A method for preparing a low-stress diamond-like carbon coating based on composite plasma enhancement

Abstract

This invention discloses a method for preparing a low-stress superhard diamond-like carbon (DLC) coating based on composite plasma enhancement. The method employs a vacuum coating apparatus combining a magnetically controlled cathode arc source and a closed-loop unbalanced magnetron sputtering source. The plasma ionization rate is increased through a closed magnetic circuit, and large particles are dually suppressed by a dynamic scanning magnetic field and bent-tube filtration. The coating is a five-layer nano-gradient composite structure, consisting of a metal activation layer, a carbonitride gradient transition layer, a doped stress control layer, a tetrahedral amorphous carbon (ta-C) superhard framework layer, and a fluorinated diamond-like carbon (F-DLC) lubricating layer, sequentially from the substrate to the surface. The preparation process involves workpiece cleaning and furnace loading, ion cleaning and etching, gradient deposition of each functional layer, and cooling before unloading. The step-by-step deposition achieves compositional and stress gradient control, making it suitable for high-end applications such as precision molds, automotive engine parts, and 3C wear-resistant components.

Description

Technical Field

[0001] This invention relates to a method for preparing a low-stress superhard diamond-like coating based on composite plasma enhancement. Background Technology

[0002] Diamond-like carbon (DLC) coatings, combining the high hardness of diamond with the low friction of graphite, have been widely used in precision automotive parts, high-end molds, and 3C electronic products. However, the industrial-scale preparation of high-performance DLC coatings often faces two major bottlenecks: the coexistence of hardness and internal stress, and large surface particle defects. While traditional cathodic arc technology can prepare ultra-hard ta-C films with high sp³ content, the macroscopic large particles generated by the explosion of cathode spots (molten droplets on metal targets and solid debris on carbon targets) severely damage the surface finish of the coating, leading to abrasive wear during friction. At the same time, the huge residual compressive stress (often >5 GPa) introduced by high-energy ion bombardment limits the film thickness to usually less than 1 µm. Once the thickness increases, catastrophic peeling is likely to occur, making it difficult to meet the requirements for long service life.

[0003] In existing technologies, magnetron sputtering, while producing smooth films, suffers from low ionization rates, resulting in a low sp³ bond ratio in the prepared DLC films and difficulty in achieving a hardness exceeding 20 GPa. While magnetically filtered cathode arc (FCVA) technology can filter large particles, it suffers from extremely low transport efficiency, slow deposition rates, and high production costs. Furthermore, existing arc-sputtering composite technologies are mostly simple hardware stacking, lacking coordinated magnetic circuit design for the two plasma fields. This often leads to unstable discharge due to magnetic field interference, and the single transition layer structure cannot effectively dissipate the interfacial shear stress accumulated in the ultra-hard layer, resulting in insufficient coating adhesion and making it impossible to achieve thick film (>3 µm) preparation while maintaining ultra-high hardness (>40 GPa). Summary of the Invention

[0004] The present invention provides a method for preparing a low-stress superhard diamond-like coating based on composite plasma enhancement in order to solve the problems existing in the prior art.

[0005] The technical solutions adopted in this invention are as follows:

[0006] A method for preparing a low-stress superhard diamond-like carbon coating based on composite plasma enhancement includes the following steps:

[0007] At least one set of magnetic field-controlled cathode arc sources and at least one set of closed-loop unbalanced magnetron sputtering sources are configured in the vacuum chamber. The magnetic field-controlled cathode arc sources are equipped with dynamic scanning magnetic field coils. The adjacent target polarities of the closed-loop unbalanced magnetron sputtering sources are arranged alternately to form a closed magnetic circuit. The substrate to be coated is placed in the center of the vacuum chamber.

[0008] The metal ions generated by the cathode arc source, controlled by the magnetic field, are bombarded, cleaned, and implanted into the substrate to be plated, depositing a metal activation layer. Then, nitrogen-containing reactive gas is introduced into the vacuum chamber to deposit a carbonitride gradient transition layer with increasing carbon content and decreasing nitrogen content along the growth direction.

