Epoxy resin surface alternate spray embedded type composite coating and preparation method

Abstract

The application discloses an epoxy resin surface alternate spraying embedded type composite coating and a preparation method, belongs to the technical field of composite coating, and mixes thermoplastic polyimide powder, thermosetting polyimide powder, nano alumina powder, deionized water and a binder, sprays and granulates after ball milling to obtain polyimide-nano Al2O3 composite powder; and the polyimide-nano Al2O3 composite powder and Al2O3 powder are alternately sprayed on a resin-based composite material. In the application, the polyimide-nano Al2O3 composite material is introduced as a transition layer, the high combination of the glass fiber reinforced resin-based composite material and the alumina ceramic layer is ensured, and the temperature resistance and wear resistance of the matrix are improved. The alumina is in an embedded structure in the polymer-based nano composite coating, the highest bonding strength reaches 20 MPa, and the highest resistivity reaches 71 TΩ.cm. Compared with a pure matrix, the bending strength is 235 MPa after ablation for 150 times, is increased by 28%, and excellent plasma ablation resistance is shown.

Description

Technical Field

[0001] This invention belongs to the field of composite coating preparation technology, and relates to an epoxy resin surface alternately sprayed embedded composite coating and its preparation method. Background Technology

[0002] Electromagnetic railguns, by converting electromagnetic energy into the instantaneous kinetic energy required for launching the payload, break through the speed and energy limits of mechanical and chemical energy launches, representing a new concept of kinetic energy weaponry. An electromagnetic railgun mainly consists of a barrel, an aluminum armature, and a power source. The barrel is primarily composed of copper alloy rails, an insulating support, and an outer cladding. The insulating support serves to support the rails and ensure electrical insulation between them. The combined effects of high-temperature plasma ablation and molten aluminum erosion can lead to a decrease in the strength and insulation performance of the support, ultimately causing the entire system to fail. Ceramic materials are unsuitable for use as structural materials for the support due to their low toughness and poor reliability. Currently, resin-based composite materials with high specific strength, good fatigue fracture resistance, and corrosion resistance are commonly used for the insulating support. However, their poor high-temperature resistance, ablation resistance, and erosion resistance are significant factors limiting the lifespan of the electromagnetic railgun barrel. Improving the mechanical properties and ablation resistance of the insulating support is of great significance for improving the performance and efficiency of electromagnetic launch systems.

[0003] Based on improving the temperature resistance of resin-based composite materials, a thermal protective coating is prepared on the resin-based surface to meet the extreme operating conditions of electromagnetic railguns. Due to the low decomposition temperature of epoxy resin-based composite materials, high requirements are placed on the coating preparation process. Currently, mainstream technologies include chemical vapor deposition (CVD), physical vapor deposition (PVD), sol-gel method, cold spraying, and thermal spraying. However, vapor deposition is difficult to prepare high-quality coatings on ultra-large components, and coatings prepared by the sol-gel method are prone to brittle cracking and peeling, and the preparation cycle is long. Cold spraying has lower heat output. In comparison, thermal spraying (TS) is highly efficient, low-cost, and suitable for large components. It involves rapidly heating the coating raw material to a molten or melted state, then causing particles to impact the substrate at high speed. The molten droplets spread, solidify, and stack to form the coating. Based on the type of heat source, it can be divided into flame spraying, supersonic flame spraying, arc spraying, and plasma spraying. Currently, the preparation of ceramic thermal protective coatings on resin-based composite surfaces using thermal spraying technology faces three prominent problems: First, most intermediate transition layers use low-melting-point metals such as Zn and Al, which cannot guarantee electrical insulation. Second, high-temperature molten particles can cause strong ablation of the resin matrix, resulting in low layer-substrate bonding strength and easy peeling and failure during use. Third, the resins selected for the intermediate layer have low heat resistance and mechanical properties, which cannot meet the layer-substrate bonding characteristics of the composite coating.

[0004] Therefore, the preparation of a ceramic thermal protective coating that combines electrical insulation and ablation resistance on the surface of a low-melting-point resin-based composite matrix is ​​a practical and feasible method to improve the service life and reliability of the electromagnetic railgun's insulating support. Summary of the Invention

[0005] To address the technical challenge of resin-based composite materials failing to simultaneously achieve electrical insulation and ablation resistance, this invention aims to provide an epoxy resin surface with an alternating spray-coated embedded composite coating and its preparation method. The composite coating prepared by this method combines electrical insulation and ablation resistance, making it better suited for harsh service environments.

