Composite coating as well as preparation method and application thereof

Abstract

The invention discloses a composite coating and a preparation method and application thereof, and relates to the field of metal material surface protection, and the composite coating is composed of silane coupling agent modified nano alumina and tungsten carbide / graphene composite particle modified polyurethane-silane hybrid. The preparation method comprises the steps that firstly, the beryllium copper alloy is subjected to acetone cleaning, multiple times of abrasive paper polishing and plasma treatment to activate the surface; coating a silane coupling agent modified nano aluminum oxide priming coat by adopting an air spraying process, and curing; mixing the tungsten carbide / graphene composite particle modified polyurethane-silane hybrid with a solvent, brushing the mixture on the surface of the bottom coating to form a middle coating, and curing; and finally, mixing and spin-coating the two modified components on the surface of the middle coating to form a surface coating, and curing. The composite coating has high bonding strength, excellent corrosion resistance and wear resistance, is suitable for surface protection of beryllium copper alloy electronic connectors, precise instrument springs and other parts, and can effectively prolong the service life of the beryllium copper alloy electronic connectors, precise instrument springs and other parts in complex environments.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material surface protection, and in particular to a composite coating and a preparation method and application thereof. Background Art

[0002] Beryllium copper alloy, due to its high electrical and thermal conductivity, fatigue resistance, and excellent processing properties, is widely used in high-end applications such as electronic connectors, precision instrument springs, and aerospace components. It is a key material supporting the development of precision and high-performance in modern industry. Its excellent physical and chemical properties make it an irreplaceable role in applications such as electronic device signal transmission and precision machinery stress transfer, placing extremely high demands on the material's long-term stability.

[0003] However, beryllium copper alloys are prone to oxidation corrosion, surface wear, and other problems in complex environments such as high temperature and humidity, salt spray corrosion, or strong friction, leading to performance degradation or even failure. If beryllium copper alloy components in electronic equipment undergo oxidation corrosion, it may cause increased contact resistance and interrupt signal transmission; if beryllium copper alloy springs in precision machinery experience surface wear, it may lead to a decrease in stress transfer efficiency, affecting the accuracy and service life of the equipment. The existence of these problems has seriously restricted the further application of beryllium copper alloys in high-end scenarios.

[0004] While traditional protective methods such as electroplating nickel / chromium and chemical copper plating can provide some protection, they have significant drawbacks: the coating has a weak bond with the substrate and is easily detached due to stress or environmental changes; its functionality is limited, offering only one of the two properties of corrosion protection or wear resistance, making it difficult to simultaneously address multiple factors of erosion; and some processes introduce harmful substances, limiting its application in high-end scenarios. Therefore, the development of a composite coating with high bonding strength, excellent corrosion resistance, and wear resistance has become an urgent need in the field of beryllium copper alloy surface protection. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite coating for beryllium copper alloy and a preparation method thereof, which solves the problems that existing beryllium copper alloy is susceptible to corrosion and wear in complex environments, and traditional coatings have weak bonding strength and single function.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions: A composite coating is composed of nano-alumina modified with a silane coupling agent and a polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles. The raw materials for preparing the nano-alumina modified with the silane coupling agent include, by mass percentage, 10-15% of γ-aminopropyltriethoxysilane and 5-10% of nano-alumina. The raw materials for preparing the polyurethane-silane hybrid modified with the tungsten carbide / graphene composite particles include 10-15% of tungsten carbide, 3-6% of graphene, 6-10% of diisocyanate, 7-12% of polyether diol, 25-35% of solvent, and 1-2% of leveling agent.

[0007] According to a preferred embodiment of the present invention, the γ-aminopropyltriethoxysilane is purchased from Hubei Xingfa Group Co., Ltd.

[0008] According to a preferred embodiment of the present invention, the nano-alumina is purchased from Jiangsu Runfeng Synthetic Technology Co., Ltd.

[0009] According to a preferred embodiment of the present invention, the tungsten carbide is purchased from Zhuzhou Cemented Carbide Group Co., Ltd.

[0010] According to a preferred embodiment of the present invention, the graphene is purchased from Changzhou Sixth Element Materials Technology Co., Ltd.

[0011] According to a preferred embodiment of the present invention, the diisocyanate is purchased from Wanhua Chemical Group Co., Ltd.

[0012] According to a preferred embodiment of the present invention, the polyether diol is purchased from BASF (China) Co., Ltd.

[0013] According to a preferred embodiment of the present invention, the solvent is an aromatic hydrocarbon organic solvent, and the aromatic hydrocarbon organic solvent is xylene, which is purchased from Sinopec Shanghai Petrochemical Co., Ltd.

