A method for preparing a surface semi-ceramic coating with enhanced bond strength to a resin

Abstract

This invention belongs to the field of material surface modification and thermal spraying technology, and provides a method for preparing a semi-ceramic coating to enhance the bonding strength of a resin surface. The method includes: preparing a composite powder using Al2O3, phenolic resin, and hexamethylenetetramine; for a cured glass fiber reinforced epoxy resin matrix, while preserving the integrity of the internal glass fiber structure, performing laser texturing pretreatment on the matrix surface to form regularly arranged micron-level concave-convex patterns; and using a supersonic plasma spraying process, spraying the composite powder onto the treated matrix surface via external powder delivery to form a semi-ceramic coating. This invention, through synergistic control of the laser texturing morphology and spraying heat input, can achieve dual enhancement of mechanical interlocking and interfacial compatibility. The resulting coating has a bonding strength with the resin matrix of no less than 20 MPa, and the interface is free of ablation or cracks. This method is particularly suitable for aerospace, electronic packaging, and other fields.

Description

Technical Field

[0001] This invention belongs to the field of material surface modification and thermal spraying technology, and relates to a method for preparing a semi-ceramic coating that enhances the bonding strength of a resin surface. Background Technology

[0002] In modern industry, resin-based composite materials are widely used in aerospace and other fields due to their excellent specific strength, electrical insulation, and designability. To meet higher performance requirements (such as ablation resistance for aerospace components or friction reduction and wear resistance for seals), preparing semi-ceramic coatings on resin surfaces has become an important technical approach. Among these, improving the bonding strength between the thermally sprayed coating and the resin matrix is ​​a key issue for realizing the engineering application of this technology.

[0003] Plasma spraying, due to its high energy density, is the mainstream process for depositing high-melting-point ceramic coatings. However, resin matrices (such as epoxy resins) have poor thermal stability (their thermal decomposition temperature is usually below 350°C), and are prone to melting, carbonization, or interfacial cracking under the action of high-temperature plasma flames, resulting in the bonding strength of coatings obtained by direct spraying generally being less than 10 MPa. Therefore, how to effectively suppress ablation damage to the resin matrix while fully melting the ceramic powder has become a technical challenge.

[0004] To address this issue, existing research attempts to improve interfacial bonding through surface pretreatment. Compared to traditional sandblasting, which can easily damage the glass fiber network, laser texturing, as a non-contact precision processing method, can construct tiny (e.g., micron-level) uneven structures on the resin surface, significantly enhancing the mechanical anchoring effect of the coating and effectively improving adhesion.

[0005] Furthermore, Chinese invention patent CN116426017A proposes a method for preparing a ceramic-resin composite coating on the surface of a resin-based composite material. This method involves first spraying a wet composite coating containing Al2O3 and phenolic resin (PF) onto a metal substrate, then transferring and adhering it to the surface of an uncured resin prepreg, followed by co-hot pressing for curing. While this method can mitigate the direct effects of high temperatures on the resin to some extent, it is only suitable for resin semi-finished products that have not yet fully cured, and cannot be used for on-site repair or post-processing of already formed service components. Simultaneously, the coating transfer process easily introduces problems such as interface contamination and uneven thickness, making the process complex and limiting its applicability.

[0006] Therefore, there is an urgent need to develop a method for preparing semi-ceramic coatings that can be directly applied to a cured resin matrix and has both high bonding strength and low thermal damage. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, such as severe thermal damage, low coating bonding strength, and inapplicability to the repair of cured finished parts, this invention provides a method for preparing a semi-ceramic coating on a resin surface that enhances bonding strength. This method employs a supersonic plasma spraying system to spray Al2O3 / phenolic resin (PF) composite powder via external powder delivery, and combines this with laser texturing pretreatment to construct a micron-level uneven structure on the resin substrate surface. This significantly improves the bonding strength between the semi-ceramic coating and the resin substrate through the synergistic effect of mechanical interlocking and interfacial compatibility, without requiring secondary curing or coating transfer of the already cured substrate.

