A method for preparing a high bond strength silicon carbide coating

Abstract

The application discloses a high-bonding-strength silicon carbide coating preparation method and belongs to the technical field of material surface treatment. The method comprises the following steps: pre-treating a base body; depositing a mixed precursor layer of silicon powder and carbon powder on the surface of the base body by ultrasonic cold spraying; rapidly cladding the precursor layer by using pulsed laser under a protective atmosphere to induce a silicon carbide transition layer at the interface; and finally performing high-temperature annealing treatment to densify the coating. The silicon carbide coating is formed on the surface of the graphite base body by the synergistic effect of pulsed laser and high-temperature annealing, and firm chemical bonding between the coating and the base body is achieved. Meanwhile, based on the combined process of ultrasonic cold spraying, laser rapid cladding and short-time annealing, the preparation period is greatly shortened. Moreover, the method can also be suitable for complex-morphology base bodies. Therefore, the application effectively solves the problems of insufficient coating bonding strength and low efficiency in the prior art.

Description

Technical Field

[0001] This invention relates to the field of material surface treatment technology, and specifically to a method for preparing a silicon carbide coating with high bonding strength. Background Technology

[0002] Graphite materials are widely used in high-temperature environments due to their excellent thermal conductivity, low coefficient of thermal expansion, and thermal shock resistance. However, graphite has poor chemical stability in oxidizing or corrosive environments and is easily oxidized at temperatures exceeding 500 °C, limiting its service life. To improve the performance of graphite materials, constructing a high-performance protective coating on its surface has become an important research direction. Among these materials, silicon carbide (SiC) is considered the most promising protective coating material due to its excellent high hardness, wear resistance, high-temperature oxidation resistance, corrosion resistance, and good matching with graphite in terms of coefficient of thermal expansion. SiC coatings can effectively isolate oxygen and corrosive media in high-temperature environments, thereby significantly improving the stability and reliability of graphite components.

[0003] However, the preparation of high-performance SiC coatings on graphite substrates still faces key challenges. Existing technologies such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and liquid-phase silicon infiltration can prepare SiC coatings, but they suffer from problems such as insufficient coating adhesion strength, long preparation cycles, low efficiency, high equipment costs, and poor coating uniformity. For example, CVD and PVD methods have slow deposition rates, and although some chemical bonding exists, the interface structure is simple and prone to peeling under thermal shock conditions; while traditional silicon infiltration methods require long-term high-temperature treatment, making them unsuitable for complex substrate morphologies.

[0004] Therefore, how to prepare SiC coatings with both high bonding strength and rapid preparation characteristics on graphite substrates is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies, such as low bonding strength between the substrate and the coating and insufficient preparation efficiency. This invention achieves a strong chemical bond between the coating and the substrate through in-situ reaction by combining ultrasonic spraying with pulsed laser rapid cladding, while also shortening the preparation cycle.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a silicon carbide coating with high bonding strength, the method comprising the following steps: S100. Select a substrate and pre-treat it to remove dust and impurities from the substrate surface; S200: Silicon powder and carbon powder are uniformly mixed according to a preset mass ratio and deposited on the pretreated substrate surface by ultrasonic cold spraying, thereby forming a uniformly distributed precursor layer on the substrate surface. S300. Under a protective gas atmosphere, a pulsed laser is used to scan the precursor layer on the substrate surface to locally melt and react the carbon powder and silicon powder in the precursor layer, thereby forming a silicon carbide transition layer of a predetermined thickness at the interface between the precursor layer and the substrate. The protective gas is one of high-purity nitrogen, argon or helium. S400: High-temperature annealing is performed in a vacuum or protective gas atmosphere to promote the diffusion reaction of silicon and carbon in the precursor layer, thereby forming a dense silicon carbide coating.

[0007] Further, step S100 specifically involves: first, selecting high-purity isostatic graphite as the matrix, with a density of 1.75-2.1 g / cm³, an average pore size of 5-20 μm, and a surface roughness of 1-5 μm; then, ultrasonically cleaning the selected matrix sequentially in deionized water and anhydrous ethanol for 20-40 min to remove dust and impurities from the matrix surface; finally, drying it in a vacuum drying oven at 100-140℃ for 1.5-3.5 h to obtain a clean and dry graphite matrix.

