Metal ceramic gradient composite coating and boiler tube screen coated with same

Abstract

The invention provides a metal ceramic gradient composite coating and a boiler tube screen coated with the coating. The coating comprises a base material, the microporous alloy bottom layer is formed on the surface of the base material; the nano activation layer is formed on the microporous alloy bottom layer; and the ceramic surface layer is formed on the nano activation layer. The microporous alloy bottom layer, the nano activation layer and the ceramic surface layer are sequentially arranged on the surface of the base material, atomic diffusion metallurgical bonding is formed between the microporous alloy bottom layer and the base material, and microporous mechanical inlaying and covalent bond dual bonding is formed between the nano activation layer and the microporous alloy bottom layer; and covalent bond combination of solid-phase diffusion sintering is formed between the ceramic surface layer and the nano activation layer, so that the ceramic surface layer and the nano activation layer have relatively high bonding strength. Experimental results show that the adhesive force of the coating reaches up to 20 MPa or above, the water-cooling thermal shock resistance frequency at 650 DEG C can reach 68 or above, and the coating does not peel off or crack after being used for 800 h or above at the temperature of 1200 DEG C.

Description

Technical Field

[0001] This application relates to the field of metal-ceramic coatings, and more particularly to a metal-ceramic gradient composite coating and a boiler tube screen coated with the coating. Background Technology

[0002] Large power plant boilers commonly blend high-sulfur coal, waste, or biomass fuels and employ low-NOx combustion technology, resulting in the generation of large amounts of corrosive gases such as sulfides and chlorides within the furnace. Under high-temperature conditions, these gases damage the oxide protective layer on the tube wall surface, reacting with the base metal and causing severe high-temperature corrosion and thinning. Simultaneously, molten ash slags and cokes on the tube walls, worsening heat conduction and causing thermal deviations, while fly ash particles carried by high-speed flue gas continuously erode the tube walls. The combined effects of corrosion, slag formation, and wear can easily lead to premature tube wall failure or even tube rupture, seriously threatening the safe, stable operation and economic efficiency of the boiler.

[0003] Currently, the main protective methods for boiler heating surface tube panels include supersonic thermal spraying of alloy coatings and cold spraying of high-temperature nano-ceramic coatings. Supersonic thermal spraying utilizes high-temperature, high-speed gas flow to propel molten or semi-molten coating material onto the substrate surface to form a coating. It offers advantages such as simple application, a wide variety of applicable alloy materials, relatively low requirements for substrate surface roughness and smoothness, and high coating-substrate bonding strength. However, the coating contains numerous pores, allowing corrosive media to easily penetrate and causing interfacial corrosion, leading to coating peeling. Cold spraying utilizes room-temperature, high-pressure gas to supersonic accelerate solid powder particles. The solid-state deposition is achieved through plastic deformation caused by the high-speed impact of these particles on the substrate. It boasts advantages such as high spraying efficiency, low operating temperature, and smooth, dense coatings. However, it has disadvantages such as high requirements for substrate surface roughness and smoothness, lower coating-substrate bonding strength, and poor matching of the coating's coefficient of thermal expansion with the substrate. Summary of the Invention

[0004] In view of this, this application provides a metal-ceramic gradient composite coating and a boiler tube screen coated with the coating. The metal-ceramic gradient composite coating provided by this application has the advantages of high bonding strength, high temperature resistance, good wear resistance and corrosion resistance.

[0005] This application provides a metal-ceramic gradient composite coating, comprising:

[0006] Substrate;

[0007] A microporous alloy underlayer is formed on the surface of the substrate;

[0008] A nano-activation layer is formed on the microporous alloy substrate;

[0009] A ceramic surface layer is formed on the nano-activated layer.

[0010] In some specific implementations, the microporous alloy substrate includes an alloy layer and a microporous alloy layer composited on the alloy layer.

[0011] In some specific implementations, the alloy layer is made of Ni95Al5 or Ni80Cr20 alloy.

[0012] The thickness of the alloy layer is 50μm~80μm;

[0013] The microporous alloy layer is made of Ni95Al5 or Ni80Cr20 alloy.

[0014] The thickness of the microporous alloy layer is 50μm~220μm;

[0015] The microporous alloy layer has a micropore diameter of 5μm to 20μm and a porosity of 5% to 15%.

[0016] In some specific implementations, the nano-activation layer is formed from nano-sol;

[0017] The nanosol includes one or more of nanoaluminum sol, nanosilica sol, and nanozirconium sol;

[0018] The thickness of the nano-activation layer is 20μm~50μm.

[0019] In some specific implementations, the ceramic surface layer includes a base layer and a top layer composited on the base layer;

[0020] The base coating comprises aluminum dihydrogen phosphate, γ-Al2O3 powder, CrO3, aluminum powder, and a first filler;

[0021] The first filler includes chrome green and / or cerium oxide;

[0022] The surface coating comprises aluminum dihydrogen phosphate, Fe2O3 powder, CrO3, and a second filler;

[0023] The second filler includes one or more of chrome green, cobalt oxide, nickel oxide, cerium oxide, quartz sand, boron nitride, and talc.

