A method for preparing a long-aging antioxidant high-emissivity alumina-silica double-layer structure coating by a pre-oxidation method

Abstract

The application discloses a method for preparing long-time aging antioxidant high-emissivity alumina-silica double-layer structure coating by a pre-oxidation method, and belongs to the technical field of coating surface modification. The application aims to solve the problems of uncontrollable coating structure and insufficient high-temperature oxidation resistance of existing coatings during long-time high-temperature service. The long-time aging antioxidant high-emissivity double-layer structure coating prepared by the application comprises an aluminum inner layer and a silicon outer layer, and the double-layer structure mainly composed of the inner layer of Al2O3 and the outer layer of SiO2 is formed in situ during the pre-oxidation process. The double-layer structure coating has good bonding performance, the bonding strength reaches above 13 MPa, the emissivity reaches 0.9, the double-layer structure of the inner layer of Al2O3 and the outer layer of SiO2 is maintained after oxidation in static air at 1150 DEG C for 50 h, the coating remains complete without falling-off phenomenon, and the coating has application potential in a long-time aging antioxidant radiation heat protection system of a high-speed aircraft.

Description

Technical Field

[0001] This invention belongs to the field of coating surface modification technology, specifically relating to a method for preparing a long-lasting, oxidation-resistant, high-emissivity alumina-silica bilayer coating using a pre-oxidation method. Background Technology

[0002] Driven by the pursuit of higher speeds, longer ranges, and enhanced performance in the aerospace industry, high-speed aircraft inevitably encounter extremely harsh thermal environments and oxidative conditions during flight. This places increasingly stringent demands on the long-term high-temperature resistance and oxidation resistance of critical aircraft components. High-temperature alloys, with their excellent high-temperature strength, creep resistance, and corrosion resistance, play a crucial role in the hot-end components of high-speed aircraft. However, high-temperature alloys primarily rely on the spontaneous formation of an oxide film on their surface by active elements such as chromium and aluminum to resist oxidation. This oxide film is highly susceptible to cracking and peeling, failing to provide effective protection. Therefore, designing and fabricating long-lasting, high-temperature resistant, and oxidation-resistant coatings to ensure the stable and reliable operation of critical components in high-speed aircraft under extreme environments is of great significance.

[0003] A published patent (CN 113278968 B) describes a high-temperature oxidation-resistant Al-Si composite modified nickel-based superalloy coating prepared using plasma cladding technology. This coating enhances oxidation resistance by increasing the Al content to rapidly form a dense alumina protective film during high-temperature oxidation. The introduction of Si promotes Cr2O3 formation, creating a SiO2 interlayer between the metal and Cr2O3 to absorb vacancies and prevent interfacial voids, thus improving the coating's oxidation and hot corrosion resistance. However, after oxidation, the oxide film formed at various temperatures is always a single Al2O3 layer, resulting in limited oxidation protection. A published patent (CN 116463589 A) discloses a Pt-Si co-modified aluminide coating and its preparation method. By adjusting the platinum and silicon content, platinum improves the coating's structural stability, while silicon enhances its hot corrosion resistance, thereby addressing the insufficient high-temperature oxidation resistance of single aluminide coatings. High-temperature oxidation experiments showed that the Pt-Si co-modified aluminide coating exhibited self-healing properties during high-temperature oxidation, significantly enhancing its high-temperature oxidation resistance. However, the coating was prepared using a magnetron sputtering-hot-dip deposition method, which failed to achieve a double-layer structure. The improvement in oxidation resistance relied solely on adding Si and Pt to the aluminide coating, resulting in limited oxidation enhancement. Furthermore, its long-term oxidation resistance at temperatures exceeding 1000℃ remains questionable. Therefore, further research is needed to develop a long-lasting high-temperature oxidation-resistant thermal protective coating on high-temperature alloy surfaces using a simple process to meet the evolving requirements of high-speed aircraft components for long-term high-temperature oxidation resistance in thermal protective coatings. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of uncontrollable coating structure and insufficient high-temperature oxidation resistance of existing coatings during long-term high-temperature service, and to provide a method for preparing a long-lasting, oxidation-resistant, high-emissivity alumina-silica bilayer coating by pre-oxidation.

[0005] A method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating via pre-oxidation, wherein the long-lasting, antioxidant, high-emissivity bilayer coating comprises an aluminum-based inner layer and a silicon-based outer layer, and the coating forms an in-situ bilayer structure with Al2O3 as the inner layer and SiO2 as the outer layer during the pre-oxidation process.

[0006] The method is specifically implemented by following these steps:

[0007] I. Pretreatment of the matrix:

[0008] First, use SiC sandpaper to smooth the surface of the high-temperature alloy substrate, then remove the oil stains from the surface of the high-temperature alloy substrate to obtain the pretreated high-temperature alloy substrate.

