Gradient functionalized composite coating applied to boiler heating surface and preparation method thereof

Abstract

The invention belongs to the technical field of thermal power heating surface treatment, and provides a gradient functional composite coating applied to a boiler heating surface and a preparation method of the gradient functional composite coating in order to solve the technical problems that an existing protective coating of the boiler heating surface is prone to abrasion and oxidation and high in cost. Collaborative design is formed, and gradient matching of mechanical properties and environmental failure resistance is achieved. The low-melting-point glass powder is combined with the rare earth catalytic effect, low-temperature ceramization is achieved, and thermal damage to a matrix is avoided. After the metal ceramic transition layer is sprayed, high-frequency induction remelting treatment is carried out, meanwhile, laser cladding is carried out on the surface of the ceramic surface layer, a nanocrystalline-amorphous composite structure is formed, and the bonding strength of the coating is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal power heating surface treatment, and particularly relates to a gradient functional composite coating applied to a boiler heating surface and a preparation method thereof. BACKGROUND

[0002] High-temperature corrosion of a thermal power boiler heating surface is a complex multi-factor problem, mainly involving fuel composition, combustion conditions, material performance and operation environment, etc., and mainly manifests as sulfide corrosion, chloride corrosion and alkali metal corrosion. A protective coating of the boiler heating surface is a key technology for guaranteeing efficient and safe operation of the boiler, and especially in a harsh environment of high temperature, corrosion and abrasion, the role of the protective coating includes preventing corrosion of corrosive gases such as sulfides and chlorides, slowing down the oxidation rate of the metal matrix, prolonging the service life of the equipment, reducing the frequency of shutdown for maintenance, etc.

[0003] In the prior art, conventional protective coatings include: a ceramic coating, which has the advantage of high-temperature resistance, but is easily scratched or abraded by metal tools during long-term use, especially in high-frequency contact scenes such as cookware, and has a short service life; a metal alloy coating, which has high-temperature oxidation and hot corrosion resistance, but has high raw material costs, and traditional air spraying processes are prone to cause oxidation of the coating; a nano coating, which enhances the compactness and thermal shock resistance, but requires high dispersion technology (such as sol-gel method) of nano particles, resulting in a production cost significantly higher than that of traditional coatings. SUMMARY

[0004] The application provides a gradient functional composite coating applied to a boiler heating surface and a preparation method thereof to solve the technical problems of easy abrasion, easy oxidation and high cost of existing protective coatings of the boiler heating surface.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the application is as follows: In a first aspect, the application provides a preparation method of a gradient functional composite coating applied to a boiler heating surface, comprising: honeycomb-like roughening treatment is performed on a surface of a base body of the boiler heating surface to obtain a pretreated base body surface; a metal fiber reinforced bottom layer is sprayed on the pretreated base body surface; the metal fiber reinforced bottom layer comprises a nickel-based alloy NiCrAlY and SiC short fibers; a ceramic fiber toughened transition layer is sprayed on the metal fiber reinforced bottom layer; the ceramic fiber toughened transition layer comprises a NiCr-Cr3C2 cermet and YSZ fibers; a ceramic top layer is sprayed on the ceramic fiber toughened transition layer, and in-situ sintering is performed at 400-450 DEG C to form a dense ceramic phase; the ceramic top layer comprises glass powder, alumina / silicon carbide whiskers and rare earth oxides; laser cladding treatment is performed on the ceramic top layer to form a nanocrystalline-amorphous composite structure.

[0006] Further, the mass ratio of SiC short fibers in the metal fiber reinforced bottom layer is 5-8wt%; The mass ratio of YSZ fibers in the ceramic fiber toughened transition layer is 10-15wt%; The mass ratio of rare earth oxides in the ceramic top layer is 5-8wt%.

[0007] Further, the honeycomb-shaped roughening treatment on the surface of the boiler heating surface substrate comprises: Degreasing cleaning of the surface of the boiler heating surface substrate; The honeycomb-shaped roughening treatment on the surface of the boiler heating surface substrate after degreasing cleaning is carried out by using a fiber laser to form a hexagonal grid groove with a depth of 50-100μm and a pitch of 200-300μm; The honeycomb-shaped roughening treatment on the surface of the boiler heating surface substrate after degreasing cleaning is carried out by using a fiber laser to form a hexagonal grid groove with a depth of 50-100μm and a pitch of 200-300μm;

[0008] Further, the degreasing cleaning of the surface of the boiler heating surface substrate comprises: chemical degreasing with a mass fraction of 5-10% NaOH solution, then ultrasonic cleaning, and finally rinsing with deionized water.

