Wear-resistant and anti-corrosion composite coating for boiler heating surface of thermal power plant and preparation process of wear-resistant and anti-corrosion composite coating

Abstract

The invention discloses a wear-resistant anti-corrosion composite coating for a boiler heating surface of a thermal power plant and a preparation process of the wear-resistant anti-corrosion composite coating, and belongs to the field of coating preparation. The composite coating sequentially comprises a matrix layer, a metal transition layer, a ceramic-based functional surface layer and a high-temperature inorganic silane hole sealing layer from a matrix to the surface. The thermal expansion coefficient difference is relieved through the metal transition layer, the functional surface layer achieves the wear-resistant and anti-corrosion core function, and the hole sealing layer blocks medium permeation. The preparation process comprises the steps of pretreatment of the base body layer, high velocity oxy-fuel spraying of the metal transition layer, laser cladding of the ceramic functional surface layer, hole sealing treatment and aftertreatment. According to the composite coating, the bonding strength is larger than or equal to 65 MPa, the microhardness is 1200-1500 HV, the long-term tolerable temperature is smaller than or equal to 1200 DEG C, the service life is larger than or equal to 24 months, the abrasion resistance and corrosion resistance of the heating surface of the boiler are remarkably improved, and the overhaul frequency and cost are reduced.

Description

Technical Field

[0001] This invention belongs to the field of composite coating technology, specifically relating to a wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler and its preparation process. Background Technology

[0002] The heating surfaces of thermal power plant boilers are exposed to harsh environments of high temperature, high dust, corrosive atmosphere, and thermal cycling shock for extended periods, making them prone to wear and corrosion, leading to shortened equipment lifespan and frequent maintenance. Existing protective coatings mostly use single ceramic or metal coatings, which suffer from low bonding strength (≤30MPa), poor thermal shock resistance, easy peeling, and insufficient hardness. Currently, the average maintenance cycle for heating surfaces is only 8-12 months. Frequent shutdowns for maintenance not only significantly increase maintenance costs but also affect the continuous and stable power supply of the power plant.

[0003] To extend the service life of boiler heating surfaces, surface protective coating technology is widely used. Chinese patent application CN120330652A proposes a NiCr-WC-Co gradient composite coating based on supersonic arc spraying. By introducing rare earth oxides, the coating's density is improved to some extent, achieving a bonding strength ≥50MPa and a hardness ≥800HV. However, the coating's hardness still falls short of the requirements for resistance to high-speed erosion in high-dust environments, and the arc spraying process itself has limitations, resulting in high coating porosity. There is still room for improvement in impermeability and bonding strength, and premature failure remains a risk during long-term high-temperature operation.

[0004] Chinese patent application CN111286224A discloses a high-temperature chlorine corrosion resistant coating for boiler heating surfaces and its preparation method. It discloses a chlorine corrosion resistant coating system based on a polysilazane precursor, employing an organic-inorganic composite structure, suitable for chlorine corrosion environments in biomass or waste incineration boilers. While this coating exhibits some corrosion resistance, its low hardness and insufficient wear resistance, coupled with the need for high-temperature (700℃) curing, make the process complex. Furthermore, the issue of thermal expansion compatibility with the metal substrate remains unresolved, limiting its widespread application on large-area heating surfaces of conventional coal-fired boilers.

[0005] Existing technologies generally suffer from problems such as low bonding strength, poor thermal shock resistance, insufficient hardness and wear resistance, and simplistic structural design, failing to meet the long-term protection requirements of boiler heating surfaces. Therefore, there is an urgent need to develop a composite coating and supporting process that combines high bonding strength, excellent wear and corrosion resistance, and good construction adaptability. Summary of the Invention

[0006] The purpose of this invention is to provide a wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler and its preparation process, so as to solve the problems of weak adhesion, poor thermal shock resistance and short service life of existing coatings.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: One objective of this invention is to provide a wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler. The coating, from the substrate to the surface, comprises, in sequence: a substrate layer, a metal transition layer, a functional surface layer, and a sealing layer. The substrate layer is made of 20G boiler steel or 12Cr1MoV heat-resistant steel. The metal transition layer is prepared from NiCrAlY alloy powder and has a thickness of 0.1~0.2 mm. The functional surface layer is an Al2O3-TiC-SiC composite system with a thickness of 0.3~0.5 mm and a microhardness ≥1200 HV. The sealing layer has a thickness of 5~10 μm.

