A gradient temperature resistant coating system and method of use thereof

Abstract

The application belongs to the technical field of metal protection, and specifically discloses a gradient temperature-resistant coating system and an application method thereof, wherein the processed coating substrate is immersed in a chemical conversion liquid to form a dense chemical conversion film on the surface of the substrate; metal powder is uniformly dispersed in epoxy-silicone resin, and the mixture is sprayed on the substrate with the chemical conversion film and dried to obtain a bottom layer; modified silicone resin paint is sprayed on the bottom layer and dried to obtain an intermediate layer; aerogel is ultrasonically dispersed in ethanol to obtain an aerogel suspension, which is sprayed on the intermediate layer to obtain an outer layer. The gradient temperature-resistant coating system breaks through the technical barriers of dual-temperature-zone protection and interlayer coordination, solves the core problems of dual-temperature-zone protection fragmentation, interlayer failure and poor structural durability, and provides a systematic solution for coating protection in an extreme high-temperature environment.

Description

Technical Field

[0001] This invention belongs to the field of metal protection technology, specifically relating to a gradient temperature-resistant coating system and its application method. Background Technology

[0002] With the development of technology, many industrial equipment require metal substrates to operate in harsh environments for extended periods, such as high temperature, humidity, high pressure, and acid / alkali conditions. This significantly shortens the service life of metal materials, making them unable to meet actual production requirements. To meet the service requirements of metal materials, it is necessary to further improve their high-temperature performance, ablation resistance, oxidation resistance, mechanical properties, and thermophysical properties. Surface coating is an effective method to improve the performance of metal materials. Surface coating preparation processes are diverse, and the composition, structure, and properties of coatings are easily controlled, making it the simplest and most practical means of material design and development. Among them, ceramic coatings have excellent wear resistance, high-temperature resistance, corrosion resistance, and oxidation resistance, and are widely used in many industrial fields such as aerospace, nuclear power, metallurgy, shipbuilding, construction, and automobiles. They have also attracted increasing attention from researchers and enterprises.

[0003] In aerospace thermal protection (such as engine hot-end components and missile reentry thermal protection structures) and industrial furnace high-temperature components (such as furnace lining inner walls and thermal barrier coating substrates), coatings need to simultaneously achieve instantaneous high-temperature barrier at 2300℃ and long-term thermal stability protection at 1000℃, while also ensuring interlayer bonding strength, thermal insulation efficiency, and structural durability. However, traditional ceramic coatings, such as the ZrO2 system, although able to withstand thermal shock at 2300℃ for a short time, have poor thermal stability and are prone to cracking and peeling due to thermal stress under repeated extreme temperature differences. To improve the thermal stability of ceramic coatings, organosilicon resins with long-term high-temperature resistance are used to modify the ceramic coatings. However, at temperatures only above 400℃, the organic phase in the organosilicon will rapidly carbonize and decompose, losing its binding effect. At the same time, under long-term thermal action, the organosilicon resin will gradually age and degrade, destroying the dispersion uniformity of the ceramic coating, reducing the coating density, and shortening the temperature resistance life. In addition to the aforementioned technical methods, inorganic nanofillers can also be added to ceramic coatings. For example, patent CN108751994A discloses a method for preparing a high-temperature resistant ceramic coating, in which tungsten carbide, nano-silica, zirconium dioxide, zinc oxide, aluminum nitride, boron nitride, titanium, and cobalt are ball-milled to obtain a mixed powder, which is then dispersed in ethanol and coated onto the surface of a stainless steel substrate to obtain a high-temperature resistant ceramic coating with good fracture toughness and thermal shock resistance. Chinese patent publication CN102863895A discloses a high-temperature resistant heat-insulating coating, in which high-temperature resistant fillers and inorganic non-metallic compounds are added to an epoxy resin-modified organosilicon resin to obtain a coating with high temperature resistance, low thermal conductivity, and strong impact resistance. However, inorganic heat-insulating coatings have low adhesion and poor resistance to temperature shock, and are prone to cracking and peeling during temperature changes. Furthermore, they will rapidly pulverize under long-term high-temperature service, and the instantaneous reflectivity will continuously decrease, causing high-temperature heat to be conducted to the metal substrate, failing to effectively block heat flow intrusion.

[0004] Therefore, there is an urgent need to develop a multi-layer gradient temperature-resistant coating system to achieve instantaneous high-temperature thermal shock resistance and long-term thermal stability at 1000℃. At the same time, it is also necessary to ensure the technical barriers of strong coating adhesion and efficient heat insulation to meet the high-temperature protection requirements in extreme environments. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problem that existing coatings cannot achieve instantaneous high-temperature barrier at 2300℃ and long-term thermal stability protection at 1000℃. It proposes a gradient temperature-resistant coating system, which breaks through the technical barriers of dual-temperature domain protection and interlayer synergy through a gradient structure design and component synergy, with strong bonding in the bottom layer, temperature stability in the middle layer and strong reflection in the top layer. It solves the core problems of dual-temperature domain protection fragmentation, interlayer failure and poor structural durability, and provides a systematic solution for coating protection in extreme high-temperature environments.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A gradient temperature-resistant coating system comprises a three-layer structure: a base layer, an intermediate layer, and an outer layer. The base layer consists of a chemical conversion film and a metallic powder primer. The intermediate layer is a modified silicone resin layer. The outer layer is an aerogel insulation layer.