[0024] The thickness of the ceramic surface layer is 0.1mm to 0.2mm.

[0025] Furthermore, this application also provides a method for preparing a metal-ceramic gradient composite coating, comprising the following steps:

[0026] a) Forming a microporous alloy underlayer on the substrate surface;

[0027] b) Forming a nano-activation layer on the microporous alloy substrate;

[0028] c) A ceramic surface layer is formed on the nano-activated layer.

[0029] In some specific implementations, step a) specifically includes:

[0030] a1) Forming an alloy layer on the surface of the substrate;

[0031] a2) A microporous alloy layer is formed on the surface of the alloy layer.

[0032] In some specific implementations, step a2) specifically includes:

[0033] a21) Forming a porous layer on the surface of the alloy layer;

[0034] a22) Supersonic electric arc thermal spraying or supersonic flame thermal spraying of alloy powder is performed on the surface of the pore-forming layer to form a microporous alloy layer.

[0035] Furthermore, this application also provides a tube screen, including: the metal-ceramic gradient composite coating described in the above technical solution; wherein the substrate of the metal-ceramic gradient composite coating is a tube screen substrate.

[0036] Furthermore, this application also provides a boiler, including the tube panel described in the above technical solution.

[0037] This application provides a metal-ceramic gradient composite coating, comprising a microporous alloy underlayer, a nano-activation layer, and a ceramic top layer sequentially formed on the surface of a substrate. By sequentially depositing the microporous alloy underlayer, nano-activation layer, and ceramic top layer on the substrate surface, this application achieves high bonding strength. The microporous alloy underlayer forms an atomic diffusion metallurgical bond with the substrate, the nano-activation layer forms a dual bond of microporous mechanical embedding and covalent bonds with the microporous alloy underlayer, and the ceramic top layer forms a solid-phase diffusion sintering covalent bond with the nano-activation layer. Simultaneously, the ceramic top layer, as the final functional layer, isolates corrosive media, prevents slagging and coking, and resists high-temperature flue gas erosion. The microporous alloy underlayer and nano-activation layer act as transitional bonding layers, enhancing the bonding strength of the ceramic top layer and buffering thermal stress. Under conditions of frequent boiler start-ups and shutdowns and significant load fluctuations, this ensures that the ceramic top layer remains unpeeled and uncracking under long-term high-temperature operation.

[0038] Experimental results show that the coating provided in this application has an adhesion of over 20 MPa, can withstand more than 68 thermal shock cycles when water-cooled at 650℃, and does not peel or crack after more than 800 hours of use at 1200℃. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the metal-ceramic gradient composite coating provided in this application;

[0040] Figure 2 SEM image of the microporous alloy substrate prepared for the embodiments of this application. Detailed Implementation

[0041] This invention provides a metal-ceramic gradient composite coating, comprising:

[0042] Substrate;

[0043] A microporous alloy underlayer is formed on the surface of the tube screen substrate;

[0044] A nano-activation layer is formed on the microporous alloy substrate;

[0045] A ceramic surface layer is formed on the nano-activated layer.

[0046] like Figure 1 As shown, Figure 1 The diagram below shows a metal-ceramic gradient composite coating provided in this application, wherein 1 is the substrate, 2 is the microporous alloy bottom layer, 3 is the nano-activation layer, and 4 is the ceramic surface layer.

[0047] The metal-ceramic gradient composite coating provided in this application includes a substrate 1, which is used to support a microporous alloy bottom layer 2, a nano-activation layer 3, and a ceramic surface layer 4. This application does not impose any special restrictions on the substrate 1, which can be a workpiece, including but not limited to boiler heating surface structural components, such as tube screen substrates.

[0048] A microporous alloy underlayer 2 is formed on the surface of the substrate 1. The microporous alloy underlayer 2 and the substrate can form a metallurgical bond, thereby improving the bonding strength of the ceramic surface layer 4 and buffering thermal stress from expansion. This application does not impose any particular limitation on the method of forming the microporous alloy underlayer 2, but it is preferably prepared using a supersonic arc spraying or supersonic flame spraying process. In some specific implementations, the thickness of the microporous alloy underlayer is 100 μm to 300 μm, preferably 150 μm to 250 μm.

[0049] In some specific implementations, the microporous alloy substrate 2 includes an alloy layer composited on the surface of the substrate 1 and a microporous alloy layer composited on the alloy layer. The alloy layer is a dense alloy layer, preferably a nickel-based alloy, and its material includes, but is not limited to, Ni95Al5 or Ni80Cr20 alloy. In some specific implementations, the thickness of the alloy layer is 50μm to 80μm, preferably 55μm to 75μm, for example, 55μm, 60μm, 65μm, 70μm, etc. In this application, the alloy layer and the substrate can be connected by metallurgical bonding, which can improve the bonding strength of the coating.