[0008] Specifically, the method includes the following steps:

[0009] Step 1: Prepare a composite powder using Al2O3, phenolic resin and hexamethylenetetramine, wherein the mass ratio of Al2O3, phenolic resin and hexamethylenetetramine in the composite powder is (6~15):9:1; Step 2: For the cured glass fiber reinforced epoxy resin matrix, while preserving the integrity of the glass fiber structure inside the matrix, laser texturing pretreatment is performed on the matrix surface to form a regularly arranged micron-level concave-convex pattern on its surface. Step 3: Using a supersonic plasma spraying process, the composite powder is sprayed onto the substrate surface treated in Step 2 by external powder delivery to form a semi-ceramic coating with a thickness of 300~400 μm.

[0010] Optionally, the micron-level convex and concave pattern is a regularly arranged square array structure with a depth of 35~85 μm.

[0011] Optionally, the process parameters of the laser texture preprocessing include: 7 to 11 laser scans, pattern spacing of 80 to 160 μm, scanning speed of 300 to 600 mm / s, and laser pulse frequency of 20 to 60 kHz.

[0012] Optionally, the particle size of the composite powder is 25~50 μm, and the mass fraction of Al2O3 is 42%~55%.

[0013] Optionally, the process parameters for the supersonic plasma spraying include: a spraying distance of 140-180 mm, a powder feeding pipe distance of 70-100 mm from the nozzle, and the plasma gas being a plasma gas formed by argon and hydrogen, wherein the argon flow rate is 3600-4800 L / h, the hydrogen flow rate is 600-1500 L / h, the current is 400-450 A, the voltage is 80-110 V, and the powder feeding rate is 5-10 g / min.

[0014] Optionally, the bonding strength between the semi-ceramic coating and the substrate is not less than 20 MPa.

[0015] This invention introduces laser-textured microstructures onto the surface of a fully cured glass fiber reinforced epoxy resin matrix, and combines this with externally fed supersonic plasma spraying of Al2O3 / phenolic resin (PF) composite powder. This achieves a synergistic enhancement mechanism of mechanical interlocking and interfacial compatibility, significantly improving the bonding strength (≥20 MPa) between the semi-ceramic coating and the resin matrix while effectively suppressing thermal damage, without requiring secondary curing or coating transfer. This method is process-controllable, environmentally friendly, and efficient, and is particularly suitable for surface strengthening and in-service repair of molded resin components, while also exhibiting excellent ablation resistance, thermal shock resistance, and engineering practicality. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The present invention provides a process for preparing a semi-ceramic coating on a resin surface to enhance its bonding strength. Figure 2 The surface morphology of sandblasted and roughened resin under a laser microscope; Figure 3 The surface morphology of laser-textured resin under a laser microscope; Figure 4 The cross-sectional morphology of the coating deposited on the roughened resin surface by sandblasting; Figure 5 The cross-sectional morphology of the coating deposited on the surface of laser-textured resin; Figure 6 The bonding strength of the coating; Figure 7 It represents the line contact rate between the coating and the substrate per unit length. Detailed Implementation

[0018] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0019] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features of the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] like Figure 1 As shown in the figure, this invention discloses a method for preparing a semi-ceramic coating that enhances the bonding strength of a resin surface. The method includes the following steps: Step 1: Prepare a composite powder using Al2O3, phenolic resin and hexamethylenetetramine, wherein the mass ratio of Al2O3, phenolic resin and hexamethylenetetramine in the composite powder is (6~15):9:1; Step 2: For the cured glass fiber reinforced epoxy resin matrix, while preserving the integrity of the glass fiber structure inside the matrix, the surface of the matrix is ​​subjected to laser texturing pretreatment to form a regularly arranged micron-level concave-convex pattern on its surface. The micron-level concave-convex pattern is a regularly arranged square array structure with a depth of 35~85 μm. Step 3: Using a supersonic plasma spraying process, the composite powder is sprayed onto the substrate surface treated in Step 2 by external powder delivery to form a semi-ceramic coating with a thickness of 300~400 μm.

[0021] In addition to laser texturing pretreatment of the substrate, step two above can also employ sandblasting. Specifically, the substrate can be roughened by low-pressure, long-distance sandblasting. The parameters for the sandblasting are: abrasive particle size 80 μm, pressure 0.3~0.6 MPa, and sandblasting spacing 100~150 mm. Analysis shows that the bonding strength of the coating prepared after laser texturing of the resin surface can reach 20~30 MPa, which is 1.5~2 times that of the composite coating on the sandblasted resin surface.

