Oriented structure graphene / copper composite filler material and preparation method and application thereof

Abstract

The application discloses an oriented structure graphene / copper composite filler metal, graphene is coated on the surface of flaky copper powder, and then is compacted, so that the graphene and copper are closely arranged in layers and intervals. The application further discloses a preparation method of the oriented structure graphene / copper composite filler metal, comprising the following steps: taking the flaky copper powder coated with graphene to perform hot-pressing sintering or discharge plasma sintering, so as to obtain the oriented structure graphene / copper composite filler metal. The application further discloses a sandwich composite brazing structure. The application further discloses application of the oriented structure graphene / copper composite filler metal and the sandwich composite brazing structure in ceramic and metal welding. The application further discloses a welding method. In the oriented structure graphene / copper composite filler metal, the graphene and copper are closely arranged in layers and intervals, and the arrangement orientation of the graphene is kept consistent; when brazing, the graphene can effectively hinder active elements such as Ti from corroding the copper matrix, reduce the residual stress of the welded joint, and improve the welding strength.

Description

Technical Field

[0001] This invention relates to the field of brazing technology, and in particular to an oriented graphene / copper composite brazing filler metal, its preparation method, and its application. Background Technology

[0002] Ceramic materials are widely used in aerospace, electronics, nuclear energy, biomedicine, and chemical industries due to their excellent characteristics such as high hardness, high corrosion resistance, good high temperature stability, high melting point, high wear resistance, and oxidation resistance.

[0003] While ceramic materials possess the advantages mentioned above, they also have some drawbacks that hinder their widespread application. For example, their poor plasticity and toughness make them difficult to process, so in many cases they need to be joined with metals to complement each other's properties and obtain components with superior performance. Brazing offers advantages such as lower heating temperatures, smooth and aesthetically pleasing joints, minimal changes in the microstructure and mechanical properties of the base material, minimal deformation, and precise weld dimensions. It is often the preferred method for joining dissimilar materials such as ceramics and metals. However, due to the significant difference in thermal expansion coefficients between ceramics and metals, large residual stresses exist in the welded joint, severely affecting its mechanical properties and even inducing cracks. Therefore, alleviating residual stress in the joint is crucial for improving its mechanical properties.

[0004] Introducing a soft interlayer into the solder is currently one of the mainstream practices for alleviating residual stress in the joint. Some researchers have introduced pure Cu sheets as an interlayer into AgCuTi solder. However, during brazing, the Cu sheets are easily corroded by active elements in the solder, such as Ti, leading to Cu agglomeration and defects in the brazed joint. Therefore, protecting the soft interlayer from corrosion by active elements in the solder is crucial for alleviating residual stress in the joint.

[0005] Currently, graphene is often added to copper to mitigate the corrosion of copper by active elements. However, graphene is prone to agglomeration, and excessive addition can lead to agglomeration, affecting the mechanical properties of the welded joint. At present, the amount of graphene added is generally low, and the distribution of graphene in copper is disordered, so its resistance to corrosion by active elements and its ability to alleviate residual stress in the joint are still low. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, this invention proposes an oriented graphene / copper composite brazing filler metal, its preparation method, and its application. In the oriented graphene / copper composite brazing filler metal of this invention, graphene and copper are arranged in a tightly packed, layer-by-layer manner, and the orientation of the graphene remains consistent. This structure gives the graphene / copper composite brazing filler metal good compactness. During brazing, the oriented graphene can effectively prevent active elements such as Ti from eroding the copper matrix, reduce the content of brittle compounds in the weld joint, and maintain the structural integrity of the soft intermediate layer (i.e., the oriented graphene / copper composite brazing filler metal), improving the strain tolerance of the joint and thus reducing the residual stress of the weld joint. This results in good bonding at the weld interface and excellent mechanical properties.

[0007] This invention proposes an oriented graphene / copper composite solder, in which graphene is coated on the surface of sheet copper powder and then compacted, so that the graphene and copper are arranged in a tightly spaced layer-by-layer configuration.

[0008] Preferably, the particle size of the flake copper powder is 1-100 μm.

[0009] Preferably, the orientation of each graphene element is consistent.

[0010] Preferably, the volume percentage of graphene in the oriented graphene / copper composite solder is 0.05-1.0 vol.%.

