase is drawn together with the base material to form a Nb filament. Therefore, it is desirable that the degree of processing in this case is 99.5% or more. In other words, if the working degree is less than this, no significant increase in the Jc value is observed. The increase in the Jc value due to such a high degree of processing is probably related to the average separation distance of the dendrites, which are generated by the diffusion process described below.
This is thought to be because the proximity effect of the Nb ₃ Sn filament comes into play. If the requirements in the field in which it will be applied are severe, the degree of processing will inevitably have to be increased. However, the remarkable feature of the present invention that should be noted here is that such high processing is performed in the form of a Cu-Nb-Ga alloy with extremely good workability, and after the Nb ₃ Sn formation described below is performed. The point is that stretching is no longer necessary. Conventionally, it was necessary to perform heat treatment in the middle of the process, so Nb ₃ Sn was produced and then stretched, which of course resulted in stretching a compound that was difficult to process, resulting in great difficulties. However, the present invention can be said to be revolutionary in that it makes this point unnecessary. The Cu-Nb-Ga alloy material drawn as described above reacts with the internal Nb filament.
An amount of Sn that can generate Nb ₃ Sn is plated.
In reality, when plotting the relationship between the amount of Sn plating and the critical current value Jc, Jc gradually increases until the amount of Sn plating reaches a predetermined amount, and when it exceeds the predetermined amount,
There is a phenomenon that Jc is already saturated. This saturated vicinity is considered to be the optimal amount of Sn. This Sn plating is then subjected to diffusion heat treatment and reacts with the Nb filament inside, converting the Nb filament into a Nb ₃ Sn filament and converting the entire wire into a superconducting material. It is desirable to perform preliminary heat treatment for about 20 to 100 hours at a lower temperature range of 240 to 500° C. before performing the diffusion treatment. This preliminary treatment allows the plated Sn to conform to the base metal, and during the subsequent diffusion treatment at high temperatures of 500 to 700℃, the molten Sn on the surface drips and becomes eccentric. This pretreatment prevents the diffusion of It is better to process it. The final diffusion treatment to form Nb filaments and Nb ₃ Sn filaments is carried out at 500-700°C. Below 500°C, the temperature is too low, diffusion is extremely poor, and no increase in Jc value is observed, so it is excluded. On the other hand, if the temperature is too high, above 700°C, the plating layer may become unstable and inhomogeneous, the shape of the filament may become unstable, or even the formation of
It is excluded because crystal growth of Nb ₃ Sn occurs and the so-called pinning effect is inhibited, resulting in a decrease in the Jc value. Through the above steps, the production of the Nb ₃ Sn-based superconducting material according to the present invention is achieved, but when looking at the process, it is simply a continuation of the usual processes of melting, casting, plating, and diffusion, which are commonly used in everyday metal materials. First, it does not involve any special steps, and it will be understood that its simplicity and economic efficiency is not comparable to the conventional method described above. Moreover, it is clear that by using the manufacturing method according to the present invention, it is possible to obtain a material that has sufficient general characteristics as a Nb ₃ Sn-based superconducting material, and it is possible to obtain a material that has sufficient general characteristics as a Nb 3 Sn-based superconducting material, and that by adding Ga, it is possible to obtain a material that has even better characteristics. It turned out that this is possible. Next, these will be explained in detail using examples. Example 1 Table 1 shows the composition of the test materials used in the examples of the present invention. However, Sn was determined by reducing the weight of Sn used for electroplating, and Ga was the nominal value.

