Preparation method of electrophoretic deposition ceramic coating on surface of heat-resistant steel

Abstract

The invention relates to the field of advanced non-ferrous metal material high-heat-insulation coating protection, in particular to a preparation method of a heat-resistant steel surface electrophoretic deposition ceramic coating. Firstly, the heat-resistant steel part for the thermal generator set is subjected to oil removal and cleaning pretreatment, and oil stains and impurities on the surface are removed; then a composite suspension is prepared, acetonitrile serves as a solvent of the suspension, 4-acetaminobutyric acid serves as an additive, and the suspension contains YSZ powder and nano ruthenium dioxide powder; then the pretreated heat-resistant steel part is placed in the composite suspension, and a uniform ceramic coating precursor is formed on the surface of the heat-resistant steel part through an electrophoretic deposition technology; and then the part deposited with the precursor is put into a high-temperature furnace, sintering densification treatment is carried out under the inert gas protection atmosphere, and the thermal barrier coating is obtained. And finally, naturally cooling to room temperature in a protective atmosphere. The thermal barrier coating prepared through the method can effectively prevent temperature from being transmitted from outside to inside, the working temperature of a heat-resistant steel part base body is remarkably reduced, and the high-temperature stability and thermal shock resistance of the heat-resistant steel part base body are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of advanced non-ferrous metal material high heat insulation coating protection, specifically a method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface. It belongs to the key technology direction of strategic emerging industries and is applicable to the surface protection of heat-resistant steel components used in thermal power generating units. Background Technology

[0002] Currently, thermal power generating units remain one of the core pieces of equipment in global energy supply, and their energy conversion efficiency is directly related to energy utilization levels and low-carbon development goals. However, the heat-resistant steel used in key components of these units (such as superheater tubes, reheater tubes, and headers) is prone to oxidation, creep deformation, and corrosion failure under complex service environments such as high temperatures, corrosion, thermal shock, and alternating loads. This severely restricts the upgrading of generating units to higher steam parameters (high temperature and high pressure), thereby limiting the improvement of energy conversion efficiency. Practice has shown that preparing a high-performance thermal barrier coating on the surface of heat-resistant steel components can effectively block the conduction of high-temperature heat to the substrate, reduce the substrate's operating temperature, and resist the erosion of corrosive media in flue gas, significantly extending the service life of components. This provides key technical support for generating units to overcome existing operating parameter limitations, improve energy conversion efficiency, and reduce operation and maintenance costs, and is of great significance for promoting the efficient and low-carbon development of the thermal power generation industry.

[0003] Currently, the mature application of thermal barrier coating technology is mainly concentrated in the field of high-temperature blades for aero-engines. This field typically uses nickel-based superalloys as the substrate and employs techniques such as plasma spraying (APS) and electron beam physical vapor deposition (EB-PVD) to prepare yttrium-stabilized zirconia (YSZ)-based coatings to meet the requirements of aero-engines operating at extreme high temperatures above 1100℃. However, these technologies suffer from drawbacks such as huge equipment investment, complex processes, high production costs, and low coating preparation efficiency. Furthermore, they are difficult to adapt to the mass production needs of large straight pipes, curved pipes, and irregularly shaped structural components in thermal power generator sets, limiting their large-scale application in the civilian energy equipment sector. In contrast, electrophoretic deposition (EPD) technology, with its significant advantages such as simple equipment structure, convenient operation, fast coating deposition rate, low production cost, strong adaptability to substrate shape (enabling uniform coating preparation on complex curved surfaces), and easy control of coating composition, has become the preferred technology path for the low-cost, large-scale preparation of thermal barrier coatings. Extending electrophoretic thermal barrier coating technology from nickel-based superalloy substrates to heat-resistant steel substrates for thermal power generating units not only fully leverages the process economy and scalability advantages of electrophoretic deposition technology, but also addresses the performance shortcomings of heat-resistant steel in high-temperature service, achieving synergy between "low-cost preparation and high-performance service." At the same time, it is suitable for engineering application scenarios in the thermal power generation industry and has broad prospects for industrial promotion.