[0008] The working principle of the gradient temperature-resistant coating system of this invention is as follows: A three-layer gradient structure is designed. The bottom layer uses a composite system to improve the adhesion between the coating and the substrate. The middle layer uses modified silicone resin to construct a stable temperature layer that can withstand 1000℃, achieving structural stability of the coating under long-term high temperatures. The outer layer uses aerogel to construct a porous network structure to block instantaneous heat radiation at 2300℃ and reduce the heating rate of the substrate surface. Through the three-layer gradient structure design of bottom layer interface thermal expansion adaptation, middle layer stable temperature and low shrinkage, and surface layer aerogel thermal barrier, the interlayer functions complement each other, synergistically regulate interlayer thermal stress, break through the performance barrier of dual-temperature domain protection, inhibit crack initiation and propagation under thermal shock cycling, improve coating durability, and achieve full life protection under extreme working conditions.

[0009] Preferably, the chemical conversion film is either a chromate conversion film or a titanate conversion film. By chemically converting the substrate (such as a high-temperature alloy or titanium alloy) to form a dense oxide film, the interfacial chemical affinity is optimized, providing anchoring points for subsequent coatings.

[0010] Preferably, the metallic primer includes aluminum powder or zinc-aluminum alloy primer, with flake-shaped metallic powder being the most preferred. Through the directional stacking of the flake-shaped metallic powder, a dual anti-corrosion mechanism of physical barrier and sacrificial anode is constructed, while simultaneously ensuring that the bonding strength between the coating and the substrate is ≥0, achieving strong adhesion between the substrate and the base layer and suppressing interfacial delamination at high temperatures.

[0011] Preferably, the modified silicone resin layer is obtained by spraying a modified silicone resin coating, which is obtained by adding ceramic filler to methylphenyl silicone resin and then dispersing it by high-speed stirring and ultrasonication. By combining silicone resin with temperature resistance and flexibility with ceramic filler with phase change regulation, the two work synergistically to achieve structural stability under long-term high temperature, solving the defects of aging cracking and density reduction in the intermediate layer.

[0012] Preferably, the organosilicon resin includes any one of methylphenyl organosilicon resin, phenyl organosilicon resin, and methyl organosilicon resin.

[0013] Preferably, the ceramic filler is any one of ZrO2 / Y2O3, Al2O3 / SiC, and TiO2 / SiO2, with ZrO2 / Y2O3 being the most preferred. ZrO2 provides high-temperature structural stability, while Y2O3 inhibits the phase transformation of ZrO2 and toughens it. The two are uniformly dispersed in the organosilicon resin, increasing the overall temperature resistance of the coating to 1000℃.

[0014] Preferably, the aerogel insulation layer is any one of nano-silicon carbide aerogel insulation layer, nano-silica aerogel insulation layer, or modified silicon carbide aerogel insulation layer. Through the microporous structure design of the aerogel, it effectively blocks instantaneous heat radiation and heat conduction at 2300℃, improves heat reflectivity, reduces heat absorption, and slows down heat diffusion, thereby reducing the temperature rise rate of the substrate surface by 75% and achieving highly efficient protection against extreme thermal shock.

[0015] Preferably, the modified silicon carbide aerogel is prepared by the following method: 10 wt% of nano-TiO2 with a particle size of 20 nm is ultrasonically dispersed and mixed with a silicon carbide precursor solution, gelled at 40-60 °C under catalysis, and aged at a constant temperature for 24-72 hours to form a wet gel; the gel is surface modified with an ethanol solution (pH=4-5) of KH-560 silane coupling agent at 50-70 °C for 24-48 hours, and dried at normal pressure by slowly increasing the temperature from 40 °C to 120-150 °C through programmed temperature rise to obtain the final modified silicon carbide aerogel with a nanoporous structure.

[0016] Another object of the present invention is to provide a method for applying a gradient temperature-resistant coating system, comprising the following steps:

[0017] (1) Substrate pretreatment: The coating substrate is sandblasted to remove oxide scale and oil stains, then ultrasonically cleaned with acetone to degrease, and dried for later use;

[0018] (2) Preparation of the base layer: The substrate after the pretreatment in step (1) is immersed in the chemical conversion solution to react and a dense chemical conversion film is formed on the surface of the substrate; the metal powder is uniformly dispersed in epoxy-organic silicone resin and sprayed onto the substrate with the chemical conversion film by air spraying process, and dried after spraying to obtain the base layer;

[0019] (3) Preparation of intermediate layer: The modified silicone resin coating is sprayed with air onto the bottom layer obtained in step (2), and then dried to obtain the intermediate layer;

[0020] (4) Preparation of outer layer: The aerogel is ultrasonically dispersed in an organic solvent to obtain an aerogel suspension, which is then sprayed onto the intermediate layer obtained in step (3) by air spraying and dried to obtain the outer layer.

