A multi-layer gradient anticorrosion and anti-coking composite coating for a boiler heating surface and a preparation method thereof

Abstract

This invention discloses a multi-layer gradient anti-corrosion and anti-coking composite coating for boiler heating surfaces and its preparation method, relating to the field of boiler heating surface protection technology. The composite coating structure is disposed on the surface of the metal substrate of the boiler heating surface, including at least a high-corrosion-dominant zone and a high-coking-dominant zone. Each functional zone, from the metal substrate outwards, sequentially includes a roughened bonding interface layer, an amorphous alloy anti-corrosion layer, a flexible buffer transition layer, a dense ceramic barrier layer, and a micro-textured anti-adhesion surface layer, with sealing phases formed within the pores, microcracks, and interface channels of each layer. Different layer thickness configurations and surface texture parameters are used for different functional zones. The construction method includes zone identification, substrate pretreatment, amorphous alloy layer construction, buffer transition layer construction, ceramic barrier layer construction, micro-textured surface layer formation, sealing treatment, and heat treatment. This structure is beneficial for improving the corrosion resistance, anti-coking performance, interlayer stability, and long-term operational reliability of boiler heating surfaces.

Description

Technical Field

[0001] This invention relates to the field of boiler heating surface protection technology, specifically to a multi-layer gradient anti-corrosion and anti-coking composite coating for boiler heating surfaces and its preparation method. Background Technology

[0002] During operation, furfural residue biomass boilers typically face both corrosion and coking issues on their heating surfaces. This is because furfural residue contains high levels of chloride ions and sulfides, which readily generate corrosive media such as HCl and SO3 upon combustion, thus corroding the boiler's heating surfaces. Simultaneously, alkali metal compounds such as potassium and sodium in the ash easily form low-melting-point eutectics at lower temperatures. When molten or semi-molten ash adheres to the tube wall surface, it gradually forms a porous coking layer. This coking layer not only affects heat transfer but also causes localized temperature increases, further exacerbating oxidation and corrosion of the heating surfaces. The interaction between corrosion products and coking deposits easily creates a cycle of "corrosion—coking—heat transfer deterioration," leading to accelerated tube wall failure and impacting the boiler's continuous operation cycle. Under certain operating conditions, some furfural residue biomass boilers require shutdown for cleaning and maintenance after approximately 45 days of continuous operation.

[0003] To address the aforementioned problems, existing technologies typically employ several treatment methods. One type is material modification, which improves service performance by enhancing the corrosion resistance of the heating surface substrate itself, such as replacing ordinary materials with alloys that have higher corrosion resistance. Another type is additive optimization, which adjusts ash characteristics by adding additives to the fuel, increasing the ash melting point or reducing coking. A third type is surface coating, which involves preparing a protective coating on the boiler heating surface to reduce corrosion rates and ash adhesion. Compared to replacing the entire substrate, surface coating is generally easier to apply on-site and more suitable for treating specific areas, thus possessing practicality in engineering applications.

[0004] For example, patent document CN121295085A discloses a gradient functionalized composite coating for boiler heating surfaces and its preparation method. This coating primarily achieves a gradient match between mechanical properties and environmental failure resistance by setting a metal fiber reinforced underlayer, a ceramic fiber toughened transition layer, and a ceramic surface layer. Patent document CN105063546A discloses a method for thermally spraying an amorphous alloy coating for boiler furnace heating surfaces. This method primarily improves corrosion resistance and wear resistance by spraying an iron-based amorphous alloy layer onto the boiler heating surface. Both of these solutions can improve the service condition of boiler heating surfaces to some extent. However, the former focuses more on the gradient composite protection structure, while the latter focuses more on single amorphous alloy spraying protection. Neither solution addresses the differentiated design for different areas of the biomass boiler heating surface where corrosion and coking coexist and the dominant failure mechanisms differ. Therefore, there is still room for further improvement in balancing corrosion prevention, coking prevention, and thermal cycle stability.

[0005] For example, patent document CN104404430A focuses on improving corrosion resistance through iron-based amorphous composite coating and remelting treatment; patent document CN120485681A focuses on improving anti-coking performance through a composite structure of porous alloy bottom layer and micro-nano ceramic surface layer. The two aforementioned solutions propose improvement ideas from the perspectives of corrosion resistance and anti-coking, respectively. However, the former mainly targets corrosion protection, while the latter mainly targets anti-coking treatment. Neither discloses a multi-layered synergistic structure for zoned configuration under the combined conditions of corrosion, coking, scouring, and thermal circulation on the heating surface of furfural residue biomass boilers. Therefore, it still differs from this application in terms of comprehensively adapting to the complex service conditions of biomass boilers. Patent document number CN107794488A uses an inorganic sealing agent formed by dissolving aluminum hydroxide in phosphoric acid. Although this solution can improve the porosity defects and corrosion resistance of the amorphous spray coating to a certain extent, its focus is mainly on deep sealing and corrosion protection enhancement of a single-layer amorphous coating. It does not propose a systematic solution for the combined failure problem of the heating surface of biomass boilers under the conditions of corrosion, coking, scouring, and thermal circulation. It still has shortcomings in taking into account corrosion prevention, anti-coking, interlayer thermal stress buffering, and long-term service stability.

[0006] However, existing surface protection solutions still have some shortcomings in practical applications. While single-metal spray coatings can improve surface hardness and corrosion resistance to a certain extent, they often still contain pores, microcracks, or interface defects. Corrosive media may diffuse inward along these defects, thus affecting long-term protective effects. Although single ceramic layers have good heat resistance and wear resistance, thermal expansion mismatch may exist between them and the metal substrate, making them prone to cracking, peeling, or localized failure during boiler start-up, shutdown, or thermal cycling. Furthermore, for boiler heating surfaces that simultaneously experience corrosion, coking, erosion, and thermal cycling, the service conditions of different parts are usually not entirely the same. If a protection method with a uniform structure, uniform layer thickness, and uniform surface parameters is adopted, it is often difficult to meet the actual protection needs of different areas. Therefore, it is necessary to further provide a composite coating structure and its preparation method suitable for furfural residue biomass boiler heating surfaces, based on existing surface protection technologies. Summary of the Invention

[0007] The technical problem this invention aims to solve is that existing boiler heating surface protection technologies struggle to simultaneously address corrosion protection, coking inhibition, interlayer thermal stress buffering, and long-term service stability, and that uniform parameter coatings lack adaptability to different dominant failure areas. This invention provides a multi-layer gradient anti-corrosion and anti-coking composite coating for boiler heating surfaces and its preparation method. By designing differentiated structures for different areas and sequentially setting an amorphous alloy anti-corrosion layer, a flexible buffer transition layer, a dense ceramic barrier layer, a micro-textured anti-adhesion surface layer, and a sealing phase, the corrosion resistance, anti-coking properties, and thermal cycling stability of the heating surface are improved. This effectively solves the problems of easy corrosion, coking, coating cracking and peeling, and short operating cycles in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a multi-layer gradient anti-corrosion and anti-coking composite coating for boiler heating surfaces, disposed on the metal substrate surface of the heating surface of a biomass boiler; the present invention also provides a method for preparing the composite coating, wherein the composite coating is disposed at least in a high corrosion-dominant zone and a high coking-dominant zone; both the high corrosion-dominant zone and the high coking-dominant zone, from the metal substrate outward, sequentially include: a roughened bonding interface layer, an amorphous alloy anti-corrosion layer, a flexible buffer transition layer, a dense ceramic barrier layer, and a micro-textured anti-adhesion surface layer; and pores in the amorphous alloy anti-corrosion layer, the flexible buffer transition layer, the dense ceramic barrier layer, and the micro-textured anti-adhesion surface layer. Sealing phases are distributed within gaps, microcracks, and interface channels; among them, the thickness of the amorphous alloy anti-corrosion layer in the high corrosion-dominant region is 0.30–0.60 mm, the thickness of the flexible buffer transition layer is 30–120 μm, and the thickness of the dense ceramic barrier layer is 0.08–0.20 mm; the thickness of the amorphous alloy anti-corrosion layer in the high coking-dominant region is 0.20–0.40 mm, the thickness of the flexible buffer transition layer is 40–100 μm, and the thickness of the dense ceramic barrier layer is 0.10–0.25 mm; the texture feature spacing of the microtextured anti-adhesion surface layer in the high coking-dominant region is smaller than that in the high corrosion-dominant region.

