RU2436197C1 - 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 multi-layer packs. ^ EFFECT: increased critical density of conductor current and improved extent of stabilisation. ^ 2 cl, 2 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 6508889, MKI Н01В 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. Moreover, 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, НВВ 12/00, publ. 11/27/1998).

However, the critical current density of such a conductor is insufficient for the current level of technology. The fixing 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 superconductor magnetic field, 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 nanostructured Nb ₃ layers Sn and Cu- (0.5-1.5) wt.% Sn alloy so that the layers adjacent to the copper shell are layers of multilayer packs.

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: (3-6) :( 10-25).

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.

Figure 1 shows the design of a 5-layer composite superconducting tape based on the Nb ₃ Sn compound.

Figure 2 shows the design of a 7-layer composite superconducting tape based on the Nb ₃ Sn compound.

The composite superconducting tape according to the invention consists of layers 1 formed by a copper sheath, adjacent multilayer packs 2, nanostructured layers of Nb ₃ Sn and a Cu- (0.5-1.5) wt.% Alloy and an alloy layer 3 located between them Cu- (0.5-1.5) wt.% Sn (Figure 1) or three multilayer packs of nanostructured layers of Nb ₃ Sn and Cu- (0.5-1.5) wt.% Alloy with two layers of the alloy Cu- (0.5-1.5) wt.% Sn 3 (Figure 2).

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

Example 1

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 a compression of 25-30% 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 a compression of 25-30% in one pass and then rolled at room temperature to tape 0.1 mm thick.

3rd stage. The package was assembled according to the following construction of Fig. 1: (5 segments of Nb / Cu tape, after the 2nd stage with a thickness of 0.1 mm) / (one strip of bronze (copper alloy with 12 wt.% Tin) 2.2 mm thick) / (5 segments of Nb / Cu tape after the second stage with a thickness of 0.1 mm) and then wrapped 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 ° С for 1 h. Then, the packet was welded by rolling in a vacuum rolling mill with preliminary heating at 750–800 ° С 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 194.7 μm, respectively; the number of niobium and bronze layers is 4650 and 1, respectively. Then the ratio t _Nb N _Nt / 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 multilayer packs placed between the outer copper layers, which are alternating nanosized layers of Nb ₃ Sn and Cu- alloy (0.5-1.5 wt% Sn) and a layer of Cu- alloy located between them (0.5-1.5 wt.% Sn) (Figure 1). The calculated thickness of the Cu- alloy layer (0.5-1.5 wt% Sn) was 194.7 microns, multilayer packs - 44.3 microns, outer layers of copper - 8.8 microns. The ratio of the thicknesses of copper, multilayer packs and Cu- alloy (0.5-1.5 wt.% Sn) was 1: 5: 22. According to scanning electron microscopy, the calculated layer thicknesses satisfactorily coincided with the measured average layer thicknesses.

The critical current was measured at a temperature of liquid helium in an external magnetic field of up to 7 Tesla with two orientations: parallel to the plane of the obtained composite (nanolaminate) and perpendicular to the transport current (in this case, the Lorentz force is directed perpendicular to the plane of nanolaminate and there is pinning on the interlayer surface) and perpendicular to the plane of the nanolaminate and the transport current (in this case, there is no pinning on the interlayer surface). The critical current density was determined by the ratio of the total transport current to the cross-sectional area occupied by multilayer layers, which included nanoscale layers of the Nb ₃ Sn compound.

The critical current density of the resulting composite is 62,000 A / cm ² in a 6 Tesla magnetic field.

Example 2

At the first stage, a packet of 14 Cu and 15 Nb foils 0.3 and 0.3 mm thick, respectively, was assembled, so that the outer foils were niobium foils, and after assembly, the packets were wrapped with one layer of annealed 0.3 mm thick copper foil and then subjected to rolling in a vacuum rolling mill with preliminary heating at 850 ° C in two passes with compression of 25-30% in one pass and then rolled at room temperature to a tape 0.3 mm thick.