[0021] Preferably, the substrate in step (1) is a high-temperature alloy. In this invention, GH4169 high-temperature alloy is selected as the substrate for experimental testing.

[0022] Preferably, the thickness of the chemical conversion film in step (2) is 5 μm, and the thickness of the bottom layer is 12-15 μm.

[0023] Preferably, the epoxy-organic silicone resin in step (2) is obtained by physically blending bisphenol type epoxy resin with phenyl organic silicone resin or methyl phenyl organic silicone resin at a mass ratio of 1:3.

[0024] Preferably, the thickness of the intermediate layer in step (3) is 25-30 μm.

[0025] Preferably, the thickness of the outer layer in step (4) is 8-10 μm.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. The coating system of this invention adopts a gradient design structure and synergy of each component to achieve a breakthrough in dual-temperature protection. Under thermal shock at 2300℃, the surface temperature of the coating rises by less than 500℃, with no cracking or peeling. Moreover, after 1000 hours of service at 1000℃, the resin carbon residue rate is greater than 30%, and the coating density decays by less than 10%. Its performance is far superior to traditional organosilicon coatings, and the overall lifespan of the coating is extended by 2-3 times.

[0028] 2. The bottom layer of the coating of this invention adopts a composite structure of chemical conversion film and metal primer. By synergistically using the anchoring effect of chemical conversion film and the physical isolation of metal primer, the bonding strength between the coating and the substrate is improved to ≥0 level, the interfacial bonding force under high temperature cycling is strengthened, the interlayer peeling caused by thermal shock is suppressed, the peeling rate is <5%, and the interlayer mechanical stability of the gradient temperature resistant coating is improved.

[0029] 3. The intermediate layer of the coating of this invention is made of ceramic filler modified organosilicon resin. Through the phase change regulation of ceramic filler and the synergistic effect of the flexibility of organosilicon resin, the coating structure stability at a long-term high temperature of 1000℃ is achieved, which solves the technical defects of traditional organosilicon coatings such as aging cracking and density reduction.

[0030] 4. The coating of this invention uses an aerogel heat insulation layer as the outer layer of the coating. The porous network structure of the aerogel can block instantaneous heat radiation at ultra-high temperature of 2300℃, reduce heat absorption, delay heat diffusion, reduce the heating rate of the substrate surface by 75%, and the coating reflectivity is >90% and thermal conductivity is <0.1W / (m・K), thus achieving safe protection of the substrate under extreme thermal shock.

[0031] 5. The gradient temperature-resistant coating system of this invention solves the core problems of dual-temperature domain protection cracking, interlayer failure, and poor structural durability through the functional synergy of strong bonding in the bottom layer, stable temperature in the middle layer, and strong reflection in the top layer. It can be applied to coating application scenarios with instantaneous ultra-high temperature and long-term medium-high temperature alternating service, such as aerospace, energy equipment, missile reentry, and industrial furnace lining. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a surface SEM image of the coating prepared in Example 3 of the present invention;

[0034] Figure 2 This is a surface SEM image of the coating prepared in Example 3 of the present invention after high-temperature oxidation. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. In the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0036] A gradient temperature-resistant coating system includes a three-layer structure: a base layer, an intermediate layer, and an outer layer. The base layer consists of a chemical conversion film and a metallic powder primer; the intermediate layer is a modified silicone resin layer; and the outer layer is an aerogel insulation layer.

[0037] It should be noted that the chemical conversion membrane can be any one of chromate conversion membrane or titanate conversion membrane, or other chemical conversion membranes with equivalent effects can be selected. In order to verify the effect, this invention selects chromate conversion membrane and commercially available chromate conversion solution, product model C3036.

[0038] It should be noted that the metallic powder primer includes aluminum powder and zinc-aluminum alloy primer. The metallic powder can be spherical or flake-shaped. In order to verify the technical effect of metallic powder of different shapes, the embodiments of the present invention preferably use spherical aluminum powder and flake-shaped aluminum powder for experimental verification. In addition to the effect of aluminum powder verified by the embodiments of the present invention, the present invention can also use other metallic powders or alloy powders with equivalent effects for replacement.

[0039] It should be noted that the modified organosilicon resin used in this invention is prepared by the following method:

[0040] ZrO2 / Y2O3 ceramic fillers with a particle size of 1-3 μm and a mass ratio of 9:1 were ball-milled for 2 hours. The mixed ceramic powder was placed in a forced-air drying oven and dried at 100℃ for 4 hours to remove the moisture from the raw materials. The dried ceramic fillers were slowly added in batches at a mass percentage of 50% to a methylphenyl organosilicon resin with a solid content of 65%. During the addition process, the mixture was continuously stirred at a low speed of 300 rpm until the powder was completely wetted and no dry powder floated. After all the fillers were added, the speed was increased to 2000 rpm and the mixture was stirred at high speed for 30 minutes. The mixture was then ultrasonically dispersed at 20 kHz for 10 minutes to obtain modified organosilicon resin coating No. 1.

