A high-entropy alloy coating for metal sheet and a method for preparing the same

Abstract

The application discloses a kind of high-entropy alloy coating for metal sheet and preparation method thereof, belong to energy-saving and environment-protecting technical field.The method with low carbon steel, galvanized steel plate or aluminum alloy plate as matrix, by alkali washing, sand blasting and preheating form suitable roughness and clean surface.High-entropy alloy nano powder is prepared by a variety of metal nitrate and cerium dioxide under the action of tannic acid and polyethylene imine, and is compounded with low VOC binder containing polyethylene butyral resin, polyvinylpyrrolidone and polyacrylic acid, and is dried and solidified after being sprayed to form precast layer.Laser cladding is used under argon atmosphere, and low-temperature cooling and tempering treatment are used, to obtain high-entropy alloy coating with dense structure and firm interface bonding on the surface of matrix.The coating has high hardness, excellent wear resistance and corrosion resistance, and good high-temperature oxidation resistance, while significantly reducing the emission of organic volatile matter, and is suitable for surface strengthening of metal components requiring high durability and environmental performance.

Description

Technical Field

[0001] This invention belongs to the field of energy conservation and environmental protection technology. Specifically, it relates to a high-entropy alloy coating for metal sheets and its preparation method. Background Technology

[0002] Metal sheets (such as low-carbon steel, galvanized steel, and aluminum alloy sheets) are widely used in industrial applications such as automobiles, machinery, construction, and energy. However, these metal materials are susceptible to corrosion, wear, and high-temperature oxidation in service environments with ambient temperature and humidity, high temperatures, and high salt spray, leading to rapid degradation of material properties, shortened service life, and significant economic losses. Statistics show that global economic losses due to corrosion amount to trillions of yuan annually, with steel corrosion accounting for the largest share. To extend the service life of metal components, surface coating protection technology has gradually become the most economical and effective solution.

[0003] Currently, commonly used industrial methods for metal surface protection mainly include hot-dip galvanizing, electroplating, and spraying. Hot-dip galvanizing, by immersing steel products in molten zinc to form a zinc coating, offers good corrosion resistance and low maintenance, but has the following drawbacks: the zinc coating is easily depleted over time (sacrificial corrosion), especially in acidic or high-salt environments, where the passivation film has poor stability and limited wear resistance; the coating thickness is uneven, and brittleness may lead to cracking or peeling at low temperatures; the process involves high-temperature chemical treatment, resulting in significant environmental pollution. Electroplating, while achieving a more uniform coating and aesthetically pleasing decorative effect, is time-consuming, costly, difficult to treat wastewater, and produces significant amounts of toxic substances; furthermore, the bonding strength between the coating and the substrate is sometimes insufficient. Organic coating spraying is suitable for surface decoration, but organic solvent-based coatings emit significant amounts of volatile organic compounds (VOCs), posing a significant threat to the environment and worker health; and single-layer coatings have relatively weak wear resistance and high-temperature oxidation resistance. Even water-based coatings, due to the high permeability of water, often have lower corrosion protection capabilities than solvent-based systems.

[0004] High-entropy alloys (HEAs) are a new type of alloy composed of five or more main elements in similar atomic percentages. Compared to traditional binary or ternary alloys, HEAs exhibit high strength, high hardness, excellent corrosion resistance, high-temperature oxidation resistance, and excellent wear resistance due to their high-entropy effect, lattice distortion, and diffusion mitigation effect, making them ideal coating materials. In recent years, HEA coatings have been widely used in high-end manufacturing fields such as aerospace, automotive, and new energy.

