A method of vacuum assisted drop-filling of defects in plasma sprayed high entropy thermal barrier coatings

Abstract

This invention discloses a method for vacuum-assisted drop-coating to fill defects in plasma-sprayed high-entropy thermal barrier coatings, relating to the field of high-temperature protective coating technology. Based on a synergistic mechanism of vacuum negative pressure drive and in-situ generation of α-alumina, this invention solves the problems of insufficient penetration depth and poor compatibility in filling techniques. The vacuum environment can expel air from the coating interior and defects, creating unobstructed penetration channels for aluminum chloride sol. Combined with a multi-drop-coating process, the sol can deeply penetrate internal defects such as pores and microcracks formed by plasma spraying. After heat treatment at 1100℃, the sol is in-situ transformed into an α-alumina filling phase. This filling phase forms a single-phase solid solution with the high-entropy rare-earth zirconate coating with defective fluorite structures, resulting in no harmful impurities and a tight interface. The small amount of free space reserved after alumina filling can release macroscopic thermal stress generated during thermal cycling, preventing new cracks from forming due to stress concentration and ensuring the stability of the coating.

Description

Technical Field

[0001] This invention relates to the field of high-temperature protective coating technology, specifically a method for filling defects in plasma-sprayed high-entropy thermal barrier coatings using vacuum-assisted droplet coating. Background Technology

[0002] Thermal barrier coatings are a key thermal protection technology for high-temperature components such as aero-engines and gas turbines. They can effectively reduce the temperature of the base metal and improve the operating temperature and efficiency of hot-end components. With the continuous improvement of engine efficiency requirements, more stringent requirements are placed on the temperature resistance and long-term stability of thermal barrier coatings. Traditional yttrium oxide stabilized zirconia coatings are prone to phase transformation and sintering at temperatures above 1200°C, which limits their further application. High-entropy rare earth zirconates have become a candidate material for the next generation of thermal barrier coatings due to their low thermal conductivity, high phase stability and excellent anti-sintering properties.

[0003] Atmospheric plasma spraying is an important process for preparing thermal barrier coatings. However, the rapid solidification and stacking of molten particles during the process inevitably introduces defects such as porosity, microcracks, and poor interlayer bonding into the coating. Although these defects can reduce thermal conductivity to some extent, excessive defects will significantly weaken the coating's bonding strength, provide diffusion channels for oxygen and corrosive media, accelerate substrate oxidation, and become stress concentration points during thermal cycling, ultimately leading to premature coating failure.

[0004] To address coating defects, existing technologies such as laser remelting, vacuum heat treatment, sol-gel sealing, and chemical vapor infiltration all have limitations. Laser remelting easily introduces new cracks and only treats the surface layer; excessively high temperatures in vacuum heat treatment can lead to over-sintering; conventional sol-gel sealing is performed at atmospheric pressure, resulting in limited penetration depth and difficulty in filling small internal defects; and chemical vapor infiltration involves complex equipment, high costs, and slow rates.

