An additive manufacturing method for a copper layer on the surface of a superconducting cavity

Abstract

This invention discloses an additive manufacturing method for a copper layer on the surface of a superconducting cavity, comprising the following steps: S1: preparing powdered brazing material; S2: depositing the brazing material onto the outer surface of the superconducting cavity by cold spraying in a solid-state molding manner to form a brazing layer, the thickness of which is 0.1-0.5 mm, and the surface of the superconducting cavity being a niobium layer; S3: electroplating copper onto the surface of the brazing layer to form a copper coating; S4: annealing the composite layer consisting of the niobium layer, the brazing layer, and the copper coating. This invention uses a high thermal conductivity brazing material to form a brazing layer on the outer surface of a superconducting cavity by cold spraying, and then electroplating a copper layer on the brazing layer, resulting in a composite coating on the outer surface of the superconducting cavity that is low in oxidation, resistant to cracking and delamination. The bonding strength between the copper layer, the brazing layer, and the niobium layer is high, while also giving the superconducting cavity excellent heat dissipation performance.

Description

Technical Field

[0001] This invention relates to the field of superconducting cavities, and more particularly to an additive manufacturing method for a copper layer on the surface of a superconducting cavity. Background Technology

[0002] Radio frequency superconducting technology is a high-tech field in accelerators, and the core component of a superconducting accelerator is the superconducting cavity. Currently, superconducting cavities are mainly manufactured using high-purity niobium with a residual resistivity greater than 300 Ω·cm. High-purity niobium has a high superconducting critical temperature, reaching 9.3 K, and a high superconducting critical magnetic field strength, reaching 200 mT. It also exhibits good chemical stability and is easy to machine and form. However, niobium has low thermal conductivity, and the wall thickness of a pure niobium superconducting cavity is only 3-4 mm, resulting in poor mechanical stability, which makes it difficult to meet the stable operation requirements of future superconducting accelerators.

[0003] The copper-niobium composite cavity, formed by adding a copper layer to the surface of a superconducting cavity, has become one of the important future development directions for cryogenic superconducting accelerator cavities due to its higher thermal conductivity and better mechanical stability. Currently, cryogenic radio frequency superconducting cavities require extremely low operating temperatures, such as maintaining a temperature between 1.6-4.5K. During operation, the inner surface of the superconducting cavity generates heat. To prevent heat accumulation and subsequent temperature rise leading to superconductivity failure, the generated heat needs to be dissipated. However, pure niobium has low thermal conductivity, making heat dissipation difficult. Pure copper has a much higher thermal conductivity at low temperatures than metallic niobium and is also inexpensive. Therefore, if a high thermal conductivity copper layer can be added to the outer surface of a pure niobium superconducting cavity, the copper layer can significantly increase the heat transfer efficiency of the superconducting cavity through effective lateral heat transfer, thereby increasing the operational stability of the superconducting cavity.

[0004] Currently, the primary method for treating pure copper as a thermally conductive layer is electroplating. This is because electroplated copper layers offer advantages such as high density, high thermal conductivity, simple fabrication process, and controllable thickness. However, electroplating is rarely used in additive manufacturing of niobium cavity surfaces. The main reason is the significant difference in physical properties between niobium and copper, making it difficult to form an effective bond between the plating layers. This leads to easy peeling of the plating, and the bonding strength of the plating significantly affects heat conduction and the mechanical stability of the superconducting cavity. Therefore, it is necessary to develop additive manufacturing methods that meet the application requirements of superconducting cavities, namely, methods with high bonding strength, good thermal conductivity, and minimal thermal impact during the additive manufacturing process. Summary of the Invention

[0005] To address the issues of poor adhesion between the niobium and copper layers and poor heat dissipation in superconducting cavities when copper is deposited on the surface of a superconducting cavity, this invention provides an additive manufacturing method for a copper layer on the surface of a superconducting cavity.

[0006] An additive manufacturing method for a copper layer on the surface of a superconducting cavity includes the following steps:

[0007] S1: Prepare powdered brazing material;

[0008] S2: The brazing material is deposited onto the outer surface of the superconducting cavity by cold spraying in a solid-state molding manner to form a brazing layer. The thickness of the brazing layer is 0.1-0.5 mm, and the surface of the superconducting cavity is a niobium layer.