[0011] The present invention also proposes a method for preparing the above-mentioned oriented graphene / copper composite solder, comprising the following steps: taking sheet copper powder coated with graphene and subjecting it to hot pressing sintering or spark plasma sintering to obtain oriented graphene / copper composite solder.

[0012] Preferably, the hot pressing sintering temperature is 900-950℃, the hot pressing sintering time is 1-3h, and the hot pressing sintering pressure is 30-50MPa.

[0013] Preferably, the temperature of the spark plasma sintering is 600-700℃, the time of the spark plasma sintering is 5-30 min, and the pressure of the spark plasma sintering is 30-50 MPa.

[0014] Flake copper powder has a small particle size. When using conventional compaction methods, the resulting bulk material has low density and many internal pores due to the lack of a sintering process. Moreover, the orientation of graphene is low after conventional compaction. In contrast, this application uses hot pressing or spark plasma sintering and selects appropriate sintering parameters to cause the flake copper powder to collapse during the sintering process. This ensures that the graphene coating on the surface of the flake copper powder maintains a consistent orientation, resulting in a dense, layered arrangement of graphene and copper in the oriented graphene / copper composite solder, thus improving the material's density.

[0015] Oriented graphene / copper composite solder can be cut into thin sheets using wire cutting; the cutting direction is consistent with the graphene alignment; the sheet thickness can be 0.05-0.3mm.

[0016] Preferably, in the preparation process of graphene-coated sheet copper powder, the carbon source and sheet copper powder are uniformly dispersed in a solvent, then the solvent is removed, and the sheet copper powder is heat-treated in an inert gas atmosphere to obtain graphene-coated sheet copper powder.

[0017] Preferably, in the preparation process of graphene-coated sheet copper powder, the carbon source is at least one of naphthol, glucose, and polymethyl methacrylate.

[0018] Preferably, in the preparation process of graphene-coated sheet copper powder, the weight ratio of carbon source to sheet copper powder is 0.05-1.5:100.

[0019] Preferably, in the preparation process of graphene-coated sheet copper powder, the heat treatment temperature is 700-900℃ and the heat treatment time is 5min-1h.

[0020] Preferably, in the preparation process of graphene-coated sheet copper powder, the solvent is at least one of ethanol and deionized water.

[0021] Preferably, in the preparation process of graphene-coated sheet copper powder, the inert gas is one of argon, hydrogen, or a mixture of hydrogen and argon.

[0022] The above method involves uniformly coating sheet copper powder with a carbon source and then heat-treating it to obtain graphene-coated sheet copper powder. This method is simple, and the graphene content can be controlled according to the size of the sheet powder to increase the graphene loading in the material.

[0023] The present invention also proposes a sandwich composite brazing structure, wherein metal brazing filler metal is provided on both sides of the above-mentioned oriented graphene / copper composite brazing filler metal, wherein the metal brazing filler metal is arranged parallel to the graphene orientation.

[0024] Preferably, the metal solder is a metal solder containing Ti.

[0025] The Ti-containing metal solder can be AgCuTi solder sheet, Ti solder sheet, etc., and its thickness can be 0.05-0.2mm.

[0026] Preferably, the size and shape of the oriented graphene / copper composite solder are the same as those of the metal solder, so that the oriented graphene / copper composite solder can cover the metal solder.

[0027] This invention also proposes the application of the above-mentioned oriented graphene / copper composite brazing filler metal and the above-mentioned sandwich composite brazing structure in ceramic-metal welding.

[0028] The present invention also proposes a welding method in which metal brazing filler metal and the above-mentioned oriented graphene / copper composite brazing filler metal are placed between the ceramic to be welded and the metal to be welded according to the above-mentioned sandwich composite brazing structure, and then welded, wherein the weld seam is parallel to the orientation of the graphene.

[0029] The welding method can be vacuum brazing, etc.

[0030] The welding conditions for the above-mentioned vacuum brazing can be: vacuum degree < 6 × 10 -3 Pa is heated to 850-950℃ at a rate of 5-10℃ / min, held for 5-60min, and then cooled to 200℃ at a rate of 5-10℃ / min, and cooled to room temperature in the furnace.

[0031] Beneficial effects:

[0032] This invention employs a suitable method to cause the sheet-like copper powder to collapse during the sintering process, thereby ensuring that the graphene coating on the surface of the sheet-like copper powder maintains a consistent orientation. This results in the graphene and copper in the oriented graphene / copper composite solder being arranged in a tightly packed, layered manner. This structure gives the graphene / copper composite solder excellent density.

