Anti-wear and anti-friction gradient nanostructure Ni coating and preparation method thereof

Abstract

The invention provides an anti-wear and anti-friction gradient nanostructure Ni coating which comprises a coating a with the grain size of 430-530 nm, an amorphous belt layer a, a coating b with the grain size of 100-140 nm, an amorphous belt layer b and a coating c with the grain size of 27-33 nm which are sequentially arranged on a metal base material from inside to outside. The thickness ratio of the plating layer a to the plating layer b to the plating layer c to the amorphous ribbon layer a to the amorphous ribbon layer b is (10-10.5) [mu] m to (8.5-9) [mu] m to (1.45-1.65) [mu] m to (30-40) nm to (3-5) nm; the content of nickel in the plating layer a, the plating layer b, the plating layer c, the amorphous ribbon layer a and the amorphous ribbon layer b is not less than 99.9 at%. Meanwhile, the invention further discloses a preparation method of the anti-wear and anti-friction gradient nanostructure Ni coating. The plating layer is the gradient nanometer Ni plating layer with the grain size in the gradient change trend from inside to outside, the amorphous zone layer exists between the plating layers with different grain sizes, the hardness value of the gradient nanometer metal Ni plating layer is higher, the friction coefficient and the wear rate are lower, and the gradient nanometer metal Ni plating layer has excellent wear resistance and friction reduction performance.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material surface protection, and particularly relates to an anti-wear and friction-reducing gradient nanostructured Ni plating layer and a preparation method thereof. Background Art

[0002] For a long time, friction and wear failure of metal surfaces has been a key factor affecting their mechanical properties and service life. Modifying or strengthening the metal surface through surface treatment technology is one of the effective methods to improve the overall wear resistance of the material, extend its service life and reduce production costs. Among them, Ni coating is not only suitable for protective decoration, but is also commonly used to repair important workpieces such as bearings. It is widely used in electronics, chemical industry, machinery, food and medical fields. In particular, in electroplating industrial production, the production volume of Ni coating ranks second only to Zn coating. Therefore, it is of great significance to develop a highly wear-resistant and friction-reducing Ni coating.

[0003] In recent years, surface nano-metallurgy has attracted much attention in surface protection. However, general nano-metal coatings are prone to surface coarsening and cracking during sliding friction due to their very limited plasticity, resulting in a coating wear rate much higher than Archard's expected value. The core idea of traditional anti-friction and anti-wear materials is to reduce the shear stress at the friction interface by adding lubricants and preparing anti-friction coatings. However, it is usually difficult to improve the friction coefficient and wear rate of metal materials through simple structural regulation. Studies have shown that one of the most promising mitigation strategies is the development of gradient nanostructured metals. By controlling the gradient distribution of spatial grain size to promote heterogeneous deformation modes, the high strength of the coating surface and the overall plastic deformation are further improved, which is expected to fundamentally improve the tribological properties of traditional metal coatings.

[0004] Currently, the main methods for preparing gradient nanostructured coatings include large surface plastic deformation (such as surface mechanical grinding and high-pressure torsion) and physical or chemical deposition (such as sputtering deposition and CVD). Large surface plastic deformation not only introduces numerous defects and makes the gradient structure difficult to control, but also alters the workpiece shape, making it difficult to apply to critical components requiring high precision and hardness. Physical or chemical deposition, on the other hand, has the disadvantages of complex equipment operation and high production costs. Therefore, there is an urgent need to develop methods for preparing gradient nanostructured metal coatings that require simple equipment, low energy consumption, ease of operation, and low cost. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and provide a wear-resistant and friction-reducing gradient nanostructured Ni coating. The grain size of the coating shows a gradient change trend from the inside to the outside, and there is also an amorphous band layer between the coatings of different grain sizes. The gradient nanometal Ni coating has a higher hardness value, a lower friction coefficient and wear rate, and thus has excellent wear-resistant and friction-reducing properties.

[0006] To solve the above technical problems, the present invention adopts a technical solution: an anti-wear and friction-reducing gradient nanostructured Ni coating, comprising a coating a with a grain size of 430-530 nm, an amorphous strip layer a, a coating b with a grain size of 100-140 nm, an amorphous strip layer b, and a coating c with a grain size of 27-33 nm, which are sequentially arranged on a metal substrate from the inside to the outside. The thickness ratio of the coating a, the coating b, the coating c, the amorphous strip layer a, and the amorphous strip layer b is (10-10.5) μm: (8.5-9) μm: (1.45-1.65) μm: (30-40) nm: (3-5) nm; and the nickel content of the coating a, the coating b, the coating c, the amorphous strip layer a, and the amorphous strip layer b is not less than 99.9 at %.

[0007] The present invention also discloses a method for preparing the anti-wear and friction-reducing gradient nanostructured Ni coating according to claim 1, the method comprising: S1, prepare electroplating solution a and electroplating solution b; S2. Using nickel as the anode and the metal substrate as the cathode, the anode and the cathode are placed in the electroplating solution a, and direct current electrodeposition is first used to prepare a coating a on the metal substrate. Then, pulse electrodeposition is continued in the electroplating solution a to first prepare an amorphous ribbon layer a on the coating a, and then prepare a coating b. Finally, pulse electrodeposition is continued in the electroplating solution b to first prepare an amorphous ribbon layer b on the coating b, and then prepare a coating c, and finally a gradient nanostructured Ni coating is obtained on the metal substrate.