[0004] Although the technical approach of preparing thermal barrier coatings by electrophoretic deposition has been disclosed in relevant research and patents, its existing technical solutions still have many shortcomings that urgently need to be addressed, and cannot meet the stringent requirements of heat-resistant steel used in thermal power generating units. For example, patent CN101805126A proposes a thermal barrier coating on a steel substrate surface and its preparation method, which adopts a composite structure of a glass adhesive layer and a rare earth zirconate ceramic surface layer. The solvents used are ethanol and acetylacetone, resulting in insufficient uniformity of powder dispersion. Furthermore, it requires the additional preparation of a glass adhesive layer and multiple heat treatment steps, making the process complex. Its ceramic surface layer is a single rare earth zirconate, and its thermal insulation and thermal shock resistance performance are insufficiently coordinated, making it unable to meet the long-term high-temperature service requirements under thermal power generation conditions. Patent CN105525867A discloses a screw drill rotor coated with a ceramic coating and its manufacturing method. The solvent used is chloroform, and the additives are CH3COONa or CH3COOK, etc. The suspension has poor stability and is prone to powder agglomeration. It is designed for the wear resistance requirements of drilling environments, not the high-temperature oxidation and thermal shock conditions of thermal power generation, and cannot meet the stability requirements for long-term service at 700–900℃. Patent CN104790013A discloses a method for preparing a sintering-resistant thermal barrier ceramic coating structure. The substrate is a high-temperature alloy FeCralloy, and the solvent is a mixture of ethanol and deionized water. The dispersion effect is limited, and the ceramic powder is a composite of YSZ and Fe2O3, with insufficient optimization of heat insulation and thermal shock resistance. The process requires additional preparation of a phase inversion coating and two-step sintering, making the process complex, and the sintering temperature is as high as 1150–1200℃, which affects the substrate properties. Patent CN120925045A discloses a method for preparing a diffusion bonding layer at the interface between a nickel-based alloy and a YSZ ceramic coating. The substrate is a nickel-based alloy, the solvent is anhydrous ethanol, and the additive is acetylacetone. However, this method offers limited improvement in suspension stability and interfacial bonding. The ceramic powder is a mixture of YSZ with cerium oxide, ytterbium oxide, etc., and requires a pressureless plasma discharge sintering step, resulting in a complex process, high production costs, and difficulty in meeting the mass production needs of thermal power generating units. Patent CN114232055A discloses a method for forming a YSZ composite coating on the surface of a nickel-based alloy substrate. The substrate is a nickel-based alloy, the solvent is a mixture of anhydrous ethanol and acetylacetone, and the additive is ammonium polyacrylate. This method fails to balance powder dispersibility and interfacial bonding. The ceramic powder is a composite of YSZ and alumina, resulting in insufficient thermal insulation and high-temperature stability. Furthermore, the sintering temperature is 1100–1250℃, which easily leads to a decline in substrate performance. The electrophoresis uses an anodic deposition mode, making it difficult to guarantee the coating's density.Reference: Huang Zhirong et al., Study on oxidation behavior of aluminized HK40 steel with surface electrodeposition-sintering Y2O3 film, Chinese Journal of Corrosion and Protection, 2003, 23(2):124-128, disclosed a method for preparing Y2O3 film on the surface of aluminized HK40 steel. The ceramic layer is composed of a single Y2O3 component, which has limited thermal insulation performance and structural stability. The solvent is an organic solution containing yttrium salt, which has insufficient uniformity of powder dispersion. In addition, repeated electrodeposition-sintering steps are required, resulting in low process efficiency and thin coating thickness, which cannot meet the thick coating protection requirements of heat-resistant steel components of thermal power generator sets.

[0005] Furthermore, existing technologies mostly focus on the basic preparation process of coatings, without fully considering the harsh environment under thermal power generation conditions such as high-temperature oxidation, sulfur / vanadium corrosion, and long-term thermal cycling. The high-temperature stability (long-term service at 700-900℃) and corrosion resistance of the prepared coatings are insufficient, and the service life is usually no more than 5000 hours, far below the maintenance cycle requirements of thermal power generating units. At the same time, some technologies have problems such as excessively high sintering temperatures (above 1200℃) leading to degradation of substrate properties and narrow process windows that are difficult to control industrially.

[0006] In summary, existing electrophoretic deposition techniques for preparing thermal barrier coatings have significant shortcomings in terms of coating structure design, interfacial bonding enhancement, service performance adaptation, and process stability. Specifically, these shortcomings include poor solvent dispersibility, easy powder agglomeration, the inability of additives to balance deposition efficiency and interfacial bonding, insufficient performance synergy due to the single ceramic composition, complex processes and excessively high sintering temperatures, and insufficient coating adhesion and thermal shock resistance. These shortcomings fail to fully meet the requirements of heat-resistant steel for thermal power generating units for high thermal insulation, high adhesion, long service life, and corrosion resistance thermal barrier coatings. Therefore, there is an urgent need to develop a targeted preparation method. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a ceramic coating by electrophoretic deposition on the surface of heat-resistant steel, which prepares a thermal barrier coating that effectively blocks temperature transfer. When applied to the surface of heat-resistant steel components for thermal power generator sets, it can improve the service life of heat-resistant steel components and solve the problems of oxidation peeling, creep deformation, and corrosion failure that easily occur in heat-resistant steel under complex service environments such as high temperature, corrosion, thermal shock and alternating loads.