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

[0007] A method for preparing an embedded composite coating by alternating spraying on an epoxy resin surface includes the following steps:

[0008] Thermoplastic polyimide powder, thermosetting polyimide powder, nano-alumina powder, deionized water, and binder are mixed to obtain a mixture;

[0009] The mixture was ball-milled and then spray-granulated to obtain polyimide-nano Al2O3 composite powder;

[0010] A wide-velocity-range high-energy plasma spraying technology was used to alternately spray polyimide-nano Al2O3 composite powder and Al2O3 powder onto a resin-based composite material to obtain an alternately sprayed embedded composite coating on the epoxy resin surface.

[0011] Furthermore, the mass solid content of the mixture is 25%.

[0012] Furthermore, the mass of the binder is 1-3% of the mass of the mixture, and the binder is polyvinyl alcohol or PEG.

[0013] Furthermore, the total mass fraction of thermoplastic polyimide powder, thermosetting polyimide powder, and nano alumina powder is 100, and the mass fraction ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano alumina powder is (0-80):(80-0):20. The thermoplastic polyimide powder and thermosetting polyimide powder cannot both be 0.

[0014] Furthermore, the particle size of thermoplastic polyimide powder is 2-10 μm, the particle size of thermosetting polyimide powder is 2-10 μm, and the particle size of nano-alumina powder is 20-30 nm.

[0015] Furthermore, the resin-based composite material undergoes pretreatment before spraying: the surface of the resin-based composite material is sandblasted and cleaned.

[0016] Furthermore, a wide-velocity high-energy plasma spraying technique is used to alternately spray polyimide-nano Al2O3 composite powder and Al2O3 powder onto a resin-based composite material, including the following steps: first, spray polyimide-nano alumina composite powder once or more, then spray Al2O3 powder once or more, then spray polyimide-nano alumina composite powder once or more, and finally spray Al2O3 powder once or more.

[0017] Furthermore, during spraying, the polyimide-nano alumina composite powder is fed into the jet via an external powder delivery method; the Al2O3 powder is fed into the jet via an internal powder delivery method.

[0018] Furthermore, during spraying, the current is 380-420 A, the voltage is 80-90 V, the main gas is argon, and the argon gas flow rate is 60-65 L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 10⁻¹⁴ L. min -1 The spraying distance is 150-180 mm, and the powder feeding distance for composite powder is 90-110 mm.

[0019] An epoxy resin surface is alternately sprayed with an embedded composite coating. The composite coating has a bonding strength of up to 20 MPa, a flexural strength of 235 MPa after 150 ablation cycles, and a resistivity of up to 71 TΩ·cm.

[0020] Compared with the prior art, the beneficial effects of the present invention include:

[0021] This invention utilizes thermoplastic polyimide powder, thermosetting polyimide powder, and nano-alumina as raw materials in the composite coating preparation process to form a polymer-ceramic composite coating. This reduces the performance differences between the substrate and the ceramic layer, ensuring high-reliability bonding of the coating and reducing substrate ablation. The addition of nano-alumina as a reinforcing filler improves the bonding strength, plasma ablation resistance, and fracture strength of the nanocomposite coating. The steric hindrance effect of nano-alumina hinders the movement of macromolecular chains, effectively pinning cracks, increasing crack propagation resistance, and improving the strength of the composite material. The alternating spraying method optimizes the composite coating structure and reduces the property differences between the coating and the substrate. Simultaneously, it effectively enhances the cohesive bonding of the coating, satisfying high bonding characteristics while also providing electrical insulation and ablation resistance, ensuring high reliability during the composite coating deposition process.

[0022] Furthermore, the present invention adds thermoplastic resin and changes the ratio of thermoplastic and thermosetting resins in the composite powder, wherein the excellent plasticity of thermoplastic polyimide significantly improves the bonding strength of the composite coating. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments;

[0024] Figure 1 The microstructure of the polyimide-nano alumina composite powder prepared in Example 5 of this invention is shown below.

