RU2088992C1 - METHOD OF PRODUCTION OF MULTIWIRE SUPERCONDUCTOR BASED ON COMPOUND nb*003SN - Google Patents

Abstract

FIELD: manufacture of current- conducting components of superconducting magnetic systems. SUBSTANCE: superconductor is obtained by placement of a niobic rod in a bag of matrix material - an alloy of copper and tin, the blank is deformed with conducting of intermediate heat treatments; the formed bar is cut, and further forming of composite is accomplished the required number of times. A barrier of copper made in the form at least of one rolled up bronze matrix material and bronze bag. EFFECT: enhanced yield of applicable conductor, enhanced quality. 2 cl, 2 dwg

Description

The invention relates to the field of electrical engineering, in particular to methods for producing superconducting wires based on an intermetallic compound Nb ₃ Sn, and can be used for the manufacture of current-carrying elements of superconducting magnetic systems for various purposes.

A known method of obtaining a superconducting wire based on Nb ₃ Sn by assembling a niobium rod in a case of matrix material, which is taken as a deformable bronze alloy of copper with tin, deformation of the obtained composite to the required lateral size with intermediate heat treatments, cutting the resulting composite rod into individual elements , the further formation of the composite the required number of times by placing composite elements in a case made of a bronze matrix material and deforming the compo zita with intermediate heat treatments, final heat treatment of the wire to form the Nb ₃ Sn compound (see TI 10.13.82 for MKNO-14641 wire).

 However, at present, in the process of serial production, there are cases of marriage of a superconductor due to a malfunction of the matrix material 1 containing niobium rods 2 with the case 3, accompanied by the detachment of the shell (case) from the matrix part of the wire (Fig. 1). In order to continue the manufacture of the conductor, it is necessary to remove the place of detachment. At the same time, the yield is reduced and the unit length of the finished wire decreases.

 For modern magnetic systems, winding wires with a unit wire length of more than 1000 m are increasingly required, which makes it necessary to receive wire from each composite billet without breaks and material losses, with the exception of losses provided by the technology. (See TI 10.13.82).

There is also a method of producing a superconducting wire based on Nb ₃ Sn, which is close in technical essence to the claimed solution and taken as a prototype: a wire of MKNOS-14641 brand, manufactured according to technological instruction TI 10.13.82. This is a method consisting in assembling a niobium rod into a case made of matrix material, which is used as a deformable bronze alloy of copper with tin, deforming the obtained niobium-bronze composite to the required lateral size with intermediate heat treatments, cutting the formed bar into separate elements, and then further the formation of a composite wire by placing composite niobium-bronze elements in a bronze case, and when forming the final workpiece in a case of stabilizer a material which is usually selected as copper, separating it from the matrix material by a barrier of niobium, tantalum or other similar materials, deforming the workpiece with intermediate annealing and final heat treatment to form the Nb ₃ Sn compound. In this way, a large number of long (up to 1000 m) stabilized superconducting wires of the MKNOS-14641 and MKNOS-44521 grades are obtained, containing, respectively, 14641 and 44521 niobium core in a bronze matrix.

 However, this method does not allow to reduce defects and wire breakage caused by poor adhesion of the matrix material, which is used bronze Cu 13 wt. tin with a bronze case, which is the case in the manufacture of intermediate 121- and 211-wire rods, from which workpieces are assembled to receive wires, MKNOS-14641 and MKNOS-44521, respectively.

 The marriage is explained by the fact that the diffusion interaction between the cover and the matrix material does not ensure the maintenance of their reliable adhesion in the process of all used technological processes.

 The aim of the invention is to improve the adhesion of the cover with a matrix material containing niobium veins, increasing the yield and unit length of the wire.

This goal is achieved by the fact that in the known method of manufacturing a composite multicore superconductor based on the Nb ₃ Sn compound, which includes the steps of assembling the composite, deforming it with intermediate heat treatments, cutting the formed rod into individual elements, then further forming the composite the required number of times and finalizing heat treatment to form a compound Nb ₃ Sn, between the matrix material containing niobium core and sheath are placed bronze Barrier , Which is made of easily deformable when machining material, not forming a deformation preventing redistribution of compounds with the matrix material and the cover. In this case, a material is used for which the diffusion coefficient of tin from the cover and the matrix material into the barrier material during all the temperature effects used in the manufacture of the conductor is greater than the coefficient of tin mutual diffusion between the cover and the matrix material. The barrier is made in the form of at least one plate rolled into a pipe and placed in an annular cavity, which is provided between the cover and the matrix material.