[0009] Furthermore, the roughened bonding interface layer is formed by sandblasting; the amorphous alloy anti-corrosion layer is one of iron-based amorphous alloy layer, iron-chromium-based amorphous alloy layer, or aluminum-containing iron-chromium-based amorphous alloy layer; the flexible buffer transition layer is a metal-ceramic composite transition layer containing Fe-Cr-Al system metal components and heat-resistant inorganic particle components; the dense ceramic barrier layer contains one or more of alumina, chromium oxide, zirconium oxide, mullite, spinel, or a composite system thereof.

[0010] Furthermore, the surface microtexture of the microtextured anti-adhesion surface layer is a microgroove unit, a micro-island unit, a mesh unit, or a combination thereof; the mesh unit may be composed of intersecting microgrooves, used to further improve the surface discrete contact characteristics and reduce the effective contact area of ​​ash and slag, the height of the microtexture is 10-300 μm, and the spacing of the texture features is 30-1000 μm; the microtexture in the high corrosion-dominant zone is preferably a microgroove unit, and the microtexture in the high coking-dominant zone is preferably a micro-island unit and / or a microgroove unit.

[0011] Furthermore, the composite coating also includes a high erosion-dominant zone and / or a thermal shock-sensitive zone; the thickness of the dense ceramic barrier layer in the high erosion-dominant zone is greater than the thickness of the dense ceramic barrier layer in the high coking-dominant zone; and the thickness of the flexible buffer transition layer in the thermal shock-sensitive zone is greater than the thickness of the flexible buffer transition layer in the high corrosion-dominant zone or the high coking-dominant zone.

[0012] Furthermore, the sealing phase is formed by curing a sealing precursor, which includes nano-wear-resistant filler, an inorganic binding phase, and a high-temperature re-densification precursor; preferably, the sealing precursor includes nano-Al2O3, silica sol, B-Si-Al inorganic glass precursor, and rare earth oxide stabilizing components; wherein the content of nano-Al2O3 is not less than 35%, and the content of silica sol is 12-15%; during thermal cycling, the sealing phase forms secondary sealing regions at pores, microcracks, and interface channels.

[0013] Furthermore, a method for preparing a zoned gradient composite coating for corrosion and coking prevention on the heating surface of a biomass boiler is characterized by comprising the following steps: S1. Zone Identification: Based on the temperature distribution, corrosive medium enrichment, ash deposition, scouring and abrasion, and thermal circulation of the heating surface of the biomass boiler, the heating surface is zoned and identified, at least dividing it into a high corrosion-dominant zone and a high coking-dominant zone. S2. Substrate pretreatment: Clean and sandblast the surface of the metal substrate in each functional area to form a roughened bonding interface layer; S3. Construction of amorphous alloy layer: An amorphous alloy anti-corrosion layer is constructed on the surface of each functional area. The thickness of the amorphous alloy anti-corrosion layer in the high corrosion-dominant area is controlled at 0.30-0.60 mm, and the thickness of the amorphous alloy anti-corrosion layer in the high coking-dominant area is controlled at 0.20-0.40 mm. S4. Construction of buffer transition layer: A flexible buffer transition layer is constructed outside the amorphous alloy anti-corrosion layer; S5. Construction of ceramic barrier layer: A dense ceramic barrier layer is constructed outside the flexible buffer transition layer; S6. Microtextured surface layer formation: A microtextured anti-adhesion surface layer is formed on the surface of the dense ceramic barrier layer, and the spacing of texture features in the high coking-dominant area is smaller than that in the high corrosion-dominant area. S7. Sealing treatment: Introduce sealing precursors into the pores, microcracks and interface channels in the amorphous alloy anti-corrosion layer, flexible buffer transition layer, dense ceramic barrier layer and microtextured anti-adhesion surface layer to form a sealing phase. S8. Heat treatment: Perform heat treatment on the treated composite coating.

[0014] Furthermore, in step S2, 10-24 mesh quartz sand is used for sandblasting, preferably 10-20 mesh quartz sand; in step S3, the preheating temperature of the metal substrate is 200℃±10℃; the amorphous alloy anti-corrosion layer is formed by supersonic arc spraying, with a wire feeding speed of 8-12m / min and a spraying distance of 150-200mm.

[0015] Furthermore, the microtextured anti-adhesion surface layer described in step S6 is formed by laser scanning reconstruction, template imprinting, selective sintering, mask spraying, or a combination thereof; wherein, the microtexture in the high corrosion-dominant region adopts microgroove units, and the microtexture in the high coking-dominant region adopts micro-island units and / or microgroove units.

[0016] Furthermore, the sealing precursor mentioned in step S7 is introduced by vacuum impregnation and sealed within 2 to 4 hours after spraying; in step S8, the temperature is increased to 850°C at 300°C / h and held for 2 hours.

[0017] Furthermore, when a failed surface layer forms on the composite coating surface, after removing the failed surface layer, the base layer is retained, and a secondary additive reconstruction layer and a secondary sealing layer are formed on the outside of the retained base layer to achieve local repair.

[0018] In a further improvement of the present invention, in order to improve the synergistic stability between different functional areas, a continuous gradient transition zone is set between adjacent functional areas, so that the thickness of the amorphous alloy anti-corrosion layer, the thickness of the flexible buffer transition layer, and the microtexture parameters change continuously in space, thereby avoiding the stress concentration problem caused by parameter abrupt changes in the traditional partitioned structure and improving the overall stability and service reliability of the composite coating structure.

[0019] Furthermore, in the microtextured anti-adhesion surface layer, the microtextured units are oriented along the flue gas flow direction or the ash migration direction, so that the surface forms a guiding ash discharge structure, thereby reducing the ash retention time and adhesion probability during operation and improving the anti-coking performance.

[0020] Meanwhile, a tiered permeation sealing phase is introduced into the coating. By controlling the distribution of the sealing phase in the thickness direction, a high-density barrier structure is formed in the surface area, while the inner area maintains a relatively low density. This not only improves the surface's impermeability but also provides a certain stress buffer space for the internal structure, further enhancing the coating's stability under thermal cycling conditions.

[0021] Through the above structural design, the present invention achieves the synergistic effect between the continuous gradient structure, directional microtexture and hierarchical sealing structure, so that the composite coating exhibits better comprehensive protective performance under the combined effects of corrosion, coking and thermal cycling.

[0022] Furthermore, a crack-preventing and release zone is set between the high corrosion-dominant zone and the high coking-dominant zone. The crack-preventing and release zone extends along the boundary direction of the regions, and the thickness of the flexible buffer transition layer in the crack-preventing and release zone is greater than the thickness of the flexible buffer transition layer at the corresponding position in the adjacent region. The dense ceramic barrier layer has a discontinuous distribution structure or a locally thinned structure in the crack-preventing and release zone to reduce stress concentration at the boundary of the regions and inhibit crack propagation.

[0023] Furthermore, the sealing phase is a reactive self-sealing phase. In addition to nano-wear-resistant fillers, inorganic bound phases, and high-temperature re-densification precursors, the reactive self-sealing phase also includes functional components that can react with alkali metal compounds and chlorine- and sulfur-containing corrosion precursors in boiler ash.