[0009] S3: Electroplating copper onto the surface of the brazing layer to form a copper coating;

[0010] S4: Anneal the composite layer consisting of the niobium layer, the brazing layer, and the copper coating. The composite coating consisting of the brazing layer and the copper layer has strong adhesion, and also strong adhesion to the niobium layer of the superconducting cavity. The superconducting cavity has good heat dissipation performance, and this method is easy to operate and control.

[0011] Optionally, the brazing material comprises the following components by mass percentage: silver ≥ 50%, copper ≥ 0%, titanium ≥ 0%, and the melting point of the brazing material is less than 1000°C. The brazing material has high thermal conductivity.

[0012] Optionally, the brazing material has a particle size of less than 300 mesh. This is beneficial for improving the strength of the brazing layer's connection to the copper and niobium layers on both sides, respectively.

[0013] Optionally, the cold spraying is performed under high pressure conditions of 1-7 MPa, with a gas flow rate of 1000-4000 SLM, using nitrogen or helium as the inert gas. This results in good spraying performance and a uniform brazing layer thickness.

[0014] Optionally, the cold spraying process uses a spray gun with a moving speed of 10-800 mm / s, a minimum distance of 10-100 mm between the spray gun and the superconducting cavity, and a gas temperature of 200-800℃. This results in good spraying performance, a uniform brazing layer thickness, and strong adhesion between the brazing layer and the niobium layer.

[0015] Optionally, the surface of the superconducting cavity can be ground and polished within 2 hours before cold spraying to reduce its surface roughness to less than 10 μm. This improves the spraying effect and enhances the adhesion between the brazing layer and the niobium layer.

[0016] Optionally, the brazing layer can be subjected to surface treatment including grinding, ultrasonic cleaning, and degreasing within 2 hours before copper plating. This improves the plating effect and enhances the adhesion between the copper layer and the brazing layer.

[0017] Optionally, the copper coating thickness is greater than 4 mm. This improves the mechanical and heat dissipation properties of the superconducting cavity.

[0018] Optionally, the annealing includes the following steps: heating from room temperature to 600°C at a rate of 1-5 min / °C and holding at that temperature for 10 h, then heating to 800-900°C at a rate of 5-10°C / min, holding at that temperature for 30 minutes, and then allowing it to cool naturally. This improves the mechanical and heat dissipation properties of the superconducting cavity.

[0019] Optionally, the annealing is performed under a vacuum condition below 1E-3 Pa. This results in a better annealing effect.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides an additive manufacturing method for a copper layer on the surface of a superconducting cavity. A brazing material with high thermal conductivity is cold-sprayed onto the outer surface of the superconducting cavity to form a brazing layer. Then, a copper layer is formed by electroplating on the brazing layer. A composite coating with low oxidation, not easy to crack or delaminate is obtained on the outer surface of the superconducting cavity. The bonding strength between the copper layer, the brazing layer and the niobium layer is high, and the superconducting cavity has good heat dissipation performance. Detailed Implementation

[0021] To illustrate the technical solutions of the present invention in detail, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1:

[0023] This embodiment provides an additive manufacturing method for a copper layer on the surface of a superconducting cavity, comprising the following steps: S1: preparing powdered brazing material; S2: depositing the brazing material onto the outer surface of the superconducting cavity using a cold spraying method to form a brazing layer with a thickness of 0.1-0.5 mm, wherein the surface of the superconducting cavity is a niobium layer; S3: electroplating copper on the surface of the brazing layer to form a copper coating; S4: annealing the composite layer consisting of the niobium layer, the brazing layer, and the copper coating.

[0024] For step S1: Prepare powdered brazing material.

[0025] The brazing material comprises the following components by mass percentage: silver ≥ 50%, copper ≥ 0%, titanium ≥ 0%, and has a melting point of less than 1000°C. The brazing material exhibits excellent thermal conductivity, and the particle size is less than 300 mesh. In some embodiments, the contents of silver, copper, and titanium are 66%, 28.01%, and 5.99%, respectively.