[0005] Therefore, it is of great significance to develop a post-processing technology that can deeply fill internal defects in coatings, is low in cost, and does not affect the performance of the coating itself. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for vacuum-assisted drop-coating to fill defects in plasma-sprayed high-entropy thermal barrier coatings. Based on the synergistic mechanism of vacuum negative pressure drive and in-situ generation of α-alumina, this method solves the problems of insufficient penetration depth and poor compatibility in filling techniques. The vacuum environment can expel air from the coating and defects, creating unobstructed penetration channels for the aluminum chloride sol. Combined with multiple drop-coating processes, the sol can deeply penetrate the pores, microcracks, and other internal defects formed by plasma spraying. After heat treatment at 1100℃, the sol is transformed in-situ into an α-alumina filling phase. This filling phase forms a single-phase solid solution with the high-entropy rare-earth zirconate coating with defective fluorite structures, without the generation of harmful impurities and with a tight interface. Simultaneously, the small amount of free space reserved after alumina filling can release macroscopic thermal stress generated during thermal cycling, preventing new cracks from forming in the coating due to stress concentration. This ensures the stability of the coating from both structural integrity and compatibility perspectives.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for vacuum-assisted drop-coating to fill defects in plasma-sprayed high-entropy thermal barrier coatings, the specific steps of which are as follows: Preparation of S100 high-entropy rare earth zirconate powder: Eu2O3, Gd2O3, Er2O3, Tm2O3, Yb2O3 and ZrO2 oxide powders with a purity ≥99.9% were weighed according to the stoichiometric molar ratio, and mixed by ball milling, drying, calcining and spray granulation with anhydrous ethanol as medium to obtain spherical high-entropy rare earth zirconate powder suitable for atmospheric plasma spraying; S200. Plasma spraying preparation of high-entropy thermal barrier coating: After sandblasting pretreatment of nickel-based alloy substrate, atmospheric plasma spraying process is adopted, using the spherical high-entropy rare earth zirconate powder as the spraying material, and an adhesive layer and a high-entropy ceramic layer are sprayed on the substrate surface to obtain the original high-entropy thermal barrier coating. Preparation of S300 aluminum chloride sol: Dissolve aluminum chloride hexahydrate in a mixed solution of deionized water and ethanol, stir and age, and then keep warm to form aluminum chloride sol for filling coating defects. S400, Vacuum-assisted drop coating filling: The original high-entropy thermal barrier coating and the aluminum chloride sol are placed in a vacuum system and vacuumed. The aluminum chloride sol is drop-coated onto the surface of the original high-entropy thermal barrier coating and completely wetted. The vacuum state is maintained so that the sol penetrates into the coating defects. After drying, one drop coating is completed. S500, Repeated Drop Coating and High-Temperature Heat Treatment: Repeat the drop coating operation of S400, and perform high-temperature heat treatment on the completed drop-coated sample to convert the aluminum chloride sol that has penetrated into the coating defects into the α-alumina filler phase, thereby completing the filling and repair of the coating defects.

[0008] Further, in S100, the stoichiometric molar ratio of the oxide powder is Eu2O3:Gd2O3:Er2O3:Tm2O3:Yb2O3:ZrO2 = 0.2:0.2:0.2:0.2:0.2:1, corresponding to the chemical formula of the high-entropy rare earth zirconate (Eu2O3:Gd2O3:Er2O3:Tm2O3:Yb2O3:ZrO2 = 0.2:0.2:0.2:0.2:1, which is (Eu2O3:Gd2O3:Er2O3:Tm2O3:Yb2O3:ZrO2:1). 0.2 Gd 0.2 Er 0.2 Tm 0.2 Yb 0.2 )2Zr2O7.

[0009] Furthermore, in S100, the ball milling and mixing are carried out using a planetary ball mill with a ball milling speed of 400 r / min and a ball milling time of 12 h. The calcination is carried out in a muffle furnace with a calcination temperature of 1600℃ and a calcination time of 5 h. After calcination, the mixture is cooled with the furnace.

[0010] Furthermore, the adhesive layer material is CoNiCrAlY, and the key parameters for atmospheric plasma spraying when spraying the high-entropy ceramic layer are: current 710A, main gas Ar pressure 60psi, auxiliary gas He pressure 50psi, voltage 40V, and spraying distance 80mm. The plasma spraying parameters for the high-entropy ceramic layer are: current 850A, main gas Ar pressure 60psi, auxiliary gas He pressure 100psi, voltage 40V, and spraying distance 80mm.

[0011] Furthermore, in the S300, the volume ratio of deionized water to ethanol is 1:1, the concentration of aluminum chloride sol is 1.5 mol / L, the holding temperature is 50℃, and the holding time is 8h.

[0012] Furthermore, in the S400, the vacuum system has a vacuum level of 20% atmospheric pressure, the initial vacuum holding time is 10 minutes, the aluminum chloride sol completely wets the surface of the original high-entropy thermal barrier coating and continues to maintain the vacuum state for 10 minutes, and the sample is completely dried after each drop coating.

[0013] Furthermore, in S500, the number of multiple drop-coating cycles is 2-6 times, and the conditions for the high-temperature heat treatment are: holding at 1050-1150℃ for 0.5-1.5 hours in an air atmosphere.

