RU2367043C1 - Method of making multi-layer tape nanostructure composite based on superconducting niobium-titanium alloy - Google Patents

Abstract

FIELD: physics; conductors. ^ SUBSTANCE: invention relates to making composites with improved current-carrying capacity and can be used, particularly, for making superconducting magnet windings. According to the invention, the method of making multi-layer tape nanostructure composites based on a niobium-titanium alloy for composite superconductors involves multi-cycle rolling, each cycle of which involves assembling a packet from alternating plates of niobium and a niobium-titanium alloy, attaching the plates to each other into a packet through diffusion welding at temperature 800-900C and pressure 20-40 MPa for 0.5-3 hours, hot vacuum rolling and cold rolling. In the first cycle, the initial plates are components of the composite, and in the second and following cycles - plates, obtained from the previous cycle. To stabilise the superconductor before the last rolling cycle, the welded packet is put into a copper casing. Thickness of the copper casing is 3-25% of the thickness of the packet. ^ EFFECT: increased critical current density. ^ 2 cl, 2 tbl, 6 ex

Description

The invention relates to the field of creating new functional materials, namely layered nanostructured composite superconducting materials based on niobium alloys with high current-carrying capacity, and can be used to create windings of superconducting magnets.

Of great interest are materials containing Nb-Ti and Nb-Zr alloys. Multilayer flat nanostructured composites based on these alloys are promising for the creation of superconducting materials with high current-carrying capacity. In a ribbon conductor, plane parallel superconducting layers, the thickness of which is 10-100 nm and, therefore, comparable with the coherence length of the superconductor, allow us to use the effect of an extended flat interlayer boundary parallel to the external magnetic field on the pinning (fixing) of the Abrikosov vortices and, therefore, critical current density value.

A known method of producing superconducting wires based on niobium-titanium alloys, including placing in a glass of copper or an alloy based on copper a blank of niobium-titanium alloy, sealing, hot extrusion and cold deformation to obtain a bar, cutting the bar into measured parts, subsequent assembly into a cup of copper or an alloy based on copper of measuring rods to obtain the required number of niobium-titanium fibers in the last composite billet, carrying out cold deformations, annealing and final deformation, p This rods and placed last in the composite preform, preliminarily deformed in the cold with an intermediate annealing at a temperature of 385-420 ^o C during 10-100 hours, after which the final assembly is deformed at room temperature until total deformation value sufficient to eliminate all the clearances existing and not less than 10%, then additional annealing is carried out at temperature-time regimes corresponding to the intermediate annealing mode, and subsequent cold deformations with annealing to obtain the wire required cheniya [RF patent №2159474, IPC H01B 13/00, opub. 2000.11.20].

However, this method does not allow to obtain multilayer composite superconducting materials in the form of ribbons.

A known method of producing a multilayer composite [patent US 5,230,748, H01L 39/24, July 19, 1991], in which the superconducting layers of the alloys of the Nb-Ti-Zr-V-Hf-Ta system at the final stage of manufacturing a superconductor are obtained by diffusion annealing of the composite from alternating layers of these metals or their alloys, the thickness of the normal and superconducting layers formed during annealing should be less than 1000 nm.

However, diffusion annealing, which requires sufficiently high temperatures, complicates the process of obtaining a superconducting material and, in addition, requires solving the issue of compatibility of the metallic components included in the composite.

Known, adopted as a prototype, a method of manufacturing a multilayer tape nanostructured composite based on a superconducting niobium-titanium alloy containing alternating layers of niobium and niobium-titanium alloy with an average thickness of each layer of 2.5 nm [Karpov MI, Vnukov VI , Volkov K.G., Medved N.V., Khodos I.I., Abrosimova G.E. "The possibilities of the vacuum rolling method as a method of producing multilayer composites with nanometric layer thicknesses." // “Material science”, 2004, No. 1, p. 48-53]. The method includes multi-cycle rolling, each cycle of which consists of assembling a package of niobium plates and a niobium-titanium alloy, fastening the package with rivets, hot vacuum rolling and cold rolling. In the first cycle, the initial plates were the components of the composite, in the second and subsequent cycles, the plates obtained in the previous cycle. Vacuum rolling in each cycle was carried out in 2 passes with heating the samples to 900 ° C and a total compression of 50%. After rolling, all samples were annealed at 400 ° C for 3 hours to isolate dispersed particles of the α phase in the layers of the Nb-50 alloy by weight of Ti.

However, the critical current density of such a superconducting composite does not satisfy modern technology requirements.

The present invention solves the problem of creating a method for manufacturing a nanostructured composite with a high critical current density, capable of carrying a large total current.

