CN101888026A - A kind of bronze process Nb3Sn superconductor multi-core wire joint and its preparation method - Google Patents

Abstract

A bronze technology Nb ₃ Sn superconductor multi-core wire joint and its preparation method. The structure of the joint is from the inner layer to the outer layer: a stable core, a superconducting connection unit, an Nb tube and a Cu tube, and the above layers are closely attached combine. The superconducting connection unit consists of Nb wire, Nb ₃ Sn compound layer, and Cu-Sn alloy coating from the inner layer to the outer layer, wherein the Nb wires of different superconductor multi-core wires to be connected in the same superconducting connection unit overlap each other, Cu-Sn alloy coating is deposited on the surface of Nb wire, and the Nb ₃ Sn compound layer is formed by solid-state diffusion between Nb wire and Cu-Sn alloy coating during the heat treatment reaction process. The Nb on the surface of different superconductor multi-core wire Nb wire The ₃ Sn compound layers are bridged and conducted with each other, and play the role of superconducting connection, so that the joint of the bronze process Nb ₃ Sn superconductor multi-core wire maintains low resistance and low loss at the superconducting temperature.

Description

A kind of bronze process Nb3Sn superconductor multi-core wire joint and its preparation method

technical field

The invention relates to a bronze process Nb ₃ Sn superconductor multi-core wire joint and a preparation method thereof.

Background technique

The Nb ₃ Sn material exhibits good superconducting properties at a low temperature of 18K. Its critical transition temperature is higher than that of NbTi superconductor materials, and it is especially suitable for the construction of high magnetic field superconducting magnets.

According to different wire structures, the methods for preparing Nb ₃ Sn superconducting wires are mainly divided into two types: bronze process and internal tin method. The wire material of the bronze process is a bronze-Nb wire multi-core mechanical composite structure. The inner-tin method wire is a mechanical composite structure in which Sn wire is inserted in a multi-Cu/Nb composite tube. Both of the above two kinds of wires need to be heat-treated at an appropriate temperature to form a superconductive Nb ₃ Sn compound layer through solid-state diffusion, which has superconducting properties. Bronze process Nb ₃ Sn superconductor multi-core wire has been widely used due to its stable use and mature technology. The schematic diagram of the cross-sectional structure of the bronze process Nb ₃ Sn superconductor multi-core wire before heat treatment (bronze-Nb wire multi-core mechanical composite wire) is shown in Figure 1, including: stable core, Nb wire, and bronze matrix.

Nb ₃ Sn is a compound of A15 structure, which itself has great brittleness, and any deformation or collision may cause damage to the superconducting property. Therefore, in the process of using bronze technology to prepare Nb ₃ Sn superconducting coils in actual engineering, it is necessary to first wind the bronze-Nb wire multi-core mechanical composite wire into a coil that meets the design requirements, and then heat-treat the coil as a whole. The reaction produces superconducting Nb ₃ Sn compounds in the multi-core mechanical composite wire, thereby obtaining Nb ₃ Sn superconducting coils with superconducting properties. After the reaction, the winding direction of the superconducting wire can no longer be changed, so as to avoid brittle fracture or damage of the Nb ₃ Sn superconducting wire and damage the superconducting performance.

During the construction of superconducting magnet coils, the welding of superconducting wires is one of the key technologies. The length of a single superconducting wire is limited, and winding a large superconducting magnet often requires tens to hundreds of kilometers of superconducting wires. In this case, multiple superconducting wires must be welded together to ensure the required length. At the same time, when manufacturing a superconducting magnet composed of multiple coils, the connection between the coils needs to be completed by welding the wires at the ends of the coils. Similarly, when manufacturing a superconducting magnet system composed of a plurality of superconducting magnets, if it is required to connect each magnet in series to be powered by a single power supply, it is also necessary to weld the ends of each magnet in series end to end. Compared with the way that each magnet is powered individually, the single power supply mode can make the magnet system have higher working reliability. In addition, if the superconducting magnet is to operate in a closed loop, it is also necessary to connect the two ends of the magnet or the magnet system with the superconducting switch to form a closed loop.

