Porous diamond coating as well as preparation method and application thereof

Abstract

The invention provides a porous diamond coating as well as a preparation method and application thereof. The porous diamond coating comprises a metal matrix, a silicon carbide composite middle layer is arranged on the surface of the metal matrix, diamond grains which are mutually dispersed are embedded in the silicon carbide composite middle layer, gaps and porous structures are formed among the dispersed diamond grains, and the porous diamond coating has the effect of preventing abrasive dust blockage. The porous diamond coating is good in machining quality, high in machining precision, low in wear rate and long in service life when being used for the cutter. In addition, the porous diamond coating is not limited by the shape of a tool, can realize rapid and controllable deposition on a miniature precision tool with any complex shape, and has the advantages of wide application range, high precision, low cost and the like. The invention further provides a preparation method and application of the porous diamond coating.

Description

Technical Field

[0001] The invention belongs to the technical field of precision machining, and in particular relates to a porous diamond coating and a preparation method and application thereof. Background Art

[0002] With the development of aerospace, micro-electromechanical systems, microelectronics, medical devices, automobiles, and communications industries, people are increasingly demanding miniature, high-precision parts, such as microchannels on microfluidic chips, micro heat converters, micro sensors, and micro gyroscopes in navigation systems for aircraft and guided weapons. Most of the key micro core components are semiconductors and ceramic materials, such as single crystal silicon for microprocessors and electrodes, quartz for bases and wafer carriers, silicon carbide, gallium nitride, and silicon carbide for 5G radio frequency chips, etc. These materials are typical difficult-to-process materials because of their high hardness, high brittleness, and easy cleavage, so the processing accuracy and surface quality are unstable, and the fragmentation rate is extremely high.

[0003] In the related technology, ultra-fine machining methods are used for micro-sized high-precision parts, using diamond tools for ultra-precision turning, ultra-precision milling and ultra-precision grinding. In addition to the difficult processing characteristics of the material itself, the core components of semiconductors are often complex and tiny in shape. The diameter of the microholes required for drilling is between 1μm and 1mm, and the processing accuracy (0.1~1μm) and surface roughness (Ra0.02~0.1μm) are high. Traditional single crystal diamond and polycrystalline diamond (PCD) superhard tool materials need to be applied through processes such as inlaying and sintering. They are prepared on the surface of complex-shaped micro-precision tools. They have the disadvantages of low density, poor uniformity, poor wear resistance and high surface roughness of the workpiece, making them difficult to apply. Summary of the invention

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

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

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

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

[0008] Micro tools are usually based on carbide or high-speed steel and coated with diamond. Ultra-fine machining requires a smaller cutting depth, and the tool used needs to have a very sharp edge and high stability. The tool base material is usually carbide or high-speed steel, and a hard coating is plated on its surface. Diamond is an ideal tool material for ultra-fine machining due to its excellent physical and chemical properties such as extremely high hardness, extremely high wear resistance, extremely high elastic modulus, chemical affinity, etc.

[0009] One of the technical solutions of the present invention regarding the porous diamond coating has at least the following beneficial effects:

[0010] In the processing of hard and brittle materials, on the one hand, the hard coating of the processing tool, such as the diamond coating, has poor bonding with the substrate, and the insufficient bonding between the diamond coating and the tool substrate will directly lead to coating failure and low tool life, which is a key technical problem of diamond coating technology. The present invention aims at the cause of poor bonding, and by arranging a silicon carbide composite intermediate layer on the surface of the metal substrate as a transition intermediate layer structure, the internal stress is reduced while suppressing the diffusion of cobalt, thereby improving the bonding between the hard coating and the substrate. On the other hand, the hard coating of the processing tool is prone to clogging the grinding wheel with grinding chips generated during the grinding process, resulting in poor processing quality. The porous diamond coating of the present invention has dispersed diamond grains embedded in the silicon carbide composite intermediate layer, and gaps and porous structures are formed between these dispersed diamond grains, which has the effect of preventing clogging of grinding chips. Therefore, the porous diamond coating of the present invention, when used for a tool, has good processing quality, high processing accuracy, low wear rate and long service life.