[0009] The closed-loop unbalanced magnetron sputtering source is turned on, and the electrons sputtered from the target material are bound around the substrate to be deposited by the closed magnetic circuit, and metal carbide nanocrystals are deposited and dispersed in the doped stress control layer of the amorphous carbon matrix.

[0010] The cathode arc source is controlled by the magnetic field, and the arc spot is rapidly scanned by the dynamic scanning magnetic field coil to suppress the generation of metal droplets and carbon debris, thereby depositing sp. 3 Tetrahedral amorphous carbon superhard framework layer with a bond content greater than 70%;

[0011] A diamond-like lubricant layer is deposited on the surface of the tetrahedral amorphous carbon superhard framework layer using the closed-loop unbalanced magnetron sputtering source, forming a five-layer nano-gradient composite structure coating consisting of the metal activation layer, carbonitride gradient transition layer, doped stress control layer, tetrahedral amorphous carbon superhard framework layer and diamond-like lubricant layer.

[0012] Furthermore, the material of the metal activation layer is selected from at least one of titanium, chromium, and tungsten, or titanium-chromium alloy, titanium-tungsten alloy, or chromium-tungsten alloy, and the thickness is 0.05µm to 0.2µm.

[0013] Furthermore, the outer surface of the carbonitride gradient transition layer is a chromium carbonitride layer with a total thickness of 0.4µm to 0.6µm.

[0014] Furthermore, the doped stress regulation layer is a metal-doped diamond-like layer, and the metal is selected from titanium, chromium or tungsten. The metal is dispersed in the amorphous carbon matrix in the form of metal carbide nanocrystals, with a thickness of 1.0µm to 2.0µm.

[0015] Furthermore, the thickness of the tetrahedral amorphous carbon superhard framework layer is 1.0µm to 2.0µm, and the nanoindentation hardness is greater than 40GPa.

[0016] Furthermore, the diamond-like lubricating layer is a fluorine-containing diamond-like layer with a surface roughness Ra of less than 0.05µm and a thickness of 0.1µm to 0.3µm.

[0017] Furthermore, the scanning frequency of the dynamic scanning magnetic field coil is 100Hz to 300Hz.

[0018] Furthermore, the magnetic field-controlled cathode arc source is equipped with a magnetic filter, which deflects the plasma flow and intercepts the metal droplets and carbon debris by bending the magnetic circuit.

[0019] Furthermore, when depositing the doped stress-controlled layer, the applied pulse bias voltage is -150V to -50V.

[0020] Furthermore, when depositing the tetrahedral amorphous carbon ultrahard framework layer, the applied bias voltage is -100V to -150V.

[0021] The present invention has the following beneficial effects:

[0022] By designing a five-layer nano-gradient composite structure, especially by utilizing the composite structure of metal carbide nanocrystals and amorphous carbon matrix in the doped stress-regulating layer to provide stress relaxation space, combined with a carbonitride transition layer with gradually changing composition, the high residual compressive stress of the tetrahedral amorphous carbon ultrahard framework layer is effectively resolved. This allows the coating to maintain an sp³ bond content of more than 70% and ultra-high hardness while achieving a thickness of more than 2µm without cracking or peeling.

[0023] By using a dynamic scanning magnetic field coil to suppress metal droplets and carbon debris generated by the electric arc source, and in conjunction with a magnetic filter to intercept residual large particles, macroscopic defects on the coating surface are reduced from the source, resulting in a smooth and dense surface of the deposited coating and reducing the workload of subsequent surface polishing.

[0024] The metal activation layer is formed by bombarding the substrate surface with metal ions to form an ion-mixed layer. The carbonitride gradient transition layer realizes the gradual transition of composition from metal to diamond-like carbon, avoiding interfacial shear failure caused by sudden hardness changes and improving the service reliability of the coating under complex stress conditions.

[0025] The closed-loop unbalanced magnetron sputtering source improves plasma ionization rate through a closed magnetic circuit, while the magnetic field-controlled cathode arc source provides a high deposition rate. The synergy of the two plasma technologies enables the coating to have both high density and reasonable deposition efficiency, shortening the preparation cycle compared to a single magnetic filtration technology.

