High reflection-high emission-low thermal conductivity synergistic thermal protection coating and preparation method

Abstract

The application provides a high-reflection-high-emission-low-thermal-conductivity synergistic thermal protection coating and a preparation method, relates to the technical field of high-temperature thermal protection and radiation heat control, and comprises a bonding transition layer arranged on the surface of a base body, and further comprises a high-reflection layer and a multi-scale pore structure low-thermal-conductivity high-emission layer in sequence; the high-reflection layer is a multilayer reflection structure designed based on refractive index mismatch, and is formed by alternately arranging high-refractive-index material layers and low-refractive-index material layers; the multi-scale pore structure low-thermal-conductivity high-emission layer comprises a low-thermal-conductivity continuous base phase, a micrometer-scale pore structure, a nanometer-scale pore structure and a high-emission second phase; and the high-emission second phase is enriched in a region close to the outer surface of the coating. The application realizes the synergistic construction of high reflection, low thermal conductivity and high emission by combining wavelength matching pore forming agent composite granulation, ultrasonic dispersion-electrostatic field assisted nanopore granulation and partition energy regulation atmospheric plasma spraying, and can improve the comprehensive thermal protection capability of the coating in a high-temperature strong radiation environment.

Description

Technical Field

[0001] This invention relates to the field of high-temperature thermal protection and radiation thermal control technology, and in particular to a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protection coating and its preparation method. Background Technology

[0002] The rapid development of aerospace technology has placed higher demands on the service temperature of engine hot-end components, high-speed aircraft outer surface components, and reusable thermal protection components. Thermal protection coatings face complex service environments characterized by high temperatures, strong radiation, and heat flux coupling. As service temperatures increase, the distribution of thermal radiation energy shifts towards shorter wavelengths, with a significant increase in the radiation contribution from the 0.5–2 μm near-infrared band. In this band, the absorption capacity of some oxide ceramics is relatively limited, and radiant heat may penetrate the coating and exert additional heating on the underlying substrate. Therefore, simply reducing the thermal conductivity of the coating is insufficient to fully meet the thermal protection requirements under high-temperature and strong radiation environments; further control of the propagation, scattering, and release processes of thermal radiation within the coating is also necessary.

[0003] Existing thermal protection coatings mostly reduce conductive heat flux through material composition optimization, pore structure control, or multilayer structure design. For example, CN115849958A discloses a ceramic matrix composite thermal protection coating, which improves temperature resistance through a sealing layer, an anti-oxidation bonding layer, and a heat-insulating and heat-resistant layer. However, it mainly focuses on sealing, anti-oxidation, and heat insulation and heat resistance, and does not adequately consider the control of high-temperature heat radiation penetration and radiation propagation path. CN112447322A discloses a multilayer radiation-resistant thermal protection material and its preparation method, which uses an outer high-reflectivity layer, a middle high-heat-capacity layer, and an inner low-thermal-conductivity layer to reduce the temperature rise of the inner wall after thermal irradiation. However, it is mainly aimed at cable thermal protection materials and is difficult to directly apply to the high-temperature long-term service environment of aerospace hot-end components. CN119016314A discloses a multi-layer thermal protection coating that combines thermal conductivity and radiation shielding. It achieves combined thermal conductivity and radiation shielding through an inner low thermal conductivity layer, an intermediate high absorption layer, and an outer high reflectivity layer. However, this scheme mainly relies on the high reflectivity layer and the high absorption layer to reduce radiation transmission. The radiation energy absorbed by the high absorption layer may still be converted into heat and participate in subsequent conduction and heat transfer.

[0004] In summary, existing thermal protection coatings still have the following shortcomings: First, traditional low thermal conductivity coatings are insufficient in controlling high-temperature radiation heat transfer; second, individual high reflectivity or high absorption structures cannot simultaneously achieve radiation blocking and outward heat release; third, if high-emissivity materials are used as continuous independent layers, it may lead to an increase in the overall thermal conductivity of the coating; fourth, existing porous thermal protection coatings mainly aim to reduce thermal conductivity, and pay insufficient attention to the matching relationship between pore size and target thermal radiation wavelength, making it difficult to fully utilize the scattering and path disturbance effects of the pore structure on near-infrared radiation. Summary of the Invention

[0005] The purpose of this invention is to provide a high-reflectivity-high-emission-low-thermal-conductivity synergistic thermal protection coating and its preparation method. It enhances interface reflection through a refractive index mismatch multilayer reflective structure, enhances body scattering through a wavelength-matched multi-scale porous structure, and enhances outward infrared radiation heat dissipation through a high-emission second phase, thereby reducing the total heat flux density transferred to the substrate under high-temperature and high-radiation environments.

