Ni-w-sic plating solution, composite coating and preparation method and application thereof

Abstract

This invention relates to a Ni-W-SiC electroplating solution, a composite coating, its preparation method, and its application. The Ni-W-SiC electroplating solution provided by this invention includes a pre-plating solution and a composite plating solution. The pre-plating solution includes NiSO4·6H2O, a buffer, and a conductive salt. The composite plating solution includes NiSO4·6H2O, Na2WO4·H2O, Na3C6H5O7·2H2O, NH4Cl, SiC nanoparticles, and a dispersant. The composite coating is formed on the surface of a metal substrate by electroplating. After vacuum heat treatment, its Vickers hardness is 650HV~780HV, and its bonding strength is 45MPa~58MPa. This invention solves the problems of low hardness, high brittleness, and insufficient bonding strength of Ni-SiC coatings, and overcomes the defects of heavy pollution and high energy consumption associated with hard chrome plating. The resulting coating has high hardness, high bonding strength, wear resistance, and is environmentally friendly, making it suitable for surface strengthening of industrial rolls.

Description

Technical Field

[0001] This invention belongs to the field of electroplating technology, specifically relating to a Ni-W-SiC electroplating solution, a composite coating, its preparation method, and its application. Background Technology

[0002] In the field of industrial rolling mill rolls, the surface properties of rolling mill rolls, as key components in metal rolling equipment, directly affect the quality of rolled products and the service life of the rolls. To improve the hardness, bonding strength, and wear resistance of rolling mill rolls and extend their service life, surface strengthening treatments are typically required. Common surface treatment processes in existing technologies include Ni-SiC composite electroplating, hard chrome plating, micro-arc oxidation, and thermal spraying.

[0003] However, existing surface treatment processes still have the following technical problems: (1) Ni-SiC composite electroplating process: Although the Ni-SiC composite coating obtained by this process can improve the wear resistance, thermal conductivity and lubricant adhesion of the metal substrate to a certain extent, its hardness is relatively low, making it difficult to meet the requirements of use under high load conditions. More importantly, the Ni-SiC composite coating is brittle and has large internal stress, resulting in insufficient bonding strength between the coating and the substrate. During service, it is prone to peeling or cracking, which seriously affects the service life of the rolls and the surface quality of the rolled products.

[0004] (2) Hard chrome plating process: Hard chrome plating is one of the most widely used processes for surface strengthening of industrial rolls. It can obtain a chrome plating layer with high hardness and good wear resistance. However, this process has significant drawbacks: First, the hexavalent chromium used in the electroplating process is highly toxic and carcinogenic. The electroplating process generates a large amount of chromium-containing waste liquid and waste gas that are difficult to treat, and the environmental treatment cost is extremely high, which does not meet the current development requirements of green manufacturing. Second, the current efficiency of the hard chrome plating process is low and the energy consumption is high. In addition, the chrome plating layer has microcrack defects and is prone to corrosion failure in corrosive environments.

[0005] (3) Other surface treatment processes: Micro-arc oxidation is mainly applicable to light metal alloys such as aluminum and magnesium, and is difficult to apply to rolls of steel substrates; Although thermal spraying technology can prepare thicker coatings, the coating and the substrate are mainly mechanically bonded, with limited bonding strength, and pores are easily generated during the spraying process, affecting the corrosion resistance of the coating.

[0006] Composite electrodeposition technology is one of the important methods for preparing high-performance metal-based composite coatings. This technology obtains composite coatings with special properties by uniformly dispersing insoluble solid particles in an electroplating solution and co-depositing them with metal ions. Among them, Ni-W-SiC composite coatings have attracted widespread attention due to their excellent comprehensive performance. Ni-W-SiC composite coatings are composed of matrix metals nickel (Ni), tungsten (W), and reinforcing phase silicon carbide (SiC) particles. Matrix metal nickel has good magnetic properties and toughness, providing good matrix support for the coating; tungsten has stable chemical properties, high hardness, and good wear resistance, which can effectively reduce the friction coefficient of the plated part, while the nickel-tungsten alloy itself has excellent corrosion resistance; silicon carbide particles, as a hard reinforcing phase, have excellent mechanical properties, high wear resistance, oxidation resistance, and a low friction coefficient. The Ni-W-SiC composite coating formed by these three components combines the advantages of high hardness, high wear resistance, good corrosion resistance, and a low friction coefficient, and is considered a promising green surface treatment technology to replace highly polluting hard chrome plating.

