A diamond composite material and a method of making the same

Abstract

This invention proposes a diamond composite material and its preparation method. The preparation method includes the following steps: ultrasonically mixing diamond micropowder, metal particles, and nano-ceramic powder in anhydrous ethanol, followed by drying to obtain a precursor powder; sequentially loading the precursor powder and a cemented carbide matrix into a reaction vessel, with an electrode mounted on the side of the cemented carbide matrix opposite to the precursor powder; subjecting the mixture to high-pressure, high-temperature heating while simultaneously applying a low-frequency alternating microcurrent to the electrode to obtain a precursor; and subjecting the precursor to secondary sintering in a vacuum environment, followed by heat preservation and natural cooling to obtain the diamond composite material. This method avoids the problems of surface conductivity, heating, and cracking caused by surface penetration, resulting in a diamond composite material with a dense, insulating, and high-hardness surface.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and particularly relates to a diamond composite material and its preparation method. Background Technology

[0002] Diamond composites are engineering materials formed by combining diamond as the main reinforcing phase with a matrix such as metal or ceramic under high temperature, high pressure, or other densification processes. Typical forms include polycrystalline diamond (PCD, where diamond microcrystals are sintered into a continuous structure under the action of binder / activator phases such as cobalt, nickel, and tantalum), diamond-metal matrix composites (such as diamond / copper and diamond / aluminate thermal management composites), and diamond-ceramic matrix composites (such as diamond / silicon carbide and diamond / alumina). These materials combine the ultra-high hardness, low coefficient of friction, and extremely high thermal conductivity of diamond with the toughness, structural support, and machinability provided by the metal or ceramic matrix.

[0003] In the fields of cutting and wear resistance, PCD composite sheets are widely used for efficient and precision machining of non-ferrous metals and non-metallic materials (aluminum alloys, copper alloys, carbon fiber composites, wood, stone, etc.), as well as PDC drill bits for oil and gas drilling, mining / geological coring tools, ultra-wear-resistant valve seats and cores, sealing rings, guide blocks, and wear bushings; this is because they can significantly reduce wear and tool change frequency under high linear speed and long life conditions. In the fields of heat dissipation and functionality, diamond / metal, with its thermal conductivity approaching or even exceeding kilowatt-level Kelvin per meter and customizable coefficient of thermal expansion, is used as a heat dissipation substrate for power devices, heat sinks for lasers, microwave devices and LED packaging substrates, and aerospace electronic thermal management components.

[0004] However, during high-temperature and high-pressure sintering, metals such as cobalt and nickel will briefly become liquid. They will be pulled upwards along the gaps between diamond particles by heat and capillary effect, forming a pathway. In the end, the diamond composite surface, which should be hard and insulating, becomes a layer doped with metal, which is more conductive and heat-generating, and its wear resistance is also reduced. It is also prone to cracking and delamination due to inconsistent thermal expansion and contraction. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a diamond composite material and its preparation method, which aims to solve the problem of surface conductivity and performance degradation caused by the infiltration of the metallic phase in the diamond composite material during the sintering process.

[0006] To address the above problems, this invention proposes a method for preparing diamond composite materials, comprising the following steps: S1. Diamond micro powder, metal particles and nano-ceramic powder are ultrasonically mixed in anhydrous ethanol and then dried to obtain precursor powder. S2. The precursor powder and the cemented carbide matrix are loaded into the reaction vessel in sequence. An electrode is mounted on the side of the cemented carbide matrix away from the precursor powder. The mixture is heated under high pressure and high temperature, and a low-frequency alternating micro-current is applied to the electrode to obtain the precursor. S3. The precursor is sintered in a vacuum environment, held at a certain temperature and then naturally cooled to obtain a diamond composite material.

[0007] In some embodiments, the metal particles include cobalt / tantalum / tungsten mixed metal powder, precious metal powder, and nickel foam particles; Step S1 includes: S1.1 Weigh diamond micro powder of different particle sizes and divide it into a first layer of powder, a second layer of powder and a third layer of powder. The particle sizes of the first layer of powder, the second layer of powder and the third layer of powder are the same or different. Cobalt / tantalum / tungsten mixed metal powder is added to the first layer of powder, precious metal powder and nano ceramic powder are added to the second layer of powder, and nickel foam particles are added to the third layer of powder. S1.2 Add dispersant to anhydrous ethanol, stir and deoxygenate at a stirring speed of 300~500 rpm under nitrogen protection, and disperse the first layer of powder, the second layer of powder and the third layer of powder separately. Perform alternating ultrasonication at a frequency of 20 / 40kHz, with an ultrasonic power of 400~600W, for 15~20min. S1.3. The first, second, and third layers of powder after ultrasonic dispersion are separately introduced into a stirring vessel preheated to 40-50°C and stirred slowly at 300-400 rpm for 10-15 minutes, so that the three layers of powder form the first, second, and third solutions under low temperature conditions. S1.4 The first solution, the second solution, and the third solution are dried by a spray drying device. The inlet air temperature of the spray drying tower is 150~165℃, the outlet air temperature is 90~110℃, the atomizing disc speed is 8000~12000rpm, the spray pressure is 1.5~2.0bar, the solid content is controlled at 6~10wt%, and the residence time of the droplets in the drying tower is 3~6s, forming the first layer of composite particles, the second layer of composite particles, and the third layer of composite particles. S1.5. The first layer of composite particles, the second layer of composite particles, and the third layer of composite particles are placed in a vacuum drying oven at 80°C for secondary drying for 2-3 hours to obtain the precursor powder, which includes the first layer of composite particles, the second layer of composite particles, and the third layer of composite particles.

[0008] In some embodiments, in step S1, the nano-ceramic powder includes at least one of alumina nanopowder, silicon carbide nanopowder, and silicon nitride nanopowder; the precious metal powder includes at least one of palladium metal powder and platinum metal powder; and the dispersant includes at least one of sodium polyacrylate, sodium dodecyl sulfate, and polyvinylpyrrolidone.