[0006] To achieve the above objectives, the present invention provides a high-reflectivity-high-emission-low-thermal-conductivity synergistic thermal protection coating, comprising a bonding transition layer disposed on the surface of a substrate, and further comprising a high-reflectivity layer and a multi-scale porous structure low-thermal-conductivity high-emission layer in sequence; The high-reflectivity layer is a multi-layered reflective structure based on refractive index mismatch design, formed by alternating layers of high-refractive-index material and low-refractive-index material. The multi-scale porous low thermal conductivity and high emission layer includes a nanoporous low thermal conductivity region, a micro-nano composite pore scattering region, and a high emission second phase enrichment region. Among them, the nanoporous low thermal conductivity region includes a low thermal conductivity continuous matrix phase and a nanoscale pore structure; the micro-nano composite pore scattering region includes a low thermal conductivity continuous matrix phase, a micron-scale pore structure, and a nanoscale pore structure; the high emission second phase enrichment region includes a low thermal conductivity continuous matrix phase and a high emission second phase; the high emission second phase enrichment region is located in the region near the outer surface of the coating.

[0007] Preferably, the difference in the real part of the refractive index between the high-refractive-index material layer and the low-refractive-index material layer in the target thermal radiation band is not less than 0.2; The high refractive index material layer is one or more of TiO2, ZrO2, HfO2, Nb2O5, and other oxide ceramic materials with a real part of refractive index not less than 1.9 in the target thermal radiation band. The low refractive index material layer is one or more of the following: SiO2, Al2O3, mullite, porous oxide ceramic materials, and other oxide ceramic materials whose real part of refractive index is not higher than 1.8 in the target thermal radiation band. The low thermal conductivity continuous matrix material is one or a combination of several of the following: zirconia-based ceramics, rare earth zirconates, rare earth tantalates, rare earth niobates, and rare earth silicate ceramics. The high-emission second phase material is one or a combination of several of the following: transition metal oxides, spinel oxides, perovskite oxides, ferrates, manganates, cobaltates, chromates, or transition metal-doped oxides.

[0008] Preferably, the pore size of the micron-sized pore structure is 0.2 to 3 times the target thermal radiation wavelength, and the pore size of the nano-sized pore structure is 20 to 500 nm.

[0009] Preferably, the total thickness of the high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating is 150~800μm; wherein, the thickness of the bonding transition layer is 25~100μm, the thickness of the high-reflectivity layer is 20~150μm, and the thickness of the multi-scale porous structure low-thermal-conductivity high-emissivity layer is 100~550μm. In the multi-scale porous structure low thermal conductivity high emission layer, the thickness of the nanopore low thermal conductivity region accounts for 20-50% of the thickness of the multi-scale porous structure low thermal conductivity high emission layer, the thickness of the micro-nano composite pore scattering region accounts for 30-60% of the thickness of the multi-scale porous structure low thermal conductivity high emission layer, and the thickness of the high emission second phase enrichment region accounts for 5-25% of the thickness of the multi-scale porous structure low thermal conductivity high emission layer.

[0010] Preferably, the transition layer powder is NiCrAlY; The matrix is ​​a high-temperature alloy, including stainless steel, nickel-based alloys, or cobalt-based alloys.

[0011] A method for preparing a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating includes the following steps: Step S1: Preparation of the bonding transition layer: The bonding transition layer powder is sprayed onto the pretreated substrate surface using an atmospheric plasma spraying method to form a bonding transition layer, thus obtaining a substrate with a bonding transition layer on the surface. Step S2, Preparation of high reflectivity layer: High refractive index layer feed and low refractive index layer feed are alternately sprayed on the surface of the bonding transition layer by atmospheric plasma spraying method to form a refractive index mismatch multilayer reflective structure with alternating high refractive index material layer and low refractive index material layer; Step S3: Fabrication of a multi-scale porous structure with low thermal conductivity and high emission: Step S31: Mix the low thermal conductivity continuous matrix feed and the nanoscale porous structure feed, and then spray it onto the surface of the high reflectivity layer to form a nanoporous low thermal conductivity region; the mass ratio of the low thermal conductivity continuous matrix feed to the nanoscale porous structure feed is (60~90):(40~10). Step S32: After mixing the low thermal conductivity continuous matrix feed, the nano-porous structure feed and the micron-porous structure feed, continue spraying to form a micro-nano composite pore scattering region; the mass ratio of the low thermal conductivity continuous matrix feed, the nano-porous structure feed and the micron-porous structure feed is (60~90):(5~20):(5~20); Step S33: After mixing the low thermal conductivity continuous matrix feed and the high emission second phase feed, continue spraying to form a high emission second phase enrichment region; the mass ratio of the low thermal conductivity continuous matrix feed to the high emission second phase feed is (30~70):(70~30); Step S4, Post-processing: The prepared coating is subjected to selective heat treatment to obtain a high-reflectivity-high-emission-low-thermal-conductivity synergistic thermal protection coating.

[0012] Preferably, the high refractive index layer feed, low refractive index layer feed, low thermal conductivity continuous matrix phase feed, micron-sized pore structure feed, high emission second phase feed, and nano-sized pore structure feed are all formed by atmospheric plasma spraying. The feedstocks for high refractive index layer, low refractive index layer, low thermal conductivity continuous matrix phase, and high emission second phase are formulated in the following proportions by mass: 60-80 parts of material powder, 1-3 parts of dispersant, 1-5 parts of binder, and 20-40 parts of solvent. Material powders include materials with high refractive index layers, materials with low refractive index layers, materials with low thermal conductivity continuous matrix phases, and materials with high emission second phases; The feedstock for the nanoscale pore structure is formulated by the following proportions by weight: 30-50 parts of low thermal conductivity continuous matrix powder, 5-15 parts of nanopore-forming agent and 40-60 parts of solvent. The feedstock for the micron-sized pore structure is formulated by the following proportions by weight: 60-80 parts micron-sized pore composite powder, 1-3 parts dispersant, 1-5 parts binder, and 20-40 parts solvent; wherein the micron-sized pore composite powder includes low thermal conductivity continuous matrix powder and micron-sized pore-forming agent, and the mass ratio of low thermal conductivity continuous matrix powder to micron-sized pore-forming agent is (70-95):(30-5).