[0011] The porous diamond coating of the present invention is provided with a silicon carbide composite intermediate layer on the surface of the metal substrate, and the silicon carbide composite intermediate layer is inlaid with dispersed diamond grains. The bonding strength between the metal substrate and the coating is related to thermal stress. During the preparation process, the temperature of the coating growth can reach more than 800 degrees Celsius. When it drops to room temperature, the thermal expansion coefficients of the substrate and the coating are different, so thermal stress exists. The expansion coefficients of cemented carbide and silicon carbide are different. After adding diamond, the expansion coefficient can be adjusted. Specifically, in the early stage of coating growth, there are more silicon carbide and less diamond, and the thermal expansion coefficient tends to silicon carbide; as the coating grows, the silicon carbide decreases, the more diamonds there are, the larger the volume, and the thermal expansion coefficient tends to diamond. Finally, the expansion coefficient becomes smaller, and the bonding force between the porous diamond coating and the metal substrate is better.

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

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

[0014] According to some embodiments of the present invention, each of the diamond grains has a portion buried in the silicon carbide composite intermediate layer and another portion exposed outside the silicon carbide composite intermediate layer to form a protrusion.

[0015] The role of the silicon carbide composite intermediate layer is similar to that of a binder. A part of the diamond grains can be buried in the silicon carbide composite intermediate layer. The silicon carbide composite intermediate layer is used to improve the bonding strength between the coating and the substrate. The hole structure formed between the diamond grains can prevent the grinding wheel from being blocked by abrasive chips, and finally improve the service life of the abrasive tool. It can be understood that as an abrasive tool, in order to facilitate grinding, a large roughness is required, and the abrasive tool requires large particles on the surface. The abrasive tool is not like a drill bit. The drill bit has threads for chip removal, but the abrasive tool does not have chip removal. If the abrasive chips generated during the working process of the abrasive tool are not removed in time, it is easy to scratch the surface of the workpiece being processed. The porous diamond coating of the present invention has a porous structure formed between the diamond grains. These porous structures provide a place to accommodate the abrasive chips generated during the working process of the abrasive tool. The abrasive chips generated during the working process of the abrasive tool will flow into the holes, thereby protecting the surface of the workpiece being processed from being scratched.

[0016] In general coatings, diamond grains are completely buried in the plating layer or binder. In the porous diamond coating of the present invention, each diamond grain is partially buried in the silicon carbide composite middle layer and the other part is exposed outside the silicon carbide composite middle layer to form 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 are equivalent to the height and width of the abrasive grain protrusion, respectively. The abrasive grain size and density will directly affect the grinding performance. The height of the diamond grain is greater than the thickness of the silicon carbide composite intermediate layer, which ensures that there are enough abrasive grain protrusions on the surface of the silicon carbide composite intermediate layer, thereby achieving better grinding effect.

[0019] According to some embodiments of the present invention, the diamond grains are oriented perpendicular to the surface of the metal substrate.

[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 substrate 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] The second aspect of the present invention provides a method for preparing the porous diamond coating, comprising the following steps: pre-treating 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] Common coating preparation processes include polycrystalline diamond (PCD), electroplating, chemical plating, chemical vapor deposition (CVD), etc. Diamond abrasives are usually made by electroplating or brazing. Among them, electroplated tools have weak grain / matrix adhesion due to the lack of chemical bonds. Brazed diamonds will cause thermal damage due to high temperature brazing.

[0026] CVD is a technology that uses precursors to generate solid thin films through decomposition and chemical reactions between atoms in an activated environment (heat, light, plasma). It is mainly based on the fact that methane and hydrogen can be decomposed into active methyl radicals and atomic hydrogen by heating with a hot wire. Through the chemical reaction of active particles, carbon-carbon is sp 3 The diamond coating is formed by bonding, and the overall chemical reaction is: CH4 (gas) - (thermal activation) → C (diamond) + 2H2 (gas). Diamond coating deposited on the surface of cemented carbide tools can greatly improve the hardness and wear resistance of the tool surface, thereby increasing the tool life. According to the different methods of generating the activation environment, the preparation methods of CVD diamond coating can be divided into hot filament CVD (Hot Filament CVD, referred to as HFCVD), electron assisted CVD (EACVD), microwave plasma CVD (MPCVD), etc. Among them, hot filament HFCVD has the advantages of large deposition area and deposition uniformity, and is suitable for high loading and high uniformity coating of complex-shaped tools.

