Method for copper coating on the surface of Nb3Al superconducting wire by rapid heating and cooling

Abstract

The present invention discloses a method for copper coating on the surface of Nb3Al superconducting wire by rapid heating and cooling. First, the metal Ga adhered to the surface of Nb3Al superconducting wire is removed; the wire after Ga removal is polished to remove the surface Nb and Ga compounds, and then ultrasonically cleaned in anhydrous ethanol with a concentration greater than 80%, and then the wire is dried until the wire shows a metallic luster and the surface of the wire has a roughness; then oxygen-free copper filaments are woven on the surface of Nb3Al superconducting wire; the wire is woven repeatedly for multiple times; the superconducting wire with oxygen-free copper braiding layer is continuously electroplated with copper and then stretched by a round die, so as to obtain Nb3Al superconducting wire with a high RRR value. The present invention uses oxygen-free copper filaments as raw materials to prepare a copper matrix with a high RRR value on the surface of Nb3Al superconducting wire after rapid heating and cooling.

Description

Technical Field

[0001] The invention belongs to the technical field of superconducting material processing, and in particular relates to a method for rapidly heating and rapidly cooling a Nb3Al superconducting wire surface to coat copper. Background Art

[0002] Nb3Al is currently the superconducting c ), critical current density (J c ) and the upper critical field (H c2 ) and other low-temperature superconducting materials with the best comprehensive practical performance. Compared with Nb3Sn, its superconducting transition temperature reaches 19.3K, and it also belongs to the A15 structure intermetallic compound and grain boundary pinning superconductor; it also has a higher upper critical field and better high-field critical current density characteristics; more importantly, it has better stress-strain tolerance than Nb3Sn. Therefore, Nb3Al superconducting wire is considered to have great potential in the application of superconducting magnets such as the next generation of thermal magnetic confinement fusion reactors (CFETR), high-energy particle accelerators (LHC) and nuclear magnetic resonance spectrometers (NMR).

[0003] At present, the preparation process of Nb3Al superconducting wire is divided into two parts: "precursor wire preparation" and "heat treatment". Among them, the preparation method of the precursor wire is usually a winding method, combined with multiple assembly composites, hydrostatic extrusion and multiple stretching to obtain a precursor wire with copper. After the multi-core precursor wire is corroded to remove copper, it is subjected to rapid heating and cooling heat treatment, so that the Nb3Al precursor wire undergoes a process of heating to ~2000℃ and then quenching to room temperature within ~0.1s, so that Nb and Al diffuse and react to generate Nb(Al) with a BCC structure. ss A supersaturated solid solution is then formed, and then a copper stabilizer is coated on the surface of the wire after rapid heating and cooling.

[0004] The copper outside the precursor wire plays a role in lubrication and preventing the hot viscous metal Nb from sticking to the mold during the multi-pass stretching process, so as to achieve the purpose of accurately controlling the final wire size and roundness. However, due to the high temperature of the rapid heating and cooling heat treatment (~2000℃), the melting point of copper is only 1083.4℃, and at high temperature, Cu, Nb, and Al will react to form CuNbAl ternary compounds, so it is necessary to remove the copper before the rapid heating and cooling heat treatment. The high-purity copper (residual resistivity ratio RRR value greater than 100) matrix material effectively conducts the heat generated by external disturbances when the superconducting wire carries high current to the outside, and at the same time, it serves as a current path when the superconducting wire quenches, which is an effective protection for the superconducting wire, preventing the superconducting wire from burning the wire instantly when the superconducting wire quenches. Therefore, the Nb3Al precursor wire must be covered with high-purity copper as a matrix after the rapid heating and cooling heat treatment.

[0005] At present, the commonly used copper coating methods are as follows: inlay method, electroplating method, and copper tube stretching method. In the inlay method, the heat-treated wire is embedded in the copper slot wire, and then stretched or tied into a flat wire. The connectivity between the superconducting wire and the copper slot wire is greatly affected by the processing amount, and the copper slot wire is difficult to process; the electroplating method is to activate the heat-treated wire with a vacuum particle beam and then electroplate it with copper. This method is inefficient and costly; the copper tube stretching method inserts the heat-treated wire into a capillary copper tube and stretches it into a round wire or a flat wire, but this method is only suitable for preparing short samples, and it is difficult to prepare long wires of more than hundreds of meters. Summary of the invention

[0006] The purpose of the present invention is to provide a method for copper coating on the surface of Nb3Al superconducting wire after rapid heating and cooling, and to prepare a copper matrix with a high RRR value on the surface of Nb3Al superconducting wire after rapid heating and cooling using multiple oxygen-free copper filaments as raw materials.