[0008] Furthermore, the NiCrAlY alloy powder used in the metal transition layer has a particle size of 50~100μm.

[0009] Furthermore, the functional surface layer is a ceramic matrix composite powder composed of Al2O3, TiC and SiC, wherein Al2O3 accounts for 65-75%, TiC accounts for 20-25%, SiC accounts for 5-10%, and the particle size of the ceramic matrix composite powder is 30-80 μm.

[0010] Furthermore, the sealing layer is characterized by being a high-temperature inorganic silane sealing agent.

[0011] The second objective of this invention is to provide a process for preparing a wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler, characterized by the following steps: S1. Mechanically grind the surface of the substrate layer to a surface roughness Ra of 3.2~6.3μm; ultrasonically clean for 15~20 minutes; preheat to 150~200℃ under inert gas protection at a heating rate of 5~10℃ / min. S2. NiCrAlY alloy powder is sprayed onto the substrate layer using a supersonic flame to form a NiCrAlY alloy transition layer on the surface of the substrate layer. S3. A functional surface layer is formed on the surface of the metal transition layer by using laser cladding technology to process ceramic matrix composite powder. S4. High-pressure airless spraying process is used to spray inorganic silane sealing agent onto the functional surface at high temperature and then cure it to form a sealing layer. S5. Grind the coating surface to ensure flatness ≤0.05mm, forming a wear-resistant and corrosion-resistant composite coating.

[0012] Furthermore, the process parameters for the supersonic flame spraying are: spraying distance 300~350mm; flame temperature 2800~3200℃; powder feeding speed 20~30g / min.

[0013] Furthermore, the process parameters for laser cladding are as follows: laser power 1800~2200W; laser scanning speed 5~8mm / s; spot diameter 3~5mm; argon protection flow rate 15~20L / min; the ceramic matrix composite powder is fed synchronously, and the powder feeding speed is matched with the laser scanning speed to ensure that the thickness uniformity error is ≤±0.02mm.

[0014] Furthermore, in the sealing process, the curing temperature is 120~150℃ and the curing time is 2 hours.

[0015] Furthermore, the temperature of the substrate layer is controlled at 200~300℃ during the spraying process of the above preparation process.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention sets a metal transition layer between the substrate layer and the ceramic-based functional surface layer. Through the bridging effect of the NiCrAlY metal transition layer, the difference in thermal expansion coefficient between the substrate layer and the ceramic-based functional surface layer is effectively alleviated, fundamentally solving the technical problem of easy cracking and peeling of traditional single coatings. The bonding strength of the composite coating of this invention is increased to ≥65MPa, which is more than twice that of traditional coatings, and the thermal shock resistance is greatly enhanced.

[0017] 2. In the preparation of the composite coating, the present invention adopts a composite process of "supersonic flame spraying + laser cladding" to achieve complementary advantages. Supersonic flame spraying ensures the density and bonding force of the metal transition layer, while the laser cladding process enables the functional surface layer and the metal transition layer to form a strong metallurgical bond, taking into account both the bonding strength and wear and corrosion resistance of the coating, and solving the problem that traditional processes cannot take into account multiple properties.

[0018] 3. The functional surface layer of this invention adopts an Al2O3-TiC-SiC composite system. TiC and SiC are dispersed in the Al2O3 matrix as hard reinforcing phases, forming a "hard particle-reinforced composite material." This maintains the high-temperature stability of Al2O3 while significantly improving the overall hardness and abrasive wear resistance. Through system optimization, synergistic performance is achieved, with a microhardness of 1200-1500 HV and wear resistance more than 5 times that of traditional coatings. The addition of SiC enhances the resistance to acid and alkali corrosion, and combined with the media blocking effect of the sealing layer, ensures long-term stable operation of the coating under harsh conditions. The service life of the coating is extended to more than 24 months, doubling the maintenance cycle of traditional coatings, saving more than 800,000 yuan in annual maintenance costs per boiler. At the same time, it reduces the risk of unplanned shutdowns and lowers the safety hazards of maintenance operations, providing a strong guarantee for the safe, stable, economical and efficient operation of thermal power plants. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the composite coating provided in this invention.

