A double barrier self-lubricating anti-coking composite coating and a preparation method thereof

Abstract

The present disclosure provides a double-barrier self-lubricating anti-coking composite coating and a preparation method thereof, and belongs to the technical field of boiler anti-coking coating. The composite coating comprises a bottom layer and a surface layer. The bottom layer is of a porous structure and is formed of an alloy material. The surface layer comprises a cladding layer on the bottom layer and an embedded layer embedded in the porous structure of the bottom layer, and the surface layer is formed of a micro-nano ceramic composite material. The porous bottom layer coating provides a "bedding" for the surface layer ceramic particles. The micro-nano particles of the surface layer can be physically embedded in the pores of the porous material of the bottom layer, thereby increasing the bonding force between the surface layer ceramic particles and the substrate, prolonging the service life of the coating, and forming a micro composite material coating interface by the multi-element corrosion-resistant alloy and the micro-nano ceramic material.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of boiler anti-coking coating, and particularly relates to a double-barrier self-lubricating anti-coking composite coating and a preparation method thereof. BACKGROUND

[0002] A coal-fired boiler is a heat energy device that generates steam or hot water by burning coal. The core heating surface, such as the water wall, is exposed to high-temperature flue gas and ash for a long time. When high-alkali coal is burned, low-melting-point ash, such as sodium and potassium compounds, is easy to coking on the heating surface, which leads to a decrease in the heat transfer efficiency of the coal-fired boiler, local over-temperature pipe explosion, and even safety accidents.

[0003] The traditional coating of the heating surface of a coal-fired boiler is mostly silicate or metal alloy. However, the silicon-based material is easy to react with sodium and potassium in high-alkali coal, which aggravates the coking problem of the heating surface. Moreover, the single-layer coating is directly coated, which needs to be combined with high-temperature curing to ensure the connection strength between the single-layer coating and the substrate, and the preparation efficiency is low. The thermal expansion coefficient of the metal alloy coating and the steel boiler substrate is quite different, which is easy to produce interface stress when the temperature fluctuates, leading to the peeling of the coating. In summary, the traditional coating is limited by materials and processes, and the anti-coking effect and service life of the coating need to be further improved. SUMMARY

[0004] The present disclosure aims to at least solve one of the technical problems existing in the prior art, and provides a double-barrier self-lubricating anti-coking composite coating and a preparation method thereof.

[0005] In one aspect of the present disclosure, a double-barrier self-lubricating anti-coking composite coating is provided, which comprises:

[0006] a bottom layer, the bottom layer being a porous structure, the bottom layer being formed of an alloy material;

[0007] a surface layer, the surface layer comprising a cladding layer on the bottom layer and an embedded layer embedded in the porous structure of the bottom layer, the surface layer being formed of a micro-nano ceramic composite material; wherein the micro-nano ceramic composite material comprises:

[0008] 15-20 parts of boron nitride;

[0009] 5-10 parts of graphene;

[0010] 15-20 parts of zirconium oxide;

[0011] 8-12 parts of silicon carbide;

[0012] 4-6 parts of chromium carbide;

[0013] 5-7 parts of silicon nitride;

[0014] 4-6 parts of molybdenum disulfide;

[0015] 3-5 parts of yttrium oxide;

[0016] 5-7 parts of titanium oxide;

[0017] 2-3 parts of cerium oxide;

[0018] 3-5 parts potassium silicate;

[0019] 3-4 parts of phenolic resin.

[0020] Optionally, the particle size of the micro-nano ceramic composite material is 50-150 nm.

[0021] Optionally, the alloy material includes any one of NiCrTi alloy, Inconel alloy, amorphous alloy, and high entropy alloy.

[0022] Optionally, the amorphous alloy is any one of an iron-based amorphous alloy, a nickel-based amorphous alloy and a cobalt-based amorphous alloy.

[0023] Optionally, the high entropy alloy is any one of CoCrFeNiAl, FeCoNiCrMo and AlCoCrFeNiTi.

[0024] Optionally, the thickness of the bottom layer is 0.2-0.4 mm; the thickness of the coating layer in the surface layer is 0.1-0.4 mm.

[0025] Another aspect of the present disclosure provides a method for preparing the composite coating described above, the method comprising:

[0026] mixing the micro-nano ceramic composite material to obtain a surface layer raw material;

[0027] Pre-treating the boiler heating surface substrate, and spraying the alloy material onto the boiler heating surface substrate to form a bottom layer;

[0028] The mixed surface layer raw materials are prepared on the bottom layer to form a surface layer on the bottom layer to obtain a composite coating.

[0029] Optionally, the alloy material is sprayed onto the boiler heating surface substrate by arc spraying, plasma spraying or flame spraying.

[0030] Optionally, the mixed surface layer raw materials are prepared on the bottom layer by spraying, cladding or mechanical coating.

[0031] Optionally, after preparing the mixed surface layer raw materials on the bottom layer to form a surface layer on the bottom layer, the method further comprises:

[0032] The surface layer is subjected to a remelting treatment.