[0007] The technical solution adopted by the present invention is a method for rapidly heating and rapidly cooling the surface of Nb3Al superconducting wire to coat copper, which is specifically implemented according to the following steps:

[0008] Step 1, removing the metal Ga on the surface of the Nb3Al superconducting wire;

[0009] Step 2, grinding the wire after Ga removal in step 1 to remove the surface Nb and Ga compounds, and then ultrasonically cleaning the wire in anhydrous ethanol with a concentration greater than 80%, and then drying the wire until the wire shows a metallic luster and the surface of the wire has a roughness;

[0010] Step 3, covering the surface of the Nb3Al superconducting wire obtained in step 2 by weaving oxygen-free copper filaments;

[0011] Step 4, the superconducting wire with the oxygen-free copper braided layer obtained in step 3 is subjected to continuous copper electroplating;

[0012] Step 5: The superconducting wire obtained in step 4 is subjected to circular die stretching to obtain a Nb3Al superconducting wire with a high RRR value.

[0013] The present invention is also characterized in that:

[0014] Specifically, step 1 is to place the Nb3Al superconducting wire subjected to rapid heating and cooling treatment in hot water greater than 90°C, and then wipe off the metal Ga attached to the surface.

[0015] In step 2, grinding is performed continuously with a grinding wheel or a scouring pad, and the thickness range of grinding removal is 0.1 to 0.5 mm. If grinding is performed with a grinding wheel, the corresponding particle size range of the grinding wheel is 400# to 800#, and the grinding time is 1 to 2 minutes;

[0016] In step 2, the frequency of ultrasonic cleaning is 25-45 Hz, the cleaning time is 15-30 min, and the drying temperature is 50-80° C.

[0017] In step 2, the surface roughness of the wire is Ra1.6 to Ra12.5.

[0018] Step 3 is as follows:

[0019] The copper cladding is woven on a braiding machine using oxygen-free copper filaments as raw material. The diameter of the oxygen-free copper wire is Φ0.05-0.2mm and the number is 12, 24, 36, or 48 wires.

[0020] The RRR value of the oxygen-free copper wire used for weaving in step 3 is greater than 150, and the number of weaving times is 1 to 3 times.

[0021] The electroplating line speed during copper plating in step 4 is 1 to 20 m / min.

[0022] In step 5, the stretching processing rate is between 15% and 50%.

[0023] In step 5, the diameter of the Nb3Al superconducting wire after braiding and copper coating is 0.60-2.00 mm.

[0024] The beneficial effect of the present invention is that a method for copper coating on the surface of Nb3Al superconducting wire by rapid heating and cooling heat treatment directly uses oxygen-free copper wire with high RRR value to weave onto the surface of Nb3Al superconducting wire after rapid heating and cooling heat treatment, and combines short-time electroplating and a round die stretching process with a certain amount of processing to achieve the composite of a copper matrix with high RRR value on the surface of Nb3Al superconducting wire. The copper matrix composited by the present invention is uniform, which improves the shortcomings of low efficiency and low coating quality of traditional electroplating copper coating, optimizes the production process, and reduces the production cost of Nb3Al superconducting wire. The method is suitable for the preparation of long superconducting wires, is conducive to large-scale promotion and application, and has great commercial value. DETAILED DESCRIPTION

[0025] The present invention is described in detail below in conjunction with specific implementation modes.

[0026] The method for rapid heating and cooling of the copper coating on the surface of Nb3Al superconducting wire of the present invention is specifically implemented according to the following steps:

[0027] Step 1, removing the metal Ga adhered to the surface of the Nb3Al superconducting wire; specifically, placing the Nb3Al superconducting wire that has been subjected to rapid heating and cooling treatment (the principle of rapid heating and cooling treatment is a special heat treatment method for Nb3Al superconducting wire, specifically, heating the ~1.0mm Nb3Al composite wire to ~2000°C within ~0.1s and then quenching it to room temperature, and this process needs to be carried out continuously and stably for a kilometer-long wire) in hot water greater than 90°C, and then wiping off the metal Ga adhered to the surface.