[0009] II. Preparation of long-lasting, oxidation-resistant, high-emissivity aluminum-based inner layer:

[0010] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the aluminum source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto one or two surfaces of a pretreated high-temperature alloy substrate to obtain the substrate for forming the aluminum-based inner layer.

[0011] III. Preparation of long-lasting, oxidation-resistant, high-emissivity silicon-based outer layers:

[0012] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the silicon source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the surface of the substrate to which the aluminum-based inner layer is to be formed, thus obtaining a substrate to which the aluminum-based inner layer and silicon-based outer layer are to be formed.

[0013] IV. Coating Pre-oxidation Treatment:

[0014] The substrate to be formed with an aluminum-based inner layer and a silicon-based outer layer is placed in a muffle furnace and pre-oxidized at 900℃~1100℃ for a period of time. After the coating is cured, a double-layer structure with Al2O3 as the inner layer and SiO2 as the outer layer is obtained, which is a long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 double-layer coating.

[0015] The principle of this invention:

[0016] This invention proposes a pre-oxidation method for preparing a long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 bilayer coating. An aluminum-based inner layer and a silicon-based outer layer are prepared via low-temperature polymerization conversion of inorganic precursors. Pre-oxidation in situ forms a bilayer structure dominated by an inner Al2O3 layer and an outer SiO2 layer. The synergistic design strategy of this bilayer structure enhances the long-lasting oxidation-resistant radiation thermal protection of high-temperature alloy substrates primarily through the following mechanisms:

[0017] (1) The outer layer of SiO2 plays a synergistic role in infrared radiation heat dissipation and oxygen diffusion blocking: After pre-oxidation, the main component of the outer layer is SiO2, which has good infrared radiation characteristics and can effectively reduce the heat load on the coating surface through radiation heat dissipation; the continuous and dense outer layer of SiO2 can serve as the first oxygen diffusion barrier, effectively preventing oxygen and other oxidizing gases from further diffusing into the coating; the high-temperature resistant and antioxidant components that provide silicon source in the outer layer can continuously oxidize to generate SiO2 oxide layer to play an antioxidant role; the fluid SiO2 at high temperature can heal defects such as cracks and pores generated during the antioxidant process, prevent cracks from further expanding, and extend the service life of the coating.

[0018] (2) The inner Al2O3 layer serves as the second oxygen shielding layer: Al2O3 also has good density, which can further hinder oxygen diffusion. After a long oxidation process, oxygen passes through the outer SiO2 barrier to reach the inner layer. The high-temperature resistant and antioxidant components that provide aluminum source in the inner layer continuously generate the Al2O3 oxygen shielding layer, which can provide more reliable protection for the substrate.

[0019] The present invention has the following beneficial effects:

[0020] I. This invention prepares an in-situ, long-lasting, antioxidant, high-emissivity Al2O3-SiO2 double-layer coating using a pre-oxidation method. The outer SiO2 layer plays a role in infrared radiation heat dissipation and serves as the first oxygen diffusion barrier, while the inner Al2O3 layer acts as the second oxygen shielding layer to prevent oxygen penetration. The synergistic effect of the dual barriers improves the coating's long-lasting antioxidant radiation heat protection performance.

[0021] II. The bonding strength of the long-lasting antioxidant high-emissivity Al2O3-SiO2 double-layer structure coating prepared by the pre-oxidation method of this invention reaches above 13MPa; the coating has excellent infrared radiation heat dissipation characteristics, with an emissivity value of 0.9; the coating thickness and structure are controllable, with a coating thickness of 50μm to 500μm. After oxidation in static air at 1150℃ for 50h, the "inner Al2O3-outer SiO2" double-layer structure is maintained, and the coating remains intact without peeling. It has application potential in long-lasting antioxidant radiation heat protection systems for high-speed aircraft. Attached Figure Description

[0022] Figure 1The XRD pattern of the long-lasting antioxidant high emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of this invention;

[0023] Figure 2 These are macroscopic and microscopic morphology photographs of the long-lasting antioxidant high-emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of the present invention.

[0024] Figure 3 This is a cross-sectional microstructure photograph of the long-lasting antioxidant high emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of the present invention.

[0025] Figure 4 The stress-strain curves of the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating prepared in Example 1 of the present invention, tested by tensile testing, are shown below.

[0026] Figure 5 The emissivity spectra of the long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 double-layer coating prepared by the pre-oxidation method in Example 1 of the present invention and the nickel-based superalloy GH4061 in Comparative Example 1 are shown.

[0027] Figure 6 The XRD patterns of the long-lasting antioxidant high emissivity Al2O3-SiO2 double-layer structure coating prepared by the pre-oxidation method in Examples 1-3 of this invention and the nickel-based high-temperature alloy GH4061 in Comparative Example 1 after static oxidation at 1150℃ for 50h are shown.

[0028] Figure 7 The images show the cross-sectional microstructure and EDS spectra of the long-lasting antioxidant high emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of this invention after static oxidation at 1150℃ for 50 hours.

