Nickel tungsten-graphite composite coating and method for preparing the same

Abstract

This invention belongs to the field of surface treatment, specifically relating to a nickel-tungsten-graphite composite coating and its preparation method. It includes the following steps: Step (1): Pretreatment of the sample to be plated; Step (2): Setting up the electroplating apparatus: The sample to be plated is set as the cathode, and a graphite anode plate is selected as the anode, with the graphite anode plate facing the cathode surface to be plated. The electroplating solution formula is 15.78-31.56 g·L⁻¹. ‑1 NiSO4·6H2O, 88.2‑147.0g·L ‑1 Na3C6H5O7·2H2O, 7.53‑35.87g·L ‑1 Na2WO4·2H2O, 21.75‑31.95g·L ‑1 NH4Cl, 10.45–20.48 g·L ‑1 NaBr; Step (3): Set the electroplating temperature, current density and electroplating time, and perform electroplating; Step (4): Sample post-treatment. This invention improves the hardness of the coating and makes the coating surface smooth and flat without micro-cracks, with roughness reaching the nanometer level.

Description

Technical Field

[0001] This invention belongs to the field of surface treatment, specifically relating to a nickel-tungsten-graphite composite coating and its preparation method. Background Technology

[0002] Electroplating is a common method in the field of metallic materials for surface modification and enhancing corresponding properties to achieve application goals. The properties of the prepared coating determine its excellent application performance, such as hardness, wear resistance, and corrosion resistance. These factors are considered key characteristics and have received considerable attention and extensive research. Currently, bright, high-strength, and high-hardness surface chromium plating technology is widely used in many fields. However, traditional chromium plating technology requires the use of plating solutions containing toxic hexavalent chromium ions. Therefore, finding safer alternatives to traditional chromium plating methods has become a recent research hotspot. In addition to using plating solutions containing trivalent chromium ions for surface electroplating, nickel-based alloys have been extensively studied as a strong alternative to chromium alloys. In terms of hardness and durability, nickel-tungsten alloys have gradually become a new material replacing surface chromium plating technology. Furthermore, microcracks generated during the production process of hard coatings are a significant factor leading to coating failure. Summary of the Invention

[0003] The purpose of this invention is to provide a smooth, high-hardness, and crack-free nickel-tungsten-graphite composite coating and its preparation method.

[0004] The technical solution to achieve the objective of this invention is: a method for preparing a nickel-tungsten-graphite composite coating, comprising the following steps:

[0005] Step (1): Pretreatment of the sample to be plated;

[0006] Step (2): Setting up the electroplating apparatus: The sample to be plated is set as the cathode, and a graphite anode plate is selected as the anode. The graphite anode plate is directly opposite the surface to be plated on the cathode. The electroplating solution formula is 15.78-31.56 g·L. -1 NiSO4·6H2O, 88.2-147.0 g·L - 1 Na3C6H5O7·2H2O, 7.53-35.87g·L -1 Na2WO4·2H2O, 21.75-31.95g·L -1 NH4Cl, 10.45-20.48 g·L -1 NaBr;

[0007] Step (3): Set the electroplating temperature, current density, and electroplating time, and perform electroplating;

[0008] Step (4): Sample post-processing.

[0009] Furthermore, the sample to be plated is steel, and step (1) specifically involves:

[0010] Step (11): Use sandpaper to smooth the surface of the steel, polish it with diamond polishing paste with a grit of 1W until the surface is bright and without scratches, wash it thoroughly with deionized water, and dry it.

[0011] Step (12): Treat the steel with dilute hydrochloric acid solution, then degrease and activate it in alkaline degreasing solution, wash it with deionized water and dry it.

[0012] Further, step (12) specifically involves treating the steel with a 1-2wt% dilute hydrochloric acid aqueous solution for 30-60 seconds, then degreasing and activating it in an alkaline degreasing solution at 40-60℃ for 3-6 minutes, washing it with deionized water, and then drying it.

[0013] Furthermore, the electroplating in step (2) is carried out in an electroplating container, and the electroplating solution is placed in a constant temperature water bath stirrer.