[0009] Further, the honeycomb-shaped roughening treatment on the surface of the boiler heating surface substrate comprises: 92-95wt% of nickel-based alloy NiCrAlY powder and 5-8wt% of SiC short fibers are prepared by ball milling dispersion process to form a composite powder; The composite powder is preheated to 80-100℃; The surface of the pretreated substrate is maintained at 200-250℃, and the composite powder is sprayed by using an axial powder feeding spray gun to form a metal fiber reinforced bottom layer with a thickness of 0.3-0.5mm.

[0010] Further, the honeycomb-shaped roughening treatment on the surface of the boiler heating surface substrate comprises: 85-90wt% of NiCr-Cr3C2 cermet and 10-15wt% of YSZ fibers are mixed by ball milling dispersion process to obtain a mixed powder; wherein the YSZ fibers have a diameter of 5-15μm, a length of 70-100μm, and a surface coated with silane coupling agent; The surface of the metal fiber reinforced bottom layer is sandblasted and roughened; The surface of the metal fiber reinforced bottom layer is sandblasted and roughened; The ceramic fiber toughened transition layer is subjected to high-frequency induction remelting at a frequency of 50kHz and a power of 15kW.

[0011] Further, the spraying ceramic surface layer on the ceramic fiber toughened transition layer, and in situ sintering at 400-450 DEG C, comprising: The glass powder, alumina / silicon carbide whisker and 5-8wt% rare earth oxide are mixed, 0.5-1.5wt% polyacrylamide dispersant is added, and ball milling is carried out for 4-6 hours to form a suspension with a solid content of 45-55%; The substrate of the sprayed ceramic fiber toughened transition layer is sprayed with the suspension at a temperature of 200-250 DEG C using an argon / hydrogen plasma spray gun to deposit a coating on the surface of the ceramic fiber toughened transition layer; during the spraying process, the glass powder is melted and catalyzed to form a dense ceramic phase at 400-450 DEG C.

[0012] Further, 0.5-1wt% hexagonal boron nitride is added to the glass powder, alumina / silicon carbide whisker, rare earth oxide and polyacrylamide dispersant.

[0013] Further, the ceramic surface layer is subjected to laser cladding treatment, comprising: The surface of the ceramic surface layer is scanned using a fiber laser, the power is 1.5kW, and the spot diameter is 2mm.

[0014] In the second aspect, the application provides a gradient functionalized composite coating applied to the heating surface of a boiler, which is prepared by the above-mentioned preparation method of the gradient functionalized composite coating applied to the heating surface of a boiler.

[0015] Compared with the prior art, the application has the following advantages: The application provides a preparation method of a gradient functionalized composite coating applied to the heating surface of a boiler, which forms a synergistic design by preparing a metal fiber reinforced bottom layer, a ceramic fiber toughened transition layer and a ceramic surface layer (rare earth modified surface layer), and realizes gradient matching of mechanical properties and environmental failure resistance. The application realizes low-temperature ceramization by using low-melting-point glass powder combined with rare earth catalytic effect, and avoids thermal damage to the substrate. After spraying the metal-ceramic transition layer, high-frequency induction remelting treatment is performed, and the surface of the ceramic surface layer is subjected to laser cladding, forming a nanocrystalline-amorphous composite structure, which, in combination, eliminates interlayer pores and cracks and improves the bonding strength of the coating.

[0016] The application also provides a gradient functionalized composite coating applied to the heating surface of a boiler, which is prepared by the above-mentioned preparation method of the gradient functionalized composite coating applied to the heating surface of a boiler and has all the advantages of the above-mentioned preparation method of the gradient functionalized composite coating applied to the heating surface of a boiler. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a flowchart of the preparation method of the gradient functionalized composite coating applied to the heating surface of a boiler. DETAILED DESCRIPTION

[0018] In order to make the technical personnel in the art have a clearer understanding and knowledge of the present application, the present application is further described in detail below in conjunction with the embodiments. It should be known that the specific embodiments described below are only for explaining the present application, facilitating understanding, and the technical solutions provided by the present application are not limited to the technical solutions provided by the following embodiments, and the technical solutions provided by the embodiments should not limit the protection scope of the present application.

