JPS63213212A - Manufacture of internal diffusion type nb3 sn superconductive wire - Google Patents

Abstract

PURPOSE:To prevent melting of a matrix and obtain a wire rod having high critical current density by setting heat treatment temperature in a prescribed range in case of manufacturing a superconductive wire of multicore structure by an internal diffusion method. CONSTITUTION:A number of Nb or Nb alloy wires whose outsides are coated with Cu or a Cu alloy are arranged inside a Cu composite tube, in whose inside a diffusion barrier is arranged, centering round an Sn or Sn alloy rod coated with Cu or a Cu alloy. Then, a surface reducing process is applied thereon to mold it into a first form followed by heat treatment in the temperature range of 650-730 deg.C for generating Nb3Sn. In the above temperature range, matrix melting is not caused so as to obtain a good characteristic, however, improvement of critical current density can not be expected under 650 deg.C, and on the other hand, the matrix is liable to be melted when 730 deg.C is exceeded, and in case of being melted, the critical current density drops remarkably.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Field of Application) The present invention relates to a method for manufacturing a Nb3Sn superconducting wire by an internal diffusion method, and the present invention relates to a method for manufacturing a Nb3Sn superconducting wire by an internal diffusion method, and particularly relates to a method for manufacturing a Nb3Sn superconducting wire using a high concentration of Sn.
This invention relates to improvement of heat treatment conditions for b3Sn formation.

(Prior art) The internal diffusion method, which is a type of manufacturing method for Nl)3sn superconducting wire, is simple and can easily improve the critical current density (JC) by increasing the amount of 5n. The following method is known as a method for producing a multicore N1)xSn superconducting wire using this internal diffusion method.

That is, in this method, a large number of Cu-coated Nb wires are arranged around the outer periphery of a Sn rod, and these are connected to a Cu-coated Nb wire with a diffusion barrier inside.
Heat treatment is performed on the final cross-sectional shape of the shell, which has been housed in a tube and subjected to area reduction processing, and this heat treatment usually involves heat treatment to form Cu-3n alloy by diffusion of 3n, and formation of Nfia3n by reaction of Nb-3n. The heat treatment is carried out in two stages. In this case, since heat treatment is performed in the final shape, the Sn matrix in the matrix after Cu-311 alloy formation is bronzed (from the viewpoint of workability, it is generally set at 13 to 14 wt%, which is below the solid solubility limit of Sn). However, since the heat treatment temperature for Nb3Sn formation is close to the melting temperature of the matrix, the matrix melts and the Nb wires aggregate, resulting in a critical current density value that is considerably lower than the designed value. The problem was that it was easy to cause

(Problems to be solved by the invention) The present invention has been made to solve the above-mentioned difficulties.
The object of the present invention is to provide a method for manufacturing a multi-core superconducting wire having good superconducting properties by maintaining heat treatment conditions for Nb3Sn production within a predetermined range to prevent melting of the matrix.

rStructure of the Invention] (Means for Solving the Problems) The method for manufacturing an internally diffused Nb 3Sn superconducting wire of the present invention is characterized in that a Cu
Or, centering around a Sn or Sn alloy rod coated with Cu alloy, a large number of Nb or Nb alloy wires coated with Cu or Cu alloy are placed on the outside, and the area is reduced to form the final shape. After molding, 650-730
Nb3S by heat treatment in the temperature range of 'C
It is characterized by generating n.

The method of the present invention is particularly effective when the 5nlit degree (Nl) 5nWi degree in the matrix excluding Nb or Nb alloy before the heat treatment for 3Sn formation is high, e.g.
This is suitable for cases where the amount is within the range of t%.

If this Sn concentration is less than 20wt%, it is not possible to expect an improvement in critical current density due to an increase in Sn concentration;
This is because if it exceeds t%, the matrix tends to melt even in the above temperature range.

In the above temperature range of 650 to 730'C, the matrix does not melt and good properties can be obtained;
If it is below 50°C, no improvement in critical current density can be expected, while if it exceeds 730°C, melting of the matrix is likely to occur.
When melted, the critical current density decreases significantly.

