Anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for front edge of hypersonic aircraft and chemical vapor deposition process of anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating

Abstract

The invention provides an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the front edge of a hypersonic aircraft and a chemical vapor deposition process of the anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating. The anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating can be suitable for thermal protection of an outer skin of the hypersonic aircraft. The coating is formed by compounding SiC and rare earth doped hafnium-based ceramic, and the coating is completely covered on a base material, compact in structure and free of defects such as cracks. And excellent high-temperature long-acting service performance is obtained through component design of the coating and optimization of a preparation process. The coating is still kept complete after being used for 3000 seconds under oxyacetylene flame flow of 1875 K or above, the mid-infrared average emissivity is still larger than 0.85, and the temperature of the back face of a sample is kept at 1200 K. Compared with a single SiC coating and an undoped hafnium-based ceramic SiC composite coating, the high-temperature ablation resistance of the composite coating is remarkably improved. The composite coating is prepared by combining a gas phase siliconizing method and a dip-coating process, the method is simple, the process is mature, operation is easy, and the method is suitable for preparing the coating on the surface of a component with a complex shape structure.

Description

Technical Field

[0001] This invention belongs to the field of thermal protection coatings and relates to an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of hypersonic vehicles and its chemical vapor deposition process. The coating's high-temperature long-term service performance is improved through composition design and process optimization. Background Technology

[0002] The pursuit and research of higher-speed aircraft by various countries has given rise to hypersonic vehicles. When an aircraft flies at hypersonic speeds near the atmosphere, aerodynamic heating is inevitable. At this time, the temperature of the aircraft's surface rises sharply, especially the nose cone and leading edge, which can reach or even exceed 1600°C. Traditional thermal protection systems have obvious disadvantages: the brittleness of high-temperature ceramics, the loss of ablated materials that alters the aerodynamic shape, and their high replacement and maintenance costs all make traditional thermal protection systems extremely unusable for hypersonic vehicles.

[0003] SiC ceramics possess high specific strength, high specific modulus, high temperature resistance, impact resistance, and good mechanical properties. They also overcome the critical drawbacks of ceramic materials, such as low fracture toughness, poor impact load resistance, and poor thermal shock resistance, making them an important heat shield material for critical components of aircraft. However, many of these advantages can only be maintained under an inert atmosphere. Although recent studies have shown that SiO2, formed after SiC oxidation, can effectively block oxygen diffusion, the resulting SiO2 is in a molten amorphous state, limiting its improvement in high-temperature, long-term service performance. Therefore, there is an urgent need to design the composition and structure of coatings to achieve better high-temperature, long-term service performance, thus solving the thermal barrier coating problem in hypersonic vehicle design. Summary of the Invention

[0004] To address the problem of insufficient high-temperature and long-term service performance of existing hypersonic thermal protective coatings, this invention provides an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of hypersonic vehicles and its chemical vapor deposition process. This composite coating achieves excellent high-temperature and long-term service performance through slurry composition design and optimized preparation process. The coating preparation process, employing a combination of dip-coating and vapor-phase silicon infiltration, offers advantages such as simplicity, stable forming quality, and applicability to complex components.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: An anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle and its chemical vapor deposition process, wherein the coating is composed of SiC and rare earth-doped hafnium-based ceramics.

[0006] Furthermore, the coating is composed of rare earth-doped hafnium-based ceramic particles encapsulated by SiC, and the thickness of the coating is 20μm-200μm.

[0007] Furthermore, the coating is composed of rare earth-doped hafnium-based ceramic particles encapsulated by SiC, and the thickness of the coating is 20μm-200μm.

[0008] A method for preparing a high-emissivity rare-earth-doped hafnium-based ceramic / silicon carbide composite ultra-high temperature thermal protection coating as described above includes the following steps: (1) Preparation of rare earth doped hafnium oxide powder: Submicron-sized rare earth oxides are ball-milled and mixed with HfO2, and treated at 900-2000℃ for 0.5-2h under an inert atmosphere to obtain rare earth doped hafnium oxide powder. (2) Preparation of slurry: Dissolve the polymer binder in the solvent and stir on a magnetic stirrer for 2 to 4 hours to form a solution. Then, ball mill and mix rare earth doped hafnium oxide powder, HfB2, SiC and the solution to obtain a slurry with a certain viscosity. (3) The substrate is immersed in the slurry prepared in step (2) by dip-coating method, so that the slurry is evenly coated on the surface of the substrate to obtain a coating. The substrate rising speed is controlled to be 30-500 μm / s. After the substrate is completely lifted out of the liquid surface, it is allowed to dry naturally and then placed in a muffle furnace to be cured at 100-230℃ for 0.5h-1.5h to obtain a cured coating. (4) The cured coating obtained in step (3) is pyrolyzed in an inert atmosphere at 500-900℃ for 0.5-2.5h to obtain a pretreated coating; (5) Place the pretreated coating obtained in step (4) into a container containing Si particles and place it in a vacuum induction heating furnace and heat it to 1500-2200℃ for 5-100 minutes.