[0050] The microporous alloy layer is an alloy layer with micropores, which can be a nickel-based alloy, such as Ni95Al5 or Ni80Cr20 alloy. In some specific implementations, the thickness of the microporous alloy layer is 50μm~220μm, preferably 70μm~200μm, for example 80μm, 110μm, 140μm, 170μm, etc. In some specific implementations, the pore size of the micropores in the microporous alloy layer is 5μm~20μm, preferably 10μm~15μm; the porosity is 5%~15%, preferably 8%~13%. The microporous alloy layer contains a microporous structure, which allows the nano-activation layer to be partially mechanically embedded in the micropores, improving the bonding strength.

[0051] A nano-activation layer 3 is formed on the surface of the microporous alloy substrate 2. The nano-activation layer 3 can penetrate and fill the micropores of the microporous alloy substrate 2, forming a stable bond with the microporous alloy substrate, which helps the ceramic surface layer to achieve solid-phase diffusion sintering to improve cohesive strength and density. This application does not have any special restrictions on the method of forming the nano-activation layer 3, but it is preferred to use an ultrasonic spraying process.

[0052] In some specific implementations, the nano-activation layer 3 is formed from a nano-sol. The nano-sol includes one or more of nano-aluminum sol, nano-silica sol, and nano-zirconium sol. In some specific implementations, the thickness of the nano-activation layer is 20 μm to 50 μm, preferably 25 μm to 45 μm, for example, 30 μm, 35 μm, 40 μm, etc. When the nano-activation layer is formed from a nano-sol, the numerous hydroxyl groups in the sol form hydrogen bonds with the alloy, tightly adsorbing onto the inner wall of the micropores. During the heating process of the tube wall, the hydrogen bonds gradually transform into covalent bonds, resulting in high bonding strength.

[0053] A ceramic surface layer 4 is formed on the surface of the nano-activated layer 3. The ceramic surface layer 4 serves to isolate the substrate 1 from corrosive media such as sulfides and CO, preventing high-temperature corrosion of the substrate. This application does not impose any special restrictions on the material of the ceramic surface layer; commercially available products or self-made products are acceptable. This application does not impose any special restrictions on the preparation method of the ceramic surface layer 4; preferably, it is prepared using compressed air spraying, high-pressure airless spraying, or cold spraying.

[0054] In some specific implementations, the ceramic surface layer can adopt the composite gradient coating and ceramic coating curing layer disclosed in Chinese Patent ZL201911051261.5. Specifically, the ceramic surface layer includes a base coating and a top coating layer composited on the base coating.

[0055] In some specific implementations, the base coating comprises the following components: aluminum dihydrogen phosphate, γ-Al2O3 powder, CrO3, aluminum powder, and a first filler;

[0056] In this process, aluminum dihydrogen phosphate undergoes a cross-linking and curing reaction with γ-Al2O3 to form a dense structure, which can effectively prevent corrosive media from penetrating the coating and corroding the substrate. The amount of aluminum dihydrogen phosphate is 10-30 parts, preferably 15-25 parts, more preferably 20 parts, and the amount of γ-Al2O3 is 5-20 parts, preferably 5-10 parts or 10-15 parts.

[0057] The role of aluminum powder is to form an alloy layer with the substrate, thereby improving the adhesion between the coating and the substrate. The amount of aluminum powder used is 10-60 parts, preferably 20-30 parts, 30-40 parts or 40-50 parts.

[0058] The amount of passivating agent CrO3 is 5 to 20 parts, preferably 5 to 10 parts or 10 to 15 parts;

[0059] The first filler refers to a substance that is substantially insoluble, preferably completely insoluble in the coating, and more particularly used to increase volume. The amount of the first filler is 0.1 to 65 parts, preferably 10 to 20 parts, 20 to 30 parts, 30 to 40 parts, or 40 to 50 parts. The first filler includes the following components: 0.1 to 50 parts of chrome green, preferably 10 to 50 parts, and / or 0.1 to 15 parts of cerium oxide, preferably 3 to 15 parts.

[0060] In some specific implementations, the base coating may further include one or more of a wetting and dispersing agent, a defoamer, and a thickener;

[0061] The wetting and dispersing agent is preferably Dow CF-10, and its dosage is 0.1 to 5 parts, preferably 1 to 3 parts;

[0062] The defoamer is preferably Henzik 6855, and its dosage is 0.1 to 5 parts, preferably 1 to 3 parts;

[0063] The thickener is preferably bentonite, and its dosage is 0.1 to 5 parts, preferably 1 to 3 parts.

