Method for preparing metal-ceramic composite coating through electrophoretic deposition

Abstract

The invention relates to the field of advanced non-ferrous metal material high-heat-insulation coating protection, in particular to a method for preparing a metal-ceramic composite coating through electrophoretic deposition. Firstly, the heat-resistant steel part for the thermal generator set is subjected to oil removal and cleaning pretreatment, and surface oil stains and oxidation impurities are removed; then nickel-based electroplating liquid containing iridium chloride and antimony chloride is prepared, the pretreated heat-resistant steel part is subjected to electro-deposition, and a nickel-iridium-antimony composite metal bonding layer is formed on the surface of the heat-resistant steel part; then preparing a ceramic suspension which takes gamma-butyrolactone as a solvent and contains YSZ and nano ruthenium dioxide powder, and putting the part with the metal bonding layer into the suspension for electrophoretic deposition to form a ceramic coating precursor; then, the part is placed in a high-temperature furnace protected by inert gas to be sintered, and interface fusion and coating densification of the metal bonding layer and the ceramic layer are achieved; and finally, the metal-ceramic composite coating is naturally cooled to the room temperature in the protective atmosphere, and the obtained metal-ceramic composite coating has the high interface bonding force and the excellent heat insulation performance.

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 metal-ceramic composite coatings by electrophoretic deposition, belonging to the core technology category of strategic emerging industries, and applicable to the surface protection of heat-resistant steel components for thermal power generating units. Background Technology

[0002] Currently, thermal power generation serves as a pillar of my country's energy supply system, and its efficient and low-carbon transformation is a key path to achieving the "dual carbon" goal. The energy conversion efficiency and operational reliability of generator units depend primarily on the service performance of key heat-resistant steel components (such as superheater tubes, reheater tubes, and high-temperature headers). However, under complex operating conditions of high temperature (600–900℃), high pressure, flue gas corrosion, and alternating thermal shock, heat-resistant steel commonly faces failure problems such as oxidation loss, creep cracking, and corrosion perforation. This not only shortens component replacement cycles and increases maintenance costs but also becomes a core bottleneck restricting the upgrading of generator units to ultra-supercritical high-parameter systems. Metal-ceramic composite coatings, with the excellent high-temperature resistance, corrosion resistance, and thermal insulation properties of the ceramic phase, combined with the good toughness and substrate bonding ability of the metal phase, can achieve the dual functions of "thermal insulation and protection - structural reinforcement." This effectively reduces the operating temperature of the heat-resistant steel substrate and resists erosion from harsh environments, which is of great practical significance for extending component service life and improving generator unit operating parameters and energy conversion efficiency. It is a key material support for promoting technological upgrading in the thermal power generation industry.

[0003] Currently, the mature application of high-performance composite coating technology is mainly concentrated in the aerospace field, especially for the protection of high-temperature blades in aero-engines. This field primarily uses nickel-based superalloys as the substrate and employs techniques such as plasma spraying (APS), high-speed flame spraying (HVOF), or electron beam physical vapor deposition (EB-PVD) to prepare coatings suitable for extreme service environments exceeding 1100℃. However, these technologies suffer from drawbacks such as high equipment investment, complex process control, high coating preparation costs, and low efficiency in large-scale production. Furthermore, they have poor adaptability to large straight pipes, bends, and irregularly shaped components in thermal power generating units, making it difficult to meet the engineering application requirements of civilian energy equipment. In contrast, electrophoretic deposition (EPD) technology offers significant advantages such as simple equipment structure, convenient operation, fast deposition rate, low production cost, uniform and controllable coating thickness, and strong adaptability to substrate shape. It can achieve batch coating preparation for complex structural components and is an ideal technological path for low-cost, large-scale production of metal-ceramic composite coatings. Extending the electrophoretic deposition technology for preparing metal-ceramic composite coatings from nickel-based superalloy substrates to heat-resistant steel substrates for thermal power generating units not only fully leverages the process economy and engineering adaptability of electrophoretic deposition technology, but also specifically compensates for the performance shortcomings of single heat-resistant steel, achieving a synergy of "low-cost preparation and high-performance protection". This lays the foundation for the large-scale application of thermal barrier coatings in the field of civilian high-temperature equipment, with broad application prospects.

