A chromium-free long-acting high-temperature oxidation-resistant coating and a preparation method thereof

Abstract

This invention discloses a chromium-free, long-lasting high-temperature anti-oxidation coating and its preparation method, belonging to the technical field of high-temperature protective materials. The coating consists of basic components such as SiO2, Al2O3, MgO, SiC, B2O3, CaO, ZnO, kaolin, and magnesium olivine powder, along with functional materials, sodium hexametaphosphate, K2SiO3, boric acid, gellan gum, and water. Its preparation mainly includes steps such as ball milling of raw materials, ultrasonic dispersion of functional materials, preparation of binder, sequential mixing, static curing, and vacuum degassing. Compared with existing technologies, this invention is completely chromium-free, environmentally friendly, and safe. Through the compounding of functional materials and optimization of the feeding sequence, its oxidation loss reduction rate can reach up to 98.1%, and the number of thermal shock cycles can reach up to 123, exhibiting excellent high-temperature oxidation resistance and thermal shock resistance, suitable for long-term protection of high-temperature alloys and steels.

Description

Technical Field

[0001] This invention relates to the field of high-temperature protective materials technology, and in particular to a chromium-free, long-lasting high-temperature anti-oxidation coating and its preparation method. Background Technology

[0002] Chromium-free, long-lasting high-temperature anti-oxidation coatings are functional coatings specifically designed to protect metal substrates (such as steel and high-temperature alloys) during long-term service in high-temperature oxidizing environments. Their core objective is to construct a dense, stable, and thermally compatible physicochemical barrier on the substrate surface through a composite ceramic phase and a special bonding system, completely eliminating toxic chromium (such as Cr2O3) or chromate components. This effectively blocks oxygen diffusion and corrosion, achieving long-lasting protection at temperatures exceeding 1000℃ and even 1300℃. The development of this type of coating is a necessary response to increasingly stringent environmental regulations and the development of industrial equipment with higher parameters. Its key technologies mainly focus on the selection of novel chromium-free functional fillers (such as borides, MAX / MAB phases, and rare earth zirconates), the construction of a high-temperature stable bonding system, and the optimized design of the coating's microstructure.

[0003] In the existing technology field, a large amount of research has been dedicated to improving the performance of high-temperature anti-oxidation coatings. For example, patent CN113943501A provides a high-temperature anti-oxidation protective coating, which achieves good synergistic anti-oxidation and anti-decarburization effects at 1300℃ through a multi-component composite containing SiO2, Al2O3, MgO, SiC, and the key component Cr2O3, supplemented by K2SiO3 binder. However, a significant drawback of this technology is that its formulation still relies on chromium as the key functional phase, which contradicts the increasingly stringent environmental protection and occupational health requirements and cannot meet the development trend of "chromium-free". Patent CN115260802A proposes an innovative approach, using a ZrO2-Al2O3 composite layer to encapsulate the SiC / TiC core, thereby improving coating stability by forming a solid solution structure at high temperatures. However, the core drawback of this technology is its extremely complex preparation process, involving pre-coating and encapsulating the core material and specific high-temperature chemical reactions. This results in a long production process, high cost, and poor process controllability, making it difficult to achieve large-scale industrial application. In addition, patent CN115260806A targets medium-high manganese steel and designs a coating with a blend of silicone resin and silicate as the adhesive matrix and the addition of components such as CeO2. However, the main drawback of this technology is its organic-inorganic composite adhesive system. Although it is effective at ≤1300℃, the silicone resin will completely decompose at higher temperatures or under prolonged heat exposure, which may lead to shrinkage cracks or pores in the coating, thus limiting its long-term reliability under extreme conditions of ultra-high temperature (e.g., >1300℃).

