Preparation method of B / Al co-doped multi-layer gradient carbon film for methanol automobile engine surface modification
By preparing B/Al co-doped multilayer gradient carbon films on the surface of engine components, the corrosion and wear problems of methanol engine components were solved, high bonding strength and stable film performance were achieved, the corrosion resistance and wear resistance of the engine were improved, and the service life was extended.
Patent Information
- Application Number
- CN202510965428.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-14
- Publication Date
- 2025-10-10
AI Technical Summary
Engine components using methanol as an alternative fuel for vehicles are susceptible to corrosion and wear under harsh working conditions such as high temperature, high pressure and mechanical friction. Traditional thermal spray coatings have high porosity and insufficient bonding between the film and the substrate. Carbon-based films have unstable performance in a methanol environment, affecting engine life and usage costs.
Magnetron sputtering technology is used to prepare B/Al co-doped multilayer gradient carbon film on the surface of engine metal parts. By depositing a Cr base layer, a CrxByCz gradient transition layer and a B/Al co-doped carbon-based functional layer, the bonding strength and stability of the film to the metal substrate are improved.
It significantly improves the corrosion resistance and wear resistance of the film, reduces the friction coefficient and wear rate, extends the service life of the engine and reduces the corrosion rate, thereby improving the service reliability of the engine in a methanol environment.
Smart Images
Figure FT_1 
Figure FT_2 
Figure FT_3
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of surface engineering, and particularly relates to a preparation method of B / Al co-doped multilayer gradient carbon film for surface modification of a methanol automobile engine. BACKGROUND
[0002] Methanol is used as a substitute fuel for vehicles, and is increasingly applied in the fields of automobiles, ships and power generation equipment, etc. due to its advantages of less environmental pollution, high octane value and good economy. However, methanol produces corrosive substances such as formaldehyde and formic acid during combustion, and the surface of engine parts is subjected to harsh conditions such as high temperature, high pressure and mechanical friction during engine operation, which puts high requirements on the material properties of engine parts. After long-term contact with methanol and its combustion products, engine metal parts are prone to corrosion and accelerated wear, which leads to performance degradation and shortened service life of the engine, and seriously restricts the promotion and application of methanol vehicles. For example, the corrosion and wear rates of traditional engine cylinder blocks, pistons, valves and other components in the methanol environment are significantly higher than those of gasoline or diesel engines, and frequent maintenance and replacement of parts increase the use cost.
[0003] At present, the commonly used method for surface modification of engines is thermal spraying technology, but it has limitations in the methanol environment. Thermal sprayed coatings have high porosity, which easily leads to the penetration of corrosive liquids such as methanol and its combustion products into the substrate, causing corrosion. Carbon-based films have excellent properties such as high hardness, low friction coefficient and good chemical stability, but their application on the surface of methanol engines still faces some challenges, such as insufficient adhesion between the film and the substrate, unstable long-term service performance in the methanol environment, etc., which need to be solved urgently.
[0004] In order to overcome the shortcomings of carbon-based films, the present application proposes an innovative technical solution, which is to prepare B / Al co-doped multilayer gradient carbon film on the surface of engine metal parts by magnetron sputtering technology. This method can effectively improve the adhesion between the film and the metal substrate, ensure the uniformity and stability of the film, and significantly improve the corrosion resistance and corrosion and wear resistance of the engine in the methanol environment. The present application not only solves the limitations of traditional film preparation technology, but also provides reliable technical support for the application of methanol as a substitute fuel for vehicles in the fields of automobiles, ships, etc. SUMMARY
[0005] In view of the problems in the above background art, the present application discloses a preparation method of B / Al co-doped multilayer gradient carbon film for surface modification of a methanol automobile engine.
[0006] 1. Preparation of B / Al co-doped multilayer gradient carbon films The preparation of the B / Al co-doped multilayer gradient carbon film of the present invention comprises the following steps: 1) Ultrasonic clean the substrate with acetone and anhydrous ethanol for 10-20 min respectively to remove surface contaminants. Dry it with nitrogen and place it on the sample holder in a vacuum chamber.
