Nickel-phosphorus-diamond plating solution, composite coating and protection method for metal substrate

Abstract

This invention belongs to the field of wear-resistant coating technology, and provides a nickel-phosphorus diamond plating solution, a composite coating, and a method for protecting a metal substrate. The nickel-phosphorus diamond plating solution of this invention comprises 35-40 g / L nickel sulfate, 25-30 g / L sodium hypophosphite, 16-20 g / L sodium malate, 12-15 g / L sodium acetate, 12-14 g / L sodium lactate, 10-50 mg / L sodium dodecyl sulfate, 10-50 mg / L hexadecyltrimethylammonium bromide, 10-30 mg / L polyoxyethylene dodecyl ether sulfate, 5-10 mg / L potassium iodate, and 0.1-1.6 g / L diamond particles. The simultaneous addition of sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and polyoxyethylene dodecyl ether sulfate ensures uniform dispersion of diamond particles in the plating solution, improves the embedding rate and dispersibility of diamond particles in the coating, and ultimately enhances the corrosion resistance, wear resistance, and hardness of the coating.

Description

Technical Field

[0001] This invention relates to the field of chemical deposition composite coating technology, and more particularly to a nickel-phosphorus diamond plating solution, a composite coating, and a method for protecting metal substrates. Background Technology

[0002] Workpieces are often damaged or even fail during operation due to fatigue, friction, corrosion, and wear, causing significant losses to my country's national economy. Chemically deposited Ni-P coatings exhibit high compatibility with various workpiece metals, making them an important means of improving workpiece performance and lifespan, thus finding widespread application in industrial production. With advancements in technology, single-layer nickel plating is insufficient to meet the requirements for long-term stable operation in harsh environments, making the research of high-performance composite coatings crucial. Based on traditional chemical Ni-P plating, a composite coating is formed by adding micron-sized diamond to the Ni-P plating solution. This coating not only possesses the uniformity of traditional chemically deposited Ni-P coatings but is also dense, and the plating process is simplified.

[0003] A common problem with Ni-P diamond composite coatings is the tendency for diamond particles to detach. Chinese patent CN106591810A discloses a method for uniformly embedding diamond particles on the surface of a Ni-P coating. This method involves coating the upper and lower surfaces of a nickel-phosphorus diamond layer with a nickel-phosphorus coating, embedding the diamond particles in the middle of the composite coating, thus preventing detachment. However, scanning electron microscopy (SEM) analysis of the micron-sized diamond particles used in this method reveals partial agglomeration and a low embedding rate, indicating that the wear resistance and corrosion resistance need further improvement. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a nickel-phosphorus diamond plating solution, a composite coating, and a method for protecting a metal substrate. The nickel-phosphorus diamond plating solution provided by this invention produces a coating with high diamond particle embedding rate and good dispersion, thereby improving the corrosion resistance of the coating.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a nickel-phosphorus diamond plating solution comprising the following components at the following concentrations:

[0007] Nickel sulfate 35-40 g / L, sodium hypophosphite 25-30 g / L, sodium malate 16-20 g / L, sodium acetate 12-15 g / L, sodium lactate 12-14 g / L, sodium dodecyl sulfate 10-50 mg / L, hexadecyltrimethylammonium bromide 10-50 mg / L, polyoxyethylene dodecyl ether sulfate 10-30 mg / L, potassium iodate 5-10 mg / L, diamond particles 0.1-1.6 g / L.

[0008] Preferably, the nickel-phosphorus diamond plating solution comprises components with the following concentrations:

[0009] Nickel sulfate 35 g / L, sodium hypophosphite 25 g / L, sodium malate 16 g / L, sodium acetate 12 g / L, sodium lactate 12 g / L, sodium dodecyl sulfate 20 mg / L, hexadecyltrimethylammonium bromide 20 mg / L, polyoxyethylene dodecyl ether sulfate 10 mg / L, potassium iodate 5 mg / L, diamond particles 0.1–1.6 g / L.

[0010] Preferably, the diamond particles have a particle size of 1–28 μm.

[0011] Preferably, the pH value of the nickel-phosphorus diamond plating solution is 4.4 to 4.6.