In the construction of large superconducting magnets, the winding of superconducting wires and the connection between superconducting wires are carried out simultaneously. The process quality of joint production directly affects the progress of the project. In addition, many joints of large magnets are inside the magnet, which cannot be disassembled, inspected and repaired. The poor quality of any joint will affect the performance of the entire magnet, and may even make the entire magnet scrapped. Therefore, the joint must have high reliability in the manufacture of large magnets. For general combined magnets or magnet systems, although the joints can be placed in places that are relatively easy to access, it is unrealistic to perform frequent inspections and repairs on the joints because the entire magnet needs to work in a closed low-temperature environment. Therefore, high reliability of joint quality must be guaranteed. For a superconducting magnet operating in a closed loop, the performance of the joint also directly determines the working performance and continuous operation time of the magnet.

The basic requirement for superconducting wire joints is, on the one hand, that the joints must have a low electrical resistance. The working current of a superconducting magnet generally reaches hundreds or even thousands of amperes. If the resistance is too large, it will cause serious Joule heat loss, which may lead to the quenching of the magnet. For a superconducting magnet operating in a closed loop, the joint resistance leads to the attenuation of the magnetic field. If the stability of the magnetic field is required to reach a certain level, the resistance of the joint must be less than a certain value. For example, for NMR magnet systems, the resistance of the superconducting joint is generally required to be no higher than 10 ^-12 ohms. On the other hand, it must have a certain mechanical strength and toughness to withstand the bending stress during the magnet winding process, the electromagnetic stress in the working state, and the shrinkage stress during the cooling process.

At present, the manufacturing methods of Nb ₃ Sn superconducting wire joints can be mainly divided into two categories according to the sequence of joint making and heat treatment: one is to make joints before superconducting wire heat treatment, and the other is to make joints after superconducting wire heat treatment.

In the first type of method, US Patent No. 5111574 discloses a method for manufacturing a Nb ₃ Sn superconducting wire joint. Mix the Nb wire and the Sn wire of the superconducting wire with the structure, wrap Sn, Cu and metal layers such as V, Nb, Ta, etc. on the outside, and generate the superconducting wire joint through heat treatment reaction. The Sn wire in this method is in a liquid state during the heat treatment process. On the one hand, the sealing performance of the sheath is very high, which is difficult to achieve in actual engineering use. On the other hand, liquid pure Sn will cause thermal corrosion to the cladding material (such as Cu), which will affect the joint effect. In addition, copper-based brazing technology has also been used to make Nb ₃ Sn superconducting wire joints. Since the superconducting connection has not really been formed, the joint resistance value is only 10 ^-9 ohms, which is not suitable for NMR and other joint resistance values. Requires higher technology. Although the above methods avoid the superconducting wire breakage risk caused by the superconducting wire becoming brittle after heat treatment, the current carrying capacity of these existing methods is very weak. In order to reduce the joint resistance, it is generally forced to extend the joint resistance, making the joint bulky.

In another method, Airco Company of the United States has directly performed resistance welding on the joints of Nb ₃ Sn wires after heat treatment, and the resistance of the joints is only 10 ^-8 ohms. GE Company of the United States once used TIG welding technology to weld Nb-Sn-Cu-Pb alloy on the ^{superconducting} wire joint to form a superconducting connection. Superconducting wires cause damage. In addition, GE Company of the United States also used chemical vapor deposition (CVD) to deposit a superconducting layer on the joint. This method is complex in process and harsh in the environment, and is not suitable for engineering use. The biggest problem with this type of method is that the Nb ₃ Sn superconducting wire itself becomes brittle after heat treatment, and accidental breakage can easily cause damage and loss of superconducting properties.

Based on the above analysis, the existing Nb ₃ Sn superconducting wire joint method can not meet the actual engineering requirements of the bronze process Nb ₃ Sn superconducting wire joint. Bronze Process Nb ₃ Sn Superconducting Wire Joint Fabrication Method.

Contents of the invention

The purpose of the present invention is to overcome the problems of non-superconducting connection of joints, easy damage of superconducting wires, complicated and harsh process conditions and other problems existing in the existing superconducting wire joint method, and propose a bronze process Nb ₃ Sn superconductor multi-core wire joint and its preparation method, the invention can realize superconducting connection and reduce joint resistance.

