High-hardness high-thermal-conductivity gradient structure copper material and preparation method thereof

Abstract

The invention discloses a high-hardness high-thermal-conductivity gradient structure copper material which is composed of a base body and a surface layer combined on the surface of the base body, the base body is oxygen-free copper, and the surface layer is a copper boron nitride alloy composed of two phases of copper grains and a boron nitride film. The surface layer and the base body are metallurgically bonded; the boron nitride thin film in the copper boron nitride alloy is clamped between copper crystal grains to form a gradient distribution structure which is in a net shape to separate and wrap the copper crystal grains, and the boron nitride content of the gradient distribution structure is continuously reduced from the outside to the inside. The invention further discloses a preparation method of the copper material, oxygen-free copper serves as a substrate to form a base body in the copper material, copper-boron alloy with boron components distributed in a gradient mode is prepared on the surface of the oxygen-free copper substrate through laser additive manufacturing, then the copper-boron alloy on the surface of the oxygen-free copper is nitrided into copper-boron nitride alloy through nitriding treatment, and then the surface layer of the copper material is formed. And the composite copper material with high hardness and high thermal conductivity is obtained. The prepared copper material can meet the service requirements of the heat management industry on the wear resistance and the heat dissipation performance of components at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and in particular relates to a high-hardness and high-thermal-conductivity gradient structure copper material and a preparation method thereof. Background Art

[0002] Copper and copper alloys are structural functional materials with excellent mechanical and physical properties, and are widely used in power electronics, aerospace, national defense, automobiles and other fields. High-hardness and high-thermal conductivity copper alloys are important structural thermal management materials. The development of science and technology and industry has continuously put forward higher requirements on the softening resistance and high-temperature performance of high-hardness and high-thermal conductivity copper alloys. Taking the crystallizer used in the foundry industry as an example, the material is required to have high thermal conductivity and high wear resistance to meet the heat transfer and transmission service requirements of the ingot. The traditional material used is oxygen-free copper, which has excellent thermal conductivity, but oxygen-free copper has low hardness and the inner wall is easily worn and deformed by the ingot, making it difficult to be used for precision casting and large-size casting. To this end, technicians have developed a variety of methods to improve the wear resistance of the inner wall of the crystallizer.

[0003] Patent application number 202210690558.1 provides a coating composite, its preparation method, coating, crystallizer copper plate, and surface treatment method thereof. The coating composite comprises a first component and a second component; the first component comprises a metal oxide and a carbon element; the metal oxide comprises at least one of titanium oxide, tungsten oxide, niobium oxide, zirconium oxide, and tantalum oxide; and the second component comprises a metal element. When applied to the surface treatment of metal products such as crystallizer copper plates, the coating composite exhibits high wear resistance and hardness after spraying, good chemical stability at high temperatures, and can extend the service life of the crystallizer copper plate.

[0004] Patent application number 201210320178.5 discloses a Cu-Co-Be alloy, the base material for copper plates used in high-speed continuous casting molds. The alloy contains 1.4% to 1.6% cobalt, 0.2% to 0.3% beryllium, and 98.1% to 98.4% copper. The resulting Cu-Co-Be alloy plate exhibits a heat-treated Brinell hardness of 190 to 210 HB, a tensile strength of 680 to 720 MPa, an elongation of 18 to 21%, and a conductivity of 33 to 34% IACS. This Cu-Co-Be alloy plate exhibits high strength, hardness, and wear resistance, extending the mold's service life, increasing steel throughput, and reducing steel leaks. This reduces mold repairs and the frequency of abnormal downtime, ultimately lowering maintenance costs and workload.

[0005] The patent with application number 201010596518.8 discloses a preparation method for a surface heat-conducting and wear-resistant coating of a continuous casting mold. Using Ni, Al, wear-resistant ceramic particles and high heat-conducting ceramic particles as raw materials, alloy powder is prepared by ball milling, and the coating is deposited on the substrate by cold spraying, and a NiAl intermetallic compound-based composite structure coating is prepared by thermal diffusion alloying treatment. This composite structure coating is based on NiAl intermetallic compound, has good bonding with the copper plate substrate and has good high-temperature wear resistance itself. The added high-hardness wear-resistant ceramic particles can further improve the wear resistance of the coating, and the added high heat-conducting ceramic particles and their good interfacial bonding with the matrix can effectively improve the heat conductivity of the coating, reduce the temperature gradient of the coating, and thus enhance the heat shock and impact wear resistance of the coating.

