RU2804454C1 - METHOD FOR MANUFACTURING SUPERCONDUCTING COMPOSITE WIRE BASED ON Nb3Sn - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention is related to creation of long-length composite wires based on superconducting compounds intended for the manufacture of electrical products. The method for producing a superconducting wire based on Nb₃Sn includes forming the first multifibre preform doped with titanium and/or tantalum by placing a diffusion barrier and a copper matrix in a copper sheath. A tin-containing rod is placed in the centre of the matrix, and niobium-containing rods are placed around it, each of which has a copper-containing shell. The second multifilament blank is formed from the obtained measured parts by assembling them in a metal case. The second multifilament preform is deformed by drawing it to obtain a wire with a diameter of 2 to 0.2 mm, followed by its stepwise heat treatment. At the first stage, heat treatment is carried out at a temperature of 410-500°C for 5-200 h, and the second stage of heat treatment is carried out at a temperature of 620-750°C for between 24 to 400 hours.

EFFECT: invention ensures a high current-carrying capacity in the superconducting composite wire based on Nb₃Sn in magnetic fields with induction above 12 T.

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Description

TECHNICAL FIELD

The invention relates to the field of electrical engineering for the creation of long composite wires based on superconducting compounds intended for the manufacture of electrical products.

BACKGROUND ART

Modern development of high-energy physics devices requires the creation of superconducting materials with high current-carrying capacity in magnetic fields up to 16 Tesla. It is known that the critical current density of a superconductor depends on the density of grain boundaries and the composition of the superconducting phase. The main operation responsible for the formation of the microstructure of the superconducting layer is diffusion heat treatment.

Superconducting composite wires based on Nb ₃ Sn, as a rule, are subjected to multi-stage heat treatments, which ensures the formation of an equiaxed fine-grained superconducting layer, and hence the high current-carrying capacity of the superconductor as a whole.

A known method for producing a superconducting composite wire based on ND3S11 [Nb ₃ Sn Phase Growth and Superconducting Properties During Heat Treatment, Emanuela Barzi and Sara Mattafirri, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 13, NO. 2, 2003], consisting in the formation of a superconducting wire using the method of an internal tin source and heat treatment of the wire of the final size according to the regime: 400°C, 80 hours (heating rate 150°C/hour)+(650-750)°C, (2 -400) h. At the first stage of diffusion heat treatment, a bronze matrix with a high tin content is formed, then at the second stage of heat treatment, tin from the bronze matrix diffuses to the niobium fibers and a superconducting Nb ₃ Sn layer is formed. In this case, at the first stage, if the heating mode is incorrectly selected, the temperature of this stage is determined and the holding time is determined, refractory niobium fibers may dissolve in the Cu-Sn matrix. The dissolution process is the destruction of the crystal lattice of a solid metal and the transition of its atoms into liquid metal. The driving force of this process is the difference in the magnitude of the thermodynamic potentials of solid metal atoms in the crystal lattice and in the liquid metal. As it dissolves, this difference gradually decreases and after a certain period of time disappears altogether. [IN AND. Nikitin “Physical and chemical phenomena under the influence of liquid metals on solid ones”, Atomizdat 1967, p. 441]. The process of formation of a superconducting compound at the second stage in this case occurs through the formation of intermediate intermetallic compounds and the layer structure is characterized by the presence of a large number of large Nb ₃ Sn grains. Their presence leads to a decrease in the density of grain boundaries, and therefore to a lower critical current density of the superconducting wire. During rapid heating to the temperature of the first stage, the processes of dissolution of tin in the copper matrix and the formation of high-tin bronze are accompanied by the presence of a liquid phase inside the conductor and lead to the formation of an intermediate nausite phase. Thus, the disadvantage of the method of manufacturing a superconductor described above is the diffusion heat treatment of a finished size conductor with the first stage at a temperature of 400°C, and with a heating rate to a temperature of this stage of 150°C/hour, since this produces a large amount of nausite phase, which then transforms into a coarse-grained superconducting Nb ₃ Sn layer.