[Table] For each sample, 150 g of Cu-Nb and Cu-Nb-Ga alloys were first arc melted and cooled in a water-cooled crucible to form a cast material of 15 mm square x 80 mm length. Then 0.24 by swaging and drawing
A wire rod of mmφ was drawn and then plated with Sn to have the Sn composition shown in Table 1. After that, each plated sample was vacuum sealed in a quartz tube and heated to 400°C for 24 hours.
After pretreatment, the sample was subjected to diffusion treatment at 600°C for 96 hours, and an external magnetic field of 9 Tesla was applied perpendicularly to the sample to measure the critical current value Jc. Figure 1 shows the results plotted in terms of Nb% and Jc value. It can be seen that the Jc value of the sample with Ga addition is clearly improved compared to the case of the same composition without the addition. As can be seen from Figure 1, when Nb is less than 15%, Jc becomes less than 3 × 10 ⁴ regardless of the presence or absence of Ga, which is a value that can be easily achieved even with alloy-based superconducting materials, and it cannot be used as a compound-based material. It is excluded because there is no reason for its existence. Figure 2 shows sample No. 9 at 400°C x 24h.
450, 500 for those with and without pretreatment,
These are the results of measuring and plotting Jc on a 9 Tesla after diffusion treatment at temperatures of 550, 600, 650, 700, and 750°C. It can be seen that the Jc value clearly improves by preprocessing. In addition, as shown in Figure 2, the temperature of the diffusion treatment is also as described above.
It can be seen that a temperature between 500 and 700°C is suitable. Such pretreatment is ineffective at temperatures below 240°C, partly due to the relationship with the melting point of Sn, and at temperatures above 500°C, the temperature is too high, causing the Sn plating layer to sag and becoming heterogeneous, causing negative effects. Also, regarding the time, less than 20 hours is too short.
Even if you do it for a long time (more than 100 hours), the effect will be saturated and there will be no opinion. Such preprocessing can be incorporated as needed, and perhaps
It is thought that it contributes to the adaptation and stabilization of the Sn plating layer, and then acts effectively for diffusion. Example 2 As shown in Table 2, Ga was applied to a sample with a nominal Nb value of 25%.
We prepared samples with various amounts of
After stretching to mmφ, Sn plating is applied to 7% Sn.
This was pretreated at 400°C for 24 hours, and then diffused at 600°C for 150 hours, and then the Jc value was measured using 9Tesla. Figure 3 plots the results.
From FIG. 3, it can be seen that the effect of Ga addition is apparent when the concentration of Ga exceeds 0.2%, and it becomes almost saturated at 4%.

【table】

[Table] This trend is almost the same for other Nb compositions, and 0.2% Ga is considered to be the lower limit. Regarding the upper limit, considering that No. 29 could not be processed up to 0.24φ, the range that can be processed is 8.0
%Ga is considered to be the upper limit. As described above, the present invention has made it possible to easily and economically obtain a Nb ₃ Sn-based superconducting material having a high Jc value by simply creating a widely used method such as melting and casting, processing, plating, and diffusion. At the same time, the Jc value was significantly improved by adding Ga, and the significance of further advancing its potential for future applications in high magnetic fields is enormous.

[Brief explanation of the drawing]

Figure 1 is a diagram comparing the effect of adding Ga to Nb of each composition, Figure 2 is a diagram comparing the effects of pretreatment and diffusion temperature on Jc value, and Figure 3 is a diagram comparing the amount of Ga added. It is a diagram plotting the relationship between changes in and Jc.

Claims (1)

[Claims] 1. An alloy consisting of 15 to 70% by weight Nb, 0.2 to 8% by weight Ga, balance Cu, and unavoidable impurities is melted and cast, and the cast material is stretched to form a filamentous Nb phase in the stretched matrix. is formed in the drawn material, and then the drawn material is coated with Nb corresponding to the amount of Nb present.
A method for producing an Nb ₃ Sn-based superconducting material, which comprises plating Sn in an amount that can generate Nb ₃ Sn, and then performing a diffusion treatment to convert the Nb filament into a filament consisting of an Nb ₃ Sn phase. 2. Melt and cast an alloy consisting of 15 to 70% by weight Nb, 0.2 to 8% by weight Ga, balance Cu, and unavoidable impurities, and stretch the cast material to form a filamentary Nb phase in the drawn matrix. Later, the drawn material was treated with the same amount of Nb as described above.
Sn is plated in an amount sufficient to generate Nb ₃ Sn, and a preliminary heat treatment is performed at 240 to 500°C for 20 to 100 hours in the middle, followed by a diffusion treatment to convert the Nb filament into a filament consisting of an Nb ₃ Sn phase.
A method for producing Nb ₃ Sn-based superconducting material.