[0019] It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner, and therefore only the components related to the present application are shown in the diagrams, not the components number, shape and size when actually implemented. The shape, number and proportion of each component when actually implemented can be arbitrarily changed, and the component layout form can also be more complex.

[0020] In the high-temperature corrosion protection scene of the heating surface of a thermal power boiler, the existing conventional protective coating (ceramic coating, metal alloy coating, nano coating) has performance short boards or application limitations. Specifically, the realization of the high-temperature resistance of the ceramic coating depends on its own ceramic phase structure (such as alumina, zirconia, etc.) with high hardness and low plasticity, but this structure also leads to high inherent brittleness of the coating and poor impact and scratch resistance. During the maintenance process of the heating surface of the thermal power boiler, metal tools are frequently used for soot cleaning or component maintenance. Under high-frequency contact, the ceramic coating is prone to micro-cracks due to external impact, and the cracks will further expand with cold and hot cycles. In addition, during the operation of the boiler, the long-term scouring of the flying ash in the flue gas on the heating surface will accelerate the abrasive wear of the coating surface, ultimately shortening the service life. The high-temperature oxidation and hot corrosion resistance of the metal alloy coating depends on the noble metal or rare metal components such as nickel-based and cobalt-based. The mineral reserves of such raw materials are limited, and the refining process is complex, resulting in a significantly higher cost of purchasing basic raw materials than ordinary metals or ceramic materials. At the same time, in order to ensure the uniformity of the coating composition, precise proportioning and pretreatment of the alloy raw materials are required, further increasing the cost investment at the raw material end. The denseness and thermal shock resistance of the nano coating are derived from the small size effect and high specific surface area of the nanoparticles. Through the close packing of the nanoparticles, the internal pores of the coating can be reduced. At the same time, the high activity of the nanoparticles can alleviate the thermal stress concentration under cold and hot cycles. However, the realization of this advantage highly depends on the precise nanoparticle dispersion technology.

[0021] In summary, the existing technology is difficult to meet the comprehensive needs of high-temperature corrosion resistance, mechanical damage resistance, low cost and easy production of the thermal power boiler at the same time.

[0022] Based on the above situation, the present application proposes a gradient functionalized composite coating applied to the heating surface of a boiler and a preparation method thereof, which will be described in detail below in conjunction with the embodiments and the drawings.

[0023] As shown in Figure 1 , it is a flowchart of the preparation method of the gradient functionalized composite coating applied to the boiler heating surface of the present application. As a basic embodiment of the preparation method of the gradient functionalized composite coating applied to the boiler heating surface of the present application, it can include: S101, the honeycomb-like roughening treatment is performed on the surface of the boiler heating surface substrate to obtain the pretreated substrate surface.

[0024] By forming honeycomb-like pits on the substrate surface, on the one hand, the contact area of the substrate and the subsequent coating is increased, and the mechanical embedding effect is improved; on the other hand, the pits can store part of the coating material, provide a buffer space for the deformation of the coating during cold and hot cycles, reduce the interfacial stress, and avoid the peeling of the coating. The honeycomb-like structure makes the substrate surface roughness higher than that after sand blasting, thereby improving the bonding strength of the coating and the substrate. At the same time, the buffering effect of the pits reduces the interfacial cracking rate after cold and hot cycles.

[0025] S102, the metal fiber reinforced bottom layer is sprayed on the pretreated substrate surface; the metal fiber reinforced bottom layer includes nickel-based alloy NiCrAlY and SiC short fibers.

[0026] NiCrAlY alloy itself has excellent high-temperature resistance and corrosion resistance, and can be well combined with the metal substrate. The addition of SiC short fibers can prevent the propagation of internal cracks in the coating through the bridging effect of the fibers, while improving the hardness and wear resistance of the coating, providing a stable connection base for the subsequent transition layer. The addition of SiC short fibers improves the fracture toughness of the bottom layer, which can effectively resist the stress impact during the spraying of the subsequent coating. At the same time, the high-temperature stability of NiCrAlY ensures that the bottom layer does not soften significantly at ultra-high temperatures.

