A diamond tool composite coating and a method for producing the same

Abstract

This invention discloses a composite coating for diamond cutting tools and its preparation method. The composite coating includes a transition layer and a main coating. The transition layer is an Fe-doped SiCN coating formed on the surface of the diamond cutting tool by a sol-gel method. The main coating is a microcrystalline diamond main coating formed on the surface of the transition layer by hot-wire chemical vapor deposition. This invention, through the design of a two-layer composite structure of an Fe-doped SiCN ceramic transition layer and a microcrystalline diamond main coating, constructs a composite coating system for diamond cutting tools suitable for different cutting conditions. This solves the technical problems of traditional WC-Co diamond cutting tools, such as Co diffusion catalytic graphitization, mismatch of thermal expansion coefficients, weak interfacial adhesion, and easy peeling and chipping of the coating.

Description

Technical Field

[0001] This invention belongs to the field of tool coating technology, specifically referring to a composite coating for diamond tools and its preparation method. Background Technology

[0002] During machining, cutting tools must withstand extreme conditions such as high temperature, high pressure, and strong abrasion. Traditional cemented carbide tools suffer from insufficient hardness and poor wear resistance, ceramic tools have low toughness and are prone to chipping, while natural diamond tools are difficult to industrialize due to resource scarcity and high cost. Therefore, developing high-performance, low-cost superhard tool coatings has become a core research direction in the machining field. Diamond, with its extremely high hardness, excellent thermal conductivity, extremely low coefficient of friction, and good chemical inertness, has become an ideal material for protective coatings on tool surfaces. Furthermore, the maturity of synthetic diamond technology has laid the foundation for the industrial application of diamond-coated tools.

[0003] Chemical vapor deposition (CVD) is the mainstream technology for preparing diamond-coated cutting tools. This technology allows for the direct growth of diamond films on the tool substrate surface, offering advantages such as low manufacturing cost and strong adhesion between the coating and the substrate. It has become the preferred tooling solution for machining non-ferrous metals and hard, brittle non-metallic materials. However, the industrial application of single-coated diamond tools still faces many technical bottlenecks, among which low adhesion strength between the coating and the substrate is the core problem leading to abnormal tool failure. In the commonly used WC-Co cemented carbide substrate, the cobalt binder phase catalyzes the graphitization transformation of diamond, destroying the sp(s) of diamond. 3 The bonding structure of diamond and cemented carbide is problematic, and the significant difference in their coefficients of thermal expansion means that the internal stress generated during deposition and cooling can easily lead to coating cracking and peeling. Even with substrate pretreatment methods such as acid leaching to remove cobalt and plasma etching, it is still difficult to completely prevent the thermal diffusion of cobalt from the substrate to the coating at high temperatures, failing to fundamentally solve the interfacial bonding problem. Furthermore, single diamond coatings lack high-temperature stability. Under high-speed dry cutting conditions above 600°C, diamond is prone to oxidation and graphitization, resulting in rapid degradation of coating performance. At the same time, diamond coatings prepared by traditional CVD processes have large grains and high surface roughness, which exacerbates friction and wear during cutting, while subsequent polishing processes can easily damage the bonding interface between the coating and the substrate, creating new performance defects.

[0004] Composite coatings achieve synergistic performance enhancements by introducing transition layers, composite ceramic / metal phases, and constructing gradient / nanocomposite structures. Composite coatings involve depositing metallic transition layers such as Ti and Cr, or ceramic transition layers such as TiN, Al2O3, and SiC, between the substrate and the diamond coating. The metallic transition layer enhances interfacial chemical bonding through the formation of covalent bonds (CM), while the ceramic transition layer effectively blocks cobalt diffusion and alleviates the problem of thermal expansion coefficient mismatch. Currently, the main technologies for preparing diamond composite coatings are CVD processes, physical vapor deposition (PVD), and combinations of both. Hot-wire CVD (HFCVD) is simple, efficient, and low-cost, suitable for industrial mass production, but the coatings have coarse grains, poor uniformity, and are prone to porosity. Microwave plasma CVD (MPCVD) can prepare high-purity, low-stress diamond coatings with good crystal nucleus uniformity, making it the preferred method for high-quality diamond coatings; however, the equipment is complex, the deposition cost is high, and it is difficult to adapt to the preparation of coatings for complex-shaped cutting tools. PVD, due to its low deposition temperature, is suitable for preparing metal / ceramic transition layers. However, it cannot grow pure crystalline diamond, only diamond-like carbon (DLC) coatings, whose performance is significantly inferior to that of diamond. To balance coating quality and preparation efficiency, CVD-PVD combined technology has become a research hotspot. This technology combines PVD to prepare the transition layer with CVD to grow the diamond coating, achieving complementary advantages. However, this technology currently suffers from poor matching of deposition parameters and inconsistencies in process integration, easily leading to low coating density and reduced interfacial adhesion, thus preventing its industrial application. Summary of the Invention

[0005] To address the above issues and overcome the shortcomings of existing technologies, this invention provides a composite coating for diamond cutting tools and its preparation method. This invention utilizes a two-layer composite structure design of an Fe-doped SiCN ceramic transition layer and a microcrystalline diamond main coating to construct a composite coating system for diamond cutting tools suitable for different cutting conditions. This solves the technical problems of traditional WC-Co diamond cutting tools, such as Co diffusion catalytic graphitization, thermal expansion coefficient mismatch, weak interfacial bonding, and easy peeling and chipping of the coating.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention proposes a composite coating for diamond cutting tools, the composite coating comprising a transition layer and a main coating; the transition layer is an Fe-doped SiCN coating formed on the surface of the diamond cutting tool by a sol-gel method; the main coating is a microcrystalline diamond main coating formed on the surface of the transition layer by hot-wire chemical vapor deposition.

[0007] Preferably, the Fe-doped SiCN coating uses Fe-polysilazane precursor as a slurry, and forms a transition layer on the surface of the diamond tool substrate through dip coating, curing and pyrolysis treatment;

[0008] Preferably, the Fe-polysilazane precursor is first formed into polysilazane from methyldichlorosilane, (chloromethyl)methyldichlorosilane and hexamethyldisilazane, and then subjected to S... N 2. Alkylation reaction: Acetylacetone is modified onto the side chain of polysilazane. Finally, Fe is modified via the acetylacetone side chain groups. 3+ The chelation reaction of the chelating agent with ferric chloride hexahydrate yields the Fe-polysilazane precursor.

[0009] Preferably, the molar ratio between methyldichlorosilane, (chloromethyl)methyldichlorosilane and hexamethyldisilazane is 4-5:2-3:3-5;

[0010] Preferably, the molar ratio of (chloromethyl)methyldichlorosilane to acetylacetone is 1:1.1-1.3;

[0011] Preferably, the molar ratio of acetylacetone to ferric chloride hexahydrate is 1:0.1-0.3;

[0012] Preferably, the thickness of the transition layer is 0.5-3 μm;

[0013] Preferably, the thickness of the main coating is 8-20 μm;

[0014] This invention also provides a method for preparing a composite coating for diamond cutting tools, specifically including the following steps:

[0015] Preparation of S1, Fe-polysilazane precursors:

[0016] S11. Dissolve methyldichlorosilane and (chloromethyl)methyldichlorosilane in anhydrous toluene, introduce flowing argon gas, raise the reaction temperature, and add hexamethyldisilazane dropwise to the reaction system. After the addition is complete, maintain the reaction temperature to carry out the condensation reaction. After the reaction is completed, cool, distill under reduced pressure, and dry to obtain polysilazane.