[0033] During brazing, a sandwich composite brazing structure is adopted, and the weld surface is parallel to the orientation of the graphene. The densely distributed graphene can effectively prevent active elements such as Ti from eroding the copper matrix and reduce the content of brittle compounds in the weld joint. On the other hand, it can maintain the structural integrity of the soft intermediate layer (i.e., the oriented graphene / copper composite brazing filler metal), improve the strain tolerance of the joint, and thus reduce the residual stress of the weld joint. This results in a good weld interface, excellent mechanical properties, high welding efficiency, low cost, and suitability for industrial production. Attached Figure Description

[0034] Figure 1 This is a SEM image of the oriented graphene / copper composite solder prepared in Example 1.

[0035] Figure 2 This is a schematic diagram of a sandwich composite brazing structure.

[0036] Figure 3 Image showing the brazed seam structure after welding using the oriented graphene / copper composite brazing filler metal described in Example 1 as a soft intermediate layer. Detailed Implementation

[0037] The technical solution of the present invention will now be described in detail through specific embodiments.

[0038] Example 1

[0039] An oriented graphene / copper composite solder is provided, wherein graphene is coated on the surface of sheet-like copper powder and then compacted, so that the graphene and copper are arranged in a tightly spaced layer-by-layer manner, and the orientation of each graphene is consistent. The particle size of the sheet-like copper powder is 30-50 μm, and the volume percentage of graphene in the oriented graphene / copper composite solder is 0.3 vol.%.

[0040] The preparation method of the above-mentioned oriented graphene / copper composite solder includes the following steps: adding naphthol and flake copper powder to ethanol at a weight ratio of 0.1:100, then stirring and ultrasonically treating for 20 minutes to uniformly disperse the naphthol and flake copper powder in ethanol, then evaporating and removing the ethanol at 130°C, and then placing it in an atmosphere furnace and heat-treating it at 800°C for 10 minutes in a mixed gas atmosphere of hydrogen and argon (hydrogen volume fraction of 5%) to obtain flake copper powder coated with graphene.

[0041] Graphene-coated sheet copper powder was hot-pressed and sintered at a temperature of 950℃ for 2 hours and a pressure of 50MPa to obtain an oriented graphene / copper composite solder.

[0042] The oriented graphene / copper composite solder prepared in Example 1 was tested, and the results are as follows: Figure 1 As shown; Figure 1 This is a SEM image of the oriented graphene / copper composite solder prepared in Example 1.

[0043] Depend on Figure 1 It can be seen that in the oriented graphene / copper composite solder, graphene and copper are arranged in a tightly packed, layered manner; the graphene coating on the surface of the sheet copper powder maintains a consistent orientation. This is because by using a suitable sintering method, the sheet copper powder collapses during the sintering process, thus ensuring that the graphene coating on the surface of the sheet copper powder maintains a consistent orientation. This results in the graphene and copper being arranged in a tightly packed, layered manner in the oriented graphene / copper composite solder, improving the density of the composite material.

[0044] Example 2

[0045] An oriented graphene / copper composite solder is provided, wherein graphene is coated on the surface of sheet copper powder and then compacted, so that the graphene and copper are arranged in a tightly spaced layer, with the orientation of each graphene being consistent. The particle size of the sheet copper powder is 50-100μm, and the volume percentage of graphene in the oriented graphene / copper composite solder is 0.15 vol.%.

[0046] The preparation method of the above-mentioned oriented graphene / copper composite solder includes the following steps: adding naphthol and flake copper powder to ethanol at a weight ratio of 0.08:100, then stirring and ultrasonically treating for 20 minutes to uniformly disperse the naphthol and flake copper powder in ethanol, then evaporating and removing the ethanol at 130°C, and then placing it in an atmosphere furnace and heat-treating it at 800°C for 20 minutes in a mixed gas atmosphere of hydrogen and argon (hydrogen volume fraction of 5%) to obtain flake copper powder coated with graphene.

[0047] Graphene-coated sheet copper powder was hot-pressed and sintered at a temperature of 900℃ for 3 hours and a pressure of 30MPa to obtain an oriented graphene / copper composite solder.