[0007] 2) Evacuate the vacuum chamber until the pressure inside is less than 3×10 −5 After the vacuum chamber reaches 0.3 Pa, high-purity argon gas is introduced, the pressure in the vacuum chamber is controlled at 0.3~0.5 Pa, the bias voltage is adjusted to −500~−800 V, and the surface of the substrate is bias cleaned to remove impurities on the substrate surface. The treatment time is 10~15 min.
[0008] 3) Depositing a B / Al co-doped multilayer gradient carbon film on the substrate surface using magnetron sputtering technology, specifically: ① Deposit Cr as a base layer: adjust the substrate bias voltage to −50–−150 V, turn on the Cr planar target, set the initial target current to 0.2–0.5 A, and increase it to 3.0–3.5 A after 30 s. Introduce argon at 15–50 sccm, control the pressure to 0.3–1.0 Pa, the duty cycle to 60–85%, and the deposition time to 15–30 min.
[0009] ② Deposition of Cr x B y C z Gradient transition layer: Turn on the C-plane target, set the initial target current to 0.2-0.5 A, and increase it to 3.0-4.0 A after 600-1800 s; turn on the B-plane target, set the initial target current to 0.1-0.3 A, and increase it to 0.5-1.0 A after 600-1800 s; the Cr target current is reduced from 3.0-5.5 A to 0 A after 1200-1800 s, the argon flow rate is 15-50 sccm, and the gas pressure reaches 0.3-1.0 Pa; adjust the bias voltage to −50-−150 V, the duty cycle to 60-85%, and the deposition time to 15-30 min.
[0010] ③ Deposition of B / Al co-doped carbon-based functional layer: Turn on the Al planar target, set the target current to 0.1~0.5 A, and keep the current of C target and B target the same as that of Cr deposition. x B y C z The gradient transition layer was consistent, and 15-50 sccm of methane gas was introduced, while the argon flow rate was maintained at 15-50 sccm and the gas pressure reached 0.3-1.0 Pa. The bias voltage was adjusted to −50-−150 V, the duty cycle was 60-85%, and the deposition time was 270-720 min.
[0011] II. Structure characterization and performance evaluation of B / Al co-doped multilayer gradient carbon thin film 1)Structure of B / Al co-doped multilayer gradient carbon thin film Figure 2 Raman spectrum of B / Al co-doped multilayer gradient carbon thin film prepared by the present application. The spectrum shows a broad asymmetric peak between 1000 cm -1 and 1800 cm -1 , indicating that the deposited B / Al co-doped multilayer gradient carbon thin film has typical Raman spectrum characteristics of amorphous carbon. The relative intensity ratio (I D / I G ) of D peak and G peak is 0.83, indicating that the carbon material has high graphitization degree and low defect content.
[0012] 2)Mechanical and tribological properties of B / Al co-doped multilayer gradient carbon thin film (1)Hardness and elastic modulus The microhardness and elastic modulus of the thin film were measured by continuous indentation method using a nanoindenter. The maximum indentation depth was set to 200 nm (to ensure that the indentation depth of the indenter was less than 1 / 10 of the thickness of the film during testing, to avoid the influence of the substrate on the hardness test); at the same time, in order to reduce the measurement error, 5 points of each sample were selected for measurement during testing, and the average value was taken as the final experimental result.
[0013] The hardness of B / Al co-doped multilayer gradient carbon thin film was measured to be between 34.56~36.32 GPa, and the elastic modulus was between 337.92~356.89 GPa.
[0014] (2)Tribological properties The friction properties of B / Al co-doped multilayer gradient carbon thin film in methanol environment were measured by ball-on-disc reciprocating friction machine. Si3N4 ceramic ball (Φ 6 mm) was selected as the friction pair, the load was 5 N, the reciprocating frequency was 1 Hz, and the reciprocating distance was 4 mm.