[0014] According to a preferred embodiment of the present invention, the leveling agent is a silicone leveling agent purchased from BYK Chemical Co., Ltd.

[0015] According to a preferred embodiment of the present invention, the preparation method of the silane coupling agent modified nano-alumina includes: mixing γ-aminopropyltriethoxysilane with anhydrous ethanol, adding nano-alumina powder, ultrasonically dispersing, then adding ammonia water to adjust the pH of the system to 8-9, transferring to a water bath for reflux reaction, cooling to room temperature and filtering, washing the filter cake with anhydrous ethanol, and vacuum drying.

[0016] According to a preferred embodiment of the present invention, the particle size of the nano-alumina powder is 50-100 nm; the frequency of ultrasonic dispersion is 30-50 kHz, and the dispersion time is 20-40 min; the temperature in the water bath is 55-65°C, and the reflux reaction time is 3-5 h; the temperature of vacuum drying is 55-65°C, and the drying time is 11-13 h.

[0017] In the preparation process of the silane coupling agent modified nano-alumina in the present invention, γ-aminopropyltriethoxysilane (KH550) is mixed with nano-alumina powder in anhydrous ethanol and then dispersed by ultrasonication to form a uniform dispersion system; ammonia water is added dropwise to adjust the pH to a weak alkaline environment of 8-9, so as to accelerate the hydrolysis of the ethoxy groups (-OC2H5) in the KH550 molecules to generate sufficient silanol groups (-Si-OH) while avoiding excessive condensation of the silanols themselves. The groups react with the hydroxyl groups (-OH) on the surface of the nano-alumina to form a stable The fixed Si-O-Al chemical bond is formed, thereby evenly anchoring the nano-alumina particles on the silane coupling agent molecular chain to form modified silane coupling agent particles with a core-shell structure. This process promotes the full hydrolysis and condensation reaction through pH control and reflux reaction (55-65°C), thereby improving the grafting rate of silane and nano-alumina. Finally, after filtration, washing and vacuum drying (55-65°C), the surface-modified silane coupling agent-modified nano-alumina is obtained, and its particle size is controlled at 50-100nm to ensure the uniformity of subsequent coating.

[0018] According to a preferred embodiment of the present invention, the preparation method of the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles includes: adding tungsten carbide powder and graphene to an agate ball mill, and ball milling with anhydrous ethanol as a medium to obtain tungsten carbide / graphene composite particles; mixing diisocyanate and polyether diol, adding dibutyltin dilaurate to react to obtain a polyurethane prepolymer; adding tungsten carbide / graphene composite particles to the polyurethane prepolymer and stirring to obtain a polyurethane prepolymer modified with tungsten carbide / graphene composite particles, and then mixing with xylene.

[0019] According to a preferred embodiment of the present invention, the dibutyltin dilaurate is purchased from Jiangsu Feixiang Chemical Co., Ltd.

[0020] According to a preferred embodiment of the present invention, the average particle size of the tungsten carbide powder is 1-3 μm; the thickness of the graphene sheet is ≤10 nm; the ball milling speed is 200-400 rpm, and the time is 5-7 hours; the diisocyanate and polyether diol are in a molar ratio of 1.2:1; the dibutyltin dilaurate accounts for 0.5% of the mass of the diisocyanate; the reaction temperature for adding dibutyltin dilaurate is 55-65° C., and the reaction time is 1.5-2.5 hours; the stirring speed is 1000-1200 rpm, and the time is 14-16 minutes.

[0021] In the preparation of the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles of the present invention, tungsten carbide (1-3 μm) and graphene (sheets ≤ 10 nm) are ball-milled at 200-400 rpm (5-7 hours) in anhydrous ethanol medium to form composite particles, the surface of which generates defect sites due to mechanical collision, thereby enhancing the interface bonding with the polymer; diisocyanate (TDI) and polyether diol (molecular weight 2000) are catalyzed by dibutyltin dilaurate (0.5% by mass) (reaction at 55-65°C for 1.5-2.5 hours), and then the reaction mixture is stirred for 1 hour. An addition reaction generates a polyurethane prepolymer, which contains a large number of urethane bonds (-NH-CO-O-) in its molecular chain, resulting in high flexibility and adhesion. Tungsten carbide / graphene composite particles are then added to the prepolymer (stirring at 1000-1200 rpm for 14-16 minutes). The particles are evenly dispersed in the polyurethane matrix through van der Waals forces and hydrogen bonding. The prepolymer is then mixed with xylene (25-35% by mass) to form a hybrid with a solid content of 35%. The viscosity is controlled at 500-800 mPa·s to ensure fluidity for subsequent coating.

