A diamond-copper composite material and a method for preparing the same

Abstract

This invention relates to a diamond-copper composite material and its preparation method. The diamond-copper composite material comprises a reinforcing phase and a matrix phase. The reinforcing phase includes a core-shell structure, which, from the inside out, comprises diamond, a ceramic interface layer, and a porous copper shell layer. The matrix phase is copper powder, and the surface of the core-shell structure is also adsorbed with a highly thermally conductive two-dimensional material. This invention solves the defects of traditional preparation processes, such as interfacial reactions and performance instability, and has good versatility and application value, meeting the needs of related fields for high-performance thermally conductive composite materials.

Description

Technical Field

[0001] This invention relates to the field of metal matrix composites, and more particularly to a diamond-copper composite material and its preparation method. Background Technology

[0002] Currently, electronic devices in fields such as 5G mobile communication, artificial intelligence computing, and aerospace are rapidly developing towards high power and high integration, with local heat flux density exceeding 1000 W / cm². 2 This places stringent requirements on the thermal conductivity, thermal expansion matching, and structural stability of thermal management materials. Diamond-copper composites, which combine the ultra-high thermal conductivity and low coefficient of thermal expansion of diamond with the good metal formability and electrical conductivity of copper, have become the core choice for fourth-generation thermal management materials and are widely used in heat dissipation scenarios with extreme heat flux densities.

[0003] In existing technologies, to address the core issues of large interfacial energy differences and poor compatibility between diamond and copper, the mainstream approach is to use processes such as PVD to deposit metal coatings such as tungsten, titanium, and chromium onto the diamond surface for interfacial modification, and then prepare diamond-copper composite materials through methods such as powder metallurgy, high-temperature melting and infiltration, or low-temperature high-pressure sintering. However, existing technologies still face many insurmountable technical bottlenecks: First, traditional metallization coatings can only partially improve the wettability of diamond and copper, failing to achieve precise lattice matching between the two. Furthermore, they introduce additional phonon scattering centers at the interface, resulting in persistently high interfacial thermal resistance and limiting the improvement of the composite material's thermal conductivity. Second, existing preparation processes often require high temperature and high pressure conditions, which not only easily cause diamond graphitization and deterioration, destroying its intrinsic high thermal conductivity, but also make it difficult to achieve a three-dimensional uniform distribution of diamond particles, easily leading to local agglomeration and severely affecting the consistency and stability of material performance. Third, the thermal expansion coefficient of composite materials is difficult to precisely control, resulting in low matching with the thermal expansion coefficients of third-generation semiconductor chips such as silicon and silicon carbide. After repeated thermal cycling, electronic devices are prone to interfacial cracking, weld layer detachment, and other problems, ultimately leading to device failure.

[0004] The aforementioned defects mean that existing diamond-copper composite materials have always been unable to simultaneously meet the technical requirements of high thermal conductivity, low interfacial thermal resistance, excellent thermal matching, and mild processing, making it difficult to meet the extreme heat dissipation requirements of high-end electronic devices. Therefore, developing a diamond-copper composite thermal management material that can fundamentally reduce interfacial thermal resistance, achieve high thermal conductivity and precise thermal expansion control, and can be efficiently prepared through low-temperature and low-pressure processes has become an urgent technical problem to be solved in the field of thermal management materials. Summary of the Invention

[0005] To address the aforementioned technical challenges, this invention optimizes the interfacial compatibility between diamond and the copper matrix by designing a core-shell structure modification system for diamond and employing a low-temperature, low-pressure densification sintering process. This effectively reduces interfacial thermal resistance and simultaneously achieves a significant increase in the thermal conductivity of the composite material while matching its coefficient of thermal expansion. Consequently, the resulting composite material possesses high thermal conductivity, low interfacial thermal resistance, excellent thermal cycling stability, and compatibility with the thermal expansion of semiconductor chips. This makes it suitable for the extreme heat flux density heat dissipation requirements of high-end electronic devices in fields such as 5G mobile communication, artificial intelligence computing, and aerospace.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a diamond-copper composite material, the diamond-copper composite material comprising a reinforcing phase and a matrix phase, the reinforcing phase comprising a core-shell structure, the core-shell structure comprising, from the inside out, diamond, a ceramic interface layer and a porous copper shell layer, the matrix phase being copper powder, and the surface of the core-shell structure also having a highly thermally conductive two-dimensional material adsorbed thereon.

[0007] This invention achieves precise interface matching between diamond and copper matrix through the synergistic design of core-shell structure and high thermal conductivity two-dimensional material, significantly reducing interfacial phonon scattering and greatly improving the overall thermal conductivity of the composite material. The porous copper shell layer can effectively buffer the thermal expansion difference between diamond and copper, reduce interfacial stress during thermal cycling, avoid interfacial cracking, and improve the structural stability and service life of the material. The high thermal conductivity two-dimensional material forms a continuous thermal conduction path between the core and shell structure, further enhancing the thermal conductivity of the composite material. At the same time, the multi-dimensional synergistic effect of the core-shell structure, graphene, and copper matrix achieves a unified balance of high thermal conductivity, low interfacial thermal resistance, and excellent thermal matching.