[0026] The diamond-like lubricant layer on the surface reduces the surface energy of the coating, giving it a lower coefficient of friction and wear rate under dry friction conditions. This makes it suitable for applications such as precision molds and engine parts that require low friction and wear resistance. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the planar structure of a composite plasma vacuum coating equipment.

[0028] Figure 2 This is a schematic diagram of the cross-sectional structure of a five-layer nanogradient composite coating.

[0029] Figure 3 This is a flowchart of the coating preparation process. Detailed Implementation

[0030] The preparation method of the low-stress superhard diamond-like carbon coating based on composite plasma enhancement according to the present invention will be further described in detail below with reference to the accompanying drawings. This embodiment takes the preparation of this type of diamond coating on the surface of an automotive engine tappet as the application scenario, and selects 20CrMnTi carburized steel as the substrate to be coated. Figure 1 This is a schematic diagram of the planar structure of the composite plasma vacuum coating equipment of the present invention, attached. Figure 2 This is a schematic cross-sectional view of the five-layer nano-gradient composite coating of the present invention, based on the attached diagram. Figure 1 The equipment completes the entire coating deposition and preparation process.

[0031] like Figure 1 As shown, the composite plasma vacuum coating equipment used in this invention mainly includes a vacuum chamber 4, a magnetic field-controlled cathode arc source 1, a closed-loop unbalanced magnetron sputtering source 2, a dynamic scanning magnetic field coil, a worktable 3, a magnetic filter, a gas inlet 5, a bias power supply, an arc power supply, a sputtering power supply, and an auxiliary electromagnetic coil.

[0032] Vacuum chamber 4 is made of stainless steel and its ultimate vacuum level can reach 8.0 × 10⁻⁶. -5 Pa, a worktable 3 is fixedly installed in the center of the vacuum chamber 4. The substrate to be coated is clamped and fixed on the worktable 3. The worktable 3 adopts a planetary rotation structure. Its revolution speed can be adjusted in the range of 0-10 rpm, and its rotation speed can be adjusted in the range of 0-30 rpm, which can ensure the uniformity of film formation on the surface of the substrate to be coated.

[0033] A gas inlet 5 is provided on the side wall of the vacuum chamber 4. The gas inlet 5 is connected to an external high-purity gas pipeline, which can introduce working gases and reaction gases such as Ar, N2, C2H2, and CF4. The vacuum chamber 4 is also connected to an external vacuum pump system, which can pump its interior to the background vacuum level required by the process.

[0034] The vacuum chamber 4 is equipped with two sets of magnetically controlled cathode arc sources 1 and a pair of closed-loop unbalanced magnetron sputtering sources 2. The two sets of magnetically controlled cathode arc sources 1 are respectively located in different positions within the vacuum chamber 4. One set is equipped with a TiCr alloy target, and the other set is equipped with a high-purity graphite target. Each set of magnetically controlled cathode arc sources 1 is equipped with a dynamic scanning magnetic field coil and a magnetic filter 6. The dynamic scanning magnetic field coil is electrically connected to the arc power supply. The magnetic filter 6 is a bent tube filter structure, which can deflect the plasma flow through the bent magnetic circuit and intercept metal droplets and carbon debris. Simultaneously, the two sets of magnetically controlled cathode arc sources Auxiliary electromagnetic coils are provided on the periphery of 1. The two sputtering targets of the closed-loop unbalanced magnetron sputtering source 2 are Cr target and C target, respectively, and the polarities of adjacent targets are arranged alternately in NS and SN. The closed-loop unbalanced magnetron sputtering source 2 is electrically connected to the sputtering power supply. The magnetic field controls the cathode arc source 1, the closed-loop unbalanced magnetron sputtering source 2 and the auxiliary electromagnetic coils to work together to form a complete closed magnetic circuit in the vacuum chamber 4, so that the magnetic lines of force form a magnetic line tunnel in the vacuum chamber 4. The substrate to be coated and the bias power supply are electrically connected, and different bias parameters can be applied to the substrate to be coated according to different deposition process stages.