[0022] The present invention also provides a method for preparing the composite coating, comprising the steps of: S1. Ultrasonic cleaning of the beryllium copper alloy surface with acetone, polishing with sandpaper of different particle sizes, ultrasonic cleaning with anhydrous ethanol, and finally treatment in a plasma cleaner; dissolving silane coupling agent-modified nano-alumina in deionized water, uniformly coating the pretreated beryllium copper alloy surface with an air spray process, and then curing in an oven to form a primer layer on the beryllium copper alloy surface; S2, mixing the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles with xylene, dispersing the mixture evenly with an electric stirrer, applying the mixture to the surface of the base coating by a brush coating process, and curing the mixture in an oven to form an intermediate coating; S3. Mix the silane coupling agent-modified nano-alumina with the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles, apply it to the surface of the intermediate coating by a spin coating process, and place it in an oven for curing to form a top coating.

[0023] According to a preferred embodiment of the present invention, in step S1, the ultrasonic cleaning time is 10-20 minutes, the particle sizes of the sandpaper are 800 mesh, 1000 mesh, and 1500 mesh respectively; the surface roughness of the beryllium copper alloy is polished to Ra≤0.8 μm; the ultrasonic cleaning time of anhydrous ethanol is 8-12 minutes; the power in the plasma cleaning machine is 40-60 W, the Ar gas flow rate is 150-250 mL / min, and the treatment time is 4-6 minutes; the mass ratio of silane coupling agent modified nano-alumina to deionized water is 1:15; the thickness of the primer layer is 5-8 μm; the curing temperature in the oven is 70-90°C, and the curing time is 10-20 minutes.

[0024] According to a preferred embodiment of the present invention, in step S2, the mass ratio of the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles to xylene is 3:1; the speed of the electric stirrer is 700-900 rpm, and the dispersion time is 8-12 min; the thickness of the intermediate coating is 15-20 μm; and the curing temperature in the oven is 110-130° C., and the time is 20-40 min.

[0025] According to a preferred embodiment of the present invention, in step S3, the mass ratio of the silane coupling agent modified nano-alumina to the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles is 1:1; the topcoat thickness is 5-10 μm; the curing temperature in the oven is 140-160° C., and the curing time is 0.8-1.2 h.

[0026] The formation process of the composite coating of the present invention is divided into three steps: the first step is to form a 5-8 μm primer layer on the surface of the beryllium copper alloy that has been pretreated (acetone ultrasonic cleaning, 800-1500 grit sandpaper polishing to Ra ≤ 0.8 μm, and plasma cleaning to activate the surface) by air spraying (0.3 MPa, nozzle 0.8 mm). After curing at 70-90 ° C (10-20 min), the silanol groups of the silane coupling agent and the hydroxyl groups (-OH) on the surface of the beryllium copper alloy undergo a condensation reaction to form Si-OM (M is Cu / Be in the beryllium copper alloy) chemical bonds, thereby achieving a strong bond between the bottom layer and the substrate; the second step is to brush a modified polyurethane-silane hybrid (with a mass ratio of 3:1 to xylene) on the surface of the primer layer to form a 15-20 μm intermediate coating, which is then cured at 110-130 ° C ( After 20-40min), the urethane bonds of the polyurethane prepolymer undergo a cross-linking reaction with the remaining active groups of the silane coupling agent of the base coating (such as incompletely reacted -Si-OH), and at the same time, the tungsten carbide / graphene particles are embedded in the interface to enhance the mechanical strength of the intermediate layer; in the third step, the modified silane coupling agent and the modified polyurethane-silane hybrid are mixed in a mass ratio of 1:1 (xylene solvent, solid content 20%) and spin-coated (500rpm×30s) to form a 5-10μm top coating on the surface of the intermediate coating. After curing at 140-160℃ (0.8-1.2h), the silane coupling agents and polyurethane molecular chains of the two further interpenetrate to form a continuous and dense cross-linked network. At the same time, the graphene sheets form a physical barrier layer in the coating to hinder the penetration of corrosive media, and the tungsten carbide particles act as a hard phase to improve the wear resistance of the coating. Precise control of temperature, time, and rotation speed in each step (e.g., reflux reaction time 3-5h, ball milling speed 200-400rpm, and curing temperature 70-160°C) ensures full reaction and uniform dispersion of each component, ultimately forming a composite coating with high adhesion, corrosion resistance, and wear resistance.

[0027] The present invention also provides an application of the composite coating or the composite coating prepared by the preparation method on the surface of a beryllium copper alloy.