[0027] CVD coated diamond abrasives, due to the small grinding space between the grains, the grinding generated during the grinding process will block the grinding space and cause grinding interruption, limiting its practical application. Some new technologies or processes are complicated, costly, or only apply to pure diamond coatings on continuous surfaces, which cannot solve the problem of grinding wheels being blocked by grinding chips during the grinding process.

[0028] A technical solution in the method for preparing a porous diamond coating of the present invention has at least the following beneficial effects:

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

[0030] In the general preparation process of diamond coating, it is necessary to pre-plant nano-diamond seeds on the surface of the substrate. The preparation method of the present invention does not require pre-planting, which further reduces the cost and simplifies the operation.

[0031] The preparation method of the present invention can make the height of the diamond grains higher than the silicon carbide layer by regulating the growth rate of the diamond grains and the silicon carbide layer, and form holes between the diamond grains, the hole depth and width of which are controllable, effectively preventing the clogging of grinding chips. Specifically, the diamond and silicon carbide grow simultaneously at first, and because the diamond grows faster, in the coating finally prepared, the diamond is higher than the silicon carbide surface, forming a protrusion.

[0032] Silicon carbide and diamond grow simultaneously on the surface of the metal substrate. From the substrate interface to the top surface, the carbide content gradually decreases, while the diamond content gradually increases to pure diamond on the top layer, so that the longitudinal thermal expansion coefficient of the coating forms a gradual change, and the thermal stress concentrated on the interface is distributed to the transition layer containing silicon carbide, which can significantly reduce the internal stress of the coating, improve the bonding strength between the coating and the metal substrate, and at the same time improve the fracture toughness of the diamond coating.

[0033] The preparation method of the invention uses an alkaline solution to pretreat the surface of the metal substrate, aiming to remove the cobalt element on the surface and inhibit the generation of harmful graphite phase on the interface.

[0034] The preparation method of the invention uses an acidic solution to pretreat the surface of the metal substrate, aiming to further remove the surface cobalt element and inhibit the generation of harmful graphite phase on the interface.

[0035] The preparation method of the present invention can affect the growth of diamond grains, including grain orientation, grain size and coating thickness, by adjusting deposition parameters, and can control the tip height and width of micron 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 the coating is deposited, does not require subsequent treatment, is simple to operate, and has low cost.

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

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

[0039] The preparation method of the present invention does not require expensive equipment and complicated process control, has undemanding reaction conditions, has readily available raw materials, has low production costs, and is easy to industrialize.

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

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

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

[0043] According to some embodiments of the present invention, after the surface of the metal substrate is pretreated with an alkaline solution, the surface of the metal substrate can be cleaned with deionized water. The number of cleanings can be multiple times, and the time for each cleaning can be 10 minutes 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 10:10-100.

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

[0047] According to some embodiments of the present invention, after the surface of the metal substrate is pretreated with an acidic solution, the surface of the metal substrate can be cleaned with deionized water, the number of cleanings can be multiple, and the time of each cleaning can be 10 minutes to 20 minutes. After cleaning, the surface of the metal substrate can be blown dry with nitrogen.

[0048] According to some embodiments of the present invention, the method of hot wire chemical vapor deposition is: adjusting the distance between the surface of the metal substrate and the hot wire, after vacuuming, 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 step of hot wire chemical vapor deposition comprises:

[0050] (1) The metal substrate is uniformly inserted into a perforated copper plate and placed under the outlet of a hot wire chemical vapor deposition device. The distance between the top of the metal substrate and the hot wire is adjusted, and then vacuum is drawn;

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

[0052] (3) turning on the hot wire power supply, adjusting the filament temperature, and continuously growing the silicon carbide composite intermediate layer and diamond grains;

[0053] (4) After growth is completed, turn off the gas, turn off the power, and evacuate the room.

[0054] According to 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.

[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 invention, the carbon source comprises methane.

[0057] According to some embodiments of the present invention, the silicon source comprises an organosilane.

[0058] According to some embodiments of the invention, the organosilane comprises 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 gas volume of the organosilane ranges from 0.05% to 1%.

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

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

[0063] The third aspect of the present invention provides the use of the porous diamond coating or the porous diamond coating prepared by the method in a cutting tool.