[0015] Figure 3 The friction coefficient curve. Under the above friction test parameters, the friction coefficient of B / Al co-doped multilayer gradient carbon thin film was stable at 0.08~0.09 ( Figure 3 a), and the friction coefficient of SUS 440C stainless steel substrate without protective film fluctuated between 0.25~0.30 ( Figure 3 b). The obtained B / Al co-doped multilayer gradient carbon thin film can significantly improve the friction reduction performance of SUS 440C stainless steel substrate.
[0016] Figure 4The three-dimensional contour of the wear scar after rubbing for 1 hour in methanol solution with Si3N4 ceramic ball (Φ 6 mm) as the friction pair, load 5 N, reciprocating frequency 1 Hz, reciprocating distance 4 mm. Figure 4 b) Compared with the obtained B / Al co-doped multilayer gradient carbon film ( Figure 4 a) The scratch morphology is relatively smooth, the scratch width is narrow and the depth is shallow. The film significantly improves the wear resistance of the stainless steel substrate.
[0017] Figure 5 The cross-sectional profile of the wear track after 1 hour of friction in methanol solution with Si3N4 ceramic ball (Φ 6 mm) as the friction pair, load 5 N, reciprocating frequency 1 Hz, reciprocating distance 4 mm. Figure 5 b) Compared with the obtained B / Al co-doped multilayer gradient carbon film ( Figure 5 The cross-sectional profile area of a) is significantly reduced, indicating that the obtained B / Al co-doped multilayer gradient carbon film has excellent anti-wear performance in methanol environment.
[0018] 3) Electrochemical performance of B / Al co-doped multilayer gradient carbon films A Gamry electrochemical workstation was used, and a three-electrode system was employed. The sample was used as the working electrode, a saturated calomel electrode was used as the reference electrode, and a platinum sheet (area 1 cm 2 ) as the counter electrode, and the open circuit potential of the B / Al co-doped multilayer gradient carbon film after immersion in methanol solution for 1800 s was evaluated. The scan range was −1 to 1 V, and the scan rate was 10 mV·s −1 Gamry Electrochemical Analysis Software was used to perform Tafel fitting analysis on the test results and record the corrosion current density and corrosion potential of the specimens.
[0019] Figure 6 The open circuit potential test after immersion in methanol solution for 1800 s showed that the open circuit potential of the B / Al co-doped multilayer gradient carbon film was stable at 0.12 V ( Figure 6 a), compared with the open circuit potential of SUS440C stainless steel substrate −0.07 V ( Figure 6 b) The open circuit potential of B / Al co-doped multilayer gradient carbon film is more positive, indicating better corrosion resistance.
[0020] Figure 7 The corrosion potential and corrosion current of the B / Al co-doped multilayer gradient carbon film were −0.172 V and 2.35×10 −8 A.cm −2 ( Figure 7a). The corrosion potential and corrosion current of the SUS 440C stainless steel substrate are-0.356 V and 2.21*10 −6 A·cm −2 Figure 7 b). Compared with the stainless steel substrate, the corrosion potential of the carbon film obtained by the method is positively shifted, and the corrosion current is reduced by about 2 orders of magnitude, indicating that the carbon film has good corrosion resistance and can effectively slow down the corrosion rate.
[0021] Compared with the prior art, the present application has the following advantages: The hydrogenated amorphous carbon content of the B / Al co-doped multilayer gradient carbon film obtained by the method of the present application is increased, while the density and hardness of the film itself are maintained; the doping elements are uniformly dispersed in the film, thereby ensuring that a small amount of element doping can significantly improve the performance of the film; the film has a low friction coefficient and a low wear rate in a methanol environment, significantly improving the tribological properties of the film. In a methanol environment, the corrosion potential can be significantly increased, the corrosion current density can be reduced, the corrosion rate can be effectively slowed down, and the corrosion resistance of the film can be significantly improved. The method of co-doping metal and non-metal carbon film can significantly improve the deposition quality of the carbon film, the method is simple, the cost is controllable, and it has guiding significance for industrial production. BRIEF DESCRIPTION OF DRAWINGS
[0022] Figure 1 The structure diagram of the B / Al co-doped multilayer gradient carbon film prepared by the present application.
