High-thermal-stability particle size gradient PCD compact and method of making same

Abstract

This invention discloses a high thermal stability particle size gradient PCD composite sheet and its preparation method. The particle size gradient PCD composite sheet is divided into a cemented carbide substrate, a diamond particle size gradient layer, and a polycrystalline diamond layer from bottom to top. The diamond particle size gradient layer is composed of N sublayers of diamond microparticles with different particle sizes, and the particle size gradient of the diamond microparticles increases or decreases along the direction away from the cemented carbide substrate. The particle size gradient PCD composite sheet is obtained by photopolymerization printing. This invention controls the diffusion of Co by setting multi-level diamond particle size gradients, reduces the Co content in the polycrystalline diamond layer, and improves the thermal stability of the composite sheet. Furthermore, through 3D printing technology, high precision, high surface quality, and complex geometric structure preparation are achieved. Combining traditional high temperature and high pressure synthesis technology, this invention overcomes the limitations of traditional PCD composite sheet manufacturing processes and can realize diamond particle size gradient structures in a high-efficiency and low-cost manner.

Description

Technical Field

[0001] This invention belongs to the field of superhard tool preparation technology, specifically relating to a high thermal stability particle size gradient PCD composite sheet and its preparation method. Background Technology

[0002] Polycrystalline diamond (PCD) composite sheets offer advantages such as high hardness and strong wear resistance. PCD inserts, made by cutting and welding large-diameter PCD composite sheets onto a cemented carbide cutting tool body, exhibit significantly superior cutting performance compared to traditional cemented carbide and ceramic inserts, and are widely used in the machining of precision components in aerospace and new energy vehicle fields. However, during cutting, the Co in the polycrystalline diamond layer catalyzes the graphitization transformation of diamond under high-temperature conditions, leading to the destruction of the diamond crystal structure and thus accelerating the wear and failure of PCD inserts. Conventional PCD composite sheets are formed by sintering diamond micropowder and a cemented carbide substrate under high temperature and pressure in a single process. Liquid Co in the cemented carbide matrix diffuses and sweeps across the polycrystalline diamond layer, catalyzing the formation of D-D bonds in the diamond layer. However, since the diffusion process is difficult to control precisely, excessive Co migration into the polycrystalline diamond layer can lead to Co enrichment or deficiency in the interface region, affecting the thermal stability and interfacial bonding strength of the PCD composite sheet. Therefore, it is crucial to improve the thermal stability of the PCD composite sheet by rationally controlling the content and distribution of Co in the polycrystalline diamond layer, controlling the catalytic process of Co on diamond, and preventing excessive Co migration. Summary of the Invention

[0003] To overcome the shortcomings of existing PCD cutting tools, such as low thermal stability and cracking and chipping caused by diamond graphitization at high temperatures, the first objective of this invention is to provide a high-thermal-stability particle size gradient PCD composite sheet. The particle size gradient PCD composite sheet provided by this invention, by setting a diamond particle size gradient layer, can rationally control the content and distribution of Co in the polycrystalline diamond layer, effectively improving the thermal stability of the PCD cutting tool. Furthermore, the particle size gradient can solve the brittle fracture caused by excessive Co migration near the interface between the cemented carbide substrate and the polycrystalline diamond layer, improving the impact toughness of the PCD composite sheet and extending the service life of the PCD cutting tool.

[0004] The second objective of this invention is to provide a method for preparing a high thermal stability PCD composite sheet with a particle size gradient. The preparation method provided by this invention can accurately control the particle size and distribution of diamond particles, thereby optimizing the microstructure of the PCD composite sheet, significantly improving its thermal stability and impact toughness, and also greatly increasing production efficiency.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The present invention provides a high thermal stability particle size gradient PCD composite sheet, wherein the particle size gradient PCD composite sheet is divided into a cemented carbide substrate, a diamond particle size gradient layer, and a polycrystalline diamond layer from bottom to top;

[0007] The diamond particle size gradient layer is composed of N sublayers of diamond microparticles with different particle sizes, and the particle size gradient of the diamond microparticles increases or decreases along the direction away from the cemented carbide substrate.