Technical scheme of the present invention is:

A bronze technology Nb ₃ Sn superconductor multi-core wire joint, the structure of the joint from the inner layer to the outer layer is respectively: a stable core, a superconducting connection unit, an Nb tube and a Cu tube, and the above layers are closely bonded. The superconducting connection unit consists of Nb wire, Nb ₃ Sn compound layer, and Cu-Sn alloy coating from the inner layer to the outer layer, wherein the Nb wires of different superconductor multi-core wires to be connected in the same superconducting connection unit overlap each other, Cu-Sn alloy coating is deposited on the surface of Nb wire, and the Nb ₃ Sn compound layer is formed by solid-state diffusion between Nb wire and Cu-Sn alloy coating during the heat treatment reaction process. The Nb on the surface of different superconductor multi-core wire Nb wire The ₃ Sn compound layers are bridged and conducted with each other, and play the role of superconducting connection, so that the joint of the bronze process Nb ₃ Sn superconductor multi-core wire maintains low resistance and low loss at the superconducting temperature.

The present invention prepares the method for the above-mentioned bronze process Nb ₃ Sn superconductor multi-core wire joint, and the sequence of preparation steps is as follows:

(1) corrode the bronze matrix at the end of the Nb ₃ Sn superconductor multi-core wire, exposing the scattered stable core and Nb wire;

(2) Mix the Nb wires of different superconductor multi-core wires to be connected, overlap each other as much as possible, and bind and fix the Cu wires;

(3) by deposition technology, make the Nb wire surface of joint generate one deck Cu-Sn alloy coating;

(4) Put the Nb tube and the Cu tube on the joint from the inside to the outside, and press the joint tightly so that the Nb wire deposited with the Cu-Sn alloy coating is tightly embedded in the Nb tube and the Cu tube;

(5) After the outer layer of the joint is coated with high-temperature resistant insulating material, it is fixed and installed at the designated position of the coil;

(6) Heat treatment is performed on the joint, and a Nb ₃ Sn superconducting bridging layer is formed by solid-state diffusion at the joint of the Nb ₃ Sn superconductor multi-core wire, so as to realize the superconducting connection of the joint.

Wherein, the deposition method may adopt electroplating deposition or electroless plating deposition.

Among them, the wall thickness of the Nb tube of the joint is 0.5-2 mm, and the wall thickness of the Cu tube is 0.5-2 mm, and the length of the Nb tube and the Cu tube should be able to cover the Nb wire.

Among them, the high-temperature-resistant insulating material coated on the outside of the joint is alkali-free glass fiber cloth.

Among them, the heat treatment temperature, holding time and heat treatment atmosphere of the joint are the same as the heat treatment temperature, holding time and heat treatment atmosphere of the Nb ₃ Sn coil where the joint is located, and the heat treatment of the joint is completed simultaneously with the heat treatment process of the Nb ₃ Sn coil where the joint is located .

Wherein, the heat treatment temperature of the butt joint is 650-690° C., the holding time is 100-190 hours, and the heat treatment atmosphere requires inert gas or vacuum.

One of the characteristics of the bronze process Nb ₃ Sn superconductor multi-core wire joint and its preparation method of the present invention is that it is formed by solid state diffusion on the Nb wire of the bronze process Nb ₃ Sn superconductor multi-core wire by means of surface deposition technology combined with heat treatment technology The Nb ₃ Sn superconducting compound layers bridge and communicate with each other, realizing the superconducting connection between different superconducting wires. This greatly reduces the resistance value of the superconducting wire joint under low-temperature working conditions, improves the current-carrying capacity of the magnet, and reduces the volume of the joint. Another feature is that the bronze process Nb ₃ Sn superconductor multi-core wire joint of the present invention is prepared before the heat treatment of the Nb ₃ Sn superconductor wire. This avoids the danger of accidental breakage of the superconducting wire due to the fact that the Nb ₃ Sn superconducting wire itself becomes brittle after heat treatment, thereby avoiding the danger of destroying the overall superconductivity.