[0029] Figure 8 The oxidation weight gain curves of the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of this invention and the comparative nickel-based superalloy GH4061 are shown. Detailed Implementation

[0030] The following embodiments further illustrate the content of the present invention, but should not be construed as limiting the present invention. Any modifications and substitutions made to the methods, steps, or conditions of the present invention without departing from the essence of the invention are within the scope of the present invention.

[0031] Specific Implementation Method 1: This implementation method is a pre-oxidation method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer structure coating. The long-lasting, antioxidant, high-emissivity bilayer structure coating includes an aluminum-based inner layer and a silicon-based outer layer. During the pre-oxidation process, the coating forms an in-situ bilayer structure with Al2O3 as the inner layer and SiO2 as the outer layer.

[0032] The method is specifically implemented by following these steps:

[0033] I. Pretreatment of the matrix:

[0034] First, use SiC sandpaper to smooth the surface of the high-temperature alloy substrate, then remove the oil stains from the surface of the high-temperature alloy substrate to obtain the pretreated high-temperature alloy substrate.

[0035] II. Preparation of long-lasting, oxidation-resistant, high-emissivity aluminum-based inner layer:

[0036] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the aluminum source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto one or two surfaces of a pretreated high-temperature alloy substrate to obtain the substrate for forming the aluminum-based inner layer.

[0037] III. Preparation of long-lasting, oxidation-resistant, high-emissivity silicon-based outer layers:

[0038] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the silicon source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the surface of the substrate to which the aluminum-based inner layer is to be formed, thus obtaining a substrate to which the aluminum-based inner layer and silicon-based outer layer are to be formed.

[0039] IV. Coating Pre-oxidation Treatment:

[0040] The substrate to be formed with an aluminum-based inner layer and a silicon-based outer layer is placed in a muffle furnace and pre-oxidized at 900℃~1100℃ for a period of time. After the coating is cured, a double-layer structure with Al2O3 as the inner layer and SiO2 as the outer layer is obtained, which is a long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 double-layer coating.

[0041] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the high-temperature alloy matrix mentioned in step one is a high-temperature alloy; the high-temperature alloy is an iron-based alloy, a nickel-based alloy, or a cobalt-based alloy. The other steps are the same as in Specific Implementation Method One.

[0042] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: in step one, the high-temperature alloy substrate is polished sequentially using 400#, 600#, 800#, and 1000# sandpaper, and then anhydrous ethanol is used to remove surface oil stains, resulting in a pretreated high-temperature alloy substrate. Other steps are the same as in Specific Implementation Method One or Two.

[0043] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the high-temperature resistant and antioxidant component for providing the aluminum source in step two is one or a mixture of several of Al, NiAl, AlSi, MCrAlY, and NiCrAlBSi powders. The other steps are the same as in Specific Implementation Methods One to Three.

[0044] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the slurry preparation method in step two is as follows: The high-temperature resistant and antioxidant component providing the aluminum source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 12 to 24 hours at a ball milling speed of 60 to 100 r / min, with a ball-to-material ratio of (2 to 4):1, to obtain a homogeneous slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the aluminum source to the low-temperature polymerized inorganic precursor binder is 1:(1 to 4). Other steps are the same as in Specific Implementation Methods One to Four.

[0045] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the high-temperature resistant and antioxidant component providing the silicon source in step three is one or a mixture of several of Si, SiC, ZrSi2, NbSi2, TaSi2, Cr3Si, SiB4, and SiB6. The other steps are the same as in Specific Implementation Methods One to Five.

[0046] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the slurry preparation method in step three is as follows: The high-temperature resistant and antioxidant component providing the silicon source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 12 to 24 hours at a ball milling speed of 60 to 100 r / min, with a ball-to-material ratio of (2 to 4):1, to obtain a homogeneous slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the silicon source to the low-temperature polymerized inorganic precursor binder is 1:(1 to 4). Other steps are the same as in Specific Implementation Methods One to Six.

[0047] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the coating method described in steps two and three is one or more of spraying, dipping, brushing, and smearing, and the coating is applied once or multiple times to control the coating thickness; the low-temperature polymerized inorganic precursor binder described in steps two and three is a phosphate binder; the preparation method of the phosphate binder is specifically completed according to the following steps:

[0048] A phosphoric acid solution with a mass fraction of 85% and deionized water are weighed and mixed evenly at a volume ratio of (1-2):1. The mixture is then heated in a water bath at 60℃-100℃ with continuous stirring for 20-60 minutes. Next, aluminum hydroxide powder is weighed and added according to a P:Al ratio of 3:(1-2). The water bath temperature is maintained at 60℃-100℃, and the mixture is heated and stirred for 1-3 hours to obtain a mixed solution. A curing agent is added to the mixed solution at a mass ratio of (1g-10g):100mL. The mixture is heated and stirred at 60℃-100℃ for 1-3 hours. The pH of the solution is then adjusted to 2-6 to obtain a phosphate binder. The curing agent is one or a mixture of several of MgO, ZnO, CuO, and CrO3. Other steps are the same as in specific embodiments one through seven.

