A high-temperature resistant mullite / SiCN composite microwave absorbing coating and its preparation method

Abstract

The present invention relates to the technical field of high-temperature absorbing coating materials, specifically to a high-temperature resistant mullite / SiCN composite absorbing coating and its preparation method. This absorbing coating is a layer greater than or equal to 0.4 mm thick, prepared on a substrate using mullite / SiCN composite powder as raw material. The mullite / SiCN composite powder comprises mullite powder and SiCN powder, with a mass ratio of mullite powder to SiCN powder ranging from 1.5 to 9:1. This high-temperature resistant mullite / SiCN composite absorbing coating and its preparation method aim to address the problem of increased overall coating weight associated with existing high-temperature resistant absorbing coatings, which require a thermal matching layer to enhance the coating's thermal shock resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature absorbing coating materials, and in particular to a high-temperature resistant mullite / SiCN composite absorbing coating and a preparation method thereof. Background Art

[0002] In recent years, research on microwave absorbing materials has facilitated the application of microwave technology in fields such as civilian communications. Through further development, these microwave absorbing materials have become thinner, lighter, and more efficient. Absorbing coatings are a key application of microwave absorbing materials, offering advantages such as easy construction, excellent absorption performance, and minimal impact on the original state of the substrate. However, most current absorbing materials that are effective at room temperature lose their magnetism at high temperatures (>700K), making the development of high-temperature absorbing coatings a critical technology that needs to be addressed urgently. At the same time, ideal high-temperature absorbing coatings require thin thickness, strong absorption, and good thermal shock resistance to better meet application requirements.

[0003] He Qing and others from the Chinese Academy of Agricultural Mechanization Sciences used phosphate glass binders and dispersants, and modified β-SiC materials as absorbers. They used arc spraying to prepare a Ni-Al metal bonding layer with a thickness of about 50 μm to reduce the difference in thermal expansion coefficient between the absorbing coating and the substrate. They also used flame spraying to prepare the absorbing coating on the carbon steel surface, with the coating thickness controlled at about 1 mm. Lu Yanhong from China Iron and Steel Research Institute Co., Ltd. used a mechanochemical method to coat nano-silicon carbide on the surface of micron nickel powder to prepare a nano-composite nickel powder absorbing material. They used plasma spraying to prepare a nano-composite nickel powder / carbonyl iron powder double-layer absorbing coating on the surface of an aluminum plate, and studied the effect of the change in SiC content in the composite material on the coating's absorbing properties. M. Bégard et al. used BaCO3, Co3O4, TiO2, and Fe2O3 as raw materials to synthesize Co and Ti substituted barium ferrite BaCoTiFe 10 O 19 , and used high velocity flame spraying (HVOF) and atmospheric plasma spraying (APS) to prepare absorbing coatings on glass ceramic substrates. The research results showed that the barium ferrite coating prepared by thermal spraying is suitable for use as a microwave and millimeter wave absorbing material.

[0004] High-temperature absorbing coating materials are mainly ceramic materials. Due to the poor thermal conductivity of ceramics, rapid heating or cooling will form a temperature difference inside the ceramics. In order to improve the absorbing performance, the absorbing coating is often thicker, which makes it easier to generate greater thermal stress inside the coating, leading to problems such as delamination, cracking, and decreased adhesion of the coating, and even damage and falling off, thereby restricting the performance of the absorbing material. The main measure currently being taken in research is to select materials with appropriate thermal expansion coefficients as transition layers for different substrates. However, this solution will increase the thickness and mass of the coating, which does not meet the coating weight reduction index and is not suitable for SiC. f There is relatively little research on coating materials for SiC ceramic matrix composites. The present invention aims to overcome the shortcomings of existing methods and provide a method for preparing a high-temperature resistant bicontinuous structure spherical wave-absorbing composite powder. The bicontinuous structure is achieved by regulating the component content and particle size of the mullite phase and SiCN phase in the composite powder. The powder component phases are all in contact with SiC. f / SiC composites have good thermal matching, and the spherical composite powder has good fluidity, which is conducive to plasma spraying to prepare coatings. The prepared coatings can be compatible with SiC f The SiC / SiC ceramic-based composite substrate maintains good thermal matching performance and does not require the introduction of a transition layer, which is conducive to the lightweighting of the material. In addition, the mullite phase can play an impedance matching role, and the SiCN phase is an absorber. The bicontinuous structure ensures the homogeneous composite of material properties. The coating prepared from the material meets the impedance matching requirements and has good absorbing performance.

