RU2436198C1 - COMPOSITE SUPERCONDUCTING TAPE BASED ON Nb3Sn COMPOUND - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: composite superconducting tape based on Nb₃Sn compound consists of at least three alternating layers arranged in a copper shell: alloy Cu-(0.5-1.5) wt % Sn and multi-layer packs of nanostructure layers Nb₃Sn and alloy Cu-(0.5-1.5) wt % Sn so that the layers adjacent to the copper shell are layers of alloy Cu-(0.5-1.5) wt % Sn.

EFFECT: increased critical density of conductor current and improved extent of stabilisation.

2 cl, 1 dwg

Description

The invention relates to the field of electrical engineering and can be used as a superconducting material in the manufacture of superconducting magnetic systems for various purposes to generate constant magnetic fields, for example, in fusion reactors for plasma confinement, particle accelerators, energy storage devices and other devices.

The superconducting compounds Nb ₃ X, where X is selected from the group of metals consisting of Al, Sn and Ge, for example, Nb ₃ Sn, Nb ₃ Ge, Nb ₃ Al, are supposed to be used for the manufacture of superconducting material, since it is suitable for creating magnetic fields such tensions for which the superconducting material based on the NbTi alloy cannot be considered satisfactory.

However, all Nb ₃ X compounds, unlike NbTi, have extremely high hardness and brittleness and, therefore, cannot be processed using plastic deformation.

Known conductors based on intermetallic compounds Nb ₃ Sn, Nb ₃ Al, Nb ₃ Al _0.8 Ge _0.2 (WO / 2005/088651, MKI H01B 1/02, publ. 09/22/2005; WO 2003/058727, MKI H01L 39 / 14, publ. 07/17/2003; US 6,508,889, MKI H01B 12/00, publ. 01, 21, 2003), which are generally a matrix of copper or aluminum with axial-shaped superconducting elements located in it.

Such conductors possess high values of the critical current, critical temperature, and upper critical magnetic field, but an unsatisfactory degree of stabilization associated with low thermal conductivity and high matrix resistance.

Known wire (prototype) for Nb ₃ X superconducting wire containing a stabilizing matrix with embedded superconducting wire cores, each of which is made of a copper rod, a layered part formed of two sheets, the first of which is made of pure niobium or its alloy, and the second - from a metal or alloy containing X atoms, which interact with niobium to form a superconducting compound. Between the copper rod and the layered part and on top of it are layers formed by the specified sheet of niobium or its alloy, and the contacting surfaces of the two sheets and the niobium sheet and the copper rod are zigzag to increase the contact area between them. In this case, niobium has a purity of at least 99.0%, and the second one is made of metal X or an alloy containing X atoms. (RU 2122758, H01B 12/00, publ. 11/27/1998.)

However, the critical current density of such a conductor is insufficient for the current level of technology. Pinning of superconducting vortices (pinning) in these wires, which determines their current carrying capacity, occurs at grain boundaries, precipitates of the second phase and other structural defects of a size on the order of or greater than the penetration depth of the magnetic field of the superconductor, i.e. pointwise. In addition, they have an unsatisfactory degree of stabilization associated with low thermal conductivity and high matrix resistance.

The present invention solves the problem of creating a composite with an increased critical current density of the conductor and an improved degree of stabilization.

According to the invention, a composite superconducting tape based on the Nb ₃ Sn compound consists of at least three alternating layers located in the copper shell: Cu- (0.5-1.5) wt.% Sn alloy and multilayer packs of Nb nanostructured layers ₃ Sn and Cu- (0.5-1.5) wt.% Sn alloy layers so that the layers adjacent to the copper shell are Cu- (0.5-1.5) wt.% Sn layers.

In the present invention, the term multilayer packs of nanostructured layers of Nb ₃ Sn and a Cu- (0.5-1.5) wt.% Sn alloy refers to a structure consisting of alternating layers of a Nb ₃ Sn compound and layers of a Cu- (0.5 -1.5) wt.% Sn nanoscale thickness.

To improve the stabilizing properties of the composite superconducting tape, the ratio of the thicknesses of the layers of the copper shell, multilayer packs and alloy is 1: (8-12) :( 10-15).

The present invention is a superconducting wire of flat geometry. In contrast to the above-described conductors, the fixing of superconducting vortices in it occurs at artificially created interlayer boundaries. Such boundaries are more effective pinning centers, since the vortex is fixed not pointwise, but over its large length. This makes an additional contribution to the critical current density of the conductor.

In addition, the outer layers of copper in the proposed flat conductor during heat treatment, which results in the formation of the Nb ₃ Sn compound, remain uncontaminated with tin and, therefore, its thermal conductivity remains high and the electrical resistance is low, which positively affects the stabilizing properties.