[0008] Preferably, the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, wherein the concentration of nickel sulfate hexahydrate in the electroplating solution a is 1.57-1.63 mol / L, the concentration of nickel chloride is 0.11-0.12 mol / L; the concentration of boric acid is 0.047-0.05 mol / L; the electroplating solution b is prepared by adding saccharin to the electroplating solution a, wherein the concentration of saccharin in the electroplating solution b is 4.8-5.2 g / L.

[0009] Preferably, when the coating layer a is plated by direct current electrodeposition, the current is 0.1-0.2A and the time is 40min; When the amorphous ribbon layer a and the coating layer b are plated by pulse electrodeposition, the current is set to 0.09-0.11 A, the power supply parameters are on-time 0.5 ms, off-time 0.5 ms, pulse current power supply working time 1 ms, and plating time 20 min; When pulse electrodeposition is used to plate the amorphous ribbon layer b and the coating layer c, the current is set to 0.09-0.11 A, the power supply parameters are on-time 0.3 ms, off-time 0.7 ms, pulse current power supply working time 1 ms, and plating time 5 min.

[0010] Preferably, when pulse electrodeposition plating is adopted, the temperature of plating solution a or plating solution b is controlled to be 48-52° C., and the stirring rate is 490-510 r / min.

[0011] Preferably, the metal substrate further includes a pretreatment before being placed in the electroplating solution a, and the pretreatment is: grinding the base Cu sheet with metallographic sandpaper to a mirror surface, then placing the base Cu sheet in a 10% volume fraction of hydrochloric acid, ultrasonically cleaning for 2 minutes, and then rinsing with distilled water, then placing the base Cu sheet in a 2% volume fraction of NaOH solution, ultrasonically cleaning for 2 minutes, and then rinsing with distilled water, and drying for use.

[0012] Compared with the prior art, the present invention has the following advantages: 1. The present invention provides an anti-wear and friction-reducing gradient nanostructured Ni coating, comprising a coating a having a grain size of 430-530 nm, an amorphous band layer a, a coating b having a grain size of 100-140 nm, an amorphous band layer b, and a coating c having a grain size of 27-33 nm, which are sequentially disposed on a metal substrate from the inside out, wherein the thickness ratio of the coating a, the coating b, the coating c, the amorphous band layer a, and the amorphous band layer b is (10-10.5) μm: (8.5-9) μm: (1.45-1.65) μm: (30-40) nm: (3-5) nm. Compared with a homogeneous nanometal Ni coating, the gradient nanometal Ni coating has a gradient grain size from the inside out, and an amorphous band layer is present between the coating layers of different grain sizes. The gradient nanometal Ni coating has a higher hardness, a lower friction coefficient, and a lower wear rate, thus having excellent anti-wear and friction-reducing properties.

[0013] 2. The present invention adopts the electroplating technology combining pulse current and direct current. By accurately controlling the process parameters such as the plating solution composition, current form and deposition time, a gradient nano-Ni plating layer with a grain size gradient from the inside to the outside can be prepared in the Ni plating layer, and an amorphous band layer exists between the plating layers with different grain sizes. Direct current electrodeposition is the most common and earliest method used to prepare nickel coatings. The coatings prepared by this method have a bright surface, uniform structure and good performance. However, the grain size of the coatings prepared by direct current electrodeposition is large. Therefore, the present invention adopts direct current electrodeposition to prepare the inner layer of large-grain-size coating. Compared with direct current electrodeposition, pulse electrodeposition has a higher deposition rate, and the grains of the nickel-based composite coating prepared are finer and the surface is denser. Therefore, the present invention adopts pulse current electrodeposition to prepare the intermediate layer coating. Since very high internal stress is generated during the electrodeposition process, adding saccharin sodium to the solution can alleviate the internal stress. In addition, saccharin sodium will be adsorbed on the electrode surface during the electrodeposition process, preventing the discharge of metal ions, causing the metal deposition potential to shift negatively, balancing the growth rate of the crystals, and helping to form a finer and more regular grain morphology. Therefore, the present invention adopts pulse current electrodeposition and adds saccharin sodium to the plating solution to prepare the outermost layer of small-grain-size coating. Compared to traditional pulsed or direct current (DC) electrodeposition techniques, the present invention's combined pulsed and DC electroplating technology overcomes the drawback of DC electrodeposition, resulting in coarse coatings. It simultaneously combines the simplicity and economy of DC electrodeposition with the high-quality coatings of pulsed electrodeposition, paving the way for the successful preparation of gradient nanostructured Ni coatings with high wear resistance and friction reduction. Its process compatibility is robust and economically feasible. The present invention achieves strain-induced localized amorphization in Ni metal by regulating the grain size within a certain gradient. Due to its poor amorphous-forming ability, amorphization of single-element metals is very difficult. Current research has shown that high stress can induce a phase transition from crystalline to amorphous. It is known that when larger and smaller grains are adjacent in the same material, localized stress concentrations may occur at the grain boundaries due to factors such as uneven strain distribution and restricted dislocation movement. Therefore, by regulating the size gradient between the coating layers, high stress-induced amorphization can be generated at the layer interfaces. However, precisely controlling the gradient and generating high stress remains a research challenge. The 480±50nm / 120±20nm / 30±3nm grain size gradient nano-Ni plating structure designed in this invention successfully induces stress amorphization at the interface and improves the subsurface strength by regulating dislocation dynamics, effectively improving the comprehensive performance of Ni metal under sliding friction conditions, showing broad application potential.