[0033] The present disclosure proposes a double-barrier self-lubricating anti-coking composite coating and its preparation method. The composite coating includes: a bottom layer and a surface layer, the bottom layer is a porous structure, and the bottom layer is formed of an alloy material; the surface layer includes a coating layer located on the bottom layer and an embedded layer embedded in the porous structure of the bottom layer, and the surface layer is formed of a micro-nano ceramic composite material. The present disclosure uses all materials with good high temperature resistance, corrosion resistance, and easy access. The coating isolates the contact between the heating surface boiler tube and the flue gas, coal ash, etc. in the furnace, playing the role of the first "physical barrier"; at the same time, all materials do not participate in the coking reaction and do not react chemically with the components in the furnace, which serves as the second barrier "chemical barrier"; the porous bottom coating provides a "bed" for the surface ceramic particles, and the micro-nano particles of the surface layer can be physically embedded in the pores of the bottom porous material, increasing the bonding force between the surface ceramic particles and the substrate and extending the coating life; and the multi-element corrosion-resistant alloy plus the micro-nano ceramic material constitutes a microscopic composite coating interface, and achieves the technical effect of 1+1 greater than 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The figure is a flowchart of a method for preparing a double-barrier self-lubricating anti-coking composite coating according to a specific embodiment of the present disclosure. DETAILED DESCRIPTION

[0035] To enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to illustrate the present disclosure and are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present disclosure.

[0036] One aspect of this disclosure proposes a dual-barrier, self-lubricating, anti-coking composite coating. The composite coating comprises a base layer and a surface layer. The base layer is a porous structure made of an alloy material. The surface layer comprises a coating layer located on the base layer and an embedded layer embedded in the porous structure of the base layer. The surface layer is made of a micro-nano ceramic composite material. Specifically, the micro-nano ceramic material is embedded in the porous structure of the base layer and coated on the surface of the base layer.

[0037] This embodiment uses physical barrier reinforcement - the bottom porous alloy (porosity 4-6%) and the surface micro-nano ceramic (50-150nm) form a gradient structure, which has the advantage of using the porous bottom coating to provide a "bed" for the surface ceramic particles. The micro-nano particles of the surface layer can be physically embedded in the pores of the bottom porous material, increasing the bonding force between the surface ceramic particles and the substrate and extending the coating life.

[0038] Furthermore, the surface layer's micro-nano ceramic composite material includes: 15-20 parts boron nitride and 5-10 parts graphene, or 8-15 parts tungsten disulfide, 15-20 parts zirconium oxide, 8-12 parts silicon carbide, 4-6 parts chromium carbide, 5-7 parts silicon nitride, 4-6 parts molybdenum disulfide, 3-5 parts yttrium oxide, 5-7 parts titanium oxide, 2-3 parts cerium oxide, 3-5 parts potassium silicate, and 3-4 parts phenolic resin. This material, which has both self-lubricating and ceramic components, can reduce ash adhesion, inhibit coke layer growth, block alkali metal penetration, and reduce defect diffusion paths.

[0039] It should be noted that the 15-20 parts boron nitride and 5-10 parts graphene, or 8-15 parts tungsten disulfide, in the composite material formula can be selected based on the specific process. For example, when preparing the surface layer raw material on the bottom layer by cladding or mechanical coating, boron nitride and graphene can be selected. When using a spraying process (such as supersonic flame spraying or activated combustion supersonic flame spraying), tungsten disulfide can be selected due to the poor high-temperature stability of boron nitride and graphene. In other words, the above-mentioned boron nitride and graphene are suitable for most processes. Only when using a spraying process, the boron nitride and graphene components are replaced with tungsten disulfide.

[0040] It should be noted that this embodiment does not impose any specific restrictions on the sources of the above-mentioned raw materials. They can be purchased directly or prepared in-house. For example, zirconium oxide can be obtained by the following method: synthesizing ZrO2-Y2O3 nanopowder by coprecipitation, calcining at 600-800°C, and spray granulating to obtain a powder. Silicon carbide can be obtained by high-temperature synthesis of crude SiC using the Acheson method, acid-washing and purification, and then airflow milling to a D50 of ≤2μm.

[0041] In some preferred embodiments, the particle size of the micro-nano ceramic composite material is 50-150 nm. For example, the size of the micro-nano ceramic composite material in the surface layer raw material is 100 nanometers. The above particle size range can make the coating have a denser microstructure, improve the hardness and wear resistance of the coating, and smaller particles help to fill the pores in the underlying porous structure to form a more uniform coating layer.

[0042] In other preferred embodiments, the thickness of the surface layer is 0.1-0.4 mm, and further preferably 0.2-0.25 mm. The appropriate thickness of the surface layer can provide sufficient chemical and physical protection while avoiding increased brittleness and thermal stress concentration caused by excessive thickness.

[0043] Furthermore, the alloy material of the bottom layer includes one of NiCrTi alloy (45CT), Inconel alloy, amorphous alloy, and high entropy alloy, which has high temperature deformation resistance, thermal shock resistance and chemical stability.