[0027] S103, the ceramic fiber toughened transition layer is sprayed on the metal fiber reinforced bottom layer; the ceramic fiber toughened transition layer includes NiCr-Cr3C2 cermet and YSZ fiber.

[0028] The metal phase of NiCr-Cr3C2 cermet can form a good metallurgical bond with the bottom layer NiCrAlY, and the ceramic phase can transition to the ceramic material of the surface layer. The addition of YSZ fiber can enhance the thermal shock resistance and toughness of the transition layer, avoid the generation of interfacial stress due to the difference in thermal expansion coefficient between the bottom layer and the surface layer, and prevent the delamination of the coating. The thermal expansion coefficient of the transition layer can achieve a smooth transition between the bottom layer and the surface layer. The YSZ fiber improves the thermal shock resistance of the transition layer, and the presence of Cr3C2 improves the wear resistance of the transition layer compared to pure metal coating.

[0029] S104, the ceramic surface layer is sprayed on the ceramic fiber toughened transition layer, and in-situ sintering is performed at 400-450°C to form a dense ceramic phase; the ceramic surface layer includes glass powder, alumina / silicon carbide whiskers and rare earth oxides.

[0030] It should be noted that during spraying, the glass powder, alumina / silicon carbide whisker and rare earth oxide are mixed to form a ceramic surface layer slurry. During in-situ sintering at 400-450 DEG C, the glass powder melts into a glass phase, filling the internal pores of the coating, and at the same time, combining with the alumina / silicon carbide whisker and rare earth oxide to form a dense ceramic phase. The alumina / silicon carbide whisker plays a role of skeleton support to improve the strength, and the rare earth oxide inhibits the grain growth at high temperature to ensure the stability of the surface layer. After in-situ sintering, the porosity of the ceramic surface layer is reduced from 15-20% after spraying to 3-5%, effectively blocking the penetration of corrosive media such as SO2 and HCl. The alumina / silicon carbide whisker increases the hardness of the surface layer, and the wear resistance is improved compared with ordinary ceramic coating. The addition of rare earth oxide makes the grain size of the surface layer not significantly increased after holding at ultrahigh temperature.

[0031] S105, laser cladding treatment is performed on the ceramic surface layer to form a nanocrystalline-amorphous composite structure.

[0032] The laser beam is focused on the surface of the ceramic surface layer, so that the material in the surface layer is melted in a very short time. Subsequently, due to the rapid heat conduction of the substrate, the molten material rapidly solidifies, and the atoms do not have time to arrange in order, part of which forms an amorphous region, and part of which forms a nanoscale grain. This composite structure not only retains the high corrosion resistance of the amorphous state, but also improves the strength through the nanocrystalline, further optimizing the performance of the surface layer.

[0033] The present application takes gradient design as the core, realizes the synergistic effect of the coating and the substrate, and the layers of the coating through the smooth transition of the performance of each layer of material and the microstructure control, and solves the problems of poor adhesion, insufficient corrosion and wear resistance, and weak thermal shock resistance of traditional coatings.

[0034] The present application is further described in detail as follows by some more specific embodiments of the present application: The present embodiment provides a preparation method of a gradient functionalized composite coating applied to a boiler heating surface, which realizes the gradient matching of mechanical properties and environmental failure resistance through the synergistic design of a metal fiber reinforced bottom layer, a ceramic fiber toughened transition layer and a ceramic surface layer. It can include: Step S1, substrate pretreatment.

[0035] After the surface of the boiler heating surface substrate is degreased and cleaned, a honeycomb-shaped roughening treatment is performed using a fiber laser (wavelength 1060 nm). The linear speed during the honeycomb-shaped roughening treatment is 600 mm / s. Specifically: Step S1.1: degrease and clean the surface of the boiler heating surface substrate. The steps of degreasing and cleaning are as follows: first, chemical degreasing is performed using a NaOH solution with a mass fraction of 5%-10%, then ultrasonic cleaning is performed at a frequency of 40 kHz, the cleaning time is 10-15 minutes, and finally, deionized water is used for rinsing.