[0049] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: the pre-oxidation treatment time in step four is 10 min to 30 min; the thickness of the inner layer in the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating in step four is 10 μm to 200 μm, and the thickness of the outer layer is 50 μm to 300 μm. Other steps are the same as in Specific Implementation Methods One to Eight.

[0050] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One through Nine in that the bonding strength of the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 double-layer coating described in step four reaches over 13 MPa; the coating exhibits excellent infrared radiation heat dissipation characteristics, with an emissivity value of 0.9, and a coating thickness of 50 μm to 500 μm. After oxidation in static air at 1150℃ for 50 hours, it maintains the "inner Al2O3-outer SiO2" double-layer structure, and the coating remains intact without peeling. Other steps are the same as in Specific Implementation Methods One through Nine.

[0051] The beneficial effects of the present invention are verified using the following embodiments:

[0052] Example 1: A method for preparing a long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating by pre-oxidation. The long-lasting, antioxidant, high-emissivity bilayer coating includes an aluminum-based inner layer and a silicon-based outer layer. During the pre-oxidation process, the coating forms a bilayer structure in situ with Al2O3 as the inner layer and SiO2 as the outer layer.

[0053] The method is specifically implemented by following these steps:

[0054] I. Pretreatment of the matrix:

[0055] The high-temperature alloy substrate was polished by using 400#, 600#, 800# and 1000# sandpaper in sequence, and then the surface oil was removed with anhydrous ethanol to obtain the pretreated high-temperature alloy substrate.

[0056] The high-temperature alloy matrix mentioned in step one is a nickel-based high-temperature alloy GH4061;

[0057] II. Preparation of long-lasting, oxidation-resistant, high-emissivity aluminum-based inner layer:

[0058] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the aluminum source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the two surfaces of a pretreated high-temperature alloy substrate to obtain the substrate for forming the aluminum-based inner layer.

[0059] The high-temperature resistant and oxidation-resistant component that provides the aluminum source in step two is Al;

[0060] The preparation method of the slurry in step two is as follows: the high-temperature resistant and antioxidant component providing the aluminum source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 12 hours at a ball milling speed of 80 r / min, with a ball-to-material ratio of 4:1, to obtain a homogeneous slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the aluminum source to the low-temperature polymerized inorganic precursor binder is 1:2.

[0061] The coating method described in step two is brush coating, which is applied multiple times to control the thickness of the coating.

[0062] III. Preparation of long-lasting, oxidation-resistant, high-emissivity silicon-based outer layers:

[0063] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the silicon source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the surface of the substrate to which the aluminum-based inner layer is to be formed, thus obtaining a substrate to which the aluminum-based inner layer and silicon-based outer layer are to be formed.

[0064] The high-temperature resistant and antioxidant component for providing the silicon source mentioned in step three is SiC;

[0065] The preparation method of the slurry in step three is as follows: the high-temperature resistant and antioxidant component providing the silicon source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 12 hours at a ball milling speed of 80 r / min, with a ball-to-material ratio of 4:1, to obtain a homogeneous slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the silicon source to the low-temperature polymerized inorganic precursor binder is 1:2.

[0066] The coating method described in step three is brush coating, which is applied multiple times to control the thickness of the coating.

[0067] The low-temperature polymerized inorganic precursor binder mentioned in steps two and three is a phosphate binder; the preparation method of the phosphate binder is specifically carried out according to the following steps:

[0068] A phosphoric acid solution with a mass fraction of 85% and deionized water were weighed and mixed evenly at a volume ratio of 2:1. The mixture was then heated in a water bath at 80°C with continuous stirring for 30 minutes. Aluminum hydroxide powder was then weighed and added according to a P:Al ratio of 3:1. The water bath temperature was maintained at 80°C, and the mixture was heated and stirred for 2 hours to obtain a mixed solution. A curing agent was added to the mixed solution at a mass ratio of 10 g to 100 mL. The mixture was heated at 80°C with stirring for 3 hours. The pH of the solution was then adjusted to 2 to obtain a phosphate binder. The curing agent was ZnO.

[0069] IV. Coating Pre-oxidation Treatment:

[0070] The substrate to be formed with an aluminum-based inner layer and a silicon-based outer layer is placed in a muffle furnace and pre-oxidized at 900℃~1100℃ for a period of time. After the coating is cured, a double-layer structure with Al2O3 as the inner layer and SiO2 as the outer layer is obtained, which is a long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 double-layer coating.

[0071] In step four, the thickness of the inner layer of the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating is 50 μm, and the thickness of the outer layer is 50 μm.