[0014] Compared to methods such as adding lubricants or alloying, electrodepositing gradient nanostructured Ni coatings has the advantages of simple operation, minimal dimensional change, ease of implementation, low cost, and wide applicability. Furthermore, the electroplating solution used in the present invention is easy to prepare, poses minimal environmental risk, and meets environmental protection requirements. Compared to alloy coatings, the gradient nanostructured pure Ni coating of the present invention has a single composition, does not produce internal metallographic segregation and phase transitions, and has excellent overall performance.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 TEM images of each layer of the gradient nanostructured Ni coating prepared in Example 1.

[0017] Figure 2 These are the cross-sectional SEM, TEM and HRTEM images of the gradient nanostructured Ni coating prepared in Example 1.

[0018] Figure 3 The hardness of the uniform elemental Ni coatings with grain sizes of 480±50 nm, 120±20 nm and 30±3 nm prepared in Comparative Examples 1-3 and the gradient nanostructured Ni coating prepared in Example 1 was measured by nanoindentation.

[0019] Figure 4 The friction coefficient and wear rate test results of the uniform elemental Ni coatings with grain sizes of 480±50nm, 120±20nm and 30±3nm prepared in Comparative Examples 1-3 and the gradient nanostructured Ni coating prepared in Example 1 were rubbed at room temperature for 20 min under a load of 5 N and a rotation speed of 100 r / min using a ball-disc rotating module.

[0020] Figure 5 The wear scar morphologies of the uniform single-element Ni coatings with grain sizes of 480±50 nm, 120±20 nm and 30±3 nm prepared in Comparative Examples 1-3 and the gradient nanostructured Ni coating prepared in Example 1 are shown. DETAILED DESCRIPTION

[0021] Example 1 This embodiment discloses a method for preparing an anti-wear and friction-reducing gradient nanostructured Ni plating layer, the method comprising: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0022] S2. Prepare electroplating solution a and electroplating solution b; the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, the concentration of nickel sulfate hexahydrate in electroplating solution a is 1.6 mol / L, the concentration of nickel chloride is 0.11 mol / L, and the concentration of boric acid is 0.048 mol / L; the electroplating solution b is prepared by adding saccharin to electroplating solution a, wherein the concentration of saccharin in electroplating solution b is 5 g / L.

[0023] S3. Using nickel as the anode and the metal substrate as the cathode, the anode and the cathode are placed in the electroplating solution a. First, direct current electrodeposition is used for plating, with a current of 0.1A and a time of 40min to prepare a coating a on the metal substrate. Then, pulse electrodeposition is used in the electroplating solution a, with a current of 0.1A, power supply parameters of on-time 0.5 ms, off-time 0.5 ms, pulse current power supply working time 1 ms, and plating time 20min. First, an amorphous ribbon layer a is prepared on the coating a, and then a coating b is prepared. Finally, pulse electrodeposition is used in the electroplating solution b, with a current of 0.1A, power supply parameters of on-time 0.3 ms, off-time 0.7 ms, pulse current power supply working time 1 ms, and plating time 5min. First, an amorphous ribbon layer b is prepared on the coating b, and then a coating c is prepared. Finally, a gradient nanostructured Ni coating is obtained on the metal substrate.

[0024] In this embodiment, the thickness of coating layer a is 10.35 μm, the thickness of coating layer b is 8.8 μm, the thickness of coating layer c is 1.55 μm, the thickness of amorphous ribbon layer a is 35 nm, and the thickness of amorphous ribbon layer b is 4 nm. The thickness of the prepared gradient nanostructured Ni coating is approximately 20.7 μm. The nickel content of coating layer a, coating layer b, coating layer c, amorphous ribbon layer a, and amorphous ribbon layer b is not less than 99.9 at%.

[0025] In this embodiment, when pulse electrodeposition plating is adopted, the temperature of plating solution a or plating solution b is controlled to be 50° C., and the stirring rate is 500 r / min.

[0026] Figure 1 TEM images of each layer of the gradient nanostructured Ni coating prepared in Example 1. The grain size distribution of each layer from the outermost layer to the innermost layer close to the substrate surface is as follows: Figure 1 (a) Figure 1 (b) Figure 1 (c), the grain size of coating c is 30±3 nm, the grain size of coating b is 120±20 nm, and the grain size of coating a is 480±50 nm.

[0027] Figure 2 The cross-sectional SEM, TEM, and HRTEM images of the gradient nanostructured Ni coating prepared in Example 1 show the change in grain size from large to small, demonstrating a gradient structure. As shown in the figure, a bright white stripe was observed at the interface of the coating layers with different grain sizes. The thickness of the two white stripes between the 480±50 nm and 120±20 nm coating layers was approximately 35 nm, and the thickness of the white stripe between the 120±20 nm and 30±3 nm coating layers was approximately 4 nm. Figure 1(a) and (b) are shown in red boxes. Further Fourier transform analysis of the white bright band revealed that the white bright band is different from the diffraction spots or diffraction rings of the crystal structure of pure Ni ( Figure 2 (c) and (d) green box illustrations), the white bright strip at the interface shows a typical amorphous halo ( Figure 2 (c) and (d) (yellow box insets) demonstrate that the atomic arrangement at the interface is relatively disordered, and the bright white stripes are amorphous. It should be noted that amorphization generally occurs in binary or ternary alloys, while the gradient nano-Ni coating is composed of pure Ni. Amorphization occurs for the following reasons: First, lattice mismatch. When there is a significant difference in grain size, microscopic strain may accumulate at the interface. This strain, arising from the sudden change in grain size, impairs local structural stability and induces an amorphous transition. Second, due to the accumulation of plastic deformation, dislocation movement is restricted at the interface between larger grains and finer grains, resulting in asymmetric plastic flow on both sides of the interface. The accumulated stress causes the local structure to enter a highly distorted state. High stress and the strong lattice and grain boundary resistance to dislocations trigger a large accumulation of dislocations, leading to solid-state amorphization. However, the grain size difference should not be too large. If the grain size difference is too large, the stress distribution at the interface and between grains will be uneven. Locally excessive stress may lead to plastic deformation or brittle fracture, affecting the overall performance of the material.

