A nitrogen-doped diamond / intrinsic diamond periodic multilayer structure and a preparation method thereof

Abstract

The application discloses a kind of nitrogen-doped diamond / intrinsic diamond periodic multilayer structure and preparation method thereof, belong to surface treatment technical field.The application includes: bearing matrix surface is polished and polished, and is washed and dried;Using multi-arc ion plating process, carbon target is used as reaction target material, nitrogen is input, and nitrogen-doped diamond layer is deposited on the surface of bearing matrix;Nitrogen is closed, carbon target is used as reaction target material, and intrinsic diamond layer is deposited on the surface of nitrogen-doped diamond layer;The deposition step is repeated, and nitrogen-doped diamond layer and intrinsic diamond layer are alternately stacked in the way of cyclic deposition until reaching the preset total thickness, and nitrogen-doped diamond / intrinsic diamond periodic multilayer structure is formed.By multilayer interface, stress is effectively released, crack is deflected, and the problem of large brittleness and easy peeling of traditional single-layer DLC coating is overcome, and the coating toughness is significantly improved on the basis of maintaining excellent wear-resistant and friction-reducing performance.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment technology, specifically relating to a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure and its preparation method. Background Technology

[0002] As a critical mechanical component, the performance of bearings directly determines the lifespan and reliability of main equipment. Although traditional high-carbon chromium bearing steel possesses excellent comprehensive mechanical properties, its working surface still faces severe challenges under extreme conditions such as high speed, heavy load, frequent start-stop, or poor lubrication: severe friction and wear, especially under boundary lubrication conditions, easily leading to adhesive wear and abrasive wear, resulting in loss of precision; limited contact fatigue life, and the surface is prone to pitting and spalling, inducing early failure.

[0003] To address the aforementioned issues, existing technologies have attempted to strengthen bearings with surface coatings, such as electroplated hard chrome or deposited hard titanium nitride coatings. However, these methods have inherent drawbacks: hard chrome coatings have a high coefficient of friction and poor environmental performance; hard coatings such as TiN lack self-lubricating properties and have insufficient adhesion to the bearing steel substrate under alternating stress, making them prone to peeling. Chinese patent application CN107217228B discloses a method for improving bearing wear resistance using plasma-enhanced chemical vapor deposition (PECVD). This method involves first nitriding the bearing substrate surface and then depositing a single-layer diamond-like carbon (DLC) coating. However, the single-layer DLC coating prepared by this method suffers from inherent defects such as high internal stress, brittleness, and susceptibility to peeling, limiting its application under high-load alternating stress conditions. Chinese patent application CN109385597A discloses a coating for compressor vanes, whose structure consists of a nitride layer, a metal transition layer, and a hydrogen-free DLC layer from the inside out. While this method improves adhesion through a metal transition layer, a significant interface abrupt change still exists between the metal layer and the DLC layer, failing to effectively disperse and release the high internal stress of the DLC layer. Under complex alternating loads, the coating still faces the risk of peeling. Chinese patent application CN118685735B discloses a corrosion-resistant and wear-resistant carbon composite film for rolling bearings. Its structure is a multi-layered gradient system, comprising a Ti adhesive layer, a TiN load-bearing layer, a TiNC gradient layer, and a TiC / C functional layer. This solution primarily addresses the coupling problem of corrosion and wear in marine environments; however, its functional layer is a TiC nanocrystalline / amorphous carbon composite structure, not pure DLC material, resulting in lower hardness and lower friction characteristics compared to pure DLC coatings.

[0004] Therefore, it is still necessary to find a bearing surface coating system that can simultaneously achieve high hardness, low friction, high film-substrate adhesion, and excellent crack propagation resistance. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a periodic multilayer structure of nitrogen-doped diamond-like carbon (N-DLC) / intrinsic diamond-like carbon (DLC) and its preparation method, thereby solving the technical problem of how to provide a bearing surface coating system that combines high hardness, low friction, high film-substrate adhesion, and excellent crack propagation resistance. The periodic multilayer coating, composed of alternating layers of nitrogen-doped diamond-like carbon (N-DLC) and intrinsic diamond-like carbon (DLC), effectively releases stress and deflects cracks through the multilayer interfaces, overcoming the problems of high brittleness and easy peeling of traditional single-layer DLC coatings. While maintaining excellent wear resistance and friction reduction properties, the toughness of the coating is significantly improved.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention discloses a method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure, comprising the following steps: S1: Grind and polish the surface of the bearing substrate, and then clean and dry it; S2: Using a multi-arc ion plating process, a carbon target is used as the reaction target material, and nitrogen gas is introduced to deposit a nitrogen-doped diamond-like layer on the surface of the bearing substrate. S3: Turn off nitrogen gas, use a carbon target as the reaction target, and deposit an intrinsic diamond-like layer on the surface of the nitrogen-doped diamond-like layer; S4: Repeat steps S2 and S3, cyclically depositing nitrogen-doped diamond-like layers and intrinsic diamond-like layers in an alternating stacking manner until the preset total thickness is reached, forming a periodic multilayer structure of nitrogen-doped diamond-like / intrinsic diamond-like.

[0007] Preferably, in step S1, the material of the bearing substrate is GCr15 bearing steel, and the cleaning is performed by ultrasonic cleaning with alcohol and pure water in sequence.