[0024] Furthermore, in the zone identification step, a zone failure risk parameter field is established based on the wall temperature distribution, flue gas velocity, chlorine and sulfur enrichment, ash deposition rate, particle erosion intensity, and temperature fluctuation amplitude of different areas of the boiler heating surface. The thickness of the amorphous alloy anti-corrosion layer, the thickness of the flexible buffer transition layer, the thickness of the dense ceramic barrier layer, the microtexture parameters, and the distribution of the sealing phase in each zone are determined according to the zone failure risk parameter field.

[0025] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention adopts a partitioned gradient composite coating structure, in which an amorphous alloy anti-corrosion layer, a flexible buffer transition layer, a dense ceramic barrier layer, a micro-textured anti-adhesion surface layer, and a sealing phase are sequentially set on the surface of the boiler heating surface, so that the same protection system can simultaneously take into account corrosion protection and coking inhibition. Compared with single metal layer or single ceramic layer schemes, this structure is more suitable for the working conditions of furfural residue biomass boiler heating surface where corrosion and coking coexist.

[0026] 2. Based on the dominant failure mechanisms of different regions of the boiler heating surface, this invention employs different layer thicknesses and surface parameter configurations for the high corrosion-dominant zone and the high coking-dominant zone. Specifically, the high corrosion-dominant zone focuses on improving the barrier capability against corrosive media, while the high coking-dominant zone focuses on reducing ash and slag adhesion and the tendency for continuous coke layer growth. Therefore, compared to protection methods with uniform parameters, this invention has better adaptability to different regions.

[0027] 3. The present invention sets a flexible buffer transition layer between the amorphous alloy anti-corrosion layer and the dense ceramic barrier layer, which helps to reduce the thermal expansion mismatch between the metal layer and the ceramic layer and alleviate the interlayer stress concentration under thermal cycling conditions. This structure can reduce the risk of coating cracking, delamination and peeling to a certain extent, thereby improving the overall stability of the composite coating.

[0028] 4. The present invention enables the sealing phase to enter the pores, microcracks and interface channels in the coating through the sealing treatment, which helps to reduce the pore connectivity and slow down the infiltration of corrosive media along the defects. At the same time, the micro-textured anti-adhesion structure set on the surface helps to reduce the effective contact area between ash and the surface, reducing the possibility of ash adhesion and continuous thickening of the coke layer, thus improving the long-term service condition of the heated surface.

[0029] 5. Under preferred implementation conditions, the composite coating of the present invention can be used to extend the continuous operation cycle of the boiler and reduce the frequency of coking and maintenance to a certain extent. This solution is implemented by surface protection, which facilitates construction and repair in local areas of the boiler heating surface, and therefore has good engineering application value. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the functional zoning of the heating surface of the biomass boiler of the present invention; Figure 2 A schematic cross-sectional view of the multi-layer gradient anti-corrosion and anti-coking composite coating structure on the boiler heating surface of the present invention. Figure 3 This is a partial structural diagram of the microtextured anti-adhesion surface layer of the present invention; Figure 4 A schematic diagram illustrating the distribution and function of the sealing phase in the composite coating of this invention; Figure 5 A schematic diagram of the process for constructing a multi-layer gradient anti-corrosion and anti-coking composite coating on the boiler heating surface according to the present invention; Figure 6 This is a schematic diagram illustrating the differentiated configuration of parameters for different functional areas of the present invention; Figure 7 This is a schematic diagram of an embodiment of the local repair type secondary additive manufacturing of the present invention; Figure 8 This is a schematic diagram of the sealing phase interaction process under thermal cycling conditions according to the present invention.

[0031] In the figure: 1 Boiler heating surface, 11 High corrosion-dominant zone, 12 High coking-dominant zone, 13 High erosion-dominant zone, 14 Thermal shock-sensitive zone, 2 Metal substrate, 21 Roughened bonding interface layer, 22 Amorphous alloy anti-corrosion layer, 23 Flexible buffer transition layer, 24 Dense ceramic barrier layer, 25 Microtextured anti-adhesion surface layer, 26 Sealing phase, 3 Microgroove unit, 31 Micro-island unit, 32 Mesh unit, 4 Pores, 41 Microcracks, 42 Interface channels, 43 Secondary sealing region, 5 zone identification, 51 substrate pretreatment, 52 amorphous alloy layer construction, 53 buffer transition layer construction, 54 ceramic barrier layer construction, 55 microtextured surface layer formation, 56 pore sealing treatment, 57 heat treatment, 7 failed surface layer, 71 retained base layer, 72 secondary additive reconstruction layer, 73 secondary pore sealing layer, 8 pre-thermal cycling state, 81 crack formation state during thermal cycling, 82 pore sealing phase migration / re-densification state, 83 post-thermal cycling sealing state. Detailed Implementation

[0032] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Example

[0033] The present invention will be further described in detail below with reference to the accompanying drawings. It should be noted that the following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions, simple modifications or conventional adjustments made by those skilled in the art based on the disclosure of this specification without departing from the technical concept of the present invention should all fall within the scope of protection of the present invention.

[0034] This invention addresses the problems encountered by biomass boilers, especially those using high-chlorine, high-sulfur, and high-ash fuels such as furfural residue, during operation, including high-temperature corrosion, ash adhesion and coking, particle erosion and wear, and interlayer thermal stress concentration caused by thermal cycling. It proposes a partitioned gradient composite coating structure and its preparation method for the boiler's heating surface. This structure, through differentiated design of different dominant failure regions, sequentially constructs a roughened bonding interface layer 21, an amorphous alloy anti-corrosion layer 22, a flexible buffer transition layer 23, a dense ceramic barrier layer 24, a micro-textured anti-adhesion surface layer 25, and a sealing phase 26 distributed in defect channels on the surface of the metal substrate 2. This simultaneously improves corrosion resistance, coking resistance, erosion resistance, and thermal cycling stability.

[0035] I. Functional Zoning and Overall Structure Implementation Method like Figure 1 and Figure 2 As shown, the composite coating structure of the present invention is disposed on the surface of the metal substrate 2 of the boiler heating surface 1; the boiler heating surface 1 includes at least a high corrosion dominant zone 11 and a high coking dominant zone 12; depending on the boiler structure layout and operating conditions, a high scouring dominant zone 13 and a thermal shock sensitive zone 14 may be further disposed.

[0036] Among them: High corrosion dominant zone 11 refers to the area that is mainly affected by high chlorine and high sulfur corrosive media during operation, with metal thinning and high temperature corrosion failure as the main risks; High coking dominant zone 12 refers to the area that is mainly affected by ash and slag adhesion, continuous coke layer growth and heat transfer deterioration during operation; High erosion dominant zone 13 refers to the area that is significantly affected by high-speed erosion and wear of flue gas particles; Thermal shock sensitive zone 14 refers to the area that is more prone to interlayer thermal stress concentration and cracking and spalling under boiler start-up and shutdown, load fluctuation or local temperature difference changes.

[0037] In actual implementation, the above-mentioned functional areas can be comprehensively divided based on the boiler structure diagram, shutdown inspection records, wall temperature distribution, corrosion thinning, coking distribution, flue gas flow field analysis results, and operation and maintenance records. The functional areas can be continuously distributed or partially overlapped, but when constructing the coating, it is preferable to select the corresponding differentiated structural parameters according to the dominant failure mechanism.

[0038] like Figure 2 As shown, both the high corrosion-dominant region 11 and the high coking-dominant region 12, from the metal substrate 2 outwards, include: a roughened bonding interface layer 21, an amorphous alloy anti-corrosion layer 22, a flexible buffer transition layer 23, a dense ceramic barrier layer 24, and a microtextured anti-adhesion surface layer 25; and a sealing phase 26 is distributed in the pores 4, microcracks 41, and interface channels 42 in the amorphous alloy anti-corrosion layer 22, the flexible buffer transition layer 23, the dense ceramic barrier layer 24, and the microtextured anti-adhesion surface layer 25.

