Nano-porous aluminized-silicon carbide gradient coating and preparation method thereof
By preparing a nanoporous aluminum-infiltrated layer and a silicon carbide nanowire gradient composite coating on the surface of a nickel-based high-temperature alloy, the problems of oxidation, thermal corrosion and insufficient catalytic activity of the nickel-based high-temperature alloy during high-temperature service are solved, and a high specific surface area, strong interface bonding strength and anti-stripping ability are achieved.
Patent Information
- Application Number
- CN202510714111.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-30
- Publication Date
- 2025-09-05
AI Technical Summary
Nickel-based high-temperature alloys face problems such as oxidation, thermal corrosion and insufficient catalytic activity when in service for a long time at temperatures above 1200°C. Existing coatings are prone to peeling under high temperature conditions, have insufficient bonding strength, small specific surface area, and stress concentration caused by thermal expansion coefficient mismatch.
A combination of dealloying corrosion and chemical vapor deposition (CVD) was used to prepare a nanoporous aluminized layer and silicon carbide (SiC) nanowire gradient composite coating on the surface of nickel-based high-temperature alloy, forming a continuous Al2O3/SiO2 composite oxide film. The SiC nanowires were used to enhance the interfacial bonding strength and anti-stripping ability.
The specific surface area and interface bonding strength of the coating were significantly improved, the stress concentration problem caused by thermal expansion coefficient mismatch was alleviated, the oxidation resistance and catalytic activity at high temperature were improved, the mass loss of the coating was reduced at 1200°C, and the anti-peeling ability was enhanced.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of material surface treatment and functional coatings, and particularly relates to a nanoporous aluminum-silicon carbide gradient coating and a preparation method thereof. Background Art
[0002] Nickel-based superalloys are core materials for aircraft engine combustion chambers, but they face challenges such as oxidation, thermal corrosion, and insufficient catalytic activity when subjected to long-term service at temperatures above 1200°C. Traditional protective technologies primarily utilize MCrAlY coatings, thermal barrier coatings, silicon carbide coatings, and single aluminized layers.
[0003] In MCrAlY coating, M refers to Ni or Co, which is deposited on the substrate surface by spraying, multi-arc ion plating, sputtering, electron beam physical vapor deposition and other methods. Due to the mutual diffusion of elements, brittle phase precipitation occurs, which is manifested as high porosity (>5%) and low specific surface area (<50 m 2 / g), weak interfacial bonding strength (<50 MPa) and reduced effective bearing area, which lead to a decrease in high-temperature endurance performance.
[0004] Thermal barrier coatings (TBCs) consist of a ceramic insulation layer, a thermally grown oxide layer, and a metallic bond layer. The insulation layer can reduce temperatures by 100-300°C, helping to increase the service temperature of engine hot-end components. However, the coating's spalling resistance is affected by the stress state of the ZrO2 layer, the microstructure of the bond layer, the thickness and stress state of the TGO layer, and the fracture resistance of the interface between the bond layer and the TGO. In particular, when cooled to ambient temperature, the mismatch in thermal expansion coefficients between the TGO and the bond layer can lead to significant residual stresses in the TGO, and TGO growth can also cause stress accumulation. These issues can lead to spalling failure of the coating.
[0005] Silicon carbide coatings are commonly produced using CVD. The SiO2 layer formed by oxidation at high temperatures exhibits low oxygen diffusion and excellent self-healing properties. However, SiC coatings offer limited protection for substrates at temperatures exceeding 1800°C. Furthermore, there is a mismatch in thermal expansion coefficients between SiC coatings and the metal substrate, making them susceptible to cracking and failure.
[0006] While a single aluminizing layer process is simple, offers stable performance, and is low-cost, it also has limitations, such as poor thermal corrosion resistance, particularly Type II thermal corrosion resistance, high coating brittleness, and rapid degradation. This is primarily due to the fact that the single Al2O3 oxide film formed by the aluminizing process easily flakes off during high-temperature cycles, resulting in insufficient surface area and limited catalytic activity.
[0007] The lack of durability in these coatings has led to the increasing interest in functionally gradient coatings (FGCs). Based on the design concept of functionally gradient materials (FGMs), FGCs combine two or more different materials to create a composite material with a gradient distribution of composition or structure along a specific direction, enabling them to achieve functions that are difficult to achieve with non-gradient structures.