[0004] Although the technology for preparing composite coatings by electrophoretic deposition has been published in relevant research and patents, existing technical solutions still have many key defects and cannot meet the stringent service requirements of heat-resistant steel used in thermal power generating units. For example, patent CN106086998A proposes an electrophoretic deposition-laser cladding composite processing method for titanium porcelain dentures. The substrate is dental pure titanium and titanium alloy, and the purpose is denture protection. This method requires secondary processing by laser cladding to ensure the coating adhesion. The process is complex and costly. The coating is a porcelain powder system and does not have high temperature resistance or thermal shock resistance. It cannot adapt to high temperature conditions of 600-900℃, and it cannot resist flue gas corrosion and alternating thermal shock. The patent with publication number CN113430621A proposes a method for preparing a water-lubricated ceramic composite coating. The substrate is copper or stainless steel, and the application is wear-resistant protection in a water-lubricated environment. The coating system is a composite coating of silicon nitride and nickel. The solvent is anhydrous ethanol. The coating needs to be deposited by electrophoresis and then filled by electroplating. The adhesion between the coating and the substrate depends on the embedding effect of nickel. The coating has extremely poor high-temperature stability and cannot withstand the high-temperature conditions of thermal power generation. It is also difficult to meet the high-temperature protection requirements of heat-resistant steel. The patent with publication number CN102732936A proposes a method for preparing a silicon oxide ceramic coating on steel parts by electrophoretic deposition. The intermediate transition layer is an electroplated dark nickel, composite nickel, or phosphating layer, which is prone to oxidation and failure at high temperatures and cannot form a stable interface buffering effect. The ceramic layer uses silicon oxide sol, which has poor powder dispersion uniformity and high coating porosity. Moreover, the thermal insulation and thermal shock resistance of single silicon oxide ceramics are limited and cannot meet the service requirements of heat-resistant steel under alternating thermal shock. At the same time, its calcination process may lead to grain growth and mechanical property degradation of the heat-resistant steel matrix. Patent CN108588796A discloses a ceramic coating containing dispersed precious metal particles and its preparation process. The substrate is a titanium-based alloy, and the purpose is to improve the high-temperature oxidation resistance of the titanium-based alloy. The coating system consists of silicon dioxide dispersed with precious metal particles such as gold and platinum. The bonding strength between the coating and the substrate depends on the chemical bonding between silicon dioxide and the titanium-based alloy, which is not stable enough. Furthermore, its solvent system is a mixture of anhydrous ethanol and saturated potassium chloride solution, which has poor suspension stability and the powder is prone to agglomeration. The coating structure is simple and cannot cope with the creep and alternating thermal shock of heat-resistant steel at high temperatures, making it unsuitable for the complex operating conditions of thermal power generation. Patent CN1312402A discloses a method for preparing metal / bioglass ceramic gradient coatings using electrophoretic co-deposition-sintering. The substrate is a metal such as titanium alloy, and the application is in the field of biomaterials. The coating system is a gradient coating of bioglass (BG) and hydroxyapatite (HA). It requires high-temperature sintering treatment, has poor high-temperature stability, and cannot withstand high-temperature corrosion conditions of 600-900℃. The bonding strength between the coating and the substrate is only above 20MPa, which is far below the requirements for heat-resistant steel used in thermal power generation. Moreover, the sintering process is complex, and the efficiency of large-scale production is low, which cannot meet the needs of mass production of large straight pipes, bends, and irregularly shaped structural components in thermal power generating units.

[0005] In addition, existing technologies mostly focus on the basic preparation process of coatings, which are not fully adapted to the long-term high-temperature oxidation, sulfur and vanadium corrosion and alternating thermal shock environment under the working conditions of thermal power generation. The high-temperature stability of the prepared coatings is insufficient, and the long-term service life above 700°C is usually no more than 4,000 hours, which is far lower than the maintenance cycle of generator sets. At the same time, some technologies have problems such as narrow process windows, difficulty in parameter control, and poor industrial replicability, making it difficult to meet the needs of mass production.

