RU2122253C1 - Composite superconductor manufacturing process - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: manufacture of Nb₃Sn base composite superconductor involves shaping primary composite blank that has matrix-material external shell and axial cylindrical niobium block with longitudinal doping component, deforming primary composite blank until hexahedral bar is obtained, cutting the latter into metered lengths, repeating assembly into tin-copper alloy or copper cans, introducing other conductor elements, such as tantalum or niobium diffusion barrier during mentioned stage of process, deforming till conductor is brought to final diameter, and diffusing at 600-800 C to produce superconductor composition Nb₃Sn; axial cylindrical niobium block is composed of at least seven longitudinal bars at least one of them being made of doping component material. Composite superconductor obtained is suited for use in magnetic fields of 12 T and higher at critical current density increased by 30%. EFFECT: improved critical current density and reduced hysteresis loss. 3 cl, 4 dwg, 2 ex

Description

 The invention relates to the field of electrical engineering and can be used in devices primarily designed to operate in magnetic fields above 10 T at high current densities and low hysteresis losses.

A known method for producing a composite stabilized superconductor based on an Nb ₃ Sn intermetallic compound, comprising the steps of forming a primary composite billet containing an outer shell of matrix material and an axial cylindrical block of niobium containing a longitudinally located alloying component, deforming the primary composite billet to produce a hexagonal bar, cutting hexagonal bar to measured lengths, the formation of a secondary composite billet, consisting of an external Lok of Cu-Sn alloy having a space for accommodating the primary preform, deformation of the second composite to the desired cross section of the superconductor and diffusion heat treated at 600-800 ^o C to form the superconducting Nb ₃ Sn compound with high critical properties in high magnetic fields (over 10 T) due to the alloying of Nb ₃ Sn layers with titanium (Russian Patent N 2069399 of 02/10/96).

The superconductor obtained in this way has high critical current densities (J _s for a section without copper — 550 A / mm ² in a field of 12 T). However, at present, to create windings of superconducting magnetic systems that generate high magnetic fields, Nb ₃ Sn based wires with an even higher current carrying capacity are required. The proposed method for manufacturing a superconductor cannot provide an appropriate increase in the critical current density.

One of the reasons is the uneven alloying of the fiber with titanium and, as a consequence, the formation of an inhomogeneous structure of the Nb ₃ Sn phase.

There is also a known method of manufacturing a composite superconductor based on Nb ₃ Sn, selected as a prototype, including the operation of forming a primary composite billet containing an outer shell of matrix material and an axial cylindrical block of niobium containing a longitudinally located alloying component, deforming the primary composite billet to obtain a hexagonal bar, cutting a hexagonal bar into measured lengths, forming a secondary composite billet, consisting of an outer cover made of alloy Ava Cu-Sn with space for placing the primary preform, deforming the second composite to the required cross section of the superconductor and conducting diffusion heat treatment at 600-800 ^o C to form the superconducting compound Nb ₃ Sn, the effect of artificial alloying achieved by forming the primary composite preform by manufacturing a small the number of (one to three) cavities along the entire length of the cylindrical niobium billet, then filling them with inserts of appropriate size and number (rods, tubes, p astynom) of additional components such as tantalum or titanium, it is sufficient and by using simple technology. (Japan Patent "Manufacture of superconductor" N 3-78914 (A) 04/04/91, "Furukawa Electric Co LTD", MKI H 01 B 13/00, C 22 C 27/02, H 01 B 12/10 - "Production of a superconductor").

The use of a limited number (1-3) of inserts from an alloying component - titanium, remote from the niobium-bronze interface, along with a simple technology avoids the formation of TiCu intermetallic and ensures efficient production of alloyed conductors with a low level of hysteresis losses and high current carrying capacity (J _with = 600 A / mm ² in the field of 12 T).

However, the known method does not allow to obtain uniform doping of the fiber throughout the volume. This is due to the presence of a certain gap between the doping sources and the tin source, different directions of grain growth of the Nb ₃ Sn phase and, as a result, the formation of an uneven structure of the Nb ₃ Sn phase.

The technical task of the present invention is to provide increased current-carrying ability of the composite due to the directed growth of grains of the Nb ₃ Sn phase by breaking the fiber into separate cell components, the boundaries between which serve as artificial ways of diffusion of tin into the fiber, and providing uniformly distributed alloying sources.

The problem is solved so that if in the known method of manufacturing a composite superconductor based on the Nb ₃ Sn compound, including the operation of forming a primary composite billet containing an outer shell of matrix material and an axial cylindrical block of niobium containing a longitudinally located alloying component, deformation of the primary composite blanks to obtain a hexagonal bar, cutting the hexagonal bar into measured lengths, the formation of a secondary composite blank, consisting of External Expansion sheath of Cu-Sn alloy having a space for accommodating the primary preform, deformation of the second composite to the desired cross section of the superconductor and diffusion heat treated at 600-800 ^o C to form a compound superconducting Nb ₃ Sn, forming a primary composite preform occurs by producing a small number (one -three) cavities along the entire length of the cylindrical niobium billet, then filling them with the appropriate size and number of inserts (rods, tubes, plates) from additional components, such as tantalum or titanium, in the proposed method the cylindrical block is represented by a composite of many rods, some of which are made of the material of the alloying insert, thereby providing a cellular structure of the fiber with the presence of artificial diffusion paths of tin and uniform doping of the entire volume.