[0008] To address the above technical bottlenecks, the present invention, through material system innovation and process optimization, adopts a combination of dealloying corrosion and chemical vapor deposition (CVD) to prepare a nanoporous aluminized layer on the surface of a nickel-based high-temperature alloy, and grows silicon carbide (SiC) nanowires through CVD to form a gradient composite structure, providing an innovative solution for the surface protection of stainless steel bipolar plates. Summary of the Invention
[0009] To address the existing problems of nickel-based superalloys facing oxidation, thermal corrosion, and insufficient catalytic activity during long-term service at temperatures above 1200°C, the present invention provides a method for preparing a gradient composite coating of a nanoporous aluminized layer and silicon carbide (SiC) nanowires. By combining dealloying corrosion with chemical vapor deposition (CVD) processes, a protective coating with high specific surface area, strong interfacial adhesion, and ultra-high-temperature stability is formed on the surface of the nickel-based superalloy. Under high-temperature service conditions, this coating forms a continuous Al2O3 / SiO2 composite oxide film, effectively inhibiting oxygen diffusion. The SiC nanowire reinforcement effect also enhances spalling resistance.
[0010] The technical solution of the present invention is: The present invention provides a method for preparing a nanoporous aluminized layer and silicon carbide nanowire gradient composite coating, the specific process of which is as follows: 1) Pretreatment of the nickel-based high-temperature alloy substrate, including sandblasting to Sa3.0 grade, pickling with immersion in a mixed solution of 10% HNO3 and 3% HF for 5-10 minutes, and then ultrasonic cleaning with deionized water to remove residual impurities on the surface.
[0011] 2) Perform chemical vapor deposition (CVD) aluminizing treatment. Place aluminum powder in a diffusing agent generator and a nickel-based high-temperature alloy substrate in a reactor. After evacuating the chamber, heat the reactor to 980°C and the diffusing agent generator to 300-450°C. Introduce HCl and H2 gas at a flow rate ratio of 1:5 and a reaction time of 2-5 hours to form a uniform aluminized layer.
[0012] 3) A nanoporous aluminized layer was formed by dealloying corrosion. The aluminized substrate was placed in a mixed solution of 10 wt.% HCl and 5 wt.% FeCl3 for 30-35 minutes to selectively dissolve the Ni-rich phase, obtaining through-hole nanopores with a pore size range of 200-500 nm and a porosity of approximately 65%.
[0013] 4) Silicon carbide nanowires were grown by chemical vapor deposition (CVD). CH₃SiCl₃ was introduced into a tube furnace as a precursor, and H₂ was used as a carrier gas. The molar ratio of H₂ to CH₃SiCl₃ was 15. The reaction temperature was set at 1100°C, and the reaction time was 1-3 hours. This produced β-SiC nanowires with a diameter of 50-100 nm, forming a silicon carbide coating. The SiC nanowires formed chemical bonds with the aluminized layer through Al-O-Si bonds, forming a gradient composite structure.
[0014] Furthermore, in the above-mentioned method for preparing a nanoporous aluminized layer and silicon carbide nanowire gradient composite coating, in step 1), the sandblasting treatment uses aluminum oxide sand particles with a particle size of 200-300 microns, the spraying angle is 45° to 60°, and the spraying pressure is 0.6 MPa.
[0015] Furthermore, in the above-mentioned method for preparing a nanoporous aluminized layer and silicon carbide nanowire gradient composite coating, in step 2), the HCl gas flow rate is 100 sccm, the H2 gas flow rate is 500 sccm, and the thickness of the aluminized layer is 50-100 microns.
[0016] Furthermore, in the above-mentioned method for preparing a nanoporous aluminized layer and silicon carbide nanowire gradient composite coating, in step 3), during the dealloying corrosion process, the temperature of the etching solution is controlled at 35°C, and the corrosion time can be adjusted according to demand. Extending it to 45 minutes can form a macroporous structure with a pore size range of 500 nm and a porosity of up to 70%, which is suitable for high catalytic activity application scenarios.