[0006] In summary, existing electrophoretic deposition techniques for preparing metal-ceramic composite coatings have significant shortcomings in terms of phase interface design, substrate compatibility, service performance adaptation, and process stability. They cannot fully meet the requirements of heat-resistant steel for thermal power generating units for composite coatings with high adhesion, long service life, corrosion resistance, and high toughness. 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 metal-ceramic composite coating by electrophoretic deposition, 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 provide a protective solution with both high heat resistance and toughness for components in high-temperature service. It can effectively solve the failure problems of heat-resistant steel under high temperature, high pressure, flue gas corrosion and alternating thermal shock conditions, such as oxidation loss, creep cracking and corrosion perforation.

[0008] The technical solution of this invention is: A method for preparing a metal-ceramic composite coating by electrophoretic deposition includes the following steps: The first step involves pre-treating the P91 heat-resistant steel plate by progressively polishing its surface with sandpaper ranging from 240 grit to 1000 grit. After polishing, the 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 5–15 minutes to thoroughly remove grease contaminants. Next, the surface is rinsed with anhydrous ethanol and dried to remove any acetone residue. Finally, the 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 involves preparing a metal bonding layer. A pretreated P91 heat-resistant steel plate is used as the cathode, and a graphite plate as the anode. The plate is placed in an electroplating solution for electrochemical deposition. The electroplating solution comprises the following components: nickel chloride 15–30 g / L, iridium chloride 5–10 g / L, antimony chloride 1–5 g / L, ethylenediaminetetraacetic acid 30–60 g / L, sodium citrate 20–40 g / L, citric acid 80–160 g / L, boric acid 25–50 g / L, saccharin 0.5–2 g / L, potassium chloride 10–20 g / L, and water as the solvent. The pH is adjusted to 2.0–4.0 using a 30% NaOH aqueous solution. During electrochemical deposition, the two electrodes are kept parallel, and the deposition current density is controlled at 1–3 A / dm² at 20–40°C. The deposition time is 30–60 min. After thorough rinsing with deionized water, the plate is dried for later use. The third step involves preparing an electrophoretic ceramic layer. A component with a metal bonding layer is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension containing the following components: 5–40 g / L ceramic powder, 0.2–2 g / L elemental iodine, 0.1–0.2 g / L polyvinyl alcohol, and γ-butyrolactone as the solvent. The ceramic powder is a mixture of 5%–20% by mass of nano-ruthenium dioxide powder and the remaining yttrium oxide-stabilized zirconium oxide powder. During electrophoretic deposition, 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. The plates are thoroughly rinsed with deionized water and then dried for later use. The fourth step is to place the electrophoretically deposited part into a heat treatment furnace with a high-purity Ar protective atmosphere. The part is heated to 900-1100°C at a heating 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 at that temperature 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 method for preparing metal-ceramic composite coatings by electrophoretic deposition, in the second step, the concentration of iridium chloride is 7-8 g / L and the concentration of antimony chloride is 2-4 g / L.

[0010] In the second step of the method for preparing metal-ceramic composite coating by electrophoretic deposition, a metal bonding layer with a thickness of 5 to 20 μm is formed on the surface of P91 heat-resistant steel plate.

[0011] In the method for preparing metal-ceramic composite coatings by electrophoretic deposition, in the third step, the amount of yttrium oxide doping in the yttrium oxide-stabilized zirconium oxide is 5wt% to 8wt%.

[0012] In the method for preparing metal-ceramic composite coatings by electrophoretic deposition, in the third step, the mass fraction of nano-ruthenium dioxide in the ceramic powder is 10-15%.

[0013] In the third step of the method for preparing a metal-ceramic composite coating by electrophoretic deposition, a ceramic layer with a thickness of 80–110 μm is obtained on the surface of the metal bonding layer.