[0025] Figure 2 The images show the microstructure of the polymer-based nanocomposite coating prepared in Example 5 of this invention; where (a) is the overall morphology of the coating; and (b) is the embedded morphology of locally alternately sprayed alumina.

[0026] Figure 3 Optical photographs of the polymer-based nanocomposite coatings prepared in Examples 2-5 of this invention after 150 plasma ablation cycles;

[0027] Figure 4 The stress-strain curves of the polymer-based nanocomposite coatings prepared in Examples 2-5 of this invention after 150 plasma ablation cycles are shown.

[0028] Figure 5 The resistivity of the polymer-based nanocomposite coatings prepared in Examples 2 and 5 of this invention. Detailed Implementation

[0029] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0030] This invention uses glass fiber reinforced epoxy resin as the matrix and polyimide-nano Al2O3 as the composite coating. Polyimide possesses excellent mechanical properties, high thermal stability, corrosion resistance, and good electrical insulation. The addition of nanoparticles can improve the wear resistance, strength, and thermal stability of the polyimide composite material. The dispersed nano-Al2O3 particles in the coating restrict the movement of molecular chains, resulting in reinforced nanocomposite behavior. High interfacial adhesion can effectively transfer the load from the polymer to the filler. The nano-Al2O3 particles increase the crack propagation path, improve mechanical properties, and also provide some thermal insulation. The effect of adjusting the ratio of thermoplastic and thermosetting polyimide on the coating bonding strength was investigated.

[0031] The method for preparing an interleaved embedded composite coating by alternating spraying on an epoxy resin surface according to the present invention includes the following steps:

[0032] (1) Preparation of polyimide (PI)-nano Al2O3 composite powder: Thermoplastic polyimide powder, thermosetting polyimide powder, and nano alumina (Al2O3) powder, deionized water, and binder are mixed and stirred at 90 °C for 2 h to fully dissolve the binder in water, resulting in a mixture. The solid content (mass) of the mixture is 25%, and the mass of the binder is 1-3% of the mixture mass. The binder is polyvinyl alcohol or PEG. The total mass fraction of thermoplastic polyimide powder, thermosetting polyimide powder, and nano alumina powder is 100, and the mass fraction ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano alumina powder is (0-80):(80-0):20. Thermoplastic polyimide powder and thermosetting polyimide powder cannot be 0. The mass ratio of thermoplastic to thermosetting polyimide is 3:7, 5:5, 7:3, or 10:0. The particle size of thermoplastic polyimide powder is 2-10 μm, the particle size of thermosetting polyimide powder is 2-10 μm, and the particle size of nano-alumina powder is 20-30 nm.

[0033] The mixture was then subjected to high-speed ball milling for 6-8 hours using a planetary ball mill to obtain a uniformly dispersed slurry. The uniformly dispersed slurry was then spray-granulated at an inlet air temperature of 130 ℃ and a centrifugal speed of 300 Hz. After drying, polyimide-nano Al2O3 composite powder was obtained.

[0034] (2) Pretreatment of the substrate before spraying: The surface of the resin-based composite material is sandblasted and cleaned. The sandblasting material is alumina with a particle size of 120-180 μm, the sandblasting air pressure is 0.3±0.05 MPa, the sandblasting angle is 70±10°, and the distance between the spray gun and the surface of the resin-based composite material is 100-150 mm. The substrate surface is cleaned with alcohol.

[0035] (3) A composite coating is prepared on the resin-based composite material using a wide-velocity high-energy plasma spraying technique. The polyimide-nano alumina (Al2O3 / PI) composite coating and the Al2O3 coating are sprayed alternately. The specific process is as follows: first, the polyimide-nano alumina composite powder is sprayed once or more times; then, the Al2O3 powder is sprayed once or more times; then, the polyimide-nano alumina composite powder is sprayed once or more times; finally, the Al2O3 powder is sprayed once or more times. This reduces the difference in physical properties between the substrate and the alumina ceramic layer, ensuring high reliability of the coating. Finally, a pure Al2O3 ceramic coating is applied to the surface. By changing the number of spraying passes of the Al2O3 coating, the optimal coating structure is optimized. The number of spraying passes is 1, 2, or 3, and the final surface is covered with a pure Al2O3 ceramic coating, resulting in an epoxy resin surface with an alternately sprayed embedded composite coating. Filling nano-Al2O3 particles into polyimide can improve the temperature resistance and mechanical properties of the nanocomposite coating, reduce the difference in thermal expansion coefficients between the ceramic layer and the substrate, reduce thermal stress, and improve the bonding strength between the ceramic surface layer and the substrate.

