A high-temperature-resistant radar wave-absorbing coating and a preparation method thereof

Abstract

The application belongs to the field of wave-absorbing materials, and particularly relates to a high-temperature-resistant radar wave-absorbing coating and a preparation method thereof. The radar wave-absorbing coating is constructed as a ceramic transition layer-modified transition layer-radar wave-absorbing layer-environmental functional layer. The ceramic transition layer is first prepared on the surface of a titanium alloy substrate through thermal spraying. Then, the modified transition layer and the radar wave-absorbing layer are prepared in sequence through a high-temperature sintering method, so as to design and control the micro-state change in the preparation process by the synergistic effect of sodium carboxymethyl cellulose, polyvinyl alcohol, glass powder and the sintering process. As a result, the multi-dimensional collaboration effect of material-to-material and material-to-process is generated between the three layers of materials, the interlayer adhesion, stress buffering and releasing of the overall material system are considered, and the wave-absorbing performance is optimized. Finally, the surface layer of the radar wave-absorbing layer is directly cladded into a dense environmental functional layer, so as to further protect the overall wave-absorbing coating without deteriorating the wave-absorbing performance of the overall coating.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of wave-absorbing materials, and particularly relates to a high-temperature-resistant radar wave-absorbing coating and a preparation method thereof. BACKGROUND

[0002] The coated radar wave-absorbing coating is an effective means for realizing the radar stealth performance without changing the original aerodynamic structure of the aircraft, and has become one of the key technologies for reducing the radar detectability of the aircraft. With the continuous improvement of the speed of the aircraft, the friction between the surface of the aircraft and the atmosphere is significantly enhanced, resulting in a sharp rise in the surface temperature during flight. At the same time, in order to realize the all-around radar stealth, higher requirements are put forward for the radar stealth performance of the high-temperature region such as the engine. Titanium alloy has the advantages of high strength and low density, and can be stably used in an environment of 500-600 DEG C, which is of great help to the lightweight design of the aircraft. Therefore, how to construct a wave-absorbing coating with excellent high-temperature resistance, structural stability and electromagnetic absorption performance on the titanium alloy substrate has become one of the core problems in the research of high-temperature stealth materials.

[0003] The traditional radar wave-absorbing coating is usually coated on the surface of the metal substrate after the uniform mixing of the organic binder and the magnetic absorber, and although it can realize good electromagnetic wave absorption effect, in the high-temperature environment, due to the thermal-mechanical coupling effect and the thermal decomposition and carbonization of the organic binder, the coating is prone to cracking and peeling. In order to improve the mechanical stability at high temperature, the thermal spraying process is used to construct the wave-absorbing coating with inorganic binder as the matrix, which significantly improves the heat resistance and mechanical strength of the coating. However, due to the limitation of the thermal spraying deposition mechanism, the absorber in the coating often presents a large flaky cluster structure with consistent orientation, which is easy to form a local conductive network, which is not conducive to the optimization design of the radar wave-absorbing performance. In recent years, glass-based binders have been widely concerned due to their low-temperature forming characteristics. By mixing the glass binder with the magnetic absorber and coating and sintering on the surface of the titanium alloy, a composite coating with excellent electromagnetic wave absorption performance can be obtained. However, such coating is combined with the surface of the titanium alloy in the form of physical adsorption and chemical bonding, and the bonding strength is low, which is difficult to meet the reliability requirements under the conditions of structural assembly or high-temperature service. In addition, the magnetic absorber is easy to be oxidized and corroded in the high-temperature oxygen / water oxygen environment, which leads to the decline of the radar wave-absorbing performance and the destruction of the coating structure. Although the surface coating of the absorber can improve its thermal stability, the process is complex and the cost is high, which is difficult to realize large-scale application. Another idea is to introduce an "environmental functional layer" on the surface of the coating for protection and isolation, but the electromagnetic performance mismatch between the environmental functional layer and the radar wave-absorbing layer often weakens the overall wave-absorbing performance.

[0004] In summary, it is urgent to develop a method for constructing a wave-absorbing coating that can realize high adhesion, excellent environmental adaptability and stable radar stealth performance on a titanium alloy substrate to meet the stringent requirements of the next generation of hypersonic vehicles for high-temperature stealth materials. SUMMARY

[0005] In view of the above problems or deficiencies, in order to solve the problem that the existing wave-absorbing coating is difficult to balance high adhesion, excellent environmental adaptability and stable radar stealth performance, the present application provides a high-temperature-resistant radar wave-absorbing coating and a preparation method thereof, solving the problem of poor compatibility of the bonding strength, environmental adaptability and radar wave-absorbing performance between the current titanium alloy substrate and the radar wave-absorbing coating.

