Graphite film / metal heterogeneous connection structure based on gradient composite coating and preparation method

Abstract

This invention relates to a graphite film / metal heterojunction structure based on a gradient composite coating and its preparation method. The graphite film / metal heterojunction structure based on the gradient composite coating involves sequentially constructing a bottom nanocrystalline copper coating, an intermediate NiP alloy coating, and a surface Ti-based diffusion layer on the graphite film surface, forming a gradient composite coating structure. This gradient composite coating structure, combined with a magnetic field-assisted brazing process, achieves the connection between the graphite film and the heterojunction material. This invention, through the synergistic effect of the gradient composite coating structure design and the magnetic field-assisted brazing process, achieves significant optimization of the graphite film heterojunction structure. The interface wetting angle is less than 15°, the shear strength is increased by 42% to over 58 MPa, and the longitudinal thermal conductivity reaches 215 W / (m‧K), a 25% improvement compared to traditional processes. The anisotropy ratio is optimized to 2.1:1 (compared to 3.6:1 in the traditional process).

Description

Technical Field

[0001] This invention relates to graphite film bonding technology in the field of high thermal conductivity materials, specifically to a graphite film / metal heterostructure bonding structure and preparation method based on gradient composite coating. Background Technology

[0002] With the rapid development of modern electronic devices and aerospace technology, the demand for high-performance heat dissipation materials is increasing. Graphite film, due to its excellent thermal conductivity, low density, and good mechanical stability, has become a key material in high-performance heat dissipation systems. However, existing technologies still face two major challenges in the connection and heat dissipation structure design of graphite films.

[0003] The first issue is the interface delamination problem in single-layer electroplated structures. In existing technologies, single-layer electroplated structures (such as copper plating) are prone to interface delamination under thermal cycling conditions due to a mismatch in their coefficients of thermal expansion. This delamination leads to a significant decrease in longitudinal thermal conductivity, affecting heat dissipation performance. If the temperature variation range is large, single-layer electroplated structures cannot meet the long-term stable heat dissipation requirements.

[0004] Secondly, the anisotropic conduction of traditional solder layers is limited. In existing technologies, traditional solder layers (such as Sn-based solders) restrict anisotropic conduction, with the difference in thermal conductivity between the horizontal and vertical directions reaching up to 3.6 times. This non-uniformity in anisotropic conduction can lead to localized overheating, reducing the overall performance and reliability of the equipment.

[0005] In summary, existing technologies have many shortcomings in the design of graphite film bonding and heat dissipation structures, making it difficult to meet the requirements of high-performance heat dissipation systems. Therefore, developing a novel graphite film bonding structure and its preparation method to overcome the deficiencies of existing technologies has significant practical importance and broad application prospects. Summary of the Invention The purpose of this invention is to provide a graphite film / metal heterojunction structure based on gradient composite coating. This graphite film / metal heterojunction structure based on gradient composite coating is used to solve the problems of poor thermal stability, high thermal resistance, and limited anisotropic conduction of graphite film connections in the prior art. Another purpose of this invention is to provide a method for preparing this graphite film / metal heterojunction structure based on gradient composite coating.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: This graphite film / metal heterostructure connection structure based on gradient composite coating is formed by sequentially constructing a bottom nanocrystalline copper coating, an intermediate NiP alloy coating, and a surface Ti-based diffusion layer on the surface of the graphite film, thus forming a gradient composite coating structure on the surface of the graphite film; the gradient composite coating structure is combined with a magnetic field-assisted brazing process to achieve the connection between the graphite film and the heteromaterial, and during the connection, a Sn-Ag-Cu-TiB2 composite system is used as the brazing filler metal, wherein Ag... The content is 0.5wt.%~1.0wt.%, Cu content is 0.5wt.%~0.7wt.%, TiB2 content is 0.3wt.%~1wt.%, and its particle size is 1~5μm. The graphite film to be welded is placed in the welding fixture, and the pre-formed brazing filler metal sheet is placed at the welding interface. A stepped temperature control method is used to control the temperature in three stages: 240~245℃ / 2~3min, 265~270℃ / 1~2min, and 255~260℃ / 3~4min, in order to achieve precise control of the brazing process. At the same time as heating, the magnetic field device is activated to apply an axial magnetic field of 0.5~1.2T to optimize the brazing process. Then, the heating device and the magnetic field device are turned off, and the welded joint is allowed to gradually cool down to room temperature under natural cooling conditions, so that the microstructure of the welded joint gradually stabilizes and a welded interface with high strength and good thermal conductivity is formed.

