Friction-resistant high-entropy alloy composite coating as well as preparation method and application thereof

Abstract

The invention provides a friction-resistant high-entropy alloy composite coating and a preparation method thereof, and belongs to the technical field of metal surface modification. A FeCoCrNiMox (x is greater than or equal to 0.18 and less than or equal to 0.25) high-entropy alloy is taken as a main component of composite powder, graphene is taken as an additive phase, and the FeCoCrNiMox high-entropy alloy composite coating is prepared on the surface of a matrix by adopting a laser cladding method. The graphene added in the composite powder can generate carbides in situ under the action of laser cladding, and second phase strengthening, solid solution strengthening and fine grain strengthening are generated, so that the friction resistance of the surface of the matrix is remarkably improved. The preparation method is easy to operate and low in cost, the prepared composite coating is high in bonding strength, good in toughness and plasticity and excellent in friction resistance, the surface performance of equipment can be effectively improved, safe and stable operation of the equipment is guaranteed, the service life of the equipment is prolonged, and maintenance expenditure is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal surface modification, and specifically relates to a friction-resistant high-entropy alloy composite coating and a preparation method thereof, and also relates to the application of the friction-resistant high-entropy alloy composite coating in equipment surface protection. Background Art

[0002] With the rapid advancement of industrial technology for extreme environments, the performance bottlenecks of traditional coating materials are becoming increasingly prominent. While traditional coatings such as nickel-chromium alloys, aluminum oxide, or fluoride coatings offer some wear resistance, they are prone to phase separation, oxidation failure, and increased brittleness in complex environments, resulting in a significant decrease in wear resistance. These coatings are unable to meet the long life and high reliability requirements of aerospace, energy equipment, marine engineering, and other fields.

[0003] High entropy alloys have four major effects due to their unique design concept of equiatomic ratios, which enable them to possess excellent properties such as high strength, high hardness, and high wear resistance that traditional alloys cannot match, giving them great application potential in the field of friction-resistant material preparation. Patent CN107699770A discloses a method for preparing a CuNiMnCoNbHf high entropy alloy coating, which has high hardness, high friction and wear resistance, and high high-temperature oxidation resistance. However, this high-entropy alloy coating is prone to brittle failure and is difficult to meet the requirements of applications under high-intensity working conditions. Patent CN114107715A discloses a FeCoCrNiMo-based high-entropy alloy composite material, its preparation method and application. It adds Ag and Ti to the FeCoCrNiMo high-entropy alloy, which effectively reduces the friction coefficient of the material and improves the friction resistance of the material. However, excessive Mo will produce intermetallic compounds, which makes the material prone to failure due to corrosion during service, and the preparation cost of bulk materials is high, making it difficult to achieve large-scale industrial applications.

[0004] To address the above problems, the present invention provides a friction-resistant high-entropy alloy composite coating and a preparation method thereof. The composite coating is simple to prepare and can form a metallurgical bond with the substrate. The single FCC structure (Face-Centered Cubic) gives the coating excellent toughness, which can effectively avoid cracking during service, and has excellent friction resistance while ensuring corrosion resistance. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a method for preparing a friction-resistant high-entropy alloy composite coating which has a simple preparation method, good bonding with a substrate, high toughness and excellent corrosion resistance.

[0006] A second object of the present invention is to provide a friction-resistant high-entropy alloy composite coating that forms a metallurgical bond with a substrate, has a single FCC structure, and can improve the toughness and corrosion resistance of the substrate.

[0007] A third object of the present invention is to provide an application of a friction-resistant high-entropy alloy composite coating in equipment surface protection.

[0008] The technical solution adopted by the present invention to achieve one of the objectives is to provide a method for preparing a friction-resistant high-entropy alloy composite coating, comprising the following steps: S1. Prepare FeCoCrNiMo according to the molar ratio of Fe, Co, Cr, Ni and Mo being 1:1:1:1:x, 0.18≤x≤0.25 x High entropy alloy powder; S2, adding graphene and FeCoCrNiMo according to the addition amount of 0.2wt.%-0.4wt.%, x High entropy alloy powders are mixed and ball-milled to obtain composite powders; S3. Prepare a high entropy alloy composite coating on the surface of the substrate by laser cladding the composite powder; in the laser cladding, the laser power is 600-800W, the flow rate of the shielding gas is 15-20L / min, and the scanning speed is 4-8mm / s.

