Method for preparing high-entropy alloy coating through atmosphere plasma spraying and laser remelting composite technology

Abstract

The invention provides a method for preparing a high-entropy alloy coating through an atmosphere plasma spraying and laser remelting composite technology, and belongs to the technical field of surface engineering. The method comprises the following steps that firstly, AlCoCrFeNi high-entropy alloy spraying powder is prepared through a vacuum gas atomization method; then, the surface of the base body is subjected to sand blasting roughening and preheating treatment; then, a high-entropy alloy spraying layer is prepared on the surface of the base body through atmospheric plasma spraying; and finally, the spraying layer is subjected to high-temperature rapid solidification through laser remelting treatment, and the composite coating which is compact in structure and high in bonding strength is formed. By optimizing spraying and remelting process parameters, the problems that a traditional plasma spraying coating is high in porosity and poor in binding force, cracks are likely to be generated in laser remelting and the like are effectively solved, the hardness, compactness and comprehensive performance of the coating are remarkably improved, and the coating is suitable for surface protection of parts under the harsh working conditions of high temperature, abrasion, corrosion and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing a high-entropy alloy coating layer by combining atmospheric plasma spraying and laser remelting, and belongs to the technical field of surface engineering. BACKGROUND

[0002] With the increasingly complex working conditions of industrial equipment, traditional alloys cannot meet the urgent demand for alloy materials with excellent comprehensive performance for parts under high-temperature, wear, strong alkali corrosion and other working conditions. Under this background, high-performance protective coatings are an important way to improve the service life of parts. Through in-depth research on materials and optimization of preparation processes, the durability of parts in harsh environments can be improved.

[0003] As a typical representative of a new multi-principal element alloy system, high-entropy alloys are a multi-element alloy system composed of five or more principal elements in an equimolar or near-equimolar ratio (3-35%). Since its inception, it has rapidly become a research hotspot in the field of advanced metal materials. Its unique "high-entropy effect", "lattice distortion effect" and "delayed diffusion effect" and other synergistic performance advantages make it have high strength, high toughness, high temperature resistance, wear resistance, corrosion resistance and lightweight, etc. This breakthrough in comprehensive performance makes it a unique advantage in the field of protective coating manufacturing, and it is expected to become an ideal candidate material for a new generation of comprehensive protective coatings with wear resistance, corrosion resistance and high-temperature oxidation resistance.

[0004] As one of the alloy coating preparation processes, plasma spraying technology can realize the industrial production of thermal barrier coatings, wear-resistant coatings and corrosion-resistant coatings. However, its unique layered structure inevitably leads to problems such as porosity, micro-cracks, poor bonding strength between the coating and the substrate, and other quality problems, hindering the development of the overall performance of the coating. Laser remelting as a non-contact precision machining technology, its high energy density and rapid cooling characteristics can effectively eliminate coating porosity, crack defects, improve coating density, refine grain structure and eliminate element segregation. However, although the laser remelted layer can refine the grain, the residual stress accumulation caused by the high cooling rate may cause interface peeling.

[0005] Therefore, there is an urgent need to develop an efficient and suitable composite process preparation method for high-entropy alloy coating to achieve controllable preparation of flexible, efficient, high-density and low-defect protective coatings. SUMMARY

[0006] In order to overcome the defects existing in the prior art, the purpose of the present application is to provide a method for preparing a high-entropy alloy coating by means of a combined process of atmospheric plasma spraying and laser remelting, which is suitable for materials such as high-entropy alloy (AlCoCrFeNi) and can obtain an AlCoCrFeNi high-entropy alloy coating which is firmly combined with the substrate, has a dense structure and excellent performance by means of coordinated control of plasma spraying process parameters and laser remelting parameters.

[0007] In order to achieve the purpose of the present application, the following technical solutions are provided.