[0008] Further, step S200 specifically involves: uniformly mixing silicon powder and carbon powder with an average particle size of 10-40 μm at a preset mass ratio, and depositing them on the surface of a graphite substrate using an ultrasonic cold spraying device, thereby forming a uniformly distributed precursor layer on the substrate surface. The preset mass ratio of silicon powder to carbon powder is 1.0-1.3:1, the nozzle frequency in the ultrasonic cold spraying device is 20-40 kHz, the spraying distance is 10-30 mm, the spraying speed is 50-200 mm / s, the number of sprays is 3-5, the thickness of the precursor layer is 20-80 μm, the porosity of the precursor layer is not greater than 10%, and the surface roughness of the precursor layer is not greater than 5 μm.

[0009] Furthermore, the ultrasonic cold spraying equipment uses helium or nitrogen as the spraying gas, with a gas purity of ≥99.99%.

[0010] Further, step S300 specifically involves: under a protective gas atmosphere, scanning the precursor layer on the substrate surface using a pulsed laser at a scanning speed of 50-300 mm / s, a scanning overlap rate of 60-80%, and scanning each region 1-3 times. The wavelength of the pulsed laser is 800-1100 nm, the pulse width is 10 μs-5 ms, the repetition frequency is 500 Hz-5 kHz, the single pulse energy is 35-45 J, and the spot diameter is 0.2-1.0 mm.

[0011] Furthermore, in step S300, the preset thickness of the silicon carbide transition layer is 1-5 μm.

[0012] Further, step S400 specifically includes: S410. Place the sample obtained in step S300 in a vacuum or protective gas atmosphere, and heat it to 1200-1800℃ at a rate of 5-15℃ / min, and keep it at that temperature for 1-4 hours. S420 is then cooled at a rate of 3–10 °C / min to promote the diffusion reaction of silicon and carbon in the precursor layer, thereby gradually forming a dense silicon carbide coating.

[0013] Furthermore, the purity of the protective gas is ≥99.99%, the flow rate of the protective gas in step S300 is 50-200 sccm, and the flow rate of the protective gas in step S400 is 50-200 sccm.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects: (1) The present invention induces the formation of a silicon carbide bonding transition layer at the interface between the substrate and the precursor layer by pulsed laser. This transition layer can effectively alleviate the difference in thermal expansion coefficient between the substrate and the silicon carbide coating, thereby achieving a strong chemical bond between the substrate and the coating, effectively overcoming the defects of poor adhesion and easy peeling in traditional methods.

[0015] (2) This invention utilizes ultrasonic cold spraying to achieve efficient deposition of the precursor layer, avoiding the problem of excessive time consumption in traditional deposition processes. At the same time, combined with the instantaneous high energy input of pulsed laser, it achieves rapid reaction and crystal nucleus generation, significantly improving the overall preparation efficiency.

[0016] (3) The present invention adopts a combination of cold spraying and pulsed laser technology. The cold spraying process can be carried out at room temperature or low temperature, while the pulsed laser only heats the local area rapidly, avoiding overall high temperature treatment, thereby effectively protecting the substrate structure and avoiding thermal damage to the substrate caused by high temperature.

[0017] (4) The present invention induces nucleation and high-temperature annealing grain growth by pulsed laser, so that the silicon carbide coating formed at the interface exhibits a gradient structure from fine grains to coarse grains, which effectively reduces the porosity and residual free silicon and free carbon content of the coating, thereby significantly improving the thermal shock resistance.

[0018] (5) The process of this invention is simple and does not rely on expensive and complex vacuum deposition equipment. It is suitable for planar, large-area and complex morphological substrates and has better potential for promotion and industrial application. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a method for preparing a high-bonding-strength silicon carbide coating according to the present invention; Figure 2 This is a diagram showing the effect of depositing a silicon carbide coating on the substrate in Example 1. Detailed Implementation

[0021] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0022] Example 1 The method for preparing a high-bonding-strength silicon carbide coating provided by this invention involves depositing a silicon carbide coating on a substrate, the specific process of which is as follows: Figure 1 As shown.

