A polycrystalline diamond compact and a method of making and using the same

Abstract

The application relates to the technical field of superhard materials, and specifically discloses a polycrystalline diamond compact as well as a preparation method and application thereof, and a preparation method of the polycrystalline diamond compact. The preparation method comprises the following steps: sintering WC-Co alloy powder to obtain a hard alloy base body; uniformly mixing nano diamond powder, micron diamond powder and cubic boron nitride, then adding a reinforcing agent and a binding agent to obtain a polycrystalline diamond layer mixture; the reinforcing agent is a nitrogen-boron doped graphene bonded amino carbon nanotube; after the hard alloy base body surface is uniformly spread with gradient transition layer raw materials and the polycrystalline diamond mixture in sequence, a composite blank is obtained through mould pressing; and the composite blank is sintered to obtain the polycrystalline diamond compact. The graphene and the carbon nanotube are compounded to form a reinforcing agent with a three-dimensional network structure, the strength and wear resistance of the material are improved, and the service life of the material under harsh working conditions is prolonged.

Description

Technical Field

[0001] This application relates to the field of superhard materials technology, and more specifically, to a polycrystalline diamond composite sheet, its preparation method, and its application. Background Technology

[0002] Polycrystalline diamond composite (PDC) is obtained by sintering diamond powder and cemented carbide substrate under ultra-high temperature and high pressure conditions with the aid of cobalt catalyst. In this composite, diamond grains are randomly distributed within the diamond layer, overcoming the anisotropy of single diamond crystals. It is widely used in superhard cutting tools, geological exploration, oil and gas extraction and other fields. In the above-mentioned geological and resource extraction fields, PDC drill bits are usually used as key components, and diamond composites are usually used as cutting teeth of the drill bit, which is the most important cutting unit in the drilling process.

[0003] However, due to the large difference in the coefficients of thermal expansion between diamond and cemented carbide, huge interfacial stresses are generated during high-temperature sintering and use, leading to crack initiation and propagation, reducing the interfacial bonding of PDC, and greatly reducing the service life of the workpiece.

[0004] In the prior art, patent application CN111957977A discloses a polycrystalline diamond composite sheet and its preparation method. The polycrystalline diamond composite sheet includes a cemented carbide substrate and a transition coating and a polycrystalline diamond layer sequentially disposed on the cemented carbide substrate. The polycrystalline diamond comprises the following raw materials by weight percentage: 69.5-79.7% coated diamond powder, 15-20% coated cubic boron nitride, 0.2-0.3% carbon nanotubes, 0.1-0.2% graphene, and 5-10% binder. This solution effectively solves the problem of... This study addresses the interfacial stress problem in traditional PDC materials caused by the large difference in thermal expansion coefficients between diamond and cemented carbide. Simultaneously, by adding carbon nanotubes and graphene to the polycrystalline diamond layer, the prepared polycrystalline diamond composite sheet exhibits excellent mechanical and thermal properties. However, it fails to form a uniformly distributed reinforcing network within the diamond matrix, and agglomerates become stress concentration points, significantly reducing the material's strength. The tubular structure advantages of carbon nanotubes and the layered reinforcement effect of graphene cannot be fully utilized, resulting in only a slight improvement in the electrical and thermal conductivity of the composite material. Furthermore, agglomerates may become the starting point for crack initiation and propagation, reducing the impact resistance and service life of the polycrystalline diamond composite sheet. Summary of the Invention

[0005] To improve the impact strength of polycrystalline diamond composite sheets, this application provides a polycrystalline diamond composite sheet, its preparation method, and its application.

[0006] In a first aspect, this application provides a method for preparing polycrystalline diamond composite sheets, employing the following technical solution:

[0007] A method for preparing a polycrystalline diamond composite sheet includes the following steps:

[0008] S1, WC-Co alloy powder is placed into a mold and cold-pressed under a pressure of 200-300MPa, and then sintered at 1400-1500℃ and vacuum degree ≤10Pa for 2h to obtain a cemented carbide matrix;

[0009] S2, nano-diamond powder, micron-diamond powder and cubic boron nitride are mixed evenly, and then a reinforcing agent and a binder are added and mixed evenly to obtain a polycrystalline diamond layer mixture; the reinforcing agent is nitrogen-boron doped graphene bonded amino carbon nanotubes.

[0010] S3, after uniformly spreading the gradient transition layer material and polycrystalline diamond mixture on the surface of the cemented carbide matrix, it is placed in a graphite mold and a composite preform is obtained under a pressure of 10-20 MPa; the composite preform is sintered to obtain a polycrystalline diamond composite sheet.

[0011] By employing the above-mentioned technical solution, a reinforcing agent that combines graphene and carbon nanotubes to form a three-dimensional network structure effectively solves the problems of easy agglomeration and poor dispersibility of single carbon nanotubes and graphene. Its interwoven network of sheets and tubes can effectively fill the gaps between nanodiamond, microdiamond powder, and cubic boron nitride, achieving efficient load transfer through the high interfacial bonding strength of covalent bonds, significantly inhibiting crack propagation and playing a crack bridging role, thus greatly improving the impact toughness and wear resistance of the polycrystalline diamond layer. Secondly, nitrogen-boron doping improves the interfacial compatibility between the reinforcing agent and diamond and cubic boron nitride, promoting the densification of the polycrystalline diamond layer during high-temperature and high-pressure sintering, while avoiding the adverse effects of traditional metal catalyst residues on performance, thus improving the thermal stability and service reliability of the composite sheet. Furthermore, this reinforcing agent exhibits good performance compatibility with the cemented carbide matrix layer and gradient transition layer, alleviating interlayer thermal stress differences and reducing the risk of delamination between the polycrystalline diamond layer and the matrix, ultimately optimizing the overall performance of the composite sheet under extreme conditions such as oil drilling and high-speed cutting.

[0012] Preferably, the preparation method of the nitrogen-boron-doped graphene-bonded amino carbon nanotubes includes the following steps:

[0013] (1) Carbon nanotubes were subjected to amino plasma treatment at 120-180W for 20-30 min to obtain amminated carbon nanotubes;

[0014] (2) Add graphene and aminoborane in a mass ratio of 10:(2-4) to anhydrous ethanol and disperse them by ultrasonication to form a suspension; dry the suspension by rotary evaporation to obtain a precursor, and anneal and dope the precursor at 700-800℃ to obtain nitrogen-boron-doped graphene.

[0015] (3) Aminated carbon nanotubes with a mass ratio of (1-3):1 and nitrogen-boron doped graphene were added to anhydrous ethanol and ultrasonically treated to obtain a dispersion. The dispersion was stirred and reacted, then washed, centrifuged and dried to obtain nitrogen-boron doped graphene bonded amino carbon nanotubes.

[0016] By employing the above-mentioned technical solution, carbon nanotubes are treated with ammonia plasma, which avoids the damage to the lattice structure of carbon nanotubes caused by traditional chemical functionalization. This process ensures that amino groups are uniformly distributed on the surface of the carbon nanotubes and maintain high activity, providing sufficient and stable reaction sites for subsequent bonding reactions. Simultaneously, the plasma etching effect can slightly optimize the surface roughness of the carbon nanotubes, further improving bonding compatibility. The amino groups on the surface of the amminated carbon nanotubes form BN covalent bonds with the boron atoms of the nitrogen-boron-doped graphene. The pyridine N and pyrrole N sites introduced by nitrogen doping can form auxiliary hydrogen bonds with the amino groups, synergistically strengthening the interfacial bonding stability with the BN covalent bonds. Ultimately, this achieves uniform bonding of the two carbon materials across the entire domain, forming a three-dimensional network structure without agglomeration and with strong interfacial bonding. Furthermore, the entire process requires no metal catalyst, avoiding the damage to the bonding effect caused by impurities. The bonded product maintains structural stability during the high-temperature and high-pressure sintering of polycrystalline diamond composite sheets, fully demonstrating its reinforcing effect.