[0014] Furthermore, in step (2), the ratio of the plating solution volume to the area to be plated is 80-120 mL·cm². -2 .

[0015] Furthermore, in step (2), the distance between the graphite anode plate and the cathode surfaces to be plated is 4-6 cm.

[0016] Furthermore, step (3) specifically involves: heating the electroplating solution using a constant temperature water bath stirrer to raise the temperature to 50-90℃ and then maintaining the temperature; setting the power supply parameters; selecting constant current mode; and gradually increasing the supply current to a specific current density of 0.1-0.2 A·cm² over 100-300 seconds. -2 Electroplating then begins, with the constant current lasting for 0.5-2 hours. During this time, the plating solution is stirred with a magnetic stirrer at a speed of 1000-1500 rpm. Once the specified time is reached, the power is disconnected, and the electroplating reaction ends.

[0017] Further, step (4) of sample post-treatment specifically involves washing the surface of the Ni-W composite coating sample with deionized water and drying it.

[0018] A nickel-tungsten-graphite composite coating is prepared using the method described above.

[0019] Compared with the prior art, the significant advantages of this invention are:

[0020] This invention, by controlling the electroplating process parameters and innovatively employing a "sacrificial anode cathodic conversion method," directly composites graphite spherical carbon materials with the nickel-tungsten electroplating layer in one step, building upon the traditional nickel-tungsten alloy surface electroplating process. This produces a smooth, high-hardness, and crack-free nickel-tungsten-graphite composite coating. The mechanism involves the surface negative potential of the fine-particle lightweight graphite carbon material being uniformly composited in the nickel-tungsten coating due to charge adsorption. This process further dops and provides active sites to control the nucleation and pinning of nickel-tungsten crystals, thereby increasing the coating's hardness and resulting in a smooth, flat surface free of micro-cracks, with a roughness reaching the nanometer level.

[0021] The selection of electrolyte composition concentration, current density, and temperature parameters in the electroplating process ensure that the nickel-tungsten-graphite composite coating obtains suitable nucleation energy during the electroplating process, achieving an amorphous nickel-tungsten structure that is difficult for cracks to penetrate, thereby possessing optimal surface smoothness and hardness performance. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the preparation method of the present invention.

[0023] Figure 2 This is a physical image of the nickel-tungsten-graphite composite coating obtained in Example 1 of the present invention.

[0024] Figure 3 This is a SEM image of the nickel-tungsten-graphite composite coating obtained in Example 1 of the present invention.

[0025] Figure 4 This is the EDS spectrum of the nickel-tungsten-graphite composite coating obtained in Example 1 of the present invention.

[0026] Figure 5 This is a physical image of the nickel-tungsten-graphite composite coating obtained in Example 2 of the present invention.

[0027] Figure 6 This is a SEM image of the nickel-tungsten-graphite composite coating obtained in Example 2 of the present invention.

[0028] Figure 7 This is the EDS spectrum of the nickel-tungsten-graphite composite coating obtained in Example 2 of the present invention.

[0029] Figure 8 This is a physical image of the nickel-tungsten-graphite composite coating obtained in Example 3 of the present invention.

[0030] Figure 9 This is a SEM image of the nickel-tungsten-graphite composite coating obtained in Example 3 of the present invention.

[0031] Figure 10 This is the EDS spectrum of the nickel-tungsten-graphite composite coating obtained in Example 3 of the present invention.

[0032] Figure 11 This is a physical image of the nickel-tungsten-graphite composite coating obtained in Example 4 of the present invention.

[0033] Figure 12 This is a SEM image of the nickel-tungsten-graphite composite coating obtained in Example 4 of the present invention.

[0034] Figure 13 This is the EDS spectrum of the nickel-tungsten-graphite composite coating obtained in Example 4 of the present invention.

[0035] Figure 14 This is a physical image of the nickel-tungsten-graphite composite coating obtained in Comparative Example 3 of the present invention. Detailed Implementation

[0036] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0037] A one-step process for producing a smooth, high-hardness, and crack-free nickel-tungsten-graphite composite coating is described below:

[0038] (1) Before electroplating, the surface of the metal steel is polished smooth with 80-grit and 2000-grit sandpaper respectively, and then polished with diamond polishing paste with a grit of 1W until the surface is bright and without scratches. Then it is thoroughly cleaned with deionized water and dried.