[0006] The patent with application number 202010377898.X discloses an alloy powder for laser cladding of a mold copper plate and a laser cladding method. By weight percentage, the mass composition of the alloy powder is: Mo: 2.1% - 2.4%, Cr: 4.5% - 4.7%, C: 1.5% - 1.6%, Si: 0.12% - 0.18%, W: 10.0% - 11.0%, V: 4.52% - 4.72%, Mn: 3.22% - 3.35%, and the balance is Fe. Its preparation method can clad the alloy powder on the surface of the copper plate under lower temperature conditions. The copper plate has good heat conductivity, so that the heat of the first alloy powder cladding layer is quickly taken away by the cooling water in the water tank, the temperature of the cladding layer drops rapidly, the copper plate near it does not melt, which does not affect the fluidity of the alloy powder, improves the surface quality of the cladding layer, and the cladding layer has a dense structure and a smooth surface.

[0007] The patent with application number 200810012662.5 discloses an alloy coating on the surface of a mold by laser cladding and its preparation method. The composition of this alloy coating is formulated according to the mechanical properties, failure conditions of the mold and the characteristics of laser cladding on the surface of the mold. This alloy coating is composed of nickel-based self-fluxing alloy powder, including elements such as Ni, Cr, W, Mo, Al, Ti, C, B, etc. By mass percentage, the coating composition is specifically composed of Ni 55 - 57, Cr 16 - 19, W 8 - 10, Mo 8 - 10, Al 0.8 - 1.0, Ti 2.5 - 3.5, C 0.2 - 0.3, Si 2.5 - 3.5 and B 2 - 2.5. After laser cladding, a high-quality coating is obtained on the surface of the mold.

[0008] Although the above methods significantly improve the surface hardness of copper materials, can alleviate the friction and wear of the casting billet, and extend the life of the mold. However, they also seriously damage the heat conductivity of copper materials, resulting in the weakening of the original advantages of using oxygen-free copper, and even unable to meet the heat transfer requirements during casting solidification. Summary of the Invention

[0009] In view of the above technical problems, the present invention provides a copper material with high hardness and high thermal conductivity. Taking oxygen-free copper as the base, a wear-resistant and high-thermal-conductivity surface copper alloy layer is metallurgically bonded to its surface to obtain a composite copper material with high hardness and high thermal conductivity, which can simultaneously meet the service requirements of the wear resistance and heat dissipation performance of components in the thermal management industry.

[0010] To achieve the above invention object, the present invention adopts the following technical solutions.

[0011] The present invention first provides a copper material with a high-hardness and high-thermal-conductivity gradient structure. The copper material is composed of a matrix and a surface layer bonded to the surface of the matrix; the matrix is oxygen-free copper; the surface layer is a copper boron nitride alloy; the surface layer and the matrix are metallurgically bonded; the copper boron nitride alloy is composed of two phases, namely copper grains and boron nitride thin films. Among them, the copper grains form a copper matrix, and the boron nitride thin films are sandwiched between the copper grains to form a network morphology to separate and wrap each copper grain; and the surface copper boron nitride alloy is a gradient distribution structure in which the boron nitride content gradually and continuously decreases from the surface (the side away from the oxygen-free copper of the matrix) to the inside (the connection surface with the oxygen-free copper of the matrix).

[0012] Boron nitride has extremely high hardness and high thermal conductivity at the same time. In copper alloys, boron nitride can be used as a reinforcing phase, which can significantly improve the hardness and strength of copper alloys; its high thermal conductivity helps copper alloys dissipate heat better in high-temperature environments. The high-hardness and high-thermal-conductivity gradient structure copper material provided by the present invention first utilizes the high hardness and high thermal conductivity characteristics of boron nitride; in addition, through the structure and microstructure design of the synthesized copper material, it is further ensured that the finally formed copper material can improve the low hardness problem of oxygen-free copper and at the same time inherit the good thermal conductivity of oxygen-free copper. The main manifestations are as follows: 1) For the copper material of the present invention, the copper boron nitride alloy is used as the surface layer, and in the copper boron nitride alloy, the boron nitride is distributed in a network thin film to separate and wrap the copper grains; this microstructure not only refines the copper grains to achieve the effect of grain refinement strengthening, but also utilizes the advantage of the extremely high hardness of boron nitride. At the same time, the boron nitride phase with a network distribution and thin film morphology can avoid problems such as large brittleness and easy cracking and falling off of coarse boron nitride phases, so that the surface layer not only has high hardness but also has good toughness and wear resistance. 2) The thermal conductivity of boron nitride is about five times that of pure copper. In the copper material of the present invention, the boron nitride is distributed in a network, which is more conducive to heat transfer. Therefore, the surface layer of the copper boron nitride alloy reaches a thermal conductivity similar to that of pure copper. 3) In the copper material, the surface layer of the copper boron nitride alloy and the oxygen-free copper matrix are metallurgically bonded, and the heat conduction is smooth, so that the entire copper material component has high thermal conductivity characteristics. 4) In the surface layer of the copper boron nitride alloy, the boron nitride content gradually decreases from the surface to the inside. This gradient structure ensures that the surface layer and the matrix can be firmly bonded and are not easily cracked or peeled off under the influence of a thermal environment with rapid cooling and heating.