A known method for manufacturing a superconducting composite wire based on Nb ₃ Sn [US 7585377 B2, publ. 2009;Cu diffusion in Nb ₃ Sn internal tin superconductors during heat treatment, Ian Pong, Luc-Rene Oberli, Luca Buttura, Supercond. Sci.Technol. 26(2013)], which consists in the formation of a superconducting wire using the method of an internal tin source and heat treatment of the wire of the final size according to the regime: at the first stage, heat treatment is carried out at a temperature of 180-220 ° C for 24-100 hours, at the second stage, heat treatment is carried out at temperature 340-410°C for 24-50 hours, at the third stage heat treatment is carried out at a temperature of 625-725°C for 12-200 hours.

Despite the fact that at the first stage of this heat treatment at sufficiently low temperatures, tin and copper should form bronze and there may not be pure tin in the conductor, at the second stage the formation of a ternary Cu-Nb-Sn phase is observed, which further prevents the diffusion of tin to niobium fibers and makes it difficult to form a superconducting layer. Also, the microstructure of the superconducting Nb ₃ Sn phase formed from the ternary Cu-Nb-Sn phase is characterized by the presence of large grains, which leads to a decrease in the density of grain boundaries and the critical current density of the superconductor.

The closest to the proposed technical solution is a method for producing a superconducting wire based on Nb ₃ Sn [US 2018/0212136 A1, publ. 2018] using the internal source method of copper-coated Nb ₃ Sn composite wire containing Nb, Sn, Cu and doped with titanium and/or tantalum, by drawing to a diameter of 2 to 0.2 mm and heat treatment in a two-stage mode: in the first stage, heat treatment is carried out at a temperature of 350-380°C for 24-400 hours, and the second stage of heat treatment is carried out at a temperature of 620-750°C and a duration of 24 to 400 hours.

According to the literature data, the nausite phase is formed at temperatures below 408°C [A new understanding of the heat treatment of Nb-Sn superconducting wires, Ch. Sanabria, 2017], and with increasing annealing duration at this stage, the layer thickness increases. Therefore, heat treatment of the wire at a first-stage temperature below 400°C leads to the formation of the nausite phase, which leads to a decrease in the critical current density of the superconductor.

DISCLOSURE OF INVENTION

The objective is to develop a method for producing a superconducting composite wire based on Nb ₃ Sn with a high current-carrying capacity for use in various magnetic systems with fields above 12 Tesla.

The technical result is to ensure high current-carrying capacity in a superconducting composite wire based on Nb ₃ Sn in magnetic fields with an induction above 12 Tesla, obtained using the developed method.

The technical result is achieved in a method for manufacturing a superconducting wire based on Nb ₃ Sn, including the formation of a first multi-fiber workpiece alloyed with titanium and/or tantalum by placing a diffusion barrier and a copper matrix in a copper case, in the center of which a tin-containing rod is placed, and niobium-containing rods are located around it, each of which has a copper-containing shell, its deformation to obtain a composite rod of the required size, cutting it into dimensional parts, forming a second multi-fiber workpiece from the resulting dimensional parts by assembling them in a metal case, deforming the second multi-fiber workpiece by drawing it to obtain a wire with a diameter of 2 up to 0.2 mm, followed by heat treatment in a stepwise mode, where the second stage of heat treatment is carried out at a temperature of 620-750°C and a duration of 24 to 400 hours, and at the first stage heat treatment is carried out at a temperature of 410-500°C for 5- 200 hours

In a particular embodiment, the first multi-fiber workpiece is alloyed with titanium and/or tantalum and at least one more element selected from the following: Zr, Hf, Al, Mg, Mn, Ga, In, Y, Ce, La, Nd, Te, Zn.

In a particular embodiment, when forming a second multi-fiber workpiece in a metal case, part of the resulting measured parts of the composite rod is replaced with copper-containing rods.

In a particular embodiment, when forming a second multi-fiber workpiece, copper-containing rods are additionally placed in a metal case.

Carrying out heat treatment in a stepwise mode, where in the first stage the heat treatment is carried out at a temperature of 410-500°C for 5-200 hours, allows one to avoid the formation of the triple nausite phase and obtain a superconducting Nb ₃ Sn layer, the microstructure of which is characterized by equiaxed grains, which ensures high current-carrying capacity superconductor.