[0039] (2) Treat the substrate with 1-2wt% dilute hydrochloric acid aqueous solution for 30-60s, then degrease and activate it in alkaline degreasing solution at 40-60℃ for 3-6min, wash with deionized water and dry.

[0040] (3) Set up an electroplating apparatus. During the electroplating process, the electroplating solution is placed in a 500mL beaker, which is fixed in a constant temperature water bath with sufficient distilled water and a stirrer. The sample to be plated is immersed in the electroplating solution, and the ratio of the volume of the plating solution to the area to be plated is 80-120mL·cm². -2 The electrolyte formulation for electroplating Ni / W alloy coatings is 15.78-31.56 g·L⁻¹. -1 NiSO4·6H2O, 88.2-147.0 g·L -1 Na3C6H5O7·2H2O, 7.53-35.87g·L -1 Na2WO4·2H2O, 21.75-31.95g·L -1 NH4Cl, 10.45-20.48 g·L -1 For NaBr, the anode is a graphite anode plate, and the cathode is the workpiece to be plated. The anode plate is directly opposite the surface to be plated on the cathode with a spacing of 4-6 cm. The positive and negative terminals of the external power supply with controllable parameters are connected to the two poles of the electroplating device using a current-carrying wire.

[0041] (4) Heat the electroplating solution using a constant temperature water bath until the temperature reaches 50-90℃, then maintain the temperature. Set the power supply parameters and select constant current mode. The power supply will gradually increase the supply current to a specific value within 100-300 seconds, achieving a specific current density (0.1-0.3 A·cm). -2 Electroplating begins after [the specified time], with a constant current for 1-2 hours. During this time, the plating solution is stirred with a magnetic stirrer at 1000-1500 rpm to ensure its uniformity. The power is then disconnected after the specified time, ending the electroplating reaction.

[0042] (5) After electroplating, the surface of the Ni-W composite coating sample is thoroughly cleaned with deionized water and dried.

[0043] Example 1

[0044] A one-step process for producing a smooth, high-hardness, and crack-free nickel-tungsten-graphite composite coating is described below:

[0045] (1) Before electroplating, the surface of the metal steel is polished smooth with 80-grit and 2000-grit sandpaper respectively, and then polished with diamond polishing paste with a particle size of 1W until the surface is bright and without scratches. Then it is thoroughly cleaned with deionized water and dried.

[0046] (2) Treat the substrate with a 2wt% dilute hydrochloric acid aqueous solution for 30s, then degrease it in an alkaline degreasing solution at 50℃ and activate it for 3min, wash it with deionized water and dry it.

[0047] (3) Set up an electroplating apparatus. During the electroplating process, the electroplating solution is placed in a 500mL beaker. The sample to be plated is immersed in the electroplating solution. The ratio of the volume of the plating solution to the area to be plated is approximately 100mL·cm². -2 The electrolyte formulation for electroplating Ni / W alloy coatings is 15.78 g·L⁻¹. -1 NiSO4·6H2O, 117.6 g·L -1 Na3C6H5O7·2H2O, 25.41 g·L -1 Na₂WO₄·2H₂O, 26.75 g·L⁻¹ -1 NH4Cl, 15.45 g·L -1 For NaBr, a graphite anode plate is used as the anode, and the workpiece to be plated is used as the cathode. The anode plate is directly opposite the workpiece to be plated on the cathode with a distance of 4 cm. The positive and negative terminals of the external power supply (SOYI-3010DM) with controllable parameters are connected to the two poles of the electroplating device using a power-conducting wire.

[0048] (4) Use a constant temperature water bath (DF-101S) to heat the electroplating solution until the temperature reaches 75℃, then maintain the temperature. Set the power supply parameters, select constant current mode, and the power supply will gradually increase the supply current to a specific value of 0.1A·cm over 300 seconds. -2 Electroplating then begins, with a constant current for 1 hour. During this time, the plating solution is stirred with a magnetic stirrer at 1500 rpm to ensure its uniformity. Once the specified time has elapsed, the power is disconnected, and the electroplating reaction ends.