[0017] Preferably, in step S11, the reaction temperature of the condensation reaction is 80-90℃, and the reaction time of the condensation reaction is 6-8h;

[0018] S12. Dissolve the polysilazane prepared in step S11 in anhydrous THF. Under an argon atmosphere, add boric anhydride and tributyl borate. After stirring and mixing evenly, add acetylacetone and raise the reaction temperature to carry out the alkylation reaction. After the reaction is completed, cool and add deionized hydrolysate excess boric anhydride and tributyl borate. After standing and separating into layers, collect the organic phase, wash the organic phase with deionized water, dry and remove water, and then perform vacuum distillation to obtain the modified polysilazane.

[0019] Preferably, in step S12, the molar ratio between acetylacetone, boric anhydride, and tributyl borate is 20-25:2:1.

[0020] Preferably, in step S12, the reaction temperature of the alkylation reaction is 50-60°C, and the reaction time of the alkylation reaction is 4-6 hours.

[0021] S13. Dissolve the modified polysilazane prepared in step S12 in a toluene / n-hexane mixed solvent. Dissolve ferric chloride hexahydrate in anhydrous ethanol and add it dropwise to the reaction system. Keep the room temperature, add KH570, and stir continuously to carry out the chelation reaction. During the reaction, the reaction system is ultrasonically dispersed. After the reaction is completed, adjust the viscosity of the reaction system to 800-2000 mPa•s, filter the membrane, and obtain the Fe-polysilazane precursor.

[0022] Preferably, in step S13, the added mass of KH-570 is 0.3%-0.8% of the mass of the modified polysilazane;

[0023] Preferably, in step S13, the stirring speed of the chelation reaction is 600-800 rpm, and the reaction time of the chelation reaction is 2.5-5 h;

[0024] S2. Pretreatment of diamond tool substrate:

[0025] S21. Cobalt removal treatment: Prepare the first and second cobalt removal solutions, and wash the diamond tool substrate in the first and second cobalt removal solutions in sequence. Then wash the surface of the diamond tool substrate with deionized water until it is neutral.

[0026] Preferably, in step S21, the first cobalt removal solution is composed of concentrated nitric acid, hydrofluoric acid and deionized water in a volume ratio of 10-15:3-5:180-187.

[0027] Preferably, in step S21, the second cobalt removal solution is composed of concentrated nitric acid and deionized water in a volume ratio of 3-5:95-97.

[0028] S22. Surface roughening treatment: Disperse diamond micro powder in deionized water to obtain diamond micro powder suspension. Place the diamond tool substrate after cobalt removal treatment in the diamond micro powder suspension for ultrasonic grinding. After rinsing with deionized water, it is ready for use.

[0029] Preferably, in step S22, the mass fraction of the diamond micropowder in deionized water is 0.3%-0.8%;

[0030] S23. Cleaning and activation treatment: The diamond tool substrate after surface roughening treatment is placed in acetone and anhydrous ethanol for ultrasonic cleaning, vacuum drying, and then sealed to obtain a pretreated diamond tool substrate for later use.

[0031] S3. Preparation of the transition layer:

[0032] S31. Pre-coating treatment: Take the Fe-polysilazane precursor prepared in step S1 and place it in the slurry tank of the dip-coating machine. After it is evenly dispersed, the pre-treated diamond tool substrate is dipped and coated. After completion, a pre-coated substrate is obtained.

[0033] Preferably, in step S31, the parameters of the immersion and lifting treatment include: immersion speed: 3000-3500μm / s, immersion time: 10-15s, pull-out speed: 3000-3200μm / s, and standing time after pull-out: 5-10min;

[0034] S32. Low-temperature curing treatment: The pre-coated substrate prepared in step S31 is placed in a forced-air drying oven for low-temperature segmented curing treatment. After the treatment is completed, it is cooled to obtain a low-temperature cured coating substrate.

[0035] Preferably, in step S32, the low-temperature segmented curing treatment parameters include: first stage: 60-80℃, holding for 30 min; second stage: heating to 120-130℃ at a heating rate of 1℃ / min, holding for 1-1.5 h; third stage: heating to 170-180℃ at a heating rate of 1℃ / min, holding for 2-3 h.

[0036] S33. Pyrolysis treatment: The low-temperature curing coating substrate prepared in step S32 is placed in a quartz boat and subjected to pyrolysis treatment in a high-purity nitrogen atmosphere. After the treatment, it is cooled to form a transition layer on the surface of the diamond tool substrate, thus obtaining the transition layer coating substrate.

[0037] Preferably, in step S33, the gradient heating program for the pyrolysis treatment includes: a first stage: heating to 300-400℃ at a heating rate of 1℃ / min and holding for 0.5-1.5h; a second stage: heating to 800-850℃ at a heating rate of 1℃ / min and holding for 2-3h.

[0038] S4. Preparation of the main coating by HFCVD: The transition layer coating substrate prepared in step S3 is transferred to the HFCVD equipment. The temperature of the hot filament and the transition layer coating substrate is adjusted. High-purity methane is introduced at a volume concentration of 1%-3%, and the pressure in the deposition chamber is maintained at 15-30 kPa. After deposition for 2-6 hours, the methane inlet valve is closed, and hydrogen is continuously introduced to maintain the temperature of the hot filament. Post-treatment is performed, heating is stopped, hydrogen is stopped, and the diamond tool is cooled under vacuum to obtain the diamond tool composite coating.

[0039] Preferably, in step S4, the hot wire temperature is 2000-2200℃, and the transition layer coating substrate temperature is 758-850℃.

[0040] The beneficial effects achieved by this invention are as follows:

[0041] This invention provides a composite coating for diamond cutting tools and its preparation method. The invention utilizes a two-layer composite structure design of an Fe-doped SiCN ceramic transition layer and a microcrystalline diamond main coating to construct a composite coating system for diamond cutting tools adaptable to different cutting conditions. This solves the technical problems of traditional WC-Co diamond cutting tools, such as Co diffusion-catalyzed graphitization, thermal expansion coefficient mismatch, weak interfacial adhesion, and easy coating peeling and chipping. In this invention, Fe molecular-level chelation doping is achieved through a three-step organic synthesis to prepare a Fe-uniformly dispersed polysilazane precursor. 3+ Fe is embedded in the polysilazane molecular chain in the form of a six-coordinate chelate, achieving molecular-level uniform dispersion. The amount of Fe doping is precisely controlled by the molar ratio of the chelation reaction, avoiding performance failure caused by excessive or insufficient Fe agglomeration. Fe is dispersed in the polysilazane precursor at the atomic / molecular scale, without micron-sized Fe particle agglomeration. After pyrolysis, Fe is uniformly distributed in the grain boundaries / lattice of the SiCN ceramic phase, without forming structural defects such as pores and cracks. The covalent bonding of the chelation reaction allows Fe to form a stable structure with the polysilazane backbone. Fe does not migrate or agglomerate during pyrolysis, ensuring the overall density and uniformity of the transition layer. Molecular-level Fe doping improves the density of the transition layer and prevents the diffusion of Co atoms from the WC-Co matrix to the diamond coating at high temperatures, thus avoiding diamond graphitization at the source. The uniformly dispersed Fe particles serve as active nucleation sites for diamond deposition, increasing the diamond nucleus density. This significantly improves the density and structural integrity of the diamond coating, addressing the problems of uneven nucleation and coarse grains in traditional diamond coatings. The dip-coating method achieves seamless coating of WC-Co matrix, followed by low-temperature segmented curing to uniformly form a film that covers critical cutting areas such as tool edges, tips, and helical grooves with a dense transition layer. This avoids the localized coating problems of traditional spraying / vapor deposition methods and eliminates Co diffusion channels caused by the absence of a transition layer in certain areas, achieving highly efficient Co barrier coating across the entire tool surface. The pre-coating is defect-free and fully cross-linked, resulting in more uniform inorganic rearrangement during high-temperature pyrolysis. The transition layer is free of microcracks and pores caused by pyrolysis, maintaining its density and ensuring stable Co barrier efficiency. The liquid-phase film-forming characteristics of dip-coating are adaptable to diamond tools of various shapes, such as end mills, drills, and inserts, solving the problem of poor coating uniformity for complex tools in traditional vapor deposition methods and expanding the application range of the transition layer. Under an argon-oxygen-free atmosphere, gradient-heating pyrolysis of the polysilazane precursor causes main chain breakage and atomic rearrangement, forming a Si / C / N covalently bonded SiCN ceramic phase. Simultaneously, chelated Fe... 3+During pyrolysis, it is reduced and undergoes in-situ bonding with Si / C / N to generate phases such as Fe3Si, FeN, and Fe3C. Furthermore, the transition layer undergoes in-situ chemical reaction at the interface with the WC-Co matrix (Fe / Si reacts with the W / C matrix to generate Fe3W and SiC). The dense SiCN covalent bond network forms a physical barrier, preventing the bulk diffusion of Co atoms. At the same time, the SiCN ceramic phase has extremely high chemical inertness, and the in-situ bonding of Fe further fills the SiCN grain boundaries, leaving no diffusion path for Co atoms. The SiCN ceramic phase formed by pyrolysis has good thermal stability, with no crystal transformation or density decrease below 850℃. Even under long-term temperature rise during high-temperature heavy cutting of titanium alloys, the transition layer structure remains stable, and the Co blocking efficiency does not decrease. This solves the problems of structural failure and decreased Co blocking ability of traditional transition layers at high temperatures. Attached Figure Description

[0042] Figure 1 The image shows the Vickers hardness results of the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 of this invention.

[0043] Figure 2 The figures show the wear resistance results of the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 of this invention.

[0044] Figure 3 The diagram shows the cutting performance results of the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 of this invention.

[0045] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0048] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the experimental materials and test strains used in the following examples were purchased from commercial channels.

[0049] Example 1

[0050] This embodiment provides a method for preparing a composite coating for diamond cutting tools, specifically including the following steps:

[0051] Preparation of S1, Fe-polysilazane precursors:

[0052] S11. Accurately weigh 5.0 mL of methyldichlorosilane and 4.7 mL of (chloromethyl)methyldichlorosilane into a three-necked flask, add 200 mL of anhydrous toluene, stir at 800 rpm, introduce flowing nitrogen into the reaction system, raise the reaction temperature to 80°C under nitrogen atmosphere, keep warm and stir for 30 min, mix the reaction system evenly, and add 12.5 mL of hexamethyldisilazane dropwise into the reaction system at a rate of 1 drop / 2 s through a constant pressure dropping funnel. After the addition is complete, keep the reaction temperature at 80°C and carry out the condensation reaction for 8 h. After the reaction is completed, let the reaction system cool naturally to room temperature, and then perform vacuum distillation to remove unreacted components and solvent to obtain polysilazane.

[0053] S12. Accurately weigh 10g of the polysilazane prepared in step S11 and place it in a three-necked flask. Add 150mL of anhydrous THF to the flask, introduce flowing argon gas, and stir at 500rpm until the reaction system is homogeneous. Then, add 0.24g of boric anhydride and 0.5mL of tributyl borate to the reaction system, increase the stirring speed to 700rpm, and stir until homogeneous. Add 4.4mL of acetylacetone, raise the reaction temperature to 50℃, and continue stirring to carry out the alkylation reaction. After 6h, the reaction system will darken in color. After the reaction is completed, turn off the heating and let the reaction system cool naturally to room temperature. Add 50mL of deionized water to the reaction system to hydrolyze the excess boric anhydride / tributyl borate. Transfer the reaction system to a separatory funnel, let it stand, and after separation, collect the upper organic phase. Wash the organic phase with deionized water, dry the organic phase with anhydrous sodium sulfate, and then distill under reduced pressure to remove the solvent to obtain the modified polysilazane.

[0054] S13. Add 10g of the modified polysilazane prepared in step S12 to the flask, add 100mL of toluene / n-hexane mixed solvent (toluene to n-hexane volume ratio is 1:1), and stir at 600rpm until the reaction system is uniformly mixed. Accurately weigh 2.3g of ferric chloride hexahydrate and dissolve it in 50mL of anhydrous ethanol. Add it dropwise to the reaction system through a constant pressure dropping funnel at a rate of 1 drop / 2s. After the addition is complete, keep at room temperature and continue stirring to carry out the chelation reaction. After 4h of reaction, add 80mg of KH-570 to the reaction system and continue stirring for 1h. Transfer the reaction system to an ultrasonic dispersion and ultrasonically disperse at 300W. After 30min, slowly add toluene / n-hexane mixed solvent to the slurry and adjust the viscosity of the reaction system to 800mPa·s. Filter through a 0.22μm organic phase membrane to obtain the Fe-polysilazane precursor.

[0055] S2. Pretreatment of diamond tool substrate:

[0056] S21. Cobalt Removal Treatment: Take 10 mL of 68% concentrated nitric acid, 3 mL of 40% hydrofluoric acid, and 187 mL of deionized water, mix them thoroughly, and let them stand at room temperature for 10 minutes to obtain the first cobalt removal solution. Take 5 mL of 68% concentrated nitric acid and 95 mL of deionized water, mix them thoroughly, and let them stand at room temperature for 10 minutes to obtain the second cobalt removal solution. Place the diamond tool substrate into the first cobalt removal solution and soak it at room temperature for 8 minutes. During this time, gently shake the container to ensure that all areas of the substrate surface are in contact with the cobalt removal solution. Remove the substrate with tweezers and place it in deionized water. Ultrasonically clean it for 5 minutes. Place the substrate into the second cobalt removal solution and soak it at room temperature for 5 minutes. After soaking, ultrasonically clean it again with deionized water for 5 minutes. Rinse the substrate surface with deionized water 3 times until the rinsing solution is neutral.

[0057] S22. Surface roughening treatment: Mix 0.5g of diamond micro powder (1μm) with 100mL of deionized water, put it into an ultrasonic cleaner, and ultrasonically disperse it for 10min to obtain a uniform diamond micro powder suspension. Put the cobalt-free substrate into the diamond micro powder suspension and ultrasonically grind it for 10min. During this period, gently turn the substrate every 2min to ensure that the surface of the substrate is roughened. Take out the substrate, ultrasonically clean it with deionized water for 5min to remove the diamond micro powder attached to the surface, and then rinse it with deionized water 3 times until there is no obvious powder residue on the surface.