[0028] The beneficial effects of the present invention are: The present invention significantly improves the bonding reliability between the coating and the beryllium copper alloy substrate through the synergistic effect of two modified components. Silane coupling agent-modified nano-alumina forms a stable chemical bonding network on the substrate surface due to its unique chemical structure. At the same time, the physical embedding of nano-alumina particles further enhances the interfacial intercalation, allowing the coating to fit tightly to the substrate. In the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles, the tungsten carbide hard particles and graphene sheets are interwoven to form a mechanical locking effect. Combined with the flexibility of the polyurethane substrate, this effectively fills the microscopic defects within the coating. The combined effect of the three makes the coating less likely to fall off due to stress changes or environmental fluctuations, significantly improving its long-term service stability.

[0029] This composite coating exhibits excellent comprehensive protective properties in complex environments. The dense molecular network formed by silane coupling agent-modified nano-alumina effectively blocks the penetration of corrosive media such as oxygen, water vapor, and chloride ions, inhibiting oxidation reactions and electrochemical corrosion of the beryllium copper alloy at the source. Tungsten carbide hard particles significantly improve the coating's hardness and friction resistance. The addition of graphene sheets not only enhances particle dispersion but also buffers external friction stress through its layered structure. The synergistic effect of these two significantly reduces surface wear rate, allowing the beryllium copper alloy to maintain good surface integrity in harsh environments such as salt spray, high humidity, and high friction, significantly extending its service life.

[0030] The preparation method of the present invention has a simple process, strong adaptability, and significant advantages in industrial application. The substrate pretreatment adopts a gradient activation process of acetone cleaning, sandpaper polishing and plasma treatment, which effectively improves the surface activity; the base coating adopts an air spray process, the middle coating adopts a brush coating process, and the top coating adopts a spin coating process. Each step is easy to operate and has low equipment requirements. The continuous construction of multi-layer coatings can be achieved without complex precision instruments; the curing process is controlled by graded temperature to ensure the full cross-linking and performance of each modified component. The overall process flow is coherent and efficient, the raw material cost is controllable, and it is easy to promote and apply on a large scale, providing an efficient and reliable solution for the surface protection of beryllium copper alloys in electronic connectors, precision instruments and other fields. DETAILED DESCRIPTION

[0031] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0032] 1. Implementation Example 1 This embodiment relates to the preparation of a composite coating for beryllium copper alloy. The specific raw materials and steps are as follows: the composite coating is composed of nano-alumina modified with a silane coupling agent (modified component A) and a polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles (modified component B). Among them, the raw materials for preparing modified component A include 12g of γ-aminopropyltriethoxysilane (KH550), 8g of nano-alumina with a particle size of 50-100nm and a specific surface area of ​​≥200m² / g, and 180g of anhydrous ethanol; the raw materials for preparing modified component B include 12g of tungsten carbide with an average particle size of 1-3μm, 5g of graphene with a layer thickness of ≤10nm, 8.5g of diisocyanate (TDI, model: Covestro Desmodur N3390), 7.1g of polyether diol (molecular weight: 2000, model: Dow DOWANOL PPH), 0.04g of dibutyltin dilaurate, 25g of xylene, and 1.5g of a leveling agent (silicone type, model: BYK-333).

[0033] The preparation steps are as follows: first, a substrate is pretreated, and beryllium copper alloy C17200 with a size of 100 mm × 50 mm × 2 mm is used, and surface oil is removed by acetone ultrasonic cleaning. The frequency of ultrasonic cleaning is 40 kHz, and the time is 15 minutes; then, the beryllium copper alloy is polished with 800 mesh, 1000 mesh, and 1500 mesh sandpaper in sequence, so that the beryllium copper alloy is first coarsely ground and then finely ground, so that the final surface roughness Ra of the beryllium copper alloy is ≤ 0.8 μm. The surface roughness of the beryllium copper alloy can be detected and confirmed by a surface roughness profiler; then, anhydrous ethanol ultrasonic cleaning is used to remove residual particles after polishing. The frequency of anhydrous ethanol ultrasonic cleaning is 40 kHz, and the time is 10 minutes; then, plasma cleaning is used to improve surface activity. The power of plasma cleaning is 50 W, the Ar gas flow rate is 200 mL / min, and the treatment time is 5 minutes.