[0008] A method for preparing a high-entropy alloy coating by means of a combined process of atmospheric plasma spraying and laser remelting, the method steps being as follows:

[0009] (1) preparing AlCoCrFeNi high-entropy alloy spraying powder by means of a vacuum gas atomization method, the atomic ratio of the powder being Al:Co:Cr:Fe:Ni=1:1:1:1:1, and the particle size range being 45-100 μm;

[0010] In step (1):

[0011] The specific steps of the vacuum gas atomization method are as follows:

[0012] The weighed alloy raw material is placed in a water-cooled copper crucible vacuum induction melting furnace for melting.

[0013] The specific parameters include: the melting vacuum degree is not higher than 5.0×10 -3 Pa; the protective atmosphere is argon with a purity of not less than 99.999%; the melting temperature is controlled at 1500-1650°C; the refining time is 5-15 minutes, and the atomization pressure is 2.0-5.0 MPa after condensation in the atomization tower.

[0014] (2) after cleaning and removing oil stains, the surface of the spraying substrate is subjected to sand blasting treatment so that the surface roughness Ra is 6um-12.5um;

[0015] In step (2):

[0016] The substrate is a metal or an alloy, preferably 316 stainless steel.

[0017] The cleaned spraying substrate surface can be obtained by the following method:

[0018] The spraying surface of the substrate is cleaned with acetone or ethanol to remove dust and oil stains and other impurities attached to the surface of the substrate, thereby obtaining a cleaned spraying substrate surface.

[0019] The sand blasting treatment can adopt 80-120 mesh white corundum sand, the sand blasting pressure is 0.3-0.6 MPa, and the surface roughness Ra reaches 6-12.5 μm.

[0020] (3) The substrate after sand blasting treatment is preheated to 150-200 DEG C, AlCoCrFeNi high-entropy alloy powder is sprayed onto the surface of the substrate to be sprayed by air plasma spraying, and a sprayed layer with a thickness of 450-500 μm and a hardness of 400-450 HV is obtained. 0.2 ;

[0021] In step (3):

[0022] The air plasma spraying process parameters are: spraying distance is 70-100 mm, current is 600-700 A, voltage is 60-80 V, flow rate of working gas Ar is 45-50 L / min, flow rate of auxiliary gas H2 is 8-10 L / min, powder feeding amount is 48-50 g / min, and carrier gas flow rate is 2-3 L / min.

[0023] After plasma spraying, a HV-1000 digital micro Vickers hardness tester is used, the test points are set at an interval of 50 μm along the cross-sectional direction with the coating surface as the starting point, each point is measured three times in the horizontal direction, the arithmetic average value is taken as the hardness representation value of the position, the test force is set to 200 g, the load holding time is 15 s, and the Vickers hardness value is calculated by the geometric relationship of the indentation diagonal line, which is 400-450 HV. 0.2 .

[0024] (4) The substrate is preheated to 150-200 DEG C, and after high-temperature heating and rapid cooling of the sprayed layer on the surface of the substrate by laser remelting, a plasma sprayed and laser remelted composite high-entropy alloy coating is obtained, and the hardness is 550-600 HV. 0.2 .

[0025] In step (4):

[0026] The substrate with the sprayed layer is preheated to 150-200 DEG C to avoid large heat accumulation during laser remelting, which causes ablation of the coating, resulting in defects such as cavities and cracks.

[0027] The laser remelting process parameters are: power 800-1000 W, scanning speed 420-450 mm / min, spot diameter 2 mm, offset 1 mm, and defocusing amount 15 mm.

[0028] The laser remelting path is parallel scanning, and the included angle between the scanning direction and the substrate plane is 90 DEG (normal incidence).

[0029] After laser remelting, an HV-1000 digital micro Vickers hardness tester was used. Starting from the coating surface along the cross-sectional direction, test sites were set at 50 μm intervals. Three independent measurements were taken at each site in the horizontal direction, and the arithmetic mean was used as the hardness value at that location. The experimental setup included a test force of 200 g and a load holding time of 15 s. The Vickers hardness value was calculated to be 550–600 HV based on the geometric relationship of the indentation diagonal. 0.2 .