[0013] In the traditional preparation method, boron nitride and copper form a copper boron nitride alloy. It is mainly made into a composite material by mixing copper powder and boron nitride powder and then pressing and sintering; or by high-energy ball milling to mix copper and boron nitride powders to form a uniform composite material. In both cases, boron nitride particles are dispersed in the copper matrix to improve the alloy performance, which is different from the bonding method in the present invention where boron nitride is distributed in a thin film network and wraps around copper grains. On the surface of an oxygen-free copper matrix to form a copper boron nitride alloy layer, conventional methods such as spraying and electroplating are used, but the surface layer prepared in this way has poor bonding with the copper matrix, is easy to peel off, and it is difficult to form a uniform and continuous gradient distribution structure of boron nitride composition.

[0014] To obtain the copper material structure of the present invention, on the oxygen-free copper matrix, a copper boron nitride alloy surface layer with boron nitride metallurgically bonded in a thin film network that wraps around copper grains and has a gradient structure is prepared by another approach. The specific technical solution is as follows.

[0015] The present invention provides a method for preparing the above-mentioned high-hardness and high-thermal-conductivity gradient structure copper material. Using oxygen-free copper as the substrate to form the matrix in the copper material, a copper boron alloy is prepared on the surface of the oxygen-free copper substrate by laser additive manufacturing, and then through nitridation treatment, the copper boron alloy on the surface of the oxygen-free copper is nitrided into a copper boron nitride alloy, which is the surface layer of the copper material. Specifically, it includes the following steps:

[0016] 1) Pre-oxidize the oxygen-free copper substrate to form a cuprous oxide layer on the surface of the oxygen-free copper. In a specific embodiment of the present invention, the pre-oxidation uses a thermal oxidation method: heat the air atmosphere in an oven to 120 °C, keep it warm for 30 min, and then cool it to room temperature in air to form a cuprous oxide layer on the surface of the oxygen-free copper. In this step, the present invention does not limit the method of pre-oxidation. As long as a cuprous oxide thin film can be formed on the surface of the oxygen-free copper substrate, the purpose of the present invention can be achieved.

[0017] 2) Laser additive manufacturing of a copper boron composite structure is carried out on the surface of the pre-oxidized oxygen-free copper substrate. The specific method includes the following steps:

[0018] 2.1) Weigh pure copper powder and pure boron powder in proportion and mechanically mix them for 30 - 60 min to obtain copper boron composite powder. Among them, the pure copper powder is spherical powder with a diameter of 50 - 105 μm, the pure boron powder is irregular nano-powder with a particle size of 10 - 200 nm, and the mass fraction of boron powder in the composite powder is 4.2% - 6%.

[0019] 2.2) Load the composite powder into the powder feeder of the laser additive manufacturing equipment, send the composite powder to the surface of the substrate through the powder feeding mechanism, and use the synchronous powder feeding laser additive manufacturing method to melt the composite powder and combine it with the substrate. Layer by layer, stack it on the substrate to form a copper-boron alloy layer with a thickness of 2 - 5 mm by controlling the laser power and scanning path of the near-infrared laser. The laser power of the first layer is the highest (4000W - 5000W), and then it decreases by 5% layer by layer until the power reaches 3000W. During the process of laser additive manufacturing of copper alloy, the magnitude of the laser power affects the boron content in the copper alloy. A higher laser power will result in a high-energy molten pool, a large penetration depth, and an obvious dilution effect of the molten pool. After solidification, the relative content of copper increases while the relative content of boron decreases. As the laser power decreases, the energy of the molten pool decreases, the penetration depth is small, and the dilution effect of the molten pool weakens. After solidification, the copper-boron content is close to the powder composition. Therefore, by adjusting the laser power, it affects the molten pool temperature, molten pool penetration depth, and molten pool dynamics, etc., indirectly affecting the boron content in the copper alloy. Selecting an appropriate laser power in this step is the key to achieving boron content control.

[0020] 2.3) Use machining equipment to mill the surface of the copper-boron alloy layer flat to process a workpiece with the required size and precision, and then clean and dry it.