[0058] S23. Cleaning and Activation Treatment: Place the roughened substrate in acetone and ultrasonically clean for 15 minutes to remove surface oil and cutting fluid residue. Remove the substrate and place it in anhydrous ethanol for ultrasonic cleaning for 15 minutes. Remove the substrate with tweezers and place it in a forced-air drying oven for vacuum drying at 80°C for 1 hour. After drying, immediately remove the substrate and place it in the fixture of the dip-coating machine. Seal the equipment to obtain the pretreated diamond tool substrate.

[0059] S3. Preparation of the transition layer:

[0060] S31. Pre-coating treatment: Take the Fe-polysilazane precursor prepared in step S1 and place it in the slurry tank of the dip-coating machine. Disperse it ultrasonically for 10 minutes. Adjust the clamps of the dip-coating machine to ensure that the pre-treated diamond tool substrate is suspended vertically with the cutting edge facing down. Set the dip-coating parameters as follows: dip speed: 3000 μm / s, dip time: 10s, pull-out speed: 3000 μm / s, and settling time after pull-out: 5 minutes. After the pull-out is completed, the pre-coated substrate is obtained.

[0061] S32. Low-temperature curing treatment: Place the pre-coated substrate prepared in step S31 in a forced-air drying oven and set the low-temperature segmented curing parameters as follows: First stage: 60℃, hold for 50 min; Second stage: heat up to 120℃ at a heating rate of 1℃ / min, hold for 1 h; Third stage: heat up to 180℃ at a heating rate of 1℃ / min, hold for 2 h, and cool to room temperature at a cooling rate of 1℃ / min to obtain the low-temperature cured coating substrate.

[0062] S33. Pyrolysis treatment: Take the low-temperature curing coating substrate prepared in step S32 out of the forced-air drying oven and immediately place it in the quartz boat of the tube furnace. Push the quartz boat into the central heating zone of the tube furnace, close the furnace door, seal it, evacuate and introduce flowing argon gas to keep the furnace free of air and oxygen. Set a gradient heating program for pyrolysis treatment: First stage: heat up to 400℃ at a heating rate of 1℃ / min and hold for 30min. Second stage: heat up to 850℃ at a heating rate of 1℃ / min and hold for 2h. Turn off the heating power and wait for the furnace temperature to cool naturally to room temperature to form a transition layer on the surface of the diamond tool substrate. The thickness of the transition layer is 1μm, and the transition layer coating substrate is obtained with a thickness of 0.5μm.

[0063] S4. Preparation of the main coating by HFCVD method:

[0064] Connect the tube furnace to the vacuum pipe of the HFCVD equipment, open the valve, and transfer the transition layer coating substrate prepared in step S3 from the tube furnace to the deposition chamber of the HFCVD equipment. Close the connecting valve, turn on the vacuum pump of the HFCVD equipment, and evacuate to 5 × 10⁻⁶. -3At 100 sccm, high-purity hydrogen gas was introduced to flush the deposition chamber for 10 minutes to remove residual impurities. The hydrogen gas was then turned off, and the vacuum was evacuated again to 5 × 10⁻⁶ Pa. -3 At kPa, turn on the hot filament power supply (tantalum wire, 0.5 mm in diameter, 50 mm in length), adjust the hot filament temperature to 2000℃ (tested with an optical pyrometer), control the distance between the hot filament and the substrate to 8-10 mm, introduce high-purity hydrogen gas (flow rate 80 sccm), maintain the deposition chamber pressure at 15 kPa, and adjust the substrate temperature (transition layer surface temperature) to 800℃ through the thermal radiation of the hot filament (slightly lower than the pyrolysis temperature of the transition layer to avoid damage to the transition layer), hold for 30 min, keep the hot filament temperature and substrate temperature constant, introduce high-purity methane (carbon source), and adjust the methane gas... The concentration was increased to 1% (methane flow rate 1 sccm, hydrogen flow rate 99 sccm), the pressure in the deposition chamber was maintained at 15 kPa, the deposition timer was started, and the deposition time was 2 hours. After the deposition time was reached, the methane inlet valve was closed first, and hydrogen was continued to be introduced. The hot wire temperature was maintained at 2000℃ for 30 minutes. The hot wire power was turned off, the hydrogen supply was stopped, and the deposition chamber was kept in a vacuum state. It was allowed to cool naturally to room temperature, and high-purity nitrogen (flow rate 50 sccm) was introduced to balance the gas pressure inside and outside the chamber (0.1 MPa). The thickness of the main coating was 10 μm, and the composite coating for diamond tools was obtained.

[0065] This embodiment also provides a composite coating for diamond tools prepared according to the above method.

[0066] Example 2

[0067] This embodiment provides a method for preparing a composite coating for diamond cutting tools, specifically including the following steps:

[0068] Preparation of S1, Fe-polysilazane precursors:

[0069] S11. Accurately weigh 8.0 mL of methyldichlorosilane and 5.6 mL of (chloromethyl)methyldichlorosilane into a three-necked flask, add 200 mL of anhydrous toluene, stir at 800 rpm, introduce flowing nitrogen into the reaction system, raise the reaction temperature to 85°C under nitrogen atmosphere, keep it at this temperature and stir for 30 min, mix the reaction system evenly, and then add 10.7 mL of hexamethyldisilazane dropwise into the reaction system at a rate of 1 drop / 2 s through a constant pressure dropping funnel. After the addition is complete, maintain the reaction temperature at 85°C and carry out the condensation reaction for 7 h. After the reaction is completed, let the reaction system cool naturally to room temperature, and then perform vacuum distillation to remove unreacted components and solvent to obtain polysilazane.

[0070] S12. Accurately weigh 15g of the polysilazane prepared in step S11 and place it in a three-necked flask. Add 150mL of anhydrous THF to the flask, introduce flowing argon gas, and stir at 500rpm until the reaction system is homogeneous. Then, add 0.29g of boric anhydride and 0.6mL of tributyl borate to the reaction system, increase the stirring speed to 700rpm, and stir until homogeneous. Add 4.8mL of acetylacetone, raise the reaction temperature to 55℃, and continue stirring to carry out the alkylation reaction. After 5h, the reaction system will darken in color. After the reaction is completed, turn off the heating and let the reaction system cool naturally to room temperature. Add 50mL of deionized water to the reaction system to hydrolyze the excess boric anhydride / tributyl borate. Transfer the reaction system to a separatory funnel, let it stand, and after separation, collect the upper organic phase. Wash the organic phase with deionized water, dry the organic phase with anhydrous sodium sulfate, and then distill under reduced pressure to remove the solvent to obtain the modified polysilazane.

[0071] S13. Add 15g of the modified polysilazane prepared in step S12 to the flask, add 100mL of toluene / n-hexane mixed solvent (toluene to n-hexane volume ratio is 1:1), and stir at 700rpm until the reaction system is uniformly mixed. Accurately weigh 1.9g of ferric chloride hexahydrate and dissolve it in 50mL of anhydrous ethanol. Add it dropwise to the reaction system through a constant pressure dropping funnel at a rate of 1 drop / 2s. After the addition is complete, maintain room temperature and continue stirring to carry out the chelation reaction. After the reaction is 3h, add 0.1g of KH-570 to the reaction system and continue stirring for 1h. Transfer the reaction system to an ultrasonic dispersion and ultrasonically disperse at 300W. After 30min, slowly add toluene / n-hexane mixed solvent to the slurry and adjust the viscosity of the reaction system to 1400mPa•s. Filter through a 0.22μm organic phase membrane to obtain the Fe-polysilazane precursor.