[0020] In the diagram: 1. Substrate layer; 2. Metal transition layer; 3. Functional surface layer; 4. Sealing layer. Detailed Implementation

[0021] The present invention will be further described below with reference to preferred embodiments. The endpoints and any values ​​of the ranges disclosed herein are not limited to precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, endpoint values ​​of various ranges, endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Unless otherwise specified, the materials, reagents, etc., used in the following embodiments are commercially available. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments are commercially available or can be obtained by existing known methods.

[0022] Example 1 Taking the water-cooled wall of a 300MW thermal power plant boiler as an example, the wear-resistant and corrosion-resistant composite coating on the heated surface includes, from the substrate to the surface, the following layers in sequence: substrate layer 1, metal transition layer 2, functional surface layer 3, and sealing layer 4. The substrate layer 1 is 20G boiler steel, the metal transition layer 2 is prepared from NiCrAlY alloy powder, the functional surface layer 3 is a ceramic matrix composite layer, which is made from ceramic matrix composite powder composed of Al2O3, TiC and SiC, of ​​which Al2O3 accounts for 65%, TiC accounts for 25% and SiC accounts for 10%, and the sealing layer 4 is an inorganic silica gel layer. The preparation process of the wear-resistant and corrosion-resistant composite coating in this embodiment includes the following steps: S1. Grind 20G boiler steel with a 120-mesh corundum grinding wheel to achieve a surface roughness Ra of 3.2-6.3μm; ultrasonically clean with anhydrous ethanol for 20 minutes; preheat 20G boiler steel to 180℃ under argon protection, with the heating rate controlled at 5℃ / min.

[0023] S2. Using a JP8000 type supersonic spraying equipment, spraying is performed on the surface of 20G boiler steel at a depth of 300mm. The flame temperature is 2800℃. NiCrAlY alloy powder with a particle size of 50μm is fed in at a powder feeding speed of 20g / min to form a NiCrAlY transition layer with a thickness of 0.1mm.

[0024] S3. Using YLS-3000 laser cladding equipment; laser power 2000W, laser scanning speed 6mm / s, spot diameter 4mm; argon protection flow rate 18L / min, ceramic matrix composite powder is fed into the laser cladding equipment, the feeding speed is consistent with the laser scanning speed, forming a ceramic matrix composite functional surface layer with a thickness of 0.3mm.

[0025] S4. Using a GPQ6C high-pressure airless spraying device, the high-temperature inorganic silane sealing agent is evenly coated onto the surface of the functional layer, ensuring no missed coating or dripping during the coating process. Then, the coated 20G boiler steel is placed in a constant temperature oven and cured at 120℃ for 2 hours, allowing the sealing agent to fully penetrate into the micropores of the functional layer and form a complete and continuous sealed layer.

[0026] S5. Use an 800-grit diamond grinding wheel to lightly polish the coating surface to remove burrs, protrusions and local defects generated during the spraying process, ensuring that the coating surface flatness is ≤0.05mm, which meets the requirements of airflow and heat exchange efficiency of the boiler heating surface.

