Modified carbon-based composite coating and preparation method, bipolar plate

Abstract

The present invention discloses a modified carbon-based composite coating, a preparation method, and a bipolar plate. The coating includes a metal substrate, a diffusion layer, a metal seed layer, a diffusion layer, a gradient transition layer, a diffusion layer, and a doped amorphous carbon coating stacked in sequence; the gradient transition layer is made of carbides or nitrides of transition metals Ti, Cr, Nb, Zr, Mo, and Ta; and the doped amorphous carbon coating is made of amorphous carbon doped with nitride particles of one or more of Cr, Ti, Zr, Mo, and Ta. In the modified carbon-based composite coating of the present invention, the metal element doped in the amorphous carbon coating is subsequently treated to nitride the doped metal to generate nitride particles, which significantly reduces the internal compressive stress of the coating, reduces the pore defects in the coating, increases the content of ordered structures in the carbon film, makes the coating more easily conductive, and thus reduces the interfacial contact resistance of the coating, thereby improving the overall density, conductivity, and corrosion resistance of the coating.

Description

Technical Field

[0001] The present invention relates to the field of coating materials, and in particular to a modified carbon-based composite coating and a preparation method thereof, and a bipolar plate. Background Art

[0002] With the extensive research on the shortage of traditional fossil energy and environmental pollution problems, there is an urgent need for a clean and renewable energy source to reduce our dependence on fossil fuels. Among the many new energy sources, hydrogen energy has attracted much attention due to its abundant resources, high calorific value and environmental friendliness. Hydrogen fuel cells are devices that directly convert the chemical energy of hydrogen into electrical energy. Compared with traditional power sources, they have the characteristics of high efficiency and zero emissions. Proton Exchange Membrane Fuel Cell (PEMFC) is considered to be one of the most promising energy sources for new energy vehicles due to its small size, fast start-up and low operating temperature. However, concerns about its reliability, durability and cost have hindered the widespread commercial application of PEMFC.

[0003] As a key multifunctional component of PEMFCs, the bipolar plate (BPP) accounts for over 80% of the weight and 30% of the total cost. It separates reactant gases, collects current, eliminates product water, and mechanically supports the entire stack, making it crucial to the lifespan of proton exchange membrane fuel cells. Metal bipolar plates have become the mainstream plate material for automotive fuel cells due to their excellent electrical and thermal conductivity, small size, mature processing technology, and low cost. However, their widespread application as BPP materials is hindered by insufficient surface conductivity caused by surface passivation and poor corrosion resistance in the acidic fuel cell environment. Studies have also shown that bare metal plates (especially stainless steel) rarely provide the required performance in long-term use. Therefore, there is an urgent need to surface modify metal BPPs to improve their corrosion resistance and electrical conductivity.

[0004] Currently, the more mature surface modification technology is to deposit precious metal coatings, metal carbide or nitride coatings, and carbon-based coatings on metal bipolar plates. Compared with precious metal coatings, metal carbide or nitride coatings, carbon-based coatings have the advantages of low price, high self-corrosion potential, and good conductivity. However, carbon-based coatings, especially amorphous carbon coatings, cannot effectively resist corrosion at high potentials and exhibit peeling after high-potential constant potentiostat polarization testing. To this end, researchers have made some improvements to carbon-based coatings to improve their corrosion resistance.

[0005] For example, Chinese patent document CN 112582634 A discloses a highly corrosion-resistant multilayer composite carbon coating for fuel cell bipolar plates, which is prepared using a plasma-assisted chemical vapor deposition method. The composite carbon coating uses non-metallic materials as a diffusion and permeation layer on the surface of the metal substrate, avoiding the phenomenon of decreased conductivity of the coating due to oxidation of the metal bottom layer. The amorphous carbon coating doped with flaky graphite, diamond or diamond-like carbon particles serves as a dense corrosion-resistant layer with a high self-corrosion potential, reducing the possibility of severe corrosion under high potential conditions. Chinese patent document CN 108060398 A discloses a fuel cell composite nanocoating and a plating method thereof. The composite nanocoating is an amorphous carbon coating inlaid with metal carbides, which improves the density of the coating, avoids pore defects in the coating, and thus improves the corrosion resistance of the coating.

