RU2371795C1 - Manufacturing method of superconducting multiply bend - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: on surface of plate made from titanium it is located powder of high-temperature superconducting (HTSC) compound and it is implemented cold deformation by means of rolling with receiving of preferred-orientation scales of HTSC compound. Scales are separated from substrate, it is collected multilayer packet from scales with alternating spacers from silver and it is pressed with formation of multilayer composite silver-HTSC-silver. Composite is placed into envelope made of silver, it is rolled with receiving of band of specified geometry and is thermal treated at temperatures in the range 800-930C during 20-100 hours. ^ EFFECT: increasing current-carrying ability of band and filling factor by superconductor. ^ 2 ex

Description

The invention relates to the development of metallurgical methods for the manufacture of superconducting HTSC wires, tapes for use in power lines, superconducting magnetic systems, electric generators, electric motors, magnetic bearings, energy storage devices, etc.

Most of the currently known high-temperature superconductors (HTSC) are brittle substances and therefore the so-called “PIT” method (powder in a pipe) is most widely used for the manufacture of wires and strips from them. This method was first applied to the Nb ₃ Sn compound by Kunzler in 1961 [JEKunzler / Rev. Mod. Phys., 1961, v. 33, p. 501]. According to this method, a niobium tube or a monel metal tube in a stoichiometric ratio (3: 1) is filled with a mixture of niobium and tin powders or a mixture of powders of the compound Nb ₃ Sn and pure tin (9: 1). Then the pipe is closed on both sides and then subjected to drawing through the die to a predetermined diameter (0.38-0.5 mm). At the final stage, during the heat treatment (970-1400 ° C), a superconducting Nb ₃ Sn phase is formed in the pipe core. In this case, for the first time, superconducting Nb ₃ Sn wires with T _c = 17.8 K and current-carrying capacity were obtained

1.5 · 10 ⁵ A / cm ² in a magnetic field of 88 kOe. Using the Kunzler method, in a vanadium shell, wires with a superconducting core of V ₃ Si and V ₃ Ga were also obtained. It was this breakthrough achievement that was the beginning of the rapid development of research on superconductors. The main disadvantage of the superconducting composites obtained by the Kunzler method is their high fragility after annealing and, as a consequence, the inability to reuse.

Later, in connection with the discovery in 1986 of HTSC compounds with values of T _c higher

77 K, this method was further developed and applied. Closest to the proposed method is the method described in [H.L. Zheng, Z.M.Yu, X.M. Xiong et al. Effect of precursor powder on microstructure and critical current density of (Bi, Pb) -2223 tapes. Physica C, 386, (2003), p. 138-141]. At the same time, various compositions of HTSC compounds (or the ingredients from which HTSC will be formed during the heat treatment) are often laid in silver in a pipe. Then the ends of the pipe with the powder are pressed and it is deformed in various ways (by rolling, drawing, pressing, etc.) to a predetermined geometric size. At the final stage, the tape or wire is subjected to heat treatment according to optimized modes.

Both single-core and multi-core conductors are made with various sizes in thickness, width and length. The level of density values of superconducting currents of HTSC tapes produced by the closest powder method in a pipe (according to American Superconductor) directly by a superconductor at nitrogen temperatures (77 K) in its own magnetic field, as a rule, is 1 · 10 ⁴ -7 · 10 ⁴ A / cm ² (maximum design current density ≈2 · 10 ⁴ A / cm ² ).

The specified method along with certain advantages, for example, relative ease of implementation, has several significant disadvantages:

- in these tapes there is a sharp decrease in the critical current density in an external magnetic field (of the order of several hundred oersteds) at a temperature of liquid nitrogen of 77 K;

- in the process of deformation processing in the HTSC core due to insufficient uniformity of the density of the powder to be poured, pinch-offs and tears arise - the so-called “sausage effect” appears;

- the fill factor for the HTSC material in the tape or wire due to the low density of the powder to be poured after deformation processing does not exceed 30-35%;

- it is not possible to achieve a sharp texture in the basal plane of HTSC conductors or interlayers;

- it is not possible to obtain a uniform section of the HTSC core in both the transverse and the longitudinal section.

The problem to which the present invention is directed, is to create a method of manufacturing a superconducting multilayer tape with increased values of current carrying capacity at a temperature of liquid nitrogen of 77 K.

The technical result of the invention is to increase the current carrying capacity of the tape and the duty cycle of the superconductor due to the formation of higher-density interlayers from HTSC compounds (Y-123, Bi-2223, Bi-2212, etc.) with a sharp base texture in the plane of the tape.

The technical result is achieved in that in a method for manufacturing a superconducting multilayer tape, comprising filling a silver shell with powder from various HTSC compounds, deforming to the required dimensions, and heat treating, according to the invention, the powder is subjected to preliminary texturing before being placed into a silver shell by cold rolling on the plate surface made of titanium with strength and hardness values 2 times higher than that of pure silver, then the rolled HTSC layer in the form of flakes is removed from the titanium substrate, a laminated bag is formed from rolled flakes with alternating silver gaskets, it is pressed to form a multilayer composite: Ag-BTCП-Ag, which is then again placed into a silver shell, deformed by rolling to the specified geometric dimensions of the tape and heat treated (depending on the specific HTSC compound) at temperatures in the range of 800-930 ° C for 20-100 hours.