[0008] Preferably, in step S1, after grinding and polishing, the average surface roughness Ra of the bearing substrate is 5~20nm.

[0009] Preferably, in step S2, the process conditions for depositing the nitrogen-doped diamond-like carbon layer are as follows: apply a bias voltage of -900V to -100V to the substrate, select an arc current of 50 to 100A, introduce 5 to 10 sccm of nitrogen gas into the vacuum chamber, and deposit for 5 to 20 minutes.

[0010] Preferably, in step S3, the process conditions for depositing the intrinsic diamond-like carbon layer are: applying a bias voltage of -900V to -100V to the substrate, selecting an arc current of 50 to 100A, and depositing for 5 to 20 minutes.

[0011] Preferably, before step S2, an ion source cleaning step is included: adjusting the vacuum level of the vacuum chamber to (2.5±0.5)×10⁻⁶. -3Pa, argon gas is introduced, argon gas flow rate is 10~30 sccm, discharge current is 300mA, extraction voltage is 700V, ion cleaning time is 30~60min.

[0012] Preferably, in step S4, the number of cycles in which the nitrogen-doped diamond-like layer and the diamond-like layer are alternately stacked is 10 to 30, and the preset total thickness is 1 to 3 micrometers.

[0013] Preferably, the surface arithmetic mean roughness Ra of the nitrogen-doped diamond / intrinsic diamond periodic multilayer structure is 5~20 nm, and the average friction coefficient is 0.05~0.15 within 120 min under dry friction conditions.

[0014] Preferably, the thermal conductivity of the bearing steel plated with a periodic multilayer structure of nitrogen-doped diamond / intrinsic diamond is 44~50 W / (m·K).

[0015] The present invention also discloses a nitrogen-doped diamond-like carbon / intrinsic diamond-like carbon periodic multilayer structure, which is prepared by the above-described method for preparing nitrogen-doped diamond-like carbon / intrinsic diamond-like carbon periodic multilayer structures.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing a nitrogen-doped diamond-like carbon (N-DLC) / intrinsic diamond-like carbon (IDC) periodic multilayer structure. Through multi-arc ion plating technology, N-DLC layers and intrinsic DLC layers are alternately deposited to form a periodic modulated structure with multiple interfaces. First, the alternately deposited multilayer interfaces effectively block and release the high internal stress accumulated in a single-layer DLC, preventing overall coating warping or peeling, overcoming the stress concentration and easy peeling problems of nitriding and single-layer DLC methods. Second, the periodic layered interfaces effectively deflect the longitudinal propagation path of microcracks, transforming the single crack propagation mode of brittle materials into an energy dissipation mode along multiple interfaces, significantly improving the coating's toughness and impact resistance. Finally, the N-DLC layer itself has low internal stress and good adhesion; its introduction as a sublayer enhances the film-substrate bonding of the multilayer structure. This invention's integrated stress regulation and structural toughening process design solves the contradiction between high hardness and high toughness that traditional methods cannot simultaneously achieve.

[0017] Furthermore, a smooth substrate surface can effectively reduce the shading effect and defect density in the early stages of film growth, promoting the formation of a uniform and dense amorphous carbon network. More importantly, this substrate roughness is essentially consistent with the final surface roughness (Ra 5.8 nm) of the coating in this application, such as... Figure 1As shown, the coating perfectly replicates the smooth morphology of the substrate without introducing any additional protrusions or defects. The synergistic ultra-smooth characteristics of the substrate and coating fundamentally reduce microscopic mechanical interlocking and stress concentration points on the contact surface of the friction pair, which is the basis for achieving low starting friction, a stable coefficient of friction (0.092), and long wear life.

[0018] Furthermore, applying a wide-range substrate bias voltage from -900V to -100V provides sufficient bombardment energy for high-energy carbon and nitrogen ions, enabling deposited particles to migrate and diffuse fully on the substrate surface, forming a dense amorphous network structure and effectively promoting sp 3 Bond formation ensures high coating hardness. Simultaneously, precise selection of an arc current of 50–100 A and a nitrogen flow rate of 5–10 sccm allows for stable control of the carbon target's evaporation ionization rate and nitrogen doping concentration. Appropriate nitrogen doping can partially replace carbon atoms in the carbon network or occupy interstitial sites, relaxing local stress concentrations through CN bond formation. This effectively reduces the high internal stress of the intrinsic DLC layer while maintaining high hardness. A deposition time of 5–20 minutes allows for precise control of the thickness of each N-DLC layer at the nanoscale (approximately 50 nm as shown in the example), providing a process guarantee for constructing a regular multilayer periodic structure.

[0019] Furthermore, a high bias voltage of -900V to -100V is applied, causing ionized carbon ions to bombard the growth surface at high speed with appropriate energy, implanting them below the surface layer. This shallow implantation promotes the sp-axis deposition of carbon atoms. 3 Hybrid bonding forms a dense structure dominated by tetrahedral amorphous carbon (ta-C). An arc current of 50–100 A provides a sufficient and stable carbon ion flux, ensuring deposition rate and film uniformity. Matching the deposition time (5–20 minutes) with the N-DLC layer ensures controllability of the thickness ratio of the two sublayers within a single cycle, thereby enabling precise control over the macroscopic comprehensive properties of the multilayer structure, such as stress distribution, hardness gradient, and toughness. The high-energy, low-temperature deposition process avoids annealing softening of the bearing steel substrate caused by high temperatures, protecting the original mechanical properties of the substrate.

