Comprehensive gradient multi-layer corrosion-resistant conductive coating as well as preparation method and application thereof

Abstract

The invention relates to the technical field of conductive coatings, and discloses a comprehensive gradient multi-layer corrosion-resistant conductive coating and a preparation method and application thereof, and the preparation method comprises the following preparation steps: (1) preparing a matrix material; (2) pretreating a base material (including grinding, polishing and argon ion etching); (3) preparing a Ti transition layer; (4) preparing a TiN / TiNC / TiC comprehensive gradient layer; (5) preparing a C layer; (6) coating heat treatment; and (7) testing the corrosion resistance, conductivity and binding force of the coating. The Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating is designed, the characteristics of TiN, TiNC and TiC are comprehensively utilized, a vacuum heat treatment mode is adopted, the Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating is prepared, the corrosion resistance, the conductivity and the binding force strength of the coating are tested, and a Ti-based corrosion-resistant conductive coating scheme is supplemented.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive coatings, and particularly relates to a preparation method of a Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating. Background Art

[0002] Proton exchange membrane fuel cells (PEMFCs) have outstanding characteristics such as high conversion efficiency (up to 60% at most), high specific power, no pollution, and long service life. It consists of an electrolyte membrane, a diffusion layer, a catalytic layer between the membrane and the diffusion layer, and bipolar plates. The bipolar plates play roles such as supporting the electrodes, conducting current, and separating the oxidant and the reductant. Metal bipolar plates are one of the commonly used bipolar plate types and are widely used due to the low mechanical strength and easy processing of stainless steel substrates, among which 316L stainless steel substrates are the most common. However, in the working environment of PEMFCs, the 316L stainless steel substrate is easily corroded by weak acidic electrolytes. On the one hand, it will reduce the ion transport efficiency of PEMFCs, and on the other hand, it will form a passivation film on the surface of the bipolar plate, thereby affecting its conductivity.

[0003] Therefore, depositing a corrosion-resistant conductive coating on the 316L stainless steel bipolar plate is an effective surface modification solution. Both TiN and TiC have excellent corrosion resistance and electrical conductivity. Shen Hongyu et al. prepared a TiN coating by plasma nitriding technology. The coating has a strong bonding force with the substrate and reduces its corrosion current density to 0.86 μA / cm 2 and maintains a low interfacial contact resistance. Liu Yang et al. compared TiN, TiNC, and TiC coatings and found that the three coatings have stable compositions and uniform distributions. The thermal expansion coefficient of TiN is closer to that of the substrate, the TiC grains are small and amorphous, and TiNC takes into account the advantages of both and has stronger corrosion resistance. CN 119481126 A publicly applied for a fuel cell metal bipolar plate with a multi-layer composite gradient coating and its preparation method. A Ti / TiN / TiCN multi-layer composite gradient coating was prepared on the substrate by multi-arc ion plating technology, and the corrosion current density of the optimal process was 0.12 μA / cm 2 and the interfacial contact resistance was 1.82 mΩ·cm under a pressure of 1.4 MPa 2 , which proves the feasibility of using multi-layer TiN / TiNC nanocrystalline coatings for the surface modification of stainless steel bipolar plates. Meng Wei et al. used vacuum heat treatment of the TiC / C layer at different temperatures to reduce the corrosion current density and interfacial contact resistance of the coating.

[0004] Existing studies have not comprehensively utilized three materials, namely TiN, TiNC, and TiC, to modify the surface of bipolar plates. Moreover, there are significant compositional and crystal structure differences between TiN and TiNC in the preparation of Ti / TiN / TiNC multi-layer composite gradient coatings, which are prone to forming geometric discontinuity regions at the interlayer interface, triggering local stress peaks. When process fluctuations occur during coating deposition, the bonding strength will be weakened and micro-defects will be induced. Heat treatment means have not been taken into account for transition metal nitride carbides to prepare comprehensive gradient multi-layer corrosion-resistant conductive coatings. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method for a Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating, in order to solve one or more technical problems existing in the prior art, and at least provide a beneficial choice or create conditions.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions.

[0007] A preparation method for a Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating includes the following steps:

[0008] 1) Preparation of the substrate material. The main purpose of this step is to remove contaminants and impurities on the surface of the substrate. Cut the substrate material into appropriate sizes, and perform ultrasonic cleaning with a cleaning agent, deionized water, and absolute ethanol respectively. The cleaned substrate material is dried under a protective atmosphere.

[0009] 2) Pretreatment of the substrate material: a. Grinding and polishing. The main purpose of this step is to remove the oxide layer on the surface of the substrate. Use grinding and polishing equipment to perform preliminary grinding, fine grinding, and final polishing in sequence. After polishing, perform ultrasonic cleaning with absolute ethanol again, and the cleaned substrate material is dried under a protective atmosphere; b. Argon ion etching. The main purpose of this step is to deeply remove the oxide layer on the surface of the substrate and increase the surface roughness. Place the dried substrate material in a vacuum chamber, turn on the ion source with a DC power supply at room temperature, and control the Ar flow rate, set power, set bias voltage, set gas pressure, and deposition time of the equipment for etching.

[0010] 3) Preparation of the Ti layer transition layer. The main purpose of this step is to better connect the substrate and the subsequent deposited coating. Select a Ti target as the DC cathode. When the set temperature is reached, under the protection of a certain flow rate of Ar gas, set the deposition power, bias voltage, deposition gas pressure, and deposition time to deposit the Ti transition layer.

[0011] 4) Preparation of the TiN / TiNC / TiC composite gradient layer. The main purpose of this step is to integrate the characteristics of the three substances, deposit a gradient multi-layer coating, avoid through defects, and ensure strong corrosion resistance. Select a Ti target as the DC cathode. After reaching the set temperature, introduce different ratios of Ar / N2 / C2H2, set the deposition power, bias voltage, deposition pressure, and deposition time, and regulate the different gas ratios to deposit the gradient layer.

[0012] 5) Preparation of the C layer. The main purpose of this step is to ensure high conductivity and reduce the interface contact resistance. Select a graphite target as the DC cathode. After reaching the set temperature, under the protection of a certain flow of Ar gas, set the deposition power, bias voltage, deposition pressure, and deposition time to deposit the C conductive layer.