[0039] Preferably, the thickness of the amorphous alloy anti-corrosion layer 22 in the high corrosion-dominant zone 11 is 0.30-0.60 mm, more preferably about 0.40 mm; the thickness of the flexible buffer transition layer 23 is 30-120 μm, more preferably 50-80 μm; and the thickness of the dense ceramic barrier layer 24 is 0.08-0.20 mm, more preferably 0.10-0.18 mm.

[0040] Preferably, the thickness of the amorphous alloy anti-corrosion layer 22 in the high coking dominance zone 12 is 0.20-0.40 mm, preferably about 0.30 mm; the thickness of the flexible buffer transition layer 23 is 40-100 μm; and the thickness of the dense ceramic barrier layer 24 is 0.10-0.25 mm, preferably 0.10-0.20 mm.

[0041] The texture feature spacing of the microtextured anti-adhesion surface layer 25 in the high coking dominance zone 12 is smaller than that in the high corrosion dominance zone 11, thereby increasing the number of textures per unit area, reducing the actual contact area of ​​ash and slag and inhibiting the continuous growth of coke layer.

[0042] For the high-scour dominant region 13, it is preferable to increase the thickness of the dense ceramic barrier layer 24 to improve wear resistance and scour resistance; for the thermal shock sensitive region 14, it is preferable to increase the thickness of the flexible buffer transition layer 23 to improve interlayer stress buffering capacity and thermal cycling cracking resistance.

[0043] II. Specific Implementation Methods of Each Functional Layer a. Coarsening the interface layer 21 The roughened bonding interface layer 21 is formed by sandblasting to remove oxide scale, deposits, corrosion products and loose layers from the surface of the metal substrate 2, and to form a uniform rough bonding surface on the substrate surface to improve the mechanical bonding ability and adhesion stability of subsequent coatings.

[0044] Preferably, 10-24 mesh quartz sand is used for sandblasting, and more preferably 10-20 mesh hard and angular quartz sand is used. After sandblasting, the substrate surface is blown and dusted to keep it clean and dry, and preferably proceeds to the subsequent spraying step as soon as possible to reduce secondary oxidation.

[0045] b. Amorphous alloy anti-corrosion layer 22 The amorphous alloy anti-corrosion layer 22 is disposed on the outside of the roughened bonding interface layer 21 to block the diffusion of chlorine-containing and sulfur-containing corrosive media into the metal substrate 2, while improving surface hardness and wear resistance. The amorphous alloy anti-corrosion layer 22 is preferably one of iron-based amorphous alloy layer, iron-chromium-based amorphous alloy layer or aluminum-containing iron-chromium-based amorphous alloy layer; in a preferred embodiment, TANK X80 type amorphous alloy material can be used as the source of amorphous alloy wire or powder; this type of amorphous alloy forms an amorphous phase structure through rapid solidification, and has high hardness, good corrosion resistance and good high temperature stability.

[0046] The amorphous alloy anti-corrosion layer 22 is preferably formed by supersonic arc spraying, but can also be formed by high-speed flame spraying, plasma spraying or a combination thereof; the preferred process parameters are: wire feeding speed 8-12m / min, preferably about 10m / min; spraying distance 150-200mm, preferably about 180mm; substrate preheating temperature 200℃±10℃.

[0047] In a preferred embodiment, the amorphous alloy anti-corrosion layer 22 can be made of Fe-Cr-B-Si system amorphous alloy material, wherein the mass fraction of Cr element is preferably 10% to 25%, the mass fraction of B element is preferably 2% to 5%, the mass fraction of Si element is preferably 1% to 4%, and the remainder is Fe and unavoidable impurity elements; through the above composition design, the corrosion resistance and high temperature stability of the coating can be improved while ensuring the amorphous formation ability; those skilled in the art can also make equivalent adjustments to the above composition according to the actual working conditions.

[0048] c. Flexible buffer transition layer 23 A flexible buffer transition layer 23 is disposed between the amorphous alloy anti-corrosion layer 22 and the dense ceramic barrier layer 24. It is used to form a gradient transition of thermal expansion and elastic modulus between the metal layer and the ceramic layer, reduce the concentration of interlayer thermal stress, and reduce the risk of cracking, delamination and peeling under thermal cycling conditions.

[0049] The flexible buffer transition layer 23 is preferably a metal-ceramic composite transition layer, comprising a Fe-Cr-Al system metal component and a heat-resistant inorganic particle component; preferably, through the matching design of material composition and thickness, a flexible transition region is formed between the amorphous alloy anti-corrosion layer 22 and the dense ceramic barrier layer 24 to improve the overall service stability of the coating.

[0050] In a preferred embodiment, the flexible buffer transition layer 23 can be formed by mixed powder plasma spraying or twin-wire arc spraying, wherein the mass ratio of metal component to ceramic component is preferably 60:40 to 80:20; by controlling the spraying parameters, the transition layer forms a gradient change in elastic modulus and coefficient of thermal expansion in the thickness direction, thereby constructing an effective stress buffer region between the amorphous alloy anti-corrosion layer 22 and the dense ceramic barrier layer 24; those skilled in the art can routinely adjust the above ratio and parameters according to different spraying equipment.

[0051] d. Dense ceramic barrier layer 24 A dense ceramic barrier layer 24 is disposed on the outside of the flexible buffer transition layer 23 to improve the surface's resistance to heat and chemical corrosion, wear resistance, and barrier ability against oxygen, water vapor, and corrosive media.

[0052] The dense ceramic barrier layer 24 preferably comprises one or more of alumina, chromium oxide, zirconium oxide, mullite, spinel or a composite system thereof; more preferably it is an alumina-based ceramic layer or an alumina-mullite composite ceramic layer; this layer can be formed by spraying and then heat-treated to obtain a relatively stable bonding structure.

[0053] e. Microtextured anti-adhesion surface layer 25 like Figure 3As shown, the microtextured anti-adhesion surface layer 25 is formed on the surface of the dense ceramic barrier layer 24. Its surface microtexture is used to reduce the actual contact area of ​​ash and slag, reduce the continuous spreading ability of molten or semi-molten ash, and improve local ash removal behavior.

[0054] The microtexture can be a microgroove unit 3, a micro-island unit 31, a mesh unit 32, or a combination thereof; preferably, the microtexture height is 10-300 μm, more preferably 20-150 μm; the texture feature spacing is 30-1000 μm, more preferably 50-500 μm.

[0055] In a preferred embodiment, the microtexture in the high corrosion-dominant region 11 adopts microgroove units 3 to balance surface integrity and ash removal guidance effect; the microtexture in the high coking-dominant region 12 adopts microisland units 31 and / or microgroove units 3 to form discrete contact features and reduce the effective contact area of ​​ash and slag; the microtextured anti-adhesion surface layer 25 can be formed by laser scanning reconstruction, template imprinting, selective sintering, mask spraying or a combination thereof.

[0056] f. Sealing phase 26 like Figure 4 As shown, the sealing phase 26 is distributed in the pores 4, microcracks 41 and interface channels 42 in the amorphous alloy anti-corrosion layer 22, flexible buffer transition layer 23, dense ceramic barrier layer 24 and microtextured anti-adhesion surface layer 25. It is used to seal capillary pores and defect channels, reduce pore connectivity, slow down the penetration of corrosive and oxidizing media, and improve the long-term stability of the coating.

[0057] Preferably, the sealing phase 26 is formed by introducing the sealing precursor through impregnation, vacuum impregnation, spray penetration or a combination thereof, followed by heat treatment and curing; the sealing precursor includes nano-wear-resistant filler, inorganic binding phase and high-temperature re-densification precursor; preferably includes nano-Al2O3, silica sol, B-Si-Al inorganic glass precursor and rare earth oxide stabilizing component; wherein, the content of nano-Al2O3 is preferably not less than 35%, and the proportion of silica sol is preferably 12-15%.