[0004] In summary, while existing high-temperature anti-oxidation coating technologies each have their own characteristics, they generally face three key issues that urgently need to be addressed: First, the environmental bottleneck, as some high-efficiency formulations still cannot escape dependence on chromium; second, the challenge of balancing process and cost, as some solutions that improve performance through complex composites or intricate structural designs often involve cumbersome preparation processes and soaring costs, hindering industrialization; and third, the challenge of long-term stability at ultra-high temperatures, particularly the durability of the bonding system at extreme temperatures and the coating's resistance to cracking and peeling during the entire thermal cycle. Therefore, developing a novel coating system that uses readily available raw materials, employs simple processes, is completely chromium-free, and can maintain long-term structural stability and protective efficacy at ultra-high temperatures has become a clear and urgent technological breakthrough in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a chromium-free, long-lasting high-temperature anti-oxidation coating with excellent high-temperature oxidation resistance and thermal shock resistance, as well as its preparation method.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A chromium-free, long-lasting, high-temperature anti-oxidation coating comprises the following components by weight: 20-40 parts SiO2, 20-30 parts Al2O3, 10-20 parts MgO, 5-15 parts SiC, 1-5 parts B2O3, 1-5 parts CaO, 1-5 parts ZnO, 1-5 parts kaolin, 3-8 parts magnesium olivine powder, 1-5 parts functional materials, 0.05-0.2 parts sodium hexametaphosphate, 10-20 parts K2SiO3, 1-2 parts boric acid, 0.4-0.8 parts gellan gum, and 80-100 parts water.

[0008] A method for preparing a chromium-free, long-lasting, high-temperature anti-oxidation coating is as follows:

[0009] Step 1: Weigh out SiO2, Al2O3, MgO, SiC, B2O3, CaO, ZnO, kaolin, and magnesium olivine powder according to the formula, put them into a mixer and mix at 100-600 r / min for 5-15 minutes, then transfer them to a ball mill and ball mill for 1-3 hours with a ball-to-powder ratio of 2-4:1 to obtain ultrafine composite powder; mix the functional materials with water, add sodium hexametaphosphate, and ultrasonically disperse to form a suspension;

[0010] Step 2: Add K2SiO3, boric acid, and gellan gum to water and stir at 100-600 r / min for 5-15 minutes to obtain a binder solution;

[0011] Step 3: Add the ultrafine composite powder obtained in Step 1 to the adhesive liquid obtained in Step 2, and stir at 100-600 r / min for 5-15 minutes. Then add the suspension obtained in Step 1 and continue stirring at 100-600 r / min for 5-15 minutes to obtain the mixed coating.

[0012] Step 4: Let the mixed coating prepared in Step 3 stand, and finally use vacuum degassing to obtain chromium-free long-lasting high-temperature anti-oxidation coating.

[0013] In step 1, the functional materials and water are mixed at a mass ratio of 1:2-4.

[0014] The ultrasonic dispersion in step 1 is ultrasonic dispersion at 100-300W and 20-60kHz for 10-50 minutes.

[0015] The standing time in step 4 is 1-5 hours at room temperature, with stirring for 3-8 minutes every 0.5-2 hours during this period.

[0016] The vacuum degassing in step 4 is performed at -0.07MPa to -0.09MPa for 5-20 minutes.

[0017] The functional material is at least one of hexagonal boron nitride, lanthanum zirconate, zirconium boride, titanium aluminum carbide, hydroxyapatite, organopolyborosilicate, hafnium boride, titanium carbonitride, and aluminum molybdenum boron.

[0018] Preferably, the functional material is composed of zirconium boride and titanium aluminum carbide in a mass ratio of 0.5-2:0.5-2.

[0019] More preferably, the functional material is composed of zirconium boride, titanium aluminum carbide, and aluminum molybdenum boron in a mass ratio of 0.5-2:0.5-2:0.1-0.3.

[0020] Preferably, step 3 can also be performed using the following method:

[0021] Add the suspension obtained in step 1 to the adhesive liquid obtained in step 2, and stir at 100-600 r / min for 5-15 minutes. Then add the ultrafine composite powder obtained in step 1 and continue stirring at 100-600 r / min for 5-15 minutes to obtain the mixed coating.

[0022] This invention first selects raw materials such as hafnium boride and zirconium boride based on the oxidation protection mechanism of single high-melting-point functional materials. The high-melting-point oxides generated by their high-temperature oxidation form a physical barrier layer, while simultaneously reacting with SiO2 in the coating to generate a glassy phase that fills the pores. This dual action constructs the basic antioxidant coating structure.

[0023] Furthermore, to address the synergistic effect of functional material blends, zirconium boride and titanium aluminum carbide are combined in an appropriate ratio. The spinel phase generated by the in-situ reaction of their oxidation products enhances high-temperature stability and thermal shock resistance. Simultaneously, the layered structure of titanium aluminum carbide alleviates coating stress, achieving a synergistic improvement in oxidation resistance and impact resistance.