[0049] (5) After electroplating, the surface of the Ni-W composite coating sample is thoroughly cleaned with deionized water and dried.

[0050] A physical image of the composite coating prepared in step (5) of this embodiment is shown below. Figure 2 As shown, the composite coating was observed using a scanning electron microscope (Quanta 250F), and the resulting SEM image is shown below. Figure 3 As shown, the coating consists of micro- and nano-sized grains, with particle sizes ranging from 400 nm to 1400 nm. No cracks were found on the coating surface. EDS characterization yielded the following results. Figure 4 As shown, the coating contains 86.83 wt% nickel, 1.43 wt% tungsten, and 11.74 wt% carbon, proving the actual presence of each element in the composite coating. The surface roughness of the coating was measured to be 50 nm using a laser confocal microscope (OLS4100), proving that the coating surface is smooth and flat.

[0051] The hardness of the coating surface was tested using a microhardness tester (HMV-G 21DT). The test result was the average of eight tests. The final hardness of the coating prepared in this embodiment was 669.4 HV. Compared with the hardness of 539.0 HV of the nickel-tungsten alloy coating prepared with nickel plate as anode given in Comparative Example 1, the hardness of the nickel-tungsten-graphite composite coating prepared by the method of this invention is significantly improved, with an improvement rate of 24.2%.

[0052] Example 2

[0053] A one-step process for producing a smooth, high-hardness, and crack-free nickel-tungsten-graphite composite coating is described below:

[0054] (1) Before electroplating, the surface of the metal substrate is polished smooth with 80-grit and 2000-grit sandpaper respectively, and then polished with diamond polishing paste with a particle size of 1W until the surface is bright and without scratches. Then it is thoroughly cleaned with deionized water and dried.

[0055] (2) Treat the substrate with a 2wt% dilute hydrochloric acid aqueous solution for 30s, then degrease it in an alkaline degreasing solution at 50℃ and activate it for 3min, wash it with deionized water and dry it.

[0056] (3) Set up an electroplating apparatus. During the electroplating process, the electroplating solution is placed in a 500mL beaker, which is fixed in a constant temperature water bath with sufficient distilled water and stirred. The sample to be plated is immersed in the electroplating solution, and the ratio of the volume of the plating solution to the area to be plated is approximately 80mL·cm². -2 The electrolyte formulation for electroplating Ni / W alloy coatings is 14.11 g·L⁻¹. -1 NiSO4·6H2O, 106.6 g·L - 1 Na3C6H5O7·2H2O, 31.62 g·L -1 Na₂WO₄·2H₂O, 22.84 g·L⁻¹ -1 NH4Cl, 17.79 g·L -1 For NaBr, a graphite anode plate is selected as the anode, and the workpiece to be plated is the cathode. The anode plate is directly opposite the surface to be plated on the cathode with a spacing of 4 cm. The positive and negative terminals of the external power supply with controllable parameters are connected to the two poles of the electroplating device using a current-carrying wire.

[0057] (4) Heat the electroplating solution using a constant temperature water bath until the temperature reaches 60℃, then maintain the temperature. Set the power supply parameters, select constant current mode, and the power supply will gradually increase the supply current to a specific value within 300 seconds, reaching a specific current density (0.2A·cm). -2 Electroplating begins after [the specified time], with a constant current for 1 hour. During this time, the plating solution is stirred with a magnetic stirrer at 1500 rpm to ensure its uniformity. The power is then disconnected after the specified time, ending the electroplating reaction.

[0058] (5) After electroplating, the surface of the Ni-W composite coating sample is thoroughly cleaned with deionized water and dried.

[0059] The coating sample obtained in step (5) of this embodiment was characterized using SEM and EDS. The results are as follows: Figure 6 and 7 As shown, the microstructure of the coating is composed of nanoscale particles containing nickel, tungsten, and carbon, demonstrating the successful preparation of the composite coating.

[0060] The hardness of the coating surface was tested using a microhardness tester. The test result was the average of eight tests. The final hardness of the coating prepared in this embodiment was 711.0 HV. Compared with the hardness of 636.9 HV of the nickel-tungsten alloy coating prepared with nickel plate as anode, the hardness of the nickel-tungsten-graphite composite coating increased due to the incorporation of graphite carbon material.