[0013] 6) Coating heat treatment. The main purpose of this step is to eliminate residual stress and prevent the coating from cracking. Take the sample out of the vacuum chamber and put it into a tube furnace with a nitrogen-containing argon mixture at 500 - 900 °C for heat treatment for 2 - 12 h to obtain a product with a composite gradient multi-layer corrosion-resistant and conductive coating.

[0014] Perform corrosion-resistant and conductive performance tests on the product with the composite gradient multi-layer corrosion-resistant and conductive coating. The main purpose of this step is to verify whether the corrosion current density, interface contact resistance, and interface and coating bonding strength of the coating meet the requirements.

[0015] a. Corrosion resistance test: In an electrochemical test cell, perform the test according to the test method of GB / T 20042.6 - 2024 to obtain the corresponding corrosion current density of the sample.

[0016] b. Conductive performance test: On a low-resistance tester, according to the test method of GB / T 20042.6 - 2024, set a certain pressure to perform the contact resistance test of the coating.

[0017] c. Bonding strength test: Perform the test with reference to the industry standard JB / T 8554 - 1997. Cut a small part of the sample for testing respectively. The scratching speed is 5 - 15 mm / min, the loading rate is 10 - 100 N / min, and the loading accuracy is 0.01 - 0.5 N.

[0018] Furthermore, the ultrasonic cleaning steps in step 1) are as follows: ultrasonically clean with a cleaning agent, deionized water, and absolute ethanol twice in sequence, with each cleaning lasting at least 30 min.

[0019] Furthermore, the grinding and polishing steps in step 2) are as follows: When initially grinding, use 80 - 200 mesh sandpaper to grind for 10 - 30 min. For fine grinding, use 200 - 400 mesh sandpaper to grind for more than 30 min. For final polishing, select 400 - 2000 mesh sandpaper to grind for more than 30 min.

[0020] Further, in the argon ion etching in step 2), the Ar flow rate is selected to be 100 - 200 sccm, the set power is 1000 - 2000 W, the set bias voltage is 600 - 800 V, the set gas pressure is 0.5 - 1.2 Pa, and the etching time is 10 - 30 min.

[0021] Further, when preparing the Ti transition layer in step 3), the purity of the Ti target is higher than 99.995%, the deposition temperature is 100 - 200 °C, the Ar gas flow rate is 50 - 100 sccm, the Ti deposition power is 1000 - 2000 W, the deposition bias voltage is 300 - 500 V, the deposition gas pressure is 0.2 - 0.8 Pa, and the deposition time is 2 - 20 min.

[0022] Further, when preparing the TiN / TiNC / TiC comprehensive gradient layer in step 4), a Ti target material with a purity higher than 99.995% is selected, the deposition temperature is 150 - 300 °C, the deposition power is 200 - 600 W, the deposition bias voltage is 50 - 150 V, the deposition gas pressure is 0.2 - 1.2 Pa, and the total deposition time is 20 - 60 min.

[0023] Further, the introduction of different ratios of Ar, N2, and C2H2 is program-controlled, and the purity of all three gases is greater than 99.999%. This makes the coating present a comprehensive gradient multi-layer state of TiN / TiNC / TiC. The Ar flow rate is 100 - 200 sccm, Ar flow rate: the sum of N2 and C2H2 flow rates = n:1 (n can take values from 1 to 4), the rated points of N2 flow rate: C2H2 flow rate are 1:0, 1:1, 0:1. x ratio points are selected between the two rated points (x can take values from 1 to 4), each rated point stays for 5 - 10 min, and each ratio point stays for 1 - 5 min.

[0024] Further, when preparing the C layer in step 5), a graphite target material with a purity greater than 99.99% is selected, the deposition temperature is 150 - 300 °C, the Ar flow rate is 50 - 100 sccm, the deposition power is 100 - 500 W, the deposition bias voltage is 50 - 150 V, the deposition gas pressure is 0.2 - 0.5 Pa, and the deposition time is 2 - 10 min.

[0025] Further, in the coating heat treatment in step 6), the ratio of the nitrogen-argon mixed gas selected is N2:Ar = (2 - 1 ~ 1 - 2), the gas flow rate is 50 - 200 sccm, and the heating rate of the tube furnace is 5 - 15 °C / min to prevent oxidation and contamination.

[0026] Further, for the corrosion resistance test in step 7), open circuit potential, potentiodynamic, and potentiostatic tests are carried out in sequence.

[0027] It should be noted that in the above steps, Ar gas can be replaced by other protective gases.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects.

[0029] By comprehensively utilizing the characteristics of strong bonding force between TiN and Ti transition layer, strong corrosion resistance of TiNC, and strong bonding force between TiC and carbon layer, the present invention prepares a Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating. Due to the gradual change of composition, the physical property differences (such as thermal expansion coefficient, etc.) between layers are reduced, and the problem of stress concentration at the interface is reduced; the electrochemical potential difference between different materials can also be reduced, reducing the risk of local corrosion. The dense TiC / C surface layer is used to further block the penetration of corrosive media and provide sufficient electron flow channels, obtaining a multi-layer gradient coating with strong bonding force with the substrate, excellent corrosion resistance, and good conductivity.

[0030] In the Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating prepared by the present invention, the middle TiNC layer of the coating is a gradient layer. By programming the control of the N2 flow rate:C2H2 flow rate, a multi-layer transition layer of TiN / TiNC / TiC is obtained, effectively reducing the existence of columnar crystals and large penetrating particles.

[0031] Additional aspects and some advantages of the present invention will be given in part in the following description, and part will become obvious from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flowchart of a preparation method of a Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating of the present invention.

[0033] Figure 2 It is a design schematic diagram of the coating in Example 1.

[0034] Figure 3 It is a test result diagram of the corrosion resistance (dynamic potential and static potential) of Example 1 and Comparative Example 1.

[0035] Figure 4 It is a test result diagram of the contact resistance of Example 1 and Comparative Example 1.