[0013] Preferably, the solvents for the high refractive index layer feed, the low refractive index layer feed, the micron-sized pore structure feed, the low thermal conductivity continuous matrix phase feed, and the high emission second phase feed are deionized water or anhydrous ethanol, the dispersant is ammonium polyacrylate or polyvinylpyrrolidone, and the binder is polyvinyl alcohol or carboxymethyl cellulose. Nanoporogens include polyethersulfone; The solvent for feeding the nanoscale porous structure is N-methylpyrrolidone; Micron-forming agents include polyhydroxybutyrate; The particle size D50 of the micron-sized pore-forming agent is 0.5~5μm.

[0014] Preferably, when preparing the bonding transition layer, the atmospheric plasma spraying process parameters are: current of 550~600A, power of 42~45kW, argon flow rate of 32~45slpm, hydrogen flow rate of 9~12slpm, carrier gas of 3~4slpm, powder feeding disc rotation speed of 30~40slpm, and spray distance of 80~110mm. When preparing the high-reflectivity layer, the atmospheric plasma spraying process parameters are as follows: current 500~600A, power 38~45kW, argon flow rate 32~45slpm, hydrogen flow rate 9~12slpm, carrier gas 3~4slpm, powder feeding tray rotation speed 30~40slpm, and spray distance 80~130mm.

[0015] Preferably, when preparing the nanoporous low thermal conductivity region, an atmospheric plasma spraying process with medium energy input is used, with a current of 500~600A, a power of 36~42kW, and a spray distance of 80~130mm. When preparing the micro-nano composite hole scattering region, a low-energy-input atmospheric plasma spraying process is used, with a current of 450~550A, a power of 32~38kW, and a spraying distance of 100~130mm. When preparing the high-emission second-phase enrichment region, an atmospheric plasma spraying process with high energy input is adopted, with a current of 550~650A, a power of 42~45kW, and a spray distance of 80~110mm.

[0016] Preferably, the heat treatment includes a low-temperature pore-forming stage and a high-temperature stabilization stage; the temperature of the low-temperature pore-forming stage is 300~600℃ and the time is 2~4h; the high-temperature stabilization temperature is 800~1100℃ and the time is 2~6h.

[0017] Therefore, the present invention employs the above-mentioned high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating and its preparation method, and the technical effects are as follows: 1. The present invention constructs a high-reflection structure based on refractive index mismatch design on the outside of the bonding transition layer. By alternating high-refractive-index material layers and low-refractive-index material layers to form a multi-interface reflection structure, the reflection, refraction and scattering in the target thermal radiation band can be enhanced, thereby reducing the penetration of high-temperature thermal radiation into the substrate. 2. This invention constructs a wavelength-matched multi-scale porous low thermal conductivity high emission layer on the outside of the high reflectivity layer. The micron-scale porous structure enhances the scattering and reflection of the target thermal radiation band, while the nano-scale porous structure enhances phonon scattering and reduces the effective thermal conductivity. At the same time, the high emission second phase enrichment region on the outer surface enhances outward infrared radiation heat dissipation, thereby achieving the synergistic effect of radiation shielding, conductive heat insulation and surface heat dissipation. 3. This invention achieves precise control of the micro- and nano-scale pore structure in the coating by using micron-sized pore-forming agent composite granulation with target wavelength matching, ultrasonic dispersion-electrostatic field-assisted nanopore granulation, zoned energy-controlled atmospheric plasma spraying, and selective heat treatment. This ensures that the micron-sized pore structure is on the same order of magnitude as the target thermal radiation wavelength, and the nano-sized pore structure effectively reduces conductive heat flow, thereby achieving a synergistic effect of radiation shielding and thermal insulation. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a high-reflectivity-high-emission-low-thermal-conductivity synergistic thermal protection coating of the present invention; Figure 2 SEM image of the cross-section of the multilayer high-reflectivity structure prepared in Example 1; Figure 3 The reflectance spectrum of the multilayer high-reflectance structure prepared in Example 1; Figure 4 SEM image of the wavelength-matched multi-scale porous high-emission-low-thermal-conductivity complex layer prepared in Example 1; Figure 5 Emissivity spectrum of the wavelength-matched multi-scale porous high-emission-low thermal conductivity complex layer prepared in Example 1; Figure 6 The reflectance spectrum of the wavelength-matched multi-scale porous high-emission-low thermal conductivity complex layer prepared in Example 1; Figure 7 The reflectance spectrum of the coating with added micron-sized pore-forming agent prepared in Example 2; Figure 8 The reflectance spectrum of the coating without micron-sized pore-forming agent prepared for Comparative Example 1. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0021] This invention achieves coordinated control of radiative and conductive heat transfer under high-temperature and high-radiation environments by designing a multi-layered reflective structure through refractive index mismatch and a multi-scale porous structure through wavelength matching.