[0058] In a preferred embodiment, the sealing treatment is performed within 2 to 4 hours after spraying, and the thickness of the resulting sealing layer is preferably 0.05 to 0.10 mm; the penetration depth of the sealing precursor preferably reaches more than 40% of the total coating thickness, and in a more preferred embodiment it can reach about 45%.

[0059] like Figure 8As shown, in the pre-thermal cycling state 8, the sealing phase 26 is distributed near the pores 4, microcracks 41, and interface channels 42. During thermal cycling, local defects may expand to form a crack formation state 81. Under subsequent temperature action, the re-densifying components in the sealing phase 26 can undergo local migration and re-densification, forming a sealing phase migration / re-densification state 82. Finally, in the closed state 83 after thermal cycling, a secondary sealing region 43 is formed at the local defects, thereby improving the local barrier capability and inhibiting further defect expansion. It should be understood that this effect is mainly manifested as local re-sealing and enhanced barrier, and does not require all defects to achieve complete macroscopic healing.

[0060] It should be noted that the re-densification and local re-sealing effect exhibited by the sealing phase 26 under thermal cycling conditions is mainly manifested as compensatory filling and enhanced barrier capacity for local defect channels, and does not require complete structural healing at all pores or cracks; those skilled in the art will understand that this effect belongs to the conventional physical or chemical response behavior of the material system under high temperature environment.

[0061] III. Implementation Method for Constructing Partitioned Gradient Composite Coatings like Figure 5 As shown, the partitioned gradient composite coating structure of the present invention can be constructed using the following steps.

[0062] Step S1: Partition Identification 5 Based on the temperature distribution, corrosive medium enrichment, ash deposition, scouring and abrasion and thermal circulation of different parts of the boiler heating surface 1, the heating surface 1 is functionally divided, at least into a high corrosion-dominant zone 11 and a high coking-dominant zone 12; if necessary, it can be further divided into a high scouring-dominant zone 13 and a thermal shock-sensitive zone 14. Zone identification can be determined by combining boiler structure diagrams, shutdown and maintenance records, wall temperature detection data, corrosion thinning data, coking thickness distribution, and flue gas flow field analysis results. The purpose of this step is to avoid using uniform parameters to cover the entire area, and instead determine more suitable structural and process parameters based on the dominant failure mechanism of each zone.

[0063] In a preferred embodiment, functional zoning can be determined by combining quantitative indicators. For example, when the wall temperature of a local area of ​​the heated surface is higher than 450°C and the content of chlorine or sulfur in the flue gas is high, it can be determined as a high corrosion-dominant zone; when the ash deposition rate is high in a local area or the coke layer thickness growth rate is significantly higher than the average level, it can be determined as a high coking-dominant zone; when the flue gas velocity is high and particle erosion is significant, it can be determined as a high scouring-dominant zone; when there are areas with frequent start-stops or large temperature fluctuations during operation, it can be determined as a thermal shock-sensitive zone. The above determination methods are illustrative examples, and those skilled in the art can make reasonable adjustments according to specific operating conditions.

[0064] Step S2: Matrix Pretreatment 51 The metal substrate 2 of each functional area is cleaned, dusted, rusted and sandblasted to form a roughened bonding interface layer 21; preferably 10-24 mesh quartz sand is used, and even more preferably 10-20 mesh quartz sand is used; after sandblasting, dust is removed by blowing to keep the substrate clean and dry.

[0065] Step S3: Construction of the amorphous alloy layer 52 The sandblasted metal substrate 2 is preheated to 200℃±10℃, and then an amorphous alloy anti-corrosion layer 22 is constructed on the surface of each functional area; preferably, supersonic arc spraying is used to form the amorphous alloy anti-corrosion layer 22, the wire feeding speed is preferably 8~12m / min, and the spraying distance is preferably 150~200mm. In this step, the thickness of the amorphous alloy anti-corrosion layer 22 in the high corrosion-dominant zone 11 is controlled to be 0.30–0.60 mm, and the thickness of the amorphous alloy anti-corrosion layer 22 in the high coking-dominant zone 12 is controlled to be 0.20–0.40 mm.

[0066] Step S4: Constructing the Buffer Transition Layer 53 A flexible buffer transition layer 23 is constructed outside the amorphous alloy anti-corrosion layer 22; the flexible buffer transition layer 23 is preferably a metal-ceramic composite transition layer, and the thickness is preferably controlled between 30 and 120 μm, more preferably between 50 and 80 μm.

[0067] Step S5: Construction of the ceramic barrier layer 54 A dense ceramic barrier layer 24 is constructed outside the flexible buffer transition layer 23; wherein, the thickness of the dense ceramic barrier layer 24 in the high corrosion dominant region 11 is preferably controlled to be 0.08 to 0.20 mm, and the thickness of the dense ceramic barrier layer 24 in the high coking dominant region 12 is preferably controlled to be 0.10 to 0.25 mm; for the high scouring dominant region 13, the thickness of the dense ceramic barrier layer 24 can be further increased.

[0068] Step S6: Microtextured surface layer formation 55 A microtextured anti-adhesion surface layer 25 is formed on the surface of the dense ceramic barrier layer 24; preferably, the spacing of texture features in the high coking region 12 is smaller than the spacing of texture features in the high corrosion region 11; the microtextured anti-adhesion surface layer 25 can be formed by laser scanning reconstruction, template imprinting, selective sintering, mask spraying or a combination thereof.

[0069] Step S7: Sealing treatment 56 A sealing precursor is introduced into the pores 4, microcracks 41 and interface channels 42 in the amorphous alloy anti-corrosion layer 22, the flexible buffer transition layer 23, the dense ceramic barrier layer 24 and the microtextured anti-adhesion surface layer 25 to form a sealing phase 26; preferably, it is introduced by vacuum impregnation, and preferably the sealing treatment is performed within 2 to 4 hours after spraying.

[0070] Step S8: Heat treatment 57 The treated composite coating is subjected to heat treatment; preferably, the temperature is raised to 850℃ at 300℃ / h and held for 2h to solidify the sealing precursor and stabilize it to form the sealing phase 26, thereby improving the bonding stability of each functional layer and the overall service reliability.

[0071] like Figure 6 As shown, this invention employs differentiated parameter configurations for different functional areas; in the figure, configuration level 1 represents low, level 2 represents medium, and level 3 represents high. The figure only illustrates the relative configuration relationship between different functional areas and is not limited to absolute values. For the high corrosion-dominant area 11, the amorphous alloy anti-corrosion layer has a high configuration level, the texture level is low, and the sealing level is high. For the high coking-dominant area 12, the texture level is high, and the amorphous alloy anti-corrosion layer has a relatively low or medium configuration level. For the high erosion-dominant area 13, the ceramic layer has a high configuration level. For the thermal shock-sensitive area 14, the transition layer has a high configuration level. Through the above differentiated configurations, different areas are respectively focused on corrosion resistance, coking resistance, erosion resistance, or thermal shock resistance. Example 1

[0072] Example 1: Standard composite protection for the high corrosion-dominant and high coking-dominant zones of water-cooled walls The water-cooled wall tubes of the furfural residue biomass boiler were selected as the boiler heating surface 1. Based on the corrosion thinning area, the continuous coke layer adhesion area and the wall temperature distribution recorded during the shutdown inspection, the parts near the strong effect of high-temperature corrosive flue gas and the obvious metal thinning were divided into the high corrosion dominant area 11, and the parts where ash and slag are easy to adhere, coke layer is easy to grow continuously and coke is frequently cleaned were divided into the high coking dominant area 12.

