A niobium-tin-copper superconducting wire prepared by a powder bronze method and a method thereof

Abstract

The invention discloses a niobium-tin-copper superconducting wire prepared by a powder bronze method and a method thereof, and relates to the technical field of superconducting wire preparation, and particularly to a niobium-tin-copper superconducting wire prepared by a powder bronze method and a method thereof, comprising the following steps: placing an oxygen-free copper rod, tin particles and titanium powder in a crucible, placing the crucible in an electrode induction gas atomization powder spraying furnace, evacuating the crucible, and simultaneously filling the crucible with nitrogen to make its pressure greater than the standard atmospheric pressure, opening the gas atomization powder spraying furnace air inlet valve and exhaust valve after being filled with nitrogen, regulating the heating current to start working, and obtaining micron-level Cu-Sn-Ti alloy powder; the invention fills the region between the pure niobium rod and the pure niobium tube with Cu-Sn-Ti alloy powder, utilizes the excellent fluidity and micron-level size advantage of the powder, improves the plasticity of the Cu-Sn-Ti alloy in the drawing process, and solves the problem of core breakage and wire breakage in the drawing of the traditional bulk Cu-Sn alloy ingot.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting wire preparation methods, and in particular to a niobium, tin, and copper superconducting wire prepared based on a powder bronze method and a method thereof. Background Art

[0002] Nb3Sn is a typical intermetallic compound with an A15-type crystal structure, with a high superconducting transition temperature Tc (~18 K), and an upper critical magnetic field Hc of up to 27 T. The preparation methods of Nb3Sn superconducting wires mainly include the internal tin method and the bronze method. Among them, the critical current density of the Nb3Sn superconducting wires produced by the internal tin method is higher, but due to the serious coupling of the core wires, its AC loss also increases; the critical current density of the Nb3Sn superconducting wires produced by the bronze method is moderate, but because the core wires are usually not coupled, its AC loss is low. Therefore, these two wires have different application fields.

[0003] At present, the bronze method and the internal tin method are the two mainstream methods for preparing Nb3Sn superconducting wires. Compared with the internal tin method, the Nb3Sn wire prepared by the bronze method has the advantages of excellent mechanical properties, low hysteresis loss and high reliability, and is widely used in the field of low-temperature superconductivity. The existing bronze method prepares superconducting wires by inserting Nb rods into bulk Cu-Sn alloys through multiple extrusion, drawing, intermediate annealing and phase heat treatment. Domestic and foreign researchers have conducted a lot of research on bulk Cu-Sn alloy modification, wire preparation process and phase heat treatment system. Studies have shown that all Sn elements in Nb3Sn superconducting wires come from bulk Cu-Sn alloys. The higher the Sn content, the greater the critical current density of the superconducting wire. However, Cu-Sn alloys with high Sn content have serious segregation, and there are a large number of brittle tin-rich phases in the organization, which leads to insufficient alloy plasticity, and serious core and wire breakage during the drawing process. Therefore, the contradictory relationship between Sn content and plasticity in bulk Cu-Sn alloys has become a bottleneck problem for the reliable preparation of Nb3Sn superconducting long wires and the improvement of critical current density. The present invention aims to prepare Cu-Sn alloy powder by gas atomization method, replace bulk Cu-Sn alloy with Cu-Sn alloy powder, directly assemble and deform with Nb rod, and then prepare Nb3Sn superconducting wire by corresponding heat treatment.

[0004] Bronze method: The bronze method is the earliest preparation method for Nb3Sn superconducting wires and is still widely used. Generally, tin bronze close to the solubility limit of Sn is used as the matrix, holes are drilled in the bronze matrix, and Nb or Nb-Ta alloy rods are inserted. The assembled composite is extruded and drawn to obtain hexagonal subcomponents. Hundreds of subcomponents are bundled together and loaded into a stabilizing copper tube with a barrier layer, and then extruded and drawn again to obtain an externally stable Nb3Sn superconductor. If Cu is used to replace part of Nb during the first assembly or a central copper rod is added to the center of the subcomponent during the second assembly, the final result is an internally stable Nb3Sn superconductor. A barrier layer (usually Ta or Nb) must be added between copper and bronze to prevent Sn in the bronze from diffusing and contaminating the stabilizing Cu.