[0036] Figure 5 It is a test result diagram of the bonding force of Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following further describes the specific embodiments of the present invention in conjunction with the accompanying drawings of the specification, making the technical solutions and their beneficial effects of the present invention clearer and more definite. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0038] The additional aspects and advantages of the present invention will become apparent in the following description section, or be learned through the practice of the present invention.

[0039] The present invention provides a preparation method for a Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating, which specifically includes the following steps:

[0040] 1) Preparation of the substrate material. The main purpose of this step is to remove contaminants and impurities on the surface of the substrate. Cut the substrate material to a suitable size, and perform ultrasonic cleaning with a cleaning agent, deionized water, and absolute ethanol respectively. The cleaned substrate material is dried under a protective atmosphere.

[0041] 2) Pretreatment of the substrate material: a. Grinding and polishing. The main purpose of this step is to remove the oxide layer on the surface of the substrate. Use grinding and polishing equipment to perform preliminary grinding, fine grinding, and final polishing in sequence. After polishing, perform ultrasonic cleaning with absolute ethanol again, and the cleaned substrate material is dried under a protective atmosphere; b. Argon ion etching. The main purpose of this step is to deeply remove the oxide layer on the surface of the substrate and increase the surface roughness. Place the dried substrate material in a vacuum chamber, turn on the ion source with a DC power supply at room temperature, and control the Ar flow rate, set power, set bias voltage, set gas pressure, and deposition time of the equipment for etching.

[0042] 3) Preparation of the Ti transition layer. The main purpose of this step is to better connect the substrate and the subsequently deposited coating. Select a Ti target as the DC cathode. After reaching the set temperature, under the protection of a certain flow rate of Ar gas, set the deposition power, bias voltage, deposition gas pressure, and deposition time to deposit the Ti transition layer.

[0043] 4) Preparation of the TiN / TiNC / TiC comprehensive gradient layer. The main purpose of this step is to combine the characteristics of the three substances, deposit a gradient multi-layer coating, avoid through defects, and ensure strong corrosion resistance. Select a Ti target as the DC cathode. After reaching the set temperature, introduce different ratios of Ar, N2, and C2H2, set the deposition power, bias voltage, deposition gas pressure, and deposition time, and regulate the different gas ratios to deposit the gradient layer.

[0044] 5) Preparation of the C layer. The main purpose of this step is to ensure high conductivity and reduce the interface contact resistance. Select a graphite target as the DC cathode. After reaching the set temperature, under the protection of a certain flow rate of Ar gas, set the deposition power, bias voltage, deposition gas pressure, and deposition time to deposit the C conductive layer.

[0045] 6) Coating heat treatment. The main purpose of this step is to eliminate residual stress and prevent coating cracking. Take the sample out of the vacuum chamber and put it into a tube furnace with nitrogen-containing argon mixture at 500 - 900 °C for heat treatment for 2 - 12 h.

[0046] 7) Coating corrosion resistance and conductivity test. The main purpose of this step is to verify whether the corrosion current density, interface contact resistance, and interface and coating bonding strength of the coating meet the requirements.

[0047] a. Corrosion resistance test: In the electrochemical test cell, test according to the test method of GB / T 20042.6 - 2024 to obtain the corresponding corrosion current density of the sample.

[0048] b. Conductivity test: On the low-resistance tester, according to the test method of GB / T 20042.6 - 2024, set a certain pressure to test the contact resistance of the coating.

[0049] c. Bonding strength test: Refer to the industry standard JB / T 8554 - 1997 for testing. Cut a small part of the sample for testing respectively. The scratch speed is 5 - 15 mm / min, the loading rate is 10 - 100 N / min, and the loading accuracy is 0.01 - 0.5 N.

[0050] Among them, in the ultrasonic cleaning step of step 1), the cleaning agent, deionized water, and absolute ethanol are ultrasonically cleaned twice in sequence, and each cleaning is at least 30 min. In the grinding and polishing step of step 2), when initially grinding, use 80 - 200 mesh sandpaper to grind for 10 - 30 min, when finely grinding, use 200 - 400 mesh sandpaper to grind for more than 30 min, and finally for polishing, use 400 - 2000 mesh sandpaper to grind for more than 30 min. In the argon ion etching of step 2), select an Ar flow rate of 100 - 200 sccm, set the power to 1000 - 2000 W, set the bias voltage to 600 - 800 V, set the gas pressure to 0.5 - 1.2 Pa, and the deposition time to 10 - 30 min. When preparing the Ti transition layer in step 3), the purity of the Ti target is higher than 99.995%, the deposition temperature is 100 - 200 °C, the Ar gas flow rate is 50 - 100 sccm, the Ti deposition power is 1000 - 2000 W, the deposition bias voltage is 300 - 500 V, the deposition gas pressure is 0.2 - 0.8 Pa, and the deposition time is 2 - 20 min. When preparing the TiN / TiNC / TiC comprehensive gradient layer in step 4), select a Ti target material with a purity higher than 99.995%, the deposition temperature is 150 - 300 °C, the deposition power is 200 - 600 W, the deposition bias voltage is 50 - 150 V, the deposition gas pressure is 0.2 - 1.2 Pa, and the total deposition time is 20 - 60 min.

[0051] In the present invention, the introduction of Ar, N2, and C2H2 in different proportions is under program control. The purity of all three gases is greater than 99.999%, enabling the coating layer to exhibit a comprehensive gradient multi-layer state of TiN / TiNC / TiC. The Ar flow rate is 100 - 200 sccm, and the Ar flow rate: the sum of the N2 and C2H2 flow rates = n:1 (n can take values from 1 to 4). The rated points of the N2 flow rate: the C2H2 flow rate are 1:0, 1:1, and 0:1. x proportional points (x can take values from 1 to 4) are selected between the two rated points, with each rated point staying for 5 - 10 minutes and each proportional point staying for 1 - 5 minutes.

[0052] In the preparation step of the C layer in step 5), a graphite target with a purity greater than 99.99% is selected. The deposition temperature is 150 - 300 °C, the Ar flow rate is 50 - 100 sccm, the deposition power is 100 - 500 W, the deposition bias voltage is 50 - 150 V, the deposition gas pressure is 0.2 - 0.5 Pa, and the deposition time is 2 - 10 minutes.

