A porous diamond coating and a method of making and using the same

Abstract

The present application provides a kind of porous diamond coating and its preparation method and application.Porous diamond coating according to the present application, including metal matrix, the metal matrix surface is equipped with silicon carbide composite intermediate layer, the silicon carbide composite intermediate layer is inlayed with mutually dispersed diamond grains, and the gap and porous structure are formed between these dispersed diamond grains, with the effect of preventing abrasive dust blockage.Porous diamond coating of the present application, when used in cutter, good machining quality, high machining precision, low wear rate, long service life.In addition, the porous diamond coating of the present application is not limited by tool shape, and can be deposited quickly and controllably on any complex-shaped micro-precision tool, with the advantages of wide application range, high precision, low cost, etc.The present application also provides a preparation method and application of porous diamond coating.

Description

Technical Field

[0001] This invention belongs to the field of precision machining technology, specifically relating to a porous diamond coating, its preparation method, and its application. Background Technology

[0002] With the development of industries such as aerospace, microelectromechanical systems, microelectronics, medical devices, automobiles, and communications, the demand for micro-sized, high-precision components is increasing. Examples include microchannels on microfluidic chips, micro heat exchangers, micro sensors, and micro gyroscopes in navigation systems for aircraft and guided weapons. Most of these micro-critical components are made of semiconductor and ceramic materials, such as single-crystal silicon for microprocessors and electrodes, quartz for substrates and wafer carriers, and silicon carbide, gallium nitride, and silicon carbide for 5G RF chips. These materials are notoriously difficult to machine due to their high hardness, brittleness, and susceptibility to cleavage, resulting in inconsistent machining accuracy and surface quality, and extremely high fragmentation rates.

[0003] In related technologies, for micro-sized high-precision parts, ultra-micro machining methods are employed, using diamond tools for ultra-precision turning, ultra-precision milling, and ultra-precision grinding. Besides the inherent difficulty in machining the materials themselves, semiconductor core components often have complex and minute shapes, requiring drilling of micro-holes with diameters between 1 μm and 1 mm, and demanding high machining accuracy (0.1–1 μm) and surface roughness (Ra 0.02–0.1 μm). Traditional single-crystal diamond and polycrystalline diamond (PCD) superhard tool materials require processes such as inlaying and sintering for application on the surfaces of complex-shaped micro-precision tools. However, these methods suffer from drawbacks such as low density, poor uniformity, poor wear resistance, and high workpiece surface roughness, making them difficult to apply. Summary of the Invention

[0004] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a porous diamond coating, which, through an intermediate layer and a porous structure formed between dispersed diamond grains to prevent wear debris from clogging, prepares a tool coating suitable for high machining accuracy, low wear rate, and long service life.

[0005] The present invention also provides a method for preparing a porous diamond coating.

[0006] The present invention also provides an application of porous diamond coating.

[0007] A first aspect of the present invention provides a porous diamond coating comprising a metal substrate, wherein a silicon carbide composite intermediate layer is disposed on the surface of the metal substrate, and dispersed diamond grains are embedded in the silicon carbide composite intermediate layer.

[0008] Micro-tools typically use cemented carbide or high-speed steel as the base material and diamond as the coating. Ultra-micro machining requires very small depths of cut, necessitating tools with extremely sharp and stable cutting edges. The tool base material is usually cemented carbide or high-speed steel with a hard coating on its surface. Diamond, due to its extremely high hardness, wear resistance, elastic modulus, and excellent physicochemical properties such as chemical affinity, is an ideal tool material for ultra-micro machining.

[0009] One technical solution of the present invention concerning porous diamond coatings has at least the following beneficial effects:

[0010] In the machining of hard and brittle materials, on the one hand, the poor adhesion between the hard coating of the machining tool, such as diamond coating, and the substrate, and insufficient adhesion between the diamond coating and the tool substrate, directly lead to coating failure and low tool life, which is a key technical problem of diamond coating technology. This invention addresses the cause of poor adhesion by setting a silicon carbide composite intermediate layer as a transitional intermediate layer structure on the surface of the metal substrate. This reduces internal stress while suppressing cobalt diffusion, thereby improving the adhesion between the hard coating and the substrate. On the other hand, the hard coating of the machining tool is prone to clogging of the grinding wheel by grinding debris generated during grinding, resulting in poor machining quality. The porous diamond coating of this invention, with dispersed diamond grains embedded in the silicon carbide composite intermediate layer, forms gaps and a porous structure between these dispersed diamond grains, which effectively prevents grinding debris clogging. Therefore, when used in cutting tools, the porous diamond coating of this invention provides good machining quality, high machining accuracy, low wear rate, and long service life.

[0011] The porous diamond coating of this invention comprises a silicon carbide composite intermediate layer on the surface of a metal substrate, wherein dispersed diamond grains are embedded in the silicon carbide composite intermediate layer. The bonding strength between the metal substrate and the coating is related to thermal stress. During the preparation process, the coating growth temperature can reach over 800 degrees Celsius. When cooled to room temperature, the thermal expansion coefficients of the substrate and the coating are different, thus thermal stress exists. Since cemented carbide and silicon carbide have different expansion coefficients, the addition of diamond can adjust the expansion coefficient. Specifically, in the early stages of coating growth, there is more silicon carbide and less diamond, and the thermal expansion coefficient favors silicon carbide. As the coating grows, silicon carbide decreases, and the number and volume of diamond increase, further favoring diamond. Ultimately, the expansion coefficient decreases, resulting in better bonding between the porous diamond coating and the metal substrate.

