JPH0676663A - Manufacture of superconducting material and nb-al superconducting wire - Google Patents

Abstract

PURPOSE:To provide a method of manufacture of superconducting material from which an Nb3Al superconducting wire excellent in both the rate of area of an Nb.Al superconducting phase in its cross section and superconducting characteristics such as critical current density can be formed, even as an element wire of higher degree which is obtainable by repeating of a process for making a primary element wire multicored. CONSTITUTION:Starting with secondary element wire 3 having in an Nb layer a number of primary element wires 3 each comprising an Al core covered with an Nb layer, a plurality of secondary element wires are either enclosed in an Nb tube 1 with an Nb and Al powder mixture 2 filling the space therein, or enclosed in the Nb tube while being surrounded by a layer of Nb and Al powder mixture. A process for forming a next element wire by drawing of the element wires enclosed is repeated by a required number of times. The ratio of a superconducting phase to a matrix phase which occupy the cross section of the superconducting wire can then readily be controlled, and the drawing process is so easy that the process of making the element wire multicored to a higher degree can efficiently and stably be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a superconducting material which has a large occupied area of Nb ₃ Al-based superconducting phase and which is excellent in superconducting properties such as critical current density, and a method for producing the Nb · Al. System superconducting wire.

[0002]

2. Description of the Related Art Conventionally, a bundle of primary wires made by coating an Al-based core made of Al or an alloy thereof with an Nb layer is housed in an Nb tube and drawn to form a secondary wire having a multi-core structure. There has been known a method of manufacturing a superconducting material in which a wire bundle is housed in a Nb tube as a starting wire and wire drawing is repeated a required number of times. Such a composite processing method (niobium tube method) has an advantage that it is possible to easily make higher-order multifilamentary wires, and the superconducting wire is subjected to heat treatment of the multifilarized material to form a Nb ₃ Al-based superconducting phase. It is obtained by generating.

However, when the wire is housed in the Nb tube, even if the cross section is formed into a hexagonal shape, which is advantageous for high packing, a gap is generated between the wire or between the wire and the Nb tube, and the filling rate is increased. There is a problem in that the number of composite strands required to bring the primary strand to a predetermined diameter, for example, about 100 nm (higher multicore) is increased, and multiple steps are required. In addition, the occurrence of a gap impairs the workability such as a reduction in the wire drawing workability, and further, the Nb layer based on the Nb pipe located on the outer periphery of each of the tertiary wires and above has an Nb layer.
The Nb layer that does not contribute to the formation of the superconducting phase increases as the primary strands are made to have a higher number of cores by repeating the compounding, and thus the Nb layer that does not contribute to the formation of the b ₃ Al superconducting phase increases. There has been a problem that the area of the Nb ₃ Al superconducting phase occupying is drastically reduced and the critical current value per unit cross section is lowered. By the way, in the fourth-order superconducting material using the third strand,
The sectional area of the Nb layer, which does not contribute to the formation of the superconducting phase, sometimes reaches about 90%.

[0004]

DISCLOSURE OF THE INVENTION The present invention has an advantage that the cross-sectional occupying area of the Nb ₃ Al based superconducting phase is excellent even when a multifilamentary primary wire is repeatedly used and the superconducting characteristics such as critical current density are excellent. The task is to develop a method of manufacturing a superconducting material capable of forming a superb Nb / Al-based superconducting wire.

[0005]

According to the present invention, a plurality of strands are formed by using as a starting strand a secondary strand having a primary strand in which an Al-based core is coated with an Nb layer in a multi-core state in the Nb layer. The book is housed in the Nb tube with the gap filled with the mixed powder of Nb powder and Al-based powder, or the bundle of wires is surrounded by the mixed powder layer of Nb powder and Al-based powder and placed in the Nb tube. A method of manufacturing a superconducting material, characterized by accommodating, and repeating the operation of wire-drawing the accommodating body to obtain the next strand a necessary number of times, and comprising a heat-treated product of the superconducting material. The present invention provides Nb / Al-based superconducting wires.

[0006]

[Function] By the above method of filling the space between the pipes and the strands and between the strands in the Nb pipe with the mixed powder of Nb powder and Al-based powder, the formation of gaps can be prevented and the workability such as wire drawing is improved. As a result, the primary wire can be efficiently thinned to a predetermined diameter with a small number of compounding times, and the mixed powder contributes to the formation of the Nb ₃ Al-based superconducting phase, and the mechanical strength, stability, and AC loss in the cross-sectional area of the superconducting material. It is possible to easily control the matrix and Al-based content ratio, which influences the above, and thus the superconducting layer ratio. As a result, it is possible to reduce the interposition of the portion that does not contribute to the formation of the Nb ₃ Al-based superconducting phase in increasing the order of the strand, and to improve the Nb ₃ Al
A large number of parts contribute to the formation of the system superconducting phase, and the multiple cores of the primary wire are repeated, and even if it is a higher-order wire, the cross-sectional area occupied by the Nb ₃ Al system superconducting phase is excellent and the superconducting characteristics such as critical current density. A superconducting material capable of forming a superb Nb / Al superconducting wire is obtained.