[0017] Further preferably, in the above-mentioned method for preparing a nanoporous aluminized layer and silicon carbide nanowire gradient composite coating, during the CVD growth of SiC nanowires, the nanowire density is controlled by adjusting the precursor flow rate and reaction time. For example, the CH3SiCl3 flow rate is set to 50 sccm, the H2 flow rate is set to 200 sccm, and the reaction time is shortened to 30 minutes, which can reduce the nanowire density to 5×10 6 / cm², suitable for gradient structure design with specific functional requirements.
[0018] The present invention also provides a nanoporous aluminized-silicon carbide gradient coating, comprising a nickel-based high-temperature alloy substrate, a nanoporous aluminized layer, and silicon carbide nanowires, wherein the nanoporous aluminized layer has a pore size range of 200-500 nm and a porosity of 65%, and the silicon carbide nanowires have a diameter of 50-100 nm.
[0019] Furthermore, in the above-mentioned nanoporous aluminized-silicon carbide gradient coating, the silicon carbide nanowires are distributed in a density gradient from the surface of the nanoporous aluminized layer to the outside, with a higher density near the surface of the aluminized layer and gradually decreasing outward.
[0020] Furthermore, in the above-mentioned nanoporous aluminized-silicon carbide gradient coating, the specific surface area of the nanoporous aluminized layer is 200 m² / g, and the thickness of the aluminized layer is 50-100 microns.
[0021] Furthermore, after the above-mentioned nanoporous aluminum-silicon carbide gradient coating is statically oxidized at 1200°C for 100 hours, a continuous Al2O3 / SiO2 composite oxide film is formed on the surface of the coating, and the thickness of the composite oxide film is 2-3 microns.
[0022] Advantages and beneficial effects of the present invention: 1. This invention uses a dealloying corrosion process to precisely dissolve Ni-rich regions, leveraging the electrochemical differences between the Ni-rich phase and the aluminized layer to form interconnected nanopores, significantly increasing the specific surface area. The nanoporous aluminized layer achieves a specific surface area of up to 200 m² / g (BET test), three times higher than traditional aluminized layers, and increases the CO oxidation conversion rate from 30% to 90%. SiC nanowires grown via CVD react with Al₂O₃ on the surface of the aluminized layer to form Al-O-Si bonds, replacing traditional physical bonding. The interfacial bonding strength reaches 75 MPa (ASTM C633 standard), a 50% increase over traditional coatings (50 MPa). 2. The SiC nanowires of the present invention are distributed in a density gradient from the surface of the aluminized layer outward, alleviating the stress concentration problem caused by the mismatch of thermal expansion coefficients. In addition, the SiC nanowires act as a "skeleton" to inhibit the cracking of the oxide film, further improving the coating's anti-stripping ability; 3. The coating prepared by this invention has a high specific surface area, strong interfacial bonding, and ultra-high-temperature stability. Under high-temperature oxidation conditions of 1200°C, the aluminum element in the aluminized layer diffuses outward to form a continuous Al2O3 film, while the SiC nanowires oxidize to form SiO2. The two composite fill the pores and prevent oxygen from diffusing into the substrate. Figure 3 It shows that after 100 hours of static oxidation at 1200℃, the coating mass loss is only 0.07-0.08 mg / cm², which is significantly lower than that of traditional MCrAlY coating (1.2 mg / cm²); 4. The present invention combines dealloying corrosion with CVD processes primarily because the Al2O3 oxide film formed by a single aluminized layer is susceptible to flaking during high-temperature cycling and has insufficient specific surface area, limiting catalytic activity. Traditional physically bonded coatings, however, are susceptible to failure under high-temperature service conditions due to weak interfacial bonding. The dealloying corrosion process allows for controlled pore formation, forming a nanoporous aluminized layer, resolving the trade-off between specific surface area and bonding strength. Simultaneously, the CVD process grows SiC nanowires, achieving a chemically bonded interface and gradient stress buffering, ensuring the coating's stability in high-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 A schematic diagram of the structure of a nanoporous aluminized layer on the surface of a nickel-based high-temperature alloy substrate according to an embodiment of the present invention, showing the structure of the composite coating; Figure 2 This is a surface SEM photograph of silicon carbide nanowires grown on the surface of the nanoporous aluminized layer in an embodiment of the present invention, showing the distribution and shape of the SiC nanowires; Figure 3 The oxidation kinetic curve of the coating in the embodiment of the present invention after static oxidation at 1200°C for 100 hours shows the oxidation resistance of the continuous Al2O3 / SiO2 composite oxide film. In the figure, 1-Nickel-based high-temperature alloy substrate; 2-Nanoporous aluminized layer; 3-Silicon carbide coating. DETAILED DESCRIPTION
[0024] The present invention provides a method for preparing a nanoporous aluminized layer and silicon carbide nanowire gradient composite coating, and the specific implementation process is as follows.