[0007] The above-mentioned method for preparing graphite film / metal heterostructure based on gradient composite coating includes the following steps: Step 1: Place the graphite film in acetone, anhydrous ethanol and deionized water in sequence for ultrasonic cleaning, and then treat it with oxygen plasma. Step 2: Prepare a bottom layer of nanocrystalline copper coating on the graphite film treated in Step 1. Use an electrolyte solution of CuSO4‧5H2O with a concentration of 250~300 g / L and H2SO4 with a concentration of 50~70 g / L, and control the current density at 1.5~2.5 A / dm³ at 20~30℃. 2 Within a certain range, mechanical stirring is used to form a nanocrystalline copper underlayer with a thickness of 0.1~10 μm on the surface of the graphite film; Step 3: Deposit an intermediate NiP alloy coating on the nanocrystalline copper coating using a chemical plating process to prepare a NiP alloy intermediate layer with a thickness of 3~8 μm. Step 4: Prepare a Ti-based diffusion layer on the surface of the NiP alloy intermediate layer by using magnetron sputtering to form a Ti-based diffusion layer with a thickness of 2~3 μm.

[0008] In the above scheme, step one specifically involves immersing the graphite film in acetone, anhydrous ethanol, and deionized water, followed by ultrasonic cleaning for 8-20 minutes, and then treating it with oxygen plasma for 2-5 minutes at a power of 200-300W.

[0009] Step three in the above scheme is as follows: depositing an intermediate NiP alloy coating on the nanocrystalline copper coating. Using a chemical plating process, a NiSO4·6H2O solution with a concentration of 20~25g / L is used as the base, and NaH2PO2·H2O with a concentration of 25-30g / L is added. The reaction temperature is controlled at 85~95℃, and the P content is adjusted to 8wt.%~12wt.%. The plating time is 60~120 min, and a NiP alloy intermediate layer with a thickness of 3~8 μm is prepared.

[0010] Step four in the above scheme specifically involves: preparing a Ti-based diffusion layer on the surface of the NiP alloy intermediate layer using magnetron sputtering with a pure titanium target ≥99.9%, high-purity Ar ≥99.9%, a flow rate of 30~40 sccm, and a vacuum degree below 6×10⁻⁶. -3 The sputtering process was carried out at Pa, with a sputtering power of 100~150 W and a time of 20~60 min. 0.5 at.%~1.2 at.% of rare earth elements were added to the Ti-based material to form a Ti-based diffusion layer with a thickness of 2~3 μm.

[0011] Beneficial effects: 1. This invention achieves significant optimization of the heterogeneous connection structure of graphite films through the synergistic effect of gradient composite coating structure design and magnetic field-assisted brazing process. The interface wetting angle is less than 15°, and the shear strength is increased by 42% to over 58 MPa. Simultaneously, the longitudinal thermal conductivity reaches 215 W / (m‧K), a 25% improvement compared to traditional processes; the anisotropy ratio is optimized to 2.1:1 (compared to 3.6:1 in traditional processes). This graphite film heterogeneous connection structure and preparation method based on gradient composite coating not only improves the connection performance between graphite films and heterogeneous materials but also effectively improves their thermal and mechanical properties, providing a new technical approach for the preparation of high-performance graphite film composite materials.

[0012] 2. The gradient coating structure of this invention adopts a structure of nanocrystalline Cu bottom layer, NiP alloy intermediate layer and Ti-based diffusion layer surface layer, which effectively solves the problem of thermal expansion coefficient mismatch and significantly improves the interfacial bonding strength; advantages of nanocrystalline copper substrate: enhanced electrical and thermal conductivity, providing a stable foundation for multi-layer coating; rare earth elements strengthen the interface: effectively inhibit the diffusion of high temperature elements and extend service life.

[0013] 3. The invention has outstanding thermal shock resistance: through material system optimization, it maintains structural integrity under extreme temperature cycling conditions and avoids interface delamination.

[0014] 4. The magnetic field brazing orientation control of this invention: magnetic field-assisted technology enables precise orientation and arrangement of brazing filler metal, reduces interface defect rate, and ensures uniform connection.

[0015] 5. The present invention optimizes the stepped temperature control process: a three-stage temperature control strategy is adopted to balance wettability and interface reaction, thereby improving connection reliability.

[0016] 6. The invention achieves uniform heat flow distribution: it significantly improves the difference between horizontal and vertical thermal conductivity, resulting in a more uniform heat flow distribution; the TiB2-reinforced solder combines high thermal conductivity with creep resistance, making it suitable for high-frequency thermal cycling scenarios.