Alloying the first multi-fiber workpiece with titanium and/or tantalum and at least one other element, for example, yttrium Y, allows not only to increase the upper critical field of the superconducting wire, and therefore its current-carrying ability in strong magnetic fields, but also to obtain a smaller amount of nausite phase during heat treatment. In addition, this promotes the formation of more equiaxed grains of the superconducting Nb ₃ Sn phase of a smaller size, which leads to an increase in the density of grain boundaries and an increase in the current-carrying capacity of the superconductor as a whole.

The technology for manufacturing a superconducting wire based on Nb ₃ Sn according to the claimed method includes the following main steps:

1. Formation of the first multi-filament blank;

2. Deformation of the first multi-fiber workpiece to a rod of the required size;

3. Cutting the resulting rod into measured parts;

4. Formation of the second multi-filament blank;

5. Deformation of the second multi-fiber workpiece by drawing to the required size;

6. Carrying out heat treatment by annealing the wire to form a superconducting compound.

The present invention is illustrated by drawings.

In fig. 1 shows a cross-section of the first multi-fiber workpiece 1. The workpiece 1 contains a copper case 2, a diffusion barrier 3, inside of which there is a copper matrix 4, in the center of which there is a tin-containing rod 5, around which there are many niobium-containing rods 6 in a copper-containing shell 7.

In fig. 2 shows a cross-section of a second multi-fiber workpiece, made by placing a plurality of workpieces 1 in a metal case 8.

In fig. Figure 3 shows a cross-section of the second multi-fiber workpiece, made by placing a plurality of workpieces 1 and copper-containing rods 9 in a metal case 8.

IMPLEMENTATION OF THE INVENTION Example.

The formation of the first multi-fiber workpiece is carried out by placing in the center of a copper sheath with a height of 300 mm, an outer diameter of 109 mm and an inner hole of 102 mm in diameter, a niobium diffusion barrier, the thickness of which is 5 mm, a tin rod with a diameter of 19.5 mm, around which 948 niobium alloyed titanium rods in a copper sheath with a turnkey size of 2.5 mm, in a copper matrix. Then the specified workpiece is deformed to a turnkey size of 3.8 mm. The resulting rod is cut into measured pieces.

The second multi-fiber preform for making a superconducting wire based on Nb ₃ Sn is formed by placing 37 dimensional parts in a copper case.

The resulting second multifilament workpiece is deformed by drawing to a diameter of 1 mm.

Annealing of a composite wire based on Nb ₃ Sn is carried out in a vacuum environment in a stepwise manner: heating to 450°C, holding for 100 hours, then heating to 665°C and holding at this temperature for 40 hours, and cooling with the furnace.

INDUSTRIAL APPLICABILITY

On a wire heat-treated according to the specified regime, a critical current density in the cross-section without copper of more than 2500 A/mm ² in a magnetic field with an induction of 12 T at a temperature of 4.2 K was obtained.

Claims (4)

1. A method for manufacturing a superconducting composite wire based on Nb ₃ Sn, including the formation of a first multi-fiber workpiece alloyed with titanium and/or tantalum by placing a diffusion barrier and a copper matrix in a copper case, in the center of which a tin-containing rod is placed, and around it there are niobium-containing rods, each of which has a copper-containing shell, its deformation to obtain a composite rod of the required size, cutting it into dimensional parts, forming a second multi-filament workpiece from the resulting dimensional parts by assembling them in a metal case, deforming the second multi-fiber workpiece by drawing it to obtain a wire with a diameter of 2 to 0.2 mm with its subsequent heat treatment in a stepwise mode, where the second stage of heat treatment is carried out at a temperature of 620-750°C and a duration of 24 to 400 hours, characterized in that at the first stage the heat treatment is carried out at a temperature of 410-500°C for 5-200 h. 2. The method according to claim 1, characterized in that the first multi-fiber workpiece is alloyed with titanium and/or tantalum and at least one more element selected from the range: Zr, Hf, Al, Mg, Μn, Ga, In, Y, Ce , La, Nd, Te, Zn. 3. The method according to claim 1, characterized in that when forming the second multi-fiber workpiece in a metal case, part of the resulting measured parts of the composite rod is replaced with copper-containing rods. 4. Method according to any one of paragraphs. 1, 3, characterized in that when forming the second multi-fiber workpiece, copper-containing rods are additionally placed in the metal case.

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