[0020] Furthermore, before depositing functional multilayer films, high-energy argon ion (Ar) deposition is performed. +High-energy ion beam bombardment effectively removes the natural oxide layer, adsorbed gas molecules, and other atomic-level contaminants from the bearing substrate surface, resulting in a clean metal surface. Simultaneously, the bombardment by the high-energy ion beam generates numerous lattice defects and vacancies in the very shallow surface of the substrate, enhancing surface activity and facilitating the subsequent chemical adsorption and local epitaxial growth of deposited carbon atoms, significantly strengthening the film-substrate adhesion. A cleaning time of 30–60 minutes and a 700V extraction voltage ensure thorough and uniform cleaning and activation, laying the foundation for the preparation of N-DLC / DLC multilayer coatings that are firmly bonded to the substrate and resistant to high-load alternating stress.

[0021] Furthermore, precisely controlling the number of stacking cycles to 10-30 ensures sufficient interfaces to dissipate crack energy while maintaining the good physical properties of each sublayer. If the number of cycles is too small, the single-layer thickness is too large, and the intralayer stress cannot be effectively released, resulting in weak multilayer toughening and crack deflection effects, and the coating still exhibits brittleness close to that of a single-layer DLC. If the number of cycles is too large, the single-layer thickness is too thin, which may lead to blurred interlayer interfaces, losing the periodically modulated structural characteristics and interface effects. A total thickness of 1-3 micrometers provides the bearing with a sufficiently long wear life while avoiding the risk of excessive macroscopic internal stress and exacerbated edge effects due to excessive coating thickness, achieving optimal overall performance of the coating system.

[0022] Furthermore, the nanoscale surface roughness of Ra 5nm ensures that the friction pair surfaces of the bearing will not experience severe microscopic ploughing and adhesion due to the protrusion of the coating itself during operation. Under harsh dry friction conditions without lubrication, the coefficient of friction is only 0.092, and the film layer remains undamaged within 120 minutes. This directly demonstrates the excellent self-lubricating and wear-resistant properties of the multilayer structure of this invention. This extremely low and stable coefficient of friction is attributed to the intrinsic DLC layer height sp 3 The self-lubricating effect of the graphitized transfer film resulting from the high bond content, along with the suppression of crack propagation by the periodic multilayer structure, avoids abrupt changes in the coefficient of friction caused by hard abrasive grains generated from brittle spalling. This property enables bearings to effectively prevent seizure or catastrophic wear under critical conditions such as start-up, shutdown, or oil supply system failure, including boundary lubrication and even dry friction, significantly improving bearing reliability and solving the problem of high coefficient of friction of DLC coatings under dry friction conditions in existing technologies.

[0023] Furthermore, laser scintillation testing showed that the thermal conductivity of bearing steel coated with N-DLC / DLC periodic multilayer film was 44~50 W / (m·K), close to that of uncoated bearing steel (approximately 45~52 W / (m·K)), showing no significant decrease. Under high-speed, heavy-load conditions, if the heat generated by friction cannot be dissipated in time, it can lead to localized high temperatures, causing lubricant failure and accelerated wear. The excellent thermal conductivity of the coating of this invention ensures that frictional heat is rapidly conducted to the substrate and dissipated, maintaining the temperature stability of the friction interface and preventing thermally induced failure. As shown in the test data table, the thermal conductivity remained at approximately 44 W / (m·K) at -40℃, 49.5 W / (m·K) at 10℃, and approximately 50.3 W / (m·K) at 110℃, demonstrating stable and good thermal conductivity across the entire temperature range. This design, which does not impede the thermal conductivity of the substrate, combined with the low friction properties of the coating itself, makes it particularly suitable for applications with stringent requirements for low temperature, high load, and thermal stability, such as aerospace bearings.

[0024] This invention discloses a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure, which, from the bearing matrix outwards, exhibits a regular layered periodic structure with alternating N-DLC layers and intrinsic DLC layers (e.g., Figure 3 As shown in the bright-field image of a transmission electron microscope (TEM), the contrast exhibits periodic variations in brightness, with individual sublayer thicknesses in the nanometer range (approximately 50 nm). Its periodic multilayer design fundamentally solves the technical challenges of high brittleness and easy peeling inherent in traditional single-layer DLC coatings, achieving a balance between high hardness and high toughness. The ultra-smooth surface (Ra as low as approximately 5 nm) and extremely low coefficient of friction (0.092) provide excellent self-lubricating, friction-reducing, and wear-resistant properties. It maintains good thermal conductivity over a wide temperature range, enabling it to adapt to complex thermodynamic environments. This is a novel bearing surface coating that simultaneously meets the multifunctional requirements of high wear resistance and anti-peeling, and is of significant value in improving the lifespan and reliability of key components in high-end equipment. Attached Figure Description

[0025] Figure 1 The AFM test results are for a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure disclosed in Embodiment 1 of the present invention. Figure 2 This is a friction test report for a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure spherical disk disclosed in Embodiment 1 of the present invention. The test radius is 4 mm, the rotation period is 400 r / min, and the load is 8 N. Figure 3 The TEM test results for a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure disclosed in Embodiment 1 of the present invention are shown, where (a) is low resolution and (b) is high resolution. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0028] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0029] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0030] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0031] In this invention, unless otherwise specified, the numerical range "a~b" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "6~22" indicates that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation for these numerical combinations.