[0044] It should be noted that the main components of NiCrTi alloy (45CT) are: usually 42%-46% chromium (Cr), 0.3%-1.0% titanium (Ti), and the rest is nickel (Ni).

[0045] As a further preferred solution, the amorphous alloy is any one of an iron-based amorphous alloy, a nickel-based amorphous alloy and a cobalt-based amorphous alloy.

[0046] As a further preferred embodiment, the high entropy alloy is any one of CoCrFeNiAl, FeCoNiCrMo and AlCoCrFeNiTi.

[0047] In other preferred embodiments, the thickness of the bottom layer is 0.2-0.4 mm, and further preferably 0.25-0.4 mm. The appropriate thickness ensures that the bottom layer has a sufficiently porous structure, provides pore space for the surface layer to "implant", and enhances the interface bonding strength between the surface layer and the bottom layer.

[0048] It should be noted that the total thickness of the composite coating formed by the base layer and the surface layer in this embodiment is less than or equal to 0.6 mm. For example, the thickness of the base layer coating is 0.3 mm, and the thickness of the coating layer in the surface layer is 0.25 mm. Of course, the thickness of the base layer and the coating layer can also be other sizes, which are not listed here. It should be understood that because the embedded layer is located in the porous structure, the thickness of the embedded layer should be less than or equal to the thickness range of the base layer.

[0049] The double-barrier self-lubricating and anti-coking composite coating provided in this embodiment is formed by combining the bottom multi-element corrosion-resistant alloy layer with corrosion resistance and other functions with the nano-ceramic coating in the surface layer to form a double-barrier self-lubricating and anti-coking composite coating, wherein the zirconium oxide in the surface layer can form a dense ceramic layer to isolate the molten ash from contact with the pipe wall of the coal-fired boiler, boron nitride and graphene synergistically reduce the adhesion ability of the coating surface, making the contact angle greater than 120 degrees, significantly reducing adhesion, titanium dioxide as a black body material can improve the thermal radiation efficiency and reduce the temperature of the heated surface, chromium oxide can resist the corrosion of sodium and potassium in high-alkali coal, and cerium dioxide can inhibit oxidation. Reaction, yttrium oxide can stabilize the zirconia lattice, silicon carbide and aluminum oxide can provide ultra-high thermal conductivity to avoid local overheating and coating failure, boron nitride and graphene are responsible for lubrication, ceramic particles are responsible for preventing coking, and other materials cannot participate in the oxidation reaction of coking. The porous underlying structure can provide a "bed" for the surface ceramic particles, and the micro-nanoparticles of the surface layer can be physically embedded in the pores of the underlying porous material, which increases the bonding force between the surface ceramic particles and the matrix and extends the coating life; moreover, the multi-element corrosion-resistant alloy plus ceramic material constitutes the microscopic composite material coating interface, and realizes the technical effect of 1+1 greater than 2.

[0050] The porous structure of the underlying layer in this embodiment provides anchoring points for the ceramic composite material in the surface layer. During spraying, the micro-nano ceramic composite material can be embedded in the pores of the alloy material, which helps to improve the interfacial bonding strength. Furthermore, the use of micro-nano ceramic composite materials in the surface layer, with their nanostructure, can reduce the diffusion path of defects. Therefore, when used in coal-fired boilers, they can effectively prevent the penetration of alkali metal ions generated by the combustion of high-alkali coal into the substrate, reducing coking and corrosion caused by alkali metal reactions. This composite coating has excellent comprehensive anti-coking and anti-corrosion properties.

[0051] like Figure 1 As shown, another aspect of the present disclosure provides a method S100 for preparing the composite coating described above, specifically comprising the following steps S110 to S130:

[0052] S110. Pour the surface layer raw materials into a mixer according to 15-20 parts of boron nitride and 5-10 parts of graphene, or 8-15 parts of tungsten disulfide, 15-20 parts of zirconium oxide, 8-12 parts of silicon carbide, 4-6 parts of chromium carbide, 5-7 parts of silicon nitride, 4-6 parts of molybdenum disulfide, 3-5 parts of yttrium oxide, 5-7 parts of titanium oxide, 2-3 parts of cerium oxide, 3-5 parts of potassium silicate and 3-4 parts of phenolic resin, and dry mix them for a preset time under nitrogen protection to avoid agglomeration of nano-graphene. Use a Hall flow meter to detect whether the powder fluidity meets the preset fluidity requirements to ensure that each group is evenly distributed. If the error of each component meets the preset error requirement, proceed to the next step.

[0053] It should be noted that the materials mixed in step S110 are randomly sampled and analyzed by XRF. In addition, the mixer used in step S110 is a V-shaped mixer with a volume of 100L, and the V-shaped mixer is preferably set to a speed of 30-50rpm.

[0054] It should be further explained that, in step S110, after the surface layer raw materials are mixed, an ultrasonic pre-dispersion process may be added to fully mix the raw materials.