[0034] Next, the modified component A was prepared as follows: 12 g of KH550 and 180 g of anhydrous ethanol were added to a beaker, and magnetic stirring was started to uniformly disperse KH550 in the anhydrous ethanol at a speed of 300 rpm. 8 g of nano-alumina was then added to the beaker and ultrasonically dispersed at a frequency of 40 kHz for 30 minutes to form a stable emulsion after uniform dispersion. About 5 mL of 25% ammonia water was added dropwise to the emulsion to adjust the pH of the system to 8-9, and then the solution was transferred to a 60°C water bath for reflux reaction for 4 hours. The reflux condenser was kept unobstructed during the reflux process. After the reaction was completed, the solution was cooled to room temperature and the reaction product was filtered. The pore size of the filter paper during filtration was 10-15 μm. The filter cake was washed with anhydrous ethanol three times, 50 mL each time, and the filtrate was clarified after washing. The washed product was vacuum dried at 60°C for 12 hours. The vacuum degree during drying was -0.09 MPa, and the temperature control accuracy of the drying oven was ±2°C to obtain silane coupling agent modified nano-alumina powder.

[0035] Then, the modified component B was prepared: 12 g of tungsten carbide and 5 g of graphene were added to an agate ball mill, the ball-to-material ratio in the ball mill was 10:1, the diameter of the agate ball was 10 mm, and the agate ball was made of zirconium oxide. 85 g of anhydrous ethanol was added to the ball mill as a dispersion medium for the ball material. The speed of the ball mill was 300 rpm, and the ball milling time was 6 h to obtain tungsten carbide / graphene composite particles. TDI was added to the ball mill. 8.5 g of tungsten carbide and 7.1 g of polyether diol were added to a reactor, and 0.04 g of dibutyltin dilaurate was added to the reactor and stirred at a stirring speed of 200 rpm during the reaction. The reaction was carried out at 60° C. for 2 h to obtain a polyurethane prepolymer; 5 g of tungsten carbide / graphene composite particles were added to the polyurethane prepolymer, and stirred at a speed of 1000 rpm for 15 min with an anchor-type stirring paddle. The stirring was stopped only after the particles were evenly dispersed and no obvious agglomeration was observed; the stirred material was then mixed with xylene (25 g) and dispersed at a speed of 800 rpm for 10 min. The viscosity of the dispersed mixture was controlled at 500-800 mPa·s to obtain a polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles.

[0036] Then, the coating is applied: first, a primer is applied, 12g of modified component A powder is dissolved in 188g of deionized water, and a primer is sprayed on the surface of the beryllium copper alloy using an air spray process, and the coating thickness is controlled to be 5-8μm. The spraying equipment model is WAGNER PRO 700, the spraying pressure is 0.3MPa, the nozzle diameter is 0.8mm, and the spraying distance is 200mm; the coating thickness is tested by a wet film card, and 3 points are measured every 10cm², so that the average value meets the requirements; after coating, the beryllium copper alloy is placed in an 80°C oven with an oven temperature control accuracy of ±5°C, and cured for 15 minutes. After curing, it is naturally cooled to room temperature, thereby forming a primer on the surface of the beryllium copper alloy.

[0037] Then apply the intermediate coating, mix the modified component B with xylene in a mass ratio of 1:1, and evenly disperse it with an electric stirrer, the speed of the electric stirrer is 700-900 rpm, and the stirring time is 8-12 minutes; apply the evenly dispersed modified component B to the surface of the base coating by a brush coating process, and control the coating thickness to 15-20 μm. The coating thickness is tested by a wet film card. The brush used in the brush coating process is a boar bristle brush with a brush width of 20 mm; after coating, place the beryllium copper alloy in a 120° C. oven and cure for 30 minutes. After curing, naturally cool to room temperature to form a layer of intermediate coating on the surface of the base coating.

[0038] Finally, a topcoat is applied and cured: modified component A and modified component B are mixed in a mass ratio of 1:1, with a total mass of 100 g after mixing. The solvent of the mixture is xylene, and the solid content of the mixture is about 20%. The mixture of modified component A and modified component B is applied to the surface of the intermediate coating by a spin coating process, and the coating thickness is controlled to be 5-10 μm. The coating thickness is detected by a thickness gauge. The spin coating equipment used in the spin coating process is a German Erichsen spin coater with a rotation speed of 500 rpm and a time of 30 seconds. After coating, the beryllium copper alloy is placed in a 150°C oven for curing for 1 hour. After curing, it is naturally cooled to room temperature to form a topcoat on the surface of the intermediate coating.