[0036] The composite powder is fed into the jet via an external powder delivery system; Al2O3 particles are fed into the jet via an internal powder delivery system. During spraying, the current is 380-420 A, the voltage is 80-90 V, the main gas is argon, and the argon gas flow rate is 60-65 L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 10⁻¹⁴ L. min -1 The spraying distance is 150-180 mm, and the powder feeding distance for composite powder is 90-110 mm.

[0037] For resin-based composite materials, compressed air is used to cool the sample surface and back side to reduce the ablation and decomposition of the substrate and composite coating during the spraying process. An infrared thermometer is used to monitor the surface temperature of the substrate between 80-150 ℃ to prevent the temperature from getting too high.

[0038] The epoxy resin surface prepared by the above-described method of the present invention is alternately sprayed with an embedded composite coating. The bonding strength of this composite coating increases with the increase of thermoplastic polyimide content. The highest bonding strength (20 MPa) is achieved when the nano-Al2O3 mass content is 20% and the resin is entirely thermoplastic polyimide. As the number of spray passes of the pure Al2O3 coating in the alternating spraying gradually increases, ablation occurs in the nanocomposite layer, and numerous cracks appear at the interface with the substrate, leading to a decrease in the coating's bonding strength. When the number of spray passes of the pure Al2O3 coating in the alternating spraying is one, the coating interface exhibits good bonding, with no ablation or decomposition. The alumina is embedded in the nanocomposite layer, improving the coating's strength.

[0039] The following are specific examples.

[0040] Example 1

[0041] Thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder were mixed with deionized water and a binder. The solid content was 25%, and the binder content was 1%. The mixture was ball-milled at high speed using a planetary ball mill to obtain a uniformly dispersed slurry. The uniformly dispersed slurry was then spray-granulated at an inlet air temperature of 130°C and a centrifugal speed of 300 Hz. After drying, polyimide-nano-Al2O3 composite powder was obtained. The mass ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder was 0:80:20.

[0042] Pre-treatment of the substrate before spraying: The surface of the resin-based composite material is sandblasted and cleaned. A wide-velocity high-energy plasma spraying technology is used to prepare a composite coating on the resin-based composite material, with alternating spraying of a polyimide-nano Al2O3 composite coating and an Al2O3 coating. Two coats of polyimide-nano Al2O3 composite powder are applied as a base coat, followed by one coat of Al2O3. This process is repeated twice, alternating between one coat of polyimide-nano Al2O3 composite powder and one coat of Al2O3 coating. Finally, three coats of pure Al2O3 coating are applied as a top coat. The composite powder is fed into the jet externally; the Al2O3 particles are fed into the jet internally. During spraying, the current is 380A, the voltage is 80V, the main gas is argon, and the argon gas flow rate is 60L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 10 L. min -1 The spraying distance is 150 mm, and the powder feeding distance of the composite powder is 90 mm, resulting in an alternating spraying and embedding composite coating on the epoxy resin surface.

[0043] The resin-based composite material is cooled before and after spraying to reduce the ablation and decomposition of the substrate and composite coating during the spraying process. An infrared thermometer is used to monitor the surface temperature of the substrate at 80 ℃ to prevent the temperature from getting too high.

[0044] Example 2

[0045] Thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder were mixed with deionized water and a binder. The solid content was 25%, and the binder content was 1%. The mixture was ball-milled at high speed using a planetary ball mill to obtain a uniformly dispersed slurry. The uniformly dispersed slurry was then spray-granulated at an inlet air temperature of 130°C and a centrifugal speed of 300 Hz. After drying, polyimide-nano-Al2O3 composite powder was obtained. The mass ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder was 24:56:20.