[0009] In some embodiments, step S2 includes: S2.1 Place the hard alloy substrate at the bottom of the reaction vessel, which is a metal cup. The electrode is attached to the side of the substrate away from the precursor powder. The electrode is a graphite sheet or a molybdenum sheet and is led out to an external power source through a high-temperature resistant insulating sleeve. A metal pressure transmission ring and a ceramic heat insulation pad are laid in sequence on the outer periphery of the metal cup. S2.2 Fill the third layer of composite particles, the second layer of composite particles, and the first layer of composite particles in the thickness direction from bottom to top. Lay a layer of tungsten carbide particles in the middle of the second layer of composite particles and the first layer of composite particles. After filling, pre-press with cold pressure at 100~200MPa 1~2 times to make the bulk density ≥60%TD. Cover the top of the metal cup with a metal pressure plate and a heat insulation pad. S2.3 Place the assembled metal cup into the six-sided high-pressure device, raise the initial pressure to 0.5~1.0GPa, then raise the pressure to 5.5~7.0GPa, first raise the temperature to 980~1120℃ and hold for 2~4 minutes, then raise the temperature to 1180~1280℃ and hold for 4~8 minutes. During the heating process, a low-frequency alternating micro-current is applied to the electrodes at a frequency of 5~20Hz, a current of 0.5~2.0A, a duty cycle of 50%, and a pressure pulsation of ±0.2GPa with a period of 30~60s. S2.4. Maintain high pressure and reduce the temperature to 400℃, then slowly depressurize to normal pressure and perform short-term heat treatment at 450~550℃ for 10~20 minutes in an inert atmosphere to obtain the precursor.

[0010] In some embodiments, the cemented carbide matrix includes at least one of tungsten carbide / cobalt alloy matrix, tungsten carbide / nickel alloy matrix, and tungsten carbide / cobalt alloy / titanium carbide / tantalum carbide alloy matrix.

[0011] In some embodiments, step S3 includes: S3.1 Place the precursor into the vacuum drying table, heat it to 120~150℃ and pre-evacuate for 30~60 minutes to make the metal cup cavity reach an equivalent vacuum. S3.2, pressurize to 8.8~10.0GPa, then heat to 1550~1700℃ at a rate of 80~120℃ / min and start timing to hold for 6~10min; S3.3. Keep the pressure constant, reduce the temperature to ≤400℃ at a rate of 100~150℃ / min, and then slowly depressurize to atmospheric pressure at a gradient of 0.2~0.4GPa / min, and remove the precursor from the metal cup. S3.4. The precursor is subjected to low-temperature annealing at 650~700℃ for 5~15min in an inert atmosphere, and then naturally cooled to obtain the diamond composite material.

[0012] In some embodiments, during step S3.2, the temperature is adjusted by ±30~50℃ around the target temperature during the heat preservation process, with a cycle of 60~120s and a duration of 4~6 cycles, during which the pressure remains stable.

[0013] This invention proposes a diamond composite material, which is prepared by the diamond composite material preparation method described above.

[0014] Compared with existing technologies, the diamond composite material and its preparation method disclosed in this invention have the following advantages: In step S1, the layered mixing and ultrasonic dispersion of diamond micron powder, metal particles, and nano-ceramic powder ensures that the metal component is uniformly coated on the diamond surface but confined to specific layers. In step S2, current field control under high pressure and high temperature ensures that the metal binder phase forms connections only in the internal layers under heating and pressure, preventing it from being carried to the surface by thermal gradients or capillary action. Finally, in step S3, vacuum secondary sintering, recrystallization and stress release prevent residual metal infiltration. This entire process avoids the problems of surface conductivity, heating, and cracking caused by infiltration, resulting in a diamond composite material with a dense, insulating, and high-hardness surface. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of a method for preparing diamond composite material according to an embodiment of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0017] Please refer to Figure 1 This invention proposes a method for preparing diamond composite materials, the steps of which include: S1. Diamond micro powder, metal particles and nano-ceramic powder are ultrasonically mixed in anhydrous ethanol and then dried to obtain precursor powder.

[0018] Metal particles include cobalt / tantalum / tungsten mixed metal powder, precious metal powder, and nickel foam particles; Step S1 includes: S1.1 Weigh diamond micron powders of different particle sizes and separate them into a first layer, a second layer, and a third layer. The particle sizes of the first, second, and third layers may be the same or different. A cobalt / tantalum / tungsten mixed metal powder is added to the first layer, precious metal powder and nano-ceramic powder are added to the second layer, and nickel foam particles are added to the third layer. The precious metal powder includes at least one of palladium metal powder and platinum metal powder. The nano-ceramic powder includes at least one of alumina nanoparticles, silicon carbide nanoparticles, and silicon nitride nanoparticles.

[0019] In this step, diamond micropowder is divided into three layers according to different particle sizes, and cobalt / tantalum / tungsten mixed metal powder, precious metal powder and nano-ceramic powder, and nickel foam particles are respectively incorporated, realizing functional stratification of the material in spatial structure. The three metal powders of cobalt, tantalum, and tungsten can form stable carbide bonds with the diamond surface at high temperature, improving the sintering reaction activity and bonding strength between grains; the precious metal powder has excellent chemical inertness, which can inhibit local graphitization reaction and form a highly conductive interface; the nano-ceramic powder can effectively disperse internal stress and improve thermal stability by pinning grain boundaries; and the nickel foam particles construct a three-dimensional thermally conductive framework, improving the thermal diffusion capability of the composite during high-pressure sintering.

[0020] This multi-component, layered design allows diamond particles of different sizes to be densified sequentially and interlocked at the interface during subsequent sintering, thereby achieving synergistic optimization of hardness, toughness, and thermal conductivity.

[0021] S1.2 Add a dispersant to anhydrous ethanol, and stir and deoxygenate at a stirring speed of 300~500 rpm under nitrogen protection to separately disperse the first, second and third powder layers. Perform alternating ultrasonication at a frequency of 20 / 40kHz with an ultrasonic power of 400~600W for 15~20min. The dispersant includes at least one of sodium polyacrylate, sodium dodecyl sulfate and polyvinylpyrrolidone.