[0025] First, nickel-based high-temperature alloy is selected as the substrate 1, which is the main body of the subsequent coating. Figure 1 The basic structure of the composite gradient coating is shown in Figure 3, which consists of a nanoporous aluminum layer and a SiC layer with a nanowire structure.
[0026] Before operation, the substrate 1 needs to be pretreated to ensure that the surface cleanliness and roughness meet the process requirements. Sandblasting uses alumina sand with a particle size of 200-300 microns, the spray angle is maintained between 45° and 60°, and the spray pressure is controlled at 0.6 MPa until the surface of the substrate 1 reaches the Sa3.0 level standard. The substrate 1 is then immersed in a mixed solution of 10% HNO3 and 3% HF for 5 minutes. During the pickling process, HF is mainly used to remove oxides on the surface of the substrate 1, while HNO3 plays a passivation role to prevent excessive corrosion. After the pickling is completed, ultrasonic cleaning is performed with deionized water. The ultrasonic frequency is set to 40 kHz and the cleaning time is 10 minutes to thoroughly remove residual impurities on the surface.
[0027] After pretreatment of substrate 1, the chemical vapor deposition (CVD) aluminization stage begins. Aluminum powder with a purity of 99.9% is loaded into the infiltrant generator. Substrate 1 is placed in a reactor and secured to a sample holder made of high-temperature resistant ceramic to prevent contamination. After evacuation, the reaction chamber is heated to 980°C. The infiltrant generator temperature is set to 300-450°C, and HCl and H2 gases are introduced at a flow rate ratio of 1:5, which can be set to 100 sccm and 500 sccm, respectively. Under these conditions, the reaction continues for 2 hours, during which aluminum elements penetrate the surface of substrate 1 through vapor diffusion to form a uniform aluminized layer. The thickness of the aluminized layer can be precisely controlled by adjusting the reaction time and temperature, typically ranging from 50-100 microns. The aluminized layer is primarily composed of Al-Ni intermetallic compounds, with a crystal structure of ordered NiAl phases.
[0028] After the aluminized layer is formed, dealloying corrosion is performed to generate a nanoporous structure. The aluminized substrate 1 is immersed in a mixed solution of 10 wt.% HCl and 5 wt.% FeCl3. The corrosion solution temperature is controlled at 35°C and the corrosion time is set to 30 minutes. FeCl3 acts as an oxidant to selectively dissolve the Ni-rich phase, while HCl is used to maintain the acidic environment of the solution to promote the dissolution reaction. During the corrosion process, the Ni-rich phase preferentially dissolves to form through-hole nanopores with a pore size range of 200-500 nm and a porosity of approximately 65%. Extending the corrosion time to 45 minutes can further increase the pore size to 500 nm and the porosity to 70%, making it suitable for scenarios requiring high catalytic activity.
[0029] The growth of silicon carbide nanowires is carried out on the basis of the nanoporous aluminized layer 2, such as Figure 2 As shown. The substrate 1 is placed in a tube furnace, and CH3SiCl3 is introduced as a precursor and H2 as a carrier gas, and the molar ratio of the two is set to 15. The reaction temperature is set to 1100 ° C, and the reaction time is controlled to 3 hours. CH3SiCl3 decomposes at high temperature to generate SiC monomers, which nucleate and grow into nanowires on the surface of the nanoporous aluminized layer 2 through vapor deposition to form a silicon carbide coating 3. The diameter of the nanowires ranges from 50 to 100 nm, and the density can be controlled by adjusting the precursor flow rate and reaction time. For example, the CH3SiCl3 flow rate is set to 50 sccm, the H2 flow rate is set to 200 sccm, and the reaction time is shortened to 30 minutes, which can reduce the nanowire density to 5×10 6 / cm². The nanowires form a chemical bond with the surface of the nanoporous aluminized layer 2 through Al-O-Si bonds, forming a gradient composite structure.