[0012] The porous diamond coating of the present invention exhibits a gradually decreasing coefficient of thermal expansion from the metal substrate to the surface.

[0013] The porous diamond coating of this invention is not limited by the shape of the tool and can be rapidly and controllably deposited on micro-precision tools of any complex shape. It has the advantages of wide application range, high precision and low cost.

[0014] According to some embodiments of the present invention, each diamond grain is partially embedded in the silicon carbide composite intermediate layer and partially exposed outside the silicon carbide composite intermediate layer, forming a protrusion.

[0015] The silicon carbide composite interlayer acts like a binder, embedding a portion of the diamond grains within it. This interlayer enhances the bond strength between the coating and the substrate. The porous structure formed between the diamond grains prevents the grinding wheel from becoming clogged with grinding debris, ultimately extending the lifespan of the grinding wheel. It's understandable that grinding wheels require a high surface roughness for effective grinding, necessitating large particles on their surface. Unlike drill bits, which have threads for chip removal, grinding wheels lack chip removal capabilities. If the grinding debris generated during operation isn't promptly removed, it can easily scratch the surface of the workpiece. The porous diamond coating of this invention, with its porous structure between the diamond grains, provides a containment space for the grinding debris generated during operation. This debris flows into the pores, protecting the workpiece surface from scratches.

[0016] In conventional coatings, diamond grains are entirely embedded in the plating or binder. However, in the porous diamond coating of this invention, each diamond grain is partially embedded in the silicon carbide composite intermediate layer, while another part is exposed outside the silicon carbide composite intermediate layer, forming a protrusion.

[0017] According to some embodiments of the present invention, the height of the diamond grains is greater than the thickness of the silicon carbide composite intermediate layer.

[0018] The height and width of the diamond grain tip correspond to the height and width of the abrasive grain protrusions, respectively. The size and density of the abrasive grains directly affect the grinding performance. The height of the diamond grain is greater than the thickness of the silicon carbide composite intermediate layer, ensuring that there are enough abrasive grain protrusions on the surface of the silicon carbide composite intermediate layer, thus achieving better grinding results.

[0019] According to some embodiments of the present invention, the orientation of the diamond grains is perpendicular to the surface of the metal matrix.

[0020] According to some embodiments of the present invention, the diamond grains include at least one of micron-sized diamond grains and submicron-sized diamond grains.

[0021] According to some embodiments of the present invention, the metal matrix comprises cemented carbide or high-speed steel.

[0022] According to some embodiments of the present invention, the cemented carbide includes YG6, YG8, YG6X and YG6M.

[0023] According to some embodiments of the present invention, the cemented carbide includes YG6 4130511, YG6X 4130511, YG84130511 and YG6M 4160511.

[0024] A second aspect of the present invention provides a method for preparing the porous diamond coating, comprising the following steps: pretreating the surface of the metal substrate with an alkaline solution and an acidic solution in sequence, and then depositing the silicon carbide composite intermediate layer and the diamond grains on the surface of the metal substrate by hot-wire chemical vapor deposition.

[0025] Commonly used coating preparation processes include polycrystalline diamond (PCD), electroplating, electroless plating, and chemical vapor deposition (CVD). Diamond abrasives are typically made by electroplating or brazing. Electroplated tools, due to the lack of chemical bonds, exhibit weaker grain / substrate adhesion. Brazed diamond abrasives suffer thermal damage due to the high-temperature brazing process.

[0026] CVD (Chemical Vapor Deposition) is a technique that uses precursor reactants to generate solid thin films through decomposition and interatomic chemical reactions in an activated environment (thermal, light, plasma). It primarily relies on the fact that methane and hydrogen, when heated by a hot filament, decompose into reactive methyl radicals and atomic hydrogen. Through the chemical reaction of these reactive particles, carbon-carbon atoms form sp(s) on the sample surface. 3 The bonding process forms a diamond coating, and the overall chemical reaction is: CH4(g) —(thermal activation) → C(diamond) + 2H2(g). Diamond coatings deposited on the surface of cemented carbide cutting tools can significantly improve the surface hardness and wear resistance, thereby increasing tool life. Depending on the method of generating the activation environment, CVD diamond coating preparation methods can be divided into hot-filament CVD (HFCVD), electron-assisted CVD (EACVD), and microwave plasma CVD (MPCVD), among others. Hot-filament HFCVD has the advantages of large deposition area and uniform deposition, making it suitable for high-load and high-uniformity coatings on complex-shaped cutting tools.

[0027] CVD-coated diamond abrasives suffer from limitations in practical applications due to the small grinding space between the grains. This space can become clogged with grinding debris during grinding, leading to grinding interruptions. Furthermore, some newer technologies or processes are complex, costly, or only applicable to pure diamond coatings on continuous planes, failing to address the problem of grinding wheel clogging during grinding.