[0022] In this step, one or more of sodium polyacrylate, sodium dodecyl sulfate, and polyvinylpyrrolidone are used as dispersants for ultrasonic dispersion and deoxygenation in anhydrous ethanol. Sodium polyacrylate forms an anion adsorption layer on the surface of diamond and metal particles, preventing agglomeration through electrostatic repulsion; sodium dodecyl sulfate acts as a surfactant, reducing the surface tension of the ethanol system and improving particle wettability and flowability; polyvinylpyrrolidone forms a molecular protective layer on the surface of noble metals and nano-ceramics, preventing oxidation and interfacial adsorption competition. Alternating ultrasound (20 / 40kHz) subjectes particles of different sizes to periodic cavitation shearing, thereby achieving efficient deagglomeration and uniform dispersion. This dispersion strategy ensures that the three-layer system remains independent and stable before mixing, allowing the metal powder, nano-ceramics, and diamond particles to achieve maximum surface activation in their respective systems. This step achieves micro-level control through independent dispersion and surface activation, ensuring the formation of a clear core-shell structure in subsequent atomization granulation, fundamentally improving the reaction consistency of the composite particles.

[0023] S1.3. The first, second, and third layers of powder, after ultrasonic dispersion, are separately introduced into a stirred tank preheated to 40-50°C. The mixture is slowly stirred at 300-400 rpm for 10-15 minutes to form the first, second, and third solutions under low-temperature conditions.

[0024] Stirring the ultrasonically dispersed three-layer powder at a low speed within the range of 40-50°C effectively avoids surface oxidation and loss of activity caused by high temperatures. This temperature range helps match the adsorption equilibrium of the dispersant with the solvent evaporation rate, allowing the metal particles to form a stable interfacial adsorption layer on the diamond surface. The first, second, and third solutions formed by separate stirring maintain their independent concentration and viscosity characteristics, providing conditions for the self-assembly of layers during the spray drying stage. During stirring, cobalt / tantalum / tungsten particles undergo mild coordination adsorption with the polar functional groups (carbonyl and hydroxyl groups) on the diamond surface; the noble metal particles are uniformly suspended due to their surface inertness; the nano-ceramic particles are dispersed in the liquid phase by the electrostatic barrier of polyacrylic acid; and the foamed nickel particles form local fluid channels due to their porous structure. This pre-established three-phase suspension state can naturally evolve into layered droplets in subsequent spraying, ensuring the spontaneous formation of the core-shell structure during the drying stage, which is a prerequisite for realizing the layered particle mechanism.

[0025] In one embodiment, camphor microparticles with a median particle size (D50) of 10–30 μm are added to the third solution at a rate of 0.5–1.0 wt% based on the solid content of the third solution. Under nitrogen protection, the temperature is controlled at 40–45 °C, and the solution is stirred at 300–400 rpm for 5–8 min to achieve uniform suspension. Subsequently, the solution is ultrasonicated at a frequency of 20 kHz and a power of 200–300 W for 2–3 min to adjust the viscosity of the third solution to 20–80 mPa·s. The camphor completely sublimates during the S1.4 hot air (150–165 °C) and S1.5 vacuum drying (80 °C, 2–3 h), leaving no residue in the powder. During droplet drying, it forms a sublimable microcavity template within the third layer system, leaving uniform and fine vacancy after spraying. This is used for subsequent metal confined penetration and stress relief in the S2 stage, preventing the formation of through-flow channels and reducing the peak value of thickness-directed thermal stress.

[0026] S1.4 The first solution, the second solution, and the third solution are dried by a spray drying device. The inlet air temperature of the spray drying tower is 150~165℃, the outlet air temperature is 90~110℃, the atomizing disc speed is 8000~12000rpm, the spray pressure is 1.5~2.0bar, the solid content is controlled at 6~10wt%, and the residence time of the droplets in the drying tower is 3~6s, forming the first layer of composite particles, the second layer of composite particles, and the third layer of composite particles.

[0027] By using a spray drying device to rapidly evaporate droplets in a high-temperature airflow, the concentration gradient between layers can be solidified in a short time. Due to the different surface tensions and evaporation rates of the three solutions, the droplets undergo inward migration and outward deposition during the drying process, thus forming a layered structure of outer shell, middle layer, and core. The first solution is rich in highly reactive cobalt / tantalum / tungsten mixed metals, which easily form an activation layer on the droplet shell; in the second solution, noble metals and nano-ceramic particles are distributed in the middle layer, providing electrical conductivity and stress buffering functions; in the third solution, foamed nickel particles and diamond are co-deposited in the core, forming a porous thermally conductive framework. This process achieves self-layering of the material at the microscale while maintaining the high fluidity and uniformity of spherical particles. This result can significantly improve the density and thermal conductivity uniformity during subsequent high-temperature and high-pressure sintering, avoiding segregation or porosity that occurs in traditional mixed powders during sintering.

[0028] S1.5. The first layer of composite particles, the second layer of composite particles, and the third layer of composite particles are placed in a vacuum drying oven at 80°C for secondary drying for 2-3 hours to obtain the precursor powder, which includes the first layer of composite particles, the second layer of composite particles, and the third layer of composite particles.

[0029] The spray-dried composite particles are then subjected to a secondary drying process under vacuum conditions. This process thoroughly removes ethanol and adsorbed moisture, preventing residual solvent from vaporizing and expanding under subsequent high temperature and pressure conditions, which could cause pores. Vacuum drying also promotes partial pyrolysis of the dispersant, enabling in-situ reduction reactions between the metal particles and the diamond surface, forming an extremely thin metallized adsorption layer. Furthermore, the vacuum environment prevents the oxidation of precious metals and nickel foam, enhancing the activity of subsequent sintering reactions. This step releases the internal stress of the three-layer composite particles, resulting in a more stable structure and a concentrated particle size distribution (30~60μm), facilitating subsequent stacking and compaction.

[0030] S2. The precursor powder and the cemented carbide matrix are sequentially loaded into a reaction vessel. An electrode is mounted on the side of the cemented carbide matrix opposite to the precursor powder. The mixture is heated under high pressure and high temperature while a low-frequency alternating micro-current is applied to the electrode to obtain the precursor. The cemented carbide matrix includes at least one of the following: tungsten carbide / cobalt alloy matrix, tungsten carbide / nickel alloy matrix, and tungsten carbide / cobalt alloy / titanium carbide / tantalum carbide alloy matrix.