[0030] The coating exhibits excellent oxidation resistance under high temperature service conditions, such as Figure 3As shown in Figure 1, when the temperature reaches 1200°C, the Al element in the nanoporous aluminized layer 2 diffuses outward and reacts with oxygen to form a continuous Al2O3 film. Simultaneously, the silicon carbide nanowires oxidize to form SiO2, which together form a dense Al2O3 / SiO2 composite oxide film. The composite oxide film is approximately 2-3 microns thick and effectively blocks oxygen diffusion into the substrate 1. After 100 hours of static oxidation at 1200°C, the coating mass loss is only 0.08 mg / cm², significantly superior to traditional MCrAlY coatings.
[0031] Silicon carbide nanowires act as a skeleton support during the oxidation process, inhibiting the cracking of the oxide film and improving its anti-stripping ability. The interface bonding strength test shows that the bonding strength between silicon carbide nanowires and the nanoporous aluminized layer 2 reaches 75MPa. This high-strength bond is derived from the formation of Al-O-Si chemical bonds, replacing the traditional physical bonding method. The nanowires are distributed in a density gradient from the surface of the nanoporous aluminized layer 2 to the outside, with a higher density near the surface of the aluminized layer 2 and gradually decreasing outward. This gradient design effectively alleviates the stress concentration problem caused by the mismatch of thermal expansion coefficients. In the 1200°C cyclic oxidation test, the coating showed good stability and no obvious peeling or cracking occurred.
[0032] The nanoporous aluminized layer 2 has a surface area of up to 200 m² / g, as measured by BET testing, three times higher than conventional aluminized layers. This high surface area significantly enhances catalytic activity, increasing CO oxidation conversion from 30% to 90%. The interconnected nanopores facilitate the transport of reactant gases and the rapid removal of products, thereby improving reaction efficiency. The nanoporous structure also exhibits excellent mechanical stability, capable of withstanding the thermal and mechanical stresses experienced under high-temperature service conditions.
[0033] Controlling key parameters throughout the entire preparation process is crucial to the final coating performance. During the dealloying corrosion process, the choice of etching solution concentration, temperature, and time directly influences the size and distribution of nanopores. Precise control of these parameters can achieve an ideal pore structure, balancing specific surface area and mechanical strength. During the growth of silicon carbide nanowires, optimizing the precursor flow rate, carrier gas ratio, and reaction time determines the density and distribution of the nanowires, which in turn influences the overall performance of the coating. The coordinated control of these parameters ensures the stability and reliability of the coating under high-temperature service conditions.
[0034] In order to better enable relevant personnel in this technical field to fully understand and implement the present invention, the specific implementation methods of the present invention are described below in conjunction with specific application scenarios. Example 1
[0035] This embodiment is to prepare a coating for the inner wall of an aircraft engine combustion chamber, and the preparation includes the following steps: 1) Inconel 718 alloy with a size of Φ50×5 mm was selected as the substrate for pretreatment. Alumina sand with a particle size of 200 μm was used for sandblasting. The spray angle was maintained at 45° and the spray pressure was controlled at 0.6 MPa until the surface of substrate 1 reached the Sa3.0 standard. The substrate was placed in a mixed solution of 10% HNO3 and 3% HF for 5 minutes, and then ultrasonically cleaned with deionized water to remove residual impurities on the surface. The ultrasonic frequency was set to 40 kHz and the cleaning time was 10 minutes.
[0036] 2) Chemical vapor deposition (CVD) aluminizing treatment was performed. Aluminum powder was placed in a diluent generator, and the nickel-based high-temperature alloy substrate was placed in a reaction furnace. After evacuation, the reaction chamber was heated to 980°C, and the diluent generator was heated to 350°C. HCl and H2 gases were introduced at a flow rate of 100 sccm for HCl and 500 sccm for H2. The reaction time was 2 hours, forming an aluminized layer with a thickness of 50 μm.
[0037] 3) A nanoporous aluminized layer was formed by dealloying corrosion. The aluminized substrate was placed in a mixed solution of 10 wt.% HCl and 5 wt.% FeCl3 for 30 minutes. The temperature of the etching solution was controlled at 35°C to selectively dissolve the Ni-rich phase, obtaining through-hole nanopores with a pore size range of 200 and a porosity of approximately 65%.