[0005] Patent "202210561667.3" discloses an internally stabilized bronze-process Nb3Sn superconducting wire and a preparation method thereof, the method comprising: first coating a barrier layer on the outside of the stabilizer, then coating a bronze / niobium composite on the outside of the barrier layer to form a composite billet, and finally sealing, extruding, stretching, and heat treating the composite billet to obtain the Nb3Sn superconducting wire. By improving the structure of the bronze-process Nb3Sn superconducting wire, the oxygen-free copper stabilizer is located inside the wire, and the superconducting region formed by the bronze / niobium composite is located outside the wire. While ensuring that the stabilizer can function normally, it can meet special requirements such as joint welding required in the design and manufacturing process of superconducting magnets such as nuclear magnetic resonance spectrometers (NMR), and has good application prospects.

[0006] Patent "201811646092.5" discloses a method for preparing a Ta-enhanced bronze-process Nb3Sn superconducting wire, which comprises (1) cleaning a bronze / Nb composite rod, a copper tube, a Ta rod, and a barrier layer; (2) taking a number of bronze / Nb alloy composite rods, bundling them in a close-packed manner, inserting a Ta rod in the middle, and then loading them into a copper tube together with a barrier layer, adding copper covers at both ends and using electron beam sealing welding to obtain a final billet; (3) heating the final billet obtained in step (2) and then extruding it to obtain a bronze-process Nb3Sn composite rod; (4) repeatedly drawing and intermediate annealing the bronze-process Nb3Sn composite rod obtained in step (3) to obtain a Ta-enhanced bronze-process Nb3Sn superconducting wire. The present invention adds Ta rods to the core of the bronze Nb3Sn superconducting wire. After the phase heat treatment, the Ta core plays a strengthening role, the overall strength of the wire is improved, the ability of the wire to resist the Lorentz force when in use is improved, and the stability of the magnet wound with the wire is increased.

[0007] Patent "201711422216.7" discloses a method for preparing bronze Nb3Sn superconducting wire by online hot drawing. The method includes: cold drawing the bronze Nb3Sn rod, placing it in a vacuum heat treatment furnace for intermediate annealing to obtain the bronze Nb3Sn wire; passing the bronze Nb3Sn wire through a heated tubular furnace; passing the bronze Nb3Sn wire through a drawing die on one side of the tubular furnace for online hot drawing; after repeated online hot drawing, the bronze Nb3Sn superconducting wire is obtained. The present invention realizes the online annealing of the bronze Nb3Sn wire, which is easy to operate, has a short annealing time, reduces the Nb3Sn phase generated by the pre-reaction, and the overall deformation of the wire is uniform, and the critical current of the wire is relatively high.

[0008] Patent "201110005146.1" discloses a method for preparing bronze Nb3Sn strands with low hysteresis loss. By adjusting the number of holes drilled in the primary billet, the subcomponents are obtained through drawing, and the final billet is obtained through secondary assembly. The strands with the required performance parameters are obtained through stretching and annealing. The strands obtained by this process have a performance of about 240A (12T, 4.2K) and a loss of about 300m / cm (12T, 4.2K), which effectively reduces the hysteresis loss of the wire.