[0005] However, current high-entropy alloy coating preparation technology still faces major bottlenecks: Complex and costly coating processes: Common methods such as laser cladding, plasma spraying, and arc spraying require high-entropy alloy powders prepared by gas atomization or mechanical alloying. These powder preparation processes involve high temperatures and high energy consumption, resulting in uneven powder mixing and difficulty in precisely controlling particle size. Furthermore, laser cladding and arc spraying processes themselves require high energy input, which can easily lead to the formation of dendrites, pores, and inclusions during coating solidification, reducing coating density and substrate adhesion. Coating costs are several to tens of times higher than traditional processes. The interfacial bonding strength between the coating and the substrate needs improvement: Many high-entropy alloy coatings use direct cladding processes, leading to thermal stress mismatch between the coating and the substrate, resulting in high residual stress and a tendency for peeling or cracking failure. Without adequate pretreatment and intermediate layer design, coating adhesion ratings are often only 3-5. Insufficient environmental performance in coating preparation: Most current high-entropy alloy coating processes use organic solvent-based binders or surfactants, resulting in VOC emissions of 40-100 mg / m³. 3 This far exceeds environmental protection requirements. Although water-based coatings have been improved, their corrosion resistance and wear resistance are often inferior to solvent-based systems. The design of the coating element system is underoptimized: existing high-entropy alloy coatings mostly use basic systems such as FeCoNiCr and CoCrFeNiTi, which have limited room for synergistic optimization of multiple indicators including corrosion resistance, wear resistance, and high-temperature oxidation resistance. The synergistic strengthening mechanism of rare earth elements (such as Ce) and refractory elements (such as Mo) has not yet been systematically and comprehensively utilized in high-entropy alloy coatings.

[0006] In summary, while traditional coating processes (hot-dip galvanizing, electroplating, and organic coatings) have high industrial maturity and relatively low cost, their durability and protective performance are limited, and they face significant environmental pressure. High-entropy alloy coatings, while exhibiting superior performance, still suffer from drawbacks such as complex processes, high costs, insufficient interfacial bonding, high VOC emissions, and limited room for elemental synergistic optimization. There is an urgent need to develop a novel coating process that combines the following characteristics: superior performance: coating hardness and wear resistance no less than existing high-entropy alloy coatings (above 650HV), strong corrosion resistance (salt spray test >1000h), and strong high-temperature oxidation resistance; reliable interfacial bonding: forming a metallurgical bond with the substrate, achieving the highest adhesion level (level 0), preventing peeling failure during service; controllable cost: relatively simplified process flow, employing scalable powder preparation and coating methods, controlling costs to within 60-80% of existing high-entropy alloy coating levels; and environmentally friendly: using low-VOC binders and coating systems, controlling VOC emissions to 10mg / m³. 3 Within the specified range, it complies with national environmental protection standards such as GB / T18582; element system optimization: through multi-element synergy (including rare earth and refractory elements) design, the comprehensive improvement of corrosion resistance, wear resistance and high temperature oxidation resistance is achieved.

[0007] Therefore, developing a method for preparing high-entropy alloy coatings for metal sheets that combines comprehensive performance and environmental protection characteristics has significant theoretical research value and practical application prospects. Summary of the Invention

[0008] Existing direct coating processes such as laser cladding and plasma spraying generate significant residual stress during high-temperature cooling due to the mismatch in thermal expansion coefficients between the substrate and the coating. This stress concentration is particularly severe with dissimilar substrates such as low-carbon steel, galvanized steel, and aluminum alloys, resulting in interfacial adhesion between the coating and substrate (typically reaching a cross-cut adhesion level of 3-5) that fails to meet high reliability requirements in industrial applications. Once the coating is subjected to mechanical shock or temperature cycling in service, it is highly susceptible to peeling, cracking, and other failures, rendering its protective function ineffective. Traditional gas atomization and mechanical alloying powder preparation processes require high-temperature, high-energy input (typically >1500℃), are expensive, and struggle to precisely control the uniformity of element distribution within the powder. Multi-element alloys are prone to micro-segregation during solidification, leading to significant differences in hardness and corrosion resistance across different regions of the coating. Furthermore, the wide particle size distribution (typically 100-300μm) hinders the formation of fine-grained structures, limiting the improvement of the coating's overall performance. Existing high-entropy alloy coatings often use binders and application systems based on organic solvents (such as dimethylformamide, acetone, etc.), with VOC emissions typically reaching 40-100 mg / m³. 3 It far exceeds the 10 mg / m³ limit specified in the "Limits of Hazardous Substances in Interior Decoration and Renovation Materials" (GB / T18582-2008). 3 These limits pose a serious threat to operator health and the environment. While water-based coatings exist as alternatives, their corrosion and abrasion resistance is often inferior to solvent-based systems due to water's high permeability. Existing high-entropy alloy coatings mostly employ relatively simple basic systems such as FeCoNiCr and CoCrFeNiTi, making it difficult to simultaneously achieve optimal performance in the three key indicators of corrosion resistance, abrasion resistance, and high-temperature oxidation resistance. The strengthening effect of rare earth elements (such as Ce) on the stability of passivation films, and the contribution of refractory elements (such as Mo) to solid solution strengthening and corrosion resistance, have not yet been systematically and comprehensively utilized in the design of high-entropy alloy coatings.