2nd stage. The bag was assembled from 31 foils after the 1st stage with a thickness of 0.3 mm. And after assembly, wrapped in a single layer of annealed copper foil with a thickness of 0.1 mm. Then the package was subjected to the same processing as in the first stage.

3rd stage. The package was assembled according to the following design: (5 cut-offs of Nb / Cu tape, after the 2nd stage 0.1 mm thick) / [one strip of bronze (copper alloy with 12 wt.% Tin) 2.2 mm thick] / ( 5 segments of Nb / Cu tape after the second stage with a thickness of 0.1 mm) and then wrapped 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 ° С for 1 h. Then, the packet was welded by rolling in a vacuum rolling mill with preliminary heating at 750–800 ° С in two passes with 30-35% reduction in one pass and then rolled 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 194.7 μm, respectively; the number of niobium and bronze layers is 4650 and 1, 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 multilayer packs placed between the outer copper layers, which are alternating nanosized layers of Nb ₃ Sn and Cu- alloy (0.5-1.5 wt% Sn) and a layer of Cu- alloy located between them (0.5-1.5 wt.% Sn). The calculated thickness of the Cu- alloy layer (0.5-1.5 wt% Sn) was 194.7 microns, multilayer packs - 44.3 microns, outer layers of copper - 8.8 microns. The ratio of the thicknesses of copper, multilayer packs and Cu- alloy (0.5-1.5 wt.% Sn) was 1: 5: 22. According to scanning electron microscopy, the calculated layer thicknesses satisfactorily coincided with the measured average layer thicknesses.

The critical current was measured at a temperature of liquid helium in an external magnetic field up to 7 Tesla with two orientations: parallel to the plane of the obtained composite (nanolaminate) and perpendicular to the transport current (in this case, the Lorentz force is directed perpendicular to the plane of nanolaminate and pinning occurs on the interlayer surface) and perpendicular to the plane of the nanolaminate and the transport current (in this case, there is no pinning on the interlayer surface). The critical current density was determined by the ratio of the total transport current to the cross-sectional area occupied by multilayer layers, which included nanoscale layers of the Nb ₃ Sn compound.

The critical current density of the resulting composite is 62,000 A / cm ² in a 6 Tesla magnetic field.

Example 3

The same as in example 1, only the package was assembled according to the following design: (4 segments of Nb / Cu tape after the 2nd stage with a thickness of 0.1 mm) / (one strip of bronze with a thickness of 1.1 mm) / (4 segments Nb / Cu tape after the 2nd stage with a thickness of 0.1 mm) / (one strip of bronze with a thickness of 1.1 mm) / (4 pieces of Nb / Cu tape after the 2nd stage with a thickness of 0.1 mm) and then wrapped in a single layer of sheet annealed copper foil 0.1 mm thick.

After the 3rd stage, the calculated thicknesses of the niobium and bronze layers are 9.2 nm and 91.7 μm, respectively; the number of niobium and bronze layers is 5580 and 3, respectively. Then the ratio t _Nb N _Nb / t _CuSn N _CuSn is 0.176. This means that the composite contains an excess of tin, relative to its calculated amount.

As a result, a composite was obtained (Figure 2), consisting of three packs of alternating nanosized layers of Nb ₃ Sn and a Cu- alloy (0.5-1.5 wt.% Sn) located between the outer copper layers and two layers of the alloy located between them Cu- (0.5-1.5 wt% Sn). The calculated thickness of the Cu- (0.5-1.5 wt% Sn) alloy layers was 91.7 μm, multilayer packs 33.3 μm, and the outer copper layers 8.3 μm. The ratio of the thicknesses of copper, multilayer packs and Cu- alloy (0.5-1.5 wt.% Sn) was 1: 4: 11.

The critical current density of the resulting composite is 41,000 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 so that the layers adjacent to the copper shell are multilayer packs of nanostructured layers. 2. The composite superconducting tape according to claim 1, characterized in that in order to improve the stabilizing properties of the tape, the ratio of the thicknesses of the layers of the copper shell, multilayer packs and alloy is 1: (3-6) :( 10-25).

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