[0008] The particle size gradient PCD composite sheet provided by this invention has a diamond particle size gradient layer composed of N sublayers of diamond micro powder with different particle sizes. During the synthesis of the composite sheet, when the temperature rises above the melting point of cobalt and high pressure is applied, cobalt changes from solid to liquid and flows. Co in the cemented carbide matrix will sweep and diffuse into the diamond layer. Setting the particle size gradient can control the sweeping process of Co and avoid excessive Co migration to the working layer, which will affect the thermal stability.

[0009] In a preferred embodiment, the mass fraction of Co in the cemented carbide substrate is 7-15%.

[0010] In a preferred embodiment, N is 2 to 6, and more preferably 4 to 5.

[0011] In a preferred embodiment, the thickness of the diamond particle size gradient layer is 0.1–0.4 mm, and the thickness of any sublayer is 0.02–0.2 mm.

[0012] In a preferred embodiment, the average particle size difference between any two adjacent sublayers in the diamond particle size gradient layer is 4~25μm, preferably 5~10μm.

[0013] In a preferred embodiment, in the diamond particle size gradient layer, the particle size gradient of the diamond micropowder decreases along the direction away from the cemented carbide substrate, and in the Nth sublayer, the average particle size of the diamond micropowder is 1μm to 25μm.

[0014] Experiments have shown that when the diamond particle size gradient layer is in a direction away from the cemented carbide substrate, the reduction in the particle size gradient of diamond microparticles not only has the function of regulating Co migration, but also significantly enhances the bonding strength of the interface by increasing the bonding interface area.

[0015] In the invention, the first sublayer is the sublayer in contact with the hard alloy substrate, while the Nth sublayer refers to the sublayer in contact with the polycrystalline diamond layer.

[0016] In a preferred embodiment, the particle size of the diamond powder in the polycrystalline diamond layer is 10–50 μm. As the working layer, the polycrystalline diamond layer ensures that the particle size of the diamond powder remains within this range during actual operation. Further optimization can be made based on the specific performance requirements of the cutting tool and the characteristics of the material being processed.

[0017] This invention also provides a method for preparing a high thermal stability particle size gradient PCD composite sheet. Diamond micro powders of different particle sizes in each sub-layer of the diamond particle size gradient layer and in the polycrystalline diamond layer are respectively mixed with excipients to obtain N+1 parts of photocurable slurry. The N+1 parts of photocurable slurry are sequentially photocured and 3D printed to obtain a green blank. The green blank is assembled with a cemented carbide substrate and then degreased to obtain a degreased blank. The degreased blank is then synthesized under high temperature and high pressure to obtain the final product.

[0018] The excipients consist of resin monomers, photoinitiators, and additives.

[0019] Diamond has a chemically inert surface and is difficult to react with other materials at room temperature. Traditional manufacturing processes cannot achieve micron-sized particle size gradient structures and cannot guarantee the uniformity of powder distribution. Even direct-write molding, due to its physical extrusion nature, has been found to be insufficient in controlling micron-sized particle distribution, preventing structural collapse, and maintaining green strength, thus failing to ensure accurate printing of particle size gradient structures. This invention utilizes photopolymerization 3D printing technology to accurately control the particle size and distribution of diamond particles, thereby optimizing the microstructure of PCD composite sheets, significantly improving their thermal stability and impact toughness, and also greatly increasing production efficiency.

[0020] In actual operation, the resin monomer is first mixed with the photoinitiator to obtain liquid photosensitive resin. The liquid photosensitive resin is divided into N+1 parts and mixed with diamond micro powder of different particle sizes. Then, additives are added to each part to obtain N+1 parts of photocurable slurry.

[0021] In a preferred embodiment, the resin monomer is selected from at least one of isooctyl acrylate, methoxyethyl acrylate, ethyl methacrylate, isobutyl methacrylate, dipropylene glycol diacrylate, o-phenylphenoxyethyl acrylate, cyclotrimethylolpropane triacrylate, ethoxyphenol acrylate, and epoxy acrylate oligomers.

[0022] In a preferred embodiment, the photoinitiator is selected from at least one of acetophenone, benzoin dimethyl ether, and isopropylthioxanthraphenone.