[0006] While existing coatings can improve the corrosion resistance and conductivity of metal bipolar plates, these surface-modified plates can fail after long-term operation, meaning their service life needs to be improved. This is particularly true for automotive fuel cell stacks, where a hydrogen-air interface forms in the anode region during startup and shutdown, leading to high potentials that are detrimental to the corrosion resistance of the metal bipolar plates and significantly shorten the fuel cell's service life. Unfortunately, amorphous carbon coatings, due to their porous structure, are not resistant to high-potential corrosion. Therefore, improvements are needed to further enhance the corrosion resistance of amorphous carbon coatings. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the defects of the amorphous carbon coating of the bipolar plate in the prior art, which cannot resist high-potential corrosion due to its loose structure and fails after long-term operation, and provide a modified carbon-based composite coating and its preparation method, and a bipolar plate.

[0008] The present invention solves the above technical problems through the following technical solutions.

[0009] The present invention provides a modified carbon-based composite coating, which comprises a metal substrate, a first diffusion layer, a metal seed layer, a second diffusion layer, a gradient transition layer, a third diffusion layer and a doped amorphous carbon coating stacked in sequence;

[0010] Among them, the material of the metal seed layer is one or more transition metals Ti, Cr, Nb and Cu; the material of the gradient transition layer is carbide or nitride of transition metals Ti, Cr, Nb, Zr, Mo and Ta; the material of the doped amorphous carbon coating is amorphous carbon doped with nitride particles of one or more of Cr, Ti, Zr, Mo and Ta.

[0011] In the present invention, the material of the metal seed layer is preferably transition metal Ti.

[0012] In the present invention, the material of the gradient transition layer is preferably transition metal Ti carbide (TiC).

[0013] In the present invention, the material of the doped amorphous carbon coating is preferably amorphous carbon doped with Ti nitride (TiN) particles.

[0014] In the present invention, the first diffusion layer is generally a layer formed by mutual diffusion of particles on the surface of the metal substrate and particles on the surface of the metal seed layer during the preparation of the modified carbon-based composite coating.

[0015] In the present invention, the second diffusion layer is generally a layer formed by mutual diffusion of particles on the surface of the metal seed layer and particles on the surface of the gradient transition layer during the preparation of the modified carbon-based composite coating.

[0016] In the present invention, the third diffusion layer is generally a layer formed by mutual diffusion of particles on the surface of the gradient transition layer and particles of the doped amorphous carbon coating during the preparation of the modified carbon-based composite coating.

[0017] In the present invention, the metal seed layer can be used to reduce the shear stress at the interface and increase the bonding strength between the coating and the metal substrate. The gradient transition layer can be used to improve the corrosion resistance of the coating. The doped amorphous carbon coating can be used to optimize the electrical conductivity and corrosion resistance of the coating.

[0018] In the present invention, the thickness of the metal seed layer may be 50-200 nm, for example, 100 nm or 150 nm.

[0019] In the present invention, the thickness of the gradient transition layer may be 100-300 nm, for example, 150 nm, 200 nm or 250 nm.

[0020] In the present invention, the thickness of the doped amorphous carbon coating may be 100-300 nm, for example, 150 nm, 200 nm or 250 nm.

[0021] In the present invention, the thickness of the first diffusion layer is generally 1-10 nm, for example, 5 nm.

[0022] In the present invention, the thickness of the second diffusion layer is generally 1-10 nm, for example, 5 nm.

[0023] In the present invention, the thickness of the third diffusion layer is generally 1-10 nm, for example, 5 nm.

[0024] In the present invention, the proportion of nitride particles in the doped amorphous carbon coating is preferably 20-45%, for example 20%, 25%, 30%, 35%, 40% or 45%, where the above percentages are the mass percentages of nitride particles in the doped amorphous carbon coating.

[0025] In a preferred embodiment, the proportion of nitride particles in the doped amorphous carbon coating may be 20%-30%, 25%-35%, 30%-40% or 35%-45%.

[0026] In the present invention, in the doped amorphous carbon coating, the particle size of the nitride particles is preferably 5-60 nm.

[0027] In a preferred embodiment, in the doped amorphous carbon coating, the particle size of the nitride particles may be 5-50 nm, 5-55 nm, 5-40 nm or 5-60 nm.