[0014] Furthermore, the specific operation steps of S400 are as follows: S410, Vacuum pretreatment: Place the original high-entropy thermal barrier coating and aluminum chloride sol into a vacuum system, evacuate to a vacuum degree of 20% atmospheric pressure, maintain the vacuum state for 10 minutes, and remove the air from the inside of the coating and the system. S420, Drop-coating and wetting: Slowly drop aluminum chloride sol onto the coating surface until the sol completely covers and wets the coating surface; S430, Vacuum Penetration: Maintain a vacuum state of 20% atmospheric pressure for 10 minutes to allow aluminum chloride sol to penetrate deeply into the pores and microcracks inside the coating under negative pressure. S440. Drying: Take out the sample after drop coating and dry it in an environment of 40-60℃ until there is no flowing liquid on the surface of the sol, thus completing one drop coating filling.

[0015] Compared with existing technologies, this method for filling defects in plasma-sprayed high-entropy thermal barrier coatings using vacuum-assisted drop-coating has the following advantages: I. This invention, based on the synergistic mechanism of vacuum negative pressure drive and in-situ generation of α-alumina, solves the problems of insufficient penetration depth and poor compatibility of filling technology. The vacuum environment can expel air from the inside of the coating and defects, creating an unobstructed penetration channel for aluminum chloride sol. Combined with the multiple drip coating process, the sol can deeply penetrate into the pores, microcracks and other internal defects formed by plasma spraying. After heat treatment at 1100℃, the sol is transformed in-situ into the α-alumina filling phase. This filling phase forms a single-phase solid solution with the high-entropy rare earth zirconate coating with defective fluorite structure, without the generation of harmful impurity phases and with tight interfacial bonding. At the same time, the small amount of free space reserved after alumina filling can release the macroscopic thermal stress generated during thermal cycling, avoiding the formation of new cracks in the coating due to stress concentration. This ensures the stability of the coating from both structural integrity and compatibility perspectives.

[0016] II. This invention achieves sol transport by constructing a synergistic mechanism of vacuum drive and capillary action, which enables the sol to penetrate internal defects of the coating. Before drop coating, the vacuum system containing the coating is pre-evacuated, which removes most of the air inside the through and semi-through defects of the coating, significantly reducing the gas resistance to sol penetration. Drop coating is carried out under this vacuum state. The negative pressure difference between the external atmospheric pressure and the inside of the defect forms a strong driving force, which, together with capillary action, promotes the rapid entry and filling of aluminum chloride sol into various pores and microcracks. This physical process ensures that the sol can not only reach the shallow area of ​​the coating, but also penetrate into the deep part of the coating and defects near the interface of the adhesive layer, laying a uniform physical foundation for the subsequent achievement of integrity through chemical reaction.

[0017] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0019] Figure 1 A flowchart of a method for filling defects in a high-entropy thermal barrier coating by vacuum-assisted drop-coating with plasma spraying; Figure 2 The high entropy (Eu) prepared for the embodiments of the present invention 0.2 Gd 0.2 Er 0.2 Tm 0.2 Yb 0.2 XRD pattern, TEM micrograph and elemental distribution map of Zr2O7 powder; Figure 3 Comparison of surface XRD patterns of Al-0 coating without drop-coating treatment and Al-5 coating after 5 drop-coating treatments; Figure 4 TG-DSC curves of Al-5 coating during the heating process from 50 to 1500°C; Figure 5 Comparison of the surface macromorphology of Al-0 coating and Al-5 coating; Figure 6 Comparative SEM images of the surface microstructures of Al-0 and Al-5 coatings; Figure 7 Figures show the three-dimensional morphology and roughness measurement results of Al-0 and Al-5 coatings; Figure 8 SEM images of the cross-sectional morphology of Al-0 and Al-5 coatings are provided to illustrate the filling state of alumina in defects. Figure 9 Comparison of TGO growth in cross sections after heat treatment at 1000°C for 10 hours for Al-0 and Al-5 coatings; Figure 10 The image shows the contact angle measurement results of molten CMAS on the Al-0 and Al-5 coating surfaces; Figure 11 Comparison of cross-sectional morphology of Al-0 and Al-5 coatings after CMAS etched at 1300°C for 5 minutes; Figure 12 This is a graph showing the effect of different alumina contents on the melt viscosity of CMAS, calculated using FactSage software. Detailed Implementation

[0020] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following description, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation methods, structures, features, and effects of the present invention. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a method for filling defects in a high-entropy thermal barrier coating by vacuum-assisted drop-coating plasma spraying,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plurality forms, unless the context clearly indicates otherwise; “plural” generally includes at least two.