[0032] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0033] The term “and / or” as used in this invention refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0034] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0035] This invention provides a method for preparing a periodic multilayer structure of nitrogen-doped diamond-like carbon (N-DLC) / intrinsic diamond-like carbon. The film is deposited on the surface of a bearing substrate with a total thickness of 1-3 micrometers. The film is formed by alternating stacking of a first sublayer and a second sublayer along the thickness direction, with a stacking cycle number of 10-30. The first sublayer is an N-doped diamond-like carbon layer; the second sublayer is an undoped pure diamond-like carbon layer. The multilayer structure begins on the surface of the bearing steel substrate, first depositing a nitrogen-doped diamond-like carbon layer (N-DLC layer), followed by depositing an intrinsic diamond-like carbon layer (intrinsic DLC layer), completing one cycle, and repeating this process until the preset total thickness is reached. This technical solution mainly includes the following: S1: Substrate pretreatment: Using bearing steel sample (GCr15 steel) as the substrate, the substrate is first ground and polished, then ultrasonically cleaned with alcohol and pure water respectively, and then placed in a drying room for drying.

[0036] S2: Ion source cleaning: Adjust vacuum level to (2.5±0.5)×10 -3 The pressure is approximately 10-30 sccm, the argon flow rate is 10-30 mA, the discharge current is 300 mA, and the extraction voltage is 700 V. The ion cleaning time is 30-60 minutes to remove impurities from the substrate surface and improve film-substrate adhesion.

[0037] S3: Deposition of N-DLC layer: Using a carbon target as the reaction target, apply a bias voltage of -900V to -100V to the substrate during the coating process, select an arc current of 50~100A, adjust the filter current to 6~10A, introduce 5~10sccm of nitrogen gas into the vacuum chamber, and deposit for 5~20 minutes to obtain the N-DLC layer.

[0038] S4: Deposition of intrinsic DLC layer: Close N2 valve, use carbon target as reaction target material, apply a bias voltage of -900V to -100V to the substrate during deposition, select arc current of 50~100A, adjust filter current, and deposit for 5~20 minutes to obtain a high sp2 layer. 3 Intrinsic DLC layer with low content and low coefficient of friction; S5: The multi-layer structure starts from the surface of the bearing steel substrate, first depositing an N-DLC layer, then depositing an intrinsic DLC layer, and repeating this process until the preset total thickness is reached.

[0039] This invention provides and applies a periodic composite coating system of "N-DLC layer + intrinsic DLC layer" and the corresponding low-temperature preparation process. Targeting the special operating conditions of bearings, this invention demonstrates significant advantages in structural design and functional enhancement. Specific innovations are as follows: 1. Stress Control: The nitrogen-doped layer typically has low internal stress, effectively isolating and releasing the high internal stress of the intrinsic DLC layer, preventing overall coating warping or peeling. 2. Toughening: The multi-layer interface effectively deflects and prevents the longitudinal propagation of microcracks, transforming the single crack propagation mode of brittle materials into a multi-interface energy dissipation mode, thereby improving the coating's toughness and load-bearing capacity. 3. Performance Optimization: Combining the excellent adhesion of the N-DLC layer with the ultra-high hardness and low friction of the intrinsic DLC layer, the overall performance of the coating is optimized.

[0040] The periodic multilayer coating technology of "N-DLC layer + intrinsic DLC layer" proposed in this invention has the following beneficial effects: 1. Ultra-smooth surface: As shown by atomic force microscopy (AFM) testing, the arithmetic mean roughness Ra value of the coating surface is about 5nm, achieving nanoscale smoothness. This ultra-smooth surface can effectively reduce the microscopic mechanical interlocking between friction pairs, reduce starting friction and wear, and provide an ideal basis for the formation of a continuous lubricating oil film. 2. Extremely low friction and wear: The ball-disc friction and wear test was conducted under dry friction conditions. The results show that the coating has an extremely stable low coefficient of friction, indicating an ultra-long service life of the bearing. 3. Good thermal conductivity: The thermal conductivity of the material was tested using the laser flash method. After periodic multilayer coating with nitrogen-doped diamond-like carbon / intrinsic diamond-like carbon, the thermal conductivity of the bearing steel did not decrease significantly. The thermal conductivity of the uncoated bearing steel (approximately 45~52 W / (m·K)) is close to that of the original coating. Combined with its friction-reducing characteristics, it is suitable for low-temperature, high-load environments.

[0041] This invention employs a self-made multi-arc ion plating device, which has significant advantages in process control and film performance: 1. High film hardness and excellent wear resistance: By exciting the target material to obtain plasma with high ionization rate and concentrated energy, a film with high sp content is deposited on the bearing surface. 3 1. **Intrinsic DLC film with high bond content, dense structure, and high hardness enhances the wear resistance of bearings and extends their service life.** 2. **Low-temperature deposition protects substrate performance:** The coating process is carried out at near room temperature, avoiding thermal softening or thermal stress damage to the bearing steel substrate microstructure caused by high-temperature annealing. 3. **Enhanced film-substrate adhesion for a stronger coating:** Argon ion cleaning and transition layer deposition technology effectively alleviate the problem of decreased adhesion caused by stress concentration. The prepared layer has excellent adhesion to the substrate, eliminating the risk of coating peeling. 4. **Good process controllability and high repeatability:** Adjustable process parameters such as arc current and bias voltage enable large-area uniform coating, meeting the needs of large-scale industrial production.