[0009] In the paper "Research on Microstructure and Electromagnetic Properties of Nb_3Sn Superconducting Wire for ITER", the author Zhang Ke found that the disadvantages of preparing Nb3Sn superconducting wire by bronze method are: tin bronze hardens very quickly during cold working, and the processing rate between two intermediate annealing of wire is generally not more than 50%. Repeated annealing is required to improve its processability, which is labor-intensive and inefficient; and there is a possibility of pre-generating Nb3Sn phase during intermediate annealing, which will lead to core breakage, wire breakage and reduced performance of finished wire. Another limitation of bronze method is that the Sn content in tin bronze restricts the volume content of Nb3Sn. The maximum solubility of Sn in bronze is 15.8wt.%, which is almost 0 at room temperature. There are a large number of brittle tin-rich phases in the organization, which leads to insufficient plasticity of high Sn content Cu-Sn alloy, fast cold working hardening, and serious core and wire breakage during drawing process, which has become a bottleneck problem for the reliable preparation of Nb3Sn superconducting long wire and the improvement of critical current density.

[0010] The above-mentioned publicly reported patents on the preparation of Nb3Sn superconducting wires by the bronze method show that: the high Sn content Cu-Sn alloy has serious segregation, and there are a large number of brittle tin-rich phases in the structure, which leads to insufficient alloy plasticity, serious core and wire breakage during the drawing process, and requires frequent annealing treatment, but frequent annealing treatment will lead to the pre-precipitation of Nb3Sn superconducting phases, reduce the plasticity of the wire, and cause core and wire breakage to occur again. Therefore, the contradictory relationship between Sn content and plasticity in bulk Cu-Sn alloy ingots has become a bottleneck problem for the reliable preparation of Nb3Sn superconducting long wires and the improvement of critical current density. Summary of the invention

[0011] The purpose of the present invention is to use micron-sized Cu-Sn-Ti alloy powder instead of bulk Cu-Sn alloy material to directly coordinate drawing deformation with Nb, utilize the advantages of powder fluidity and micron-sized size to improve alloy plasticity, inhibit component segregation, and solve the problems of core breakage, wire breakage, and the need for frequent intermediate annealing treatment when preparing Nb3Sn wire by bronze method.

[0012] The present invention provides a method for preparing a niobium-tin-copper superconducting wire based on a powder bronze method, comprising the following steps:

[0013] In the first step, oxygen-free copper rod, tin particles and titanium powder are placed in a crucible, and the mass fraction ratio of the three is: oxygen-free copper rod 80-90%wt, tin particles 9.5-19.5%wt, titanium powder 0.3-0.5%wt, and the crucible is placed in an electrode induction gas atomization powder spraying furnace, and the vacuum is evacuated to a vacuum degree of less than 3×10 -3 Pa, and at the same time, nitrogen is filled into the electrode induction gas atomization powder spraying furnace to make its pressure greater than the standard atmospheric pressure. After being filled with nitrogen, the gas atomization powder spraying furnace inlet valve and exhaust valve are opened, and the heating current is adjusted to start working, so as to obtain micron-sized Cu-Sn-Ti alloy powder;

[0014] The second step is to select a pure niobium rod, and to arrange a pure niobium tube outside the pure niobium rod, and to fill the area between the pure niobium rod and the pure niobium tube with Cu-Sn-Ti alloy powder under vacuum conditions, and to seal both ends of the area between the pure niobium rod and the pure niobium tube with pure niobium to ensure that the Cu-Sn-Ti alloy powder does not leak, thereby forming an intermediate billet;

[0015] Placing the intermediate blank sleeve in the first oxygen-free copper tube, and sealing both ends of the first oxygen-free copper tube with pure copper to form a combined blank;

[0016] The third step is to place the combined blank on a drawing machine and perform multiple drawing on the combined blank at room temperature to obtain a wire;

[0017] Step 4: Cut the wire obtained in the previous step into short wires according to the required length, and closely arrange the short wires in the second oxygen-free copper tube to form a multi-core billet, and the second oxygen-free copper tube is closely fitted with the short wires in the second oxygen-free copper tube;

[0018] Step 5: placing the multi-core blank on a drawing machine and continuing to draw at room temperature until the required diameter size is reached;

[0019] The sixth step is to wind the wire obtained in the fifth step, and perform phase sintering integration treatment in a vacuum atmosphere heat treatment furnace. After the heating is completed, the wire is cooled with the furnace to finally obtain the Nb3Sn superconducting wire.