[0024] Furthermore, this invention leverages the self-healing mechanism of trace molybdenum-based materials by adding a small amount of molybdenum-aluminum-boron to the zirconium boride and aluminum-titanium carbide composite system. The low-melting-point glassy phase generated by its high-temperature oxidation fills micro-cracks in the coating, and its layered structure enhances fracture toughness, endowing the coating with high-temperature self-healing capabilities and further improving its protective performance.

[0025] Finally, the feeding sequence was optimized to achieve uniform dispersion of the functional phase. The functional material suspension was first mixed with the binder, and then the ultrafine composite powder was added. This avoids the functional material being coated with a large amount of base material, ensuring that the functional phase is evenly distributed in the coating, allowing for rapid generation of high-temperature antioxidants and effective stress dispersion by the layered buffer phase, thereby maximizing the protective effect of the coating.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects:

[0027] 1) This invention abandons the traditional chromium-containing components and selects a high-melting-point functional material compound system, which can generate a dense barrier layer and a filling glass phase in situ at high temperature, thus avoiding chromium contamination and achieving long-term high-temperature anti-oxidation protection of the substrate.

[0028] 2) Through the synergistic effect of functional materials, this invention can form a stable composite ceramic phase at high temperatures and use the layered structure to relieve thermal stress, effectively reducing cracks and peeling of the coating during thermal cycling, and adapting to complex high-temperature working conditions.

[0029] 3) This invention optimizes the batching sequence and dispersion process to ensure that the functional phase is evenly distributed in the coating, thereby improving the coating properties and film quality; the self-healing mechanism at high temperature can fill in minor defects, further extending the service life of the coating and reducing maintenance costs. Detailed Implementation

[0030] Some material parameters and their sources:

[0031] Hexagonal boron nitride, average particle size: 1μm, density: 2.27g / cm³, Mohs hardness: 2.

[0032] Lanthanum zirconate, particle size: 1-3 μm, chemical formula La₂Zr₂O₇, fluorite-type structure, melting point up to 2300℃, density 6.09 g / cm³ 3 .

[0033] Zirconium boride, average particle size: 1 μm, chemical formula ZrB2, hexagonal crystal system, melting point 3040℃, density 6.1 g / cm³3 Its Vickers hardness is 22 GPa.

[0034] Titanium aluminum carbide, average particle size: 5 μm, layered ternary compound, melting point 1900℃, density 4.23 g / cm³ 3 .

[0035] Hydroxyapatite, grain size: 60-80 nm, hexagonal crystal system, density 3.16 g / cm³ 3 Mohs hardness 5.

[0036] Organic polyborosilazane, model: PB93792, Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0037] Hafnium boride, average particle size: 2μm, chemical formula HfB2, hexagonal crystal system, melting point 3250℃, Vickers hardness 20-25GPa.

[0038] Titanium carbonitride, particle size: 50-200 nm, face-centered cubic structure, melting point 2900℃, density 5.4-5.6 g / cm³ 3 .

[0039] Molybdenum aluminum boron, particle size: ≤38μm, layered ternary compound, melting point 1600℃, density 5.3g / cm³ 3 .

[0040] SiO2, particle size: 10-35μm.

[0041] Al2O3, particle size: 5-20μm, crystal form: α-type.

[0042] MgO, particle size: 10-30μm.

[0043] SiC, particle size: 15-35μm.

[0044] B2O3, particle size: 15-35μm.

[0045] CaO, particle size: 10-30μm

[0046] ZnO, particle size: 10-25μm

[0047] Kaolin, particle size: 15-35μm.

[0048] Magnesium olivine powder, particle size: 15-35μm.

[0049] In the embodiments and comparative examples of this invention, all raw materials are commercially available products.