[0021] 3) Nitridize the copper-boron composite structure: Load the above workpiece into a nitriding furnace for nitriding treatment. In a specific embodiment of the present invention, the specific method of nitriding treatment is to use ammonia gas as the nitrogen source, nitriding at 500 - 600 °C for 1 - 12 h, and nitriding the copper-boron alloy on the surface layer of the copper material into a copper boron nitride alloy, that is, forming the surface layer of the copper material.

[0022] The principle of the above-mentioned laser additive manufacturing method and process of the present invention is as follows: First, laser additive manufacturing is used to achieve metallurgical bonding between the surface layer and the substrate. The laser power of the first layer is the highest and then gradually decreases. Such laser power not only ensures the gradient change of boron content, but also realizes a large melting depth and a large dilution rate of the oxygen-free copper substrate with the highest laser power of the first layer, achieving better metallurgical bonding between the substrate and the surface layer. At the same time, copper boron nitride with a gradient structure is realized, obtaining a firm bond between the surface layer and the substrate, while ensuring mechanical properties and thermal conductivity. Second, since the oxygen-free copper substrate has a very high reflectivity to laser, especially near-infrared laser, it is easy to burn out the laser. In the present invention, the oxygen-free copper substrate is pre-oxidized first to form a thin layer of cuprous oxide on the substrate surface. Cuprous oxide has a very small reflectivity to near-infrared laser, thus overcoming the problem of high laser reflectivity of the original oxygen-free copper substrate. And cuprous oxide decomposes above 1000 °C and will not form residues and slag inclusions. In addition, boron nitride has no solid solubility in copper. If boron nitride powder and copper powder are directly mixed for laser additive manufacturing, large agglomerates of boron nitride and coarse structures are often obtained. In the present invention, a copper-boron binary eutectic system is used. First, a copper-boron eutectic is prepared so that boron wraps and separates copper grains in the form of a network film. Then, through nitriding treatment, the boron film reacts with diffused and penetrated nitrogen atoms to form boron nitride, thereby obtaining a network boron nitride structure. In this way, not only high hardness is obtained, but also the thermal conductivity of the film can be significantly improved. And copper cannot be nitrided, so the pure copper substrate will not change during the nitriding process.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1) The surface of the gradient structure copper material provided by the present invention has high hardness and can effectively resist the friction and wear of the casting billet. And the surface layer is a copper boron nitride composite layer with high thermal conductivity. Cooperating with the oxygen-free copper substrate, it can quickly conduct the heat of the melt, ensuring the solidification speed and quality in the mold used in the casting industry.

[0025] 2) Boron nitride has a melting point as high as 2700 °C, good thermal stability, and is not easy to react with metals or alloys. Therefore, as the surface directly in contact with the melt and the casting billet, it can maintain the original state for a long time without polluting the melt.

[0026] 3) The preparation method provided by the present invention is precisely controllable and can be mass-produced, having good application prospects. Description of the Drawings

[0027] Figure 1 X-ray diffraction pattern of the copper boron nitride surface layer prepared in Example 1. Detailed Embodiments

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0029] Example 1

[0030] The preparation of a high-hardness and high-thermal-conductivity gradient-structured copper material includes the following steps:

[0031] 1. Pre-oxidize the oxygen-free copper substrate. Heat it in an oven under an air atmosphere to 120 °C, keep it warm for 30 minutes, and then air-cool it to room temperature.

[0032] 2. Conduct laser additive manufacturing of a copper-boron composite structure on the surface of the pre-oxidized oxygen-free copper substrate. The specific method includes the following steps:

[0033] 2.1 Weigh pure copper powder and boron powder according to the designed ratio and mechanically mix them for 30 minutes to obtain a composite powder. The pure copper powder is spherical powder with a diameter of 50 - 105 μm, and the boron powder is irregular nano-powder with a particle size of 10 - 200 nm. The mass fraction of boron powder in the composite powder is 4.2%.

[0034] 2.2 Load the composite powder into the powder feeder of the laser additive manufacturing equipment. Send the composite powder to the surface of the substrate through the powder feeding mechanism. Adopt the synchronous powder feeding laser additive manufacturing method to melt the composite powder and compound it with the substrate. Layer by layer, stack it on the substrate to form a copper-boron alloy layer with a thickness of 5 mm by controlling the laser power and scanning path of a near-infrared laser. The laser power of the first layer is 5000 W, and then it decreases by 5% layer by layer until the power reaches 3000 W.

[0035] 2.3 Use machining equipment to mill the surface of the copper-boron alloy layer flat, process it to the required size and precision, and clean and dry it to obtain the processed workpiece.