[0028] One technical solution of the present invention relating to the preparation method of porous diamond coating has at least the following beneficial effects:

[0029] The preparation method of the present invention involves pretreating the surface of the metal substrate with an alkaline solution and an acidic solution in sequence, and then depositing a silicon carbide composite intermediate layer on the surface of the metal substrate by hot-wire chemical vapor deposition, while simultaneously forming diamond grains. The diamond grains are dispersed among each other, forming gaps and a porous structure, which produces the effect of preventing wear debris clogging and ultimately solves the problem of wear debris clogging.

[0030] In the general process of preparing diamond coatings, it is necessary to pre-plant and adsorb nanodiamond seeds onto the substrate surface. The preparation method of the present invention does not require pre-planting, which further reduces costs and simplifies the operation.

[0031] The preparation method of this invention, by controlling the growth rate of diamond grains and silicon carbide layers, allows the height of the diamond grains to be higher than that of the silicon carbide layer, and forms pores between the diamond grains. The depth and width of these pores are controllable, effectively preventing wear debris clogging. Specifically, diamond and silicon carbide are grown simultaneously. Due to the faster growth rate of diamond, the final coating has diamonds protruding above the silicon carbide surface, forming protrusions.

[0032] Silicon carbide and diamond grow simultaneously on the surface of the metal substrate. From the substrate interface to the top surface, the content of carbide gradually decreases, while the content of diamond gradually increases until the top layer is pure diamond. This causes a gradual change in the longitudinal thermal expansion coefficient of the coating, distributing the thermal stress concentrated at the interface to the transition layer containing silicon carbide. This can significantly reduce the internal stress of the coating, improve the adhesion between the coating and the metal substrate, and improve the fracture toughness of the diamond coating.

[0033] The preparation method of the present invention involves pretreating the surface of the metal substrate with an alkaline solution to remove surface cobalt elements and inhibit the formation of harmful graphite phases at the interface.

[0034] The preparation method of the present invention involves pretreating the surface of the metal substrate with an acidic solution to further remove surface cobalt elements and inhibit the formation of harmful graphite phases at the interface.

[0035] The preparation method of the present invention can affect the growth of diamond grains by adjusting deposition parameters, including grain orientation, grain size and coating thickness, and can control the tip height and width of micron-sized diamond grains, thereby adjusting the grinding performance of the tool.

[0036] The preparation method of the present invention can naturally form a porous structure after coating deposition, without the need for subsequent processing, and is simple to operate and low in cost.

[0037] The preparation method of the present invention is applicable not only to planar tools, but also to micro tools with complex shapes.

[0038] The preparation method of the present invention can achieve uniform coating on the surface of micro-tools by depositing a porous composite diamond structure.

[0039] The preparation method of the present invention does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are readily available, the production cost is low, and it is easy to industrialize.

[0040] According to some embodiments of the present invention, the alkaline solution comprises an inorganic base, ferricyanide, and water.

[0041] According to some embodiments of the present invention, the mass ratio of the inorganic base, the mass of the ferricyanide, and the volume of water is 1:1:10 to 100.

[0042] According to some embodiments of the present invention, during the pretreatment of the surface of the metal substrate with an alkaline solution, ultrasound can be applied, the ultrasonic etching time is 5 min to 50 min, and the ultrasonic frequency is 80 Hz to 120 Hz.

[0043] According to some embodiments of the present invention, after pretreating the surface of the metal substrate with an alkaline solution, the surface of the metal substrate can be cleaned with deionized water. The cleaning can be performed multiple times, and each cleaning can last from 10 to 20 minutes.

[0044] According to some embodiments of the present invention, the acidic solution is a mixture of concentrated sulfuric acid and hydrogen peroxide.

[0045] According to some embodiments of the present invention, the volume ratio of concentrated sulfuric acid to hydrogen peroxide is 10:10 to 100.

[0046] According to some embodiments of the present invention, the surface of the metal substrate is pretreated with an acidic solution for 5 to 60 seconds.

[0047] According to some embodiments of the present invention, after pretreating the surface of the metal substrate with an acidic solution, the surface of the metal substrate can be cleaned with deionized water. The cleaning can be performed multiple times, with each cleaning session lasting 10 to 20 minutes. After cleaning, the surface of the metal substrate can be dried with nitrogen gas.

[0048] According to some embodiments of the present invention, the hot filament chemical vapor deposition method is as follows: adjusting the distance between the surface of the metal substrate and the hot filament, evacuating the vacuum, introducing a mixed gas, heating the filament, and depositing a silicon carbide composite intermediate layer and diamond grains on the surface of the metal substrate.

[0049] According to some embodiments of the present invention, the hot-filament chemical vapor deposition step includes:

[0050] (1) Insert the metal substrate evenly into the perforated copper disk, place it under the outlet of the hot filament chemical vapor deposition, adjust the distance from the top of the metal substrate to the hot filament, and then evacuate.

[0051] (2) After evacuating (1), hydrogen, carbon source and silicon source are introduced, and the gas pressure is maintained at 1 kPa to 10 kPa.

[0052] (3) Turn on the hot wire power supply, adjust the filament temperature, and continue to grow the silicon carbide composite intermediate layer and diamond grains.