[0048] Example 3

[0049] An oriented graphene / copper composite solder is provided, wherein graphene is coated on the surface of sheet-like copper powder and then compacted, so that the graphene and copper are arranged in a tightly spaced layer-by-layer manner, and the orientation of each graphene is consistent. The particle size of the sheet-like copper powder is 30-50 μm, and the volume percentage of graphene in the oriented graphene / copper composite solder is 0.3 vol.%.

[0050] The preparation method of the above-mentioned oriented graphene / copper composite solder includes the following steps: adding naphthol and flake copper powder to ethanol at a weight ratio of 0.1:100, then stirring and ultrasonically treating for 20 minutes to uniformly disperse the naphthol and flake copper powder in ethanol, then evaporating and removing the ethanol at 130°C, and then placing it in an atmosphere furnace and heat-treating it at 800°C for 30 minutes in a mixed gas atmosphere of hydrogen and argon (hydrogen volume fraction of 5%) to obtain flake copper powder coated with graphene.

[0051] Graphene-coated sheet copper powder was hot-pressed and sintered at a temperature of 950℃ for 1 hour and a pressure of 50MPa to obtain an oriented graphene / copper composite solder.

[0052] Example 4

[0053] An oriented graphene / copper composite solder is provided, wherein graphene is coated on the surface of sheet-like copper powder and then compacted, so that the graphene and copper are arranged in a tightly spaced layer-by-layer manner, and the orientation of each graphene is consistent. The particle size of the sheet-like copper powder is 1-30 μm, and the volume percentage of graphene in the oriented graphene / copper composite solder is 0.5 vol.%.

[0054] The preparation method of the above-mentioned oriented graphene / copper composite solder includes the following steps: adding naphthol and flake copper powder to ethanol at a weight ratio of 0.3:100, then stirring and ultrasonically treating for 20 minutes to uniformly disperse the naphthol and flake copper powder in ethanol, then evaporating and removing the ethanol at 130°C, and then placing it in an atmosphere furnace and heat-treating it at 800°C for 30 minutes in a mixed gas atmosphere of hydrogen and argon (hydrogen volume fraction of 5%) to obtain flake copper powder coated with graphene.

[0055] Graphene-coated sheet copper powder was subjected to spark plasma sintering at a temperature of 600℃ for 30 minutes and a pressure of 30 MPa to obtain an oriented graphene / copper composite solder.

[0056] Comparative Example 1

[0057] Replace the flake copper powder with spherical copper powder of the same particle size, otherwise the same as in Example 1.

[0058] Comparative Example 2

[0059] Replace the flake copper powder with dendritic copper powder of the same particle size, otherwise the same as in Example 1.

[0060] Example 6

[0061] The graphene / copper composite solders prepared in Examples 1-5 and Comparative Examples 1-2 were wire-cut into 0.3 mm thick sheets, with the wire-cutting direction consistent with the graphene alignment. They were then polished to 0.1 mm thickness with 200-1000 grit SiC sandpaper and ultrasonically cleaned with anhydrous ethanol for 10-30 min to serve as soft intermediate layers for later use.

[0062] The Nb metal to be welded and the 0.08mm thick AgCuTi welding sheet are polished sequentially using 200-1000 mesh SiC sandpaper. The ZrB2-SiC ceramic to be welded is polished sequentially using 400-3000 mesh diamond sandpaper. Then, the Nb metal to be welded, the AgCuTi welding sheet, and the ZrB2-SiC ceramic to be welded are ultrasonically cleaned with anhydrous ethanol for 10-30 minutes and set aside.

[0063] AgCuTi brazing sheets are placed on both sides of each flexible interlayer (each flexible interlayer and the AgCuTi brazing sheet have the same shape, length, and width). The AgCuTi brazing sheets are arranged parallel to the graphene orientation to obtain a sandwich composite brazing structure (its structure is as follows). Figure 2 As shown, this sandwich composite brazing structure was placed between the ZrB2-SiC ceramic to be brazed and the Nb metal to be brazed, with the weld seam direction parallel to the graphene alignment. It was then transferred to a brazing furnace for brazing under the following conditions: the vacuum level of the brazing furnace was reduced to below 6 × 10⁻⁶.-3 Pa, then heat to the brazing temperature of 880℃ at a rate of 5-10℃ / min, hold for 10min, then cool to 200℃ at a rate of 5-10℃ / min, and then cool to room temperature in the furnace.

[0064] Comparative Example 3

[0065] Without a soft intermediate layer, welding is performed according to the method of Example 6.