(Example) A Nb-1,1 wt% Ti alloy rod with an outer diameter of 38.1 mm is housed in a Cu tube with an outer diameter of 50 mm and an inner diameter of 38.3 mm. Distance 1.94
A wire rod with a hexagonal cross section of mm was manufactured. Then this 409
Books are densely assembled to form an outer diameter of 49mmφ and a thickness of 4mm.
It was placed in a pipe, subjected to surface reduction processing in the same way, and subjected to strain relief annealing to form a CU coated N with a hexagonal cross section of parallel plane type @ 2.13 mm.
B alloy wire was manufactured. These 180 pieces have an outer diameter of 22.8 mm.
A Ta tube with an outer diameter of 45 mm and a thickness of 2 mm and an outer diameter of 58 mm are assembled on the outer periphery of a Cu-coated Sn rod of φ.
A composite was fabricated by sequentially arranging Cu tubes with a diameter of 6 mm and a thickness of 6 mm. This composite was subjected to surface reduction processing to produce sample No. 1. On the other hand, Cu-coated Sn with an outer diameter of 18.9 mmφ
On the outer periphery of the rod, the Cu used in the production of sample No. 1 was placed.
216 coated Nb alloy wires were collected, and Ta tubes and C
No. 1 is achieved by reducing the surface area of a composite body in which tl tubes are arranged in order.
Two samples were produced. The specifications of samples No. 1 and No. 2 are shown in the table below', where the 3n concentration indicates the concentration in the matrix excluding the Nb--Ti alloy filament in the Ta tube.

FIG. 1 shows the critical current density values of superconducting wires subjected to heat treatment in the temperature range of 725 to 650'C for 1 to 6 days with respect to an external magnetic field.

From this result, it shows good characteristics at a temperature of 725 to 750'C, but the value of critical current density becomes low at a temperature of 800C or higher. Figure 2 shows sample No. 1 at 650-750℃.
Figure 1 shows the case where heat treatment is performed for 1 to 8 days in the temperature range of 650 to 725°C. descend. As a result of microscopic observation of the cross-sections of these samples, it was observed that the filaments of the samples with low critical current density were aggregated due to melting of the matrix. However, no aggregation of filaments was observed in the samples heat-treated at temperatures below 725°C. No agglomeration of filaments was observed in the sample shown in FIG. 1 which was heat treated at 750'C, but significant aggregation of filaments was observed in the sample shown in FIG. From this result, it is not possible to stably achieve 1q of predetermined characteristics at a heat treatment temperature of 750°C.

[Effects of the Invention] As described above, according to the present invention, melting of the matrix can be prevented by setting the heat treatment temperature within a predetermined range when manufacturing a superconducting wire with a multicore structure by the internal diffusion method. Therefore, it is possible to produce a wire having a high critical current density.

The method of the present invention is suitable for a wire having a structure using a high concentration of Sni in which the melting temperature of the matrix tends to decrease.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are graphs showing the relationship between critical current density and external magnetic field of a superconducting wire manufactured by the method of the present invention and a superconducting wire manufactured by another method, respectively. Applicant Showa Cable and Wire Co., Ltd. Agent Patent Attorney Sa Suyama - (1 other person) No. 12 9F - Tsuya 1&J (T) A2T

Claims (3)

[Claims] (1) Inside the Cu composite tube with a diffusion barrier placed inside,
Centering around a Sn or Sn alloy rod coated with Cu or Cu alloy, a large number of Nb or Nb alloy wires coated with Cu or Cu alloy are arranged on the outside, and the area is reduced to form the final shape. After molding to 650-7
Nb_3Sn by heat treatment in the temperature range of 30℃
Internal diffusion type Nb_3S characterized by generating
A method for manufacturing an n-superconducting wire. (2) The method for manufacturing an internally diffused Nb_3Sn superconducting wire according to claim 1, wherein the Nb or Nb alloy wire has a hexagonal cross section. (3) The method for manufacturing an internally diffused Nb_3Sn superconducting wire according to claim 1 or 2, wherein the amount of Sn in the diffusion barrier is 20 to 35 wt% of the total amount excluding Nb.