[0006] A preparation method of a high-temperature-resistant radar wave-absorbing coating, comprising the following steps:

[0007] Step 1, ceramic transition layer preparation;

[0008] The surface of the titanium alloy substrate is cleaned and pretreated and roughened, a ceramic transition layer with a thickness of 80-120 μm is prepared on the surface of the titanium alloy substrate by using thermal spraying technology, and the composition of the ceramic transition layer is Al2O3-13wt.%TiO2.

[0009] The role of the ceramic transition layer:

[0010] The thermal expansion coefficient of Al2O3-13wt.%TiO2 is between the titanium alloy substrate and the radar wave-absorbing coating; compared with the traditional double-layer structure of the titanium alloy substrate and the radar wave-absorbing coating, this structure can avoid the cracking failure problem caused by the difference in thermal expansion coefficient during high-temperature sintering and use, and mainly plays the roles of stress release and improving the interlayer bonding strength.

[0011] The advantage of preparing the ceramic transition layer by using thermal spraying technology is that this technology has concentrated energy and high deposition efficiency, can fully melt the ceramic powder to form a liquid phase, and accelerate the deposition on the surface of the titanium alloy substrate. During high-temperature and high-speed deposition, the molten particles form a local molten pool by contacting the substrate and react with the titanium alloy substrate elements to generate intermetallic compounds such as TiAl and AlTi3. These products significantly improve the bonding strength between the coating and the substrate under the combined action of mechanical riveting effect and metallurgical bonding effect.

[0012] In the ceramic transition layer, the Al 3+ ceramic phase provides abundant Al 3+ , which is significantly higher than the Al 3+ in the subsequently prepared modified transition layer, forming a stable concentration gradient diffusion mechanism under high-temperature conditions; and is conducive to the diffusion of Al 2+ to the modified transition layer and the diffusion of Ca 4+The reaction occurs to form a dense CaAl2Si2O8 phase, thereby constructing a dense structure at the interface and improving the interlayer bonding strength. In addition, the ceramic transition layer prepared by thermal spraying technology provides abundant diffusion channels due to its inherent porous structure, crack network and high grain boundary density, further promoting interfacial reaction and element migration. 3+ TiO2 not only improves the wettability of the ceramic transition layer to the modified transition layer, increases the interfacial reaction area, and promotes effective diffusion of elements, but also adjusts the difference in thermal expansion coefficient, optimizes the overall stress distribution, and enhances the structural stability and high-temperature service reliability of the coating.

[0013] Step 2, preparation of the modified transition layer;

[0014] The glass powder, deionized water and sodium carboxymethyl cellulose are prepared into a glass slurry, which is coated on the surface of the ceramic transition layer. After drying, a modified transition layer with a thickness of 5-10 μm is prepared by high-temperature sintering.

[0015] The glass powder is CaO-B2O3-SiO2-Al2O3-TiO 2- ZrO2, with a particle size of less than 2 μm, and a mass ratio of 30-36% CaO, 33-37% SiO2, 18-22% B2O3, 4-9% Al2O3, 2-5% TiO2, and 1-4% ZrO2, with a total amount of 1.

[0016] The dispersion medium of the glass slurry is deionized water, and the solid content of the slurry is 40-60 wt.%. The sodium carboxymethyl cellulose accounts for 1-5 wt.% of the total mass of the glass powder, and the sodium carboxymethyl cellulose is a thickening agent.

[0017] The high-temperature sintering is specifically: the atmosphere is argon, the gas flow is 10-30 mL / min; the sintering temperature is 800-900℃, and the heating rate is 5-10℃ / min.

[0018] The drying conditions are specifically: temperature 10-30℃, humidity 30-50%, drying time 2-24h, ventilation environment, to avoid surface cracking caused by too fast drying.

[0019] The role of the modified transition layer:

[0020] On the one hand, the modified transition layer provides a high-temperature environment by high-temperature sintering, promoting liquid flow and fully contacting with the ceramic transition layer, so that the materials between the two layers form a cooperative effect to achieve dense bonding. In addition, the dense modified transition layer prepared by high-temperature sintering also has the effect of protecting the titanium alloy substrate, which can isolate corrosive media such as water and oxygen from oxidizing the titanium alloy substrate.