[0022] The refractive index mismatch multilayer reflective structure reduces the penetration of the target thermal radiation band into the substrate through multi-interface reflection, refraction, and scattering between high- and low-refractive-index material layers. The wavelength-matched multi-scale porous structure, with its micron-scale pores in the high-emission, low-thermal-conductivity composite layer, is on the same order of magnitude as the target thermal radiation wavelength, enhancing volume scattering and propagation path perturbation of the target band radiation; the nanoscale pore structure enhances phonon scattering and reduces effective thermal conductivity; and the high-emission second phase enriched on the outer surface enhances outward infrared radiation heat dissipation from the coating.

[0023] To achieve the above structure, this invention further introduces a target wavelength-matched micron-sized pore-forming agent composite granulation, ultrasonic dispersion-electrostatic field-assisted nanopore precursor granulation, zoned energy-controlled atmospheric plasma spraying, and selective heat treatment pore-forming processes. Specifically, the micron-sized pore-forming agent particle size is determined according to the target thermal radiation band, allowing the pore-forming agent to be dispersed, embedded, or partially coated within the low thermal conductivity matrix phase or between particles, thereby improving the uniformity of pore-forming agent distribution and reducing its excessive burn-off in the plasma flame. The ultrasonic dispersion-electrostatic field-assisted nano-granulation process reduces powder agglomeration and can be transformed into a feedstock with a nanoscale pore structure during heat treatment. The zoned energy-controlled atmospheric plasma spraying process controls the feedstock melting state, pore structure retention, and interlayer bonding state, ensuring the formation of the target structure. Selective heat treatment, through a low-temperature pore-forming stage and a high-temperature stabilization stage, gradually decomposes or volatilizes the pore-forming agent and stabilizes the ceramic structure, thereby obtaining a micron-sized pore structure with a pore size matching the target thermal radiation band.

[0024] Through the above structural design and process control, the radiative heat flow entering the coating is suppressed by the scattering of the micron-sized pore structure and the interface reflection of the refractive index mismatch multilayer reflection structure. The conductive heat flow is suppressed by the low thermal conductivity continuous matrix phase and the nano-sized pore structure. The heat of the coating can also be released outward through radiation by the high emission second phase, thereby reducing the total heat flow transferred to the substrate.

[0025] Example 1 A structure of a high-reflectivity-high-emission-low-thermal-conductivity synergistic thermal protective coating is as follows: Figure 1 As shown, a method for preparing a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating includes the following steps: S1. Substrate surface pretreatment A nickel-based high-temperature alloy was selected as the substrate. The substrate surface was ground and polished with sandpaper. The substrate surface was then ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water in sequence to remove surface oil, dust, and impurities. The substrate surface was then roughened by sandblasting with 60# corundum sand as the sandblasting medium, a sandblasting pressure of 0.3 MPa, a sandblasting distance of 100 mm, and a sandblasting angle of 45° to obtain the pretreated substrate. S2, Preparation of the transition layer NiCrAlY powder was sprayed onto the pretreated substrate surface using atmospheric plasma spraying to form a NiCrAlY bonding transition layer. This NiCrAlY bonding transition layer enhances the bonding strength between the substrate and the outer ceramic layer, and mitigates the thermal expansion mismatch between the metal substrate and the ceramic layer. The NiCrAlY powder particle size was 15–45 μm. The atmospheric plasma spraying parameters were: current 500 A, power 42.5 kW, argon flow rate 32 slpm, hydrogen flow rate 10 slpm, carrier gas flow rate 3 slpm, powder feed tray speed 25 rpm, and nozzle distance 100 mm.

[0026] S3. Preparation of high-refractive-index material layer spray feed and low-refractive-index material layer spray feed ZrO2 was selected as the high-refractive-index oxide ceramic material, and Al2O3 as the low-refractive-index oxide ceramic material. The preparation method is as follows: 75 parts of ZrO2 powder or Al2O3 powder, 1 part of polyvinylpyrrolidone, 2 parts of carboxymethyl cellulose, and 22 parts of deionized water are added to a sealed bottle according to the mass ratio. Zirconia balls are added at a ball-to-material mass ratio of 5:1. After ball milling and dispersion, a uniform slurry is obtained. The slurry is then spray-granulated and dried to obtain either a high-refractive-index material feed or a low-refractive-index material feed. The ball milling speed is 150 rpm, and the ball milling time is 12 h. The spray granulation parameters are: inlet air temperature 220℃, outlet air temperature 100℃, and atomization pressure 0.3 MPa. The drying temperature is 80℃, and the drying time is 12 h. The size of the high-refractive-index material feed and the low-refractive-index material feed is 30~100 μm. S4. Fabrication of a high-reflectivity layer Atmospheric plasma spraying method is used to alternately spray high refractive index layer feed and low refractive index layer feed on the surface of NiCrAlY bonding transition layer to form a refractive index mismatch multilayer reflection structure with alternating high refractive index material layer and low refractive index material layer; The high-reflectivity layer has a five-layer alternating structure, consisting of ZrO2 layer, Al2O3 layer, ZrO2 layer, Al2O3 layer and ZrO2 layer from the side closest to the substrate outwards. The atmospheric plasma spraying process parameters are: current of 500 A, power of 40 kW, argon gas flow rate of 40 slpm, hydrogen gas flow rate of 10 slpm, carrier gas flow rate of 3 slpm, powder feeding tray rotation speed of 30 rpm, and spray distance of 100 mm.