[0064] A technical solution of the present invention regarding the application of porous diamond coating in cutting tools has at least the following beneficial effects:

[0065] The porous diamond coating of the invention, when used for cutting tools, has good processing quality, high processing precision, low wear rate and long service life.

[0066] The porous diamond coating of the present invention is provided with a silicon carbide composite intermediate layer on the surface of the metal substrate, and the silicon carbide composite intermediate layer is inlaid with dispersed diamond grains. The bonding strength between the metal substrate and the coating is related to thermal stress. During the preparation process, the temperature of the coating growth can reach more than 800 degrees Celsius. When it drops to room temperature, the thermal expansion coefficients of the substrate and the coating are different, so thermal stress exists. The expansion coefficients of cemented carbide and silicon carbide are different. After adding diamond, the expansion coefficient can be adjusted. Specifically, in the early stage of coating growth, there are more silicon carbide and less diamond, and the thermal expansion coefficient tends to silicon carbide; as the coating grows, the silicon carbide decreases, the more diamonds there are, the larger the volume, and the thermal expansion coefficient tends to diamond. Finally, the expansion coefficient becomes smaller, and the bonding force between the porous diamond coating and the metal substrate is better.

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

[0068] The porous diamond coating of the present invention is not limited by the shape of the tool, can achieve rapid and controllable deposition on micro-precision tools of any complex shape, has a wide range of applications, high precision and low cost.

[0069] According to some embodiments of the present invention, the tool comprises a grinder, a reamer, a broach, a riving knife or a slotting knife. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 Schematic diagram of the preparation process of porous diamond coating.

[0071] Figure 2 The graph of coating silane prepared for base material YG6 and working time.

[0072] Figure 3 This is the microscopic morphology of the coating surface of Example 22.

[0073] Figure 4 This is the microscopic morphology of the coating surface of Example 23. DETAILED DESCRIPTION

[0074] The following are specific embodiments of the present invention, and the technical solutions of the present invention are 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, the present invention provides a porous diamond coating, comprising a metal substrate, a silicon carbide composite intermediate layer is provided on the surface of the metal substrate, and dispersed diamond grains are embedded in the silicon carbide composite intermediate layer.

[0076] Micro tools are usually based on carbide or high-speed steel and coated with diamond. Ultra-fine machining requires a smaller cutting depth, and the tool used needs to have a very sharp edge and high stability. The tool base material is usually carbide or high-speed steel, and a hard coating is plated on its surface. Diamond is an ideal tool material for ultra-fine machining due to its excellent physical and chemical properties such as extremely high hardness, extremely high wear resistance, extremely high elastic modulus, chemical affinity, etc.

[0077] It can be understood that in the processing of hard and brittle materials, on the one hand, the hard coating of the processing tool, such as the diamond coating, has poor bonding with the substrate, and the insufficient bonding between the diamond coating and the tool substrate will directly lead to coating failure and low tool life, which is a key technical problem of diamond coating technology. The present invention aims at the reason for the poor bonding force, and by arranging a silicon carbide composite intermediate layer on the surface of the metal substrate as a transition intermediate layer structure, the internal stress is reduced while suppressing the diffusion of cobalt, and the bonding force between the hard coating and the substrate is improved. On the other hand, the hard coating of the processing tool, the grinding chips generated during the grinding process are easy to block the grinding wheel, and the processing quality is poor. The porous diamond coating of the present invention has dispersed diamond grains inlaid in the silicon carbide composite intermediate layer, and gaps and porous structures are formed between these mutually dispersed diamond grains, which has the effect of preventing grinding chips from clogging. Therefore, the porous diamond coating of the present invention, when used for a tool, has good processing quality, high processing accuracy, low wear rate and long service life.

[0078] The porous diamond coating of the present invention is provided with a silicon carbide composite intermediate layer on the surface of the metal substrate, and the silicon carbide composite intermediate layer is inlaid with dispersed diamond grains. The bonding strength between the metal substrate and the coating is related to thermal stress. During the preparation process, the temperature of the coating growth can reach more than 800 degrees Celsius. When it drops to room temperature, the thermal expansion coefficients of the substrate and the coating are different, so thermal stress exists. The expansion coefficients of cemented carbide and silicon carbide are different. After adding diamond, the expansion coefficient can be adjusted. Specifically, in the early stage of coating growth, there are more silicon carbide and less diamond, and the thermal expansion coefficient tends to silicon carbide; as the coating grows, the silicon carbide decreases, the more diamonds there are, the larger the volume, and the thermal expansion coefficient tends to diamond. Finally, the expansion coefficient becomes smaller, and the bonding force between the porous diamond coating and the metal substrate is better.