[0014] The design concept of this invention is: When existing heat-resistant steels are used under high-temperature, alternating thermal shock, and corrosive conditions, traditional metal-ceramic composite coatings often suffer from the dual defects of "weak interfacial bonding" and "insufficient thermal insulation and thermal shock resistance." Single ceramic coatings are prone to peeling from the substrate, while conventional metal bonding layers (such as pure nickel and nickel-chromium alloys) are easily oxidized and fail at high temperatures, leading to rapid heat conduction to the substrate, causing creep deformation and oxidation loss, thus limiting the application of heat-resistant steel in high-parameter equipment. This invention proposes a method for preparing metal-ceramic composite coatings by electrophoretic deposition. First, a metal bonding layer (mainly nickel, containing small amounts of iridium and antimony) is constructed on the surface of the heat-resistant steel using an electrodeposition process. Then, a ceramic coating mainly composed of YSZ (yttrium-stabilized zirconium oxide) and supplemented with nano-ruthenium dioxide powder is prepared on the surface of the bonding layer using electrophoretic deposition technology. Finally, high-temperature sintering is used to achieve coating densification and enhanced interfacial bonding. The metal bonding layer acts as a "transition buffer layer," improving the interfacial compatibility between the ceramic coating and the heat-resistant steel substrate while resisting high-temperature oxidation. The composite ceramic layer, relying on the excellent thermal insulation properties of YSZ and the synergistic modification effect of nano-ruthenium dioxide, effectively hinders heat transfer from the outside to the inside, significantly reducing the actual operating temperature of the heat-resistant steel substrate. The overall solution, through the synergistic design of the "bonding layer-ceramic layer," simultaneously addresses the problems of poor adhesion and rapid degradation of thermal insulation performance in traditional composite coatings, comprehensively improving the high-temperature service performance and service life of heat-resistant steel while considering process controllability and industrial adaptability. Therefore, this invention provides an efficient solution for high-performance surface protection of heat-resistant steel through innovative coating structure design, component optimization, and process combination.

[0015] This invention prepares a ceramic layer by electrophoretic deposition in a suspension comprising ceramic powder, elemental iodine, polyvinyl alcohol, and γ-butyrolactone. The ceramic powder consists of yttrium-stabilized zirconia (YSZ) powder and nano-ruthenium dioxide powder. YSZ itself possesses excellent thermal insulation and high-temperature stability, while nano-ruthenium dioxide reduces the thermal conductivity of the coating and inhibits YSZ grain growth; the two work synergistically to enhance the coating's thermal insulation and thermal shock resistance. Elemental iodine undergoes slight dissociation in the γ-butyrolactone solvent and adsorbs onto the surfaces of YSZ and nano-ruthenium dioxide powder, giving the originally uncharged or weakly charged ceramic particles a stable surface charge. Polyvinyl alcohol adsorbs onto the surface of the ceramic powder, ensuring dispersion and adhesion, further improving the stability of the suspension. Compared to traditional solvents such as water, alcohols, or acetonitrile, γ-butyrolactone is highly polar and chemically stable, effectively dissolving elemental iodine and being compatible with polyvinyl alcohol, while also providing excellent wetting of the YSZ and nano-ruthenium dioxide powder.