[0027] The coatings obtained in the above embodiments were subjected to comprehensive performance testing, and the results are as follows: Coating bond strength: Tested using the pull-out method (according to GB / T 8642-2002 standard), the result is 72MPa, which is far superior to traditional coatings (≤30MPa). Microhardness: Tested using an HV-1000 Vickers hardness tester, five test points were selected in different areas of the coating, and the average value was 1350 HV, which is higher than that of traditional coatings (800-1000 HV). High temperature resistance: The sample was placed in a high-temperature box furnace at 1200℃ for 720 hours. After the sample was removed, the coating was observed to be free of cracks and peeling, indicating stable performance. Wear resistance: Tested using an MM-200 pin-disc wear tester with a loading pressure of 10N and a rotation speed of 200r / min, the wear amount after 1000 revolutions was 0.025g, which is only 1 / 6 of that of traditional coatings; Actual operating results: After the water-cooled wall was treated with the composite coating of this invention, it operated continuously for 18 months. Regular inspections showed no obvious wear or corrosion on the coating. The maintenance cycle is expected to be extended from the original 10 months to more than 24 months. The annual maintenance cost of a single boiler is reduced by 850,000 yuan, resulting in significant economic benefits.

[0028] Example 2 The difference between this embodiment and Embodiment 1 is that: the substrate layer 1 is 12Cr1MoV heat-resistant steel; the ceramic matrix composite layer is made of ceramic matrix composite powder composed of Al2O3, TiC and SiC, with Al2O3 accounting for 70%, TiC accounting for 23% and SiC accounting for 7%; The preparation process of the wear-resistant and corrosion-resistant composite coating in this embodiment includes the following steps: S1. Grind 20G boiler steel with a 120-mesh corundum grinding wheel to achieve a surface roughness Ra of 3.2-6.3μm; ultrasonically clean with anhydrous ethanol for 20 minutes; preheat 20G boiler steel to 180℃ under argon protection, with the heating rate controlled at 10℃ / min.

[0029] S2. Using a JP8000 type supersonic spraying equipment, spraying is performed on the surface of 20G boiler steel at a depth of 330mm. The flame temperature is 3000℃. NiCrAlY alloy powder is fed in with a particle size of 75μm and a powder feeding speed of 25g / min to form a NiCrAlY transition layer with a thickness of 0.15mm.

[0030] S3. Use YLS-3000 laser cladding equipment; laser power 2000W, laser scanning speed 6mm / s, spot diameter 4mm; argon protection flow rate 18L / min. Feed the ceramic matrix composite powder into the laser cladding equipment at the same speed as the laser scanning speed to form a ceramic matrix composite functional surface layer with a thickness of 0.4mm.

[0031] S4. Using a GPQ6C high-pressure airless spraying device, the high-temperature inorganic silane sealing agent is evenly coated onto the surface of the functional layer, ensuring no missed coating or dripping during the coating process. Then, the coated 20G boiler steel is placed in a constant temperature oven and cured at 135℃ for 2 hours, allowing the sealing agent to fully penetrate into the micropores of the functional layer and form a complete and continuous sealed layer.

[0032] S5. Use an 800-grit diamond grinding wheel to lightly polish the coating surface to remove burrs, protrusions and local defects generated during the spraying process, ensuring that the coating surface flatness is ≤0.05mm, which meets the requirements of airflow and heat exchange efficiency of the boiler heating surface.

[0033] Example 3 The difference between this embodiment and Embodiment 1 is that the ceramic matrix composite layer is made of ceramic matrix composite powder composed of Al2O3, TiC and SiC, with Al2O3 accounting for 70%, TiC accounting for 23% and SiC accounting for 7%. The preparation process of the wear-resistant and corrosion-resistant composite coating in this embodiment includes the following steps: S1. Grind 20G boiler steel with a 120-mesh corundum grinding wheel to achieve a surface roughness Ra of 3.2-6.3μm; ultrasonically clean with anhydrous ethanol for 20 minutes; preheat 20G boiler steel to 180℃ under argon protection, with the heating rate controlled at 10℃ / min.

[0034] S2. Using a JP8000 type supersonic spraying equipment, spraying is performed on the surface of 20G boiler steel at a depth of 350mm. The flame temperature is 3200℃. NiCrAlY alloy powder is fed in with a particle size of 100μm and a powder feeding speed of 30g / min to form a NiCrAlY transition layer with a thickness of 0.2mm.

