A high-entropy alloy coating and a method of making the same

Abstract

The present application relates to the field of advanced metal materials and surface engineering, and particularly relates to a high-entropy alloy coating and a preparation method thereof, comprising the following steps: physically mixing tantalum reinforced high-entropy alloy powder and silane coated nano yttrium oxide composite particles to obtain a composite powder; performing surface pretreatment on a nickel-based high-temperature alloy substrate; under the protection of an inert atmosphere, using a synchronous powder feeding method, delivering the composite powder to the focal point area of a high-power laser beam, and scanning the surface of the substrate to make the composite powder and the surface layer of the substrate melt synchronously to form a co-melt pool, and rapidly solidify after the laser beam moves away to form a coating that is metallurgically bonded with the substrate; and performing stress relief annealing treatment on the cladded workpiece; the present application effectively solves the problem of high-temperature oxidation peeling of traditional coatings.

Description

Technical Field

[0001] This invention relates to the field of advanced metallic materials and surface engineering, specifically to a high-entropy alloy coating and its preparation method. Background Technology

[0002] Protective coating technology for high-temperature components such as turbine blades of aero-engines aims to solve the oxidation and peeling problems of existing coatings under operating conditions above 1150℃. Traditional MCrAlY coatings are prone to forming brittle phases at high temperatures, leading to severe oxidation. After 100 hours of oxidation at 1150℃, the weight gain is as high as 2.13 mg / cm³. 2 Furthermore, the oxide film is loose and partially peels off. In addition, these traditional coatings mainly form a mechanical bond with the substrate with low bonding strength, only about 55 MPa. This bonding interface is prone to failure during thermal cycling. At the same time, in the rapid solidification process of laser cladding, if subsequent stress-relieving annealing is lacking, the coating will exhibit significant brittleness due to the large residual stress inside, resulting in unsatisfactory bonding strength. It is prone to cracking when subjected to impact, affecting the reliability of the component. Therefore, developing a new coating system that has high metallurgical strength when bonded to the substrate, excellent high-temperature oxidation resistance, and eliminates brittleness through process optimization is the key to solving the above technical problems. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a high-entropy alloy coating and its preparation method, which solves the problems of poor wettability and weak interfacial adhesion between ceramic particles and nickel-based superalloy substrates. The specific technical solution of this invention is as follows:

[0004] A method for preparing a high-entropy alloy coating by laser cladding includes the following steps:

[0005] A tantalum-reinforced high-entropy alloy powder was physically mixed with a silane-coated nano-yttrium oxide composite particle to obtain a composite powder.

[0006] Surface pretreatment of nickel-based high-temperature alloy substrate;

[0007] Under an inert atmosphere, the composite powder is fed to the focal area of ​​a high-power laser beam using a synchronous powder feeding method. The surface of the substrate is then scanned, causing the composite powder and the substrate surface to melt synchronously to form a eutectic pool. After the laser beam is removed, the composite powder solidifies rapidly to form a coating that is metallurgically bonded to the substrate.

[0008] The workpiece that has been clad is subjected to stress-relieving annealing.

[0009] Preferably, the weight ratio of the tantalum-reinforced high-entropy alloy powder to the silane-coated nano-yttrium oxide composite particles is (96-99):(1-4).

[0010] Preferably, the preparation of the tantalum-reinforced high-entropy alloy powder includes the following steps:

[0011] Al, Co, Cr, Ni, and Ta metal raw materials are smelted in a vacuum induction melting furnace according to a preset atomic ratio, and a master alloy ingot with uniform composition is obtained by electromagnetic stirring and repeated remelting.

[0012] The master alloy ingot is heated to complete melting and then atomized at high speed using high-pressure argon gas, causing the molten droplets to solidify rapidly into powder.

[0013] The powder is subjected to vibratory sieving and vacuum drying.

[0014] Preferably, the atomic ratio of Al, Co, Cr, Ni, and Ta in the metal raw material is 1:1.5:1.5:2:0.3; and the particle size of the powder selected by the vibrating sieve is 50-150 μm.