[0030] The beneficial effects of this invention are:

[0031] This study provides a method for preparing high-entropy alloy coatings using a combined atmospheric plasma spraying and laser remelting process. The method involves plasma spraying an AlCoCrFeNi high-entropy alloy onto a 316 stainless steel substrate to create the coating layer. This avoids the coating peeling problem caused by the difference in thermal expansion coefficients between the 316 stainless steel substrate and the AlCoCrFeNi high-entropy alloy under a single heat source. Plasma spraying, through its unique method of instantaneous regional heating and layer-by-layer deposition, successfully transforms macroscopic thermal stress problems into microscopically controllable stress problems, thus effectively overcoming the coating peeling problem caused by the difference in thermal expansion coefficients between the 316 stainless steel substrate and the AlCoCrFeNi high-entropy alloy.

[0032] To address the challenges of poor density, porosity, and bonding strength in plasma spraying coating preparation, the melting and spreading area of ​​entropy alloy powder can be increased by adjusting the spraying distance, current, and voltage parameters in the atmospheric plasma spraying process. This results in a high-entropy alloy coating with a smooth and dense surface, interlocking layers, tight bonding, and fewer pores and gaps.

[0033] This study provides a method for preparing high-entropy alloy coatings using a combined atmospheric plasma spraying and laser remelting process. The method, through laser remelting, completely alters the typical layered, porous structure of plasma-sprayed coatings, eliminating unmelted particles and oxide inclusions, resulting in a dense and uniform metallurgical coating. As shown in the data from the examples, after laser remelting, the microhardness of the coating increases from 400-450 HV in the sprayed state. 0.2 Significantly improved to 550~600HV 0.2 .

[0034] The present application ensures excellent bonding performance through the multiple synergistic effects of "sand blasting roughening + substrate preheating + laser remelting". The sand blasting treatment provides the necessary mechanical embedding basis; the substrate is preheated to 150-200 DEG C before spraying, effectively reducing the thermal stress caused by the large temperature difference between the substrate and the powder particles during the spraying process, and reducing the generation of micro cracks; the final laser remelting process causes the interface between the coating and the substrate to melt together, forming a firm metallurgical bonding interface, which fundamentally overcomes the shortcomings of insufficient bonding strength of single APS coating and avoids the risk of coating peeling under high temperature, high load or thermal shock conditions.

[0035] The present application adjusts the solidification process of the molten pool by optimizing the laser remelting process parameters (especially the matching of power 800-1000 W and scanning speed 420-450 mm / min), and preheating the substrate with the sprayed layer to 150-200 DEG C before remelting. The preheating treatment effectively reduces the thermal gradient in the laser processing process, avoids the macroscopic cracks, pores and ablation defects caused by rapid cooling shrinkage. The finally obtained coating has a dense and uniform structure, no visible cracks and holes, and has good surface and internal structure. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The surface morphology diagram of the AlCoCrFeNi powder material for the sprayed layer prepared in Example 1.

[0037] Figure 2 The surface morphology diagram of the surface powder melting of the plasma sprayed layer prepared in Example 1.

[0038] Figure 3 The field emission scanning electron microscope diagram of the surface of the plasma sprayed layer prepared in Example 1.

[0039] Figure 4 The field emission scanning electron microscope diagram of the cross section of the plasma sprayed layer prepared in Example 1.

[0040] Figure 5 The field emission scanning electron microscope diagram of the cross section of the laser remelting coating prepared in Example 1.

[0041] Figure 6 The surface morphology diagram of the AlCoCrFeNi powder material for the sprayed layer prepared in Example 2.

[0042] Figure 7 The surface morphology diagram of the surface powder melting of the plasma sprayed layer prepared in Example 2.

[0043] Figure 8 The field emission scanning electron microscope diagram of the surface of the plasma sprayed layer prepared in Example 2.

[0044] Figure 9 Field emission scanning electron microscope image of the cross section of the plasma sprayed coating prepared in Example 2.

[0045] Figure 10 Field emission scanning electron microscope image of the cross section of the laser remelted coating prepared in Example 2.

[0046] Figure 11 Surface topography image of the surface powder melting of the plasma sprayed coating prepared in Comparative Example 1.