[0023] In a preferred embodiment, the additive is composed of polyvinyl butyral, polyethylene glycol diacrylate, methoxyphenol, and hydroquinone, in a mass ratio of 0.05-0.5:0.05-0.5:0.05-0.5:0.05-0.5, preferably 0.2-0.5:0.1-0.5:0.4-0.5:0.5.

[0024] Experiments revealed that adding the aforementioned additives resulted in the optimal printing effect. Polyvinyl butyral exhibited excellent film-forming and adhesive properties, improving the interfacial bonding between the resin system and diamond micropowder. Polyethylene glycol diacrylate demonstrated good dilution properties, reducing slurry viscosity and improving slurry flowability. Methoxyphenol and hydroquinone captured free radicals in the slurry system, preventing premature resin polymerization and thus ensuring the stability of the printing slurry.

[0025] This invention employs photopolymerization molding, which ensures the stability of the slurry through a specific slurry composition and improves the accuracy of photopolymerization printing. This ensures that diamond particles are precisely arranged in the green body according to a preset gradient, and provides a more complete diamond particle size gradient skeleton for subsequent high-temperature and high-pressure sintering.

[0026] In a preferred embodiment, the excipients, by mass percentage, consist of: 90-98% resin monomer, 0.5-5% photoinitiator, and 0.25-5% additives.

[0027] In a further preferred embodiment, the excipients, by mass percentage, consist of the following: 95-98% resin monomer, 0.5-3% photoinitiator, and 0.25-2.5% additives.

[0028] In this invention, all portions of the photocurable slurry use additives with the same composition.

[0029] In the preferred embodiment, the volume fraction of diamond micro powder in N+1 parts of the photocurable slurry is 40-75%, preferably 60-75%.

[0030] Experiments have shown that controlling the mass fraction of diamond powder in each slurry within the above-mentioned range yields the best printing results. If the mass fraction of diamond powder is too low, it will cause misalignment of the particle size gradient structure during the synthesis process.

[0031] In a preferred embodiment, the parameters for photopolymer 3D printing are as follows: exposure time: 3–60 s, printing layer thickness: 20–100 μm, light intensity: 50–1000 mW / cm², and wavelength: 100–500 nm.

[0032] In a further preferred embodiment, the parameters for the photopolymer 3D printing are as follows: exposure time: 10-30s, printing layer thickness: 20-40μm, light intensity: 60-150 mW / cm², and wavelength: 120-400nm.

[0033] By using the above photocuring parameters, the degree of resin curing can be ensured, resulting in excellent interlayer bonding strength.

[0034] In actual operation, models of each sublayer in the diamond particle size gradient layer and the polycrystalline diamond layer are drawn in the computer. The models are then imported into the slicing software to set the printing parameters. A photopolymerization 3D printer with a multi-feed system is used to automatically switch the corresponding slurry according to the slicing program, expose and form layer by layer, and print a PCD composite green sheet with a particle size gradient structure. Then, the excess slurry is blown off the green sheet, and after assembling it with a cemented carbide substrate, it is placed in a high-temperature degreasing furnace for degreasing.

[0035] In a preferred embodiment, the degreasing process is as follows: first, the temperature is increased from room temperature to 60-150°C at a heating rate of 0.1-5°C / min, and held for 30-180 min; then, the temperature is increased to 160-250°C at a heating rate of 0.1-3°C / min, and held for 120-240 min; next, the temperature is increased to 300-350°C at a heating rate of 0.1-1°C / min, and held for 30-180 min; finally, the temperature is increased to 400-450°C at a heating rate of 0.1-3°C / min, and held for 60-120 min, and then cooled to room temperature in the furnace.

[0036] In the preferred embodiment, the high-temperature and high-pressure synthesis is carried out at a temperature of 1400℃~2000℃, a pressure of 5~8GPa, and a time of 240s~700s.

[0037] In actual operation, the degreased preform is placed in a six-sided press for high-temperature and high-pressure synthesis. After the synthesis is completed, the pressure is slowly released to obtain a particle size gradient PCD composite sheet.