[0055] S120. Pre-sandblast the boiler heating surface substrate to roughen its surface and remove impurities generated by the sandblasting. Then, spray the alloy raw material onto the boiler heating surface substrate to form a porous structure coating. After spraying, the substrate is immediately air-cooled to prevent thermal deformation. The surface layer material is physically embedded in the porous structure of the underlying layer until it is cooled and formed.

[0056] It should be noted that after sandblasting, the heating surface of the boiler needs to be cleaned with acetone to remove oil and impurities.

[0057] In step S120, the alloy raw material is sprayed onto the steel pipe substrate by a spraying method such as arc spraying, plasma spraying or flame spraying, which is a method for preparing a strong-bonding porous coating.

[0058] In some preferred embodiments, when the electric arc spraying process is adopted, the electric arc spraying system is equipped with a double-wire feeding mechanism, and the process parameters can include an electric arc voltage: 32-36 V DC, an electric arc current: 180-200 A, a compressed air pressure: 0.65 MPa (after oil removal and drying treatment), a spraying distance: 150-180 mm, a spray gun moving speed: 300-400 mm / s, and a wire feeding speed: 2.5-3.0 m / min.

[0059] In some preferred embodiments, when the flame spraying process is adopted, the flame spraying process parameters include: a fuel system is propane (C3H8) + oxygen (O2) mixed combustion (oxygen fuel ratio 1.2:1), a gas flow is propane: 200-220 L / min; oxygen: 800-850 L / min (dynamic adjustment to maintain neutral flame), a gas distance is 180-220 mm, a powder feeding rate is 45-50 g / min, a spraying angle is 85-90°, a substrate preheating temperature is 150-180℃, and air cooling.

[0060] S130, the mixed surface layer raw material is prepared on the bottom layer to form a surface layer on the bottom layer, to obtain a composite coating, and the formed coating is slightly polished to make the surface roughness Ra less than 1 μm.

[0061] In step S130, the mixed surface layer raw material can be prepared on the bottom layer by spraying, cladding or mechanical coating. It should be understood that the micro-nano ceramic composite material herein not only embeds in the porous structure of the alloy material to form an embedded layer, but also coats the surface of the bottom layer to form a coating layer.

[0062] It should be noted that the present embodiment does not specifically limit the method of spraying, for example, the spraying includes supersonic flame spraying or activated combustion supersonic flame spraying. It should be noted that when supersonic flame spraying or activated combustion supersonic flame spraying is adopted, 15-20 parts of boron nitride and 5-10 parts of graphene in the surface layer raw material are replaced by 8-15 parts of tungsten disulfide. That is, in the formula of the micro-nano ceramic composite material of the surface layer, the selection of components also has certain differences according to the preparation process. When the surface layer raw material is prepared on the bottom layer by cladding or mechanical coating, boron nitride and graphene components can be selected, and when the spraying process is adopted, tungsten disulfide can be selected due to the poor high-temperature stability of boron nitride and graphene.

[0063] It should be further noted that the present embodiment does not specifically limit the mechanical coating method. For example, mechanical coating includes blade coating, roller coating, dip coating, air spray coating, airless spray coating, etc. Of course, the mechanical coating process may also include an ultrasonic dispersion process, wherein the ultrasonic power density is 50-100 W / L and the ultrasonic dispersion time is 20-40 minutes.

[0064] In other preferred embodiments, after preparing the mixed surface layer raw materials on the base layer to form a surface layer on the base layer, the method further includes: remelting the surface layer, wherein the remelting treatment is plasma arc remelting or laser remelting.

[0065] This embodiment uses laser remelting to process the surface layer, so that the coating absorbs laser energy and the surface temperature rises sharply to above the melting point, forming a molten pool. After the laser beam is removed, the molten pool quickly dissipates heat to the surrounding substrate, quickly cools and solidifies, and the composite coating obtains grain refinement, changes in phase composition, and increases infrared emissivity, thereby enhancing heat dissipation performance.

[0066] The preparation process of this embodiment omits the heat treatment process after spraying, that is, the coating does not enter the heat treatment furnace after spraying, and realizes its own ceramicization or high-temperature curing under the heat action of the furnace startup process, thereby enhancing on-site applicability.

[0067] The preparation method of the composite coating will be further described below with reference to specific examples:

[0068] Example 1

[0069] In this embodiment, the method for preparing the double-barrier self-lubricating anti-coking composite coating includes the following steps:

[0070] S1: Weigh and proportion the material components shown in Table 1. Then, pour the weighed powder into a 100L V-type mixer and set the speed to 30rpm. Dry mix under nitrogen for 2 hours to prevent nano-graphene from agglomerating and absorbing moisture. Use a Hall effect flowmeter to check whether the powder flowability is greater than or equal to 25s / 50g. Randomly sample and perform XRF composition analysis to ensure that the components are evenly distributed and the error of each component is within ±1%.