[0047] Figure 12 Field emission scanning electron microscope image of the surface of the plasma sprayed coating prepared in Comparative Example 1.

[0048] Figure 13 Field emission scanning electron microscope image of the cross section of the plasma sprayed coating prepared in Comparative Example 1.

[0049] Figure 14 Field emission scanning electron microscope image of the cross section of the laser remelted coating prepared in Comparative Example 1. DETAILED DESCRIPTION

[0050] The present application is further described below in connection with specific embodiments, wherein the methods are conventional techniques in the art unless otherwise specified, and the raw materials are available from public sources unless otherwise specified. In the following examples:

[0051] The surface roughness was measured by using a Japanese Keyence VHX-6000 ultra-depth microscope system.

[0052] An atmospheric plasma spraying device (APS-MF-P1000) was used.

[0053] A ZKZM-2000 high-speed laser device was used as the laser remelting device.

[0054] A ZEISS Gemini SEM 300 device was used to observe the microstructure of the sprayed powder, the sprayed coating and the remelted layer prepared in the examples and comparative examples.

[0055] Image J image analysis software was used to measure and calculate the porosity of the sprayed coating prepared in the examples and comparative examples.

[0056] An HV-1000 digital microscope Vickers hardness tester was used to calculate the Vickers hardness of the sprayed coating and the remelted layer according to the ISO 6507 standard by the geometric relationship of the indentation diagonal.

[0057] Example 1

[0058] A method for preparing a high-entropy alloy coating by a combined process of atmospheric plasma spraying and laser remelting, the method steps being as follows:

[0059] Purity ≥99.9% Al, Co, Cr, Fe, Ni elemental metal raw materials are weighed with a total mass of 240g according to the atomic ratio Al:Co:Cr:Fe:Ni=1:1:1:1:1, and the weighed metal raw materials are placed in a water-cooled copper crucible vacuum induction melting furnace for melting. The melting vacuum degree is not higher than 5.0×10 -3 Pa; fill in protective high-purity argon with a concentration of 99.999%; the melting temperature is controlled at 1550°C; the refining time is 10 minutes, and the atomized powder is condensed after being placed in an atomization tower with an atomization pressure of 3MPa. The atomized powder is sieved, and the part with a particle size of 45-100μm is selected as the spraying powder, which has a near-spherical morphology.

[0060] The surface to be sprayed of the 316 stainless steel substrate is cleaned with ethanol to remove dust and oil stains and other impurities attached to the surface of the substrate, obtaining a clean surface to be sprayed. A 100-mesh white corundum sand is used to sand the cleaned surface under a sandblasting pressure of 0.4MPa, and the sandblasting distance is 100mm. The surface roughness after sandblasting is Ra=8.5μm.

[0061] The sandblasted substrate is placed in a preheating furnace and heated to 150°C and kept for at least 30 minutes to ensure uniform temperature of the whole substrate. The purpose of preheating is to reduce the thermal stress between the powder particles and the substrate during spraying, and to improve the deposition efficiency and bonding strength.

[0062] The preheated substrate is fixed on the spraying tooling rack, and atmospheric plasma spraying equipment is used for spraying. The plasma spraying process parameters are as follows: spraying distance 100mm, spraying current 700A, arc voltage 80V, protective gas argon (purity 99.99%), flow rate 50L / min, auxiliary gas hydrogen, flow rate 8L / min. The powder feeder is controlled at a powder feeding rate of 45g / min, and the carrier gas (argon) flow rate is 3L / min. Through multi-pass spraying, an AlCoCrFeNi high-entropy alloy spraying layer with a thickness of 500μm is prepared on the surface of the substrate.

[0063] The substrate with the sprayed coating is placed back into the preheating furnace and preheated to 150°C. Then, the surface of the sprayed coating is laser-remelted. The laser remelting process parameters are as follows: laser power 1000 W, scanning speed 420 mm / min, spot diameter 2 mm, offset 1 mm, defocusing amount 15 mm. The laser beam is scanned perpendicular to the substrate surface (normal incidence 90°), and a parallel scanning strategy is used. After remelting, the coating is rapidly cooled in air, resulting in a composite coating of plasma spraying and laser remelting.

