Thermal barrier coating resistant to high-temperature gradient change and preparation method thereof

Abstract

The invention discloses a thermal barrier coating resistant to high-temperature gradient change and a preparation method thereof, and relates to the technical field of high-performance coatings, the thermal barrier coating sequentially comprises a base bonding layer, a buffer transition layer, a thermal insulation layer and a surface closing layer from bottom to top, and the thermal barrier coating is prepared based on the layered structure. According to the invention, a multi-layer structure is arranged, and a heat-resistant filler and a composite bonding system are reasonably configured in each layer, so that the coating forms a thermal expansion characteristic and a structural gradient in step-by-step transition from a matrix to the surface, thermal stress generated in a cooling and heating alternation process can be effectively dispersed, and interface cracking and peeling risks are reduced; meanwhile, a low-heat-conduction structure constructed in the heat insulation layer can obviously slow down the transfer of heat to the matrix direction, and the surface sealing layer improves the oxidation resistance and medium infiltration resistance of the coating, so that the coating can still keep stable adhesion and good heat insulation effect under the conditions of high temperature and rapid temperature change; the material is suitable for long-term use of automobile exhaust systems and other high-temperature parts.

Description

Technical Field

[0001] This invention relates to the field of high-performance coatings technology, specifically to a thermal barrier coating resistant to high-temperature gradient changes and its preparation method. Background Technology

[0002] As automotive engines evolve towards higher power density and higher thermal efficiency, components such as exhaust manifolds, turbocharger housings, exhaust pipe tips, and high-temperature protective parts are subjected to severe temperature fluctuations during operation. This is especially true during cold starts, rapid acceleration, high-load operation, and engine shutdown cooling, where component surface temperatures can change dramatically in a short period, creating significant temperature gradients. To reduce damage to the metal substrate from high temperatures and minimize heat transfer to surrounding structures, heat-resistant or heat-insulating coatings are typically applied to the surfaces of these components. However, existing thermal barrier coatings often employ single-layer or simple multi-layer structures with significantly different coefficients of thermal expansion compared to the metal substrate. During repeated thermal cycles, these coatings are prone to generating substantial thermal stress, leading to cracking, peeling, or powdering, and resulting in a limited lifespan. Furthermore, while some coatings exhibit good high-temperature resistance, their dense internal structure and short heat conduction paths make them insufficiently buffered against rapidly changing temperature gradients, making it difficult to simultaneously achieve adhesion, heat insulation, and thermal shock resistance. Therefore, there is an urgent need to provide a thermal barrier coating and its preparation method that can maintain structural stability under rapid temperature changes, have high thermal insulation capacity, and are not prone to cracking and peeling, so as to meet the requirements of long-term reliable operation of high-temperature automotive components. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a thermal barrier coating resistant to high-temperature gradient changes and its preparation method, thereby solving the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a thermal barrier coating resistant to high temperature gradient changes, wherein the thermal barrier coating comprises, from bottom to top, a base bonding layer, a buffer transition layer, a heat insulation layer and a surface sealing layer; in, The base bonding layer comprises the following components in parts by weight: The ingredients are: 20-35 parts silicone resin, 25-45 parts aluminum powder, 10-25 parts nickel powder, 8-20 parts alumina powder, 5-12 parts talc powder, 10-22 parts silica sol, 0.5-2 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 15-40 parts solvent. The buffer transition layer comprises the following components in parts by mass: The ingredients are: 18-30 parts silicone resin, 20-35 parts alumina powder, 15-30 parts zirconium oxide powder, 10-25 parts mullite powder, 5-15 parts mica powder, 8-20 parts silica sol, 3-10 parts glass powder, 0.5-2 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 10-35 parts solvent. The insulation layer comprises the following components in parts by weight: Zirconia powder 35-60 parts, alumina powder 10-25 parts, hollow ceramic microspheres 15-35 parts, diatomaceous earth powder 5-15 parts, mullite powder 8-18 parts, silica sol 10-25 parts, silicone resin 8-18 parts, glass powder 2-8 parts, dispersant 0.5-2 parts, defoamer 0.2-1 part, leveling agent 0.2-1 part, and solvent 10-30 parts; The surface sealing layer comprises the following components in parts by weight: The ingredients are: 20-35 parts silicone resin, 15-30 parts silica sol, 10-20 parts alumina powder, 8-18 parts zirconium oxide powder, 5-12 parts mica powder, 5-15 parts glass powder, 2-8 parts titanium dioxide, 0.3-1.5 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 15-35 parts solvent.

[0005] To further optimize this technical solution, the preparation process of the base bonding layer includes: First, add silicone resin, solvent, dispersant and defoamer to a stirring container and premix at a speed of 300-800 r / min for 5-15 min to form an initial liquid phase system; Then slowly add alumina powder and talc powder, and increase the stirring speed to 800-1500 r / min, and disperse for 20-40 min; Add aluminum powder and nickel powder and continue stirring for 10-30 minutes to ensure that the metal powder and ceramic powder are evenly distributed in the resin system. After the slurry is evenly dispersed, silica sol and leveling agent are added, and solvent is added to adjust the construction viscosity, finally obtaining the base layer coating.

[0006] To further optimize this technical solution, the preparation process of the buffer transition layer includes: First, add silicone resin, silica sol, solvent, and dispersant to a dispersion vessel and stir at 500-1000 r / min for 10-20 min to form a composite binder phase; Subsequently, alumina powder, zirconium oxide powder and mullite powder are added sequentially and dispersed at a high speed of 800-1500 r / min, with the dispersion time preferably being 20-50 min; After the mixture is evenly dispersed, add mica powder and glass powder, and continue mixing at a speed of 500-1000 r / min for 10-20 min. Finally, defoamer, leveling agent, and solvent are added and adjusted to a viscosity suitable for application to obtain a buffer transition layer coating.

[0007] To further optimize this technical solution, the preparation process of the heat insulation layer includes: First, silica sol, silicone resin, solvent and dispersant are added to a mixing container and stirred to form a liquid phase binder matrix; Subsequently, zirconium oxide powder, alumina powder, mullite powder and diatomaceous earth powder are added in sequence and dispersed at 800-1600 r / min for 20-40 min to form a uniform thermal insulation skeleton slurry. Then reduce the rotation speed to 300-600 r / min, slowly add hollow ceramic microspheres and glass powder, and continue mixing for 5-15 min to ensure that the hollow ceramic microspheres are evenly dispersed without significant breakage; Finally, defoamer, leveling agent and solvent are added, the viscosity is adjusted and then filtered to obtain the heat insulation coating.

[0008] To further optimize this technical solution, the preparation process of the surface sealing layer includes: First, mix silicone resin, silica sol, solvent and dispersant to form a basic liquid phase, then add alumina powder, zirconium oxide powder, titanium dioxide and glass powder in sequence, and disperse at a medium-high speed of 500-1000 r / min for 20-40 min. Then add mica powder and continue stirring at a low speed of 300-500 r / min for 5-15 min to maintain the morphology of the flaky particles; Finally, defoamer and leveling agent are added to adjust the viscosity, and the surface sealing layer coating is obtained after filtration.

[0009] To further optimize this technical solution, the coating uses a composite bonding system of silicone resin and silica sol. The silicone resin is a high-temperature resistant organosilicon resin with a temperature resistance of not less than 500℃ and a solid content of 40% to 70%. The silica sol is an aqueous or alcoholic silica dispersion system with a particle size of 10 to 50 nm and a solid content of 20% to 40%. The mass ratio of the silicone resin to the silica sol is 0.5:1 to 2:1.

[0010] To further optimize this technical solution, the glass powder used in the coating is low-softening-temperature inorganic glass particles with a softening temperature of 450–750℃, an average particle size of 1–30 μm, and a coefficient of thermal expansion of 4 × 10⁻⁶. -6 ~9×10 -6 / ℃; the glass powder includes borosilicate glass or aluminosilicate glass systems.

[0011] To further optimize this technical solution, the hollow ceramic microspheres in the heat insulation layer are ceramic particles with a closed hollow structure. Their outer shell is made of alumina or alumina-silicon composite ceramic, with an average particle size of 10-80 μm, a shell thickness of 1-8 μm, an apparent density of 0.2-0.8 g / cm³, and the cavity volume accounts for 60%-90% of the total particle volume.