[0053] In the coating heat treatment step of step 6), the proportion of the nitrogen-argon mixed gas selected is N2:Ar = 2 - 1 to 1 - 2, the gas flow rate is 50 - 200 sccm, and the heating rate of the tubular furnace is 5 - 15 °C / min to prevent oxidation and contamination. In the corrosion resistance test step of step 6), open circuit potential, potentiodynamic, and potentiostatic tests are carried out in sequence. Example 1

[0054] Refer to Figure 1 As shown, a preparation method for a Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant and conductive coating specifically includes the following steps: 1) Substrate material preparation. The main purpose of this step is to remove contaminants and impurities on the substrate surface. Cut the 316L stainless steel substrate material into 3 pieces with a size of 5 cm * 5 cm * 0.1 mm, numbered A1, A2, and A3 respectively. Select a cleaning agent, deionized water, and anhydrous ethanol in sequence and clean each twice, with ultrasonic cleaning for 30 minutes each time. After cleaning, put A1, A2, and A3 into a nitrogen atmosphere drying oven and dry at 40 °C for 2 hours.

[0055] 2) Substrate material pretreatment: a. Grinding and polishing. The main purpose of this step is to remove the oxide layer on the substrate surface. Use a grinding and polishing device to initially grind on 100-mesh sandpaper for 10 minutes, finely grind on 320-mesh sandpaper for 30 minutes, and finally polish on 2000-mesh sandpaper for 30 minutes in sequence. After polishing, perform ultrasonic cleaning with absolute ethanol twice, 20 minutes each time. Put A1, A2, and A3 after cleaning into a nitrogen atmosphere drying oven and dry at 40°C for 2 hours; b. Argon ion etching. The main purpose of this step is to deeply remove the oxide layer on the substrate surface and increase the surface roughness. Put the dried A1, A2, and A3 into the magnetron sputtering vacuum chamber, turn on the ion source with a DC power supply at room temperature, and etch with the Ar flow rate of the device controlled at 200 sccm, the set power at 1500 W, the set bias voltage at 700 V, the set gas pressure at 0.8 Pa, and the deposition time at 10 minutes.

[0056] 3) Preparation of Ti transition layer. The main purpose of this step is to better connect the substrate and the subsequently deposited coating. Select a Ti target with a purity greater than 99.995% as the DC cathode. After reaching 150°C, introduce 100 sccm of Ar, set the deposition power at 1000 W, the bias voltage at 400 V, the deposition gas pressure at 0.5 Pa, and the deposition time at 5 minutes to deposit the Ti transition layer.

[0057] 4) Preparation of TiN / TiNC / TiC comprehensive gradient layer. The main purpose of this step is to integrate the characteristics of the three substances, deposit a gradient multi-layer coating, avoid through defects, and ensure strong corrosion resistance. Select a Ti target with a purity greater than 99.995% as the DC cathode. After reaching 200°C, the Ar flow rate is 200 sccm, Ar flow rate: the sum of N2 and C2H2 flow rates = 2:1. Introduce different ratios of N2 / C2H2 as shown in Table 1. The rated points of N2 flow rate: C2H2 flow rate are 1:0, 1:1, 0:1. Select 3 ratio points between the rated points, stay at each rated point for 10 minutes, and stay at each ratio point for 3 minutes. Set the deposition power at 300 W, the bias voltage at 100 V, the deposition gas pressure at 1.0 Pa, and the total deposition time at 48 minutes, and regulate different gas ratios to deposit the gradient layer.

[0058] Table 1. Different ratios and residence times of Ar, N2, and C2H2 <![CDATA[N2:C2H2 (volume ratio)]]> <![CDATA[N2 flow rate (sccm)]]> <![CDATA[C2H2 flow rate (sccm)]]> Deposition Time (min) Rated Point 1: 0 100 0 10 Ratio Point 4: 1 80 20 3 Ratio Point 2: 1 66.66 33.33 3 Ratio Point 4: 3 57.14 42.86 3 Rated Point 1: 1 50 50 10 Ratio Point 3: 4 42.86 57.14 3 Ratio Point 1: 2 33.33 66.66 3 Ratio Point 1: 4 20 80 3 Rated Point 0: 1 0 100 10

[0059] 5) Preparation of layer C. The main purpose of this step is to ensure high conductivity and reduce the interfacial contact resistance. A graphite target with a purity greater than 99.99% is selected as the DC cathode. After reaching 200 °C, 80 sccm of Ar is introduced, and the deposition power is set to 250 W, the bias voltage is 50 V, the deposition pressure is 0.2 Pa, and the deposition time is 5 min to deposit the C conductive layer. The structure of the deposited coating is as shown in Figure 2 shown.

[0060] 6) Heat treatment of the coating. The main purpose of this step is to eliminate residual stress and prevent the coating from cracking. Samples A1, A2, and A3 are taken out of the vacuum chamber and placed in a tubular furnace filled with a nitrogen-argon mixed gas of 100 sccm (N2:Ar = 1:1, volume ratio), and heated to 800 °C at a rate of 10 °C / min for heat treatment for 5 h.

[0061] 7) Testing of the corrosion resistance, conductivity, and adhesion of the coating. The main purpose of this step is to verify whether the corrosion current density, interfacial contact resistance, and interfacial and coating adhesion of the coating meet the requirements.

[0062] a. Corrosion resistance test: In the electrochemical test cell, open circuit potential, potentiodynamic, and potentiostatic tests are carried out in sequence according to the test method of GB / T 20042.6-2024 to obtain the corresponding corrosion current density of the sample, as shown in Figure 3 shown.

[0063] b. Conductivity test: On a low-resistance tester, the contact resistance of the coating is tested at a pressure of 1.4 Mpa according to the test method of GB / T 20042.6-2024, and the results are as shown in Figure 4 shown.

[0064] c. Adhesion test: The test is carried out with reference to the industry standard JB / T 8554-1997. A small part of the sample is cut and tested respectively. The scratching speed is 10 mm / min, the loading rate is 20 N / min, and the loading accuracy is 0.03 N. The test results are as shown in Figure 5 shown.