[0022] This invention utilizes a supersonic plasma spraying device to spray Al2O3 / phenolic resin (PF) composite powder via external powder delivery. Combined with laser texturing pretreatment, a micron-level uneven structure is constructed on the resin matrix surface. Thus, without the need for secondary curing or coating transfer of the already cured matrix, a semi-ceramic coating is prepared on the matrix surface through the synergistic effect of mechanical interlocking and interfacial compatibility. This method can significantly improve the bonding strength between the semi-ceramic coating and the resin matrix.

[0023] This invention provides a detailed description of a method for preparing a semi-ceramic coating on the surface of a glass fiber reinforced epoxy resin matrix through the following examples: Example 1: Step 1: Use Al2O3 / PF composite powder with a particle size of 25~50 µm as the spraying material. The mass ratio of Al2O3 to PF in the material is 1:1. At the same time, add a certain amount of curing agent hexamethylenetetramine. Step 2: Select cured 3420 glass fiber reinforced epoxy resin as the matrix, and perform low-pressure long-distance sandblasting roughening pretreatment on the matrix. The effect of the sandblasting roughening pretreatment is as follows: Figure 2 As shown, the sand particles were 80 µm, the sandblasting pressure was 0.4 MPa, and the sandblasting spacing was 150 mm during the sandblasting pretreatment. The pretreated sample was then subjected to ultrasonic cleaning with alcohol for 10 min to remove stains from the resin matrix surface.

[0024] Step 3: Place the composite powder in the spraying equipment and use a supersonic plasma spraying system to spray the material to be coated using an external powder delivery method. The effect of the coating after spraying is as follows: Figure 4 As shown, the resin matrix is ​​150 mm away from the nozzle, the powder feeding pipe is 95 mm away from the nozzle, and a mixture of argon (Ar) and hydrogen (H2) is used as the plasma gas during the spraying process. The plasma pressure is 1.1 MPa, the Ar gas flow rate is 4200 L / h, the H2 gas flow rate is 1080 L / h, the current is 425 A, the voltage is 95 V, and the powder feeding rate is 8 g / min.

[0025] Example 2: Step 1: Use Al2O3 / PF composite powder with a particle size of 25~50 µm as the spraying material. The mass ratio of Al2O3 to PF in the material is 12:9. At the same time, a certain amount of curing agent hexamethylenetetramine is added. Step 2: Select cured 3420 glass fiber reinforced epoxy resin as the matrix, and perform laser texturing pretreatment on the matrix. The effect after treatment is as follows: Figure 3As shown, the laser scanning number during the laser texture pretreatment was 9, the pattern spacing was 160 µm, the current was 1A, the frequency was 40 kHz, and the laser scanning speed was 500 mm / s. The pretreated sample was ultrasonically cleaned with alcohol for 10 min to remove stains from the resin matrix surface. After treatment, a square array structure with regular arrangement of micron-level concave and convex patterns can be formed on the matrix surface, with a depth of 35~85 μm.

[0026] Step 3: Place the composite powder in the spraying equipment and spray the material to be coated using an external powder feeding method with a supersonic plasma spraying device. The resin substrate is 150 mm away from the nozzle, and the powder feeding pipe is 95 mm away from the nozzle. During the spraying process, a mixture of argon (Ar) and hydrogen (H2) is used as the plasma gas. The plasma pressure is 1.1 MPa, the Ar gas flow rate is 4200 L / h, the H2 gas flow rate is 1080 L / h, the current is 425 A, the voltage is 95 V, and the powder feeding rate is 8 g / min. The effect of the coating after spraying is shown in [reference needed]. Figure 5 As shown.

[0027] It should be noted that when setting the process parameters for supersonic plasma spraying, the surface temperature of the resin substrate must not exceed its thermal decomposition temperature, and no secondary curing treatment of the substrate is required.

[0028] The pretreated substrate surfaces of Examples 1 and 2 are respectively shown in the figure. Figure 2 and Figure 3 As shown, the surface pattern of the resin matrix after laser texturing pretreatment is regularly arranged and the glass fibers are intact.