[0036] Step S1.2: honeycomb texturing treatment is performed on the cleaned substrate surface using a fiber laser with a wavelength of 1060 nm, wherein the laser power is 15-20 W, the pulse frequency is 20-50 kHz, and the scanning line speed is 600 mm / s. As a preferred solution, a galvanometer scanning system can be used, the spot diameter is 50-100 μm, the single scanning coverage width is 0.5-1.0 mm, a hexagonal grid groove with a depth of 50-100 μm and a pitch of 200-300 μm is formed on the substrate surface, the hexagonal side length of the honeycomb grid is 100-150 μm, and the roughness Ra of the groove bottom is ≤3.2 μm.

[0037] Step S1.3: the texturing treatment is completed in an argon or nitrogen protection environment, and the surface oxidation layer thickness is controlled to be ≤1 μm.

[0038] Through the above method, the honeycomb texturing structure can have the following advantages: increasing the coating contact area and improving the bonding strength. The hexagonal grid uniformly distributes the thermal stress and avoids local stress concentration leading to cracking. Compared with the traditional sand blasting process, the laser texturing can reduce the generation of the substrate surface oxide scale.

[0039] Step S2: preparation of the metal fiber reinforced bottom layer.

[0040] Based on the pretreated substrate surface, an ultrasonic flame spraying technology is used to prepare a metal fiber reinforced bottom layer on the substrate surface, the metal fiber reinforced bottom layer includes a nickel-based alloy NiCrAlY and 5-8 wt% SiC short fibers, and the thickness is 0.3-0.5 mm.

[0041] Specifically, the following method can be used: Step S2.1: a composite powder of 92-95 wt% nickel-based alloy NiCrAlY powder and 5-8 wt% SiC short fibers is prepared by a ball milling dispersion process. The SiC short fibers have a length of 50-150 μm and a diameter of 5-10 μm, the surface is treated by chemical nickel plating, the plating layer thickness is 1-2 μm, and the wettability with the metal matrix is enhanced. The ball-to-material ratio is 5:1, the rotation speed is 200 r / min, the dispersion time is 2 h, and the uniform distribution of the fibers is ensured. The NiCrAlY alloy powder has a particle size of 15-45 μm, and the composition ratio is Ni-20Cr-10Al-0.5Y (wt%).

[0042] Step S2.2: Based on the pretreated substrate surface, spray the composite powder using an axial powder feeding spray gun (such as a JP8000 type spray gun), with aviation kerosene and oxygen as the fuel, an oxygen-to-oil mass ratio of 2.5:1, a carrier gas flow rate of 800 L / min, a spraying distance of 150 mm, a powder feeding rate of 30-50 g / min, a combustion chamber pressure of ≥150 PSI, and a flame flow rate of ≥2200 m / s, to form a metal fiber reinforced bottom layer with a thickness of 0.3-0.5 mm.

[0043] Before spraying, the composite powder is preheated to 80-100°C to prevent interface cracking caused by the difference in thermal expansion between the fiber and the substrate. During the spraying process, the substrate temperature is 200-250°C to avoid the accumulation of thermal stress. The substrate temperature and the powder preheating work together to avoid microcracks caused by thermal mismatch between the fiber and the substrate.

[0044] The metal fiber reinforced bottom layer prepared by the above method has a microhardness of 750-900 HV and a salt spray corrosion resistance of ≥1500 h. Its role is to match the thermal expansion coefficient of the substrate and provide initial corrosion resistance. Step S3: Preparation of the ceramic fiber toughened transition layer.

[0046] On the surface of the metal fiber reinforced bottom layer, a ceramic fiber toughened transition layer is prepared using plasma spraying technology. The ceramic fiber toughened transition layer is composed of NiCr-Cr3C2 cermet and 10-15 wt% YSZ fiber, with a fiber length of 70-100 μm.