[0012] The present invention also provides a composite coating, which is obtained by heat treatment of a nickel-phosphorus coating and a nickel-phosphorus diamond coating stacked in sequence; the nickel-phosphorus diamond coating is obtained by plating with the nickel-phosphorus diamond plating solution described in the above technical solution.

[0013] Preferably, the nickel-phosphorus plating layer is obtained by plating with a nickel-phosphorus plating solution; the nickel-phosphorus plating solution comprises components of the following concentrations:

[0014] Nickel sulfate 35-40 g / L, sodium hypophosphite 25-30 g / L, sodium malate 16-20 g / L, sodium acetate 12-15 g / L, sodium lactate 12-14 g / L.

[0015] Preferably, the thickness of the nickel-phosphorus coating is 3-4 μm, and the thickness of the nickel-phosphorus diamond coating is 14-16 μm.

[0016] Preferably, the heat treatment temperature is 170–200°C, the atmosphere is argon, and the time is 1–1.5 hours.

[0017] The present invention also provides a method for protecting a metal substrate, comprising the following steps:

[0018] Prepare composite coatings on metal substrates;

[0019] The composite coating is the composite coating described in the above technical solution;

[0020] The nickel-phosphorus coating in the composite coating is in contact with the metal substrate.

[0021] Preferably, the metal substrate mainly comprises steel.

[0022] This invention provides a nickel-phosphorus diamond plating solution comprising the following components at the following concentrations: nickel sulfate 35-40 g / L, sodium hypophosphite 25-30 g / L, sodium malate 16-20 g / L, sodium acetate 12-15 g / L, sodium lactate 12-14 g / L, sodium dodecyl sulfate 10-50 mg / L, hexadecyltrimethylammonium bromide 10-50 mg / L, polyoxyethylene dodecyl ether sulfate 10-30 mg / L, potassium iodate 5-10 mg / L, and diamond particles 0.1-1.6 g / L.

[0023] This invention involves simultaneously adding surfactants sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, and sodium polyoxyethylene dodecyl ether sulfate to a nickel-phosphorus diamond plating bath. This ensures uniform dispersion and high embedding rate of diamond particles in the plating bath, thereby improving the dispersibility of diamond particles in the coating. The uniform dispersion and high embedding rate of diamond particles enhance the corrosion resistance, wear resistance, and hardness of the coating. Furthermore, the diamond particle content in the nickel-phosphorus diamond plating bath is 0.1–1.6 g / L, which also ensures that the diamond particles do not easily settle in the plating bath and are uniformly dispersed, further improving the corrosion resistance, wear resistance, and hardness of the coating.

[0024] Furthermore, this invention controls the diamond particle size to be 1–28 μm, which prevents the diamond particles from being too small, causing them to easily agglomerate in the coating and easily peel off in sheets during wear. It also avoids the defects caused by excessively large diamond particles, which result in poor bonding between the diamond particles and the Ni-P coating and easy peeling of the diamond particles during friction. Attached Figure Description

[0025] Figure 1 The image shows the SEM spectrum of the composite coating obtained in Example 3. Detailed Implementation

[0026] This invention provides a nickel-phosphorus diamond plating solution comprising the following components at the following concentrations:

[0027] Nickel sulfate 35-40 g / L, sodium hypophosphite 25-30 g / L, sodium malate 16-20 g / L, sodium acetate 12-15 g / L, sodium lactate 12-14 g / L, sodium dodecyl sulfate 10-50 mg / L, hexadecyltrimethylammonium bromide 10-50 mg / L, polyoxyethylene dodecyl ether sulfate 10-30 mg / L, potassium iodate 5-10 mg / L, diamond particles 0.1-1.6 g / L.

[0028] Unless otherwise specified, all raw materials used in this invention are preferably commercially available products.

[0029] The nickel-phosphorus diamond plating solution provided by the present invention comprises 35-40 g / L of nickel sulfate, preferably 36-39 g / L, and more preferably 37-38 g / L.

[0030] The nickel-phosphorus diamond plating solution provided by the present invention includes sodium hypophosphite at a concentration of 25-30 g / L, preferably 26-29 g / L, and more preferably 27-28 g / L.

[0031] The nickel-phosphorus diamond plating solution provided by the present invention comprises sodium malate at a concentration of 16-20 g / L, preferably 17-19 g / L, and more preferably 18 g / L.