[0046] Pre-treatment of the substrate was performed before spraying: the surface of the resin-based composite material was sandblasted and cleaned. A wide-velocity high-energy plasma spraying technique was used to prepare a composite coating on the resin-based composite material, with alternating spraying of a polyimide-nano Al2O3 composite coating and an Al2O3 coating. Two coats of polyimide-nano Al2O3 composite powder were applied as a base coat, followed by one coat of Al2O3. This process was repeated twice, alternating between one coat of polyimide-nano Al2O3 composite powder and one coat of Al2O3 coating. Finally, three coats of pure Al2O3 were applied as a top coat. The composite powder was fed into the jet externally; the Al2O3 particles were fed into the jet internally. During spraying, the current was 400A, the voltage was 85V, the main gas was argon, and the argon gas flow rate was 62 L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 12L. min -1 The spraying distance is 160 mm, and the powder feeding distance of the composite powder is 100 mm, resulting in an alternating spraying embedded composite coating on the epoxy resin surface.

[0047] The resin-based composite material is cooled before and after spraying to reduce the ablation and decomposition of the substrate and composite coating during the spraying process. An infrared thermometer is used to monitor the surface temperature of the substrate at 100 ℃ to prevent the temperature from getting too high.

[0048] Example 3

[0049] Thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder were mixed with deionized water and a binder. The solid content was 25%, and the binder content was 1%. The mixture was ball-milled at high speed using a planetary ball mill to obtain a uniformly dispersed slurry. The uniformly dispersed slurry was then spray-granulated at an inlet air temperature of 130°C and a centrifugal speed of 300 Hz. After drying, polyimide-nano-Al2O3 composite powder was obtained. The mass ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder was 40:40:20.

[0050] Pre-treatment of the substrate was performed before spraying: the surface of the resin-based composite material was sandblasted and cleaned. A wide-velocity high-energy plasma spraying technique was used to prepare a composite coating on the resin-based composite material, with alternating spraying of a polyimide-nano Al2O3 composite coating and an Al2O3 coating. Two coats of polyimide-nano Al2O3 composite powder were applied as a base coat, followed by one coat of Al2O3. This process was repeated twice, alternating between one coat of polyimide-nano Al2O3 composite powder and one coat of Al2O3 coating. Finally, three coats of pure Al2O3 were applied as a top coat. The composite powder was fed into the jet externally; the Al2O3 particles were fed into the jet internally. During spraying, the current was 400A, the voltage was 85V, the main gas was argon, and the argon gas flow rate was 62 L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 12L. min -1 The spraying distance is 160 mm, and the powder feeding distance of the composite powder is 100 mm, resulting in an alternating spraying embedded composite coating on the epoxy resin surface.

[0051] The resin-based composite material is cooled before and after spraying to reduce the ablation and decomposition of the substrate and composite coating during the spraying process. An infrared thermometer is used to monitor the surface temperature of the substrate at 100 ℃ to prevent the temperature from getting too high.

[0052] Example 4

[0053] Thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder were mixed with deionized water and a binder. The solid content was 25%, and the binder content was 1%. The mixture was ball-milled at high speed using a planetary ball mill to obtain a uniformly dispersed slurry. The uniformly dispersed slurry was then spray-granulated at an inlet air temperature of 130°C and a centrifugal speed of 300 Hz. After drying, polyimide-nano-Al2O3 composite powder was obtained. The mass ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder was 56:24:20.

[0054] Pre-treatment of the substrate was performed before spraying: the surface of the resin-based composite material was sandblasted and cleaned. A wide-velocity high-energy plasma spraying technique was used to prepare a composite coating on the resin-based composite material, with alternating spraying of a polyimide-nano Al2O3 composite coating and an Al2O3 coating. Two coats of polyimide-nano Al2O3 composite powder were applied as a base coat, followed by one coat of Al2O3. This process was repeated twice, alternating between one coat of polyimide-nano Al2O3 composite powder and one coat of Al2O3 coating. Finally, three coats of pure Al2O3 were applied as a top coat. The composite powder was fed into the jet externally; the Al2O3 particles were fed into the jet internally. During spraying, the current was 400A, the voltage was 85V, the main gas was argon, and the argon gas flow rate was 62 L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 12L. min -1 The spraying distance is 160 mm, and the powder feeding distance of the composite powder is 100 mm, resulting in an alternating spraying embedded composite coating on the epoxy resin surface.

[0055] The resin-based composite material is cooled before and after spraying to reduce the ablation and decomposition of the substrate and composite coating during the spraying process. An infrared thermometer is used to monitor the surface temperature of the substrate at 120 ℃ to prevent the temperature from getting too high.