[0022] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or device comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or device comprising said element. This embodiment discloses a method for filling defects in high-entropy thermal barrier coatings by vacuum-assisted drop-coating and plasma spraying. This method is mainly applied to the post-processing of thermal barrier coatings for high-temperature components such as aero-engines and gas turbines. It aims to solve problems such as reduced bonding strength, insufficient oxidation / corrosion resistance, and premature failure caused by defects such as pores and microcracks in high-entropy rare earth zirconate coatings sprayed by atmospheric plasma spraying.

[0023] This invention utilizes vacuum-assisted drop-coating technology to penetrate coating defects to a specific depth and then transforms the sol into an α-alumina filler phase with excellent compatibility with the coating through in-situ heat treatment, thereby significantly improving the coating's density, insulation performance, and service life.

[0024] Specifically, in this embodiment, (Eu) 0.2 Gd 0.2 Er 0.2 Tm 0.2 Yb 0.2 Taking the Zr2O7 high-entropy rare-earth zirconate thermal barrier coating as an example, such as... Figure 1 As shown, a method for filling defects in plasma-sprayed high-entropy thermal barrier coatings using vacuum-assisted droplet coating is provided, specifically including the following steps: Preparation of S100 high-entropy rare earth zirconate powder: Eu2O3, Gd2O3, Er2O3, Tm2O3, Yb2O3 and ZrO2 oxide powders with a purity ≥99.9% were weighed according to the stoichiometric molar ratio, and mixed by ball milling, drying, calcining and spray granulation with anhydrous ethanol as medium to obtain spherical high-entropy rare earth zirconate powder suitable for atmospheric plasma spraying; S200. Plasma spraying preparation of high-entropy thermal barrier coating: After sandblasting pretreatment of nickel-based alloy substrate, atmospheric plasma spraying process is adopted, using the spherical high-entropy rare earth zirconate powder as the spraying material, and an adhesive layer and a high-entropy ceramic layer are sprayed on the substrate surface to obtain the original high-entropy thermal barrier coating. Preparation of S300 aluminum chloride sol: Dissolve aluminum chloride hexahydrate in a mixed solution of deionized water and ethanol, stir and age, and then keep warm to form aluminum chloride sol for filling coating defects. S400, Vacuum-assisted drop coating filling: The original high-entropy thermal barrier coating and the aluminum chloride sol are placed in a vacuum system and vacuumed. The aluminum chloride sol is drop-coated onto the surface of the original high-entropy thermal barrier coating and completely wetted. The vacuum state is maintained so that the sol penetrates into the coating defects. After drying, one drop coating is completed. S500, Repeated Drop Coating and High-Temperature Heat Treatment: Repeat the drop coating operation of S400, and perform high-temperature heat treatment on the completed drop-coated sample to convert the aluminum chloride sol that has penetrated into the coating defects into the α-alumina filler phase, thereby completing the filling and repair of the coating defects.

[0025] In the specific implementation, for the preparation of S100 high-entropy rare earth zirconate spraying powder, according to the stoichiometric molar ratio of Eu2O3:Gd2O3:Er2O3:Tm2O3:Yb2O3:ZrO2=0.2:0.2:0.2:0.2:0.2:1, the oxide powders of Eu2O3, Gd2O3, Er2O3, Tm2O3, Yb2O3 and ZrO2 with a purity ≥99.9% are accurately weighed. The weighed powders are placed together with anhydrous ethanol medium in the ball mill jar of a planetary ball mill. The ball milling process is carried out continuously at a speed of 400 r / min for 12 hours to ensure that the powder components are uniformly mixed at the atomic scale. After the ball milling is completed, the slurry is placed in a drying oven to dry thoroughly to completely remove the ethanol medium. The uniformly mixed dry powder was placed in an alumina crucible and then placed in a muffle furnace. The crucible was heated to 1600℃ at a heating rate of 5℃ / min and held at this temperature for 5 hours to complete the solid-phase reaction. After calcination, the powder was cooled to room temperature with the furnace to obtain a high-entropy rare-earth zirconate bulk with a defective fluorite structure. The calcined bulk was then slightly crushed and ground, and prepared into spherical powders with good flowability and uniform particle size distribution using a spray granulation process. These spherical powders can be directly used for atmospheric plasma spraying. Phase analysis of the prepared powder was performed by X-ray diffraction (XRD), and the results are as follows:Figure 2 As shown, its diffraction peaks are consistent with the standard Er2Zr2O3 card, with no impurity peaks, confirming the successful synthesis of a single-phase high-entropy solid solution. Transmission electron microscopy observation and elemental surface distribution analysis further show that the lattice fringes are clear, the rare earth elements are uniformly distributed, and there is no segregation.