[0073] First, the area to be treated is cleaned by removing dust, rust, and surface. Then, it is sandblasted with 10-20 mesh quartz sand to form a roughened bonding interface layer 21. After sandblasting, the surface is blown with compressed air to ensure that the surface is clean and dry. Then, the metal substrate 2 is preheated to 200℃±10℃.

[0074] Supersonic arc spraying is used to form an iron-chromium-based amorphous alloy anti-corrosion layer 22 with a thickness of about 0.40 mm in the high corrosion-dominant zone 11 and an iron-chromium-based amorphous alloy anti-corrosion layer 22 with a thickness of about 0.30 mm in the high coking-dominant zone 12. The wire feeding speed is controlled at about 10 m / min and the spraying distance is controlled at about 180 mm during spraying.

[0075] Subsequently, a flexible buffer transition layer 23 with a thickness of about 50 to 80 μm is constructed outside the amorphous alloy anti-corrosion layer 22, and then a dense ceramic barrier layer 24 with a thickness of about 0.10 to 0.18 mm is constructed outside it.

[0076] In the high corrosion-dominant region 11, microgroove units 3 are formed on the surface of the dense ceramic barrier layer 24; in the high coking-dominant region 12, a combination of micro-island units 31 and microgroove units 3 is formed on the surface of the dense ceramic barrier layer 24, so that the texture feature spacing of the high coking-dominant region 12 is smaller than that of the high corrosion-dominant region 11.

[0077] The sealing precursor is then introduced by vacuum impregnation. The sealing precursor includes nano-Al2O3, silica sol, B-Si-Al inorganic glass precursor and rare earth oxide stabilizing components. The content of nano-Al2O3 is not less than 35%, and the content of silica sol is 12-15%. The sealing treatment is carried out within 2-4 hours after the spraying is completed.

[0078] Finally, the composite coating is heat-treated by raising the temperature to 850℃ at 300℃ / h and holding it for 2h to solidify the sealing precursor and form the sealing phase 26. The resulting composite coating structure combines corrosion resistance, coking prevention, and thermal cycling stability. Under preferred implementation conditions, the coating bonding strength can reach more than 32MPa, preferably about 34MPa, the porosity can be controlled below 3%, preferably about 2.9-3.0%, and the sealing penetration depth can reach more than 40% of the total coating thickness, preferably about 45%.

[0079] Example 2: Enhanced Implementation of High-Scrubber Dominant Region In the high scour dominant region 13, it is preferable to set the thickness of the dense ceramic barrier layer 24 to be greater than that in the high coking dominant region 12, and appropriately reduce the microtexture height or increase the continuous support area of ​​the surface to balance the ability to resist particle scour and the ability to resist adhesion.

[0080] After completing the amorphous alloy anti-corrosion layer 22 and the flexible buffer transition layer 23, a dense ceramic barrier layer 24 with a thickness higher than the set value of the high coking dominance zone 12 is constructed, preferably using an alumina-based or alumina-mullite composite ceramic system; then, depending on the degree of erosion, a shallow textured microtextured anti-adhesion surface layer 25 is constructed, and pore sealing and heat treatment are performed to improve the long-term stability of the windward area or the high-speed particle erosion area.

[0081] Example 3: Enhanced Implementation of Thermal Shock Sensitive Area In the thermal shock sensitive area 14, it is preferable to increase the thickness of the flexible buffer transition layer 23 to improve the interlayer thermal stress buffering capacity, and the amount of sealing precursor introduced can be appropriately increased to enhance the local resealing capacity under thermal cycling conditions.

[0082] After the amorphous alloy anti-corrosion layer 22 is constructed in this area, a relatively thick flexible buffer transition layer 23 is formed first, followed by the construction of a dense ceramic barrier layer 24 and a micro-textured anti-adhesion surface layer 25, and finally sealing and heat treatment are performed. This structure can reduce the risk of cracking and peeling under boiler start-up and shutdown and load fluctuation conditions.

[0083] Example 4: Local Repair Implementation Method like Figure 7 As shown, when a failed surface layer 7 forms on the surface of the composite coating, the protective capability can be restored by local repair. Specifically, the failed area is located first, and the surface layer that has cracked, peeled, severely worn, or severely coked is removed. The base layer 71 that is stable with the metal substrate 2 and has not undergone obvious delamination is retained.

[0084] Subsequently, the exposed area and the surface of the retained base layer 71 are cleaned and roughened as necessary, and a secondary additive reconstruction layer 72 is reconstructed on its outer side. The secondary additive reconstruction layer 72 preferably includes a dense ceramic barrier layer 24 and / or a micro-textured anti-adhesion surface layer 25. Then, the sealing precursor is introduced again to form a secondary sealing layer 73, which is then stabilized by heat treatment.

[0085] This localized repair method restores the corrosion resistance, coking resistance, and wear resistance of a localized area without removing the entire original protective layer, thereby shortening the maintenance cycle and reducing maintenance costs.

[0086] V. Comparative Experiments and Verification of Technical Effects To further verify the technical effect of the partitioned gradient composite coating structure of the present invention, metal substrate samples with the same material as the boiler heating surface were used to prepare Example A and Comparative Examples 1 to 5 under the same substrate pretreatment conditions, the same spraying equipment conditions and the same heat treatment conditions. The coating structure performance, corrosion resistance performance, anti-coking performance, thermal cycle stability and field operation verification of each group of samples were carried out respectively. The results are shown in Tables 1 to 7.

[0087] In this example, Example A uses the same partitioned differential gradient composite coating structure and preparation process as Example 1; Comparative Example 1 uses a uniform parameter structure for the entire region; Comparative Example 2 does not have a microtextured anti-adhesion surface layer 25; Comparative Example 3 does not have a flexible buffer transition layer 23; Comparative Example 4 does not perform pore sealing treatment 56; and Comparative Example 5 uses a region parameter interchange configuration.

[0088] Table 1 Sample Grouping and Test Objectives

[0089] Table 2 Main preparation parameters of each group of samples

[0090] Table 3 Test results of coating structure performance

[0091] Table 4 Corrosion Resistance Test Results

[0092] Table 5. Test results of anti-coking performance

[0093] As shown in Table 5, Example A, through the synergistic effect of the micro-textured anti-adhesion surface layer and the zoned differentiated structural design, is superior to the comparative examples in terms of ash adhesion amount, coking layer thickness and adhesion strength, indicating that the present invention has a better effect in inhibiting coking.

[0094] Table 6 Thermal Cycling Stability Test Results

[0095] Table 7. On-site operation verification results

[0096] As shown in Tables 1 to 7, Example A, by implementing differentiated configurations in the high corrosion-dominant region 11 and the high coking-dominant region 12, achieves a synergistic effect among the amorphous alloy anti-corrosion layer 22, the flexible buffer transition layer 23, the dense ceramic barrier layer 24, the microtextured anti-adhesion surface layer 25, and the sealing phase 26. This results in superior performance compared to the comparative examples in terms of corrosion resistance, anti-coking, thermal cycling stability, and on-site operating cycle. The results indicate that the technical effect of this invention stems from the matching relationship between structural parameters and the dominant failure mechanism, rather than the effect achievable by a single-layer structure or uniform parameter configuration.

[0097] This invention is not superior to the comparative example in a single performance indicator, but simultaneously improves multiple indicators such as corrosion resistance, coking resistance, structural stability, and operating cycle. For the heating surface of biomass boilers, simply improving corrosion resistance does not naturally lead to a simultaneous improvement in coking resistance, and simply increasing the thickness of the ceramic layer does not naturally lead to an improvement in thermal cycle stability. However, this invention achieves synergistic optimization of multiple performance objectives through zoned differentiated configuration.