 Another difference is that the barrier is made with discontinuities, uniformly perforated, such as holes, or mesh.

 A significant difference from the prototype lies in the fact that as a result of the proposed operation of introducing the barrier, diffusion welding zones are formed between the cover and the matrix material, passing through the volume of the barrier and along the entire length of the composite. This difference is due to the diffusion interaction between the components of the barrier, the sheath, and the matrix material, which proceeds quite effectively under thermal stresses during extrusion and intermediate heat treatments necessary to relieve stresses arising from deformation.

 As a barrier material, satisfying all the requirements, it is possible to use a number of metals and alloys: copper, brass, iron. However, there is no strong evidence that there are metals or alloys that are better than copper, suitable for this purpose.

 It is also important that, as a result of technological conversions on the final wire size, the copper barrier will completely merge with the sheath and matrix, being saturated with tin diffusing from them into copper, which will ensure the fast delivery of tin during the final diffusion heat treatment from the peripheral regions of the conductor (i.e. case) into the internal (i.e., into the matrix) where niobium veins are located.

где X расстояние от исходной границы между чехлом (или матричным материалом) и медным барьером, принимаемое равным половине достаточной толщины медного барьера;
τ суммарная длительность равнозначных температурных воздействий;
D коэффициент диффузии олова из бронзы Cu 13 мас. Sn в медь; (см. книгу Л. С. Даркен и Р. В. Гурри "Физическая химия металлов". М. "Металлургия, 1960).When calculating the diffusion penetration of tin from bronze Cu-13 wt. the tin case and the matrix material into the copper barrier to the tin concentration in the barrier equal to the arithmetic mean value between the initial and final tin concentrations in the case and the matrix, you can apply the ratio

where X is the distance from the initial boundary between the cover (or matrix material) and the copper barrier, taken equal to half the sufficient thickness of the copper barrier;
τ total duration of equivalent temperature effects;
D diffusion coefficient of tin from bronze Cu 13 wt. Sn in copper; (see the book by L. S. Darken and R. V. Gurri "Physical chemistry of metals." M. "Metallurgy, 1960).

Substituting in the formula the values of D _Sn-Cu 6.5 • 10 ^-12 cm ² / s for extrusion temperatures of 600-650 ^o C and D _Sn-Cu 1.5 • 120 ^-12 cm ² / s for the temperature of intermediate heat treatment 500-550 ^o C and the total value of t ₁ = 3600 s for the extrusion operation, τ ₂ = 36000 s for intermediate heat treatments, we find that when redistributing the initial billet with a diameter of d _outer 93.5 mm in a wire d _pr 3 mm, it is enough to lay a copper barrier with a thickness of 20 microns. (There are assemblies in which, in order to save the more expensive bronze Cu 13 wt. Sn, the cover is made of bronze Cu (7-10) wt. Sn. In this case, in the above calculations, a different numerical value of the diffusion coefficient D _Sn-Cu should be used, however, the order all parameters will not change).

 Based on the practice of assembling composite billets, we can say that it is more technologically advanced to manufacture and install a barrier in the workpiece greater than the specified thickness.

In cases where the tin reserves in the wire are limited or absent (as a rule, these are all stabilized conductors) it is advisable to use a perforated copper barrier in the form of a mesh or a plate with holes in order to accelerate the delivery of tin to niobium veins. With this approach, it is necessary to pre-process copper billets. However, as a result of accelerating the delivery of tin from the case through the perforated barrier to the inner regions of the conductor (this parameter is controlled by the diffusion heat treatment of the superconductor), it is possible to form the grain structure of the Nb ₃ Sn superconducting compound most favorable for a specific working range of magnetic fields in morphology and proximity to the stoichiometric composition, t .e. to provide the maximum current carrying capacity of the superconductor used.

 Comparative analysis with the prototype shows that the inventive method is different from the prototype and thus meets the criteria of the invention of "novelty."

 In the study of other well-known technical solutions in this technical field, signs that distinguish the claimed invention from the prototype were not identified, that is, the claimed technical solution meets the criterion of "significant differences".

 Examples of specific performance.