[0017] 7. The present invention has upgraded corrosion resistance: it provides excellent corrosion resistance to meet the requirements of harsh environments; it has strong process compatibility: it is suitable for heterogeneous bonding of graphite film with various substrates (metals / composite materials). Attached Figure Description

[0018] Figure 1 The microstructure of the graphite film / metal heterojunction joint. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings: This graphite film / metal heterojunction structure based on gradient composite coating involves sequentially constructing a bottom nanocrystalline copper coating, an intermediate NiP alloy coating, and a surface Ti-based diffusion layer on the graphite film surface, forming a gradient composite coating structure on the graphite film surface.

[0020] The gradient composite coating structure, combined with magnetic field-assisted brazing, enables the connection of graphite films with dissimilar materials. During the connection, magnetic field-assisted brazing is used to join the graphite films. A Sn-Ag-Cu-TiB2 composite system is selected as the brazing filler metal, wherein the Ag content is 0.5wt.%~1.0wt.%, the Cu content is 0.5wt.%~0.7wt.%, and the TiB2 content is 0.3wt.%~1wt.%, with a particle size of 1~5μm. This composite brazing filler metal system exhibits good wettability and mechanical properties, enabling efficient connection of graphite films with dissimilar materials under magnetic field assistance. At the start of the welding process, the graphite film to be welded is placed in the welding fixture, ensuring the pre-formed brazing filler metal sheet is positioned at the welding interface. Heating begins, employing a stepped temperature control method, sequentially controlling the temperature at three stages: 240~245 ℃ / 2~3 min, 265~270 ℃ / 1~2 min, and 255~260 ℃ / 3~4 min, to achieve precise control of the brazing process. Simultaneously, a magnetic field device is activated, applying an axial magnetic field of 0.5~1.2T to optimize the brazing process. The heating equipment is then turned off, followed by the magnetic field device, allowing the weld joint to gradually cool to room temperature under natural cooling conditions. This allows the microstructure of the weld joint to gradually stabilize, forming a weld interface with high strength and good thermal conductivity.

[0021] Through the synergistic effect of the aforementioned gradient composite coating structure design and magnetic field-assisted brazing process, this invention achieves significant optimization of the heterogeneous connection structure of graphite films. The interface wetting angle is less than 15°, and the shear strength is increased by 42% to over 58 MPa. Simultaneously, the longitudinal thermal conductivity reaches 215 W / (m‧K), a 25% improvement compared to traditional processes; the anisotropy ratio is optimized to 2.1:1 (compared to 3.6:1 in traditional processes). This graphite film heterogeneous connection structure and preparation method based on gradient composite coating not only improves the connection performance between graphite films and heterogeneous materials but also effectively enhances their thermal and mechanical properties, providing a new technical approach for the preparation of high-performance graphite film composite materials.

[0022] This invention addresses two major pain points in existing technologies through the synergistic effect of gradient composite coating and directional brazing, significantly improving the thermal stability and thermal conductivity of graphite film connections.

[0023] The fabrication method of this graphite film / metal heterostructure based on gradient composite coating is as follows: The graphite membrane was sequentially immersed in acetone, anhydrous ethanol, and deionized water, with each step involving ultrasonic cleaning for 8–20 minutes. It was then treated with oxygen plasma at a power of 200–300 W for 2–5 minutes.

[0024] A bottom layer of nanocrystalline copper was prepared on the graphite film surface using a CuSO4·5H2O (copper sulfate pentahydrate) electrolyte with a concentration of 250–300 g / L and an H2SO4 electrolyte concentration of 50–70 g / L, at a temperature of 20–30 °C, and with a current density controlled at 1.5–2.5 A / dm³. 2 Within a certain range, mechanical stirring is performed to form a nanocrystalline copper substrate with a thickness of 0.1~10 μm.

[0025] A NiP alloy intermediate layer was deposited on a nanocrystalline copper substrate. Using a chemical plating process, a solution with a NiSO4·6H2O concentration of 20–25 g / L was used as the base, with the addition of sodium hypophosphite (NaH2PO2·H2O) at a concentration of 25–30 g / L. The reaction temperature was controlled at 85–95 °C, and the P content was adjusted to 8 wt.%–12 wt.%. The plating time was 60–120 min, resulting in a NiP alloy intermediate layer with a thickness of 3–8 μm.