[0072] Figure 1 The XRD pattern of the long-lasting antioxidant high emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of this invention;

[0073] from Figure 1 It can be seen that the coating surface after pre-oxidation mainly includes the binder phase and the SiO2 phase after pre-oxidation of the silicon-based outer layer, indicating that the coating surface has an in-situ outer layer SiO2 structure after pre-oxidation. However, due to the limited depth of X-ray testing, the inner layer Al2O3 phase was not detected.

[0074] Figure 2 These are macroscopic and microscopic morphology photographs of the long-lasting antioxidant high-emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of the present invention.

[0075] Figure 3 This is a cross-sectional microstructure photograph of the long-lasting antioxidant high emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of the present invention.

[0076] from Figures 2-3It can be seen that after pre-oxidation, the filler oxidizes to form a continuous coating, and the other part of the PO-Al macromolecular network backbone extends and grows at high temperature. The cross-sectional morphology of the coating shows that the final double-layer structure coating includes an aluminum-based inner layer with a thickness of about 50 μm and a silicon-based outer layer with a thickness of 50 μm, and the total thickness of the coating is about 100 μm.

[0077] Figure 4 The stress-strain curves of the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating prepared in Example 1 of the present invention, tested by tensile testing, are shown below.

[0078] from Figure 4 It can be seen that the bonding strength of the long-lasting antioxidant high emissivity Al2O3-SiO2 double-layer structure coating prepared by the pre-oxidation method in Example 1 reaches above 13MPa, which shows good bonding performance.

[0079] Example 2: A method for preparing a long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating by pre-oxidation. The long-lasting, antioxidant, high-emissivity bilayer coating includes an aluminum-based inner layer and a silicon-based outer layer. During the pre-oxidation process, the coating forms a bilayer structure in situ with Al2O3 as the inner layer and SiO2 as the outer layer.

[0080] The method is specifically implemented by following these steps:

[0081] I. Pretreatment of the matrix:

[0082] The high-temperature alloy substrate was polished by using 400#, 600#, 800# and 1000# sandpaper in sequence, and then the surface oil was removed with anhydrous ethanol to obtain the pretreated high-temperature alloy substrate.

[0083] The high-temperature alloy matrix mentioned in step one is a nickel-based high-temperature alloy GH4061;

[0084] II. Preparation of long-lasting, oxidation-resistant, high-emissivity aluminum-based inner layer:

[0085] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the aluminum source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the two surfaces of a pretreated high-temperature alloy substrate to obtain the substrate for forming the aluminum-based inner layer.

[0086] The high-temperature resistant and oxidation-resistant component for providing the aluminum source mentioned in step two is NiAl;

[0087] The preparation method of the slurry in step two is as follows: the high-temperature resistant and antioxidant component providing the aluminum source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 18 hours at a ball milling speed of 60 r / min, with a ball-to-material ratio of 3:1, to obtain a homogeneous slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the aluminum source to the low-temperature polymerized inorganic precursor binder is 1:1.

[0088] The coating method described in step two is brush coating, which is applied multiple times to control the thickness of the coating.

[0089] III. Preparation of long-lasting, oxidation-resistant, high-emissivity silicon-based outer layers:

[0090] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the silicon source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the surface of the substrate to which the aluminum-based inner layer is to be formed, thus obtaining a substrate to which the aluminum-based inner layer and silicon-based outer layer are to be formed.

[0091] The high-temperature resistant and antioxidant component for providing the silicon source mentioned in step three is ZrSi2;

[0092] The preparation method of the slurry in step three is as follows: the high-temperature resistant and antioxidant component providing the silicon source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 18 hours at a ball milling speed of 60 r / min, with a ball-to-material ratio of 3:1, to obtain a homogeneous slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the silicon source to the low-temperature polymerized inorganic precursor binder is 1:1.

[0093] The coating method described in step three is brush coating, which is applied multiple times to control the thickness of the coating.

[0094] The low-temperature polymerized inorganic precursor binder mentioned in steps two and three is a phosphate binder; the preparation method of the phosphate binder is specifically carried out according to the following steps:

[0095] A phosphoric acid solution with a mass fraction of 85% and deionized water were weighed and mixed evenly at a volume ratio of 3:2. The mixture was then heated in a water bath at 90°C with continuous stirring for 20 minutes. Aluminum hydroxide powder was then weighed and added at a P:Al ratio of 2:1. The water bath temperature was maintained at 90°C, and the mixture was heated and stirred for 1 hour to obtain a mixed solution. A curing agent was added to the mixed solution at a mass ratio of 5 g:100 mL. The mixture was heated and stirred at 90°C for 2 hours. The pH of the solution was then adjusted to 4 to obtain a phosphate binder. The curing agent was CuO.

[0096] IV. Coating Pre-oxidation Treatment:

[0097] The substrate to be formed with an aluminum-based inner layer and a silicon-based outer layer is placed in a muffle furnace and pre-oxidized at 900℃~1100℃ for a period of time. After the coating is cured, a double-layer structure with Al2O3 as the inner layer and SiO2 as the outer layer is obtained, which is a long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 double-layer coating.