[0008] The technical solution of this invention is: A method for preparing an electrophoretic deposition ceramic coating on a heat-resistant steel surface includes the following steps: The first step involves pre-treating the P91 heat-resistant steel plate by progressively polishing the surface with sandpaper ranging from 240 grit to 1000 grit. After polishing, the steel plate is immersed in anhydrous ethanol and ultrasonically cleaned for 10–15 minutes to remove residual contaminants. Then, it is ultrasonically cleaned in a fume hood with acetone solution for 3–10 minutes to thoroughly remove grease contaminants from the steel plate surface. Next, the surface of the P91 heat-resistant steel plate is rinsed with coarse anhydrous ethanol and dried to remove acetone residue. Finally, the P91 heat-resistant steel plate is immersed in a 10% (v / v) HCl aqueous solution for 5–15 minutes to remove the surface oxide film and activate the surface. After rinsing thoroughly with deionized water, it is dried for later use. The second step is to prepare a suspension, which includes the following components: 5-40 g / L ceramic powder, 0.2-2 g / L elemental iodine, 0.01-1 g / L additives, and acetonitrile as the solvent. The ceramic powder is a mixture of 5%-20% by mass of nano-oxide powder and the remaining yttrium-stabilized zirconium oxide powder. The nano-oxide is nano-ruthenium dioxide, and the additive is 4-acetaminophen. After magnetic stirring for 1-3 hours, the suspension is used within a temperature range of 40℃-80℃. The third step is to prepare the electrophoretic deposition ceramic layer. P91 heat-resistant steel plate is used as the cathode and graphite plate is used as the anode. Electrophoretic deposition is carried out in the suspension. During the electrophoretic deposition process, the distance between the two plates is 10-20 mm, the deposition voltage is 30-120 V, and the deposition time is 30-120 s. After being thoroughly rinsed with deionized water, the plates are dried for later use. The fourth step is the sintering of the electrophoretic deposited ceramic layer. The part after electrophoretic deposition is placed in a heat treatment furnace with a high-purity Ar protective atmosphere. The temperature is raised to 900-1100°C at a rate of 5-10°C / min in the high-purity Ar protective atmosphere with a flow rate of 2-4 L / min, and then held for 60-300 min. The part is then cooled to room temperature in the furnace under a continuous high-purity Ar protective atmosphere.

[0009] In the second step of the method for preparing the electrophoretic deposition ceramic coating on the surface of heat-resistant steel, the doping amount of yttrium oxide in the yttrium oxide-stabilized zirconium oxide is 5wt% to 8wt%.

[0010] In the second step of the method for preparing the electrophoretic deposition ceramic coating on the surface of heat-resistant steel, the mass fraction of nano-ruthenium dioxide in the ceramic powder is 10-15%.

[0011] In the second step of the method for preparing the electrophoretic deposition ceramic coating on the surface of heat-resistant steel, the 4-acetaminophen content in the suspension is 0.05–0.8 g / L.

[0012] In the third step of the method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface, a ceramic layer with a thickness of 90-150 μm is obtained on the surface of a P91 heat-resistant steel plate by adjusting the electrophoretic deposition parameters.

[0013] In the fourth step of the method for preparing the electrophoretic deposition ceramic coating on the surface of heat-resistant steel, the volume purity of the high-purity Ar protective atmosphere is ≥99.99%.

[0014] The design concept of this invention is: Existing heat-resistant steels, when operating under high-temperature, thermal shock, and complex corrosion conditions, are prone to rapid heat conduction leading to increased substrate temperature, which in turn causes oxidation loss, creep deformation, and performance degradation, limiting their application in high-parameter equipment. This invention addresses the material characteristics of P91 heat-resistant steel and the harsh operating environment of thermal power generation by proposing a method for preparing an electrophoretic deposition ceramic coating on the surface of heat-resistant steel. YSZ (yttrium-stabilized zirconium oxide) is used as the coating matrix, combined with nano-oxide powder (nano-ruthenium dioxide) for doping modification, utilizing the synergistic effect of the two to improve thermal insulation and structural stability. Acetonitrile is selected as the solvent to ensure uniform dispersion of YSZ and nano-ruthenium dioxide, solving the problem of poor dispersibility in traditional solvents. 4-Acetaminobutyric acid (4-Acetoaminobutyric acid) is used as an additive to balance deposition efficiency and interfacial bonding. Elemental iodine can act as a conductive medium to adjust the conductivity of the suspension, ensuring uniform particle migration during electrophoretic deposition. Composite ceramic powder is uniformly deposited on the surface of heat-resistant steel using electrophoretic deposition technology, and then the coating is densified by high-temperature sintering. By optimizing the electrophoretic deposition and sintering process parameters, the coating densification can be achieved without additional adhesive layers or complex processing steps.

[0015] This design leverages the excellent intrinsic thermal insulation properties of YSZ and the synergistic effect of nano-ruthenium dioxide to create a thermal barrier coating that effectively prevents heat transfer from the outside to the inside, significantly reducing the actual operating temperature of the heat-resistant steel substrate. Simultaneously, it enhances the coating's high-temperature stability, thermal shock resistance, and adhesion to the substrate, thereby comprehensively improving the performance of the heat-resistant steel and expanding its application scenarios in higher-temperature and more demanding conditions. Overall, this invention achieves a significant improvement in the high-temperature protection performance of heat-resistant steel through innovative coating system design and process adaptation, while also considering the controllability and practicality of the preparation process. Therefore, this invention, through its innovative coating composition design and electrophoretic deposition-high-temperature sintering process combination, effectively solves the problem of insufficient high-temperature service performance of traditional heat-resistant steel, providing a highly efficient and reliable surface protection solution for heat-resistant steel.