[0026] Finally, a Ti-based diffusion layer was prepared on the surface of the NiP alloy intermediate layer. Magnetron sputtering was used with a pure titanium target (≥99.9%), and the flow rate of high-purity Ar (99.9%) was controlled at 30–40 sccm, with a vacuum level below 6 × 10⁻⁶. -3The sputtering process was carried out at Pa, with a sputtering power of 100~150 W and a time of 20~60 min. 0.5 at.%~1.2 at.% of rare earth elements were added to the Ti-based material to form a Ti-based diffusion layer with a thickness of 2~3 μm.

Claims

1. A graphite film / metal heterojunction structure based on gradient composite coating, characterized in that: This graphite film / metal heterostructure connection structure based on gradient composite coating involves sequentially constructing a bottom nanocrystalline copper coating, an intermediate NiP alloy coating, and a surface Ti-based diffusion layer on the graphite film surface, forming a gradient composite coating structure. This gradient composite coating structure is combined with a magnetic field-assisted brazing process to connect the graphite film to the heteromaterial. During the connection, a Sn-Ag-Cu-TiB2 composite system is used as the brazing filler metal, wherein the Ag content is 0.5wt.%~1.0wt.%, the Cu content is 0.5wt.%~0.7wt.%, and the TiB2 content is 0.3wt.%~1wt.%, with a particle size of 1~5μm. The graphite film to be welded is placed in a welding fixture, and a pre-formed brazing filler metal sheet is placed at the welding interface. A stepped temperature control method is used, with the temperature sequentially controlled at 240~245℃ / 2~3min, 265~270℃ / 1~2min, and 255~260℃ / 3~4min. The process involves three stages: heating and magnetic field equipment. An axial magnetic field of 0.5 to 1.2 T is applied to optimize the brazing process. Then, the heating and magnetic field equipment are turned off, allowing the welded joint to gradually cool to room temperature under natural cooling conditions. This allows the microstructure of the welded joint to gradually stabilize, forming a welded interface with high strength and good thermal conductivity.

2. The method for preparing a graphite film / metal heterostructure based on a gradient composite coating according to claim 1, characterized in that... Includes the following steps: Step 1: Place the graphite film in acetone, anhydrous ethanol and deionized water in sequence for ultrasonic cleaning, and then treat it with oxygen plasma. Step 2: Prepare a bottom layer of nanocrystalline copper coating on the graphite film treated in Step 1. Use an electrolyte solution of CuSO4‧5H2O with a concentration of 250~300 g / L and H2SO4 with a concentration of 50~70 g / L, and control the current density at 1.5~2.5 A / dm³ at 20~30℃. 2 Within a certain range, mechanical stirring is used to form a nanocrystalline copper underlayer with a thickness of 0.1~10 μm on the surface of the graphite film; Step 3: Deposit an intermediate NiP alloy coating on the nanocrystalline copper coating using a chemical plating process to prepare a NiP alloy intermediate layer with a thickness of 3~8 μm. Step 4: Prepare a Ti-based diffusion layer on the surface of the NiP alloy intermediate layer by using magnetron sputtering to form a Ti-based diffusion layer with a thickness of 2~3 μm.

3. The method for preparing a graphite film / metal heterostructure based on a gradient composite coating according to claim 2, characterized in that: Step one specifically involves immersing the graphite film in acetone, anhydrous ethanol, and deionized water, followed by ultrasonic cleaning for 8-20 minutes, and then treating it with oxygen plasma for 2-5 minutes at a power of 200-300W.

4. The method for preparing a graphite film / metal heterostructure based on a gradient composite coating according to claim 3, characterized in that: Step three specifically involves depositing an intermediate NiP alloy coating on a nanocrystalline copper coating. This is achieved using a chemical plating process, with a NiSO4·6H2O solution of 20-25 g / L as the base, and the addition of NaH2PO2·H2O of 25-30 g / L. The reaction temperature is controlled at 85-95°C, and the P content is adjusted to 8 wt.%-12 wt.%. The plating time is 60-120 min, resulting in a NiP alloy intermediate layer with a thickness of 3-8 μm.

5. The method for preparing a graphite film / metal heterostructure based on a gradient composite coating according to claim 4, characterized in that: Step four specifically involves: preparing a Ti-based diffusion layer on the surface of the NiP alloy intermediate layer using magnetron sputtering with a pure titanium target ≥99.9%, high-purity Ar ≥99.9%, a flow rate of 30-40 sccm, and a vacuum level below 6×10⁻⁶. -3 The sputtering process was carried out at Pa, with a sputtering power of 100~150 W and a time of 20~60 min. 0.5 at.%~1.2 at.% of rare earth elements were added to the Ti-based material to form a Ti-based diffusion layer with a thickness of 2~3 μm.

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