[0065] Comparative Example 1

[0066] According to Example 1, which comprehensively utilizes the material properties of TiN, TiNC, and TiC, in this comparative example, only TiN and TiNC are used to prepare a Ti / TiN / TiNC / C composite gradient multi-layer corrosion-resistant conductive coating. The specific steps are as follows: 1) Substrate material preparation. The main purpose of this step is to remove contaminants and impurities on the substrate surface. Cut the 316L stainless steel substrate material into 3 pieces with a size of 5 cm * 5 cm * 0.1 mm, numbered B1, B2, and B3 respectively. Select a cleaning agent, deionized water, and anhydrous ethanol in sequence and clean each twice. Each time, perform ultrasonic cleaning for 30 min. After cleaning, put B1, B2, and B3 into a nitrogen atmosphere drying oven and dry at 40 °C for 2 h.

[0067] 2) Substrate material pretreatment: a. Grinding and polishing. The main purpose of this step is to remove the oxide layer on the substrate surface. Use a grinding and polishing device to initially grind on 100-mesh sandpaper for 10 min, finely grind on 320-mesh sandpaper for 30 min, and finally polish on 2000-mesh sandpaper for 30 min. After polishing, perform ultrasonic cleaning with anhydrous ethanol twice, each time for 20 min. After cleaning, put B1, B2, and B3 into a nitrogen atmosphere drying oven and dry at 40 °C for 2 h; b. Argon ion etching. The main purpose of this step is to deeply remove the oxide layer on the substrate surface and increase the surface roughness. Put the dried B1, B2, and B3 into a magnetron sputtering vacuum chamber. At room temperature, turn on the ion source using a DC power supply, control the Ar flow rate of the device to be 200 sccm, set the power to 1500 W, set the bias voltage to 700 V, set the gas pressure to 0.8 Pa, and the deposition time to 10 min for etching.

[0068] 3) Preparation of the Ti transition layer. The main purpose of this step is to better connect the substrate and the subsequently deposited coating. Select a Ti target with a purity greater than 99.995% as the DC cathode. After reaching 150 °C, introduce 100 sccm of Ar, set the deposition power to 1000 W, the bias voltage to 400 V, the deposition gas pressure to 0.5 Pa, and the deposition time to 5 min to deposit the Ti transition layer.

[0069] 4) Preparation of the TiN / TiNC composite gradient layer. The main purpose of this step is to deposit a gradient multi-layer coating using only the material properties of TiN and TiNC, avoid through-thickness defects, and ensure strong corrosion resistance. A Ti target with a purity greater than 99.995% is selected as the DC cathode. After reaching 200 °C, the Ar flow rate is 200 sccm, and the ratio of Ar flow rate to the sum of N2 and C2H2 flow rates is 2:1. Different ratios of N2 / C2H2 are introduced as shown in Table 2. The rated points for the N2 flow rate to C2H2 flow rate are 1:0 and 1:1. Seven ratio points are selected between the rated points, with each rated point staying for 10 min and each ratio point staying for 4 min. The deposition power is set at 300 W, the bias voltage is 100 V, the deposition pressure is 1.0 Pa, and the total deposition time is 48 min. Different gas ratios are adjusted to deposit the gradient layer.

[0070] Table 2. Different ratios and residence times of Ar, N2, and C2H2 <![CDATA[N2:C2H2 (volume ratio)]]> <![CDATA[N2 flow rate (sccm)]]> <![CDATA[C2H2 flow rate (sccm)]]> Deposition Time (min) Rated Point 1: 0 100 0 10 Ratio Point 8: 1 88.88 11.12 4 Ratio Point 4: 1 80 20 4 Ratio Point 8: 3 72.72 27.28 4 Ratio Point 2: 1 66.66 33.34 4 Ratio Point 8: 5 61.53 38.47 4 Ratio Point 4: 3 57.14 42.86 4 Ratio Point 8: 7 53.33 46.67 4 Rated Point 1: 1 50 50 10

[0071] 5) Preparation of the C layer. The main purpose of this step is to ensure high conductivity and reduce the interfacial contact resistance. A graphite target with a purity greater than 99.99% is selected as the DC cathode. After reaching 200 °C, 80 sccm of Ar is introduced. The deposition power is set at 250 W, the bias voltage is 50 V, the deposition pressure is 0.2 Pa, and the deposition time is 5 min to deposit the C conductive layer.

[0072] 6) Coating heat treatment. The main purpose of this step is to eliminate residual stress and prevent coating cracking. Samples B1, B2, and B3 are taken out of the vacuum chamber and placed in a tubular furnace filled with a nitrogen-argon mixture (N2:Ar = 1:1, volume ratio) with a flow rate of 100 sccm. The temperature is raised to 800 °C at a rate of 10 °C / min for heat treatment for 5 h.

[0073] 7) Testing of the corrosion resistance, conductivity, and adhesion of the coating. The main purpose of this step is to verify whether the corrosion current density, interfacial contact resistance, and interfacial and coating adhesion of the coating meet the requirements.

[0074] a. Corrosion resistance testing: In the electrochemical test cell, open-circuit potential, potentiodynamic, and potentiostatic tests are carried out in sequence according to the test method of GB / T 20042.6-2024 to obtain the corresponding corrosion current density of the sample, as Figure 3 shown.

[0075] b. Conductivity testing: On the low-resistance tester, the contact resistance of the coating is tested at a pressure of 1.4 Mpa according to the test method of GB / T 20042.6-2024. The results are as Figure 4 shown.

[0076] c. Bonding force test: The test was carried out with reference to the industry standard JB / T 8554-1997. A small part of the sample was cut for testing respectively. The scratching speed was 10 mm / min, the loading rate was 20 N / min, and the loading accuracy was 0.03 N. The test results are as Figure 5 shown.