[0012] To further optimize this technical solution, the zirconium powder used in the heat insulation layer is stabilized zirconium oxide particles, and its stabilizer is yttrium oxide or magnesium oxide. The mass percentage of the stabilizer is 3% to 10%, the average particle size is 0.5 to 10 μm, the specific surface area is 1 to 10 m² / g, and the main crystal form is tetragonal or cubic phase.

[0013] A method for preparing a thermal barrier coating resistant to high temperature gradient changes, based on the above-mentioned thermal barrier coating, includes the following steps: S1. Pre-treat the substrate to be coated; S2. Apply and cure the base bonding layer on the substrate surface; S3. Apply and cure a buffer transition layer on the surface of the base bonding layer; S4. Apply and cure the heat insulation layer on the surface of the buffer transition layer; S5. Coating and forming a surface sealing layer on the surface of the insulation layer; S6. Perform staged heat treatment and performance stabilization treatment on the overall thermal barrier coating.

[0014] Compared with the prior art, the present invention provides a thermal barrier coating resistant to high temperature gradient changes and its preparation method, which has the following beneficial effects: This high-temperature gradient-resistant thermal barrier coating and its preparation method utilize a multi-layer structure consisting of a base bonding layer, a buffer transition layer, a heat insulation layer, and a surface sealing layer. By rationally configuring heat-resistant fillers and composite bonding systems in each layer, the coating achieves a progressively changing thermal expansion characteristic and structural gradient from the substrate to the surface. This effectively disperses thermal stress generated during alternating hot and cold periods, reducing the risk of interface cracking and peeling. Simultaneously, the low thermal conductivity structure constructed in the heat insulation layer significantly slows heat transfer towards the substrate, while the surface sealing layer enhances the coating's resistance to oxidation and media penetration. This allows the coating to maintain stable adhesion and excellent thermal insulation performance even under high-temperature and rapidly changing temperature conditions, making it suitable for long-term use in automotive exhaust systems and other high-temperature components. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0016] Figure 1 This is a schematic diagram of the layered structure of a thermal barrier coating resistant to high temperature gradient changes proposed in this invention. Detailed Implementation

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0019] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0020] Reference Figure 1 A thermal barrier coating resistant to high temperature gradient changes, wherein the thermal barrier coating comprises, from bottom to top, a base bonding layer, a buffer transition layer, a heat insulation layer and a surface sealing layer.

[0021] The base bonding layer comprises the following components in parts by weight: The ingredients are: 20-35 parts silicone resin, 25-45 parts aluminum powder, 10-25 parts nickel powder, 8-20 parts alumina powder, 5-12 parts talc powder, 10-22 parts silica sol, 0.5-2 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 15-40 parts solvent.

[0022] The base bonding layer is used for direct adhesion to the surface of metal substrates, suitable for high-temperature automotive parts substrates such as cast iron, stainless steel, heat-resistant steel, and nickel-based alloys. Silicone resin is used to form a heat-resistant bonding network, ensuring the coating maintains its basic structural stability at high temperatures. Powder and nickel powder are used to enhance heat-resistant adhesion and improve thermal compatibility with the metal substrate. Alumina powder is used to increase coating hardness and abrasion resistance. Talc powder is used to improve workability and help regulate thermal expansion behavior. Silica sol is used to enhance the stability of the inorganic skeleton. Dispersants, defoamers, and leveling agents are used to ensure uniform coating application. Solvents are used to adjust viscosity for easy spraying or brushing.

[0023] The buffer transition layer comprises the following components in parts by mass: The ingredients are: 18-30 parts silicone resin, 20-35 parts alumina powder, 15-30 parts zirconium oxide powder, 10-25 parts mullite powder, 5-15 parts mica powder, 8-20 parts silica sol, 3-10 parts glass powder, 0.5-2 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 10-35 parts solvent.

[0024] A buffer transition layer is placed between the base bonding layer and the insulation layer. Its main function is to absorb interlayer stress generated during thermal cycling, reducing the risk of cracking and peeling. Alumina powder and zirconium oxide powder together constitute the heat-resistant matrix. Mullite powder is used to improve high-temperature stability and thermal shock resistance. Mica powder helps to form a lamellar barrier structure, dispersing thermal stress during rapid temperature changes. Glass powder helps to improve the interparticle bonding state during subsequent curing and high-temperature use. Silicone resin and silica sol together provide organic-inorganic composite bonding ability, giving this layer both a certain degree of toughness and high-temperature stability.

[0025] The insulation layer comprises the following components in parts by weight: The ingredients are: 35-60 parts zirconium oxide powder, 10-25 parts alumina powder, 15-35 parts hollow ceramic microspheres, 5-15 parts diatomaceous earth powder, 8-18 parts mullite powder, 10-25 parts silica sol, 8-18 parts silicone resin, 2-8 parts glass powder, 0.5-2 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 10-30 parts solvent.

[0026] The thermal insulation layer is the core layer of the thermal barrier coating, primarily responsible for its thermal barrier function. This layer should minimize heat conduction and maintain structural stability under high-temperature gradient changes. Zirconia powder is the main thermal insulation and high-temperature resistant filler, suitable as the main body of the thermal barrier. Alumina powder is used to enhance structural strength and prevent the insulation layer from being too porous. Hollow ceramic microspheres can significantly increase the microporous structure within the layer and reduce the thermal conductivity rate. Diatomaceous earth powder further improves the thermal insulation effect and helps to construct low thermal conductivity paths. Mullite powder is used to improve thermal cycling stability. Silica sol and silicone resin together form a bonding network, fixing the thermal insulation particles and maintaining the integrity of the layer. Glass powder helps to improve the sintering bonding effect and surface density.

[0027] The surface sealing layer comprises the following components in parts by weight: The ingredients are: 20-35 parts silicone resin, 15-30 parts silica sol, 10-20 parts alumina powder, 8-18 parts zirconium oxide powder, 5-12 parts mica powder, 5-15 parts glass powder, 2-8 parts titanium dioxide, 0.3-1.5 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 15-35 parts solvent.

[0028] The outermost surface sealing layer serves to prevent media such as oxygen, water vapor, salt spray, and oil from penetrating the insulation layer, while also reducing pulverization and microcrack propagation caused by high-temperature airflow. Silicone resin and silica sol are used to form a dense, heat-resistant sealing film. Alumina powder and zirconium oxide powder improve surface heat resistance and abrasion resistance. Mica powder forms a sheet-like barrier structure, slowing the penetration of oxidizing media. Glass powder helps the surface layer form a more stable sealing state after heat treatment. Titanium dioxide improves weather resistance and surface uniformity.

[0029] The preparation process of the base bonding layer includes: First, add silicone resin, solvent, dispersant, and defoamer to a mixing container and premix at 300–800 rpm for 5–15 minutes to form an initial liquid phase system. Then, slowly add alumina powder and talc powder, and increase the stirring speed to 800–1500 rpm for 20–40 minutes. Next, add aluminum powder and nickel powder and continue stirring for 10–30 minutes to ensure that the metal powder and ceramic powder are evenly distributed in the resin system. After the slurry is evenly dispersed, add silica sol and leveling agent, and add solvent to adjust the application viscosity to finally obtain the base layer coating.

[0030] The preparation process of the buffer transition layer includes: First, silicone resin, silica sol, solvent, and dispersant are added to a dispersion vessel and stirred at 500–1000 rpm for 10–20 min to form a composite binder phase. Then, alumina powder, zirconium oxide powder, and mullite powder are added sequentially and dispersed at a high speed of 800–1500 rpm for a preferred dispersion time of 20–50 min. After uniform dispersion, mica powder and glass powder are added and mixed at 500–1000 rpm for another 10–20 min. Finally, defoamer, leveling agent, and solvent are added and the viscosity is adjusted to a suitable level for application to obtain a buffer transition layer coating.

[0031] The preparation process of the heat insulation layer includes: First, silica sol, silicone resin, solvent, and dispersant are added to a mixing container and stirred to form a liquid-phase binder matrix. Then, zirconium oxide powder, alumina powder, mullite powder, and diatomaceous earth powder are added sequentially and dispersed at 800–1600 r / min for 20–40 min to form a uniform heat-insulating skeleton slurry. Afterward, the rotation speed is reduced to 300–600 r / min, and hollow ceramic microspheres and glass powder are slowly added. Mixing continues for 5–15 min to ensure that the hollow ceramic microspheres are uniformly dispersed without significant breakage. Finally, defoamer, leveling agent, and solvent are added, the viscosity is adjusted, and the mixture is filtered to obtain the heat-insulating coating.