[0017] Preferably, the graphene is obtained by chemically exfoliating graphite to obtain few-layer graphene, followed by oxygen plasma activation treatment.

[0018] By adopting the above technical solutions, the chemical exfoliation process can effectively break the interlayer van der Waals forces of graphite, obtaining few-layer graphene with controllable layer number and large specific surface area, while preserving the integrity of its sheet structure, providing a stable structural basis for subsequent doping and bonding. Oxygen plasma activation, under mild conditions, precisely introduces oxygen-containing groups (-OH, -COOH) and controllable edge defects on the graphene surface, avoiding the destructive damage to the graphene lattice caused by traditional chemical oxidation, and significantly increasing the density of surface active sites. These active sites can serve as anchoring points for N and B doping, promoting the uniform bonding of N and B active species generated by the decomposition of aminoborane with the graphene lattice, improving doping efficiency and doping uniformity, while optimizing the surface charge distribution and interfacial compatibility of graphene, creating favorable conditions for the subsequent formation of BN coordination covalent bonds with aminated carbon nanotubes and auxiliary hydrogen bonds between pyridine N, pyrrole N and amino groups, effectively inhibiting graphene sheet aggregation, and ensuring the formation of a uniform and stable three-dimensional network structure with aminated carbon nanotubes.

[0019] Preferably, the graphene is obtained by chemically exfoliating graphite to obtain few-layer graphene, followed by expansion treatment and then oxygen plasma activation treatment.

[0020] By adopting the above technical solution, the expansion treatment can effectively increase the spacing between graphene sheets, weaken the tendency of aggregation between sheets, and increase the specific surface area of ​​graphene, creating sufficient contact space for subsequent processing. This not only allows the active sites generated by subsequent plasma activation to be more evenly distributed on the sheet surface and between layers, but also facilitates the penetration and diffusion of active species during the doping process, avoiding uneven local doping. At the same time, when bonding with aminated carbon nanotubes, it provides flexible space for the insertion of tubular structures, helping to form a regular three-dimensional network structure.

[0021] Preferably, in step (2), the precursor is annealed in stages during annealing and doping, specifically: the temperature is increased to 350-400℃ at a heating rate of 5℃ / min and held for 30-40min; then the temperature is increased to 550-600℃ at a heating rate of 5℃ / min and held for 60-90min; finally the temperature is increased to 700-800℃ at a heating rate of 5℃ / min and held for 90-120min.

[0022] By adopting the above technical solution, segmented annealing utilizes a synergistic design of gradient heating and staged holding. In the low-temperature stage, residual dispersion media in the precursor are effectively removed, while the dopant source is slowly decomposed, preventing the instantaneous escape or local aggregation of active species caused by rapid heating. The medium-temperature stage provides sufficient time for the bonding of active species to the active sites on the graphene surface, promoting uniform anchoring of doped atoms and reducing local overdoping or underdoping. The high-temperature stage promotes the stable embedding of anchored doped atoms into the graphene lattice, while simultaneously repairing minor lattice defects generated during doping, thus improving the stability of the doped structure. This entire process avoids the problems of graphene sheet stacking and uneven doping caused by single high-temperature annealing, while ensuring efficient and uniform doping of nitrogen and boron elements, laying a solid foundation for subsequent stable bonding with aminated carbon nanotubes and the construction of a high-performance reinforcement network.

[0023] Preferably, the Co content of the WC-Co alloy powder is 6-12 wt%;

[0024] The polycrystalline diamond layer comprises the following raw materials: 30-50 wt% nano-diamond powder, 20-40 wt% micron-diamond powder, 8-15 wt% reinforcing agent, 5-15 wt% cubic boron nitride, and 5-12 wt% binder;

[0025] The binder is a Co-Ni-Si-B quaternary composite binder, and the mass fractions of each component are: Co 38-42wt%, Ni 33-37wt%, Si 14-16wt%, and B 9-11wt%.

[0026] By adopting the above technical solution, the Co-Ni-Si-B quaternary composite binder achieves a highly efficient synergistic effect through the balanced ratio of each component, resulting in multiple beneficial effects: appropriate amounts of Co and Ni construct a stable and tough matrix, which can effectively absorb impact energy during sintering and service, alleviate thermal stress, and inhibit crack propagation; Si and B form a dispersed hard phase in an appropriate ratio, complementing the properties of diamond, cubic boron nitride, and reinforcing agents, significantly improving the overall hardness and wear resistance of the polycrystalline diamond layer; the precise matching of the proportions of each component ensures that the binder can completely melt under high temperature and high pressure sintering conditions to form a liquid phase with suitable fluidity, fully wetting each raw material particle and filling the gaps, and also strengthens the interfacial bonding strength through chemical bonding with the active sites on the surface of the reinforcing agent and metallurgical bonding with the hard alloy matrix, while avoiding performance imbalance caused by excessive amounts of a single component, ultimately achieving comprehensive optimization of wear resistance, impact toughness, and structural stability of the polycrystalline diamond composite sheet.

[0027] Preferably, the gradient transition layer comprises, from bottom to top, a first transition layer, a second transition layer, and a third transition layer;

[0028] The first transition layer comprises the following raw materials: 60-70 wt% WC-Co powder, 20-30 wt% micron-sized diamond powder, 5-10 wt% TiC powder, and 3-5 wt% Mo2C powder;

[0029] The second transition layer comprises the following raw materials: 40-50 wt% WC-Co powder, 30-40 wt% micron diamond powder, 5-10 wt% nano diamond powder, 3-8 wt% TiC powder, and 2-4 wt% Mo2C powder;

[0030] The third transition layer comprises the following raw materials: 20-30wt% WC-Co powder, 40-50wt% micron diamond powder, 10-15wt% nano diamond powder, 3-6wt% TiC powder, and 1-3wt% Mo2C powder.

[0031] By adopting the above technical solution, the polycrystalline diamond composite sheet effectively solves the interfacial stress problem caused by the large difference in thermal expansion coefficients between diamond and cemented carbide in traditional PDC materials through a multi-layer gradient structure design. At the same time, the gradient transition layer adopts a compositional gradient design, which realizes a smooth transition of material properties from the cemented carbide matrix layer to the functional layer, improves the interfacial bonding strength, and effectively suppresses the generation and propagation of cracks.

[0032] Preferably, in S2, the nanodiamond powder, microdiamond powder and cubic boron nitride are mixed and then subjected to acidification followed by amino plasma treatment.

[0033] By adopting the above technical solutions, acidification treatment can efficiently remove residual metal catalysts, oil stains, and oxidation impurities from the surfaces of the three powders, purifying the surface active sites and laying a pure foundation for subsequent modification. Ammonia plasma treatment can controllably introduce amino groups and micro-nano rough structures into the powder surface, forming stable amide covalent bonds and strong hydrogen bonds with oxygen-containing functional groups on the surface of oxygen plasma-modified graphene, and forming coordination bonds with metal ions in the Co-Ni-Si-B alloy binder, constructing a strong bonding network across the entire interface of graphene-powder-binder, significantly improving the dispersion uniformity and interfacial bonding strength of the multi-components. At the same time, this treatment not only fully preserves the original high hardness and high wear resistance of the three powders, but also increases the specific surface area through the surface micro-nano rough structure, promoting densification during high-temperature and high-pressure sintering, effectively preventing particle shedding and interfacial separation under working conditions, and finally, synergistically enhancing the three-dimensional network reinforcement effect of the reinforcing agent, improving the overall strength and impact and wear resistance of the polycrystalline diamond composite sheet.

[0034] Secondly, this application provides a polycrystalline diamond composite sheet, which adopts the following technical solution:

[0035] A polycrystalline diamond composite sheet is prepared using the above-described preparation method.