[0028] Step 2: Grind the wire after Ga removal in step 1 to remove the surface Nb and Ga compounds. The metallic Ga is silvery white. The surface of the wire after Ga removal is dark gray, which is the reaction product of Nb and Ga and has a certain thickness. Then, ultrasonic cleaning is performed in anhydrous ethanol with a concentration greater than 80%, and then the wire is dried until the wire shows a metallic luster. At the same time, the surface of the wire has a roughness, which is convenient for the close bonding between the copper wire and the superconducting wire in the subsequent weaving process. During grinding, a grinding wheel or a scouring pad is used for continuous grinding. The thickness range of grinding removal is 0.1-0.5 mm. If it is a grinding wheel, the particle size range corresponding to the grinding wheel is 400#-800#, and the grinding time is 1-2 minutes. The frequency of ultrasonic cleaning is 25-45 Hz, the cleaning time is 15-30 min, and the drying temperature is 50-80°C. The surface roughness of the wire is Ra1.6-Ra12.5.

[0029] Step 3, braiding and copper-cladding the Nb3Al superconducting wire obtained in step 2; the braiding tension is preferably set so as not to break the copper wire, the thickness of the braided layer is designed according to the final copper ratio requirement of the wire, and the wire is braided repeatedly; the details are as follows:

[0030] The oxygen-free copper wire is used as the raw material on the braiding machine to braid the copper. The diameter of the oxygen-free copper wire is Φ0.05-0.2mm, and the number is 12, 24, 36, or 48. The RRR value of the oxygen-free copper wire used in braiding is greater than 150, and the number of braiding is 1-3 times. The specific design is based on the final copper ratio requirements of the wire.

[0031] Step 4: The superconducting wire with oxygen-free copper braided layer obtained in step 3 is continuously electroplated with copper, and the electroplating line speed is 1-20 m / min. The small gaps in the braiding process are filled; the short-time electroplating treatment is aimed at filling the braided gaps with the electroplating process. The wire with a certain roughness ensures good contact between the fine copper wires in the braiding process and forms a good bonding state in the subsequent stretching process.

[0032] Step 5: The superconducting wire obtained in step 4 is subjected to round die stretching, and the stretching processing rate is 15-50%, so as to obtain a Nb3Al superconducting wire with a high RRR value. The diameter of the Nb3Al superconducting wire after braiding and copper coating is 0.60-2.00 mm.

[0033] The present invention selects oxygen-free copper wire with a high RRR value, and coats the surface of the Nb3Al superconducting wire with a copper matrix with a high RRR value by a weaving method combined with electroplating and subsequent stretching, thereby changing the traditional inefficient electroplating process, reducing costs, and more importantly, realizing continuous weaving and copper coating of long wires.

[0034] Example 1

[0035] Take Φ1.31mm Nb3Al superconducting wire, and after rapid heating and cooling, remove the metal Ga in 100-degree hot water; then continuously polish the wire to remove the Nb and Ga reactants on the surface of the wire. After removing the surface reactants, the wire diameter is Φ1.20mm, and the surface roughness of the wire is Ra6.3. Then wash the wire with anhydrous ethanol for 20 minutes, and dry it in a drying oven at a drying temperature of 50°C for 30 minutes.

[0036] The cleaned superconducting wire is placed on a braiding machine, and oxygen-free copper wire is used as the raw material. The diameter of the oxygen-free copper wire is 0.08 mm, and the number is 18. The braided wire is continuously electroplated in the electroplating tank, and the electroplating line speed is 5m / min;

[0037] The braided and electroplated wire is stretched through a round die with a total stretching amount of 20% to obtain a copper-clad Nb3Al superconducting wire.

[0038] The length of a single copper-clad Nb3Al superconducting wire produced exceeds 1000m. After the final transformation heat treatment, its RRR value is tested to be 205.

[0039] Example 2

[0040] Take Φ1.35mm Nb3Al superconducting wire, and after rapid heating and cooling, remove the metal Ga in 100-degree hot water. Then polish the wire continuously to remove the Nb and Ga reactants on the surface of the wire. The diameter of the wire after cleaning is 1.21mm, and the surface roughness of the wire is Ra3.2. Then clean the wire with anhydrous ethanol for 25 minutes, and dry it in a drying oven at a drying temperature of 70°C for 20 to 30 minutes.

[0041] The cleaned superconducting wire is braided on a braiding machine, using oxygen-free copper wire as the raw material. The diameter of the oxygen-free copper wire is 0.05mm, and the number is 24. The braided wire is continuously electroplated in the electroplating tank, and the electroplating line speed is 10m / min;

[0042] The braided and electroplated wire is stretched through a round die with a total stretching amount of 30%, thereby obtaining a copper-clad Nb3Al superconducting wire.

[0043] The length of a single copper-clad Nb3Al superconducting wire produced exceeds 1500m. After the final transformation heat treatment, its RRR value is tested to be 193.