[0023] Figure 2 The Raman spectrum of the B / Al co-doped multilayer gradient carbon film prepared by the present application.
[0024] Figure 3 The B / Al co-doped multilayer gradient carbon film prepared by the present application Figure 3 a) and the SUS 440C stainless steel substrate (b) in the methanol environment. Figure 3 b) in the methanol environment for 1 h (5 N load, 1 Hz frequency).
[0025] Figure 4 The B / Al co-doped multilayer gradient carbon film prepared by the present application Figure 4 a) and the SUS 440C stainless steel substrate (b) in the methanol environment. Figure 4 b) in the methanol environment for 1 h (5 N load, 1 Hz frequency).
[0026] Figure 5 The B / Al co-doped multilayer gradient carbon film prepared by the present application Figure 5 a) and the SUS 440C stainless steel substrate (b) in the methanol environment. Figure 5 b) Cross-section profile of wear tracks rubbed in methanol environment for 1 h (5 N load, 1 Hz frequency).
[0027] Figure 6 B / Al co-doped multilayer gradient carbon thin film prepared for the present application Figure 6 a) and SUS 440C stainless steel substrate Figure 6 b) Open circuit potential of immersion in methanol environment for 1800 s.
[0028] Figure 7 B / Al co-doped multilayer gradient carbon thin film prepared for the present application Figure 7 a) and SUS 440C stainless steel substrate Figure 7 b) Potentiodynamic polarization curve in methanol environment. DETAILED DESCRIPTION
[0029] The present application will be further explained in conjunction with specific embodiments.
[0030] Example 1 (1) The substrates were cleaned with acetone and anhydrous ethanol respectively by ultrasonic cleaning for 10-20 min to remove surface contaminants, and then dried by nitrogen and placed on the sample holder in the vacuum chamber.
[0031] (2) After the vacuum chamber was vacuumed to a pressure less than 3x10 −5 Pa, high-purity argon was introduced, the pressure in the vacuum chamber was controlled at 0.3-0.5 Pa, the bias voltage was adjusted to -500 to -800 V, the surface of the substrate was cleaned by bias voltage to remove impurities on the surface of the substrate, and the treatment time was 10-15 min.
[0032] (3) B / Al co-doped multilayer gradient carbon thin film was deposited on the surface of the substrate by magnetron sputtering technology, specifically: ① Depositing Cr base layer: adjusting the substrate bias voltage to -70 V, turning on the Cr plane target, setting the starting target current to 0.2 A, increasing to 3 A after 30 s; introducing argon at a flow rate of 16 sccm, controlling the gas pressure at 0.37 Pa, the duty cycle at 60%, and the deposition time at 15 min.
[0033] ② Depositing Cr x B y C z Gradient transition layer: turning on the C plane target, setting the starting target current to 0.2 A, increasing to 3 A after 1800 s; turning on the B plane target, setting the starting target current to 0.2 A, increasing to 0.5 A after 1800 s; the Cr target current decreases from 3 A to 0 A after 1800 s, the argon flow rate remains at 16 sccm, the gas pressure reaches 0.34 Pa; adjusting the bias voltage to -70 V, the duty cycle to 60%, and the deposition time to 30 min.
[0034] ③ Depositing B / Al co-doped carbon-based functional layer: turning on the Al plane target, setting the target current to 0.2 A, keeping the C target and B target current unchanged, and depositing Cr x B y C z The gradient transition layer remains unchanged, 16 sccm of methane gas is introduced, the argon flow rate is kept at 16 sccm, the gas pressure reaches 0.34 Pa; the bias voltage is adjusted to-70 V, the duty cycle is 60%, and the deposition time is 270 min.