An increase in the number of layers of the Cu- (0.5-1.5) wt.% Sn alloy and multilayer packs of nanostructured layers of Nb ₃ Sn and the Cu- (0.5-1.5) wt.% Sn alloy leads to an increase in the number of intermediate annealing upon receipt of such a composite tape, which in turn significantly increases the cost of the process and increases the time it takes.

The drawing shows the design of a 5-layer composite superconducting tape based on the compound Nb ₃ Sn.

The composite superconducting tape according to the invention consists of layers 1 formed by a copper sheath, adjacent layers 2 of a Cu- (0.5-1.5) wt.% Sn alloy and a multilayer bundle 3 of nanostructured Nb ₃ Sn and alloy layers located between them Cu- (0.5-1.5) wt.% Sn (drawing).

The following examples confirm, but do not limit, the invention.

Example

At the first stage, a packet of 16 Cu and 15 Nb foils 0.3 and 0.3 mm thick, respectively, was assembled, so that the outer foils were copper foils. Then the package was first subjected to diffusion welding under a pressure of 25 MPa at 800-850 ° C for 40 minutes and then rolling on a vacuum rolling mill with preliminary heating at 850 ° C in two passes with 25-30% compression in one pass and then rolled at room temperature to tape 0.3 mm thick.

2nd stage. The bag was assembled from 31 foils after the 1st cycle with a thickness of 0.3 mm. Then the package was first subjected to diffusion welding under a pressure of 25 MPa at 800-850 ° C for 40 minutes and then rolling on a vacuum rolling mill with preliminary heating at 850 ° C in two passes with 25-30% compression in one pass and then rolled at room temperature to tape 0.1 mm thick. To form layers of the superconducting compound Nb ₃ Sn, the composite was annealed at 750 ° C for 5 h and at 600-650 ° C for up to 300-350 h.

3rd stage. The bag was assembled according to the following design (drawing): (one strip of bronze with a thickness of 1.1 mm) / (10 pieces of Nb / Cu - tape after the 2nd stage with a thickness of 0.1 mm) / (one plate of bronze with a thickness of 1.1 mm) and then turned around with one layer of sheet annealed copper foil with a thickness of 0.1 mm.

The volume contents of bronze and niobium in the preform were selected so as to satisfy the ratio t _Nb N _Nb / t _CuSn N _CuSn = 0.150-0.300, where t _Nb and t _CuSn are the thicknesses of the niobium and bronze layers, N _Nb and N _CuSn are the number of niobium layers and bronzes respectively. When this ratio is fulfilled, the maximum amount of tin from bronze and all niobium will be spent on the formation of the superconducting compound Nb ₃ Sn.

Before assembly, the bronze plate was annealed at 700–750 ° C for 1 h. Then, the packet was welded by rolling in a vacuum rolling mill with preliminary heating at 750–800 ° C in two passes with 30–35% reduction in one pass and then rolled at room temperature at room temperature to a tape 0.3 mm thick.

After the 3rd stage, the calculated thicknesses of the niobium and bronze layers are 9.7 nm and 97.3 μm, respectively; the number of niobium and bronze layers is 4650 and 2, respectively. Then the ratio t _Nb N _Nb / t _CuSn N _CuSn is 0.232. This is close enough to the theoretical value of the ratio (0.288), but with a certain excess of tin in relation to its calculated amount.

As a result, a composite was obtained consisting of two layers of Cu- alloy (0.5-1.5 wt% Sn) located between the outer copper layers and a multilayer stack of alternating nanosized layers of Nb ₃ Sn and Cu- (0.5 -1.5 wt.% Sn). The calculated thickness of the Cu- (0.5-1.5 wt% Sn) alloy layers was 97.3 μm, of the multilayer bundle 88.5 μm, and the outer copper layers 8.8 μm. The ratio of the thicknesses of copper, multilayer pack and Cu- alloy (0.5-1.5 wt.% Sn) was 1:10:11.

The critical current density of the resulting composite is 64,000 A / cm ² in a 6 Tesla magnetic field.

As can be seen from the above examples, the present invention allows to obtain a composite superconducting tape based on the Nb ₃ Sn compound with a high critical current density, capable of carrying a large total current and at the same time having enhanced stabilizing properties.

Claims (2)

1. A composite superconducting tape based on the Nb ₃ Sn compound, consisting of at least three alternating layers located in the copper shell: Cu- (0.5-1.5) wt.% Sn alloy and multilayer packs of Nb nanostructured layers ₃ Sn and Cu- (0.5-1.5) wt.% Sn alloy layers so that the layers adjacent to the copper shell are Cu- (0.5-1.5) wt.% Sn layers. 2. The composite superconducting tape according to claim 1, characterized in that for improving the stabilizing properties of the tape, the ratio of the thicknesses of the layers of copper, multilayer packs and alloy is 1: (8-12) :( 10-15).

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