[0009] A method for preparing a high-entropy alloy coating for metal sheets, comprising the following steps by weight: (1) Substrate pretreatment: metal sheets are selected as the substrate, and after alkaline washing to remove oil and sandblasting, preheating treatment is performed; (2) Preparation of high-entropy alloy nanopowder: iron nitrate, cobalt nitrate, chromium nitrate, nickel nitrate, manganese nitrate, aluminum nitrate, ammonium molybdate, and cerium dioxide are mixed in a mass ratio of (10-20):(10-20):(5-10):(10-20):(5-10):(10-20):(5-10):(5-10) to obtain a mixture, then 10-20 times the mass of the mixture of tannic acid solution is added, and after mixing, 5-10 times the mass of the mixture of polyethyleneimine is added, the pH is adjusted to 8-9, the temperature is raised to 60-70℃, and stirring is continued for 3-6 hours, followed by vacuum freeze drying, and then... Calcination treatment to obtain particles and ball milling treatment to obtain dry powder; (3) Preparation of binder: Polyvinyl butyral resin, polyvinylpyrrolidone, polyacrylic acid, sodium dodecyl sulfate, anhydrous ethanol and deionized water are mixed in mass ratio (5-10): (2-6): (1-4): (1-3): (10-30): (20-40), and vacuum degassing is performed to obtain binder; (4) Preparation of prefabricated layer: The dry powder of step (2) and the binder of step (3) are ultrasonically dispersed in mass ratio (1-3): 1 to obtain slurry and applied to the substrate after preheating treatment in step (1), and then dried to obtain a prefabricated layer with a thickness of 100-200μm; (5) Control of prefabricated layer: The prefabricated layer of step (4) is clad under argon atmosphere, then cooled to -20℃, and then tempered.

[0010] Preferably, the thickness of the metal plate in step (1) is 0.5-3mm; the metal plate in step (1) is low carbon steel, galvanized steel plate or aluminum alloy plate; the alkaline washing solution in step (1) is a sodium hydroxide solution with a concentration of 0.4-3.5g / L; the parameters of the sandblasting treatment in step (1) are as follows: sand particles with a diameter of 125μm, pressure of 0.3-0.7MPa, time of 2min, and surface roughness Ra controlled at 1.0-5.0μm; the parameters of the preheating treatment in step (1) are as follows: preheating at 250-350℃ for 10-30min.

[0011] Preferably, the mixing temperature in step (2) is 40-50℃ and the mixing speed is 120-140 rpm; the concentration of the tannic acid solution in step (2) is 0.2-0.6 g / L; and the pH adjustment solution in step (2) is sodium hydroxide solution.

[0012] Preferably, the stirring speed in step (2) is 100-200 rpm; the calcination treatment in step (2) is as follows: calcination at 700-900℃ for 12-24h under nitrogen atmosphere; the ball milling parameters in step (2) are as follows: ball-to-material mass ratio is 5:1-15:1, ball milling speed is 200-500 r / min, and ball milling time is 4-12h.

[0013] Preferably, the mixing parameters in step (3) are as follows: stirring at 60-80 rpm for 60-100 min; the vacuum degassing parameters in step (3) are as follows: temperature 60-80℃, time 20-40 min.

[0014] Preferably, the parameters for ultrasonic dispersion in step (4) are as follows: power 200-600W, frequency 20-40kHz, time 20-40min, and temperature 20-40℃.

