CN111243820A - Bronze process Nb3Sn superconducting wire joint and preparation method thereof - Google Patents

Abstract

A bronze process Nb ₃ Sn superconducting joint and a preparation method thereof are respectively composed of a copper tube, a Ta film, a superconducting joint connecting part and a support core from the outside to the inside. The Ta film is attached to the inner wall of the copper tube, the support core is located in the center of the copper tube, and the connection part of the superconducting joint is between the Ta film and the support core. The preparation method of the superconducting wire joint is as follows: (1) Etch the copper at the incoming end and the outgoing end of the Nb ₃ Sn coil to be connected with FeCl ₃ solution, exposing the Nb multifilament and supporting core in the Nb ₃ Sn wire; (2) Divide the Nb multifilaments into multiple bundles and weave them into a bundle; (3) insert the Ta film into the copper tube and attach to the inner wall of the copper tube wall; insert the braided Nb multifilament bundles into the copper tube; (4) insert the Nb multifilament bundle into the copper tube; The powder and bronze alloy powder are mixed, poured into a mortar and ground; (5) the mixed Nb powder and bronze alloy powder are poured into a copper tube with Nb multifilament inserted, and both ends of the copper tube are sealed. Place the copper tube horizontally on the press for pressure; (6) perform high temperature heat treatment on the Nb ₃ Sn coil together with the copper tube at the incoming wire end and the outgoing wire end.

Description

A kind of bronze process Nb3Sn superconducting wire joint and preparation method thereof

technical field

The invention relates to a Nb ₃ Sn superconducting wire joint and a preparation method thereof.

Background technique

With the rapid development of superconducting magnet technology, scientific research devices and facilities with ultra-high magnetic fields have come out one after another. These devices are characterized by extremely high magnetic fields, which are great challenges for superconducting magnet high-field coils that provide strong magnetic fields under extreme environmental multiphysics operating conditions. At present, the low-temperature superconducting magnets in the strong magnetic field device are mainly composed of NbTi and Nb ₃ Sn superconducting coils. Compared with the low-temperature NbTi superconducting coils, the Nb ₃ Sn superconducting transition temperature is higher than 18K, and the upper critical magnetic field is at 4.2K. It can reach 25T, and the critical current density carried under the magnetic field of 4.2K/10T is about 5×10 ⁵ A/cm ² . However, the manufacturing process of superconducting coils is very complicated, and the resulting A15 crystal structure is an intermetallic compound with high brittleness and high hardness. At present, there are still many technological difficulties that restrict the use of Nb ₃ Sn superconducting coils.

Bronze process and inner tin process are currently the most widely used methods for preparing Nb ₃ Sn superconducting wires. The bronze process mainly uses tin bronze as the substrate of the superconducting wire. Insert the Nb alloy rod into the hole punched in the tin bronze matrix, then extrude and draw the combined composite for several times to obtain sub-components, and then bundle several sub-components together into the stabilizer copper tube, and again It is extruded and drawn to the final size, and finally the wire is subjected to heat treatment at 600° C. to 800° C. to obtain an A15 phase Nb ₃ Sn superconductor.

_Nb3Sn superconducting magnets require superconducting joints to connect multiple independent _Nb3Sn magnet coils. Because for Nb ₃ Sn low-temperature superconducting wire, winding large-scale superconducting magnets usually requires tens or even hundreds of kilometers of superconducting wire. Due to the limitation of superconducting wire processing technology and equipment, it is extremely difficult and costly to manufacture a single superconducting wire with a length of several tens of kilometers. Therefore, the length of each superconducting wire actually manufactured is often several hundred meters to several thousand. meters, which requires the production of superconducting joints that connect several superconducting wires. In addition, for applications such as magnetic resonance, the requirements for the magnet space and the uniformity of the magnetic field are very high. At the same time, it is necessary to ensure that the superconducting magnet can operate in a closed loop in a low temperature environment, and high-field superconducting joints need to be fabricated. For closed-loop Nb ₃ Sn superconducting magnets, especially for magnetic resonance high-field superconducting magnets that require high magnetic field uniformity, the superconducting joints of Nb ₃ Sn are required to have low resistance properties. Since the superconducting phase _of Nb3Sn superconductor turns into a fragile ceramic phase after heat treatment, it is difficult to operate on superconducting wires, otherwise it will cause unrecoverable damage in _Nb3Sn superconductor, which further limits high performance Fabrication of Nb ₃ Sn superconducting magnets.