[0032] The preparation process of the surface sealing layer includes: First, silicone resin, silica sol, solvent, and dispersant are mixed to form a basic liquid phase. Then, alumina powder, zirconium oxide powder, titanium dioxide, and glass powder are added sequentially and dispersed at a medium-high speed of 500-1000 r / min for 20-40 min. Next, mica powder is added and stirred at a lower speed of 300-500 r / min for 5-15 min to maintain the morphology of the flaky particles. Finally, defoamer and leveling agent are added to adjust the viscosity, and the mixture is filtered to obtain a surface sealing layer coating.

[0033] The hollow ceramic microspheres in the insulation layer are preferably closed-cell hollow ceramic particles with an outer shell made of alumina or alumina-silicon composite ceramic. The average particle size is 10–80 μm, the shell thickness is 1–8 μm, the apparent density is 0.2–0.8 g / cm³, and the cavity volume accounts for 60%–90% of the total particle volume. The outer surface of the hollow ceramic microspheres is preferably treated with a silane coupling agent to form a stable inorganic-organic interface layer, thereby improving its dispersion stability in silicone resin or silica sol systems and reducing pore connectivity. This closed-cell hollow structure can form dispersed low-thermal-conductivity units within the coating, thereby reducing the rate of heat transfer to the substrate during rapid temperature changes and reducing thermal stress concentration caused by localized temperature differences.

[0034] The zirconia powder used in the heat insulation layer is preferably stabilized zirconia particles, with yttrium oxide or magnesium oxide as the stabilizer. The stabilizer content is 3% to 10% (mass percentage), the average particle size is 0.5 to 10 μm, the specific surface area is 1 to 10 m² / g, and the main crystal form is tetragonal or cubic phase. The zirconia powder is preferably prepared by spray granulation or mechanical ball milling to make the particles have an approximately spherical or obtuse-angled polyhedral structure, so as to improve the filler packing density and coating compactness. The stabilized zirconia has low thermal conductivity and high resistance to phase transformation under high temperature conditions, which can avoid volume expansion caused by crystal transformation, thereby improving the structural stability of the coating during repeated thermal cycling.

[0035] The glass powder used in the coating is low-softening-temperature inorganic glass particles with a softening temperature of 450–750°C, an average particle size of 1–30 μm, and a coefficient of thermal expansion of 4 × 10⁻⁶. -6 ~9×10 -6 / ℃; The glass powder is preferably a borosilicate glass or aluminosilicate glass system, which can partially soften and fill the gaps between particles during heat treatment or high-temperature use, thereby forming a continuous inorganic bonded phase; This bonded phase maintains the stability of the overall structure and does not form a completely dense molten layer, which can avoid overall cracking caused by thermal expansion mismatch and help improve the coating's resistance to peeling and gas penetration.

[0036] The coating uses a composite bonding system of silicone resin and silica sol. The silicone resin is a high-temperature resistant organosilicon resin with a temperature resistance rating of not less than 500℃ and a solid content of 40%–70%. The silica sol is an aqueous or alcoholic silica dispersion system with a particle size of 10–50 nm and a solid content of 20%–40%. The mass ratio of silicone resin to silica sol is 0.5:1 to 2:1. During the curing process, the organic components cross-link to form a flexible network, while the inorganic components form a rigid framework, thus constituting an organic-inorganic synergistic composite structure. This structure provides initial adhesion and toughness, maintains basic morphological stability at high temperatures, and absorbs thermal stress through local deformation of the organic phase during rapid temperature changes.

[0037] The mica powder used in the buffer transition layer is preferably natural or artificial mica with a sheet-like structure, having a sheet diameter of 20–150 μm, a thickness of 0.5–5 μm, and an aspect ratio of 10–80. The sheet-like particles are oriented and arranged along the plane of the coating during the coating process. This oriented structure forms a multi-layered barrier path within the layer, which can reduce the direct conduction of gas and heat. At the same time, during thermal cycling, it disperses local stress through micro-slippage between the sheet layers, thereby mitigating the interface stress concentration caused by the difference in thermal expansion between the base layer and the insulation layer.

[0038] The mullite powder used in the buffer transition layer and the heat insulation layer is preferably aluminosilicate ceramic particles with an Al2O3 content of 60% to 75%, an average particle size of 1 to 20 μm, a temperature resistance rating of not less than 1500℃, and an irregular blocky or short columnar morphology. Mullite has a low coefficient of thermal expansion and good thermal shock stability, which can maintain structural stability and reduce the tendency of crack propagation inside the coating during rapid changes in high temperature, thereby improving the durability of the entire thermal barrier system under repeated thermal cycling conditions.

[0039] A method for preparing a thermal barrier coating resistant to high temperature gradient changes, based on the above-mentioned thermal barrier coating, includes the following steps: S1. Pre-treat the substrate to be coated; The metal substrate of a high-temperature automotive component is selected as the object to be treated. The metal substrate is preferably cast iron, stainless steel, heat-resistant steel, or nickel-based alloy. First, the substrate surface is degreased and cleaned using an alkaline cleaning solution or industrial degreaser to remove surface oil, cutting fluid residue, and oxide deposits. The cleaning temperature is preferably 40–60°C, and the cleaning time is preferably 5–20 minutes. After cleaning, the surface is rinsed with deionized water until no obvious residual liquid remains. Subsequently, the substrate surface is roughened, preferably by sandblasting. The sandblasting medium is preferably brown corundum sand, quartz sand, or steel grit, and the blasting pressure is preferably 0.4–0.8 MPa. After treatment, the surface roughness Ra of the substrate reaches 3–12 μm. The roughened substrate is then purged with compressed air and dried at 80–120°C for 10–30 minutes to remove residual moisture and ensure good adhesion interface conditions.

[0040] S2. Apply and cure the base bonding layer on the substrate surface; The base coat coating is applied to the pretreated substrate surface by spraying, brushing, or rolling, preferably using air spraying or airless spraying. The wet film thickness of a single coat is preferably controlled at 20–60 μm. After spraying, allow it to stand and level for 5–15 minutes, then pre-bake at 80–150°C for 10–30 minutes to evaporate the solvent and form a preliminary adhesion layer. Depending on the designed thickness, 1–3 coats can be applied repeatedly, resulting in a dry film thickness of 30–120 μm for the base coat. After the base coat is applied, allow it to cure in stages at 180–300°C for 20–60 minutes to allow the silicone resin to undergo initial cross-linking, forming an inorganic network of silica sol, thereby constructing a base bonding structure on the substrate surface that combines adhesion and heat resistance.

[0041] S3. Apply and cure a buffer transition layer on the surface of the base bonding layer; After the base bonding layer has cured and cooled to room temperature, the buffer transition layer coating is applied to the surface of the base bonding layer. This layer is preferably applied using a multi-coat, thin-layer method, with each wet film thickness preferably 30–80 μm. After each coat, allow it to stand for 5–10 minutes to level, then pre-bake at 80–120°C for 10–20 minutes. Repeat the application 1–3 times to achieve a dry film thickness of 50–180 μm for the buffer transition layer. During this step, the continuity of interlayer adhesion should be controlled to avoid sagging, bubbles, or localized cracking caused by applying a thick coat all at once. After the buffer transition layer is applied, cure it at 200–350°C for 30–90 minutes to further cross-link the composite bonding system, forming a more stable particle bond between the glass powder and inorganic particles, thereby constructing a thermal expansion gradient transition zone.

[0042] S4. Apply and cure the heat insulation layer on the surface of the buffer transition layer; The heat insulation coating is applied to the surface of the cured buffer transition layer, preferably by spraying to form a uniform heat insulation layer. A multi-coat application process is used, with each wet film thickness preferably 40–100 μm. After each coat, pre-dry at 60–100°C for 5–15 minutes to gradually remove solvent and reduce internal stress. Repeat the application 2–5 times according to design requirements, so that the dry film thickness of the heat insulation layer preferably reaches 100–500 μm. After all the heat insulation layers are applied, maintain the temperature at 100–150°C for 20–40 minutes, then raise the temperature to 250–400°C and maintain it for 30–120 minutes to allow the organic-inorganic composite bonding system to gradually cure and stably coat the various heat insulation particles. After curing, this layer forms a low thermal conductivity layer mainly composed of zirconia powder and hollow ceramic microspheres, which is used to block the transmission of high temperature to the substrate.