[0038] Beneficial effects

[0039] This invention provides a high thermal stability particle size gradient PCD composite sheet. A gradient layer with different diamond particle sizes is set between the cemented carbide and the PCD layer. Its particle size structure can regulate the migration behavior of Co element from the cemented carbide substrate to the polycrystalline diamond layer during sintering, effectively reducing the Co content in the polycrystalline diamond layer and thus improving its thermal stability. At the same time, it avoids the formation of brittle fracture zones in the cemented carbide substrate due to excessive Co migration, improves the overall impact toughness of the composite sheet, and enhances the interfacial bonding strength.

[0040] This invention uses DLP3D printing technology to manufacture PCD composite preforms with particle size structure, which can achieve rapid manufacturing of high precision and complex structures, significantly shorten the product development and performance verification cycle, and reduce the overall production cost while improving production efficiency. Attached Figure Description

[0041] Figure 1 A schematic diagram of the PCD composite sheet described in this invention.

[0042] Figure 2 A schematic diagram of the particle size gradient structure of the PCD composite sheet described in this invention. Detailed Implementation

[0043] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments.

[0044] Example 1

[0045] The raw materials used are diamond micron powder, diamond photopolymer DLP printing paste with different particle sizes, and cemented carbide substrate. The diamond micron powder in the PCD layer has a particle size of 10 micrometers, the cemented carbide substrate contains 9% Co, the diamond concentration in the diamond photopolymer printing paste is 70%, and the liquid photosensitive resin and additives include: 60% isooctyl acrylate, 35% methoxyethyl acrylate, 2% epoxy acrylate oligomer, 1% acetophenone, 0.5% polyvinyl butyral, 0.5% polyethylene glycol diacrylate, 0.5% methoxyphenol, and 0.5% hydroquinone.

[0046] The total thickness of the diamond particle size gradient layer is 0.2 mm, with each layer being 0.05 mm thick. From the cemented carbide substrate to the polycrystalline diamond layer, the diamond microparticle size gradient is as follows:

[0047] The first layer of diamond micro powder has a particle size of 50μm;

[0048] The second layer of diamond micro powder has a particle size of 40μm;

[0049] The third layer of diamond micro powder has a particle size of 30μm;

[0050] The fourth layer of diamond micro powder has a particle size of 20μm;

[0051] This example provides a 3D printing fabrication process for high thermal stability particle size gradient PCD composite sheets, including the following steps:

[0052] 1) Slurry preparation: Mix diamond micro powder with photosensitive resin, photoinitiator and additives evenly according to the requirements to prepare photocurable printing slurries with corresponding diamond particle sizes.

[0053] 2) Printing parameter settings: Exposure time: 10s, printing layer thickness: 25μm, light intensity: 125 mW / cm², wavelength: 400nm.

[0054] 3) Printing: Add diamond photocurable printing paste of different particle sizes to the DLP printer in batches, and print the green blanks of each structural layer of the particle size gradient PCD composite sheet by matching the corresponding printing model in sequence.

[0055] 4) Hot degreasing: After the green body is assembled, it is placed in a vacuum degreasing furnace for hot degreasing. First, the temperature is raised from room temperature to 100℃ at 5℃ / min and held at 100℃ for 0.5h; then the temperature is raised from 100℃ to 200℃ at 1℃ / min and held at 200℃ for 1h; then the temperature is raised from 200℃ to 350℃ at 0.5℃ / min and held at 350℃ for 1h; finally, the temperature is raised from 350℃ to 450℃ at 0.5℃ / min and held at 450℃ for 1h before being cooled with the furnace.

[0056] 5) High temperature and high pressure synthesis: The degreased parts and hard alloy substrate are put into the mold and sintered in a six-sided press at a temperature of 1500℃ and a pressure of 5GPa for 240s. After sintering, the pressure is slowly released to obtain a particle size gradient PCD composite sheet.

[0057] After coarse grinding and polishing, the particle size gradient PCD composite sheet obtained in Example 1 was subjected to wear resistance, thermal stability and bending strength tests. The relative wear ratio was ≥500,000 when measured by silicon carbide grinding wheel method. In terms of thermal stability, after the sample was heated at 700℃ in a protective atmosphere for 20 minutes, no cracks, delamination or carbonization of the diamond layer were observed. In terms of mechanical properties, the bending strength was tested according to the three-point bending method, and the results showed that its bending strength was 1200MPa, which is better than the average level of commercial PDC products.