[0027] In this embodiment, multiple refractive index mismatch interfaces are formed between the ZrO2 layer and the Al2O3 layer. After the target thermal radiation enters the high reflectivity layer, multiple interface reflections, refractions and scattering occur between the high refractive index material layer and the low refractive index material layer, thereby enhancing the reflection blocking effect in the target thermal radiation band.

[0028] Figure 2This demonstrates the successful fabrication of a multilayer high-reflectivity structure; Figure 3 This demonstrates that the multi-layer high-reflectivity structure design based on refractive index differences achieves efficient shielding against thermal radiation.

[0029] S5. Preparation of feedstock for multi-scale porous structures with low thermal conductivity and high emission layer S51, Preparation of low thermal conductivity continuous matrix feed and high emission second phase feed La2Zr2O7 was selected as the low thermal conductivity continuous matrix material and NiFe2O4 was selected as the high emission second phase material. The La2Zr2O7 powder and NiFe2O4 powder were spray granulated to obtain the low thermal conductivity continuous matrix feed and the high emission second phase feed. The preparation method was the same as that of S3. The low thermal conductivity continuous matrix feed is formulated as follows by mass: 75 parts La2Zr2O7 powder, 1 part polyvinylpyrrolidone, 2 parts carboxymethyl cellulose and 22 parts deionized water.

[0030] The high-emission second-phase feed is formulated by mass ratio as follows: 75 parts NiFe2O4 powder, 1 part polyvinylpyrrolidone, 2 parts carboxymethyl cellulose and 22 parts deionized water.

[0031] The dimensions of the low thermal conductivity continuous matrix feed and the high emission second phase feed are 30~100μm.

[0032] S52, Preparation of nanoscale porous structure feed Ten parts by weight of polyethersulfone (PES) were added to a beaker containing 50 parts of N-methylpyrrolidone (NMP) and stirred in a water bath at 60°C for 1 hour to completely dissolve the PES. Then, 40 parts of La2Zr2O7 powder were added and stirred for 1 hour. After ultrasonic dispersion at 20 kHz for 10 minutes, the mixture was prepared into a nanoscale slurry. After electrostatic field-assisted granulation and drying, a nanoporous feedstock was obtained. The specific process parameters for electrostatic field-assisted granulation are as follows: voltage is 15 kV, receiving distance is 10 cm, slurry flow rate is 23 ml / min, receiving system is deionized water; drying temperature is 80℃, drying time is 12 h; the particle size range of the nanoporous feed is 20~80 μm. S53, Preparation of feed with micron-sized pore structure 90 parts by weight of La2Zr2O7 powder and 10 parts by weight of polyhydroxybutyrate (PHB), a micron-sized pore-forming agent, are mixed to prepare a composite slurry containing the micron-sized pore-forming agent. The composite slurry containing the micron-sized pore-forming agent is then spray-granulated, and dried after spray granulation to obtain a micron-sized pore structure feedstock. The preparation method is the same as that of S52. The particle size D50 of PHB is 1~5μm. The particle size range of the micron-sized pore structure feedstock is 10~100μm. S6. Preparation of low thermal conductivity nanoporous regions An atmospheric plasma spraying method was used to mix 70 parts by weight of low thermal conductivity continuous matrix feed and 30 parts by weight of nanoscale porous structure feed and then spray it onto the surface of a high reflectivity layer to form a nanoporous low thermal conductivity region.

[0033] The atmospheric plasma spraying process parameters are as follows: current of 500 A, power of 40 kW, argon flow rate of 32 slpm, hydrogen flow rate of 12 slpm, carrier gas of 3 slpm, powder feeding tray speed of 30 rpm, and spray distance of 130 mm.

[0034] S7. Fabrication of micro / nano composite pore scattering regions An atmospheric plasma spraying method was used to mix 60 parts of low thermal conductivity continuous matrix feed, 20 parts of nanoscale pore structure feed and 20 parts of micron-scale pore structure feed and then sprayed to form a micro-nano composite pore scattering region in the middle.

[0035] The spraying parameters for the micro-nano composite pore scattering region are as follows: current of 500 A, power of 35 kW, argon flow rate of 32 slpm, hydrogen flow rate of 12 slpm, carrier gas of 3 slpm, powder feeding disc rotation speed of 30 rpm, and spray distance of 130 mm.

[0036] S8. Preparation of a high-emission second-phase enrichment region An atmospheric plasma spraying method was used to mix 70 parts of low thermal conductivity continuous matrix feed and 30 parts of high emission second phase feed and then sprayed to form a high emission second phase enrichment region near the outer surface.