[0035] The microhardness of the film is 35.1 GPa and the elastic modulus is 347.52 GPa, measured by nanoindentation through continuous indentation. Raman spectroscopy shows that the carbon material has a high degree of graphitization and a low defect content. The friction coefficient of the co-doped carbon film in the methanol environment is stable at 0.08. The co-doped carbon film in the methanol environment has a low friction coefficient (0.08) and a low wear rate (7.8×10 -7 mm 3 ·m -1 ·N -1 ), the wear scar morphology is smooth and flat, and has excellent tribological properties. The corrosion potential and corrosion current in the methanol environment are-0.172 V and 2.35×10 −8 A·cm −2 , respectively, which can significantly reduce the corrosion current density and effectively slow down the corrosion rate.
[0036] Example 2 (1) The substrate is ultrasonically cleaned with acetone and anhydrous ethanol for 10-20 min to remove surface contaminants, and then dried with nitrogen and placed on a sample holder in a vacuum chamber.
[0037] (2) After the vacuum chamber is evacuated to a pressure of less than 3×10 −5 Pa, high-purity argon is introduced, the pressure in the vacuum chamber is controlled to be 0.3-0.5 Pa, the bias power is adjusted to-500 to-800 V, and the substrate surface is cleaned by bias to remove impurities on the substrate surface. The treatment time is 10-15 min.
[0038] (3) B / Al co-doped multilayer gradient carbon film is deposited on the substrate surface by magnetron sputtering technology, specifically: ① Depositing Cr primer layer: adjusting the substrate bias to-90 V, turning on the Cr plane target, setting the initial target current to 0.5 A, increasing to 3.5 A after 30 s; introducing argon at a flow rate of 30 sccm, controlling the gas pressure to be 0.42 Pa, the duty cycle to be 65%, and the deposition time to be 15 min.
[0039] ② Depositing Cr x By C z Gradient transition layer: open C-plane target, set the starting target current 0.3 A, increase to 3.5 A for 1800 s; open B-plane target, set the starting target current 0.2 A, increase to 1.0 A for 1800 s; Cr target current decreases from 3.5 A to 0 A for 1800 s, argon flow rate remains 30 sccm, gas pressure reaches 0.42 Pa; adjust the bias voltage to-90 V, duty cycle 65%, deposition time 30 min.
[0040] ③ Deposition of B / Al co-doped carbon functional layer: open Al-plane target, set the target current 0.3 A, keep C target and B target current and deposition of Cr x B y C z Gradient transition layer remains unchanged, introduce 16 sccm of methane gas, keep argon flow rate at 30 sccm, gas pressure reaches 0.45 Pa; adjust the bias voltage to-90 V, duty cycle 65%, deposition time 270 min.
[0041] The microhardness of the film is 34.9 GPa and the elastic modulus is 340.26 GPa, measured by continuous indentation method using a nanoindenter; the Raman spectrum shows that the carbon material has a high degree of graphitization and a low defect content. The friction coefficient of the co-doped carbon film in the methanol environment is stable at 0.09. The three-dimensional morphology of the wear scar of the co-doped carbon film in the methanol environment under a load of 5 N and a frequency of 1 Hz is smooth, has a low friction coefficient (0.09) and a low wear rate (9.3×10 -7 mm 3 ·m -1 ·N -1 ), which improves the tribological properties of the film. The corrosion potential and corrosion current in the methanol environment are-0.169 V and 2.27×10 −8 A·cm −2 , respectively, which can significantly reduce the corrosion current density and effectively slow down the corrosion rate.
[0042] Comparative Example 1 In order to highlight the advantages of the B / Al co-doped multilayer gradient carbon film prepared by the application for surface modification of a methanol automobile engine, which can realize low wear, strong corrosion resistance and long service life in a methanol environment, the application uses the application of SUS 440C stainless steel commonly used in methanol automobile engines in methanol solution as a control, and the specific process is as follows: The friction performance of SUS 440C stainless steel in a methanol environment was determined using a ball-on-disc reciprocating friction machine. Si3N4 ceramic balls (Φ 6 mm) were selected as the friction pair, the load was 5 N, the reciprocating frequency was 1 Hz, and the reciprocating distance was 4 mm.