[0064] Specifically, in a typical technical solution of this application, the base coating comprises: aluminum dihydrogen phosphate (40wt%): 50 parts, γ-Al2O3 powder: 5 parts, CrO3: 6 parts, aluminum powder: 33 parts, chrome green powder: 20 parts, cerium oxide powder: 8 parts, Dow CF-10: 0.5 parts, Heinz 6855: 0.5 parts, and bentonite: 0.1 parts.

[0065] In this application, the surface coating comprises the following components: aluminum dihydrogen phosphate, Fe2O3 powder, CrO3, and a second filler;

[0066] In this process, aluminum dihydrogen phosphate undergoes a condensation reaction with Fe2O3 and forms a transition layer rich in Al, Fe, P and O with the aluminum powder in the undercoating layer at the bonding surface. The amount of aluminum dihydrogen phosphate used is 10 to 30 parts, preferably 15 to 25 parts.

[0067] Fe2O3 also acts as a curing agent, enabling the coating to cure at a lower curing temperature. The amount of Fe2O3 powder used is 5 to 20 parts, preferably 10 to 15 parts.

[0068] The amount of passivating agent CrO3 is 3 to 20 parts, preferably 5 to 10 parts or 10 to 15 parts;

[0069] The second filler has high emissivity, and the amount of the second filler is 0.1 to 200 parts, preferably 30 to 60 parts or 70 to 90 parts. The second filler includes the following components:

[0070] Chrome green powder: 0.1~30 parts, preferably 5~30 parts; cobalt oxide powder: 0.1~20 parts, preferably 5~10 parts; nickel oxide powder: 0.1~20 parts, preferably 5~10 parts; cerium oxide powder: 0.1~10 parts, preferably 5~10 parts; quartz sand: 0.1~80 parts, preferably 20~80 parts; boron nitride powder: 0.1~20 parts, preferably 3~20 parts; talc powder: 0.1~20 parts.

[0071] In some specific implementations, the surface coating further includes one or more of the following: spherical aluminum powder, wetting and dispersing agent, defoamer, and thickener;

[0072] The amount of spherical aluminum powder used is 0.1 to 30 parts, preferably 5 to 10 parts;

[0073] The wetting and dispersing agent is preferably Dow CF-10, and its dosage is 0.1 to 5 parts, preferably 1 to 3 parts;

[0074] The defoamer is preferably Henzik 6855, and its dosage is 0.1 to 5 parts, preferably 1 to 3 parts;

[0075] The thickener is preferably bentonite, and its dosage is 0.1 to 5 parts, preferably 1 to 3 parts.

[0076] Specifically, in a typical technical solution of this application, the surface coating comprises: aluminum dihydrogen phosphate (40wt%): 50 parts, Fe2O3 powder: 12 parts, CrO3: 8 parts, chrome green powder: 10 parts, cobalt oxide powder: 5 parts, nickel oxide powder: 5 parts, cerium oxide powder: 3 parts, quartz sand: 40 parts, boron nitride powder: 10 parts, talc powder: 5 parts, Dow CF-10: 1 part, Heinz 6855: 1 part, bentonite: 0.6 parts.

[0077] The thickness of the ceramic surface layer is 0.1mm to 0.2mm, preferably 0.15mm; the ceramic surface layer serves as the final functional layer, which isolates corrosive media, prevents slagging and coking, and resists erosion and wear from high-temperature flue gas.

[0078] The metal-ceramic gradient composite coating provided in this application has the characteristics of high bonding strength with the substrate, strong adaptability of expansion coefficient and high cohesive strength, and can be used for high-temperature corrosion, slagging, coking and wear protection of the heating surfaces of coal-fired boilers, waste and biomass incineration boilers.

[0079] This application also provides a method for preparing a metal-ceramic gradient composite coating, comprising:

[0080] a) Forming a microporous alloy underlayer on the substrate surface;

[0081] b) Forming a nano-activation layer on the microporous alloy substrate;

[0082] c) A ceramic surface layer is formed on the nano-activated layer.

[0083] This application first forms a microporous alloy underlayer on the surface of a substrate. The microporous alloy underlayer includes an alloy layer and a microporous alloy layer composite on the alloy layer. In some specific implementations, this application forms the microporous alloy underlayer according to the following method:

[0084] a1) Forming an alloy layer on the surface of the substrate;

[0085] a2) A microporous alloy layer is formed on the surface of the alloy layer.

[0086] This application first forms an alloy layer on the surface of a substrate. The material and thickness of the alloy layer are as described above and will not be repeated here. This application does not impose any special restrictions on the method for forming the alloy layer. Supersonic arc or flame thermal spraying is preferred to achieve metallurgical bonding between the substrate and the alloy layer, thereby improving the bonding strength. This application does not impose any restrictions on the specific parameters of the supersonic arc or flame thermal spraying, as long as it can form an alloy layer. In some specific implementations, the parameters of the supersonic arc thermal spraying process can be: arc spraying voltage of 32V~40V, preferably 35V~38V; current of 250A~350A, preferably 280A~320A; compressed air pressure of 0.5MPa~0.7MPa, preferably 0.55MPa~0.65MPa; and wire feed speed of 4m / min~8m / min, preferably 5m / min~7m / min.