[0007] Therefore, there is an urgent need to develop a new type of composite coating and its preparation method that has high hardness, high bonding strength, good wear resistance and corrosion resistance, and is environmentally friendly and cost-controllable, so as to meet the surface treatment needs of metal components such as industrial rolls. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention aims to provide a Ni-W-SiC electroplating solution, a composite coating, its preparation method, and its application, in order to solve the problems of low hardness, high brittleness, insufficient bonding strength, and easy detachment of existing Ni-SiC composite coatings. At the same time, it overcomes the problems of severe environmental pollution and high energy consumption in hard chromium plating processes, and obtains a composite coating that has high hardness, high bonding strength, good wear resistance, and is environmentally friendly.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: The first objective of this invention is to provide a Ni-W-SiC electroplating solution, comprising a pre-plating solution and a composite plating solution, wherein the pre-plating solution comprises 100-150 g / L NiSO4·6H2O, 30-35 g / L buffer, and 68-130 g / L conductive salt; The composite plating solution comprises NiSO4·6H2O 30~40g / L, Na2WO4·H2O 60~80g / L, Na3C6H5O7·2H2O 110~130g / L, NH4Cl 30~40g / L, SiC nanoparticles 20~40g / L, and dispersant 0.1~0.2g / L.

[0010] Preferably, the SiC nanoparticles include SiC nanoparticles with a particle size of 500~700nm and SiC nanoparticles with a particle size of 80~120nm, and the mass ratio of the two is (2~4):1.

[0011] Preferably, the buffer is H3BO3, the conductive salt includes Na2SO4 and NaCl; the dispersant is a compound of hexadecyltrimethylammonium bromide and OP emulsifier in a mass ratio of 1:(2~5).

[0012] Preferably, the pre-plating solution comprises NiSO4·6H2O 100~150g / L, H3BO3 30~35g / L, Na2SO4 60~120g / L and NaCl 8~10g / L.

[0013] Another object of the present invention is to provide a method for preparing a Ni-W-SiC composite coating, comprising the following steps: S1. Pre-treat the metal substrate; S2. A pre-plating layer is formed by electroplating a pre-plating solution onto a pre-treated metal substrate. S3. A composite plating layer is formed by electroplating the pre-plating layer using a composite plating solution; S4. The composite coating is subjected to vacuum heat treatment and cooled to obtain the Ni-W-SiC composite coating. The pre-plating solution comprises 100-150 g / L NiSO4·6H2O, 30-35 g / L buffer, and 68-130 g / L conductive salt; the composite plating solution comprises 30-40 g / L NiSO4·6H2O, 60-80 g / L Na2WO4·H2O, 110-130 g / L Na3C6H5O7·2H2O, 30-40 g / L NH4Cl, 20-40 g / L SiC nanoparticles, and 0.1-0.2 g / L dispersant.

[0014] Preferably, step S1 pre-treats the metal substrate, including mechanical leveling, sandblasting, and degreasing cleaning; the sandblasting process makes the surface roughness of the metal substrate reach 3~5μm.

[0015] Preferably, in step S2, the electroplating process conditions for forming the pre-plating layer are: pH value of 5~6, temperature of 20~30℃, current density of 1~3A / dm², magnetic stirring speed of 60~90r / min, and time of 5~10min.

[0016] Preferably, in step S3, the electroplating process conditions for forming the composite coating are: pH value of 8~9, temperature of 60~70℃, current density of 1~3A / dm², magnetic stirring speed of 150~180r / min, and time of 120~180min.

[0017] Preferably, in step S4, the process conditions for vacuum heat treatment are as follows: under vacuum conditions, the heating rate is 3~8℃ / min, the heat treatment temperature is 300~500℃, and the holding time is 1~3h.

[0018] Another object of the present invention is to provide a Ni-W-SiC composite coating prepared according to the above preparation method, the composite coating comprising a Ni-W alloy matrix and SiC nanoparticles dispersed in the Ni-W alloy matrix.

[0019] like Figure 1 As shown, this invention addresses the technical problems of existing Ni-SiC composite coatings, such as low hardness, high brittleness, insufficient bonding strength, and easy detachment, as well as the heavy environmental pollution and high energy consumption of hard chromium plating processes. It proposes a Ni-W-SiC electroplating solution, a composite coating, its preparation method, and its applications. The design principle and concept of this invention are as follows: This invention uses a Ni-W alloy as the matrix metal for the coating, instead of the traditional Ni or Ni-SiC. The principle is that W atoms have a large atomic radius, and when dissolved into the Ni lattice, they cause lattice distortion, resulting in a solid solution strengthening effect. Simultaneously, a Ni4W intermetallic compound phase can be formed during electrodeposition, further enhancing the coating hardness through precipitation strengthening. Addressing the issue that single-size SiC particles cannot simultaneously achieve high composite content and fine-grained strengthening, this invention employs nanoscale mixed-size SiC particles to further improve coating hardness. The inventors believe the mechanism may be that large-size particles are easier to co-deposit, helping to increase the SiC composite content in the coating; small-size particles provide more nucleation sites, which is beneficial for grain refinement and dislocation pinning. The synergistic effect of these two factors significantly improves the coating hardness.