[0015] Preferably, the preparation of the silane-coated yttrium oxide nanocomposite particles includes the following steps:

[0016] Nano-yttrium oxide powder was added to anhydrous ethanol and ultrasonically dispersed under nitrogen protection to form a uniform suspension.

[0017] A silane coupling agent is added dropwise to the suspension, and a constant-temperature reflux reaction is carried out at a specific temperature.

[0018] The reaction products were then subjected to centrifugation, washing with anhydrous ethanol, and vacuum drying.

[0019] Preferably, the process parameters for laser cladding scanning are: laser power 1.8-2.2kW, scanning speed 8-12mm / s, and overlap rate of adjacent cladding channels 30-50%.

[0020] Preferably, the surface pretreatment of the substrate includes sandblasting the substrate surface and then ultrasonic cleaning in anhydrous ethanol.

[0021] Preferably, the process parameters for the stress-relief annealing treatment are: annealing temperature 500-700℃, and holding time 1-3 hours.

[0022] A high-entropy alloy coating prepared by the above preparation method.

[0023] The application of the aforementioned high-entropy alloy coating in the protection of high-temperature components such as turbine blades or combustion chamber liners of aero-engines.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. Excellent high-temperature oxidation resistance effectively solves the problem of traditional coatings peeling off during high-temperature oxidation. The tantalum-reinforced high-entropy alloy powder used in this invention can form a dense and stable protective oxide film, while the added silane-coated nano-yttrium oxide greatly enhances the adhesion of the oxide film. The synergistic effect of these two factors results in a weight gain of only 0.51 mg / cm³ after 100 hours of oxidation at 1150℃. 2 It is far lower than the 2.13 mg / cm³ of traditional MCrAlY coatings. 2 Furthermore, the oxide film is dense and does not peel off.

[0026] 2. The coating and the substrate achieve a high-strength metallurgical bond, with a bonding strength far exceeding that of traditional coatings. Through laser cladding, the coating powder and the substrate surface melt synchronously to form a eutectic pool, achieving inter-element diffusion and forming a strong metallurgical bond. The bonding strength of the embodiments all exceed 85MPa, with a maximum of 92.15MPa. Fracture occurs inside the coating rather than at the interface, solving the problem that traditional MCrAlY coatings are prone to failure during thermal cycling due to mechanical bonding.

[0027] 3. A combination of high hardness and high toughness was achieved; the high-entropy alloy exhibits high hardness due to solid solution strengthening and laser rapid cooling resulting in fine grain strengthening; the subsequent crucial stress-relief annealing treatment effectively eliminated the enormous residual stress generated during the cladding process; this step resolved the contradiction that high hardness is usually accompanied by high brittleness, allowing the coating to maintain a hardness of 610.25 HV. 0.2 While achieving high hardness, it also significantly improves toughness, thus avoiding the risk of cracking under impact loads.

[0028] 4. The preparation process has a wide window and strong adaptability, providing a reliable technical option for different working conditions; coatings with excellent bonding strength and good oxidation resistance can be obtained by varying the powder ratio, laser parameters and annealing process within a wide range. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the preparation process of the present invention;

[0030] Figure 2 SEM comparison images of the surface oxide film morphology of different coatings after oxidation at 1150℃ for 100 hours, where:

[0031] (a) is the coating of Example 1 of the present invention, whose oxide film is dense and without peeling;

[0032] (b) is the coating of Comparative Example 1, in which microcracks appear in the oxide film;

[0033] (c) is the coating of Comparative Example 2, whose oxide film is loose and partially peeled off;

[0034] Figure 3This is a bar chart comparing the coating bonding strength of various embodiments and comparative examples in this invention. Detailed Implementation

[0035] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1:

[0037] This embodiment provides a laser cladding method for preparing high-entropy alloy coatings. The coatings prepared by this method can be applied to the protection of high-temperature components such as turbine blades of aero-engines. The preparation method first prepares two core raw materials:

[0038] like Figures 1-3 As shown, the preparation of a tantalum-reinforced high-entropy alloy powder includes the following steps: Al, Co, Cr, Ni, and Ta metal raw materials are melted in a vacuum induction melting furnace at an atomic ratio of 1:1.5:1.5:2:0.3, and a homogeneous master alloy ingot is obtained by electromagnetic stirring and repeated remelting four times; the master alloy ingot is then heated to complete melting and atomized at high speed by high-pressure argon gas, causing the molten droplets to solidify rapidly into powder; finally, the powder is vibrated and sieved, and the portion with a particle size of 50-150 μm is selected and vacuum dried.

[0039] The preparation of silane-coated yttrium oxide nanoparticles includes the following steps: adding yttrium oxide nanoparticles to anhydrous ethanol and ultrasonically dispersing them under nitrogen protection to form a uniform suspension; adding a silane coupling agent dropwise to the suspension, wherein the amount of silane coupling agent added is 3% of the mass of the yttrium oxide nanoparticles, and performing a constant temperature reflux reaction at 80°C; and sequentially centrifuging, washing with anhydrous ethanol, and vacuum drying the reaction product.

[0040] The tantalum-reinforced high-entropy alloy powder prepared above was physically mixed with silane-coated nano-yttrium oxide composite particles at a weight ratio of 98:2 to obtain composite powder. The nickel-based superalloy used as the target substrate was subjected to surface pretreatment, which included sandblasting and ultrasonic cleaning in anhydrous ethanol. Under the protection of an argon atmosphere with a flow rate of 20 L / min, the composite powder was transported to the focal area of ​​a high-power laser beam using a synchronous powder feeding method, and the substrate surface was scanned. The process parameters of the laser cladding scanning were: laser power 2.0 kW, scanning speed 10 mm / s, overlap rate of adjacent cladding channels 40%, laser spot diameter 3 mm, and powder feeding rate 15 g / min.

[0041] This process allows the composite powder and the substrate surface to melt synchronously to form a eutectic pool, and then solidify rapidly after the laser beam is removed, forming a coating that is metallurgically bonded to the substrate. The workpiece that has been clad is then subjected to stress-relief annealing, with the following process parameters: annealing temperature 550℃, holding time 2 hours.

[0042] The high-entropy alloy coating prepared in this embodiment aims to solve the oxidation and peeling problems of existing coatings under operating conditions above 1150℃. The resulting coating has a dense structure and achieves excellent metallurgical bonding with the substrate, with a bonding strength of up to 92 MPa. When applied to the combustion chamber lining of an aero-engine, its weight gain after 100 hours of high-temperature oxidation at 1150℃ is only 0.51 mg / cm³. 2 It exhibits excellent high-temperature oxidation resistance, which helps extend the service life of hot-end components.

[0043] Example 2:

[0044] This embodiment provides a laser cladding method for preparing high-entropy alloy coatings, characterized by comprising the following steps:

[0045] First, the tantalum-reinforced high-entropy alloy powder is prepared, and the specific steps are the same as in Example 1; second, the silane-coated yttrium oxide nanocomposite particles are prepared, and the specific steps are also the same as in Example 1.

[0046] The prepared tantalum-reinforced high-entropy alloy powder was physically mixed with silane-coated nano-yttrium oxide composite particles at a weight ratio of 99:1 to obtain composite powder. The nickel-based high-temperature alloy substrate underwent surface pretreatment, which included sandblasting followed by ultrasonic cleaning with anhydrous ethanol. Laser cladding was performed under an inert atmosphere using a synchronous powder feeding method. In this embodiment, the laser cladding scanning process parameters were set as follows: laser power 1.8kW, scanning speed 12mm / s, and overlap rate of adjacent cladding channels 50%. Laser beam scanning caused the composite powder and substrate surface to melt synchronously and solidify rapidly, forming a metallurgically bonded coating. Finally, the workpiece underwent stress-relief annealing, with the following process parameters: annealing temperature 500℃ and holding time 3 hours.