[0009] The overall idea and inventive principle of the present invention are as follows: The present invention adopts the method of laser cladding to prepare a high entropy alloy composite coating on the substrate surface to improve the surface properties of the substrate. The raw material powder used for laser cladding is FeCoCrNiMo x High entropy alloy is used as the main component, and a small amount of graphene is used as an added phase.

[0010] First, the present invention adopts FeCoCrNiMo x High entropy alloy is the main component of the cladding layer. The addition of Fe can significantly reduce the composition difference between the coating and the substrate, reduce the thermal expansion coefficient mismatch and chemical potential gradient at the interface, thereby enhancing the metallurgical bonding between the coating and the substrate and avoiding peeling or cracking; Co has excellent high-temperature oxidation resistance and thermal stability, which can enhance the softening resistance of the coating in high-temperature environments caused by friction and wear, and reduce performance degradation during thermal cycling; Cr can form a dense Cr2O3 passivation film, effectively blocking the intrusion of oxygen, water and other corrosive media, and improving the coating's resistance to acidic, alkaline or Cl-containing environments. - The corrosion resistance in the environment increases the application field of the coating; Ni can promote the formation of FCC phase in high entropy alloys, improve the ductility and toughness of the coating, avoid brittle fracture, and thus improve the fatigue resistance and creep resistance of the coating. For Mo, the oxidation products of Mo can be adsorbed in the defects of the passivation film, inhibiting Cl -At the same time, Mo has a large atomic radius, and its introduction will aggravate the lattice distortion, enhance the solid solution strengthening effect, and improve the hardness and wear resistance of the coating. However, too much Mo will cause σ phase to be generated in the coating, forming a Mo / Cr-poor area, which reduces the corrosion resistance of the coating. Thermodynamic calculation results also show that when the Mo content is <0.17, it is difficult to form a high entropy alloy. When the Mo content is >0.25, the average number of electron holes is too high, and too much intermetallic compound precipitates, affecting its corrosion resistance. Therefore, based on the consideration of comprehensive performance, the present application limits the molar ratio of Fe, Co, Cr, Ni, and Mo in the high entropy alloy powder to 1:1:1:1:x, and 0.18≤x≤0.25.

[0011] Secondly, the composite powder of this invention also incorporates a certain amount of graphene. Graphene decomposes into carbon atoms under the high energy of a laser. These carbon atoms not only dissolve into the high-entropy alloy matrix as interstitial atoms, resulting in solid-solution strengthening, but also in situ form micronized carbides (3-15μm in diameter) with matrix elements, simultaneously refining the grains and inducing second-phase strengthening and grain refinement. Furthermore, to ensure the effective functioning of all three strengthening mechanisms, the amount of graphene added must be strictly controlled. Too little graphene will not achieve sufficient strengthening, while excessive addition will result in the in-situ formation of large carbides within the coating, increasing abrasive wear and reducing the friction resistance of the composite coating. Furthermore, excessive graphene can lead to layer agglomeration due to van der Waals forces and the π-π stacking effect, further reducing the wear resistance of the composite coating. Therefore, this application limits the addition amount of graphene in the composite powder to 0.2wt.%-0.4wt.%, so as to ensure the synergistic effect of the three strengthening mechanisms, thereby significantly improving the hardness and friction resistance of the substrate surface.

[0012] Finally, in view of the particularity of the composite powder composition, especially considering the high thermal conductivity of graphene, the laser energy can be evenly dispersed during the laser cladding process, reducing the temperature gradient of the molten pool and thus affecting the forming effect and performance of the coating. The present invention also optimizes and adjusts the parameters of laser cladding: among them, the laser power is controlled to 600-800W to maintain a balance between the dilution rate and metallurgical bonding; the shielding gas flow rate is controlled to 15-20L / min, and a high-flow shielding gas is used to ensure the cladding effect of graphene and prevent severe oxidation of the coating; the scanning speed is controlled to 4-8mm / s to balance the forming and cladding efficiency of the coating.

[0013] Based on the above-mentioned inventive concept, the present invention adopts a suitable laser cladding process to process composite powder containing graphene, and the obtained high-entropy alloy composite coating has better toughness and corrosion resistance, and at the same time generates carbides in situ; the three strengthening mechanisms (solid solution strengthening, second phase strengthening and fine grain strengthening) triggered by the addition of graphene can also significantly improve the hardness and friction resistance of the substrate surface.