[0031] Step S2 includes: S2.1 Place the cemented carbide substrate at the bottom of the reaction vessel, which is a metal cup. An electrode is attached to the side of the substrate away from the precursor powder. The electrode is a graphite sheet or a molybdenum sheet, which is led out to an external power source through a high-temperature resistant insulating sleeve. A metal pressure transmission ring and a ceramic heat insulation pad are laid in sequence on the outer periphery of the metal cup.

[0032] In this step, a cemented carbide substrate is placed at the bottom of a metal cup and connected to an external power source via graphite or molybdenum electrodes, achieving stable separation between the current transmission path and the heat conduction path. Graphite sheets possess excellent electrical conductivity and high-temperature oxidation resistance, ensuring stable conduction of microcurrents under high pressure. Molybdenum sheets, with their high melting point and low thermal expansion, prevent electrode warping or breakage due to thermal shock. The outer metal pressure-transmitting ring evenly distributes the external load, avoiding localized stress concentration. Ceramic insulation pads (such as alumina or silicon nitride) isolate current leakage and stabilize the thermal field distribution. Through this design, the reaction system forms a layered energy flow structure in the longitudinal direction, consisting of a current path, a heat conduction channel, and a thermal isolation layer. This arrangement ensures uniform distribution of the subsequent microcurrent within the sample, enabling electric field-assisted diffusion and thermal gradient to couple, providing stable conditions for subsequent interlayer electropercolation and reaction activation.

[0033] S2.2 Fill the third layer of composite particles, the second layer of composite particles, and the first layer of composite particles in the thickness direction from bottom to top. Lay a layer of tungsten carbide particles in the middle between the second layer of composite particles and the first layer of composite particles. After filling, pre-press with cold pressure at 100~200MPa 1~2 times to make the bulk density ≥60%TD. Cover the top of the metal cup with a metal pressure plate and a heat insulation pad.

[0034] In this step, the composite particles of the third, second, and first layers are sequentially loaded, with a tungsten carbide particle layer laid between the second and first layers. The addition of the tungsten carbide particle layer forms a diffusion valve layer; its high melting point and low diffusion coefficient limit the excessive penetration of the highly active cobalt phase from the upper layer to the lower layer at high temperatures, thus preventing catalyst segregation. Simultaneously, the WC layer provides additional interfacial matching, helping to disperse high-temperature stress and inhibit hot crack propagation. After loading, cold pressing at 100-200 MPa is applied to pre-form the particle, achieving a bulk density of over 60% of the theoretical density, effectively eliminating macroscopic voids and increasing the contact probability of the powder. During cold pressing, the plastic deformation of the metal powder promotes mechanical interlocking between particles, forming a preliminary mechanically interlocked skeleton. This provides the initial structural conditions for densification in the subsequent high-pressure sintering stage, reducing the porosity residue and improving the overall uniformity and dimensional stability of the composite material.

[0035] S2.3 Place the assembled metal cup into the six-sided high-pressure device, raise the initial pressure to 0.5~1.0GPa, then raise the pressure to 5.5~7.0GPa, first raise the temperature to 980~1120℃ and hold for 2~4 minutes, then raise the temperature to 1180~1280℃ and hold for 4~8 minutes. During the heating process, a low-frequency alternating micro-current with a frequency of 5~20Hz, a current of 0.5~2.0A, a duty cycle of 50% is applied to the electrodes, and a pressure pulsation of ±0.2GPa with a period of 30~60s is superimposed.

[0036] Under high pressure (5.5~7.0 GPa) and segmented heating (980~1280℃), a low-frequency alternating microcurrent (frequency 5~20Hz, current 0.5~2.0A, duty cycle 50%) was applied, simultaneously superimposed with ±0.2 GPa pressure fluctuations, achieving synergistic sintering of thermal, electric, and stress fields. The alternating microcurrent generates Joule heating and electromigration effects in the multiphase system, promoting the directional migration of metal ions along grain boundaries and pores, allowing the metal phase to permeate uniformly within the diamond, thereby increasing the neck formation rate. The cobalt / tantalum / tungsten mixed metal forms a transient liquid phase under current-driven conditions, enhancing the wettability and carbonization reaction ability of the metal on the diamond surface; the noble metal powders (palladium, platinum) remain stable during this process, acting as an electron potential buffer and inhibiting diamond graphitization. Simultaneously, the ±0.2 GPa pressure fluctuations induce periodic flow of the liquid metal phase within the pores of the nickel foam, forming nanoscale permeation channels, improving interfacial thermal conductivity and the continuity of the internal metal phase. The combined field effect enables the interlayer interface to achieve a triple enhancement effect of conductivity, thermal conductivity, and adhesion.

[0037] S2.4. Maintain high pressure and reduce the temperature to 400℃, then slowly depressurize to normal pressure and perform short-term heat treatment at 450~550℃ for 10~20 minutes in an inert atmosphere to obtain the precursor.

[0038] After maintaining high pressure and lowering the temperature to 400℃, the pressure is slowly released, followed by a short-term heat treatment at 450-550℃ for 10-20 minutes in an inert atmosphere (such as argon). This effectively releases residual thermal stress and electromigration-induced stress generated during sintering. At this temperature range, some metallic phases (Ni, Co) undergo lattice rearrangement, making the solid solution more stable; simultaneously, nano-ceramic particles achieve secondary pinning at the interface, preventing abnormal grain growth. In the direction of the current channel, the residual electromigration effect gradually diminishes, and the carbide layer at the metal-diamond interface solidifies into a continuous phase, thus achieving stable shaping of the conductive and thermal paths. The annealed precursor exhibits dense interlayer bonding, significantly improved thermal conductivity and mechanical toughness, while maintaining excellent thermal stability and crack resistance. This isobaric slow cooling and short-term annealing design is an innovative extension of traditional sintering. Through thermal stress redistribution and grain boundary self-healing, it lays a solid structural foundation for subsequent secondary sintering.