[0087] Before forming the alloy layer, this application preferably pre-treats the substrate surface. In some specific implementations, the pre-treatment is sandblasting to remove grease and rust from the substrate surface. In some specific implementations, the sandblasting process gives the substrate surface a surface finish of Ra2.5 or higher.

[0088] After forming the alloy layer, this application forms a microporous alloy layer on the surface of the alloy layer. The material, thickness, pore size, porosity, etc., of the microporous alloy layer are as described above, and will not be repeated here. In a specific implementation, the microporous alloy layer is formed according to the following method:

[0089] a21) Forming a porous layer on the surface of the alloy layer;

[0090] a22) Apply supersonic electric arc thermal spraying or supersonic flame thermal spraying of nickel-based alloy material to the surface of the porous layer to form a microporous alloy layer.

[0091] Specifically, this application first sprays a pore-forming slurry onto the surface of an alloy layer to form a pore-forming layer. In some specific implementations, the pore-forming slurry includes a binder, a pore-forming agent, and water. The binder can adhere to the alloy layer and includes, but is not limited to, polyvinyl alcohol and sodium carboxymethyl cellulose. The pore-forming agent is used to subsequently form micropores and includes, but is not limited to, graphite powder and urea particles. This application does not have any special restrictions on the ratio of binder, pore-forming agent, and water, as long as it can form a pore-forming layer on the alloy surface. In some specific implementations, the pore-forming slurry includes 10wt%~20wt% binder, 25wt%~50wt% pore-forming agent, and the balance deionized water. In some specific implementations, the pore-forming slurry includes 10wt%~20wt% binder, 25wt%~50wt% pore-forming agent, and the balance deionized water. In some specific implementations, the spraying temperature is room temperature, for example, 10℃~30℃, preferably 15℃~25℃; the compressed air pressure is 0.5MPa~0.8MPa, preferably 0.6MPa~0.7MPa; and the spraying distance is 200mm~300mm, preferably 220mm~280mm. In some specific implementations, the thickness of the dry film of the pore-forming layer is 60μm~100μm, preferably 70μm~90μm, and more preferably 75μm~85μm.

[0092] After forming the pore-forming layer, this application applies supersonic electric arc thermal spraying or supersonic flame thermal spraying of alloy materials to the surface of the pore-forming layer. During the spraying process, high-temperature molten droplets impact the pore-forming layer, causing the pore-forming agent, binder, and other materials in the pore-forming layer to rapidly volatilize or oxidize, forming a large amount of gas. This creates numerous interconnected micro-explosive pores within the alloy layer, forming a microporous alloy layer. Compared to conventional thermal spraying pore-forming processes, this application avoids premature volatilization and failure of the pore-forming agent by setting an independent pore-forming layer. Furthermore, it allows for the use of multiple pore-forming layers, flexibly adjusting the thickness and number of micropores in the microporous alloy layer. In some specific implementations, the parameters of the supersonic arc thermal spraying process can be: arc spraying voltage of 32V~40V, preferably 35V~38V; current of 250A~350A, preferably 280A~320A; compressed air pressure of 0.5MPa~0.7MPa, preferably 0.55MPa~0.65MPa; and wire feeding speed of 4m / min~8m / min, preferably 5m / min~7m / min.

[0093] In some specific implementations, the steps of forming a porous layer and applying supersonic electric arc thermal spraying or supersonic flame thermal spraying alloy material can be repeated to form a microporous alloy layer of predetermined thickness, while flexibly adjusting the thickness and number of micropores in the microporous alloy layer.

[0094] After forming the microporous alloy layer, this application forms a nano-activation layer on its surface. Specifically, this application sprays a nano-sol onto the surface of the microporous alloy layer. Utilizing the high permeability and capillary effect of nanoparticles, the nano-sol penetrates into the micropores of the microporous alloy layer and forms hydrogen bonds with the alloy through the large number of hydroxyl groups contained in the sol, tightly adsorbing onto the inner wall of the micropores. During the heating process of the wall, the hydrogen bonds gradually transform into covalent bonds, ultimately forming the nano-activation layer. The type of nano-sol and the thickness of the nano-activation layer are as described above and will not be repeated here. This application preferably uses an ultrasonic spraying process to spray the nano-sol onto the surface of the microporous alloy substrate. This application does not have special limitations on the specific parameters of the ultrasonic spraying, as long as the nano-activation layer can be formed. In some specific implementations, the process parameters of the ultrasonic spraying can be: ultrasonic frequency 50kHz~120kHz, preferably 80kHz~100kHz; spraying power 100W~200W, preferably 120W~180W; compressed air pressure 0.3MPa~0.5MPa, preferably 0.35MPa~0.45MPa; spraying distance 120mm~300mm, preferably 150mm~250mm.