[0014] Furthermore, in step S1, FeCoCrNiMo is prepared by gas atomization powder making. x High-entropy alloy powder. Research has found that excessively fine high-entropy alloy powder particles can reduce powder fluidity due to van der Waals forces and electrostatic adsorption, leading to powder blockage. Furthermore, the large specific surface area resulting from excessively fine powders can increase coating surface activity, making it susceptible to oxidation and vaporization during the cladding process, reducing coating performance. Excessively large high-entropy alloy powder particles can lead to low laser energy absorption efficiency, resulting in unfused areas and reduced coating quality. Preferably, the high-entropy alloy powder has a particle size of 45-105 μm.

[0015] Furthermore, in step S2, the graphene is few-layer graphene with three or fewer atomic layers. Compared to graphite or multi-layer graphene, few-layer graphene has higher thermal conductivity. During the laser cladding process, it can evenly disperse the laser energy, reduce the temperature gradient of the molten pool, and avoid cracking. It also helps to quickly dissipate heat, reduce residual stress, and improve the bonding strength between the cladding layer and the substrate. In addition, compared to graphite and multi-layer graphene, few-layer graphene is easier to disperse during the ball milling process, making the in-situ formed carbides more evenly distributed in the coating, avoiding uneven coating performance.

[0016] Furthermore, in step S2, the ball milling treatment is performed in an intermittent operation mode, the rotation speed of the ball milling treatment is 250-350 rpm, and the ball milling treatment time is 3-5 hours.

[0017] Preferably, ball milling uses 5 mm and 10 mm 304L austenitic stainless steel balls, with a mass ratio of 5 mm:10 mm = 4:1. Intermittent milling is performed for 20 minutes, followed by a 10-minute pause and then a subsequent re-milling. This intermittent milling method prevents oxidation or cold welding of the raw materials due to heat generation during milling.

[0018] Furthermore, the FeCoCrNiMo in step S1 x The preparation process of the high entropy alloy powder and the composite powder in step S2 both includes a drying process, which is carried out at a temperature of 90-110°C for 2-4 hours. The drying process protects the powder from moisture and prevents the formation of pores in the prepared coating.

[0019] Furthermore, in step S3, before laser cladding, the substrate is polished, ultrasonically cleaned, and preheated in sequence. Preferably, the ultrasonic cleaning medium includes acetone or anhydrous ethanol, which is beneficial for removing impurities on the surface of the pretreated substrate and is easy to clean the ultrasonic medium.

[0020] Furthermore, preheating the substrate can prevent cracks on the substrate surface during laser cladding. If the preheating temperature is too low, residual stresses cannot be eliminated, and the coating is prone to deformation or cracking. Excessively high temperatures can cause grain growth and degrade substrate performance. Preferably, the preheating temperature is 100-200°C, and the preheating time is 20-30 minutes.

[0021] Furthermore, in step S3, the parameter selection of laser cladding determines the quality of cladding. The present invention adopts the parameter conditions of laser power of 600-800W, flow rate of shielding gas of 15-20L / min, and scanning speed of 4-8mm / s to ensure the comprehensive performance of the coating. When the power of laser cladding is too low, the dilution rate of the coating and the substrate is low, and the metallurgical bonding strength is poor; when the power is too high, it will cause the matrix elements to diffuse into the coating, reducing the coating performance; when the gas flow rate is too small, the coating is easily oxidized; and when the gas flow rate is too large, it is easy to cause waste of resources. When the scanning speed is too slow, the coating cannot be formed; and when the scanning speed is too fast, it will cause the deposition rate to decrease, reducing the powder utilization rate and coating thickness. Preferably, in laser cladding, the powder feeding speed is 5-7rad / min, the overlap distance is 10-16μm, and the shielding gas is one of argon, nitrogen or helium.

[0022] The technical solution adopted by the present invention to achieve the second purpose is: to provide a friction-resistant high-entropy alloy composite coating, which is prepared by the preparation method according to one of the purposes of the present invention.

[0023] The technical solution adopted by the present invention to achieve the third purpose is: to provide an application of the friction-resistant high-entropy alloy composite coating described in the second purpose of the present invention in equipment surface protection.