[0016] This invention involves the electrochemical deposition of a metal bonding layer in an electroplating solution. The electroplating solution comprises main salts (nickel chloride, iridium chloride, antimony chloride), complexing agents (ethylenediaminetetraacetic acid, sodium citrate, citric acid), buffers (boric acid), additives (saccharin), and conductive salts (potassium chloride). Nickel chloride provides the core component of the plating layer, nickel ions (Ni...). 2+ ) is the main body of the metal bonding layer, ensuring the basic toughness of the bonding layer; iridium chloride provides iridium ions (Ir) 3+ Antimony chloride, as a functional dopant, can refine nickel grains, improve the high-temperature stability and creep resistance of the binder layer, prevent oxidation and peeling of the binder layer at high temperatures, and enhance the interfacial compatibility between the binder layer and the ceramic layer; antimony chloride provides antimony ions (Sb). 3+ EDTA forms a solid solution with nickel, strengthening the bidirectional interfacial bonding strength between the adhesive layer and the heat-resistant steel substrate, and between the adhesive layer and the ceramic coating. EDTA reacts with nickel chloride, iridium chloride, and antimony chloride in the electroplating solution to form Ni... 2+ Ir 3+ Sb 3+ Ions form complexes, preventing premature precipitation of metal ions and ensuring long-term stability of the electroplating solution. Sodium citrate and EDTA work synergistically to further enhance the stability of the complex system, strengthen the hydrolysis resistance of the complex, and prevent turbidity in the plating solution. Citric acid has both complexing and pH buffering functions, forming weak complexes with metal ions to prevent defects such as porosity and cracks in the plating layer caused by excessively rapid local deposition. The metal ions provided by nickel chloride, iridium chloride, and antimony chloride form a multi-component complex system with EDTA, sodium citrate, and citric acid, ensuring that the three ions are reduced and deposited synchronously and uniformly, avoiding the enrichment of single elements. Boric acid prevents the precipitation of metal hydroxides caused by an increase in the pH value of the plating solution, ensuring the stability of the complex system and controllable deposition process. Saccharin adsorbs on the cathode surface, inhibiting excessive growth of nickel grains, refining the grain structure, and reducing internal porosity and defects in the plating layer; it also reduces the surface tension of the plating layer, making the plating layer uniform and smooth, providing a good interface foundation for subsequent ceramic layer deposition. Potassium chloride (K) + and Cl - Increasing the ion concentration in the plating solution improves its conductivity, allowing the current to be evenly distributed on the cathode surface, reducing the hydrogen evolution reaction at the cathode, and preventing cracks in the plating layer due to hydrogen embrittlement.

[0017] Compared with the prior art, the present invention has the following advantages: (1) The present invention innovatively designs a nickel-iridium-antimony composite metal adhesive layer as a nickel-based composite system (containing a small amount of iridium and antimony elements). The composition is controlled by adding iridium chloride and antimony chloride to the electroplating solution. Compared with traditional pure nickel or nickel-chromium adhesive layers, iridium can refine nickel grains, improve the high-temperature stability and creep resistance of the adhesive layer, and prevent the adhesive layer from oxidizing and peeling off at high temperatures. Antimony can form a solid solution with nickel, enhance the bidirectional interfacial bonding strength between the adhesive layer and the heat-resistant steel substrate, and between the adhesive layer and the ceramic coating, and solve the defect of "weak unidirectional bonding" in traditional adhesive layers. At the same time, iridium chloride and antimony chloride have good solubility and uniform dispersion in the electroplating solution, and the amount of iridium and antimony added can be precisely controlled (mass fraction 0.5% to 2%), avoiding the instability of coating performance caused by composition fluctuations, and overcoming the problems of difficult composition control and easy failure at high temperatures in existing adhesive layers.

[0018] (2) In this invention, γ-butyrolactone is selected as the suspension solvent for electrophoretic deposition of ceramic coating. Compared with traditional water-based solvents (which are prone to powder agglomeration), alcohol solvents (which evaporate too quickly and easily produce pinholes in the coating) or acetonitrile solvents (which have limited solubility for some nanoparticles), γ-butyrolactone has stronger polarity and chemical stability, which can enable YSZ powder and nano ruthenium dioxide powder to form a uniformly dispersed and stable suspension system (the suspension does not show obvious sedimentation after standing for 48 hours); at the same time, its evaporation rate is mild (boiling point 204℃), which can form a uniform thickness and crack-free wet film during electrophoretic deposition, laying the foundation for the subsequent high-temperature sintering to prepare a dense ceramic layer, and solving the problems of poor dispersibility and easy formation of pore defects in coatings by traditional solvents.