[0058] Example 2

[0059] The raw materials used are diamond micron powder, diamond photopolymer DLP printing paste with different particle sizes, and cemented carbide substrate. The diamond micron powder in the PCD layer has a particle size of 30 micrometers, the cemented carbide substrate contains 15% Co, the diamond concentration in the diamond photopolymer printing paste is 75%, and the liquid photosensitive resin and additives include: 30% isooctyl acrylate, 44% methoxyethyl acrylate, 24% epoxy acrylate oligomer, 0.8% isopropylthioxanthone, 0.2% polyvinyl butyral, 0.1% polyethylene glycol diacrylate, 0.4% methoxyphenol, and 0.5% hydroquinone.

[0060] The total thickness of the diamond particle size gradient layer is 0.1 mm, with each layer being 0.05 mm thick. From the cemented carbide substrate to the polycrystalline diamond layer, the diamond microparticle size gradient is as follows:

[0061] The first layer of diamond micro powder has a particle size of 25μm;

[0062] The second layer of diamond micro powder has a particle size of 20μm;

[0063] The third layer of diamond micro powder has a particle size of 15μm;

[0064] The fourth layer of diamond micro powder has a particle size of 10μm;

[0065] This example provides a 3D printing fabrication process for high thermal stability particle size gradient PCD composite sheets, including the following steps:

[0066] 1) Slurry preparation: Mix diamond micro powder with photosensitive resin, photoinitiator and additives evenly according to the requirements to prepare photocurable printing slurries with corresponding diamond particle sizes.

[0067] 2) Printing parameter settings: Exposure time: 30s, printing layer thickness: 20μm, light intensity: 60mW / cm², wavelength: 120nm.

[0068] 3) Printing: Add diamond photocurable printing paste of different particle sizes to the DLP printer in batches, and print the green blanks of each structural layer of the particle size gradient PCD composite sheet by matching the corresponding printing model in sequence.

[0069] 4) Hot degreasing: After the green body is assembled, it is placed in a vacuum degreasing furnace for hot degreasing. First, the temperature is raised from room temperature to 120°C at 5°C / min and held at 120°C for 1 hour. Then, the temperature is raised from 120°C to 180°C at 0.5°C / min and held at 180°C for 1.5 hours. Next, the temperature is raised from 180°C to 350°C at 0.5°C / min and held at 350°C for 0.5 hours. Finally, the temperature is raised from 350°C to 400°C at 1°C / min and held at 400°C for 1 hour before being cooled in the furnace.

[0070] 5) High temperature and high pressure synthesis: The degreased parts and hard alloy substrate are put into the mold and sintered in a six-sided press at a temperature of 1550℃, a pressure of 7GPa, and a sintering time of 300s. After sintering, the pressure is slowly released to obtain a particle size gradient PCD composite sheet.

[0071] After coarse grinding and polishing, the particle size gradient PCD composite sheet obtained in Example 2 was subjected to wear resistance, thermal stability and bending strength tests. The relative wear ratio was ≥520,000 when measured by silicon carbide grinding wheel method. In terms of thermal stability, after the sample was heated at 750℃ in a protective atmosphere for 15 minutes, no cracks, delamination or carbonization of the diamond layer were observed. In terms of mechanical properties, the bending strength was tested according to the three-point bending method, and the results showed that its bending strength was 1400MPa, which is better than the average level of commercial PDC products.

[0072] Comparative Example 1

[0073] Other conditions remained the same as in Example 1, except for the photopolymerization printing parameters: the light intensity was set to 40 mW / cm² and the wavelength to 100 nm. Experimental results showed that due to insufficient resin curing under this parameter combination, the interlayer bonding was weak, causing the particle size gradient layer preform to collapse during printing, resulting in the failure to obtain a complete molded part.

[0074] Comparative Example 2

[0075] The other conditions are the same as in Example 2, except that the diamond concentration in the printing paste is different. The diamond concentration in the paste is 25%. After degreasing, the green body shows bulging and cracking, which may cause misalignment of the particle size gradient structure during the synthesis process, making it impossible to synthesize high-quality PCD composite sheets.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high thermal stability particle size gradient PCD composite sheet, characterized in that: The particle size gradient PCD composite sheet is divided into a hard alloy substrate, a diamond particle size gradient layer, and a polycrystalline diamond layer from bottom to top. The diamond particle size gradient layer is composed of N sublayers of diamond microparticles with different particle sizes, and the particle size gradient of the diamond microparticles increases or decreases along the direction away from the cemented carbide substrate.