[0050] Example 1

[0051] A method for preparing a chromium-free, long-lasting, high-temperature anti-oxidation coating is as follows:

[0052] Step 1: Weigh out 30 parts SiO2, 28 parts Al2O3, 15 parts MgO, 10 parts SiC, 2.5 parts B2O3, 2.5 parts CaO, 3 parts ZnO, 3 parts kaolin, and 5 parts magnesium olivine powder according to the formula. Put them into a mixer and mix at 400 r / min for 10 minutes. Then transfer them to a ball mill and ball mill for 2 hours with a ball-to-powder ratio of 3:1 to obtain ultrafine composite powder. Mix 2.5 parts of functional material with 7.5 parts of water, then add 0.1 parts of sodium hexametaphosphate. Disperse the mixture using ultrasonication at 200W and 40kHz for 30 minutes to form a suspension.

[0053] Step 2: Add 16 parts K2SiO3, 1.5 parts boric acid, and 0.6 parts gellan gum to 82.5 parts water, and stir at 500 r / min for 10 minutes to obtain the adhesive solution;

[0054] Step 3: Add the ultrafine composite powder obtained in Step 1 to the adhesive liquid obtained in Step 2, and stir at 300 r / min for 10 minutes. Then add the suspension obtained in Step 1 and continue stirring at 300 r / min for 10 minutes to obtain the mixed coating.

[0055] Step 4: Let the mixed coating prepared in Step 3 stand at room temperature for 3 hours, stirring for 5 minutes every hour during this period. Finally, use a vacuum degassing machine to degas for 15 minutes at -0.07MPa to obtain a chromium-free long-lasting high-temperature anti-oxidation coating.

[0056] The functional material is hexagonal boron nitride.

[0057] Example 2

[0058] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is lanthanum zirconate.

[0059] Example 3

[0060] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is zirconium boride.

[0061] Example 4

[0062] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is aluminum titanium carbide.

[0063] Example 5

[0064] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is hydroxyapatite.

[0065] Example 6

[0066] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is an organic polyborosilazane.

[0067] Example 7

[0068] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is hafnium boride.

[0069] Example 8

[0070] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is titanium carbonitride.

[0071] Example 9

[0072] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is composed of zirconium boride and aluminum titanium carbide in a mass ratio of 1:1.

[0073] Example 10

[0074] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is composed of hexagonal boron nitride and hydroxyapatite in a mass ratio of 1:1.

[0075] Example 11

[0076] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is composed of zirconium boride, aluminum titanium carbide and molybdenum aluminum boron in a mass ratio of 1:1:0.2.

[0077] Example 12

[0078] A method for preparing a chromium-free, long-lasting, high-temperature anti-oxidation coating is as follows:

[0079] Step 1: Weigh out 30 parts SiO2, 28 parts Al2O3, 15 parts MgO, 10 parts SiC, 2.5 parts B2O3, 2.5 parts CaO, 3 parts ZnO, 3 parts kaolin, and 5 parts magnesium olivine powder according to the formula. Put them into a mixer and mix at 400 r / min for 10 minutes. Then transfer them to a ball mill and ball mill for 2 hours with a ball-to-powder ratio of 3:1 to obtain ultrafine composite powder. Mix 2.5 parts of functional material with 7.5 parts of water, then add 0.1 parts of sodium hexametaphosphate. Disperse the mixture using ultrasonication at 200W and 40kHz for 30 minutes to form a suspension.

[0080] Step 2: Add 16 parts K2SiO3, 1.5 parts boric acid, and 0.6 parts gellan gum to 82.5 parts water, and stir at 500 r / min for 10 minutes to obtain the adhesive solution;

[0081] Step 3: Add the suspension obtained in Step 1 to the adhesive liquid obtained in Step 2, and stir at 300 r / min for 10 minutes. Then add the ultrafine composite powder obtained in Step 1, and continue stirring at 300 r / min for 10 minutes to obtain the mixed coating.

[0082] Step 4: Let the mixed coating prepared in Step 3 stand at room temperature for 3 hours, stirring for 5 minutes every hour during this period. Finally, use a vacuum degassing machine to degas for 15 minutes at -0.07MPa to obtain a chromium-free long-lasting high-temperature anti-oxidation coating.

[0083] The functional material is composed of zirconium boride, titanium aluminum carbide, and aluminum molybdenum boron in a mass ratio of 1:1:0.2.

[0084] Comparative Example 1

[0085] The preparation method of a chromium-free long-lasting high-temperature anti-oxidation coating is basically the same as that in Example 1, except that the functional material is not added.