[0009] Furthermore, in step (1), the mass ratio of rare earth oxides to HfO2 is 1:0.2 to 5.

[0010] Furthermore, the rare earth oxide in step (1) includes one or a mixture of several of praseodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, and thulium oxide; the substrate is one of graphite, C / C composite material, C / Cf composite material, and C / SiC composite material.

[0011] Furthermore, the polymeric adhesive mentioned in step (2) includes one or a mixture of phenolic resin, epoxy resin, and polyimide.

[0012] Furthermore, the solvent mentioned in step (2) includes one or a mixture of several of ethanol, propanol, and deionized water.

[0013] Furthermore, in step (2), the ratio of hafnium compound to SiC is 1:0.5 to 3, and the solid content in the slurry is 20wt% to 60wt%.

[0014] The present invention has the following beneficial effects: 1. This invention provides a novel approach to enhance the high-temperature, long-term service performance of silicon carbide composite coatings through rare-earth doping. By synthesizing a solid solution of hafnium oxide and rare-earth oxides, rare-earth-doped HfC and HfSi2 are obtained after a vapor-phase silicon infiltration reaction. The resulting rare-earth-doped silicon carbide composite coating exhibits exceptionally superior high-temperature, long-term service performance. After being ablated for 3000 seconds in an oxyacetylene flame at temperatures above 1600°C, the vapor-phase silicon infiltrated coating remains intact, with the average backside temperature remaining below 910.3°C. 2. This invention utilizes vapor-phase silicon infiltration to generate a SiC layer between the substrate surface and the coating, thereby improving the adhesion between the coating and the substrate and achieving excellent thermal shock resistance. 3. The rare-earth-doped hafnium-based ceramic and silicon carbide composite coating of this invention is prepared using a combination of vapor-phase silicon infiltration and impregnation processes. This method allows for the preparation of a thicker coating while ensuring good adhesion to the substrate. The preparation process is simple, convenient, and applicable to surfaces of complex-shaped components. It is highly repeatable and suitable for large-scale production. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1

[0017] A high-emissivity rare-earth-doped hafnium-based ceramic / silicon carbide composite ultra-high temperature thermal protection coating is prepared by the following method: 1. Use 1200# sandpaper to smooth the graphite substrate, then sonicate with ethanol for 10 minutes and deionize clean before use.

[0018] 2. Rare earth oxides and HfO2 were weighed at a mass ratio of 1:2, ball-milled and mixed, and then treated at 1400℃ for 0.5h in an inert atmosphere to obtain rare earth-doped hafnium oxide powder.

[0019] 3. Weigh phenolic resin and ethanol at a mass ratio of 2:13 to prepare an ethanol solution of phenolic resin.

[0020] 4. Weigh rare earth-doped hafnium oxide and silicon carbide at a mass ratio of 1:0.5, and weigh phenolic resin ethanol solution at a solid phase ratio of 30wt%. Ball mill the powder and solution to obtain a slurry.

[0021] 5. Immerse the substrate in the slurry, set the lifting speed of the lifting machine to 100 μm / s, and allow the coating to air dry naturally after lifting. Then, cure it at 150℃ for 0.5 h, place it in a tube furnace, and pyrolyze it at 500℃ for 1 h in an inert atmosphere. Finally, place it in a vacuum induction furnace at 1700℃ for 10 min for silicon infiltration.

[0022] Example 2

[0023] A high-emissivity rare-earth-doped hafnium-based ceramic / silicon carbide composite ultra-high temperature thermal protection coating is prepared by the following method: 1. Use 1200# sandpaper to smooth the graphite substrate, then sonicate with ethanol for 10 minutes and deionize clean before use.

[0024] 2. Rare earth oxides and HfO2 were weighed at a mass ratio of 1:2, ball-milled and mixed, and then treated at 1400℃ for 0.5h in an inert atmosphere to obtain rare earth-doped hafnium oxide powder.

[0025] 3. Weigh phenolic resin and ethanol at a mass ratio of 2:15 to prepare an ethanol solution of phenolic resin.

[0026] 4. Weigh hafnium carbide and silicon carbide in a 1:1 mass ratio, and weigh phenolic resin ethanol solution in a 30wt% solid phase ratio. Ball mill the powder and solution together to obtain the coating slurry.