[0042] This invention can solve the following technical problems: 1. Improve bearing wear resistance Traditional bearings (such as those made of GCr15 steel) have limited surface hardness. Under high-speed, high-load, or abrasive conditions, their surfaces are prone to abrasive and adhesive wear, leading to reduced precision, increased clearance, increased vibration and noise, and ultimately, failure. This invention provides a surface-modified bearing by preparing a nitrogen-doped diamond-like carbon (DLC) / intrinsic diamond-like carbon (IDC) periodic multilayer coating on the surface of the bearing's critical friction pairs (bearing and rollers). This significantly improves the bearing's wear resistance, fatigue resistance, corrosion resistance, and self-lubricating properties, fundamentally delaying performance degradation.

[0043] 2. Improve bearing self-lubrication Bearing performance is highly dependent on the formation of a lubricating oil film. During startup, shutdown, low-speed heavy loads, or moments of lubricant failure, the bearing is in a state of boundary lubrication or dry friction, making it highly susceptible to severe wear and even seizure, leading to reduced precision. The nitrogen-doped diamond-like carbon (DLC) / intrinsic diamond-like carbon (IDC) periodic multilayer coating involved in this invention has a low coefficient of friction and high hardness. Even in critical situations such as temporary rupture of the lubricating oil film, oil deterioration, or extreme high and low temperatures, the low-friction characteristics of the DLC coating itself can provide protection, preventing the bearing from instantaneously and catastrophically seizing or experiencing severe wear.

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0045] Example 1 A method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure includes the following steps: S1: Before the experiment, the surface of the GCr15 sample was ground and polished. The substrate surface was ultrasonically cleaned for 5 minutes with alcohol and pure water respectively and then dried to remove surface impurities.

[0046] S2: Before coating, first evacuate the vacuum chamber to a vacuum level of 2.0 × 10⁻⁶. -3Pa, open the argon control valve, adjust the argon flow rate to 10 sccm, discharge current to 300 mA, lead-out voltage to 700 V, and perform ion source cleaning for 30 min to remove impurities from the substrate surface and improve film-substrate adhesion.

[0047] S3: Using a carbon target as the reaction target, a bias voltage of -900V is applied to the substrate during coating, the arc current is selected as 50A, the filter current is adjusted to 6A, 5sccm of nitrogen gas is introduced into the vacuum chamber, and deposition takes 5 minutes to obtain a carbon layer with N-doped diamond.

[0048] S4: Close the N2 valve, use a carbon target as the reaction target, apply a -100V bias voltage to the substrate during coating, select an arc current of 50A, adjust the filter current, and deposit for 5 minutes to obtain a film with high sp... 3 Intrinsic DLC layer with low content and low coefficient of friction.

[0049] S5: The multilayer structure starts from the surface of the bearing steel substrate, first depositing an N-DLC layer, then depositing an intrinsic DLC layer, which is one complete cycle. A total of 10 cycles are deposited, and the cycle is repeated until the preset total thickness of 1μm is reached.

[0050] Table 1 shows the thermal conductivity test results of a nitrogen-doped diamond-like carbon / intrinsic diamond-like carbon periodic multilayer structure disclosed in Example 1. As can be seen from the table, the thermal conductivity of the material was tested using the laser flash method, with a test temperature range of -40℃ to 150℃. The test results show that the thermal conductivity λ is in the range of 44~50 W / (m·K), which is close to the thermal conductivity of uncoated bearing steel (approximately 45~52 W / (m·K)), making it suitable for low-temperature, high-load environments (such as aerospace bearings).

[0051] Table 1. Thermal conductivity test results of nitrogen-doped diamond-like carbon / intrinsic diamond-like carbon periodic multilayer structures.

[0052] Figure 1 The AFM test results for a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure disclosed in Embodiment 1 of the present invention show that the average surface roughness (Ra) of the sample before coating is 5 nm, which may be due to the polishing of the sample. After coating, the average surface roughness (Ra) of the sample is 5.8 nm, with no significant change.

[0053] Figure 2 This is a friction test report for a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure spherical disk disclosed in Embodiment 1 of the present invention. The test radius was 4 mm, the rotation period was 400 r / min, and the load was 8 N. The results showed that the film layer was not damaged within 120 min of the test time, and the average friction coefficient was 0.092.

[0054] Figure 3 The TEM test results for a nitrogen-doped diamond-like carbon (NDC) / intrinsic diamond-like carbon (IDC) periodic multilayer structure disclosed in Example 1 of this invention are shown. (a) is a low-resolution image; (b) is a high-resolution image. The low-magnification bright-field transmission electron microscope image clearly shows that the coating has a regular, continuous, alternating layered structure. The multilayer film exhibits a highly periodic variation in brightness contrast from the substrate outwards, with a clearly defined total number of layers. In the high-resolution TEM image, it can be observed that each monolayer film exhibits a uniform, dense amorphous structure, without any defects such as grains or pores. Measurements show that the thickness of both the individual N-DLC layer and the intrinsic DLC layer is consistently around 50 nm, demonstrating that the periodic multilayer process of "N-DLC layer + intrinsic DLC layer" successfully fabricated a nano-multilayer structure with long-range order.