[0026] For the preparation of high-entropy thermal barrier coatings by S200 plasma spraying, nickel-based high-temperature alloys are selected as the substrate material. The substrate surface is pretreated by sandblasting with brown corundum gravel to obtain a clean and rough surface, thereby enhancing the mechanical bonding between the coating and the substrate.

[0027] The coating was prepared using an atmospheric plasma spraying system. CoNiCrAlY (PraxairCO-110) alloy was sprayed onto the pretreated substrate as an adhesive layer. The spraying parameters for the adhesive layer were: current 710A, main gas Ar pressure 60psi, auxiliary gas He pressure 50psi, voltage 40V, and spraying distance 80mm.

[0028] After the adhesive layer is applied, use the spherical (Eu) mold prepared in S100. 0.2 Gd 0.2 Er 0.2 Tm 0.2 Yb 0.2 High-entropy powder (Zr2O7) was used as raw material to spray a high-entropy ceramic layer. The spraying parameters of the high-entropy ceramic layer were: current 850A, main gas Ar pressure 60psi, auxiliary gas He pressure 100psi, voltage 40V, and spraying distance 80mm.

[0029] Using the above process, a pristine high-entropy thermal barrier coating with a typical layered structure but containing defects such as pores and microcracks was prepared on the substrate. For subsequent performance testing, an uncoated adhesive layer was prepared, and the high-entropy ceramic layer was directly sprayed after sandblasting. After spraying, the sample was immersed in hydrochloric acid for 24 hours, and the substrate was peeled off to obtain the pure high-entropy ceramic layer.

[0030] For the preparation of S300 aluminum chloride sol, aluminum chloride hexahydrate (AlCl3•6H2O) reagent was weighed and dissolved in a mixed solvent prepared by deionized water and anhydrous ethanol at a volume ratio of 1:1. The mixture was continuously stirred on a magnetic stirrer until the solid was completely dissolved, resulting in a clear aluminum chloride solution with a concentration of 1.5 mol / L. The clear aluminum chloride solution was then transferred to a constant temperature oven at 50°C and aged for 8 hours. During this process, the clear aluminum chloride solution gradually transformed into a stable aluminum chloride sol with a certain viscosity. This aluminum chloride sol will be used as a filling medium in the subsequent vacuum-assisted drop coating process.

[0031] For S400 vacuum-assisted drop-coating filling, the synergistic effect of vacuum negative pressure and capillary action allows aluminum chloride sol to deeply penetrate coating defects, achieving deep defect filling. The specific operation process is as follows: S410, Vacuum Pretreatment: Place the original high-entropy thermal barrier coating sample obtained in S200 and the aluminum chloride sol prepared in S300 into the vacuum chamber, seal it, start the vacuum pump, and pump the pressure in the vacuum system to about 20% of the standard atmospheric pressure. Maintain this vacuum state for 10 minutes. This process is used to remove as much air as possible from the through and semi-through defects inside the coating, creating a gas-free channel for sol penetration.

[0032] S420, Drop Coating and Wetting: Under the condition of maintaining the vacuum level of S410, use a dropper to slowly and evenly drop aluminum chloride sol onto the surface of the coating sample, control the dropping rate to ensure that the sol can fully spread and completely wet the entire coating surface until a continuous liquid film is formed.

[0033] S430, Vacuum Penetration: After the addition is complete, maintain the vacuum system at 20% atmospheric pressure and let it stand for 10 minutes. During this period, the pressure difference between the atmospheric pressure outside the cavity and the negative pressure inside the coating defects is used as the main driving force, in conjunction with the capillary action of the sol itself, to jointly promote the aluminum chloride sol to penetrate deep into the pores, microcracks and other defects inside the coating.