[0024] Furthermore, the substrate material of the equipment surface includes carbon steel, aluminum alloy, titanium alloy and other traditional alloys with poor friction resistance or corrosion resistance and certain high temperature resistance.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for preparing a friction-resistant high-entropy alloy composite coating, which uses a laser cladding method to prepare a cladding layer on the surface of a substrate using composite powder. In the composite powder, FeCoCrNiMo xHigh-entropy alloy, the primary component of the coating, controls the Mo content to prevent corrosion failure during service and induce significant lattice distortion, resulting in a coating with excellent hardness and friction resistance. Furthermore, the addition of a small amount of graphene to the composite powder triggers three strengthening mechanisms, effectively improving the coating's hardness and friction resistance. Furthermore, due to its small size, graphene facilitates uniform distribution during the composite powder preparation process. Once formed, the coating avoids stress concentration caused by uneven composition, thereby enhancing the coating's deformation resistance and friction resistance.

[0026] (2) The friction-resistant high entropy alloy composite coating provided by the present invention forms a metallurgical bond with the substrate and has good bonding strength. x High-entropy alloys present a single FCC structure, and the addition of graphene does not change its crystal structure. They have good plasticity and toughness, which can reduce the initiation and expansion of cracks during friction and wear, thereby improving fatigue wear resistance.

[0027] (3) The friction-resistant high-entropy alloy composite coating provided by the present invention has a simple preparation method, low cost, high bonding strength, good toughness and plasticity and excellent friction resistance, which can effectively improve the surface performance of the equipment, ensure the safe and stable operation of the equipment, increase the service life of the equipment, and reduce maintenance expenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the friction-resistant high-entropy alloy composite coating near the fusion line prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of in-situ synthesized carbides in the friction-resistant high-entropy alloy composite coating prepared in Example 1 of the present invention; Figure 3 FeCoCrNiMo prepared with different Mo contents in the examples and comparative examples of the present invention x Comparison of corrosion resistance of high entropy alloy composite coatings; Figure 4 Schematic diagram of wear volume calculation for testing the wear amount of composite coatings in the embodiments of the present invention and comparative examples; Figure 5 1 is a comparison chart of the wear loss of the composite coatings with different graphene contents and the Q235 substrate in the embodiments of the present invention and the comparative examples; Figure 6 The effects of different laser powers on FeCoCrNiMo in the embodiments of the present invention and the comparative examples are shown in FIG. 0.2 Comparison of dilution rates of high entropy alloy coatings; Figure 7 The effects of different shielding gas flow rates on FeCoCrNiMo in the embodiments of the present invention and the comparative examples are shown in FIG.0.2 Comparison of the effects of high-entropy alloy coating macromorphology; (a) shielding gas flow rate is 10 L / min; (b) shielding gas flow rate is 12.5 L / min; (c) shielding gas flow rate is 15 L / min; Figure 8 FeCoCrNiMo prepared at different scanning speeds in the embodiments of the present invention and the comparative examples 0.2 Comparison of high-entropy alloy coating morphologies; (a) scanning speed is 2 mm / s; (b) scanning speed is 3 mm / s; (c) scanning speed is 4 mm / s; (d) scanning speed is 6 mm / s; (e) scanning speed is 8 mm / s; (f) scanning speed is 10 mm / s. DETAILED DESCRIPTION

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0031] An embodiment of the present invention provides a method for preparing a friction-resistant high-entropy alloy composite coating, comprising the following steps: Step 1: Prepare FeCoCrNiMo by gas atomization powdering according to the molar ratio of Fe, Co, Cr, Ni and Mo being 1:1:1:1:x, 0.18≤x≤0.25 x High entropy alloy powder is dried at a temperature of 90-110° C. for 2-4 hours, and the particle size of the high entropy alloy powder is 45-105 μm; Step 2: Add 0.2wt.%-0.4wt.% of few-layer graphene (atomic layer is 3 layers or less) and FeCoCrNiMo x The high entropy alloy powders are mixed and ball milled in an intermittent operation mode at a rotation speed of 250-350 rpm for 3-5 hours to obtain a composite powder, which is then dried at a temperature of 90-110° C. for 2-4 hours. Step 3: The substrate is polished, ultrasonically cleaned and preheated in sequence, the preheating temperature is 100-200°C, and the preheating time is 20-30 min; the composite powder is laser clad to prepare a high-entropy alloy composite coating on the surface of the substrate; in the laser cladding, the laser power is 600-800W, the flow rate of the shielding gas is 15-20L / min, the scanning speed is 4-8mm / s, the powder feeding speed is 5-7rad / min, and the overlap distance is 10-16μm.

[0032] The present invention will be further described below with reference to specific examples, but they are not intended to limit the present invention.

[0033] The main parameters and variables of the embodiments and comparative examples of the present invention are shown in Table 1 below.