[0064] Performance characterization and testing:

[0065] (1) The microstructure of the AlCoCrFeNi high-entropy alloy powder for spraying prepared in Example 1 was observed. Figure 1 As can be seen, the prepared powder is spherical with a particle size of 45μm to 100μm.

[0066] (2) The surface powder melting state of the sprayed coating prepared in Example 1 was observed, and the SEM image of the coating surface was obtained. Figure 2 Observations revealed no obvious unmelted powder particles, indicating a good molten state. This facilitates good contact between molten particles, thereby reducing porosity.

[0067] (3) The microstructure morphology of the surface and cross-section of the sprayed coating prepared in Example 1 was observed using a scanning electron microscope (SEM, ZEISS Gemini SEM 300); the results are as follows:

[0068] SEM image of the surface of the sprayed coating Figure 3 As can be seen from the SEM image of the sprayed coating, the powder particles spread sufficiently after melting, with good inter-particle bonding and a small number of small pores. Figure 4 It can be seen that it has a typical layered structure of atmospheric plasma spraying coating, with layers embedded and tightly bonded, exhibiting mechanical bonding with the 316 stainless steel substrate.

[0069] (4) Image analysis test using Image J showed that the average porosity of the prepared spray coating was 9.56%.

[0070] (5) The cross-sectional SEM image of the remelted layer prepared in Example 1 was observed using a scanning electron microscope (SEM, ZEISS Gemini SEM 300). Figure 5 Microscopic examination revealed that the layered structure of the sprayed coating was eliminated after laser remelting, resulting in a dense and smooth coating without obvious pores, cracks, or other defects. The presence of a bright white bonding line between the remelted layer and the 316 stainless steel substrate indicates that the bond between the remelted layer and the substrate has shifted from mechanical to metallurgical.

[0071] Hardness test

[0072] The microhardness distribution of the coating was tested by HV-1000 digital micro-vickers hardness tester along the normal gradient of the coating-substrate cross section. The test sites were set at an interval of 50 μm, and each site was measured three times in the horizontal direction to obtain the arithmetic mean value as the hardness characterization value of the position. The hardness gradient distribution data of the coating to the substrate were obtained. The hardness of the sprayed coating after laser remelting was increased from 453.2 HV 0.2 to 591.3 HV 0.2 , with an increase of 30.5%.

[0073] Example 2

[0074] A method for preparing a high-entropy alloy coating by a combined process of atmospheric plasma spraying and laser remelting, the steps of which are as follows:

[0075] The pure Al, Co, Cr, Fe and Ni elemental metal raw materials with a purity of ≥99.9% are weighed to a total mass of 240g according to the atomic ratio Al:Co:Cr:Fe:Ni=1:1:1:1:1, and then placed in a water-cooled copper crucible vacuum induction melting furnace for melting. The melting vacuum degree is not higher than 5.0×10 -3 Pa; the protective argon gas with a high purity of 99.999% is filled; the melting temperature is controlled at 1500°C; the refining time is 10 minutes, and then the condensed material is placed in an atomization tower with an atomization pressure of 3MPa. The atomized powder is sieved, and the part with a particle size of 45~100 μm is selected as the sprayed powder, which has a near-spherical morphology.

[0076] The surface to be sprayed of the 316 stainless steel substrate is cleaned with ethanol to remove dust and oil stains and other impurities attached to the surface of the substrate, so as to obtain a clean surface to be sprayed. The cleaned surface is subjected to sandblasting treatment under the condition of a sandblasting pressure of 0.4MPa by using 100-mesh white corundum sand, and the sandblasting distance is 100mm. The surface roughness after sandblasting is Ra=8.5 μm.

[0077] The substrate after sandblasting is placed in a preheating furnace and heated to 150°C and kept for at least 30 minutes to ensure that the overall temperature of the substrate is uniform. The purpose of preheating is to reduce the thermal stress between the powder particles and the substrate during the spraying process, and to improve the deposition efficiency and bonding strength.