[0041] It should be noted that the other modified silicone resin layer used in this invention is prepared by the following method:

[0042] ZrO2 / Y2O3 ceramic fillers with a particle size of 0.5-2μm and a mass ratio of 8:2 were ball-milled for 2 hours. The mixed ceramic powder was placed in a forced-air drying oven and dried at 110℃ for 3 hours to remove the moisture from the raw materials. The dried ceramic fillers were slowly added in batches at a mass percentage of 55% to methylphenyl silicone resin with a solid content of 65%. During the addition process, the mixture was continuously stirred at a low speed of 400 rpm until the powder was completely wetted and no dry powder floated. After all the fillers were added, the speed was increased to 2000 rpm and the mixture was stirred at high speed for 30 minutes. The mixture was then ultrasonically dispersed at 20kHz for 10 minutes to obtain modified silicone resin coating No. 2.

[0043] It should be noted that the other modified silicone resin layer used in this invention is prepared by the following method:

[0044] Al2O3 / SiC ceramic fillers with a particle size of 0.5-2μm and a mass ratio of 8:2 were ball-milled for 2 hours. The mixed ceramic powder was placed in a forced-air drying oven and dried at 120℃ for 2 hours to remove the moisture from the raw materials. The dried ceramic fillers were slowly added in batches at a mass percentage of 55% to methylphenyl organosilicon resin with a solid content of 65%. During the addition process, the mixture was continuously stirred at a low speed of 500 rpm until the powder was completely wetted and no dry powder floated. After all the fillers were added, the speed was increased to 2000 rpm and the mixture was stirred at high speed for 30 minutes. The mixture was then ultrasonically dispersed at 20kHz for 10 minutes to obtain modified organosilicon resin coating No. 3.

[0045] It should be noted that the other modified silicone resin layer used in this invention is prepared by the following method:

[0046] TiO2 / SiO2 ceramic fillers with a particle size of 0.5-2μm and a mass ratio of 8:2 were mixed and ball-milled for 2 hours. The mixed ceramic powder was placed in a forced-air drying oven and dried at 120℃ for 2 hours to remove the moisture from the raw materials. The dried ceramic fillers were slowly added in batches at a mass percentage of 55% to methylphenyl organosilicon resin with a solid content of 65%. During the addition process, the mixture was continuously stirred at a low speed of 500 rpm until the powder was completely wetted and no dry powder floated. After all the fillers were added, the speed was increased to 2000 rpm and the mixture was stirred at high speed for 30 minutes. The mixture was then ultrasonically dispersed at 20kHz for 10 minutes to obtain modified organosilicon resin coating #4.

[0047] It should be noted that the aerogel insulation layer is any one of the following: nano-silicon carbide aerogel insulation layer, nano-silica aerogel insulation layer, and modified silicon carbide aerogel insulation layer; wherein the modified silicon carbide aerogel is prepared by the following method: 10wt% nano-TiO2 with a particle size of 20nm is ultrasonically dispersed and mixed with a silicon carbide precursor solution, gelled at 50℃ under catalysis, and aged at a constant temperature for 40 hours to form a wet gel; the gel is surface modified at 60℃ for 32 hours using an ethanol solution (pH=4-5) of KH-560 silane coupling agent, and dried at normal pressure by slowly increasing the temperature from 40℃ to 130℃ through programmed temperature rise to obtain the final modified silicon carbide aerogel with a nanoporous structure.

[0048] It should be noted that, in order to verify the application effect of the coating system of the present invention, GH4169 high-temperature alloy was selected as the coating substrate for the coating system effect verification test. The same type of substrate was used in all the embodiments described below.

[0049] Example 1

[0050] A method for applying a gradient temperature-resistant coating system includes the following steps:

[0051] (1) Substrate pretreatment: High-temperature alloy GH4169 was used as the coating substrate. The oxide scale and oil were removed by sandblasting, and then degreased by ultrasonic cleaning with acetone for 10 minutes. After drying, it was ready for use.

[0052] (2) Preparation of the base layer: The substrate after the pretreatment in step (1) is immersed in chromate conversion solution at 60℃ for 12 min to form a dense chemical conversion film with a thickness of 5 μm on the substrate surface; spherical aluminum powder with a particle size of 5-10 μm is uniformly dispersed in epoxy-silicone resin obtained by blending bisphenol epoxy resin and phenyl silicone resin at a mass ratio of 1:3. After uniform dispersion and mixing, it is sprayed onto the substrate with the chemical conversion film by air spraying process and baked at 80℃ for 30 min to obtain a 15 μm thick aluminum powder primer layer;

[0053] (3) Preparation of intermediate layer: The modified silicone resin coating No. 1 is sprayed with air onto the bottom layer obtained in step (2), and baked at 150°C for 60 min to obtain a 30 μm thick intermediate layer;

[0054] (4) Preparation of outer layer: The nano-silica aerogel with a particle size of 30-80nm and a porosity of 85% is ultrasonically dispersed in ethanol for 30min to obtain an aerogel suspension. The intermediate layer obtained in step (3) is sprayed by air spraying and dried at room temperature for 24h to form an outer layer with a thickness of 10μm.