[0061] Example 3

[0062] A one-step process for producing a smooth, high-hardness, and crack-free nickel-tungsten-graphite composite coating is described below:

[0063] (1) Before electroplating, the surface of the metal steel is polished smooth with 80-grit and 2000-grit sandpaper respectively, and then polished with diamond polishing paste with a grit of 1W until the surface is bright and without scratches. Then it is thoroughly cleaned with deionized water and dried.

[0064] (2) Treat the substrate with a 2wt% dilute hydrochloric acid aqueous solution for 30s, then degrease it in an alkaline degreasing solution at 50℃ and activate it for 3min, wash it with deionized water and dry it.

[0065] (3) Set up an electroplating apparatus. During the electroplating process, the electroplating solution is placed in a 500mL beaker, which is fixed in a constant temperature water bath with sufficient distilled water and stirred. The sample to be plated is immersed in the electroplating solution. The ratio of the volume of the plating solution to the area to be plated is approximately 110mL·cm². -2 The electrolyte formulation for electroplating Ni / W alloy coatings is 29.44 g·L⁻¹. -1 NiSO4·6H2O, 96.12 g·L - 1 Na3C6H5O7·2H2O, 16.88 g·L -1 Na₂WO₄·2H₂O, 29.65 g·L⁻¹ -1 NH4Cl, 13.48 g·L -1 For NaBr, a graphite anode plate is selected as the anode, and the workpiece to be plated is the cathode. The anode plate is directly opposite the surface to be plated on the cathode with a spacing of 4 cm. The positive and negative terminals of the external power supply with controllable parameters are connected to the two poles of the electroplating device using a current-carrying wire.

[0066] (4) Heat the electroplating solution using a constant temperature water bath until the temperature reaches 90℃, then maintain the temperature. Set the power supply parameters, select constant current mode, and the power supply will gradually increase the supply current to a specific value within 300 seconds, reaching a specific current density (0.1 A·cm). -2 Electroplating begins after [the specified time], with a constant current for 1.2 hours. During this time, the plating solution is stirred with a magnetic stirrer at 1500 rpm to ensure its uniformity. The power is then disconnected after the specified time, ending the electroplating reaction.

[0067] (5) After electroplating, the surface of the Ni-W composite coating sample is thoroughly cleaned with deionized water and dried.

[0068] The composite coating prepared in step (5) of this embodiment was observed using a scanning electron microscope (Quanta 250F), and the obtained SEM image is shown below. Figure 9 As shown, the coating consists of micro- and nano-sized grain aggregates with no surface cracks. EDS characterization yielded the following results: Figure 10As shown, the coating contains 83.9 wt% nickel, 1.1 wt% tungsten, and 13 wt% carbon, proving the actual presence of each element in the composite coating. The surface roughness of the coating was measured to be 74 nm using a laser confocal microscope (OLS4100), proving that the coating surface is smooth and flat.

[0069] The hardness of the coating surface was tested using a microhardness tester (HMV-G 21DT). The test result was the average of eight tests, and the hardness of the coating prepared in this embodiment was finally found to be 752 HV.

[0070] Example 4

[0071] A one-step process for producing a smooth, high-hardness, and crack-free nickel-tungsten-graphite composite coating is described below:

[0072] (1) Before electroplating, the surface of the metal steel is polished smooth with 80-grit and 2000-grit sandpaper respectively, and then polished with diamond polishing paste with a grit of 1W until the surface is bright and without scratches. Then it is thoroughly cleaned with deionized water and dried.

[0073] (2) Treat the substrate with a 2wt% dilute hydrochloric acid aqueous solution for 30s, then degrease it in an alkaline degreasing solution at 50℃ and activate it for 3min, wash it with deionized water and dry it.