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

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

[0081] In some embodiments of the present invention, a portion of each diamond grain is buried in the silicon carbide composite intermediate layer, and another portion is exposed outside the silicon carbide composite intermediate layer to form a protrusion.

[0082] The role of the silicon carbide composite intermediate layer is similar to that of a binder. A part of the diamond grains can be buried in the silicon carbide composite intermediate layer. The silicon carbide composite intermediate layer is used to improve the bonding strength between the coating and the substrate. The hole structure formed between the diamond grains can prevent the grinding wheel from being blocked by abrasive chips, and finally improve the service life of the abrasive tool. It can be understood that as an abrasive tool, in order to facilitate grinding, a large roughness is required, and the abrasive tool requires large particles on the surface. The abrasive tool is not like a drill bit. The drill bit has threads for chip removal, but the abrasive tool does not have chip removal. If the abrasive chips generated during the working process of the abrasive tool are not removed in time, it is easy to scratch the surface of the workpiece being processed. The porous diamond coating of the present invention has a porous structure formed between the diamond grains. These porous structures provide a place to accommodate the abrasive chips generated during the working process of the abrasive tool. The abrasive chips generated during the working process of the abrasive tool will flow into the holes, thereby protecting the surface of the workpiece being processed from being scratched.

[0083] In general coatings, diamond grains are completely buried in the plating layer or binder. In the porous diamond coating of the present invention, each diamond grain is partially buried in the silicon carbide composite middle layer and the other part is exposed outside the silicon carbide composite middle layer to form 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 intermediate layer.

[0085] The height and width of the diamond grain tip are equivalent to the height and width of the abrasive grain protrusion, respectively. The abrasive grain size and density will directly affect the grinding performance. The height of the diamond grain is greater than the thickness of the silicon carbide composite intermediate layer, which ensures that there are enough abrasive grain protrusions on the surface of the silicon carbide composite intermediate layer, thereby achieving better grinding effect.

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

[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 substrate comprises 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: pre-treating the surface of a metal substrate with an alkaline solution and an acidic solution in sequence, and then depositing a silicon carbide composite intermediate layer and diamond grains on the surface of the metal substrate by hot wire chemical vapor deposition.

[0092] Common coating preparation processes include polycrystalline diamond (PCD), electroplating, chemical plating, chemical vapor deposition (CVD), etc. Diamond abrasives are usually made by electroplating or brazing. Among them, electroplated tools have weak grain / matrix adhesion due to the lack of chemical bonds. Brazed diamonds will cause thermal damage due to high temperature brazing.

[0093] CVD is a technology that uses precursors to generate solid thin films through decomposition and chemical reactions between atoms in an activated environment (heat, light, plasma). It is mainly based on the fact that methane and hydrogen can be decomposed into active methyl radicals and atomic hydrogen by heating with a hot wire. Through the chemical reaction of active particles, carbon-carbon is sp 3 The diamond coating is formed by bonding, and the overall chemical reaction is: CH4 (gas) - (thermal activation) → C (diamond) + 2H2 (gas). Diamond coating deposited on the surface of cemented carbide tools can greatly improve the hardness and wear resistance of the tool surface, thereby increasing the tool life. According to the different methods of generating the activation environment, the preparation methods of CVD diamond coating can be divided into hot filament CVD (Hot Filament CVD, referred to as HFCVD), electron assisted CVD (EACVD), microwave plasma CVD (MPCVD), etc. Among them, hot filament HFCVD has the advantages of large deposition area and deposition uniformity, and is suitable for high loading and high uniformity coating of complex-shaped tools.

[0094] CVD coated diamond abrasives, due to the small grinding space between the grains, the grinding generated during the grinding process will block the grinding space and cause grinding interruption, limiting its practical application. Some new technologies or processes are complicated, costly, or only apply to pure diamond coatings on continuous surfaces, which cannot solve the problem of grinding wheels being blocked by grinding chips during the grinding process.