[0077] Comparative Example 2

[0078] Based on the comprehensive utilization of the material properties of TiN, TiNC, and TiC in Example 1, this comparative example only uses TiNC and TiC to prepare a Ti / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating. The specific steps are as follows: 1) Preparation of the substrate material. The main purpose of this step is to remove contaminants and impurities on the surface of the substrate. Cut the 316L stainless steel substrate material into 3 pieces with a size of 5 cm * 5 cm * 0.1 mm, numbered C1, C2, and C3 respectively. Select a cleaning agent, deionized water, and anhydrous ethanol to clean 2 times in sequence, with ultrasonic cleaning for 30 min each time. After cleaning, put C1, C2, and C3 into a nitrogen atmosphere drying oven and dry at 40 °C for 2 h.

[0079] 2) Pretreatment of the substrate material: a. Grinding and polishing. The main purpose of this step is to remove the oxide layer on the surface of the substrate. Use a grinding and polishing device to initially grind on 100-mesh sandpaper for 10 min, finely grind on 320-mesh sandpaper for 30 min, and finally polish on 2000-mesh sandpaper for 30 min. After polishing, perform ultrasonic cleaning with anhydrous ethanol 2 times, 20 min each time. After cleaning, put C1, C2, and C3 into a nitrogen atmosphere drying oven and dry at 40 °C for 2 h; b. Argon ion etching. The main purpose of this step is to deeply remove the oxide layer on the surface of the substrate and increase the surface roughness. Put the dried C1, C2, and C3 into the magnetron sputtering vacuum chamber. At room temperature, turn on the ion source with a DC power supply, control the Ar flow rate of the device to be 200 sccm, set the power to 1500 W, set the bias voltage to 700 V, set the gas pressure to 0.8 Pa, and the deposition time to 10 min for etching.

[0080] 3) Preparation of the Ti transition layer. The main purpose of this step is to better connect the substrate and the subsequent deposited coating. Select a Ti target with a purity greater than 99.995% as the DC cathode. After reaching 150 °C, introduce 100 sccm of Ar, set the deposition power to 1000 W, the bias voltage to 400 V, the deposition gas pressure to 0.5 Pa, and the deposition time to 5 min to deposit the Ti transition layer.

[0081] 4) Preparation of TiNC / TiC composite gradient layer. The main purpose of this step is to deposit a gradient multi-layer coating by only utilizing the material properties of TiNC and TiC. A Ti target with a purity greater than 99.995% is selected as the DC cathode. After reaching 200 °C, the Ar flow rate is 200 sccm, and the ratio of Ar flow rate to the sum of N2 and C2H2 flow rates is 2:1. Different ratios of N2 / C2H2 are introduced as shown in Table 3. The rated points for the N2 flow rate to C2H2 flow rate are 1:1 and 0:1. Seven ratio points are selected between the rated points, with a 10-minute stay at each rated point and a 4-minute stay at each ratio point. The deposition power is set at 300 W, the bias voltage is 100 V, the deposition pressure is 1.0 Pa, and the total deposition time is 48 minutes. Different gas ratios are adjusted to deposit the gradient layer.

[0082] Table 3. Different ratios and residence times of Ar, N2, and C2H2 <![CDATA[N2:C2H2 (volume ratio)]]> <![CDATA[N2 flow rate (sccm)]]> <![CDATA[C2H2 flow rate (sccm)]]> Deposition Time (min) Rated Point 1: 1 50 50 10 Ratio Point 7: 8 46.67 53.33 4 Ratio Point 3: 4 42.86 57.14 4 Ratio Point 5: 8 38.47 61.53 4 Ratio Point 1: 2 33.34 66.66 4 Ratio Point 3: 8 27.28 72.72 4 Ratio Point 1: 4 20 80 4 Ratio Point 1: 8 11.12 88.88 4 Rated Point 0: 1 0 100 10

[0083] 5) Preparation of C layer. The main purpose of this step is to ensure high conductivity and reduce the interface contact resistance. A graphite target with a purity greater than 99.99% is selected as the DC cathode. After reaching 200 °C, 80 sccm of Ar is introduced. The deposition power is set at 250 W, the bias voltage is 50 V, the deposition pressure is 0.2 Pa, and the deposition time is 5 minutes to deposit the C conductive layer.

[0084] 6) Coating heat treatment. The main purpose of this step is to eliminate residual stress and prevent coating cracking. Samples C1, C2, and C3 are taken out of the vacuum chamber and placed in a tube furnace filled with a nitrogen-argon mixture (N2:Ar = 1:1, volume ratio) with a flow rate of 100 sccm. Heat treatment is carried out at a heating rate of 10 °C / min to 800 °C for 5 hours.

[0085] 7) Testing of the corrosion resistance, conductivity, and adhesion of the coating. The main purpose of this step is to verify whether the corrosion current density, interface contact resistance, and interface-to-coating adhesion of the coating meet the requirements.

[0086] a. Corrosion resistance testing: In the electrochemical test cell, open circuit potential, potentiodynamic, and potentiostatic tests are carried out in sequence according to the test method of GB / T 20042.6-2024 to obtain the corresponding corrosion current density of the sample, as Figure 3 shown.

[0087] b. Conductivity testing: On the low-resistance tester, the contact resistance of the coating is tested at a pressure of 1.4 Mpa according to the test method of GB / T 20042.6-2024. The results are as Figure 4 shown.

[0088] c. Bonding force test: The test was carried out with reference to the industry standard JB / T 8554-1997. A small part of the sample was cut for testing respectively. The scratching speed was 10 mm / min, the loading rate was 20 N / min, and the loading accuracy was 0.03 N. The test results are as Figure 5 shown.

[0089] Comparative Example 3

[0090] According to Example 1, by comprehensively utilizing the material properties of TiN, TiNC and TiC, a fuel cell metal bipolar plate with a multi-layer composite gradient coating and its preparation method were disclosed in CN 119481126A to prepare a Ti / TiN / TiNC / C multi-layer alternating composite gradient coating. The specific steps are as follows: 1) Preparation of the substrate material. The main purpose of this step is to remove contaminants and impurities on the surface of the substrate. The 316L stainless steel substrate material was cut into 3 pieces with a size of 5 cm * 5 cm * 0.1 mm, numbered D1, D2 and D3 respectively. They were successively cleaned 2 times with a cleaning agent, deionized water and anhydrous ethanol, and ultrasonically cleaned for 30 min each time. After cleaning, D1, D2 and D3 were placed in a nitrogen atmosphere drying oven and dried at 40 °C for 2 h.