[0043] S5. Coating and forming a surface sealing layer on the surface of the insulation layer; The surface sealing layer coating is uniformly applied to the surface of the insulation layer, preferably using a 1-3 coat thin-coat method. The wet film thickness of each coat is preferably 15-50 μm. After each coat, allow it to stand and level for 5-10 minutes, and then pre-bake at 80-120℃ for 10-20 minutes. After all coats are applied, cure at 200-350℃ for 30-90 minutes to form a continuous coating structure. The dry film thickness of the surface sealing layer is preferably controlled at 20-100 μm, thereby improving the coating's oxidation resistance, media penetration resistance, and surface chalking resistance without significantly increasing the overall thermal stress.

[0044] S6. Perform staged heat treatment and performance stabilization treatment on the overall thermal barrier coating; After the four-layer structure is fully constructed, the overall coating undergoes a phased heat treatment. Preferably, it is first held at 100–150℃ for 20–40 minutes to further remove residual volatiles; then held at 250–350℃ for 30–60 minutes to promote cross-linking of the organic phase and aggregation of the inorganic phase; finally, depending on the temperature resistance rating of the applied component, it is held at 400–650℃ for 30–120 minutes to achieve a more stable interlayer bonding. After heat treatment, it is cooled to room temperature using slow furnace cooling or stepped cooling methods to reduce thermal shock damage caused by rapid cooling. This process yields a high-temperature gradient thermal barrier coating with strong interlayer bonding, stable thermal insulation performance, and the ability to withstand alternating hot and cold operating conditions of automotive components.

[0045] This thermal barrier coating is particularly suitable for the following automotive components: The outer surface of the engine exhaust manifold; the outer surface of the turbocharger housing; the outer surface of the front section of the exhaust pipe and the three-way catalytic converter housing; the inner or outer side of the high-temperature heat shield; the surface of the metal brackets or protective parts in the engine compartment near the heat source area.

[0046] In these scenarios, components often undergo cyclical changes from cold start to heating up, high load, and then to shutdown and cooling. The temperature changes rapidly and the gradient is large. Ordinary single-layer heat-resistant paint is prone to cracking, peeling, or insufficient heat insulation. The four-layer structure of this thermal barrier coating is more suitable for such working conditions.

[0047] Example 1: A thermal barrier coating resistant to high temperature gradient changes comprises the following formulation: The base bonding layer includes: 20 parts silicone resin, 25 parts aluminum powder, 10 parts nickel powder, 8 parts alumina powder, 5 parts talc powder, 10 parts silica sol, 0.5 parts dispersant, 0.2 parts defoamer, 0.2 parts leveling agent, and 15 parts solvent.

[0048] The buffer transition layer comprises: 18 parts silicone resin, 20 parts alumina powder, 15 parts zirconium oxide powder, 10 parts mullite powder, 5 parts mica powder, 8 parts silica sol, 3 parts glass powder, 0.5 parts dispersant, 0.2 parts defoamer, 0.2 parts leveling agent, and 10 parts solvent.

[0049] The heat insulation layer comprises: 35 parts zirconium oxide powder, 10 parts alumina powder, 15 parts hollow ceramic microspheres, 5 parts diatomaceous earth powder, 8 parts mullite powder, 10 parts silica sol, 8 parts silicone resin, 2 parts glass powder, 0.5 parts dispersant, 0.2 parts defoamer, 0.2 parts leveling agent, and 10 parts solvent.

[0050] The surface sealing layer comprises: 20 parts silicone resin, 15 parts silica sol, 10 parts alumina powder, 8 parts zirconium oxide powder, 5 parts mica powder, 5 parts glass powder, 2 parts titanium dioxide, 0.3 parts dispersant, 0.2 parts defoamer, 0.2 parts leveling agent, and 15 parts solvent.

[0051] The preparation process of the base bonding layer includes: First, add silicone resin, solvent, dispersant, and defoamer to a mixing container and premix at 550 rpm for 10 minutes to form an initial liquid phase system. Then, slowly add alumina powder and talc powder and increase the stirring speed to 1150 rpm for 30 minutes. Next, add aluminum powder and nickel powder and continue stirring for 20 minutes to ensure that the metal powder and ceramic powder are evenly distributed in the resin system. After the slurry is evenly dispersed, add silica sol and leveling agent, and add solvent to adjust the application viscosity to finally obtain the base layer coating.

[0052] The preparation process of the buffer transition layer includes: First, silicone resin, silica sol, solvent, and dispersant are added to a dispersion vessel and stirred at 750 rpm for 15 minutes to form a composite binder phase. Then, alumina powder, zirconium oxide powder, and mullite powder are added sequentially and dispersed at 1150 rpm for 35 minutes. After uniform dispersion, mica powder and glass powder are added and mixed at 750 rpm for another 15 minutes. Finally, defoamer, leveling agent, and solvent are added and the viscosity is adjusted to a suitable level for application to obtain a buffer transition layer coating.

[0053] The preparation process of the heat insulation layer includes: First, silica sol, silicone resin, solvent, and dispersant are added to a mixing container and stirred to form a liquid-phase binder matrix. Then, zirconium oxide powder, alumina powder, mullite powder, and diatomaceous earth powder are added sequentially and dispersed at 1200 r / min for 30 min to form a uniform heat-insulating skeleton slurry. Afterward, the rotation speed is reduced to 450 r / min, and hollow ceramic microspheres and glass powder are slowly added and mixed for another 10 min to ensure that the hollow ceramic microspheres are uniformly dispersed without significant breakage. Finally, defoamer, leveling agent, and solvent are added, the viscosity is adjusted, and the mixture is filtered to obtain the heat-insulating coating.

[0054] The preparation process of the surface sealing layer includes: First, silicone resin, silica sol, solvent, and dispersant are mixed to form a basic liquid phase. Then, alumina powder, zirconium oxide powder, titanium dioxide, and glass powder are added sequentially and dispersed at a medium-high speed of 750 r / min for 30 min. Next, mica powder is added and stirred at a lower speed of 400 r / min for 10 min to maintain the morphology of the flaky particles. Finally, defoamer and leveling agent are added to adjust the viscosity. After filtration, a surface sealing layer coating is obtained.

[0055] The hollow ceramic microspheres in the insulation layer are ceramic particles with a closed hollow structure. Their outer shell is made of alumina-silicon composite ceramic with an average particle size of 45 μm, a shell thickness of 4.5 μm, an apparent density of 0.5 g / cm³, and the cavity volume accounts for 75% of the total particle volume. The outer surface of the hollow ceramic microspheres is treated with silane coupling agent KH-550 to form a stable inorganic-organic interface layer on its surface.

[0056] The zirconia powder used in the heat insulation layer is stabilized zirconia particles, with yttrium oxide as the stabilizer, a stabilizer content of 6.5%, an average particle size of 5 μm, a specific surface area of ​​5.5 m² / g, and a tetragonal phase as the main crystal form; the zirconia powder is prepared by spray granulation process, so that the particles have an approximately spherical structure.

[0057] The glass powder used in the coating is low-softening-temperature inorganic glass particles with a softening temperature of 600℃, an average particle size of 15μm, and a coefficient of thermal expansion of 6.5×10⁻⁶. -6 / ℃; The glass powder is a borosilicate glass system, which can partially soften and fill the gaps between particles during heat treatment or high-temperature use, thereby forming a continuous inorganic bonded phase.

[0058] The coating uses a composite bonding system of silicone resin and silica sol. The silicone resin is a high-temperature resistant organosilicon resin with a temperature resistance rating of 600℃ and a solid content of 55%. The silica sol is an aqueous silica dispersion system with a particle size of 30nm and a solid content of 30%. The mass ratio of the silicone resin to the silica sol is 1:1.

[0059] The mica powder used in the buffer transition layer is natural phlogopite powder with a sheet-like structure, a sheet diameter of 85 μm, a thickness of 2.75 μm, an aspect ratio of 45, and the sheet-like particles are oriented and arranged along the plane of the coating during the coating process.