[0015] Preferably, the parameters for coating in step (4) are as follows: spray gun temperature 130-160℃, spray gun nozzle diameter 2mm, spray pressure 0.3-0.5MPa, spray gun distance 15cm, spray angle 60-70°, and spray speed 20-30cm / s.

[0016] Preferably, the drying parameters in step (4) are as follows: temperature 80-120℃, time 30-60min.

[0017] Preferably, the parameters for the cladding process in step (5) are as follows: laser power is 2000-3000W, scanning speed is 10-20mm / s, and spot diameter is 2-4mm; the tempering temperature in step (5) is 300-500℃ and the time is 2-4h.

[0018] A high-entropy alloy coating for metal sheets, wherein the high-entropy alloy coating for metal sheets is obtained by the preparation method described above.

[0019] Compared to existing technologies, this invention achieves the following significant technical effects through the comprehensive innovation of introducing a multi-element synergistic strengthening system and a green preparation process: the high-entropy alloy coating prepared by this invention achieves a Vickers hardness (HV) of 685.2-765.8 HV. This hardness level has reached the international advanced level for similar laser-clad high-entropy alloy coatings. Correspondingly, the wear resistance of the coating is also significantly improved.

[0020] Friction and wear tests conducted according to GB / T3960 standard show that the wear rate of the coating of this invention is 0.27-0.38 mg / cm². 2 The control group had a concentration of 0.78-0.92 mg / cm³. 2The improvement in hardness reaches 60-70%. The mechanism of hardness enhancement comes from the fact that the elements in the Fe-Co-Cr-Ni-Mn-Al-Mo-Ce octet form solid solutions in the high-entropy alloy matrix, increasing lattice distortion and atomic packing density, thereby improving the strength and hardness of the material. Molybdenum (Mo) has an extremely high melting point (2623℃), and its solid solution in the high-entropy alloy matrix provides strong solid solution strengthening. At the same time, the addition of Mo inhibits grain growth in the coating during high-temperature cooling, ensuring a fine-grained structure.

[0021] Rare earth oxide CeO2 is uniformly dispersed in the alloy matrix in particulate form, significantly hindering dislocation movement. This is an innovation that distinguishes it from existing FeCoNiCr or CoCrFeNiTi systems, contributing an additional 100-150 HV of hardness increase. Through controlled low-temperature cooling (-20℃) and medium-temperature tempering, a finer grain structure (estimated grain size <10μm) was obtained compared to direct laser cladding. According to the Hall-Petch relationship, fine-grained strengthening also significantly contributes to the hardness improvement. The 5% NaCl salt spray test conducted according to GB / T10125-2012 standard is an important indicator for evaluating the coating's corrosion resistance.

[0022] The salt spray test time (until rust spots appear) of this invention reached 1180.3-1320.9 hours, with an average of approximately 1250 hours, representing an improvement of approximately 92.3%, or nearly double. This significant improvement stems from a multi-layered protective mechanism: chromium (12-15 wt% equivalent) forms a dense passivation film primarily composed of Cr2O3 on the coating surface, which is the foundation of the high-entropy alloy's corrosion resistance. Compared to the passivation film of traditional elemental Cr, the presence of multiple elements in the high-entropy alloy enhances the stability of the passivation film. Rare earth oxide CeO2 is not only a hardening phase, but more importantly, it can be adsorbed onto the coating surface, enhancing the density and defect repair capability of the passivation film. When the passivation film is locally damaged, CeO2 can promote its rapid reformation, which is a key advantage of this invention compared to systems without CeO2. Manganese lowers the corrosion potential, improving the coating's resistance to localized corrosion; molybdenum, through the formation of MoO4... 2- The presence of anions further stabilizes the passivation film. Nickel provides excellent thermodynamic stability, forming a dense protective layer on the coating surface.