The task is achieved by a method of manufacturing multilayer tape nanostructured composites based on a niobium-titanium alloy by the multi-cycle rolling method, each cycle of which included assembling a package of alternating niobium and niobium-titanium alloy plates, bonding the plates together, hot vacuum rolling and cold rolling. In the first cycle, the initial plates were the components of the composite, and in the second and subsequent cycles, the plates obtained in the previous cycle. The novelty of the proposed method lies in the fact that the fastening of the plates together in a package is carried out using diffusion welding at a temperature of 800-900 ^about C and a pressure of 20-40 MPa for 0.5-3 hours

To stabilize the superconductor before the last rolling cycle, the welded bag is placed in a copper shell. The thickness of the copper shell is 3-25% of the thickness of the package.

The technical result of the invention is to increase the critical current density of multilayer tape nanostructured composites by increasing the uniformity of the thickness of the rolled layers, which is the result of a decrease in their undulation.

When studying the microstructure of the cross sections of composite samples cut parallel to the rolling direction, we found that the critical current density was the higher, the less wavy the niobium layers and the niobium-titanium alloy layers. By analogy with vibrational processes, the wavelength of one wave L and its amplitude A were taken to characterize the undulation of the layered structure. It was also noted that in layers with a strongly pronounced undulation (small L and large A), local decreases (up to zero) of the layer thickness were noted both niobium and niobium-titanium alloy.

The least noticeable undulating structure was manifested in the case when the package was rolled, pre-bonded using diffusion welding, carried out in the intervals declared by us.

At the same time, placing it before the last rolling cycle in a copper shell of the thickness declared by us led to stabilization of multilayer tape nanostructured composites with a high critical current density.

Table 1 shows the data on the change in the critical current density of composites with different compositions of niobium-titanium alloy, obtained both by the present method and by the prototype method.

Table 2 shows the data on the change in the critical current density of the obtained composites depending on the modes of bonding the plates to each other using diffusion welding.

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

Example 1

Samples of a multilayer tape nanostructured composite in the form of a tape with a width of 30-40 mm and a thickness of 0.3 mm were obtained as in the prototype by the method of multi-cycle rolling. Each cycle consisted of four sequential operations: assembling the bag from the original plates, fastening the bag with rivets, hot vacuum rolling, and cold rolling. In the first cycle, the initial plates were the components of the composite, in the second and subsequent cycles, the plates obtained in the previous cycle.

The first assembly of the Nb / (Nb-50 wt.% Ti) composite consisted of 20 layers of niobium and 19 layers of the alloy. The thickness of the initial plates of niobium and alloy was equal to 0.3 mm Cold rolling in each cycle was also completed at a thickness of 0.3 mm. In the third cycle, rolling was carried out until a final thickness of 0.15 mm was reached. Vacuum rolling in each cycle was carried out in 2 passes with heating the samples to 900 ° C and a total compression of 50%. The result was a composite consisting of 64,000 layers with an average layer thickness of 2.5 nm.

After rolling, all samples were annealed at 400 ° C for 3 hours to isolate dispersed particles of the α phase in the layers of the Nb-50 alloy by weight of Ti.

The critical current was measured at a temperature of liquid helium in an external magnetic field of up to 7 T with two orientations: parallel to the plane of the obtained composite (nanolaminate) and perpendicular to the transport current (in this case, the Lorentz force acting on the Abrikosov vortices is directed perpendicular to the plane of nanolaminate, and pinning to the interlayer surface takes place) 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 entire cross-sectional area of the composite.

The structure of the samples was studied by scanning electron and transmission electron microscopy. The plane of the sections and foils for these studies was parallel to the direction of rolling of the composite.

The microstructure of the obtained composite was characterized by such values of the wave-like parameters: L≈170 μm, A≈10 μm.

The critical current density of the obtained composite is 30,000 A / cm ² in a magnetic field of 6 T.

Example 2

The same as in example 1, only the bonding of the plates to each other is carried out using diffusion welding. Diffusion bonding was carried out using the apparatus of an induction heating at ⁸⁵⁰ ° C and a pressure of 25 MPa for 1 h.

The microstructure of the obtained composite was characterized by such values of the wave-like parameters: amplitude A≈0.5 μm, period L more than 300 μm.

The critical current density of the resulting composite is 38,000 A / cm ² in a magnetic field of 6 T.

Example 3

The same as in example 1, only as a niobium-titanium alloy was taken an alloy of the composition Nb-30 wt.% Ti.

The microstructure of the obtained composite was characterized by such values of the wave-like parameters: L≈170 μm, A≈10 μm.

The critical current density of the obtained composite is 40,000 A / cm ² in a magnetic field of 6 T.

Example 4

The same as in example 3, only the bonding of the plates to each other is carried out using diffusion welding. Diffusion bonding was carried out using the apparatus of an induction heating at ⁸⁵⁰ ° C and a pressure of 25 MPa for 1 h.