[0060] The mullite powder used in the buffer transition layer and the heat insulation layer is aluminosilicate ceramic particles with an Al2O3 content of 67.5%, an average particle size of 10.5 μm, a temperature resistance rating of 1500℃, and an irregular blocky morphology.

[0061] The preparation of the thermal barrier coating described above includes the following steps: S1. Pre-treat the substrate to be coated; The metal substrate of a high-temperature automotive component, specifically a heat-resistant steel substrate, was selected as the object to be treated. First, the substrate surface was degreased and cleaned using an alkaline cleaning solution to remove surface oil, cutting fluid residue, and oxide deposits. The cleaning temperature was 50°C, and the cleaning time was 12 minutes. After cleaning, the substrate was rinsed with deionized water until no obvious residual liquid remained. Subsequently, the substrate surface was roughened using sandblasting with brown corundum abrasive at a pressure of 0.6 MPa, achieving a surface roughness Ra of 7.5 μm. The roughened substrate was then purged with compressed air and dried at 100°C for 20 minutes to remove residual moisture and ensure good adhesion interface conditions.

[0062] S2. Apply and cure the base bonding layer on the substrate surface; The thickness of a single wet film is controlled at 40 μm. After spraying, allow it to stand and level for 10 min, then pre-bake at 115℃ for 20 min. Repeat the coating twice to achieve a dry film thickness of 75 μm for the substrate bonding layer. Then cure at 240℃ for 40 min.

[0063] S3. Apply and cure a buffer transition layer on the surface of the base bonding layer; Each wet film thickness is 55μm. After each application, allow it to stand and level for 7 minutes, then pre-bake at 100℃ for 15 minutes. Repeat the application twice to achieve a dry film thickness of 115μm for the buffer transition layer. Then cure at 275℃ for 60 minutes.

[0064] S4. Apply and cure the heat insulation layer on the surface of the buffer transition layer; Each wet film thickness is 70μm, and each layer is pre-dried at 80℃ for 10 minutes after application; repeat the application 3 times to achieve a dry film thickness of 300μm for the insulation layer. Then, maintain the insulation at 125℃ for 30 minutes, and then at 325℃ for 75 minutes.

[0065] S5. Coating and forming a surface sealing layer on the surface of the insulation layer; Each wet film thickness is 32μm. After each application, the film is allowed to stand and level for 7 minutes, and then pre-baked at 100℃ for 15 minutes. Two applications are made to achieve a dry film thickness of 60μm for the surface sealing layer. The film is then cured at 275℃ for 60 minutes.

[0066] S6. Perform staged heat treatment and performance stabilization treatment on the overall thermal barrier coating; First, hold at 125℃ for 30 minutes, then at 300℃ for 45 minutes, and finally at 525℃ for 75 minutes. After the heat treatment, use a slow cooling method with the furnace to cool to room temperature in order to reduce thermal shock damage caused by rapid cooling.

[0067] Example 2: A thermal barrier coating resistant to high temperature gradient changes comprises the following formulation: The base bonding layer includes: 28 parts silicone resin, 35 parts aluminum powder, 18 parts nickel powder, 14 parts alumina powder, 9 parts talc powder, 16 parts silica sol, 1.25 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 28 parts solvent.

[0068] The buffer transition layer comprises: 24 parts silicone resin, 28 parts alumina powder, 23 parts zirconium oxide powder, 18 parts mullite powder, 10 parts mica powder, 14 parts silica sol, 6.5 parts glass powder, 1.25 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 22.5 parts solvent.

[0069] The heat insulation layer comprises: 48 parts zirconium oxide powder, 18 parts alumina powder, 25 parts hollow ceramic microspheres, 10 parts diatomaceous earth powder, 13 parts mullite powder, 18 parts silica sol, 13 parts silicone resin, 5 parts glass powder, 1.25 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 20 parts solvent.

[0070] The surface sealing layer comprises: 28 parts silicone resin, 23 parts silica sol, 15 parts alumina powder, 13 parts zirconium oxide powder, 8.5 parts mica powder, 10 parts glass powder, 5 parts titanium dioxide, 0.9 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 25 parts solvent.

[0071] The preparation process of the base bonding layer includes: First, add silicone resin, solvent, dispersant, and defoamer to a mixing container and premix at 550 rpm for 10 minutes to form an initial liquid phase system. Then, slowly add alumina powder and talc powder and increase the stirring speed to 1150 rpm for 30 minutes. Next, add aluminum powder and nickel powder and continue stirring for 20 minutes to ensure that the metal powder and ceramic powder are evenly distributed in the resin system. After the slurry is evenly dispersed, add silica sol and leveling agent, and add solvent to adjust the application viscosity to finally obtain the base layer coating.

[0072] The preparation process of the buffer transition layer includes: First, silicone resin, silica sol, solvent, and dispersant are added to a dispersion vessel and stirred at 750 rpm for 15 minutes to form a composite binder phase. Then, alumina powder, zirconium oxide powder, and mullite powder are added sequentially and dispersed at 1150 rpm for 35 minutes. After uniform dispersion, mica powder and glass powder are added and mixed at 750 rpm for another 15 minutes. Finally, defoamer, leveling agent, and solvent are added and the viscosity is adjusted to a suitable level for application to obtain a buffer transition layer coating.

[0073] The preparation process of the heat insulation layer includes: First, silica sol, silicone resin, solvent, and dispersant are added to a mixing container and stirred to form a liquid-phase binder matrix. Then, zirconium oxide powder, alumina powder, mullite powder, and diatomaceous earth powder are added sequentially and dispersed at 1200 r / min for 30 min to form a uniform heat-insulating skeleton slurry. Afterward, the rotation speed is reduced to 450 r / min, and hollow ceramic microspheres and glass powder are slowly added and mixed for another 10 min to ensure that the hollow ceramic microspheres are uniformly dispersed without significant breakage. Finally, defoamer, leveling agent, and solvent are added, the viscosity is adjusted, and the mixture is filtered to obtain the heat-insulating coating.

[0074] The preparation process of the surface sealing layer includes: First, silicone resin, silica sol, solvent, and dispersant are mixed to form a basic liquid phase. Then, alumina powder, zirconium oxide powder, titanium dioxide, and glass powder are added sequentially and dispersed at a medium-high speed of 750 r / min for 30 min. Next, mica powder is added and stirred at a lower speed of 400 r / min for 10 min to maintain the morphology of the flaky particles. Finally, defoamer and leveling agent are added to adjust the viscosity. After filtration, a surface sealing layer coating is obtained.

[0075] The hollow ceramic microspheres in the insulation layer are ceramic particles with a closed hollow structure. Their outer shell is made of alumina-silicon composite ceramic with an average particle size of 45 μm, a shell thickness of 4.5 μm, an apparent density of 0.5 g / cm³, and the cavity volume accounts for 75% of the total particle volume. The outer surface of the hollow ceramic microspheres is treated with silane coupling agent KH-550 to form a stable inorganic-organic interface layer on its surface.

[0076] The zirconia powder used in the heat insulation layer is stabilized zirconia particles, with yttrium oxide as the stabilizer, a stabilizer content of 6.5%, an average particle size of 5 μm, a specific surface area of ​​5.5 m² / g, and a tetragonal phase as the main crystal form; the zirconia powder is prepared by spray granulation process, so that the particles have an approximately spherical structure.

[0077] The glass powder used in the coating is low-softening-temperature inorganic glass particles with a softening temperature of 600℃, an average particle size of 15μm, and a coefficient of thermal expansion of 6.5×10⁻⁶. -6 / ℃; The glass powder is a borosilicate glass system, which can partially soften and fill the gaps between particles during heat treatment or high-temperature use, thereby forming a continuous inorganic bonded phase.

[0078] The coating uses a composite bonding system of silicone resin and silica sol. The silicone resin is a high-temperature resistant organosilicon resin with a temperature resistance rating of 600℃ and a solid content of 55%. The silica sol is an aqueous silica dispersion system with a particle size of 30nm and a solid content of 30%. The mass ratio of the silicone resin to the silica sol is 1:1.

[0079] The mica powder used in the buffer transition layer is natural phlogopite powder with a sheet-like structure, a sheet diameter of 85 μm, a thickness of 2.75 μm, an aspect ratio of 45, and the sheet-like particles are oriented and arranged along the plane of the coating during the coating process.