[0016] Compared with the prior art, the present invention has the following advantages: (1) This invention innovatively uses acetonitrile as a suspension solvent. Compared with traditional water-based or alcohol-based solvents, acetonitrile has stronger chemical stability and powder solubility, which can enable YSZ powder and nano-ruthenium dioxide powder to form a uniformly dispersed and stable system, avoiding powder agglomeration during the deposition process. At the same time, acetonitrile has a mild evaporation rate, which can form a uniform thickness, pinhole-free and crack-free wet film during electrophoretic deposition, providing a good foundation for the subsequent high-temperature sintering to prepare a dense coating, and solving the problems of poor dispersibility of traditional solvents and easy generation of pore defects in coatings.

[0017] (2) In this invention, 4-acetaminobutyric acid is selected as a suspension additive. The amide group and carboxyl group in its molecular structure can synergistically regulate the zeta potential of the suspension, enhance the charge stability of the powder particles, and improve the electrophoretic deposition rate and coating uniformity. At the same time, the additive can form a thin layer of highly active adsorption layer on the surface of heat-resistant steel substrate, improve the interfacial compatibility between ceramic powder and substrate, significantly enhance the bonding force between coating and substrate, and overcome the defect of traditional additives that are difficult to balance deposition efficiency and interfacial bonding strength.

[0018] (3) This invention innovatively introduces nano-ruthenium dioxide powder into the ceramic layer composition. Compared with single YSZ coating, nano-ruthenium dioxide has excellent thermal stability and low thermal conductivity, and can form a synergistic heat insulation effect with YSZ, further reducing the overall thermal conductivity rate of the coating and improving the heat barrier effect. At the same time, nano-ruthenium dioxide particles can act as grain refiners, inhibiting the growth of YSZ grains during high-temperature sintering, reducing stress concentration inside the coating, enhancing the thermal shock resistance and structural stability of the coating, and solving the problems of easy aging and rapid decay of heat insulation performance of traditional single YSZ coating at high temperature.

[0019] (4) The present invention is designed for P91 heat-resistant steel. It does not require additional preparation of glass bonding layer, phase transformation coating, or complex steps such as hydrogen flame cladding or pressureless plasma discharge sintering. Its process is simple. The sintering temperature is controlled at 900-1100℃, which avoids the degradation of the matrix performance, is easy to industrialize, and meets the mass production needs of thermal power generator set components.

[0020] The advantages and beneficial effects of this invention are: 1. This invention uses acetonitrile as the suspension solvent, which effectively improves the dispersion uniformity of YSZ and nano ruthenium dioxide powder and the stability of the suspension, ensuring consistent coating thickness and dense structure, thus laying the material foundation for high-performance coating.

[0021] 2. The present invention uses 4-acetaminophen as a suspension additive, which not only improves the efficiency and uniformity of electrophoretic deposition, but also strengthens the interfacial bonding between the ceramic coating and the heat-resistant steel substrate, thus preventing the coating from peeling off during high-temperature thermal shock or long-term service.

[0022] 3. This invention achieves synergistic optimization of coating thermal insulation performance, high-temperature stability and thermal shock resistance through composite doping design of nano-ruthenium dioxide powder and YSZ powder, which can significantly reduce the working temperature of heat-resistant steel substrate and comprehensively improve its high-temperature service performance.

[0023] 4. The method for preparing a ceramic coating by electrophoretic deposition on the surface of heat-resistant steel described in this invention effectively improves the high-temperature protection capability and performance of heat-resistant steel through innovative solvent selection, additive matching and coating composition design, overcomes the shortcomings of the prior art, and provides an efficient and reliable technical solution for the application of heat-resistant steel in high-parameter equipment, which has important industrial application value.

[0024] 5. After preparing the ceramic coating using this invention, the adhesion between the coating and the P91 substrate is tested using an automatic scratch tester and is ≥40N. According to the ASTM-D3359-09 standard test method for measuring adhesion by tape method, the coating adhesion reaches level 5B. In the thermal shock resistance test, after being kept at 700℃ for 20 minutes and then cooled to room temperature by water, the number of cycles is ≥300, and the coating does not peel off or crack. Attached Figure Description

[0025] Figure 1 The image shows the morphology of the cross-section of the electroceramic coating on the heat-resistant steel surface in Example 1.

[0026] Figure 2 The image shows the morphology of the cross-section of the electroceramic coating on the heat-resistant steel surface in Example 2.

[0027] Figure 3 The image shows the morphology of the cross-section of the electroceramic coating on the heat-resistant steel surface in Example 3.