[0053] (4) After growth is complete, turn off the gas and power supply, and evacuate the vacuum.

[0054] According to some embodiments of the present invention, the distance between the surface of the metal substrate and the hot wire is 15mm to 30mm.

[0055] According to some embodiments of the present invention, the mixed gas includes hydrogen, a carbon source, and a silicon source.

[0056] According to some embodiments of the present invention, the carbon source includes methane.

[0057] According to some embodiments of the present invention, the silicon source includes organosilanes.

[0058] According to some embodiments of the present invention, the organosilane includes tetramethylsilane.

[0059] According to some embodiments of the present invention, methane accounts for 1% to 10% of the total gas volume.

[0060] According to some embodiments of the present invention, the total volume of organosilane gas ranges from 0.05% to 1%.

[0061] According to some embodiments of the present invention, the filament is heated to a temperature of 1500°C to 2800°C.

[0062] According to some embodiments of the present invention, the deposition and growth time of the silicon carbide composite intermediate layer and diamond grains is 1h to 15h.

[0063] A third aspect of the invention provides the application of the porous diamond coating or the porous diamond coating prepared by the method in cutting tools.

[0064] The present invention relates to a technical solution for the application of porous diamond coatings in cutting tools, which has at least the following beneficial effects:

[0065] The porous diamond coating of this invention, when used in cutting tools, results in good machining quality, high machining accuracy, low wear rate, and long service life.

[0066] The porous diamond coating of this invention comprises a silicon carbide composite intermediate layer on the surface of a metal substrate, wherein dispersed diamond grains are embedded in the silicon carbide composite intermediate layer. The bonding strength between the metal substrate and the coating is related to thermal stress. During the preparation process, the coating growth temperature can reach over 800 degrees Celsius. When cooled to room temperature, the thermal expansion coefficients of the substrate and the coating are different, thus thermal stress exists. Since cemented carbide and silicon carbide have different expansion coefficients, the addition of diamond can adjust the expansion coefficient. Specifically, in the early stages of coating growth, there is more silicon carbide and less diamond, and the thermal expansion coefficient favors silicon carbide. As the coating grows, silicon carbide decreases, and the number and volume of diamond increase, further favoring diamond. Ultimately, the expansion coefficient decreases, resulting in better bonding between the porous diamond coating and the metal substrate.

[0067] The porous diamond coating of the present invention exhibits a gradually decreasing coefficient of thermal expansion from the metal substrate to the surface.

[0068] The porous diamond coating of this invention is not limited by the shape of the tool and can be rapidly and controllably deposited on micro-precision tools of any complex shape. It has a wide range of applications, high precision, and low cost.

[0069] According to some embodiments of the present invention, the cutting tool includes a grinding wheel, a reamer, a broach, a cleaver, or a grooving tool. Attached Figure Description

[0070] Figure 1 This is a schematic diagram of the preparation process of porous diamond coating.

[0071] Figure 2 The curve of the coating silane prepared for the YG6 substrate material and its working time.

[0072] Figure 3 The microstructure of the coating surface in Example 22 is shown.

[0073] Figure 4 The microstructure of the coating surface in Example 23 is shown. Detailed Implementation

[0074] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0075] In some embodiments of the present invention, a porous diamond coating is provided, comprising a metal substrate, a silicon carbide composite intermediate layer disposed on the surface of the metal substrate, and dispersed diamond grains embedded in the silicon carbide composite intermediate layer.

[0076] Micro-tools typically use cemented carbide or high-speed steel as the base material and diamond as the coating. Ultra-micro machining requires very small depths of cut, necessitating tools with extremely sharp and stable cutting edges. The tool base material is usually cemented carbide or high-speed steel with a hard coating on its surface. Diamond, due to its extremely high hardness, wear resistance, elastic modulus, and excellent physicochemical properties such as chemical affinity, is an ideal tool material for ultra-micro machining.

[0077] It is understandable that in the machining of hard and brittle materials, on the one hand, poor adhesion between the hard coating of the machining tool, such as diamond coating, and the substrate, and insufficient adhesion between the diamond coating and the tool substrate, directly leads to coating failure and low tool life, which is a key technical problem of diamond coating technology. This invention addresses the cause of poor adhesion by setting a silicon carbide composite intermediate layer as a transitional intermediate layer structure on the surface of the metal substrate. This reduces internal stress while suppressing cobalt diffusion, thereby improving the adhesion between the hard coating and the substrate. On the other hand, the hard coating of the machining tool is prone to clogging the grinding wheel with grinding debris generated during grinding, resulting in poor machining quality. The porous diamond coating of this invention has dispersed diamond grains embedded in the silicon carbide composite intermediate layer. These dispersed diamond grains form gaps and a porous structure, which has the effect of preventing grinding debris clogging. Therefore, when used in cutting tools, the porous diamond coating of this invention provides good machining quality, high machining accuracy, low wear rate, and long service life.