[0021] On the other hand, the radar wave absorbing coating is mainly composed of glass powder and magnetic absorber. The glass powder needs to be softened and form a glass liquid phase in the high-temperature sintering process, but the flow of the glass liquid phase will be hindered by the magnetic absorber, so the sintering temperature needs to be increased to completely infiltrate the lower ceramic transition layer to achieve dense sintering. However, the element diffusion phenomenon (including the reaction between the magnetic absorber and the glass liquid phase components) will be intensified at high temperature, and the cracking problem of the radar wave absorbing coating caused by the mismatch of thermal shrinkage will reduce the electromagnetic wave absorption effect of the radar wave absorbing coating. By preparing a modified transition layer with similar element composition on the surface of the ceramic transition layer, when the heat treatment temperature is higher than the glass softening temperature, the flowability of the glass powder in the radar wave absorbing layer is enhanced, which can cause adhesion, flow diffusion and rearrangement on the surface of the modified transition layer, so that the radar wave absorbing coating and the lower structure are fused and form a tight bond. This enables the radar wave absorbing coating to be formed at a lower sintering temperature, thereby effectively avoiding the element diffusion phenomenon and the cracking problem of the absorbing coating caused by the mismatch of thermal shrinkage in the high-temperature sintering process, improving the electromagnetic wave absorption effect and overall bonding strength of the radar wave absorbing coating.

[0022] Step 3, preparation of the radar wave absorbing layer;

[0023] The glass powder, magnetic absorber, deionized water, polyvinyl alcohol and sodium carboxymethyl cellulose are prepared into a mixed slurry, which is coated on the surface of the modified transition layer, and then dried to obtain the radar wave absorbing layer by high-temperature sintering; the thickness of the radar wave absorbing layer is 500-700 μm.

[0024] The magnetic absorber accounts for 20-35% of the total volume of the glass powder and the magnetic absorber, the solid content of the mixed slurry is 50-70 wt.%, the polyvinyl alcohol accounts for 3-5 wt.% of the total volume of the glass powder and the magnetic absorber, and the sodium carboxymethyl cellulose accounts for 1-5 wt.% of the total mass of the glass powder and the magnetic absorber; wherein the polyvinyl alcohol is a dispersant and the sodium carboxymethyl cellulose is a thickening agent; the magnetic absorber is a high-temperature resistant magnetic absorber (such as Fe-based), the particle size is less than 5 μm, and the Curie temperature is greater than 600 ℃.

[0025] The glass powder has the same composition and particle size as the glass powder in step 2.

[0026] The high-temperature sintering process is: the atmosphere is air or argon, the gas flow is 10-30 mL / min; the sintering temperature is 720-800 ℃, and the heating rate is 2-5 ℃ / min.

[0027] The drying conditions are specifically: the temperature is 10-30 ℃, the humidity is 30-50%, the drying time is 2-24 h, and the environment is ventilated; avoid surface cracking caused by too fast drying.

[0028] In the present application, the sodium carboxymethyl cellulose used has good solubility in water, and its long-chain high molecular backbone can significantly increase the viscosity of the slurry system, effectively inhibit the settlement of the magnetic absorbent caused by its large density, and improve the dispersion uniformity of the magnetic absorbent and the microcrystalline glass in the slurry. In addition, the hydroxyl and carboxyl groups in the sodium carboxymethyl cellulose molecule can form hydrogen bonds with water molecules and cross-link with polyvinyl alcohol to construct a three-dimensional network structure in the system.

[0029] On the one hand, during the drying process, the slurry viscosity further increases, and the three-dimensional network structure also plays a role in assisting the dispersion of the magnetic absorbent and the microcrystalline glass to provide space support, prevent the structure from being uneven due to gravity stratification, and improve the integrity of the coating, effectively inhibiting the cracks that occur during the drying process.

[0030] On the other hand, the three-dimensional network structure constructed by sodium carboxymethyl cellulose and polyvinyl alcohol plays a transitional role in the uniform dispersion of the magnetic absorbent and microcrystalline powder particles in the coating after sintering. This is because the microcrystalline glass powder will soften during high-temperature sintering, and the microcrystalline glass powder will fuse to form a new three-dimensional network support structure, providing overall support for the coating. The softened microcrystalline glass powder has a high viscosity, so the magnetic absorbent powder can still be uniformly dispersed in the wave-absorbing coating, making the final prepared wave-absorbing coating have excellent performance.

[0031] During the final sintering process, sodium carboxymethyl cellulose will undergo thermal decomposition in a high-temperature environment, forming CO2 and Na2O. The removal of CO2 gas will form a micro-pore structure inside the material, which can provide electromagnetic scattering effect to further improve the electromagnetic wave absorption performance of the material. Secondly, the residual Na2O will destroy the glass network, forming non-bridging oxygen, thereby reducing the glass transition temperature and viscosity, and reducing the sintering temperature. Promote the flow of glass phase during sintering, so that it can better wet and wrap around the surface of the magnetic absorbent.

[0032] Through the cooperation of sodium carboxymethyl cellulose, polyvinyl alcohol, glass powder and sintering process, the micro-state change during the process is designed and controlled, so that the magnetic absorbent can always be uniformly dispersed in the radar wave-absorbing coating, making the coating have excellent electromagnetic wave absorption effect, and also have other excellent performances required by wave-absorbing materials.