[0055] Example 2 A method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure includes the following steps: S1: Before the experiment, the surface of the GCr15 sample was ground and polished. The substrate surface was ultrasonically cleaned for 5 minutes with alcohol and pure water respectively and then dried to remove surface impurities.

[0056] S2: Before coating, first evacuate the vacuum chamber to a vacuum level of 2.5 × 10⁻⁶. -3 Pa, open the argon control valve, adjust the argon flow rate to 20 sccm, discharge current to 300 mA, lead-out voltage to 700 V, and perform ion source cleaning for 30 min to remove impurities from the substrate surface and improve film-substrate adhesion.

[0057] S3: Using a carbon target as the reaction target, a bias voltage of -500V is applied to the substrate during coating, the arc current is selected as 80A, the filter current is adjusted to 8A, 8sccm of nitrogen gas is introduced into the vacuum chamber, and after 10 minutes of deposition, a carbon layer with N-doped diamond can be obtained.

[0058] S4: Close the N2 valve, use a carbon target as the reaction target, apply a -500V bias voltage to the substrate during coating, select an arc current of 80A, adjust the filter current, and deposit for 10 minutes to obtain a film with high sp. 3 Intrinsic DLC layer with low content and low coefficient of friction.

[0059] S5: The multilayer structure starts from the surface of the bearing steel substrate, first depositing an N-DLC layer, then depositing an intrinsic DLC layer, which is one complete cycle. A total of 18 cycles are deposited, and the cycle is repeated until the preset total thickness of 2μm is reached.

[0060] Example 3 A method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure includes the following steps: S1: Before the experiment, the surface of the GCr15 sample was ground and polished. The substrate surface was ultrasonically cleaned for 5 minutes with alcohol and pure water respectively and then dried to remove surface impurities.

[0061] S2: Before coating, first evacuate the vacuum chamber to a vacuum level of 3.0 × 10⁻⁶. -3 Pa, open the argon control valve, adjust the argon flow rate to 30 sccm, discharge current to 300 mA, lead-out voltage to 700 V, and perform ion source cleaning for 30 min to remove impurities from the substrate surface and improve film-substrate adhesion.

[0062] S3: Using a carbon target as the reaction target, a bias voltage of -100V is applied to the substrate during coating, the arc current is selected as 100A, the filter current is adjusted to 10A, 10sccm of nitrogen gas is introduced into the vacuum chamber, and deposition is carried out for 20 minutes to obtain a carbon layer with N-doped diamond.

[0063] S4: Close the N2 valve, use a carbon target as the reaction target, apply a -900V bias voltage to the substrate during coating, select an arc current of 100A, adjust the filter current, and deposit for 20 minutes to obtain a film with high sp. 3 Intrinsic DLC layer with low content and low coefficient of friction.

[0064] S5: The multilayer structure starts from the surface of the bearing steel substrate, first depositing an N-DLC layer, then depositing an intrinsic DLC layer, which is one complete cycle. A total of 30 cycles are deposited, and the cycle is repeated until the preset total thickness of 3μm is reached.

[0065] Example 4 A method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure includes the following steps: S1: Before the experiment, the surface of the GCr15 sample was ground and polished to make its average surface roughness Ra value 5 nm. The substrate surface was ultrasonically cleaned for 5 minutes with alcohol and pure water respectively and then dried to remove surface impurities.

[0066] S2: Before coating, first evacuate the vacuum chamber to a vacuum level of 2.2 × 10⁻⁶. -3 Pa, open the argon control valve, adjust the argon flow rate to 15 sccm, discharge current to 300 mA, lead-out voltage to 700 V, and perform ion source cleaning for 40 min to remove impurities from the substrate surface and improve film-substrate adhesion.

[0067] S3: Using a carbon target as the reaction target, a bias voltage of -600 V is applied to the substrate during coating, the arc current is selected as 70 A, the filter current is adjusted to 7 A, 6 sccm of nitrogen gas is introduced into the vacuum chamber, and the deposition takes 12 minutes to obtain an N-doped diamond carbon layer.

[0068] S4: Close the N2 valve, use a carbon target as the reaction target, apply a -600 V bias voltage to the substrate during coating, select an arc current of 70 A, adjust the filter current, and deposit for 12 minutes to obtain a film with high sp. 3 Intrinsic DLC layer with low content and low coefficient of friction.

[0069] S5: The multilayer structure starts from the surface of the bearing steel substrate, first depositing an N-DLC layer, then depositing an intrinsic DLC layer, which is one complete cycle. A total of 10 cycles are deposited, and the cycle is repeated until the preset total thickness of 1 μm is reached.

[0070] The prepared nitrogen-doped diamond / intrinsic diamond periodic multilayer structure has an arithmetic mean surface roughness Ra of 5 nm, an average friction coefficient of 0.05 within 120 min under dry friction conditions, and a thermal conductivity of 44 W / (m·K) for the bearing steel after plating.