[0034] Table 1

[0035] Example 1 This embodiment provides a method for preparing a friction-resistant high-entropy alloy composite coating, comprising the following steps: Step 1: Prepare FeCoCrNiMo by atomization powdering according to the molar ratio of Fe, Co, Cr, Ni and Mo being 1:1:1:1:0.2 0.2 High entropy alloy powder, which is dried at 100° C. for 3 hours, and has a particle size of 45-105 μm; Step 2: 0.2wt.% few-layer graphene and 99.8wt.% FeCoCrNiMo 0.2 High entropy alloy powder was added to a planetary ball mill for mixing. The grinding balls used were 5 mm and 10 mm 304L austenitic stainless steel balls with a mass ratio of 5 mm:10 mm=4:1. The rotation speed was 300 rpm. The milling was carried out for 20 minutes and then stopped for 10 minutes in an intermittent operation mode. The milling time was 4 hours. The composite powder was dried in a vacuum drying oven at 100 °C for 3 hours.

[0036] Step 3: After polishing the oxides on the Q235 substrate, the substrate was ultrasonically cleaned in anhydrous ethanol for 30 minutes. After drying the ethanol, the substrate was preheated at 150°C for 25 minutes. Laser cladding composite coatings were deposited on the Q235 substrate using a laser power of 700W, a shielding gas (argon) flow rate of 15 L / min, a scan speed of 4 mm / s, a powder feed rate of 6 rad / min, and an overlap distance of 13 μm. The resulting coating exhibited good formation and excellent metallurgical bonding with the substrate.

[0037] Figure 1This is a scanning electron micrograph of the composite coating prepared in Example 1 near the fusion line. Observation shows that the addition of graphene did not change the primary morphology of the coating. Three characteristic regions can be observed from the fusion line to the center of the coating: the metallurgical bonding interface, the planar crystal region, and the columnar crystal region. The smooth, bright white band at the fusion line interface represents the metallurgical bonding interface, indicating a diffusion-type metallurgical bond between the coating and the Q235 substrate. Above the metallurgical bonding interface lies the planar crystal region, with columnar crystals growing perpendicular to the fusion line toward the coating.

[0038] Figure 2 The scanning electron microscope image of the in-situ synthesized carbide in the composite coating obtained in Example 1 is a SEM image of the precipitated phase region magnified 50,000 times. According to the scale, the precipitated phase length is 4.667 microns, indicating that the addition of graphene can form micron-sized carbides in the coating in situ. This also shows that after graphene is added, carbon atoms, in addition to being dissolved into the high-entropy alloy lattice, will also form micron-sized carbides in situ. This micron-sized carbide has a high melting point and preferentially deposits, causing the non-uniform nucleation of the high-entropy alloy, reducing grain size, and producing fine grain strengthening. In addition, these micron-sized carbides can hinder dislocation motion, improve the coating's ability to resist deformation, and produce second-phase strengthening.

[0039] Example 2 This embodiment provides a method for preparing a friction-resistant high-entropy alloy composite coating, comprising the following steps: Step 1: FeCoCrNiMo was prepared by atomization powdering according to the molar ratio of Fe, Co, Cr, Ni and Mo being 1:1:1:1:0.18. 0.18 High entropy alloy powder, which is dried at 100° C. for 3 hours, and has a particle size of 45-105 μm; Step 2: 0.2wt.% few-layer graphene and 99.8wt.% FeCoCrNiMo 0.18 High entropy alloy powder was added to a planetary ball mill for mixing. The grinding balls used were 5 mm and 10 mm 304L austenitic stainless steel balls with a mass ratio of 5 mm:10 mm=4:1. The rotation speed was 300 rpm. The milling was carried out for 20 minutes and then stopped for 10 minutes in an intermittent operation mode. The milling time was 4 hours. The composite powder was dried in a vacuum drying oven at 100 °C for 3 hours.

[0040] Step 3: After polishing the oxides on the Q235 substrate, the substrate was ultrasonically cleaned in anhydrous ethanol for 30 minutes. After drying the ethanol, the substrate was preheated at 150°C for 25 minutes. Laser cladding composite coatings were deposited on the Q235 substrate using a laser power of 800W, a shielding gas (argon) flow rate of 15 L / min, a scan speed of 8 mm / s, a powder feed rate of 5 rad / min, and an overlap distance of 10 μm. The resulting coatings exhibited excellent metallurgical bonding with the substrate.