[0039] Example 2 The specific implementation method is basically the same as that of Example 1, except that the raw materials for preparing the modified component A in the composite coating include 10 g of KH550, 5 g of nano-alumina, and 150 g of anhydrous ethanol; the raw materials for preparing the modified component B include 10 g of tungsten carbide, 3 g of graphene, 6 g of TDI, 7 g of polyether glycol, 0.03 g of dibutyltin dilaurate, 25 g of xylene, and 1 g of a leveling agent. The preparation steps are adjusted as follows: the substrate pretreatment is the same as in Example 1; when preparing the modified component A, the ultrasonic dispersion time is 20 minutes, the frequency is 30 kHz, the pH is adjusted to 8 with ammonia water, refluxed in a water bath at 55°C for 3 hours, vacuum dried at 55°C for 11 hours, the coating thickness is 5 μm, and cured at 70°C for 10 minutes; when preparing the modified component B, the ball milling time is 5 hours, the ball milling speed is 200 rpm, the stirring speed is 1000 rpm, the stirring time is 14 minutes, the coating thickness is 15 μm, and cured at 110°C for 20 minutes; in the topcoat, the mixing ratio of the modified component A and the modified component B by mass is 1:1, the spin coating thickness is 5 μm, and the coating is cured at 140°C for 0.8 hours.

[0040] Example 3 The specific implementation method is basically the same as Example 1, except that the raw materials for preparing the modified component A in the composite coating include 15 g of KH550, 10 g of nano-alumina, and 225 g of anhydrous ethanol; the raw materials for preparing the modified component B include 15 g of tungsten carbide, 6 g of graphene, 10 g of TDI, 12 g of polyether glycol, 0.05 g of dibutyltin dilaurate, 35 g of xylene, and 2 g of a leveling agent. The preparation steps are adjusted as follows: the substrate pretreatment is the same as in Example 1; when preparing the modified component A, the ultrasonic dispersion time is 40 minutes, the frequency is 50 kHz, the pH is adjusted to 9 with ammonia water, refluxed in a water bath at 65°C for 5 hours, vacuum dried at 65°C for 13 hours, the coating thickness is 8 μm, and cured at 90°C for 20 minutes; when preparing the modified component B, the ball milling time is 7 hours, the speed is 400 rpm, the stirring speed is 1200 rpm, the stirring time is 16 minutes, the coating thickness is 20 μm, and the curing is carried out at 130°C for 40 minutes; the topcoat mixing ratio is 1:1, the spin coating thickness is 10 μm, and the curing is carried out at 160°C for 1.2 hours.

[0041] Comparative Example 1 The coating (total mass, approximately 90 g) was formed by directly coating a polyurethane prepolymer on the surface of a beryllium copper alloy. The polyurethane prepolymer was prepared using a raw material comprising 10 g of polyether glycol, 6 g of TDI, 0.03 g of dibutyltin dilaurate, 25 g of xylene, and 1 g of a leveling agent, according to the polyurethane prepolymer preparation method described in Example 1. The coating was free of silane coupling agent-modified nano-alumina. The coating was prepared by pretreating the substrate as in Example 1, then directly coating the polyurethane prepolymer (formed by the reaction of TDI and polyether glycol) (10 μm thick) on the beryllium copper alloy surface and curing at 120°C for 30 minutes.

[0042] Comparative Example 2 The coating (total mass, approximately 90 g) was formed by directly coating a beryllium copper alloy surface with silane-coupling-agent-modified nanoalumina. The silane-coupling-agent-modified nanoalumina was prepared using 12 g of KH550, 8 g of nanoalumina, and 180 g of anhydrous ethanol according to the preparation method for silane-coupling-agent-modified nanoalumina described in Example 1. The coating was free of tungsten carbide / graphene composite particles. The coating was prepared by pretreating the substrate as in Example 1, then directly coating the beryllium copper alloy surface with the silane-coupling-agent-modified nanoalumina in the same manner as the primer coating in Example 1, without applying an intermediate or topcoat, and curing at 80°C for 15 minutes.

[0043] Comparative Example 3 The raw materials for preparing the composite coating (total mass, approximately 95g) include modified component A and modified component B'. The ingredients and preparation method of modified component A are the same as those in Example 1. The raw materials for preparing modified component B' include 12g tungsten carbide, 8g TDI, 10g polyether glycol, 0.04g dibutyltin dilaurate, 30g xylene, and 1.5g leveling agent. The preparation method for modified component B' is identical to that for modified component B in Example 1, except that graphene is omitted in the corresponding steps. The composite coating preparation steps are as follows: substrate pretreatment and basecoat application are the same as in Example 1. For the midcoat and topcoat, graphene-free modified component B' is used instead of modified component B. All other steps are the same as in Example 1.