[0023] This invention employs a three-layer progressive design of "pre-formed layer buffer + low-temperature cooling + tempering control," enabling the coating to achieve a cross-cut adhesion rating of 0 (the optimal rating in GB / T9286-2021) on all substrates (low-carbon steel, galvanized steel sheet, aluminum alloy sheet), while the comparative samples generally show a rating of 3-4. This means that the coating exhibits no peeling at the cross-cut marks, and its bonding strength is significantly superior to traditional processes. Mechanism analysis: Compared to direct laser cladding, the introduction of the pre-formed layer ensures that the cladding layer does not directly act on the substrate but rather fuses with the pre-formed layer, significantly reducing thermal stress concentration during the cladding process. The alkaline washing, sandblasting (roughness Ra 1.0-5.0 μm), and preheating (250-350℃) in the substrate pretreatment also provide mechanical bonding and thermal matching. Directly cooling from a high temperature (>1300℃) to −20℃ produces a higher cooling rate compared to room temperature cooling, suppressing the formation of coarse dendrites and obtaining a fine-grained martensite or metastable phase structure. These structures have higher surface energy, which is beneficial for metallurgical bonding with the matrix. Tempering treatment partially recovers the supercooled martensite, precipitating a hard phase that forms a stronger interface with the matrix, while reducing residual stress. According to the data from the examples, the fracture location of the tempered specimens in tensile tests occurred in the matrix rather than at the interface, fully demonstrating the superiority of the interface strength. In the 800℃ oxidation test conducted according to the experimental procedure for 24 hours, the weight gain of the coating of the present invention was 1.08-1.42% (average about 1.25%), while that of the comparative example was 3.48-3.82% (average about 3.65%), a reduction of about 65.8%. This indicates that the oxidation resistance of the coating in high-temperature service environments is far superior to that of the comparative scheme. Antioxidation Mechanism: Aluminum preferentially oxidizes at high temperatures to form Al2O3, one of the densest and most protective metal oxide films, effectively preventing further oxidation of the inner alloy layers. In conjunction with Al2O3, Cr2O3 forms a multi-layered oxide film structure, enhancing the barrier effect. CeO2, with its high melting point (2400℃) and thermal stability, acts as a framework phase in high-temperature oxide films, significantly reducing the tendency for oxide film peeling. The complex crystal structure of multiple principal elements and high lattice distortion in high-entropy alloys slow down the diffusion rate of oxygen and metal ions, thereby reducing the oxidation rate.

[0024] The low-VOC binder system used in this invention has a VOC emission of 8.1-9.4 mg / m³. 3 The VOC emissions of the comparative example (using traditional organic solvent-based binders) were 43.6-48.2 mg / m³. 3 The reduction rate is 82-84%, fully complying with the ≤10mg / m³ limit of hazardous substances in GB / T18582-2017 "Limits of Hazardous Substances in Interior Decoration and Renovation Materials". 3The key to this improvement lies in using deionized water and anhydrous ethanol as the main solvents, resulting in extremely low volatile organic compound (VOC) content compared to traditional organic solvents such as dimethylformamide (DMF) and acetone. Sodium dodecyl sulfate (SDS), as a food-grade surfactant, exhibits significantly lower toxicity and VOC contribution compared to traditional organophosphates or long-chain alkylbenzene sulfonates. The optimized mass ratio of PVB, PVP, and PAA minimizes the required organic solvent usage while ensuring adhesion and flowability. By avoiding high-temperature gas atomization and prolonged heating, the overall energy consumption and pollutant emissions of this process are far lower than traditional high-entropy alloy powder preparation methods. Compared to gas atomization powder production (equipment investment > 10 million RMB) and high-power laser direct cladding (laser price > 1 million RMB), this invention achieves: costs only 20-30% of gas atomization powder production and is easily scalable; compared to single laser cladding, laser power requirements are reduced by 30-40%, significantly lowering equipment and operating costs.

[0025] In summary, this invention has achieved breakthroughs in coating performance, environmental performance, and industrial feasibility through multi-level innovation (multi-element system, rare earth reinforcement, low VOC binder, and step-by-step control process). It is a rare comprehensive optimization solution in the prior art that combines "high performance + green environmental protection + controllable cost". Attached Figure Description

[0026] Figure 1 This is a transmission electron microscope image of the dry powder prepared in Example 1.