[0008] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0009] As a preferred embodiment of the present invention, the diamond in the core-shell structure is a single-crystal diamond particle.

[0010] The core-shell structure of this invention uses single-crystal diamond particles, which have the characteristics of no grain boundaries and few lattice defects. This can minimize the scattering loss of phonons inside the diamond, give full play to the advantages of diamond's ultra-high intrinsic thermal conductivity, and have good structural integrity. The coating and bonding with the ceramic interface layer and the porous copper shell layer are more uniform and tighter, further reducing the interface thermal resistance and improving the overall structural stability and thermal conductivity continuity of the core-shell structure.

[0011] Preferably, the diamond particle size is 50~150μm, for example, it can be 50μm, 70μm, 90μm, 120μm or 150μm. This particle size range ensures the complete formation of the core-shell structure, and avoids excessive specific surface area and superposition of interfacial thermal resistance due to excessively small particle size, or stress concentration and decreased density of the material due to excessively large particle size. Furthermore, multiple particle size distribution designs within this particle size range can be adopted at the same time, which can realize the close packing of the diamond core-shell structure in the copper matrix, greatly improve the packing density of the composite material, reduce internal porosity defects, and further improve the thermal conductivity continuity and structural compactness of the material.

[0012] As a preferred technical solution of the present invention, the ceramic interface layer is made of any one of aluminum nitride, silicon nitride, or titanium nitride. These materials have excellent lattice matching and efficient phonon transport characteristics with diamond and copper substrates, which can effectively eliminate the interface compatibility differences between diamond and copper, reduce heat flow loss at the interface, and at the same time have good chemical stability and interface bonding force. They can form a uniform and dense coating layer on the diamond surface, ensuring the interface stability and thermal conductivity continuity of the core-shell structure.

[0013] Preferably, the thickness of the ceramic interface layer is 2~5nm, for example, it can be 2nm, 2.5nm, 3nm, 4nm or 5nm. This thickness design can minimize the thermal resistance of the interface layer itself, avoid hindering the cross-interface conduction of phonons and heat flow due to excessive layer thickness, and at the same time achieve precise bonding with the diamond surface and porous copper shell layer, which not only ensures the interface modification effect, but also prevents internal stress concentration caused by uneven layer thickness, further improving the overall adaptability and thermal conductivity of the core-shell structure.

[0014] As a preferred technical solution of the present invention, the thickness of the porous copper shell layer is 50~200nm, for example, it can be 50nm, 80nm, 120nm, 160nm or 200nm, etc.

[0015] As a preferred technical solution of the present invention, the porosity of the porous copper shell layer is 20-30%, for example, it can be 20%, 22%, 25%, 28% or 30%, etc., to avoid the copper shell layer being too dense due to excessively low porosity, making it difficult to melt and diffuse at low temperature, and to prevent the copper shell layer structure from being loose and the covering support from being too high porosity; at the same time, the porosity of the copper shell layer can realize the effective adsorption and embedding of high thermal conductivity two-dimensional materials, increase the contact area and bonding tightness of the two, adapt to the subsequent low temperature sintering process, and take into account the modification effect of the core-shell structure and the overall density of the composite material.

[0016] As a preferred technical solution of the present invention, the high thermal conductivity two-dimensional material includes graphene nanosheets or hexagonal boron nitride nanosheets. Both of them have ultra-high intrinsic thermal conductivity and excellent in-plane phonon transport performance, which can build an efficient cross-particle thermal conduction bridge between the core and shell structures, make up for the shortcomings of thermal conduction of the copper matrix. Moreover, the sheet structure of the two materials is easily adsorbed and embedded by pores, and has good interfacial compatibility with the core and shell structure and the copper matrix, without introducing additional interfacial thermal resistance.

[0017] Preferably, the thickness of the high thermal conductivity two-dimensional material is 3 to 5 layers, and the lateral dimension is 1 to 5 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, etc., where the lateral dimension is the average equivalent circle diameter (ECD) of the high thermal conductivity two-dimensional material in the planar direction of the layers. The lateral dimension of 1 to 5 μm matches the particle size of the core-shell structure and the pore size of the porous copper shell layer, ensuring effective bridging, avoiding agglomeration, and making it difficult to be adsorbed and embedded by pores, further improving the consistency of the thermal conductivity of the composite material.

[0018] As a preferred technical solution of the present invention, the mass ratio of the high thermal conductivity two-dimensional material to the core-shell structure is 1:20~40, for example, it can be 1:20, 1:25, 1:30, 1:35 or 1:40, etc.

[0019] Preferably, the mass ratio of the reinforcing phase to the matrix phase is 50:50 to 60:40, for example, it can be 1:20, 1:25, 1:30, 1:35 or 1:40, etc.