[0047] This embodiment aims to verify the adaptability of the technical solution within a wide process window; the obtained coating also forms an effective metallurgical bond, and the internal structure of the coating is fine; when applied to components such as turbine guide vanes, it can effectively suppress the formation and peeling of oxides under high temperature environment while meeting the bonding strength, providing a reliable technical option for component protection under different working conditions.

[0048] Example 3:

[0049] This embodiment provides a laser cladding method for preparing high-entropy alloy coatings, characterized by comprising the following steps:

[0050] Preparation of the tantalum-reinforced high-entropy alloy powder and the silane-coated yttrium oxide nanocomposite particles;

[0051] The two powder raw materials were physically mixed at a weight ratio of 96:4 to obtain composite powder; the nickel-based high-temperature alloy substrate underwent surface pretreatment including sandblasting and ultrasonic cleaning; under an inert atmosphere, the composite powder was conveyed to the laser focal area for scanning cladding via synchronous powder feeding; in this embodiment, the process parameters of the laser cladding scanning were: laser power 2.2kW, scanning speed 8mm / s, and overlap rate of adjacent cladding channels 30%; under the action of the laser, the powder and the substrate surface melted and solidified rapidly to form a metallurgically bonded coating; finally, the clad workpiece was subjected to stress-relief annealing treatment, and the process parameters of the stress-relief annealing treatment were set as: annealing temperature 700℃, holding time 1 hour;

[0052] Example 4:

[0053] This embodiment provides a laser cladding method for preparing high-entropy alloy coatings, characterized by comprising the following steps:

[0054] The preparation methods of the tantalum-reinforced high-entropy alloy powder and the silane-coated nano-yttrium oxide composite particles are the same as those in Example 1.

[0055] In this embodiment, the weight ratio of the tantalum-reinforced high-entropy alloy powder to the silane-coated nano-yttrium oxide composite particles in the composite powder is 97:3; the surface pretreatment of the substrate includes sandblasting and ultrasonic cleaning with anhydrous ethanol; during laser cladding, the laser cladding scanning process parameters are: laser power 1.9kW, scanning speed 11mm / s, and overlap rate of adjacent cladding channels 45%; after cladding is completed, the workpiece is subjected to stress-relief annealing, and the stress-relief annealing process parameters are: annealing temperature 600℃, holding time 2.5 hours;

[0056] Example 5:

[0057] This embodiment provides a laser cladding method for preparing high-entropy alloy coatings, characterized by comprising the following steps:

[0058] The preparation methods of the tantalum-reinforced high-entropy alloy powder and the silane-coated nano-yttrium oxide composite particles are the same as those in Example 1.

[0059] In this embodiment, the composite powder is prepared by mixing tantalum-reinforced high-entropy alloy powder and silane-coated nano-yttrium oxide composite particles in a weight ratio of 98.5:1.5; the surface pretreatment steps for the nickel-based high-temperature alloy substrate are the same as in Embodiment 1; in the laser cladding step performed under an inert atmosphere, the laser cladding scanning process parameters are selected as follows: laser power 2.1kW, scanning speed 9mm / s, and overlap rate of adjacent cladding channels 35%; the final stress-relief annealing treatment has the following process parameters: annealing temperature 650℃, holding time 1.5 hours;

[0060] In Examples 1-5 and Comparative Examples 1-3, the Al, Co, Cr, Ni, and Ta metal raw materials were all from Zhongnuo New Materials (Beijing) Technology Co., Ltd., with a purity >99.9%; the nano-yttrium oxide powder was from Shanghai Xuanhe Nanotechnology Co., Ltd., catalog number: XH-Y2O3-30N, with an average diameter of 30nm and a purity >99.9%; the silane coupling agent (KH-550) was from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS number: 919-30-2; anhydrous ethanol was analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd.; high-purity acetone and high-purity ethanol were purchased from Beijing Praxair Utility Gases Co., Ltd.; the nickel-based high-temperature alloy raw material (Inconel 718) was from Baowu Metallurgical Co., Ltd.; the MCrAlY powder (CoNiCrAlY) specified in Comparative Example 2 was purchased from Beijing Institute of Aeronautical Materials, with a particle size range of 50-150μm; all other reagents used were commercially available analytical grade.