Example 1. Composite unstabilized multicore superconductor 1, containing 14641 core 2 in bronze Cu 13mas. Sn matrix 3 was obtained by the "bronze" technology, initially assembling the niobium rod d _ref. 44 ^-0.1 mm, in a matrix bronze case d _ext. 93.5 ^-0.3 mm, and d _int. 44.6 ^+0.2 mm.

The obtained preform was then subjected to deformation by hot pressing and cold drawing with intermediate annealing and profiling onto a hexagon with a key size S 6.3 mm. After cutting into measuring parts during further assembly, hexagonal composite niobium bronze rods with sizes S 6.3 mm in an amount of 121 pieces were placed in a matrix bronze case with an outer diameter of 93.5 ^-0.3 mm, an inner diameter of 44.6 ^+0.2 mm, and in the ring cavity formed between the cover and the matrix material (represented by the 121st composite rod), the barrier element 4 was made in the form of a copper plate rolled into an overlap tube. Based on the minimum calculated value of the thickness of the copper plate (see above, 20 μm) and the manufacturability of the assembly, the initial barrier thickness was chosen equal to 0.3 mm. Then, the composite rod was further formed, deforming it by hot pressing and cold drawing with intermediate annealing and profiling onto hexagon S 6.3 mm-5. Then, cutting the bar into measuring parts, the final 14641-core (121 x 121) assembly 1 was performed in the same way as when forming the 121-core blank (Fig. 2): 6 case. The finished conductor d _pr 1.0 mm was subjected to final heat treatment according to the regime of 700 ^o C 72 hours

 Example 2. Composite stabilized multicore superconductor containing 14641 wires in bronze Cu 13 wt. The Sn matrix was obtained by bronze technology, as described in Example 1, but with the exception that a barrier element was made in the annular cavity between the cover and the matrix material containing 121 niobium core, which was a 0.3 mm thick copper plate rolled into an overlap pipe in which 105 holes with a diameter of 5 mm were made with a distance between them and between the rows of holes of ten mm (these values were chosen experimentally). In addition, during the final assembly, a copper barrier was not installed, because a niobium barrier was placed between the matrix material containing 14641 wires and a cover made of copper taken as a stabilizer to prevent poisoning of the stabilizing copper with tin during diffusion heat treatment.

 Using the proposed method for producing a multicore superconducting wire allows to completely eliminate the marriage of products caused by poor adhesion of the bronze matrix material and the bronze case. Thus, an increase in the yield is achieved, the unit length of the finished wire increases.

To obtain comparative data on the adhesion of the sheath (cover) of a composite niobium-bronze rod to a matrix material containing 121 or 14641 niobium veins, shear tests were carried out using a hydraulic press with a force of 10 tons of two series of samples with a diameter of d _arr. 22 mm and a length of 40 mm. In one of the series, a copper continuous barrier was placed in all samples between the matrix material and the bronze shell (case). Each series consisted of three samples containing 121 veins in a bronze matrix, and three samples containing 14,641 veins. To carry out the tests, a groove was made in the upper part of all samples with a diameter of 0.9 • d ₀ mm, where d _{0 was the} diameter of the bar zone occupied by the cores with a depth of 1.5 mm, and the casing was ground from the bottom to a height of 2 mm. The shear value was taken to be the force shown at the time of the beginning of the forcing of the bar zone occupied by the veins. For all samples containing a copper barrier, the extrusion force is 15–20% higher than for samples without a barrier. Thus, it was shown that in samples with a copper barrier, the adhesion of a matrix material containing niobium veins with a sheath (case) is better compared to samples without such a barrier.

Claims (2)

1. A method of producing a multicore superconducting wire based on an Nb ₃ Sn compound, in which a composite is formed by placing a niobium rod in a case made of a matrix material, which is an alloy of copper with tin, the resulting workpiece is deformed to the required transverse size with intermediate heat treatments, the formed bar is cut into individual elements and produce further composite formation the required number of times by placing composite niobium-bronze elements in a matrix case material, deform the preforms with intermediate annealing to the required size and carry out the final heat treatment to form the Nb ₃ Sn compound, characterized in that, in order to improve the adhesion of the cover to the matrix material containing niobium veins, increase the yield and single length of the wire, an annular cavity between the bronze matrix material and the bronze case is placed a copper barrier made in the form of at least one plate rolled into a pipe.  2. The method according to p. 1, characterized in that the barrier is performed with uniformly perforated holes.

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