[0074] (3) Set up an electroplating apparatus. During the electroplating process, the electroplating solution is placed in a 500mL beaker, which is fixed in a constant temperature water bath with sufficient distilled water and stirred. The sample to be plated is immersed in the electroplating solution. The ratio of the volume of the plating solution to the area to be plated is approximately 100mL·cm². -2 The electrolyte formulation for electroplating Ni / W alloy coatings is 17.23 g·L⁻¹. -1 NiSO4·6H2O, 142.6 g·L - 1 Na3C6H5O7·2H2O, 8.66 g·L -1 Na₂WO₄·2H₂O, 23.99 g·L⁻¹ -1 NH4Cl, 11.25 g·L -1 For NaBr, a graphite anode plate is used as the anode, and the workpiece to be plated is the cathode. The anode plate is directly opposite the surface to be plated on the cathode with a spacing of 6 cm. The positive and negative terminals of the external power supply with controllable parameters are connected to the two poles of the electroplating device using a current-carrying wire.

[0075] (4) Heat the electroplating solution using a constant temperature water bath until the temperature reaches 60℃, then maintain the temperature. Set the power supply parameters, select constant current mode, and the power supply will gradually increase the supply current to a specific value within 300 seconds, reaching a specific current density (0.1 A·cm). -2Electroplating begins after [the specified time], with a constant current for 1.5 hours. During this time, the plating solution is stirred with a magnetic stirrer at 1500 rpm to ensure its uniformity. The power is then disconnected after the specified time, ending the electroplating reaction.

[0076] (5) After electroplating, the surface of the Ni-W composite coating sample is thoroughly cleaned with deionized water and dried.

[0077] The composite coating prepared in step (5) of this embodiment was observed using a scanning electron microscope (Quanta 250F), and the obtained SEM image is shown below. Figure 12 As shown, the coating consists of numerous microparticle clusters, and no cracks were found on the surface. EDS characterization yielded the following results: Figure 13 As shown, the coating contains 57.57 wt% nickel, 27.97 wt% tungsten, and 14.46 wt% carbon, proving the actual presence of each element in the composite coating. The surface roughness of the coating was measured to be 123 nm using a laser confocal microscope (OLS4100), proving that the coating surface is smooth and flat.

[0078] The hardness of the coating surface was tested using a microhardness tester (HMV-G 21DT). The test result was the average of eight tests, and the hardness of the coating prepared in this embodiment was finally found to be 582.5 HV.

[0079] Comparative Example 1

[0080] A method for preparing a nickel-tungsten-graphite composite coating is as follows:

[0081] (1) Before electroplating, the surface of the metal steel is polished smooth with 80-grit and 2000-grit sandpaper respectively, and then polished with diamond polishing paste with a grit of 1W until the surface is bright and without scratches. Then it is thoroughly cleaned with deionized water and dried.

[0082] (2) Treat the substrate with a 2wt% dilute hydrochloric acid aqueous solution for 30s, then degrease it in an alkaline degreasing solution at 50℃ and activate it for 3min, wash it with deionized water and dry it.

[0083] (3) Set up an electroplating apparatus. During the electroplating process, the electroplating solution is placed in a 500mL beaker, which is fixed in a constant temperature water bath with sufficient distilled water and stirred. The sample to be plated is immersed in the electroplating solution, and the ratio of the volume of the plating solution to the area to be plated is approximately 120mL·cm². -2 The electrolyte formulation for electroplating Ni / W alloy coatings is 15.78 g·L⁻¹. -1 NiSO4·6H2O, 107.6 g·L - 1 Na3C6H5O7·2H2O, 25.42 g·L -1Na₂WO₄·2H₂O, 25.85 g·L⁻¹ -1 NH4Cl, 15.44 g·L -1 NaBr, the anode is a pure nickel plate, the cathode is the workpiece to be plated, the anode plate is directly opposite the surface to be plated on the cathode and the distance is 5cm, and the positive and negative terminals of the external power supply with controllable parameters are connected to the two poles of the electroplating device using a current-carrying wire.

[0084] (4) Heat the electroplating solution using a constant temperature water bath until the temperature reaches 75℃, then maintain the temperature. Set the power supply parameters, select constant current mode, and the power supply will gradually increase the supply current to a specific value within 300 seconds, reaching a specific current density (0.1 A·cm). -2 Electroplating begins after [the specified time], with a constant current for 1 hour. During this time, the plating solution is stirred with a magnetic stirrer at 1500 rpm to ensure its uniformity. The power is then disconnected after the specified time, ending the electroplating reaction.