[0028] Figure 4 The image shows the morphology of the cross-section of the electroceramic coating on the heat-resistant steel surface in Example 4. Detailed Implementation

[0029] In its specific implementation, this invention proposes a method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface. The specific process is as follows: First, the heat-resistant steel components for thermal power generator sets are subjected to degreasing and cleaning pretreatment to remove surface oil and impurities. Then, a composite suspension is prepared, which uses acetonitrile as a solvent, 4-acetaminophen as an additive, and contains YSZ (yttrium-stabilized zirconium oxide) powder and nano-ruthenium dioxide powder, with an average particle size of 40-70 nm. Next, the pretreated heat-resistant steel components are placed in the composite suspension, and a uniform ceramic coating precursor is formed on its surface by electrophoretic deposition technology. Then, the components with the deposited precursor are placed in a high-temperature furnace and sintered and densified under an inert gas protective atmosphere to obtain a thermal barrier coating. Finally, the components are naturally cooled to room temperature in a protective atmosphere.

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] In this embodiment, a method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface includes the following steps: The first step is to pre-treat the P91 heat-resistant steel plate by progressively grinding the surface with sandpaper ranging from coarse to fine (240 mesh → 400 mesh → 600 mesh → 800 mesh → 1000 mesh) to remove surface oxide scale and impurities, ensuring that Ra is within the range of 0.8–1.6 μm. The ground steel plate is then immersed in anhydrous ethanol and ultrasonically cleaned for 10 minutes to remove residual contaminants. Next, it is ultrasonically cleaned in acetone solution for 5 minutes in a fume hood to thoroughly remove grease contaminants from the steel plate surface. Afterward, the surface of the P91 heat-resistant steel plate is rinsed with a large amount of anhydrous ethanol and dried to remove acetone residue. Finally, the P91 heat-resistant steel plate is immersed in a 10% (v / v) HCl aqueous solution for 15 minutes to remove the surface oxide film and activate the surface. It is then thoroughly rinsed with deionized water and dried for later use.

[0033] The second step involves preparing a suspension comprising the following components: 5 g / L ceramic powder, 1.5 g / L elemental iodine, and 0.01 g / L additives, with acetonitrile as the solvent. The ceramic powder primarily consists of 5% YSZ powder with an average particle size of 40 nm, and 10% by mass of nano-oxide powder with an average particle size of 50 nm. The nano-oxide is ruthenium dioxide, and the additive is 4-acetaminophen. The suspension is magnetically stirred for 3 hours and then used at 40°C to maintain its stability.

[0034] The third step involves preparing the electrophoretic deposition ceramic layer. A P91 heat-resistant steel plate is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension. During the electrophoretic deposition process, the distance between the two plates is 10 mm, the deposition voltage is 60 V, and the deposition time is 40 s. The sample is thoroughly rinsed with deionized water and then dried for later use.

[0035] The fourth step is the sintering of the ceramic layer. The sample after electrophoretic deposition is placed in a heat treatment furnace with a protective atmosphere of high-purity Ar (volume purity 99.995%). The temperature is raised to 900°C at a rate of 10°C / min in the high-purity Ar protective atmosphere at a flow rate of 2L / min, and held for 60min. The sample is then cooled to room temperature in the furnace in the high-purity Ar protective atmosphere.

[0036] like Figure 1As shown in the cross-sectional morphology of the ceramic coating on the heat-resistant steel surface in Example 1, the coating exhibits a clear double-layer structure. The bottom layer is a P91 heat-resistant steel substrate, providing a good foundation for mechanical properties; a dense ceramic layer, approximately 99 μm thick, covers this substrate, with ruthenium dioxide particles uniformly distributed within the YSZ, resulting in a dense coating structure. This ceramic layer is primarily composed of YSZ with a yttrium oxide doping mass fraction of 5%, and contains ruthenium dioxide particles with a mass fraction of 10%. The cross-sectional view shows that the ruthenium dioxide particles are uniformly distributed within the YSZ, and the ceramic coating becomes denser after high-temperature sintering. This ruthenium dioxide YSZ composite ceramic coating achieves synergistic optimization of the coating's thermal insulation performance, high-temperature stability, and thermal shock resistance, significantly reducing the operating temperature of the heat-resistant steel substrate and comprehensively improving its high-temperature service performance.

[0037] In this embodiment, after preparing the ceramic coating using the present invention, the adhesion between the coating and the P91 substrate was tested using an automatic scratch tester and found to be 44N. According to the ASTM-D3359-09 standard test method for adhesion measurement, the coating adhesion was rated as 5B. In the thermal shock resistance test, after cycling at 700°C for 20 minutes and then water-cooled to room temperature, the coating began to peel and crack after 320 cycles.