[0078] The preheated substrate was fixed on a spraying tooling rack, and atmospheric plasma spraying equipment was used for spraying. The plasma spraying process parameters are as follows: spraying distance 90 mm, spraying current 600 A, arc voltage 60 V, protective gas is argon (purity 99.99%), flow rate is 50 L / min, auxiliary gas is hydrogen, flow rate is 10 L / min. The powder feeder is controlled at a powder feeding rate of 50 g / min, and the carrier gas (argon) flow rate is 3 L / min. Through multi-pass spraying, an AlCoCrFeNi high-entropy alloy sprayed layer with a thickness of 450 μm is prepared on the surface of the substrate.

[0079] The substrate with the sprayed layer was again placed in the preheating furnace and preheated to 200℃. Subsequently, the surface of the sprayed layer was subjected to laser remelting treatment using a laser. The laser remelting process parameters are as follows: laser power 800 W, scanning speed 450 mm / min, spot diameter 2 mm, offset 1 mm, defocusing amount 15 mm. The laser beam is scanned perpendicular to the surface of the substrate (normal incidence 90°), and the scanning path adopts parallel scanning strategy. After remelting, the coating is rapidly cooled in air to obtain a plasma sprayed and laser remelted composite coating.

[0080] Performance characterization and detection:

[0081] (1) The micro-morphology of the sprayed AlCoCrFeNi high-entropy alloy powder prepared in this embodiment 2 was observed, and it was found from the SEM image of the powder that the prepared powder was spherical, and the particle size was 45 μm-100 μm. Figure 6

[0082] (2) The surface powder melting state of the sprayed layer prepared in this embodiment 2 was observed, and it was found from the SEM image of the coating surface that there were a small amount of partially melted powder particles. The partially melted powder particles increase the generation of pores. Figure 7

[0083] (3) The scanning electron microscope (SEM, ZEISS Gemini SEM 300) was used to observe the microstructure morphology of the surface and cross section of the sprayed layer prepared in embodiment 2; the results are as follows:

[0084] From the SEM image of the surface of the sprayed layer Figure 8 , it can be seen that the powder particles spread fully after melting, the particles are well combined, and the pores are slightly increased. From the SEM image of the cross section of the sprayed layer Figure 9 , it can be seen that the sprayed layer has a typical lamellar structure of atmospheric plasma sprayed coating, and the layers are inlaid, the combination is relatively tight, and the 316 stainless steel substrate presents mechanical combination.

[0085] (4) Image J image analysis test shows that the average porosity of the prepared sprayed layer is 11.42%.​​

[0086] (5) The cross-section SEM of the remelted layer prepared in Example 2 was observed by a scanning electron microscope (SEM, ZEISS Gemini SEM 300) Figure 10 It was found from the microstructure morphology of the sprayed layer that although the porosity of the sprayed layer slightly increased under this parameter, the layered structure of the sprayed layer was eliminated after laser remelting, and the coating was dense and smooth, and no obvious pores, cracks and other defects could be seen. The remelted layer and the 316 stainless steel substrate were still metallurgically bonded.

[0087] Hardness test

[0088] A digital micro-Vickers hardness tester (HV-1000) was used to test the microhardness distribution along the normal gradient of the coating-substrate cross section. The test sites were set at an interval of 50 μm, and each site was measured three times in the horizontal direction to obtain the arithmetic mean value as the hardness characterization value of the site. The hardness of the sprayed layer was increased from 448.8 HV 0.2 to 588.9 HV 0.2 , with an increase of 31.2%.

[0089] Comparative Example 1

[0090] A method for preparing a high-entropy alloy coating by a combined process of atmospheric plasma spraying and laser remelting, the steps of which are as follows:

[0091] Pure Al, Co, Cr, Fe and Ni metals with a purity of ≥99.9% were weighed to a total mass of 240g in the atomic ratio of Al:Co:Cr:Fe:Ni=1:1:1:1:1, and then placed in a water-cooled copper crucible vacuum induction melting furnace for melting. The melting vacuum degree was not higher than 5.0x10 -3 Pa; protective argon with a high purity of 99.999% was filled; the melting temperature was controlled at 1550°C; the refining time was 10 minutes, and the condensed powder was placed in an atomization tower with an atomization pressure of 3MPa. The atomized powder was sieved, and the part with a particle size of 45-100 μm was selected as the spraying powder, which had a near-spherical morphology.