[0026] For step S2: The brazing material is deposited onto the outer surface of the superconducting cavity by cold spraying in a solid forming manner to form a brazing layer with a thickness of 0.1-0.5 mm. The surface of the superconducting cavity is a niobium layer.

[0027] Cold spraying is performed under high pressure conditions of 1-7 MPa, with a gas flow rate of 1000-4000 SLM, using nitrogen or helium as the inert gas. The spray gun movement speed is 10-800 mm / s, the minimum distance between the spray gun and the superconducting cavity is 10-100 mm, and the gas temperature is 200-800℃. The cold spraying can utilize a PCS-1000 high-pressure cold spraying system with a Laval nozzle. In one embodiment, the working gas is nitrogen, the working gas pressure is 4 MPa, the working gas temperature is 600℃, the spraying distance is 30 mm, the spray gun movement speed is 10 mm / s, and a brazing layer with a thickness of approximately 0.4 mm is prepared.

[0028] To improve the interparticle bonding effect of the brazing layer, the brazing material is deposited onto the surface of the superconducting cavity under high pressure via cold spraying, employing a low-temperature, high-speed, and solid-state molding process. The brazing layer is relatively thin, ranging from 0.1 to 0.5 mm. A thickness less than 0.1 mm cannot ensure diffusion bonding between the brazing layer and the copper coating, while a thickness greater than 0.5 mm will cause changes in the copper coating structure. The contact surface between the brazing layer and the niobium layer exhibits good bonding, resulting in a dense coating structure free from cracks, delamination, and oxide residue. The powdered brazing material also possesses high thermal conductivity at low temperatures.

[0029] This invention utilizes a cold spraying process, employing high-pressure inert gas to accelerate the brazing material, causing it to undergo intense plastic deformation at low temperatures and in a solid state to form a surface coating. The brazing layer prepared by this cold spraying process effectively avoids oxidation during coating formation due to the use of a high-pressure inert protective gas. High-pressure cold spraying also promotes bonding between the brazing layer particles and the niobium layer particles, thereby ensuring the quality of the brazing layer and a high-strength bond between the brazing layer and the superconducting cavity surface.

[0030] For step S3: Electroplating copper on the surface of the brazing layer to form a copper coating.

[0031] The copper coating is thicker than 4 mm. To improve the adhesion between the copper layer and the brazing layer, the surface of the superconducting cavity can be treated before electroplating. The anode for electroplating is pure copper, resulting in a copper layer with low porosity and good adhesion between the copper layer and the brazing layer.

[0032] For S4: Anneal the composite layer consisting of the niobium layer, the brazing layer, and the copper coating.

[0033] Annealing improves the bonding strength between coatings and removes impurity gases. Annealing includes the following steps: heating from room temperature to 600°C at a rate of 1-5 min / °C and holding for 10 hours, then heating to 800-900°C at a rate of 5-10°C / min, holding for 30 minutes, and then allowing to cool naturally. Annealing needs to be performed under a vacuum of less than 1E-3 Pa. In one embodiment, annealing is performed by heating from room temperature to 600°C at a rate of 3 min / °C and holding for 10 hours, followed by heating to 850°C at a rate of 8.3°C / min, holding for 30 minutes, and then allowing to cool naturally. The copper layer exhibits a thermal conductivity greater than 350 W / mK at a low temperature of 4.2 K and shows no bubbles after 10 hours of annealing.

[0034] The bonding strength of the copper layer, brazing layer, and niobium layer was tested using the national standard GB / T 6396-2008 Test Methods for Mechanical and Technological Properties of Composite Steel Plates. The results showed that even if the copper layer was torn, the copper layer, brazing layer, and niobium layer remained tightly bonded. This indicates that the copper layer, brazing layer, and niobium layer have extremely high bonding strength, far exceeding the bonding strength of the composite layer composed of the copper layer and niobium layer, and also far exceeding the tensile strength of metallic copper. This completely solves the problem of the lack of mutually soluble phases and poor bonding strength between the copper layer and niobium layer.

[0035] As shown in the table below, the copper layer before annealing has a high thermal conductivity of more than 516 W / (m·K) at a temperature of 4.2K, and after annealing, it is even higher than 1768 W / (m·K), which shows that the copper layer has excellent thermal conductivity.