[0055] Example 2

[0056] An application method for a gradient temperature-resistant coating system includes the following steps:

[0057] (1) Substrate pretreatment: High-temperature alloy GH4169 was used as the coating substrate. The oxide scale and oil were removed by sandblasting, and then degreased by ultrasonic cleaning with acetone for 10 minutes. After drying, it was ready for use.

[0058] (2) Preparation of the base layer: The substrate after the pretreatment in step (1) is immersed in chromate conversion solution at 60℃ and reacted for 12 min to form a dense chemical conversion film with a thickness of 5 μm on the substrate surface; spherical aluminum powder with a particle size of 5-10 μm is uniformly dispersed in epoxy-silicone resin obtained by blending bisphenol epoxy resin and methylphenyl silicone resin at a mass ratio of 1:3. After uniform dispersion and mixing, it is sprayed onto the substrate with the chemical conversion film by air spraying process and baked at 90℃ for 25 min to obtain a 12 μm thick aluminum powder primer layer;

[0059] (3) Preparation of intermediate layer: The modified silicone resin coating No. 2 is sprayed with air onto the bottom layer obtained in step (2), and baked at 160°C for 50 min to obtain a 25 μm thick intermediate layer;

[0060] (4) Preparation of outer layer: The nano-silicon carbide aerogel with a particle size of 30-80nm and a porosity of 85% is ultrasonically dispersed in isopropanol for 40min to obtain an aerogel suspension. The intermediate layer obtained in step (3) is sprayed by air spraying and baked at 60℃ for 12h to form an outer layer with a thickness of 8μm.

[0061] Example 3

[0062] An application method for a gradient temperature-resistant coating system includes the following steps:

[0063] (1) Substrate pretreatment: High-temperature alloy GH4169 was used as the coating substrate. The oxide scale and oil were removed by sandblasting, and then degreased by ultrasonic cleaning with acetone for 10 minutes. After drying, it was ready for use.

[0064] (2) Preparation of the base layer: The substrate after the pretreatment in step (1) is immersed in chromate conversion solution at 60℃ and reacted for 12 min to form a dense chemical conversion film with a thickness of 5 μm on the substrate surface; flaky aluminum powder with a thickness-to-diameter ratio of 50:1 and a particle size of 10 μm is uniformly dispersed in epoxy-silicone resin obtained by blending bisphenol epoxy resin and methylphenyl silicone resin at a mass ratio of 1:3. After uniform dispersion and mixing, it is sprayed onto the substrate with the chemical conversion film by air spraying process and baked at 90℃ for 25 min to obtain a 12 μm thick aluminum powder primer layer;

[0065] (3) Preparation of intermediate layer: The modified silicone resin coating No. 2 is sprayed with air onto the bottom layer obtained in step (2), and baked at 160°C for 50 min to obtain a 25 μm thick intermediate layer;

[0066] (4) Preparation of outer layer: Modified silicon carbide aerogel with a particle size of 30-80nm and a porosity of 85% is ultrasonically dispersed in ethanol for 40min to obtain an aerogel suspension. The intermediate layer obtained in step (3) is sprayed by air spraying and baked at 60℃ for 12h to form an outer layer with a thickness of 8μm.

[0067] Example 4

[0068] An application method for a gradient temperature-resistant coating system includes the following steps:

[0069] (1) Substrate pretreatment: High-temperature alloy GH4169 was used as the coating substrate. The oxide scale and oil were removed by sandblasting, and then degreased by ultrasonic cleaning with acetone for 10 minutes. After drying, it was ready for use.

[0070] (2) Preparation of the base layer: The substrate after the pretreatment in step (1) is immersed in chromate conversion solution at 60℃ and reacted for 12 min to form a dense chemical conversion film with a thickness of 5 μm on the substrate surface; flaky zinc-aluminum alloy powder with a thickness-to-diameter ratio of 50:1 and a particle size of 10 μm is uniformly dispersed in epoxy-silicone resin obtained by blending bisphenol epoxy resin and phenyl silicone resin at a mass ratio of 1:3. After uniform dispersion and mixing, it is sprayed onto the substrate with the chemical conversion film by air spraying process and baked at 90℃ for 25 min to obtain a 13 μm thick aluminum powder primer layer;

[0071] (3) Preparation of intermediate layer: The modified silicone resin coating No. 3 is sprayed with air onto the bottom layer obtained in step (2), and baked at 160°C for 50 min to obtain an intermediate layer with a thickness of 27 μm;

[0072] (4) Preparation of outer layer: Modified silicon carbide aerogel with a particle size of 30-80nm and a porosity of 85% is ultrasonically dispersed in ethanol for 40min to obtain an aerogel suspension. The intermediate layer obtained in step (3) is sprayed by air spraying and baked at 60℃ for 12h to form an outer layer with a thickness of 9μm.

[0073] Example 5

[0074] An application method for a gradient temperature-resistant coating system includes the following steps:

[0075] (1) Substrate pretreatment: High-temperature alloy GH4169 was used as the coating substrate. The oxide scale and oil were removed by sandblasting, and then degreased by ultrasonic cleaning with acetone for 10 minutes. After drying, it was ready for use.