[0036] Thirdly, this application provides an application of polycrystalline diamond composite sheets, employing the following technical solution:

[0037] The aforementioned polycrystalline diamond composite sheets are used in oil and gas drilling, geological exploration, superhard cutting tools, or wear-resistant tools.

[0038] By adopting the above technical solutions, the polycrystalline diamond composite sheet of this application, with its high hardness, excellent impact and wear resistance, and stable interlayer strength and interfacial bonding strength of each component, can withstand extreme loads and wear in complex and harsh formation operations in oil and gas drilling and geological exploration. It can also achieve long-life stable operation in high-efficiency cutting or wear-resistant conditions of superhard tools and wear-resistant tools, significantly improving operational efficiency and reliability.

[0039] In summary, this application has the following beneficial effects:

[0040] 1. The three-dimensional network reinforcing agent formed by combining graphene and carbon nanotubes in this application can solve the problem of agglomeration of single carbon materials and synergistically exert the layer and tubular reinforcement effects. After uniform distribution, it significantly improves the strength and wear resistance of polycrystalline diamond composite sheets and extends the service life under harsh working conditions.

[0041] 2. In this application, graphene is obtained by chemical exfoliation of graphene to obtain few-layer graphene and then treated with oxygen plasma. This not only enhances the dispersion stability of graphene, but also enables uniform and stable loading of alloy nanoparticles, providing efficient catalytic sites for in-situ directional growth of carbon nanotubes, and finally constructing a three-dimensional interconnected and enhanced network of graphene-metal particles-carbon nanotubes.

[0042] 3. In this application, the mixture of nano-diamond powder, micron-diamond powder and cubic boron nitride is first acidified and then subjected to amino plasma treatment. This process forms a strong bonding network across the entire interface with the oxygen-containing functional groups of graphene and the Co-Ni-Si-B binder, while retaining the high hardness and wear resistance of the powder and promoting sintering densification. Ultimately, the synergistic reinforcing agent significantly improves the overall strength and impact and wear resistance of the polycrystalline diamond composite sheet. Detailed Implementation

[0043] The present application will be further described in detail below with reference to preparation examples, embodiments and comparative examples. Unless otherwise specified, all raw materials involved in the present application can be obtained commercially.

[0044] Preparation Example 1

[0045] This preparation example discloses a method for preparing an enhancer, specifically including the following steps:

[0046] (1) Spread carbon nanotubes with a diameter of 20-50 nm and a length of 5-10 μm evenly on the sample holder of the plasma processing equipment, close the equipment cavity and evacuate to ≤5 Pa, pass ammonia gas with a purity of ≥99.99% and adjust the ammonia gas flow rate to 35 sccm to maintain the pressure inside the cavity at 20 Pa; turn on the plasma generator and process for 25 min at a power of 150 W; after the processing is completed, continue to pass ammonia gas until the cavity temperature drops to room temperature to obtain aminated carbon nanotubes.

[0047] (2) 10g of graphene powder (3-5 layers, particle size 5-10μm) and 3g of aminoborane were added to 250mL of anhydrous ethanol and ultrasonically treated for 35min at a power of 400W and a frequency of 30kHz to obtain a suspension. The suspension was transferred to a rotary evaporator and rotary evaporated for 1.5h at 65℃ and a vacuum of -0.08MPa to obtain a precursor. The precursor was transferred to a tube furnace and heated to 750℃ at a rate of 10℃ / min with 99.99% pure argon gas at a flow rate of 40sccm as a protective gas. The temperature was held for 2.5h for annealing and doping. After annealing, argon gas was continued to be introduced until the temperature inside the furnace dropped to room temperature to obtain nitrogen-boron doped graphene.

[0048] (3) 20g of aminated carbon nanotubes and 10g of nitrogen-boron doped graphene were added to 2L of anhydrous ethanol. The mixture was first sonicated at 400W power and 30kHz frequency for 25min to obtain a dispersion. The dispersion was transferred to a constant temperature stirred reactor and stirred continuously at 55℃ and 350r / min for 5h. After the reaction was completed, the product was washed three times with anhydrous ethanol. The washed mixture was transferred to a high-speed centrifuge and centrifuged at 10000r / min for 15min to collect the precipitate. The precipitate was placed in a vacuum drying oven and dried to constant weight at 90℃ and -0.08MPa vacuum to obtain nitrogen-boron doped graphene bonded amino carbon nanotubes.

[0049] Preparation Example 2

[0050] This preparation example is basically the same as Preparation Example 1, except that the graphene powder in step (1) is obtained by the following preparation method:

[0051] S1. Natural flake graphite with a particle size of 50-100 nm was vacuum-dried for 4 hours at 80℃ and a vacuum degree ≤10 Pa to pretreat the graphite. Then, 1720.8 mL of 98 wt% concentrated sulfuric acid and 191.2 mL of 95% fuming nitric acid were mixed thoroughly and cooled to room temperature to form a mixed acid. 80 g of potassium permanganate was added to the mixed acid at a stirring rate of 2 g / min at 300 r / min. After the addition was complete, stirring continued for 30 min until the potassium permanganate dissolved to obtain 2 L of intercalation reaction solution. Maintaining the stirring conditions, 100 g of pretreated graphite was added to the intercalation reaction solution at 25℃ at a rate of 8 g / min. After the addition was complete, the reaction was stirred at a constant temperature for 6 hours. After the reaction was completed, 6 L of deionized water was slowly added to the system to finish the reaction. To stop the reaction, add 5wt% hydrochloric acid solution to adjust the pH of the system to 2-3, stir for 30 min, filter, and disperse the filter cake in 160 L of deionized water to obtain a dispersion. Under ice-water bath conditions (temperature ≤10℃), perform intermittent ultrasonic treatment at 120 W and 20 kHz (3 s on, 2 s off) for a total time of 60 min. After ultrasonication, centrifuge the dispersion at 3000 r / min for 10 min, collect the supernatant, and then centrifuge at 12000 r / min for 30 min, discarding the supernatant. Wash the precipitate repeatedly with deionized water until the pH of the filtrate is 7, then wash twice with 500 mL of anhydrous ethanol, and finally place it in a freeze dryer and dry it at -50℃ and vacuum degree ≤5 Pa for 12 h to obtain few-layer graphene powder.

[0052] S2, the few-layer graphene powder obtained above is evenly spread on a quartz glass slide, the glass slide is placed in the plasma reaction chamber, the chamber is closed and the vacuum pump is started to evacuate the chamber to a vacuum degree ≤20Pa; then, the reaction chamber is purged three times with high-purity argon gas at a flow rate of 50sccm, each time for 5min. After purging, the reaction atmosphere is adjusted to an argon-oxygen mixture with a volume ratio of 8.5:1.5, and the total flow rate of the mixed gas is controlled at 20sccm to maintain the vacuum degree of the reaction chamber at a stable 30Pa; the radio frequency plasma generator is started, the processing frequency is set to 200W, the processing temperature is 80℃, and the processing time is 10min to start the plasma activation treatment; after the treatment, the argon gas is kept in the state and the reaction chamber is continued to be purged until the chamber temperature drops to room temperature. The graphene powder is taken out and placed in a vacuum drying oven and dried at 80℃ for 2h to obtain modified graphene.