[0056] Example 5

[0057] Thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder were mixed with deionized water and a binder. The solid content was 25%, and the binder content was 1%. The mixture was ball-milled at high speed using a planetary ball mill to obtain a uniformly dispersed slurry. The uniformly dispersed slurry was then spray-granulated at an inlet air temperature of 130°C and a centrifugal speed of 300 Hz. After drying, polyimide-nano-Al2O3 composite powder was obtained. The mass ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder was 80:0:20.

[0058] Pre-treatment of the substrate was performed before spraying: the surface of the resin-based composite material was sandblasted and cleaned. A wide-velocity high-energy plasma spraying technique was used to prepare a composite coating on the resin-based composite material, with alternating spraying of a polyimide-nano Al2O3 composite coating and an Al2O3 coating. Two coats of polyimide-nano Al2O3 composite powder were applied as a base coat, followed by one coat of Al2O3. This process was repeated twice, alternating between one coat of polyimide-nano Al2O3 composite powder and one coat of Al2O3 coating. Finally, three coats of pure Al2O3 were applied as a top coat. The composite powder was fed into the jet externally; the Al2O3 particles were fed into the jet internally. During spraying, the current was 420A, the voltage was 90V, the main gas was argon, and the argon gas flow rate was 65 L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 14L. min -1 The spraying distance is 180 mm, and the powder feeding distance of the composite powder is 110 mm, resulting in an alternating spraying embedded composite coating on the epoxy resin surface.

[0059] The resin-based composite material is cooled before and after spraying to reduce the ablation and decomposition of the substrate and composite coating during the spraying process. An infrared thermometer is used to monitor the surface temperature of the substrate at 150 ℃ to prevent the temperature from getting too high.

[0060] from Figure 1 It can be seen that the composite powder prepared in Example 5 has a high sphericity and a particle size of 20-80 μm.

[0061] See Figure 2 In (a) and (b), from Figure 2 It can be seen that the alumina in the prepared coating is embedded in the polyimide-nano alumina composite coating, with good interfacial bonding. The alumina coating is pinned, which ensures the high bonding strength of the composite coating.

[0062] See Figure 3 Examples 2-5 show the plasma ablation morphology, in which a wide-velocity high-energy plasma jet is used to ablate the coating surface, and the ablation power is 40kW.

[0063] See Figure 4 Through three-point bending mechanical property testing, the bending strengths of Examples 2-5 were 210 MPa, 220 MPa, 225 MPa, and 235 MPa, respectively. Compared with the pure matrix, the bending strength of the sample with a plastic:solid ratio of 3:7 after 150 ablation cycles was 235 MPa, which is 28% higher.

[0064] See Figure 5Through resistivity testing, the coatings obtained in Examples 2 and 5 were found to be superior to the pure substrate. The resistivity of the samples with a plastic:solid ratio of 10:0 and 3:7 were 71 TΩ·cm and 51 TΩ·cm, respectively.

[0065] Example 6

[0066] Thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder were mixed with deionized water and a binder. The solid content was 25%, and the binder content was 1%. The mixture was ball-milled at high speed using a planetary ball mill to obtain a uniformly dispersed slurry. The uniformly dispersed slurry was then spray-granulated at an inlet air temperature of 130°C and a centrifugal speed of 300 Hz. After drying, polyimide-nano-Al2O3 composite powder was obtained. The mass ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder was 80:0:20.

[0067] Pre-treatment of the substrate was performed before spraying: the surface of the resin-based composite material was sandblasted and cleaned. A wide-velocity high-energy plasma spraying technique was used to prepare a composite coating on the resin-based composite material, with alternating spraying of a polyimide-nano Al2O3 composite coating and an Al2O3 coating. Two coats of polyimide-nano Al2O3 composite powder were applied as a base coat, followed by two coats of Al2O3 coating. Then, one coat of polyimide-nano Al2O3 composite powder and two coats of Al2O3 coating were alternated, repeated twice. Finally, two coats of pure Al2O3 coating were applied as a top coat. The composite powder was fed into the jet externally; the Al2O3 particles were fed into the jet internally. During spraying, the current was 420A, the voltage was 90V, the main gas was argon, and the argon gas flow rate was 65 L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 14L. min -1 The spraying distance is 180 mm, and the powder feeding distance of the composite powder is 110 mm, resulting in an alternating spraying embedded composite coating on the epoxy resin surface.