[0036] 3. Nitride the copper-boron composite structure to obtain a copper material with a copper-nitride-boron composite structure: Load the above workpiece into a nitriding furnace for nitriding treatment. The treatment process is to use ammonia gas as the nitrogen source and nitride it at 500 °C for 12 hours to nitride the copper-boron alloy into a copper-nitride-boron gradient-structured composite layer.

[0037] Example 2

[0038] The preparation of a high-hardness and high-thermal-conductivity gradient-structured copper material includes the following steps:

[0039] 1. Pre-oxidize the oxygen-free copper substrate. Heat it in an oven under an air atmosphere to 120 °C, keep it warm for 30 minutes, and then air-cool it to room temperature.

[0040] 2. Laser additive manufacturing of copper-boron composite structure is carried out on the surface of the pre-oxidized oxygen-free copper substrate. The specific method includes the following steps:

[0041] 2.1 Weigh pure copper powder and boron powder according to the designed ratio and mechanically mix them for 60 min to obtain composite powder. The pure copper powder is spherical powder with a diameter of 50 - 105 μm, and the boron powder is irregular nano-powder with a particle size of 10 - 200 nm. The mass fraction of boron powder in the composite powder is 6%.

[0042] 2.2 Load the composite powder into the powder feeder of the laser additive manufacturing equipment, send the composite powder to the substrate surface through the powder feeding mechanism, and use the synchronous powder feeding laser additive manufacturing method to melt the composite powder and combine it with the substrate. Layer by layer stacking on the substrate to form a copper-boron alloy layer with a thickness of 2 mm by controlling the laser power and scanning path of the near-infrared laser. The laser power of the first layer is 4000 W, and then it decreases by 5% layer by layer until the power reaches 3000 W.

[0043] 2.3 Use machining equipment to mill the surface of the copper-boron alloy layer flat, process it to the required size and precision, and clean and dry to obtain the processed workpiece.

[0044] 3. Nitriding treatment is carried out on the copper-boron composite structure to obtain copper material of copper boron nitride composite structure: Load the above workpiece into a nitriding furnace for nitriding treatment. The treatment process is using ammonia as the nitrogen source and nitriding at 600 °C for 1 h to nitride the copper-boron alloy into a composite layer with a copper boron nitride gradient structure.

[0045] Example 3

[0046] Preparation of a high-hardness and high-thermal-conductivity gradient structure copper material includes the following steps:

[0047] 1. Pre-oxidize the oxygen-free copper substrate, heat it in an oven under air atmosphere to 120 °C, keep it warm for 30 min, and then air-cool it to room temperature.

[0048] 2. Laser additive manufacturing of copper-boron composite structure is carried out on the surface of the pre-oxidized oxygen-free copper substrate. The specific method includes the following steps:

[0049] 2.1 Weigh pure copper powder and boron powder according to the designed ratio and mechanically mix them for 45 min to obtain composite powder. The pure copper powder is spherical powder with a diameter of 50 - 105 μm, and the boron powder is irregular nano-powder with a particle size of 10 - 200 nm. The mass fraction of boron powder in the composite powder is 5%.

[0050] 2.2 Load the composite powder into the powder feeder of the laser additive manufacturing equipment, send the composite powder to the surface of the substrate through the powder feeding mechanism, and use the synchronous powder feeding laser additive manufacturing method to melt the composite powder and compound it with the substrate. By controlling the laser power and scanning path of the near-infrared laser, layer by layer stacking is carried out on the substrate to form a copper-boron alloy layer with a thickness of 3 mm. The laser power of the first layer is 4500 W, and then it is reduced by 5% layer by layer until the power reaches 3000 W.

[0051] 2.3 Use machining equipment to mill the surface of the copper-boron alloy layer flat, process it to the required size and precision, and clean and dry it to obtain the processed workpiece.

[0052] 3. Nitride the copper-boron composite structure to obtain copper material with a copper-nitride-boron composite structure: Load the above workpiece into a nitriding furnace for nitriding treatment. The treatment process is to use ammonia gas as the nitrogen source and nitriding at 560 °C for 8 h to nitride the copper-boron alloy into a composite layer with a copper-nitride-boron gradient structure.

[0053] Comparative Example 1

[0054] In this comparative example, a lower mass fraction of boron powder was used in the laser-based manufacturing of copper-boron alloy. The specific process for preparing copper material is as follows:

[0055] 1. Pre-oxidize the oxygen-free copper substrate, heat it in an oven under air atmosphere to 120 °C, hold for 30 min, and then air-cool to room temperature.