[0032] The nickel-phosphorus diamond plating solution provided by the present invention includes 12-15 g / L of sodium acetate, preferably 13-14 g / L.

[0033] The nickel-phosphorus diamond plating solution provided by the present invention comprises sodium lactate at 12-14 g / L, preferably 12.5-13.5 g / L, and more preferably 13 g / L.

[0034] The nickel-phosphorus diamond plating solution provided by the present invention comprises sodium dodecyl sulfate at a concentration of 10-50 mg / L, preferably 20-40 mg / L, and more preferably 30 mg / L.

[0035] The nickel-phosphorus diamond plating solution provided by the present invention comprises 10-50 mg / L of hexadecyltrimethylammonium bromide, preferably 20-40 mg / L, and more preferably 30 mg / L.

[0036] The nickel-phosphorus diamond plating solution provided by the present invention comprises 10-30 mg / L of sodium polyoxyethylene dodecyl ether sulfate, preferably 15-25 mg / L, and more preferably 20 mg / L.

[0037] The nickel-phosphorus diamond plating solution provided by this invention comprises 5-10 mg / L potassium iodate, preferably 6-9 mg / L, and more preferably 7-8 mg / L. In this invention, the potassium iodate can stabilize nickel ions in the nickel-phosphorus diamond plating solution, stabilize the nickel plating rate, prevent self-decomposition, and make the nickel-phosphorus diamond plating layer more uniform.

[0038] The nickel-phosphorus diamond plating solution provided by this invention comprises diamond particles at a concentration of 0.1–1.6 g / L, preferably 0.1–0.4 g / L, and more preferably 0.2–0.3 g / L. In this invention, the particle size of the diamond particles is preferably 1–28 μm. In this invention, the diamond particles are preferably pretreated before use, and the pretreatment preferably includes: sequentially subjecting the diamond particles to alkaline boiling and acid leaching. In this invention, the reagent for alkaline boiling is preferably a 50 wt% NaOH solution, the temperature for alkaline boiling is preferably 50–60°C, and the time is preferably 30 minutes; after alkaline boiling, the solution preferably further includes removing the alkaline-boiled diamond particles, washing them with water until neutral, and then drying them. In this invention, the reagent for acid leaching is preferably 50 wt% sulfuric acid, the temperature for acid leaching is preferably room temperature, and the time is preferably 10 minutes; after acid leaching, the solution preferably further includes: removing the acid-leached diamond particles, washing them with water until neutral, and then drying them.

[0039] The solvent of the nickel-phosphorus diamond plating solution provided by the present invention is preferably water, and the water is preferably deionized water.

[0040] The nickel-phosphorus diamond plating solution provided by this invention preferably further includes sodium saccharin, and the concentration of sodium saccharin is preferably 20-25 mg / L. In this invention, the sodium saccharin can reduce the roughness of the nickel-phosphorus diamond plating layer, making the nickel-phosphorus diamond plating layer smoother.

[0041] In this invention, the nickel-phosphorus diamond plating solution preferably comprises components with the following concentrations:

[0042] Nickel sulfate 35 g / L, sodium hypophosphite 25 g / L, sodium malate 16 g / L, sodium acetate 12 g / L, sodium lactate 12 g / L, sodium dodecyl sulfate 20 mg / L, hexadecyltrimethylammonium bromide 20 mg / L, polyoxyethylene dodecyl ether sulfate 10 mg / L, potassium iodate 5 mg / L, diamond particles 0.1–1.6 g / L; Further preferred components include the following concentrations:

[0043] Nickel sulfate 35 g / L, sodium hypophosphite 25 g / L, sodium malate 16 g / L, sodium acetate 12 g / L, sodium lactate 12 g / L, sodium dodecyl sulfate 20 mg / L, hexadecyltrimethylammonium bromide 20 mg / L, polyoxyethylene dodecyl ether sulfate 10 mg / L, potassium iodate 5 mg / L, diamond particles 0.1–0.5 g / L.

[0044] In this invention, the pH value of the nickel-phosphorus diamond plating solution is preferably 4.4 to 4.6. In this invention, the reagent used to adjust the pH value of the nickel-phosphorus diamond plating solution to 4.4 to 4.6 is preferably acetic acid.