[0028] Example 2 This embodiment discloses a method for preparing an anti-wear and friction-reducing gradient nanostructured Ni plating layer, the method comprising: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0029] S2. Prepare electroplating solution a and electroplating solution b; the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, the concentration of nickel sulfate hexahydrate in electroplating solution a is 1.57 mol / L, the concentration of nickel chloride is 0.11 mol / L, and the concentration of boric acid is 0.047 mol / L; the electroplating solution b is prepared by adding saccharin to electroplating solution a, wherein the concentration of saccharin in electroplating solution b is 4.8 g / L.

[0030] S3. Using nickel as the anode and the metal substrate as the cathode, the anode and the cathode are placed in the electroplating solution a. First, direct current electrodeposition is used for plating, with a current of 0.1A and a time of 40min to prepare a coating a on the metal substrate. Then, pulse electrodeposition is used in the electroplating solution a, with a current of 0.09A, power supply parameters of on-time 0.5ms, off-time 0.5ms, pulse current power supply working time 1ms, and plating time 20min. First, an amorphous ribbon layer a is prepared on the coating a, and then a coating b is prepared. Finally, pulse electrodeposition is used in the electroplating solution b, with a current of 0.09A, power supply parameters of on-time 0.3ms, off-time 0.7ms, pulse current power supply working time 1ms, and plating time 5min. First, an amorphous ribbon layer b is prepared on the coating b, and then a coating c is prepared. Finally, a gradient nanostructured Ni coating is obtained on the metal substrate.

[0031] In this embodiment, when pulse electrodeposition plating is adopted, the temperature of plating solution a or plating solution b is controlled to be 48° C., and the stirring rate is 490 r / min.

[0032] In this embodiment, the thicknesses of the coating a, coating b, coating c, amorphous ribbon layer a, and amorphous ribbon layer b are 10 μm, 8.5 μm, 1.45 μm, 30 nm, and 3 nm, respectively; the nickel content in the coating a, coating b, coating c, amorphous ribbon layer a, and amorphous ribbon layer b is not less than 99.9 at%.

[0033] Example 3 This embodiment discloses a method for preparing an anti-wear and friction-reducing gradient nanostructured Ni plating layer, the method comprising: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0034] S2. Prepare electroplating solution a and electroplating solution b; the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, the concentration of nickel sulfate hexahydrate in electroplating solution a is 1.63 mol / L, the concentration of nickel chloride is 0.12 mol / L, and the concentration of boric acid is 0.05 mol / L; the electroplating solution b is prepared by adding saccharin to electroplating solution a, wherein the concentration of saccharin in electroplating solution b is 5.2 g / L.

[0035] S3. Use nickel as the anode and the metal substrate as the cathode, place the anode and the cathode in the electroplating solution a, first use direct current electrodeposition for plating, the current is 0.2A, the time is 40min, and a coating a is prepared on the metal substrate, then continue to use pulse electrodeposition in the electroplating solution a, set the current to 0.11A, the power supply parameters are on-time 0.5 ms, off-time 0.5 ms, pulse current power supply working time 1 ms, and plating time 20min; first prepare an amorphous ribbon layer a on the coating a, and then prepare the coating b, finally continue to use pulse electrodeposition in the electroplating solution b, set the current to 0.11 A, the power supply parameters are on-time 0.3 ms, off-time 0.7 ms, pulse current power supply working time 1 ms, and plating time 5min, first prepare an amorphous ribbon layer b on the coating b, and then prepare the coating c, and finally obtain a gradient nanostructured Ni coating on the metal substrate.

[0036] In this embodiment, when pulse electrodeposition plating is adopted, the temperature of plating solution a or plating solution b is controlled to be 52° C., and the stirring rate is 510 r / min.

[0037] In this embodiment, the thicknesses of the coating a, coating b, coating c, amorphous ribbon layer a, and amorphous ribbon layer b are 10.5 μm, 9 μm, 1.65 μm, 40 nm, and 5 nm, respectively; the nickel content in the coating a, coating b, coating c, amorphous ribbon layer a, and amorphous ribbon layer b is not less than 99.9 at%.

[0038] The hardness and wear rate of the gradient nanostructured Ni coatings prepared in Examples 1 to 3 are shown in Table 1.

[0039] Table 1 Hardness and wear rate of gradient nanostructured Ni coatings prepared in Examples 1-3 Comparative Example 1 This comparative example discloses a method for preparing a homogeneous Ni plating layer a1, which comprises: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0040] S2. Prepare electroplating solution a; the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, wherein the concentration of nickel sulfate hexahydrate in the electroplating solution a is 1.6 mol / L, the concentration of nickel chloride is 0.11 mol / L; and the concentration of boric acid is 0.048 mol / L.