[0033] It should be noted that: too high sodium carboxymethyl cellulose will increase the viscosity of the material slurry, hinder the dispersion of the magnetic absorbent and microcrystalline glass powder in the slurry, and cause agglomeration, thereby reducing the performance of the electromagnetic wave absorber. And during the high-temperature sintering process, the excessive CO2 gas will cause a large number of holes in the material, forming a through crack in the coating, which will reduce the integrity and stiffness of the coating.

[0034] The forming performance and various physical properties of the glass-ceramics are improved by adjusting the composition of the glass-ceramics: SiO2 mainly plays a role of network intermediate to enhance the strength of the glass skeleton in the glass matrix. CaO2 can reduce the glass viscosity, improve the glass flowability, promote the flow and forming effect of the particles in the high-temperature sintering process, and form a low-dielectric β-CaSiO3 phase with SiO2. B2O3 can reduce the melting temperature of the glass. Al2O3 can promote the formation of glass liquid phase, so that the glass can occur at a lower temperature. TiO2 can enhance the surface wetting performance between the ceramic transition layer and the surface wetting performance between the glass-ceramics powder and the lower layer substrate, so that it can fully contact and improve the chemical diffusion. ZrO2 material can adjust the thermal expansion coefficient of the glass, reduce the coating cracking caused by temperature change during cooling and rising of the material. By adjusting the component distribution in the glass-ceramics, the sintering temperature, forming performance and final functionality of the material are changed.

[0035] Step 4, preparation of the environmental functional layer;

[0036] The surface of the radar wave absorbing layer is instantaneously heated by using plasma surface treatment technology or laser cladding technology, so that a dense environmental functional layer is prepared on the surface layer of the radar wave absorbing layer.

[0037] The role of the environmental functional layer:

[0038] The plasma surface treatment technology or laser cladding method has the significant advantages of concentrated heat source and high energy density in constructing the environmental functional layer. After high-temperature sintering, there are pore structures on the surface of the coating (the surface of the radar wave absorbing layer) due to liquid phase shrinkage and exhaust. Such pore structures can allow corrosive media such as oxygen and water vapor to enter the coating, and some magnetic absorbing agent particles in the coating that are not completely wrapped during the sintering process will be oxidized and corroded. The generation of oxides will cause the coating to crack and the electromagnetic wave absorption performance to decrease.

[0039] The preparation of the environmental functional layer can form a short-term high heat source on the surface of the coating layer, generate a local liquid phase, and fill the coating layer surface pores and cracks under the driving of surface tension and capillary action, thereby blocking the penetration channel of corrosion media such as oxygen or water oxygen. Compared with the traditional overall heat treatment process, only the surface layer is heated, avoiding the volume shrinkage stress caused by overall densification and reducing the risk of cracking failure of the coating. At the same time, compared with the traditional preparation of a layer of environmental functional layer (such as glaze) on the surface coating as an environmental isolation layer, the method is more convenient and reduces the complexity of coating preparation. The densified environmental functional layer is directly prepared by melting the surface layer of the radar wave absorbing layer, and the interlayer bonding force is exceptionally strong. The porosity shrinkage caused by densification will increase the dielectric constant, but some low dielectric constant crystal particles will appear on the surface of the particles, which can reduce the influence on the electromagnetic parameters, have better electromagnetic wave absorption effect, and the thickness of the environmental functional layer is much smaller than the wavelength of the radar wave, so the influence on the electromagnetic wave absorption performance is small.

[0040] The traditional environmental functional layer is prepared by selecting different materials, which will cause the electromagnetic wave absorbing coating to have obvious deterioration of the wave absorbing performance.

[0041] Further, the coating method of step 2 is screen printing, which has stronger film uniformity.

[0042] Further, the mixing method of the mixed slurry prepared in step 3 is: first, deionized water, polyvinyl alcohol, sodium carboxymethyl cellulose and magnetic absorber are mixed for 2-5h by horizontal ball mill, then glass powder is added and mixed for 10-24h. The horizontal ball mill has small momentum, which can avoid polymer degradation and reaction caused by temperature rise of the slurry. Secondly, the magnetic absorber is mixed first to improve the dispersion uniformity of the magnetic absorber and avoid agglomeration when the magnetic absorber and the glass powder are mixed at the same time.

[0043] Further, the thickness of the radar wave absorbing coating is designed by multiple repeated sintering in step 3, and the single radar wave absorbing coating sintering thickness is 80-100μm, which can release stress and further improve the linearity of interlayer stress to make the interlayer bonding force better.

[0044] Further, the thickness of the environmental functional layer is 20-50μm.

[0045] Further, a high-temperature-resistant radar wave absorbing coating is prepared by the above method.