The microstructure of the obtained composite was characterized by such values of the wave-like parameters: amplitude A≈0.5 μm, period L more than 550 μm.

The critical current density of the resulting composite is 57200 A / cm ² in a magnetic field of 6 T.

Data on the change in the critical current density of composites with different compositions of niobium-titanium alloy obtained both by the present method and the prototype method are shown in table 1.

As can be seen from the above examples, the bonding of the plates together, carried out using diffusion welding according to the proposed method, reduces the undulation of the layers and thereby increases the critical current density.

Example 5

The same as in example 4, only the bonding of the plates to each other is carried out using diffusion welding, carried out under various conditions. The data on the change in the critical current density depending on the modes of bonding the plates to each other using diffusion welding are shown in table 2.

As seen from the table that the optimal modes of diffusion welding are: temperature 800-900 ^{° C,} pressure 20-40 MPa, time of 0.5-3 hours.

Example 6

Samples of a multilayer tape nanostructured composite in the form of a tape with a width of 30-40 mm and a thickness of 0.15 mm were obtained by the multi-cycle rolling method. Each cycle consisted of four sequential operations: assembling the bag from the original plates, fastening the bag using diffusion welding, hot vacuum rolling, and cold rolling. In the first cycle, the initial plates were the components of the composite, in the second and subsequent cycles, the plates obtained in the previous cycle.

The first assembly of the Nb / (Nb-30 wt.% Ti) composite consisted of 16 layers of niobium and 15 layers of the alloy. The thickness of the initial plates of niobium and alloy was equal to 0.3 mm Cold rolling in each cycle was also completed at a thickness of 0.3 mm. Before the third rolling cycle, the welded bag was placed in a copper shell, the thickness of which is 10% of the thickness of the package and rolling was carried out until a final thickness of 0.3 mm was reached. Vacuum rolling in each cycle was carried out in 2 passes with heating the samples to 900 ° C and a total compression of 50%. The result was a composite consisting of 28,830 layers of niobium and a niobium-titanium alloy and two outer layers of copper, in which the thickness of each alloy layer was 5.9 nm.

Studies of the effect of the thickness of the copper shell on the preparation of the composite showed that a decrease in the thickness of the copper shell of less than 3% of the thickness of the packet is impractical so as not to impair its stabilizing effect. An increase in the thickness of the copper shell of more than 25% of the thickness of the packet leads to an unjustified increase in the non-bearing cross-sectional area, i.e. to reduce the critical current density.

As can be seen from the above examples, the manufacture of a multilayer tape nanostructured composite based on the superconducting niobium-titanium alloy by the proposed method leads to an increase in the critical current density due to a decrease in the wave-like parameters of the layers.

Table 1 No. p / p Composition of niobium-titanium alloy Prototype method: rivet the package The inventive method: fastening the package by diffusion welding Parameters of wave-like layers The critical current density at 6 T, A / cm ² Parameters of wave-like layers The critical current density at 6 T, A / cm ² one 25 A≈10 μm
L = 170 μm 39700 A≈0.5 μm
L> 500 μm 56000 2 thirty A≈10 μm
L = 170 μm 40,000 A≈0.5 μm
L> 500 μm 57200 3 40 A≈10 μm
L = 170 μm 40500 A≈0.5 μm
L> 500 μm 57000 four fifty A≈10 μm
L = 170 μm 30120 A≈0.5 μm
L> 300 μm 38000 5 55 A≈10 μm
L = 170 μm 25,400 A≈0.5 μm
L> 300 μm 36000

table 2 No. p / p Modes of fastening plates together using diffusion welding The critical current density at 6 T, A / cm ² Temperature, ^о С Pressure, MPa Time hour one 750 fifteen 0.3 No connection 2 800 twenty 0.5 57600 3 850 thirty 1,5 57000 four 900 40 3 56500 5 950 45 3,5 Cross diffusion between layers

Claims (2)

1. A method of manufacturing a multilayer tape nanostructured composite based on a niobium-titanium superconducting alloy, including multi-cycle rolling, each cycle of which consists of assembling a packet of plane plates parallel to the composite plane of alternating niobium and niobium-titanium alloys, bonding the plates together followed by hot vacuum and cold rolling, moreover, in the first cycle, the initial plates are the components of the composite, and in the second and subsequent cycles, the plates obtained in the previous cycle are excellent sistent with the fact that the bond between the plates is carried out by means of diffusion bonding at a temperature of 800-900 ° C and a pressure of 20-40 MPa for 0.5-3 hours. 2. The method according to claim 1, characterized in that before the last rolling cycle, the welded bag is placed in a copper shell with a wall thickness of 3-25% of the thickness of the bag.