[0035] As shown in Figure 3, the preparation process of the present invention includes the following steps in sequence:

[0036] Workpiece cleaning, furnace loading, and vacuuming;

[0037] Ion heating and cleaning etching (Ar) + Cr + / Ti + );

[0038] Deposited metal activation layer (TiCr);

[0039] Deposition of gradient transition layer (TiCrN--CrCN) (arc + magnetron sputtering, N2 and C2H2 pass through);

[0040] Deposition stress-controlled layer (Me-DLC) (magnetron sputtering Cr / C target, C2H2+Ar pass through);

[0041] Deposition of ultrahard ta-C framework layer (magnetic splitting arc C target + bent tube filter, high pulse bias -120V);

[0042] Deposited surface lubricating layer (F-DLC) (magnetron sputtering C target, Ar pass through, CF4 gradually introduced);

[0043] Cool and remove from the oven.

[0044] After completing the equipment debugging and preparation, the 20CrMnTi carburized steel engine tappet substrate to be plated was first pretreated. The substrate was placed in an ultrasonic cleaner and ultrasonically cleaned sequentially using an alkaline degreasing agent, deionized water, and anhydrous ethanol. Each cleaning process took 15 minutes. After cleaning, the substrate was dried. Then, the dried substrate was clamped and fixed on the worktable 3 in the center of vacuum chamber 4. Vacuum chamber 4 was closed and the vacuum pump system was started to evacuate the vacuum chamber 4 to a background vacuum of 2.0 × 10⁻⁶. -3 Pa, at the same time, turn on the heater in vacuum chamber 4 to raise the chamber temperature to 150°C and keep it at that temperature for 30 minutes to fully remove water vapor and adsorbed gas from the substrate surface and complete the preliminary preparation of the substrate.

[0045] Next, the magnetic field-controlled cathode arc source 1 is activated, utilizing the generated metal ions to bombard, clean, and inject the substrate. First, Ar gas at a flow rate of 80 sccm is introduced into the vacuum chamber 4 through gas inlet 5, maintaining the chamber pressure at 0.8 Pa. The bias power supply is then activated, applying a mid-frequency pulse bias of -800V, 40kHz, and 60% duty cycle to the substrate, causing a high-density glow discharge on the substrate surface. This utilizes the Ar... + The substrate surface was bombarded with ions for 15 minutes for cleaning.

[0046] Subsequently, the magnetic field-controlled cathode arc source 1, equipped with a TiCr alloy target, was activated, and the arc current was set to 80A. Simultaneously, the matching dynamic scanning magnetic field coil was activated, and its scanning frequency was adjusted to 100Hz, causing the arc spot on the target surface to fission and rapidly scan. At the same time, the substrate bias voltage was instantaneously increased to -600V, utilizing high-energy Ti (greater than 100eV) cathode arcs. + and Cr + The substrate is etched with ions for 3 minutes. While removing deep contaminants from the substrate surface, a 10-50nm ion mixing layer is formed on the substrate surface. After the substrate bombardment cleaning and ion implantation are completed, the magnetic field-controlled cathode arc source 1 is kept on, the arc current is maintained at 80A, and the substrate bias voltage is reduced to -120V to enter the deposition mode.

[0047] High-energy TiCr metal ions adsorb, nucleate, and grow on the substrate surface, depositing a metal activation layer. This metal activation layer uses a TiCr alloy as the deposition material, belonging to the titanium-chromium alloy category. The deposition time is controlled at 10 minutes, and the final metal activation layer thickness is 0.15 μm. Figure 2 As shown, the metal activation layer is directly attached to the surface of the substrate, serving as an anchoring layer between the coating and the substrate.

[0048] After the metal activation layer is deposited, nitrogen-containing reactive gas N2 is introduced into the vacuum chamber 4 to begin the deposition of the carbonitride gradient transition layer. This deposition process is divided into two stages.

[0049] In the first stage, the magnetic field-controlled cathode arc source 1, which carries the TiCr alloy target, continues to operate. N2 is introduced through the gas inlet 5 and its flow rate is linearly increased from 0 sccm to 100 sccm. The cavity pressure in the vacuum chamber 4 is maintained at about 0.5 Pa. After 20 minutes of deposition, a TiCrN hard support layer is formed on the surface of the metal activation layer.