[0092] The surface to be sprayed of the 316 stainless steel substrate was cleaned with ethanol to remove dust and oil stains and other impurities attached to the surface of the substrate, thereby obtaining a clean surface to be sprayed. A 100-mesh white corundum sand was used to sand the cleaned surface under the condition of a sandblasting pressure of 0.4MPa, and the sandblasting distance was 100mm. The surface roughness after sandblasting was Ra=8.5 μm.

[0093] Put the sandblasted substrate into a preheating furnace, heat to 150℃, and keep for at least 30 minutes to ensure the uniformity of the overall temperature of the substrate. The purpose of preheating is to reduce the thermal stress between the powder particles and the substrate during spraying, improve the deposition efficiency and bonding strength.

[0094] Fix the preheated substrate on the spraying tooling rack, and use atmospheric plasma spraying equipment for spraying. The plasma spraying process parameters are as follows: spraying distance 70 mm, spraying current 700 A, arc voltage 80 V, protective gas argon (purity 99.99%), flow rate 50 L / min, auxiliary gas hydrogen, flow rate 8 L / min. The powder feeding rate of the powder feeder is controlled at 45 g / min, and the carrier gas (argon) flow rate is 3 L / min. Through multi-pass spraying, an AlCoCrFeNi high-entropy alloy sprayed layer with a thickness of 500 μm is prepared on the surface of the substrate.

[0095] Put the substrate with the sprayed layer into the preheating furnace again, and preheat to 150℃. Then, use a laser to perform laser remelting treatment on the surface of the sprayed layer. The laser remelting process parameters are as follows: laser power 600 W, scanning speed 420 mm / min, spot diameter 2 mm, offset 1 mm, and defocusing amount 15 mm. The laser beam is scanned perpendicular to the surface of the substrate (normal incidence 90°), and the scanning path adopts parallel scanning strategy. After remelting, the coating is rapidly cooled in air to obtain a plasma sprayed and laser remelted composite coating.

[0096] Performance characterization and detection:

[0097] (1) The surface powder melting state of the sprayed layer prepared in Comparative Example 1 was observed, and it was found from the SEM image of the surface of the coating that a large number of powder particles were not completely melted, which caused insufficient contact between the melted particles and resulted in the generation of a large number of pores. Figure 11

[0098] (2) The microstructure morphology of the surface and cross-section of the sprayed layer prepared in Comparative Example 1 was observed by scanning electron microscope (SEM, ZEISS Gemini SEM 300); the results are as follows:

[0099] It can be seen from the SEM image of the surface of the sprayed layer that the powder particles are not fully spread after melting, the inter-particle bonding is poor, and there are a large number of pores. It can be seen from the SEM image of the cross-section of the sprayed layer that it has a typical lamellar structure of atmospheric plasma sprayed coating, and the layers are inlaid, the bonding is not tight, and it presents an incomplete continuous mechanical bonding with the 316 stainless steel substrate. Figure 12 Figure 13

[0100] ​​​(3) The average porosity of the prepared sprayed layer is 17.28% by using Image J image analysis test.

[0101] (4) The microstructure morphology of the cross-section SEM image of the prepared remelted layer in Comparative Example 1 is observed by using a scanning electron microscope (SEM, ZEISS Gemini SEM 300), and it is found that the remelted layer eliminates defects such as pores and cracks, the layered structure of the sprayed layer after laser remelting is eliminated, and the finally obtained coating has a dense and uniform structure, no visible cracks and pores, and good surface and internal structure. Figure 14