[0095] After forming the nano-activated layer, this application forms a ceramic surface layer on its surface. The composition and thickness of the ceramic surface layer are as described above and will not be repeated here. This application does not impose any special restrictions on the method for forming the ceramic surface layer, but a cold spraying process is preferred. This application does not impose any restrictions on the specific parameters of the cold spraying, as long as it can form a ceramic surface layer. In some specific implementations, the process parameters of the cold spraying can be: operating temperature at room temperature, for example, 10℃~30℃, preferably 15℃~25℃; compressed air pressure 0.5MPa~0.8MPa, preferably 0.6MPa~0.7MPa; spraying distance 300mm~500mm, preferably 350mm~450mm. During the cold spraying process, the ceramic coating penetrates into the micropores under the capillary effect. The nano-alumina, silica, and zirconium dioxide activation layer on the inner wall of the micropores can act as a curing agent for the ceramic coating, promoting its rapid curing to form a ceramic surface layer. As the tube wall heats up, the nano-activation layer promotes solid-phase diffusion sintering inside the ceramic surface layer, and the ceramic surface layer and the nano-activation layer form covalent bonds, which improves the bonding strength.

[0096] This application also provides a tube screen, including the metal-ceramic gradient composite coating described in the above technical solution, wherein the substrate of the metal-ceramic gradient composite coating is a tube screen substrate.

[0097] Tube panel substrate is the core manufacturing material for tube panel components in boiler thermal energy equipment. It refers to the basic material that constitutes the main structure of the tube panel, directly bears the operating load, and serves as the substrate for functional coatings. This application does not impose any special restrictions on the tube panel substrate; commonly used tube panel substrates are acceptable.

[0098] This application also provides a boiler, including the tube panel described in the above technical solution.

[0099] The metal-ceramic gradient composite coating provided in this application comprises a microporous alloy underlayer, a nano-activation layer, and a ceramic top layer sequentially formed on the surface of a substrate. By sequentially depositing the microporous alloy underlayer, nano-activation layer, and ceramic top layer on the substrate surface, this application achieves high bonding strength. The microporous alloy underlayer forms an atomic diffusion metallurgical bond with the substrate, the nano-activation layer forms a dual bond of microporous mechanical embedding and covalent bonding with the microporous alloy underlayer, and the ceramic top layer forms a solid-phase diffusion sintering covalent bond with the nano-activation layer. Experimental results show that the coating provided in this application has an adhesion strength exceeding 20 MPa, withstands over 68 thermal shock cycles at 650℃ with water cooling, and does not peel or crack after more than 800 hours of use at 1200℃.

[0100] The present application is further illustrated below with reference to embodiments. The scope of protection of the present application is not limited to the following embodiments.

[0101] In the following embodiments, the first coating is composed of: aluminum dihydrogen phosphate (40wt%): 50 parts, γ-Al2O3 powder: 5 parts, CrO3: 6 parts, aluminum powder: 33 parts, chrome green powder: 20 parts, cerium oxide powder: 8 parts, Dow CF-10: 0.5 parts, Heinz 6855: 0.5 parts, bentonite suspension: 0.1 parts, and water: 40 parts;

[0102] The second coating composition is as follows: aluminum dihydrogen phosphate (40wt%): 50 parts, Fe2O3 powder: 12 parts, CrO3: 8 parts, chrome green powder: 10 parts, cobalt oxide powder: 5 parts, nickel oxide powder: 5 parts, cerium oxide powder: 3 parts, quartz sand: 40 parts, boron nitride powder: 10 parts, talc powder: 5 parts, Dow CF-10: 1 part, Henschke 6855: 1 part, bentonite suspension: 0.6 parts, water: 50 parts.

[0103] In the following embodiments, the supersonic arc thermal spraying process parameters are as follows: the arc spraying voltage is 38V, the current is 300A, the compressed air pressure is 0.6MPa, and the wire feeding speed is 6m / min;

[0104] The cold spraying process parameters for the slurry are as follows: cold spraying from a spray bottle, operation at room temperature, compressed air pressure of 0.7MPa, and spraying distance of 250mm;

[0105] The ultrasonic spraying process parameters are as follows: ultrasonic frequency 100kHz, spraying power 150W, compressed air pressure 0.4MPa, and spraying distance 200mm.

[0106] The cold spraying process parameters for the coating are as follows: cold spraying from a spray bottle, operation at room temperature, compressed air pressure of 0.7MPa, and spraying distance of 400mm.