[0039] S3. The precursor is sintered in a vacuum environment, held at a certain temperature and then naturally cooled to obtain a diamond composite material.

[0040] Step S3 includes: S3.1 Place the precursor into a vacuum drying table, heat it to 120~150℃ and pre-evacuate for 30~60 minutes to make the metal cup cavity reach an equivalent vacuum.

[0041] Placing the precursor on a vacuum drying table and pre-evacuating it at 120~150℃ can effectively remove adsorbed moisture, residual ethanol, and impurities such as oxygen and nitrogen from the air inside the metal cup cavity and the precursor body, achieving a vacuum degree of 10. - 2 Pa level. If residual gases are not removed, they will expand or react with metal particles under high temperature and pressure to form oxides, causing interface defects or porosity. A vacuum environment can significantly reduce the reaction of metals such as Co, Ni, and Ta with oxygen, preventing the formation of low-conductivity oxides such as CoO and NiO, while also avoiding surface passivation of noble metals (palladium, platinum). Furthermore, at temperatures of 120–150°C, the physically adsorbed water and oxide film on the surface of the nickel foam begin to peel off, forming an activated surface, providing conditions for subsequent liquid-phase infiltration. Through this step, the contact energy between the metal phase and the diamond and ceramic phases in the system is significantly improved, forming a high-purity, low-oxidation, and interface-activated initial reaction state, which is an important prerequisite for ensuring the uniformity of subsequent high-pressure densification.

[0042] S3.2, pressurize to 8.8~10.0GPa, then heat to 1550~1700℃ at a rate of 80~120℃ / min and start timing to hold for 6~10min; during the holding process, reciprocate the temperature rise and fall by ±30~50℃ around the target temperature, with a cycle of 60~120s, for 4~6 cycles, during which the pressure remains stable.

[0043] In this step, the pressure is increased to 8.8~10.0 GPa and the temperature is raised to 1550~1700℃ to enter the secondary sintering range. The cobalt / tantalum / tungsten mixed metal in the system partially melts, forming a transient liquid phase that penetrates into the intergranular spaces of the diamond crystals. Cobalt and carbon undergo a limited carburization reaction at high temperature to generate Co3W3C or Co6W6C. These phases act as bonding bridges for the diamond grains, improving the bonding strength. Tantalum forms a TaC nanolayer at the interface, playing a dual role of isolation and reinforcement, preventing diamond graphitization. Noble metal powders (palladium, platinum) maintain a stable phase in this high-temperature region. Their high electrical conductivity and chemical inertness allow them to form an electron buffer layer at the interface, promoting uniform charge distribution and suppressing the formation of localized carbon supersaturated regions. The periodic temperature cycle of ±30~50℃ induces micro-amplitude thermal stress cycling between grains, promoting grain boundary migration, porosity contraction, and grain boundary rearrangement, achieving higher densification and stress homogenization. In this stage, the nanoceramics exert a pinning effect on the liquid metal phase, limiting abnormal grain growth and ensuring microstructure uniformity. Therefore, this process achieves simultaneous densification and structural reorganization of the metal, diamond, and ceramic phases through temperature periodic waves and high-pressure liquid phase infiltration mechanisms, resulting in composite materials with high bonding strength, low internal stress, and high thermal stability.

[0044] S3.3 Keep the pressure constant, reduce the temperature to ≤400℃ at a rate of 100~150℃ / min, and then slowly depressurize to atmospheric pressure at a gradient of 0.2~0.4GPa / min, and remove the precursor from the metal cup.

[0045] Cooling to 400℃ while maintaining pressure avoids instantaneous structural cracking caused by thermo-pressure coupling. At this temperature, the liquid metal gradually solidifies, forming a continuous thermally conductive network; cobalt, nickel, and tungsten preferentially precipitate at grain boundaries, forming refined metallic carbide phases. Slow pressure release (0.2~0.4 GPa / min) prevents microcracks caused by sudden stress release within the material. Simultaneously, as the temperature decreases, the thermal expansion difference between the metallic phase and diamond gradually balances, and the TaC / WC interface phase acts as a stress buffer layer. The porous channels remaining in the nickel foam are partially filled and solidified by the metallic phase during this stage, forming efficient thermal diffusion paths. At this point, a structural gradient of rigid, buffer, and thermally conductive layers is formed within the material, and thermal stress is released stepwise along the thickness direction, preventing interlayer delamination and crack propagation. This step achieves stable coupling between the thermal and force fields, transforming the composite from a sintered dense state to a structurally balanced state, laying the foundation for a final stable diamond composite material.

[0046] S3.4. The precursor is subjected to low-temperature annealing at 650~700℃ for 5~15min in an inert atmosphere, and then naturally cooled to obtain the diamond composite material.

[0047] Short-term annealing at 650–700 °C in an inert atmosphere achieves diffusion equilibrium and stress relaxation at the multiphase interface. This temperature range promotes the recoordination of the metal carbide phase and the carbon layer on the diamond surface, further enhancing the interfacial bonding energy. Some Co and Ni atoms diffuse into the residual pores during this stage, completing microscale rewetting and sealing interfacial defects. Furthermore, the noble metals (palladium and platinum) remain stable during annealing, acting as an electron buffer and homogenizing conductivity, smoothing the conductivity gradient of the material. The nano-ceramic particles undergo slight lattice rearrangement during this process, forming a stable pinning network to prevent interfacial drift caused by thermal cycling during subsequent use. After annealing, the overall structure achieves stable thermal channels, enhanced interfacial bonding energy, and full release of internal stress, significantly improving the thermal stability, crack resistance, and conductivity uniformity of the composite material.

[0048] This invention proposes a diamond composite material, which is prepared by the diamond composite material preparation method described above.