[0098] Upon testing, the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in this embodiment includes an aluminum-based inner layer with a thickness of 100 μm and a silicon-based outer layer with a thickness of approximately 100 μm, with a total coating thickness of approximately 200 μm.

[0099] Example 3: A method for preparing a long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating by pre-oxidation. The long-lasting, antioxidant, high-emissivity bilayer coating includes an aluminum-based inner layer and a silicon-based outer layer. During the pre-oxidation process, the coating forms a bilayer structure in situ with Al2O3 as the inner layer and SiO2 as the outer layer.

[0100] The method is specifically implemented by following these steps:

[0101] I. Pretreatment of the matrix:

[0102] The high-temperature alloy substrate was polished by using 400#, 600#, 800# and 1000# sandpaper in sequence, and then the surface oil was removed with anhydrous ethanol to obtain the pretreated high-temperature alloy substrate.

[0103] The high-temperature alloy matrix mentioned in step one is a nickel-based high-temperature alloy GH4061;

[0104] II. Preparation of long-lasting, oxidation-resistant, high-emissivity aluminum-based inner layer:

[0105] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the aluminum source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the two surfaces of a pretreated high-temperature alloy substrate to obtain the substrate for forming the aluminum-based inner layer.

[0106] The high-temperature resistant and oxidation-resistant component for providing the aluminum source mentioned in step two is NiCrAlBSi;

[0107] The preparation method of the slurry in step two is as follows: the high-temperature resistant and antioxidant component providing the aluminum source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 24 hours at a ball milling speed of 100 r / min with a ball-to-material ratio of 2:1 to obtain a homogeneous slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the aluminum source to the low-temperature polymerized inorganic precursor binder is 1:3.

[0108] The coating method described in step two is brush coating, which is applied multiple times to control the thickness of the coating.

[0109] III. Preparation of long-lasting, oxidation-resistant, high-emissivity silicon-based outer layers:

[0110] A slurry is made by combining a high-temperature resistant and antioxidant component that provides the silicon source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the surface of the substrate to which the aluminum-based inner layer is to be formed, thus obtaining a substrate to which the aluminum-based inner layer and silicon-based outer layer are to be formed.

[0111] The high-temperature resistant and antioxidant component for providing the silicon source mentioned in step three is SiB4;

[0112] The preparation method of the slurry in step three is as follows: the high-temperature resistant and antioxidant component providing the silicon source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 24 hours at a ball milling speed of 100 r / min with a ball-to-material ratio of 2:1 to obtain a homogeneous slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the silicon source to the low-temperature polymerized inorganic precursor binder is 1:3.

[0113] The coating method described in step three is brush coating, which is applied multiple times to control the thickness of the coating.

[0114] The low-temperature polymerized inorganic precursor binder mentioned in steps two and three is a phosphate binder; the preparation method of the phosphate binder is specifically carried out according to the following steps:

[0115] A phosphoric acid solution with a mass fraction of 85% was weighed and mixed with deionized water at a volume ratio of 1:1. The mixture was then heated in a water bath at 60°C with continuous stirring for 60 minutes. Aluminum hydroxide powder was then weighed and added according to a P:Al ratio of 3:2. The water bath temperature was maintained at 60°C, and the mixture was heated and stirred for 3 hours to obtain a mixed solution. A curing agent was added to the mixed solution at a mass ratio of 2 g:100 mL. The mixture was heated and stirred at 60°C for 1 hour. The pH of the solution was then adjusted to 6 to obtain a phosphate binder. The curing agent was MgO.

[0116] IV. Coating Pre-oxidation Treatment:

[0117] The substrate to be formed with an aluminum-based inner layer and a silicon-based outer layer is placed in a muffle furnace and pre-oxidized at 900℃~1100℃ for a period of time. After the coating is cured, a double-layer structure with Al2O3 as the inner layer and SiO2 as the outer layer is obtained, which is a long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 double-layer coating.

[0118] Upon testing, the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in this embodiment includes an aluminum-based inner layer with a thickness of 10 μm and a silicon-based outer layer with a thickness of approximately 50 μm, with a total coating thickness of approximately 60 μm.

[0119] Comparative Example 1:

[0120] This comparative example uses nickel-based superalloy GH4061.

[0121] Experimental example:

[0122] The emissivity performance of the long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 bilayer coatings prepared by the pre-oxidation method in Examples 1-3 and the nickel-based superalloy GH4061 in Comparative Example 1 were tested, and static high-temperature oxidation tests were conducted at 1150℃. The testing methods are as follows:

[0123] (1) The emissivity of the long-lasting antioxidant high emissivity Al2O3-SiO2 double-layer structure coating prepared by the pre-oxidation method in Example 1 and the comparative nickel-based high-temperature alloy GH4061 were tested using an emissivity testing device.