[0045] In this invention, the preparation method of the nickel-phosphorus diamond plating solution preferably includes the following steps:

[0046] Nickel sulfate, sodium malate, sodium acetate, sodium lactate, and sodium hypophosphite were added to the solvent in sequence and stirred thoroughly. The pH value was adjusted to 4.4–4.6 with acetic acid to obtain the plating solution precursor.

[0047] Diamond particles are dispersed in a solvent to obtain a diamond particle dispersion; sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, sodium polyoxyethylene dodecyl ether sulfate and potassium iodate are added to the diamond particle dispersion to obtain a diamond particle suspension.

[0048] The plating solution precursor and the diamond particle suspension are mixed to obtain the nickel-phosphorus diamond plating solution.

[0049] In this invention, the diamond particles are preferably pretreated before use. The pretreatment preferably includes: sequentially subjecting the diamond particles to alkaline washing, a first water wash, acid washing, and a second water wash. In this invention, the reagent for the alkaline washing is preferably a 50 wt% NaOH solution, the temperature for the alkaline washing is preferably 50°C, and the washing time is preferably 30 minutes. In this invention, the first water wash is performed until the pH value is neutral. In this invention, the reagent for the acid washing is preferably 50 wt% sulfuric acid, and the acid washing method is preferably immersion, with the immersion time preferably being 10 minutes. In this invention, the second water wash is performed until the pH value is neutral.

[0050] The present invention also provides a composite coating, which is obtained by heat treatment of a nickel-phosphorus coating and a nickel-phosphorus diamond coating stacked in sequence; the nickel-phosphorus diamond coating is obtained by plating with the nickel-phosphorus diamond plating solution described in the above technical solution.

[0051] In this invention, the nickel-phosphorus plating layer is obtained by plating with a nickel-phosphorus plating solution; the nickel-phosphorus plating solution preferably comprises the following components at the following concentrations: nickel sulfate 35-40 g / L, sodium hypophosphite 25-30 g / L, sodium malate 16-20 g / L, sodium acetate 12-15 g / L, and sodium lactate 12-14 g / L. In this invention, the nickel-phosphorus plating solution preferably comprises nickel sulfate 35-40 g / L, more preferably 36-39 g / L, and even more preferably 37-38 g / L. In this invention, the nickel-phosphorus plating solution preferably comprises sodium hypophosphite 25-30 g / L, more preferably 26-29 g / L, and even more preferably 27-28 g / L. In this invention, the nickel-phosphorus plating solution preferably comprises sodium malate 16-20 g / L, more preferably 17-19 g / L, and even more preferably 18 g / L. In this invention, the nickel-phosphorus plating solution preferably comprises 12-15 g / L sodium acetate, more preferably 13-14 g / L. In this invention, the nickel-phosphorus plating solution preferably comprises 12-14 g / L sodium lactate, more preferably 12.5-13.5 g / L, and more preferably 13 g / L. In this invention, the nickel-phosphorus plating solution preferably comprises the following components at the following concentrations: 35 g / L nickel sulfate, 25 g / L sodium hypophosphite, 16 g / L sodium malate, 12 g / L sodium acetate, and 12 g / L sodium lactate. In this invention, the preparation method of the nickel-phosphorus plating solution preferably comprises the following steps: adding nickel sulfate, sodium malate, sodium acetate, sodium lactate, and sodium hypophosphite sequentially to a solvent and stirring thoroughly; adjusting the pH value to 4.4-4.6 with acetic acid to obtain the nickel-phosphorus plating solution.

[0052] In this invention, the thickness of the nickel-phosphorus coating is preferably 3 to 4 μm, and the thickness of the nickel-phosphorus diamond coating is preferably 14 μm.

[0053] In this invention, the heat treatment temperature is preferably 170-200°C, the atmosphere is preferably argon, and the time is preferably 1-1.5 hours.

[0054] In this invention, the preparation methods of the nickel-phosphorus coating and the nickel-phosphorus diamond coating are preferably described in the subsequent section on the protection methods of metal substrates, and will not be repeated here.