[0091] 2) Pretreatment of the substrate material: a. Grinding and polishing. The main purpose of this step is to remove the oxide layer on the surface of the substrate. The grinding and polishing equipment was used to initially grind on 100-mesh sandpaper for 10 min, finely grind on 320-mesh sandpaper for 30 min and finally polish on 2000-mesh sandpaper for 30 min. After polishing, it was ultrasonically cleaned 2 times with anhydrous ethanol for 20 min each time. After cleaning, D1, D2 and D3 were placed in a nitrogen atmosphere drying oven and dried at 40 °C for 2 h; b. Argon ion etching. The main purpose of this step is to deeply remove the oxide layer on the surface of the substrate and increase the surface roughness. The dried D1, D2 and D3 were placed in a magnetron sputtering vacuum chamber. At room temperature, the ion source was turned on with a DC power supply, and the Ar flow rate of the equipment was controlled at 200 sccm, the set power was 1500 W, the set bias voltage was 700 V, the set gas pressure was 0.8 Pa and the deposition time was 10 min for etching.

[0092] 3) Preparation of the Ti transition layer. The main purpose of this step is to better connect the substrate and the subsequently deposited coating. A Ti target with a purity greater than 99.995% was selected as the DC cathode. After reaching 150 °C, 100 sccm of Ar was introduced, and the deposition power was set at 1000 W, the bias voltage was 400 V, the deposition gas pressure was 0.5 Pa and the deposition time was 5 min to deposit the Ti transition layer.

[0093] 4) Preparation of TiN / TiNC alternating composite gradient layer. The main purpose of this step is to deposit a composite gradient coating by only utilizing the material properties of TiN and TiNC. A Ti target with a purity greater than 99.995% is selected as the DC cathode. After reaching 200 °C, the Ar flow rate is 200 sccm, and the Ar flow rate: the sum of the N2 and C2H2 flow rates = 2:1. Different ratios of N2 / C2H2 are introduced as shown in Table 4. The rated points of the N2 flow rate: C2H2 flow rate are 1:0 and 1:1. Each rated point is alternated 4 times, and each rated point stays for 6 min. The deposition power is set to 300 W, the bias voltage is 100 V, the deposition pressure is 1.0 Pa, and the total deposition time is 48 min to obtain an 8-layer TiN / TiNC alternating composite gradient coating.

[0094] Table 4. Different ratios and residence times of N2 and C2H2 <![CDATA[N2:C2H2 (volume ratio)]]> <![CDATA[N2 flow rate (sccm)]]> <![CDATA[C2H2 flow rate (sccm)]]> Deposition Time (min) Rated Point 1: 0 100 0 6 Rated Point 1: 1 50 50 6

[0095] 5) Preparation of the C layer. The main purpose of this step is to ensure high conductivity and reduce the interface contact resistance. A graphite target with a purity greater than 99.99% is selected as the DC cathode. After reaching 200 °C, 80 sccm of Ar is introduced, and the deposition power is set to 250 W, the bias voltage is 50 V, the deposition pressure is 0.2 Pa, and the deposition time is 5 min to deposit a C conductive layer.

[0096] 6) Coating heat treatment. The main purpose of this step is to eliminate residual stress and prevent coating cracking. Samples C1, C2, and C3 are taken out of the vacuum chamber and placed in a tubular furnace filled with a nitrogen-argon mixture (N2:Ar = 1:1, volume ratio) with a flow rate of 100 sccm, and heated to 800 °C at a rate of 10 °C / min for heat treatment for 5 h.

[0097] 7) Testing of the corrosion resistance, conductivity, and adhesion of the coating. The main purpose of this step is to verify whether the corrosion current density, interface contact resistance, and interface and coating adhesion of the coating meet the requirements.

[0098] a. Corrosion resistance testing: In an electrochemical test cell, open circuit potential, potentiodynamic, and potentiostatic tests are carried out in sequence according to the test method of GB / T 20042.6-2024 to obtain the corresponding corrosion current density of the sample, as Figure 3 shown.

[0099] b. Conductivity testing: On a low-resistance tester, the contact resistance of the coating is tested at a pressure of 1.4 Mpa according to the test method of GB / T 20042.6-2024, and the results are as Figure 4 shown.

[0100] c. Adhesion test: The test was carried out with reference to the industry standard JB / T 8554-1997. A small part of the sample was cut for testing respectively. The scratching speed was 10 mm / min, the loading rate was 20 N / min, and the loading accuracy was 0.03 N. The test results are as Figure 5 shown.

[0101] Through Figure 3 , Figure 4 and Figure 5 comparing the experimental results, it can be found that the prepared Ti / TiN / TiNC / TiC / C composite gradient multi-layer corrosion-resistant conductive coating has better potentiodynamic corrosion current density, galvanostatic corrosion current density and adhesion strength than the Ti / TiN / TiNC / C composite gradient multi-layer corrosion-resistant conductive coating, the Ti / TiNC / TiC / C composite gradient multi-layer corrosion-resistant conductive coating and the Ti / TiN / TiNC / C multi-layer alternating composite gradient coating, while the interface contact resistance results are comparable. Among them, the Ti / TiN / TiNC / TiC / C composite gradient layer has better corrosion resistance and conductivity than the Ti / TiN / TiNC / C composite gradient layer. This is mainly because the TiC structure is dense and has a similar coefficient of thermal expansion to the C layer, making the binding force between TiC and C stronger, enhancing the corrosion resistance while ensuring sufficient electron flow channels; the Ti / TiN / TiNC / TiC / C composite gradient layer has stronger corrosion resistance and adhesion than the Ti / TiNC / TiC / C composite gradient layer because the binding force between TiN and the Ti transition layer is stronger, which can ensure that the subsequent coating will not fall off in a whole piece and reduce the occurrence of interlayer corrosion; the Ti / TiN / TiNC / TiC / C composite gradient layer has stronger adhesion, corrosion resistance and conductivity than the Ti / TiN / TiNC / C multi-layer alternating composite gradient coating. The binding force between TiC and the C layer is stronger than that between TiNC and the C layer, and TiC itself has a lower conductivity. The use of a gradient layer method can reduce problems such as geometric stress concentration and differences in coefficients of thermal expansion caused by abrupt changes at the interlayer interface, thereby enhancing the binding strength of the coating; in addition, by gradually changing the composition, the electrochemical potential difference between different materials is reduced, the risk of local corrosion is lowered, and a dense corrosion-resistant conductive coating is formed.