[0020] In a second aspect, the present invention provides a method for preparing the diamond-copper composite material as described in the first aspect, the method comprising the following steps: (1) A ceramic interface layer and a porous copper shell layer are sequentially deposited on the surface of diamond particles to prepare a core-shell structure; (2) The core-shell structure and the high thermal conductivity two-dimensional material are dispersed in a dispersant, and ultrasonic-assisted dispersion and adsorption are used. The mixture is then spray-dried and granulated to obtain the reinforcing phase precursor. (3) The reinforcing phase precursor is mixed with copper powder and then loaded into a mold for sintering. After cooling and demolding, the diamond copper composite material is obtained.

[0021] The dispersant described in this invention may be of a type commonly used in the art, including but not limited to ethanol.

[0022] As a preferred technical solution of the present invention, the deposition in step (1) is performed by atomic layer deposition.

[0023] Atomic layer deposition (ALD) is used to prepare a ceramic interface layer and a porous copper shell layer. This ensures that the ceramic interface layer is ultrathin and uniformly coated on the diamond surface, while controlling the porosity and structural morphology of the porous copper shell layer. The deposition has strong adhesion, which allows the ceramic interface layer, porous copper shell layer and diamond particles to form a tight bond, greatly improving the interfacial stability of the core-shell structure. Moreover, the deposition process is gentle and will not damage the intrinsic structure of the diamond particles, thus fully preserving their high thermal conductivity.

[0024] As a preferred technical solution of the present invention, the sintering in step (3) adopts spark plasma sintering, which can effectively suppress the interfacial reaction between diamond and ceramic interface layer and copper matrix, avoid the generation of brittle phase at high temperature or cause diamond graphitization and deterioration, and retain the intrinsic high thermal conductivity of each component to the maximum extent. The pulse current can promote the local melting and diffusion connection of porous copper shell layer, so that the core-shell structure and copper matrix form a good metallurgical bond. Under low temperature and low pressure, a high density and low defect microstructure can be obtained, and the mechanical properties and thermal conductivity of the material can be improved simultaneously.

[0025] Preferably, during the spark plasma sintering process, an axial magnetic field is applied to induce the highly thermally conductive two-dimensional material to align in a direction perpendicular to the pressing direction.

[0026] Preferably, the sintering temperature is 650~800℃, for example, 650℃, 700℃, 720℃, 760℃ or 800℃; the pressure is 20~40MPa, for example, 20MPa, 25MPa, 30MPa, 35MPa or 40MPa; and the vacuum degree is <10Pa.

[0027] Preferably, the sintering is a stepped heating sintering, wherein the temperature is increased from room temperature to a first temperature at a first heating rate, and then increased from the first temperature to a second temperature at a second heating rate, while the pressure is increased to the sintering pressure. After holding the temperature and pressure for sintering, the furnace is cooled to a third temperature and the pressure is unloaded. The second heating rate is less than the first heating rate. The first temperature can be 500°C, the first heating rate can be 100°C / min, the second heating rate can be 50°C / min, the second temperature can be 750°C, the third temperature can be 300°C, and the holding time for sintering can be 5 min.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects: (1) This invention solves the problems of poor compatibility between diamond and copper interface, high interface thermal resistance, mismatch of thermal expansion and harsh preparation process by the overall design of core-shell structure and copper matrix, which significantly improves the thermal conductivity, structural stability and process applicability of diamond-copper composite material. (2) This invention uses a ceramic interface layer as a phonon matching transition layer between diamond and copper, which significantly reduces the interfacial thermal resistance compared to traditional tungsten coatings. Combined with the synergistic bridging effect of the porous copper shell and the high thermal conductivity two-dimensional material, a continuous and efficient thermal conduction path can be constructed, which significantly improves the thermal conductivity of the composite material. The measured thermal conductivity can exceed 800 W / (m·K), and the thermal expansion coefficient of the composite material is controlled within 5×10. -6 / K~8×10 -6 / K, improves the overall mechanical properties and reliability of the material; (3) The present invention adopts low temperature and low pressure discharge plasma sintering, which can effectively avoid the graphitization of diamond. The material has a performance decay of less than 5% after 1000 thermal cycles at -55℃~125℃, and has excellent thermal cycling stability and long-term service reliability. Furthermore, applying an axial magnetic field during the sintering process can induce the directional arrangement of high thermal conductivity two-dimensional materials, thereby improving thermal uniformity and structural compactness. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the core-shell structure in the diamond-copper composite material provided in Embodiment 1 of the present invention; Figure 2 This is a scanning electron microscope image of the diamond-copper composite material provided in Embodiment 1 of the present invention. Detailed Implementation