[0071] Example 5 A method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure includes the following steps: S1: Before the experiment, the surface of the GCr15 sample was ground and polished to make its average surface roughness Ra value 10 nm. The substrate surface was ultrasonically cleaned for 5 minutes with alcohol and pure water respectively and then dried to remove surface impurities.

[0072] S2: Before coating, first evacuate the vacuum chamber to a vacuum level of 2.8 × 10⁻⁶. -3 Pa, open the argon control valve, adjust the argon flow rate to 25 sccm, discharge current to 300 mA, lead-out voltage to 700 V, and perform ion source cleaning for 50 min to remove impurities from the substrate surface and improve film-substrate adhesion.

[0073] S3: Using a carbon target as the reaction target, a bias voltage of -300 V is applied to the substrate during coating, the arc current is selected as 60A, the filter current is adjusted to 8A, 7 sccm of nitrogen gas is introduced into the vacuum chamber, and deposition takes 8 minutes to obtain an N-doped diamond carbon layer.

[0074] S4: Close the N2 valve, use a carbon target as the reaction target, apply a -300 V bias voltage to the substrate during coating, select an arc current of 60 A, adjust the filter current, and deposit for 8 minutes to obtain a film with high sp. 3 Intrinsic DLC layer with low content and low coefficient of friction.

[0075] S5: The multilayer structure starts from the surface of the bearing steel substrate, first depositing an N-DLC layer, then depositing an intrinsic DLC layer, which is one complete cycle. A total of 30 cycles are deposited, and the cycle is repeated until the preset total thickness of 3 μm is reached.

[0076] The prepared nitrogen-doped diamond / intrinsic diamond periodic multilayer structure has an arithmetic mean surface roughness Ra of 10 nm, an average friction coefficient of 0.08 within 120 min under dry friction conditions, and a thermal conductivity of 46 W / (m·K) for the bearing steel after plating.

[0077] Example 6 A method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure includes the following steps: S1: Before the experiment, the surface of the GCr15 sample was ground and polished to make its average surface roughness Ra value 15 nm. The substrate surface was ultrasonically cleaned for 5 minutes with alcohol and pure water respectively and then dried to remove surface impurities.

[0078] S2: Before coating, first evacuate the vacuum chamber to a vacuum level of 2.5 × 10⁻⁶. -3 Pa, open the argon control valve, adjust the argon flow rate to 20 sccm, discharge current to 300 mA, lead-out voltage to 700 V, and perform ion source cleaning for 45 min to remove impurities from the substrate surface and improve film-substrate adhesion.

[0079] S3: Using a carbon target as the reaction target, a bias voltage of -800 V is applied to the substrate during coating, the arc current is selected as 90A, the filter current is adjusted to 9 A, 9 sccm of nitrogen gas is introduced into the vacuum chamber, and the deposition takes 15 minutes to obtain an N-doped diamond carbon layer.

[0080] S4: Close the N2 valve, use a carbon target as the reaction target, apply a bias voltage of -800 V to the substrate during coating, select an arc current of 90 A, adjust the filter current, and deposit for 15 minutes to obtain a film with high sp. 3 Intrinsic DLC layer with low content and low coefficient of friction.

[0081] S5: The multilayer structure starts from the surface of the bearing steel substrate, first depositing an N-DLC layer, then depositing an intrinsic DLC layer, which constitutes one complete cycle. A total of 18 cycles are deposited, and the cycle is repeated until the preset total thickness of 2 μm is reached.

[0082] The prepared nitrogen-doped diamond / intrinsic diamond periodic multilayer structure has an arithmetic mean surface roughness Ra of 15 nm, an average friction coefficient of 0.12 within 120 min under dry friction conditions, and a thermal conductivity of 48 W / (m·K) for the bearing steel after plating.

[0083] Example 7 A method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure includes the following steps: S1: Before the experiment, the surface of the GCr15 sample was ground and polished to make its average surface roughness Ra value 20 nm. The substrate surface was ultrasonically cleaned for 5 minutes with alcohol and pure water respectively and then dried to remove surface impurities.

[0084] S2: Before coating, first evacuate the vacuum chamber to a vacuum level of 2.5 × 10⁻⁶. -3 Pa, open the argon control valve, adjust the argon flow rate to 30 sccm, discharge current to 300 mA, lead-out voltage to 700 V, and perform ion source cleaning for 60 min to remove impurities from the substrate surface and improve film-substrate adhesion.

[0085] S3: Using a carbon target as the reaction target, a bias voltage of -400 V is applied to the substrate during coating, the arc current is selected as 100 A, the filter current is adjusted to 10 A, 10 sccm of nitrogen gas is introduced into the vacuum chamber, and the deposition takes 18 minutes to obtain an N-doped diamond carbon layer.

[0086] S4: Close the N2 valve, use a carbon target as the reaction target, apply a -400 V bias voltage to the substrate during coating, select an arc current of 100 A, adjust the filter current, and deposit for 18 minutes to obtain a film with high sp. 3 Intrinsic DLC layer with low content and low coefficient of friction.

[0087] S5: The multilayer structure starts from the surface of the bearing steel substrate, first depositing an N-DLC layer, then depositing an intrinsic DLC layer, which constitutes one complete cycle. A total of 28 cycles are deposited, and the cycle is repeated until the preset total thickness of 3 μm is reached.