[0086] Test Example 1

[0087] High-temperature oxidation loss reduction rate test:

[0088] Q235 steel plates were cut into 100mm×100mm×10mm samples. The surface oxide layer was removed by sanding with 800-grit sandpaper, and the samples were cleaned with anhydrous ethanol and dried. The initial mass of the samples was weighed and recorded as m1. The coatings of each example and comparative example were uniformly coated, and the coating thickness was controlled to be 0.8mm. The samples were dried at a constant temperature of 60℃ for 5 hours.

[0089] The coated sample was placed in a muffle furnace at 1300℃ and kept at that temperature for 10 hours. After cooling to room temperature with the furnace, the surface iron oxide scale was removed, and the final mass of the sample was weighed and recorded as m2. The blank control experiment used a Q235 steel plate sample of the same specification without coating and carried out a high-temperature oxidation test according to the above steps.

[0090] Indicator Calculation:

[0091] The mass difference of the blank sample is denoted as Δm. 空白 =m 1空白 -m 2空白

[0092] The mass difference of the sample is Δm = m1 - m2

[0093] Oxidation loss reduction rate δ = 100% × (Δm) 空白 -Δm) / Δm空白

[0094] Each group was tested 3 times, and the average value of the results was taken. The test results are shown in Table 1.

[0095] Table 1

[0096] Experimental protocol Oxidation loss reduction rate δ (%) Example 1 78.2 Example 2 82.7 Example 3 87.6 Example 4 86.8 Example 5 75.4 Example 6 80.3 Example 7 88.3 Example 8 84.0 Example 9 94.2 Example 10 76.9 Example 11 97.5 Example 12 98.1 Comparative Example 1 63.5

[0097] Test Example 2

[0098] High-temperature thermal shock cycle performance test

[0099] GH3535 alloy steel substrates were cut into 50mm×50mm×5mm samples. The coating was applied using an air spray method, with the coating thickness controlled at 0.8mm, and cured at 100℃ for 2 hours. The samples were then placed in a 1200℃ resistance furnace for 30 minutes, and quickly removed and cooled in flowing room temperature water for 5 minutes. The surface condition of the coating was recorded before and after each cycle, observing for cracks, peeling, or flaking.

[0100] The termination criteria are as follows:

[0101] Cracks with a length of ≥5mm appear on the coating surface

[0102] Coating area ≥10mm 2 peeling area

[0103] If any of the above situations occur, record the number of thermal shock cycles that have been completed.

[0104] Each group was tested 5 times, and the average value of the results was taken. The relevant test data are summarized in Table 2.

[0105] Table 2

[0106] Experimental protocol Number of thermal shock cycles (times) Example 1 45 Example 2 52 Example 3 68 Example 4 65 Example 5 42 Example 6 58 Example 7 70 Example 8 60 Example 9 95 Example 10 44 Example 11 115 Example 12 123 Comparative Example 1 28

[0107] In Example 7, hafnium boride is slowly oxidized at high temperature to generate HfO2 and B2O3. HfO2 has an extremely high melting point and can form a dense physical barrier layer. B2O3 reacts with SiO2 in the coating to generate a borosilicate glass phase that fills the pores of the coating. This dual effect significantly improves the oxidation resistance and thermal stability of the coating at 1300℃. Therefore, the oxidation burn-off reduction rate and the number of thermal shock cycles are the highest among single-functional materials.

[0108] Example 9 uses a 1:1 composite of zirconium boride and titanium aluminum carbide. The Al2O3 generated by the decomposition of titanium aluminum carbide at high temperature reacts in situ with the ZrO2 generated by the oxidation of zirconium boride to form a spinel phase of ZrAl2O4. This spinel has better high-temperature stability and thermal shock resistance than ZrO2 or Al2O3 alone. At the same time, the layered structure of titanium aluminum carbide can also alleviate the stress concentration of the coating during thermal cycling, achieving a dual synergy of anti-oxidation and anti-impact, which is better than the effect of using the two materials alone.

[0109] Example 11 adds a small amount of molybdenum-aluminum-boron to Example 9. The MoO3 generated by the oxidation of molybdenum-aluminum-boron at high temperature will form a low-melting-point borosilicate glass phase with B2O3 in the coating. This glass phase can quickly flow and fill defects when micro-cracks appear in the coating, achieving high-temperature self-repair. In addition, the layered structure of molybdenum-aluminum-boron further enhances the fracture toughness of the coating, making it more difficult for the coating to crack during thermal shock. Therefore, the performance is further improved compared to Example 9.