[0041] S3. Using nickel as the anode and the metal substrate as the cathode, the anode and cathode are placed in the electroplating solution a. Direct current electrodeposition is first used for plating with a current of 0.1 A and a time of 80 min to prepare a homogeneous Ni plating layer a1 on the metal substrate.

[0042] In this comparative example, the electroplating method of the Ni plating layer a1 is the same as that of the plating layer a in the embodiment, except that the DC deposition time is extended. The grain size of the Ni plating layer a1 is the same as that of the plating layer a, and the thickness is about 20.7 μm, which is the same as the gradient nanostructured Ni plating prepared in Example 1.

[0043] Comparative Example 2 This comparative example discloses a method for preparing a homogeneous Ni plating layer b1, which comprises: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0044] S2. Prepare electroplating solution a and electroplating solution b; the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, the concentration of nickel sulfate hexahydrate in electroplating solution a is 1.6 mol / L, the concentration of nickel chloride is 0.11 mol / L, and the concentration of boric acid is 0.048 mol / L; the electroplating solution b is prepared by adding saccharin to electroplating solution a, wherein the concentration of saccharin in electroplating solution b is 5 g / L.

[0045] S3. Use nickel as the anode and the metal substrate as the cathode. Place the anode and cathode in the electroplating solution a and use pulse electrodeposition for plating. Set the current to 0.11 A, the power supply parameters to on-time 0.5 ms, off-time 0.5 ms, pulse current power supply working time 1 ms, and plating time 50 min. Prepare a homogeneous Ni plating layer b1 on the substrate Cu sheet.

[0046] In this comparative example, the electroplating method of the homogeneous Ni coating b1 is the same as that of the coating b in the embodiment, except that the pulse electrodeposition time is extended. The grain size of the Ni coating b1 is the same as that of the coating b, and the thickness is about 20.7 μm, which is the same as the gradient nanostructured Ni coating prepared in Example 1.

[0047] When pulse electrodeposition plating is adopted, the temperature of the plating solution a is controlled at 50° C. and the stirring rate is 500 r / min.

[0048] Comparative Example 3 This comparative example discloses a method for preparing a homogeneous Ni plating layer c1, which comprises: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0049] S2. Prepare electroplating solution b; the electroplating solution b is prepared by adding saccharin to electroplating solution a, wherein the concentration of saccharin in electroplating solution b is 5 g / L; the electroplating solution a is prepared by nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, wherein the concentration of nickel sulfate hexahydrate in electroplating solution a is 1.6 mol / L, the concentration of nickel chloride is 0.11 mol / L; and the concentration of boric acid is 0.048 mol / L; S3. Use nickel as the anode and the metal substrate as the cathode. Place the anode and cathode in the electroplating solution b. Continue to use pulse electrodeposition to plate the substrate Cu sheet in the electroplating solution b. Set the current to 0.1 A, the power supply parameters to on-time 0.3 ms, off-time 0.7 ms, pulse current power supply working time 1 ms, and plating time 70 min to prepare a homogeneous Ni plating layer c1 with a grain size of 27-33 nm.

[0050] In this comparative example, the thickness of the Ni plating layer c1 is about 20.7 μm, which is the same as that of the gradient nanostructured Ni plating layer prepared in Example 1.

[0051] In this comparative example, the electroplating method of the homogeneous Ni coating c1 is the same as that of the coating c in the embodiment, except that the pulse electrodeposition time is extended. The grain size of the Ni coating c1 is the same as that of the coating c, and the thickness is about 20.7 μm, which is the same as the gradient nanostructured Ni coating prepared in Example 1.

[0052] In this comparative example, when pulse electrodeposition plating is adopted, the temperature of the plating solution b is controlled to be 50° C. and the stirring rate is 500 r / min.

[0053] Figure 3 The hardness of the uniform elemental Ni coatings with grain sizes of 480±50 nm, 120±20 nm, and 30±3 nm prepared in Comparative Examples 1-3, respectively, and the gradient nanostructured Ni coating prepared in Example 1 was measured using nanoindentation. The hardness of the gradient nanostructured Ni coating was 4.734 GPa, while the hardness of the uniform elemental Ni coatings with grain sizes of 480±50 nm, 120±20 nm, and 30±3 nm were 1.32 GPa, 3.18 GPa, and 3.80 GPa, respectively. The hardness of the gradient nanostructured Ni coating was increased by 258.3%, 48.7%, and 23.0%, respectively, compared to the three homogeneous nanostructured Ni coatings.

[0054] Figure 4 The friction coefficient and wear rate of the uniform elemental Ni coatings with grain sizes of 480±50nm, 120±20nm, and 30±3nm prepared in Comparative Examples 1-3, respectively, and the gradient nanostructured Ni coating prepared in Example 1 were tested using a ball-disc rotating module. The friction coefficient and wear rate were tested at room temperature for 20 minutes under a load of 5 N and a rotation speed of 100 r / min. In the stable friction stage, the friction coefficient of the gradient nanostructured Ni coating (0.5±0.02) was reduced by 28.6%, 20.0%, and 6.0% compared to the uniform elemental Ni coatings with grain sizes of 480±50nm, 120±20nm, and 30±3nm prepared in Comparative Examples 1-3, respectively. The wear volume was measured by a three-dimensional optical profilometer, and the formula was used to calculate the wear volume. ω=V / FS The wear rate is calculated as F To load the load, S is the total sliding distance. The results show that the wear rate of the gradient nanostructured Ni coating prepared in Example 1 is 0.97452×10 -4 mm 3 ·N -1 ·m -1 ) Compared with the uniform elemental Ni coatings with grain sizes of 480±50 nm, 120±20 nm and 30±3 nm prepared in Comparative Examples 1-3, the wear rates were reduced by 80.7%, 75.6% and 71.1%, respectively, and the wear resistance was significantly improved.