[0043] The open circuit potential of SUS 440C stainless steel after immersion in methanol solution for 1800 s was evaluated using a three-electrode system with a Gamry electrochemical workstation, the sample as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum sheet (area 1 cm 2 ) as the counter electrode. After the open circuit potential of the system was stable, the potentiodynamic polarization curve test was performed with a scanning range of -1-1 V and a scanning rate of 10 mV / s. The test results were analyzed by Tafel fitting using Gamry electrochemical analysis software, and the corrosion current density and corrosion potential of the sample were recorded.
[0044] The friction coefficient and wear rate of SUS 440C stainless steel in a methanol environment under a 5 N load and a 1 Hz frequency were 0.29 and 2.7 x 10 -6 mm 3 ·m -1 ·N -1 , respectively. The corrosion potential and corrosion current in the methanol environment were -0.356 V and 2.21 x 10 −6 A·cm −2 , respectively. Compared with the B / Al co-doped multilayer gradient carbon film prepared in Example 1, the friction coefficient, wear rate, corrosion potential, and corrosion current density of SUS 440C stainless steel in the methanol environment were significantly increased.
[0045] Comparative Example 2 In order to highlight the advantages of the B / Al co-doped multilayer gradient carbon film prepared by the present application for surface modification of a methanol automobile engine, which can achieve low wear, strong corrosion resistance, and long service life in a methanol environment, the present application uses a H-containing carbon film as a control, and the specific preparation process is as follows: (1) The substrate was ultrasonically cleaned with acetone and anhydrous ethanol for 10-20 min to remove surface contaminants, and then dried with nitrogen and placed on a sample holder in a vacuum chamber; (2) After the vacuum chamber was evacuated to a pressure of less than 3 x 10 −5 Pa, high-purity argon was introduced, the pressure in the vacuum chamber was controlled to be 0.3-0.5 Pa, the bias power supply was adjusted to -500 to -800 V, and the substrate surface was bias cleaned to remove impurities on the substrate surface, and the treatment time was 10-15 min; (3) A H-containing carbon film was deposited on the substrate surface using a magnetron sputtering technique, specifically: ① Depositing a Cr primer layer: adjusting the substrate bias to -35 V, turning on the Cr plane target, setting the starting target current to 0.5 A, increasing it to 3.0 A after 30 s; introducing argon at a flow rate of 120 sccm, controlling the gas pressure to be 0.62 Pa, the duty cycle to be 65%, and the deposition time to be 15 min.
[0046] ② Deposition of the WC transition layer: Turn on the WC planar target and set the initial target current to 0.3 A, which was increased to 4 A after 1800 s. Turn off the Cr planar target and introduce 50 sccm of acetylene gas, maintaining an argon flow rate of 120 sccm and a pressure of 0.64 Pa. Adjust the bias voltage to −45 V, the duty cycle to 65%, and the deposition time to 60 min.
[0047] ③ H-containing carbon thin film functional layer: Turn off the WC planar target, increase the acetylene gas to 300 sccm, reduce the argon gas flow to 0 sccm, and reach a gas pressure of 0.68 Pa; adjust the bias voltage to −700 V, the duty cycle to 65%, and the deposition time to 120 min.
[0048] The difference between this comparative example and Example 1 is that WC is used as the transition layer during the preparation process of this comparative example, and the functional layer is not doped with B and Al elements.
[0049] The friction coefficient and wear rate of H-containing carbon film under 5 N load and 1 Hz frequency in methanol environment are 0.11 and 9.7×10 -7 mm 3 ·m -1 ·N -1 The corrosion potential and corrosion current in methanol environment are -0.186V and 5.67×10 − 8 A.cm −2 Compared with the B / Al co-doped multilayer gradient carbon film prepared in Example 1, the friction coefficient, wear rate, corrosion potential and corrosion current density of the H-containing carbon film in a methanol environment are significantly increased.