[0034] S440, Drying: Introduce air into the vacuum chamber to release the vacuum. Remove the sample that has completed the drop-coating process and allow it to air dry at room temperature for 24 hours, or place it in an oven at 40-60℃ to accelerate drying, until the sol is completely cured and there is no flowing liquid on the coating surface. This completes one complete drop-coating cycle.

[0035] In the specific implementation process, in order to ensure the filling effect, the drop-coating filling cycle described in S400 was repeated on the experimental group samples. In this embodiment, the drop-coating was repeated 5 times, and the final sample was marked as Al-5; in contrast, the original coating without drop-coating treatment was marked as Al-0.

[0036] After multiple drop coatings, the sample was placed in a high-temperature box furnace for heat treatment. The heat treatment was carried out in an air atmosphere, heated to 1100°C at a heating rate of 5°C / min, and held at this temperature for 1 hour, and then cooled to room temperature with the furnace. This heat treatment process caused the aluminum chloride sol that had penetrated into the coating defects to decompose and undergo phase transformation, eventually transforming into thermodynamically stable α-alumina (α-Al2O3) crystals with high melting point and excellent chemical stability, thereby filling the coating defects and achieving defect repair.

[0037] In this implementation process, to verify the effectiveness of the method for vacuum-assisted drop-coating to fill defects in plasma-sprayed high-entropy thermal barrier coatings, the performance of the Al-0 and Al-5 coatings before and after treatment was characterized, specifically including: Phase and structure analysis: XRD tests were performed on the Al-5 coating, and the results are as follows: Figure 3 As shown, compared with the Al-0 coating, the XRD pattern of the Al-5 coating clearly shows the diffraction peak of α-Al2O3, while the main phase of the defective fluorite structure of the high-entropy rare earth zirconate remains unchanged, and no other impurity phases are observed. This indicates that the filling treatment successfully introduced α-Al2O3, which has good chemical compatibility with the coating matrix and did not induce harmful phase transformation.

[0038] Thermal stability assessment: The Al-5 coating was analyzed by thermogravimetric-differential scanning calorimetry (TGC), and the results are as follows: Figure 4 As shown, within the temperature range of 50-1500℃, no significant weight change was observed in the TG curve, and no significant endothermic or exothermic peaks were observed in the DSC curve, proving that the Al-5 coating has excellent thermal stability and phase stability in this wide temperature range, meeting the application requirements of high-temperature thermal barrier coatings.

[0039] Surface and cross-sectional morphology observation: Macroscopic morphology: such as Figure 5 As shown, obvious pores are visible on the surface of the Al-0 coating, while the surface of the Al-5 coating is denser and the pores are almost invisible, which intuitively demonstrates the healing effect of alumina filling.

[0040] Microscopic morphology: such as Figure 6 As shown, the Al-0 coating exhibits a typical plasma-sprayed "fish scale" morphology, with unmelted particles and unevenness; the Al-5 coating surface becomes relatively smooth and continuous, presumably due to the formation of an extremely thin aluminum oxide coating layer on the surface.

[0041] Surface roughness: such as Figure 7 As shown, the surface roughness Ra of the Al-0 coating was 4.69 μm, as measured by a three-dimensional profilometer, while that of the Al-5 coating decreased to 4.27 μm. This reduction can be attributed to the formation of a continuous surface layer, where alumina effectively covers unmelted and semi-melted particles that appear during spraying, resulting in a smoother overall coating surface. Roughness directly affects the spreading behavior of molten CMAS.

[0042] Cross-sectional morphology: such as Figure 8The cross-sectional SEM image shown reveals bright white alumina filler within the pores of the Al-5 coating. The alumina does not completely fill the pores but rather partially, leaving a small amount of free space between it and the pore walls. This structure helps release macroscopic thermal stress caused by the difference in thermal expansion coefficients between the alumina and the high-entropy ceramic, preventing new cracks from forming during thermal cycling. Observations at the interface indicate that the alumina and the high-entropy coating are well bonded.