[0055] Figure 5The wear scar morphology of the uniform elemental Ni coatings with grain sizes of 480±50nm, 120±20nm, and 30±3nm prepared in Comparative Examples 1-3, respectively, and the gradient nanostructured Ni coating prepared in the example. As can be seen from the figure, the homogeneous Ni coating with a grain size of 480±50nm prepared in Comparative Example 1 exhibits significant flaking, accompanied by a large amount of powdered wear debris and protruding particles (indicated by white arrows), indicating severe abrasive wear and adhesive wear. The wear scar of the homogeneous coating with a grain size of 120±20nm prepared in Comparative Example 2 shows significantly less powdered wear debris, accompanied by a small number of scratches and furrows. In addition, a large number of surface cracks continue to expand and connect above the wear scar, indicating that abrasive wear and delamination wear are the main causes. The wear scar surface of the homogeneous coating with a grain size of 30±3nm prepared in Comparative Example 3 is smoother than the previous two, but still has a certain number of scratches and furrows, indicating that abrasive wear is still the main cause of wear. The number of protruding particles and furrows in the wear scar of the gradient nanostructured Ni coating prepared in Example 1 is significantly reduced, the furrows are more gentle and the surface is smoother, and the deterioration of wear resistance is alleviated. This means that the wear mechanism has been transformed into mild abrasive wear, thereby significantly improving the wear resistance of the coating. Comparing the wear scar morphology of the uniform elemental Ni coating and the gradient nanostructured Ni coating, the friction performance of the gradient nanostructured Ni coating is significantly higher than that of the elemental Ni coating sample.

[0056] The improved wear resistance achieved in this invention is attributed to the gradient design of the pure Ni coating with different grain sizes and the amorphous state generated between adjacent layers. The grain size and thickness of the three layers are particularly critical in the gradient design, as they determine whether an amorphous transition layer forms between the two layers. Differences in thermal expansion coefficient and dislocation density (higher dislocation density in fine-grained layers) between layers of different grain sizes lead to stress concentration at the interface. When the stress exceeds a critical value, the lattice loses its long-range order, releasing energy through amorphization.

[0057] During the preparation of layer a to layer b, layer a was deposited using direct current electrodeposition to form coarse grains, resulting in a relatively ordered lattice arrangement at the interface. When layer b was then deposited on layer a using pulsed electrodeposition, the grain size dropped sharply from 430-530 nm to 100-140 nm, and the grain boundary density increased significantly. This sudden change in grain size also hindered dislocation motion in high-stress regions, slowed grain growth, increased nucleation density, and led to disordered atomic stacking and stress release, resulting in the formation of amorphous ribbon layer a before layer b. Layer b was deposited using pulsed electrodeposition with an on-off ratio of 1:1 (0.5 ms on / 0.5 ms off), which facilitated the maintenance of a dynamic adsorption-desorption equilibrium and reduced interface mutation.

[0058] During the preparation of layer b to layer c, the grain size dropped sharply from 100-140 nm to 27-33 nm, and the grain boundary density increased exponentially. Furthermore, during the pulsed electrodeposition process, the plating solution was switched from solution a to solution b. The most critical factor in the plating solution was the change from a saccharin-free solution to a saccharin-containing solution. The saccharin concentration in the plating solution changed dramatically, leading to the reconstruction of the adsorption layer on the cathode surface. The sudden introduction of saccharin inhibited the directional growth of nickel grains, forcing atoms to deposit rapidly in a disordered manner, thus first forming an amorphous ribbon layer b as a stress buffer, followed by the formation of layer c. The pulse parameters during the plating process of layer c were an on-off ratio of 3:7 (0.3 ms on / 0.7 ms off). The longer off time allowed saccharin molecules to adsorb more fully on the cathode surface, causing the adsorption layer to approach saturation and severely suppressing the lattice order. As a result, atoms were first deposited in a disordered manner on layer b to form an amorphous ribbon layer.

[0059] Therefore, it can be said that coating a is first deposited in bath a using direct current electrodeposition. Then, the parameters are changed to produce amorphous strips a using pulsed electrodeposition. Then, coating b is deposited in bath a. Finally, pulsed electrodeposition is continued in bath b to produce amorphous strips b on coating b, followed by coating c, ultimately resulting in a gradient nanostructured Ni coating on the metal substrate.

[0060] Comparative Example 4 This comparative example discloses a method for preparing a gradient nanostructured Ni coating, the method comprising: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0061] S2. Prepare electroplating solution a and electroplating solution b; the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, the concentration of nickel sulfate hexahydrate in electroplating solution a is 1.6 mol / L, the concentration of nickel chloride is 0.11 mol / L, and the concentration of boric acid is 0.048 mol / L; the electroplating solution b is prepared by adding saccharin to electroplating solution a, wherein the concentration of saccharin in electroplating solution b is 6 g / L.