[0049] Example 1: In S1, diamond micron powder is prepared into a three-layer system according to S1.1: The first layer consists of 120g of diamond micron powder, of which 84g is 8~12μm and 36g is 3~6μm, and 0.60g of cobalt / tantalum / tungsten mixed metal powder is added; the second layer consists of 100g of diamond micron powder, of which 96.00g is 5~10μm equivalent gradation, and 3.00g of precious metal powder (palladium metal powder) and 1.00g of nano-ceramic powder (silicon carbide nanoparticles) are added; the third layer consists of 80g of diamond micron powder, of which 40g is 1~5μm and 38.8g is 8~12μm, and 1.20g of nickel foam particles are added. In step S1.2, a dispersant was added to anhydrous ethanol to disperse three layers of powder: the first layer used 0.06 g of sodium dodecyl sulfate; the second layer used 0.10 g of polyvinylpyrrolidone and 0.05 g of sodium polyacrylate; and the third layer used 0.04 g of sodium dodecyl sulfate and 0.04 g of sodium polyacrylate. Each of the three systems was deoxygenated by stirring at 300 rpm for 10 min under nitrogen protection, followed by alternating ultrasonication at 20 / 40 kHz (500 W) for 18 min. In step S1.3, the three ultrasonically dispersed slurries were respectively introduced into a stirred tank preheated to 45°C and stirred at 320 rpm for 12 min to obtain the first, second, and third solutions. In step S1.4, the three solutions are dried separately in a spray drying device with an inlet air temperature of 160℃, an outlet air temperature of 100℃, an atomizing disc speed of 10000rpm, a spray pressure of 1.8bar, a solid content of 8wt%, and a droplet residence time of 5s, yielding 114.5g of the first layer of composite particles, 96.8g of the second layer of composite particles, and 77.2g of the third layer of composite particles. In step S1.5, the three composite particles are vacuum dried again at 80℃ for 2.5h and combined as the precursor powder. In step S2, in step S2.1, a tungsten carbide / cobalt alloy substrate is placed at the bottom of a metal cup. A graphite sheet electrode is attached to the side of the substrate away from the precursor powder and led out through an alumina insulating sleeve. An iron-based metal pressure transmission ring and an alumina ceramic insulation pad are laid on the outer periphery of the metal cup. S2.2 The third layer of composite particles (40.0g), the second layer of composite particles (45.0g), and the first layer of composite particles (55.0g) are filled from bottom to top along the thickness direction, with 0.30g of tungsten carbide particles laid between the second and first layers. Then, the mixture is cold-pressed twice at 150MPa to achieve a bulk density of not less than 60%TD. The cup mouth is then covered with a metal pressure-transmitting plate and a ceramic insulation pad. In S2.3, the metal cup is placed in a six-sided high-pressure device, and the pressure is increased to an initial 0.8GPa and then to 6.2GPa. The temperature is first raised to 1100℃ and held for 3 minutes, then raised to 1250℃ and held for 6 minutes. During the heating process, a low-frequency alternating micro-current (12Hz, 1.2A, 50% duty cycle) is applied to the electrodes, superimposed with ±0.2GPa pressure pulsations with a period of 45s.In S2.4, the temperature is lowered to 400℃ under high pressure, and then slowly depressurized to atmospheric pressure. After removal, it is subjected to a short-term heat treatment at 480℃ for 15 minutes in an inert atmosphere to obtain the precursor. In S3, S3.1 the precursor is placed in a vacuum drying table and pre-evacuated at 140℃ for 45 minutes; S3.2 the pressure is increased to 9.5 GPa, the temperature is increased to 1650℃ at 100℃ / min and held for 8 minutes, while the temperature is repeatedly increased and decreased by ±40℃ around the target temperature, with a cycle of 90 seconds, for a total of 5 cycles, during which the pressure remains stable; S3.3 the pressure is kept constant, the temperature is lowered to 400℃ at 120℃ / min and then slowly depressurized to atmospheric pressure at 0.3 GPa / min; S3.4 annealing is performed at 680℃ for 10 minutes in an inert atmosphere, followed by natural cooling to obtain the diamond composite material.

[0050] Example 2: In S1, the first layer of powder is still 120g of diamond micro powder (78g for 8~12μm and 42g for 3~6μm) with 0.60g of cobalt / tantalum / tungsten mixed metal powder added; the second layer of powder is 100g of diamond micro powder (97.00g for 5~10μm equivalent gradation), with 2.00g of precious metal powder (platinum metal powder) and 1.00g of nano-ceramic powder (alumina nano powder) added; the third layer of powder is 80g of diamond micro powder (38g for 1~5μm and 40.8g for 8~12μm) with 1.20g of nickel foam particles added. The dispersant used was 0.06 g sodium dodecyl sulfate for the first layer, 0.10 g polyvinylpyrrolidone for the second layer, and 0.06 g sodium polyacrylate for the third layer. The ultrasonic conditions were 20 / 40 kHz alternating, 500 W power, and dispersion for 18 min. The drying and secondary drying parameters for S1.3–S1.5 were the same as in Example 1. In S2, the cemented carbide matrix was replaced with a tungsten carbide / nickel alloy matrix. The loading amounts were 38.0 g of the third layer composite particles, 47.0 g of the second layer composite particles, 55.0 g of the first layer composite particles, and 0.30 g of the intermediate tungsten carbide particles. Pre-compression at 150 MPa was performed twice. HPHT was performed with the following parameters: voltage boosted to 6.4 GPa, held at 1100℃ for 3 min, then held at 1250℃ for 6 min. The microcurrent parameters were 10 Hz, 1.0 A, duty cycle 50%, and pressure pulsation ±0.2 GPa with a cycle of 45 s. The precursor was then obtained by heat treatment at 480℃ for 12 min in an inert atmosphere. In S3, the precursor was pre-evacuated to 140℃ for 45 min. The secondary sintering conditions were 9.2 GPa, heated to 1620℃ and held for 8 min, followed by 5 cycles of temperature increases and decreases of ±40℃ with a cycle of 90 s. The precursor was then slowly cooled to 400℃ under isobaric pressure and depressurized at 0.3 GPa / min. The annealing conditions were 660℃ for 12 min.