[0076] (2) Preparation of the base layer: The substrate after the pretreatment in step (1) is immersed in chromate conversion solution at 60℃ and reacted for 12 min to form a dense chemical conversion film with a thickness of 5 μm on the substrate surface; spherical zinc-aluminum powder with a particle size of 5-10 μm is uniformly dispersed in epoxy-silicone resin obtained by blending bisphenol epoxy resin and phenyl silicone resin at a mass ratio of 1:3. After uniform dispersion and mixing, it is sprayed onto the substrate with the chemical conversion film by air spraying process and baked at 80℃ for 30 min to obtain a 15 μm thick aluminum powder primer layer;

[0077] (3) Preparation of intermediate layer: The modified silicone resin coating No. 4 is sprayed with air onto the bottom layer obtained in step (2), and baked at 150°C for 60 min to obtain a 30 μm thick intermediate layer;

[0078] (4) Preparation of outer layer: The modified silicon carbide aerogel insulation layer with a particle size of 30-80nm and a porosity of 85% is ultrasonically dispersed in ethanol for 30min to obtain an aerogel suspension. The intermediate layer obtained in step (3) is sprayed by air spraying and dried at room temperature for 24h to form an outer layer with a thickness of 10μm.

[0079] Comparative Example 1

[0080] An application method for a temperature-resistant coating system, compared with Example 3, uses a single-layer chemical conversion film as the bottom layer and removes the metal primer layer. The specific preparation includes the following steps:

[0081] (1) Substrate pretreatment: High-temperature alloy GH4169 was used as the coating substrate. The oxide scale and oil were removed by sandblasting, and then degreased by ultrasonic cleaning with acetone for 10 minutes. After drying, it was ready for use.

[0082] (2) Preparation of the bottom layer: The substrate after the pretreatment in step (1) is immersed in chromate conversion solution at 60℃ for 12 min to form a dense chemical conversion film with a thickness of 5 μm on the substrate surface to obtain the bottom layer;

[0083] (3) Preparation of intermediate layer: The modified silicone resin coating No. 2 is sprayed with air onto the bottom layer obtained in step (2), and baked at 160°C for 50 min to obtain a 25 μm thick intermediate layer;

[0084] (4) Preparation of outer layer: Modified silicon carbide aerogel with a particle size of 30-80nm and a porosity of 85% is ultrasonically dispersed in ethanol for 40min to obtain an aerogel suspension. The intermediate layer obtained in step (3) is sprayed by air spraying and baked at 60℃ for 12h to form an outer layer with a thickness of 8μm.

[0085] Comparative Example 2

[0086] An application method for a temperature-resistant coating system, compared with Example 3, uses a single-layer metallic primer layer as the base layer and removes the chemical conversion film, specifically including the following steps:

[0087] (1) Substrate pretreatment: High-temperature alloy GH4169 was used as the coating substrate. The oxide scale and oil were removed by sandblasting, and then degreased by ultrasonic cleaning with acetone for 10 minutes. After drying, it was ready for use.

[0088] (2) Preparation of the base layer: Spherical aluminum powder with a particle size of 5-10 μm is uniformly dispersed in epoxy-silicone resin obtained by blending bisphenol epoxy resin and methylphenyl silicone resin at a mass ratio of 1:3. After uniform dispersion and mixing, it is sprayed onto the substrate treated in step (1) by air spraying process. The coating is baked at 90℃ for 25 min to obtain a 12 μm thick aluminum powder base coat layer.

[0089] (3) Preparation of intermediate layer: The modified silicone resin coating No. 2 is sprayed with air onto the bottom layer obtained in step (2), and baked at 160°C for 50 min to obtain a 25 μm thick intermediate layer;

[0090] (4) Preparation of outer layer: Modified silicon carbide aerogel with a particle size of 30-80nm and a porosity of 85% is ultrasonically dispersed in ethanol for 40min to obtain an aerogel suspension. The intermediate layer obtained in step (3) is sprayed by air spraying and baked at 60℃ for 12h to form an outer layer with a thickness of 8μm.

[0091] Comparative Example 3

[0092] An application method for a heat-resistant coating system, compared with Example 3, removes the underlying layer, i.e., removes step (2), specifically including the following steps:

[0093] (1) Substrate pretreatment: High-temperature alloy GH4169 was used as the coating substrate. The oxide scale and oil were removed by sandblasting, and then degreased by ultrasonic cleaning with acetone for 10 minutes. After drying, it was ready for use.

[0094] (2) Preparation of the base layer: The modified silicone resin coating No. 2 was sprayed onto the pretreated substrate by air spraying and baked at 160℃ for 50 min to obtain a 25μm thick base layer;

[0095] (3) Preparation of outer layer: Modified silicon carbide aerogel with a particle size of 30-80nm and a porosity of 85% is ultrasonically dispersed in ethanol for 40min to obtain an aerogel suspension. The suspension is then sprayed onto the bottom layer obtained in step (2) by air spraying and baked at 60℃ for 12h to form an outer layer with a thickness of 8μm.