[0050] In the second stage, the magnetic field-controlled cathode arc source 1 with the TiCr alloy target is shut down, and the closed-loop unbalanced magnetron sputtering source 2 is turned on. The sputtering power of the Cr target is adjusted to 5kW and the sputtering power of the C target is adjusted to 2kW. The closed magnetic circuit is kept open, and the flow rate of N2 is gradually reduced from 100sccm to 15sccm. At the same time, C2H2 gas is introduced through gas inlet 5 and its flow rate is increased from 0sccm to 30sccm. The substrate bias voltage is maintained at -100V. During this process, the composition of the film layer changes with the change of gas flow rate, and a gradient transition structure composed of TiCrN, CrN / Cr (C,N) and CrCN is gradually formed. Finally, a chromium carbonitride layer (CrCN) is formed on the outer surface of the transition layer. The total thickness of the entire carbonitride gradient transition layer is 0.5μm.

[0051] like Figure 2 As shown, the carbonitride gradient transition layer is attached to the surface of the metal activation layer. Its carbon content increases along the coating growth direction, while its nitrogen content decreases along the coating growth direction, thus achieving a smooth transition of composition from the metal layer to the diamond-like carbon layer.

[0052] After the carbonitride gradient transition layer is deposited, the closed-loop unbalanced magnetron sputtering source 2 is kept in operation to begin depositing the doped stress-controlled layer. The sputtering power of the Cr target in the closed-loop unbalanced magnetron sputtering source 2 is adjusted to 3kW, and the sputtering power of the C target is increased to 5kW. 50 sccm of C2H2 and 30 sccm of Ar are stably introduced into the vacuum chamber 4 through gas inlet 5. At this time, the Cr and C targets in the closed-loop unbalanced magnetron sputtering source 2 are in a closed magnetic circuit coupling state. The closed magnetic circuit confines the electrons sputtered from the target material around the substrate to be deposited, extending the electron movement path and significantly improving the plasma ionization rate of C2H2. Simultaneously, a -100°C bias voltage is applied to the substrate. With a pulsed bias voltage of V, the pulse frequency is adjusted to 50kHz and the duty cycle is adjusted to 50%. Under these process parameters, Cr atoms react with C atoms to generate nanoscale chromium carbide grains. These metal carbide nanocrystals exist in the amorphous carbon matrix in a dispersed form, forming a metal-doped diamond-like carbon layer. The deposition time of this doped stress-controlled layer is controlled to be 60 minutes. During the deposition process, the substrate temperature is strictly controlled to be below 150℃ by the back water cooling system of vacuum chamber 4. The final thickness of the doped stress-controlled layer is 1.5μm. This doped stress-controlled layer is attached to the surface of the carbonitride gradient transition layer. The chromium carbide nanocrystals, as the doped metal phase, provide stress relaxation space for the coating.

[0053] After the doped stress-controlled layer is deposited, the closed-loop unbalanced magnetron sputtering source 2 and the C2H2 gas path are closed, and the vacuum chamber 4 is evacuated to a high vacuum state again. Only 20 sccm of Ar gas is introduced through the gas inlet 5 to maintain the discharge.

[0054] Subsequently, the magnetic field-controlled cathode arc source 1, equipped with a high-purity graphite target, was activated to begin depositing a tetrahedral amorphous carbon ultrahard framework layer. The arc current of the magnetic field-controlled cathode arc source 1 was set to 60A, and its matching dynamic scanning magnetic field coil was activated. The scanning frequency of the dynamic scanning magnetic field coil was adjusted to 300Hz. The arc spot was driven to rapidly fission and scan on the graphite target surface by the dynamic scanning magnetic field, suppressing the generation of solid carbon debris from the source. At the same time, the matching magnetic filter 6 was used to spatially intercept residual metal droplets and carbon debris, achieving dual suppression of large particles and outputting pure carbon plasma. Simultaneously, the substrate bias voltage was increased to -120V through the bias power supply, utilizing the C plasma with an average kinetic energy of 100-120eV. + Ions create a "sub-implantation" effect on the coating surface, forcing carbon atoms to spread at a high density. 3 Diamond bonding was used in the deposition process, which was controlled to take 50 minutes, resulting in a tetrahedral amorphous carbon ultrahard framework layer with sp 3The bond content is greater than 70%, the coating thickness is 1.2μm, and the nanoindentation hardness of the tetrahedral amorphous carbon superhard framework layer is greater than 40Gpa. The tetrahedral amorphous carbon superhard framework layer is attached to the surface of the doped stress-regulating layer, serving as the superhard core framework of the entire coating.