[0037] The atmospheric plasma spraying parameters are as follows: current of 550 A, power of 45 kW, argon flow rate of 32 slpm, hydrogen flow rate of 12 slpm, carrier gas of 3 slpm, powder feeding disc speed of 30 rpm, and spray distance of 110 mm.

[0038] S9, Post-processing: The coating prepared by spraying was subjected to heat treatment to remove residual pore-forming agent, stabilize the coating phase and improve the coating bonding state. The heat treatment process parameters were as follows: in air atmosphere, the temperature was increased to 600℃ at a heating rate of 2℃ / min and held for 2h to complete low-temperature pore formation; the temperature was increased to 900℃ at a heating rate of 1℃ / min and held for 4h to complete high-temperature stabilization.

[0039] Figure 4 SEM image of the wavelength-matched multi-scale porous high-emission-low-thermal-conductivity complex layer prepared in Example 1.

[0040] Figure 5 This demonstrates that the coating prepared in this embodiment has a high infrared emissivity, which is beneficial for the outward radiation heat dissipation of the coating.

[0041] Figure 6 This demonstrates that the coating prepared in this embodiment has a high near-infrared reflectivity, which is beneficial for achieving radiation shielding from the outside to the substrate.

[0042] Example 2 The difference between this embodiment and Embodiment 1 is that in step S53, the particle size D50 of the micron-sized pore-forming agent PHB is adjusted to 8~15μm. The composite slurry containing the micron-sized pore-forming agent is formulated according to the following mass ratio: 80 parts La2Zr2O7 powder, 20 parts PHB, 2 parts polyvinylpyrrolidone, 3 parts carboxymethyl cellulose, and 25 parts deionized water, in order to study the influence of the particle size of the micron-sized pore-forming agent and the composite granulation process on the pore structure and reflectivity of the coating. Other steps and parameters are the same as in Embodiment 1.

[0043] Compared to Example 1, this example features increased PHB particle size and a higher PHB content, resulting in larger micron-sized pore structures, a wider pore distribution range, and a tendency for larger pores or interconnected pore structures to form in localized areas. While this structure increases the number of scattering interfaces within the coating, the excessively large pore size reduces the compatibility with the target thermal radiation band and may weaken the integrity of the localized continuous ceramic skeleton of the coating.

[0044] Depend on Figure 7 It can be seen that the reflectivity of the coating obtained in this embodiment is slightly lower than that in Example 1, indicating that the micron-sized pore structure is not necessarily more beneficial to the improvement of reflectivity by the larger the pore size or the higher the pore content. When the pore size deviates from the target thermal radiation wavelength matching range or the pore distribution is too wide, the effective scattering and reflection of the coating on the target thermal radiation band is reduced. Furthermore, this embodiment shows that the size and distribution of the micro-nano pore structure can be controlled by the particle size of the micron-sized pore-forming agent and the feeding ratio, so as to achieve the optimal control of the coating reflectivity.

[0045] Example 3 The difference from Example 1 is that polyvinylpyrrolidone is replaced with ammonium polyacrylate and carboxymethyl cellulose is replaced with polyvinyl alcohol.

[0046] Example 4 The difference between this embodiment and Embodiment 1 is that: the ZrO2 high refractive index material layer in the high reflectivity layer is replaced with a TiO2 material layer, and the Al2O3 low refractive index material layer is replaced with a SiO2 layer; the La2Zr2O7 low thermal conductivity continuous matrix phase in the multi-scale porous low thermal conductivity high emission layer is replaced with rare earth silicate Y2Si2O7, and the NiFe2O4 high emission second phase is replaced with spinel-type oxide CoAl2O4; the remaining structural design, feed preparation method, and APS process parameters are the same as in Embodiment 1.

[0047] Example 5 The difference between this embodiment and Embodiment 1 is that: the ZrO2 high refractive index material layer in the high reflectivity layer is replaced with an HfO2 material layer, and the Al2O3 low refractive index material layer is replaced with a mullite material layer; the La2Zr2O7 low thermal conductivity continuous matrix phase in the multi-scale porous low thermal conductivity high emission layer is replaced with rare earth tantalate GdTaO4, and the NiFe2O4 high emission second phase is replaced with perovskite oxide LaMnO3; the remaining structural design, feed preparation method, and APS process parameters are the same as in Embodiment 1.

[0048] Example 6 The difference between this embodiment and Embodiment 1 is that: the ZrO2 high refractive index material layer in the high reflectivity layer is replaced with a Nb2O5 material layer, and the Al2O3 low refractive index material layer is replaced with a porous oxide ceramic material layer; the La2Zr2O7 low thermal conductivity continuous matrix phase in the multi-scale porous low thermal conductivity high emission layer is replaced with rare earth niobate Sm3NbO7, and the NiFe2O4 high emission second phase is replaced with Co2O3; the remaining structural design, feed preparation method, and APS process parameters are the same as in Embodiment 1.

[0049] Example 7 The difference between this embodiment and Embodiment 1 is that the substrate material is replaced by a cobalt-based high-temperature alloy instead of a nickel-based high-temperature alloy, while the remaining bonding transition layer, high-reflection structure, multi-scale porous structure low thermal conductivity high-emissivity layer, and spraying parameters remain the same.