Description of drawings

Figure 1 Schematic diagram of the cross-sectional structure of the bronze process Nb ₃ Sn superconductor multi-core wire before heat treatment (bronze-Nb wire multi-core mechanical composite wire);

Fig. 2 Schematic diagram of the structure of the bronze process Nb ₃ Sn superconductor multi-core wire joint;

Fig. 3 is a flow chart of the preparation method of the Nb ₃ Sn superconductor multi-core wire joint in the bronze process;

Fig. 4 is a schematic diagram showing that the bronze matrix at the end of the Nb ₃ Sn superconductor multi-core wire to be connected is corroded and the Nb wire is exposed;

Fig. 5 is a schematic diagram of the Nb filaments of the bronze process Nb ₃ Sn superconductor multi-core wires to be connected together and overlapping each other;

Fig. 6 is a schematic diagram of the structure of the bronze process Nb ₃ Sn superconductor multi-core wire joint before heat treatment.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

As shown in Fig. 2, the structure of the bronze process Nb ₃ Sn superconductor multi-core wire joint of the present invention is respectively from the inner layer to the outer layer: a stable core, a superconducting connection unit, a Nb tube and a Cu tube. There is a tight fit between the layers. The superconducting connection unit is respectively composed of Nb wire, Nb ₃ Sn compound layer and Cu-Sn alloy coating from inside to outside, wherein the Nb wires of different superconductor multi-core wires to be connected in the same superconducting connection unit overlap each other.

The manufacture method of bronze process Nb ₃ Sn superconductor multi-core wire joint of the present invention is as follows:

As shown in Figure 3, first corrode the bronze matrix at the end of two or more bronze process Nb ₃ Sn superconductor multi-core wires to be connected without heat treatment, and expose a section of evenly spread Nb wires, as shown in Figure 3. 4. Thoroughly clean the Nb wires to remove surface oil stains and dust; then put the stable cores of two or more Nb ₃ Sn superconductor multi-core wires to be connected together with the Nb wires so that the Nb wires are in contact with each other as much as possible lap, as shown in Figure 5. The overlapping Nb wires are bound and fixed with thin Cu wires; then the superconductor multi-core wire Nb wires of the joints are plated with Cu-Sn alloy coatings by electroless deposition or electroplating deposition, and the Cu-Sn alloy coatings combine different superconductors The Nb wires of the multi-core wires are connected as one. Then, the Cu-Sn alloy plated joint is cleaned and dried to completely remove the plating solution or oxide impurity layer on the joint. Put the cleaned joints on the pure Nb tube and the pure Cu tube sequentially from the inside to the outside. The wall thickness of the pure Nb tube and the pure Cu tube are both 0.5-2.0mm, and the length of the pure Nb tube and the pure Cu tube is slightly longer than that of the superconductor multi-core The length of the Nb wire exposed by wire corrosion, one end of the pure Nb tube and pure Cu tube is longer than the end of the Nb wire, and the other end is longer than the root of the Nb wire. Flatten the pure Cu tube and the pure Nb tube so that the Nb wire deposited with the Cu-Sn alloy coating is tightly embedded in the Nb tube and the Cu tube to prevent the Nb wire from moving inside the pure Cu tube and the pure Nb tube, as shown in Figure 6 Shown is a schematic diagram of the structure of the bronze process Nb ₃ Sn superconductor multi-core wire joint before heat treatment. Coat the overall outer surface of the joint with high-temperature-resistant insulating material, and fix it at the designated position of the coil; finally, the joint is placed along with the Nb ₃ Sn coil where it is located - and placed in a heat treatment furnace for diffusion heat treatment. The bronze-Nb wire multi-core in the coil While the mechanical composite wire forms a Nb ₃ Sn compound layer with superconducting properties through solid-state diffusion, the Nb wire in the joint reacts with the Cu-Sn alloy coating to form a Nb ₃ Sn superconducting compound layer with superconducting properties through solid-state diffusion. The heat treatment temperature is 650-690°C, the holding time is 100-190 hours, and the heat treatment atmosphere requires inert gas or vacuum. The heat treatment temperature, holding time and heat treatment atmosphere of the joint are the same as those of the Nb ₃ Sn coil where the joint is located. The Nb ₃ Sn superconducting compound layers communicate with each other, and can bridge different superconducting multi-core wires, so as to realize the superconducting connection of joints.

Wherein the high temperature resistant insulating material may be alkali-free glass core fiber cloth.