[0124] (2) The long-term antioxidant high emissivity Al2O3-SiO2 double-layer structure coatings prepared by the pre-oxidation method in Examples 1-3 and the nickel-based high-temperature alloy GH4061 in Comparative Example 1 were subjected to static high-temperature oxidation test at 1150℃ using a high-temperature muffle furnace to evaluate their high-temperature antioxidant performance.

[0125] Figure 5 The emissivity spectra of the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of the present invention and the nickel-based high-temperature alloy GH4061 in Comparative Example 1 are shown.

[0126] from Figure 5 It can be seen that the emissivity of the nickel-based high-temperature alloy GH4061 in Comparative Example 1 is about 0.3, while the emissivity of the long-term oxidation-resistant high-emissivity Al2O3-SiO2 double-layer structure coating prepared by the pre-oxidation method in Example 1 of this invention is as high as 0.9, which is 3 times higher. This indicates that the long-term oxidation-resistant high-emissivity Al2O3-SiO2 double-layer structure coating designed and prepared by this invention has good infrared radiation heat dissipation characteristics and can play an effective role in radiation heat dissipation.

[0127] The XRD patterns of the sample surfaces of Examples 1-3 and Comparative Example 1 after static oxidation at 1150℃ for 50 hours are as follows: Figure 6 As shown. By Figure 6 It can be seen that the surface of the nickel-based superalloy GH4061 in Comparative Example 1 after oxidation mainly includes the γ-Ni phase and the oxidation products NiO, Cr2O3, and Al2O3 phases; the long-term oxidation-resistant high-emissivity Al2O3-SiO2 double-layer structure coatings prepared by the pre-oxidation method in Examples 1 to 3 mainly include the SiO2 phase on the surface after oxidation, which can play a good role in oxygen diffusion blocking and provide effective high-temperature oxidation protection for the substrate.

[0128] Figure 7 The images show the cross-sectional microstructure and EDS spectra of the long-lasting antioxidant high emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of this invention after static oxidation at 1150℃ for 50 hours.

[0129] Depend on Figure 7 It is known that after high-temperature oxidation, the coating maintains a double-layer structure of "inner layer Al2O3-outer layer SiO2". This double-layer structure plays a synergistic role in the high-temperature oxidation process. The double oxygen diffusion barrier can block the diffusion of oxygen and has excellent long-term antioxidant radiation heat protection performance.

[0130] The weight gain curves of high-temperature oxidation over time for Example 1 and the comparative example are plotted as follows: Figure 8 As shown;

[0131] Figure 8 The oxidation weight gain curves of the long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 double-layer coating prepared by the pre-oxidation method in Example 1 of this invention and the comparative nickel-based superalloy GH4061 are shown.

[0132] Depend on Figure 8 It can be seen that the long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of this invention and the comparative nickel-based superalloy GH4061 both exhibit segmented oxidation behavior throughout the oxidation process, but the oxidation rates are significantly different. The long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 bilayer coating prepared by the pre-oxidation method in Example 1 of this invention shows rapid weight gain during the oxidation process from 0 to 1 hour, indicating that the high-temperature resistant and oxidation-resistant components in the coating react with oxygen in the initial stage of oxidation. The weight gain curve slows significantly from 2 to 50 hours, indicating a slow oxidation rate. This suggests that the "inner Al2O3-outer SiO2" structure in the coating acts as an oxygen diffusion barrier, preventing the oxidizing atmosphere from diffusing into the coating interior, thus delaying the oxidation rate. After 50 hours of oxidation, the sample weight gain was 2.197 mg / cm³. 2 In contrast, the comparative nickel-based superalloy GH4061 exhibited a relatively high oxidation rate within the range of 0–50 h, resulting in a significant weight gain. After 50 h of oxidation, the sample weight gain was 2.461 mg / cm³. 2 This indicates that the matrix is ​​severely oxidized, and the high-temperature oxidation products NiO and Cr2O3 cannot provide effective thermal protection for the matrix.