[0028] The present invention also provides a method for preparing the modified carbon-based composite coating, which comprises the following steps:

[0029] S1 forms the metal seed layer on one side of the metal substrate by a single deposition;

[0030] S2 secondary deposition on the surface of the metal seed layer to form the gradient transition layer;

[0031] S3 forms the doped amorphous carbon coating by depositing the coating three times on the surface of the gradient transition layer;

[0032] S4 nitrides the metal substrate after three coating depositions. After the nitridation, the first diffusion layer is formed between the metal substrate and the metal seed layer; the second diffusion layer is formed between the metal seed layer and the gradient transition layer; and the third diffusion layer is formed between the gradient transition layer and the doped amorphous carbon coating.

[0033] In S1, before the primary deposition, the substrate is generally pretreated. The pretreatment method can be conventional in the art, such as cleaning to remove oil stains and oxide films on the surface of the metal substrate.

[0034] The cleaning method may be conventional in the art, and generally ultrasonic cleaning is performed first, and then the oxide film on the surface of the substrate is etched to increase the bonding strength of the coating.

[0035] The ultrasonic cleaning process is typically performed in acetone, anhydrous ethanol, and deionized water for 10-20 minutes each to remove surface oil and oxide film. After ultrasonic cleaning, the substrate is typically dried in a dust-free environment using N2 to remove the water film and prevent further oxidation and contamination.

[0036] The operation of etching the substrate generally adopts plasma cleaning, ion beam cleaning, pulse cleaning or other similar methods. The plasma cleaning is generally carried out in vacuum coating equipment.

[0037] When the plasma cleaning is used, the cleaning temperature may be 50-500°C.

[0038] When the plasma cleaning method is used, the bias voltage may range from -500V to 1000V.

[0039] When the plasma cleaning is adopted, the inert gas introduced may be Ar or He.

[0040] When the plasma cleaning is used, the cleaning time may be 10 to 60 minutes, preferably 10 to 30 minutes.

[0041] In S1, the primary deposition may be performed by a vacuum multi-arc ion plating method.

[0042] In S1, during the one deposition process, the Ti multi-arc target deposition current may be 0.5-12A, preferably 2-5A, for example 3A.

[0043] In S1, during the primary deposition process, the deposition temperature may be 50-800°C, preferably 100-600°C, such as 380°C, 400°C or 420°C.

[0044] In S1, during the one deposition process, the deposition time may be 1-300 min, preferably 1-100 min, such as 30 min or 60 min.

[0045] In S1, the primary deposition process preferably first increases the bias voltage to 780-1000V and the low pressure to 0.05-0.1Pa, allowing the metal ions to bombard and embed into the substrate. The bias voltage is then reduced to 200-500V and the high pressure to 0.5-1Pa, allowing the metal ions to diffuse and grow a dense thin film material on the substrate surface under the action of argon ion bombardment. For example, the primary deposition process may first increase the bias voltage to 800V and the low pressure to 0.1Pa, and then reduce the bias voltage to 400V and the high pressure to 0.8Pa.

[0046] In S2, the secondary deposition may be performed by vacuum multi-arc ion plating, which has a high ionization rate and is more conducive to the reaction between metal ions and carbon or nitrogen to form metal carbides or metal nitrides.

[0047] In S2, during the secondary deposition process, the Ti multi-arc target deposition current may be 0.5-12A, preferably 2-5A, for example 3A.

[0048] In S2, during the secondary deposition process, the deposition temperature may be 50-800°C, preferably 100-600°C, such as 380°C, 400°C or 420°C.

[0049] In S2, during the secondary deposition process, preferably, the bias voltage is (-90)-(-110) V, and the deposition pressure is 0.4-0.6 Pa, for example, the bias voltage is -100 V, and the deposition pressure is 0.5 Pa.

[0050] In S2, during the secondary deposition process, the deposition time may be 1-300 min, preferably 1-100 min.

[0051] In S3, the three deposition methods can adopt vacuum magnetron sputtering and multi-arc ion plating co-deposition methods. In the present invention, the amorphous carbon adopts the vacuum magnetron sputtering method to ensure the fine density of the amorphous carbon layer; the doped metal adopts the multi-arc ion plating method, and the doped metal has a high degree of ionization and can be effectively embedded in the amorphous carbon layer under the action of bias voltage.

[0052] In S3, during the three deposition processes, the sputtering power of the graphite target may be 6 kW.

[0053] In S3, during the three deposition processes, the Ti multi-arc target deposition current may be 88-92A, for example, 90A.