[0044] 2. Performance Testing The materials prepared in Examples 1-3 and Comparative Examples 1-3 were tested for performance according to the following method: 1. Abrasion resistance test: According to ASTM G65 standard, dry sand / rubber wheel testing machine was used, using CS-10 rubber wheel (load 10N±0.1N, speed 60±1rpm), sample size 25mm×75mm×2mm, after 1000 revolutions of abrasion, the mass loss was measured with an electronic balance with an accuracy of 0.01mg, according to the formula W v =Δm / (ρFL) to calculate the volume wear rate (W v is the volume wear rate, in mm 3 / Nm; ρ is the coating density, in g / cm³; F is the load, in N; L is the sliding distance, in m). The test was repeated three times in parallel and the average value was taken.

[0045] 2. Adhesion test: Use the cross-hatch method according to ISO 2409. Use a 6-blade cutter (blade spacing 2.0±0.1mm) to scratch a 10×10 grid (depth to the substrate) on the coating surface. Apply 3M 600 tape (width 25mm) and peel it off at a constant speed (1.0±0.1m / min) at an angle of 60°±5°. Immediately evaluate the proportion of peeled grids under a 100× optical microscope (Grade 0: 0%; Grade 1: ≤5%; Grade 2: 5-15%; Grade 3: 15-35%; Grade 4: 35-65%; Grade 5: >65%).

[0046] 3. Salt spray corrosion test: Follow ASTM B117 standard, prepare 5.0±0.1wt% NaCl solution (pH=6.8±0.1), salt spray chamber temperature 35.0±0.5℃, salt spray deposition rate 1.5±0.1mL / h·80cm², tilt the sample at 45±2°, spray continuously for 1000 hours, remove the sample, and use ImageJ software to analyze the surface rust area percentage (%). Take the average value of the three groups of samples.

[0047] 4. Friction coefficient test: A UMT-5 friction and wear testing machine was used, with a Φ6.00±0.01mm GCr15 steel ball (hardness 62±1HRC) as the wear part, a normal load of 5.0±0.1N, a sliding speed of 0.10±0.01m / s, a total sliding distance of 100±1m, and the friction coefficient curve was recorded in real time and the average value of the stable stage (the last 50m) was taken. The ambient temperature was 25±1℃ and the humidity was 50±5%.

[0048] 5. Microhardness test: Use HXD-1000TMC microhardness tester, Knoop indenter, test load 25.00±0.01gf, hold time 15.0±0.5s, take 5 measurement points at equal intervals in the center area of ​​the coating cross section (spacing ≥50μm), remove the highest and lowest values ​​and take the average hardness of the remaining 3 points (HK 0.025 ), calibrated in accordance with ISO 4545.

[0049] 6. Performance test results: Table 1: Performance test results of various embodiments and comparative examples As can be seen from Table 1, Examples 1-3 of the present invention solve the problems of corrosion and wear of beryllium copper alloy in complex environments and weak bonding and single function of traditional coatings through composite coating design: In terms of wear resistance, the volume wear rate of Examples 1-3 (1.92–2.87×10 -6 mm³ / N·m) is significantly lower than that of traditional polyurethane coating (Comparative Example 1: 8.74×10 -6 ), attributed to the synergistic effect of hard reinforcement and lubrication of tungsten carbide / graphene composite particles, which improves wear resistance by more than 67%. In terms of corrosion resistance, the rust area after 1000 hours of salt spray is only 2.8-4.5% (much lower than the 38.6% in Comparative Example 1), thanks to the dual protection mechanism of the dense passivation film of silane coupling agent-modified nano-alumina (Component A) and the physical barrier of Component B. In terms of bonding strength, all examples have adhesion of ISO 2409, the highest grade 0 (no shedding), while the traditional single-layer coating (Comparative Example 1) has shedding of 18%. The key lies in the chemical bonding (Si-O-Cu) between Component A and the beryllium copper substrate and the interpenetrating cross-linking of the multi-layer coating (bottom / middle / surface). In terms of multifunctional integration, the examples simultaneously achieve a low friction coefficient (0.16-0.21, a 51-63% reduction compared to Comparative Example 1) and a high hardness (298-347 HK 0.025 ), confirming the functional complementarity of nano-alumina (corrosion protection / hardness) and graphene (lubrication / wear resistance). This also highlights the engineering applicability of this invention under harsh working conditions.

[0050] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A composite coating, characterized in that: The invention is composed of nano-alumina modified with a silane coupling agent and a polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles. The raw materials for preparing the nano-alumina modified with the silane coupling agent include, by mass percentage, 10-15% of γ-aminopropyltriethoxysilane and 5-10% of nano-alumina. The raw materials for preparing the polyurethane-silane hybrid modified with the tungsten carbide / graphene composite particles include 10-15% of tungsten carbide, 3-6% of graphene, 6-10% of diisocyanate, 7-12% of polyether diol, 25-35% of solvent, and 1-2% of leveling agent.