Claims

1. A method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating using a pre-oxidation method, characterized in that... The long-lasting, antioxidant, high-emissivity dual-layer coating includes an aluminum-based inner layer and a silicon-based outer layer. During the pre-oxidation process, the coating forms a dual-layer structure in situ with the inner layer being mainly Al2O3 and the outer layer being mainly SiO2. The method is specifically implemented by following these steps: I. Pretreatment of the matrix: First, use SiC sandpaper to smooth the surface of the high-temperature alloy substrate, then remove the oil stains from the surface of the high-temperature alloy substrate to obtain the pretreated high-temperature alloy substrate. II. Preparation of long-lasting, oxidation-resistant, high-emissivity aluminum-based inner layer: A slurry is made by combining a high-temperature resistant and antioxidant component that provides the aluminum source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto one or two surfaces of a pretreated high-temperature alloy substrate to obtain the substrate for forming the aluminum-based inner layer. The high-temperature resistant and oxidation-resistant component for providing the aluminum source mentioned in step two is one or a mixture of several of Al, NiAl, AlSi, MCrAlY, and NiCrAlBSi powder; III. Preparation of long-lasting, oxidation-resistant, high-emissivity silicon-based outer layers: A slurry is made by combining a high-temperature resistant and antioxidant component that provides the silicon source with a low-temperature polymerized inorganic precursor binder. This slurry is then coated onto the surface of the substrate to which the aluminum-based inner layer is to be formed, thus obtaining a substrate to which the aluminum-based inner layer and silicon-based outer layer are to be formed. The high-temperature resistant and antioxidant component for providing the silicon source mentioned in step three is one or a mixture of several of Si, SiC, ZrSi2, NbSi2, TaSi2, Cr3Si, SiB4, and SiB6. The low-temperature polymerization inorganic precursor binder mentioned in steps two and three is a phosphate binder; IV. Coating Pre-oxidation Treatment: The substrate to be formed with an aluminum-based inner layer and a silicon-based outer layer is placed in a muffle furnace and pre-oxidized at 900℃~1100℃ for a period of time. After the coating is cured, a double-layer structure with Al2O3 as the inner layer and SiO2 as the outer layer is obtained, which is a long-lasting, oxidation-resistant, high-emissivity Al2O3-SiO2 double-layer coating.

2. The method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating by pre-oxidation according to claim 1, characterized in that... The high-temperature alloy matrix mentioned in step one is a high-temperature alloy; the high-temperature alloy is an iron-based alloy, a nickel-based alloy, or a cobalt-based alloy.

3. The method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating according to claim 1, characterized in that... In step one, the high-temperature alloy substrate is polished with 400#, 600#, 800# and 1000# sandpaper in sequence. Then, anhydrous ethanol is used to remove the oil stains on the surface to obtain the pretreated high-temperature alloy substrate.

4. The method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating according to claim 1, characterized in that... The preparation method of the slurry in step two is as follows: the high-temperature resistant and antioxidant component providing the aluminum source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the ball milling is carried out for 12h to 24h at a ball milling speed of 60r / min to 100r / min, with a ball-to-material ratio of (2 to 4):1, to obtain a uniform slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the aluminum source to the low-temperature polymerized inorganic precursor binder is 1:(1 to 4).

5. The method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating according to claim 1, characterized in that... The preparation method of the slurry in step three is as follows: the high-temperature resistant and antioxidant component providing the silicon source and the low-temperature polymerized inorganic precursor binder are placed in a ball mill jar, zirconia balls are added, and the mixture is ball-milled for 12h to 24h at a ball milling speed of 60r / min to 100r / min, with a ball-to-material ratio of (2 to 4):1, to obtain a uniform slurry; the mass ratio of the high-temperature resistant and antioxidant component providing the silicon source to the low-temperature polymerized inorganic precursor binder is 1:(1 to 4).

6. The method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating according to claim 1, characterized in that... The coating methods described in steps two and three are one or more of spraying, dipping, brushing, and slurry coating, and the coating is applied once or multiple times to control the coating thickness; the preparation method of the phosphate binder is specifically completed according to the following steps: Weigh out an 85% phosphoric acid solution and deionized water at a volume ratio of (1~2):1 and mix thoroughly. Then heat in a water bath at 60℃~100℃ and stir continuously for 20min~60min. Next, weigh out aluminum hydroxide powder at a P:Al ratio of 3:(1~2), maintain the water bath temperature at 60℃~100℃, heat and stir for 1h~3h to obtain a mixed solution. Add a curing agent to the mixed solution at a mass ratio of (1g~10g):100mL, heat and stir at 60℃~100℃ for 1h~3h, and then adjust the pH value of the solution to 2~6 to obtain a phosphate binder. The curing agent is one or a mixture of several of MgO, ZnO, CuO, and CrO3.

7. The method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating according to claim 1, characterized in that... The pre-oxidation treatment time in step four is 10 min to 30 min; the thickness of the inner layer of the long-lasting antioxidant high emissivity Al2O3-SiO2 double-layer structure coating in step four is 10 μm to 200 μm, and the thickness of the outer layer is 50 μm to 300 μm.

8. The method for preparing a long-lasting, antioxidant, high-emissivity alumina-silica bilayer coating according to claim 1, characterized in that... The bonding strength of the long-lasting, antioxidant, high-emissivity Al2O3-SiO2 double-layer coating described in step four reaches over 13 MPa; the coating has excellent infrared radiation heat dissipation characteristics, with an emissivity value of 0.9, and a coating thickness of 50 μm to 500 μm. After oxidation in static air at 1150℃ for 50 hours, it maintains the "inner Al2O3-outer SiO2" double-layer structure, and the coating remains intact without peeling.

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