[0055] The present invention also provides a method for protecting a metal substrate, comprising the following steps:

[0056] Prepare composite coatings on metal substrates;

[0057] The composite coating is the composite coating described in the above technical solution;

[0058] The nickel-phosphorus coating in the composite coating is in contact with the metal substrate.

[0059] In this invention, the metal substrate preferably includes steel.

[0060] In this invention, before preparing the composite coating on the metal substrate, it is preferable to pretreat the metal substrate. The pretreatment preferably includes, sequentially, sandblasting, rinsing with clean water, degreasing, water washing, acid pickling activation, rinsing with clean water, alcohol rinsing, and drying. In this invention, the sandblasting time is preferably 10 minutes. In this invention, the degreasing agent is preferably a degreasing agent, preferably including one or more of a soda ash solution and a caustic soda solution. The concentration of the soda ash solution is preferably 40%–50%, and the concentration of the caustic soda solution is preferably 30%–40%. The degreasing temperature is preferably 50–60°C, and the time is preferably 30 minutes. In this invention, the acid pickling activation agent is preferably 5% sulfuric acid (by volume), and the acid pickling time is preferably 1–2 minutes.

[0061] In this invention, the plating parameters of the nickel-phosphorus coating include: a temperature preferably of 80-90°C and a time preferably of 15 minutes.

[0062] In this invention, the plating parameters of the nickel-phosphorus diamond coating include: a temperature preferably of 80-85°C, a time preferably of 70 minutes, and the plating of the nickel-phosphorus diamond coating is preferably carried out under bubbling conditions.

[0063] The following detailed description, in conjunction with embodiments, of the nickel-phosphorus diamond plating solution, composite coating, and protective method for metal substrates provided by the present invention, should not be construed as limiting the scope of protection of the present invention.

[0064] Comparative Example 1

[0065] Preparation of Ni-P plating solution: Add 35g / L nickel sulfate, 25g / L sodium hypophosphite, 16g / L sodium malate, 12g / L sodium acetate, and 12g / L sodium lactate to water and stir thoroughly. Adjust the pH value to 4.6 with acetic acid.

[0066] The workpiece to be plated is pretreated as follows: First, the workpiece is sandblasted for 10 minutes. After sandblasting, the workpiece is rinsed with clean water. Then, it is placed in a heated 40% sodium hydroxide aqueous solution at 50°C for 30 minutes to remove oil. Then, it is washed with water and acid-washed in 5% sulfuric acid for 2 minutes. Then, it is washed with water and rinsed with alcohol. Finally, it is dried and ready for use.

[0067] The pretreated workpiece is placed in the Ni-P plating solution and pre-plated at 80°C for 15 minutes.

[0068] Place the pre-plated workpiece into a heating furnace and bake at 200°C for 1 hour.

[0069] Example 1

[0070] Diamond particles are pretreated before use. The pretreatment includes: immersing the diamond particles in a 50wt% NaOH solution at 50℃ for 30 minutes, washing with water until neutral, and then drying to obtain alkali-treated diamond particles; then soaking the alkali-treated diamond particles in 50wt% sulfuric acid for 10 minutes, washing with water until neutral, and then drying for later use.

[0071] Preparation of Ni-P plating solution: Add 35 g / L nickel sulfate, 25 g / L sodium hypophosphite, 16 g / L sodium malate, 12 g / L sodium acetate, and 12 g / L sodium lactate to water and stir thoroughly. Adjust the pH to 4.6 with acetic acid.

[0072] Preparation of Ni-P diamond plating solution: 35 g / L nickel sulfate, 25 g / L sodium hypophosphite, 16 g / L sodium malate, 12 g / L sodium acetate, 12 g / L sodium lactate, 20 mg / L sodium dodecyl sulfate, 10 mg / L polyoxyethylene-dodecyl ether sulfate, 20 mg / L hexadecyltrimethylammonium bromide, 5 mg / L potassium iodate, 0.1 g / L diamond particles (particle size 3.5 μm), and acetic acid to adjust the pH to 4.6.

[0073] The workpiece to be plated is pretreated as follows: First, the workpiece is sandblasted for 10 minutes. After sandblasting, the workpiece is rinsed with clean water. Then, it is placed in a heated 40% sodium hydroxide aqueous solution at 50°C for 30 minutes to remove oil. Then, it is washed with water and acid-washed in 5% sulfuric acid for 2 minutes. Then, it is washed with water and rinsed with alcohol. Finally, it is dried and ready for use.