SUMMARY OF THE INVENTION

Due to the development of a new method of cold deformation by rolling the HTSC powder on the surface of a stronger and harder metal substrate than silver, in particular titanium, high-density (up to 95-98%), thin (10-40 microns) coatings or HTSC-flakes are obtained compounds with a sharp base texture and most importantly easily detachable from the substrate after cold rolling. This advantage allows us to use pre-textured and compacted flakes instead of loose powder, interlayers for use as current-carrying material in wires and multilayer HTSC tapes with a silver sheath. In addition, the use of pre-textured HTSC powders can increase core density, uniformity of filling along the length, and fill factor. At the same time, the density of the transport current increases more than 2 times in comparison with the known analogues and prototype.

Example 1

1. From pure titanium, the method of rolling is to produce ribbons 8-10 mm wide and 3.2-3.4 mm thick.

2. After rolling, recrystallization annealing is carried out at 800 ° C for 15 minutes.

3. After annealing, a longitudinal groove 4-5 mm wide and a depth of 1.0 mm is extruded onto the surface of the tape by pressing.

4. Then, the recess is filled with HTSC powder.

5. After this, the tape with the powder is subjected to subsequent cold rolling. To prevent powder from sticking to the rolls of the rolling mill, a titanium foil is laid between the roll and the rolled strip. It is the use of gaskets made of titanium that allows cold rolling of HTSC powders without powder sticking to the surface of the rolls. Thinning during cold deformation in 1 pass is 0.2-0.3 mm.

6. After reaching a tape thickness of 2.0-2.2 mm, the coating rolled on a titanium substrate is separated in the form of a thin high-density layer with a sharp base texture (the degree of texture is 1.5-2 times higher than in the case of rolling on silver )

7. From these interlayers in an amount of 5 to 10 or more, a bag is made up of alternating interlayers of silver, which is placed in a silver shell, and then cold rolling is carried out in a strip to a predetermined thickness (0.3-0.4 mm). At the final stage, the tape containing the Bi-2223 phase is annealed in air at temperatures of 830-850 ° C for 50-100 hours, the tape containing the Bi-2212 phase is annealed in argon at temperatures in the range 800-830 ° C. and in the case of compound Y-123, annealing is carried out in an oxygen atmosphere at temperatures in the range of 900-930 ° C for 24-100 hours.

As a result of carrying out the indicated technological operations at the stage after cold rolling on titanium of the Bi-2223 phase, the dispersion of grain orientations (A), determined by the half-width of the maximum, decreases from Δ≈15 ° (for the case of a silver substrate) to Δ≈10 ° (for a titanium substrate ) The fill factor in the HTSC phase in the tape increases to 50%, and the density of the superconducting layer also increases to 95-98%. These factors contribute to a 2-fold increase in the constructive critical current density of a multilayer superconducting tape (J _c to ~ 3-4 · 10 ⁴ A / cm ² in its own magnetic field at a temperature of 77 K) in comparison with many well-known companies producing HTSC tapes powder method "PIT". In this case, the cross-section (thickness) of the rolled HTSC layers practically does not change (the “sausage effect” practically does not appear along the length of the rolled tape), and the fill factor along the superconductor in the tape volume due to the use of high-density HTSC flakes instead of powder increases by 1.5 times.

Example 2

After cold rolling powders of HTSC compounds on the surface of a titanium substrate to a thickness of ≈100 μm or less, a thin layer of silver with a thickness of 5-20 μm is applied by spraying to a coating of HTSC.

At the next stage, the HTSC coating is separated from the titanium substrate and cut into 5-10 pieces of the same length and then a multilayer composite of (5-10 layers) is pressed into a recess on the surface of the silver substrate. A prepared preform (composite) containing a multilayer package of HTSC layers and silver interlayers is then again deformed by cold rolling into a tape to the specified thickness (0.25-0.4 mm).

At the final stage, the tapes are subjected to prolonged annealing, depending on the HTSC compound used, either in air in the case of the Bi-2223 phase, in oxygen in the case of Y-123, and in argon as applied to the Bi-2212 phase at temperatures of 800–930 ° С for 20 -100 hours.

As a result of these technological operations, the texture in the HTSC layer is enhanced, due to the small thickness of the silver interlayers, the fill coefficient in the HTSC phase increases to 55%, and the density of the superconducting layer also increases to 95-98%. These factors contribute to a 2-3-fold increase in the constructive critical current density of a multilayer superconducting tape (J _c to ~ 4-5 · 10 ⁴ A / cm ² in its own magnetic field at a temperature of 77 K) in comparison with many well-known companies producing HTSCs - tapes by the powder method "PIT". In this case, the cross section (thickness) of the rolled HTSC interlayers practically does not change along the length of the tape (the “sausage effect” practically does not appear). In the proposed method, unlike the known ones, an easier access of oxygen is provided during the heat treatment, which reduces the annealing time at the final stage of tape production.

Claims (1)

A method of manufacturing a superconducting multilayer tape, comprising placing on the surface of a titanium plate a powder of a high temperature superconducting (HTSC) compound, cold deformation by rolling to obtain textured flakes of an HTSC compound, separating the flakes from the titanium substrate, assembling a multilayer bag of flakes with alternating silver spacers, pressing the resulting package with the formation of a multilayer composite silver-HTSC-silver, the placement of the composite in a shell of silver, deformation by rolling to obtain a tape of specified geometric dimensions and heat treatment at temperatures in the range of 800-930 ° C for 20-100 hours