[0047] This can be achieved by the following method: Step S3.1: Mix 85-90 wt% NiCr-Cr3C2 cermet and 10-15 wt% YSZ fiber by ball milling dispersion process to obtain a mixed powder. The YSZ fiber has a diameter of 5-15 μm and a length of 70-100 μm, and is coated with a silane coupling agent on the surface to improve the interfacial bonding strength with the metal cermet. The NiCr-Cr3C2 composite powder (Cr3C2 content 25-30 wt%) has a NiCr alloy composition of Ni-20Cr-10Al-0.5Y (wt%). The process parameters of the ball milling dispersion process can use the aforementioned parameters, which are not repeated here. As a preferred solution, the YSZ fiber is yttria-stabilized zirconia (Y2O3 content 8 wt%).

[0048] Step S3.2: Sand blast the surface of the metal fiber reinforced bottom layer. As a preferred solution, it can be roughened to Sa≥3.5, and laser cleaning is used to remove the oxide scale.

[0049] Step S3.3: Based on the surface of the processed metal fiber reinforced bottom layer, the substrate temperature is 200-250°C, and the mixed powder is sprayed by atmospheric plasma spraying process. In practical application, the process parameters can be set as follows: main gas flow 40-45 L / min, spraying power 45-55 kW, spraying distance 100-120 mm, powder particle size 10-75 μm, powder feeding rate 25-35 g / min, and ceramic fiber toughened transition layer with thickness of 0.2-0.4 mm is formed.

[0050] Step S3.4: High frequency induction remelting of the ceramic fiber toughened transition layer, process parameters are as follows: frequency 50 kHz, power 15 kW. Its role is to eliminate pores and improve interlayer bonding strength. High frequency induction remelting is an advanced surface modification technology that uses high frequency current induction heating principle to perform secondary melting treatment on the surface coating of metal, mainly used to improve the density, bonding strength and service performance of the coating, and its principle is that when high frequency current (usually frequency is 7-50 kHz) passes through the induction coil, eddy current is generated on the surface of the workpiece, and the coating and substrate surface layer are rapidly heated to a molten or semi-molten state by using "skin effect".

[0051] The ceramic fiber toughened transition layer prepared by the above method can gradiently adjust thermal stress and enhance the erosion resistance of the coating.

[0052] Step S4: Preparation of ceramic top layer.

[0053] On the surface of the ceramic fiber toughened transition layer, a ceramic top layer is prepared by suspension plasma spraying technology, the thickness of the ceramic top layer is 300-400 μm, the single deposition thickness is about 50-80 μm, and the target thickness is achieved by multiple spraying and stacking, the ceramic top layer is composed of low melting point glass powder, alumina / silicon carbide whisker (3:1 mass ratio) and 5-8 wt% rare earth oxide, and a dense ceramic phase is formed by in-situ sintering at low temperature of 400-450°C.

[0054] Specifically, the following method can be used: Step S4.1: Mix the low melting point glass powder, alumina / silicon carbide whisker and 5-8 wt% rare earth oxide, add 0.5-1.5 wt% ammonium polyacrylate dispersant, and ball mill for 4-6 hours to form a suspension with solid content of 45-55%. The low melting point glass powder is Bi2O3-B2O3-ZnO system, the melting point is 350-420°C, the alumina whisker diameter is 1-3 μm, and the silicon carbide whisker diameter is 0.5-2 μm. The rare earth oxide is a mixture of La2O3 and CeO2 with a mass ratio of 1:1, and is uniformly coated on the surface of the whisker by ball milling and dispersion process. In a further preferred embodiment, 0.5-1 wt% hexagonal boron nitride (h-BN) can also be added.

[0055] As a preferred solution, the content of h-BN is 0.8wt%, the particle size of hexagonal boron nitride is 0.5-5um, the purity is greater than or equal to 98%, the layered structure and low surface energy characteristics (surface energy is about 30mJ / m 2 ) of h-BN can reduce the coking adhesion rate of the coating surface, at the same time, the Mohs hardness of h-BN is only 2, which can absorb impact energy and improve the fracture toughness of the coating, and the inertness to molten metal and acid and alkali can improve the corrosion resistance of the coating in sulfur-containing flue gas.

[0056] Step S4.2: Based on the ceramic fiber toughened transition layer, the substrate temperature is 200-250℃, the argon / hydrogen plasma spray gun is used to spray the suspension, the spraying temperature is 400-450℃, the power is 35-45kW, the spraying distance is 80-120mm, and the coating is deposited on the surface of the ceramic fiber toughened transition layer.