[0027] Figure 2 This is a state diagram of the adhesive prepared in Example 1.

[0028] Figure 3 This is the infrared spectrum of the adhesive prepared in Example 1. Detailed Implementation

[0029] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to restrict the scope of protection of the invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected. Also, for mass ratios not explicitly stated or mentioned, the mass ratio after addition generally refers to the mass ratio. Furthermore, in the present invention, the unit of mass is grams (g).

[0030] Example 1

[0031] The preparation method of high entropy alloy coating for metal sheet includes the following steps: (1) Substrate pretreatment: low carbon steel with a thickness of 2 mm is selected as the substrate, and sodium hydroxide solution with a concentration of 2 g / L is used for alkaline washing to remove oil. Then, sandblasting is performed. The sandblasting parameters are sand particles with a diameter of 125 μm, pressure of 0.5 MPa, time of 2 min, and surface roughness Ra controlled at 3 μm. Finally, preheating is performed with the parameters of preheating at 300℃ for 20 min.

[0032] (2) Preparation of high-entropy alloy nanopowder: Ferric nitrate, cobalt nitrate, chromium nitrate, nickel nitrate, manganese nitrate, aluminum nitrate, ammonium molybdate, and cerium dioxide were mixed in a mass ratio of 15:15:7.5:15:7.5:15:7.5:7.5 (total mass of 90g, i.e., 15g ferric nitrate, 15g cobalt nitrate, 7.5g chromium nitrate, 15g nickel nitrate, 7.5g manganese nitrate, 15g aluminum nitrate, 7.5g ammonium molybdate, and 7.5g cerium dioxide) at 45℃ and 130rpm to obtain a mixture. Then, 15 times the mass of the mixture was added ( A 0.4 g / L tannic acid solution (1350 g) was mixed thoroughly, and then 7.5 times the mass of the mixture (675 g) of polyethyleneimine was added. The pH was adjusted to 8.5 (using sodium hydroxide solution). The mixture was heated to 65°C and stirred continuously at 150 rpm for 4.5 h. Vacuum freeze-drying followed by calcination at 800°C for 18 h under a nitrogen atmosphere yielded granules, which were then ball-milled. The ball-milling parameters were: ball-to-material mass ratio 10:1, ball milling speed 350 r / min, and ball milling time 8 h. A dry powder was obtained, and its elemental distribution diagram under transmission electron microscopy is shown below. Figure 1 As shown.

[0033] (3) Preparation of adhesive: Polyvinyl butyral resin, polyvinylpyrrolidone, polyacrylic acid, sodium dodecyl sulfate, anhydrous ethanol and deionized water were mixed in a mass ratio of 7.5:4:2.5:2:20:30 (total mass of 66g, i.e., 7.5g polyvinyl butyral resin, 4g polyvinylpyrrolidone, 2.5g polyacrylic acid, 2g sodium dodecyl sulfate, 20g anhydrous ethanol and 30g deionized water) at 70 rpm for 80 min. The vacuum degassing parameters were 70℃ and 30 min to obtain the adhesive, the state diagram of which is shown in the figure. Figure 2 As shown, its infrared spectrum is as follows Figure 3 As shown.

[0034] (4) Preparation of the prefabricated layer: The dry powder from step (2) and the binder from step (3) are ultrasonically dispersed at a mass ratio of 2:1 (total mass of dry powder is 60g and total mass of binder is 30g). The parameters are power 400W, frequency 30kHz, time 30min and temperature 30℃. The slurry is obtained and applied to the substrate after the preheating treatment in step (1). The application parameters are spray gun temperature 145℃, spray gun diameter 2mm, spraying pressure 0.4MPa, spray gun distance 15cm, spraying angle 65° and spraying speed 25cm / s. Then, it is dried with the parameters of temperature 100℃ and time 45min to obtain a prefabricated layer with a thickness of 150μm.

[0035] (5) Control of the prefabricated layer: The prefabricated layer from step (4) was clad under an argon atmosphere with a laser power of 2500W, a scanning speed of 15mm / s, and a spot diameter of 3mm. Then, it was cooled to -20℃ and subsequently tempered at 400℃ for 3 hours to obtain a high-entropy alloy coating. The obtained high-entropy alloy coating for metal sheets has the following physical parameters: a thickness of 150μm and good wear resistance.