[0102] Through the description of the above structure and principle, those skilled in the art should understand that the present invention is not limited to the above specific embodiments. Improvements and substitutions using well-known technologies in the art based on the present invention all fall within the protection scope of the present invention. The protection scope of the present invention shall be defined by each claim item and its equivalents. Parts not described in the specific embodiments are all prior art or common general knowledge.

Claims

1. A preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating, characterized in that Used to prepare a Ti / TiN / TiNC / TiC / C comprehensive gradient multi-layer corrosion-resistant conductive coating on a substrate, including the following steps: 1) Substrate material preparation, removing contaminants and impurities on the substrate surface; 2) Substrate material pretreatment, removing the oxide layer on the substrate surface; 3) Preparation of the Ti transition layer, selecting a Ti target as the DC cathode. After reaching the set temperature, under the protection of a certain flow rate of protective gas, set the deposition power, bias voltage, deposition pressure and deposition time to deposit the Ti transition layer; 4) Preparation of the TiN / TiNC / TiC comprehensive gradient layer, selecting a Ti target as the DC cathode. After reaching the set temperature, sequentially introduce protective gas, N2 and C2H2 in different proportions, set the deposition power, bias voltage, deposition pressure and deposition time, and regulate the proportion of different gases to deposit the gradient layer; 5) Preparation of the C layer, selecting a graphite target as the DC cathode. After reaching the set temperature, under the protection of a certain flow rate of protective gas, set the deposition power, bias voltage, deposition pressure and deposition time to deposit the C conductive layer; 6) Coating heat treatment, putting the sample obtained in step 5) into a heat treatment furnace with a nitrogen-containing argon mixture at 500 - 900 °C for heat treatment for 2 - 12 h to obtain a product with a comprehensive gradient multi-layer corrosion-resistant conductive coating.

2. The preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating according to claim 1, characterized in that, In step 1) of the substrate material preparation step, the substrate material is ultrasonically cleaned with a cleaning agent, deionized water and anhydrous ethanol, and the cleaned substrate material is dried under a protective atmosphere.

3. The preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating according to claim 1, characterized in that, In step 2) of the substrate material pretreatment step, it includes a grinding and polishing step. In the grinding and polishing step, a grinding and polishing device is used to perform preliminary grinding, fine grinding and final polishing work in sequence to initially remove the oxide layer on the substrate surface; after polishing is completed, it is ultrasonically cleaned with anhydrous ethanol again, and the cleaned substrate material is dried under a protective atmosphere.

4. The preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating according to claim 1, characterized in that, In step 2) of the substrate material pretreatment step, it includes an argon ion etching step; in the argon ion etching step, the substrate material is placed in a vacuum chamber, the ion source is turned on with a DC power supply at room temperature, and the Ar flow rate, set power, set bias voltage, set pressure and etching time of the equipment are controlled for etching to deeply remove the oxide layer on the substrate surface and increase the surface roughness.

5. The preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating according to claim 1, characterized in that, In step 3) of the Ti transition layer preparation step, the purity of the Ti target is higher than 99.995%, the deposition temperature is 100 - 200 °C, the flow rate of the protective gas is 50 - 100 sccm, the Ti deposition power is 1000 - 2000 W, the deposition bias voltage is 300 - 500 V, the deposition pressure is 0.2 - 0.8 Pa, and the deposition time is 2 - 20 min.

6. The preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating according to claim 1, characterized in that, In step 4) of the TiN / TiNC / TiC comprehensive gradient layer preparation step, a Ti target material with a purity higher than 99.995% is selected, the deposition temperature is 150 - 300 °C, the deposition power is 200 - 600 W, the deposition bias voltage is 50 - 150 V, the deposition pressure is 0.2 - 1.2 Pa, and the total deposition time is 20 - 60 min; The introduction of protective gas, N2, and C2H2 in different proportions is under program control. The purity of all three gases is greater than 99.999%. The flow rate of the protective gas is 100 - 200 sccm. The flow rate of the protective gas : the sum of the flow rates of N2 and C2H2 = n : 1, where the value of n is 1 - 4. The rated points of the flow rate of N2 : the flow rate of C2H2 are 1 : 0, 1 : 1, and 0 :

1. x proportional points are selected between the two rated points, where the value of x is 1 - 4. Each rated point stays for 5 - 10 min, and each proportional point stays for 1 - 5 min.

7. A method for preparing a comprehensive gradient multi-layer corrosion-resistant conductive coating according to claim 1, characterized in that, In the preparation of the C layer in step 5), a graphite target with a purity greater than 99.99% is selected. The deposition temperature is 150 - 300 °C, the flow rate of the protective gas is 50 - 100 sccm, the deposition power is 100 - 500 W, the deposition bias voltage is 50 - 150 V, the deposition gas pressure is 0.2 - 0.5 Pa, and the deposition time is 2 - 10 min.

8. The preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating according to claim 1, characterized in that In the coating heat treatment step of step 6), the volume mixing ratio of the nitrogen-argon mixed gas selected is N2 : Ar = 2 - 1 ~ 1 - 2, the gas flow rate is 50 - 200 sccm, and the heating rate of the tubular furnace is 5 - 15 °C / min.

9. A comprehensive gradient multi-layer corrosion-resistant conductive coating, characterized in that, It is prepared by using the preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating according to any one of claims 1 - 8.

10. The application of the preparation method of a comprehensive gradient multi-layer corrosion-resistant conductive coating according to any one of claims 1 - 8 in the preparation of stainless steel bipolar plates.

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