[0056] 2. Conduct laser additive manufacturing of the copper-boron composite structure on the surface of the pre-oxidized oxygen-free copper substrate. The specific method includes the following steps:

[0057] 2.1 Weigh pure copper powder and boron powder according to the designed ratio and mechanically mix them for 30 min to obtain the composite powder. The pure copper powder is spherical powder with a diameter of 50 - 105 μm, and the boron powder is irregular nano-powder with a particle size of 10 - 200 nm. The mass fraction of boron powder in the composite powder is 1%.

[0058] 2.2 Load the composite powder into the powder feeder of the laser additive manufacturing equipment, send the composite powder to the surface of the substrate through the powder feeding mechanism, and use the synchronous powder feeding laser additive manufacturing method to melt the composite powder and compound it with the substrate. By controlling the laser power and scanning path of the near-infrared laser, layer by layer stacking is carried out on the substrate to form a copper-boron alloy layer with a thickness of 5 mm. The laser power of the first layer is 5000 W, and then it is reduced by 5% layer by layer until the power reaches 3000 W.

[0059] 2.3 Use machining equipment to mill the surface of the copper-boron alloy layer flat, process it to the required size and precision, and clean and dry it to obtain the processed workpiece.

[0060] 3. Copper material with a copper boron nitride composite structure obtained by nitriding a copper boron composite structure: The above workpiece is loaded into a nitriding furnace for nitriding treatment. The treatment process uses ammonia gas as the nitrogen source and nitrides at 500 °C for 12 h to nitride the copper boron alloy into a composite layer with a copper boron nitride gradient structure.

[0061] Comparative Example 2

[0062] In the laser substrate manufacturing of copper boron alloy in this comparative example, a relatively high mass fraction of boron powder is used. The specific process for preparing the copper material is as follows:

[0063] 1. Pre-oxidize the oxygen-free copper substrate by heating it in an oven under an air atmosphere to 120 °C, holding for 30 min, and then air-cooling to room temperature.

[0064] 2. Laser additive manufacturing of a copper boron composite structure is carried out on the surface of the pre-oxidized oxygen-free copper substrate. The specific method includes the following steps:

[0065] 2.1 Weigh pure copper powder and boron powder according to the designed ratio and mechanically mix them for 30 min to obtain a composite powder. The pure copper powder is spherical powder with a diameter of 50 - 105 μm, and the boron powder is irregular nano-powder with a particle size of 10 - 200 nm. The mass fraction of boron powder in the composite powder is 10%.

[0066] 2.2 Load the composite powder into the powder feeder of the laser additive manufacturing equipment, send the composite powder to the surface of the substrate through the powder feeding mechanism, and use the synchronous powder feeding laser additive manufacturing method to melt the composite powder and combine it with the substrate. Layer by layer, a copper boron alloy layer with a thickness of 5 mm is deposited on the substrate by controlling the laser power and scanning path of the near-infrared laser. The laser power of the first layer is 5000 W, and then it decreases by 5% layer by layer until the power reaches 3000 W.

[0067] 2.3 Use machining equipment to mill the surface of the copper boron alloy layer flat, process it to the required size and accuracy, and clean and dry it to obtain the processed workpiece.

[0068] 3. Copper material with a copper boron nitride composite structure obtained by nitriding a copper boron composite structure: The above workpiece is loaded into a nitriding furnace for nitriding treatment. The treatment process uses ammonia gas as the nitrogen source and nitrides at 500 °C for 12 h to nitride the copper boron alloy into a composite layer with a copper boron nitride gradient structure.

[0069] Comparative Example 3

[0070] In the laser substrate manufacturing of copper boron alloy in this comparative example, a constant laser power is used, and finally a copper boron nitride alloy without a gradient structure is prepared as the surface layer of the copper material. The specific process for preparing the copper material is as follows:

[0071] 1. Pre-oxidize the oxygen-free copper substrate by heating it in an oven under an air atmosphere to 120 °C, holding for 30 min, and then air-cooling to room temperature.

[0072] 2. Laser additive manufacturing of a copper-boron composite structure is carried out on the surface of a pre-oxidized oxygen-free copper substrate. The specific method includes the following steps:

[0073] 2.1 Weigh pure copper powder and boron powder according to the designed ratio and mechanically mix them for 30 minutes to obtain composite powder. The pure copper powder is spherical powder with a diameter of 50 - 105 μm, and the boron powder is irregular nano-powder with a particle size of 10 - 200 nm. The mass fraction of boron powder in the composite powder is 1%.

[0074] 2.2 Load the composite powder into the powder feeder of the laser additive manufacturing equipment, send the composite powder to the surface of the substrate through the powder feeding mechanism, and use the synchronous powder feeding laser additive manufacturing method to melt and compound the composite powder with the substrate. Layer by layer, stack the composite powder on the substrate to form a copper-boron alloy layer with a thickness of 5 mm by controlling the laser power and scanning path of the near-infrared laser. The laser power is kept constant at 3000 W.