[0074] The pretreated workpiece is placed in the Ni-P plating solution and pre-plated at 80°C for 15 minutes.

[0075] After pre-plating, the workpiece is placed in Ni-P diamond plating solution and plated for 75 minutes at 80°C under bubbling conditions.

[0076] The plated workpiece is placed in a heating furnace and baked at 200°C for 1 hour.

[0077] Example 2

[0078] The difference from Example 1 is that the concentration of diamond particles in the Ni-P diamond plating solution is 0.2 g / L.

[0079] Example 3

[0080] The difference from Example 1 is that the concentration of diamond particles in the Ni-P diamond plating solution is 0.3 g / L.

[0081] Example 4

[0082] The difference from Example 1 is that the concentration of diamond particles in the Ni-P diamond plating solution is 0.4 g / L.

[0083] Example 5

[0084] The difference from Example 3 is that the particle size of the diamond particles in the Ni-P diamond plating solution is 1 μm.

[0085] Example 6

[0086] The difference from Example 3 is that the diamond particles in the Ni-P diamond plating solution have a particle size of 7 μm.

[0087] Example 7

[0088] The difference from Example 3 is that the diamond particles in the Ni-P diamond plating solution have a particle size of 14 μm.

[0089] Example 8

[0090] The difference from Example 3 is that the particle size of the diamond particles in the Ni-P diamond plating solution is 28 μm.

[0091] Comparative Example 2

[0092] The difference from Example 1 is that sodium dodecyl sulfate in the nickel-phosphorus diamond plating solution is omitted.

[0093] Comparative Example 3

[0094] The difference from Example 1 is that hexadecyltrimethylammonium bromide in the nickel-phosphorus diamond plating solution is omitted.

[0095] Comparative Example 4

[0096] The difference from Example 1 is that sodium polyoxyethylene dodecyl ether sulfate in the nickel-phosphorus diamond plating solution is omitted.

[0097] Comparative Example 5

[0098] The difference from Example 1 is that sodium dodecyl sulfate in the nickel-phosphorus diamond plating solution is replaced with 2-mercaptobenzimidazole.

[0099] Comparative Example 6

[0100] The difference from Example 1 is that the cetyltrimethylammonium bromide in the nickel-phosphorus diamond plating solution is replaced with 2-mercaptobenzimidazole.

[0101] Comparative Example 7

[0102] The difference from Example 1 is that the sodium polyoxyethylene dodecyl ether sulfate in the nickel-phosphorus diamond plating solution is replaced with 2-mercaptobenzimidazole.

[0103] The composite coatings obtained in the examples and comparative examples were subjected to friction and wear tests on a CSM friction and wear testing machine in Switzerland. The load was 15 N, the frequency was 2 Hz, and the time was 30 minutes. The test standards were DIN 50324 and ASTM G99. The results are shown in Table 1.

[0104] Table 1. Tribological and wear test results of the composite coatings obtained in the examples and comparative examples.

[0105] Serial Number Diamond content (g / L) Diamond particle size (micrometers) Wear volume (millimeters) Comparative Example 1 0 - 0.02679 Example 1 0.1 3.5 0.01481 Example 2 0.2 3.5 0.01205 Example 3 0.3 3.5 0.00919 Example 4 0.4 3.5 0.02168 Example 5 0.3 1 0.02315 Example 6 0.3 7 0.04322 Example 7 0.3 14 0.03073 Example 8 0.3 28 0.03318 Comparative Example 2 0.3 3.5 0.04184 Comparative Example 3 0.3 3.5 0.03753 Comparative Example 4 0.3 3.5 0.0249 Comparative Example 5 0.3 3.5 0.0535 Comparative Example 6 0.3 3.5 0.04632 Comparative Example 7 0.3 3.5 0.03995

[0106] As shown in Table 1, under a load of 15N, the introduction of unsuitable diamonds (including the particle size and concentration of diamond particles in the plating solution) not only fails to enhance the wear resistance of the Ni-P coating, but also causes diamonds that are easily detached from the Ni-P coating to become trapped within it, becoming a source of damage to the integrity of the Ni-P coating. Example 3 was selected for formulation, and by adding appropriate diamond particle content and size, the bonding force between diamond and the Ni-P coating was improved. This invention provides a basis for the composite coating to operate under high-load friction conditions.