[0030] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0031] Example 1 This embodiment provides a diamond-copper composite material, which includes a reinforcing phase and a matrix phase. The reinforcing phase includes a core-shell structure, such as... Figure 1 The core-shell structure shown comprises, from the inside out, single-crystal diamond, an aluminum nitride ceramic interface layer, and a porous copper shell layer. The matrix phase is copper powder, and graphene nanosheets are also adsorbed on the surface of the core-shell structure. The specific steps of the preparation method are as follows: (1) The weighed single crystal diamond particles are evenly spread in the ALD special sample tray. The sample tray is loaded into the reaction chamber of the ALD equipment of model: Beneq TFS 200. The chamber is closed and vacuuming is started. The following basic steps are executed in a cycle: "Pulse-injecting trimethylaluminum into the reaction chamber, purging excess precursor with inert gas, pulse-injecting ammonia, and purging again", deposition temperature 300℃, trimethylaluminum pulse time 0.1s, ammonia pulse time 0.2s, purging time 10s, single cycle growth rate 0.1Å / cycle, start the deposition program, run 400 cycles automatically, and obtain an AlN interface layer with a target thickness of 4nm. The following basic steps were performed cyclically: "Pulse-injection of Cu(II)-2,2,6,6-tetramethyl-3,5-heptadecane, purging, pulse-injection of hydrogen, purging". The deposition temperature was 180℃, the precursor pulse time was 1.0s, the purging time was 15s, the hydrogen pulse time was 0.5s, the single-cycle growth rate was 0.2Å / cycle, the deposition program was started, and it ran automatically for 500 cycles to obtain a porous copper shell layer with a target thickness of 100nm. After the program was completed, the cavity was opened and the powder was removed to obtain a core-shell structure with a metallic luster. (2) The core-shell structure and graphene nanosheets were mixed at a mass ratio of 30:1 and added together to a beaker containing anhydrous ethanol (analytical grade). The beaker was placed in the water tank of the Binensin ultrasonic cleaner. The ultrasonic cleaning was turned on, with a power of 300W, a time of 2h, and a temperature of 25℃, so that the graphene sheets were peeled off and uniformly adsorbed on the surface of the core-shell particles. The thickness of the graphene nanosheets was 3~5 layers and the lateral size was 1~5μm. After the ultrasonic cleaning was completed, a uniform suspension with a solid content of 15wt% was obtained. The above suspension was poured into the feed tank of the BUCHI B-290 spray dryer. The equipment was started, and the inlet air temperature was set to 180°C, the outlet air temperature to 80°C, and the atomizer speed to 25,000 rpm. The suspension was atomized into tiny droplets, and the ethanol evaporated instantly in the hot air flow. A dry, uniformly composed, and highly fluid reinforcing phase precursor was obtained in the collection tank.

[0032] (3) Apply a layer of graphite paper to the inner wall of the graphite mold and the upper and lower pressure heads to facilitate demolding. Mix the above-mentioned reinforcing phase precursor with copper powder of 99.9% purity and 5μm particle size at a mass ratio of 55:45, and slowly pour it into the mold cavity. Vibrate it slightly to make it fill evenly. Assemble the entire mold. Place the assembled mold into the FCT Systeme HP D. The 25-type SPS equipment is set with the following sintering program: Stage 1: From room temperature to 500℃, heating rate 100℃ / min, no pressure; Stage 2: From 500℃ to 750℃, heating rate 50℃ / min, pressure linearly increased to 30MPa; Stage 3: Hold at 750℃ for 5 minutes, pressure maintained at 30MPa; Stage 4: Cool with furnace to 300℃ and then unload pressure, with vacuum protection throughout (vacuum degree <10Pa). The sintering program is then started. After sintering is complete, the mold is removed, and the sintered composite material columnar ingot is ejected using a demolding tool. The surface of the ingot is gently sanded with sandpaper to remove the attached graphite paper, resulting in the final diamond-copper composite material block.

[0033] The scanning electron microscope image of the diamond-copper composite material prepared in this embodiment is shown below. Figure 2 As shown, the diamond content is 75 vol%, the aluminum nitride layer thickness is (4.2 ± 0.3) nm, the Cu shell porosity is 25%, and the specific surface area is 2.5 m². 2 / g, theoretical density is 5.82g / cm³ 3 The measured density is 5.78 g / cm³. 3 It has a relative density of 99.3%, a room temperature thermal conductivity of 825±15 W / (m•K), a specific heat capacity of 0.65 J / (g•K), and a thermal diffusivity of 218 mm. 2 / s, the coefficient of thermal expansion at 25~150℃ is (6.3±0.2)×10 -6 The flexural strength is 455±20 MPa, and the Vickers hardness is 185±10 HV1. After 1000 thermal cycles at -55℃ to 125℃, the thermal conductivity decreased from 825 W / (m•K) to 815 W / (m•K), a decrease of 1.2%, and the coefficient of thermal expansion decreased from 6.3×10⁻⁶. -6 / K becomes 6.4×10 -6 / K, flexural strength retention rate is 98.5%, and there is no delamination or cracks at the interface.