[0075] 2.3 Use machining equipment to mill the surface of the copper-boron alloy layer flat, process it to the required size and precision, and clean and dry it to obtain the processed workpiece.

[0076] 3. Nitriding treatment is carried out on the copper-boron composite structure to obtain copper material of a copper boron nitride composite structure: Load the above workpiece into a nitriding furnace for nitriding treatment. The treatment process is to use ammonia gas as the nitrogen source and nitrify at 500 °C for 12 hours to nitride the copper-boron alloy into copper boron nitride.

[0077] Comparative Example 4

[0078] In the laser-based manufacturing of copper-boron alloy in this comparative example, a copper-boron alloy with a relatively large thickness is obtained. The specific process of preparing the copper material is as follows:

[0079] 1. Pre-oxidize the oxygen-free copper substrate, heat it in an air atmosphere in an oven to 120 °C, keep it warm for 30 minutes, and then air-cool it to room temperature.

[0080] 2. Laser additive manufacturing of a copper-boron composite structure is carried out on the surface of the pre-oxidized oxygen-free copper substrate. The specific method includes the following steps:

[0081] 2.1 Weigh pure copper powder and boron powder according to the designed ratio and mechanically mix them for 30 minutes to obtain composite powder. The pure copper powder is spherical powder with a diameter of 50 - 105 μm, and the boron powder is irregular nano-powder with a particle size of 10 - 200 nm. The mass fraction of boron powder in the composite powder is 1%.

[0082] 2.2 Load the composite powder into the powder feeder of the laser additive manufacturing equipment, send the composite powder to the surface of the substrate through the powder feeding mechanism, and use the synchronous powder feeding laser additive manufacturing method to melt the composite powder and compound it with the substrate. By controlling the laser power and scanning path of the near-infrared laser, layer by layer stacking is carried out on the substrate to form a copper-boron alloy layer with a thickness of 8 mm. The laser power of the first layer is 5000 W, and then it is reduced by 5% layer by layer until the power reaches 3000 W.

[0083] 2.3 Use machining equipment to mill the surface of the copper-boron alloy layer to be flat, process it to the required size and precision, and clean and dry it to obtain the processed workpiece.

[0084] 3. Nitride the copper-boron composite structure to obtain copper material with a copper boron nitride composite structure: Load the above workpiece into a nitriding furnace for nitriding treatment. The treatment process is to use ammonia gas as the nitrogen source and nitriding at 500 °C for 12 h to nitride the copper-boron alloy into a composite layer with a copper boron nitride gradient structure.

[0085] Comparative Example 5

[0086] The difference between this comparative example and Example 1 is that the oxygen-free copper substrate was not pre-oxidized before the laser-based manufacturing of the copper-boron alloy.

[0087] Comparative Example 6

[0088] The difference between this comparative example and Example 1 is that after the laser-based manufacturing of the copper-boron alloy, Step 3 was omitted, that is, the copper-boron alloy on the surface layer was not nitrided.

[0089] Perform X-ray diffraction tests on the copper boron nitride surface layers prepared in each example, and confirm that the surface layer is composed of a copper phase and a boron nitride phase, as Figure 1 is the X-ray diffraction test pattern of the copper boron nitride surface layer prepared in Example 1. It can be seen from the figure that the diffraction peaks of the copper and boron nitride two phases are contained in the pattern of the surface layer.

[0090] Perform hardness and thermal conductivity tests, as well as preliminary microstructure observations on the copper materials prepared in each example and comparative example. The results are shown in Table 1.

[0091] Table 1 Summary of test results of copper materials prepared in each example and comparative example

[0092]

[0093] The copper materials of Examples 1 to 3 all exhibit excellent comprehensive properties of high hardness and high thermal conductivity, indicating that the material design and preparation technical solutions disclosed in the present invention can obtain high-performance materials.

[0094] From the test results of Example 1 and Comparative Example 1, it can be seen that if the boron content is too low, insufficient boron film can be generated to separate copper grains, resulting in insufficient hardness of the material. At the same time, it also leads to the inability to form sufficient high-thermal-conductivity boron nitride during the subsequent nitridation treatment, making the overall thermal conductivity of the material low.

[0095] By analyzing the test results of Example 1 and Comparative Example 2, it can be seen that if the boron content is too high, although the hardness of the material is very high, due to the too large mismatch in hardness between the copper matrix and the surface layer, the bonding is not firm and the surface layer is prone to peeling off.

[0096] By analyzing the test results of Example 1 and Comparative Example 3, it can be seen that if a single laser power is used, it will lead to insufficient initial additive energy, poor bonding quality between the surface layer and the copper matrix, and an ineffective surface layer cannot be obtained.