[0072] S2. Pretreatment of diamond tool substrate:

[0073] S21. Cobalt Removal Treatment: Take 12 mL of 68% concentrated nitric acid, 4 mL of 40% hydrofluoric acid, and 184 mL of deionized water, mix them evenly, and let them stand at room temperature for 10 minutes to obtain the first cobalt removal solution. Take 3 mL of 68% concentrated nitric acid and 97 mL of deionized water, mix them evenly, and let them stand at room temperature for 10 minutes to obtain the second cobalt removal solution. Place the diamond tool substrate into the first cobalt removal solution and soak it at room temperature for 8 minutes. During this time, gently shake the container to ensure that all areas of the substrate surface are in contact with the cobalt removal solution. Remove the substrate with tweezers and place it in deionized water. Ultrasonically clean it for 5 minutes. Place the substrate into the second cobalt removal solution and soak it at room temperature for 5 minutes. After soaking, ultrasonically clean it again with deionized water for 5 minutes. Rinse the substrate surface with deionized water 3 times until the rinsing solution is neutral.

[0074] S22. Surface roughening treatment: Mix 0.65g of diamond micro powder (1μm) with 100mL of deionized water, put it into an ultrasonic cleaner, and ultrasonically disperse it for 10min to obtain a uniform diamond micro powder suspension. Put the cobalt-free substrate into the diamond micro powder suspension and ultrasonically grind it for 10min. During this period, gently turn the substrate every 2min to ensure that the surface of the substrate is roughened. Take out the substrate, ultrasonically clean it with deionized water for 5min to remove the diamond micro powder attached to the surface, and then rinse it with deionized water 3 times until there is no obvious powder residue on the surface.

[0075] S23. Cleaning and Activation Treatment: Place the roughened substrate in acetone and ultrasonically clean for 15 minutes to remove surface oil and cutting fluid residue. Remove the substrate and place it in anhydrous ethanol for ultrasonic cleaning for 15 minutes. Remove the substrate with tweezers and place it in a forced-air drying oven for vacuum drying at 80°C for 1 hour. After drying, immediately remove the substrate and place it in the fixture of the dip-coating machine. Seal the equipment to obtain the pretreated diamond tool substrate.

[0076] S3. Preparation of the transition layer:

[0077] S31. Pre-coating treatment: Take the Fe-polysilazane precursor prepared in step S1 and place it in the slurry tank of the dip-coating machine. Disperse it ultrasonically for 10 minutes. Adjust the clamps of the dip-coating machine to ensure that the pre-treated diamond tool substrate is suspended vertically with the cutting edge facing down. Set the dip-coating parameters as follows: dip speed: 3200 μm / s, dip time: 15s, pull-out speed: 3100 μm / s, and settling time after pull-out: 7 minutes. After the pull-out is completed, the pre-coated substrate is obtained.

[0078] S32. Low-temperature curing treatment: Place the pre-coated substrate prepared in step S31 in a forced-air drying oven and set the low-temperature segmented curing parameters as follows: First stage: 70℃, hold for 30 min; Second stage: heat up to 125℃ at a heating rate of 1℃ / min, hold for 1.5 h; Third stage: heat up to 170℃ at a heating rate of 1℃ / min, hold for 3 h, and cool to room temperature at a cooling rate of 1℃ / min to obtain the low-temperature cured coating substrate.

[0079] S33. Pyrolysis treatment: Take the low-temperature curing coating substrate prepared in step S32 out of the forced-air drying oven and immediately place it in the quartz boat of the tube furnace. Push the quartz boat into the central heating zone of the tube furnace, close the furnace door, seal it, evacuate and introduce flowing argon gas to keep the furnace free of air and oxygen. Set a gradient heating program for pyrolysis treatment: First stage: heat up to 300℃ at a heating rate of 1℃ / min and hold for 1.5h. Second stage: heat up to 800℃ at a heating rate of 1℃ / min and hold for 3h. Turn off the heating power and wait for the furnace temperature to cool naturally to room temperature to form a transition layer on the surface of the diamond tool substrate. The thickness of the transition layer is 2μm, and the transition layer coating substrate is obtained. The thickness of the transition layer is 2μm.

[0080] S4. Preparation of the main coating by HFCVD method:

[0081] Connect the tube furnace to the vacuum pipe of the HFCVD equipment, open the valve, and transfer the transition layer coating substrate prepared in step S3 from the tube furnace to the deposition chamber of the HFCVD equipment. Close the connecting valve, turn on the vacuum pump of the HFCVD equipment, and evacuate to 5 × 10⁻⁶. -3 At 100 sccm, high-purity hydrogen gas was introduced to flush the deposition chamber for 10 minutes to remove residual impurities. The hydrogen gas was then turned off, and the vacuum was evacuated again to 5 × 10⁻⁶ Pa. -3 At kPa, turn on the hot filament power supply (tantalum wire, 0.5 mm in diameter, 50 mm in length), adjust the hot filament temperature to 2100℃ (tested with an optical pyrometer), control the distance between the hot filament and the substrate to 8-10 mm, introduce high-purity hydrogen gas (flow rate 80 sccm), maintain the deposition chamber pressure at 15 kPa, and adjust the substrate temperature (transition layer surface temperature) to 750℃ (slightly below the transition layer pyrolysis temperature to avoid damage to the transition layer) through the thermal radiation of the hot filament, hold for 30 min, keep the hot filament temperature and substrate temperature constant, introduce high-purity methane (carbon source), and adjust the methane gas... The concentration was increased to 2% (methane flow rate 2 sccm, hydrogen flow rate 98 sccm), the pressure in the deposition chamber was maintained at 20 kPa, the deposition timer was started, and the deposition time was 4 hours. After the deposition time was reached, the methane inlet valve was closed first, and hydrogen was continued to be introduced. The hot wire temperature was maintained at 2000℃ for 30 minutes. The hot wire power was turned off, the hydrogen supply was stopped, and the deposition chamber was kept in a vacuum state. It was allowed to cool naturally to room temperature, and high-purity nitrogen (flow rate 50 sccm) was introduced to balance the gas pressure inside and outside the chamber (0.1 MPa). The thickness of the main coating was 15 μm, and the composite coating for diamond tools was obtained.

[0082] This embodiment also provides a composite coating for diamond tools prepared according to the above method.

[0083] Example 3

[0084] This embodiment provides a method for preparing a composite coating for diamond cutting tools, specifically including the following steps:

[0085] Preparation of S1, Fe-polysilazane precursors:

[0086] S11. Accurately weigh 10.0 mL of methyldichlorosilane and 5.1 mL of (chloromethyl)methyldichlorosilane into a three-necked flask, add 200 mL of anhydrous toluene, stir at 800 rpm, introduce flowing nitrogen into the reaction system, raise the reaction temperature to 90°C under nitrogen atmosphere, keep warm and stir for 30 min, mix the reaction system evenly, and add 16.0 mL of hexamethyldisilazane dropwise into the reaction system at a rate of 1 drop / 2 s through a constant pressure dropping funnel. After the addition is complete, keep the reaction temperature at 90°C and carry out the condensation reaction for 6 h. After the reaction is completed, let the reaction system cool naturally to room temperature, and then perform vacuum distillation to remove unreacted components and solvent to obtain polysilazane.