[0023] 1) High-purity isostatic graphite with a density of 1.85 g / cm³, a pore size of 15 μm, and a surface roughness of 3 μm was selected as the matrix and ultrasonically cleaned in deionized water and anhydrous ethanol for 30 min in sequence, and then dried in a vacuum drying oven at 120℃ for 2 h. 2) Silicon powder with a particle size of 20 μm and carbon powder with a particle size of 15 μm were uniformly mixed at a preset mass ratio of 1.2:1, ball-milled for 6 hours, and then dried in a vacuum drying oven at 100℃ for 2 hours. Then, an ultrasonic cold spraying device was used to deposit a precursor layer, wherein the nozzle frequency was 30 kHz, the spray gas was high-purity nitrogen (purity of 99.99%), the nitrogen gas flow rate was 150 sccm, the spraying distance was 20 mm, the spraying speed was 100 mm / s, the nozzle step size was 0.3 mm, and the number of scans was 4, resulting in a precursor layer with a thickness of 50 μm. 3) Pulsed laser rapid cladding is performed in a high-purity argon atmosphere. The wavelength of the pulsed laser is 1064nm, the pulse width is 100μs, the repetition frequency is 1kHz, the single pulse energy is 40J, the spot diameter is 0.5mm, and the power density is calculated based on the laser energy, pulse width, and spot area, i.e., power density = single pulse energy / (spot area × pulse width). The scanning speed is 150mm / s, the scanning overlap rate is 70%, each area is scanned twice, and the instantaneous temperature of the laser action area during the cladding process is 2000℃. A silicon carbide transition layer with a thickness of 3μm is formed at the interface between the precursor layer and the substrate. 4) The sample obtained in step 3) was placed in a vacuum tube furnace and annealed under a high-purity argon atmosphere (99.999% purity, flow rate 150 sccm). The temperature was increased to 1450℃ at a rate of 10℃ / min and held for 2 hours, then cooled at a rate of 5℃ / min to obtain a dense silicon carbide coating with a thickness of 50 μm. Figure 2 As shown, Figure 2 The image shows the effect of depositing a silicon carbide coating on a graphite substrate using a high-bonding-strength silicon carbide coating preparation method.

[0024] Example 2 1) High-purity isostatic graphite with a density of 1.75 g / cm³, a pore size of 5 μm, and a surface roughness of 1 μm was selected as the matrix and ultrasonically cleaned in deionized water and anhydrous ethanol for 20 min in sequence, and then dried in a vacuum drying oven at 100℃ for 1.5 h. 2) Silicon powder with a particle size of 10 μm and carbon powder with a particle size of 25 μm were mixed uniformly at a preset mass ratio of 1:1, ball-milled for 4 hours, and then dried in a vacuum drying oven at 120℃ for 1.5 hours. Then, an ultrasonic cold spraying device was used to deposit a precursor layer, wherein the nozzle frequency was 20 kHz, the spray gas was high-purity nitrogen (purity of 99.99%), the nitrogen gas flow rate was 50 sccm, the spraying distance was 10 mm, the spraying speed was 50 mm / s, the nozzle step size was 0.2 mm, and the number of scans was 3, resulting in a precursor layer with a thickness of 20 μm. 3) Pulsed laser rapid cladding is performed in a high-purity argon atmosphere. The wavelength of the pulsed laser is 800 nm, the pulse width is 10 μs, the repetition frequency is 500 Hz, the single pulse energy is 35 J, the spot diameter is 0.2 mm, the power density is calculated based on the laser energy, pulse width and spot area, the scanning speed is 50 mm / s, the scanning overlap rate is 60%, each area is scanned once, the instantaneous temperature of the laser action area during the cladding process is 1800℃, and a silicon carbide transition layer with a thickness of 1 μm is formed at the interface between the precursor layer and the substrate. 4) The sample obtained in step 3) was placed in a vacuum tube furnace and annealed in a high-purity argon atmosphere (purity of 99.999% and flow rate of 50 sccm). The temperature was increased to 1200℃ at a rate of 5℃ / min and held for 4 hours. Then it was cooled at a rate of 3℃ / min to obtain a dense silicon carbide coating with a thickness of 20μm.