[0068] The resin-based composite material is cooled before and after spraying to reduce the ablation and decomposition of the substrate and composite coating during the spraying process. An infrared thermometer is used to monitor the surface temperature of the substrate at 150 ℃ to prevent the temperature from getting too high.

[0069] Example 7

[0070] Thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder were mixed with deionized water and a binder. The solid content was 25%, and the binder content was 1%. The mixture was ball-milled at high speed using a planetary ball mill to obtain a uniformly dispersed slurry. The uniformly dispersed slurry was then spray-granulated at an inlet air temperature of 130°C and a centrifugal speed of 300 Hz. After drying, polyimide-nano-Al2O3 composite powder was obtained. The mass ratio of thermoplastic polyimide powder, thermosetting polyimide powder, and nano-Al2O3 powder was 80:0:20.

[0071] Pre-treatment of the substrate was performed before spraying: the surface of the resin-based composite material was sandblasted and cleaned. A wide-velocity high-energy plasma spraying technique was used to prepare a composite coating on the resin-based composite material, alternating between polyimide-nano Al2O3 composite coatings and Al2O3 coatings. Two coats of polyimide-nano Al2O3 composite powder were applied as a base coat, followed by three coats of Al2O3 coating. Then, one coat of polyimide-nano Al2O3 composite powder and three coats of Al2O3 coating were alternated, repeated twice. Finally, a single coat of pure Al2O3 was applied as a top coat. The composite powder was fed into the jet externally; the Al2O3 particles were fed into the jet internally. During spraying, the current was 420A, the voltage was 90V, the main gas was argon, and the argon gas flow rate was 65 L. min -1 The secondary gas is hydrogen, and the hydrogen gas flow rate is 14L. min -1 The spraying distance is 180 mm, and the powder feeding distance of the composite powder is 110 mm, resulting in an alternating spraying embedded composite coating on the epoxy resin surface.

[0072] The resin-based composite material is cooled before and after spraying to reduce the ablation and decomposition of the substrate and composite coating during the spraying process. An infrared thermometer is used to monitor the surface temperature of the substrate at 150 ℃ to prevent the temperature from getting too high.

[0073] The bonding strength of polymer-based nanocomposite coatings with different proportions prepared in this invention is shown in Table 1.

[0074] Table 1. Bond strength of polymer-based nanocomposite coatings with different proportions prepared in this invention.

[0075]

[0076] Referring to Table 1, it can be seen that the bonding strength of the coating increases with the increase of thermoplastic polyimide content, with the highest bonding strength reaching 20 MPa for pure thermoplastic resin. Increasing the number of alternating Al2O3 powder spraying passes to 2 and 3 leads to coating ablation and cracking, resulting in a decrease in bonding strength. The best bonding strength is achieved when the number of alternating Al2O3 powder spraying passes is 1. Compared to the pure substrate, the flexural strength after 150 ablation cycles is 235 MPa, an increase of 28%, and it exhibits excellent resistance to plasma ablation.

[0077] In this invention, the incorporation of nano-Al2O3 particles into polyimide improves the temperature resistance and mechanical properties of the nanocomposite coating, reduces the difference in thermal expansion coefficients between the ceramic layer and the substrate, decreases thermal stress, and enhances the bonding strength between the ceramic surface layer and the substrate. The introduction of a polyimide-nano-Al2O3 composite material as a transition layer in the composite coating ensures high bonding between the glass fiber reinforced resin matrix composite material and the alumina ceramic layer, thereby improving the temperature resistance and wear resistance of the substrate. The alumina exhibits an embedded structure in the polymer-based nanocomposite coating, resulting in excellent interfacial bonding.