[0078] The porous diamond coating of this invention comprises a silicon carbide composite intermediate layer on the surface of a metal substrate, wherein dispersed diamond grains are embedded in the silicon carbide composite intermediate layer. The bonding strength between the metal substrate and the coating is related to thermal stress. During the preparation process, the coating growth temperature can reach over 800 degrees Celsius. When cooled to room temperature, the thermal expansion coefficients of the substrate and the coating are different, thus thermal stress exists. Since cemented carbide and silicon carbide have different expansion coefficients, the addition of diamond can adjust the expansion coefficient. Specifically, in the early stages of coating growth, there is more silicon carbide and less diamond, and the thermal expansion coefficient favors silicon carbide. As the coating grows, silicon carbide decreases, and the number and volume of diamond increase, further favoring diamond. Ultimately, the expansion coefficient decreases, resulting in better bonding between the porous diamond coating and the metal substrate.

[0079] The porous diamond coating of the present invention exhibits a gradually decreasing coefficient of thermal expansion from the metal substrate to the surface.

[0080] It is understood that the porous diamond coating of the present invention is not limited by the shape of the tool and can be rapidly and controllably deposited on micro-precision tools of any complex shape, with advantages such as wide application range, high precision and low cost.

[0081] In some embodiments of the present invention, each diamond grain is partially embedded in the silicon carbide composite intermediate layer and partially exposed outside the silicon carbide composite intermediate layer, forming a protrusion.

[0082] The silicon carbide composite interlayer acts like a binder, embedding a portion of the diamond grains within it. This interlayer enhances the bond strength between the coating and the substrate. The porous structure formed between the diamond grains prevents the grinding wheel from becoming clogged with grinding debris, ultimately extending the lifespan of the grinding wheel. It's understandable that grinding wheels require a high surface roughness for effective grinding, necessitating large particles on their surface. Unlike drill bits, which have threads for chip removal, grinding wheels lack chip removal capabilities. If the grinding debris generated during operation isn't promptly removed, it can easily scratch the surface of the workpiece. The porous diamond coating of this invention, with its porous structure between the diamond grains, provides a containment space for the grinding debris generated during operation. This debris flows into the pores, protecting the workpiece surface from scratches.

[0083] In conventional coatings, diamond grains are entirely embedded in the plating or binder. However, in the porous diamond coating of this invention, each diamond grain is partially embedded in the silicon carbide composite intermediate layer, while another part is exposed outside the silicon carbide composite intermediate layer, forming a protrusion.

[0084] In some embodiments of the present invention, the height of the diamond grains is greater than the thickness of the silicon carbide composite interlayer.

[0085] The height and width of the diamond grain tip correspond to the height and width of the abrasive grain protrusions, respectively. The size and density of the abrasive grains directly affect the grinding performance. The height of the diamond grain is greater than the thickness of the silicon carbide composite intermediate layer, ensuring that there are enough abrasive grain protrusions on the surface of the silicon carbide composite intermediate layer, thus achieving better grinding results.

[0086] In some embodiments of the present invention, the orientation of the diamond grains is perpendicular to the surface of the metal matrix.

[0087] In some embodiments of the present invention, the diamond grains include at least one of micron-sized diamond grains and submicron-sized diamond grains.

[0088] In some embodiments of the present invention, the metal matrix includes cemented carbide or high-speed steel.

[0089] In some embodiments of the present invention, the cemented carbide includes YG6, YG8, YG6X and YG6M.

[0090] In some embodiments of the present invention, the cemented carbide includes YG6 4130511, YG6X 4130511, YG84130511 and YG6M 4160511.

[0091] In some other embodiments of the present invention, the present invention provides a method for preparing the porous diamond coating of the present invention, comprising the following steps: after pretreating the surface of a metal substrate with an alkaline solution and an acidic solution in sequence, a silicon carbide composite intermediate layer and diamond grains are deposited on the surface of the metal substrate by hot-wire chemical vapor deposition.

[0092] Commonly used coating preparation processes include polycrystalline diamond (PCD), electroplating, electroless plating, and chemical vapor deposition (CVD). Diamond abrasives are typically made by electroplating or brazing. Electroplated tools, due to the lack of chemical bonds, exhibit weaker grain / substrate adhesion. Brazed diamond abrasives suffer thermal damage due to the high-temperature brazing process.

[0093] CVD (Chemical Vapor Deposition) is a technique that uses precursor reactants to generate solid thin films through decomposition and interatomic chemical reactions in an activated environment (thermal, light, plasma). It primarily relies on the fact that methane and hydrogen, when heated by a hot filament, decompose into reactive methyl radicals and atomic hydrogen. Through the chemical reaction of these reactive particles, carbon-carbon atoms form sp(s) on the sample surface. 3 The bonding process forms a diamond coating, and the overall chemical reaction is: CH4(g) —(thermal activation) → C(diamond) + 2H2(g). Diamond coatings deposited on the surface of cemented carbide cutting tools can significantly improve the surface hardness and wear resistance, thereby increasing tool life. Depending on the method of generating the activation environment, CVD diamond coating preparation methods can be divided into hot-filament CVD (HFCVD), electron-assisted CVD (EACVD), and microwave plasma CVD (MPCVD), among others. Hot-filament HFCVD has the advantages of large deposition area and uniform deposition, making it suitable for high-load and high-uniformity coatings on complex-shaped cutting tools.