[0062] S3. Using nickel as the anode and the metal substrate as the cathode, the anode and the cathode are placed in the electroplating solution a. First, direct current electrodeposition is used for plating, with a current of 0.1A and a time of 40min to prepare a coating a on the metal substrate. Then, pulse electrodeposition is used in the electroplating solution a, with a current of 0.1A, power supply parameters of on-time 0.5 ms, off-time 0.5 ms, pulse current power supply working time 1 ms, and plating time 20min. First, an amorphous ribbon layer a is prepared on the coating a, and then a coating b is prepared. Finally, pulse electrodeposition is used in the electroplating solution b, with a current of 0.1A, power supply parameters of on-time 0.3 ms, off-time 0.7 ms, pulse current power supply working time 1 ms, and plating time 5min. First, an amorphous ribbon layer b is prepared on the coating b, and then a coating c is prepared. Finally, a gradient nanostructured Ni coating is obtained on the metal substrate.

[0063] In this comparative example, the thickness of coating layer a was 10.35 μm, the thickness of coating layer b was 8.8 μm, the thickness of coating layer c was 1.55 μm, the thickness of amorphous ribbon layer a was 35 nm, and the thickness of amorphous ribbon layer b was 4 nm. The thickness of the prepared gradient nanostructured Ni coating was approximately 20.7 μm. The nickel content of coating layer a, coating layer b, coating layer c, amorphous ribbon layer a, and amorphous ribbon layer b was not less than 99.9 at%.

[0064] Comparative Example 5 This comparative example discloses a method for preparing a gradient nanostructured Ni coating, the method comprising: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0065] S2. Prepare electroplating solution a and electroplating solution b; the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, the concentration of nickel sulfate hexahydrate in electroplating solution a is 1.6 mol / L, the concentration of nickel chloride is 0.11 mol / L, and the concentration of boric acid is 0.048 mol / L; the electroplating solution b is prepared by adding saccharin to electroplating solution a, wherein the concentration of saccharin in electroplating solution b is 5 g / L.

[0066] S3. Using nickel as the anode and the metal substrate as the cathode, the anode and the cathode are placed in the electroplating solution a. First, direct current electrodeposition is used for plating, with a current of 0.1A and a time of 30min to prepare a coating a on the metal substrate. Then, pulse electrodeposition is used in the electroplating solution a, with a current of 0.1A, power supply parameters as on-time 0.5 ms, off-time 0.5 ms, pulse current power supply working time 1 ms, and plating time 25min; an amorphous ribbon layer a is first prepared on the coating a, and then a coating b is prepared. Finally, pulse electrodeposition is used in the electroplating solution b, with a current of 0.1A, power supply parameters as on-time 0.3 ms, off-time 0.7 ms, pulse current power supply working time 1 ms, and plating time 3min to first prepare an amorphous ribbon layer b on the coating b, and then a coating c is prepared, and finally a gradient nanostructured Ni coating is obtained on the metal substrate.

[0067] In this comparative example, the thickness of coating layer a was 7.76 μm, the thickness of coating layer b was 11 μm, the thickness of coating layer c was 0.93 μm, the thickness of amorphous ribbon layer a was 35 nm, and the thickness of amorphous ribbon layer b was 4 nm. The thickness of the prepared gradient nanostructured Ni coating was approximately 19.7 μm. The nickel content of coating layer a, coating layer b, coating layer c, amorphous ribbon layer a, and amorphous ribbon layer b was not less than 99.9 at %.

[0068] In this comparative example, when pulse electrodeposition plating is used, the temperature of plating solution a or plating solution b is controlled to be 50°C and the stirring rate is 500r / min. This comparative example discloses a method for preparing a gradient nanostructured Ni coating, the method comprising: S1. The Cu sheet was linearly cut to a φ=20 mm base Cu sheet. The base Cu sheet was polished with metallographic sandpaper, with the sandpaper grain size ranging from coarse to fine, and the finest grain size was 2000#. Then it was polished to a mirror surface. The base Cu sheet was then placed in a 10% volume fraction of hydrochloric acid, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. The base Cu sheet was then placed in a 2% volume fraction of NaOH solution, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. It was blown dry for use.

[0069] S2. Prepare electroplating solution a and electroplating solution b; the electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, the concentration of nickel sulfate hexahydrate in electroplating solution a is 1.6 mol / L, the concentration of nickel chloride is 0.11 mol / L, and the concentration of boric acid is 0.048 mol / L; the electroplating solution b is prepared by adding saccharin to electroplating solution a, wherein the concentration of saccharin in electroplating solution b is 6 g / L.

[0070] S3. Use nickel as the anode and the metal substrate as the cathode, place the anode and the cathode in the electroplating solution a, first use direct current electrodeposition for plating, the current is 0.1A, the time is 30min, and a coating a is prepared on the metal substrate, then continue to use pulse electrodeposition in the electroplating solution a, set the current to 0.1A, the power supply parameters are on-time 0.5 ms, off-time 0.5 ms, pulse current power supply working time 1 ms, and plating time 25min; first prepare an amorphous ribbon layer a on the coating a, and then prepare the coating b, finally continue to use pulse electrodeposition in the electroplating solution b, set the current to 0.1A, the power supply parameters are on-time 0.3 ms, off-time 0.7 ms, pulse current power supply working time 1 ms, and plating time 3min, first prepare an amorphous ribbon layer b on the coating b, and then prepare the coating c, and finally obtain a gradient nanostructured Ni coating on the metal substrate.

[0071] In this comparative example, the thickness of coating layer a was 7.76 μm, the thickness of coating layer b was 11 μm, the thickness of coating layer c was 0.93 μm, the thickness of amorphous ribbon layer a was 35 nm, and the thickness of amorphous ribbon layer b was 4 nm. The thickness of the prepared gradient nanostructured Ni coating was approximately 19.7 μm. The nickel content of coating layer a, coating layer b, coating layer c, amorphous ribbon layer a, and amorphous ribbon layer b was not less than 99.9 at %.