[0046] In summary, the present application constructs a 4-layer radar absorbing coating of ceramic transition layer-modified transition layer-radar absorbing layer-environmental functional layer; firstly, a ceramic transition layer of Al2O3-13wt.%TiO2 is made on the surface of the titanium alloy substrate by thermal spraying; then a specially designed modified transition layer and a radar absorbing layer are prepared in turn by high temperature sintering, so as to design and control the micro-state change in the preparation process by the synergistic effect of sodium carboxymethyl cellulose, polyvinyl alcohol, glass powder and sintering process, so that the multi-dimensional collaboration effect (interface, microstructure distribution) between materials and between materials and process is generated between the three layers of materials, not only the interlayer adhesion, but also the stress buffering and release of the overall material system, but also the optimization of the absorbing performance; finally, the surface of the radar absorbing layer is directly cladded into a dense environmental functional layer, which further protects the overall radar absorbing coating without deteriorating the absorbing performance of the overall radar absorbing coating. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is the interlayer structure diagram of the high-temperature radar absorbing coating of the present application.

[0048] Figure 2 is the physical picture of the high-temperature radar absorbing coating of example 1.

[0049] Figure 3 is the SEM picture of the cross section of the high-temperature radar absorbing coating of example 1.

[0050] Figure 4 is the SEM enlarged picture of the cross section of the modified transition layer and the ceramic transition layer in the high-temperature radar absorbing coating of example 1.

[0051] Figure 5 is the SEM picture of the coating surface of the high-temperature radar absorbing coating of example 1.

[0052] Figure 6 is the SEM picture of the coating surface of the high-temperature radar absorbing coating of comparative example 4.

[0053] Figure 7 is the XRD comparison chart of the high-temperature radar absorbing coating of example 1 at 600 DEG C high temperature test for 0h and 300h.

[0054] Figure 8 is the oxidation weight gain chart of the high-temperature radar absorbing coating of example 1 at 600 DEG C high temperature test for 0-300h.

[0055] Figure 9 is the vertical reflectivity comparison chart of the high-temperature radar absorbing coating of example 1 at 600 DEG C high temperature test for 0h and 300h.

[0056] Figure 10is a comparison chart of the vertical reflectivity of the high-temperature resistant radar wave absorbing coating of Example 1 at room temperature and 600℃.

[0057] Figure 11 is a comparison chart of the vertical reflectivity of the high-temperature resistant radar wave absorbing coating of Example 1, Comparative Example 4 and Comparative Example 6 at room temperature.

[0058] Figure 12 is a cracking failure chart of Comparative Example 9 and Comparative Example 10 occurring during preparation. DETAILED DESCRIPTION

[0059] The application will be further described in detail below in combination with the drawings and examples.

[0060] Example 1

[0061] A preparation method of a high-temperature resistant radar wave absorbing coating, comprising the following steps:

[0062] Step 1, preparation of a ceramic transition layer;

[0063] The titanium alloy substrate is TC4, first, the surface rust layer is removed by shot blasting, then the surface is cleaned by using kerosene, acetone, alcohol and deionized water in sequence, and then the substrate is sandblasted by using corundum to obtain a uniform roughness on the surface. The preparation method is atmospheric plasma spraying, and the atmospheric plasma spraying process parameters are: a spraying distance of 120 mm, an argon flow rate of 160 SCFH, a nitrogen flow rate of 60 SCFH, a hydrogen flow rate of 60 SCFH, and a spraying power of 55 kW. An Al2O3-13wt.%TiO2 ceramic transition layer with a thickness of 100 μm is sprayed.

[0064] Step 2, preparation of a modified transition layer;

[0065] The mass ratio composition of the glass raw material powder is: 36% CaO, 37% SiO2, 20% B2O3, 4% Al2O3, 2% TiO2 and 1% ZrO2. The glass raw material powder is mixed and uniformly and is melted at 1400℃ for 2h to obtain a glass solution; then the glass solution is poured into deionized water for quenching to obtain glass slag, and is ball milled to obtain glass powder. The glass powder is mixed with deionized water and sodium carboxymethyl cellulose to prepare a glass slurry, wherein the solid content of the glass slurry is 50%, the sodium carboxymethyl cellulose accounts for 3wt.% of the total mass of the solids, the mixing is performed by using a horizontal ball mill at a speed of 100 RPM for 24h, and the particle size is less than 2 μm after ball milling.

[0066] The modified transition coating layer with a thickness of 10 μm is prepared on the surface of the ceramic transition layer by using a screen printing technique; and the sample is dried in an environment with a temperature of 20℃ and a humidity of 40% for 2 hours.