[0055] After the tetrahedral amorphous carbon ultrahard framework layer was deposited, the magnetic field-controlled cathode arc source 1 with a high-purity graphite target was shut down, and the C target in the closed-loop unbalanced magnetron sputtering source 2 was restarted. Its sputtering power was adjusted to 3kW, and the deposition of the diamond-like carbon lubricant layer began. Initially, 50 sccm of Ar gas was introduced only through gas inlet 5. A pure carbon transition layer was deposited on the surface of the tetrahedral amorphous carbon ultrahard framework layer using the C target for 1 minute. Subsequently, CF4 gas was gradually introduced through gas inlet 5, increasing its flow rate from 0 sccm to 10 sccm. The substrate bias voltage was reduced to -50V, and a low-energy deposition method was used to gradually incorporate fluorine atoms into the diamond-like carbon (DLC) film to form a fluorine-containing DLC ​​layer. The deposition time of this DLC lubricant layer was controlled to be 10 minutes, and the final coating thickness was 0.2 μm. Furthermore, through the atomic-level deposition effect of magnetron sputtering, the microscopic pits on the surface of the tetrahedral amorphous carbon superhard framework layer were filled, making the surface roughness Ra of this DLC lubricant layer less than 0.05 μm. This DLC lubricant layer is attached to the surface of the tetrahedral amorphous carbon superhard framework layer and is the outermost layer of the entire coating.

[0056] After the diamond-like carbon (DLC) lubricant layer is deposited, all arc power supplies, sputtering power supplies, and bias power supplies are stopped, all gas passages are closed, and the vacuum chamber 4 is kept in a vacuum state. The substrate to be coated is cooled to below 150°C using the self-cooling system of the vacuum chamber 4. Then, nitrogen gas is introduced into the vacuum chamber 4 through the vacuum pump system to restore the pressure inside the vacuum chamber 4 to atmospheric pressure. Finally, the vacuum chamber 4 is opened, and the engine tappet substrate with the coating deposited is removed. This completes the entire preparation process of the low-stress superhard diamond-like carbon coating based on composite plasma enhancement. Finally, a five-layer nano-gradient composite structure coating is formed on the substrate surface, consisting of a metal activation layer, a carbonitride gradient transition layer, a doped stress control layer, a tetrahedral amorphous carbon superhard framework layer, and a diamond-like carbon lubricant layer stacked sequentially. The total thickness of this composite coating can reach 3.55 μm, achieving film deposition of thicknesses greater than 2 μm without cracking or peeling.

[0057] The composite coating prepared by the above process was subjected to performance testing. According to ISO 14577 standard, the nanoindentation hardness of the coating was measured to be 48 GPa using the continuous stiffness method, and the elastic modulus was 420 GPa. The residual compressive stress of the coating was measured to be only 1.8 GPa using the curvature method. Scratch test results showed that the critical load of the coating reached 92 N, and the indentation test showed HF1 level adhesion. Atomic force microscopy showed that the surface roughness Ra of the coating was 0.028 μm, with no obvious macroscopic large particle defects. Under dry friction conditions, when polished against a GCr15 ball, the coefficient of friction of the coating remained stable between 0.04 and 0.06, and the wear rate was as low as 3.2 × 10⁻⁶. -17 m 3 / Nm, meeting the requirements of high-end working conditions such as precision molds and engine parts for low friction, wear resistance and high bonding strength.