[0097] By analyzing the test results of Example 1 and Comparative Example 4, it can be seen that if the copper-boron alloy layer is too thick, the surface layer will lose its bonding with the copper substrate and peel off due to the accumulation of internal stress.

[0098] By analyzing the test results of Example 1 and Comparative Example 5, it can be seen that if the pure copper substrate is not pre-oxidized, the laser will be reflected back to the laser. In the light case, the laser will alarm and stop, and in the severe case, the laser will be burned out.

[0099] By analyzing the test results of Example 1 and Comparative Example 6, it can be seen that if the nitridation treatment is not carried out, the low-thermal-conductivity boron film cannot be transformed into high-thermal-conductivity boron nitride, and only a performance level with relatively high hardness and relatively low thermal conductivity can be achieved.

Claims

1. A high-hardness and high-thermal-conductivity gradient-structured copper material, characterized in that: The copper material is composed of a matrix and a surface layer covering the surface of the matrix; Among them, the matrix of the copper material is oxygen-free copper; the surface layer is a copper boron nitride alloy; the surface layer and the matrix are metallurgically bonded; The copper boron nitride alloy is composed of two phases, copper grains and boron nitride thin films. Among them, the copper grains form a copper matrix, and the boron nitride thin films are sandwiched between the copper grains to form a network morphology to separate and wrap each copper grain; and the surface layer copper boron nitride alloy is a gradient distribution structure in which the boron nitride content gradually and continuously decreases from the surface to the inside.

2. A method for preparing a high-hardness and high-thermal-conductivity gradient-structured copper material as claimed in claim 1, characterized in that: The matrix in the copper material is formed with oxygen-free copper as the substrate. Copper boron alloy is prepared on the surface of the oxygen-free copper substrate by laser additive manufacturing, and then through nitridation treatment, the copper boron alloy on the surface of the oxygen-free copper is nitrided into a copper boron nitride alloy, which is the surface layer of the copper material.

3. The preparation method of a high-hardness and high-thermal-conductivity gradient-structured copper material according to claim 2, characterized in that, It includes the following steps: 1) Pre-oxidize the oxygen-free copper substrate to form a cuprous oxide layer on the surface of the oxygen-free copper; 2) Laser additive manufacturing of copper boron alloy on the surface of the pre-oxidized oxygen-free copper substrate: 2.1) Weigh pure copper powder and pure boron powder in proportion and mechanically mix them to obtain copper boron composite powder; 2.2) Load the composite powder into the powder feeder of the laser additive manufacturing equipment, send the composite powder to the surface of the substrate through the powder feeding mechanism, and use the synchronous powder feeding laser additive manufacturing method to melt the composite powder and combine it with the substrate. Layer by layer, a copper boron alloy layer with a thickness of 2-5 mm is deposited on the substrate; and the laser power of the first layer is the highest, and then decreases layer by layer; a copper boron alloy layer with a gradient structure is prepared on the surface of the substrate; 2.3) Use machining equipment to mill the surface of the copper boron alloy layer to be flat, process it into a workpiece with the required size and precision, and clean and dry it; 3) Nitridation treatment: Load the workpiece in step 2.3) into a nitriding furnace for nitridation treatment, so that the copper boron alloy layer on the surface of the copper material is nitrided into a copper boron nitride alloy, that is, the surface layer of the copper material is formed.

4. The preparation method of a high-hardness and high-thermal-conductivity gradient structure copper material according to claim 3, wherein: In step 1), the pre-oxidation adopts a thermal oxidation method: heat the air atmosphere in the oven to 120 °C, keep it warm for 30 min, and cool it to room temperature in air to form a cuprous oxide layer on the surface of the oxygen-free copper.

5. The preparation method of a high-hardness and high-thermal-conductivity gradient structure copper material according to claim 3, characterized in that: In step 2.1), the pure copper powder is spherical powder with a diameter of 50-105 μm, the pure boron powder is irregular nano powder with a particle size of 10-200 nm, and the mass fraction of boron powder in the composite powder is 4.2%-6%.

6. The preparation method of a high-hardness and high-thermal-conductivity gradient structure copper material according to claim 3, characterized in that: In step 2.2), the laser power of the first layer is 4000W-5000W, and then it decreases by 5% layer by layer until the laser power is 3000W.

7. The preparation method of a high-hardness and high-thermal-conductivity gradient structure copper material according to claim 3, wherein: In step 3), the specific method of nitridation treatment is to use ammonia as the nitrogen source and nitrify at 500-600 °C for 1-12 h.

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