[0053] Preparation Example 3

[0054] This preparation example is basically the same as Preparation Example 2, except that in S2, the few-layer graphene powder is first spread evenly in a quartz boat and placed in a tube furnace; the furnace door is closed and a vacuum is drawn until the vacuum degree inside the chamber is ≤10Pa, then argon gas with a purity ≥99.99% is introduced, the argon gas flow rate is adjusted to 50sccm, and it is continuously purged for 15min; the temperature is raised to 900℃ at a heating rate of 6℃ / min and held for 18min for high-temperature expansion treatment; after the holding period, argon gas is continuously introduced and the material is naturally cooled to below 100℃ to obtain expanded graphene; the expanded graphene is transferred to an agate mortar and ground at a rate of 120r / min for 5min, then transferred to a vacuum drying oven and dried at 80℃ and a vacuum degree of 5Pa for 3h to obtain expanded graphene powder; the few-layer graphene powder obtained above is evenly spread on a quartz boat. Place the glass slide into the plasma reaction chamber, close the chamber, and start the vacuum pump to evacuate the chamber to a vacuum level ≤20Pa. Then, purge the reaction chamber three times with high-purity argon gas at a flow rate of 50 sccm, each time for 5 minutes. After purging, adjust the reaction atmosphere to an argon-oxygen mixture with a volume ratio of 8.5:1.5, control the total flow rate of the mixture to 20 sccm, and maintain the vacuum level of the reaction chamber at 30Pa. Start the radio frequency plasma generator, set the processing frequency to 200W, the processing temperature to 80℃, and the processing time to 10 minutes to begin plasma activation treatment. After treatment, keep the argon gas inlet and continue purging the reaction chamber until the chamber temperature drops to room temperature. Remove the graphene powder and place it in a vacuum drying oven to dry at 80℃ for 2 hours to obtain modified graphene.

[0055] Preparation Example 4

[0056] This preparation example is basically the same as Preparation Example 1, except that (2) 10g of graphene powder and 3g of aminoborane were added to 250mL of anhydrous ethanol and ultrasonically treated for 35min at a power of 400W and a frequency of 30kHz to obtain a suspension; the suspension was transferred to a rotary evaporator and rotary evaporated for 1.5h at 65℃ and a vacuum of -0.08MPa to obtain a precursor; the precursor was transferred to a tube furnace and heated to 380℃ at a heating rate of 5℃ / min and held for 35min with 99.99% pure argon gas at a flow rate of 40sccm as a protective gas; then heated to 580℃ at a heating rate of 5℃ / min and held for 75min; finally heated to 750℃ at a heating rate of 5℃ / min and held for 105min for annealing and doping; after annealing, argon gas was continued to be introduced until the furnace temperature dropped to room temperature to obtain nitrogen-boron doped graphene.

[0057] Preparation Example 5

[0058] This preparation example discloses a method for preparing an enhancer, specifically including the following steps:

[0059] (1) Spread carbon nanotubes with a diameter of 20-50 nm and a length of 5-10 μm evenly on the sample holder of the plasma processing equipment, close the equipment cavity and evacuate to ≤5 Pa, pass ammonia gas with a purity of ≥99.99% and adjust the ammonia gas flow rate to 35 sccm to maintain the pressure inside the cavity at 20 Pa; turn on the plasma generator and process for 30 min at a power of 120 W; after the processing is completed, continue to pass ammonia gas until the cavity temperature drops to room temperature to obtain aminated carbon nanotubes;

[0060] (2) 10g of graphene powder (3-5 layers, particle size 5-10μm) and 2g of aminoborane were added to 250mL of anhydrous ethanol and ultrasonically treated for 35min at a power of 400W and a frequency of 30kHz to obtain a suspension. The suspension was transferred to a rotary evaporator and rotary evaporated for 1.5h at 65℃ and a vacuum of -0.08MPa to obtain a precursor. The precursor was transferred to a tube furnace and heated to 350℃ at a rate of 5℃ / min and held for 40min with 99.99% pure argon gas at a flow rate of 40sccm as a protective gas. Then the temperature was increased to 550℃ at a rate of 5℃ / min and held for 90min. Finally, the temperature was increased to 700℃ at a rate of 5℃ / min and held for 120min for annealing and doping. After annealing, argon gas was continued to be introduced until the temperature inside the furnace dropped to room temperature to obtain nitrogen-boron doped graphene.

[0061] (3) 10g of aminated carbon nanotubes and 10g of nitrogen-boron doped graphene were added to 2L of anhydrous ethanol. The mixture was first sonicated at 400W power and 30kHz frequency for 25min to obtain a dispersion. The dispersion was transferred to a constant temperature stirred reactor and stirred continuously at 55℃ and 350r / min for 5h. After the reaction was completed, the product was washed three times with anhydrous ethanol. The washed mixture was transferred to a high-speed centrifuge and centrifuged at 10000r / min for 15min to collect the precipitate. The precipitate was placed in a vacuum drying oven and dried to constant weight at 90℃ and -0.08MPa vacuum to obtain nitrogen-boron doped graphene bonded amino carbon nanotubes.

[0062] Preparation Example 6

[0063] This preparation example discloses a method for preparing an enhancer, specifically including the following steps:

[0064] (1) Spread carbon nanotubes with a diameter of 20-50 nm and a length of 5-10 μm evenly on the sample holder of the plasma processing equipment, close the equipment cavity and evacuate to ≤5 Pa, pass ammonia gas with a purity of ≥99.99% and adjust the ammonia gas flow rate to 35 sccm to maintain the pressure inside the cavity at 20 Pa; turn on the plasma generator and process for 20 min at a power of 180 W; after the processing is completed, continue to pass ammonia gas until the cavity temperature drops to room temperature to obtain aminated carbon nanotubes;

[0065] (2) 10g of graphene powder (3-5 layers, particle size 5-10μm) and 4g of aminoborane were added to 250mL of anhydrous ethanol and ultrasonically treated for 35min at a power of 400W and a frequency of 30kHz to obtain a suspension. The suspension was transferred to a rotary evaporator and rotary evaporated for 1.5h at 65℃ and a vacuum of -0.08MPa to obtain a precursor. The precursor was transferred to a tube furnace and heated to 400℃ at a rate of 5℃ / min and held for 30min with 99.99% pure argon gas at a flow rate of 40sccm as a protective gas. Then the temperature was increased to 600℃ at a rate of 5℃ / min and held for 60min. Finally, the temperature was increased to 800℃ at a rate of 5℃ / min and held for 90min for annealing and doping. After annealing, argon gas was continued to be introduced until the temperature inside the furnace dropped to room temperature to obtain nitrogen-boron doped graphene.

[0066] (3) 30g of aminated carbon nanotubes and 10g of nitrogen-boron doped graphene were added to 2L of anhydrous ethanol. The mixture was first sonicated at 400W power and 30kHz frequency for 25min to obtain a dispersion. The dispersion was transferred to a constant temperature stirred reactor and stirred continuously at 55℃ and 350r / min for 5h. After the reaction was completed, the product was washed three times with anhydrous ethanol. The washed mixture was transferred to a high-speed centrifuge and centrifuged at 10000r / min for 15min to collect the precipitate. The precipitate was placed in a vacuum drying oven and dried at 90℃ and -0.08MPa vacuum to constant weight to obtain nitrogen-boron doped graphene bonded amino carbon nanotubes.

[0067] Example 1

[0068] In this embodiment, the polycrystalline diamond composite sheet is prepared according to the following steps:

[0069] S1, First Transition Layer: Weigh 65g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 25g of micron-sized diamond powder (particle size 2-4μm), 7g of TiC powder (particle size 0.8-1.5μm), and 3g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the first mixture;

[0070] Second transition layer: Weigh 45g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 35g of micron diamond powder (particle size 2-4μm), 8g of nano diamond powder (particle size 50-80nm), 8g of TiC powder (particle size 0.8-1.5μm), and 4g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the second mixture;

[0071] Third transition layer: Weigh 30g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 46g of micron diamond powder (particle size 2-4μm), 15g of nano diamond powder (particle size 50-80nm), 6g of TiC powder (particle size 0.8-1.5μm), and 3g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the third mixture;

[0072] Polycrystalline diamond layer raw material mixing: Weigh 40g of nanodiamond powder (particle size 50-80nm), 30g of micron diamond powder (particle size 2-4μm), and 12g of cubic boron nitride (particle size 3-6μm) and add them to a planetary mixer. Stir at 300r / min for 60min to obtain a mixed powder. Then add 10g of reinforcing agent and 8g of Ni-Co binder (particle size ≤3μm, Ni:Co mass ratio 7:3), add 300mL of anhydrous ethanol for dispersion, stir at 400r / min for 90min, and then place in an 80℃ vacuum drying oven for 6h to obtain polycrystalline diamond layer mixture; wherein the reinforcing agent is the one obtained in Preparation Example 1.