[0080] The mullite powder used in the buffer transition layer and the heat insulation layer is aluminosilicate ceramic particles with an Al2O3 content of 67.5%, an average particle size of 10.5 μm, a temperature resistance rating of 1500℃, and an irregular blocky morphology.

[0081] The preparation of the thermal barrier coating described above includes the following steps: S1. Pre-treat the substrate to be coated; The metal substrate of a high-temperature automotive component, specifically a heat-resistant steel substrate, was selected as the object to be treated. First, the substrate surface was degreased and cleaned using an alkaline cleaning solution to remove surface oil, cutting fluid residue, and oxide deposits. The cleaning temperature was 50°C, and the cleaning time was 12 minutes. After cleaning, the substrate was rinsed with deionized water until no obvious residual liquid remained. Subsequently, the substrate surface was roughened using sandblasting with brown corundum abrasive at a pressure of 0.6 MPa, achieving a surface roughness Ra of 7.5 μm. The roughened substrate was then purged with compressed air and dried at 100°C for 20 minutes to remove residual moisture and ensure good adhesion interface conditions.

[0082] S2. Apply and cure the base bonding layer on the substrate surface; The thickness of a single wet film is controlled at 40 μm. After spraying, allow it to stand and level for 10 min, then pre-bake at 115℃ for 20 min. Repeat the coating twice to achieve a dry film thickness of 75 μm for the substrate bonding layer. Then cure at 240℃ for 40 min.

[0083] S3. Apply and cure a buffer transition layer on the surface of the base bonding layer; Each wet film thickness is 55μm. After each application, allow it to stand and level for 7 minutes, then pre-bake at 100℃ for 15 minutes. Repeat the application twice to achieve a dry film thickness of 115μm for the buffer transition layer. Then cure at 275℃ for 60 minutes.

[0084] S4. Apply and cure the heat insulation layer on the surface of the buffer transition layer; Each wet film thickness is 70μm, and each layer is pre-dried at 80℃ for 10 minutes after application; repeat the application 3 times to achieve a dry film thickness of 300μm for the insulation layer. Then, maintain the insulation at 125℃ for 30 minutes, and then at 325℃ for 75 minutes.

[0085] S5. Coating and forming a surface sealing layer on the surface of the insulation layer; Each wet film thickness is 32μm. After each application, the film is allowed to stand and level for 7 minutes, and then pre-baked at 100℃ for 15 minutes. Two applications are made to achieve a dry film thickness of 60μm for the surface sealing layer. The film is then cured at 275℃ for 60 minutes.

[0086] S6. Perform staged heat treatment and performance stabilization treatment on the overall thermal barrier coating; First, hold at 125℃ for 30 minutes, then at 300℃ for 45 minutes, and finally at 525℃ for 75 minutes. After the heat treatment, use a slow cooling method with the furnace to cool to room temperature in order to reduce thermal shock damage caused by rapid cooling.

[0087] Example 3: A thermal barrier coating resistant to high temperature gradient changes comprises the following formulation: The base bonding layer includes: 35 parts silicone resin, 45 parts aluminum powder, 25 parts nickel powder, 20 parts alumina powder, 12 parts talc powder, 22 parts silica sol, 2 parts dispersant, 1 part defoamer, 1 part leveling agent, and 40 parts solvent.

[0088] The buffer transition layer comprises: 30 parts silicone resin, 35 parts alumina powder, 30 parts zirconium oxide powder, 25 parts mullite powder, 15 parts mica powder, 20 parts silica sol, 10 parts glass powder, 2 parts dispersant, 1 part defoamer, 1 part leveling agent, and 35 parts solvent.

[0089] The heat insulation layer comprises: 60 parts zirconium oxide powder, 25 parts alumina powder, 35 parts hollow ceramic microspheres, 15 parts diatomaceous earth powder, 18 parts mullite powder, 25 parts silica sol, 18 parts silicone resin, 8 parts glass powder, 2 parts dispersant, 1 part defoamer, 1 part leveling agent, and 30 parts solvent.

[0090] The surface sealing layer comprises: 35 parts silicone resin, 30 parts silica sol, 20 parts alumina powder, 18 parts zirconium oxide powder, 12 parts mica powder, 15 parts glass powder, 8 parts titanium dioxide, 1.5 parts dispersant, 1 part defoamer, 1 part leveling agent, and 35 parts solvent.

[0091] The preparation process of the base bonding layer includes: First, add silicone resin, solvent, dispersant, and defoamer to a mixing container and premix at 550 rpm for 10 minutes to form an initial liquid phase system. Then, slowly add alumina powder and talc powder and increase the stirring speed to 1150 rpm for 30 minutes. Next, add aluminum powder and nickel powder and continue stirring for 20 minutes to ensure that the metal powder and ceramic powder are evenly distributed in the resin system. After the slurry is evenly dispersed, add silica sol and leveling agent, and add solvent to adjust the application viscosity to finally obtain the base layer coating.

[0092] The preparation process of the buffer transition layer includes: First, silicone resin, silica sol, solvent, and dispersant are added to a dispersion vessel and stirred at 750 rpm for 15 minutes to form a composite binder phase. Then, alumina powder, zirconium oxide powder, and mullite powder are added sequentially and dispersed at 1150 rpm for 35 minutes. After uniform dispersion, mica powder and glass powder are added and mixed at 750 rpm for another 15 minutes. Finally, defoamer, leveling agent, and solvent are added and the viscosity is adjusted to a suitable level for application to obtain a buffer transition layer coating.

[0093] The preparation process of the heat insulation layer includes: First, silica sol, silicone resin, solvent, and dispersant are added to a mixing container and stirred to form a liquid-phase binder matrix. Then, zirconium oxide powder, alumina powder, mullite powder, and diatomaceous earth powder are added sequentially and dispersed at 1200 r / min for 30 min to form a uniform heat-insulating skeleton slurry. Afterward, the rotation speed is reduced to 450 r / min, and hollow ceramic microspheres and glass powder are slowly added and mixed for another 10 min to ensure that the hollow ceramic microspheres are uniformly dispersed without significant breakage. Finally, defoamer, leveling agent, and solvent are added, the viscosity is adjusted, and the mixture is filtered to obtain the heat-insulating coating.

[0094] The preparation process of the surface sealing layer includes: First, silicone resin, silica sol, solvent, and dispersant are mixed to form a basic liquid phase. Then, alumina powder, zirconium oxide powder, titanium dioxide, and glass powder are added sequentially and dispersed at a medium-high speed of 750 r / min for 30 min. Next, mica powder is added and stirred at a lower speed of 400 r / min for 10 min to maintain the morphology of the flaky particles. Finally, defoamer and leveling agent are added to adjust the viscosity. After filtration, a surface sealing layer coating is obtained.

[0095] The hollow ceramic microspheres in the insulation layer are ceramic particles with a closed hollow structure. Their outer shell is made of alumina-silicon composite ceramic with an average particle size of 45 μm, a shell thickness of 4.5 μm, an apparent density of 0.5 g / cm³, and the cavity volume accounts for 75% of the total particle volume. The outer surface of the hollow ceramic microspheres is treated with silane coupling agent KH-550 to form a stable inorganic-organic interface layer on its surface.

[0096] The zirconia powder used in the heat insulation layer is stabilized zirconia particles, with yttrium oxide as the stabilizer, a stabilizer content of 6.5%, an average particle size of 5 μm, a specific surface area of ​​5.5 m² / g, and a tetragonal phase as the main crystal form; the zirconia powder is prepared by spray granulation process, so that the particles have an approximately spherical structure.

[0097] The glass powder used in the coating is low-softening-temperature inorganic glass particles with a softening temperature of 600℃, an average particle size of 15μm, and a coefficient of thermal expansion of 6.5×10⁻⁶. -6 / ℃; The glass powder is a borosilicate glass system, which can partially soften and fill the gaps between particles during heat treatment or high-temperature use, thereby forming a continuous inorganic bonded phase.

[0098] The coating uses a composite bonding system of silicone resin and silica sol. The silicone resin is a high-temperature resistant organosilicon resin with a temperature resistance rating of 600℃ and a solid content of 55%. The silica sol is an aqueous silica dispersion system with a particle size of 30nm and a solid content of 30%. The mass ratio of the silicone resin to the silica sol is 1:1.