[0034] Example 2 This embodiment provides a diamond-copper composite material, which includes a reinforcing phase and a matrix phase. The reinforcing phase includes a core-shell structure, which, from the inside out, includes single-crystal diamond, an aluminum nitride ceramic interface layer, and a porous copper shell layer. The matrix phase is copper powder, and the surface of the core-shell structure is also adsorbed with graphene nanosheets.

[0035] The specific steps of the preparation method are as follows: (1) The weighed single crystal diamond particles are evenly spread in the ALD special sample tray. The sample tray is placed into the reaction chamber of the ALD equipment of model: Beneq TFS 200. The chamber is closed and vacuuming is started. The following basic steps are executed in a cycle: "Pulse-injecting tris(dimethylamino)silane (TDMAS) into the reaction chamber, purging unreacted precursors and by-products with high-purity nitrogen, pulse-injecting ammonia, and purging again". The deposition temperature is set to 320℃, the pulse time of TDMAS precursor is 0.15s, the pulse time of ammonia is 0.25s, and the high-purity nitrogen purging time after each step is 12s. The single-cycle growth rate of this process is about 0.12 Å / cycle. The automatic deposition program is started and run for about 167 cycles to obtain a silicon nitride interface layer with a target thickness of about 2nm on the surface of the diamond particles. The following basic steps were performed cyclically: "Pulse-injection of Cu(II)-2,2,6,6-tetramethyl-3,5-heptadecane, purging, pulse-injection of hydrogen, purging". The deposition temperature was 170℃, the precursor pulse time was 0.8s, the purging time was 14s, the hydrogen pulse time was 0.4s, the single-cycle growth rate was 0.18Å / cycle, the deposition program was started, and it ran automatically for 278 cycles to obtain a porous copper shell layer with a target thickness of 50nm. After the program was completed, the cavity was opened and the powder was removed to obtain a core-shell structure with a metallic luster. (2) The core-shell structure and hexagonal boron nitride nanosheets were mixed at a mass ratio of 20:1 and added together to a beaker containing anhydrous ethanol (analytical grade). The beaker was placed in the water tank of a Binensin ultrasonic cleaner. The ultrasonic cleaning was turned on, with a power of 280W, a time of 1.5h, and a temperature of 24℃, so that the hexagonal boron nitride sheets were peeled off and uniformly adsorbed on the surface of the core-shell particles. The thickness of the hexagonal boron nitride nanosheets was 3~5 layers, and the transverse size was 1~5μm. After the ultrasonic cleaning was completed, a uniform suspension with a solid content of 12wt% was obtained. The above suspension was poured into the feed tank of the BUCHI B-290 spray dryer. The equipment was started, and the inlet air temperature was set to 170°C, the outlet air temperature to 75°C, and the atomizer speed to 22,000 rpm. The suspension was atomized into tiny droplets, and the ethanol evaporated instantly in the hot air flow. A dry, uniformly composed, and highly fluid reinforcing phase precursor was obtained in the collection tank.

[0036] (3) Apply a layer of graphite paper to the inner wall of the graphite mold and the upper and lower pressure heads to facilitate demolding. Mix the above-mentioned reinforcing phase precursor with copper powder of 99.9% purity and 5μm particle size at a mass ratio of 50:50, and slowly pour it into the mold cavity. Vibrate it slightly to make it fill evenly. Assemble the entire mold. Place the assembled mold into the FCT Systeme HP D. The 25-type SPS equipment is set with the following sintering program: Stage 1: From room temperature to 480℃, heating rate 90℃ / min, no pressure; Stage 2: From 480℃ to 650℃, heating rate 45℃ / min, pressure linearly increased to 20MPa; Stage 3: Hold at 650℃ for 4 minutes, pressure maintained at 20MPa; Stage 4: Cool with furnace to 280℃ and then unload pressure, with full vacuum protection, vacuum degree <10Pa, start the sintering program, remove the mold after sintering, use a demolding tool to eject the sintered composite material columnar ingot, gently sand the surface of the ingot with sandpaper to remove the attached graphite paper, and obtain the final diamond-copper composite material block.

[0037] The diamond-copper composite material prepared in this embodiment has a diamond content of 75 vol%, a silicon nitride layer thickness of (2 ± 0.3) nm, a Cu shell porosity of 20%, and a specific surface area of ​​2.3 m². 2 / g, theoretical density is 5.82 g / cm³ 3The measured density is 5.77 g / cm³. 3 It has a relative density of 99.1%, a room temperature thermal conductivity of 820±15 W / (m•K), a specific heat capacity of 0.65 J / (g•K), and a thermal diffusivity of 215 mm. 2 / s, the coefficient of thermal expansion at 25~150℃ is (6.3±0.2)×10 -6 The flexural strength is 450±20 MPa, and the Vickers hardness is 185±10 HV1. After 1000 thermal cycles at -55℃ to 125℃, the thermal conductivity decreased from 820 W / (m•K) to 811 W / (m•K), a decrease of 1.1%, while the coefficient of thermal expansion remained at 6.3×10⁻⁶. -6 / K, flexural strength retention rate is 98.5%, and there is no delamination or cracks at the interface.