[0020] To address the problem of insufficient coating-substrate bonding strength in existing composite coatings due to the presence of second-phase particles (SiC), this invention designs a pre-plated pure Ni layer as a transition layer. The principle is that pure Ni and the Ni-W-SiC composite coating have similar lattice constants and chemical affinities, enabling good lattice matching. Simultaneously, the pure Ni pre-plating layer avoids direct contact between SiC particles and the metal substrate, effectively alleviating stress concentration at the interface. Building upon this, this invention further introduces a vacuum heat treatment process: at high temperatures, Ni atoms in the pre-plating layer interdiffusion with atoms in the substrate, forming a metallurgical bond; simultaneously, atomic diffusion also occurs between the pre-plating layer and the composite coating, transforming the original mechanical bond (or weak chemical bond) into a metallic bond, thereby significantly improving the overall bonding strength of the coating.

[0021] This invention employs a two-step electroplating method of "pre-plating followed by composite plating," controlling process parameters such as composition, pH value, temperature, current density, and stirring speed of the pre-plating and composite plating solutions respectively to ensure a dense and uniform pre-plating layer and well-dispersed SiC particles in the composite plating layer. In the heat treatment stage, this invention achieves precise control over the microstructure of the coating (such as grain size and phase composition) and the degree of interfacial diffusion by controlling the heat treatment temperature, holding time, and heating rate. Experiments show that the solid solution strengthening effect reaches its peak and the hardness is highest at 300℃ heat treatment; and the interfacial diffusion is most complete and the bonding strength is highest at 500℃ heat treatment. A suitable heat treatment temperature can be selected within the range of 300~500℃ according to actual needs to achieve a balance between hardness and bonding strength.

[0022] In summary, this invention addresses the hardness issue through the synergistic effect of a Ni-W alloy matrix and mixed-size SiC particles; it resolves the bonding strength issue through the synergistic effect of a pre-plated pure Ni layer and vacuum heat treatment; and it achieves controllable adjustment of coating performance through an optimized electroplating process and adjustable heat treatment temperature. Ultimately, a composite coating with high hardness, high bonding strength, excellent wear resistance, and environmental friendliness is obtained, which can replace traditional hard chrome plating technology and is particularly suitable for surface strengthening of metal parts under heavy-duty conditions such as industrial rolls.

[0023] Compared with the prior art, the present invention has the following beneficial effects: The electroplating solution of this invention adopts a hexavalent chromium-free system, which has high current efficiency and low energy consumption, and avoids the generation of toxic chromium-containing waste liquid and waste gas.

[0024] The method for preparing composite coatings using the electroplating solution of this invention, through pre-plating, mixing SiC particles of different sizes, and vacuum heat treatment, achieves a Vickers hardness of 777.3 HV and a bonding strength of 57.02 MPa, significantly improving both hardness and bonding strength, and effectively solving the problem of easy coating peeling.

[0025] The Ni-W-SiC composite coating prepared by this invention has high hardness, high bonding strength and excellent wear resistance, which can meet the requirements of high load conditions such as industrial rolls. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation and heat treatment process of the Ni-W-SiC composite coating of the present invention. Figure 2 This is a schematic diagram of the electroplating experimental apparatus of the present invention; Figure 3 The XRD patterns of the Ni-W-SiC composite coating of the present invention at different heat treatment temperatures are shown; where the horizontal axis is the diffraction angle 2θ (unit: degrees, °) and the vertical axis is the diffraction intensity (unit: au). Figure 4 Vickers hardness diagrams of the Ni-W-SiC composite coating of the present invention at different heat treatment temperatures are shown; where the horizontal axis represents the heat treatment temperature (unit: °C), and the vertical axis represents the Vickers hardness value (unit: HV) under a test force of 0.2 kgf. 0.2 ); Figure 5 This is a schematic diagram of the tensile strength test of the present invention; Figure 6 The diagram shows the bonding strength of the Ni-W-SiC composite coating of the present invention at different heat treatment temperatures; where the horizontal axis represents the heat treatment temperature (unit: °C) and the vertical axis represents the bonding strength of the coating (unit: MPa). Figure 7 The diagram shows the wear rate of the Ni-W-SiC composite coating of the present invention under different heat treatment temperatures and different loads; where the horizontal axis represents the heat treatment temperature (unit: °C) and the vertical axis represents the wear rate (unit: %). Detailed Implementation

[0027] Unless otherwise specified, the experimental methods described in the following embodiments of the present invention are generally performed under conventional conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the embodiments are commercially available products.