2. The high thermal stability particle size gradient PCD composite sheet according to claim 1, characterized in that: In the hard alloy substrate, the mass fraction of Co is 7-15%.

3. The high thermal stability particle size gradient PCD composite sheet according to claim 1, characterized in that: The value of N is 2 to 6; The thickness of the diamond grain size gradient layer is 0.1–0.4 mm, and the thickness of any sublayer is 0.02–0.2 mm. In the diamond particle size gradient layer, the average particle size difference between any two adjacent sub-layers is 4~25μm. In the diamond particle size gradient layer, the particle size gradient of diamond powder decreases along the direction away from the cemented carbide substrate, and in the Nth sublayer, the average particle size of diamond powder is 1μm to 25μm.

4. The high thermal stability particle size gradient PCD composite sheet according to claim 1, characterized in that: The diamond microparticles in the polycrystalline diamond layer have a particle size of 10–50 μm.

5. A high thermal stability particle size gradient PCD composite sheet according to any one of claims 1-4, characterized in that: Diamond micro powders of different particle sizes in each sublayer of the diamond particle size gradient layer and in the polycrystalline diamond layer are respectively prepared and mixed with auxiliary materials to obtain N+1 parts of photocurable slurry. The N+1 parts of photocurable slurry are sequentially photocured 3D printed to obtain a green blank. The green blank is assembled with a cemented carbide substrate and then degreased to obtain a degreased blank. The degreased blank is then synthesized under high temperature and high pressure to obtain the final product. The excipients consist of resin monomers, photoinitiators, and additives.

6. The high thermal stability particle size gradient PCD composite sheet according to claim 5, characterized in that: The resin monomer is selected from at least one of isooctyl acrylate, methoxyethyl acrylate, ethyl methacrylate, isobutyl methacrylate, dipropylene glycol diacrylate, o-phenylphenoxyethyl acrylate, cyclotrimethylolpropane triacrylate, ethoxyphenol acrylate, and epoxy acrylate oligomers. The photoinitiator is selected from at least one of acetophenone, benzoin dimethyl ether, and isopropylthioxanthone. The additive is composed of polyvinyl butyral, polyethylene glycol diacrylate, methoxyphenol, and hydroquinone, in a mass ratio of 0.05-0.5: 0.05-0.5: 0.05-0.5: 0.05-0.5; The excipients, by mass percentage, consist of: 90-98% resin monomer, 0.5-5% photoinitiator, and 0.25-5% additives.

7. The high thermal stability particle size gradient PCD composite sheet according to claim 5, characterized in that: In N+1 parts of the light-cured slurry, the volume fraction of diamond micro powder is 40-75%.

8. The high thermal stability particle size gradient PCD composite sheet according to claim 5, characterized in that: The parameters for the photopolymer 3D printing are as follows: exposure time: 3-60s, printing layer thickness: 20-100μm, light intensity: 50-1000 mW / cm², wavelength: 100-500nm.

9. A high thermal stability particle size gradient PCD composite sheet according to claim 5, characterized in that: The degreasing process is as follows: first, the temperature is increased from room temperature to 60-150℃ at a heating rate of 0.1-5℃ / min, and held for 30-180 min; then, the temperature is increased to 160-250℃ at a heating rate of 0.1-3℃ / min, and held for 120-240 min; then, the temperature is increased to 300-350℃ at a heating rate of 0.1-1℃ / min, and held for 30-180 min; finally, the temperature is increased to 400-450℃ at a heating rate of 0.1-3℃ / min, and held for 60-120 min, and then cooled to room temperature in the furnace.

10. A high thermal stability particle size gradient PCD composite sheet according to claim 5, characterized in that: The high-temperature and high-pressure synthesis is carried out at a temperature of 1400℃~2000℃, a pressure of 5~8GPa, and a time of 240s~700s.

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