[0110] In Example 12, by adjusting the feeding sequence, the functional material suspension was first mixed with the binder before the ultrafine composite powder was added. This effectively avoided the problem of uneven dispersion of the functional material due to being encapsulated by a large amount of base material, and made the functional phase more uniformly distributed in the coating. The uniform phase distribution not only ensured the rapid generation of antioxidants at high temperatures, but also allowed the layered buffer phase to more effectively disperse stress, ultimately resulting in a slight improvement in the coating's antioxidant and thermal shock resistance compared to Example 11.

Claims

1. A chromium-free, long-lasting, high-temperature anti-oxidation coating, characterized in that, It comprises the following components by weight: 20-40 parts SiO2, 20-30 parts Al2O3, 10-20 parts MgO, 5-15 parts SiC, 1-5 parts B2O3, 1-5 parts CaO, 1-5 parts ZnO, 1-5 parts kaolin, 3-8 parts magnesium olivine powder, 1-5 parts functional materials, 0.05-0.2 parts sodium hexametaphosphate, 10-20 parts K2SiO3, 1-2 parts boric acid, 0.4-0.8 parts gellan gum, and 80-100 parts water.

2. A method for preparing the chromium-free, long-lasting, high-temperature anti-oxidation coating as described in claim 1, characterized in that, The method is as follows: Step 1: Weigh out SiO2, Al2O3, MgO, SiC, B2O3, CaO, ZnO, kaolin, and magnesium olivine powder according to the formula, put them into a mixer and mix at 100-600 r / min for 5-15 minutes, then transfer them to a ball mill and ball mill for 1-3 hours with a ball-to-powder ratio of 2-4:1 to obtain ultrafine composite powder; mix the functional materials with water, add sodium hexametaphosphate, and ultrasonically disperse to form a suspension; Step 2: Add K2SiO3, boric acid, and gellan gum to water and stir at 100-600 r / min for 5-15 minutes to obtain a binder solution; Step 3: Add the ultrafine composite powder obtained in Step 1 to the adhesive liquid obtained in Step 2, and stir at 100-600 r / min for 5-15 minutes. Then add the suspension obtained in Step 1 and continue stirring at 100-600 r / min for 5-15 minutes to obtain the mixed coating. Step 4: Let the mixed coating prepared in Step 3 stand, and finally use vacuum degassing to obtain chromium-free long-lasting high-temperature anti-oxidation coating.

3. The method as described in claim 2, characterized in that, In step 1, the functional materials and water are mixed at a mass ratio of 1:2-4.

4. The method as described in claim 2, characterized in that, The ultrasonic dispersion in step 1 is ultrasonic dispersion at 100-300W and 20-60kHz for 10-50 minutes.

5. The method as described in claim 2, characterized in that, The standing time in step 4 is 1-5 hours at room temperature, with stirring for 3-8 minutes every 0.5-2 hours during this period.

6. The method as described in claim 2, characterized in that, The vacuum degassing in step 4 is performed at -0.07MPa to -0.09MPa for 5-20 minutes.

7. The method as described in claim 2, characterized in that, The functional material is at least one of hexagonal boron nitride, lanthanum zirconate, zirconium boride, titanium aluminum carbide, hydroxyapatite, organopolyborosilicate, hafnium boride, titanium carbonitride, and aluminum molybdenum boron.

8. The method as described in claim 2, characterized in that, The functional material is composed of zirconium boride and titanium aluminum carbide in a mass ratio of 0.5-2:0.5-2.

9. The method as described in claim 2, characterized in that, The functional material is composed of zirconium boride, titanium aluminum carbide, and aluminum molybdenum boron in a mass ratio of 0.5-2:0.5-2:0.1-0.

3.

10. The method as described in claim 2, characterized in that, Step 3 can also be performed using the following method: Add the suspension obtained in step 1 to the adhesive liquid obtained in step 2, and stir at 100-600 r / min for 5-15 minutes. Then add the ultrafine composite powder obtained in step 1 and continue stirring at 100-600 r / min for 5-15 minutes to obtain the mixed coating.