[0038] Example 3 This embodiment provides a diamond-copper composite material, which includes a reinforcing phase and a matrix phase. The reinforcing phase includes a core-shell structure, which, from the inside out, includes single-crystal diamond, a titanium nitride ceramic interface layer, and a porous copper shell layer. The matrix phase is copper powder, and the surface of the core-shell structure is also adsorbed with graphene nanosheets.

[0039] The specific steps of the preparation method are as follows: (1) The weighed single crystal diamond particles are evenly spread in the ALD special sample tray. The sample tray is loaded into the reaction chamber of the ALD equipment of model: Beneq TFS 200. The chamber is closed and vacuuming is started. The following basic steps are executed in a cycle: "Tetrazolite (dimethylamino)titanium (TDMAT) is pulsed into the reaction chamber, unreacted precursors and by-products are purged with high-purity nitrogen, ammonia is pulsed in, and purging is performed again". The deposition temperature is set to 320℃. The TDMAT precursor tank needs to be heated and stabilized at 75℃. Its pulse time is set to 0.8s, the ammonia pulse time is 1.2s, and the high-purity nitrogen purging time after each step is 20s. The single-cycle growth rate of this process is about 0.4 Å / cycle. The automatic deposition program is started and 125 cycles are run to obtain a titanium nitride interface layer with a target thickness of about 5 nm on the surface of the diamond particles. The following basic steps were repeated cyclically: "Pulse-injection of Cu(II)-2,2,6,6-tetramethyl-3,5-heptadecane, purging, pulse-injection of hydrogen, purging". The deposition temperature was 190℃, the precursor pulse time was 1.2s, the purging time was 16s, the hydrogen pulse time was 0.6s, the single-cycle growth rate was 0.22Å / cycle, the deposition program was started, and it ran automatically for 909 cycles to obtain a porous copper shell layer with a target thickness of 200nm. After the program was completed, the cavity was opened and the powder was removed to obtain a core-shell structure with a metallic luster. (2) The core-shell structure and graphene nanosheets were mixed at a mass ratio of 40:1 and added together to a beaker containing anhydrous ethanol (analytical grade). The beaker was placed in the water tank of a Binensin ultrasonic cleaner. The ultrasonic cleaning was turned on, with a power of 320W, a time of 2.5h, and a temperature of 26℃, so that the graphene sheets were peeled off and uniformly adsorbed on the surface of the core-shell particles. The graphene nanosheets were 3~5 layers thick and had a lateral size of 1~5μm. After the ultrasonic cleaning was completed, a uniform suspension with a solid content of 18wt% was obtained. The above suspension was poured into the feed tank of the BUCHI B-290 spray dryer. The equipment was started, and the inlet air temperature was set to 190°C, the outlet air temperature to 85°C, and the atomizer speed to 28,000 rpm. The suspension was atomized into tiny droplets, and the ethanol evaporated instantly in the hot air stream. A dry, uniformly composed, and highly fluid reinforcing phase precursor was obtained in the collection tank.

[0040] (3) Apply a layer of graphite paper to the inner wall of the graphite mold and the upper and lower pressure heads to facilitate demolding. Mix the above-mentioned reinforcing phase precursor with copper powder of 99.9% purity and 5μm particle size at a mass ratio of 60:40, and slowly pour it into the mold cavity. Vibrate it slightly to make it fill evenly. Assemble the entire mold. Place the assembled mold into the FCT Systeme HP D. The 25-type SPS equipment is set with the following sintering program: Stage 1: From room temperature to 520℃, heating rate 110℃ / min, no pressure; Stage 2: From 520℃ to 800℃, heating rate 55℃ / min, pressure linearly increased to 40MPa; Stage 3: Hold at 800℃ for 6 minutes, pressure maintained at 40MPa; Stage 4: Cool with furnace to 320℃ and then unload pressure, with full vacuum protection, vacuum degree <10Pa, start the sintering program, remove the mold after sintering, use a demolding tool to eject the sintered composite material columnar ingot, gently sand the surface of the ingot with sandpaper to remove the attached graphite paper, and obtain the final diamond-copper composite material block.

[0041] The diamond-copper composite material prepared in this embodiment has a diamond content of 75 vol%, a titanium nitride layer thickness of (5±0.5) nm, a Cu shell porosity of 18%, and a specific surface area of ​​2.1 m². 2 / g, theoretical density is 5.87 g / cm³ 3 The measured density is 5.81 g / cm³. 3 It has a relative density of 99.0%, a room temperature thermal conductivity of 880±20 W / (m·K), a specific heat capacity of 0.63 J / (g·K), and a thermal diffusivity of 240 mm. 2 / s, the coefficient of thermal expansion at 25~150℃ is (6.1±0.2)×10 -6The flexural strength is 460±25 MPa, and the Vickers hardness is 195±12 HV1. After 1000 thermal cycles at -55℃ to 125℃, the thermal conductivity decreased from 880 W / (m·K) to 870 W / (m·K), a decrease of 1.1%, while the coefficient of thermal expansion remained at 6.1×10⁻⁶. -6 / K, flexural strength retention rate is 98.7%, and there is no delamination or cracks at the interface.