[0038] Example 2

[0039] In this embodiment, a method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface includes the following steps: The first step involves pre-treating the P91 heat-resistant steel plate. The surface is progressively polished using sandpaper ranging from coarse to fine (240 mesh → 400 mesh → 600 mesh → 800 mesh → 1000 mesh) to remove oxide scale and impurities, ensuring an Ra value within the range of 0.8–1.6 μm. The polished steel plate is then immersed in anhydrous ethanol and ultrasonically cleaned for 12 minutes to remove residual contaminants. Next, it is ultrasonically cleaned in acetone solution for 3 minutes in a fume hood to thoroughly remove grease contaminants from the steel plate surface. Afterward, the surface of the P91 heat-resistant steel plate is rinsed with a large amount of anhydrous ethanol and dried to remove any acetone residue. Finally, the P91 heat-resistant steel plate is immersed in a 10% (v / v) HCl aqueous solution for 12 minutes to remove the surface oxide film and activate the surface. The plate is then thoroughly rinsed with deionized water and dried for later use.

[0040] The second step involves preparing a suspension comprising the following components: 15 g / L ceramic powder, 2 g / L elemental iodine, and 0.8 g / L additives. The suspension solvent is acetonitrile. The ceramic powder primarily consists of 6% YSZ powder with an average particle size of 50 nm, and 15% by mass of nano-oxide powder with an average particle size of 60 nm. The nano-oxide is ruthenium dioxide, and the additive is 4-acetaminophen. The suspension is magnetically stirred for 1 hour and then used at 55°C to maintain its stability.

[0041] The third step involves preparing the electrophoretic deposition ceramic layer. A P91 heat-resistant steel plate is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension. During the electrophoretic deposition process, the distance between the two plates is 14 mm, the deposition voltage is 30 V, and the deposition time is 30 s. The sample is thoroughly rinsed with deionized water and then dried for later use.

[0042] The fourth step is the sintering of the ceramic layer. The sample after electrophoretic deposition is placed in a heat treatment furnace with a protective atmosphere of high-purity Ar (volume purity 99.995%). The temperature is raised to 1000℃ at a rate of 5℃ / min in the high-purity Ar protective atmosphere at a flow rate of 2.5L / min, and then held for 300min. The sample is then cooled to room temperature in the furnace in the high-purity Ar protective atmosphere.

[0043] like Figure 2 As shown in the cross-sectional morphology of the ceramic coating on the heat-resistant steel surface in Example 2, the coating exhibits a clear double-layer structure. The bottom layer is a P91 heat-resistant steel substrate, providing a good foundation for mechanical properties; a dense ceramic layer, approximately 93 μm thick, covers this substrate, with ruthenium dioxide particles uniformly dispersed and tightly bonded to the substrate. This ceramic layer is primarily composed of YSZ doped with 6% yttrium oxide, and contains 15% ruthenium dioxide particles. The cross-sectional view shows that the ruthenium dioxide particles are uniformly distributed within the YSZ, and the ceramic coating is densified after high-temperature sintering. This ruthenium dioxide YSZ composite ceramic coating achieves synergistic optimization of the coating's thermal insulation performance, high-temperature stability, and thermal shock resistance, significantly reducing the operating temperature of the heat-resistant steel substrate and comprehensively improving its high-temperature service performance.

[0044] In this embodiment, after preparing the ceramic coating using the present invention, the adhesion between the coating and the P91 substrate was tested using an automatic scratch tester and found to be 40N. According to the ASTM-D3359-09 standard test method for adhesion measurement, the coating adhesion was rated as 5B. In the thermal shock resistance test, after cycling at 700°C for 20 minutes and then water-cooled to room temperature, the coating began to peel and crack after 331 cycles.

[0045] Example 3

[0046] In this embodiment, a method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface includes the following steps: The first step involves pre-treating the P91 heat-resistant steel plate. The surface is progressively polished using sandpaper ranging from coarse to fine (240 mesh → 400 mesh → 600 mesh → 800 mesh → 1000 mesh) to remove oxide scale and impurities, ensuring an Ra value within the range of 0.8–1.6 μm. The polished steel plate is then immersed in anhydrous ethanol and ultrasonically cleaned for 13 minutes to remove residual contaminants. Next, it is ultrasonically cleaned in acetone solution for 10 minutes in a fume hood to thoroughly remove grease contaminants from the steel plate surface. Afterward, the surface of the P91 heat-resistant steel plate is rinsed with a large amount of anhydrous ethanol and dried to remove any acetone residue. Finally, the P91 heat-resistant steel plate is immersed in a 10% (v / v) HCl aqueous solution for 5 minutes to remove the surface oxide film and activate the surface. The plate is then thoroughly rinsed with deionized water and dried for later use.

[0047] The second step involves preparing a suspension comprising the following components: 25 g / L ceramic powder, 1 g / L elemental iodine, 0.3 g / L additives, and acetonitrile as the solvent. The ceramic powder primarily consists of 7% YSZ powder with an average particle size of 60 nm, and 5% by mass of nano-oxide powder with an average particle size of 70 nm. The nano-oxide is ruthenium dioxide, and the additive is 4-acetaminophen. The suspension is magnetically stirred for 1.5 h and then used at 65°C to maintain its stability.