[0050] Comparative Example 1 Since the micron-sized pore structure feed is not prepared, i.e. step S53 is not performed, the mass ratio of the low thermal conductivity continuous matrix feed to the nano-sized pore structure feed is 60:40 when preparing the micro-nano composite pore scattering region; the remaining steps and atmospheric plasma spraying process parameters are consistent with those in Example 2.

[0051] Since this comparative example did not include micron-sized pore structure feedstock, the wavelength-matching micron-sized pore structure generated by PHB could not be formed during the post-processing. The coating mainly retained the nano-sized pore structure formed by electrostatic field-assisted nanopore granulation feedstock and the inherent interlayer pores formed during the spraying process.

[0052] Depend on Figure 8 It can be seen that the reflectivity of the coating obtained in this comparative example is lower than that of Example 1 and Example 2, indicating that it is difficult to fully enhance the scattering and reflection of the target thermal radiation band by relying solely on the nanoscale pore structure; introducing wavelength-matched micron-sized pore-forming agent composite granulation feed helps to form an effective micron-sized pore structure, thereby improving the reflectivity of the coating.

[0053] Therefore, the present invention adopts the above-mentioned high reflectivity-high emission-low thermal conductivity synergistic thermal protection coating and preparation method. By combining wavelength matching pore-forming agent composite granulation, ultrasonic dispersion-electrostatic field assisted nanopore granulation and partitioned energy-controlled atmospheric plasma spraying, the synergistic construction of high reflectivity, low thermal conductivity and high emission functions is achieved, which can improve the comprehensive thermal protection capability of the coating in high temperature and strong radiation environment.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating, comprising a bonding transition layer disposed on the surface of a substrate, characterized in that, It also includes, in sequence, a high-reflectivity layer and a multi-scale porous structure with low thermal conductivity and high emission; The high-reflectivity layer is a multi-layered reflective structure based on refractive index mismatch design, formed by alternating layers of high-refractive-index material and low-refractive-index material. The multi-scale porous low thermal conductivity and high emission layer includes a nanoporous low thermal conductivity region, a micro-nano composite pore scattering region, and a high emission second phase enrichment region. Among them, the nanoporous low thermal conductivity region includes a low thermal conductivity continuous matrix phase and a nanoscale pore structure; the micro-nano composite pore scattering region includes a low thermal conductivity continuous matrix phase, a micron-scale pore structure, and a nanoscale pore structure; the high emission second phase enrichment region includes a low thermal conductivity continuous matrix phase and a high emission second phase; the high emission second phase enrichment region is located in the region near the outer surface of the coating.

2. The high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protection coating according to claim 1, characterized in that, The difference in the real part of the refractive index between the high-refractive-index material layer and the low-refractive-index material layer in the target thermal radiation band is not less than 0.2; The high refractive index material layer is one or more of TiO2, ZrO2, HfO2, Nb2O5, and other oxide ceramic materials with a real part of refractive index not less than 1.9 in the target thermal radiation band. The low refractive index material layer is one or more of the following: SiO2, Al2O3, mullite, porous oxide ceramic materials, and other oxide ceramic materials whose real part of refractive index is not higher than 1.8 in the target thermal radiation band. The low thermal conductivity continuous matrix material is one or a combination of several of the following: zirconia-based ceramics, rare earth zirconates, rare earth tantalates, rare earth niobates, and rare earth silicate ceramics. The high-emission second phase material is one or a combination of several of the following: transition metal oxides, spinel oxides, perovskite oxides, ferrates, manganates, cobaltates, chromates, or transition metal-doped oxides.

3. The high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protection coating according to claim 1, characterized in that, The pore size of micron-sized pore structures is 0.2 to 3 times the target thermal radiation wavelength, while the pore size of nano-sized pore structures is 20 to 500 nm.

4. The high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protection coating according to claim 1, characterized in that, The total thickness of the high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating is 150~800μm; among which, the thickness of the bonding transition layer is 25~100μm, the thickness of the high-reflectivity layer is 20~150μm, and the thickness of the multi-scale porous structure low-thermal-conductivity high-emissivity layer is 100~550μm. In the multi-scale porous structure low thermal conductivity high emission layer, the thickness of the nanopore low thermal conductivity region accounts for 20-50% of the thickness of the multi-scale porous structure low thermal conductivity high emission layer, the thickness of the micro-nano composite pore scattering region accounts for 30-60% of the thickness of the multi-scale porous structure low thermal conductivity high emission layer, and the thickness of the high emission second phase enrichment region accounts for 5-25% of the thickness of the multi-scale porous structure low thermal conductivity high emission layer.

5. The high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protection coating according to claim 1, characterized in that, The transition layer powder is NiCrAlY; The matrix is ​​a high-temperature alloy, including stainless steel, nickel-based alloys, or cobalt-based alloys.