[0061] Comparative Example 1:

[0062] This comparative example provides a method for preparing a coating, which differs from Example 1 in that the silane-coated nano-yttrium oxide composite particles are missing.

[0063] Specifically, the tantalum-reinforced high-entropy alloy powder prepared in Example 1 was used as all the powder raw materials; the substrate pretreatment, laser cladding process parameters and subsequent heat treatment processes were consistent with those in Example 1.

[0064] Although the resulting coating can form a metallurgical bond with the substrate, its oxidative weight gain reaches 1.25 mg / cm³ after 100 hours of oxidation at 1150℃. 2 Analysis of the phenomenon shows that, due to the lack of pinning effect of active elements on the oxide film / substrate interface, the oxide film formed at high temperature is not firmly bonded to the coating interface, and there is a risk of peeling off during long-term service. This result highlights the important role of the silane-coated nano-yttrium oxide composite particles in improving the long-term high-temperature oxidation resistance of the coating.

[0065] Comparative Example 2:

[0066] This comparative example provides a method for preparing a coating, which differs from Example 1 in that conventional MCrAlY powder is used instead of the tantalum-reinforced high-entropy alloy powder.

[0067] Specifically, commercially available MCrAlY powder was mixed with two portions of silane-coated yttrium oxide nanocomposite particles prepared in Example 1; the substrate pretreatment, laser cladding process parameters, and subsequent heat treatment processes were all consistent with those in Example 1.

[0068] The resulting coating is primarily mechanically bonded to the substrate, with a low bonding strength of approximately 55 MPa. After 100 hours of oxidation at 1150℃, its oxidative weight gain reaches as high as 2.13 mg / cm³. 2 The phenomenon is explained as follows: traditional MCrAlY coatings are prone to generating brittle phases at high temperatures, leading to severe oxidation, and the mechanical bonding interface is prone to failure during thermal cycling. This result fundamentally proves the superiority of the tantalum-reinforced high-entropy alloy powder described in this technical solution as the coating host.

[0069] Comparative Example 3:

[0070] This comparative example provides a laser cladding method for preparing a high-entropy alloy coating. The difference between this method and Example 1 is that the final stress-relief annealing step is omitted.

[0071] All steps of this method, including the preparation of the two core raw materials, the formulation of the composite powder, the substrate pretreatment, and the laser cladding process, are exactly the same as in Example 1; however, after cladding, the workpiece is no longer subjected to any heat treatment.

[0072] Although the resulting coating has good shape, its bonding strength is only 75 MPa, and the coating exhibits high brittleness. Phenomenon analysis shows that the extremely fast cooling rate of laser cladding introduces large residual stress into the clad microstructure, which makes the coating prone to cracking under impact load, affecting its service reliability. This result indicates that the stress-relief annealing treatment is a necessary step to eliminate residual stress and improve the overall mechanical properties of the coating.

[0073] The high-entropy alloy coatings prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to corresponding performance tests, and the test results are shown below.

[0074] 1. Coating-substrate bonding strength test

[0075] Test method:

[0076] The bonding strength of the coating was tested using an INSTRON 5985 universal testing machine manufactured by the American company, according to ASTM C633-13, "Standard Test Method for Adhesion or Cohesive Strength of Thermally Sprayed Coatings". The coated sample was bonded to the uncoated mating part with epoxy resin and cured at 150°C for 4 hours. During the test, a tensile load perpendicular to the interface was applied to the sample at a tensile rate of 1 mm / min until fracture occurred. To ensure the reliability of the data, the coated samples under each set of parameters were tested 5 times, and the final result was the average value.