[0067] Step 3, preparation of the radar wave absorbing layer;

[0068] The high-temperature-resistant magnetic absorber Fe 90 Si7Cr3, the same glass powder in Step 2, deionized water, polyvinyl alcohol and sodium carboxymethyl cellulose are mixed to prepare a slurry; the solid content of the slurry is 60%, the FeSiCr accounts for 25 vol.% of the total volume of solids, the polyvinyl alcohol accounts for 3 wt.% of the total mass of solids, and the sodium carboxymethyl cellulose accounts for 3 wt.% of the total mass of solids; the horizontal ball mill is used for mixing at a speed of 100 RPM for 24 hours.

[0069] The radar wave absorbing coating layer with a thickness of 100 μm is prepared on the surface of the modified transition layer by using a doctor blade method, and is dried in an environment with a temperature of 20℃ and a humidity of 40% for 24 hours. The sample after drying is subjected to high-temperature sintering, and the sintering parameters are as follows: a sintering temperature of 750℃, a holding time of 0.5 hours, a temperature rising rate of 5℃ / min, an atmosphere of argon, and a gas flow rate of 20 mL / min. The above process is repeated for several times until the thickness of the radar wave absorbing layer reaches 700 μm.

[0070] Step 4, preparation of the environmental functional layer;

[0071] The surface of the radar wave absorbing layer obtained in Step 3 is instantaneously heated by using a plasma surface treatment technology (atmospheric plasma surface treatment), so that a 30 μm dense environmental functional layer is prepared on the surface layer of the radar wave absorbing layer by cladding.

[0072] The atmospheric plasma surface treatment process parameters are as follows: a workpiece distance of 80 mm, an argon flow rate of 180 SCFH, a nitrogen flow rate of 80 SCFH, a hydrogen flow rate of 80 SCFH, and a treatment power of 85 kW, and the process is stopped when the surface temperature reaches 800℃. The interlayer structure of the high-temperature-resistant radar wave absorbing coating layer finally prepared is shown in Figure 1 . Figure 2 is a physical picture of the high-temperature-resistant radar wave absorbing coating layer of Example 1, Figure 3 is an SEM picture of the cross section of the high-temperature-resistant radar wave absorbing coating layer of Example 1, Figure 4 is an SEM enlarged picture of the cross section of the modified transition layer and the ceramic transition layer in the high-temperature-resistant radar wave absorbing coating layer of Example 1, Figure 5 is an SEM picture of the coating surface of the high-temperature-resistant radar wave absorbing coating layer of Example 1.

[0073] Example 2

[0074] Example 2 differs from Example 1 only in that the glass raw material powder is composed of the following mass ratio: CaO: 30%, SiO2: 33%, B2O3: 19%, Al2O3: 9%, TiO2: 5%, ZrO2: 4%.

[0075] Example 3

[0076] Example 3 differs from Example 1 only in that the glass raw material powder is composed of the following mass ratio: CaO: 35%, SiO2: 37%, B2O3: 18%, Al2O3: 5%, TiO2: 3%, ZrO2: 2%.

[0077] Example 4

[0078] Example 4 differs from Example 1 only in that the sodium carboxymethyl cellulose content in Step 3 is 1 wt.%.

[0079] Example 5

[0080] Example 5 differs from Example 1 only in that the sodium carboxymethyl cellulose content in Step 3 is 5 wt.%.

[0081] Comparative Example 1

[0082] Comparative Example 1 differs from Example 1 only in that no ceramic transition layer is prepared.

[0083] Comparative Example 2

[0084] Comparative Example 2 differs from Example 1 only in that no modified transition layer is prepared.

[0085] Comparative Example 3

[0086] Comparative Example 3 differs from Example 1 only in that the ceramic transition layer is composed of an alumina coating layer only.

[0087] Comparative Example 4

[0088] Comparative Example 4 differs from Example 1 only in that no environmental functional layer is prepared.

[0089] Comparative Example 5

[0090] Comparative Example 5 differs from Example 1 only in that no ceramic transition layer and no modified transition layer are prepared.

[0091] Comparative Example 6

[0092] Comparative Example 6 differs from Example 1 only in that no sodium carboxymethyl cellulose is added in Step 3.

[0093] Comparative Example 7

[0094] The difference between Comparative Example 7 and Example 1 is only that the sodium carboxymethyl cellulose content in step 3 is 6 wt.%.

[0095] Comparative Example 8

[0096] The difference between Comparative Example 8 and Example 1 is only that the glass raw material is composed of the following mass ratio: CaO: 37%, SiO2: 41%, B2O3: 22%. Without the addition of Al2O3, TiO2 and ZrO2, the liquidus flowability of the glass powder and the surface wettability of the lower ceramic transition layer will be reduced, and the thermal expansion coefficient will be increased. During the coating preparation process, it will not be able to be shaped due to thermal shrinkage mismatch and other reasons.

[0097] Comparative Example 9

[0098] The difference between Comparative Example 9 and Example 1 is only that the drying temperature is 60°C.