[0057] During the spraying process, the low-melting-point glass powder is melted and catalytically formed into a dense ceramic phase at 400-450℃, the ceramic conversion rate is greater than or equal to 75%, the porosity is less than or equal to 2%, the plasma jet (temperature 6000-8000℃) makes the suspension evaporate quickly, the low-melting-point glass powder is melted at 400-450℃, and the rare earth oxide catalytically forms an Al2O3-SiC eutectic phase by “dissolution-precipitation” to fill the pores.

[0058] Step S5: Laser cladding treatment.

[0059] The fiber laser is used to scan the surface of the ceramic surface layer to form an amorphous-nanocrystalline composite structure, the power is 1.5kW, the spot diameter is 2mm, and the h-BN can be arranged in a direction.

[0060] In order to verify the effect of the preparation method of the application, the following experimental examples are set.

[0061] Experimental example: 1. Experimental purpose: (1) Verify the interlayer bonding strength, thermal shock resistance and anti-coking performance of the coating.

[0062] (2) Compare the performance difference between the traditional single coating (such as pure NiCrAlY coating or single ceramic layer) and the scheme.

[0063] 2. Experimental materials and equipment:

[0064] The coating is prepared according to the scheme provided in the above embodiment.

[0065] 3. Comparison group setting Control group 1: traditional single NiCrAlY coating (without fiber reinforcement, without gradient structure).

[0066] Control group 2: single ceramic coating (directly sprayed on the substrate without a transition layer).

[0067] Experimental group: the aforementioned embodiments of the application.

[0068] 4. Performance test and results, as shown in the following table:

[0069] 5. Functional test (1) Thermal shock resistance: Method: The sample was cycled at room temperature ↔ 600℃ for 1000 times (water quenching method); Results: The experimental group had no peeling, and the control group 1 had edge cracks, and the ceramic layer of the control group 2 completely fell off.

[0070] (2) Corrosion resistance: Salt spray test: the experimental group was ≥2000h without substrate corrosion, and the control group 1 was ≤800h with rust spots.

[0071] (3) High temperature corrosion: exposed to 850℃ SO2-containing atmosphere for 500h, the mass loss rate of the experimental group was 0.8mg / cm 2 , which was much lower than that of the control group 1 (5.2mg / cm 2 ).

[0072] (4) Anti-coking property: coking thickness: the experimental group was 0.3mm in 600℃ coal ash, and the control group was 1.1mm.

[0073] Based on the above experiments, the interlayer bonding strength of the coating prepared by the present application is improved, and the thermal shock resistance, corrosion resistance and anti-coking performance are obviously improved compared with traditional coatings.

[0074] In addition, the application also provides a gradient functionalized composite coating applied to the heating surface of a boiler, which is prepared by the above-mentioned preparation method of the gradient functionalized composite coating applied to the heating surface of a boiler.

[0075] The above embodiments are only illustrative of the principles and effects of the application, and are not intended to limit the application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea disclosed by the application should be covered by the claims of the application.

Claims

1. A method for preparing a gradient functionalized composite coating for use on boiler heating surfaces, characterized in that, include: The surface of the boiler heating surface substrate is subjected to honeycomb texturing treatment to obtain the pretreated substrate surface. A metal fiber reinforced underlayer is sprayed onto the pretreated substrate surface; the metal fiber reinforced underlayer comprises a nickel-based alloy NiCrAlY and SiC short fibers. A ceramic fiber toughening transition layer is sprayed onto a metal fiber reinforced substrate; the ceramic fiber toughening transition layer comprises NiCr-Cr3C2 cermet and YSZ fibers. A ceramic surface layer is sprayed onto a ceramic fiber toughened transition layer and sintered in situ at 400-450℃ to form a dense ceramic phase; the ceramic surface layer includes glass powder, alumina / silicon carbide whiskers and rare earth oxides. The ceramic surface layer is subjected to laser cladding to form a nanocrystalline-amorphous composite structure.