[0096] Comparative Example 4

[0097] An application method for a heat-resistant coating system, compared with Example 3, is to replace the modified organosilicon resin coating 2# with the traditional methylphenyl organosilicon resin coating, and the remaining preparation steps are the same as in Example 3.

[0098] Comparative Example 5

[0099] An application method for a heat-resistant coating system, compared with Example 3, is to replace the modified organosilicon resin coating 2# with a pure ZrO2 coating, while the remaining preparation steps are the same as in Example 3.

[0100] Comparative Example 6

[0101] An application method for a heat-resistant coating system, compared with Example 3, removes the outer layer in step (4), while the other preparation steps are the same as in Example 3.

[0102] Comparative Example 7

[0103] An application method for a temperature-resistant coating system, compared with Example 3, is to replace the modified organosilicon resin coating 2# with the traditional methyl phenyl organosilicon resin coating, delete the outer layer in step (4), and the other preparation steps are the same as in Example 3.

[0104] Comparative Example 8

[0105] An application method for a heat-resistant coating system, compared with Example 3, is to replace the modified organosilicon resin coating 2# with pure ZrO2 coating, delete the outer layer in step (4), and the other preparation steps are the same as in Example 3.

[0106] Test case

[0107] The coatings prepared in the above embodiments and comparative examples were subjected to application performance testing. The specific test content and methods are as follows:

[0108] Microscopic morphology characterization: The coating prepared in Example 3 was subjected to surface scanning electron microscopy (SEM) testing, and the surface SEM of the coating after high-temperature oxidation was also tested.

[0109] Adhesion: Tested according to GB / T 9286-2021 "Cross-cut test for paints and varnishes"; use a cross-cut tester to cut a grid of squares with a spacing of 1mm or 2mm on the coating surface, penetrating to the substrate. After cleaning, apply pressure-sensitive adhesive tape tightly to the grid area and quickly peel it off at a 60° angle. Observe the area of ​​the coating that the tape has peeled off according to the standard's grading (grades 0 to 5). Grade 0 represents a completely smooth coating edge with no squares peeling off, indicating excellent coating adhesion.

[0110] Temperature resistance test: According to GJB·323B-2018 standard, the performance of the coating is evaluated by oxy-acetylene ablation test: After the coating sample is subjected to a severe thermal shock cycle of 5 minutes from the highest flame temperature of about 2300℃ to room temperature, the coating cross section and surface morphology are observed by using an optical microscope or scanning electron microscope to detect the presence of microcracks, whether the interface with the substrate is intact, characterize the integrity of the coating, calculate the weight loss rate, and test the thermal radiation reflectivity.

[0111] The method for calculating the weight loss rate is as follows: with an initial mass of M1, gently sweep away any loose dust that may be attached to the surface with a soft brush, weigh the sample again accurately, record the final mass M2, and calculate the weight loss rate = (M1-M2) / M1×100%.

[0112] Thermal reflectivity: Tested according to ASTM E903-20, "Test method for measuring the solar absorptivity, reflectivity and transmittance of materials using an integrating sphere". The spectral reflectivity R(λ) of the coating surface was measured within the wavelength range of 250 nm to 2500 nm, using a standard white plate (barium sulfate pellet) as a reference. The spectral reflectivity was weighted and integrated according to the formula in the standard to obtain the solar reflectance or to directly report the hemispherical reflectivity within the characteristic wavelength range of blackbody radiation at a specific temperature.

[0113] Thermal shock test: Referring to GB / T 30873-2014 "Test Method for Thermal Shock Resistance of Refractory Materials", the sample is placed in a muffle furnace preheated to 1000℃ and held for 5 minutes to allow the entire sample to reach the test temperature. The sample is then removed and cooled in still air at 25℃ for 5 minutes, completing one cycle. The above steps are repeated until cracks appear in the coating, and the number of cycles is recorded.

[0114] Specific test results are as follows: Figure 1 , Figure 2 As shown in Table 1. Figure 2 This is the high-temperature oxidized surface state of the coating in Embodiment 3 of the present invention after undergoing a thermal cycle of 1000℃ to room temperature. Figure 1 , Figure 2 The scanning electron microscope (SEM) images show that the surface conditions of both surfaces did not change significantly. Figure 2The surface electron microscopy image shows that the coating prepared by the present invention does not show obvious cracks or peeling, indicating that the coating prepared by the present invention has good high temperature resistance, heat resistance and thermal stability under extreme thermal shock environment, ensuring the long-term stability and integrity of the coating.