[0094] CVD-coated diamond abrasives suffer from limitations in practical applications due to the small grinding space between the grains. This space can become clogged with grinding debris during grinding, leading to grinding interruptions. Furthermore, some newer technologies or processes are complex, costly, or only applicable to pure diamond coatings on continuous planes, failing to address the problem of grinding wheel clogging during grinding.

[0095] It is understood that the preparation method of the present invention, after pretreating the surface of the metal substrate with alkaline solution and acidic solution in sequence, can form a silicon carbide composite intermediate layer on the surface of the metal substrate by hot filament chemical vapor deposition, and at the same time form diamond grains. The diamond grains are dispersed among each other, forming gaps and porous structures, which produces the effect of preventing wear debris clogging, and finally solves the problem of wear debris clogging.

[0096] In the general process of preparing diamond coatings, it is necessary to pre-plant and adsorb nanodiamond seeds onto the substrate surface. The preparation method of the present invention does not require pre-planting, which further reduces costs and simplifies the operation.

[0097] The preparation method of this invention, by controlling the growth rate of diamond grains and silicon carbide layers, allows the height of the diamond grains to be higher than that of the silicon carbide layer, and forms pores between the diamond grains. The depth and width of these pores are controllable, effectively preventing wear debris clogging. Specifically, diamond and silicon carbide are grown simultaneously. Due to the faster growth rate of diamond, the final coating has diamonds protruding above the silicon carbide surface, forming protrusions.

[0098] Silicon carbide and diamond grow simultaneously on the surface of the metal substrate. From the substrate interface to the top surface, the content of carbide gradually decreases, while the content of diamond gradually increases until the top layer is pure diamond. This causes a gradual change in the longitudinal thermal expansion coefficient of the coating, distributing the thermal stress concentrated at the interface to the transition layer containing silicon carbide. This can significantly reduce the internal stress of the coating, improve the adhesion between the coating and the metal substrate, and improve the fracture toughness of the diamond coating.

[0099] The method for creating a porous diamond coating according to the present invention includes the following steps: after pretreating the surface of a metal substrate with an alkaline solution and an acidic solution in sequence, a silicon carbide composite intermediate layer and diamond grains are deposited on the surface of the metal substrate by hot-wire chemical vapor deposition.

[0100] Combination Figure 1 To better understand the preparation process of the porous diamond coating of the present invention, the surface of the hard alloy metal substrate has cobalt 1 and tungsten carbide 2. After the surface of the metal substrate is pretreated with alkaline solution and acidic solution in sequence, a silicon carbide composite intermediate layer 3 and diamond grains 4 are simultaneously deposited on the surface of the metal substrate by hot filament chemical vapor deposition.

[0101] By adjusting deposition parameters, the growth of diamond grains 4 can be influenced, including grain orientation, grain size, and coating thickness. The height and width of the micron-sized diamond grain tips can be controlled, thereby adjusting the grinding performance of the cutting tool. The dispersed diamond grains 4 can naturally form a porous structure, requiring no further processing, making the operation simple and cost-effective.

[0102] The preparation method of the present invention is applicable not only to planar tools, but also to micro tools with complex shapes.

[0103] The preparation method of the present invention can achieve uniform coating on the surface of micro-tools by depositing a porous composite diamond structure.

[0104] The preparation method of the present invention does not require expensive equipment and complex process control, the reaction conditions are not harsh, the raw materials are readily available, the production cost is low, and it is easy to industrialize.

[0105] In some embodiments of the present invention, the alkaline solution comprises an inorganic base, ferricyanide, and water.

[0106] In some embodiments of the present invention, the mass ratio of the inorganic base, the mass of the ferricyanide, and the volume of water is 1:1:10 to 100.

[0107] In some embodiments of the present invention, during the pretreatment of the surface of the metal substrate with an alkaline solution, ultrasound can be applied, and the ultrasonic etching time is 5 min to 50 min, and the ultrasonic frequency is 80 Hz to 120 Hz.

[0108] In some embodiments of the present invention, after pretreating the surface of the metal substrate with an alkaline solution, the surface of the metal substrate can be cleaned with deionized water, and the cleaning can be performed multiple times.

[0109] In some embodiments of the present invention, the acidic solution is a mixture of concentrated sulfuric acid and hydrogen peroxide.

[0110] In some embodiments of the present invention, the volume ratio of concentrated sulfuric acid to hydrogen peroxide is 10:10 to 100.

[0111] In some embodiments of the present invention, the surface of the metal substrate is pretreated with an acidic solution for 5 to 60 seconds.

[0112] In some embodiments of the present invention, after pretreating the surface of the metal substrate with an acidic solution, the surface of the metal substrate can be cleaned with deionized water, and the cleaning can be performed multiple times. After cleaning, the surface of the metal substrate can be dried with nitrogen gas.

[0113] In some embodiments of the present invention, the hot filament chemical vapor deposition method is as follows: adjusting the distance between the surface of the metal substrate and the hot filament, evacuating the vacuum, introducing a mixed gas, heating the filament, and depositing a silicon carbide composite intermediate layer and diamond grains on the surface of the metal substrate.

[0114] In some embodiments of the present invention, the hot-filament chemical vapor deposition step includes:

[0115] (1) Insert the metal substrate evenly into the perforated copper disk, place it under the outlet of the hot filament chemical vapor deposition, adjust the distance from the top of the metal substrate to the hot filament, and then evacuate.