[0005] The shortcomings of the existing methods mainly include: in order to achieve the absorption performance index of the existing high temperature resistant absorbing coating materials, the final coating often needs to use a thermal matching layer to enhance the thermal shock resistance of the coating, and the introduction of the thermal matching layer will increase the overall weight of the coating, which does not meet the lightweight index. In addition, at this stage, the SiC f There is relatively little research on absorbing coatings based on / SiC ceramic matrix composite materials, and there is a lack of corresponding high-temperature resistant coating material systems with good absorbing performance and thermal shock resistance for reference.

[0006] Therefore, the inventors provide a high-temperature resistant mullite / SiCN composite microwave absorbing coating and a preparation method thereof. Summary of the Invention

[0007] (1) Technical problems to be solved

[0008] The embodiments of the present invention provide a high-temperature resistant mullite / SiCN composite absorbing coating and a preparation method thereof, which solves the technical problem that the existing high-temperature resistant absorbing coating requires a thermal matching layer to enhance the thermal shock resistance of the coating, resulting in an increase in the overall weight of the coating.

[0009] (2) Technical solution

[0010] A first aspect of the present invention provides a high-temperature resistant mullite / SiCN composite absorbing coating, which is a 0.4 mm thick absorbing coating prepared on a substrate using mullite / SiCN composite powder as a raw material; wherein the mullite / SiCN composite powder comprises mullite powder and SiCN powder, and the mass ratio of the mullite powder to the SiCN powder is 1.5 to 9:1.

[0011] Furthermore, the substrate is SiC f / SiC ceramic matrix composites.

[0012] Furthermore, the thickness of the absorbing coating is 0.4 mm to 0.6 mm.

[0013] Furthermore, the mullite / SiCN composite powder is a spherical composite powder with a bicontinuous structure prepared by a spray drying granulation process.

[0014] Furthermore, the particle size of the mullite / SiCN composite powder is 30 μm to 80 μm.

[0015] A second aspect of the present invention provides a method for preparing a high-temperature resistant mullite / SiCN composite radar absorbing coating, comprising the following steps:

[0016] Mullite powder, SiCN powder, binder and deionized water are mixed uniformly to obtain a suspension;

[0017] The suspension is subjected to a spray drying granulation process to prepare a powder, the obtained powder is dried and passed through a test sieve to obtain a mullite / SiCN bicontinuous structure composite powder;

[0018] Roughen the surface of the substrate to be sprayed and remove the residual sand on the surface of the substrate to make the surface of the substrate reach the preset roughness;

[0019] Preheating the substrate at a set temperature;

[0020] The mullite / SiCN bicontinuous structure composite powder is sprayed on the substrate to form a mullite / SiCN composite microwave absorbing coating.

[0021] Furthermore, the mullite powder, SiCN powder, binder and deionized water are uniformly mixed to obtain a suspension, specifically:

[0022] The suspension is obtained by mixing in a ball milling manner, with a ball milling speed of 150 rpm to 420 rpm, a ball milling time of 2.5 h to 5 h, and a ball-to-material ratio of 4 to 6:1.

[0023] Furthermore, the parameters of the spray drying granulation process are: inlet temperature 200°C to 300°C, outlet temperature 120°C to 160°C, nozzle speed 25Hz to 40Hz, and peristaltic pump speed 30rpm to 45rpm.

[0024] Furthermore, the substrate is preheated at a set temperature, specifically:

[0025] The substrate is preheated by using a plasma spray gun, and the temperature of the substrate is controlled to be 110° C. to 150° C.

[0026] Furthermore, the mass percentage of the mullite powder to the SiCN powder is 1.5 to 9:1.