[0085] (5) After electroplating, the surface of the Ni-W coating sample is thoroughly cleaned with deionized water and dried.

[0086] The coating prepared in this comparative example was tested and found to have a hardness of 539.0 HV, which is slightly lower than the coating prepared by the method of this invention.

[0087] Comparative Example 2

[0088] A method for preparing a nickel-tungsten-graphite composite coating is as follows:

[0089] (1) Before electroplating, the surface of the metal steel is polished smooth with 80-grit and 2000-grit sandpaper respectively, and then polished with diamond polishing paste with a grit of 1W until the surface is bright and without scratches. Then it is thoroughly cleaned with deionized water and dried.

[0090] (2) Treat the substrate with a 2wt% dilute hydrochloric acid aqueous solution for 30s, then degrease it in an alkaline degreasing solution at 50℃ and activate it for 3min, wash it with deionized water and dry it.

[0091] (3) Set up an electroplating apparatus. During the electroplating process, the electroplating solution is placed in a 500mL beaker, which is fixed in a constant temperature water bath with sufficient distilled water and stirred. The sample to be plated is immersed in the electroplating solution. The ratio of the volume of the plating solution to the area to be plated is approximately 100mL·cm². -2 The electrolyte formulation for electroplating the Ni / W alloy coating is 29.66 g·L⁻¹. -1 NiSO4·6H2O, 132.9 g·L - 1 Na3C6H5O7·2H2O, 26.42 g·L -1 Na₂WO₄·2H₂O, 28.54 g·L⁻¹ -1NH4Cl, 12.26 g·L -1 NaBr, the anode is a pure nickel plate, the cathode is the workpiece to be plated, the anode plate is directly opposite the cathode surface to be plated with a distance of 4 cm, and the positive and negative terminals of the external power supply with controllable parameters are connected to the two poles of the electroplating device using a current-carrying wire.

[0092] (4) Heat the electroplating solution using a constant temperature water bath until the temperature reaches 60℃, then maintain the temperature. Set the power supply parameters, select constant current mode, and the power supply will gradually increase the supply current to a specific value within 300 seconds, reaching a specific current density (0.1 A·cm). -2 Electroplating begins after [the specified time], with a constant current for 1.2 hours. During this time, the plating solution is stirred with a magnetic stirrer at 1500 rpm to ensure its uniformity. The power is then disconnected after the specified time, ending the electroplating reaction.

[0093] (5) After electroplating, the surface of the Ni-W coating sample is thoroughly cleaned with deionized water and dried.

[0094] The coating prepared in this comparative example was tested and found to have a hardness of 493.5 HV, which is lower than the coating prepared by the method of this invention.

[0095] Comparative Example 3

[0096] A method for preparing a nickel-tungsten-graphite composite coating is as follows:

[0097] (1) Before electroplating, the surface of the metal steel is polished smooth with 80-grit and 2000-grit sandpaper respectively, and then polished with diamond polishing paste with a grit of 1W until the surface is bright and without scratches. Then it is thoroughly cleaned with deionized water and dried.

[0098] (2) Treat the substrate with a 2wt% dilute hydrochloric acid aqueous solution for 30s, then degrease it in an alkaline degreasing solution at 50℃ and activate it for 3min, wash it with deionized water and dry it.

[0099] (3) Set up an electroplating apparatus. During the electroplating process, the electroplating solution is placed in a 500mL beaker, which is fixed in a constant temperature water bath with sufficient distilled water and stirred. The sample to be plated is immersed in the electroplating solution. The ratio of the volume of the plating solution to the area to be plated is approximately 100mL·cm². -2 The electrolyte formulation for electroplating Ni / W alloy coatings is 31.44 g·L⁻¹. -1 NiSO4·6H2O, 136.8 g·L - 1 Na3C6H5O7·2H2O, 31.48 g·L -1 Na2WO4·2H2O, 29.96 g·L -1 NH4Cl, 17.11 g·L -1For NaBr, a graphite anode plate is used as the anode, and the workpiece to be plated is used as the cathode. The anode plate is directly opposite the workpiece to be plated on the cathode with a spacing of 5 cm. The positive and negative terminals of the external power supply with controllable parameters are connected to the two poles of the electroplating device using a current-carrying wire.