[0028] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the invention.

[0030] The following embodiments further describe the present invention, but these embodiments are not intended to limit the scope of protection of the present invention.

[0031] Equipment and Instruments: The X-ray diffractometer was purchased from Rigaku Corporation, model Rigakud Ultima IV; The digital microhardness tester was purchased from Shanghai Sichangyue Optical Instrument Co., Ltd., model HXD-1000TMSC / LCD; The material mechanics testing system was purchased from China Machinery Testing Equipment Co., Ltd., and is a model MTA material mechanics testing system. The high-speed reciprocating friction and wear testing machine was purchased from Lanzhou Zhongke Kaihua Technology Development Co., Ltd., model HSR-2M. The multi-functional friction and wear testing machine was purchased from Rtec Instruments, USA, model MFT-5000.

[0032] Example 1: The Ni-W-SiC electroplating solution, composite coating, and their preparation according to the present invention. The Ni-W-SiC electroplating solution in this embodiment: The pre-plating solution consists of: NiSO4·6H2O 120g / L, H3BO3 30g / L, Na2SO4 120g / L and NaCl 10g / L; The composite plating solution consists of: NiSO4·6H2O 40 g / L, Na2WO4·H2O 80 g / L, Na3C6H5O7·2H2O 130 g / L, NH4Cl 40 g / L, SiC particles 30 g / L, and dispersant 0.1 g / L. The SiC particles include SiC particles with diameters of 600 nm and 100 nm, with a mass ratio of 3:1. The dispersant is a mixture of hexadecyltrimethylammonium bromide and OP emulsifier, with a mixing ratio of 1:3.

[0033] The method for preparing the Ni-W-SiC composite coating in this embodiment includes the following steps: S1. Pretreatment of the metal substrate: Industrial rolling mill steel was used as the metal matrix. The metal parts were cut into flat, appropriately sized sheet structures using a wire EDM machine. The samples were then degreased with an alkaline solution, followed by cleaning with alcohol and deionized water to remove stains and residual organic matter from the surface of the metal matrix.

[0034] S2. Electroplating a pre-plating layer is formed on the pretreated metal substrate, using the above-mentioned pre-plating solution for electroplating. The electroplating process conditions were: pH value 5.5, temperature 25℃, current density 2A / dm², magnetic stirring speed 80r / min, and time 5min.

[0035] S3. Electroplating a composite coating is formed on the pre-plating layer, using the aforementioned composite plating solution for electroplating. The electroplating process conditions were: pH value 8.5, temperature 65℃, current density 2A / dm², magnetic stirring speed 150r / min, and time 180min.

[0036] S4. Vacuum heat treatment of the electroplated metal substrate: The electroplated sample was vacuum sealed and placed in a heat treatment furnace. It was heated to 400°C at a heating rate of 5°C / min and held at that temperature for 2 hours. The cooling method was furnace cooling to obtain the Ni-W-SiC composite coating.

[0037] like Figure 2 The diagram shown is a schematic of the electroplating experimental apparatus of the present invention, which can help to understand the electroplating conditions in the embodiments.

[0038] Example 2: The Ni-W-SiC electroplating solution, composite coating, and their preparation according to the present invention. Compared with Example 1, the vacuum heat treatment temperature of the Ni-W-SiC composite coating in step S4 of this example is 200℃, and the remaining steps and parameters are the same as in Example 1.

[0039] Example 3: The Ni-W-SiC electroplating solution, composite coating, and their preparation according to the present invention. Compared with Example 1, the vacuum heat treatment temperature of the Ni-W-SiC composite coating in step S4 of this example is 300℃, and the remaining steps and parameters are the same as in Example 1.

[0040] Example 4: The Ni-W-SiC electroplating solution, composite coating, and their preparation according to the present invention. Compared with Example 1, the vacuum heat treatment temperature of the Ni-W-SiC composite coating in step S4 of this example is 500℃, and the remaining steps and parameters are the same as in Example 1.

[0041] Example 5: The Ni-W-SiC electroplating solution, composite coating, and their preparation according to the present invention. The Ni-W-SiC electroplating solution in this embodiment: The pre-plating solution consists of: NiSO4·6H2O 100g / L, H3BO3 35g / L, Na2SO4 60g / L and NaCl 8g / L; The composite plating solution consists of: NiSO4·6H2O 30 g / L, Na2WO4·H2O 60 g / L, Na3C6H5O7·2H2O 110 g / L, NH4Cl 30 g / L, SiC particles 20 g / L, and dispersant 0.2 g / L. The SiC particles include SiC particles with diameters of 500 nm and 80 nm, with a mass ratio of 2:1. The dispersant is a mixture of hexadecyltrimethylammonium bromide and OP emulsifier, with a mass ratio of 1:2.