[0036] The specific parameters for Examples 2-8 and Comparative Examples 1-8 are listed in the following tables. The tables are designed according to the progression of the steps, with each table reflecting different parameter values ​​for the examples / comparative examples, covering all endpoint and intermediate values. Only the parameters that have changed from those in Example 1 are listed in the tables; the descriptions of the remaining parameters are the same as in Example 1.

[0037] Table 1: Parameters for matrix pretreatment in step (1)

[0038]

[0039] Table 2: Preparation parameters of high-entropy alloy nanopowder in step (2)

[0040]

[0041] Table 3: Preparation parameters of high-entropy alloy nanopowder in step (2)

[0042]

[0043] Table 4: Preparation parameters of adhesive in step (3)

[0044]

[0045] Table 5: Preparation parameters of the prefabricated layer in step (4)

[0046]

[0047] Table 6: Preparation parameters of the prefabricated layer in step (4)

[0048]

[0049] Table 7: Control parameters of the precast layer in step (5)

[0050]

[0051] To verify the performance of the high-entropy alloy coating for metal sheets described in this invention, multi-dimensional tests were conducted on the products prepared in Examples 1-8 and Comparative Examples 1-8. The tests included coating hardness (Vickers hardness), corrosion resistance (salt spray test time), abrasion resistance (wear rate), adhesion (cross-cut test grade), heat resistance (high-temperature oxidation weight gain rate), and environmental performance (VOC emissions). The test methods are as follows: Coating hardness test: Measured using a Vickers hardness tester (model: HV-1000), with a load of 500g and a loading time of 10s. Corrosion resistance test: According to GB / T10125-2012 standard, a salt spray test chamber (model: YWX-60) was used, with 5% NaCl solution and a temperature of 35℃, and the time until rust spots appeared was recorded (h). Abrasion resistance test: According to GB / T3960-2016 standard, a friction and wear testing machine (model: MM-200) was used, with a load of 200N, a rotation speed of 200r / min, and a time of 30min, and the wear rate (mg / cm²) was calculated. 2 Adhesion test: According to GB / T9286-2021 standard, the cross-cut test was used to evaluate the grade (0-5, grade 0 being the best). Heat resistance test: Oxidation at 800℃ for 24 hours, and the weight gain rate (%) was calculated. Environmental performance test: According to GB / T18582-2017 standard, VOC emissions (mg / m³) were measured using a gas chromatograph (model: GC-7890). 3 The sample was placed in a sealed chamber and collected 24 hours later.

[0052] Table 8: Performance Test Results

[0053]

[0054] Table 9: Performance Test Results II

[0055]

[0056] The test results show that the coating hardness of the products in the examples ranges from 685.2 to 765.8 HV, the salt spray time ranges from 1180.3 to 1320.9 h, and the wear rate ranges from 0.27 to 0.38 mg / cm². 2 The original sample exhibited excellent performance; the comparative sample, due to component deficiency or parameter deviation, showed a significant decrease in performance (e.g., hardness decreased to 465.3-510.9 HV, and salt spray time decreased to 620.8-680.4 h). This demonstrates the superiority of the preparation method of this invention.

[0057] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted herein.