[0027] (3) Beneficial effects

[0028] In summary, the present invention can achieve a bicontinuous structure of the composite powder by regulating the component content and powder particle size, which can give full play to the impedance matching performance of the mullite phase and the wave absorbing performance of the SiCN phase, so that the prepared coating has good wave absorbing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] Figure 1 1 is a schematic flow chart of a method for preparing a high-temperature resistant mullite / SiCN composite microwave-absorbing coating provided by an embodiment of the present invention;

[0031] Figure 2 This is a comparison chart of the reflection loss performance of a SiC / SiC flat plate surface before and after preparation of a high-temperature resistant mullite / SiCN absorbing coating, provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention. That is, the present invention is not limited to the described embodiments.

[0033] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] An embodiment of the present invention provides a high-temperature resistant mullite / SiCN composite absorbing coating, which is a 0.4 mm thick absorbing coating prepared on a substrate using mullite / SiCN composite powder as a raw material. The mullite / SiCN composite powder includes mullite powder and SiCN powder, the mass ratio of mullite powder to SiCN powder is 1.5 to 9:1, and the particle size of the SiCN powder is 1 to 10 μm.

[0035] In the above-described embodiment, the coating exhibits excellent thermal compatibility with the SiC / SiC ceramic-based composite material, is resistant to cracking, exhibits strong adhesion, and eliminates the need for a transition layer, thereby avoiding the associated mass increase. By manipulating the component content and powder particle size, a bicontinuous structure of the composite powder can be achieved, fully utilizing the impedance matching properties of the mullite phase and the microwave absorption properties of the SiCN phase. The resulting coating exhibits excellent microwave absorption performance. The composite powder used in the coating exhibits excellent flowability and uniform component distribution.

[0036] The binder may be polyvinyl alcohol (PVA).

[0037] As an optional embodiment, the substrate is SiC f / SiC ceramic matrix composite material. Among them, the component phases of the composite absorbing coating are all SiC f / SiC composites have similar thermal expansion coefficients, and the prepared coating can f / SiC ceramic matrix composite substrate maintains good thermal matching performance.

[0038] As an optional embodiment, the thickness of the absorbing coating is 0.4mm-0.6mm. The thickness of the absorbing coating is determined based on the specific absorbing performance. A smaller thickness will result in poor absorbing performance, while a larger thickness will weaken the bonding strength between the coating and the substrate.

[0039] As an optional embodiment, the mullite / SiCN composite powder is a spherical composite powder with a bicontinuous structure produced by a spray drying granulation process. Specifically, spray drying granulation is a conventional process for preparing powders, but the specific process parameters vary depending on the type of powder. The spray drying granulation process parameters are: inlet temperature 200°C to 300°C, outlet temperature 120°C to 160°C, nozzle speed 25Hz to 40Hz, and peristaltic pump speed 30rpm to 45rpm.

[0040] As an optional embodiment, the particle size of the mullite / SiCN composite powder is 30 μm to 80 μm, wherein the composite powder in this particle size range is conducive to the coating.

[0041] Figure 1Schematic diagram of a process for preparing a high temperature resistant mullite / SiCN composite absorbing coating according to an embodiment of the present invention. Figure 1 As shown, the method may include the following steps:

[0042] S100, mixing mullite powder, SiCN powder, a binder and deionized water to obtain a suspension;

[0043] S200, preparing a powder from the suspension by a spray drying granulation process, drying the obtained powder and passing it through a test sieve to obtain a mullite / SiCN bicontinuous structure composite powder;

[0044] S300, roughening the surface of the substrate to be sprayed and removing the sand particles remaining on the surface of the substrate so that the surface of the substrate reaches a preset roughness;

[0045] S400, preheating the substrate at a set temperature;

[0046] S500, spraying the mullite / SiCN bicontinuous structure composite powder on the substrate to form a mullite / SiCN composite absorbing coating.

[0047] In the above embodiment, in step S300, the surface of the substrate to be sprayed is roughened using 20-60 mesh white corundum sand, and the sand particles remaining on the surface of the substrate are blown away using compressed air to make the surface roughness (Ra) of the substrate reach 4μm to 7μm.

[0048] In step S400, a plasma spray gun is used to preheat the substrate, and the substrate temperature is controlled to be 110°C to 150°C.

[0049] In step S500, a mullite / SiCN composite powder is sprayed onto a substrate using a plasma spraying process. Compressed air is used to cool the substrate during the spraying process, forming a mullite / SiCN composite absorbing coating. This facilitates plasma spraying, resulting in a more uniform distribution of the coating material and reduced internal defects.