[0116] (2) After evacuating (1), hydrogen, methane and organosilanes (tetramethylsilane or silane) are introduced, and the pressure is maintained at 1 kPa to 10 kPa.

[0117] (3) Turn on the hot wire power supply, adjust the filament temperature, and continue to grow the silicon carbide composite intermediate layer and diamond grains.

[0118] (4) After growth is complete, turn off the gas and power supply, and evacuate the vacuum.

[0119] In some embodiments of the present invention, the distance between the surface of the metal substrate and the hot wire is 15 mm to 30 mm.

[0120] In some embodiments of the present invention, the combined gas includes hydrogen, methane, and organosilane.

[0121] In some embodiments of the present invention, methane accounts for 1% to 10% of the total gas volume.

[0122] In some embodiments of the present invention, the total volume of organosilane gas ranges from 0.05% to 1%.

[0123] In some embodiments of the present invention, the filament is heated to a temperature of 1500°C to 2800°C.

[0124] In some embodiments of the present invention, the deposition and growth time of the silicon carbide composite intermediate layer and diamond grains is 1h to 15h.

[0125] In other embodiments of the present invention, the present invention provides the application of porous diamond coatings or porous diamond coatings prepared by the porous diamond coating or method of the present invention in cutting tools.

[0126] It is understood that the porous diamond coating of the present invention, when used in cutting tools, results in good processing quality, high processing accuracy, low wear rate, and long service life.

[0127] The porous diamond coating of this invention is not limited by the shape of the tool and can be rapidly and controllably deposited on micro-precision tools of any complex shape. It has a wide range of applications, high precision, and low cost.

[0128] In some embodiments of the present invention, the cutting tool includes a grinding wheel, a reamer, a broach, a cleaver, or a grooving tool.

[0129] The technical solution of the present invention will be better understood below with reference to specific embodiments.

[0130] This invention improves the bonding strength between the coating and the substrate by adding a silicon carbide composite interlayer between the substrate and the diamond coating. The silicon carbide acts as a binder, embedding a portion of the diamond grains within the silicon carbide layer. Specifically, at the beginning of the preparation process, diamond and silicon carbide grow simultaneously; however, due to the faster growth rate of diamond, the final coating has diamond protruding above the silicon carbide surface, forming protrusions. Furthermore, pores are formed between the diamond grains, with controllable pore depth and width, effectively preventing wear debris clogging.

[0131] Table 1 below shows examples 1-20, which illustrate coating preparation on the surfaces of several different substrate materials, categorized as having an intermediate layer and not having an intermediate layer, as well as different silane contents. The working time of these coatings is compared.

[0132] The specific preparation steps are as follows:

[0133] 1. First, perform chemical pretreatment on the cemented carbide precision abrasive. Immerse the working area of ​​the cemented carbide precision abrasive in a mixed alkaline solution (K3Fe(CN)6∶KOH∶H2O=1:1:10) and ultrasonically corrode it for 15 minutes in an ultrasonic bath (100Hz). Then, remove the cemented carbide precision abrasive and ultrasonically clean it three times with deionized water, 10 minutes each time. After cleaning, prepare a mixed acid solution (a mixture of concentrated sulfuric acid and hydrogen peroxide). Weigh 10 mL of concentrated sulfuric acid solution and 100 mL of hydrogen peroxide solution, and mix them thoroughly. Immerse the cleaned cemented carbide precision abrasive in the mixed acid solution for 30 seconds, then remove it and ultrasonically clean it three times with deionized water, 10 minutes each time. After cleaning, dry it with nitrogen gas.

[0134] 2. Evenly insert the cemented carbide micro-mold into the perforated copper disk, placing it below the outlet of the hot-wire chemical vapor deposition (CVD) system. Adjust the distance from the tip of the cemented carbide precision mold to the hot wire to 15 mm, then evacuate the system. Introduce hydrogen, methane, and tetramethylsilane (1% tetramethylsilane, 99% hydrogen) at flow rates of 800 sccm and 16 sccm respectively, maintaining a pressure of 3 kPa. Turn on the hot wire power supply, setting the filament temperature to 2200℃. Allow the mold to grow for 2 hours, then turn off the tetramethylsilane and continue growth for another 5 hours.

[0135] Table 1 Comparison of the presence or absence of an intermediate layer and changes in silane content.

[0136]

[0137] As can be seen from the table above, the working time of coatings prepared from the four substrate materials shows the same trend: the working time of abrasives with added silicon carbide composite interlayers is significantly improved compared to abrasives without added silicon carbide composite interlayers. Furthermore, for the same substrate material, the working time of the abrasive increases with the increase of tetramethylsilane content. (See table below.)Figure 2 As shown, Figure 2 The graph shows the silane coating and working time curves prepared for the YG6 substrate material. This indicates that the silicon carbide composite intermediate layer used in this invention can effectively increase the adhesion of the diamond coating and increase the working time of the abrasive.

[0138] It should be noted that "working time" refers to the time from the start of processing the mold until the processing quality deteriorates and cracks appear on the surface of the processed area.