[0041] Example 3 This embodiment provides a method for preparing a friction-resistant high-entropy alloy composite coating, comprising the following steps: Step 1: Prepare FeCoCrNiMo by atomization powdering according to the molar ratio of Fe, Co, Cr, Ni and Mo being 1:1:1:1:0.25 0.25 High entropy alloy powder, which is dried at 100° C. for 3 hours, and has a particle size of 45-105 μm; Step 2: 0.2wt.% few-layer graphene and 99.8wt.% FeCoCrNiMo 0.25 High entropy alloy powder was added to a planetary ball mill for mixing. The grinding balls used were 5 mm and 10 mm 304L austenitic stainless steel balls with a mass ratio of 5 mm:10 mm=4:1. The rotation speed was 300 rpm. The milling was carried out for 20 minutes and then stopped for 10 minutes in an intermittent operation mode. The milling time was 4 hours. The composite powder was dried in a vacuum drying oven at 100 °C for 3 hours.

[0042] Step 3: After polishing the oxides on the Q235 substrate, the substrate was ultrasonically cleaned in anhydrous ethanol for 30 minutes. After drying the ethanol, the substrate was preheated at 150°C for 25 minutes. Laser cladding composite coatings were deposited on the Q235 substrate using a laser power of 700W, a shielding gas (argon) flow rate of 20 L / min, a scan speed of 4 mm / s, a powder feed rate of 6 rad / min, and an overlap distance of 13 μm. The resulting coatings exhibited excellent metallurgical bonding with the substrate.

[0043] Example 4 This embodiment provides a method for preparing a friction-resistant high-entropy alloy composite coating, comprising the following steps: Step 1: Prepare FeCoCrNiMo by atomization powdering according to the molar ratio of Fe, Co, Cr, Ni and Mo being 1:1:1:1:0.2 0.2 High entropy alloy powder, which is dried at 100° C. for 3 hours, and has a particle size of 45-105 μm; Step 2: 0.3wt.% few-layer graphene and 99.7wt.% FeCoCrNiMo 0.2 High entropy alloy powder was added to a planetary ball mill for mixing. The grinding balls used were 5 mm and 10 mm 304L austenitic stainless steel balls with a mass ratio of 5 mm:10 mm=4:1. The rotation speed was 300 rpm. The milling was carried out for 20 minutes and then stopped for 10 minutes in an intermittent operation mode. The milling time was 4 hours. The composite powder was dried in a vacuum drying oven at 100 °C for 3 hours.

[0044] Step 3: After polishing the oxides on the Q235 substrate, the substrate was ultrasonically cleaned in anhydrous ethanol for 30 minutes. After drying the ethanol, the substrate was preheated at 150°C for 25 minutes. Laser cladding composite coatings were deposited on the Q235 substrate using a laser power of 600W, a shielding gas (argon) flow rate of 15 L / min, a scanning speed of 6 mm / s, a powder feed rate of 7 rad / min, and an overlap distance of 16 μm. The resulting coatings exhibited excellent metallurgical bonding with the substrate.

[0045] Example 5 This embodiment provides a method for preparing a friction-resistant high-entropy alloy composite coating, comprising the following steps: Step 1: Prepare FeCoCrNiMo by atomization powdering according to the molar ratio of Fe, Co, Cr, Ni and Mo being 1:1:1:1:0.2 0.2 High entropy alloy powder, which is dried at 100° C. for 3 hours, and has a particle size of 45-105 μm; Step 2: 0.4wt.% few-layer graphene and 99.6wt.% FeCoCrNiMo 0.2 High entropy alloy powder was added to a planetary ball mill for mixing. The grinding balls used were 5 mm and 10 mm 304L austenitic stainless steel balls with a mass ratio of 5 mm:10 mm=4:1. The rotation speed was 300 rpm. The milling was carried out for 20 minutes and then stopped for 10 minutes in an intermittent operation mode. The milling time was 4 hours. The composite powder was dried in a vacuum drying oven at 100 °C for 3 hours.

[0046] Step 3: After polishing the oxides on the Q235 substrate, the substrate was ultrasonically cleaned in anhydrous ethanol for 30 minutes. After drying the ethanol, the substrate was preheated at 150°C for 25 minutes. Laser cladding composite coatings were deposited on the Q235 substrate using a laser power of 700W, a shielding gas (argon) flow rate of 18 L / min, a scan speed of 4 mm / s, a powder feed rate of 6 rad / min, and an overlap distance of 13 μm. The resulting coatings exhibited excellent metallurgical bonding with the substrate.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that the graphene content in the composite powder of step S2 of Example 1 is adjusted to 0 and 0.1 wt.%, respectively, and the other conditions remain unchanged, and the composite coating is prepared on the surface of the Q235 substrate by laser cladding.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that the high entropy alloy FeCoCrNiMo in step S1 of Example 1 is replaced by x The molar fraction x of Mo in the composite coating was adjusted to 0.1 and 0.5 respectively, and the other conditions remained unchanged. The composite coating was prepared on the surface of the Q235 substrate by laser cladding.