[0073] S2, 100g of WC-Co alloy powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm) was placed in a mold and cold-pressed under 250MPa pressure. Then it was placed in a vacuum sintering furnace and sintered at 1450℃ and 5Pa vacuum for 2h to obtain a cemented carbide matrix with a thickness of 4mm. The first mixture (thickness 100μm), the second mixture (thickness 80μm), and the third mixture (thickness 60μm) were spread evenly on the cemented carbide matrix in sequence. After each layer was spread, it was smoothed with a scraper. Finally, a polycrystalline diamond layer mixture (thickness 3mm) was spread. The whole thing was placed in a graphite mold and subjected to room temperature unidirectional static pressing at 15MPa for 2min to obtain a composite green body.

[0074] S3. The composite blank is placed in a six-sided press, high-purity Ar gas is introduced, the temperature is raised to 1450℃ at 6℃ / min, and the pressure is raised to 7GPa at 0.8GPa / min, and held at the temperature and pressure for 5min. After sintering, the temperature is lowered at 4℃ / min and the pressure is lowered to room temperature and atmospheric pressure at 0.4GPa / min, and the sintered body is removed. The sintered body is ground and polished with a diamond grinding wheel to control the surface roughness Ra of the polycrystalline diamond layer to 0.08μm and the bottom surface roughness Ra of the cemented carbide substrate to 0.2μm. The composite sheet is ultrasonically cleaned in 60℃ deionized water for 15min, and then immersed in anhydrous ethanol for 10min. After removal, it is dried in a drying oven at 80℃ and vacuum degree 5Pa for 2h to obtain the polycrystalline diamond composite sheet.

[0075] The polycrystalline diamond composite sheet prepared in this embodiment is processed into φ16mm×8mm PDC cutting teeth, which can be used for drilling bits.

[0076] Example 2

[0077] This embodiment is basically the same as Embodiment 1, except that in S1, the polycrystalline diamond layer raw material is mixed as follows: 40g of nanodiamond powder (particle size 50-80nm), 30g of micron diamond powder (particle size 2-4μm), and 10g of cubic boron nitride (particle size 3-6μm) are weighed and added to a planetary mixer. The mixture is stirred at 300r / min for 60min to obtain a mixed powder. 1.2L of 6wt% dilute nitric acid solution is added, and the mixture is stirred at 350r / min at 60℃ for 30min. After stirring, the mixture is filtered, and the filtrate is washed to pH=7. The filter cake is placed in a vacuum drying oven and dried at 80℃ and a vacuum degree ≤10Pa for 4h to obtain acidified powder. The acidified powder is evenly spread on a quartz glass slide, which is then placed in a plasma reaction chamber. After closing the chamber, a vacuum pump is started, and the vacuum is evacuated until the vacuum degree inside the chamber is ≤20Pa. Then, high-purity argon gas is introduced at a flow rate of 50sccm. The reaction chamber was purged three times, each time for 5 minutes. After purging, the reaction atmosphere was adjusted to an argon-ammonia mixture with a volume ratio of 9:1, and the total flow rate of the mixture was controlled at 30 sccm to maintain the vacuum degree of the reaction chamber at 40 Pa. The radio frequency plasma generator was started, and the processing power was set to 200 W, the processing temperature to 70 °C, and the processing time to 12 minutes to start the plasma activation treatment. After the treatment, the argon gas was kept in the state, and the reaction chamber was purged until the chamber temperature dropped to room temperature. The mixed powder was taken out and placed in a vacuum drying oven and dried at 80 °C for 2 hours to obtain the mixed powder. Then, 12 g of reinforcing agent and 8 g of Ni-Co binder (particle size ≤3 μm, Ni:Co mass ratio 7:3) were added and dispersed in 300 mL of anhydrous ethanol. The mixture was stirred at 400 r / min for 90 minutes and then placed in a vacuum drying oven at 80 °C for 6 hours to obtain the polycrystalline diamond layer mixture. The reinforcing agent was the one obtained in Preparation Example 1.

[0078] Example 3

[0079] This embodiment is basically the same as Example 1, except that the reinforcing agent in S1 is the one obtained in Preparation Example 2.

[0080] Example 4

[0081] This embodiment is basically the same as Example 1, except that the reinforcing agent in S1 is the one obtained in Preparation Example 3.

[0082] Example 5

[0083] This embodiment is basically the same as Example 1, except that the reinforcing agent in S1 is the one obtained in Preparation Example 4.

[0084] Example 6

[0085] This embodiment is basically the same as Example 1, except that the polycrystalline diamond layer raw materials are mixed as follows: 40g of nanodiamond powder (particle size 50-80nm), 30g of micron diamond powder (particle size 2-4μm), and 12g of cubic boron nitride (particle size 3-6μm) are weighed and added to a planetary mixer, and stirred at 300r / min for 60min to obtain a mixed powder; then 10g of reinforcing agent and 8g of Co-Ni-Si-B binder (particle size ≤3μm, Co 40wt%, Ni 35wt%, Si 15wt%, B 10wt%) are added and dispersed in 300mL of anhydrous ethanol, and stirred at 400r / min for 90min, and then placed in an 80℃ vacuum drying oven for 6h to obtain a polycrystalline diamond layer mixture; wherein the reinforcing agent is the one obtained in Preparation Example 1.

[0086] Example 7

[0087] In this embodiment, the polycrystalline diamond composite sheet is prepared according to the following steps:

[0088] S1, First Transition Layer: Weigh 60g of WC-Co powder (particle size 1-5μm, Co content 8wt% and WC particle size 1-3μm), 30g of micron-sized diamond powder (particle size 2-4μm), 7g of TiC powder (particle size 0.8-1.5μm), and 3g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the first mixture;

[0089] Second transition layer: Weigh 40g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 40g of micron diamond powder (particle size 2-4μm), 10g of nano diamond powder (particle size 50-80nm), 6g of TiC powder (particle size 0.8-1.5μm), and 4g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the second mixture;

[0090] Third transition layer: Weigh 26g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 50g of micron diamond powder (particle size 2-4μm), 15g of nano diamond powder (particle size 50-80nm), 6g of TiC powder (particle size 0.8-1.5μm), and 3g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the third mixture;

[0091] Polycrystalline diamond layer raw material mixing: Weigh 40g of nanodiamond powder (particle size 50-80nm), 30g of micron diamond powder (particle size 2-4μm), and 10g of cubic boron nitride (particle size 3-6μm) and add them to a planetary mixer. Stir at 300r / min for 60min to obtain a mixed powder. Add 1.2L of [unspecified material]. A 6wt% dilute nitric acid solution was stirred at 350 r / min for 30 min at 60℃. After stirring, the mixture was filtered, and the filtrate was washed until pH=7. The filter cake was placed in a vacuum drying oven and dried for 4 h at 80℃ and a vacuum degree ≤10 Pa to obtain acidified powder. The acidified powder was evenly spread on a quartz glass slide, which was then placed in a plasma reaction chamber. After the chamber was closed, the vacuum pump was started, and the vacuum degree inside the chamber was evacuated to ≤20 Pa. The reaction chamber was then purged three times with high-purity argon gas at a flow rate of 50 sccm, each time for 5 min. After purging, the reaction atmosphere was adjusted to a 9:1 volume ratio argon-ammonia mixture, and the total flow rate of the mixed gas was controlled at 30 sccm to maintain a stable vacuum degree of 40 Pa in the reaction chamber. The radio frequency plasma generator was started, and the processing power was set to 200W, the processing temperature to 70℃, and the processing time to 12min. The plasma activation treatment was then initiated. After the treatment, argon gas was kept flowing through the reaction chamber, which was then purged until the chamber temperature dropped to room temperature. The mixed powder was then removed and placed in a vacuum drying oven and dried at 80℃ for 2 hours to obtain the mixed powder. 12g of reinforcing agent and 8g of Co-Ni-Si-B binder (particle size ≤3μm, Co 38wt%, Ni 37wt%, Si 16wt%, B 9wt%) were added and dispersed in 300mL of anhydrous ethanol. The mixture was stirred at 400r / min for 90min and then placed in an 80℃ vacuum drying oven for 6 hours to obtain the polycrystalline diamond layer mixture. The reinforcing agent used was the one obtained in Preparation Example 5.