2. The method for preparing a gradient functionalized composite coating applied to a boiler heating surface according to claim 1, characterized in that: In the metal fiber reinforced substrate, the mass ratio of SiC short fibers is 5-8 wt%. In the ceramic fiber toughening transition layer, the mass ratio of YSZ fibers is 10-15 wt%. In the ceramic surface layer, the mass ratio of rare earth oxides is 5-8 wt%.

3. The method for preparing a gradient functionalized composite coating applied to a boiler heating surface according to claim 1, characterized in that, The honeycomb-like roughening treatment of the boiler heating surface substrate includes: Degreased and cleaned the surface of the boiler heating surface substrate; A fiber laser is used to perform honeycomb texturing on the surface of the boiler heating surface substrate after degreasing and cleaning, forming hexagonal grid grooves with a depth of 50-100μm and a spacing of 200-300μm. Under protective gas, the surface of the boiler heating surface substrate after honeycomb texturing is texturized.

4. The method for preparing a gradient functionalized composite coating applied to a boiler heating surface according to claim 3, characterized in that, The degreasing and cleaning of the boiler heating surface substrate includes: chemical degreasing with a 5-10% NaOH solution, followed by ultrasonic cleaning, and finally rinsing with deionized water.

5. The method for preparing a gradient functionalized composite coating applied to a boiler heating surface according to claim 1, characterized in that, The process of spraying a metal fiber reinforced underlayer onto the pretreated substrate surface includes: A composite powder consisting of 92-95 wt% nickel-based alloy NiCrAlY powder and 5-8 wt% SiC short fibers was prepared by ball milling dispersion process. Preheat the composite powder to 80-100℃; Keep the pretreated substrate surface at 200-250℃, and use an axial powder feeding spray gun to spray composite powder to form a metal fiber reinforced underlayer with a thickness of 0.3-0.5mm.

6. The method for preparing a gradient functionalized composite coating applied to a boiler heating surface according to claim 1, characterized in that, The process of spraying a ceramic fiber toughening transition layer onto a metal fiber reinforced substrate includes: A mixed powder was obtained by mixing 85-90 wt% NiCr-Cr3C2 cermet with 10-15 wt% YSZ fiber through a ball milling dispersion process; wherein the YSZ fiber has a diameter of 5-15 μm, a length of 70-100 μm, and is coated with a silane coupling agent. The surface of the metal fiber reinforced substrate is roughened by sandblasting. The substrate with the metal fiber reinforced underlayer is kept at a temperature of 200-250℃, and the mixed powder is sprayed using an atmospheric plasma spraying process to form a ceramic fiber toughened transition layer with a thickness of 0.2-0.4mm. The ceramic fiber toughened transition layer was subjected to high-frequency induction remelting at a frequency of 50kHz and a power of 15kW.

7. The method for preparing a gradient functionalized composite coating applied to a boiler heating surface according to claim 1, characterized in that, The process of spraying a ceramic surface layer onto a ceramic fiber-reinforced transition layer and sintering it in situ at 400-450°C includes: Glass powder, alumina / silicon carbide whiskers and 5-8 wt% rare earth oxides are mixed, and 0.5-1.5 wt% ammonium polyacrylate dispersant is added. The mixture is ball-milled for 4-6 hours to form a suspension with a solid content of 45-55%. The substrate for the ceramic fiber toughening transition layer is sprayed with a suspension using an argon / hydrogen plasma spray gun at a temperature of 200-250℃, depositing a coating on the surface of the ceramic fiber toughening transition layer; during the spraying process, glass powder is melted and catalyzed to form a dense ceramic phase at 400-450℃.

8. The method for preparing a gradient functionalized composite coating applied to a boiler heating surface according to claim 1, characterized in that, The glass powder, alumina / silicon carbide whiskers, rare earth oxides and ammonium polyacrylate dispersant also contain 0.5-1 wt% hexagonal boron nitride.

9. The method for preparing a gradient functionalized composite coating applied to a boiler heating surface according to claim 1, characterized in that, Laser cladding of the ceramic surface layer includes: A fiber laser with a power of 1.5kW and a spot diameter of 2mm was used to scan the surface of the ceramic layer.

10. A gradient functionalized composite coating for boiler heating surfaces, prepared by any one of the preparation methods for gradient functionalized composite coatings for boiler heating surfaces as described in claims 1 to 9.

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