[0071] S2: The boiler steel tube substrate is sandblasted in advance to roughen its surface and remove impurities generated by sandblasting. Then, NiCrTi alloy (45CT) is arc sprayed onto the steel tube substrate to form a porous structure base layer with a thickness of 0.2 mm. The arc spraying system is equipped with a double-wire feeding mechanism. The wire material is NiCrTi alloy (45CT) with a wire diameter of Φ1.6 mm. Further process parameters may include arc voltage: 34 V DC, arc current: 190 A, compressed air pressure: 0.65 MPa (after degreasing and drying treatment), spraying distance: 160 mm, spray gun movement speed: 350 mm / s, and wire feeding speed: 2.8 m / min.

[0072] S3: Apply the surface layer material to the base layer by scraping. Specifically, adjust the scraper gap to 0.3mm and scrape at a constant speed of 15mm / s to control the surface layer thickness to 0.25mm. The formed coating is lightly polished to a surface roughness Ra of less than 1μm.

[0073] It should be noted that the base layer and surface layer materials used in this embodiment can be obtained commercially. The thickness of the base layer coating formed in steps S2 and S3 in the above preparation process, the base layer coating material and the surface layer coating thickness are shown in Table 2.

[0074] Example 2

[0075] As shown in Table 1, the mass fraction of boron nitride was changed to 20 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer were consistent with those in Example 1. The thickness of the formed surface layer was 0.4 mm. The results are shown in Table 2.

[0076] Example 3

[0077] As shown in Table 1, the mass fraction of zirconium oxide was changed to 20 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer were consistent with those in Example 1. The thickness of the bottom layer formed was 0.4 mm, and the thickness of the surface layer was 0.2 mm. The results are shown in Table 2.

[0078] Example 4

[0079] As shown in Table 1, the mass fraction of graphene was changed to 6 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer were consistent with those in Example 1. The thickness of the bottom layer formed was 0.25 mm, and the thickness of the surface layer was 0.25 mm. The results are shown in Table 2.

[0080] Example 5

[0081] As shown in Table 1, the mass fraction of potassium silicate was changed to 5 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer were consistent with those in Example 1. The thickness of the bottom layer formed was 0.4 mm, and the thickness of the surface layer was 0.1 mm. The results are shown in Table 2.

[0082] Example 6

[0083] The bottom coating material was changed to an iron-based amorphous alloy, and the other material components and their mass fractions, as well as the steps included in the preparation method of the surface layer, were consistent with those in Example 1.

[0084] Example 7

[0085] The bottom coating material was changed to a CoCrFeNiAl high entropy alloy, and the other material components and their mass fractions, as well as the steps included in the preparation method of the surface layer, were consistent with those in Example 1.

[0086] Example 8

[0087] The base coating material was changed to Inconel alloy, and the other material components and their mass fractions, as well as the steps included in the preparation method of the surface layer, were consistent with those in Example 1.

[0088] Example 9

[0089] On the basis of Example 1, the spraying method in step S2 was changed from arc spraying to flame spraying. The other components and preparation process parameters were consistent with those in Example 1. The flame spraying process parameters included: the fuel system was propane (C3H8) + oxygen (O2) mixed combustion (oxygen-fuel ratio 1.2:1), the gas flow rate was propane: 210 L / min; oxygen: 830 L / min (dynamically adjusted to maintain a neutral flame), the gas distance was 200 mm, the powder feeding rate was 47 g / min, the spraying angle was 88°, the substrate preheating temperature was 165°C, and the cooling was air-cooled.

[0090] Example 10

[0091] On the basis of Example 1, an ultrasonic dispersion process is added. Specifically, an ultrasonic pre-dispersion process is added after S1 mixing. An immersion titanium alloy probe (Φ20 mm) can be used, and the parameters are set to ultrasonic frequency: 20 kHz ± 1.5%, power density: 80 W / L, and processing time: 30 min (pulse mode, working cycle 1 s on / 0.5 s off).

[0092] Example 11

[0093] On the basis of Example 1, in step S3, a laser remelting process is added to the surface layer, wherein the laser remelting parameters include: laser wavelength of 1064nm, power density of 3.2×10 4W / cm², spot diameter is 1.2mm, scanning speed is 450mm / s, and pulse frequency is 200kHz (effectively avoiding thermal damage to the graphene structure).

[0094] Furthermore, in order to further explore the coating formulation performance of the embodiments of the present application and study the influence of the surface layer component content on the coating performance, the present disclosure also provides the following comparative examples 1 to 10, and the coating thickness is the same as that of Example 1 in Table 2.