[0107] Example 1: The substrate of the tube screen was pretreated by sandblasting. A supersonic arc thermal spraying process was used to spray Ni80Cr20 welding wire onto the pretreated substrate surface, forming a 70μm thick alloy layer. A slurry was formed by uniformly mixing 20wt% polyvinyl alcohol, 40wt% urea particles, and the remainder deionized water, and then cold-sprayed onto the alloy layer to form a 70μm thick pore-forming layer. Using a supersonic arc thermal spraying process, Ni80Cr20 welding wire was sprayed onto the surface of the pore-forming layer. The pore-forming layer rapidly vaporized, forming interconnected micro-explosive pores inside, creating an 80μm microporous alloy layer. Finally, a 150μm thick microporous alloy underlayer was obtained. (See also...) Figure 2 , Figure 2 This is a SEM image of the microporous alloy substrate prepared according to an embodiment of this application. Figure 2 It is known that the microporous alloy substrate prepared in this application has a porosity of 5% to 15% and a micropore diameter of 5 μm to 20 μm.

[0108] Nano-aluminum sol and silica sol were mixed evenly at a weight ratio of 1:1. The sol mixture was then sprayed onto the microporous alloy layer using an ultrasonic spraying process. After surface drying, a nano-activation layer with a thickness of 30 μm was formed.

[0109] After the surface of the nano-activated layer dries, the first coating is sprayed onto the surface of the nano-activated layer using a cold spraying process, and left to stand for 1 hour to form a base coating. After the base coating is surface dry, the second coating is sprayed onto the surface of the base coating using a cold spraying process, and left to stand for 12 hours. After surface dry, a ceramic surface layer with a thickness of 0.15 mm is formed, thus obtaining the tube screen.

[0110] The tube screen is installed on the boiler, and the boiler is started and heated. During the heating process, covalent bonds are formed between the nano-activated layer and the microporous alloy bottom layer, and covalent bonds are formed between the nano-activated layer and the ceramic surface layer, ultimately forming a gradient composite coating on the surface of the tube screen.

[0111] Example 2

[0112] The substrate of the tube screen is pretreated by sandblasting. Then, using a supersonic arc thermal spraying process, Ni95Al5 powder is sprayed onto the pretreated substrate surface to form a 60μm thick alloy layer. A slurry is formed by uniformly mixing 15wt% sodium carboxymethyl cellulose, 40wt% graphite powder, and the remainder deionized water. This slurry is then applied to the alloy layer surface using a cold spraying process to form a first pore-forming layer with a thickness of 80μm. Finally, Ni80C is sprayed onto the surface of the first pore-forming layer using a supersonic arc thermal spraying process. R20 welding wire causes rapid vaporization of the pore-forming layer, forming interconnected micro-explosive pores within the alloy layer, thus forming the first microporous alloy layer. The aforementioned slurry is then sprayed onto the surface of the first microporous alloy coating to form a second pore-forming layer with a thickness of 80 μm. Using a supersonic arc thermal spraying process, Ni80Cr20 welding wire is sprayed onto the surface of the second pore-forming layer, causing rapid vaporization of the pore-forming layer and the formation of interconnected micro-explosive pores within the alloy layer, thus forming the second microporous alloy layer. Finally, a microporous alloy underlayer with a thickness of 260 μm is obtained.

[0113] Nano-aluminum sol, silica sol and zirconium sol were mixed evenly in a weight ratio of 2:1:1. The sol mixture was then sprayed onto the microporous alloy substrate using an ultrasonic spraying process. After surface drying, a nano-activation layer with a thickness of 50 μm was formed.

[0114] After the surface of the nano-activated layer dries, the first coating is sprayed onto the surface of the nano-activated layer using a cold spraying process, and left to stand for 1 hour to form a base coating. After the base coating is surface dry, the second coating is sprayed onto the surface of the base coating using a cold spraying process, and left to stand for 12 hours. After surface dry, a ceramic surface layer with a thickness of 0.15 mm is formed, thus obtaining the tube screen.

[0115] The tube screen is installed on the boiler, and the boiler is started and heated. During the heating process, covalent bonds are formed between the nano-activated layer and the microporous alloy bottom layer, and covalent bonds are formed between the nano-activated layer and the ceramic surface layer, ultimately forming a gradient composite coating on the surface of the tube screen.

[0116] Comparative Example 1

[0117] The substrate of the tube screen is pretreated by sandblasting. Then, a supersonic arc thermal spraying process is used to spray Ni80Cr20 welding wire onto the surface of the pretreated substrate to form an alloy layer with a thickness of 150μm. Subsequently, a first coating is sprayed onto the surface of the microporous alloy underlayer using a cold spraying process, and allowed to stand for 1 hour to form a base layer. After the base layer is surface dry, a second coating is sprayed onto the surface of the base layer using a cold spraying process, and allowed to stand for 12 hours to form a ceramic surface layer with a thickness of 0.15mm, thus obtaining the tube screen.

[0118] The tube screen is installed on the boiler, the boiler is started and heated, the ceramic surface layer is sintered and cured, and finally a composite coating is formed on the surface of the tube screen.