[0020] Preferably, in the third step, when the combined blank is drawn, the intermediate drawing dies are all circular dies, and the last drawing die is a regular hexagonal die, until a wire with a regular hexagonal cross section is obtained.

[0021] Preferably, in the fourth step, the obtained wire with a regular hexagonal cross-section is cut into multiple short wires, and the short wires are closely arranged in a regular hexagonal arrangement in the second oxygen-free copper tube to form a multi-core billet, and the second oxygen-free copper tube is tightly fitted with the short wires located in the second oxygen-free copper tube.

[0022] Preferably, in the fifth step, when drawing the multi-core blank, the drawing process parameters are: the cross-sectional shrinkage rate of each pass is 15%-25%, and the drawing speed is 35-50 mm / s.

[0023] Preferably, the diameter of the pure niobium rod is 5-10 mm, the inner diameter of the pure niobium tube is twice the diameter of the pure niobium rod, and the wall thickness of the pure niobium tube is 1-2 mm;

[0024] The inner diameter of the first oxygen-free copper tube is 1-2 mm larger than the outer diameter of the pure niobium tube, the wall thickness of the first oxygen-free copper tube is 1-2 mm, and the wall thickness of the second oxygen-free copper tube is 1-2 mm.

[0025] Preferably, the final diameter of the wire after drawing is 1 mm.

[0026] Preferably, in the third step, when the combined blank is drawn, the drawing process parameters are: cross-sectional shrinkage rate per pass is 20%-35%, and the drawing speed is 60-70 mm / s.

[0027] Preferably, the heat treatment temperature of the phase sintering integration treatment is 700-740° C., and the heat treatment time is 150-250 hours.

[0028] Preferably, the mass ratio of oxygen-free copper rod, tin particles and titanium powder is 84:15.5:0.5.

[0029] A superconducting wire is prepared by a method for preparing niobium-tin-copper superconducting wire based on a powder bronze method.

[0030] The present invention fills the area between the pure niobium rod and the pure niobium tube with Cu-Sn-Ti alloy powder, utilizes the excellent fluidity and micron-level size advantages of the powder to improve the plasticity of the Cu-Sn-Ti alloy during the drawing process, and solves the problem of core breakage and wire breakage in drawing of traditional bulk Cu-Sn alloy ingots.

[0031] The present invention not only retains the advantages of preparing Nb3Sn / Cu superconducting wires by the bronze method, but also solves the problems of core breakage and wire breakage during CuSn / Nb drawing by using the excellent fluidity of the powder. At the same time, the ultra-high cooling rate in the powder preparation process can refine the grains under the condition of obtaining a saturated CuSn alloy, which is conducive to the formation of fine Nb3Sn superconducting phases in the phase formation process, improves the magnetic flux pinning ability, and enhances superconducting properties such as the critical current density of the superconducting wire.

[0032] The gas atomization method for preparing powder can refine the grains, which is beneficial to obtaining a fine and uniform microstructure Nb3Sn superconducting phase, and further improving the critical current density of the superconducting wire.

[0033] The present invention does not require intermediate annealing during the wire drawing process. Compared with the bronze method which requires annealing once in three passes during the drawing process, the process is simple and labor costs are saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0035] The present invention provides a method for preparing a niobium-tin-copper superconducting wire based on a powder bronze method, comprising the following steps:

[0036] In the first step, oxygen-free copper rod, tin particles and titanium powder are placed in a crucible, and the mass fraction ratio of the three is: oxygen-free copper rod 80-90%wt, tin particles 9.5-19.5%wt, titanium powder 0.3-0.5%wt, and the crucible is placed in an electrode induction gas atomization powder spraying furnace, and the vacuum is evacuated to a vacuum degree of less than 3×10 -3 Pa, and at the same time, nitrogen is filled into the electrode induction gas atomization powder spraying furnace to make its pressure greater than the standard atmospheric pressure. After being filled with nitrogen, the gas atomization powder spraying furnace inlet valve and exhaust valve are opened, and the heating current is adjusted to start working, so as to obtain micron-sized Cu-Sn-Ti alloy powder;

[0037] The second step is to select a pure niobium rod, and to arrange a pure niobium tube outside the pure niobium rod, and to fill the area between the pure niobium rod and the pure niobium tube with Cu-Sn-Ti alloy powder under vacuum conditions, and to seal both ends of the area between the pure niobium rod and the pure niobium tube with pure niobium to ensure that the Cu-Sn-Ti alloy powder does not leak, thereby forming an intermediate billet;

[0038] Placing the intermediate blank sleeve in the first oxygen-free copper tube, and sealing both ends of the first oxygen-free copper tube with pure copper to form a combined blank;

[0039] The third step is to place the combined blank on a drawing machine and perform multiple drawing on the combined blank at room temperature to obtain a wire;

[0040] Step 4: Cut the wire obtained in the previous step into short wires according to the required length, and closely arrange the short wires in the second oxygen-free copper tube to form a multi-core billet, and the second oxygen-free copper tube is closely fitted with the short wires in the second oxygen-free copper tube;

[0041] Step 5: placing the multi-core blank on a drawing machine and continuing to draw at room temperature until the required diameter size is reached;

[0042] The sixth step is to wind the wire obtained in the fifth step, and perform phase sintering integration treatment in a vacuum atmosphere heat treatment furnace. After the heating is completed, the wire is cooled with the furnace to finally obtain the Nb3Sn superconducting wire.

[0043] In one embodiment, in the third step, when the combined blank is drawn, the intermediate drawing dies are all circular dies, and the last drawing die is a regular hexagonal die, until a wire with a regular hexagonal cross section is obtained.

[0044] In one embodiment, in the fourth step, the obtained wire with a regular hexagonal cross-section is cut into multiple short wires, and the short wires are closely arranged in a regular hexagonal arrangement in the second oxygen-free copper tube to form a multi-core billet, and the second oxygen-free copper tube is tightly fitted with the short wires located in the second oxygen-free copper tube.

[0045] In one embodiment, in the fifth step, when drawing the multi-core blank, the drawing process parameters are: the cross-sectional shrinkage rate of each pass is 15%-25%, and the drawing speed is 35-50 mm / s.

[0046] The diameter of the pure niobium rod is 5-10 mm, the inner diameter of the pure niobium tube is twice the diameter of the pure niobium rod, and the wall thickness of the pure niobium tube is 1-2 mm;

[0047] The inner diameter of the first oxygen-free copper tube is 1-2 mm larger than the outer diameter of the pure niobium tube, the wall thickness of the first oxygen-free copper tube is 1-2 mm, and the wall thickness of the second oxygen-free copper tube is 1-2 mm.

[0048] The final diameter of the wire after drawing is 1mm.

[0049] In the third step, when the combined billet is drawn, the drawing process parameters are: cross-sectional shrinkage rate per pass 20%-35%, and drawing speed 60-70 mm / s.

[0050] The heat treatment temperature of the phase sintering integrated treatment is 700-740°C, and the heat treatment time is 150-250 hours.

[0051] In one embodiment, the mass ratio of oxygen-free copper rod, tin particles and titanium powder is 84:15.5:0.5.