[0095] It can be understood that the preparation method of the present invention, after pre-treating the surface of the metal substrate with an alkaline solution and an acidic solution in sequence, can deposit a silicon carbide composite intermediate layer on the surface of the metal substrate through hot wire chemical vapor deposition, and at the same time form diamond grains. The diamond grains are dispersed with each other to form gaps and a porous structure, which produces the effect of preventing clogging by grinding chips, and ultimately solves the problem of clogging by grinding chips.

[0096] In the general preparation process of diamond coating, it is necessary to pre-plant nano-diamond seeds on the surface of the substrate. The preparation method of the present invention does not require pre-planting, which further reduces the cost and simplifies the operation.

[0097] The preparation method of the present invention can make the height of the diamond grains higher than the silicon carbide layer by regulating the growth rate of the diamond grains and the silicon carbide layer, and form holes between the diamond grains, the hole depth and width of which are controllable, effectively preventing the clogging of grinding chips. Specifically, the diamond and silicon carbide grow simultaneously at first, and because the diamond grows faster, in the coating finally prepared, the diamond is higher than the silicon carbide surface, forming a protrusion.

[0098] Silicon carbide and diamond grow simultaneously on the surface of the metal substrate. From the substrate interface to the top surface, the carbide content gradually decreases, while the diamond content gradually increases to pure diamond on the top layer, so that the longitudinal thermal expansion coefficient of the coating forms a gradual change, and the thermal stress concentrated on the interface is distributed to the transition layer containing silicon carbide, which can significantly reduce the internal stress of the coating, improve the bonding strength between the coating and the metal substrate, and at the same time improve the fracture toughness of the diamond coating.

[0099] The porous diamond coating method of the present invention comprises the following steps: pre-treating the surface of a metal substrate with an alkaline solution and an acidic solution in sequence, and then depositing a silicon carbide composite intermediate layer and diamond grains 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 metal substrate cemented carbide has cobalt 1 and tungsten carbide 2. After the surface of the metal substrate is pretreated with an alkaline solution and an acidic solution in turn, a silicon carbide composite intermediate layer 3 and diamond grains 4 are simultaneously deposited on the surface of the metal substrate by hot wire chemical vapor deposition.

[0101] By adjusting the deposition parameters, the growth of diamond grains 4 can be affected, including grain orientation, grain size and coating thickness, and the height and width of the tip of the micron diamond grains can be controlled, thereby adjusting the grinding performance of the tool. The mutually dispersed diamond grains 4 can naturally form a porous structure, without the need for subsequent treatment, simple operation and low cost.

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

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

[0104] The preparation method of the present invention does not require expensive equipment and complicated process control, has undemanding reaction conditions, has readily available raw materials, has low production costs, and is easy to industrialize.

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

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

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

[0108] In some embodiments of the present invention, after the surface of the metal substrate is pretreated with an alkaline solution, the surface of the metal substrate may be cleaned with deionized water, and the cleaning may 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 10:10-100.

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

[0112] In some embodiments of the present invention, after the surface of the metal substrate is pretreated with an acidic solution, the surface of the metal substrate can be cleaned with deionized water for multiple times. After cleaning, the surface of the metal substrate can be blown dry with nitrogen.

[0113] In some embodiments of the present invention, the method of hot wire chemical vapor deposition is: adjusting the distance between the surface of the metal substrate and the hot wire, after vacuuming, 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 step of hot wire chemical vapor deposition includes:

[0115] (1) The metal substrate is uniformly inserted into a perforated copper plate and placed under the outlet of a hot wire chemical vapor deposition device. The distance between the top of the metal substrate and the hot wire is adjusted, and then vacuum is drawn;

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

[0117] (3) turning on the hot wire power supply, adjusting the filament temperature, and continuously growing the silicon carbide composite intermediate layer and diamond grains;

[0118] (4) After growth is completed, turn off the gas, turn off the power, and evacuate the room.

[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 gas volume of the organosilane is in the range of 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 growth time of the silicon carbide composite intermediate layer and the diamond grains is 1 hour to 15 hours.

[0125] In some other embodiments of the present invention, the present invention provides the use of the porous diamond coating of the present invention or the porous diamond coating prepared by the method in a cutting tool.