[0099] The mica powder used in the buffer transition layer is natural phlogopite powder with a sheet-like structure, a sheet diameter of 85 μm, a thickness of 2.75 μm, an aspect ratio of 45, and the sheet-like particles are oriented and arranged along the plane of the coating during the coating process.

[0100] The mullite powder used in the buffer transition layer and the heat insulation layer is aluminosilicate ceramic particles with an Al2O3 content of 67.5%, an average particle size of 10.5 μm, a temperature resistance rating of 1500℃, and an irregular blocky morphology.

[0101] The preparation of the thermal barrier coating described above includes the following steps: S1. Pre-treat the substrate to be coated; The metal substrate of a high-temperature automotive component, specifically a heat-resistant steel substrate, was selected as the object to be treated. First, the substrate surface was degreased and cleaned using an alkaline cleaning solution to remove surface oil, cutting fluid residue, and oxide deposits. The cleaning temperature was 50°C, and the cleaning time was 12 minutes. After cleaning, the substrate was rinsed with deionized water until no obvious residual liquid remained. Subsequently, the substrate surface was roughened using sandblasting with brown corundum abrasive at a pressure of 0.6 MPa, achieving a surface roughness Ra of 7.5 μm. The roughened substrate was then purged with compressed air and dried at 100°C for 20 minutes to remove residual moisture and ensure good adhesion interface conditions.

[0102] S2. Apply and cure the base bonding layer on the substrate surface; The thickness of a single wet film is controlled at 40 μm. After spraying, allow it to stand and level for 10 min, then pre-bake at 115℃ for 20 min. Repeat the coating twice to achieve a dry film thickness of 75 μm for the substrate bonding layer. Then cure at 240℃ for 40 min.

[0103] S3. Apply and cure a buffer transition layer on the surface of the base bonding layer; Each wet film thickness is 55μm. After each application, allow it to stand and level for 7 minutes, then pre-bake at 100℃ for 15 minutes. Repeat the application twice to achieve a dry film thickness of 115μm for the buffer transition layer. Then cure at 275℃ for 60 minutes.

[0104] S4. Apply and cure the heat insulation layer on the surface of the buffer transition layer; Each wet film thickness is 70μm, and each layer is pre-dried at 80℃ for 10 minutes after application; repeat the application 3 times to achieve a dry film thickness of 300μm for the insulation layer. Then, maintain the insulation at 125℃ for 30 minutes, and then at 325℃ for 75 minutes.

[0105] S5. Coating and forming a surface sealing layer on the surface of the insulation layer; Each wet film thickness is 32μm. After each application, the film is allowed to stand and level for 7 minutes, and then pre-baked at 100℃ for 15 minutes. Two applications are made to achieve a dry film thickness of 60μm for the surface sealing layer. The film is then cured at 275℃ for 60 minutes.

[0106] S6. Perform staged heat treatment and performance stabilization treatment on the overall thermal barrier coating; First, hold at 125℃ for 30 minutes, then at 300℃ for 45 minutes, and finally at 525℃ for 75 minutes. After the heat treatment, use a slow cooling method with the furnace to cool to room temperature in order to reduce thermal shock damage caused by rapid cooling.

[0107] Comparative Example 1: The same formulation system as in Example 2 was used, but hollow ceramic microspheres were not added to the insulation layer and were replaced with the same amount of alumina powder to investigate the effect of the hollow insulation structure on thermal barrier performance and thermal shock resistance.

[0108] The base bonding layer includes: 28 parts silicone resin, 35 parts aluminum powder, 18 parts nickel powder, 14 parts alumina powder, 9 parts talc powder, 16 parts silica sol, 1.25 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 28 parts solvent.

[0109] The buffer transition layer comprises: 24 parts silicone resin, 28 parts alumina powder, 23 parts zirconium oxide powder, 18 parts mullite powder, 10 parts mica powder, 14 parts silica sol, 6.5 parts glass powder, 1.25 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 22.5 parts solvent.

[0110] The heat insulation layer comprises: 48 parts zirconium oxide powder, 43 parts alumina powder, 10 parts diatomaceous earth powder, 13 parts mullite powder, 18 parts silica sol, 13 parts silicone resin, 5 parts glass powder, 1.25 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 20 parts solvent.

[0111] The surface sealing layer comprises: 28 parts silicone resin, 23 parts silica sol, 15 parts alumina powder, 13 parts zirconium oxide powder, 8.5 parts mica powder, 10 parts glass powder, 5 parts titanium dioxide, 0.9 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 25 parts solvent.

[0112] Comparative Example 2: Comparative Example 2 uses a formulation system that is basically the same as that of Example 2, but the buffer transition layer is removed. That is, the insulation layer is formed directly on the base layer bonding layer, and then a surface sealing layer is formed on the surface of the insulation layer. This is used to examine the effect of the multi-layer gradient structure on the ability to resist cracking and peeling.

[0113] The base bonding layer includes: 28 parts silicone resin, 35 parts aluminum powder, 18 parts nickel powder, 14 parts alumina powder, 9 parts talc powder, 16 parts silica sol, 1.25 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 28 parts solvent.

[0114] The heat insulation layer comprises: 48 parts zirconium oxide powder, 18 parts alumina powder, 25 parts hollow ceramic microspheres, 10 parts diatomaceous earth powder, 13 parts mullite powder, 18 parts silica sol, 13 parts silicone resin, 5 parts glass powder, 1.25 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 20 parts solvent.

[0115] The surface sealing layer comprises: 28 parts silicone resin, 23 parts silica sol, 15 parts alumina powder, 13 parts zirconium oxide powder, 8.5 parts mica powder, 10 parts glass powder, 5 parts titanium dioxide, 0.9 parts dispersant, 0.6 parts defoamer, 0.6 parts leveling agent, and 25 parts solvent.

[0116] The coatings prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to the tests shown in Table 1 below to verify the actual effect of the coatings.

[0117] Table 1 Test Summary: Multiple tests were conducted on the thermal barrier coatings prepared in Examples 1, 2, and 3, as well as Comparative Examples 1 and 2, including evaluation of appearance, adhesion, impact resistance, thermal conductivity change, high-temperature resistance, thermal shock cycling performance, high and low temperature cycling performance, oxidation resistance, salt spray resistance, damp heat resistance, and microstructural integrity. These tests revealed that the examples employing a four-layer synergistic structure consisting of a base bonding layer, a buffer transition layer, a thermal insulation layer, and a surface sealing layer all exhibited better overall performance. Example 1, due to its relatively low addition of functional components in each layer, although forming a complete thermal barrier system, showed only moderate performance compared to the other two examples in terms of sustained high-temperature protection, thermal gradient buffering capacity, and structural retention after multiple thermal cycles. However, it still meets the thermal insulation protection requirements for general automotive high-temperature components. Example 2 uses an intermediate ratio of each component layer, balancing bond strength, thermal insulation performance, and interlayer stress buffering capacity. Tests showed a relatively balanced overall performance, particularly in adhesion stability, surface integrity after thermal shock cycling, and back-temperature reduction. This indicates that using a moderate filler ratio and composite bonding system is more conducive to forming a thermal barrier coating with continuous structure and good interlayer matching. Example 3, due to the higher addition of heat-resistant ceramic components, hollow ceramic microspheres, and sealing layer materials, exhibits stronger high-temperature resistance and thermal insulation capabilities, showing advantages in sustained high temperatures and heat barrier performance. However, due to the higher proportion of inorganic phase, its application viscosity and layer rigidity are also relatively increased. Improper process control can easily affect interlayer stress release. Therefore, it is more suitable for applications with higher high-temperature protection requirements and more stable process control conditions.

[0118] Compared to the examples, in Comparative Example 1, the hollow ceramic microspheres in the insulation layer were replaced with alumina powder. Although it still possessed certain high-temperature resistance, the lack of a closed, hollow, low-thermal-conductivity structure within the insulation layer resulted in a decrease in thermal barrier capacity. This led to a weaker back-temperature reduction effect in the thermal conductivity change evaluation test. Furthermore, after thermal shock cycling and high / low temperature cycling tests, localized microcracks were more likely to appear on its surface, indicating that the hollow ceramic microspheres played a significant role in constructing low-thermal-conductivity paths and mitigating localized thermal stress caused by rapid temperature changes. In Comparative Example 2, the removal of the buffer transition layer resulted in a lack of a transition area for thermal expansion and structural stiffness between the base layer and the insulation layer. Although a multi-layered adhesion structure could initially be formed, repeated thermal shock and thermal cycling tests made it more prone to interfacial stress concentration, localized cracking, and even edge lifting. This demonstrates that the buffer transition layer plays a crucial role in coordinating the thermal expansion differences between the base layer and the insulation layer and improving overall anti-peeling performance.