[0036]

[0037]

[0038] Copper coatings not only improve the thermal conductivity of superconducting cavities and significantly reduce cryogenic losses and operating costs, but also greatly enhance the mechanical strength of pure niobium superconducting cavities. Because superconducting cavities operate at high frequencies, even minute mechanical deformations can have a significant impact on the frequency; a change of only 1 micrometer can cause a frequency shift of tens of hertz. Therefore, superconducting cavities are highly sensitive to geometric disturbances and require high mechanical stability. Vibrations, pressure changes in cryogenic fluids, overpressure during superconducting cavity cooling, or Lorentz forces generated by high electromagnetic fields within the superconducting cavity can all cause shape changes, thereby reducing the performance of the superconducting cavity. Covering the surface of the superconducting cavity with a copper layer not only enhances its mechanical properties and reduces the impact of factors such as Lorentz stress on its performance, but also allows for a reduction in the niobium layer thickness, lowering the manufacturing cost of the superconducting cavity.

[0039] Compared to methods such as electroplating and spraying copper directly on the surface of the superconducting cavity, this invention improves the bonding strength of different materials in the superconducting cavity through the welding effect of a high thermal conductivity brazing layer, while ensuring the thermal conductivity of the superconducting cavity. This meets the requirements for stable operation of the superconducting cavity under extreme conditions of extremely low temperature, high radio frequency electromagnetic field, and extremely low loss, and is conducive to expanding the application range of the superconducting cavity.

[0040] The copper coating of the superconducting cavity has the characteristics of large thickness, high reliability, high mechanical strength and high thermal conductivity. The copper coating also has the characteristics of low porosity, low oxidation rate and high purity, and can also have high bonding strength with the brazing layer and the surface of the superconducting cavity.

[0041] This embodiment provides an additive manufacturing method for a copper layer on the surface of a superconducting cavity. A brazing material with high thermal conductivity is cold-sprayed onto the outer surface of the superconducting cavity to form a brazing layer. Then, a copper layer is electroplated on the brazing layer to form a composite coating with low oxidation, which is not easy to crack or delaminate, is obtained on the outer surface of the superconducting cavity. The bonding strength between the copper layer, the brazing layer and the niobium layer is high, and the superconducting cavity has good heat dissipation performance.

[0042] Example 2:

[0043] This embodiment provides an additive manufacturing method for a copper layer on the surface of a superconducting cavity, comprising the following steps: S1: preparing powdered brazing material; S2: depositing the brazing material onto the outer surface of the superconducting cavity using a cold spraying method to form a brazing layer with a thickness of 0.1-0.5 mm, the surface of the superconducting cavity being a niobium layer; S3: electroplating copper onto the surface of the brazing layer to form a copper coating; S4: annealing the composite layer consisting of the niobium layer, the brazing layer, and the copper coating. The brazing material comprises the following components by mass percentage: silver ≥ 50%, copper ≥ 0%, titanium ≥ 0%, the melting point of the brazing material is less than 1000℃, and the brazing material has excellent thermal conductivity. The thickness of the copper coating is greater than 4 mm.

[0044] Two hours before cold spraying, the surface of the superconducting cavity is ground and polished to make its surface roughness less than 10μm.

[0045] Grinding and polishing the surface of the superconducting cavity improves the bonding between the brazing material particles and the niobium layer surface. Specifically, grinding is performed sequentially using 200-grit, 400-grit, 800-grit, 1500-grit, and 2500-grit sandpaper, followed by chemical polishing with a chemical reagent. This grinding and polishing treatment of the niobium layer surface before spraying improves the surface cleanliness for bonding with the brazing layer, thus enhancing the subsequent spraying effect.

[0046] This embodiment provides an additive manufacturing method for a copper layer on the surface of a superconducting cavity. A brazing material with high thermal conductivity is cold-sprayed onto the outer surface of the superconducting cavity to form a brazing layer. Then, a copper layer is electroplated on the brazing layer to form a composite coating with low oxidation, which is not easy to crack or delaminate, is obtained on the outer surface of the superconducting cavity. The bonding strength between the copper layer, the brazing layer and the niobium layer is high, and the superconducting cavity has good heat dissipation performance.