[0029] The cross-sectional morphologies of the coatings prepared in Examples 1 and 2 are as follows: Figure 4 and 5 As shown, the coating and substrate interface have good adhesion, and the absence of large cracks at the interface indicates that a large number of Al2O3 particles did not completely melt during the spraying process, thus failing to ablate the substrate surface, or that a small portion of the Al2O3 droplets did not have a large-scale ablation effect on the substrate surface. After the laser-textured resin surface is coated, the substrate still retains a relatively complete pattern.

[0030] The bonding strength of the coatings prepared in Examples 1 and 2 is as follows: Figure 6 As shown, the average bonding strength of the laser-textured resin surface coating is 22.3 MPa, which is 1.6 times that of the sandblasted roughened resin surface coating (13.5).

[0031] The interfacial contact rates of the coatings prepared in Examples 1 and 2 with the substrate are as follows: Figure 7As shown in the figure, this method uses Image ProPlus software to calculate the linear contact length L1 between the substrate and the coating. The ratio of L1 to the SEM image width value L2 is the linear contact rate. This figure reflects that laser-textured resin surfaces can improve the contact rate and reliability of the coating's mechanical bonding, thereby increasing its bonding strength.

[0032] This invention introduces laser-textured microstructures onto the surface of a fully cured glass fiber reinforced epoxy resin matrix, and combines this with externally fed supersonic plasma spraying of Al2O3 / phenolic resin (PF) composite powder. This achieves a synergistic enhancement mechanism of mechanical interlocking and interfacial compatibility, significantly improving the bonding strength (≥20 MPa) between the semi-ceramic coating and the resin matrix while effectively suppressing thermal damage, without requiring secondary curing or coating transfer. This method is process-controllable, environmentally friendly, and efficient, and is particularly suitable for surface strengthening and in-service repair of molded resin components, while also exhibiting excellent ablation resistance, thermal shock resistance, and engineering practicality.

[0033] Obviously, those skilled in the art should understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations of the embodiments of the present invention are possible for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a semi-ceramic coating that enhances the bonding strength of a resin surface, characterized in that, include: Step 1: Prepare a composite powder using Al2O3, phenolic resin and hexamethylenetetramine, wherein the mass ratio of Al2O3, phenolic resin and hexamethylenetetramine in the composite powder is (6~15):9:1; Step 2: For the cured glass fiber reinforced epoxy resin matrix, while preserving the integrity of the glass fiber structure inside the matrix, laser texturing pretreatment is performed on the matrix surface to form a regularly arranged micron-level concave-convex pattern on its surface. Step 3: Using a supersonic plasma spraying process, the composite powder is sprayed onto the substrate surface treated in Step 2 by external powder delivery to form a semi-ceramic coating with a thickness of 300~400 μm.

2. The method for preparing a semi-ceramic coating to enhance the bonding strength of the resin surface according to claim 1, characterized in that, The micron-level convex and concave patterns are regularly arranged square array structures with a depth of 35~85 μm.

3. The method for preparing a semi-ceramic coating to enhance the bonding strength of the resin surface according to claim 1 or 2, characterized in that, The process parameters for the laser texture pretreatment include: 7 to 11 laser scans, pattern spacing of 80 to 160 μm, scanning speed of 300 to 600 mm / s, and laser pulse frequency of 20 to 60 kHz.

4. The method for preparing a semi-ceramic coating to enhance the bonding strength of the resin surface according to claim 1, characterized in that, The composite powder has a particle size of 25-50 μm and an Al2O3 mass fraction of 42%-55%.

5. The method for preparing a semi-ceramic coating to enhance the bonding strength of the resin surface according to claim 1, characterized in that, The process parameters for supersonic plasma spraying include: spraying distance of 140-180 mm, distance between powder feeding pipe and nozzle of 70-100 mm, plasma gas being a plasma gas formed by argon and hydrogen, wherein the argon flow rate is 3600-4800 L / h, the hydrogen flow rate is 600-1500 L / h, the current is 400-450 A, the voltage is 80-110 V, and the powder feeding rate is 5-10 g / min.

6. The method for preparing a semi-ceramic coating to enhance the bonding strength of the resin surface according to claim 1, characterized in that, The bonding strength between the semi-ceramic coating and the substrate is not less than 20 MPa.

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