[0048] The third step involves preparing the electrophoretic deposition ceramic layer. A P91 heat-resistant steel plate is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension. During the electrophoretic deposition process, the distance between the two plates is 20 mm, the deposition voltage is 90 V, and the deposition time is 50 s. The sample is thoroughly rinsed with deionized water and then dried for later use.

[0049] The fourth step is the sintering of the ceramic layer. The sample after electrophoretic deposition is placed in a heat treatment furnace with a protective atmosphere of high-purity Ar (volume purity 99.995%). The temperature is raised to 1050°C at a rate of 7°C / min in the high-purity Ar protective atmosphere at a flow rate of 4L / min, and held for 150min. The sample is then cooled to room temperature in the furnace in the high-purity Ar protective atmosphere.

[0050] like Figure 3As shown in the cross-sectional morphology of the ceramic coating on the heat-resistant steel surface in Example 3, the coating exhibits a clear double-layer structure. The bottom layer is a P91 heat-resistant steel substrate, providing a good foundation for mechanical properties; a dense ceramic layer, approximately 106 μm thick, covers this substrate with a clear cross-sectional structure and no obvious porosity defects. This ceramic layer is mainly composed of YSZ with a yttrium oxide doping mass fraction of 7%, and contains ruthenium dioxide particles with a mass fraction of 5%. The cross-sectional image shows that the ruthenium dioxide particles are uniformly distributed within the YSZ, and the ceramic coating is densified after high-temperature sintering. This composite ceramic coating of ruthenium dioxide and YSZ achieves synergistic optimization of the coating's thermal insulation performance, high-temperature stability, and thermal shock resistance, significantly reducing the operating temperature of the heat-resistant steel substrate and comprehensively improving its high-temperature service performance.

[0051] In this embodiment, after preparing the ceramic coating using the present invention, the adhesion between the coating and the P91 substrate was tested using an automatic scratch tester and found to be 48N. According to the ASTM-D3359-09 standard test method for adhesion measurement, the coating adhesion was rated as 5B. In the thermal shock resistance test, after cycling at 700°C for 20 minutes and then water-cooled to room temperature, the coating began to peel and crack after 315 cycles.

[0052] Example 4

[0053] In this embodiment, a method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface includes the following steps: The first step involves pre-treating the P91 heat-resistant steel plate. The surface is progressively polished using sandpaper ranging from coarse to fine (240 mesh → 400 mesh → 600 mesh → 800 mesh → 1000 mesh) to remove oxide scale and impurities, ensuring an Ra value within the range of 0.8–1.6 μm. The polished steel plate is then immersed in anhydrous ethanol and ultrasonically cleaned for 15 minutes to remove residual contaminants. Next, it is ultrasonically cleaned in acetone solution for 8 minutes in a fume hood to thoroughly remove grease contaminants from the steel plate surface. Afterward, the surface of the P91 heat-resistant steel plate is rinsed with a large amount of anhydrous ethanol and dried to remove any acetone residue. Finally, the P91 heat-resistant steel plate is immersed in a 10% (v / v) HCl aqueous solution for 8 minutes to remove the surface oxide film and activate the surface. The plate is then thoroughly rinsed with deionized water and dried for later use.

[0054] The second step involves preparing a suspension comprising the following components: 40 g / L ceramic powder, 0.2 g / L elemental iodine, 1 g / L additive, and acetonitrile as the solvent. The ceramic powder primarily consists of 8% YSZ powder with an average particle size of 70 nm, and 20% by mass of nano-oxide powder with an average particle size of 40 nm. The nano-oxide is ruthenium dioxide, and the additive is 4-acetaminophen. The suspension is magnetically stirred for 2.5 h and then used at 80°C to maintain its stability.

[0055] The third step involves preparing the electrophoretic deposition ceramic layer. A P91 heat-resistant steel plate is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension. During the electrophoretic deposition process, the distance between the two plates is 18 mm, the deposition voltage is 120 V, and the deposition time is 120 s. The sample is thoroughly rinsed with deionized water and then dried for later use.

[0056] The fourth step is the sintering of the ceramic layer. The sample after electrophoretic deposition is placed in a heat treatment furnace with a protective atmosphere of high-purity Ar (volume purity 99.995%). The temperature is raised to 1100℃ at a heating rate of 8℃ / min in the high-purity Ar protective atmosphere at a flow rate of 3.5L / min, and then held for 210min. The sample is then cooled to room temperature in the furnace in the high-purity Ar protective atmosphere.