[0078] This invention uses glass fiber reinforced epoxy resin with low density and high specific strength as the matrix. By introducing a polymer-ceramic composite coating, the performance difference between the matrix and the ceramic layer can be reduced, ensuring high-reliability bonding of the coating, improving the thermal stability and wear resistance of the polymer composite material, and further enhancing its performance. Polyimide-nano Al2O3, with its excellent comprehensive properties, is used as a transition coating. Compared with traditional microstructured composite coatings, the nanocomposite coating exhibits superior characteristics in mechanical properties such as hardness, elastic modulus, fracture toughness, and bond strength. The addition of nanoparticles can improve the wear resistance, strength, and thermal stability of the polyimide composite material. The dispersed nano-Al2O3 particles in the composite coating restrict the movement of molecular chains, leading to enhanced nanocomposite behavior. High interfacial adhesion can effectively transfer the load from the polymer to the filler. The nano-Al2O3 particles increase the crack propagation path, improve mechanical properties, and also provide some thermal insulation. The influence of adjusting the ratio of thermoplastic and thermosetting polyimide on the coating bond strength is investigated.

[0079] This invention optimizes the coating structure by adjusting the ratio of thermoplastic and thermosetting polyimide and changing the number of Al2O3 powder spraying passes during alternating spraying. It obtains the composite powder composition ratio and Al2O3 powder spraying passes with high bonding strength, explores the intrinsic relationship between microstructure and mechanical properties, and features simple operation, good repeatability, significant economic benefits, and accurate and reliable results. In the prepared composite coating, alumina is embedded in the polyimide-nano alumina composite coating, showing high bonding strength.

[0080] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0081] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for producing an epoxy resin surface alternate spray-embedded composite coating, characterized by, The method comprises the following steps: The thermoplastic polyimide powder, the thermosetting polyimide powder and the nano-aluminum oxide powder, deionized water and a binder are mixed to obtain a mixture with a mass solid content of 25%; the total mass fraction of the thermoplastic polyimide powder, the thermosetting polyimide powder and the nano-aluminum oxide powder is 100, the mass fraction ratio of the thermoplastic polyimide powder, the thermosetting polyimide powder and the nano-aluminum oxide powder is (0-80):(80-0):20, the thermoplastic polyimide powder and the thermosetting polyimide powder cannot be 0 at the same time; the mass ratio of the thermoplastic polyimide and the thermosetting polyimide is 3:7, 5:5, 7:3 or 10:0; the particle size of the thermoplastic polyimide powder is 2-10 μm, the particle size of the thermosetting polyimide powder is 2-10 μm, and the particle size of the nano-aluminum oxide powder is 20-30 nm; The mixture is ball milled and then spray granulated to obtain a polyimide-nano-Al2O3 composite powder; The polyimide-nano-Al2O3 composite powder and the Al2O3 powder are alternately sprayed on the resin-based composite material by using a wide-speed-range high-energy plasma spraying technology, and the method comprises the following steps: the polyimide-nano-aluminum oxide composite powder is sprayed for 2 times, then the Al2O3 powder is sprayed for 1 time, the polyimide-nano-Al2O3 composite powder is sprayed for 1 time and the Al2O3 coating is sprayed for 1 time alternately, the alternating process is repeated twice, and finally the Al2O3 powder is sprayed for 3 times to obtain an embedded type composite coating alternately sprayed on the surface of the epoxy resin; During spraying, the polyimide-nano-aluminum oxide composite powder is sent into the jet flow by using an external powder feeding mode, and the Al2O3 powder is sent into the jet flow by using an internal powder feeding mode.

2. The method for preparing an epoxy resin surface-alternating spray-embedded composite coating according to claim 1, characterized by, The mass of the binder is 1-3% of the mass of the mixture, and the binder is polyvinyl alcohol or PEG.

3. The method for preparing an embedded composite coating by alternating spraying on an epoxy resin surface according to claim 1, characterized in that, The resin-based composite material is pretreated before spraying: the surface of the resin-based composite material is sandblasted and cleaned.

4. The method for preparing an embedded composite coating by alternating spraying on an epoxy resin surface according to claim 1, characterized in that, The current is 380-420 A, the voltage is 80-90 V, the main gas is argon, the argon gas flow is 60-65 L·min -1 , the secondary gas is hydrogen, the hydrogen gas flow is 10-14 L·min -1 , the spraying distance is 150-180 mm, and the powder feeding distance of the composite powder is 90-110 mm.

5. An epoxy resin surface alternating spray-embedded composite coating prepared according to the method of any one of claims 1 to 4, characterized by, The highest bonding strength of the composite coating is 20 MPa, the bending strength after ablation for 150 times is 235 MPa, and the highest resistivity reaches 71 TΩ·cm.

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