There are many technologies for the preparation of superconducting joints, such as brazing, cold pressing, diffusion welding, fusion welding, sintering and so on. Among them, brazing, fusion welding and cold-pressing welding appeared earlier and are widely used at present; diffusion welding and sintering appeared later and are still basically at the laboratory level. Due to the complex physical structure and special material properties of superconducting materials, it is very difficult to ensure that the properties of superconducting materials are not changed at all in the joint part of the connection. The physical makeup of a joint is often quite complex compared to a busbar. The application of chemical and thermomechanical processes to the filaments perturbs the chemistry and microstructure, locally altering the superconducting properties, most notably their upper critical field (Hc2) and critical current density (Jc).

Superconducting joints in superconducting magnets are very fragile and easily damaged parts of the magnet system. Production downtime caused by joint problems during the manufacturing process of superconducting magnets will affect the delivery of the overall magnet system. Mainly because the Nb ₃ Sn superconducting magnet is made by the reaction-winding method, that is, by first winding the unreacted Nb ₃ Sn superconducting wire into a coil, and then subjecting the coil to a long-term high-temperature heat treatment to generate Nb ₃ Sn superconducting wire. Mutually. This process is very complicated, and there are many factors that affect the final superconducting magnet, including the heat treatment temperature, the temperature uniformity zone, the stress induced by the heat treatment, and the volume fraction of the superconducting phase generated by the reaction. In the production process of Nb ₃ Sn superconducting joints, not only must go through the above-mentioned severe heat treatment reactions, but also ensure that the superconducting joints can generate superconducting connections, the superconducting joints can meet the critical magnetic field strength, and the conduction is not lower than The excitation current of the superconducting magnet has an extremely low resistance not higher than the magnitude of E-12, and at the same time, it also meets the stress under the multi-field coupling of the extreme environment such as the strong magnetic field during the low-temperature excitation of the superconducting joint, extremely low temperature and high current. Require.

At present, in the production method of Nb ₃ Sn superconducting joints, the American Airco company has directly resistance welded the Nb ₃ Sn wire joints after the heat treatment reaction, and the joint resistance is only 10 ^-8 Ω. The Nb ₃ Sn superconducting joint was prepared by chemical vapor deposition at the University of Washington, and the critical current density of the joint was 500,000 A/cm ² under a comparative magnetic field of 5T. This method has high requirements on technology and equipment, and is not suitable for engineering applications. The patent CN201010221920.8 adopts the deposition method to prepare the Nb ₃ Sn superconducting joint, which needs to adopt the electroplating process, and the process is relatively complicated, so it is not an environment-friendly processing method.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the disadvantages of high equipment requirements, complex process and unfriendly environment in the prior art, and propose a bronze process Nb ₃ Sn superconducting wire joint and a preparation method thereof. The process of the invention is simple and reliable, can obtain Nb ₃ Sn superconducting joints with low resistance, and is suitable for industrialized manufacturing.

The purpose of the present invention is achieved through the following technical solutions.

A bronze process Nb ₃ Sn superconducting wire joint, from outside to inside are respectively a Cu tube, a Ta film, a superconducting joint connecting part and a support core, the Ta film is attached to the inner wall of the Cu tube, the support core is located in the center of the copper tube, and the superconducting joint The connecting portion is located between the support core and the Ta film.

The connecting part of the superconducting joint is composed of Nb multifilament and Nb ₃ Sn bulk material formed by sintering metal powder. The Nb multifilaments are woven together and twisted with each other to form multiple bundles of silk strands. Electric current flows through the Nb3Sn bulk material, forming a non _- resistance or low-resistance superconducting connection.

The Nb ₃ Sn superconducting wire joint of the invention is formed by the diffusion reaction of Nb multifilament, Nb powder and bronze alloy powder through high temperature heat treatment.

The bronze process Nb ₃ Sn superconducting wire joint of the present invention is used for connecting two Nb ₃ Sn wires with limited length, or for connecting multiple Nb ₃ Sn coils in series to form a current superconducting connection.