6. The method for preparing a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating according to claim 1, characterized in that, Includes the following steps: Step S1: Preparation of the bonding transition layer: The bonding transition layer powder is sprayed onto the pretreated substrate surface using an atmospheric plasma spraying method to form a bonding transition layer, thus obtaining a substrate with a bonding transition layer on the surface. Step S2, Preparation of high reflectivity layer: High refractive index layer feed and low refractive index layer feed are alternately sprayed on the surface of the bonding transition layer by atmospheric plasma spraying method to form a refractive index mismatch multilayer reflective structure with alternating high refractive index material layer and low refractive index material layer; Step S3: Fabrication of a multi-scale porous structure with low thermal conductivity and high emission: Step S31: Mix the low thermal conductivity continuous matrix feed and the nanoscale porous structure feed, and then spray it onto the surface of the high reflectivity layer to form a nanoporous low thermal conductivity region; the mass ratio of the low thermal conductivity continuous matrix feed to the nanoscale porous structure feed is (60~90):(40~10). Step S32: After mixing the low thermal conductivity continuous matrix feed, the nano-porous structure feed and the micron-porous structure feed, continue spraying to form a micro-nano composite pore scattering region; the mass ratio of the low thermal conductivity continuous matrix feed, the nano-porous structure feed and the micron-porous structure feed is (60~90):(5~20):(5~20); Step S33: After mixing the low thermal conductivity continuous matrix feed and the high emission second phase feed, continue spraying to form a high emission second phase enrichment region; the mass ratio of the low thermal conductivity continuous matrix feed to the high emission second phase feed is (30~70):(70~30); Step S4, Post-processing: The prepared coating is subjected to selective heat treatment to obtain a high-reflectivity-high-emission-low-thermal-conductivity synergistic thermal protection coating.

7. The method for preparing a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating according to claim 6, characterized in that, High refractive index layer feed, low refractive index layer feed, low thermal conductivity continuous matrix phase feed, micron-sized pore structure feed, high emission second phase feed, and nano-sized pore structure feed are all formed by atmospheric plasma spraying. The feedstocks for high refractive index layer, low refractive index layer, low thermal conductivity continuous matrix phase, and high emission second phase are formulated in the following proportions by mass: 60-80 parts of material powder, 1-3 parts of dispersant, 1-5 parts of binder, and 20-40 parts of solvent. Material powders include materials with high refractive index layers, materials with low refractive index layers, materials with low thermal conductivity continuous matrix phases, and materials with high emission second phases; The feedstock for the nanoscale pore structure is formulated by the following proportions by weight: 30-50 parts of low thermal conductivity continuous matrix powder, 5-15 parts of nanopore-forming agent and 40-60 parts of solvent. The feedstock for the micron-sized pore structure is formulated by the following proportions by weight: 60-80 parts micron-sized pore composite powder, 1-3 parts dispersant, 1-5 parts binder, and 20-40 parts solvent; wherein the micron-sized pore composite powder includes low thermal conductivity continuous matrix powder and micron-sized pore-forming agent, and the mass ratio of low thermal conductivity continuous matrix powder to micron-sized pore-forming agent is (70-95):(30-5).

8. The method for preparing a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating according to claim 7, characterized in that, The solvents for high refractive index layer feed, low refractive index layer feed, micron-sized pore structure feed, low thermal conductivity continuous matrix phase feed, and high emission second phase feed are deionized water or anhydrous ethanol, the dispersant is ammonium polyacrylate or polyvinylpyrrolidone, and the binder is polyvinyl alcohol or carboxymethyl cellulose. Nanoporogens include polyethersulfone; The solvent for feeding the nanoscale porous structure is N-methylpyrrolidone; Micron-forming agents include polyhydroxybutyrate; The particle size D50 of the micron-sized pore-forming agent is 0.5~5μm.

9. The method for preparing a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating according to claim 6, characterized in that, When preparing the bonding transition layer, the atmospheric plasma spraying process parameters are as follows: current 550~600A, power 42~45kW, argon flow rate 32~45slpm, hydrogen flow rate 9~12slpm, carrier gas 3~4slpm, powder feeding disc rotation speed 30~40slpm, and spray distance 80~110mm. When preparing the high-reflectivity layer, the atmospheric plasma spraying process parameters are as follows: current 500~600A, power 38~45kW, argon flow rate 32~45slpm, hydrogen flow rate 9~12slpm, carrier gas 3~4slpm, powder feeding tray rotation speed 30~40slpm, and spray distance 80~130mm.

10. The method for preparing a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating according to claim 6, characterized in that, When preparing the low thermal conductivity nanopore region, an atmospheric plasma spraying process with medium energy input is used, with a current of 500~600A, a power of 36~42kW, and a spray distance of 80~130mm. When preparing the micro-nano composite hole scattering region, a low-energy-input atmospheric plasma spraying process is used, with a current of 450~550A, a power of 32~38kW, and a spraying distance of 100~130mm. When preparing the high-emission second-phase enrichment region, an atmospheric plasma spraying process with high energy input is adopted, with a current of 550~650A, a power of 42~45kW, and a spray distance of 80~110mm.

11. The method for preparing a high-reflectivity-high-emissivity-low-thermal-conductivity synergistic thermal protective coating according to claim 6, characterized in that, The heat treatment includes a low-temperature pore-forming stage and a high-temperature stabilization stage; the temperature of the low-temperature pore-forming stage is 300~600℃, and the time is 2~4h. The high-temperature stability temperature is 800~1100℃, and the time is 2~6h.

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