[0025] Example 3 1) High-purity isostatic graphite with a density of 2.1 g / cm³, a pore size of 20 μm, and a surface roughness of 5 μm was selected as the matrix and ultrasonically cleaned in deionized water and anhydrous ethanol for 40 min in sequence, and then dried in a vacuum drying oven at 140℃ for 3.5 h. 2) Silicon powder with a particle size of 40 μm and carbon powder with a particle size of 40 μm were uniformly mixed at a preset mass ratio of 1.3:1, ball-milled for 8 hours, and then dried in a vacuum drying oven at 140℃ for 3 hours. Then, an ultrasonic cold spraying device was used to deposit a precursor layer, wherein the nozzle frequency was 40 kHz, the spray gas was high-purity nitrogen (purity of 99.99%), the nitrogen gas flow rate was 200 sccm, the spraying distance was 30 mm, the spraying speed was 200 mm / s, the nozzle step size was 0.5 mm, and the number of scans was 5, resulting in a precursor layer with a thickness of 80 μm. 3) Pulsed laser rapid cladding is performed in a high-purity argon atmosphere. The wavelength of the pulsed laser is 1100nm, the pulse width is 5ms, the repetition frequency is 5kHz, the single pulse energy is 45J, the spot diameter is 1.0mm, the power density is calculated based on the laser energy, pulse width and spot area, the scanning speed is 300mm / s, the scanning overlap rate is 80%, each area is scanned 3 times, the instantaneous temperature of the laser action area during the cladding process is 2200℃, and a silicon carbide transition layer with a thickness of 5μm is formed at the interface between the precursor layer and the substrate. 4) Place the sample obtained in step 3) in a vacuum tube furnace and anneal it in a high-purity argon atmosphere (purity of 99.999% and flow rate of 200 sccm). Heat it to 1800℃ at a rate of 15℃ / min, hold it for 1 h, and then cool it at a rate of 10℃ / min to obtain a dense silicon carbide coating with a thickness of 100 μm.

[0026] Comparative Example 1 The same substrate as in Example 1 was selected, and a silicon carbide coating was deposited on the substrate using a conventional CVD process.

[0027] Comparative Example 2 The same substrate as in Example 2 was selected, and a silicon carbide coating was deposited on the substrate using a conventional CVD process.

[0028] Comparative Example 3 The same substrate as in Example 3 was selected, and a silicon carbide coating was deposited on the substrate using a conventional CVD process.

[0029] The substrates in Examples 1-3 and Comparative Examples 1-3 with deposited silicon carbide coatings were subjected to thermal shock cycles and silicon carbide coating adhesion strength tests. The test results are shown in Tables 1 and 2.

[0030] Table 1. Results of thermal shock cycle tests for Examples 1-3 and Comparative Examples 1-3 Example 1 No cracks or peeling, surface intact Example 2 No cracks or peeling, surface intact Example 3 No cracks or peeling, surface intact Comparative Example 1 The coating cracked and peeled off over a large area. Comparative Example 2 The coating cracked and peeled off over a large area. Comparative Example 3 The coating cracked and peeled off over a large area. As can be seen from Table 1, after 50 thermal shock cycles at 1000℃, no cracks or peeling were observed in Examples 1-3, and the surface remained intact. In contrast, the coatings of Comparative Examples 1-3 cracked and peeled off over a large area. Therefore, compared with Comparative Examples 1-3, Examples 1-3 have better thermal shock resistance. This means that the high bonding strength silicon carbide coating preparation method provided by the present invention can significantly improve the thermal shock resistance of silicon carbide coatings.

[0031] Table 2. Test results of coating bond strength in Examples 1-3 and Comparative Examples 1-3 Example 1 72 Example 2 68 Example 3 75 Comparative Example 1 19 Comparative Example 2 25 Comparative Example 3 21 As can be seen from Table 2, the bonding strength between the coating and the substrate in Examples 1-3 is above 65 MPa, while the bonding strength between the coating and the substrate in Comparative Examples 1-3 is below 25 MPa. Since Comparative Examples 1-3 use traditional CVD process, the silicon carbide coating deposited on the substrate mostly relies on physical adhesion, and the bonding force is weak. Examples 1-3 use ultrasonic spraying combined with pulsed laser rapid cladding process, and a metallurgical bonding transition layer is formed at the interface between the silicon carbide coating and the substrate. This transition layer can effectively improve the bonding strength between the silicon carbide coating and the substrate.