[0050] Among them, the process parameters of the plasma spraying process are as follows: spraying distance is 80mm~95mm, current is 800A~900A, main gas (argon) flow rate is 70L / min~90L / min, auxiliary gas (helium) flow rate is 30L / min~50L / min, carrier gas (argon) flow rate is 8L / min~12L / min, and powder feeding rate is 3~4RPM.

[0051] As an optional embodiment, mullite powder, SiCN powder, binder and deionized water are mixed evenly to obtain a suspension. Specifically, the suspension is obtained by mixing by ball milling, the ball milling speed is 150rpm420rpm, the ball milling time is 2.5h5h, and the ball-to-material ratio is 4-6:1.

[0052] The specific process parameters of the ball milling are specifically selected based on the specific components and content of the suspension selected in the present invention.

[0053] As an optional embodiment, the substrate is preheated at a set temperature, specifically, a plasma spray gun is used to preheat the substrate, and the temperature of the substrate is controlled to be 110°C to 150°C.

[0054] The temperature parameters of the above-mentioned preheating process are conventionally selected in order to improve the bonding strength between the coating and the substrate.

[0055] As an optional embodiment, the combined mass percentage of mullite and SiCN powders in the powder suspension is 30% to 50%, the mass percentage of the binder is 0.21% to 0.54%, and the mass ratio of mullite to SiCN powder is 1.5 to 9:1. The composition of the suspension is specifically chosen to facilitate the preparation of a high-temperature resistant bicontinuous spherical absorbing powder, significantly different from existing high-temperature absorbing coating materials. This ensures homogeneous integration of the impedance-matching mullite phase and the absorbent SiCN phase in the composite powder.

[0056] Example 1

[0057] (1) Add 268 g of mullite powder, 32 g of SiCN powder, 1.5 g of PVA (polyvinyl alcohol), and 450 g of deionized water into a ball mill with a ball-to-material ratio of 5:1. Mill the mixture at a speed of 200 rpm for 4.5 h to uniformly mix the components and obtain a suspension.

[0058] (2) The suspension was transferred to a spray drying granulation tower for powder preparation, and the collected powder was placed in an oven at 130°C for 24 hours and passed through a test sieve to obtain a mullite / SiCN bicontinuous structure composite powder with a particle size of 30 μm to 80 μm; wherein the spray drying granulation process parameters are as follows: inlet temperature 220°C, outlet temperature 150°C, nozzle speed 35 Hz, and peristaltic pump speed 40 rpm;

[0059] (3) Use 20-60 mesh white corundum sand to roughen the surface of the substrate to be sprayed, and use compressed air to blow away the sand particles remaining on the surface of the substrate to make the surface roughness (Ra) of the substrate reach 6μm;

[0060] (4) Preheat the substrate using a plasma spray gun and control the substrate temperature to 140°C;

[0061] (5) The mullite / SiCN composite powder is sprayed on the substrate by a plasma spraying process, and the substrate is cooled by compressed air during the spraying process to form a mullite / SiCN composite absorbing coating on the substrate with a coating thickness of 0.6 mm;

[0062] The process parameters of the plasma spraying process are as follows: spraying distance is 85 mm, current is 850 A, main gas (argon) flow rate is 80 L / min, auxiliary gas (helium) flow rate is 38 L / min, carrier gas (argon) flow rate is 10 L / min, and powder feeding rate is 3.8 RPM.

[0063] like Figure 2 As shown, the reflection loss performance of the composite absorbing coating prepared in Example 1 is much improved compared with that before spraying the coating, thereby improving the overall absorbing performance of the absorbing coating.

[0064] Example 2

[0065] (1) Add 257 g of mullite powder, 43 g of SiCN powder, 1.6 g of PVA (polyvinyl alcohol), and 460 g of deionized water into a ball mill with a ball-to-material ratio of 4:1. Mill the mixture at a speed of 300 rpm for 4 h to uniformly mix the components and obtain a suspension.