[0042] Example 4 This embodiment provides a diamond-copper composite material. In the preparation of the diamond-copper composite material, two types of single-crystal diamond particles with particle sizes of 50μm and 150μm are graded in a ratio of 3:7 to improve the packing density. The mass ratio of graphene nanosheets to core-shell structure is adjusted to 20:1. During SPS sintering, a 1.5T axial magnetic field is applied along the pressing direction to induce the graphene nanosheets to align perpendicular to the pressing direction. The rest is the same as in the embodiment.

[0043] The material prepared in this embodiment has a parallel thermal conductivity of 950±20 W / (m•K), a perpendicular thermal conductivity of 520±15 W / (m•K), an anisotropy ratio of 1.83, and a radial thermal expansion coefficient of 5.8×10⁻⁶. -6 / K, the axial thermal expansion coefficient is 7.2×10 -6 After 1000 thermal cycles, the parallel thermal conductivity was maintained at 98.8%, the interfacial shear strength was 85 MPa, and the orientation of graphene in the microstructure was well maintained.

[0044] Example 5 This embodiment provides a diamond-copper composite material. The composite material is prepared by a high-temperature melting infiltration process with a temperature of 1100℃ and a holding time of 30min. The rest is the same as in Example 1.

[0045] The theoretical density of the prepared diamond-copper composite material is 5.82 g / cm³. 3 The measured density is 5.45 g / cm³. 3 It has a relative density of 93.6%, a room temperature thermal conductivity of 680±40 W / (m·K), a specific heat capacity of 0.65 J / (g·K), and a thermal diffusivity of 130 mm. 2 / s, the coefficient of thermal expansion at 25~150℃ is (7.8±0.3)×10 -6 The flexural strength is 320±35 MPa, and the Vickers hardness is 145±15 HV1. After 1000 thermal cycles at -55℃ to 125℃, the thermal conductivity decreased from 680 W / (m·K) to 637 W / (m·K), a decrease of 6.3%, while the coefficient of thermal expansion increased to 8.1×10⁻⁶. -6 / K, the flexural strength retention rate is 90.2%, and local microcracks and a small amount of delamination were observed at the interface.

[0046] Comparative Example 1 This comparative example provides a diamond-copper composite material, which uses single-crystal diamond particles of the same size as in Example 1, but does not use the ceramic interface layer and atomic deposition method of the present invention. Instead, it uses conventional magnetron sputtering to deposit tungsten with a thickness of about 1 μm as the interface layer. The preparation process adopts a high-temperature melting infiltration process with a temperature of 1100°C and a holding time of 30 min. All other aspects are the same as in Example 1.

[0047] The prepared diamond-copper composite material has a thermal conductivity of 650 W / (m·K); due to high-temperature treatment, a significant WC reaction layer exists at the interface, increasing the material's brittleness and reducing its flexural strength to only 280 MPa; the coefficient of thermal expansion is 8.5 × 10⁻⁶. -6 / K; After 1000 thermal cycles at -55℃ to 125℃, the thermal conductivity drops to 580 W / (m·K), and the performance decreases by 10.8%.

[0048] Comparative Example 2 This comparative example provides a diamond-copper composite material, which is the same as Example 1 except that the surface of the core-shell structure does not adsorb highly thermally conductive two-dimensional materials.

[0049] The prepared diamond-copper composite material has the same mechanical properties as in Example 1, with a room temperature thermal conductivity of 715±18 W / (m•K), a specific heat capacity of 0.64 J / (g•K), and a thermal diffusivity of 195 mm. 2 / s.

[0050] Test methods This invention employs the laser flash method for thermal conductivity testing, referring to ASTM E1461 standard, with a test temperature of room temperature; the thermomechanical analysis (TMA) method is used for thermal expansion coefficient testing, with a test temperature range of 25℃ to 150℃ and the heating rate set according to the equipment's standard parameters; the thermal cycling stability test involves placing the sample in a high and low temperature test chamber and conducting a cycle test from -55℃ to 125℃, accumulating 1000 cycles, and testing the changes in thermal conductivity, thermal expansion coefficient, and mechanical properties before and after the cycle; the BET method is used for porosity testing to measure the porosity of the porous copper shell layer; the Archimedes' drainage method is used for relative density testing; the ellipsometry is used to measure the thickness of the ceramic interface layer; and the three-point bending method (span 20mm) is used for mechanical property testing of flexural strength, and the Vickers hardness test (HV1) is used for hardness testing.

[0051] (1) As can be seen from Examples 1 to 3, the present invention adopts a core-shell structure of single crystal diamond, ceramic interface layer and porous copper shell layer, combined with atomic layer deposition, spark plasma sintering process and high thermal conductivity two-dimensional material adsorption, which can achieve the effects of high material density, excellent thermal conductivity and thermal cycling stability.