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

[0127] The porous diamond coating of the present invention is not limited by the shape of the tool, can achieve rapid and controllable deposition on micro-precision tools of any complex shape, has a wide range of applications, high precision and low cost.

[0128] In some embodiments of the present invention, the tool comprises a grinder, a reamer, a broach, a riving knife or a slotting knife.

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

[0130] The present invention adds a silicon carbide composite intermediate layer between the substrate and the diamond coating. Silicon carbide is similar to a binder, burying part of the diamond grains in the silicon carbide layer, thereby improving the bonding strength between the coating and the substrate. Specifically, at the beginning of preparation, diamond and silicon carbide grow simultaneously. However, due to the faster growth rate of diamond, in the final prepared coating, the diamond is higher than the silicon carbide surface, forming a protrusion. In addition, holes are formed between the diamond grains, and the hole depth and width are controllable, which effectively prevents the clogging of grinding chips.

[0131] Examples 1-20 in Table 1 below are coating preparations on the surfaces of several different substrate materials, divided into those with and without an intermediate layer added, and those with different silane contents, and their working times are compared.

[0132] The specific preparation steps are as follows:

[0133] 1. First, chemically pretreat the carbide precision grinding tool; immerse the working area of ​​the carbide precision grinding tool in a mixed alkaline solution (K3Fe(CN)6∶KOH∶H2O=1:1:10), and ultrasonically corrode it in an ultrasonic tank (100Hz) for 15 minutes. Then take out the carbide precision grinding tool and ultrasonically clean it with deionized water for 3 times, 10 minutes each time. After cleaning, prepare a mixed acid solution (a mixture of concentrated sulfuric acid and hydrogen peroxide), weigh 10mL of concentrated sulfuric acid solution and 100mL of hydrogen peroxide solution, and mix the two thoroughly. Put the cleaned carbide precision grinding tool into the mixed acid solution for corrosion for 30 seconds, then take it out and ultrasonically clean it in deionized water for 3 times, 10 minutes each time. After cleaning, blow it dry with nitrogen.

[0134] 2. Insert the carbide micro-abrasive tool evenly into the perforated copper plate, place it under the outlet of the hot wire chemical vapor deposition, adjust the distance from the top of the carbide precision abrasive tool to the hot wire to 15mm, and then evacuate. Introduce hydrogen, methane and tetramethylsilane (1% tetramethylsilane, 99% hydrogen), with gas flow rates of 800sccm and 16sccm respectively, and keep the gas pressure at 3kPa. Turn on the hot wire power supply, the filament temperature is 2200℃, grow for 2h, then turn off tetramethylsilane and continue to grow for 5h.

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

[0136]

[0137] From the above table, we can see that the working time of the coatings prepared from the four base materials shows the same rule: the working time of the abrasive tool with the silicon carbide composite intermediate layer is significantly longer than that of the abrasive tool without the silicon carbide composite intermediate layer, and for the same base material, as the content of tetramethylsilane increases, the working time of the abrasive tool also increases, see Figure 2 As shown, Figure 2 The graph of coating silane and working time prepared for base material YG6 shows that the silicon carbide composite intermediate layer used in the present invention can effectively increase the bonding force of the diamond coating and increase the working time of the abrasive tool.

[0138] It should be noted that "working time" refers to the time from the start of machining of the abrasive tool to the time when the machining quality deteriorates and cracks appear on the surface of the machined position.

[0139] The method of the invention can realize the growth of diamond coatings on the surfaces of different cemented carbide substrate materials, and the controllable growth of the diamond coatings can be realized by adjusting the growth temperature (wire-to-bottom distance), methane content, silane content, gas pressure, growth time and other conditions, so as to obtain diamond coatings with different thicknesses and different grain sizes.

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

[0141] 1. First, chemically pretreat the carbide precision grinding tool; immerse the working area of ​​the carbide precision grinding tool in a mixed alkaline solution (K3Fe(CN)6∶KOH∶H2O=1:1:20), and ultrasonically corrode it in an ultrasonic tank (100Hz) for 15 minutes. Then take out the carbide precision grinding tool and ultrasonically clean it with deionized water for 3 times, 10 minutes each time. After cleaning, prepare a mixed acid solution (a mixture of concentrated sulfuric acid and hydrogen peroxide), weigh 10mL of concentrated sulfuric acid solution and 100mL of hydrogen peroxide solution, and mix the two thoroughly. Put the cleaned carbide precision grinding tool into the mixed acid solution for corrosion for 30 seconds, then take it out and ultrasonically clean it in deionized water for 3 times, 10 minutes each time. After cleaning, blow it dry with nitrogen.