[0047] Example 3:

[0048] This embodiment provides an additive manufacturing method for a copper layer on the surface of a superconducting cavity, comprising the following steps: S1: preparing powdered brazing material; S2: depositing the brazing material onto the outer surface of the superconducting cavity using a cold spraying method to form a brazing layer with a thickness of 0.1-0.5 mm, the surface of the superconducting cavity being a niobium layer; S3: electroplating copper onto the surface of the brazing layer to form a copper coating; S4: annealing the composite layer consisting of the niobium layer, the brazing layer, and the copper coating. The brazing material comprises the following components by mass percentage: silver ≥ 50%, copper ≥ 0%, titanium ≥ 0%, the melting point of the brazing material is less than 1000℃, and the brazing material has excellent thermal conductivity. The thickness of the copper coating is greater than 4 mm.

[0049] Two hours before copper electroplating, the brazing layer undergoes surface treatment including grinding, ultrasonic cleaning, and degreasing to improve the adhesion between the copper layer and the brazing layer. Specifically, grinding and ultrasonic cleaning of the brazing layer improves its cleanliness, allowing for better bonding between the brazing material particles and the niobium layer surface.

[0050] This embodiment provides an additive manufacturing method for a copper layer on the surface of a superconducting cavity. A brazing material with high thermal conductivity is cold-sprayed onto the outer surface of the superconducting cavity to form a brazing layer. Then, a copper layer is electroplated on the brazing layer to form a copper layer. A composite coating with low oxidation, which is not easy to crack or delaminate, is obtained on the surface of the superconducting cavity. The bonding strength between the copper layer, the brazing layer and the niobium layer is high, and the superconducting cavity has good heat dissipation performance.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention.

[0052] In the description of this invention, it should be understood that the terms indicating orientation or positional relationship are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the protection scope of the present invention.

Claims

1. An additive manufacturing method for a copper layer on the surface of a superconducting cavity, characterized in that: The steps are as follows: S1: Prepare a powdered brazing material, wherein the brazing material comprises the following components by mass percentage: silver ≥ 50%, copper ≥ 0%, titanium ≥ 0%, the melting point of the brazing material is less than 1000℃, and the particle size of the brazing material is less than 300 mesh; S2: The brazing material is deposited onto the outer surface of the superconducting cavity in a solid-state molding manner using cold spraying to form a brazing layer. The thickness of the brazing layer is 0.1-0.5 mm, and the surface of the superconducting cavity is a niobium layer. The cold spraying is carried out under high pressure conditions of 1-7 MPa, with a gas flow rate of 1000-4000 SLM. The inert gas used is nitrogen or helium. The moving speed of the spray gun used in the cold spraying is 10-800 mm / s, the shortest distance between the spray gun and the superconducting cavity is 10-100 mm, and the gas temperature is 200-800℃. S3: Electroplating copper onto the surface of the brazing layer to form a copper coating; S4: Anneal the composite layer consisting of the niobium layer, the brazing layer, and the copper coating.

2. The additive manufacturing method for a copper layer on the surface of a superconducting cavity according to claim 1, characterized in that: Two hours before cold spraying, the surface of the superconducting cavity is ground and polished to make its surface roughness less than 10μm.

3. The additive manufacturing method for a copper layer on the surface of a superconducting cavity according to claim 1, characterized in that: Two hours before copper electroplating, the brazing layer is subjected to surface treatment including grinding, ultrasonic cleaning, and degreasing.

4. The additive manufacturing method for a copper layer on the surface of a superconducting cavity according to claim 1, characterized in that: The thickness of the copper coating is greater than 4 mm.

5. The additive manufacturing method for a copper layer on the surface of a superconducting cavity according to claim 1, characterized in that: The annealing process includes the following steps: heating from room temperature to 600°C at a rate of 1-5 min / °C and holding at that temperature for 10 h, then heating to 800-900°C at a rate of 5-10°C / min, holding at that temperature for 30 minutes, and then allowing the temperature to cool naturally.

6. The additive manufacturing method for a copper layer on the surface of a superconducting cavity according to claim 1 or 5, characterized in that: The annealing is performed under a vacuum of less than 1E-3 Pa.

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