JPS6347086B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a method for producing a compound superconducting wire by supplying solute metal to an unreacted composite superconducting wire through a diffusion process. Conventionally, supplying a solute metal to an unreacted composite superconducting wire by a diffusion treatment method has had the following drawbacks. Specifically, the method for manufacturing a Nb ₃ Sn superconducting wire as an example of a compound superconducting wire will be described in detail. As shown in Figure 1, a plurality of niobium 2 is embedded in a copper matrix 1 and subjected to area reduction processing to obtain the final shape. Thereafter, tin plating 3 is applied to this, and tin 3 is diffused into copper 1 by heating to form a Nb ₃ Sn compound superconductor 4 at the interface with niobium. As another method, as shown in Figure 2, copper powder and niobium powder are melted in an arc melting furnace or the like, solidified, and then subjected to area reduction processing to form the final shape.
Apply tin 3 to this and heat it to make tin 3
is diffused into the copper and at the interface with niobium.
This is what forms the Nb ₃ Sn compound superconductor 4. These methods are usually called in-situ methods. However, in the case of the above method, a large number of Kirkendall voids 6 with a size of 5 to 20 μm ² are dispersed and formed due to diffusion, which promotes the brittleness of the compound superconductor and deteriorates the tensile strength and Significantly reduces bending resistance. Furthermore, in order to reduce the crystal grain size and increase the layer thickness of the Nb ₃ Sn layer through the reaction between tin and niobium, it is necessary to control the diffusion temperature to 750°C or less, but within a specified time. In order to complete the reaction, the diffusion distance (depth) of tin is greatly limited, and the outer diameter of the wire is limited to 0.3 mm. In other words, it was impossible to obtain a conductor with a diameter larger than 0.3 mmφ. Furthermore, since the plating layer is a low melting point material, the diameter change in the longitudinal direction is large in the final annealing, making the winding operation difficult. In this way, in the conventional method, after tin is diffused, no further processing is performed until Nb ₃ Sn is formed, so Kirkendall Void occurs due to the difference in diffusion rate between tin and copper or niobium. However, no measures had been taken to remove this. As a result of extensive research aimed at improving these drawbacks, the present invention has discovered a method for eliminating Kirkendall voids and producing a compound superconductor with excellent mechanical strength and bending resistance. That is, the method of the present invention is a method for producing a compound superconducting wire by supplying solute metals such as Sn and Ga from the surface layer of an unreacted composite superconducting wire through a diffusion process, in which a composite of copper or a copper alloy and niobium is subjected to an area-reducing process. a second step of plating with solute metal and performing diffusion heat treatment; a third step of reducing the area by 5 to 80%; and a fourth step of repeating the second and third steps. and a fifth step of performing diffusion annealing. Note that in the above, the surface layer portion of the unreacted composite superconducting wire usually refers to the outer surface, but when the composite superconducting wire is made of a hollow body, it also includes the surface of this circular hole. An example of the manufacturing process of the present invention will be explained with reference to the drawings. As shown in Fig. 3, copper 1 and niobium 2 are composited in the same manner as in the conventional method, and after surface reduction processing and before reaching the final shape, tin plating 3 is applied, and the temperature required to diffuse the tin is 250 to 450. C. for 5 to 50 hours to obtain an unreacted composite superconducting wire 8 in which niobium 2 is embedded in the bronze matrix 5. This superconducting wire 8 is subjected to a surface reduction process of 5 to 80% by die drawing or rolling to obtain a final shape. The shapes include round wire, square wire as shown in Fig. 4, smooth body stranded wire 10 as shown in Fig. 5, and
It may be of any shape, such as a shaped stranded wire 11 as shown in the figure. Next, the Nb ₃ Sn compound superconductor is diffusion annealed at a temperature of 500 to 800° C. for 10 to 100 hours to form a Nb ₃ Sn layer 4 at the interface between the bronze 5 and the niobium 2, thereby forming the inventive compound superconductor. This is the one that obtains line 9. In addition, in the process of manufacturing the unreacted composite superconducting wire of copper and niobium in the above, copper and niobium may be a dilute alloy or may contain impurities such as oxygen and hydrogen. Also, there is no problem even if an element such as potassium is mixed into the tin in the tin plating process. In order to obtain a conductor with an even larger current capacity, as shown in FIG. This can be obtained by embedding it in The reason why the unreacted composite superconducting wire that has been subjected to tin plating is processed after annealing in the method of the present invention will be explained as follows. (1) Kirkendall voids, which are generated during the process of tin diffusion into copper, are made small and dispersed to a size that does not pose a practical problem. (2) In the final diffusion heat treatment step in which Nb ₃ Sn is formed by accumulating strain energy in the bronze matrix, diffusion of Sn can be promoted and Nb ₃ Sn nuclei can be made fine. (3) The final shape of the conductor can be made into any desired shape. (4) By annealing the unreacted composite superconducting wire that has been tin-plated, it is possible to correct the deformation of the conductor shape during the bronze matrix composite process. The method of the present invention can be applied not only to single substances such as Sn and Ga as solute metals, but also to multiple diffusion in which Ga is diffused after Sn, and alloy diffusion such as Sn--Mg alloy and Ga--Zn alloy. Next, examples of the present invention will be described. Example Copper powder and niobium powder were mixed in a weight percent ratio of 65:35, compressed, and then melted in an arc melting furnace.
An ingot of mmφ×180mm was obtained. This ingot was heated at 450° for 2 hours and then hot extruded to obtain an extruded rod of 15 mmφ×800 mm. This extruded rod was made into a wire rod with a diameter of 0.3 mm by cold area reduction processing. Using a part of this wire, tin plate it to a thickness of about 10μm, annealing it at 400℃ for 24 hours, and then cutting it into a wire diameter of 0.22mmφ by die drawing.
Diffusion heat treatment was performed at 750°C for 50 hours to obtain a superconducting wire of the compound of the present invention. In addition, for comparison with the compound superconducting wire of the present invention, the above 0.3 mmφ composite wire was cut into 0.22 mmφ by die drawing.
After drawing the wire to 7 μm, the wire was plated to an equivalent thickness of approximately 7 μm, and diffusion heat treatment was performed at 750°C for 50 hours to obtain a conventional compound superconducting wire. Table 1 shows the results of measuring the metal structure, mechanical properties, and electrical properties of the superconducting wire of the present invention and the conventional superconducting wire.