Embodiment 1: In this embodiment, the outer diameter of the bronze process Nb ₃ Sn superconductor multi-core wire to be connected is 0.9 mm, and the diameter of a single Nb wire is 4.5 microns. First use concentrated nitric acid to corrode the bronze substrates at the ends of the two bronze process Nb ₃ 8n superconductor multi-core wires to be connected, and expose the pure Nb wire part with a length of 30 mm. Clean and dry the Nb wire at the joint. Then put the Nb wires of the superconductor multi-core wires together so that the Nb wires of the two wires overlap each other as much as possible, and bind and fix them with thin Cu wires. Then the joint is subjected to electroplating and deposition of Cu-Sn alloy layer. The composition ratio of electroplating deposition electrolyte is: SnCl ₂ 2H ₂ O——40 g/L, NaF——30 g/L, N(CH ₂ COOH) ₃ - 20 g/l, CuSO ₄ 5H ₂ O - 30 g/l, EDTA - 45 g/l, citric acid - 10 g/l, polyoxyethylene fatty ether - 2 g/l, Deionized water—the balance, PH=5.5. During the electroplating deposition process, the pure tin plate and pure Cu plate with the same surface area are used as the anode, and the joint part is used as the cathode, and a low-voltage direct current with a current density of 0.1-0.6A/ ^dm2 is passed through, and the electroplating deposition temperature requires 30°C±2°C . Then, the electroplating deposition part of the joint is cleaned and dried with a chemical pure alcohol solution. Then put the pure Nb tube and the pure Cu tube on the joint from the inside to the outside respectively. The inner diameter of the Nb tube is 3.5 mm, the wall thickness is 0.5 mm, and the length is 40 mm; the inner diameter of the Cu tube is 4.5 mm, the wall thickness is 0.5 mm, and the length is 40 mm. The pure Nb tube and the pure Cu tube are aligned to cover the entire joint part, and the two ends of the pure Nb tube and the pure Cu tube are 5 mm longer than the Nb wire. The pure Nb tube and the pure Cu tube are compressed and deformed by hydraulic pliers, so that the Nb wire deposited with Cu-Sn alloy coating is fixed and embedded in the Nb tube and the Cu tube, so that the joint is sealed and firm, and the outer layer of the joint is coated with alkali-free After the glass fiber cloth is fixed on the specified position of the magnet coil. Then the joint is put into a heat treatment furnace together with the coil for diffusion heat treatment. The heat treatment temperature is 650°C, the holding time is 190 hours, and the vacuum heat treatment is carried out at a vacuum degree of 10 ^-3 Pa. Slowly cool to room temperature after heat treatment. The superconducting joint is prepared. After testing, the joint resistance is 9×10 ^-12 ohms.

Embodiment 2: In this embodiment, the diameters of the bronze process Nb ₃ Sn superconductor multi-core wires to be connected are all 0.7 mm, and the diameter of a single Nb wire is 4.5 microns. First use concentrated nitric acid to corrode the bronze matrix part at the end of the two bronze process Nb ₃ Sn superconductor multi-core wires to be connected, and expose the pure Nb wire part, and the length of the exposed Nb wire is 40 mm. Clean and dry the Nb wire at the joint. Then, the Nb filaments of the superconductor multi-core wires are brought together so that the Nb filaments of two Nb ₃ Sn superconductor multi-core wires overlap each other as much as possible, and are bound and fixed with thin Cu wires. Then the joint is subjected to electroless plating deposition Cu-Sn alloy layer treatment, the composition ratio of electroless plating deposition electrolyte is: SnCl ₂ 2H ₂ O——30 g/L, NaF——30 g/L, N(CH ₂ COOH) ₃ - 25 g/L, CuSO ₄ 5H ₂ O - 20 g/L, EDTA - 25 g/L, citric acid - 7 g/L, polyoxyethylene fatty ether - 1 g/L liters, deionized water—residue, PH=4. The electroless plating deposition temperature requires 30°C±2°C. Subsequently, the electroless plating deposition part of the joint is cleaned and dried with pure alcohol solution. Then put the pure Nb tube and the pure Cu tube on the joint from the inside to the outside respectively. The inner diameter of the Nb tube is 3 mm, the wall thickness is 2 mm, and the length is 50 mm; the inner diameter of the Cu tube is 7 mm, the wall thickness is 2 mm, and the length is 50 mm. The pure Nb tube and the pure Cu tube are aligned to cover the entire joint part, and the pure Nb tube and the pure Cu tube are pressed and deformed by hydraulic pliers, so that the Nb wire deposited with Cu-Sn alloy coating is tightly embedded in the Nb tube and the Cu tube, so that the joint The parts are closed and firm, and after the outer layer of the joint is covered with alkali-free glass fiber cloth, it is fixed at the specified position of the magnet coil. Then the joint is put into a heat treatment furnace together with the coil for diffusion heat treatment. The heat treatment temperature is 690°C, the holding time is 100 hours, the heat treatment atmosphere is flowing argon, and the flow rate is 0.1-0.2 liters/minute. Slowly cool to room temperature after heat treatment. The superconducting joint is prepared. After testing, the joint resistance is 8×10 ^-12 ohms.