The joint resistance test method of the present invention is as follows: winding a bronze process Nb ₃ Sn wire into a Nb ₃ Sn coil, making its incoming wire and outgoing wire a Nb ₃ Sn joint to form a closed loop, using the method of electromagnetic induction to make The joint loop induces current and tests the current decay to calculate the resistance of the joint.

The present invention adopts the preparation method of the bronze process Nb ₃ Sn superconducting wire joint as follows:

(1) use FeCl ₃ solution to corrode the incoming wire end of the Nb ₃ Sn coil to be connected, the copper at the outgoing wire end, the length of the corrosion section is 2cm-20cm, and the Nb multifilament and the support core in the Nb ₃ Sn wire are exposed;

(2) Divide the Nb multifilaments in the incoming end and outgoing end of the corroded Nb ₃ Sn coil into multiple bundles, and weave them into one bundle in pairs;

(3) The Ta film is inserted into the copper tube and attached to the inner wall of the copper tube wall to form an inner wall layer. Then insert the braided Nb multifilament bundle into the copper tube;

(4) Mix the Nb powder and the bronze alloy powder, pour it into a mortar and grind for half an hour to make it evenly mixed;

(5) The mixed Nb powder and bronze alloy powder are poured into the copper tube with Nb multi-wire inserted, and the two ends of the copper tube are pressed and sealed with pressure pliers. Then put the copper tube horizontally on the press to pressurize, and compact the Ta film, Nb multi-filament bundle, Nb powder and bronze alloy powder in the copper tube;

(6) The Nb ₃ Sn coil together with the copper tubes at the incoming and outgoing ends are subjected to high temperature heat treatment, the heat treatment temperature is 640°C-670°C, and the holding time is 200h-220h to form a joint. The joint part generates Nb ₃ Sn superconducting connection through high temperature diffusion reaction.

Wherein, the bronze alloy powder is copper-tin alloy powder, the molar ratio of copper-tin is 10:1-1:1, and the molar ratio of Nb powder to Sn in the bronze powder is 6:1-0.5:1. The particle size of Nb powder and bronze powder is from micrometer to nanometer.

Wherein, the wall thickness of the copper tube is 0.2mm-1mm, and the thickness of the Ta film is 0.1mm-1mm.

Among them, put it horizontally on the press to pressurize the joint, and the pressure is 0.1 tons to 10 tons.

The bronze alloy powder used in the present invention is obtained by smelting copper and tin metal. Pure Sn will become liquid at temperatures above 230 °C. If it is directly heat treated, it will melt when the temperature exceeds the melting point of Sn. Liquid Sn will gradually volatilize and form a liquid-solid interface, which is difficult to react with solid Nb to obtain the required Nb. ₃ Sn superconducting phase. Moreover, the diffusion reaction is carried out at the liquid-solid interface, and it is difficult to have chemical reactions according to the temperature range and atomic composition range on the binary phase diagram of Nb and Sn. The reaction of Nb and Sn is prone to generate many impurity phases, such as Nb ₆ Sn ₅ , NbSn ₂ impurity. Using a quantitative and precise chemical percentage of copper-tin alloy powder, Sn atoms form a solid solution with copper atoms in a solid form, which can avoid the problem of Sn melting beyond the melting point. In the present invention, the Nb powder and the copper-tin alloy powder are evenly mixed, and the thermal diffusion reaction in the solid reactant occurs during the high-temperature heat treatment diffusion reaction, and it is easier to control the thermal diffusion reaction to be carried out according to the stoichiometric ratio and temperature range to obtain the required Nb ₃ Sn product.

Description of drawings

Figure 1 is a schematic cross-sectional view of a Nb3Sn superconducting wire;

Figure ₂ is a schematic diagram of the cross-section of the end of the Nb3Sn superconducting wire after being etched by FeCl3 solution;

Figure 3 is a schematic diagram of the Nb multifilament structure that is twisted with each other;

4 is a schematic structural diagram of the copper tube and the Ta film of the Nb ₃ Sn superconducting wire joint of the present invention;

Fig. 5 is a schematic diagram of the distribution of Nb and bronze powder in the bulk Nb ₃ Sn;

FIG. 6 is a schematic structural diagram of the Nb3Sn superconducting joint of the present invention.