[0054] In S3, during the three deposition processes, the deposition temperature may be 480-520°C, for example, 500°C.

[0055] In S3, during the three deposition processes, preferably, the bias voltage is (-90)-(-110) V, and the deposition pressure is 0.4-0.6 Pa, for example, the bias voltage is -100 V, and the deposition pressure is 0.5 Pa.

[0056] In S4, during the nitriding process, the deposited metal may be transformed into corresponding nitride particles, for example, Ti metal may be transformed into TiN particles.

[0057] In S4, during the nitriding treatment, NH3 or a mixed gas of N2 and H2 is generally introduced. The flow rate of the NH3 or mixed gas can be conventional in the art.

[0058] In S4, the temperature of the nitriding treatment is preferably 500-1000°C, more preferably 580-740°C, for example 700°C.

[0059] In S4, the pressure of the nitriding treatment is preferably below 400 Pa, such as 0.01 Pa, 100 Pa, 200 Pa or 300 Pa, more preferably 200-300 Pa.

[0060] In S4, the nitriding treatment time is preferably 1-4 hours, for example 4 hours.

[0061] The present invention also provides a metal bipolar plate comprising the modified carbon-based composite coating as described above.

[0062] In the present invention, “first, second, and third” are only used to distinguish the diffusion layers and have no special meaning.

[0063] In the present invention, “one time, two times, three times” is only used to distinguish four different deposition operations and has no special meaning.

[0064] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0065] The reagents and raw materials used in the present invention are commercially available.

[0066] The positive progress effect of the present invention is:

[0067] In the modified carbon-based composite coating of the present invention, the amorphous carbon coating is doped with metal elements and the doped metal is nitrided in the subsequent treatment to generate nitride particles, which greatly reduces the internal compressive stress of the coating, reduces the pore defects in the coating, and improves the ordered structure (sp 2 The increase in carbon content makes the coating's electronic conduction easier, thereby reducing the coating's interfacial contact resistance and improving the coating's overall density, conductivity, and corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 Schematic diagram of the structure of the metal bipolar plate modified carbon-based composite coating prepared in Example 1.

[0069] Among them, 1 is a metal substrate, 2 is a metal seed layer, 3 is a gradient transition layer, 4 is a doped amorphous carbon coating, 5 is nitride particles, 6 is a first diffusion layer, 7 is a second diffusion layer, and 8 is a third diffusion layer.

[0070] Figure 2 The potentiodynamic corrosion current test diagram of the modified carbon-based composite coating of Example 1 and Comparative Example 2

[0071] Figure 3 This is a diagram showing the dynamic potential corrosion current test of the modified carbon-based composite coating of Example 2.

[0072] Figure 4 This is a constant potential corrosion current test diagram of the modified carbon-based composite coating in Example 1.

[0073] Figure 5 This is a constant potential corrosion current test diagram of the modified carbon-based composite coating of Example 2.

[0074] Figure 6 This is a grid test chart of the adhesion of the modified carbon-based composite coating in Example 1.

[0075] Figure 7 This is a hundred-grid test chart of the adhesion of the modified carbon-based composite coating of Comparative Example 1. DETAILED DESCRIPTION

[0076] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0077] Example 1

[0078] A metal bipolar plate modified carbon-based composite coating for fuel cells, the structure of which is as follows Figure 1 As shown, the thickness of the metal seed layer 2 is 100 nm, the thickness of the gradient transition layer 3 is 200 nm, the thickness of the doped amorphous carbon coating 4 is 200 nm; the thickness of the first diffusion layer 6 is about 5 nm; the thickness of the second diffusion layer 7 is about 5 nm; and the thickness of the third diffusion layer 8 is about 5 nm.

[0079] In the doped amorphous carbon coating 4 , the proportion of the nitride particles 5 is 25-35%, where the above percentage is the mass percentage of the nitride particles 5 in the doped amorphous carbon coating 4 ; the particle size of the nitride particles 5 is 5-50 nm.

[0080] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0081] The preparation method of the modified carbon-based composite coating comprises the following steps:

[0082] (1) The metal substrate 1 was ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 15 min each to remove surface oil and oxide film. The substrate was then dried with N2 in a dust-free environment to remove the water film and prevent the substrate from being oxidized and contaminated again.