[0051] Example 3: In S1, the first layer of powder consists of 120g of diamond micro powder (84g for 8~12μm and 36g for 3~6μm) and 0.60g of cobalt / tantalum / tungsten mixed metal powder; the second layer of powder consists of 100g of diamond micro powder (95.50g for 5~10μm), mixed with precious metal powder (1.50g of palladium metal powder and 2.00g of platinum metal powder) and 1.00g of nano-ceramic powder (silicon nitride nano powder); the third layer of powder consists of 80g of diamond micro powder (40g for 1~5μm and 38.6g for 8~12μm) and 1.40g of nickel foam particles. The dispersant used was 0.06g sodium dodecyl sulfate for the first layer, 0.12g polyvinylpyrrolidone and 0.05g sodium polyacrylate for the second layer, and 0.06g sodium polyacrylate for the third layer; ultrasonic dispersion was performed at 20 / 40kHz, 520W, for 18min; spray drying and secondary drying were performed as in Example 1. In S2, the matrix was a tungsten carbide / cobalt alloy / titanium carbide / tantalum carbide alloy matrix; the filling amount was 39.0g of the third layer composite particles, 46.0g of the second layer composite particles, and 56.0g of the first layer composite particles, with 0.35g of tungsten carbide particles in the middle; pre-compression was performed twice at 160MPa. The high-temperature, high-pressure, and electrical parameters were as follows: pressure increased to 6.3 GPa, held at 1100℃ for 3 min, then held at 1260℃ for 6 min; micro-current parameters were 15 Hz, 1.1 A, duty cycle 50%; pressure pulsation ±0.2 GPa, cycle 60 s; subsequently, the precursor was obtained by heat treatment at 500℃ for 12 min in an inert atmosphere. In S3, vacuum pre-evacuation was performed at 140℃ for 45 min; the secondary sintering conditions were 9.6 GPa, heating rate 100℃ / min to 1660℃ and held for 8 min, while simultaneously performing ±40℃, cycle 90 s, for a total of 5 cycles of reciprocating heating and cooling; isobaric slow cooling to 400℃ and depressurization at 0.3 GPa / min; annealing conditions were 700℃ for 10 min.

[0052] Comparative Example 1: This comparative example is identical to Example 1 except for the low-frequency alternating microcurrent and pressure pulsation in S2.3. That is, during the process of boosting the pressure to 6.2 GPa and holding at 1100°C for 3 min and 1250°C for 6 min, no alternating microcurrent is applied to the electrode, and no pressure pulsation is superimposed.

[0053] Comparative Example 2: This comparative example only omits the temperature cycling process in step S3.2, replacing it with a constant temperature holding at 1650℃ and 9.5 GPa for 8 minutes. The remaining steps are identical to those in Example 1. The obtained sample was tested using the same method, showing a Vickers hardness of 84 GPa, a fracture toughness of 10.9 MPa·m^0.5, a bulk electrical conductivity of 1.1 × 10^4 S / m, a thermal conductivity of 1040 W / (m·K), an interlaminar shear strength of 410 MPa, and a surface roughness Ra of 28 nm.

[0054] In the experiment, all samples were cut into circular pieces with a diameter of 10 mm and a composite layer thickness of 3.5 mm. These were then precision ground with a diamond wheel until no visible machining marks were visible on the surface, and polished to a mirror finish with a 0.25 μm diamond blasting agent. Vickers hardness testing was performed using a load of 1 kgf for 15 seconds, with 10 points on the same sample being averaged. Fracture toughness was determined using the indentation method, calculated based on the indentation diagonal and crack length using a commonly used empirical formula. Bulk conductivity was measured along the thickness using a four-probe method with a probe spacing of 1.0 mm and a constant current source set to 100 mA. The steady-state voltage was recorded and the conductivity was calculated. Thermal conductivity was measured using the laser flash method to measure thermal diffusivity, combined with Archimedes' density method and differential scanning calorimetry to obtain the specific heat. Interlaminar shear strength was measured using a double-lapped shear fixture on a universal testing machine under transverse loading. The cross-layer shear area was uniformly calibrated, and the average of three samples was taken. Surface roughness was measured using a white light interferometer, and the average of five values ​​was taken. The experimental results are shown in Table 1.

[0055] Table 1: The experimental data above show that the diamond composite material preparation method proposed in this invention significantly improves the comprehensive performance of the material under multi-physics field coupling and structural hierarchical control. The hardness of Examples 1 to 3 remains above 85 GPa, and the fracture toughness is between 12.4 and 13.5 MPa·m^0.5, indicating that the system achieves high hardness while also possessing excellent crack resistance and energy absorption capacity. This is mainly attributed to the composite carbide network formed by the synergistic effect of cobalt / tantalum / tungsten mixed metals and noble metals, as well as the stress buffer and thermal conductivity channels jointly constructed by nickel foam and nano-ceramics, enabling stable interfacial bonding of diamond microcrystals under high temperature and high pressure. The bulk electrical conductivity and thermal conductivity data show that the electrical conductivity of Examples 1 to 3 is all above 10. 3 With a thermal conductivity on the order of S / m and exceeding 1100 W / (m·K), the metallic conductive channel induced by low-frequency alternating microcurrent and temperature reciprocating wave exhibits uniform electron and phonon transport characteristics. In contrast, the conductivity of Comparative Example 1 drops sharply to 6.5 × 10⁻⁶ W / (m·K) after the electric field is removed. 1 The S / m indicates that the electro-diffusion process plays a crucial role in the redistribution of the metallic phase. Comparative Example 2, although its conductivity increased to 1.1 × 10⁻⁶ under constant high-temperature holding conditions... 4While the interlaminar shear strength decreased significantly to 410 MPa, the excessively continuous metal infiltration channels led to interfacial stress concentration and weakened bonding, further confirming the importance of temperature reciprocating waves in controlling grain boundary migration and suppressing stress accumulation. Furthermore, comparing interlaminar shear strength and surface roughness, Example 3 exhibited the highest interlaminar bonding strength at 540 MPa, while having the lowest surface roughness at only 17 nm. This indicates that the use of a WC / Co / TiC / TaC multi-component matrix and a dual noble metal system can form a more ideal thermal expansion matching and grain boundary transition layer during high-pressure sintering and annealing, thereby obtaining a composite with a complete structure and smooth interface. Overall, the experimental results show that the electric field-temperature field-pressure field synergistic control process of this invention can achieve coordinated densification and energy gradient homogenization of the diamond, metal, and ceramic phases, significantly improving the thermal conductivity, mechanical toughness, and interfacial stability of the composite material.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a diamond composite material, characterized in that the steps include... include: S1. Diamond micro powder, metal particles and nano-ceramic powder are ultrasonically mixed in anhydrous ethanol and then dried to obtain precursor powder. The metal particles include cobalt / tantalum / tungsten mixed metal powder, precious metal powder, and nickel foam particles; the nano-ceramic powder includes at least one of alumina nanopowder, silicon carbide nanopowder, and silicon nitride nanopowder; the precious metal powder includes at least one of palladium metal powder and platinum metal powder; and the dispersant includes at least one of sodium polyacrylate, sodium dodecyl sulfate, and polyvinylpyrrolidone. Step S1 includes: S1.1 Weigh diamond micro powder of different particle sizes and divide it into a first layer of powder, a second layer of powder and a third layer of powder. The particle sizes of the first layer of powder, the second layer of powder and the third layer of powder are the same or different. Cobalt / tantalum / tungsten mixed metal powder is added to the first layer of powder, precious metal powder and nano ceramic powder are added to the second layer of powder, and nickel foam particles are added to the third layer of powder. S1.2 Add dispersant to anhydrous ethanol, stir and deoxygenate at a stirring speed of 300~500 rpm under nitrogen protection, and disperse the first layer of powder, the second layer of powder and the third layer of powder separately. Perform alternating ultrasonication at a frequency of 20 / 40kHz, with an ultrasonic power of 400~600W, for 15~20min. S1.