[0100] (4) Heat the electroplating solution using a constant temperature water bath until the temperature reaches 90℃, then maintain the temperature. Set the power supply parameters, select constant current mode, and the power supply will gradually increase the supply current to a specific value within 300 seconds, reaching a specific current density (0.3A·cm). -2 Electroplating begins after [the specified time], with a constant current for 1.8 hours. During this time, the plating solution is stirred with a magnetic stirrer at 1500 rpm to ensure its uniformity. The power is then disconnected after the specified time, ending the electroplating reaction.

[0101] (5) After electroplating, the surface of the Ni-W composite coating sample is thoroughly cleaned with deionized water and dried.

[0102] The surface photograph of the graphite-nickel-tungsten composite coating prepared in step (5) of this comparative example is shown below. Figure 14 As shown, when the preparation method exceeds the scope given in this invention, the coating exhibits surface cracking, and the roughness increases from the nanoscale to the level of several micrometers, losing its smooth and flat characteristics.

[0103] Table 1

[0104]

[0105] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-tungsten-graphite composite coating, characterized in that, Includes the following steps: Step (1): Pretreatment of the sample to be plated; Step (2): Setting up the electroplating apparatus: The sample to be plated is set as the cathode, and a graphite anode plate is selected as the anode. The graphite anode plate is directly opposite the surface to be plated on the cathode. The electroplating solution formula is 15.78-31.56 g·L. -1 NiSO4·6H2O, 88.2-147.0 g·L -1 Na3C6H5O7·2H2O, 7.53-35.87 g·L -1 Na2WO4·2H2O, 21.75-31.95 g·L -1 NH4Cl, 10.45-20.48 g·L -1 NaBr; Step (3): Set the electroplating temperature, current density, and electroplating time, and perform electroplating; Step (4): Sample post-processing; Step (3) specifically involves: heating the electroplating solution using a constant temperature water bath stirrer to raise the temperature to 50-90°C and then maintaining the temperature; setting the power supply parameters; selecting constant current mode; and gradually increasing the supply current to a specific current density of 0.1-0.2 A·cm² over 100-300 seconds. -2 Electroplating then begins, with the constant current lasting for 0.5-2 hours. During this time, the plating solution is stirred with a magnetic stirrer at a speed of 1000-1500 rpm. Once the specified time has elapsed, the power is disconnected, and the electroplating reaction is complete.

2. The preparation method according to claim 1, characterized in that, The sample to be plated is steel. Step (1) is as follows: Step (11): Use sandpaper to smooth the steel surface, polish it with diamond polishing paste with a grit size of W1 until the surface is bright and free of scratches, wash it thoroughly with deionized water, and dry it. Step (12): Treat the steel with dilute hydrochloric acid solution, then degrease and activate it in alkaline degreasing solution, wash it with deionized water and dry it.

3. The preparation method according to claim 2, characterized in that, Step (12) specifically involves treating the steel with a 1-2 wt% dilute hydrochloric acid aqueous solution for 30-60 seconds, then degreasing and activating it in an alkaline degreasing solution at 40-60 °C for 3-6 minutes, washing it with deionized water, and then drying it.

4. The preparation method according to claim 3, characterized in that, The electroplating in step (2) is carried out in an electroplating container, and the electroplating solution is placed in a constant temperature water bath stirrer.

5. The preparation method according to claim 4, characterized in that, In step (2), the ratio of the plating solution volume to the area to be plated is 80-120 mL·cm². -2 .

6. The preparation method according to claim 5, characterized in that, In step (2), the distance between the graphite anode plate and the cathode surface to be plated is 4-6 cm.

7. The preparation method according to claim 6, characterized in that, Step (4) Sample post-processing specifically involves washing the surface of the Ni-W composite coating sample with deionized water and drying it.

8. A nickel-tungsten-graphite composite coating, characterized in that, Prepared using the method described in any one of claims 1-7.

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