[0066] Comparative Example 4

[0067] The flexible intermediate layer is a 0.1 mm thick copper foil, which is soldered according to the method of Example 6.

[0068] The strength of each group of welded joints was tested, and the results are shown in Table 1.

[0069] Table 1 Test Results

[0070] Grouping Welded joint strength (MPa) Example 1 116 Example 2 97 Example 3 112 Example 4 109 Comparative Example 1 74 Comparative Example 2 65 Comparative Example 3 20 Comparative Example 4 31

[0071] As can be seen from Table 1, when using graphene / copper composite brazing filler metal with an oriented structure to braze ceramics and metals, the residual stress of the joint is low, resulting in a brazed joint with high strength.

[0072] Figure 3 Image showing the brazed seam structure after welding using the oriented graphene / copper composite brazing filler metal described in Example 1 as a soft intermediate layer.

[0073] Depend on Figure 3 It can be seen that in the brazing seam structure, the white area is the silver-based solid solution Ag(s,s), and the gray area is the copper / matrix solid solution. The white area is mostly distributed in the parts adjacent to the metal Nb and ceramic ZS, and is distributed on both sides of the brazing seam structure. The gray area is distributed in the middle region of the brazing seam structure. It can be seen that when brazing with oriented graphene / copper composite brazing filler metal, graphene can effectively prevent active elements such as Ti from eroding the copper matrix. This improves the strain tolerance of the joint, reduces the residual stress of the welded joint, and improves the welding strength.

[0074] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an oriented graphene / copper composite solder, characterized in that, The process includes the following steps: taking sheet copper powder coated with graphene and hot-pressing or spark plasma sintering to obtain oriented graphene / copper composite solder. The hot pressing sintering temperature is 900-950℃, the hot pressing sintering time is 1-3h, and the hot pressing sintering pressure is 30-50MPa; The temperature of the spark plasma sintering is 600-700℃, the time of the spark plasma sintering is 5-30min, and the pressure of the spark plasma sintering is 30-50MPa. In the preparation process of graphene-coated sheet copper powder, carbon source and sheet copper powder are uniformly dispersed in solvent, then the solvent is removed, and heat treatment is performed in an inert gas atmosphere to obtain graphene-coated sheet copper powder. In the preparation of graphene-coated sheet copper powder, the carbon source is at least one of naphthol, glucose, and polymethyl methacrylate. In the preparation of graphene-coated sheet copper powder, the weight ratio of carbon source to sheet copper powder is 0.05-1.5:

100. In the preparation of graphene-coated sheet copper powder, the heat treatment temperature is 700-900℃ and the heat treatment time is 5min-1h.

2. The method for preparing the oriented graphene / copper composite solder according to claim 1, characterized in that, In the preparation of graphene-coated sheet copper powder, the solvent is at least one of ethanol and deionized water.

3. The method for preparing the oriented graphene / copper composite solder according to claim 1, characterized in that, In the preparation of graphene-coated sheet copper powder, the inert gas is one of argon, hydrogen, or a mixture of hydrogen and argon.

4. An oriented graphene / copper composite solder, characterized in that, It is prepared according to the method for preparing oriented graphene / copper composite solder according to any one of claims 1-3; Graphene is coated onto the surface of sheet-like copper powder and then compacted, so that the graphene and copper are arranged in a tightly spaced layer; the orientation of each graphene is consistent.

5. The oriented graphene / copper composite solder according to claim 4, characterized in that, The particle size of the flake copper powder is 1-100μm.

6. The oriented graphene / copper composite solder according to claim 4, characterized in that, The volume percentage of graphene in oriented graphene / copper composite solder is 0.05-1.0 vol.%.

7. A sandwich composite brazing structure, characterized in that, Metal solder is disposed on both sides of the oriented graphene / copper composite solder as described in any one of claims 4-6, wherein the metal solder is oriented parallel to the graphene.

8. The sandwich composite brazing structure according to claim 7, characterized in that, The metal solder is a metal solder containing Ti.

9. The application of an oriented graphene / copper composite brazing filler metal as described in any one of claims 4-6 in ceramic-metal welding.

10. The application of a sandwich composite brazing structure as described in claim 7 or 8 in ceramic-metal welding.

11. A welding method, characterized in that, Metal brazing filler metal is placed between the ceramic and the metal to be welded according to the sandwich composite brazing structure described in claim 7 or 8, and then welded, wherein the weld surface is parallel to the orientation of the graphene.

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