[0035] S3. Use YLS-3000 laser cladding equipment; laser power 2000W, laser scanning speed 6mm / s, spot diameter 4mm; argon protection flow rate 18L / min. Feed the ceramic matrix composite powder into the laser cladding equipment at the same speed as the laser scanning speed to form a ceramic matrix composite functional surface layer with a thickness of 0.5mm.

[0036] S4. Using a GPQ6C high-pressure airless spraying device, the high-temperature inorganic silane sealing agent is evenly coated onto the surface of the functional layer, ensuring no missed coating or dripping during the coating process. Then, the coated 20G boiler steel is placed in a constant temperature oven and cured at 150℃ for 2 hours, allowing the sealing agent to fully penetrate into the micropores of the functional layer and form a complete and continuous sealed layer.

[0037] S5. Use an 800-grit diamond grinding wheel to lightly polish the coating surface to remove burrs, protrusions and local defects generated during the spraying process, ensuring that the coating surface flatness is ≤0.05mm, which meets the requirements of airflow and heat exchange efficiency of the boiler heating surface.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler, characterized in that, The structure from the substrate to the surface comprises: a substrate layer (1), a metal transition layer (2), a functional surface layer (3), and a sealing layer (4); the substrate layer (1) is 20G boiler steel or 12Cr1MoV heat-resistant steel; the metal transition layer (2) is prepared from NiCrAlY alloy powder with a thickness of 0.1~0.2mm; the functional surface layer (3) is an Al2O3-TiC-SiC composite system with a thickness of 0.3~0.5mm and a microhardness ≥1200HV; and the sealing layer (4) has a thickness of 5~10μm.

2. The wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler according to claim 1, characterized in that, The NiCrAlY alloy powder used in the metal transition layer (2) has a particle size of 50~100μm.

3. The wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler according to claim 1, characterized in that, The functional surface layer (3) is a ceramic matrix composite powder composed of Al2O3, TiC and SiC, wherein Al2O3 accounts for 65~75%, TiC accounts for 20~25%, SiC accounts for 5~10%, and the particle size of the ceramic matrix composite powder is 30~80μm.

4. The wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler according to claim 1, characterized in that, The sealing layer (4) is a high-temperature inorganic silane sealing agent.

5. A preparation process for a wear-resistant and corrosion-resistant composite coating for the heating surface of a thermal power plant boiler as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Mechanically grind the surface of the substrate layer (1) to a surface roughness Ra of 3.2~6.3μm; ultrasonically clean for 15~20 minutes; preheat to 150~200℃ under inert gas protection at a heating rate of 5~10℃ / min. S2. NiCrAlY alloy powder is sprayed onto the substrate layer (1) using a supersonic flame to form a NiCrAlY alloy transition layer on the surface of the substrate layer (1). S3. The ceramic matrix composite powder is treated by laser cladding process, so that the ceramic matrix composite powder is bonded to the surface of the metal transition layer (2) to form a functional surface layer (3). S4. High-pressure airless spraying process is used to spray inorganic silane sealing agent on the functional surface layer (3) at high temperature and then cure it to form a sealing layer (4). S5. Grind the coating surface to ensure flatness ≤0.05mm, forming a wear-resistant and corrosion-resistant composite coating.

6. The preparation process according to claim 5, characterized in that, The process parameters for supersonic flame spraying are: spraying distance 300~350mm; flame temperature 2800~3200℃; powder feeding speed 20~30g / min.

7. The preparation process according to claim 5, characterized in that, The laser cladding process parameters are as follows: laser power 1800~2200W; laser scanning speed 5~8mm / s; spot diameter 3~5mm; argon protection flow rate 15~20L / min; the ceramic matrix composite powder is fed synchronously, and the powder feeding speed is matched with the laser scanning speed to ensure that the thickness uniformity error is ≤±0.02mm.

8. The preparation process according to claim 5, characterized in that, In the sealing process, the curing temperature is 120~150℃ and the curing time is 2 hours.

9. According to claim 5 8. The preparation process described in any one of the above is characterized in that, During the preparation process, the temperature of the substrate layer (1) is controlled at 200~300℃.

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