[0052] A superconducting wire is prepared by a method for preparing niobium-tin-copper superconducting wire based on a powder bronze method. Example

[0053] The present invention provides a method for preparing a niobium-tin-copper superconducting wire based on a powder bronze method, comprising the following steps:

[0054] In the first step, oxygen-free copper rods, tin particles, and titanium powder are placed in a crucible at a mass ratio of 84:15.5:0.5, and the crucible is placed in an electrode induction atomization powder spraying furnace, and the vacuum is evacuated to a vacuum degree of less than 3×10-3 Pa, and nitrogen is filled into the electrode induction gas atomization powder spraying furnace at the same time to make its pressure greater than the standard atmospheric pressure. After being filled with nitrogen, the gas atomization powder spraying furnace intake valve and exhaust valve are opened, and the heating current is adjusted to start working. The atomization medium is nitrogen and the atomization pressure is 30MPa. After the alloy particles are melted and the charge reaches the atomization temperature, the molten liquid metal is poured into the insulation tundish of the electrode induction gas atomization powder spraying furnace under the protection of inert gas. The liquid metal will enter the atomization chamber through the guide pipe at the bottom of the tundish. In this process, it is impacted by the high-pressure airflow from the nozzle, and the metal liquid is atomized and broken into a large number of fine metal droplets. The droplets form spheres under the action of surface tension during the flight and sedimentation process and solidify into micron-sized alloy powders. The powder prepared by the vacuum gas atomization method is tested for particle size, and the median particle size of the powder is measured to be about 44 microns;

[0055] The second step is to select a pure niobium rod with a length of 500 mm, and to arrange a pure niobium tube on the outer surface of the pure niobium rod with a length of 530 mm. The area between the pure niobium rod and the pure niobium tube is filled with Cu-Sn-Ti alloy powder under vacuum conditions, and both ends of the area between the pure niobium rod and the pure niobium tube are sealed with pure niobium to ensure that the Cu-Sn-Ti alloy powder does not leak, thereby forming an intermediate billet.

[0056] The intermediate blank sleeve is placed in the first oxygen-free copper tube, the length of the first oxygen-free copper tube is 560 mm, and the total length of the first oxygen-free copper tube is 30 mm longer than the total length of the intermediate blank sleeve, and both ends of the first oxygen-free copper tube are sealed with pure copper to form a combined blank;

[0057] The third step is to place the combined blank on a drawing machine and perform multiple drawing on the combined blank at room temperature. The drawing process parameters are: a cross-sectional shrinkage rate of 20% per pass, a drawing speed of 60 mm / s, a circular die for the intermediate passes, and a regular hexagonal die for the last pass, until a wire with a regular hexagonal cross section is obtained, and the side length of the regular hexagon is 2 mm.

[0058] Step 4: Cut the wires in the previous step into 300 mm long short wires, 19 in number, and arrange the short wires in a regular hexagonal pattern in a second oxygen-free copper tube to form a 19-core billet. The second oxygen-free copper tube is tightly fitted with the short wires in the second oxygen-free copper tube.

[0059] The fifth step is to place the 19-core billet on a drawing machine for further drawing. The drawing process parameters are: the cross-sectional shrinkage rate of each pass is 20%, the drawing speed is 40 mm / s, the drawing temperature is room temperature drawing, and the final diameter of the drawn wire is 1 mm.

[0060] The sixth step is to wind the wire obtained in the fifth step and carry out phase sintering integration treatment in a vacuum atmosphere heat treatment furnace. The heat treatment temperature of the phase sintering integration treatment is 740°C and the heat treatment time is 200 hours. After the heating is completed, the wire is cooled with the furnace to finally obtain the Nb3Sn / Cu superconducting wire.