Detailed ways

The present invention is further described below with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 6 , the structures of the bronze process Nb ₃ Sn superconducting wire joint of the present invention are, from outside to inside, respectively: copper tube, Ta film, superconducting joint connecting part and support core. The Ta film is attached to the inner wall of the Cu tube, the support core is located in the center of the copper tube, and the connecting part of the superconducting joint is located between the support core and the Ta film.

The connection part of the superconducting joint is composed of Nb multifilament and Nb ₃ Sn bulk material formed by sintering. The Nb multifilaments are woven together and twisted with each other to form multiple bundles of silk strands. The Nb ₃ Sn joint is formed by the diffusion reaction of Nb multifilament, Nb powder and bronze alloy powder through high temperature heat treatment.

The preparation method of the bronze process Nb ₃ Sn superconducting wire joint of the present invention is as follows:

The structure of the Nb ₃ Sn superconducting wire is shown in FIG. 1 . Fix the incoming and outgoing ends of the superconducting coil, leaving the length of the connector. First, use FeCl ₃ solution to corrode the copper at the incoming and outgoing ends of the Nb ₃ Sn coil. The length of the etched section is 2cm-20cm, exposing the Nb multifilament and the support core, as shown in Figure 2. The Nb multifilament and the support core were cleaned with deionized water, then the Nb multifilament and the support core were cleaned with alcohol, and then the Nb multifilament and the support core were placed to dry. Then, the Nb multifilaments at the incoming end and the outgoing end are divided into multiple bundles, and part of the multifilaments from one bundle is cross-woven with part of the other multifilaments to form a new bundle, as shown in Figure 3. Continue to weave other multifilaments until all multifilaments are braided and the support cores are arranged side by side in parallel. As shown in Figure 4, the Ta film was inserted into the copper tube and attached to the inner side of the tube arm to form an inner wall layer. When the subsequent high temperature heat treatment diffusion reaction occurs, the Ta layer can prevent the interdiffusion of the inner layer atoms into the outer layer copper, and change the purity of the outermost copper layer. Among them, the thickness of the Ta film is 0.1mm-1mm, and the wall thickness of the copper tube is 0.2mm-1mm. Then insert the braided Nb multifilament into the copper tube and spread it out.

Mix Nb powder and bronze alloy powder, then pour into a mortar and grind for half an hour and mix well. The bronze alloy powder is copper-tin alloy powder, the molar ratio of copper-tin is 10:1-1:1, and the molar ratio of Nb to Sn in the bronze powder is 6:1-0.5:1. The scale of Nb powder and bronze powder is from micrometer to nanometer.

Then, pour the mixed Nb powder and bronze alloy powder into the copper tube with Nb multifilament inserted, as shown in Figure 5. Use pressure pliers to seal the ends of the copper tube. Then, the copper tube is placed horizontally on a press to pressurize, and the pressure is 0.1 tons to 10 tons, and the Ta film, Nb multi-filament bundle, Nb powder and bronze alloy powder in the copper tube are compacted. Finally, the Nb ₃ Sn coil together with the copper tubes at the incoming and outgoing ends are subjected to high temperature heat treatment. The heat treatment temperature is 640°C-670°C, and the holding time is 200h-220h to form a joint. The joint part generates Nb ₃ Sn through a high temperature diffusion reaction, thereby forming a superconducting connection, as shown in Fig. 6 . The high temperature heat treatment adopts the mature heat treatment process of superconducting wires.