[0032] The above provides a detailed description of a method for preparing a high-bonding-strength silicon carbide coating. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of these examples are merely for the purpose of helping to understand the core ideas of this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for preparing a silicon carbide coating with high bonding strength, characterized in that, The method includes the following steps: S100. Select a substrate and pre-treat it to remove dust and impurities from the substrate surface; S200: Silicon powder and carbon powder are uniformly mixed according to a preset mass ratio and deposited on the pretreated substrate surface by ultrasonic cold spraying, thereby forming a uniformly distributed precursor layer on the substrate surface. S300. Under a protective gas atmosphere, a pulsed laser is used to scan the precursor layer on the substrate surface to locally melt and react the carbon powder and silicon powder in the precursor layer, thereby forming a silicon carbide transition layer of a predetermined thickness at the interface between the precursor layer and the substrate. The protective gas is one of high-purity nitrogen, argon or helium. S400: High-temperature annealing is performed in a vacuum or protective gas atmosphere to promote the diffusion reaction of silicon and carbon in the precursor layer, thereby forming a dense silicon carbide coating.

2. The method for preparing a high-bonding-strength silicon carbide coating according to claim 1, characterized in that, The specific steps of step S100 are as follows: First, high-purity isostatic graphite is selected as the matrix, with a density of 1.75-2.1 g / cm³, an average pore size of 5-20 μm, and a surface roughness of 1-5 μm; then, the selected matrix is ​​ultrasonically cleaned in deionized water and anhydrous ethanol for 20-40 min in sequence to remove dust and impurities from the matrix surface; finally, it is dried in a vacuum drying oven at 100-140℃ for 1.5-3.5 h to obtain a clean and dry graphite matrix.

3. The method for preparing a high-bonding-strength silicon carbide coating according to claim 2, characterized in that, Step S200 specifically involves: uniformly mixing silicon powder and carbon powder with an average particle size of 10-40 μm at a preset mass ratio, and depositing them on the surface of a graphite substrate using an ultrasonic cold spraying device, thereby forming a uniformly distributed precursor layer on the substrate surface. The preset mass ratio of silicon powder to carbon powder is 1.0-1.3:1, the nozzle frequency in the ultrasonic cold spraying device is 20-40 kHz, the spraying distance is 10-30 mm, the spraying speed is 50-200 mm / s, the number of sprays is 3-5, the thickness of the precursor layer is 20-80 μm, the porosity of the precursor layer is not greater than 10%, and the surface roughness of the precursor layer is not greater than 5 μm.

4. The method for preparing a high-bonding-strength silicon carbide coating according to claim 3, characterized in that, The ultrasonic cold spraying equipment uses helium or nitrogen as the spray gas, with a purity of ≥ 99.99%.

5. The method for preparing a high-bonding-strength silicon carbide coating according to claim 4, characterized in that, Step S300 specifically involves: under a protective gas atmosphere, scanning the precursor layer on the substrate surface using a pulsed laser at a scanning speed of 50-300 mm / s, a scanning overlap rate of 60-80%, and scanning each region 1-3 times. The wavelength of the pulsed laser is 800-1100 nm, the pulse width is 10 μs-5 ms, the repetition frequency is 500 Hz-5 kHz, the single pulse energy is 35-45 J, and the spot diameter is 0.2-1.0 mm.

6. The method for preparing a high-bonding-strength silicon carbide coating according to claim 5, characterized in that, In step S300, the preset thickness of the silicon carbide transition layer is 1-5 μm.

7. The method for preparing a high-bonding-strength silicon carbide coating according to claim 6, characterized in that, Step S400 specifically includes: S410. Place the sample obtained in step S300 in a vacuum or protective gas atmosphere, and heat it to 1200-1800℃ at a rate of 5-15℃ / min, and keep it at that temperature for 1-4 hours. S420 is then cooled at a rate of 3–10 °C / min to promote the diffusion reaction of silicon and carbon in the precursor layer, thereby gradually forming a dense silicon carbide coating.

8. The method for preparing a high-bonding-strength silicon carbide coating according to claim 7, characterized in that, The purity of the protective gas is ≥99.99%, the flow rate of the protective gas in step S300 is 50-200 sccm, and the flow rate of the protective gas in step S400 is 50-200 sccm.

Images