[0049] Comparative Example 3 The difference between this comparative example and Example 1 is that in step S3 of Example 1, the laser power in the laser cladding is adjusted to 1000 W and 1200 W respectively, and the other conditions remain unchanged, and the composite coating is prepared on the surface of the Q235 substrate by laser cladding.

[0050] Comparative Example 4 The difference between this comparative example and Example 1 is that in step S3 of Example 1, the shielding gas flow rate in the laser cladding is adjusted to 10 L / min and 12.5 L / min respectively, and the other conditions remain unchanged, and the composite coating is prepared on the surface of the Q235 substrate by laser cladding.

[0051] Comparative Example 5 The difference between this comparative example and Example 1 is that in step S3 of Example 1, the scanning speed in the laser cladding is adjusted to 2 mm / s, 3 mm / s and 10 mm / s respectively, and the other conditions remain unchanged, and the composite coating is prepared on the surface of the Q235 substrate by laser cladding.

[0052] Performance Testing (1) Annualized corrosion rate High-entropy alloy coatings were machined into Φ8 × 10 mm cylindrical specimens using wire electrospark cutting. The end surface of the coating was used as the working surface, and the other surface was soldered to a copper conductor. The specimens were then cold-mounted and cured at room temperature for 10 hours. The working surface was then polished to a mirror finish. Polarization curves of the composite coatings were measured using a CS310H electrochemical workstation.

[0053] Electrochemical experiments were conducted using a saturated calomel electrode as the reference electrode and a platinum sheet as the auxiliary electrode. Before testing, the saturated calomel electrode was inspected for bubbles. After removing any bubbles, a saturated KCl solution was added. The open-circuit potential was then measured in a 3.5 wt.% NaCl corrosive medium. After the open-circuit potential stabilized, a potentiodynamic polarization curve was performed. The polarization curve was determined using a potentiodynamic sweep method with a sweep potential from -2 V to 2 V and a sweep rate of 0.5 mV / s. The measured polarization curve was fitted with a Tafel equation to obtain the annualized corrosion rate.

[0054] Figure 3 The figure is a comparison chart of the annualized corrosion rates of the composite coatings prepared in Examples 1-3 and Comparative Example 2. Figure 3 It can be seen that for FeCoCrNiMo x With the increase of Mo content x, the corrosion resistance of the high-entropy alloy coating shows a trend of first strengthening and then weakening. When 0.18≤x≤0.25, the annualized corrosion rate can be controlled in the range of 1.00mm / a, and the best corrosion resistance is achieved when x=0.2.

[0055] (2) Friction and wear performance test like Figure 4 As shown, the friction and wear properties of the composite coatings prepared in the examples and comparative examples of the present invention were tested using an MS-T3001 ball-on-disc friction and wear testing machine. The composite coatings were first processed into standard specimens (15 × 15 × 10 mm) using wire-cut electrical discharge technology. After being polished to 2000# using metallographic sandpaper, surface contaminants were removed using acetone ultrasonic cleaning. The specimens were then secured to a rotating table using adhesive. The friction and wear experimental parameters are shown in Table 2 below.

[0056] Table 2

[0057] After the experiment, the wear amount was calculated based on the wear scar width according to the following formula.

[0058]

[0059]

[0060]

[0061]

[0062]

[0063] Where, V loss is the wear volume (mm 3 ); C is the wear scar circumference (mm); S is the wear cross-sectional area (mm2 ); β is the friction arc angle (rad); d is the wear scar width (mm); r is the grinding ball radius (mm); R is the wear scar radius (mm).

[0064] Figure 5 The figure is a comparison of the wear amount of the composite coatings obtained in Examples 1, 4, 5 and Comparative Example 1. Figure 5 It can be seen that under the same other conditions, with the increase of graphene addition, the wear loss of the composite coating shows a trend of first decreasing and then increasing. When the addition amount of graphene in the composite powder is controlled at 0.2wt.%-0.3wt.%, the wear performance of the composite coating is better, and the wear loss is controlled at 0.012mm. 3 within the range.