[0042] The method for preparing the Ni-W-SiC composite coating in this embodiment includes the following steps: S1. Pretreatment of the metal substrate: Industrial rolling mill steel was used as the metal substrate. The metal substrate was cut into flat, appropriately sized sheet samples using an electrical discharge wire cutting machine; sandblasting was performed to achieve a surface roughness of 4μm; then, the substrate was degreased with an alkaline solution, followed by cleaning with alcohol and deionized water to remove surface stains and residual organic matter.

[0043] S2. Electroplating a pre-plating layer is formed on the pretreated metal substrate, using the above-mentioned pre-plating solution for electroplating. The electroplating process conditions were: pH value 5.0, temperature 20℃, current density 1A / dm², magnetic stirring speed 60r / min, and time 10min.

[0044] S3. Electroplating a composite coating is formed on the pre-plating layer, using the aforementioned composite plating solution for electroplating. The electroplating process conditions were: pH value 8.0, temperature 60℃, current density 1A / dm², magnetic stirring speed 180r / min, and time 120min.

[0045] S4. Vacuum heat treatment of the electroplated metal substrate: The electroplated sample was vacuum sealed and placed in a heat treatment furnace. It was heated to 300°C at a heating rate of 3°C / min and held at that temperature for 3 hours. The cooling method was furnace cooling to obtain the Ni-W-SiC composite coating.

[0046] Example 6: The Ni-W-SiC electroplating solution, composite coating, and their preparation according to the present invention. The Ni-W-SiC electroplating solution in this embodiment: The pre-plating solution consists of: NiSO4·6H2O 150g / L, H3BO3 30g / L, Na2SO4 120g / L and NaCl 10g / L; The composite plating solution consists of: NiSO4·6H2O 40 g / L, Na2WO4·H2O 80 g / L, Na3C6H5O7·2H2O 130 g / L, NH4Cl 40 g / L, SiC particles 40 g / L, and dispersant 0.1 g / L. The SiC particles include SiC particles with diameters of 700 nm and 120 nm, with a mass ratio of 4:1. The dispersant is a mixture of hexadecyltrimethylammonium bromide and OP emulsifier, with a mass ratio of 1:4.

[0047] The method for preparing the Ni-W-SiC composite coating in this embodiment includes the following steps: S1. Pretreatment of the metal substrate: Industrial rolling mill steel was used as the metal substrate. The metal substrate was cut into flat, appropriately sized sheet samples using an electrical discharge wire cutting machine; sandblasting was performed to achieve a surface roughness of 4μm; then, the substrate was degreased with an alkaline solution, followed by cleaning with alcohol and deionized water to remove surface stains and residual organic matter.

[0048] S2. Electroplating a pre-plating layer is formed on the pretreated metal substrate, using the above-mentioned pre-plating solution for electroplating. The electroplating process conditions were: pH value 6.0, temperature 30℃, current density 3A / dm², magnetic stirring speed 90r / min, and time 5min.

[0049] S3. Electroplating a composite coating is formed on the pre-plating layer, using the aforementioned composite plating solution for electroplating. The electroplating process conditions were: pH value 9.0, temperature 70℃, current density 3A / dm², magnetic stirring speed 150r / min, and time 180min.

[0050] S4. Vacuum heat treatment of the electroplated metal substrate: The electroplated sample was vacuum sealed and placed in a heat treatment furnace. It was heated to 500°C at a heating rate of 8°C / min and held at that temperature for 1 hour. The cooling method was furnace cooling to obtain the Ni-W-SiC composite coating.

[0051] Example 7: The Ni-W-SiC electroplating solution, composite coating, and their preparation according to the present invention. Compared with Example 1, the metal substrate and the method of pretreatment of the metal substrate are different in this example, but the rest is the same as in Example 1.

[0052] The method for preparing the Ni-W-SiC composite coating in this embodiment includes the following steps: Pretreatment of the metal substrate: Using aluminum alloy as the metal substrate, the metal parts are cut into flat, appropriately sized sheet structures using a wire EDM machine. They are then sanded, first with 800# sandpaper for rough sanding, then with 1500# sandpaper for fine sanding, and finally with 2000# sandpaper for finishing sanding until the surface is smooth and shiny. Finally, they are polished with diamond polishing compound on a polishing machine. To prevent corrosion of the metal substrate by the acidic plating solution, a zinc plating layer is pre-deposited on the metal substrate through two zinc immersion processes. After a simple rinse with ethanol, the surface is cleaned with a plasma cleaner to remove residual organic matter, thereby enhancing the bonding strength between the plating layer and the substrate.