[0142] 2. Insert the carbide micro-abrasive tool evenly into the perforated copper plate, place it under the outlet of the hot wire chemical vapor deposition, and evacuate. Set different growth temperatures and pressures. After evacuating, introduce hydrogen, methane, and silane, and control and adjust the percentage of methane and silane. Turn on the hot wire power supply, first grow for 2 hours under the condition of introducing tetramethylsilane, then turn off the tetramethylsilane and continue to grow for different times. After the growth is completed, turn off the gas, turn off the power supply, and evacuate.

[0143] Table 2 Different growth parameters and coating growth

[0144]

[0145] It can be seen from Table 2 that the method of the present invention can realize the growth of diamond coatings with different thicknesses and different grain sizes on the surfaces of different cemented carbide substrate materials. Figure 3 , Figure 4The surface morphologies of the coatings of Example 22 and Example 23 respectively show that the corresponding diamond coatings are successfully deposited on the surfaces of the abrasive tools, and the coatings are porous composite structures, which can solve the problem of chip clogging.

[0146] The present invention has been described in detail above in conjunction with the embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A porous diamond coating, characterized in that: It comprises a metal matrix, the surface of which is provided with a silicon carbide composite intermediate layer, and the silicon carbide composite intermediate layer is inlaid with dispersed diamond grains.

2. The porous diamond coating according to claim 1, characterized in that A portion of each diamond grain is buried in the silicon carbide composite intermediate layer, and another portion is exposed outside the silicon carbide composite intermediate layer to form a protrusion.

3. The porous diamond coating according to claim 1, characterized in that The height of the diamond grains is greater than the thickness of the silicon carbide composite intermediate layer.

4. The porous diamond coating according to claim 1, characterized in that The diamond grains are oriented perpendicular to the surface of the metal substrate.

5. The porous diamond coating according to any one of claims 1 to 4, characterized in that: The diamond grains include at least one of micron-sized diamond grains and submicron-sized diamond grains.

6. The porous diamond coating according to any one of claims 1 to 4, characterized in that: The metal matrix includes cemented carbide or high speed steel.

7. A method for preparing a porous diamond coating according to any one of claims 1 to 6, characterized in that: The following steps are involved: After the surface of the metal substrate is pretreated with an alkaline solution and an acidic solution in sequence, the silicon carbide composite intermediate layer and the diamond grains are deposited on the surface of the metal substrate by hot wire chemical vapor deposition.

8. The method according to claim 7, characterized in that The alkaline solution includes an inorganic base, ferrocyanide and water.

9. The method according to claim 8, characterized in that The volume ratio of the mass of the inorganic base, the mass of the ferrocyanide and the water is 1:1:10-100.

10. The method according to claim 7, characterized in that The acidic solution is a mixture of concentrated sulfuric acid and hydrogen peroxide.

11. The method according to claim 10, characterized in that The volume ratio of the concentrated sulfuric acid to the hydrogen peroxide solution is 10:10-100.

12. The method according to claim 7, characterized in that The method of hot wire chemical vapor deposition is: adjusting the distance between the surface of the metal substrate and the hot wire, after vacuuming, introducing mixed gas, heating the filament, and depositing a silicon carbide composite intermediate layer and diamond grains on the surface of the metal substrate.

13. The method according to claim 12, characterized in that The distance between the surface of the metal substrate and the hot wire is 15 mm to 30 mm.

14. The method according to claim 12, characterized in that The mixed gas includes hydrogen, methane and organic silane.

15. The method according to claim 12, characterized in that The heating filament is heated to a temperature of 1500°C to 2800°C.

16. The method according to claim 12, characterized in that The deposition growth time of the silicon carbide composite intermediate layer and the diamond grains is 1 h to 15 h.

17. Use of the porous diamond coating according to any one of claims 1 to 6 or the porous diamond coating prepared by the method according to any one of claims 7 to 16 in a cutting tool.

18. The use according to claim 17, characterized in that The tool comprises a grinder, a reamer, a broach, a riving knife or a slotting knife.

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