Claims

1. A method for preparing a high-entropy alloy coating for metal sheets, characterized in that: The process, by weight, includes the following steps: (1) Pretreatment of the matrix: metal plates are selected as the matrix, and the substrate is preheated after being degreased by alkaline washing and sandblasting; (2) Preparation of high-entropy alloy nanopowder: iron nitrate, cobalt nitrate, chromium nitrate, nickel nitrate, manganese nitrate, aluminum nitrate, ammonium molybdate, and cerium dioxide are mixed in a mass ratio of (10-20): (10-20): (5-10): (10-20): (5-10): (10-20): (5-10): (5-10) to obtain a mixture. Then, tannic acid solution of 10-20 times the mass of the mixture is added, and after mixing, polyethyleneimine of 5-10 times the mass of the mixture is added. The pH is adjusted to 8-9, the temperature is raised to 60-70℃, and the mixture is stirred continuously for 3-6 hours. Then, vacuum freeze-drying is carried out, followed by calcination to obtain particles and further processing. (2) Ball milling to obtain dry powder; (3) Preparation of binder: Polyvinyl butyral resin, polyvinylpyrrolidone, polyacrylic acid, sodium dodecyl sulfate, anhydrous ethanol and deionized water are mixed in mass ratio (5-10): (2-6): (1-4): (1-3): (10-30): (20-40), and vacuum degassing is performed to obtain binder; (4) Preparation of prefabricated layer: The dry powder of step (2) and the binder of step (3) are ultrasonically dispersed in mass ratio (1-3): 1 to obtain slurry and applied to the substrate after preheating treatment in step (1), and then dried to obtain a prefabricated layer with a thickness of 100-200μm; (5) Control of prefabricated layer: The prefabricated layer of step (4) is clad under argon atmosphere, then cooled to -20℃, and then tempered.

2. The method for preparing a high-entropy alloy coating for metal sheets according to claim 1, characterized in that: The thickness of the metal sheet in step (1) is 0.5-3mm; the metal sheet in step (1) is low carbon steel, galvanized steel sheet or aluminum alloy sheet; the alkaline washing solution in step (1) is a sodium hydroxide solution with a concentration of 0.4-3.5g / L; the parameters of the sandblasting treatment in step (1) are as follows: sand particles with a diameter of 125μm, pressure of 0.3-0.7MPa, time of 2min, and surface roughness Ra controlled at 1.0-5.0μm; the parameters of the preheating treatment in step (1) are as follows: preheating at 250-350℃ for 10-30min.

3. The method for preparing a high-entropy alloy coating for metal sheets according to claim 1, characterized in that: The mixing temperature in step (2) is 40-50℃ and the mixing speed is 120-140rpm; the concentration of tannic acid solution in step (2) is 0.2-0.6g / L; the pH adjustment solution in step (2) is sodium hydroxide solution.

4. The method for preparing a high-entropy alloy coating for metal sheets according to claim 1, characterized in that: The stirring speed in step (2) is 100-200 rpm; the calcination treatment in step (2) is as follows: calcination at 700-900℃ for 12-24h under nitrogen atmosphere; the ball milling parameters in step (2) are as follows: ball-to-material mass ratio is 5:1-15:1, ball milling speed is 200-500 r / min, and ball milling time is 4-12h.

5. The method for preparing a high-entropy alloy coating for metal sheets according to claim 1, characterized in that: The mixing parameters in step (3) are as follows: stir at 60-80 rpm for 60-100 min; the vacuum degassing parameters in step (3) are as follows: temperature 60-80℃, time 20-40 min.

6. The method for preparing a high-entropy alloy coating for metal sheets according to claim 1, characterized in that: The parameters for ultrasonic dispersion in step (4) are as follows: power 200-600W, frequency 20-40kHz, time 20-40min, temperature 20-40℃.

7. The method for preparing a high-entropy alloy coating for metal sheets according to claim 1, characterized in that: The parameters for application in step (4) are as follows: spray gun temperature 130-160℃, spray gun nozzle diameter 2mm, spray pressure 0.3-0.5MPa, spray gun distance 15cm, spray angle 60-70°, and spray speed 20-30cm / s.

8. The method for preparing a high-entropy alloy coating for metal sheets according to claim 1, characterized in that: The drying parameters in step (4) are as follows: temperature 80-120℃, time 30-60min.

9. The method for preparing a high-entropy alloy coating for metal sheets according to claim 1, characterized in that: The parameters for the cladding process in step (5) are as follows: laser power is 2000-3000W, scanning speed is 10-20mm / s, and spot diameter is 2-4mm; the tempering temperature in step (5) is 300-500℃ and the time is 2-4h.

10. A high-entropy alloy coating for metal sheets, characterized in that: The high-entropy alloy coating for metal sheets is obtained by the preparation method described in any one of claims 1-9.

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