[0019] (3) This invention innovatively introduces nano-ruthenium dioxide powder into the ceramic layer. Compared with a single YSZ ceramic layer, nano-ruthenium dioxide not only has a lower thermal conductivity and can form a "synergistic thermal insulation effect" with YSZ, further reducing the overall thermal conductivity rate of the coating; it can also act as a "grain growth inhibitor" during high-temperature sintering, inhibiting excessive growth of YSZ grains, reducing stress concentration inside the coating, and significantly improving the thermal shock resistance of the ceramic layer. At the same time, nano-ruthenium dioxide has good compatibility with the nickel-based bonding layer, which can avoid the formation of harmful phases at the interface between the ceramic layer and the bonding layer, solving the problem of rapid thermal insulation performance decay and easy stress cracking of traditional single YSZ coatings at high temperatures.

[0020] The advantages and beneficial effects of this invention are: 1. This invention constructs a nickel-iridium-antimony composite bonding layer by adding iridium chloride and antimony chloride to the electroplating solution. This not only improves the high-temperature stability and oxidation resistance of the bonding layer, but also strengthens the interfacial bonding strength between the coating and the substrate and within the coating, effectively preventing the composite coating from peeling off during high-temperature service.

[0021] 2. This invention uses γ-butyrolactone as the suspension solvent, which significantly improves the dispersion uniformity of YSZ and nano ruthenium dioxide powder and the stability of the suspension, ensuring that the ceramic coating has a consistent thickness and a dense structure, providing structural protection for the high thermal insulation performance of the coating, while simplifying the preparation and storage process of the suspension.

[0022] 3. This invention achieves synergistic optimization of the coating's thermal insulation and thermal shock resistance performance by doping and modifying the YSZ ceramic layer with nano-ruthenium dioxide powder. This can further reduce the working temperature of the heat-resistant steel substrate (by 30°C to 50°C more than that of a single YSZ coating) and delay the oxidation and creep damage of the substrate.

[0023] 4. The method for preparing metal-ceramic composite coatings by electrophoretic deposition as described in this invention solves the problems of poor adhesion and insufficient thermal insulation performance of traditional composite coatings through the synergistic design of the "adhesive layer-ceramic layer" and multi-dimensional composition and process innovation. It significantly improves the high-temperature performance of heat-resistant steel, has strong process controllability, and is suitable for industrial mass production. It provides reliable technical support for the application of heat-resistant steel in high-parameter thermal power generation, aerospace and other fields, and 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 ≥50N. 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 ≥350, and the coating does not peel off or crack. Attached Figure Description

[0025] Figure 1 The image shows the morphology of the metal-ceramic composite coating on the heat-resistant steel surface in Example 1.

[0026] Figure 2 The image shows the morphology of the metal-ceramic composite coating on the heat-resistant steel surface in Example 2.

[0027] Figure 3 The image shows the morphology of the metal-ceramic composite coating on the heat-resistant steel surface in Example 3.

[0028] Figure 4 The image shows the morphology of the metal-ceramic composite 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 metal-ceramic composite coating by electrophoretic deposition. The specific process is as follows: First, the heat-resistant steel components of the thermal power generator set are degreased and cleaned to remove surface oil and oxide impurities. Then, a nickel-based electroplating solution containing iridium chloride and antimony chloride is prepared, and the pretreated heat-resistant steel components are placed in it for electrodeposition to form a nickel-iridium-antimony composite metal bonding layer on its surface. Next, a ceramic suspension containing YSZ (yttrium-stabilized zirconium oxide) powder and nano-ruthenium dioxide powder is prepared using γ-butyrolactone as a solvent. The average particle size of the powder is 40-60 nm. The components with the metal bonding layer are placed in the suspension for electrophoretic deposition to form a ceramic coating precursor. Then, the components are placed in a high-temperature furnace under inert gas protection for sintering to achieve interfacial fusion between the metal bonding layer and the ceramic layer and to densify the 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 metal-ceramic composite coating by electrophoretic deposition includes the following steps: The first step involves pre-treating the P91 heat-resistant steel plate by progressively polishing its surface with sandpaper ranging from coarse to fine (240 mesh → 400 mesh → 600 mesh → 800 mesh → 1000 mesh). The polished steel plate is then immersed in anhydrous ethanol and ultrasonically cleaned for 10 minutes to remove residual contaminants. Next, it is ultrasonically cleaned in a fume hood with acetone solution for 15 minutes to thoroughly remove grease contaminants from the steel plate surface. Afterward, the surface of the P91 heat-resistant steel plate is rinsed with coarse 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.