[0087] S12. Accurately weigh 20g of the polysilazane prepared in step S11 and place it in a three-necked flask. Add 150mL of anhydrous THF to the flask, introduce flowing argon gas, and stir at 500rpm until the reaction system is homogeneous. Then, add 0.35g of boric anhydride and 0.7mL of tributyl borate to the reaction system, increase the stirring speed to 700rpm, and stir until homogeneous. Add 5.1mL of acetylacetone, raise the reaction temperature to 60℃, and continue stirring to carry out the alkylation reaction. After 4h, the color of the reaction system darkens. After the reaction is completed, turn off the heating and let the reaction system cool naturally to room temperature. Add 50mL of deionized water to the reaction system to hydrolyze the excess boric anhydride / tributyl borate. Transfer the reaction system to a separatory funnel, let it stand, and after separation, collect the upper organic phase. Wash the organic phase with deionized water, dry the organic phase with anhydrous sodium sulfate, and then distill under reduced pressure to remove the solvent to obtain the modified polysilazane.

[0088] S13. Add 20g of the modified polysilazane prepared in step S12 to the flask, add 100mL of toluene / n-hexane mixed solvent (toluene to n-hexane volume ratio is 1:1), and stir at 800rpm until the reaction system is uniformly mixed. Accurately weigh 1.4g of ferric chloride hexahydrate and dissolve it in 50mL of anhydrous ethanol. Add it dropwise to the reaction system through a constant pressure dropping funnel at a rate of 1 drop / 2s. After the addition is complete, maintain room temperature and continue stirring to carry out the chelation reaction. After 2h of reaction, add 90mg of KH-570 to the reaction system and continue stirring for 0.5h. Transfer the reaction system to an ultrasonic dispersion and ultrasonically disperse at 300W. After 30min, slowly add toluene / n-hexane mixed solvent to the slurry and adjust the viscosity of the reaction system to 2000mPa•s. Filter through a 0.22μm organic phase membrane to obtain the Fe-polysilazane precursor.

[0089] S2. Pretreatment of diamond tool substrate:

[0090] S21. Cobalt Removal Treatment: Take 15 mL of 68% concentrated nitric acid, 5 mL of 40% hydrofluoric acid, and 180 mL of deionized water, mix them thoroughly, and let them stand at room temperature for 10 minutes to obtain the first cobalt removal solution. Take 4 mL of 68% concentrated nitric acid and 96 mL of deionized water, mix them thoroughly, and let them stand at room temperature for 10 minutes to obtain the second cobalt removal solution. Place the diamond tool substrate into the first cobalt removal solution and soak it at room temperature for 8 minutes. During this time, gently shake the container to ensure that all areas of the substrate surface are in contact with the cobalt removal solution. Remove the substrate with tweezers and place it in deionized water. Ultrasonically clean it for 5 minutes. Place the substrate into the second cobalt removal solution and soak it at room temperature for 5 minutes. After soaking, ultrasonically clean it again with deionized water for 5 minutes. Rinse the substrate surface with deionized water 3 times until the rinsing solution is neutral.

[0091] S22. Surface roughening treatment: Mix 0.8g of diamond micro powder (1μm) with 100mL of deionized water and place it in an ultrasonic cleaner. Disperse the mixture ultrasonically for 10min to obtain a uniform diamond micro powder suspension. Place the cobalt-free substrate into the diamond micro powder suspension and ultrasonically grind for 10min. During this period, gently turn the substrate every 2min to ensure that the substrate surface is roughened. Remove the substrate and ultrasonically clean it with deionized water for 5min to remove the diamond micro powder attached to the surface. Rinse it with deionized water 3 times until there is no obvious powder residue on the surface.

[0092] S23. Cleaning and Activation Treatment: Place the roughened substrate in acetone and ultrasonically clean for 15 minutes to remove surface oil and cutting fluid residue. Remove the substrate and place it in anhydrous ethanol for ultrasonic cleaning for 15 minutes. Remove the substrate with tweezers and place it in a forced-air drying oven for vacuum drying at 80°C for 1 hour. After drying, immediately remove the substrate and place it in the fixture of the dip-coating machine. Seal the equipment to obtain the pretreated diamond tool substrate.

[0093] S3. Preparation of the transition layer:

[0094] S31. Pre-coating treatment: Take the Fe-polysilazane precursor prepared in step S1 and place it in the slurry tank of the dip-coating machine. Disperse it ultrasonically for 10 minutes. Adjust the clamps of the dip-coating machine to ensure that the pre-treated diamond tool substrate is suspended vertically with the cutting edge facing down. Set the dip-coating parameters as follows: dip speed: 3500 μm / s, dip time: 12s, pull-out speed: 3200 μm / s, and settling time after pull-out: 10 minutes. After the pull-out is completed, the pre-coated substrate is obtained.

[0095] S32. Low-temperature curing treatment: Place the pre-coated substrate prepared in step S31 in a forced-air drying oven and set the low-temperature segmented curing parameters as follows: First stage: 80℃, hold for 30 min; Second stage: heat up to 130℃ at a heating rate of 1℃ / min, hold for 1 h; Third stage: heat up to 175℃ at a heating rate of 1℃ / min, hold for 2.5 h, and cool to room temperature at a cooling rate of 1℃ / min to obtain the low-temperature cured coating substrate.

[0096] S33. Pyrolysis treatment: Take the low-temperature curing coating substrate prepared in step S32 out of the forced-air drying oven and immediately place it in the quartz boat of the tube furnace. Push the quartz boat into the central heating zone of the tube furnace, close the furnace door, seal it, evacuate and introduce flowing argon gas to keep the furnace free of air and oxygen. Set a gradient heating program for pyrolysis treatment: First stage: heat up to 250℃ at a heating rate of 1℃ / min and hold for 1h. Second stage: heat up to 850℃ at a heating rate of 1℃ / min and hold for 2.5h. Turn off the heating power and wait for the furnace temperature to cool naturally to room temperature to form a transition layer on the surface of the diamond tool substrate. The thickness of the transition layer is 3μm, and the transition layer coating substrate is obtained. The thickness of the transition layer is 3μm.