 The manufacture of a niobium block from a plurality of rods greatly simplifies the layout of the block with a uniform distribution of alloying inserts over the cross section, eliminating the time-consuming drilling operations or any other, providing several cavities in a continuous blank for the entire length of the block.

 The formation of a niobium block from many rods with a uniform distribution of the alloying component allows the use of titanium or an NbTi alloy with a titanium content of 20 to 55 wt.% Without intermediate layers of high strength niobium or a high titanium niobium alloy as an alloying insert. Other materials, such as tantalum, zirconium, etc., can also be used as an alloying component.

 The number of alloying inserts is selected in such a way as to ensure the necessary content of the alloying component in the volume of the axial composite block and the possibility of uniform distribution over the cross section.

 The number of rods forming a niobium block is chosen so that their transverse size in the finished wire is a multiple of the lattice parameter of magnetic fluxoids in the working range of magnetic fields.

 The distribution of alloying inserts among the niobium rods forming the block is chosen in such a way as to ensure directed grain growth during the final diffusion annealing.

 The distribution of alloying inserts among the niobium rods forming the block is chosen in such a way as to avoid the formation of Cu-Ti intermetallic in the process of manufacturing the composite.

The process of forming a niobium block with uniformly distributed alloying inserts can be carried out both in a case made of a copper alloy with tin, and in a case made of copper with subsequent operations of forming into a hexagonal bar, cutting to length and subsequent single or multiple assembly operations into a case or pipe from copper or Cu-Sn alloy, deformation to a finite diameter with the introduction of additional elements in the intermediate stage in the form of a diffusion barrier from tantalum and a stabilizing shell, uzionnoy heat treatment at 600-800 ^o C to form a compound superconducting Nb ₃ Sn.

 The process of the final stage of formation of a composite with a cellular structure of a fiber can be carried out both by the hot pressure treatment method and by the cold pressure treatment method.

Case Studies
Example 1

 In FIG. 1 shows a superconductor, the manufacturing process of which includes the operation of forming a primary composite billet containing an outer shell 1 of matrix material and an axial composite block made of six niobium rods 2 and one alloying insert 3.

 In FIG. 2 shows a superconductor, the manufacturing process of which includes the operation of forming a primary composite billet containing an outer shell 1 of matrix material and an axial composite block made of 16 niobium rods 2 and three alloying inserts 3.

 In FIG. 3 shows a superconductor, the manufacturing process of which includes the operation of forming a primary composite billet containing an outer shell 1 of matrix material and an axial composite block made of 81 niobium rod 2 and four alloying inserts 3.

 Example 2

In FIG. Figure 4 shows a composite copper-stabilized 1 with a diffusion barrier 2 multi-fiber superconductor containing 12,684 fibers, each of which is formed of 81 niobium fiber and 4 alloying inserts, obtained by the "bronze" technology. The final diameter of the conductor is 0.8 mm, the transverse size of the rods forming the niobium block at this size is comparable with the lattice parameter of magnetic fluxoids. The critical current density in a magnetic field of 12 T is 790 A / mm ² .

The technical result of the proposed method for manufacturing a composite superconductor based on the Nb ₃ Sn compound is to increase the critical current density in a magnetic field of 12 T by more than 30% compared to a composite superconductor, the fibers of which are obtained from a niobium cylindrical monolithic block with cavities filled with alloying inserts.

Claims (3)

1. A method of manufacturing a composite superconductor based on the Nb ₃ Sn compound, comprising the steps of forming a primary composite billet containing an outer shell of matrix material and an axial cylindrical block of niobium containing a longitudinally located alloying component, deforming the primary composite billet to produce a hexagonal rod, cutting hex a bar for measured lengths, the formation of a secondary composite billet consisting of an external cover made of Cu-Sn alloy with space for placement Nia primary preform, deformation of the second composite to the desired cross section of the superconductor and conducting diffusion heat treatment at 600 - 800 ^o C to form a superconducting compound Nb ₃ Sn, characterized in that the axial cylindrical block of niobium operate a composite of a plurality, but not less than seven longitudinally located rods, and at least one of these rods is made of an alloying component.  2. The method according to claim 1, characterized in that the axial cylindrical block of niobium is made of composite of at least nineteen longitudinally spaced rods, and at least at least three rods uniformly distributed over the cross section of the cylindrical block are made of an alloying component.  3. The method according to p. 1 or 2, characterized in that the number of rods of which the cylindrical block of niobium is made is chosen so that their transverse size in the finished wire is a multiple of the lattice parameter of the magnetic fluxoids in the working range of magnetic fields.

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