[0050] A method for preparing B / Al co-doped multilayer gradient carbon films significantly improves the film quality and the corrosion and wear resistance of the substrate in a methanol environment. The preparation method is simple, cost-effective, and has guiding significance for industrial production.
[0051] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.
Claims
1. A method for preparing a B / Al co-doped multilayer gradient carbon film for surface modification of a methanol automobile engine, characterized by: Cr base layer, Cr x B y C z Gradient transition layer and B / Al co-doped carbon-based functional layer; The Cr base layer was prepared by DC magnetron sputtering with a substrate bias of −50 to −150 V, a Cr target current increased from 0.2 to 0.5 A to 3.0 to 3.5 A over 30 s, an argon flow rate of 15 to 50 sccm, a gas pressure of 0.3 to 1.0 Pa, a duty cycle of 60 to 85%, and a deposition time of 15 to 30 min. The Cr x B y C z The gradient transition layer was deposited by DC magnetron sputtering. The C target current was increased from 0.2-0.5 A to 3.0-4.0 A over 600-1800 s; the B target current was increased from 0.1-0.3 A to 0.5-1.0 A over 600-1800 s; and the Cr target current was decreased from 3.0-5.5 A to 0 A over 1200-1800 s. The substrate bias voltage was −50-−150 V, the argon flow rate was 15-50 sccm, the pressure was 0.3-1.0 Pa, the duty cycle was 60-85%, and the deposition time was 15-30 min. The B / Al co-doped carbon-based functional layer was prepared by DC magnetron sputtering. The Al target current was 0.1-0.5 A, the C target current was increased from 0.2-0.5 A to 3.0-4.0 A over 600-1800 s, and the B target current was increased from 0.1-0.3 A to 0.5-1.0 A over 600-1800 s. Methane gas flow rate was 15-50 sccm, argon gas flow rate was 15-50 sccm, and the gas pressure was 0.3-1.0 Pa. The substrate bias was −50-−150 V, the duty cycle was 60-85%, and the deposition time was 270-720 min.
2. The preparation method according to claim 1, wherein: The Cr bottom layer is a nanocrystalline structure with a thickness of 0.1-0.4 μm; x B y C z The gradient transition layer is an amorphous-nanocrystalline composite structure with a thickness of 0.1-0.4 μm; the B / Al co-doped carbon-based functional layer is an amorphous structure with a thickness of 1.0-4.0 μm.
3. The preparation method according to claim 1 or 2, characterized in that: The substrate is pre-treated before deposition, including: Ultrasonic cleaning was performed with acetone and anhydrous ethanol for 10–20 min in sequence; Vacuum plasma glow cleaning, evacuate to a pressure of <3×10 -5 After the argon gas is introduced at a rate of 100–200 sccm, the pressure is controlled at 0.3–0.5 Pa, the bias voltage is −500–−800 V, and the cleaning is performed for 10–20 min.
4. A B / Al co-doped multilayer gradient carbon film prepared by the method according to any one of claims 1 to 3, characterized in that: include: Cr primer bonded to the metal substrate; Cr on the Cr base layer x B y C z A gradient transition layer; and a B / Al co-doped carbon-based functional layer located on the gradient transition layer.
5. The B / Al co-doped multilayer gradient carbon film according to claim 4, characterized in that: The hardness of the film is 34.56-36.32 GPa, and the elastic modulus is 337.92-356.89 GPa.
6. The B / Al co-doped multilayer gradient carbon film according to claim 4, characterized in that: The friction coefficient of the film in methanol environment is 0.08-0.09, and the corrosion current density is 2.35×10 −8 A.cm −2 .
7. The B / Al co-doped multilayer gradient carbon film according to claim 4, characterized in that: The film is used for surface modification of metal parts of methanol automobile engines.