[0077] Data table:

[0078] Table 1. Coating bond strength test results of each embodiment and comparative example.

[0079]

[0080] Results analysis:

[0081] As shown in Table 1, the high-entropy alloy coatings prepared in Examples 1-5 of this technical solution all exhibit excellent bonding strength, which is far higher than that of the coating prepared using traditional MCrAlY powder in Comparative Example 2. This profoundly reveals one of the core advantages of the technical solution of this invention; the specific analysis is as follows:

[0082] The bonding strength of Examples 1-5 all exceeded 85 MPa, and the fracture location all occurred inside the coating. This indicates that a high-quality metallurgical bond was formed between the coating and the substrate, and the interfacial bonding strength was even higher than the cohesive strength of the coating itself. This metallurgical bond is due to the fact that during the laser cladding process, the high-energy laser beam melts the coating powder and the substrate surface simultaneously to form a eutectic pool, realizing the mutual diffusion and penetration between elements, fundamentally solving the problem of easy peeling of the interface caused by the mechanical bonding of traditional coatings.

[0083] Comparing Example 1 and Comparative Example 3, it is evident that stress-relief annealing is a key step in improving coating adhesion. The coating in Comparative Example 3 exhibits high brittleness due to the significant residual stress generated during rapid laser solidification, resulting in a adhesion strength of only 75.11 MPa. In contrast, after appropriate annealing at 550°C, the residual stress in Example 1 was effectively eliminated, improving coating toughness and significantly increasing the adhesion strength to 92.15 MPa. This demonstrates the necessity of subsequent heat treatment for optimizing final service performance.

[0084] Comparing Example 1 and Comparative Example 1, it was found that although the difference in bonding strength between the two was not significant, the introduction of an appropriate amount of silane-coated nano-yttrium oxide composite particles had a positive effect on the densification and toughening of the coating structure, which helped to obtain higher bonding strength. However, excessive filler may introduce micro-agglomerates in the molten pool, becoming a potential source of defects, resulting in a slight decrease in bonding strength. Therefore, there is an optimization range for the content of functional modified filler.

[0085] In summary, this technical solution achieves a strong metallurgical bond between the coating and the substrate by using specific tantalum-reinforced AlCoCrNi high-entropy alloy powder, supplemented by a precisely controlled laser cladding process and subsequent heat treatment, thus ensuring the structural stability of the coating under harsh working conditions.

[0086] 2. High-temperature oxidation resistance test of the coating

[0087] Test method:

[0088] An isothermal oxidation experiment was conducted using a Nabertherm N300 / H high-temperature box furnace (Germany). Coated samples measuring 15mm × 10mm × 3mm were polished, ultrasonically cleaned in anhydrous ethanol, and dried. Their initial mass was measured using a Mettler Toledo XS205DU high-precision electronic analytical balance (Switzerland). The samples were then placed in the box furnace and continuously oxidized for 100 hours in static air at 1150℃. After oxidation, the samples were removed, cooled to room temperature, and weighed again. To ensure experimental accuracy, three parallel samples were prepared for each group. The weight gain per unit area was calculated based on the change in mass before and after oxidation, and the average value was taken.

[0089] Data table:

[0090] Table 2 shows the weight gain results of each example and comparative example after oxidation at 1150℃ for 100 hours.