[0083] The cleaned and dried metal substrate 1 is placed in a vacuum coating device, and the inert gas introduced is Ar. Plasma cleaning is performed for 10 minutes at a bias voltage of -1000V and a pressure of 2.5Pa to remove the oxide film on the surface of the metal substrate 1 and increase the bonding strength of the coating;

[0084] A vacuum multi-arc ion plating method was used to deposit Ti metal on the surface of the pretreated metal substrate 1 to form a metal seed layer 2. The Ti target deposition current was 3 A, the deposition temperature was 400° C., and the deposition time was 30 min. A high bias voltage of 800 V and a low pressure of 0.1 Pa were first applied; then the bias voltage was reduced to 400 V and the high pressure was 0.8 Pa.

[0085] (2) TiC crystals were deposited on the surface of the metal seed layer 2 by vacuum multi-arc ion plating to form a gradient transition layer 3; wherein, the Ti target deposition current was 3 A, the deposition temperature was 400°C, the deposition time was 50 min, the bias voltage was -100 V, and the deposition pressure was 0.5 Pa;

[0086] (3) depositing an amorphous carbon coating on the surface of the gradient transition layer 3 by a vacuum magnetron sputtering method and a multi-arc ion plating method, and doping Ti metal during the deposition of the amorphous carbon coating to form a doped amorphous carbon coating 4;

[0087] (4) The metal substrate 1 after three-layer plating deposition is nitrided. After the nitridation treatment, a first diffusion layer 6 is formed between the metal substrate 1 and the metal seed layer 2; a second diffusion layer 7 is formed between the metal seed layer 2 and the gradient transition layer 3; and a third diffusion layer 8 is formed between the gradient transition layer 3 and the doped amorphous carbon coating 4.

[0088] The graphite target sputtering power was 6 kW, the Ti multi-arc target current was set to 90 A, the bias voltage was -100 V, the deposition temperature was 500 °C, and the deposition pressure was 0.5 Pa.

[0089] During the nitriding process, NH3 was introduced, the temperature was maintained at 700°C, and the pressure was 300 Pa. The deposited coating was nitrided for 4 hours to convert the Ti metal in the doped carbon layer into nitride particles 5 (TiN particles).

[0090] Examples 2-4

[0091] The preparation methods of the modified carbon-based composite coatings in Examples 2-4 are the same as those in Example 1 except for the conditions shown in Table 1.

[0092] In the modified carbon-based composite coatings of Examples 1-4, the particle size range of TiN particles and the mass percentage of TiN particles in the doped amorphous carbon coating were analyzed by the metal material foreign matter analysis method (EDS+SEM), as shown in Table 1.

[0093] Table 1 Preparation conditions and test structure data of modified carbon-based composite coatings of Examples 1-4

[0094]

[0095] Comparative Example 1

[0096] Compared with Example 1, Comparative Example 1 has only no metal seed layer, and other operations and conditions are the same as those of Example 1, thereby obtaining a modified carbon-based composite coating without a metal seed layer.

[0097] Comparative Example 2

[0098] Comparative Example 1 is compared with Example 1, except that the nitriding treatment is not performed. Other operations and conditions are the same as those in Example 1, and a modified carbon-based composite coating without nitriding treatment is obtained.

[0099] Effect Example 1

[0100] Figure 2These are the potentiodynamic corrosion current test diagrams of the modified carbon-based composite coatings of Example 1 and Comparative Example 2. Figure 3 This is a diagram showing the dynamic potential corrosion current test of the modified carbon-based composite coating of Example 2. Figure 2-Figure 3 Used to characterize the corrosion resistance of materials. Test conditions: dynamic potential -0.3V ~ 1V, water temperature 80℃, H2SO4 solution with pH=3, F - Concentration 0.1mg / L.

[0101] Depend on Figure 2 It can be seen that the corrosion voltage of the modified carbon-based composite coating prepared in Example 1 is 300 mV, and the corrosion current density is 0.124 μA / cm 2 The corrosion voltage of the modified carbon-based composite coating prepared in Comparative Example 2 is 284 mV, and the corrosion current density is 0.228 μA / cm 2 It can be seen that the corrosion voltage of the modified carbon-based composite coating prepared in Example 1 is higher than that of Comparative Example 2, and the corrosion current density is lower than that of Comparative Example 2.

[0102] Depend on Figure 3 It can be seen that the corrosion voltage of the modified carbon-based composite coating prepared in Example 2 is 295 mV, and the corrosion current density is 0.137 μA / cm 2 .