[0072] Comparative Examples 1-5 differ in that: Comparative Examples 1-3 are homogeneous Ni coatings, Comparative Example 4 changes the grain size of the outermost layer relative to Example 1, Comparative Example 5 changes the thickness ratio relative to Example 1, and Comparative Example 6 changes both the grain size and thickness ratio relative to Example 1. The specific examples of the present invention only present a portion of the experiments conducted during the research process, as considerable experimentation with thickness ratio and grain size was conducted. The comparative examples presented here merely illustrate the impact of grain size and thickness on the hardness and wear rate of the gradient nanostructured Ni coating.

[0073] Table 2 Hardness and wear rate of gradient nanostructured Ni coatings prepared in Comparative Examples 1-6 Comparing the hardness and wear rate in Table 1 and Table 2, it is obvious that the hardness and wear rate in the comparative example are worse. The difference between Example 1 and Comparative Example 4 is that the amount of saccharin added is different and the size of the outermost grain is different. In Comparative Example 4, the preparation method of coating a and coating b is the same as that in Example 1, so their grain sizes are consistent with those in Example 1. However, the amount of saccharin added to the plating solution b in Comparative Example 4 exceeds the saccharin addition limit range of the plating solution b in Examples 1-3. The experimental results show that with the increase in the amount of saccharin added, the hardness and wear rate of the coating did not increase as expected, but decreased. In addition, the test results of coating c in Comparative Example 4 showed that its grain size was 12-18nm. This result shows that the grain size of coating c is not the smaller the better, but there is an optimal range. Therefore, the amount of saccharin added in the plating solution of this application affects the grain size of the outermost coating, and thus affects the anti-wear and friction reduction performance of the coating. According to research, the anti-wear and friction reduction of the coating is best when the concentration of saccharin in the plating solution b is 4.8-5.2 g / L.

[0074] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A wear-resistant and friction-reducing gradient nanostructured Ni coating, characterized in that: The invention comprises a coating a with a grain size of 430-530 nm, an amorphous strip layer a, a coating b with a grain size of 100-140 nm, an amorphous strip layer b, and a coating c with a grain size of 27-33 nm, which are sequentially placed on a metal substrate from the inside out. The thickness ratio of the coating a, the coating b, the coating c, the amorphous strip layer a, and the amorphous strip layer b is (10-10.5) μm: (8.5-9) μm: (1.45-1.65) μm: (30-40) nm: (3-5) nm. The nickel content in the coating a, the coating b, the coating c, the amorphous strip layer a, and the amorphous strip layer b is not less than 99.9 at %.

2. A method for preparing the anti-wear and friction-reducing gradient nanostructured Ni coating according to claim 1, characterized in that: The method includes: S1, prepare electroplating solution a and electroplating solution b; S2. Using nickel as the anode and the metal substrate as the cathode, the anode and the cathode are placed in the electroplating solution a, and direct current electrodeposition is first used to prepare a coating a on the metal substrate. Then, pulse electrodeposition is continued in the electroplating solution a to first prepare an amorphous ribbon layer a on the coating a, and then prepare a coating b. Finally, pulse electrodeposition is continued in the electroplating solution b to first prepare an amorphous ribbon layer b on the coating b, and then prepare a coating c, and finally a gradient nanostructured Ni coating is obtained on the metal substrate.

3. The preparation method according to claim 2, characterized in that The electroplating solution a is prepared from nickel sulfate hexahydrate, nickel chloride, boric acid and distilled water, wherein the concentration of nickel sulfate hexahydrate in the electroplating solution a is 1.57-1.63 mol / L, the concentration of nickel chloride is 0.11-0.12 mol / L, and the concentration of boric acid is 0.047-0.05 mol / L. The electroplating solution b is prepared by adding saccharin to the electroplating solution a, wherein the concentration of saccharin in the electroplating solution b is 4.8-5.2 g / L.

4. The preparation method according to claim 2, characterized in that When the coating layer a is plated by direct current electrodeposition, the current is 0.1-0.2A and the time is 40min; When the amorphous ribbon layer a and the coating layer b are plated by pulse electrodeposition, the current is set to 0.09-0.11A, the power supply parameters are on-time 0.5ms, off-time 0.5ms, pulse current power supply working time 1ms, and plating time 20min; When pulse electrodeposition is used to plate the amorphous ribbon layer b and the coating layer c, the current is set to 0.09-0.11A, the power supply parameters are on-time 0.3ms, off-time 0.7ms, pulse current power supply working time 1ms, and plating time 5min.

5. The preparation method according to any one of claims 2 to 4, characterized in that: When pulse electrodeposition plating is adopted, the temperature of plating solution a or plating solution b is controlled at 48-52° C., and the stirring rate is 490-510 r / min.

6. The method for preparing an anti-wear and friction-reducing gradient nanostructured Ni coating according to any one of claims 2 to 4, characterized in that: The metal substrate also includes a pretreatment before being placed in the electroplating solution a. The pretreatment is as follows: the base Cu sheet is polished to a mirror surface with metallographic sandpaper, and then the base Cu sheet is placed in a hydrochloric acid solution with a volume fraction of 10%, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water. Then, the base Cu sheet is placed in a NaOH solution with a volume fraction of 2%, ultrasonically cleaned for 2 minutes, and then rinsed with distilled water, and blown dry for use.

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