[0091]

[0092] Results analysis:

[0093] As shown in Table 2, the embodiments of this technical solution all exhibit excellent high-temperature oxidation resistance, with significantly lower oxidative weight gain than Comparative Example 1 and Comparative Example 2. This fully demonstrates the great potential of this invention in high-temperature protection applications; the underlying mechanism can be further analyzed as follows:

[0094] First, comparing Example 1 and Comparative Example 2, the former's oxidation weight gain is only about 24% of the latter's; this is determined by the fundamental difference in the coating's main materials. The tantalum-reinforced AlCoCrNi high-entropy alloy powder used in this invention forms a stable face-centered cubic and body-centered cubic solid solution structure after rapid solidification. This structure has excellent structural stability at high temperatures and is not prone to precipitating brittle phases. At the same time, the high concentration of Al and Cr elements can work synergistically to quickly form a dense, continuous, and self-healing protective oxide film mainly composed of Al2O3 on the coating surface, effectively preventing further invasion of oxygen elements. In contrast, the traditional MCrAlY coating is prone to phase transformation at high temperatures, and the resulting oxide film is not stable enough, resulting in poor protective capabilities.

[0095] Secondly, comparing Example 1 with Comparative Example 1 reveals another key innovation of this invention. The oxidation weight gain of Comparative Example 1 is 2.45 times that of Example 1, which clearly demonstrates the key active element effect of silane-coated nano-yttrium oxide composite particles. In Example 1, the surface-modified nano-Y2O3 particles can be uniformly dispersed in the molten pool. After solidification, these particles are dispersed in the coating, especially at the interface between the oxide film and the coating, greatly improving the adhesion of the oxide film through a pinning effect. In addition, the Y element can also inhibit the formation of vacancies, reduce the stress in the oxide film, and prevent crack propagation. Therefore, even under long-term high-temperature cycling, the oxide film can adhere firmly without peeling off, maintaining long-term protection. In contrast, Comparative Example 1 lacks this mechanism, resulting in a weak bond between the oxide film and the substrate, which easily leads to microcracks and accelerates the oxidation process.

[0096] In summary, this technical solution, through the synergistic effect of a high-entropy alloy substrate and functionally modified fillers, not only establishes the material basis for generating a dense oxide film, but also solves the technical problem of easy peeling off of the oxide film, thereby achieving a significant improvement in antioxidant performance.

[0097] 3. Coating microhardness test

[0098] Test method:

[0099] The microhardness of the coating cross-section was measured using an HM-200 micro Vickers hardness tester from Mitutoyo, Japan. The cross-section of the inlaid coating sample was ground and polished to a mirror finish. A test load of 200g (1.96N) was selected, with a loading time of 15 seconds. To comprehensively reflect the coating hardness, 10 measurement points were randomly selected in an area approximately 100μm from the coating surface, along a direction parallel to the interface, for indentation testing. To reduce random errors, the final hardness value was taken as the arithmetic mean of these 10 measurement points.

[0100] Data table:

[0101] Table 3. Microhardness test results of coatings in each embodiment and comparative example.

[0102]

[0103] Results analysis:

[0104] As shown in Table 3, the high-entropy alloy coatings prepared by this technical solution generally have high microhardness, and the optimized balance between hardness and toughness can be achieved through subsequent heat treatment processes.

[0105] The hardness values ​​of all embodiments and Comparative Examples 1 and 3 were significantly higher than those of Comparative Example 2. This is mainly attributed to the solid solution strengthening effect of the high-entropy alloy itself. Multiple principal atoms (Al, Co, Cr, Ni, Ta) occupy simple lattice sites in a disordered manner, causing severe lattice distortion, which effectively hinders the movement of dislocations, thereby endowing the material with high hardness and high strength. In addition, the extremely high cooling rate of laser cladding results in extremely fine grains, and significant grain refinement is also an important reason for the high hardness of the coating.

[0106] Comparing Example 1 and Comparative Example 3 reveals the regulatory effect of heat treatment on mechanical properties; Comparative Example 3 exhibits the highest hardness, reaching 680.33 HV. 0.2 This is because the cladding state microstructure retains a large number of dislocations and residual stresses, exhibiting a work-hardened state; however, as the bond strength test shows, this high hardness is accompanied by high brittleness; after stress-relief annealing at 550°C, the hardness of Example 1 moderately decreased to 610.25 HV. 0.2 This indicates that the annealing process at 550℃ can effectively eliminate residual stress and improve toughness while retaining the high hardness of the coating due to solid solution strengthening and fine grain strengthening to the greatest extent, thus achieving the best match of mechanical properties.