[0097] S4. Preparation of the main coating by HFCVD method:

[0098] Connect the tube furnace to the vacuum pipe of the HFCVD equipment, open the valve, and transfer the transition layer coating substrate prepared in step S3 from the tube furnace to the deposition chamber of the HFCVD equipment. Close the connecting valve, turn on the vacuum pump of the HFCVD equipment, and evacuate to 5 × 10⁻⁶. -3At 100 sccm, high-purity hydrogen gas was introduced to flush the deposition chamber for 10 minutes to remove residual impurities. The hydrogen gas was then turned off, and the vacuum was evacuated again to 5 × 10⁻⁶ Pa. -3 At kPa, turn on the hot filament power supply (tantalum wire, 0.5 mm in diameter, 50 mm in length), adjust the hot filament temperature to 2200℃ (tested with an optical pyrometer), control the distance between the hot filament and the substrate to 8-10 mm, introduce high-purity hydrogen gas (flow rate 80 sccm), maintain the deposition chamber pressure at 25 kPa, and adjust the substrate temperature (transition layer surface temperature) to 780℃ (slightly lower than the transition layer pyrolysis temperature to avoid damage to the transition layer) through the thermal radiation of the hot filament, hold for 30 min, keep the hot filament temperature and substrate temperature constant, introduce high-purity methane (carbon source), and adjust the methane gas... The concentration was increased to 3% (methane flow rate 3 sccm, hydrogen flow rate 97 sccm), the pressure in the deposition chamber was maintained at 30 kPa, the deposition timer was started, and the deposition time was 5 hours. After the deposition time was reached, the methane inlet valve was closed first, and hydrogen was continued to be introduced. The hot wire temperature was maintained at 2000℃ for 30 minutes. The hot wire power was turned off, the hydrogen supply was stopped, and the deposition chamber was kept in a vacuum state. It was allowed to cool naturally to room temperature, and high-purity nitrogen (flow rate 50 sccm) was introduced to balance the gas pressure inside and outside the chamber (0.1 MPa). The thickness of the main coating was 28 μm, and the composite coating for diamond tools was obtained.

[0099] This embodiment also provides a composite coating for diamond tools prepared according to the above method.

[0100] Comparative Example 1

[0101] This comparative example provides a composite coating and its preparation method. The only difference between this example and Example 1 is that in the preparation method of the composite coating, step S1 does not include steps S12 and S13. In step S31, the polysilazane prepared in step S11 is used for pre-coating treatment. The remaining components and component contents are the same as in Example 1.

[0102] Comparative Example 2

[0103] This comparative example provides a composite coating and its preparation method. The only difference between this example and Example 1 is that the preparation method of the composite coating does not include steps S1 and S3. That is, the composite coating does not include a transition layer, and the remaining components and component contents are the same as in Example 1.

[0104] Experimental Example 1

[0105] Hardness tests were conducted on the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 using a Warbert 402MVD Vickers microhardness tester. The sample surfaces were clean and dry, and fixed on the testing platform. For the hardness test of the diamond coating, the load was strictly controlled, and the test parameters were set as follows: load 0.2 N, holding time 10 s. Tests were conducted in five different areas on the diamond coating surface, avoiding cutting edges and coating defects. Based on the diagonal length of the indentation, the Vickers hardness (HV) was calculated using the formula: HV = 1.8544 × F / d 2 (F is the load, d is the average length of the indentation diagonal), take the average of 5 tests;

[0106] Figure 1 The figures show the Vickers hardness results of the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 of this invention. As shown in the figures, Examples 1-3 maintain the ultra-high hardness characteristics of the diamond coating. The Fe doping in Examples 1-3 completely avoids the agglomeration of Fe particles during the nucleation / growth process of the diamond coating, and only acts as an active nucleation site, without causing distortion of the diamond lattice structure, thus ensuring the high hardness of the diamond. 3 The high purity of the phase; at the same time, the low doping amount increases the density of the transition layer, effectively improving the Co blocking efficiency and avoiding graphitization caused by Co atom diffusion; Comparative Example 1 is an ordinary SiCN transition layer without Fe doping, which leads to a decrease in the density of the transition layer, the existence of tiny interconnected pores, and a decrease in Co blocking efficiency. During HFCVD deposition, a small number of Co atoms in the matrix diffuse through the pores to the diamond coating interface, catalyzing part of the sp. 3 Phase transition sp 2 The graphite phase, being a soft phase, directly reduces the overall hardness of the coating. Comparative Example 2, which has no transition layer, deposits a diamond coating directly on the WC-Co matrix. The fundamental reason for its sharp drop in hardness and complete loss of superhard properties is that severe diffusion of Co atoms leads to large-area graphitization of diamond, resulting in coating structural failure.

[0107] Experiment Example 2

[0108] Wear resistance tests were conducted on the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 using a ball-and-disc wear tester. The coating surface of the tool under test was used as the grinding disc, and Si3N4 grinding balls were used as the grinding balls. After cleaning, the grinding balls were installed to ensure line contact with the coating surface. The dry wear test parameters were set as follows: load 5N, wear speed 300r / min, wear radius 5mm, and wear time 30min. The friction curve was recorded. All samples were tested under the same working conditions. After wear, the samples were ultrasonically cleaned with anhydrous ethanol, dried, and weighed. The wear volume (V) was calculated according to the following formula: V=Δm / ρ, (Δm is the mass difference before and after wear, and ρ is the density of the diamond coating 3.5g / cm³).

[0109] Figure 2The figures show the wear resistance results of the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 of this invention. As shown in the figures, the diamond coatings in Examples 1-3 are high-purity sp³ phases with high density and strong interfacial bonding. The wear is mainly slight abrasive wear on the surface, and the amount of material removed is very small. Comparative Example 1 is a low-density coating with slight graphitization. The wear is abrasive wear, accompanied by slight adhesive wear and local micro-peeling. The amount of material removed increases significantly. Comparative Example 2 is a cracked coating with large-area graphitization. The wear is adhesive wear, and the coating peels off in large areas. At the same time, the substrate is exposed and eroded. The amount of material removed increases exponentially.

[0110] Experimental Example 3

[0111] Actual cutting performance tests were conducted on the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2. The test conditions were divided into conventional cutting and heavy cutting, respectively adapted to different examples and comparative examples. The cutting materials were carbon fiber composite (CFRP) and titanium alloy (TC4), typical machining objects of diamond tools. Dry cutting was performed, and the cutting parameters were set as follows: cutting material CFRP, cutting speed vc=100m / min, feed rate f=0.1mm / r, depth of cut ap=0.5mm. Every 50m of cutting, the flank wear amount VB of the main cutting edge of the tool was measured using a tool microscope (magnification 200x). When VB≥0.2mm, the tool was judged to have failed. The surface Ra value of the CFRP workpiece after cutting was measured using a surface roughness meter, and the average value of 5 different positions was taken. The cumulative cutting length from the start of cutting to when the flank wear amount VB=0.2mm was also recorded.

[0112] Figure 3 The figures show the cutting performance results of the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 of this invention. As shown in the figures, the composite coatings prepared in Examples 1-3 achieved excellent performance in CFRP cutting, including high surface finish, long cutting life, and no failed cutting edge. In Comparative Example 1, the Ra value increased significantly and the cumulative cutting length dropped sharply when cutting CFRP. The functional defects of the ordinary SiCN transition layer led to slight graphitization of the diamond coating, reduced density, and weak interfacial bonding. The coating lost its superhardness and wear resistance. During the cutting process, the cutting edge eroded quickly, stuck to the tool, and the coating peeled off slightly. In Comparative Example 2, the diamond coating was deposited directly on the WC-Co substrate. When cutting CFRP, the cutting edge immediately chipped and the coating peeled off in large areas, making it impossible to complete effective cutting. Severe atomic diffusion led to large-area graphitization of the diamond, and the mismatch of the thermal expansion coefficient caused network cracking of the coating, resulting in complete failure of the coating structure.