[0119] Comparative Example 2

[0120] The substrate of the tube screen is pretreated by sandblasting. Then, a supersonic arc thermal spraying process is used to spray Ni80Cr20 welding wire onto the surface of the pretreated substrate to form an alloy layer with a thickness of 70μm. 20wt% polyvinyl alcohol, 40wt% urea particles, and the balance deionized water are mixed evenly to form a slurry. The slurry is cold-sprayed onto the alloy layer to form a pore-forming layer with a thickness of 70μm. Using a supersonic arc thermal spraying process, Ni80Cr20 welding wire is sprayed onto the surface of the pore-forming layer. The pore-forming layer rapidly vaporizes, forming interconnected micro-explosive pores inside, forming a microporous alloy layer. Finally, a microporous alloy underlayer with a thickness of 150μm is obtained.

[0121] Subsequently, a first coating is applied to the surface of the microporous alloy substrate using a cold spraying process, and allowed to stand for 1 hour to form a base coating. After the base coating is surface dry, a second coating is applied to the surface of the base coating using a cold spraying process, and allowed to stand for 12 hours to form a ceramic surface layer with a thickness of 0.15 mm, thus obtaining the tube screen.

[0122] The tube screen is installed on the boiler, the boiler is started and heated, the ceramic surface layer is sintered and cured, and finally a composite coating is formed on the surface of the tube screen.

[0123] The performance of the tube screens prepared in Examples 1-2 and Comparative Examples 1-2 was tested according to the following methods. The results are shown in Table 1. Table 1 shows the performance test results of the tube screens prepared in the examples and comparative examples of this application.

[0124] Table 1 Performance test results of the tube screens prepared in the embodiments and comparative examples of this application.

[0125]

[0126] As shown in Table 1, the metal alloy ceramic coating provided in this application has high bonding strength with the tube screen substrate and excellent thermal shock resistance and high temperature resistance. The adhesion of this coating is as high as 20MPa or more, and the number of thermal shock resistance cycles under water cooling at 650℃ can reach more than 68. It does not peel off or crack after being used at 1200℃ for more than 800 hours.

[0127] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and application concept of this application, should be included within the scope of protection of this application.

Claims

1. A metal-ceramic gradient composite coating, characterized in that, include: Substrate; A microporous alloy underlayer is formed on the surface of the substrate; A nano-activation layer is formed on the microporous alloy substrate; A ceramic surface layer is formed on the nano-activated layer.

2. The metal-ceramic gradient composite coating according to claim 1, characterized in that, The microporous alloy substrate includes an alloy layer and a microporous alloy layer composite on the alloy layer.

3. The metal-ceramic gradient composite coating according to claim 1, characterized in that, The alloy layer is made of Ni95Al5 or Ni80Cr20 alloy. The thickness of the alloy layer is 50μm~80μm; The microporous alloy layer is made of Ni95Al5 or Ni80Cr20 alloy. The thickness of the microporous alloy layer is 50μm~220μm; The microporous alloy layer has a pore size of 5μm to 20μm and a porosity of 5% to 15%.

4. The metal-ceramic gradient composite coating according to claim 1, characterized in that, The nano-activation layer is formed from nano-sol; The nanosol includes one or more of nanoaluminum sol, nanosilica sol, and nanozirconium sol; The thickness of the nano-activation layer is 20μm~50μm.

5. The metal-ceramic gradient composite coating according to claim 1, characterized in that, The ceramic surface layer includes a base coating and a surface coating layer laminated on the base coating; The base coating comprises aluminum dihydrogen phosphate, γ-Al2O3 powder, CrO3, aluminum powder, and a first filler; The first filler includes chrome green and / or cerium oxide; The surface coating comprises aluminum dihydrogen phosphate, Fe2O3 powder, CrO3, and a second filler; The second filler includes one or more of chrome green, cobalt oxide, nickel oxide, cerium oxide, quartz sand, boron nitride, and talc. The thickness of the ceramic surface layer is 0.1mm to 0.2mm.

6. A method for preparing a metal-ceramic gradient composite coating, characterized in that, Includes the following steps: a) Forming a microporous alloy underlayer on the substrate surface; b) Forming a nano-activation layer on the microporous alloy substrate; c) A ceramic surface layer is formed on the nano-activated layer.

7. The method for preparing a metal-ceramic gradient composite coating according to claim 6, characterized in that, Step a) specifically includes: a1) Forming an alloy layer on the surface of the substrate; a2) A microporous alloy layer is formed on the surface of the alloy layer.

8. The method for preparing the metal-ceramic gradient composite coating according to claim 7, characterized in that, Step a2) specifically includes: a21) Forming a porous layer on the surface of the alloy layer; a22) Supersonic electric arc thermal spraying or supersonic flame thermal spraying of alloy powder is performed on the surface of the porous layer to form a microporous alloy layer.

9. A type of tube screen, characterized in that, include: The metal-ceramic gradient composite coating as described in any one of claims 1 to 8; In the aforementioned metal-ceramic gradient composite coating, the substrate is a tube screen substrate.

10. A boiler, comprising the tube panel as described in claim 9.

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