Example 1

First, the copper at both ends of the inlet and outlet wires of the Nb ₃ Sn coil was etched with FeCl ₃ solution with a mass fraction of 50%. The Nb multifilament and the support core were cleaned with deionized water, then the Nb multifilament and the support core were cleaned with alcohol, and the Nb multifilament and the support core were left to dry. Then divide the Nb multifilaments of the two threads into 10 bundles, respectively take part of the multifilaments from one bundle and cross-knit part of the multifilaments from the other bundle to form a new bundle, and continue to weave other multifilaments until all multifilaments are woven. The support cores are arranged side by side in parallel. Insert a 0.1mm Ta film into a 0.2mm thick copper tube and stick it to the inside of the tube arm to form an inner wall layer. Then the braided Nb multifilament bundles are inserted into the copper tube and dispersed. 10 g of 45-micron Nb powder and 45-micron bronze alloy powder with a copper-tin molar ratio of 10:1 were mixed, and the molar ratio of Nb to Sn in the bronze powder was 6:1. Then pour into a mortar and grind for half an hour and mix well. Then, pour the mixed Nb powder and bronze alloy powder into the copper tube with Nb multi-wire inserted, and press and seal the two ends of the copper tube with pressure pliers. Put the copper tube horizontally on the press with a pressure of 10 tons to compact the internal material components tightly. Finally, the copper tube and the Nb ₃ Sn coil are jointly subjected to high temperature heat treatment, the heat treatment temperature is 640 ° C, and the holding time is 200 h to form a joint. The joint part generates Nb ₃ Sn superconducting connection through high temperature diffusion reaction. The high temperature heat treatment adopts the mature heat treatment process of superconducting wires. After testing, the resistance of the joint is 8.5×10 ^-12 Ω.

Embodiment 2

First, the copper at both ends of the inlet and outlet wires _of the Nb3Sn coil was etched with FeCl3 solution ₅ with a mass fraction of 30%. The Nb multifilament and the support core were rinsed with deionized water, then the Nb multifilament and the support core were cleaned with alcohol and then left to dry until the Nb multifilament and the support core were dry. Divide the Nb multifilaments of the two Nb ₃ Sn wires into 15 bundles, respectively take part of the multifilaments in one bundle and cross-knit part of the multifilaments in the other bundle to form a new bundle, and continue to weave other multifilaments until all multifilaments are woven. Completion, the support cores are arranged side by side in parallel. Insert a 1mm Ta film into a 1mm thick copper tube and stick it to the inside of the tube arm to form the inner wall. Then the braided Nb multifilament bundles are inserted into the copper tube and dispersed. 10 g of 0.5-micron Nb powder and 45-micron bronze alloy powder with a copper-tin molar ratio of 1:1 were mixed, and the molar ratio of Nb to Sn in the bronze powder was 0.5:1. Pour the mixed Nb powder and bronze alloy powder into a mortar and grind for half an hour, then pour the mixed Nb powder and bronze alloy powder into a copper tube with Nb multi-wire inserted, and press both ends of the copper tube with a pressure clamp Seal tightly. Put the copper tube horizontally on the press with a pressure of 0.1 ton to compact the internal material components tightly. Finally, the copper tube and the Nb ₃ Sn coil are jointly subjected to high temperature heat treatment, the heat treatment temperature is 670 ° C, and the holding time is 220 h to form a joint. The joint part generates Nb ₃ Sn superconducting connection through high temperature diffusion reaction. The high temperature heat treatment adopts the mature heat treatment process of superconducting wires. The joint resistance tested was 5.5 x ^10-12 Ω.

Embodiment 3

First, the copper at both ends of the inlet and outlet wires _of the Nb3Sn coil was etched with FeCl3 solution ₅ with a mass fraction of 40%. The Nb multifilament and the support core were washed three times with deionized water, then the Nb multifilament and the support core were washed three times with alcohol and then left to dry until the Nb multifilament and the support core were dry. Then divide the Nb multifilaments of the two threads into 15 bundles, respectively take part of the multifilaments from one bundle and cross-knit part of the multifilaments from the other bundle to form a new bundle, and continue to weave other multifilaments until all multifilaments are woven. The support cores are arranged side by side in parallel. Insert a 0.5mm Ta film into a 0.5mm thick copper tube and stick it to the inside of the tube arm to form an inner wall. Then the braided Nb multifilament bundles are inserted into the copper tube and dispersed. 10 g of 0.5-micron Nb powder and 45-micron bronze alloy powder with a copper-tin molar ratio of 5:1 were mixed, and the molar ratio of Nb to Sn in the bronze powder was 3:1. Then pour into a mortar and grind for half an hour and mix well. Then, pour the mixed Nb powder and bronze alloy powder into the copper tube with Nb multi-wire inserted, and press and seal the two ends of the copper tube with pressure pliers. Then, the joint part is placed horizontally on the press with a pressure of 5 tons to compact the internal material components tightly. Finally, the copper tube and the Nb ₃ Sn coil are jointly subjected to high temperature heat treatment, the heat treatment temperature is 660 ° C, and the holding time is 210 h to form a joint. The joint part generates Nb ₃ Sn superconducting connection through high temperature diffusion reaction. The high temperature heat treatment adopts the mature heat treatment process of superconducting wires. The joint resistance tested was 6.5 x ^10-12 Ω.