[0115] From the adhesion, weight loss rate, and integrity test data in Table 1, it can be concluded that the gradient temperature-resistant coatings prepared in Examples 1-5 of this invention have strong interfacial bonding strength under high-temperature cycling. The adhesion test data from Comparative Examples 1-3 show that traditional substrates such as single chemical oxide layers or pure aluminum powder coatings have poor interfacial chemical properties. The weight loss rate test data shows that the coatings prepared in the examples of this invention have a weight loss rate of <5% after high-temperature cycling, while the weight loss rate of the comparative examples is much higher than that of the examples. This further illustrates that the coating of this invention utilizes the anchoring effect of a chemical conversion film to bond with the metal powder substrate. The synergistic effect of the barrier strengthens the interfacial bonding force under high-temperature cycling, inhibits interlayer delamination caused by thermal shock, and maintains the mechanical stability of the interlayer. As can be seen from the integrity data of Comparative Examples 3 and 6, if the heat-resistant coating only has a double-layer structure and lacks the structural design of a composite bottom layer or an outer aerogel insulation layer, the coating will show varying degrees of cracking and peeling after several high-temperature thermal cycles. This shows that the three-layer structure of the gradient heat-resistant coating of this invention is complementary and indispensable. Through the gradient design of the three-layer structure, the initiation and propagation of cracks under thermal shock cycling are inhibited, and the durability of the coating is improved.

[0116] As shown in Table 1, the gradient temperature-resistant coating prepared in the embodiments of the present invention can withstand more than 100 thermal shock cycles under long-term high-temperature conditions without cracking or peeling. In contrast, the coatings designed in the comparative examples all had fewer than 60 cycles. The test data from Comparative Examples 1-2 and 4-5 show that even with a three-layer structure design, the technical performance of the coating using a traditional single bottom layer or silicone resin is significantly worse than that of the embodiments. The test data from Comparative Examples 4 and 5 show that the temperature resistance of the silicone resin coating without ceramic filler modification is significantly reduced. This is because ordinary silicone resin will gradually age and degrade under long-term heat at 1000℃, resulting in decreased coating density and shortened temperature resistance life. The test results from Comparative Example 6 show that if the outer layer lacks an aerogel insulation layer, heat is easily conducted to the substrate under instantaneous high temperatures, and the instantaneous reflectivity continuously decreases, failing to effectively block heat flow and reducing the heat resistance and lifespan of the coating.

[0117]

[0118] In summary, this invention employs a gradient structure design with a strong bottom layer, a stable middle layer, and a strong outer layer. Specifically, it uses a composite structure of a chemical conversion film and a metallic primer as the bottom layer of the coating, ceramic filler-modified silicone resin as the middle layer, and an aerogel insulation layer as the outer layer. This strengthens the interfacial bonding under high-temperature cycling, suppresses interlayer delamination caused by thermal shock, and achieves structural stability under long-term high temperatures. At the same time, it blocks instantaneous heat radiation and heat conduction at 2300℃, breaking through the performance barrier of dual-temperature protection and achieving full-life protection under extreme working conditions.

[0119] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention.

Claims

1. A gradient temperature resistant coating system, characterized in that, The system comprises a three-layer structure of a bottom layer, an intermediate layer and an outer layer, the bottom layer is composed of a chemical conversion film and a metal powder primer; the intermediate layer is a modified silicone resin layer; the outer layer is an aerogel thermal insulation layer; wherein the chemical conversion film is any one of a chromate conversion film and a titanate conversion film; the metal powder primer comprises an aluminum powder and a zinc-aluminum alloy powder primer; the modified silicone resin layer is obtained by spraying a modified silicone resin coating, the modified silicone resin coating is obtained by adding ceramic fillers to a silicone resin and then performing high-speed stirring and ultrasonic dispersion; the aerogel thermal insulation layer is any one of a nano-silicon carbide aerogel thermal insulation layer, a nano-silicon oxide aerogel thermal insulation layer and a modified silicon carbide aerogel thermal insulation layer.

2. The gradient temperature resistant coating system of claim 1, wherein, The ceramic fillers are any one of ZrO2 / Y2O3, Al2O3 / SiC and TiO2 / SiO2.

3. A method of applying the gradient temperature resistant coating system of any of claims 1-2, characterized in that, The method comprises the following steps: (1) substrate pretreatment: the coating substrate is subjected to sand blasting treatment to remove oxide scale and oil stains, and then is subjected to ultrasonic cleaning with acetone for degreasing, and is dried for standby; (2) preparation of the bottom layer: the substrate pretreated in step (1) is immersed in a chemical conversion liquid for reaction, so as to form a dense chemical conversion film on the surface of the substrate; metal powder is uniformly dispersed in epoxy-silicone resin, and is sprayed on the substrate with the chemical conversion film by an air spraying process, and the bottom layer is obtained after drying; (3) preparation of the intermediate layer: the modified silicone resin coating is sprayed on the bottom layer obtained in step (2) by air spraying, and the intermediate layer is obtained after drying; (4) preparation of the outer layer: aerogel is dispersed in an organic solvent to obtain an aerogel suspension, and the outer layer is obtained by air spraying the intermediate layer obtained in step (3) and drying.

4. The method of application of a graded temperature resistant coating system according to claim 3, characterized in that, The thickness of the chemical conversion film in step (2) is 5 μm, and the thickness of the bottom layer is 12-15 μm.

5. The method of application of a graded temperature resistant coating system according to claim 3, characterized in that, The thickness of the intermediate layer in step (3) is 25-30 μm.

6. The method of application of a graded temperature resistant coating system according to claim 3, characterized in that, The thickness of the outer layer in step (4) is 8-10 μm.

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