[0043] Antioxidant performance test: Al-0 and Al-5 coated samples were subjected to a 10-hour heat exposure test in air at 1000℃. The growth of thermally grown oxide (TGO) on their cross-sections was compared. The results are as follows: Figure 9 As shown, the TGO at the interface between the Al-0 coating and the adhesive layer is thicker and grows unevenly; while the TGO thickness at the interface of the Al-5 coating is significantly reduced and more uniform. This indicates that the alumina filling the defects effectively hinders the rapid diffusion of oxygen through the internal defects of the coating to the interface, thereby slowing down the oxidation rate of the adhesive layer.

[0044] Evaluation of resistance to CMAS corrosion: Wettability: CMAS glass frit was placed on Al-0 and Al-5 coated surfaces and heated at 1200℃ for 5 minutes. The contact angle of the molten CMAS was measured. Figure 10 As shown, the contact angle of the Al-5 coating surface is about 28° higher than that of the Al-0 coating, indicating that the spreading ability of molten CMAS on the Al-5 coating surface is significantly reduced and the wettability is worse. This is attributed to the formation of a thin layer of alumina on the surface and the reduction of surface roughness.

[0045] Penetration behavior: Al-0 and Al-5 coatings were etched with CMAS at 1300℃ for 5 minutes, and the cross-sectional morphology was observed, such as... Figure 11 As shown, CMAS exhibits rapid localized penetration in the Al-0 coating, clearly invading along the coating defect channels; while in the Al-5 coating, the penetration of CMAS is more uniform and shallower, and no rapid penetration channels were observed. This indicates that the alumina filling effectively blocked the rapid penetration path of CMAS.

[0046] Mechanism analysis: The effect of different Al2O3 contents on the melt viscosity of CMAS was calculated using FactSage software. The results are as follows: Figure 12 As shown, when the Al2O3 content in CMAS increases from 10% to 16%, its viscosity increases significantly, especially in the lower temperature range. This indicates that the alumina dissolved from coating defects into the CMAS melt acts as a "viscosity modifier," increasing the melt viscosity and thus kinetically slowing its penetration rate into the coating interior.

[0047] This specific embodiment details a method for vacuum-assisted drop-coating to fill defects in plasma-sprayed high-entropy thermal barrier coatings. By driving the deep penetration of aluminum chloride sol in a vacuum environment, combined with in-situ generation of αAl₂O₃ filler phase through heat treatment, effective repair of internal defects in the coating is successfully achieved. This treatment significantly improves the structural integrity of the coating, enhances its resistance to high-temperature oxidation and CMAS corrosion, and does not affect the inherent thermal stability of the coating. This method is simple, low-cost, and highly effective, providing an effective technical approach to solving the inherent defect problem of plasma-sprayed thermal barrier coatings.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for filling defects in a high-entropy thermal barrier coating by vacuum-assisted drop-coating with plasma spraying, characterized in that, The specific steps of this method are as follows: Preparation of S100 high-entropy rare earth zirconate powder: Eu2O3, Gd2O3, Er2O3, Tm2O3, Yb2O3 and ZrO2 oxide powders with a purity ≥99.9% were weighed according to the stoichiometric molar ratio, and mixed by ball milling, drying, calcining and spray granulation with anhydrous ethanol as medium to obtain spherical high-entropy rare earth zirconate powder suitable for atmospheric plasma spraying; S200. Plasma spraying preparation of high-entropy thermal barrier coating: After sandblasting pretreatment of nickel-based alloy substrate, atmospheric plasma spraying process is adopted, using the spherical high-entropy rare earth zirconate powder as the spraying material, and an adhesive layer and a high-entropy ceramic layer are sprayed on the substrate surface to obtain the original high-entropy thermal barrier coating. Preparation of S300 aluminum chloride sol: Dissolve aluminum chloride hexahydrate in a mixed solution of deionized water and ethanol, stir and age, and then keep warm to form aluminum chloride sol for filling coating defects. S400, Vacuum-assisted drop coating filling: The original high-entropy thermal barrier coating and the aluminum chloride sol are placed in a vacuum system and vacuumed. The aluminum chloride sol is drop-coated onto the surface of the original high-entropy thermal barrier coating and completely wetted. The vacuum state is maintained so that the sol penetrates into the coating defects. After drying, one drop coating is completed. S500, Repeated Drop Coating and High-Temperature Heat Treatment: Repeat the drop coating operation of S400, and perform high-temperature heat treatment on the completed drop-coated sample to convert the aluminum chloride sol that has penetrated into the coating defects into the α-alumina filler phase, thereby completing the filling and repair of the coating defects.