[0119] The test results above demonstrate that this invention, by sequentially constructing a base bonding layer, a buffer transition layer, a thermal insulation layer, and a surface sealing layer on the surface of a metal substrate, achieves clear division of labor and synergistic cooperation among the layers in terms of adhesion, stress buffering, thermal barrier, and surface sealing. This effectively improves the overall performance of the coating in the high-temperature service environment of automotive components. The low thermal conductivity structure constructed from hollow ceramic microspheres and the stress transition effect provided by the buffer transition layer are key factors in enhancing the resistance to high-temperature gradient changes. Compared to the comparative example lacking key structural units, the embodiment using this four-layer structure exhibits superior results in terms of thermal insulation, thermal cycling stability, and interlayer integrity, indicating that the formulation design and hierarchical structure of this invention have good rationality and application value.

[0120] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. 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 be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A thermal barrier coating resistant to high temperature gradient changes, characterized in that, The thermal barrier coating comprises, from bottom to top, a base bonding layer, a buffer transition layer, a heat insulation layer, and a surface sealing layer; in, The base bonding layer comprises the following components in parts by weight: The ingredients are: 20-35 parts silicone resin, 25-45 parts aluminum powder, 10-25 parts nickel powder, 8-20 parts alumina powder, 5-12 parts talc powder, 10-22 parts silica sol, 0.5-2 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 15-40 parts solvent. The buffer transition layer comprises the following components in parts by mass: The ingredients are: 18-30 parts silicone resin, 20-35 parts alumina powder, 15-30 parts zirconium oxide powder, 10-25 parts mullite powder, 5-15 parts mica powder, 8-20 parts silica sol, 3-10 parts glass powder, 0.5-2 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 10-35 parts solvent. The insulation layer comprises the following components in parts by weight: Zirconia powder 35-60 parts, alumina powder 10-25 parts, hollow ceramic microspheres 15-35 parts, diatomaceous earth powder 5-15 parts, mullite powder 8-18 parts, silica sol 10-25 parts, silicone resin 8-18 parts, glass powder 2-8 parts, dispersant 0.5-2 parts, defoamer 0.2-1 part, leveling agent 0.2-1 part, and solvent 10-30 parts; The surface sealing layer comprises the following components in parts by weight: The ingredients are: 20-35 parts silicone resin, 15-30 parts silica sol, 10-20 parts alumina powder, 8-18 parts zirconium oxide powder, 5-12 parts mica powder, 5-15 parts glass powder, 2-8 parts titanium dioxide, 0.3-1.5 parts dispersant, 0.2-1 part defoamer, 0.2-1 part leveling agent, and 15-35 parts solvent.

2. The thermal barrier coating resistant to high temperature gradient changes according to claim 1, characterized in that, The preparation process of the base bonding layer includes: First, add silicone resin, solvent, dispersant and defoamer to a stirring container and premix at a speed of 300-800 r / min for 5-15 min to form an initial liquid phase system; Then slowly add alumina powder and talc powder, and increase the stirring speed to 800-1500 r / min, and disperse for 20-40 min; Add aluminum powder and nickel powder and continue stirring for 10-30 minutes to ensure that the metal powder and ceramic powder are evenly distributed in the resin system. After the slurry is evenly dispersed, silica sol and leveling agent are added, and solvent is added to adjust the construction viscosity, finally obtaining the base layer coating.

3. The thermal barrier coating resistant to high temperature gradient changes according to claim 1, characterized in that, The preparation process of the buffer transition layer includes: First, add silicone resin, silica sol, solvent, and dispersant to a dispersion vessel and stir at 500-1000 r / min for 10-20 min to form a composite binder phase; Subsequently, alumina powder, zirconium oxide powder and mullite powder are added sequentially and dispersed at a high speed of 800-1500 r / min, with the dispersion time preferably being 20-50 min; After the mixture is evenly dispersed, add mica powder and glass powder, and continue mixing at a speed of 500-1000 r / min for 10-20 min. Finally, defoamer, leveling agent, and solvent are added and adjusted to a viscosity suitable for application to obtain a buffer transition layer coating.

4. The thermal barrier coating resistant to high temperature gradient changes according to claim 1, characterized in that, The preparation process of the heat insulation layer includes: First, silica sol, silicone resin, solvent and dispersant are added to a mixing container and stirred to form a liquid phase binder matrix; Subsequently, zirconium oxide powder, alumina powder, mullite powder and diatomaceous earth powder are added in sequence and dispersed at 800-1600 r / min for 20-40 min to form a uniform thermal insulation skeleton slurry. Then reduce the rotation speed to 300-600 r / min, slowly add hollow ceramic microspheres and glass powder, and continue mixing for 5-15 min to ensure that the hollow ceramic microspheres are evenly dispersed without significant breakage; Finally, defoamer, leveling agent and solvent are added, the viscosity is adjusted and then filtered to obtain the heat insulation coating.

5. The thermal barrier coating resistant to high temperature gradient changes according to claim 1, characterized in that, The preparation process of the surface sealing layer includes: First, mix silicone resin, silica sol, solvent and dispersant to form a basic liquid phase, then add alumina powder, zirconium oxide powder, titanium dioxide and glass powder in sequence, and disperse at a medium-high speed of 500-1000 r / min for 20-40 min. Then add mica powder and continue stirring at a low speed of 300-500 r / min for 5-15 min to maintain the morphology of the flaky particles; Finally, defoamer and leveling agent are added to adjust the viscosity, and the surface sealing layer coating is obtained after filtration.

6. The thermal barrier coating resistant to high temperature gradient changes according to claim 1, characterized in that, The coating uses a composite bonding system of silicone resin and silica sol. The silicone resin is a high-temperature resistant organosilicon resin with a temperature resistance of not less than 500°C and a solid content of 40% to 70%. The silica sol is an aqueous or alcoholic silica dispersion system with a particle size of 10 to 50 nm and a solid content of 20% to 40%. The mass ratio of the silicone resin to the silica sol is 0.5:1 to 2:

1.

7. The thermal barrier coating resistant to high temperature gradient changes according to claim 1, characterized in that, The glass powder used in the coating is low-softening-temperature inorganic glass particles with a softening temperature of 450–750°C, an average particle size of 1–30 μm, and a coefficient of thermal expansion of 4 × 10⁻⁶. -6 ~9×10 -6 / ℃; the glass powder includes borosilicate glass or aluminosilicate glass systems.

8. The thermal barrier coating resistant to high temperature gradient changes according to claim 1, characterized in that, The hollow ceramic microspheres in the insulation layer are ceramic particles with a closed hollow structure. Their outer shell is made of alumina or alumina-silicon composite ceramic, with an average particle size of 10-80 μm, a shell thickness of 1-8 μm, an apparent density of 0.2-0.8 g / cm³, and the cavity volume accounts for 60%-90% of the total particle volume.

9. The thermal barrier coating resistant to high temperature gradient changes according to claim 1, characterized in that, The zirconia powder used in the heat insulation layer is stabilized zirconia particles, and its stabilizer is yttrium oxide or magnesium oxide. The mass percentage of the stabilizer is 3% to 10%, the average particle size is 0.5 to 10 μm, the specific surface area is 1 to 10 m² / g, and the main crystal form is tetragonal or cubic phase.

10. A method for preparing a thermal barrier coating resistant to high-temperature gradient changes, comprising preparing the coating based on any one of claims 1-9, characterized in that, Includes the following steps: S1. Pre-treat the substrate to be coated; S2. Apply and cure the base bonding layer on the substrate surface; S3. Apply and cure a buffer transition layer on the surface of the base bonding layer; S4. Apply and cure the heat insulation layer on the surface of the buffer transition layer; S5. Coating and forming a surface sealing layer on the surface of the insulation layer; S6. Perform staged heat treatment and performance stabilization treatment on the overall thermal barrier coating.

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