[0102] Hardness test

[0103] A digital micro-Vickers hardness tester (HV-1000) is used to test the microhardness distribution along the normal gradient of the coating-substrate cross section. The test sites are set at an interval of 50 μm, each site is measured three times in the horizontal direction, and the arithmetic mean is taken as the hardness value of the site. The hardness of the sprayed layer after laser remelting is increased from 423.6 HV 0.2 to 503.3 HV 0.2 , with an increase of 18.8%. Compared with the sprayed layer and the remelted layer in Examples 1 and 2, the difference in the preparation process parameters of the sprayed layer and the remelted layer affects the forming quality of the sprayed layer and the remelted layer. In this comparative example, changing the spraying distance and the laser power is not conducive to forming a sprayed layer with small porosity and a remelted layer with excellent density, which affects the use effect of the coating.​

Claims

1. A method for preparing high-entropy alloy coating by combined atmospheric plasma spraying and laser remelting process, characterized in that: The preparation method comprises the following steps: (1) preparing an AlCoCrFeNi high-entropy alloy spraying powder by a vacuum gas atomization method, the atom ratio of the powder being Al:Co:Cr:Fe:Ni=1:1:1:1:1, and the particle size range being 45-100 μm; (2) performing sand blasting treatment on the surface of the cleaned and oil-stain-removed spraying substrate, so that the surface roughness Ra is 6-12.5 μm; (3) preheat the substrate after the sand blasting treatment in step (2) to 150-200 DEG C, use atmospheric plasma spraying to spray AlCoCrFeNi high-entropy alloy powder onto the surface of the substrate to be sprayed to obtain a sprayed layer with a thickness of 450-500 mu m and a hardness of 400-450 HV 0.2 ; (4) Preheat the substrate with the sprayed layer of step (3) to 150-200 DEG C, and after high-temperature heating and rapid cooling of the sprayed layer on the surface of the substrate by laser remelting method, a plasma sprayed and laser remelted composite high-entropy alloy coating is obtained, with a hardness of 550-600 HV 0.2 .

2. The method of claim 1, wherein the method is characterized by: The vacuum gas atomization method is as follows: the weighed high-entropy alloy raw material is placed in a water-cooled copper crucible vacuum induction melting furnace for melting; the specific parameters include: the melting vacuum degree is not higher than 5.0*10-3 Pa; the protective atmosphere is argon with a purity of not less than 99.999%; the melting temperature is controlled at 1500-1650°C; the refining time is 5-15 minutes, and the condensation is performed in an atomization tower, and the atomization pressure is 2.0-5.0 MPa.

3. The method of claim 1, wherein the method is characterized by In step (2), the surface of the spraying substrate is cleaned with acetone or ethanol to remove dust and oil stains and other impurities attached to the surface of the substrate, so as to obtain a clean spraying substrate surface. The sand blasting uses 80-120 mesh white corundum sand, the sand blasting pressure is 0.3-0.6 MPa, and the surface roughness Ra is 6-12.5 μm.

4. The method of claim 1, wherein the high-entropy alloy coating is prepared by a combined atmospheric plasma spraying and laser remelting process. In step (3), the initial atmospheric plasma spraying layer preparation process parameters are as follows: the spraying distance is 90-110 mm, the current is 600-700 A, the voltage is 60-80 V, the flow rate of the working gas Ar is 45-50 L / min, the flow rate of the auxiliary gas H2 is 8-10 L / min, the powder feeding amount is 48-50 g / min, and the carrier gas flow rate is 2-3 L / min.

5. The method of claim 1, wherein the method is characterized by: In step (4), the initial spraying layer is remelted by laser remelting, and the process parameters are as follows: the power is 800-1000 W, the scanning speed is 420-450 mm / min, the spot diameter is 2 mm, the offset is 1 mm, the defocusing amount is 15 mm, the laser remelting path is parallel scanning, and the included angle between the scanning direction and the substrate plane is 90° (normal incidence).

6. The method of claim 1, wherein the high-entropy alloy coating is prepared by a combined atmospheric plasma spraying and laser remelting process. The substrate is a metal or an alloy.

7. The method of claim 6, wherein the high-entropy alloy coating is prepared by a combined atmospheric plasma spraying and laser remelting process. The substrate is a 316 stainless steel alloy.

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