[0053] Then, pre-plating, composite plating, and vacuum heat treatment are performed according to steps S2-S4 of Example 1.

[0054] Comparative Example 1 Compared with Example 1, the Ni-W-SiC composite coating in this comparative example was not subjected to vacuum heat treatment. That is, after completing the S3 composite electroplating, the S4 step was not performed, but the coating was left to stand naturally at room temperature of 25°C. Other steps and parameters were the same as in Example 1.

[0055] Comparative Example 2 Compared with Example 1, this comparative example replaces the SiC particles in the composite plating solution with single SiC particles with a particle size of 600 nm, while other steps and parameters are the same as in Example 1.

[0056] Comparative Example 3 Compared with Example 1, this comparative example replaces the SiC particles in the composite plating solution with single SiC particles with a particle size of 100nm. Other steps and parameters are the same as in Example 1.

[0057] Comparative Example 4 Compared with Example 1, this comparative example omits step S2, that is, no pure Ni layer is pre-plated on the pretreated metal substrate, and composite electroplating is performed directly (S3). Other steps and parameters are the same as in Example 1.

[0058] Experiment 1 XRD Phase Analysis The Ni-W-SiC composite coating samples prepared in Examples 1-4 of this invention and the untreated sample of Comparative Example 1 were used as controls.

[0059] Test method: Phase analysis of each sample was performed using an X-ray diffractometer. Test conditions: Cu-Ka radiation was used as the X-ray source. The scanning rate was 5° / min, and the scanning range was set to 20~80°.

[0060] Experimental results: such as Figure 3As shown, temperature-varying XRD analysis of the samples within the range of 200–500 °C indicates that SiC maintains a stable cubic crystal structure within this temperature range, with no new phase formation or crystal transformation, demonstrating excellent thermal stability. Compared to the control group (untreated), the characteristic diffraction peak intensity of the experimental group samples significantly increased with increasing temperature, while the full width at half maximum (FWHM) narrowed, indicating a continuous increase in crystallinity and gradual grain growth. When the temperature reached 500 °C, sharp peaks began to appear in the XRD pattern, indicating the transformation from an amorphous structure to a crystalline structure. These results demonstrate that high-temperature treatment can effectively optimize the crystal quality of the coating, providing experimental evidence for its high-temperature applications.

[0061] Experimental two-dimensional hardness test The Ni-W-SiC composite coating samples prepared in Examples 1-4 of this invention and the untreated sample of Comparative Example 1 were used as controls.

[0062] Test method: The microhardness of the coating surface was characterized using an HXD-1000TMSC / LCD digital microhardness tester (Shanghai Sichangyue Optical Instrument Co., Ltd., model HXD-1000TMSC / LCD). The load was 200g and the holding time was 40s.

[0063] Experimental results: such as Figure 4 As shown, the Vickers hardness of the untreated composite coating is 648.9 HV. 0.2 The high hardness of the composite coating primarily stems from solid solution strengthening caused by W atoms in the Ni lattice and the precipitation of the Ni4W phase. Heat treatment can increase the diffusion rate of W atoms in the coating, thereby enhancing the solid solution strengthening effect. As the heat treatment temperature increases, the hardness of the composite coating first increases and then decreases, reaching a maximum hardness of 777.3 HV at 300℃. 0.2 Therefore, the heat treatment method provided by this invention can improve the hardness of the coating, and achieve the highest hardness at around 300°C.

[0064] Based on the above variable-temperature XRD analysis results, it can be seen that medium-low temperature heat treatment (around 300℃) can promote the diffusion of W atoms in the coating, enhance the solid solution strengthening effect, and effectively enhance the resistance to plastic deformation and improve the mechanical properties of the Ni-W-SiC composite coating. However, when the temperature reaches 400℃, grain growth begins, leading to a deterioration in material hardness. This pattern provides direct experimental evidence for the optimal heat treatment process and high-temperature service temperature selection of Ni-W-SiC composite coating materials.

[0065] Experiment 3 Bond Strength Test The Ni-W-SiC composite coating samples prepared in Examples 1-4 of this invention and the untreated sample of Comparative Example 1 were used as controls.