[0007]

EXAMPLE As shown in FIG. 1, the manufacturing method of the present invention is
A plurality of strands are accommodated in the Nb tube 1 with the secondary strand 3 made of Nb-based multi-core strand as a starting strand, and the gap is a mixed powder 2 made of Nb powder and Al-based powder. The superconducting material is obtained by repeating the operation of drawing the container filled with the step 1 to draw the next strand.

As the Al / Nb-based multifilamentary starting wire, as shown in FIG. 3, an Al-based core 34 made of Al or an alloy thereof is covered with a Nb layer 33 to form a primary wire 32 and an Nb layer 31. The secondary strand 3 having a multi-core state is used inside the. The primary wire 32 can be obtained by, for example, a method of loading an Al system wire into an Nb tube and performing a wire drawing process, and the secondary wire 3 accommodates a large number of the primary wire inside the Nb tube. It can be obtained by a method of wire drawing treatment. The primary strand, the secondary strand, and the strand for accommodating the Nb tube, which is formed by making the secondary strand higher-order multicore, can have any cross-sectional shape,
The hexagonal shape is preferable from the viewpoint of high filling property in the Nb tube.

A method for accommodating a plurality of strands in a Nb pipe in a state where the gaps between the strands and the Nb pipes and the gaps between the strands are filled with the mixed powder 2 of Nb powder and Al-based powder is, for example, A method of filling the gap with the mixed powder after accommodation is arbitrary. The number of wires to be accommodated may be appropriately determined, but is generally about 10 to 300.

The mixing ratio of the Nb powder and the Al-based powder in the mixed powder to be filled may be appropriately determined, but from the viewpoint of efficiently forming the Nb ₃ Al-based superconducting phase between the Nb powder and the Al-based powder. It is preferable that the amount is 1/3 of Nb powder, especially about 1/4.

The particle diameters of the Nb powder and the Al-based powder to be used may be appropriately determined, but in general, from the viewpoint of the formation of the superconducting phase, Al is particularly preferable.
It is preferable that the powder of the system has a diameter as equal as possible to the Al-based core of the primary wire in the wire at each stage of wire drawing. As a result, the heat treatment conditions for producing the Nb ₃ Al-based superconducting phase can be unified within the material. By the way, when an Al-based powder having a diameter different from the above-mentioned Al-based core diameter is used, the heating conditions for producing the superconducting phase are different between the Al-based core portion and the Al-based powder portion. A problem that the Nb ₃ Al-based superconducting phase is not generated due to a shortage or a problem that the superconducting characteristic is deteriorated due to coarsening of crystal grains of the Nb ₃ Al-based superconducting phase due to excessive heat treatment is easily induced.

In the present invention, an operation of accommodating a plurality of strands and the mixed powder in a Nb tube and performing wire drawing is first performed on the above-mentioned starting strand, and then obtained. Repeat the required number of times by using the wire drawing product for the next strand, and thus make the Al-based core diameter of the starting strand one by one, while making the Al-based core diameter higher It is considered to be a superconducting material. The wire drawing process may be performed by an appropriate method such as a swaging method, a groove roll method, or a die method, and the cross-sectional shape to be formed is arbitrary as described above.

In another manufacturing method of the present invention, as shown in FIG. 2, the secondary wire 3 described above is used as a starting wire, and the bundle of the wire is a mixed powder layer 2 of Nb powder and Al-based powder. The superconducting material is obtained by surrounding and accommodating it in the Nb tube 4 and drawing the accommodating body into the next strand to repeat the necessary number of times.
Therefore, a superconducting material is obtained according to the method described above except that the bundle of strands is surrounded by a layer of mixed powder of Nb powder and Al powder.

As a method of enclosing the bundle of strands with the layer of the mixed powder, an appropriate method such as densifying the mixed powder layer by a hydrostatic molding method can be used.
The thickness of the mixed powder layer to be formed is arbitrary. In general, 10 to 100 strands, in particular 20 to 50 strands, are bundled and a mixed powder layer is provided on the outer periphery thereof with a thickness of 1 to 100 times, especially 2 to 10 times the diameter of the strands. It is said that

Nb for accommodating the primary strands and secondary strands used in the present invention, as well as their composite higher order strands
The tube may be covered with a Cu-based material made of copper or a copper alloy, if necessary. By providing a Cu-based coating layer, wire drawing can be performed efficiently without damaging the wires or surrounding powder,
Due to its excellent wire drawing workability, it is possible to easily increase the order of the wire and efficiently perform the multi-core of the primary wire,
It is possible to form a matrix that is advantageous in improving mechanical strength and stability, preventing AC loss, and the like.