[0092] S2, 100g of WC-Co alloy powder (particle size 1-5μm, Co content 8wt% and WC particle size 1-3μm) was placed in a mold and cold-pressed under 250MPa pressure. Then it was placed in a vacuum sintering furnace and sintered at 1400℃ and 5Pa vacuum for 2h to obtain a cemented carbide matrix with a thickness of 4mm. The first mixture (thickness 100μm), the second mixture (thickness 80μm), and the third mixture (thickness 60μm) were spread evenly on the cemented carbide matrix in sequence. After each layer was spread, it was smoothed with a scraper. Finally, a polycrystalline diamond layer mixture (thickness 3mm) was spread. The whole thing was placed in a graphite mold and subjected to room temperature unidirectional static pressing at 10MPa for 2min to obtain a composite green body.

[0093] S3. The composite blank is placed in a six-sided press, high-purity Ar gas is introduced, the temperature is raised to 1450℃ at 6℃ / min, and the pressure is raised to 7GPa at 0.8GPa / min, and held at the temperature and pressure for 5min. After sintering, the temperature is lowered at 4℃ / min and the pressure is lowered to room temperature and atmospheric pressure at 0.4GPa / min, and the sintered body is removed. The sintered body is ground and polished with a diamond grinding wheel to control the surface roughness Ra of the polycrystalline diamond layer to 0.08μm and the bottom surface roughness Ra of the cemented carbide substrate to 0.2μm. The composite sheet is ultrasonically cleaned in 60℃ deionized water for 15min, and then immersed in anhydrous ethanol for 10min. After removal, it is dried in a drying oven at 80℃ and vacuum degree 5Pa for 2h to obtain the polycrystalline diamond composite sheet.

[0094] Example 8

[0095] In this embodiment, the polycrystalline diamond composite sheet is prepared according to the following steps:

[0096] S1, First Transition Layer: Weigh 70g of WC-Co powder (particle size 1-5μm, Co content 12wt% and WC particle size 1-3μm), 20g of micron-sized diamond powder (particle size 2-4μm), 5g of TiC powder (particle size 0.8-1.5μm), and 5g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the first mixture;

[0097] Second transition layer: Weigh 50g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 35g of micron diamond powder (particle size 2-4μm), 5g of nano diamond powder (particle size 50-80nm), 8g of TiC powder (particle size 0.8-1.5μm), and 2g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the second mixture;

[0098] Third transition layer: Weigh 30g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 50g of micron diamond powder (particle size 2-4μm), 15g of nano diamond powder (particle size 50-80nm), 4g of TiC powder (particle size 0.8-1.5μm), and 1g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the third mixture;

[0099] Polycrystalline diamond layer raw material mixing: Weigh 40g of nanodiamond powder (particle size 50-80nm), 30g of micron diamond powder (particle size 2-4μm), and 10g of cubic boron nitride (particle size 3-6μm) and add them to a planetary mixer. Stir at 300r / min for 60min to obtain a mixed powder. Add 1.2L of [unspecified material]. A 6wt% dilute nitric acid solution was stirred at 350 r / min for 30 min at 60℃. After stirring, the mixture was filtered, and the filtrate was washed until the pH reached 7. The filter cake was placed in a vacuum drying oven and dried for 4 h at 80℃ and a vacuum degree ≤10 Pa to obtain acidified powder. The acidified powder was evenly spread on a quartz glass slide, which was then placed in the plasma reaction chamber. After closing the chamber, the vacuum pump was started, and the chamber was evacuated until the vacuum degree was ≤20 Pa. Subsequently, the reaction chamber was purged three times with high-purity argon gas at a flow rate of 50 sccm, each time for 5 min. After purging, the reaction atmosphere was adjusted to a 9:1 volume ratio argon-ammonia mixture, with the total flow rate of the mixed gas controlled at 30 sccm, maintaining the vacuum degree of the reaction chamber at a stable 40 Pa. A radio frequency plasma generator was used, with the processing power set to 200W, the processing temperature to 70℃, and the processing time to 12min. The plasma activation treatment was then initiated. After the treatment, argon gas was kept flowing through the reaction chamber, which was then purged until the chamber temperature dropped to room temperature. The mixed powder was then removed and placed in a vacuum drying oven, where it was dried at 80℃ for 2 hours to obtain the mixed powder. 12g of reinforcing agent and 8g of Co-Ni-Si-B binder (particle size ≤3μm, Co 42wt%, Ni 33wt%, Si 14wt%, B 11wt%) were added and dispersed in 300mL of anhydrous ethanol. The mixture was stirred at 400r / min for 90min and then placed in an 80℃ vacuum drying oven for 6 hours to obtain the polycrystalline diamond layer mixture. The reinforcing agent used was the one obtained in Preparation Example 6.

[0100] S2, 100g of WC-Co alloy powder (particle size 1-5μm, Co content 12wt% and WC particle size 1-3μm) was placed in a mold and cold-pressed under 250MPa pressure. Then it was placed in a vacuum sintering furnace and sintered at 1500℃ and 5Pa vacuum for 2h to obtain a cemented carbide matrix with a thickness of 4mm. The first mixture (thickness 100μm), the second mixture (thickness 80μm), and the third mixture (thickness 60μm) were spread evenly on the cemented carbide matrix in sequence. After each layer was spread, it was smoothed with a scraper. Finally, a polycrystalline diamond layer mixture (thickness 3mm) was spread. The whole thing was placed in a graphite mold and subjected to room temperature unidirectional static pressing at 20MPa for 2min to obtain a composite green body.

[0101] S3. The composite blank is placed in a six-sided press, high-purity Ar gas is introduced, the temperature is raised to 1450℃ at 6℃ / min, and the pressure is raised to 7GPa at 0.8GPa / min, and held at the temperature and pressure for 5min. After sintering, the temperature is lowered at 4℃ / min and the pressure is lowered to room temperature and atmospheric pressure at 0.4GPa / min, and the sintered body is removed. The sintered body is ground and polished with a diamond grinding wheel to control the surface roughness Ra of the polycrystalline diamond layer to 0.08μm and the bottom surface roughness Ra of the cemented carbide substrate to 0.2μm. The composite sheet is ultrasonically cleaned in 60℃ deionized water for 15min, and then immersed in anhydrous ethanol for 10min. After removal, it is dried in a drying oven at 80℃ and vacuum degree 5Pa for 2h to obtain the polycrystalline diamond composite sheet.