[0107] The corrosion resistance of the obtained composite coating was tested by electrochemical methods, and the hardness of the obtained composite coating was tested by a hardness tester. The results are shown in Table 2.

[0108] Table 2. Test results of corrosion resistance and hardness of the composite coatings obtained in the examples and comparative examples.

[0109]

[0110] Table 2 shows that corrosion potential indicates the tendency of corrosion to occur; a more positive corrosion potential indicates a lower tendency for corrosion to occur, and a higher corrosion current density indicates a higher corrosion rate. The composite coating prepared by adding 3.5-micron diamond showed improved corrosion resistance. The combined use of sodium dodecyl sulfate, polyoxyethylene-dodecyl ether sulfate, and hexadecyltrimethylammonium bromide improved the surface smoothness and diamond dispersion of the coating. Therefore, Example 3 was selected for formulation, resulting in the coating with the best corrosion resistance.

[0111] Figure 1 The image shows the SEM spectrum of the composite coating obtained in Example 3. Figure 1 It can be seen that the diamond particles on the surface of the composite coating are distinct and evenly distributed. Most of the diamonds exposed outside the Ni-P layer have a high embedding rate and are wrapped by the Ni layer, and the diamonds are firmly bonded to the Ni layer.

[0112] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A nickel-phosphorus diamond plating solution, characterized by, The components include the following concentrations: ​ Nickel sulfate 35~40g / L, sodium hypophosphite 25~30g / L, sodium malate 16~20g / L, sodium acetate 12~15g / L, sodium lactate 12~14g / L, sodium dodecyl sulfate 10~50mg / L, hexadecyltrimethylammonium bromide 10~50mg / L, polyoxyethylene dodecyl ether sulfate sodium 10~30mg / L, potassium iodate 5~10mg / L, diamond particles 0.1~0.4g / L; The diamond particles have a particle size of 3.5 μm.

2. The nickel-phosphorus diamond plating solution according to claim 1, wherein, The components include the following concentrations: Nickel sulfate 35 g / L, sodium hypophosphite 25 g / L, sodium malate 16 g / L, sodium acetate 12 g / L, sodium lactate 12 g / L, sodium dodecyl sulfate 20 mg / L, hexadecyltrimethylammonium bromide 20 mg / L, polyoxyethylene dodecyl ether sulfate 10 mg / L, potassium iodate 5 mg / L, diamond particles 0.1~0.4 g / L.

3. The nickel-phosphorus diamond plating solution according to claim 1 or 2, characterized in that, The pH value of the nickel-phosphorus diamond plating solution is 4.4~4.

6.

4. A composite coating, characterized in that, The coating is obtained by heat treatment of a nickel-phosphorus plating layer and a nickel-phosphorus diamond plating layer stacked in sequence; the nickel-phosphorus diamond plating layer is obtained by plating with the nickel-phosphorus diamond plating solution according to any one of claims 1 to 3.

5. The composite coating according to claim 4, characterized in that, The nickel-phosphorus plating layer is obtained by plating with a nickel-phosphorus plating solution; the nickel-phosphorus plating solution comprises the following components at the following concentrations: Nickel sulfate 35~40g / L, sodium hypophosphite 25~30g / L, sodium malate 16~20g / L, sodium acetate 12~15g / L, sodium lactate 12~14g / L.

6. The composite coating according to claim 4, characterized in that, The thickness of the nickel-phosphorus coating is 3~4μm, and the thickness of the nickel-phosphorus diamond coating is 14~16μm.

7. The composite coating according to claim 4, characterized in that, The heat treatment is performed at a temperature of 170℃ to 200℃, in an argon atmosphere, for a time of 1 to 1.5 hours.

8. A method for protecting a metal substrate, characterized in that, Includes the following steps: Prepare composite coatings on metal substrates; The composite coating is the composite coating described in any one of claims 4 to 7; The nickel-phosphorus coating in the composite coating is in contact with the metal substrate.

9. The protection method according to claim 8, characterized in that, The metal substrate is steel.

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