In the present invention, the superconducting material to be formed can be arbitrarily determined, and therefore the number of times of repeating the above operation is also arbitrary. Generally, in order to prevent deterioration of mechanical strength and stability due to lack of matrix portion that is not Nb / Al superconducting phase, or to prevent AC loss, about 10 to 300 primary strands are multifilamented. Nb area ratio is 0.2 to 20%
/99.8-80% secondary strand as a starting strand, and mixed powder of Nb powder and Al-based powder is added to it, and the number of cores is 10 core to 10,000 in units of the secondary strand. Core, diameter 0.1-2
mm, area ratio of secondary wire portion / added portion such as mixed powder occupying in the cross-sectional area from 1/9 to 9/1, Al system / Nb area ratio in the cross section of about 2 to 20% / 98 to 80% It is considered to be a superconducting material.

The Nb / Al superconducting wire can be obtained by processing the superconducting material into a desired cross-sectional shape such as a circle, a rectangle, or a tape, if necessary, and then heat-treating it. The heating conditions are appropriately determined depending on the Al-based core diameter in the superconducting material, the thickness of the mixed powder layer, etc., but the heating is generally performed in the temperature range of 700 to 1600 ° C.

By heat treatment, for example, an Al-based core (34) based on, for example, a primary strand, its coated Nb layer (33), and a secondary strand existing inside the wire-drawing layer of the Nb tube finally enclosed. Nb ₃ Al-based superconducting phase by reacting all or part of the Nb portion and the Al-based portion adjacent to the Nb portion and the Al-based portion such as the outer peripheral Nb layer (31) and the mixed powder layer (2) of Nb powder and Al-based powder. To form.

The Nb ₃ Al type superconducting phase produced by the heat treatment is usually about 4 times as much as the contained Al type component. Therefore, the content of the Nb ₃ Al-based superconducting phase in the obtained superconducting wire can be controlled by adjusting the Al-based portion in the cross-sectional area of the superconducting material. For example, the Nb / Al ratio of the multifilamentary wire layer is 98% / 2%, and the Nb / Al mixed powder layer is Nb / Al.
Assuming that the Al ratio is 80% / 20%, the Al ratio is changed to 2 by changing the filling ratio of the Nb-Al mixed powder layer.
Since it can be varied within the range of up to 20%, Nb ₃
A superconducting wire in which the Al superconducting phase occupies a cross-sectional area in the range of 8 to 80% is obtained.

[0020]

According to the present invention, the content ratio of the Al-based substance that contributes to the formation of the superconducting phase can be easily adjusted so that the superconducting phase occupies the cross-sectional area of the superconducting wire and the matrix phase related to the strength and the like. The ratio can be easily controlled, moreover, the wire drawing can be easily performed by the pipe system, and the higher-order multicore of the wire can be efficiently and stably performed. As a result, the Nb ₃ Al-based superconducting phase occupies a large area even if a high-order element is obtained by repeating the multi-core structure of the primary element, and the superconducting characteristics such as the critical current density are excellent.
b · Al superconducting wire can be obtained efficiently.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view of an embodiment.

FIG. 2 is an explanatory sectional view of another embodiment.

FIG. 3 is an explanatory cross-sectional view illustrating the structure of a secondary wire.

[Explanation of Codes] 1: Nb tube 2: Mixed powder layer of Nb powder and Al-based powder 3: Secondary strand (starting strand) 31: Nb layer 32: Primary strand 33: Nb layer 34: Al-based core 4: Nb tube

Claims (3)

[Claims] 1. A secondary strand having a primary strand in which an Al-based core is coated with an Nb layer in a multi-core state in the Nb layer is used as a starting strand, and a plurality of strands are provided in a Nb tube with a gap of Nb. A method for producing a superconducting material, characterized in that the operation of accommodating in a state of being filled with a mixed powder of powder and Al-based powder and drawing it to obtain the next strand is repeated a necessary number of times. 2. A secondary strand having a primary strand in which an Al-based core is covered with an Nb layer in a multi-core state in the Nb layer is used as a starting strand, and a bundle of strands is composed of Nb powder and Al-based powder. The method for producing a superconducting material, which is characterized in that the operation of enclosing the mixed powder layer in a Nb tube, accommodating it in a Nb tube, and drawing it to obtain the next strand is repeated a necessary number of times. 3. A Nb · comprising a heat-treated material of a superconducting material obtained by the manufacturing method according to claim 1 or 2.
Al-based superconducting wire.