[0066] Test methods: such as Figure 5 As shown, a symmetrical columnar sample structure is used. The coating to be tested is sandwiched between the two end faces of the sample using E7 structural adhesive. During the test, a tensile force F in opposite directions is applied along the axial direction of the sample. The bonding strength is determined by breaking the interface between the coating and the substrate / adhesive layer. This method can accurately characterize the interfacial adhesion performance of the coating and provides a direct experimental means to evaluate its mechanical reliability. The specific steps are as follows: The coating to be tested was bonded to the clamps at both ends using E7 structural adhesive. The mixture was then cured in a 100℃ drying oven for 3 hours. Subsequently, the clamps were mounted on an MTA-type material mechanics testing system, and the sample was stretched at a rate of 1 mm / min. The tensile force at the moment of fracture was recorded, and the result was analyzed using the formula... Calculate the bond strength, where Bond strength (MPa). This represents the tensile force (N) recorded when the wire breaks. Contact area (mm) 2 The test results are as follows: Figure 6 As shown.

[0067] Experimental results are as follows Figure 6 As shown, the bonding strength of the coating first decreases and then increases with the increase of heat treatment temperature: the bonding strength of the untreated sample (25℃) is 49.80 MPa; after heat treatment at 200℃ and 300℃, the bonding strength drops to 48.32 MPa and 45.67 MPa respectively, showing a gradual decreasing trend; after heat treatment at 400℃, the bonding strength rebounds to 53.53 MPa; after heat treatment at 500℃, the bonding strength reaches a peak of 57.02 MPa, which is significantly higher than that of the untreated sample.

[0068] Based on the analysis of the Vickers hardness variation curves at different heat treatment temperatures, the decrease in strength at low temperatures (≤300℃) may be related to micro-defects, interfacial element segregation, or slight oxidation generated during the stress release process of the coating. As the temperature further increases (≥400℃), the degassing and stress relief effects of vacuum heat treatment, as well as the interdiffusion of metal atoms between the coating and the substrate, begin to dominate. The bonding mode gradually transitions from the initial chemical layer bonding to interatomic metal bonding, thereby significantly improving the bonding strength between the coating and the substrate and the toughness of the coating.

[0069] Experiment 4 Wear Resistance Test The Ni-W-SiC composite coating samples prepared in Examples 1-4 of this invention and the untreated sample of Comparative Example 1 were used as controls.

[0070] Test method: The friction and wear test was carried out using the HSR-2M high-speed reciprocating friction and wear tester. The loads were 5N, 7N and 9N respectively, the running length was 5mm, the frequency was 5Hz and the time was 2h. After the test, the wear track was characterized in three dimensions and the wear rate was calculated using the MFT-5000 multi-functional friction and wear tester.

[0071] Experimental results are as follows Figure 7 As shown, the wear rate of the coating varies with heat treatment temperature under different loads (5N, 7N, 9N): the wear rate remains at a very low level under low load (5N), and the effect of temperature is not significant; under medium and high loads (7N, 9N), the wear rate reaches the lowest value when heat treated at 300℃, among which the wear rate at 300℃ under 9N load is about 35% lower than that at 25℃, and the wear resistance is the best; as the temperature further increases to 400℃ and 500℃, the wear rate under medium and high loads increases significantly, and the wear rate reaches its peak at 500℃, and the wear resistance deteriorates significantly.

[0072] Based on Vickers hardness and bond strength data, heat treatment at 300℃ yields the highest hardness (approximately 775 HV) and optimal wear resistance, representing the optimal temperature for coating wear resistance. While heat treatment at 500℃ achieves the highest bond strength (57.02 MPa), both hardness and wear resistance decrease significantly. Therefore, a suitable heat treatment temperature within the range of 300–500℃ can be selected based on the actual load and service requirements to achieve a balance between coating hardness, wear resistance, and bond strength.

[0073] Experiment 5: Performance testing of comparative samples 2-4 This experiment used the same testing methods and equipment as Experiments 1 to 3 to conduct XRD phase and microstructure analysis, Vickers hardness test, bonding strength test and wear rate test on the test samples prepared by Comparative Examples 2, 3 and 4. The test results are shown in Table 1.

[0074] Table 1. Experimental results of Comparative Examples 2-4

[0075] As shown in the table above, compared with Example 1, Comparative Example 2 used a single large-diameter SiC particle, Comparative Example 3 used a single small-diameter SiC particle, and Comparative Example 4 omitted the pure Ni pre-plating transition layer. The results showed that the microstructure of the coatings in all three comparative examples had different defects, the overall bonding strength decreased significantly, the wear rate increased significantly under multi-load conditions, and the wear resistance was significantly deteriorated. Only the surface hardness increased slightly, but the overall service performance was not as good as that of Example 1. It can be seen that the composite plating solution using SiC particles of mixed sizes with a pre-plated pure Ni transition layer, combined with a reasonable vacuum heat treatment process, can optimize the microstructure of the coating and effectively improve the interfacial bonding strength and wear resistance stability of the coating. The preparation process of single-diameter hard particles and omitting the transition layer will deteriorate the overall comprehensive performance of the coating.