[0103] Figure 4 This is a constant potential corrosion current test diagram of the modified carbon-based composite coating in Example 1. Figure 5 This is a constant potential corrosion current test diagram of the modified carbon-based composite coating of Example 2. Figure 4-Figure 5 Used to characterize the life of the coating in an electrochemical corrosion environment for a long time. Test conditions: using the US DOE test standard, constant potential 0.6V, water temperature 80℃, pH=3 H2SO4 solution, F - The concentration is 0.1 mg / L and the test time is 3600 s (1 h).

[0104] Depend on Figure 4 It can be seen that the corrosion current density of the modified carbon-based composite coating prepared in Example 1 is 0.295 μA / cm 2 , which is far lower than the corrosion current requirement published by DOE, indicating that it has good electrochemical corrosion resistance. Figure 5 It can be seen that the corrosion current of the modified carbon-based composite coating prepared in Example 2 is 0.298 μA / cm 2 , which is far lower than the corrosion current requirement published by DOE, indicating that it has good electrochemical corrosion resistance.

[0105] The modified carbon-based composite coating of the present invention is nitrided during the nitriding treatment, and the internal doped metal particles are nitrided. At the same time, the high-temperature treatment relaxes the internal stress of the film, thereby improving the density of the film and reducing internal defects. The dangling bonds on the surface of the amorphous carbon coating are saturated and passivated, which not only reduces the surface energy of the composite film, but also improves the corrosion resistance, reduces the corrosion current density, and increases the corrosion voltage.

[0106] The surface contact resistance (ICR) of the modified carbon-based composite coating of Example 1 was tested. Using the US DOE test standard, under a pressure of 1.5 MPa, a 5 cm*5 cm sample, and carbon paper contact, the surface contact resistance (ICR) of the modified carbon-based composite coating of Example 1 was approximately 3.5 mΩ·cm. 2 .

[0107] Effect Example 2

[0108] The adhesion of the modified carbon-based composite coatings of Comparative Example 1 and Example 1 was tested using an ASTM standard crosshatch knife.

[0109] Figure 6 This is a grid test chart of the adhesion of the modified carbon-based composite coating in Example 1. Figure 7 This is a hundred-grid test chart of the adhesion of the modified carbon-based composite coating of Comparative Example 1.

[0110] The adhesion of the modified carbon-based composite coating in Example 1 is 5B. Figure 6 It can be seen that the edges of the cuts are completely smooth and there is no peeling at the edges of the lattice. The adhesion of the modified carbon-based composite coating in Comparative Example 1 is 4B. Figure 7 It can be seen that there are small pieces peeling off at the intersection of the cuts, and the actual damage in the cross-cut area does not exceed 5%.

[0111] The modified carbon-based composite coating prepared in Example 1 contains a metal seed layer, which increases the adhesion between the modified carbon-based composite coating and the substrate. If the film adhesion is poor, it will cause the film to fall off in a high-temperature acidic environment for a long time, thus shortening the service life of the plate.

Claims

1. A method for preparing a modified carbon-based composite coating, characterized in that: It includes the following steps: S1 forms a metal seed layer on one side of the metal substrate by a single deposition; S2 secondary deposition on the surface of the metal seed layer to form a gradient transition layer; S3 depositing a metal-doped amorphous carbon coating three times on the surface of the gradient transition layer; S4 nitriding the metal substrate after the three-layer plating deposition, forming a first diffusion layer between the metal substrate and the metal seed layer; forming a second diffusion layer between the metal seed layer and the gradient transition layer; forming a third diffusion layer between the gradient transition layer and the metal-doped amorphous carbon coating; and nitriding the metal in the metal-doped amorphous carbon coating to generate nitride particles. Among them, the material of the metal seed layer is one or more transition metals Ti, Cr, Nb and Cu; the material of the gradient transition layer is carbide or nitride of transition metals Ti, Cr, Nb, Zr, Mo and Ta; the material of the metal-doped amorphous carbon coating after nitridation is amorphous carbon doped with nitride particles of one or more of Cr, Ti, Zr, Mo and Ta.

2. The method for preparing a modified carbon-based composite coating according to claim 1, wherein: It meets one or more of the following conditions ①-③: ① The material of the metal seed layer is transition metal Ti; ② The material of the gradient transition layer is transition metal Ti carbide; and, ③ The material of the metal-doped amorphous carbon coating after nitridation is amorphous carbon doped with Ti nitride particles.