Claims (7)

1. A bronze process Nb ₃ Sn superconductor multi-core wire joint, characterized in that the structure of the joint is from inner layer to outer layer: stable core, superconducting connection unit, Nb tube and Cu tube, above-mentioned each level The superconducting connecting unit is composed of Nb wire, Nb ₃ Sn compound layer, and Cu-Sn alloy coating from the inner layer to the outer layer, and the different superconducting multi-core wires to be connected in the same superconducting connecting unit Nb wires overlap each other, Cu-Sn alloy coatings are deposited on the surface of Nb wires, and the Nb ₃ Sn compound layer is formed by solid-state diffusion between Nb wires and Cu-Sn alloy coatings during the heat treatment reaction process. Different superconductor multi-core The Nb ₃ Sn compound layers on the surface of the wire Nb wire are bridged and conducted with each other, which acts as a superconducting connection, so that the joint of the bronze process Nb ₃ Sn superconductor multi-core wire maintains low resistance and low loss at the superconducting temperature. 2. The method for preparing the bronze process Nb ₃ Sn superconductor multi-core wire joint according to claim 1 is characterized in that the order of manufacturing steps is as follows: (1) corrode the bronze matrix at the end of the Nb ₃ Sn superconductor multi-core wire, exposing the scattered stable core and Nb wire; (2) The Nb wires of different superconductor multi-core wires to be connected are mixed with each other, overlapped with each other, and bound and fixed with Cu wires; (3) by deposition technology, make the Nb wire surface of described joint generate one deck Cu-Sn alloy coating; (4) Put the Nb tube and the Cu tube on the joint from the inside to the outside, and press the joint tightly so that the Nb wire deposited with the Cu-Sn alloy coating is tightly embedded in the Nb tube and the Cu tube; (5) After the outer layer of the joint is coated with high-temperature resistant insulating material, it is fixed and installed at the designated position of the coil; (6) The joint is heat-treated, and a Nb ₃ Sn superconducting bridging layer is formed by solid-state diffusion at the joint of the Nb ₃ Sn superconductor multi-core wire, so as to realize the superconducting connection of the joint. 3. The method for preparing the Nb ₃ Sn superconductor multi-core wire connector with bronze technology according to claim 2, characterized in that the deposition method adopts electroplating deposition or electroless plating deposition. 4. The preparation method of the bronze process Nb ₃ Sn superconductor multi-core wire joint according to claim 2, characterized in that the wall thickness of the Nb tube is 0.5-2 mm, the wall thickness of the Cu tube is 0.5-2 mm, and the Nb tube wall thickness is 0.5-2 mm. And the length of Cu tube can cover Nb wire. 5. The method for preparing the joint of Nb ₃ Sn superconductor multi-core wire with bronze technology according to claim 2, characterized in that the high temperature resistant insulating material coated on the outside of the joint is alkali-free glass fiber cloth. 6. The preparation method of the bronze process Nb ₃ Sn superconductor multi-core wire joint according to claim 2 is characterized in that the heat treatment temperature, heat preservation time and heat treatment atmosphere of the joint and the heat treatment temperature of the Nb ₃ Sn coil where the joint is located , the holding time and the heat treatment atmosphere are the same, and the heat treatment of the joint is completed at the same time as the heat treatment of the Nb ₃ Sn coil where the joint is located. 7. The method for preparing a bronze process Nb ₃ Sn superconductor multi-core wire joint according to claim 2, characterized in that the heat treatment temperature of the butt joint is 650-690°C, the holding time is 100-190 hours, and the heat treatment atmosphere requires inert gas or vacuum.

Images