[0099] Comparative Example 10

[0100] The difference between Comparative Example 10 and Example 1 is only that the environmental functional layer in step 4 is prepared by heat treatment, the heat treatment temperature is 800°C, the heat treatment time is 0.5h, the atmosphere is argon, the gas flow is 20mL / min, the heating rate is 5°C / min, and the furnace cooling is used.

[0101] The coating samples prepared in Examples 1-5 and Comparative Examples 1-6 were tested for performance, including temperature resistance and adhesion tests. The adhesion test results were divided into pre-high temperature test (600°C-0h) and post-high temperature test (600°C-10h). The high temperature test conditions were: temperature 600°C for 10h. Among them, Comparative Examples 7-10 had no test results because: the slurry of Comparative Example 7 was too thick to achieve coating preparation, and obvious cracking and alligatoring phenomenon occurred during the coating preparation of Comparative Examples 8-10, so they were not included. The specific test characterization analysis is as follows: the temperature resistance performance uses 600°C / 300h, and the coating surface does not crack, alligator and fall off as the qualified standard; the adhesion test is divided into 0h and 10h at 600°C, and the test results are shown in Table 1.

[0102] Table 1:

[0103] Number Temperature resistance Adhesion before high temperature test (MPa) Adhesion after high temperature test (MPa) Example 1 Pass 22 22 Example 2 Pass 29 28 Example 3 Pass 26 25 Example 4 Pass 23 22 Example 5 Pass 19 18 Comparative Example 1 Failure 12 7 Comparative Example 2 Failure 13 6 Comparative Example 3 Failure 18 8 Comparative Example 4 Failure 21 10 Comparative Example 5 Failure 10 5 Comparative Example 6 Failure 20 6 According to Table 1, the coating of Examples 1-5 can be used at 600°C for a long time, and the adhesion has no obvious change before and after high temperature test. The test results show that the addition of ceramic transition layer and modified transition layer can effectively improve the bonding strength of radar absorbing coating and titanium alloy substrate; the preparation of environmental functional layer can inhibit the corrosion of magnetic absorber and improve the adhesion of coating; improving the dispersibility of magnetic absorber in the coating can improve the adhesion of the coating.

[0104] By comparison Figure 5 and Figure 6 It can be seen that the prepared environmental functional layer has significantly reduced porosity compared to the radar absorbing layer, and the surface magnetic absorbent is obviously wrapped by glass.

[0105] By Figure 7 and Figure 8 It can be seen that by preparing the environmental functional layer, the overall phase of the coating does not change significantly and the oxidation weight gain trend is not obvious. The test results show that the environmental functional layer can effectively improve the oxidation resistance of the coating.

[0106] Figure 9 The vertical reflectivity comparison chart of Example 1 after 0h and 300h high temperature test at 600℃. The test results show that the radar absorbing effect of the coating is stable, and the vertical reflectivity changes little after long-term service in high temperature environment, which meets the application requirements.

[0107] Figure 10 The vertical reflectivity comparison chart of Example 1 at room temperature and 600℃. The test results show that during the temperature change process, the vertical reflectivity result changes little, which can meet the use under high temperature.

[0108] Figure 11 The vertical reflectivity comparison chart of Example 1, Comparative Example 4 and Comparative Example 6. The test results show that the environmental functional layer does not significantly change the absorption effect of the coating on electromagnetic waves; due to the lack of the dispersing effect of sodium carboxymethyl cellulose in the slurry and drying process, the magnetic absorbent is obviously settled and agglomerated, which makes the electromagnetic wave absorption effect of the coating worse.

[0109] Figure 12 The cracking failure chart of Comparative Example 9 and Comparative Example 10 during preparation. The test results show that when the drying temperature is too high, due to the accelerated evaporation rate of water, the coating surface cracks; high sintering temperature will cause the radar absorbing coating to crack due to mismatched thermal shrinkage.

[0110] It can be seen from the above examples that, compared with the prior art, the present application solves the problems of poor compatibility of the bonding strength, environmental adaptability and radar wave absorbing performance between the titanium alloy substrate and the radar wave absorbing coating by the multi-layer structure design and the adjustment of material components and proportions. The present application prepares a high-temperature-resistant radar wave absorbing coating by the multi-layer structure design and the adjustment of material components and proportions. The ceramic transition layer and the modified transition layer have good bonding performance to the titanium alloy substrate and the radar wave absorbing layer by the combined action of mechanical bonding and chemical bonding, and significantly improve the adhesion between the titanium alloy substrate and the radar wave absorbing layer under the combined action of the ceramic transition layer and the modified transition layer. The synergistic effect of sodium carboxymethyl cellulose and glass powder in the slurry preparation, drying and high-temperature sintering process promotes the dispersibility of the magnetic absorbent in the radar wave absorbing coating, and improves the radar wave absorbing performance of the coating. And the environmental functional layer is directly remelted on the surface layer of the radar wave absorbing layer for the first time, which improves the chemical stability of the overall radar wave absorbing coating in the high-temperature environment without damaging the original radar absorbing effect. The present application effectively solves the problems of poor compatibility of the bonding strength, environmental adaptability and radar wave absorbing performance between the titanium alloy substrate and the radar wave absorbing coating. The coating can be used stably for a long time in an environment temperature of 600 DEG C, and has excellent bonding strength and radar wave absorbing effect.