[0139] The method of this invention can achieve the growth of diamond coatings on the surface of different cemented carbide substrates, and the diamond coatings can be grown in a controlled manner by adjusting the growth temperature (wire-to-base distance), methane content, silane content, gas pressure and growth time, so as to obtain diamond coatings with different thicknesses and different grain sizes.

[0140] The instance variable parameters and coating growth conditions are shown in Table 2, while other parameters remain consistent. The specific steps are as follows:

[0141] 1. First, perform chemical pretreatment on the cemented carbide precision abrasive. Immerse the working area of ​​the cemented carbide precision abrasive in a mixed alkaline solution (K3Fe(CN)6∶KOH∶H2O=1:1:20) and ultrasonically corrode it for 15 minutes in an ultrasonic bath (100Hz). Then, remove the cemented carbide precision abrasive and ultrasonically clean it three times with deionized water, 10 minutes each time. After cleaning, prepare a mixed acid solution (a mixture of concentrated sulfuric acid and hydrogen peroxide). Weigh 10 mL of concentrated sulfuric acid solution and 100 mL of hydrogen peroxide solution, and mix them thoroughly. Immerse the cleaned cemented carbide precision abrasive in the mixed acid solution for 30 seconds, then remove it and ultrasonically clean it three times with deionized water, 10 minutes each time. After cleaning, dry it with nitrogen gas.

[0142] 2. Insert the cemented carbide micro-mold evenly into the perforated copper disk, place it under the outlet of the hot-wire chemical vapor deposition system, and evacuate. Set different growth temperatures and gas pressures. After evacuation, introduce hydrogen, methane, and silane, and control the percentage of methane and silane content. Turn on the hot-wire power supply and grow for 2 hours with tetramethylsilane introduced, then turn off the tetramethylsilane and continue growth for different times. After growth is complete, turn off the gas and power supply, and evacuate again.

[0143] Table 2. Different growth parameters and coating growth.

[0144]

[0145] As can be seen from Table 2, the method of the present invention can achieve the growth of diamond coatings with different thicknesses and different grain sizes on the surface of different cemented carbide substrate materials. Figure 3 , Figure 4The coating surface morphology of Examples 22 and 23 are shown respectively. It can be seen that the corresponding diamond coating was successfully deposited on the surface of the grinding wheel, and the coating has a porous composite structure, which can solve the problem of grinding debris clogging.

[0146] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for preparing a porous diamond coating, characterized in that, The porous diamond coating includes a metal substrate, on the surface of which a silicon carbide composite intermediate layer is provided. Dispersed diamond grains are embedded in the silicon carbide composite intermediate layer. Each diamond grain has a portion embedded in the silicon carbide composite intermediate layer and another portion exposed outside the silicon carbide composite intermediate layer, forming a protrusion. The height of the diamond grain is greater than the thickness of the silicon carbide composite intermediate layer, and the orientation of the diamond grain is perpendicular to the surface of the metal substrate. The porous diamond coating forms a porous structure that prevents wear debris from clogging through the intermediate layer and the dispersed diamond grains. The porous diamond coating exhibits a gradually decreasing coefficient of thermal expansion from the metal substrate to the surface. The porous diamond coating is obtained through the following steps: (1) First, chemical pretreatment is performed on the cemented carbide precision abrasive. The working area of ​​the cemented carbide precision abrasive is immersed in a mixed alkaline solution with a volume ratio of K3Fe(CN)6:KOH:H2O of 1:1:

10. The abrasive is ultrasonically etched in an ultrasonic bath at a frequency of 100Hz for 15 minutes. Then, the cemented carbide precision abrasive is taken out and ultrasonically cleaned with deionized water 3 times for 10 minutes each time. After cleaning, a mixed acid solution of concentrated sulfuric acid and hydrogen peroxide is prepared. Weigh 10 mL of concentrated sulfuric acid solution and 100 mL of hydrogen peroxide solution, mix them thoroughly, and then put the cleaned cemented carbide precision abrasive into the mixed acid solution for 30 seconds. After cleaning, it is taken out and ultrasonically cleaned with deionized water 3 times for 10 minutes each time. After cleaning, it is dried with nitrogen. (2) Insert the cemented carbide micro-mold evenly into the perforated copper disk and place it under the outlet of the hot filament chemical vapor deposition. Adjust the distance from the top of the cemented carbide precision mold to the hot filament to 15 mm. Then, evacuate the vacuum and introduce hydrogen, methane and tetramethylsilane. The gas flow rates are 800 sccm and 16 sccm, respectively. The introduced tetramethylsilane is 1% tetramethylsilane and 99% hydrogen. The gas pressure is maintained at 3 kPa. Turn on the hot filament power supply and the filament temperature is 2200ºC. Grow for 2 hours first, then turn off the tetramethylsilane and continue growing for 5 hours.

2. The method for preparing a porous diamond coating according to claim 1, characterized in that, The diamond grains include at least one of micron-sized diamond grains and submicron-sized diamond grains.

3. The application of the porous diamond coating preparation method as described in claim 1 or 2 in cutting tools.

4. The application according to claim 3, characterized in that, The cutting tools include abrasives, reamers, broaches, cleavers, or grooving tools.

Images