Claims

1. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method, characterized in that: The following steps are involved: In the first step, oxygen-free copper rod, tin particles and titanium powder are placed in a crucible, and the mass fraction ratio of the three is: oxygen-free copper rod 80-90%wt, tin particles 9.5-19.5%wt, titanium powder 0.3-0.5%wt, and the crucible is placed in an electrode induction gas atomization powder spraying furnace, and the vacuum is evacuated to a vacuum degree of less than 3×10 -3 Pa, and at the same time, nitrogen is filled into the electrode induction gas atomization powder spraying furnace to make its pressure greater than the standard atmospheric pressure. After being filled with nitrogen, the gas atomization powder spraying furnace inlet valve and exhaust valve are opened, and the heating current is adjusted to start working, so as to obtain micron-sized Cu-Sn-Ti alloy powder; The second step is to select a pure niobium rod, and to arrange a pure niobium tube outside the pure niobium rod, and to fill the area between the pure niobium rod and the pure niobium tube with Cu-Sn-Ti alloy powder under vacuum conditions, and to seal both ends of the area between the pure niobium rod and the pure niobium tube with pure niobium to ensure that the Cu-Sn-Ti alloy powder does not leak, thereby forming an intermediate billet; Placing the intermediate blank sleeve in the first oxygen-free copper tube, and sealing both ends of the first oxygen-free copper tube with pure copper to form a combined blank; The third step is to place the combined blank on a drawing machine and perform multiple drawing on the combined blank at room temperature to obtain a wire; Step 4: Cut the wire obtained in the previous step into short wires according to the required length, and closely arrange the short wires in the second oxygen-free copper tube to form a multi-core billet, and the second oxygen-free copper tube is closely fitted with the short wires in the second oxygen-free copper tube; Step 5: placing the multi-core blank on a drawing machine and continuing to draw at room temperature until the required diameter size is reached; The sixth step is to wind the wire obtained in the fifth step, and perform phase sintering integration treatment in a vacuum atmosphere heat treatment furnace. After the heating is completed, the wire is cooled with the furnace to finally obtain the Nb3Sn superconducting wire.

2. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method as claimed in claim 1, characterized in that: In the third step, when the combined billet is drawn, the intermediate drawing dies are all circular dies, and the last drawing die is a regular hexagonal die, until a wire with a regular hexagonal cross section is obtained.

3. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method as claimed in claim 2, characterized in that: In the fourth step, the obtained wire with a regular hexagonal cross-section is cut into multiple short wires, and the short wires are closely arranged in a regular hexagonal arrangement in the second oxygen-free copper tube to form a multi-core billet, and the second oxygen-free copper tube is tightly fitted with the short wires located in the second oxygen-free copper tube.

4. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method as claimed in claim 3, characterized in that: In the fifth step, when drawing the multi-core billet, the drawing process parameters are: the cross-sectional shrinkage rate of each pass is 15%-25%, and the drawing speed is 35-50mm / s.

5. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method as claimed in claim 4, characterized in that: The diameter of the pure niobium rod is 5-10 mm, the inner diameter of the pure niobium tube is twice the diameter of the pure niobium rod, and the wall thickness of the pure niobium tube is 1-2 mm; The inner diameter of the first oxygen-free copper tube is 1-2 mm larger than the outer diameter of the pure niobium tube, the wall thickness of the first oxygen-free copper tube is 1-2 mm, and the wall thickness of the second oxygen-free copper tube is 1-2 mm.

6. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method as claimed in claim 5, characterized in that: The final diameter of the wire after drawing is 1mm.

7. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method as claimed in claim 1, characterized in that: In the third step, when the combined blank is drawn, the drawing process parameters are: the cross-sectional shrinkage rate of each pass is 20%-35%, and the drawing speed is 60-70 mm / s.

8. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method as claimed in claim 1, characterized in that: The heat treatment temperature of the phase sintering integration treatment is 700-740° C., and the heat treatment time is 150-250 hours.

9. A method for preparing niobium-tin-copper superconducting wire based on powder bronze method as claimed in claim 1, characterized in that: The mass ratio of oxygen-free copper rod, tin particles and titanium powder is 84:15.5:0.

5.

10. A superconducting wire prepared by the method for preparing a niobium-tin-copper superconducting wire based on a powder bronze method as claimed in any one of claims 1 to 9.

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