[0102] Comparative Example 1

[0103] In this comparative example, the polycrystalline diamond composite sheet was prepared according to the following steps:

[0104] S1, First Transition Layer: Weigh 65g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 25g of micron-sized diamond powder (particle size 2-4μm), 7g of TiC powder (particle size 0.8-1.5μm), and 3g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the first mixture;

[0105] Second transition layer: Weigh 45g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 35g of micron diamond powder (particle size 2-4μm), 8g of nano diamond powder (particle size 50-80nm), 8g of TiC powder (particle size 0.8-1.5μm), and 4g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the second mixture;

[0106] Third transition layer: Weigh 30g of WC-Co powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm), 46g of micron diamond powder (particle size 2-4μm), 15g of nano diamond powder (particle size 50-80nm), 6g of TiC powder (particle size 0.8-1.5μm), and 3g of Mo2C powder (particle size 0.8-1.5μm), add them to a planetary mixer, and stir at 300r / min for 60min to obtain the third mixture;

[0107] Polycrystalline diamond layer raw material mixing: Weigh 40g of nanodiamond powder (particle size 50-80nm), 30g of micron diamond powder (particle size 2-4μm), and 12g of cubic boron nitride (particle size 3-6μm) and add them to a planetary mixer. Stir at 300r / min for 60min to obtain a mixed powder. Then add 5g of graphene (3-5 layers, particle size 5-10μm), 5g of single-walled carbon nanotubes (outer diameter 3-5nm, length 5-30μm), and 8g of Ni-Co binder (particle size ≤3μm, Ni:Co mass ratio 7:3). Add 300mL of anhydrous ethanol for dispersion and stir at 400r / min for 90min. Then place in an 80℃ vacuum drying oven and dry for 6h to obtain polycrystalline diamond layer mixture.

[0108] S2, 100g of WC-Co alloy powder (particle size 1-5μm, Co content 6wt% and WC particle size 1-3μm) was placed in a mold and cold-pressed under 250MPa pressure. Then it was placed in a vacuum sintering furnace and sintered at 1450℃ and 5Pa vacuum for 2h to obtain a cemented carbide matrix with a thickness of 4mm. The first mixture (thickness 100μm), the second mixture (thickness 80μm), and the third mixture (thickness 60μm) were spread evenly on the cemented carbide matrix in sequence. After each layer was spread, it was smoothed with a scraper. Finally, a polycrystalline diamond layer mixture (thickness 3mm) was spread. The whole thing was placed in a graphite mold and subjected to room temperature unidirectional static pressing at 15MPa for 2min to obtain a composite green body.

[0109] S3. The composite blank is placed in a six-sided press, high-purity Ar gas is introduced, the temperature is raised to 1450℃ at 6℃ / min, and the pressure is raised to 7GPa at 0.8GPa / min, and held at the temperature and pressure for 5min. After sintering, the temperature is lowered at 4℃ / min and the pressure is lowered to room temperature and atmospheric pressure at 0.4GPa / min, and the sintered body is removed. The sintered body is ground and polished with a diamond grinding wheel to control the surface roughness Ra of the polycrystalline diamond layer to 0.08μm and the bottom surface roughness Ra of the cemented carbide substrate to 0.2μm. The composite sheet is ultrasonically cleaned in 60℃ deionized water for 15min, and then immersed in anhydrous ethanol for 10min. After removal, it is dried in a drying oven at 80℃ and vacuum degree 5Pa for 2h to obtain the polycrystalline diamond composite sheet.

[0110] Performance testing

[0111] 1. The PDC cutting teeth (φ16mm×8mm) prepared in each embodiment and comparative example were subjected to impact resistance test according to the falling hammer method (the mass of the falling hammer used in the test was 1kg, the falling distance was 30cm, and the single impact potential energy was 2.94J). Five parallel samples were tested for each sample, and the cumulative impact energy when visible damage first appeared in each parallel sample was recorded (cumulative impact energy = single impact potential energy × number of impacts). Finally, the average value of the five parallel samples was taken as the impact resistance test result of the sample. The test results are shown in Table 1.

[0112] 2. The wear resistance of polycrystalline diamond composite sheets prepared in each embodiment and comparative example was tested according to standard JB / T3235-2013. A pin-disc wear tester was used, with the grinding disc made of 45# steel and W14 (1000 mesh) SiC abrasive cloth fixed on the surface. The test load was 30N, the grinding disc speed was 300r / min, and the wear stroke was 1000m. The test was conducted at room temperature and normal pressure. The test results are shown in Table 1.

[0113] 3. The polycrystalline diamond composite sheets prepared in each embodiment and comparative example were used to make SNMG120404-M tool specimens with a tool tip radius of R0.4. According to GB / T16461-1996 standard, 6061-T6 aluminum alloy test bar material (50mm in diameter and 300mm in length) was intermittently cut on a CNC lathe with intermittent grooves (groove width 5mm, groove spacing 20mm, groove depth 1.5mm). The cutting speed was 830m / min, the cutting depth was 0.15mm, and the feed rate was 0.15mm / r. The machine was stopped every 500m of cutting. After cooling to room temperature, the tool was disassembled, and the wear on the flank face was measured with a tool microscope. When the wear was close to 0.20mm, the measurement interval was shortened to once every 200m of cutting. When the dulling standard was reached (i.e., the flank face wear Vb=0.25mm), the cutting mileage of the specimen at this time was checked, and the results were recorded in Table 1.

[0114] Table 1 Performance test data of Examples 1-8 and Comparative Example 1

[0115]

[0116] As can be seen from Example 1 and Comparative Example 1, and referring to Table 1, Example 1 uses a three-dimensional network reinforcement formed by nitrogen-boron-doped graphene bonded to amino carbon nanotubes. The bonding design avoids carbon material agglomeration, and nitrogen-boron doping optimizes the interfacial compatibility with diamond, cubic boron nitride, and the binder. The interwoven network structure of sheets and tubes can efficiently transfer loads, inhibit crack propagation, and play a crack bridging role. In contrast, Comparative Example 1 directly uses unbonded, undoped single graphene and carbon nanotubes, which easily form agglomerates and become stress concentration points, making it impossible to construct a uniform reinforcement network, resulting in weak interfacial bonding and insufficient structural density. This makes Example 1 significantly superior to Comparative Example 1 in impact resistance and wear resistance, and also demonstrates a longer service life in actual cutting conditions, fully demonstrating the key role of the reinforcement design in overcoming the defects of the prior art and improving the performance of polycrystalline diamond composite sheets.

[0117] Combining Examples 1 and 2 and referring to Table 1, it can be seen that Example 2 additionally subjected the mixed powder of nanodiamond, microdiamond, and cubic boron nitride to acidification and ammonia plasma treatment, while Example 1 did not employ this surface modification process. Acidification effectively removed residual impurities from the powder surface and purified the active sites. Ammonia plasma treatment introduced amino groups and micro / nano rough structures onto the powder surface, which not only form stable chemical bonds and strong hydrogen bonds with the active groups on the reinforcing agent surface but also form coordination bonds with metal ions in the binder, constructing a strong bonding network across the entire interface. This significantly improved the dispersion uniformity and interfacial bonding strength of the multi-component mixture, reducing the risk of particle shedding and interfacial separation during sintering and service. This resulted in Example 2 exhibiting superior impact resistance and wear resistance compared to Example 1, with a longer service life under actual cutting conditions. This fully demonstrates the synergistic effect of the powder surface modification process with the reinforcing agent and binder, further verifying the effectiveness of this modification design in optimizing the overall performance of polycrystalline diamond composite sheets.