3. The method for preparing a modified carbon-based composite coating according to claim 1, wherein: It meets one or more of the following conditions ①-⑥: ① The thickness of the metal seed layer is 50-200 nm; ② The thickness of the gradient transition layer is 100-300nm; ③ The thickness of the metal-doped amorphous carbon coating is 100-300 nm; ④ The thickness of the first diffusion layer is 1-10 nm; ⑤ The thickness of the second diffusion layer is 1-10 nm; ⑥ The thickness of the third diffusion layer is 1-10 nm.

4. The method for preparing a modified carbon-based composite coating according to claim 3, wherein: It meets one or more of the following conditions ①-⑥: ① The thickness of the metal seed layer is 100 nm or 150 nm; ② The thickness of the gradient transition layer is 150nm, 200nm or 250nm; ③ The thickness of the metal-doped amorphous carbon coating is 150 nm, 200 nm or 250 nm; ④ The thickness of the first diffusion layer is 5 nm; ⑤The thickness of the second diffusion layer is 5 nm; ⑥ The thickness of the third diffusion layer is 5 nm.

5. The method for preparing a modified carbon-based composite coating according to claim 1, wherein: In the metal-doped amorphous carbon coating after nitridation, the proportion of nitride particles is 20-45%, and the above percentages are the mass percentages of nitride particles in the metal-doped amorphous carbon coating after nitridation; And / or, in the metal-doped amorphous carbon coating after nitridation, the particle size of nitride particles is 5-60 nm.

6. The method for preparing a modified carbon-based composite coating according to claim 5, wherein: In the metal-doped amorphous carbon coating after nitridation, the proportion of nitride particles is 20%, 25%, 30%, 35%, 40% or 45%, and the above percentages are the mass percentages of nitride particles in the metal-doped amorphous carbon coating after nitridation.

7. The method for preparing a modified carbon-based composite coating according to claim 5, wherein: In the metal-doped amorphous carbon coating after nitridation, the particle size of nitride particles is 5-50 nm.

8. The method for preparing a modified carbon-based composite coating according to claim 5, wherein: In the metal-doped amorphous carbon coating after nitridation, the particle size of nitride particles is 5-55 nm.

9. The method for preparing a modified carbon-based composite coating according to claim 5, wherein: In the metal-doped amorphous carbon coating after nitridation, the particle size of nitride particles is 5-40 nm.

10. The method for preparing a modified carbon-based composite coating according to claim 5, wherein: In the metal-doped amorphous carbon coating after nitridation, the proportion of nitride particles is 20%-30%, and the above percentage is the mass percentage of nitride particles in the metal-doped amorphous carbon coating after nitridation.

11. The method for preparing a modified carbon-based composite coating according to claim 5, wherein: In the metal-doped amorphous carbon coating after nitridation, the proportion of nitride particles is 25%-35%, and the above percentage is the mass percentage of nitride particles in the metal-doped amorphous carbon coating after nitridation.

12. The method for preparing a modified carbon-based composite coating according to claim 5, wherein: In the metal-doped amorphous carbon coating after nitridation, the proportion of nitride particles is 30%-40%, and the above percentage is the mass percentage of nitride particles in the metal-doped amorphous carbon coating after nitridation.

13. The method for preparing a modified carbon-based composite coating according to claim 5, wherein: In the metal-doped amorphous carbon coating after nitridation, the proportion of nitride particles is 35%-45%, and the above percentages are the mass percentages of nitride particles in the metal-doped amorphous carbon coating after nitridation.

14. The method for preparing a modified carbon-based composite coating according to claim 1, wherein: The preparation method satisfies one or more of the following conditions ①-⑥: ① In S1, before performing the first deposition, the substrate is cleaned; ② In S1, the primary deposition method is a vacuum multi-arc ion plating method; ③ In S1, during the one deposition process, the Ti multi-arc target deposition current is 0.5-12A; ④ In S1, during the primary deposition process, the deposition temperature is 50-800° C.; ⑤ In S1, the deposition time during the first deposition process is 1-300 min; and, ⑥ In S1, during the one deposition process, the bias voltage is first increased to 780-1000V and the low pressure is 0.05-0.1Pa; then the bias voltage is reduced to 200-500V and the high pressure is 0.5-1Pa.