3. The first, second, and third layers of powder after ultrasonic dispersion are separately introduced into a stirring vessel preheated to 40-50°C and stirred slowly at 300-400 rpm for 10-15 minutes, so that the three layers of powder form the first, second, and third solutions under low temperature conditions. S1.4 The first solution, the second solution, and the third solution are dried by a spray drying device. The inlet air temperature of the spray drying tower is 150~165℃, the outlet air temperature is 90~110℃, the atomizing disc speed is 8000~12000rpm, the spray pressure is 1.5~2.0bar, the solid content is controlled at 6~10wt%, and the residence time of the droplets in the drying tower is 3~6s, forming the first layer of composite particles, the second layer of composite particles, and the third layer of composite particles. S1.

5. The first layer of composite particles, the second layer of composite particles, and the third layer of composite particles are placed in a vacuum drying oven at 80°C for secondary drying for 2-3 hours to obtain precursor powder, which includes the first layer of composite particles, the second layer of composite particles, and the third layer of composite particles. S2. The precursor powder and the cemented carbide matrix are loaded into the reaction vessel in sequence. An electrode is mounted on the side of the cemented carbide matrix away from the precursor powder. The mixture is heated under high pressure and high temperature, and a low-frequency alternating micro-current is applied to the electrode to obtain the precursor. S3. The precursor is sintered in a vacuum environment, held at a certain temperature and then naturally cooled to obtain a diamond composite material.

2. The method for preparing a diamond composite material according to claim 1, characterized in that, Step S2 includes: S2.1 Place the hard alloy substrate at the bottom of the reaction vessel, which is a metal cup. The electrode is attached to the side of the substrate away from the precursor powder. The electrode is a graphite sheet or a molybdenum sheet and is led out to an external power source through a high-temperature resistant insulating sleeve. A metal pressure transmission ring and a ceramic heat insulation pad are laid in sequence on the outer periphery of the metal cup. S2.2 Fill the third layer of composite particles, the second layer of composite particles, and the first layer of composite particles in the thickness direction from bottom to top. Lay a layer of tungsten carbide particles in the middle of the second layer of composite particles and the first layer of composite particles. After filling, pre-press with cold pressure at 100~200MPa 1~2 times to make the bulk density ≥60%TD. Cover the top of the metal cup with a metal pressure plate and a heat insulation pad. S2.3 Place the assembled metal cup into the six-sided high-pressure device, raise the initial pressure to 0.5~1.0GPa, then raise the pressure to 5.5~7.0GPa, first raise the temperature to 980~1120℃ and hold for 2~4 minutes, then raise the temperature to 1180~1280℃ and hold for 4~8 minutes. During the heating process, a low-frequency alternating micro-current is applied to the electrodes at a frequency of 5~20Hz, a current of 0.5~2.0A, a duty cycle of 50%, and a pressure pulsation of ±0.2GPa with a period of 30~60s. S2.

4. Maintain high pressure and reduce the temperature to 400℃, then slowly depressurize to normal pressure and perform short-term heat treatment at 450~550℃ for 10~20 minutes in an inert atmosphere to obtain the precursor.

3. A method for preparing a diamond composite material according to claim 1 or 2, characterized in that, The cemented carbide matrix includes at least one of tungsten carbide / cobalt alloy matrix, tungsten carbide / nickel alloy matrix, and tungsten carbide / cobalt alloy / titanium carbide / tantalum carbide alloy matrix.

4. The method for preparing a diamond composite material according to claim 1, characterized in that, Step S3 includes: S3.1 Place the precursor into the vacuum drying table, heat it to 120~150℃ and pre-evacuate for 30~60 minutes to make the metal cup cavity reach an equivalent vacuum. S3.2, pressurize to 8.8~10.0GPa, then heat to 1550~1700℃ at a rate of 80~120℃ / min and start timing to hold for 6~10min; S3.

3. Keep the pressure constant, reduce the temperature to ≤400℃ at a rate of 100~150℃ / min, and then slowly depressurize to atmospheric pressure at a gradient of 0.2~0.4GPa / min, and remove the precursor from the metal cup. S3.

4. The precursor is subjected to low-temperature annealing at 650~700℃ for 5~15min in an inert atmosphere, and then naturally cooled to obtain the diamond composite material.

5. The method for preparing a diamond composite material according to claim 4, characterized in that, In step S3.2, during the heat preservation process, the temperature is adjusted back and forth by ±30~50℃ around the target temperature, with a cycle of 60~120s, lasting for 4~6 cycles, during which the pressure remains stable.

6. A diamond composite material, characterized in that, It is prepared by the method for preparing a diamond composite material as described in any one of claims 1-5.

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