[0038] 4) Silicon carbide nanowires were grown by chemical vapor deposition (CVD) in a tube furnace. CH₃SiCl₃ was introduced as a precursor, and H₂ was introduced as a carrier gas. The CH₃SiCl₃ flow rate was set to 50 sccm, the H₂ flow rate was set to 200 sccm, the reaction temperature was set to 1100°C, and the pressure was set to 10 kPa. The reaction time was 1 hour, resulting in β-SiC nanowires with a diameter of 50 nm. The SiC nanowires formed chemical bonds with the aluminized layer surface through Al-O-Si bonds, forming a gradient composite structure.
[0039] The performance indicators of the coating in this embodiment are: After static oxidation at 1200℃ for 100 hours, the mass loss is only 0.07 mg / cm²; The oxide film is a continuous Al2O3 / SiO2 composite structure with a thickness of 2 microns; Bonding strength: Using the pull-out method, the interfacial bonding strength was measured to be 78 MPa (ASTM C633 standard tensile test), which is 56% higher than that of traditional coatings (50 MPa); Thermal shock stability: After 100 thermal cycles (room temperature ↔ 1200°C), the coating has no cracks or peeling. Example 2
[0040] This embodiment is to prepare a coating for the inner wall of a chemical catalytic reactor. The difference between this embodiment and embodiment 1 is that; Step 1) A Hastelloy X alloy plate with a thickness of 2 mm was selected as the substrate for pretreatment, and the spray angle was maintained at 60° during sandblasting.
[0041] Step 2) forming an aluminized layer with a thickness of 100 μm.
[0042] In the dealloying corrosion process of step 3), extending the corrosion time to 45 minutes can form a macroporous structure with a pore size range of 500 nm and a porosity of up to 70%.
[0043] Step 4) During the CVD growth of SiC nanowires, the reaction time was shortened to 30 minutes, and the nanowire density was reduced to 5×10 6 / cm². SiC nanowires are used as carriers of catalytic active sites, and their surface is modified with Pt nanoparticles (5 nm in diameter, 1 wt.% loading), resulting in nanowires with a diameter of 100 nm.
[0044] The performance indicators of the coating in this embodiment are: The specific surface area of the nanoporous aluminized layer can reach 200 m² / g (BET test); Catalytic activity: CO oxidation conversion rate: up to 92% at 350°C (only 35% for traditional coatings); Anti-carbon deposition performance: After 100 hours of methane cracking reaction, the carbon deposition amount is <1wt.% (traditional coating >5wt.%); Corrosion resistance: In an acidic environment (450°C) containing H2S (5 vol.%), the annual corrosion rate is <0.005 mm; Thermal conductivity: The thermal conductivity of the coating is 35 W / (m·K), which avoids catalyst deactivation caused by local hot spots. Example 3
[0045] This embodiment is for preparing a coating for a nuclear reactor cladding tube. The difference between the preparation method and that of Example 1 is as follows: In step 1), a zirconium alloy Zircaloy-4 with a size of Φ10×1 mm is selected as the substrate; Step 2) The aluminizing treatment was changed to ion implantation assisted aluminizing method, with a reaction temperature of 450°C and a reaction time of 2 hours to avoid phase transformation of the zirconium matrix; Step 3: The nanoporous aluminized layer is formed with a pore size of 300 nm and a porosity of 50%. Step 4) During the CVD growth of SiC nanowires, boron-doped SiC nanowires (B content 5 at.%) were introduced to enhance neutron absorption capability, resulting in B-SiC nanowires with a diameter of 80 nm, forming a radiation shielding layer (thermal neutron absorption cross section 950 barn).
[0046] The performance indicators of the coating in this embodiment are: Anti-hydrogen permeation: In a high-pressure hydrogen environment (10 MPa) at 400°C, the hydrogen permeability is reduced to 1×10 -11 mol / (m·s·Pa 0.5 ) (Bare zirconium alloy is 5×10 -9 ); Radiation resistance: after fast neutron irradiation (5×10 21 n / cm 2 ) after treatment, the coating hardness only decreased by 8% (conventional coatings decreased by 30%); After oxidation in steam at 1200℃ for 30 minutes, the coating integrity rate is >95% (the bare zirconium alloy is completely powdered).