2. The method for filling defects in a high-entropy thermal barrier coating using vacuum-assisted drop-coating and plasma spraying according to claim 1, characterized in that, In S100, the stoichiometric molar ratio of the oxide powder is Eu2O3:Gd2O3:Er2O3:Tm2O3:Yb2O3:ZrO2 = 0.2:0.2:0.2:0.2:0.2:1, corresponding to the chemical formula of the high-entropy rare earth zirconate (Eu2O3:Gd2O3:Er2O3:Tm2O3:Yb2O3:ZrO2 = 0.2:0.2:0.2:0.2:1, and the chemical formula of the corresponding high-entropy rare earth zirconate is (Eu2O3:Gd2O3:Er2O3:Tm2O3:Yb2O3:ZrO2 = 0.2:0.2:0.2:0.2:1). 0.2 Gd 0.2 Er 0.2 Tm 0.2 Yb 0.2 )2Zr2O7.

3. The method for filling defects in a high-entropy thermal barrier coating using vacuum-assisted drop-coating and plasma spraying according to claim 1, characterized in that, In S100, the ball milling and mixing are carried out using a planetary ball mill with a ball milling speed of 400 r / min and a ball milling time of 12 h. The calcination is carried out in a muffle furnace with a calcination temperature of 1600℃ and a calcination time of 5 h. After calcination, the mixture is cooled with the furnace.

4. The method for filling defects in a high-entropy thermal barrier coating using vacuum-assisted drop-coating and plasma spraying according to claim 1, characterized in that, The adhesive layer material is CoNiCrAlY. The key parameters for atmospheric plasma spraying when spraying the high-entropy ceramic layer are: current 710A, main gas Ar pressure 60psi, auxiliary gas He pressure 50psi, voltage 40V, and spraying distance 80mm. The plasma spraying parameters for the high-entropy ceramic layer are: current 850A, main gas Ar pressure 60psi, auxiliary gas He pressure 100psi, voltage 40V, and spraying distance 80mm.

5. The method for filling defects in a high-entropy thermal barrier coating by vacuum-assisted drop-coating with plasma spraying according to claim 1, characterized in that, In the S300, the volume ratio of deionized water to ethanol is 1:1, the concentration of aluminum chloride sol is 1.5 mol / L, the holding temperature is 50℃, and the holding time is 8h.

6. The method for filling defects in a high-entropy thermal barrier coating by vacuum-assisted drop-coating with plasma spraying according to claim 1, characterized in that, In the S400, the vacuum system has a vacuum level of 20% atmospheric pressure, the initial vacuum holding time is 10 minutes, the aluminum chloride sol completely wets the surface of the original high-entropy thermal barrier coating and continues to maintain the vacuum state for 10 minutes, and the sample is completely dried after each drop coating.

7. The method for filling defects in a high-entropy thermal barrier coating by vacuum-assisted drop-coating with plasma spraying according to claim 1, characterized in that, In S500, the number of multiple drop-coating cycles is 2-6 times, and the conditions for high-temperature heat treatment are: holding at 1050-1150℃ for 0.5-1.5 hours in an air atmosphere.

8. The method for filling defects in a high-entropy thermal barrier coating by vacuum-assisted drop-coating with plasma spraying according to claim 6, characterized in that, The specific operation steps of S400 are as follows: S410, Vacuum pretreatment: Place the original high-entropy thermal barrier coating and aluminum chloride sol into a vacuum system, evacuate to a vacuum degree of 20% atmospheric pressure, maintain the vacuum state for 10 minutes, and remove the air from the inside of the coating and the system. S420, Drop-coating and wetting: Slowly drop aluminum chloride sol onto the coating surface until the sol completely covers and wets the coating surface; S430, Vacuum Penetration: Maintain a vacuum state of 20% atmospheric pressure for 10 minutes to allow aluminum chloride sol to penetrate deeply into the pores and microcracks inside the coating under negative pressure. S440. Drying: Take out the sample after drop coating and dry it in an environment of 40-60℃ until there is no flowing liquid on the surface of the sol, thus completing one drop coating filling.

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