Claims

1. A method for preparing a high-temperature resistant radar absorbing coating, characterized in that, The method comprises the following steps: Step 1, ceramic transition layer preparation; The surface of the titanium alloy substrate is cleaned and pretreated and roughened, and a ceramic transition layer with a thickness of 80-120 μm is prepared on the surface of the titanium alloy substrate by thermal spraying technology, and the composition of the ceramic transition layer is Al2O3-13wt.%TiO2; Step 2, modified transition layer preparation; Glass powder, deionized water and sodium carboxymethyl cellulose are prepared into a glass slurry, which is coated on the surface of the ceramic transition layer, and after drying, a modified transition layer with a thickness of 5-10 μm is prepared by high temperature sintering; The glass powder is CaO-B2O3-SiO2-Al2O3-TiO2, the particle size is less than 2 μm, and the mass ratio of each component is: 30-36% CaO, 33-37% SiO2, 18-22% B2O3, 4-9% Al2O3, 2-5% TiO2, and 1-4% ZrO2, with a total amount of 1; The solid content of the glass slurry is 40-60wt.%; the sodium carboxymethyl cellulose accounts for 1-5wt.% of the total mass of the glass powder, and the sodium carboxymethyl cellulose is a thickening agent; The high temperature sintering is specifically: the atmosphere is argon, the gas flow is 10-30 mL / min; the sintering temperature is 800-900℃, and the heating rate is 5-10℃ / min; The drying conditions are specifically: temperature 10-30℃, humidity 30-50%, drying time 2-24h, and ventilation environment; Step 3, radar wave absorbing layer preparation; Glass powder, magnetic absorber, deionized water, polyvinyl alcohol and sodium carboxymethyl cellulose are prepared into a mixed slurry, which is coated on the surface of the modified transition layer, and after drying, a radar wave absorbing layer is prepared by high temperature sintering; the thickness of the radar wave absorbing layer is 500-700 μm; The magnetic absorber accounts for 20-35% of the total volume of the glass powder and the magnetic absorber solid, the solid content of the mixed slurry is 50-70wt.%, the polyvinyl alcohol accounts for 3-5wt.% of the total mass of the glass powder and the magnetic absorber solid, and the sodium carboxymethyl cellulose accounts for 1-5wt.% of the total mass of the glass powder and the magnetic absorber solid; wherein the polyvinyl alcohol is a dispersing agent, the sodium carboxymethyl cellulose is a thickening agent; the magnetic absorber is a high-temperature-resistant magnetic absorber, the particle size is less than 5 μm, and the Curie temperature is greater than 600℃; The composition and particle size of the glass powder in step 3 are the same as those of the glass powder in step 2; The high temperature sintering process in step 3 is: the atmosphere is air or argon, the gas flow is 10-30 mL / min; the sintering temperature is 720-800℃, and the heating rate is 2-5℃ / min; The drying conditions in step 3 are specifically: temperature 10-30℃, humidity 30-50%, drying time 2-24h, and ventilation environment; Step 4, environmental functional layer preparation; The surface of the radar wave absorbing layer is instantaneously heated by plasma surface treatment technology or laser cladding technology, so that a dense environmental functional layer is prepared on the surface layer of the radar wave absorbing layer.

2. The method for preparing the high-temperature resistant radar absorbing coating as described in claim 1, characterized in that: The coating method of step 2 is screen printing.

3. The preparation method of the high-temperature-resistant radar wave absorbing coating according to claim 1, characterized in that: The mixing method of the mixed slurry prepared in the step 3 is that: firstly, the deionized water, polyvinyl alcohol, sodium carboxymethyl cellulose and magnetic absorbent are mixed for 2-5 h by using a horizontal ball mill, then the glass powder is added and mixed for 10-24 h.

4. The method for preparing the high-temperature resistant radar absorbing coating as described in claim 1, characterized in that: The step 3 is repeated by multiple times of sintering to a specific designed thickness of the wave-absorbing coating, and the single-time sintering thickness of the radar wave-absorbing coating is 80-100 μm.

5. The method for preparing the high-temperature resistant radar absorbing coating as described in claim 1, characterized in that: The thickness of the environmental functional layer is 20-50 μm.

6. A high temperature resistant radar absorbing coating, characterized by: The method is prepared by any one of the above claims 1-5.

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