[0113] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

[0114] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A composite coating for cutting tools, characterized in that: The composite coating comprises a transition layer and a main coating; the transition layer is an Fe-doped SiCN coating formed on the tool substrate surface by a sol-gel method; the main coating is a micron-crystalline diamond main coating formed on the transition layer surface by hot-wire chemical vapor deposition; the Fe-doped SiCN coating uses an Fe-polysilazane precursor as a slurry, which is dip-coated, cured, and pyrolyzed to form the transition layer on the tool substrate surface; the Fe-polysilazane precursor first forms a polysilazane from methyldichlorosilane, (chloromethyl)methyldichlorosilane, and hexamethyldisilazane, and then through S... N 2. Alkylation reaction: Acetylacetone is modified onto the side chain of polysilazane. Finally, Fe is modified via the acetylacetone side chain groups. 3+ The chelation reaction of the chelate with ferric chloride hexahydrate yields the Fe-polysilazane precursor.

2. The composite coating for cutting tools according to claim 1, characterized in that: The molar ratio of methyldichlorosilane, (chloromethyl)methyldichlorosilane and hexamethyldisilazane is 4-5:2-3:3-5; the molar ratio of (chloromethyl)methyldichlorosilane to acetylacetone is 1:1.1-1.3; and the molar ratio of acetylacetone to ferric chloride hexahydrate is 1:0.1-0.

3.

3. The composite coating for cutting tools according to claim 2, characterized in that: The thickness of the transition layer is 0.5-3 μm; the thickness of the main coating layer is 8-20 μm.

4. A method for preparing a composite coating for cutting tools according to claim 3, characterized in that: Specifically, the following steps are included: Preparation of S1, Fe-polysilazane precursors: S11. Dissolve methyldichlorosilane and (chloromethyl)methyldichlorosilane in anhydrous toluene, introduce flowing argon gas, raise the reaction temperature, and add hexamethyldisilazane dropwise to the reaction system. After the addition is complete, maintain the reaction temperature to carry out the condensation reaction. After the reaction is completed, cool, distill under reduced pressure, and dry to obtain polysilazane. S12. Dissolve the polysilazane prepared in step S11 in anhydrous THF. Under an argon atmosphere, add boric anhydride and tributyl borate. After stirring and mixing evenly, add acetylacetone and raise the reaction temperature to carry out the alkylation reaction. After the reaction is completed, cool and add deionized water to hydrolyze the excess boric anhydride and tributyl borate. After standing and separating into layers, collect the organic phase, wash the organic phase with deionized water, dry and remove water, and then perform vacuum distillation to obtain the modified polysilazane. S13. Dissolve the modified polysilazane prepared in step S12 in a toluene / n-hexane mixed solvent. Dissolve ferric chloride hexahydrate in anhydrous ethanol and add it dropwise to the reaction system. Keep the room temperature, add KH570, and stir continuously to carry out the chelation reaction. During the reaction, the reaction system is ultrasonically dispersed. After the reaction is completed, adjust the viscosity of the reaction system to 800-2000 mPa•s, filter the membrane, and obtain the Fe-polysilazane precursor. S2. Tool substrate pretreatment: S21. Cobalt removal treatment: Prepare the first and second cobalt removal solutions, and wash the tool substrate in the first and second cobalt removal solutions in sequence. Then wash the surface of the tool substrate with deionized water until it is neutral. S22. Surface roughening treatment: Disperse diamond micro powder in deionized water to obtain diamond micro powder suspension. Place the cobalt-free treated tool substrate in the diamond micro powder suspension for ultrasonic grinding. Rinse with deionized water and set aside for use. S23. Cleaning and activation treatment: The tool substrate after surface roughening treatment is placed in acetone and anhydrous ethanol for ultrasonic cleaning, vacuum drying, and then sealed to obtain a pretreated tool substrate for later use. S3. Preparation of the transition layer: S31. Pre-coating treatment: Take the Fe-polysilazane precursor prepared in step S1 and place it in the slurry tank of the dip-coating machine. After it is evenly dispersed, dip-coat the tool substrate and obtain the pre-coated substrate. S32. Low-temperature curing treatment: The pre-coated substrate prepared in step S31 is placed in a forced-air drying oven for low-temperature segmented curing treatment. After the treatment is completed, it is cooled to obtain a low-temperature cured coating substrate. S33. Pyrolysis treatment: The low-temperature curing coating substrate prepared in step S32 is placed in a quartz boat and subjected to pyrolysis treatment in a high-purity nitrogen atmosphere. After the treatment, it is cooled to form a transition layer on the surface of the tool substrate, thus obtaining the transition layer coating substrate. S4. Preparation of the main coating by HFCVD: The transition layer coating substrate prepared in step S3 is transferred to the HFCVD equipment. The temperature of the hot filament and the transition layer coating substrate is adjusted. High-purity methane is introduced at a volume concentration of 1%-3%, and the pressure in the deposition chamber is maintained at 15-30 kPa. After deposition for 2-6 hours, the methane inlet valve is closed, and hydrogen is continuously introduced to maintain the temperature of the hot filament. Post-treatment is then performed. Heating and hydrogen are stopped, and the tool is allowed to cool under vacuum to obtain the tool composite coating.

5. The method for preparing a composite coating for a cutting tool according to claim 4, characterized in that: In step S11, the reaction temperature of the condensation reaction is 80-90℃, and the reaction time of the condensation reaction is 6-8h.

6. The method for preparing a composite coating for a cutting tool according to claim 5, characterized in that: In step S12, the molar ratio of acetylacetone to boric anhydride and tributyl borate is 20-25:2:1; the reaction temperature of the alkylation reaction is 50-60℃, and the reaction time of the alkylation reaction is 4-6h.

7. The method for preparing a composite coating for a cutting tool according to claim 6, characterized in that: In step S13, the mass of KH570 added is 0.3-0.8% of the mass of the modified polysilazane; the stirring speed of the chelation reaction is 600-800 rpm, and the reaction time of the chelation reaction is 2.5-5 h.

8. The method for preparing a composite coating for a cutting tool according to claim 7, characterized in that: In step S21, the first cobalt removal solution is composed of concentrated nitric acid, hydrofluoric acid, and deionized water in a volume ratio of 10-15:3-5:180-187; in step S21, the second cobalt removal solution is composed of concentrated nitric acid and deionized water in a volume ratio of 3-5:95-97; in step S22, the mass fraction of the diamond micron powder in the deionized water is 0.3%-0.8%.

9. The method for preparing a composite coating for a cutting tool according to claim 8, characterized in that: In step S31, the parameters of the immersion and lifting treatment include: immersion speed: 3000-3500μm / s, immersion time: 10-15s, pull-out speed: 3000-3200μm / s, and standing time after pull-out: 5-10min; In step S32, the low-temperature segmented curing treatment parameters include: first stage: 60-80℃, holding for 30 min; second stage: heating to 120-130℃ at a heating rate of 1℃ / min, holding for 1-1.5 h; third stage: heating to 170-180℃ at a heating rate of 1℃ / min, holding for 2-3 h. In step S33, the gradient heating program for pyrolysis treatment includes: first stage: heating to 300-400℃ at a heating rate of 1℃ / min and holding for 0.5-1.5h; second stage: heating to 800-850℃ at a heating rate of 1℃ / min and holding for 2-3h.

10. The method for preparing a composite coating for a cutting tool according to claim 9, characterized in that: In step S4, the hot wire temperature is 2000-2200℃, and the transition layer coating substrate temperature is 758-850℃.

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