15. The method for preparing the modified carbon-based composite coating according to claim 14, wherein: The preparation method satisfies one or more of the following conditions ①-④: ① In S1, during the one deposition process, the Ti multi-arc target deposition current is 2-5A; ② In S1, during the primary deposition process, the deposition temperature is 100-600° C.; ③ In S1, the deposition time during the one deposition process is 1-100 min; and, ④ In S1, during the one deposition process, the bias voltage is first increased to 800V and the low pressure is 0.1Pa, and then the bias voltage is reduced to 400V and the high pressure is 0.8Pa.

16. The method for preparing the modified carbon-based composite coating according to claim 15, wherein: The preparation method satisfies one or more of the following conditions ①-③: ① In S1, during the one deposition process, the Ti multi-arc target deposition current is 3A; ② In S1, during the primary deposition process, the deposition temperature is 380° C., 400° C., or 420° C.; ③ In S1, during the one deposition process, the deposition time is 30 min and 60 min.

17. The method for preparing a modified carbon-based composite coating according to claim 1, wherein: The preparation method satisfies one or more of the following conditions ①-④: ① In S2, during the secondary deposition process, the Ti multi-arc target deposition current is 0.5-12A; ② In S2, during the secondary deposition process, the deposition temperature is 50-800° C.; ③ In S2, during the secondary deposition process, the bias voltage is (-90)-(-110) V and the deposition pressure is 0.4-0.6 Pa; ④ In S2, during the secondary deposition process, the deposition time is 1-300 min.

18. The method for preparing the modified carbon-based composite coating according to claim 17, wherein: The preparation method satisfies one or more of the following conditions ①-④: ① In S2, during the secondary deposition process, the Ti multi-arc target deposition current is 2-5A; ② In S2, during the secondary deposition process, the deposition temperature is 100-600° C.; ③ In S2, during the secondary deposition process, the bias voltage is -100 V and the deposition pressure is 0.5 Pa; ④ In S2, during the secondary deposition process, the deposition time is 1-100 minutes.

19. The method for preparing a modified carbon-based composite coating according to claim 18, wherein: The preparation method satisfies one or both of the following conditions ①-②: ① In S2, during the secondary deposition process, the Ti multi-arc target deposition current is 3A; ② In S2, during the secondary deposition process, the deposition temperature is 380°C, 400°C or 420°C.

20. The method for preparing a modified carbon-based composite coating according to claim 1, wherein: The preparation method satisfies one or more of the following conditions ①-④: ① In S3, during the three deposition processes, the sputtering power of the graphite target is 6 kW; ② In S3, during the three deposition processes, the Ti multi-arc target deposition current is 88-92A; ③ In S3, during the three deposition processes, the deposition temperature is 480-520°C; ④ In S3, during the three deposition processes, the bias voltage is (-90)-(-110) V, and the deposition pressure is 0.4-0.6 Pa.

21. The method for preparing a modified carbon-based composite coating according to claim 20, wherein: The preparation method satisfies one or more of the following conditions ①-③: ① In S3, during the three deposition processes, the Ti multi-arc target deposition current is 90A; ② In S3, during the three deposition processes, the deposition temperature is 500° C.; ③ In S3, during the three deposition processes, the bias voltage is -100 V and the deposition pressure is 0.5 Pa.

22. The method for preparing the modified carbon-based composite coating according to claim 1, wherein: The preparation method satisfies one or more of the following conditions ①-③: ① In S4, the temperature of the nitriding treatment is 500-1000° C.; ② In S4, the pressure of the nitriding treatment is 400 Pa or less; and, ③ In S4, the nitriding treatment time is 1-4 hours.

23. The method for preparing a modified carbon-based composite coating according to claim 22, wherein: The preparation method satisfies one or more of the following conditions ①-③: ① In S4, the temperature of the nitriding treatment is 580-740°C; ② In S4, the pressure of the nitriding treatment is 0.01Pa, 100Pa, 200Pa or 300Pa; and, ③ In S4, the nitriding treatment time is 4 hours.

24. The method for preparing a modified carbon-based composite coating according to claim 22, wherein: The preparation method satisfies one or both of the following conditions ①-②: ① In S4, the temperature of the nitriding treatment is 700° C.; ② In S4, the pressure of the nitriding treatment is 200-300 Pa.

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