[0066] (2) The suspension was transferred to a spray drying granulation tower for powder preparation, and the collected powder was placed in an oven at 130°C for 24 hours and passed through a test sieve to obtain a mullite / SiCN bicontinuous structure composite powder with a particle size of 30 μm to 80 μm; wherein the spray drying granulation process parameters are as follows: inlet temperature 240°C, outlet temperature 150°C, nozzle speed 30 Hz, and peristaltic pump speed 35 rpm;

[0067] (3) Use 20-60 mesh white corundum sand to roughen the surface of the substrate to be sprayed, and use compressed air to blow away the sand particles remaining on the surface of the substrate to make the surface roughness (Ra) of the substrate reach 6μm;

[0068] (4) Preheat the substrate using a plasma spray gun and control the substrate temperature to 120°C;

[0069] (5) The mullite / SiCN composite powder is sprayed on the substrate by a plasma spraying process, and the substrate is cooled by compressed air during the spraying process to form a mullite / SiCN composite absorbing coating on the substrate with a coating thickness of 0.5 mm; wherein, the process parameters of the plasma spraying process are as follows: spraying distance is 90 mm, current is 880 A, main gas (argon) flow rate is 84 L / min, auxiliary gas (helium) flow rate is 42 L / min, carrier gas (argon) flow rate is 11 L / min, and powder feeding rate is 3.6 RPM.

[0070] It should be noted that the various embodiments in this specification are described in a progressive manner. References to the same or similar parts between the various embodiments are sufficient. Each embodiment focuses on the differences from the other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and technologies are omitted here.

[0071] The above are merely embodiments of the present application and are not intended to limit the present application. Various modifications and variations are possible for those skilled in the art without departing from the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included within the scope of the claims of the present application.

Claims

1. A high temperature resistant mullite / SiCN composite microwave absorbing coating, characterized in that: The invention relates to a microwave-absorbing coating having a thickness greater than or equal to 0.4 mm and prepared on a substrate using mullite / SiCN composite powder as raw material; wherein the mullite / SiCN composite powder comprises mullite powder and SiCN powder, and the mass ratio of the mullite powder to the SiCN powder is 1.5 to 9:1; and the thickness of the microwave-absorbing coating is 0.4 to 0.6 mm.

2. The high temperature resistant mullite / SiCN composite microwave absorbing coating according to claim 1, characterized in that: The matrix is ​​a SiCf / SiC ceramic-based composite material.

3. The high temperature resistant mullite / SiCN composite microwave absorbing coating according to claim 1, characterized in that: The mullite / SiCN composite powder is a spherical composite powder with a bicontinuous structure prepared by a spray drying granulation process.

4. The high temperature resistant mullite / SiCN composite radar absorbing coating according to claim 1, characterized in that: The particle size of the mullite / SiCN composite powder is 30 μm to 80 μm.

5. A method for preparing a high temperature resistant mullite / SiCN composite radar absorbing coating according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: Mullite powder, SiCN powder, binder and deionized water are mixed uniformly to obtain a suspension; The suspension is subjected to a spray drying granulation process to prepare a powder, the obtained powder is dried and passed through a test sieve to obtain a mullite / SiCN bicontinuous structure composite powder; Roughen the surface of the substrate to be sprayed and remove the residual sand on the surface of the substrate to make the surface of the substrate reach the preset roughness; Preheating the substrate at a set temperature; The mullite / SiCN bicontinuous structure composite powder is sprayed on the substrate to form a mullite / SiCN composite microwave absorbing coating.

6. The preparation method according to claim 5, characterized in that The mullite powder, SiCN powder, binder and deionized water are uniformly mixed to obtain a suspension, specifically: The suspension is obtained by mixing in a ball milling manner, with a ball milling speed of 150 rpm to 420 rpm, a ball milling time of 2.5 h to 5 h, and a ball-to-material ratio of 4 to 6:

1.

7. The preparation method according to claim 5, characterized in that The parameters of the spray drying granulation process are: inlet temperature 200°C to 300°C, outlet temperature 120°C to 160°C, nozzle speed 25Hz to 40Hz, and peristaltic pump speed 30rpm to 45rpm.

8. The preparation method according to claim 5, characterized in that The preheating treatment of the substrate at a set temperature is specifically as follows: The substrate is preheated by using a plasma spray gun, and the temperature of the substrate is controlled to be 110° C. to 150° C.

9. The preparation method according to claim 5, characterized in that The mass ratio of the mullite powder to the SiCN powder is 1.5 to 9:1.

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