[0057] like Figure 4 As shown in the cross-sectional morphology of the ceramic coating on the heat-resistant steel surface in Example 4, the coating exhibits a clear double-layer structure. The bottom layer is a P91 heat-resistant steel substrate, providing a good foundation for mechanical properties; a dense ceramic layer, approximately 144 μm thick, is then applied over it, exhibiting good density and strong bonding with the substrate interface. This ceramic layer is primarily composed of YSZ doped with 8% yttrium oxide, with 20% ruthenium dioxide particles doped internally. The cross-sectional view shows that the ruthenium dioxide particles are uniformly distributed within the YSZ, and the ceramic coating is densified after high-temperature sintering. This ruthenium dioxide-YSZ composite ceramic coating achieves synergistic optimization of the coating's thermal insulation performance, high-temperature stability, and thermal shock resistance, significantly reducing the operating temperature of the heat-resistant steel substrate and comprehensively improving its high-temperature service performance.

[0058] In this embodiment, after preparing the ceramic coating using the present invention, the adhesion between the coating and the P91 substrate was tested using an automatic scratch tester and found to be 52N. According to the ASTM-D3359-09 standard test method for adhesion measurement, the coating adhesion was rated as 5B. In the thermal shock resistance test, after cycling at 700°C for 20 minutes and then water-cooled to room temperature, the coating began to peel and crack after 300 cycles.

[0059] The results show that the use of acetonitrile as a suspension solvent in this invention effectively improves the dispersion uniformity and suspension stability of YSZ and nano-ruthenium dioxide powder. The use of 4-acetaminophen as a suspension additive strengthens the interfacial bonding between the ceramic coating and the heat-resistant steel substrate. Through the composite doping design of nano-ruthenium dioxide powder and YSZ powder, the synergistic optimization of the coating's thermal insulation performance, high-temperature stability, and thermal shock resistance is achieved. This significantly reduces the operating temperature of the heat-resistant steel substrate, greatly improves its high-temperature stability and thermal shock resistance, comprehensively improves its high-temperature service performance, and thus extends the service life of heat-resistant steel components used in thermal power generator sets.

Claims

1. A method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface, characterized in that, Includes the following steps: The first step involves pre-treating the P91 heat-resistant steel plate by progressively polishing the surface with sandpaper ranging from 240 grit to 1000 grit. After polishing, the steel plate is immersed in anhydrous ethanol and ultrasonically cleaned for 10–15 minutes to remove residual contaminants. Then, it is ultrasonically cleaned in a fume hood with acetone solution for 3–10 minutes to thoroughly remove grease contaminants from the steel plate surface. Next, the surface of the P91 heat-resistant steel plate is rinsed with coarse anhydrous ethanol and dried to remove acetone residue. Finally, the P91 heat-resistant steel plate is immersed in a 10% (v / v) HCl aqueous solution for 5–15 minutes to remove the surface oxide film and activate the surface. After rinsing thoroughly with deionized water, it is dried for later use. The second step is to prepare a suspension, which includes the following components: 5-40 g / L ceramic powder, 0.2-2 g / L elemental iodine, 0.01-1 g / L additives, and acetonitrile as the solvent. The ceramic powder is a mixture of 5%-20% by mass of nano-oxide powder and the remaining yttrium-stabilized zirconium oxide powder. The nano-oxide is nano-ruthenium dioxide, and the additive is 4-acetaminophen. After magnetic stirring for 1-3 hours, the suspension is used within a temperature range of 40℃-80℃. The third step is to prepare the electrophoretic deposition ceramic layer. P91 heat-resistant steel plate is used as the cathode and graphite plate is used as the anode. Electrophoretic deposition is carried out in the suspension. During the electrophoretic deposition process, the distance between the two plates is 10-20 mm, the deposition voltage is 30-120 V, and the deposition time is 30-120 s. After being thoroughly rinsed with deionized water, the plates are dried for later use. The fourth step is the sintering of the electrophoretic deposited ceramic layer. The part after electrophoretic deposition is placed in a heat treatment furnace with a high-purity Ar protective atmosphere. The temperature is raised to 900-1100°C at a rate of 5-10°C / min in the high-purity Ar protective atmosphere with a flow rate of 2-4 L / min, and then held for 60-300 min. The part is then cooled to room temperature in the furnace under a continuous high-purity Ar protective atmosphere.

2. The method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface according to claim 1, characterized in that, In the second step, yttrium oxide stabilizes the yttrium oxide doping content in zirconium oxide at 5wt% to 8wt%.

3. The method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface according to claim 1, characterized in that, In the second step, the mass fraction of nano-ruthenium dioxide in the ceramic powder is 10-15%.

4. The method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface according to claim 1, characterized in that, In the second step, the concentration of 4-acetaminophen in the suspension is 0.05–0.8 g / L.

5. The method for preparing an electrophoretic deposition ceramic coating on a heat-resistant steel surface according to claim 1, characterized in that, In the third step, a ceramic layer with a thickness of 90 to 150 μm is obtained on the surface of P91 heat-resistant steel plate by adjusting the electrophoretic deposition parameters.

6. The method for preparing a ceramic coating by electrophoretic deposition on a heat-resistant steel surface according to claim 1, characterized in that, In the fourth step, the volume purity of the high-purity Ar protective atmosphere is ≥99.99%.

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