Claims (7)

1. Bronze process Nb₃An Sn superconducting wire joint, characterized in that: the joints are respectively from outside to inside: the device comprises a copper pipe, a Ta film, a superconducting joint connecting part and a supporting core; the Ta film is attached to the inner wall of the copper pipe, and the supporting core is positioned on the copperThe superconducting joint connecting part is positioned between the Ta film and the support core; nb₃The Sn superconducting wire joint is generated by carrying out high-temperature heat treatment diffusion reaction on Nb multifilaments, Nb powder and bronze alloy powder.

2. Bronze process Nb according to claim 1₃An Sn superconducting wire joint, characterized in that: the superconducting joint connecting part is formed by Nb multifilaments and Nb₃Composite of Sn bulk material, Nb₃The Sn bulk material is generated by sintering metal powder; current at said Nb₃The Sn bulk material forms a resistance-free or low-resistance superconducting connection.

3. Bronze process Nb according to claim 1₃An Sn superconducting wire joint, characterized in that: the Nb multiple wires are combined and woven and are mutually spliced to form a multi-bundle wire strand.

4. Bronze process Nb according to claim 1₃The preparation method of the Sn superconducting wire joint is characterized by comprising the following steps: the preparation steps are as follows:

(1) using FeCl₃Solution etching of Nb to be joined₃The copper at the wire inlet end and the wire outlet end of the Sn coil has the corrosion section length of 2cm-20cm and exposes Nb₃A Nb multifilament in Sn wire and a support core;

(2) corroding Nb₃Multiple Nb wires in the wire inlet end and the wire outlet end of the Sn coil are divided into multiple beams, and the multiple beams are woven pairwise to form a beam;

(3) inserting a Ta film into the copper pipe, and attaching the Ta film to the inner wall of the copper pipe to form an inner wall layer; then inserting the woven Nb multi-filament bundles into the copper pipe;

(4) mixing Nb powder and bronze alloy powder, pouring into a mortar, and grinding for half an hour to uniformly mix the Nb powder and the bronze alloy powder;

(5) pouring the mixed Nb powder and bronze alloy powder into a copper pipe inserted with Nb multifilaments, and tightly pressing and sealing two ends of the copper pipe by using a pressure clamp; then horizontally placing the copper pipe on a press machine for pressurizing, and compacting the Ta film, the Nb multi-filament bundle, the Nb powder and the bronze alloy powder in the copper pipe;

(6) will Nb₃The Sn coil together with the copper pipes at the wire inlet end and the wire outlet end are subjected to high-temperature heat treatment at 640-670 ℃, the heat preservation time is 200-220 h, and the joint part generates Nb through high-temperature diffusion reaction₃And Sn is connected in a superconducting way.

5. Bronze process Nb according to claim 4₃The preparation method of the Sn superconducting wire joint is characterized by comprising the following steps: the Nb powder and the bronze alloy powder are added in proportion, the bronze alloy powder is copper-tin alloy powder, the molar ratio of copper to tin is 10:1-1:1, and the molar ratio of Nb to Sn in the bronze powder is 6:1-0.5: 1; the grain sizes of the Nb powder and the bronze powder are micron-sized to nanometer-sized.

6. Bronze process Nb according to claim 4₃The preparation method of the Sn superconducting wire joint is characterized by comprising the following steps: the thickness of the Ta film is 0.1mm-1mm, and the wall thickness of the copper pipe is 0.2mm-1 mm.

7. Bronze process Nb according to claim 4₃The preparation method of the Sn superconducting wire joint is characterized by comprising the following steps: the pressure of the press is 0.1 ton to 10 tons.

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