[0098] As one implementation method, an optimization is made based on the aforementioned embodiments, by setting a continuous gradient transition zone between the high corrosion-dominant zone and the high coking-dominant zone, and by synergistically regulating the microtexture structure and the sealing structure.

[0099] The composite coating sets a continuous gradient transition zone between adjacent functional areas, so that the thickness of the amorphous alloy anti-corrosion layer, the thickness of the flexible buffer transition layer, and the microtexture parameters change continuously; the microtexture units in the microtexture anti-adhesion surface layer are oriented along the flue gas flow direction or the ash migration direction; the sealing phase forms a hierarchical penetration structure in the coating thickness direction, and the sealing density of the surface area is higher than that of the inner layer area.

[0100] First, the metal substrate of the boiler heating surface is sandblasted. The preferred sandblasting particle size is 40-80 mesh. After treatment, the surface roughness Ra is 3-8 μm to form a stable roughened bonding interface.

[0101] Subsequently, an amorphous alloy anti-corrosion layer was prepared on the surface of the metal substrate using a high-speed arc spraying process, wherein the spraying distance was 150-200 mm and the wire feeding speed was 8-12 m / min; in the high corrosion-dominant zone, the thickness of the amorphous alloy anti-corrosion layer was controlled at 0.40-0.60 mm, and in the high coking-dominant zone, it was controlled at 0.20-0.40 mm.

[0102] A continuous gradient transition zone is set between adjacent functional areas, with a width preferably of 10 to 30 mm. Within this transition zone, by adjusting the spraying speed and wire feeding rate, the thickness of the amorphous alloy anti-corrosion layer gradually transitions from a larger value in the high corrosion-dominant zone to a smaller value in the high coking-dominant zone, thus achieving continuous thickness variation.

[0103] A flexible buffer transition layer is formed on the outside of the amorphous alloy anti-corrosion layer. This transition layer is preferably formed by a mixed powder feeding plasma spraying process, with the mass ratio of metal components to ceramic components being 60:40 to 80:20. In the continuous gradient transition zone, the thickness of the flexible buffer transition layer is gradually transitioned from 60 μm to 80 μm by adjusting the powder feeding ratio, thereby forming a gradual structure with varying elastic modulus.

[0104] A dense ceramic barrier layer is prepared on the outside of the flexible buffer transition layer using a plasma spraying process. The thickness is 0.08–0.20 mm in the high corrosion-dominant zone and 0.10–0.25 mm in the high coking-dominant zone, with continuous thickness variation within the continuous gradient transition zone.

[0105] A microtextured anti-adhesion surface layer is formed on the surface of a dense ceramic barrier layer. The microtexture is formed by laser etching to create a micro-groove structure with a width of 20–80 μm, a depth of 10–40 μm, and a spacing of 50–150 μm. In particular, the microtexture density is higher in the high coking-dominant region, and the spacing is preferably 50–80 μm.

[0106] Furthermore, the microgroove units are oriented along the flue gas flow direction, and the angle between their extension direction and the mainstream flue gas direction is preferably 0 to 20°, thereby forming a guiding ash discharge path during operation and reducing the residence time of ash and slag on the surface.

[0107] After completing the above structure, the coating is subjected to a pore-sealing treatment. The pore-sealing treatment preferably adopts the sol-gel impregnation method, and the particle size of the pore-sealing precursor is preferably 50-200 nm. By controlling the impregnation time to 10-30 min and the number of repeated impregnations to 2-5 times, the pore-sealing phase forms a hierarchical penetration structure inside the coating.

[0108] Specifically, in the area near the surface, the penetration depth of the sealing phase is preferably 40% to 50% of the total coating thickness to form a dense closed structure; in the area near the inner layer, the penetration depth of the sealing phase is preferably 15% to 25% to retain a certain stress buffer space.

[0109] Finally, the entire coating is subjected to heat treatment, preferably at a temperature of 850℃±10℃ and a holding time of 2 hours, to promote the curing of the sealing phase and improve the overall bonding strength of the coating.

[0110] Through the above structural design, this embodiment avoids the problem of sudden performance change at the boundary of the region. At the same time, the directional micro-texture structure improves the migration behavior of ash and slag, and the hierarchical permeable sealing structure takes into account both the surface barrier ability and the internal stress release ability, thus exhibiting a lower crack propagation tendency and higher structural stability under thermal cycling conditions.

[0111] The composite coating features a continuous gradient transition zone between adjacent functional areas, allowing for continuous variation in the thickness of the amorphous alloy anti-corrosion layer, the thickness of the flexible buffer transition layer, and the microtexture parameters. In a preferred embodiment, to further reduce stress concentration and crack propagation risk at the boundary between the high corrosion-dominant area 11 and the high coking-dominant area 12, a crack-resistant release zone is further provided within the continuous gradient transition zone. The crack-resistant release zone extends along the boundary direction, with a width preferably 3–15 mm, more preferably 5–10 mm. The thickness of the flexible buffer transition layer 23 within the crack-resistant release zone is greater than the thickness of the corresponding flexible buffer transition layer 23 in the adjacent area, preferably increasing by 10%–30%. Simultaneously, the dense ceramic barrier layer 24 forms a discontinuous distribution within this area. The structure can be locally thinned, with the local thickness preferably reduced by 5% to 20% compared to adjacent areas, to reduce rigid constraints and thermal stress concentration at the boundary between areas. Preferably, discrete stress relief units can also be set within the crack-resistant and slow-release zone. These stress relief units can be micro-depressions, short grooves, island-shaped discontinuities, or combinations thereof, with a preferred size of 50 to 300 μm and a spacing of 100 to 800 μm, thereby dispersing local stress and inhibiting the continuous propagation of cracks along the boundary direction under thermal cycling conditions. Through the above structural design, not only can a smooth transition between different functional areas be achieved, but also a dedicated stress dissipation and crack-resistant structure can be formed at the boundary of areas, thereby improving the overall interlayer stability and long-term service reliability of the composite coating.

[0112] As a preferred embodiment, this embodiment further optimizes the aforementioned embodiments by introducing a reverse design mechanism for failure risk parameter fields based on regional service conditions during the construction of composite coatings in different functional areas of the boiler heating surface. A reactive self-sealing phase is set inside the composite coating. The failure risk parameter field is established by comprehensively considering wall temperature distribution, flue gas velocity, enrichment of chlorine and sulfur elements, ash deposition rate, particle erosion intensity, and temperature fluctuation amplitude. Based on this, the thickness of the amorphous alloy anti-corrosion layer, the thickness of the flexible buffer transition layer, the thickness of the dense ceramic barrier layer, the microtexture parameters, and the distribution of the sealing phase are reverse-configured to match the coating structure parameters of different regions with their dominant failure mechanisms.

[0113] In this embodiment, the sealing phase is a reactive self-sealing phase, which includes not only nano-wear-resistant fillers, inorganic bonding phases, and high-temperature re-densification precursors, but also functional components that can react with alkali metal compounds and chlorine- and sulfur-containing corrosion precursors in boiler ash. During thermal cycling, the reactive self-sealing phase can locally compensate for and fill pores, microcracks, and interface channels, and capture and fix coking and corrosion precursors, thereby improving the corrosion resistance, coking resistance, and long-term operational stability of the composite coating.

[0114] VI. Effect Description After adopting the partitioned gradient composite coating structure of the present invention, the high corrosion-dominant zone 11 can improve its barrier ability against corrosive media through a thicker amorphous alloy anti-corrosion layer 22 and sealing phase 26; the high coking-dominant zone 12 can reduce ash and slag adhesion and continuous coke layer growth through a micro-textured anti-adhesion surface layer 25 with smaller texture spacing; the high scouring-dominant zone 13 can enhance wear resistance through a thickened dense ceramic barrier layer 24; and the thermal shock-sensitive zone 14 can improve thermal cycle stability through a thickened flexible buffer transition layer 23. In summary, this structure can effectively extend the operating cycle of the boiler heating surface, reduce the frequency of maintenance, improve the heat transfer state, and enhance operational stability.