[0095] Comparative Example 1

[0096] As shown in Table 3, the mass fraction of boron nitride is set to 25 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0097] Comparative Example 2

[0098] As shown in Table 3, the mass fraction of zirconium oxide is set to 25 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0099] Comparative Example 3

[0100] As shown in Table 3, the mass fraction of potassium silicate is set to 6 parts, and the other material components and mass fractions thereof, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0101] Comparative Example 4

[0102] As shown in Table 3, the mass fraction of graphene is set to 8 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0103] Comparative Example 5

[0104] As shown in Table 3, the mass fraction of titanium oxide is set to 8 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0105] Comparative Example 6

[0106] As shown in Table 3, the mass fraction of boron nitride is set to 10 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0107] Comparative Example 7

[0108] As shown in Table 3, the mass fraction of zirconium oxide is set to 10 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0109] Comparative Example 8

[0110] As shown in Table 3, the mass fraction of potassium silicate is set to 2 parts, and the other material components and mass fractions thereof, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0111] Comparative Example 9

[0112] As shown in Table 3, the mass fraction of graphene is set to 3 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0113] Comparative Example 10

[0114] As shown in Table 3, the mass fraction of titanium oxide is set to 4 parts, and the other material components and their mass fractions, and the steps included in the preparation method of the surface layer are consistent with those in Example 1.

[0115] Furthermore, the coatings prepared from the components of Examples 1 to 11 and Comparative Examples 1 to 10 were tested for porosity, bonding strength and coking rate, and the steps included (1) to (3).

[0116] (1) Porosity detection steps:

[0117] a. Sampling: Cut the coating specimen (10×10 mm), embed it with resin and polish it to a mirror finish;

[0118] b. Microscopic observation: Use a metallographic microscope (200× magnification) to photograph the coating cross section and randomly select five fields of view;

[0119] c. Image analysis: Calculate the pore area ratio using ImageJ software and take the average value.

[0120] Testing standard: Porosity = total pore area / total field area × 100%.

[0121] (2) Binding strength detection steps:

[0122] a. Sample preparation: Spray the coating onto a standard cylindrical substrate (Φ25mm) with a thickness of 200μm-300μm;

[0123] b. Adhesion test: Use epoxy resin to bond the coating sample to the substrate (ASTM C633 standard);

[0124] c. Tensile test: Use a universal material testing machine to stretch at a rate of 1 mm / min until the coating falls off. Record the maximum load: Bond strength = maximum load (N) / bonding area (mm²).

[0125] (3) Coking rate detection steps:

[0126] a. Simulated combustion: Burn Zhundong high-sodium coal (ash melting point 1200°C) in a one-dimensional flame furnace for 24 hours;

[0127] b. Coke layer measurement: After cooling, peel off the coke blocks and weigh the coke layer mass (coke layer mass / initial fly ash mass × 100%).

[0128] c. Surface analysis: SEM was used to observe the interface between the focal layer and the coating and evaluate the adhesion strength.

[0129] The performance data of each group in Examples 1 to 11 are shown in Table 4, and the performance data of each group in Comparative Examples 1 to 10 are shown in Table 5 below.

[0130] It can be seen from Tables 4 and 5 that in the anti-coking coatings of Examples 1 to 5, zirconium oxide (15 parts-20 parts) constructs a dense ceramic layer with stable porosity (less than 5%) and strong high temperature resistance. Graphene (5 parts-6 parts) and boron nitride (15 parts-20 parts) increase the contact angle to greater than 120°, significantly reduce the coking rate, and have strong anti-adhesion properties. Titanium oxide (5 parts-7 parts) radiates heat to suppress local overheating and has high thermal stability. Potassium silicate has good chemical stability and has good tolerance to chemical substances present in the boiler operating environment, such as some common alkaline substances and weakly acidic substances, thereby ensuring the stability of the bonding layer. The bonding structure formed after curing has a certain strength and hardness, which helps to maintain the connection between the surface coating and the substrate in the presence of material scouring, airflow impact, etc., and reduces the risk of coating shedding. Phenolic resin is used for bonding and is known for its excellent heat resistance and corrosion resistance. Phenolic resin can undergo further condensation reaction and solidify during the heating process. It performs excellently in some bonding applications under high-temperature environments. The material is firmly bonded to the metal backboard and can withstand high temperatures and large friction. Potassium silicate and phenolic resin do not require preliminary high-temperature heat treatment to achieve bonding. During the heating process of the furnace body, the active groups in the thermal curing agent molecules will react chemically with the cured substance in a certain stoichiometric ratio to form chemical bonds, continuously connecting and expanding the molecular chains and finally forming a three-dimensional network cross-linked structure, thereby significantly changing the physical and chemical properties of the material, achieving the purpose of curing and molding and improving performance. It can be cured as the furnace temperature rises to ensure bonding stability.

[0131] In Comparative Example 1, when the mass fraction of boron nitride is 25 parts, the porosity is 6.5% and the coking rate is 12%. This may be due to the deterioration of its fluidity during the coating formation process caused by excessive boron nitride. In Comparative Example 2, the mass fraction of zirconium oxide is 25 parts, the bonding strength is 42 MPa, and the coking rate is 18%. This may be due to the lattice instability caused by excessive zirconium oxide, thereby reducing the coating strength. The bonding strength in Comparative Example 3 is only 38 MPa, which may be due to the increase in the brittleness of the coating caused by excessive potassium silicate binder. In Comparative Example 4, the graphene leads to aggravated nano-agglomeration, decreased thermal conductivity, and increased coking rate. In Comparative Example 5, the excessive titanium oxide content leads to increased brittleness of the coating, and the coking rate (16%) also increases. The performance data in Comparative Examples 6 to 10 are also significantly inferior to those in the embodiments.