[0076] In summary, this invention solves the problems of insufficient performance of existing Ni-SiC composite coatings and high pollution and energy consumption in hard chrome plating processes by synergistically combining Ni-W alloy matrix with mixed-size SiC particles, optimizing the interface of the pre-plated pure Ni transition layer, and precisely controlling vacuum heat treatment. Experiments show that the coating performance of preparation methods using single-size SiC particles or omitting the pre-plated Ni layer is inferior to that of the composite coating prepared by this invention. The composite coating prepared by this invention achieves a Vickers hardness of 777.3 HV after heat treatment at 300℃ (an improvement of about 20% compared to the untreated layer) and has the best wear resistance. After heat treatment at 500℃, the bonding strength reaches a maximum of 57.02 MPa. It has both excellent comprehensive performance and environmental friendliness, and can replace hard chrome plating technology. It is suitable for surface strengthening of high-load metal parts, with significant application prospects and economic benefits.

[0077] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A Ni-W-SiC electroplating solution, characterized in that, The plating solution includes a pre-plating solution and a composite plating solution. The pre-plating solution includes 100-150 g / L NiSO4·6H2O, 30-35 g / L buffer, and 68-130 g / L conductive salt. The composite plating solution comprises NiSO4·6H2O 30~40g / L, Na2WO4·H2O 60~80g / L, Na3C6H5O7·2H2O 110~130g / L, NH4Cl 30~40g / L, SiC nanoparticles 20~40g / L, and dispersant 0.1~0.2g / L.

2. The Ni-W-SiC electroplating solution according to claim 1, characterized in that, The SiC nanoparticles include SiC nanoparticles with a particle size of 500~700nm and SiC nanoparticles with a particle size of 80~120nm, and the mass ratio of the two is (2~4):

1.

3. The Ni-W-SiC electroplating solution according to claim 1, characterized in that, The buffer is H3BO3, and the conductive salt includes Na2SO4 and NaCl; the dispersant is a compound of hexadecyltrimethylammonium bromide and OP emulsifier in a mass ratio of 1:(2~5).

4. The Ni-W-SiC electroplating solution according to claim 3, characterized in that, The pre-plating solution comprises 100~150g / L NiSO4·6H2O, 30~35g / L H3BO3, 60~120g / L Na2SO4, and 8~10g / L NaCl.

5. A method for preparing a Ni-W-SiC composite coating, characterized in that, Includes the following steps: S1. Pre-treat the metal substrate; S2. A pre-plating layer is formed by electroplating a pre-plating solution onto a pre-treated metal substrate. S3. A composite plating layer is formed by electroplating the pre-plating layer using a composite plating solution; S4. The composite coating is subjected to vacuum heat treatment and cooled to obtain the Ni-W-SiC composite coating. The pre-plating solution comprises 100-150 g / L NiSO4·6H2O, 30-35 g / L buffer, and 68-130 g / L conductive salt; the composite plating solution comprises 30-40 g / L NiSO4·6H2O, 60-80 g / L Na2WO4·H2O, 110-130 g / L Na3C6H5O7·2H2O, 30-40 g / L NH4Cl, 20-40 g / L SiC nanoparticles, and 0.1-0.2 g / L dispersant.

6. The preparation method according to claim 5, characterized in that, Step S1 involves pre-treating the metal substrate, including mechanical leveling, sandblasting, and degreasing cleaning; the sandblasting process reduces the surface roughness of the metal substrate to 3-5 μm.

7. The preparation method according to claim 5, characterized in that, In step S2, the electroplating process conditions for forming the pre-plating layer are: pH value of 5~6, temperature of 20~30℃, current density of 1~3A / dm², magnetic stirring speed of 60~90r / min, and time of 5~10min.

8. The preparation method according to claim 5, characterized in that, In step S3, the electroplating process conditions for forming the composite coating are: pH value of 8~9, temperature of 60~70℃, current density of 1~3A / dm², magnetic stirring speed of 150~180r / min, and time of 120~180min.

9. The preparation method according to claim 5, characterized in that, In step S4, the process conditions for vacuum heat treatment are as follows: under vacuum conditions, the heating rate is 3~8℃ / min, the heat treatment temperature is 300~500℃, and the holding time is 1~3h.

10. The Ni-W-SiC composite coating prepared by the preparation method according to any one of claims 5 to 9, characterized in that, The composite coating comprises a Ni-W alloy matrix and SiC nanoparticles dispersed in the Ni-W alloy matrix.

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