[0065] (3) Influence of laser cladding parameters on coating processing performance Figure 6 The effect of different laser powers on FeCoCrNiMo in laser cladding is shown. 0.2 The effect of dilution rate on high entropy alloy coating. Figure 6 It can be seen that when the laser power is less than 600W, the dilution rate between the coating and the substrate is low and the metallurgical bonding strength is poor, which will affect the bonding strength between the coating and the substrate and cause the coating to easily fall off. When the laser power is above 800W, the coating dilution rate is too high, and a large number of Fe atoms from Q235 diffuse into the coating, causing the coating to lose the inherent ratio of each element in the original high-entropy alloy coating, which will cause the coating performance to deteriorate. At the same time, considering the absorption and dispersion effect of graphene on laser energy and its inherent heat dissipation ability, the coating dilution rate will become wider at 600W and narrower at 800W. Therefore, the embodiment of the present invention sets the laser power to 600W-800W.

[0066] Figure 7 The effects of different shielding gas flow rates on FeCoCrNiMo 0.2 The influence of high entropy alloy coating macromorphology. Figure 7 It can be seen that when the shielding gas flow rate is less than 15 L / min, there is severe oxidation on the coating surface. Taking into account the absorption effect of graphene on laser energy, the present invention should set the gas flow rate to no less than 15 L / min. At the same time, in order to avoid waste, the upper limit of the gas flow rate is set to 20 L / min.

[0067] Figure 8 Demonstrates FeCoCrNiMo prepared at different laser scanning speeds 0.2 The influence of high entropy alloy coating morphology. Figure 8 It can be seen that when the scanning speed is less than 4 mm / s, the coating is difficult to form; and when the scanning speed is greater than 8 mm / s, the coating thickness is significantly reduced, which will lead to a decrease in powder utilization.

[0068] In summary, the present invention uses a suitable laser cladding process to process composite powder containing graphene. The addition of graphene can generate carbides in situ and trigger three strengthening mechanisms (solid solution strengthening, second phase strengthening and fine grain strengthening), which give the high-entropy alloy composite coating better toughness and corrosion resistance. Its application in equipment surface protection can significantly improve the hardness and friction resistance of the substrate surface.

[0069] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A method for preparing a friction-resistant high-entropy alloy composite coating, characterized in that: The following steps are involved: S1. Prepare FeCoCrNiMo according to the molar ratio of Fe, Co, Cr, Ni and Mo being 1:1:1:1:x, 0.18≤x≤0.25 x High entropy alloy powder; S2, adding graphene and FeCoCrNiMo according to the addition amount of 0.2wt.%-0.4wt.%, x High entropy alloy powders are mixed and ball-milled to obtain composite powders; S3. Prepare a high entropy alloy composite coating on the surface of the substrate by laser cladding the composite powder; in the laser cladding, the laser power is 600-800W, the flow rate of the shielding gas is 15-20L / min, and the scanning speed is 4-8mm / s.

2. The preparation method according to claim 1, characterized in that In step S1, FeCoCrNiMo is prepared by gas atomization powder making. x High entropy alloy powder, the particle size of the high entropy alloy powder is 45-105 μm.

3. The preparation method according to claim 1, characterized in that In step S2, the graphene is a few-layer graphene having 3 or fewer atomic layers.

4. The preparation method according to claim 1, characterized in that In step S2, the ball milling process is performed in an intermittent operation mode, the rotation speed of the ball milling process is 250-350 rpm, and the ball milling process time is 3-5 hours.

5. The preparation method according to claim 1, characterized in that FeCoCrNiMo in step S1 x The preparation of the high entropy alloy powder and the preparation of the composite powder in step S2 both include a drying process; the drying process is performed at a temperature of 90-110° C. for 2-4 hours.

6. The preparation method according to claim 1, characterized in that In step S3, before laser cladding, the substrate is polished, ultrasonically cleaned and preheated in sequence.

7. The preparation method according to claim 6, characterized in that The temperature of the preheating treatment is 100-200° C., and the time of the preheating treatment is 20-30 minutes.

8. The preparation method according to claim 1, characterized in that In step S3, during the laser cladding, the powder feeding speed is 5-7 rad / min, the overlap distance is 10-16 μm, and the shielding gas is one of argon, nitrogen or helium.

9. A friction-resistant high-entropy alloy composite coating, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the friction-resistant high-entropy alloy composite coating according to claim 9 in equipment surface protection.

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