[0132] By comparing Examples 1-5 and Examples 6-8, it is not difficult to see that the use of high entropy alloy as the underlying material can further reduce the coking rate of the coating, which may be because the Al element migrates to the surface to form an Al2O3 nanosheet layer, which synergistically reduces the ash wettability with the surface layer BN and can improve the bonding strength of the coating. The multi-principal element alloy of the CoCrFeNiAl high entropy alloy forms a gradient interface with the surface ceramic, and the bonding is enhanced by the chemical bonding of Cr2O3 / ZrO2. The coating with the underlying material of the iron-based amorphous alloy has a lower porosity, mainly because the molten droplets solidify rapidly during the spraying of the amorphous alloy to form a dense structure, and the ultra-high-speed cooling inhibits the formation of grain boundary pores.

[0133] In summary, a comparative analysis of the data from the Examples and Comparative Examples reveals that coating performance is highly correlated with component optimization, structural design, and preparation process. In Examples 1-5, when the top layer contains a reasonable ratio of boron nitride (15-20 parts) to zirconium oxide (15-20 parts), the coating porosity remains stable at 4%-5%, the bonding strength reaches 22-28 MPa, and the coking rate is as low as 6%-10%. This demonstrates that the synergistic effect of boron nitride and zirconium oxide effectively improves compactness and anti-adhesion properties, while the lubricating effect of graphene (5-10 parts) further reduces ash wettability. In Comparative Examples 1-5, however, excessive boron nitride or zirconium oxide content (e.g., 25 parts boron nitride in Comparative Example 1 and 25 parts zirconium oxide in Comparative Example 2) results in an increase in porosity to 6.5%-7.2%, a decrease in bonding strength to 15-19 MPa, and an increase in coking rate to 12%-18%, indicating that the excess ceramic phase induces particle agglomeration, disrupting coating uniformity.

[0134] Further, according to the data of the examples and comparative examples, it can be known that optimization of the underlayer material significantly affects the coating service life and protection effect. In examples 6-8, high-entropy alloys (such as CoCrFeNiAl system) or amorphous alloys are used to replace traditional NiCrTi alloys, and the bonding strength is increased to 23-35 MPa, and the coking rate is further reduced to 5%-9%. This can be attributed to the multi-principal element structure of high-entropy alloys forming a gradient transition layer (such as Al2O3 nanosheet) at the interface through element diffusion, which together with the densification characteristics of amorphous alloys enhances the mechanical interlocking of the coating and the substrate. In comparative examples 6-10, when the content of the key components (such as boron nitride, graphene) of the surface layer is insufficient, the coking rate soars to 15%-24%, verifying the irreplaceability of each component in the composite coating formula of the present disclosure.

[0135] Further, according to the data of the examples and comparative examples, it can be known that the innovation of the preparation process greatly improves the coating performance. In examples 9-11, supersonic flame spraying combined with laser remelting reduces the porosity of the coating to 1.2%-2.9%, the bonding strength breaks through 52 MPa, and the coking rate is as low as 2.3%. This benefits from the rapid solidification of laser remelting to refine the grains (such as zirconia grain size <200 nm) and in-situ generation of amorphous / nanocrystalline composite structure. In contrast, traditional mechanical coating (comparative examples 4-5) lacks interface strengthening, and the bonding strength is less than 15 MPa, which shows that the patented process realizes the optimization of the "double barrier" protection mechanism through the synergy of physical embedding (microparticle filling pores) and chemical bonding (potassium silicate / phenolic resin high-temperature curing).

[0136] In summary, the present disclosure builds a dual anti-coking system by synergizing micro-nanoparticles, and the core mechanism is as follows: 1) physical barrier strengthening: the gradient structure is formed by the bottom layer of porous alloy (porosity 4-6%) and the surface layer of micro-nanoceramics (50-150 nm), and the dense layer (porosity <5%) is formed by zirconium oxide (15-20 parts) and silicon carbide (8-12 parts) nanoparticles through supersonic flame spraying (>2000 m / s), and the ash penetration path is lengthened by 83%; 2) chemical inertness blocking: boron nitride (15-20 parts) and graphene (5-10 parts) form a non-polar surface (contact angle >120°), and molybdenum disulfide (4-6 parts) and cerium oxide (2-3 parts) inhibit the interfacial diffusion reaction of Na / K in ash (XPS verifies that no new phase is generated); 3) dynamic lubrication compensation: the h-BN and graphene sheets in the surface layer slip along the shear direction at high temperature (800°C), and the friction coefficient is reduced from 0.35 to 0.12 (ASTM G99), combined with the infrared radiation strengthening (emissivity >0.92) of titanium oxide (5-7 parts), so that the stress in the coking layer breaks through the adhesion and self-peels. The data of the examples show that in the high-alkali coal combustion environment at 1200°C, the coking rate is stably <6% (the traditional coating is >22%), the bonding strength is maintained at 28 MPa after 100 thermal shock cycles, and the wear resistance is improved by 5 times (the wear width is <50 μm), which verifies the synergistic effect of the micro-nanomultiphase system in anti-coking, wear resistance and thermal shock resistance.