[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.
Claims
1. A method for preparing a nanoporous aluminum-silicon carbide gradient coating, characterized in that: The specific steps include: 1) Pre-treat the nickel-based high-temperature alloy substrate by sandblasting to Sa3.0, then soak it in a mixed solution of 10% HNO3 and 3% HF by mass for 5-10 minutes, and then ultrasonically clean it with deionized water; 2) Using a chemical vapor deposition aluminizing process, a nickel-based high-temperature alloy substrate is heated to 980°C in a reactor, a dilution generator is heated to 300-450°C, HCl and H2 gases are introduced at a flow ratio of 1:5, and the reaction time is 2-5 hours to form a uniform aluminized layer; 3) Forming a nanoporous aluminized layer by dealloying corrosion: The aluminized nickel-based superalloy substrate is placed in a mixed solution of 10% HCl and 5% FeCl3 by mass. The corrosion solution temperature is controlled at 30-35°C and the corrosion time is 30-40 minutes. The Ni-rich phase is selectively dissolved to form a nanoporous aluminized layer with a pore size range of 200-500 nm and a porosity of 65%. 4) Growing silicon carbide nanowires by chemical vapor deposition (CVD) in a tubular furnace. CH3SiCl3 is introduced as a precursor, H2 is introduced as a carrier gas, the molar ratio of H2 to CH3SiCl3 is 15, the reaction temperature is 1100-1300°C, and the reaction time is 1-3 hours. Silicon carbide nanowires with a diameter of 50-100 nm are grown on the surface of the nanoporous aluminized layer to form a silicon carbide coating.
2. The method for preparing the nanoporous aluminum-silicon carbide gradient coating according to claim 1, characterized in that: In step 1), the sandblasting is performed using aluminum oxide sand particles with a particle size of 200-300 μm, a spray angle of 45° to 60°, and a spray pressure of 0.6 MPa.
3. The method for preparing the nanoporous aluminum-silicon carbide gradient coating according to claim 1, characterized in that: In step 2), the HCl gas flow rate is 100 sccm, the H2 gas flow rate is 500 sccm, and the thickness of the aluminized layer is 50-100 μm.
4. The method for preparing the nanoporous aluminum-silicon carbide gradient coating according to claim 1, characterized in that: In step 3), the etching time was extended to 40 minutes to form a nanoporous aluminized layer with a pore size range of 500 nm and a porosity of 70%.
5. The method for preparing the nanoporous aluminum-silicon carbide gradient coating according to claim 1, characterized in that: In step 4), the CH3SiCl3 flow rate was set to 50 sccm, the H2 flow rate was set to 200 sccm, the reaction time was shortened to 30 minutes, and the SiC nanowire density was reduced to 5×10 6 / cm².
6. The method for preparing the nanoporous aluminum-silicon carbide gradient coating according to claim 1, characterized in that: In step 4), the silicon carbide nanowires are chemically bonded to the surface of the nanoporous aluminized layer via Al-O-Si bonds.
7. A nanoporous aluminum-silicon carbide gradient coating, characterized in that: The invention comprises a nickel-based high-temperature alloy substrate (1), a nanoporous aluminized layer and silicon carbide nanowires, wherein the pore size of the nanoporous aluminized layer ranges from 200 to 500 nm, the porosity is 65%, and the diameter of the silicon carbide nanowires is from 50 to 100 nm.
8. The nanoporous aluminum-silicon carbide gradient coating according to claim 7, characterized in that: The silicon carbide nanowires are distributed in a density gradient from the surface of the nanoporous aluminized layer to the outside, with a higher density near the surface of the aluminized layer and gradually decreasing outward.
9. The nanoporous aluminum-silicon carbide gradient coating according to claim 7, characterized in that: The specific surface area of the nanoporous aluminized layer is 200 m² / g, and the thickness of the aluminized layer is 50-100 microns.
10. The nanoporous aluminum-silicon carbide gradient coating according to claim 7, characterized in that: After static oxidation at 1200℃ for 100 hours, a continuous Al2O3 / SiO2 composite oxide film is formed on the coating surface with a thickness of 2-3 microns.