[Table] As is clear from the above table, the void size of the compound superconducting wire produced by the method of the present invention is significantly smaller and more dispersed than that of the compound superconducting wire produced by the conventional method. In addition, Nb ₃ Sn has a fine grain size and a thick layer. Furthermore, wire pressure, bending resistance,
It was observed that the critical current density and the critical current density were significantly improved. As detailed above, the method of the present invention has the following effects. (1) Eliminating Kirkendall voids and significantly improving the mechanical strength and bending resistance of unreacted composite superconducting wires. (2) Superconducting wires with high critical current density and large current capacity can be obtained. (3) Since the shape of the conductor can be changed as it is processed with a maximum area reduction rate of 80%, there is no need to limit the shape of the conductor to stranded wire forming, stranded wire, tape, etc.

[Brief explanation of the drawing]

1 and 2 are manufacturing process explanatory diagrams showing one example of a conventional method for manufacturing a compound superconducting wire, FIG. 3 are manufacturing process explanatory diagrams showing an example of a manufacturing method for a compound superconducting wire according to the present invention, 4, 5 and 6 are cross-sectional views showing an example of the shape of an unreacted composite superconducting wire,
Figure 7 shows an example of an unreacted composite superconducting wire with a large current capacity, where A is a cross-sectional view of the round wire, and B is a cross-sectional view of the round wire A.
FIG. 1... Copper matrix, 2... Niobium, 3... Suzmetsuki, 4... Nb ₃ Sn compound superconductor, 5... Bronze matrix, 6... Kirkendall void, 7... Conventional unreacted composite superconducting wire, 8... Unreacted of the present invention Composite superconducting wire, 9...Compound superconducting wire of the present invention, 10...
Smooth body stranded wire, 11... Molded stranded wire, 12... Diffusion barrier.

Claims (1)

[Claims] 1. In a method for producing a compound superconducting wire by supplying solute metal from the surface layer of an unreacted composite superconducting wire by diffusion treatment, a first step of reducing the area of a composite of copper or copper alloy and niobium; The second step is plating and diffusion heat treatment, and 5 to 80%
A method for manufacturing a compound superconducting wire, comprising: a third step of performing surface reduction processing; a fourth step of repeatedly performing the second and third steps; and a fifth step of performing diffusion annealing.