[0137] Table 1 Material components of the surface layer coating in Examples 1 to 5 and their mass parts

[0138]

[0139] Table 2 Coating thickness and data of each group of bottom layer coating materials in Examples 1 to 5

[0140]

[0141] Table 3 Material components of the surface layer in Comparative Examples 1 to 10 and their mass parts

[0142]

[0143] Table 4 Performance data of each group in Examples 1 to 11

[0144]

[0145] Table 5 Performance data of each group in Comparative Examples 1 to 10

[0146]

[0147] The present disclosure proposes a double-barrier self-lubricating anti-coking composite coating and a preparation method thereof, and has the following beneficial effects compared with the prior art:

[0148] First, the present invention discloses that all materials have good high temperature resistance, corrosion resistance, and easy access. The coating isolates the contact between the heating surface boiler tube and the flue gas, coal ash, etc. in the furnace, and plays the role of the first "physical barrier"; at the same time, all materials do not participate in the coking reaction and do not react chemically with the components in the furnace, which serves as the second barrier "chemical barrier"; the porous bottom coating provides a "bed" for the surface ceramic particles, and the micro-nano particles of the surface layer can be physically embedded in the pores of the bottom porous material, increasing the bonding force between the surface ceramic particles and the matrix, and extending the coating life; and the multi-element corrosion-resistant alloy plus ceramic material constitutes a microscopic composite material coating interface, and realizes the technical effect of 1+1 greater than 2. The potassium silicate and phenolic resin cooperate to realize self-solidification of the coating as the furnace temperature rises.

[0149] Second, the present disclosure eliminates the need for a heat treatment process after spraying, that is, the coating does not enter a heat treatment furnace after spraying, and achieves its own ceramicization or high-temperature curing under the heat of the furnace startup process, thereby enhancing on-site applicability.

[0150] It is understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Those skilled in the art may make various modifications and improvements without departing from the spirit and substance of the present disclosure, and such modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A double-barrier self-lubricating anti-coking composite coating, characterized in that: The composite coating comprises: A bottom layer, the bottom layer is a porous structure, and the bottom layer is formed of an alloy material; A surface layer, comprising a coating layer located on the bottom layer and an embedded layer embedded in the porous structure of the bottom layer, wherein the surface layer is formed of a micro-nano ceramic composite material; wherein the micro-nano ceramic composite material comprises: 15-20 parts of boron nitride; 5-10 parts of graphene; 15-20 parts of zirconium oxide; 8-12 parts of silicon carbide; 4-6 parts of chromium carbide; 5-7 parts of silicon nitride; 4-6 parts of molybdenum disulfide; 3-5 parts of yttrium oxide; 5-7 parts of titanium oxide; 2-3 parts of cerium oxide; 3-5 parts potassium silicate; 3-4 parts of phenolic resin; The composite coating is formed by the following method: mixing the micro-nano ceramic composite material to obtain a surface layer raw material; Pre-treating the boiler heating surface substrate, and spraying the alloy material onto the boiler heating surface substrate to form a bottom layer; The mixed surface layer raw materials are prepared on the bottom layer to form a surface layer on the bottom layer, and the surface layer is remelted to obtain a composite coating.

2. The double-barrier self-lubricating anti-coking composite coating according to claim 1, characterized in that: The particle size of the micro-nano ceramic composite material is 50-150 nm.

3. The double-barrier self-lubricating anti-coking composite coating according to claim 1, characterized in that: The alloy material includes any one of NiCrTi alloy, Inconel alloy, amorphous alloy, and high entropy alloy.

4. The double-barrier self-lubricating anti-coking composite coating according to claim 3, characterized in that: The amorphous alloy is any one of an iron-based amorphous alloy, a nickel-based amorphous alloy and a cobalt-based amorphous alloy.

5. The double-barrier self-lubricating anti-coking composite coating according to claim 3, characterized in that: The high entropy alloy is any one of CoCrFeNiAl, FeCoNiCrMo and AlCoCrFeNiTi.

6. The double-barrier self-lubricating anti-coking composite coating according to any one of claims 1 to 5, characterized in that: The thickness of the bottom layer is 0.2-0.4 mm; the thickness of the coating layer in the surface layer is 0.1-0.4 mm.

7. The double-barrier self-lubricating anti-coking composite coating according to claim 1, characterized in that: The alloy material is sprayed onto the boiler heating surface substrate by arc spraying, plasma spraying or flame spraying.

8. The double-barrier self-lubricating anti-coking composite coating according to claim 1, characterized in that: The mixed surface layer raw materials are prepared on the bottom layer by using cladding or mechanical coating.

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