[0118] Combining Examples 1 and 3 and referring to Table 1, it can be seen that the graphene in Example 3, after chemical exfoliation to obtain few-layer graphene, underwent additional oxygen plasma activation treatment, while Example 1 did not use this activation process. Oxygen plasma activation, under mild conditions, precisely introduces oxygen-containing active functional groups and controllable edge defects to the graphene surface. This avoids the damage to the graphene lattice caused by traditional chemical oxidation and significantly increases the density of surface active sites, making subsequent nitrogen-boron doping more uniform and the bonding with aminated carbon nanotubes stronger. This, in turn, results in better dispersion and interfacial bonding strength of the three-dimensional network reinforcing agent. In contrast, the ordinary graphene in Example 1 has fewer surface active sites, leading to a slightly weaker synergistic effect with other components. This makes Example 3 superior to Example 1 in impact resistance, wear resistance, and actual cutting service life, fully demonstrating that after oxygen plasma activation treatment, graphene can synergize with the bonding and doping design of the reinforcing agent, further optimizing the overall performance of the polycrystalline diamond composite sheet.

[0119] Combining Examples 3 and 4 and referring to Table 1, it can be seen that in Example 4, after obtaining few-layer graphene through chemical exfoliation, an additional high-temperature expansion treatment was added before oxygen plasma activation, while in Example 3, only oxygen plasma activation was used without expansion treatment. Expansion treatment effectively widens the interlayer spacing of graphene sheets, weakens the tendency for aggregation between sheets, and increases the specific surface area. This allows the oxygen-containing active sites generated by subsequent oxygen plasma activation to be more uniformly distributed on the sheet surface and between layers. It also facilitates the penetration and diffusion of active species during nitrogen-boron doping and creates more flexible space for tubular structure insertion when bonding with aminated carbon nanotubes, helping to form a more regular, continuous, and agglomerated three-dimensional network reinforcing agent. In contrast, the graphene in Example 3, lacking expansion treatment, is prone to localized stacking of sheets, resulting in slightly weaker network uniformity and interfacial bonding integrity of the reinforcing agent. This makes Example 4 superior to Example 3 in terms of impact resistance, wear resistance and actual cutting service life, which fully demonstrates that the combined treatment of graphene expansion and oxygen plasma activation can give fuller play to the synergistic effect of bonding with reinforcing agents and doping design compared with single oxygen plasma activation, and further optimize the structural stability and comprehensive service performance of polycrystalline diamond composite sheets.

[0120] Combining Examples 1 and 6 and referring to Table 1, it can be seen that Example 6 used a Co-Ni-Si-B quaternary composite binder, while Example 1 used a traditional Ni-Co binary binder. The quaternary binder, through the synergistic design of the tough matrix (Co-Ni) and the hard phase dispersion reinforcement (Si-B), retains the excellent toughness, catalytic activity, and thermal expansion coefficient matching of the Ni-Co binder. The introduced Si element improves the wettability and interfacial compatibility of the binder with diamond, cubic boron nitride, and reinforcing agents. The B element forms a hard boride phase with Co and Ni, dispersed in the binder matrix, significantly improving the overall hardness and wear resistance of the polycrystalline diamond layer. This multi-component synergistic effect allows the polycrystalline diamond composite sheet of Example 6 to maintain high impact toughness while exhibiting better wear resistance and service life under actual cutting conditions than that of Example 1, fully verifying the effectiveness of the Co-Ni-Si-B quaternary composite binder in improving the overall performance of PDC.

[0121] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method of producing a polycrystalline diamond compact, characterized by, The method comprises the following steps: S1, WC-Co alloy powder is put into a mold and cold-pressed into shape under a pressure of 200-300 MPa, and then sintered at 1400-1500 DEG C under a vacuum degree of less than or equal to 10 Pa for 2 hours to obtain a cemented carbide substrate; S2, nano diamond powder, micron diamond powder and cubic boron nitride are uniformly mixed, and then a reinforcing agent and a binder are added and uniformly mixed to obtain a polycrystalline diamond layer mixture; the reinforcing agent is nitrogen-boron doped graphene bonded amino carbon nanotubes; S3, the gradient transition layer raw material and the polycrystalline diamond mixture are uniformly spread on the surface of the cemented carbide substrate in sequence, and then the composite blank is obtained by placing the composite blank in a graphite mold under a pressure of 10-20 MPa; and the polycrystalline diamond composite sheet is obtained by sintering the composite blank.

2. The method of producing a polycrystalline diamond compact according to claim 1, wherein The preparation method of the nitrogen-boron doped graphene bonded amino carbon nanotubes comprises the following steps: (1) The carbon nanotubes are subjected to amino plasma treatment at 120-180 W for 20-30 min to obtain amino carbon nanotubes; (2) The graphene and aminoborane are added to anhydrous ethanol in a mass ratio of 10: (2-4), ultrasonic dispersion is performed to form a suspension, the suspension is rotary evaporated and dried to obtain a precursor, and the precursor is annealed and doped at 700-800 DEG C to obtain nitrogen-boron doped graphene; (3) The amino carbon nanotubes and the nitrogen-boron doped graphene are added to anhydrous ethanol in a mass ratio of (1-3): 1, ultrasonic treatment is performed to obtain a dispersion liquid, and the dispersion liquid is stirred and reacted, washed, centrifuged and dried to obtain nitrogen-boron doped graphene bonded amino carbon nanotubes.

3. The method of producing a polycrystalline diamond compact according to claim 2, wherein The graphene is obtained by preparing few-layer graphene from graphite by using a chemical exfoliation method and then performing oxygen plasma activation treatment.

4. The method of producing a polycrystalline diamond compact according to claim 2, wherein The graphene is obtained by preparing few-layer graphene from graphite by using a chemical exfoliation method, performing expansion treatment first, and then performing oxygen plasma activation treatment.

5. The method of producing a polycrystalline diamond compact as claimed in claim 2, wherein In step (2), the precursor is subjected to staged annealing during the annealing and doping, specifically: increasing the temperature to 350-400 DEG C at a rate of 5 DEG C / min, and maintaining the temperature for 30-40 min; then increasing the temperature to 550-600 DEG C at a rate of 5 DEG C / min, and maintaining the temperature for 60-90 min; finally, increasing the temperature to 700-800 DEG C at a rate of 5 DEG C / min, and maintaining the temperature for 90-120 min.

6. The method of producing a polycrystalline diamond compact as claimed in claim 1, wherein The Co content of the WC-Co alloy powder is 6-12 wt%; The polycrystalline diamond layer comprises the following raw materials: nano diamond powder 30-50 wt%, micron diamond powder 20-40 wt%, reinforcing agent 8-15 wt%, cubic boron nitride 5-15 wt%, and binder 5-12 wt%; The binder is a Co-Ni-Si-B quaternary composite binder, and the mass fractions of the components are as follows: Co 38-42 wt%, Ni 33-37 wt%, Si 14-16 wt%, and B 9-11 wt%.

7. The method of producing a polycrystalline diamond compact as claimed in claim 1, wherein The gradient transition layer comprises a first transition layer, a second transition layer and a third transition layer from bottom to top; The first transition layer comprises the following raw materials: WC-Co powder 60-70 wt%, micron diamond powder 20-30 wt%, TiC powder 5-10 wt%, and Mo2C powder 3-5 wt%; The second transition layer comprises the following raw materials: WC-Co powder 40-50wt%, micron diamond powder 30-40wt%, nano diamond powder 5-10wt%, TiC powder 3-8wt%, Mo2C powder 2-4wt%; The third transition layer comprises the following raw materials: WC-Co powder 20-30wt%, micron diamond powder 40-50wt%, nano diamond powder 10-15wt%, TiC powder 3-6wt%, Mo2C powder 1-3wt%.

8. The method of producing a polycrystalline diamond compact of claim 1, wherein In S2, the nano diamond powder, the micron diamond powder and the cubic boron nitride are mixed, and then subjected to acidization and then amino plasma treatment.

9. A polycrystalline diamond compact characterised in that, The polycrystalline diamond compact is prepared by the method of any one of claims 1-8.

10. Use of the polycrystalline diamond compact according to claim 9, characterized in that The polycrystalline diamond compact is used in oil and gas drilling, geological exploration, superhard cutters or wear-resistant tools.

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