[0058] The preparation method of the present invention is not limited to the process parameters of the above embodiments. In practical applications, the process parameters of each deposition stage can be reasonably adjusted according to the material of the substrate to be deposited, the operating conditions, and the performance requirements of the coating. For example, the scanning frequency of the dynamic scanning magnetic field coil can be adjusted as needed between 100Hz and 300Hz, the pulse bias voltage of the deposited doped stress-controlled layer can be adjusted between -150V and -50V, the bias voltage of the deposited tetrahedral amorphous carbon superhard framework layer can be varied between -100V and -150V, and the thickness of each coating can also be adjusted accordingly within the range defined by the present invention. At the same time, the number of magnetic field-controlled cathode arc sources and the target material selection of the closed-loop unbalanced magnetron sputtering source can also be adapted according to actual needs. For example, the material of the metal activation layer can be selected from titanium, chromium, and tungsten alone, or titanium-tungsten alloy, chromium-tungsten alloy, etc., and the doped metal of the doped stress-controlled layer can also be titanium, tungsten, etc., all of which can achieve the technical effects of the present invention.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-stress superhard diamond-like coating based on composite plasma enhancement, characterized in that: Includes the following steps: At least one set of magnetic field-controlled cathode arc sources and at least one set of closed-loop unbalanced magnetron sputtering sources are configured in the vacuum chamber. The magnetic field-controlled cathode arc sources are equipped with dynamic scanning magnetic field coils. The adjacent target polarities of the closed-loop unbalanced magnetron sputtering sources are arranged alternately to form a closed magnetic circuit. The substrate to be coated is placed in the center of the vacuum chamber. The metal ions generated by the cathode arc source, controlled by the magnetic field, are bombarded, cleaned, and implanted into the substrate to be plated, depositing a metal activation layer. Then, nitrogen-containing reactive gas is introduced into the vacuum chamber to deposit a carbonitride gradient transition layer with increasing carbon content and decreasing nitrogen content along the growth direction. The closed-loop unbalanced magnetron sputtering source is turned on, and the electrons sputtered from the target material are bound around the substrate to be deposited by the closed magnetic circuit, and metal carbide nanocrystals are deposited and dispersed in the doped stress control layer of the amorphous carbon matrix. The cathode arc source is controlled by the magnetic field, and the arc spot is rapidly scanned by the dynamic scanning magnetic field coil to suppress the generation of metal droplets and carbon debris, thereby depositing sp. 3 Tetrahedral amorphous carbon superhard framework layer with a bond content greater than 70%; A diamond-like lubricant layer is deposited on the surface of the tetrahedral amorphous carbon superhard framework layer using the closed-loop unbalanced magnetron sputtering source, forming a five-layer nano-gradient composite structure coating consisting of the metal activation layer, carbonitride gradient transition layer, doped stress control layer, tetrahedral amorphous carbon superhard framework layer and diamond-like lubricant layer.

2. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1, characterized in that: The material of the metal activation layer is selected from at least one of titanium, chromium, and tungsten, or titanium-chromium alloy, titanium-tungsten alloy, or chromium-tungsten alloy, and the thickness is 0.05µm to 0.2µm.

3. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1 or 2, characterized in that: The outer surface of the carbonitride gradient transition layer is a chromium carbonitride layer with a total thickness of 0.4µm to 0.6µm.

4. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1, characterized in that: The doped stress regulation layer is a metal-doped diamond-like layer, with the metal selected from titanium, chromium, or tungsten. The metal is dispersed in the amorphous carbon matrix in the form of metal carbide nanocrystals, with a thickness of 1.0µm to 2.0µm.

5. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1 or 4, characterized in that: The thickness of the tetrahedral amorphous carbon superhard framework layer is 1.0µm to 2.0µm, and the nanoindentation hardness is greater than 40GPa.

6. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1, characterized in that: The diamond-like lubricating layer is a fluorine-containing diamond-like layer with a surface roughness Ra of less than 0.05µm and a thickness of 0.1µm to 0.3µm.

7. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1, characterized in that: The scanning frequency of the dynamic scanning magnetic field coil is 100Hz to 300Hz.

8. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1, characterized in that: The magnetic field-controlled cathode arc source is equipped with a magnetic filter, which deflects the plasma flow and intercepts the metal droplets and carbon debris by bending the magnetic circuit.

9. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1, characterized in that: When depositing the doped stress-controlled layer, the applied pulse bias voltage is -150V to -50V.

10. The method for preparing low-stress superhard diamond-like coating based on composite plasma enhancement as described in claim 1, characterized in that: When depositing the tetrahedral amorphous carbon ultrahard framework layer, the applied bias voltage is -100V to -150V.

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