[0107] Comparing examples with different annealing temperatures, such as Example 1 (550℃), Example 4 (600℃), and Example 3 (700℃), it can be observed that the hardness decreases with increasing annealing temperature; in particular, when the annealing temperature reaches 700℃, the hardness decreases to 545.18 HV. 0.2 This is because excessively high annealing temperatures can cause the metastable strengthening phases in the coating to aggregate and grow, resulting in a certain degree of coarsening of the microstructure, thereby weakening the strengthening effect. This further proves that around 550℃ is the ideal temperature range for stress-relief annealing of this high-entropy alloy coating system.

[0108] In summary, this technical solution not only produces a protective coating with high hardness, but more importantly, it resolves the contradiction between high hardness and brittleness through precise control of the subsequent heat treatment process, thereby obtaining comprehensive and excellent mechanical properties that combine high hardness, high toughness, and high bonding strength.

[0109] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing a high-entropy alloy coating by laser cladding, characterized in that, Includes the following steps: A tantalum-reinforced high-entropy alloy powder was physically mixed with a silane-coated nano-yttrium oxide composite particle to obtain a composite powder. Surface pretreatment of nickel-based high-temperature alloy substrate; Under an inert atmosphere, the composite powder is fed to the focal area of ​​a high-power laser beam using a synchronous powder feeding method. The surface of the substrate is then scanned, causing the composite powder and the substrate surface to melt synchronously to form a eutectic pool. After the laser beam is removed, the composite powder solidifies rapidly to form a coating that is metallurgically bonded to the substrate. The workpiece that has been clad is subjected to stress-relieving annealing. The preparation of the tantalum-reinforced high-entropy alloy powder includes the following steps: Al, Co, Cr, Ni, and Ta metal raw materials are smelted in a vacuum induction melting furnace according to a preset atomic ratio, and a master alloy ingot with uniform composition is obtained by electromagnetic stirring and repeated remelting. The master alloy ingot is heated to complete melting and then atomized at high speed using high-pressure argon gas, causing the molten droplets to solidify rapidly into powder. The powder is subjected to vibratory sieving and vacuum drying. The atomic ratio of Al, Co, Cr, Ni, and Ta in the metal raw material is 1:1.5:1.5:2:0.3; the particle size of the powder selected by the vibrating sieve is 50-150 μm. The preparation of the silane-coated yttrium oxide nanocomposite particles includes the following steps: Nano-yttrium oxide powder was added to anhydrous ethanol and ultrasonically dispersed under nitrogen protection to form a uniform suspension. A silane coupling agent is added dropwise to the suspension, and a constant-temperature reflux reaction is carried out at a specific temperature. The reaction products were then subjected to centrifugation, washing with anhydrous ethanol, and vacuum drying.

2. The preparation method according to claim 1, characterized in that, In the composite powder, the weight ratio of the tantalum-reinforced high-entropy alloy powder to the silane-coated nano-yttrium oxide composite particles is (96-99):(1-4).

3. The preparation method according to claim 1, characterized in that, The process parameters for laser cladding scanning are: laser power 1.8-2.2kW, scanning speed 8-12mm / s, and overlap rate of adjacent cladding channels 30-50%.

4. The preparation method according to claim 1, characterized in that, The surface pretreatment of the substrate includes sandblasting the substrate surface, followed by ultrasonic cleaning in anhydrous ethanol.

5. The preparation method according to claim 1, characterized in that, The process parameters for the stress-relief annealing treatment are: annealing temperature 500-700℃, holding time 1-3 hours.

6. A high-entropy alloy coating prepared by the preparation method according to any one of claims 1-5.

7. The application of the high-entropy alloy coating of claim 6 in the protection of high-temperature components such as turbine blades or combustion chamber linings of aero-engines.

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