2. The composite coating according to claim 1, characterized in that The preparation method of the nano-alumina modified silane coupling agent comprises: mixing γ-aminopropyltriethoxysilane with anhydrous ethanol, adding nano-alumina powder, ultrasonically dispersing, then dripping ammonia water to adjust the pH of the system to 8-9, transferring the mixture to a water bath for reflux reaction, cooling to room temperature and filtering, washing the filter cake with anhydrous ethanol, and vacuum drying.

3. The composite coating according to claim 2, characterized in that The particle size of the nano-alumina powder is 50-100 nm; the frequency of ultrasonic dispersion is 30-50 kHz, and the dispersion time is 20-40 min; the temperature in the water bath is 55-65° C., and the reflux reaction time is 3-5 h; the temperature of vacuum drying is 55-65° C., and the drying time is 11-13 h.

4. The composite coating according to claim 1, characterized in that The preparation method of the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles comprises: adding tungsten carbide powder and graphene into an agate ball mill, and ball milling with anhydrous ethanol as a medium to obtain tungsten carbide / graphene composite particles; mixing diisocyanate and polyether diol, and adding dibutyltin dilaurate to react to obtain a polyurethane prepolymer; adding the tungsten carbide / graphene composite particles into the polyurethane prepolymer and stirring to obtain a polyurethane prepolymer modified with the tungsten carbide / graphene composite particles, and then mixing with xylene.

5. The composite coating according to claim 4, characterized in that The average particle size of the tungsten carbide powder is 1-3 μm; the thickness of the graphene sheet is ≤10 nm; the ball milling speed is 200-400 rpm, and the time is 5-7 hours; the diisocyanate and polyether diol have a molar ratio of 1.2:1; the dibutyltin dilaurate accounts for 0.5% of the mass of the diisocyanate; the reaction temperature for adding dibutyltin dilaurate is 55-65° C., and the reaction time is 1.5-2.5 hours; the stirring speed is 1000-1200 rpm, and the time is 14-16 minutes.

6. A method for preparing a composite coating according to any one of claims 1 to 5, characterized in that the steps include: S1. The surface of the beryllium copper alloy is ultrasonically cleaned with acetone, polished with sandpaper of different grits, then ultrasonically cleaned with anhydrous ethanol, and finally placed in a plasma cleaner for treatment; The silane coupling agent-modified nano-alumina is dissolved in deionized water, and is evenly coated on the surface of the pretreated beryllium copper alloy by an air spraying process, and then placed in an oven for curing, thereby forming a primer layer on the surface of the beryllium copper alloy; S2, mixing the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles with xylene, dispersing the mixture evenly with an electric stirrer, applying the mixture to the surface of the base coating by a brush coating process, and curing the mixture in an oven to form an intermediate coating; S3. Mix the silane coupling agent-modified nano-alumina with the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles, apply it to the surface of the intermediate coating by a spin coating process, and place it in an oven for curing to form a top coating.

7. The preparation method according to claim 6, characterized in that In step S1, the ultrasonic cleaning time is 10-20 minutes, and the particle sizes of the sandpaper are 800 mesh, 1000 mesh, and 1500 mesh respectively; the surface roughness of the beryllium copper alloy is polished to Ra≤0.8 μm; The ultrasonic cleaning time of anhydrous ethanol is 8-12 minutes; the power of the plasma cleaning machine is 40-60W, the Ar gas flow rate is 150-250mL / min, and the processing time is 4-6 minutes; the mass ratio of silane coupling agent modified nano-alumina to deionized water is 1:15; the thickness of the primer layer is 5-8μm; the curing temperature in the oven is 70-90℃, and the curing time is 10-20 minutes.

8. The preparation method according to claim 6, characterized in that In step S2, the mass ratio of the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles to xylene is 3:1; the speed of the electric stirrer is 700-900 rpm, and the dispersion time is 8-12 minutes; the thickness of the intermediate coating is 15-20 μm; and the curing temperature in the oven is 110-130° C., and the curing time is 20-40 minutes.

9. The preparation method according to claim 6, characterized in that In step S3, the mass ratio of the silane coupling agent modified nano-alumina to the polyurethane-silane hybrid modified with tungsten carbide / graphene composite particles is 1:1; the topcoat thickness is 5-10 μm; the curing temperature in the oven is 140-160° C., and the curing time is 0.8-1.2 hours.

10. An application of the composite coating according to any one of claims 1 to 5, characterized in that: Application of the composite coating on the surface of beryllium copper alloy.

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