[0044] Example 3

[0045] Take Φ1.03mm Nb3Al superconducting wire, and after rapid heating and cooling, remove the metal Ga in 200℃ hot water. Then polish the wire continuously to remove the Nb and Ga reactants on the surface of the wire. The diameter of the wire after cleaning is 0.83mm, and the surface roughness of the wire is Ra6.3. Then clean the wire with anhydrous ethanol for 30 minutes, and dry it in a drying oven at 80℃ for 25 minutes.

[0046] The cleaned superconducting wire is placed on a braiding machine, and oxygen-free copper wire is used as the raw material. The diameter of the oxygen-free copper wire is 0.10 mm, and the number is 36. The braided wire is continuously electroplated in the electroplating tank, and the electroplating line speed is 15m / min;

[0047] The braided and electroplated wire is stretched through a round die with a total stretching amount of 20% to obtain a copper-clad Nb3Al superconducting wire.

[0048] The length of a single copper-clad Nb3Al superconducting wire produced exceeds 2000m. After the final transformation heat treatment, its RRR value is tested to be 227.

Claims

1. A method for rapidly heating and cooling a Nb3Al superconducting wire surface to coat copper, characterized in that: Follow the steps below to implement it: Step 1, removing the metal Ga on the surface of the Nb3Al superconducting wire that has been subjected to rapid heating and cooling heat treatment; Step 2, grinding the wire after Ga removal in step 1 to remove the surface Nb and Ga compounds, and then ultrasonically cleaning the wire in anhydrous ethanol with a concentration greater than 80%, and then drying the wire until the wire shows a metallic luster and the surface of the wire has a roughness; The surface roughness of the wire in step 2 is Ra1.6~Ra12.5; Step 3, coating the oxygen-free copper filaments on the surface of the Nb3Al superconducting wire obtained in step 2 by weaving; repeatedly weaving the wire for multiple times, and the RRR value of the oxygen-free copper filaments is greater than 150; Step 4, the superconducting wire with the oxygen-free copper braided layer obtained in step 3 is subjected to continuous copper electroplating; Step 5: The superconducting wire obtained in step 4 is subjected to circular die stretching to obtain a Nb3Al superconducting wire with a high RRR value.

2. The method for rapid heating and cooling heat treatment of Nb3Al superconducting wire surface copper coating according to claim 1, characterized in that: Specifically, the step 1 is to place the Nb3Al superconducting wire subjected to rapid heating and cooling treatment in hot water greater than 90° C., and then wipe off the metal Ga attached to the surface.

3. The method for rapid heating and cooling heat treatment of Nb3Al superconducting wire surface copper coating according to claim 1, characterized in that: In step 2, grinding is performed continuously with a grinding wheel or a scouring pad, and the thickness range of grinding removal is 0.1-0.5 mm. If grinding is performed with a grinding wheel, the particle size range corresponding to the grinding wheel is 400#-800#, and the grinding time is 1-2 minutes.

4. The method for rapid heating and cooling heat treatment of Nb3Al superconducting wire surface copper coating according to claim 1, characterized in that: The frequency of ultrasonic cleaning in step 2 is 25-45 Hz, the cleaning time is 15-30 min, and the drying temperature is 50-80° C.

5. The method for rapid heating and cooling heat treatment of Nb3Al superconducting wire surface copper coating according to claim 1, characterized in that: The step 3 is as follows: The copper cladding is woven on a braiding machine using oxygen-free copper filaments as raw material. The diameter of the oxygen-free copper filaments is Φ0.05~0.2mm, and the number is 12, 24, 36, or 48.

6. The method for rapid heating and cooling heat treatment of Nb3Al superconducting wire surface copper coating according to claim 1, characterized in that: The RRR value of the oxygen-free copper wire used for weaving in step 3 is greater than 150, and the number of weaving times is 1 to 3 times.

7. The method for rapid heating and cooling heat treatment of Nb3Al superconducting wire surface copper coating according to claim 1, characterized in that: The electroplating line speed during the copper electroplating in step 4 is 1-20 m / min.

8. The method for rapid heating and cooling heat treatment of Nb3Al superconducting wire surface copper coating according to claim 1, characterized in that: In step 5, the stretching processing rate is between 15% and 50%.

9. The method for rapid heating and cooling heat treatment of Nb3Al superconducting wire surface copper coating according to claim 1, characterized in that: In step 5, the diameter of the Nb3Al superconducting wire after braiding and copper coating is 0.60-2.00 mm.