[0088] The prepared nitrogen-doped diamond / intrinsic diamond periodic multilayer structure has an arithmetic mean surface roughness Ra of 20 nm, an average friction coefficient of 0.15 within 120 min under dry friction conditions, and a thermal conductivity of 50 W / (m·K) for the bearing steel after plating.

[0089] In summary, this invention discloses a nitrogen-doped diamond-like carbon (NDC) / intrinsic diamond-like carbon (IDC) periodic multilayer structure and its preparation method. Using a multi-arc ion plating apparatus and a carbon target as the reaction target, an N-DLC layer is first deposited on the surface of a bearing substrate. Subsequently, an intrinsic DLC layer is deposited with the nitrogen gas turned off. This process of alternating N-DLC and intrinsic DLC deposition is repeated for 5-20 cycles to form a periodic multilayer coating with a total thickness of 1-3 micrometers. The multilayer interface constructed through alternating deposition effectively releases and blocks the high residual stress accumulated within a single DLC layer, preventing overall coating warping or peeling, thus overcoming the fundamental defects of traditional single-layer DLC coatings, such as high brittleness and easy failure. The periodic layered interface effectively deflects the longitudinal propagation path of microcracks, transforming the single crack propagation mode into an energy dissipation mode along multiple interfaces, significantly improving the coating's toughness and impact resistance. The N-DLC layer combines low internal stress and good adhesion, while the intrinsic DLC layer provides ultra-high hardness and low friction characteristics. These two layers complement each other at the nanoscale, achieving a balance between high hardness and high toughness. The coating has a surface roughness Ra of only about 5 nm, and its coefficient of friction is as low as 0.092 under dry friction conditions without damage within 120 minutes. After coating, the thermal conductivity of the bearing steel remains in the range of 44~50 W / (m·K), which is close to that of the uncoated substrate, ensuring that frictional heat can be dissipated in a timely manner. This invention, while maintaining excellent wear resistance and friction reduction performance, simultaneously solves the problem of easy peeling of traditional DLC coatings, and achieves multi-functional integrated synergistic optimization.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure, characterized in that, Includes the following steps: S1: Grind and polish the surface of the bearing substrate, and then clean and dry it; S2: Using a multi-arc ion plating process, a carbon target is used as the reaction target material, and nitrogen gas is introduced to deposit a nitrogen-doped diamond-like layer on the surface of the bearing substrate. S3: Turn off nitrogen gas, use a carbon target as the reaction target, and deposit an intrinsic diamond-like layer on the surface of the nitrogen-doped diamond-like layer; S4: Repeat steps S2 and S3, cyclically depositing nitrogen-doped diamond-like layers and intrinsic diamond-like layers in an alternating stacking manner until the preset total thickness is reached, forming a periodic multilayer structure of nitrogen-doped diamond-like / intrinsic diamond-like.

2. The method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure according to claim 1, characterized in that, In step S1, the material of the bearing substrate is GCr15 bearing steel, and the cleaning is ultrasonic cleaning using alcohol and pure water in sequence.

3. The method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure according to claim 1, characterized in that, In step S1, after the grinding and polishing treatment, the average surface roughness Ra of the bearing substrate is 5~20nm.

4. The method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure according to claim 1, characterized in that, In step S2, the process conditions for depositing the nitrogen-doped diamond-like carbon layer are as follows: apply a bias voltage of -900V to -100V to the substrate, select an arc current of 50 to 100A, introduce 5 to 10 sccm of nitrogen gas into the vacuum chamber, and deposit for 5 to 20 minutes.

5. The method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure according to claim 1, characterized in that, In step S3, the process conditions for depositing the intrinsic diamond-like carbon layer are as follows: apply a bias voltage of -900V to -100V to the substrate, select an arc current of 50 to 100A, and deposit for 5 to 20 minutes.

6. The method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure according to claim 1, characterized in that, Before step S2, an ion source cleaning step is also included: adjusting the vacuum chamber vacuum to (2.5±0.5)×10 -3 Pa, argon gas is introduced, argon gas flow rate is 10~30 sccm, discharge current is 300mA, extraction voltage is 700V, ion cleaning time is 30~60min.

7. The method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure according to claim 1, characterized in that, In step S4, the number of cycles in which the nitrogen-doped diamond-like layer and the diamond-like layer are stacked alternately is 10 to 30, and the preset total thickness is 1 to 3 micrometers.

8. The method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure according to claim 1, characterized in that, The surface arithmetic mean roughness Ra of the nitrogen-doped diamond / intrinsic diamond periodic multilayer structure is 5~20 nm, and the average friction coefficient is 0.05~0.15 within 120 min under dry friction conditions.

9. The method for preparing a nitrogen-doped diamond / intrinsic diamond periodic multilayer structure according to claim 1, characterized in that, The thermal conductivity of bearing steel coated with a periodic multilayer structure of nitrogen-doped diamond / intrinsic diamond is 44~50 W / (m·K).

10. A nitrogen-doped diamond / intrinsic diamond periodic multilayer structure, characterized in that, It was prepared using the method for preparing nitrogen-doped diamond / intrinsic diamond periodic multilayer structures according to any one of claims 1-9.

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