[0115] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope thereof, and all such changes and modifications shall fall within the scope of protection claimed by the present invention.

Claims

1. A multi-layer gradient anticorrosion and anti-coking composite coating for the heating surface of a boiler, arranged on the surface of a metal base (2) of a biomass boiler heating surface (1), characterized in that: The composite coating is at least set in the high corrosion-dominant zone (11) and the high coking-dominant zone (12); the high corrosion-dominant zone (11) and the high coking-dominant zone (12) both include, from the metal substrate (2) outwards: a roughened bonding interface layer (21), an amorphous alloy anti-corrosion layer (22), a flexible buffer transition layer (23), a dense ceramic barrier layer (24), and a microtextured anti-adhesion surface layer (25); a sealing phase (26) is distributed in the pores (4), microcracks (41), and interface channels (42) of the amorphous alloy anti-corrosion layer (22), the flexible buffer transition layer (23), the dense ceramic barrier layer (24), and the microtextured anti-adhesion surface layer (25); among them, the high corrosion-dominant zone (11) and the high coking-dominant zone (12) are at least set in the high corrosion-dominant zone (11) and the high coking-dominant zone (12); The thickness of the amorphous alloy anti-corrosion layer (22) in the guiding zone (11) is 0.30-0.60 mm, the thickness of the flexible buffer transition layer (23) is 30-120 μm, and the thickness of the dense ceramic barrier layer (24) is 0.08-0.20 mm; the thickness of the amorphous alloy anti-corrosion layer (22) in the high coking dominant zone (12) is 0.20-0.40 mm, the thickness of the flexible buffer transition layer (23) is 40-100 μm, and the thickness of the dense ceramic barrier layer (24) is 0.10-0.25 mm; the texture feature spacing of the microtextured anti-adhesion surface layer (25) in the high coking dominant zone (12) is smaller than that in the high corrosion dominant zone (11).

2. The multi-layer gradient anticorrosion and anti-coking composite coating of a boiler heating surface according to claim 1, characterized in that: The roughened bonding interface layer (21) is formed by sandblasting; the amorphous alloy anti-corrosion layer (22) is one of iron-based amorphous alloy layer, iron-chromium-based amorphous alloy layer or aluminum-containing iron-chromium-based amorphous alloy layer; the flexible buffer transition layer (23) is a metal-ceramic composite transition layer containing Fe-Cr-Al system metal components and heat-resistant inorganic particle components; the dense ceramic barrier layer (24) contains one or more of alumina, chromium oxide, zirconium oxide, mullite, spinel or their composite system.

3. The multi-layer gradient anti-corrosion and anti-coking composite coating for boiler heating surfaces according to claim 1, characterized in that: The surface microtexture of the microtextured anti-adhesion surface layer (25) is a microgroove unit (3), a micro-island unit (31), a mesh unit (32) or a combination thereof; the height of the microtexture is 10 to 300 μm and the spacing between texture features is 30 to 1000 μm; the microtexture in the high corrosion-dominant zone (11) is preferably a microgroove unit (3), and the microtexture in the high coking-dominant zone (12) is preferably a micro-island unit (31) and / or a microgroove unit (3).

4. The multi-layer gradient anti-corrosion and anti-coking composite coating for boiler heating surfaces according to claim 1, characterized in that: The composite coating is also provided with a high scour dominant zone (13) and / or a thermal shock sensitive zone (14); the thickness of the dense ceramic barrier layer (24) in the high scour dominant zone (13) is greater than the thickness of the dense ceramic barrier layer (24) in the high coking dominant zone (12); the thickness of the flexible buffer transition layer (23) in the thermal shock sensitive zone (14) is greater than the thickness of the flexible buffer transition layer (23) in the high corrosion dominant zone (11) or the high coking dominant zone (12).

5. The multi-layer gradient anti-corrosion and anti-coking composite coating for boiler heating surfaces according to claim 1, characterized in that: The sealing phase (26) is formed by curing a sealing precursor, which includes nano-wear-resistant filler, inorganic bonding phase and high-temperature re-densification precursor; preferably, the sealing precursor includes nano-Al2O3, silica sol, B-Si-Al inorganic glass precursor and rare earth oxide stabilizing component; wherein, the content of nano-Al2O3 is not less than 35% and the silica sol accounts for 12-15%; during thermal cycling, the sealing phase (26) forms a secondary sealing region (43) at pores (4), microcracks (41) and interface channels (42).

6. A method for preparing a zoned gradient composite coating for corrosion and coking prevention on the heating surface of a biomass boiler as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Zone identification (5): Based on the temperature distribution, corrosive medium enrichment, ash deposition, scouring and wear and thermal circulation of the heating surface (1) of the biomass boiler, the heating surface (1) is zoned and identified, and at least the high corrosion-dominant zone (11) and the high coking-dominant zone (12) are divided. S2, Substrate pretreatment (51): Clean and sandblast the surface of the metal substrate (2) in each functional area to form a roughened bonding interface layer (21). S3, Amorphous alloy layer construction (52): An amorphous alloy anti-corrosion layer (22) is constructed on the surface of each functional area. The thickness of the amorphous alloy anti-corrosion layer (22) in the high corrosion-dominant area (11) is controlled to be 0.30-0.60 mm, and the thickness of the amorphous alloy anti-corrosion layer (22) in the high coking-dominant area (12) is controlled to be 0.20-0.40 mm. S4, Construction of buffer transition layer (53): A flexible buffer transition layer (23) is constructed outside the amorphous alloy anti-corrosion layer (22); S5, Construction of ceramic barrier layer (54): A dense ceramic barrier layer (24) is constructed outside the flexible buffer transition layer (23). S6, Microtextured surface layer formation (55): A microtextured anti-adhesion surface layer (25) is formed on the surface of a dense ceramic barrier layer (24), and the spacing of texture features in the high coking-dominant region (12) is smaller than the spacing of texture features in the high corrosion-dominant region (11). S7, Sealing treatment (56): Introduce sealing precursors into the pores (4), microcracks (41) and interface channels (42) in the amorphous alloy anti-corrosion layer (22), flexible buffer transition layer (23), dense ceramic barrier layer (24) and microtextured anti-adhesion surface layer (25) to form a sealing phase (26). S8, Heat treatment (57): Heat treatment is performed on the treated composite coating.

7. The preparation method according to claim 6, characterized in that: In step S2, 10-24 mesh quartz sand is used for sandblasting, preferably 10-20 mesh quartz sand; in step S3, the preheating temperature of the metal substrate (2) is 200℃±10℃; the amorphous alloy anti-corrosion layer (22) is formed by supersonic arc spraying, with a wire feeding speed of 8-12m / min and a spraying distance of 150-200mm.

8. The preparation method according to claim 6, characterized in that: The microtextured anti-adhesion surface layer (25) described in step S6 is formed by laser scanning reconstruction, template imprinting, selective sintering, mask spraying or a combination thereof; wherein, the microtexture in the high corrosion-dominant region (11) adopts microgroove units (3), and the microtexture in the high coking-dominant region (12) adopts microisland units (31) and / or microgroove units (3).

9. The preparation method according to claim 6, characterized in that: The sealing precursor mentioned in step S7 is introduced by vacuum impregnation and sealed within 2 to 4 hours after spraying; in step S8, the temperature is increased to 850℃ at 300℃ / h and held for 2 hours.

10. The preparation method according to claim 6, characterized in that: When a failed surface layer (7) is formed on the surface of the composite coating, the failed surface layer (7) is removed, the base layer (71) is retained, and a secondary additive reconstruction layer (72) and a secondary sealing layer (73) are formed on the outside of the retained base layer (71) to achieve local repair.

Images