[0027] 5. Immerse the substrate in the slurry, set the lifting speed of the lifting machine to 200 μm / s, and allow the coating to air dry naturally after lifting. Then, cure it at 150℃ for 0.5 h, place it in a tube furnace, and pyrolyze it at 500℃ for 1 h in an inert atmosphere. Finally, place it in a vacuum induction furnace at 1700℃ for 10 min for silicon infiltration.

[0028] Example 3

[0029] A high-emissivity rare-earth-doped hafnium-based ceramic / silicon carbide composite ultra-high temperature thermal protection coating is prepared by the following method: 1. Use 1200# sandpaper to smooth the graphite substrate, then sonicate with ethanol for 10 minutes and deionize clean before use.

[0030] 2. Rare earth oxides and HfO2 were weighed at a mass ratio of 1:2, ball-milled and mixed, and then treated at 1400℃ for 0.5h in an inert atmosphere to obtain rare earth-doped hafnium oxide powder.

[0031] 3. Weigh phenolic resin and ethanol at a mass ratio of 2:10 to prepare an ethanol solution of phenolic resin.

[0032] 4. Weigh hafnium boride and silicon carbide at a mass ratio of 1:1.5, and weigh phenolic resin ethanol solution at a solid phase ratio of 40wt%. Ball mill the powder and solution together to obtain the coating slurry.

[0033] 5. Immerse the substrate in the slurry, set the lifting speed of the lifting machine to 300 μm / s, and allow the coating to air dry naturally after lifting. Then, cure it at 150℃ for 0.5 h, place it in a tube furnace, and pyrolyze it at 500℃ for 1 h in an inert atmosphere. Finally, place it in a vacuum induction furnace at 1700℃ for 10 min for silicon infiltration.

[0034] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle, characterized in that: The coating is composed of SiC and rare earth-doped hafnium-based ceramics.

2. The anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle as described in claim 1, characterized in that: The coating consists of rare earth-doped hafnium-based ceramic particles encapsulated by SiC, and the thickness of the coating is 20μm-200μm.

3. The anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle as described in claim 1, characterized in that: The hafnium-based ceramics include one or a mixture of several of hafnium oxide, hafnium carbide, hafnium boride, and hafnium silicide.

4. A method for preparing an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle as described in any one of claims 1-3, characterized in that, The process includes the following steps: (1) Preparation of rare earth-doped hafnium oxide powder: Submicron-sized rare earth oxides are ball-milled and mixed with HfO2, and treated at 900-2000℃ for 0.5-2h under an inert atmosphere to obtain rare earth-doped hafnium oxide powder; (2) Preparation of slurry: The polymer binder is dissolved in a solvent and stirred on a magnetic stirrer for 2-4h to form a solution. Then, the hafnium-containing compound, SiC and the solution are ball-milled and mixed to obtain a slurry with a certain viscosity. The hafnium-containing compound is rare earth-doped hafnium oxide and hafnium silicide, hafnium carbide and boron. (2) A mixture of one or more of hafnium compounds; (3) The substrate is immersed in the slurry prepared in step (2) by dip-coating method, so that the slurry is uniformly coated on the surface of the substrate to obtain a coating. The substrate rising speed is controlled to be 30-500 μm / s. After the substrate is completely lifted out of the liquid surface, it is allowed to dry naturally and placed in a muffle furnace to be cured at 100-230℃ for 0.5h-1.5h to obtain a cured coating; (4) The cured coating obtained in step (3) is pyrolyzed in an inert atmosphere at 500-900℃ for 0.5h-2.5h to obtain a pretreated coating; (5) Place the pretreated coating obtained in step (4) into a container containing Si particles and place it in a vacuum induction heating furnace and heat it to 1500-2200℃ for 5-100 minutes.

5. The method for preparing an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle as described in claim 4, characterized in that: The mass ratio of rare earth oxides to HfO2 in step (1) is 1:0.2 to 5.

6. The method for preparing an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle as described in claim 4, characterized in that: The rare earth oxides in step (1) include one or a mixture of several of praseodymium oxide, samarium oxide, europium oxide, gadolinium oxide, terbium oxide, and thulium oxide; the substrate is one of graphite, C / C composite material, C / Cf composite material, and C / SiC composite material.

7. The method for preparing an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle as described in claim 4, characterized in that: The polymeric adhesive mentioned in step (2) includes one or a mixture of phenolic resin, epoxy resin, and polyimide.

8. The method for preparing an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle as described in claim 4, characterized in that: The solvent mentioned in step (2) includes one or a mixture of several of ethanol, propanol, and deionized water.

9. The method for preparing an anti-oxidation / anti-ablation silicon carbide-based composite ceramic coating for the leading edge of a hypersonic vehicle as described in claim 4, characterized in that: In step (2), the ratio of hafnium compound to SiC is 1:0.5 to 3, and the solid content in the slurry is 20wt% to 60wt%.