[0052] (2) By comparing Example 1 with Examples 4 and 5, it can be seen that the present invention can further optimize the thermal conductivity by using diamond particle size distribution and magnetic field-induced directional arrangement of high thermal conductivity two-dimensional materials; by using spark plasma sintering, rapid sintering can be achieved, effectively improving the material density, strengthening the interface bonding state, suppressing interface reaction, and ensuring the material's excellent thermal cycling stability and thermal conductivity.

[0053] (3) As can be seen from the comparison between Example 1 and Comparative Examples 1 and 2, the present invention uses a ceramic interface layer and atomic layer deposition (ALD) to replace the traditional tungsten plating and high-temperature melting infiltration process, which can effectively avoid the defects such as interface reaction, increased material brittleness, and significant performance degradation that are prone to occur in the traditional process, and ensure the integrity of the interface bonding; Comparative Example 1 lacks a nano-ceramic interface layer and ALD process, and uses traditional tungsten plating and high-temperature melting infiltration, which easily generates brittle phases at the interface, resulting in reduced thermal conductivity, mechanical properties, and thermal cycling performance. Adsorbing highly thermally conductive two-dimensional materials on the surface of the core-shell structure can construct a continuous, low-defect, three-dimensional, highly efficient thermally conductive path between the diamond particles and the copper matrix; Comparative Example 2 lacks highly thermally conductive two-dimensional materials, cannot construct a continuous thermally conductive path, and has a significantly reduced thermal conductivity.

[0054] In summary, this invention achieves high density, high thermal conductivity, excellent thermal matching, and superior thermal cycling stability in diamond-copper composite materials by employing a core-shell structure design using single-crystal diamond, a ceramic interface layer, and a porous copper shell layer. This is achieved through atomic layer deposition (ALD) to prepare the interface layer and porous copper shell layer, adsorbing highly thermally conductive two-dimensional materials, and using spark plasma sintering (SPCS). Simultaneously, it overcomes the defects of traditional preparation processes, such as interfacial reactions and performance instability, demonstrating good versatility and application value.

[0055] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A diamond-copper composite material, characterized in that, The diamond-copper composite material includes a reinforcing phase and a matrix phase. The reinforcing phase includes a core-shell structure, which consists of diamond, a ceramic interface layer, and a porous copper shell layer from the inside out. The matrix phase is copper powder, and the surface of the core-shell structure is also adsorbed with a highly thermally conductive two-dimensional material.

2. The diamond-copper composite material according to claim 1, characterized in that, The diamond in the core-shell structure is a single-crystal diamond particle. Preferably, the diamond has a particle size of 50~150μm.

3. The diamond-copper composite material according to claim 1 or 2, characterized in that, The ceramic interface layer is made of any one of aluminum nitride, silicon nitride, or titanium nitride. Preferably, the thickness of the ceramic interface layer is 2~5nm.

4. The diamond-copper composite material according to any one of claims 1 to 3, characterized in that, The thickness of the porous copper shell layer is 50~200nm.

5. The diamond-copper composite material according to any one of claims 1 to 4, characterized in that, The porosity of the porous copper shell is 20-30%.

6. The diamond-copper composite material according to any one of claims 1 to 5, characterized in that, The highly thermally conductive two-dimensional material includes graphene nanosheets or hexagonal boron nitride nanosheets; Preferably, the thickness of the high thermal conductivity two-dimensional material is 3 to 5 layers, and the lateral dimension is 1 to 5 μm.

7. The diamond-copper composite material according to any one of claims 1 to 6, characterized in that, The mass ratio of the high thermal conductivity two-dimensional material to the core-shell structure is 1:20~40; Preferably, the mass ratio of the reinforcing phase to the matrix phase is 50:50 to 60:

40.

8. A method for preparing the diamond-copper composite material as described in any one of claims 1 to 7, characterized in that, The method includes the following steps: (1) A ceramic interface layer and a porous copper shell layer are sequentially deposited on the surface of diamond particles to prepare a core-shell structure; (2) The core-shell structure and the high thermal conductivity two-dimensional material are dispersed in a dispersant, and ultrasonic-assisted dispersion and adsorption are used. The mixture is then spray-dried and granulated to obtain the reinforcing phase precursor. (3) The reinforcing phase precursor is mixed with copper powder and then loaded into a mold for sintering. After cooling and demolding, the diamond copper composite material is obtained.

9. The method according to claim 8, characterized in that, The deposition in step (1) is performed using atomic layer deposition.

10. The method according to claim 8 or 9, characterized in that, The sintering process described in step (3) is performed using spark plasma sintering. Preferably, during the spark plasma sintering process, an axial magnetic field is applied to induce the highly thermally conductive two-dimensional material to align in a direction perpendicular to the pressing direction; Preferably, the sintering temperature is 650~800℃, the pressure is 20~40MPa, and the vacuum degree is <10Pa.

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