[0033] The second step involves preparing the metal bonding layer. A pre-treated steel plate is used as the cathode, and a graphite plate as the anode. The plate is placed in an electroplating solution for electrochemical deposition. The electroplating solution comprises the following components: nickel chloride 20 g / L; iridium chloride 7 g / L; antimony chloride 2 g / L; ethylenediaminetetraacetic acid (EDTA) 40 g / L; sodium citrate 20 g / L; citric acid 110 g / L; boric acid 32 g / L; saccharin 0.5 g / L; potassium chloride 12 g / L; and water as the solvent. The pH is adjusted to 2.5 using a 30% (w / w) NaOH aqueous solution. During electrochemical deposition, the two electrodes are kept parallel, and the deposition current density is controlled at 1.5 A / dm² at 20°C for 50 min. The sample is thoroughly rinsed with deionized water and dried for later use, forming a 20 μm thick metal bonding layer on the surface of the P91 heat-resistant steel plate.

[0034] The third step involves preparing the electrophoretic deposition ceramic layer. The sample with the attached metal binder layer is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension containing the following components: 5 g / L ceramic powder, 1.5 g / L elemental iodine, 0.13 g / L polyvinyl alcohol, and γ-butyrolactone as the solvent. The ceramic powder consists of 6% YSZ powder with an average particle size of 40 nm and 15% ruthenium dioxide nanoparticles with an average particle size of 50 nm. During electrophoretic deposition, the distance between the two electrodes is 14 mm, the deposition voltage is 60 V, and the deposition time is 90 s. The sample is thoroughly rinsed with deionized water and dried for later use, resulting in a 100 μm thick ceramic layer on the surface of the metal binder layer.

[0035] The fourth step involves placing the electrophoretically deposited sample into a heat treatment furnace with a protective atmosphere of high-purity Ar (99.995% volume purity). The temperature is raised to 1000°C at a rate of 10°C / min in the high-purity Ar protective atmosphere at a flow rate of 4L / min, and then held for 300min. The sample is then cooled to room temperature in the furnace under a continuous protective atmosphere.

[0036] like Figure 1As shown in the image, the surface morphology of the metal-ceramic composite coating on the heat-resistant steel surface in Example 1 reveals a uniform and dense coating surface, with no cracks or peeling observed. In the backscattered electron microscope (SEM) image mode, the light-colored area represents the ceramic matrix formed after sintering 6% YSZ powder, exhibiting a continuous distribution, as indicated by the white arrow in the image. The dark-colored area represents the state after sintering nano-ruthenium dioxide powder mixed with 6% yttrium oxide-doped YSZ powder, exhibiting a fine and uniform distribution, as indicated by the black arrow in the image. Pure YSZ powder, after sintering, forms a ceramic coating with high porosity, while the nano-ruthenium dioxide powder, after doping and sintering, fills these gaps, making the coating more dense. The metal-ceramic composite coating prepared in Example 1 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 coating adhesion scratch tester and found to be 61N. According to the ASTM-D3359-09 standard test method for adhesion measurement, the coating adhesion reached level 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 353 cycles.

[0038] Example 2

[0039] In this embodiment, a method for preparing a metal-ceramic composite coating by electrophoretic deposition includes the following steps: The first step is to pre-treat the P91 heat-resistant steel plate by progressively polishing the surface with sandpaper ranging from coarse to fine (240 mesh → 400 mesh → 600 mesh → 800 mesh → 1000 mesh). After polishing, the steel plate is immersed in anhydrous ethanol and ultrasonically cleaned for 12 minutes to remove residual contaminants. Then, it is ultrasonically cleaned in a fume hood with acetone solution for 5 minutes to thoroughly remove grease contaminants from the steel plate surface. Next, 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 8 minutes to remove the surface oxide film and activate the surface. After rinsing thoroughly with deionized water, it is dried for later use.

[0040] The second step involves preparing the metal bonding layer. A pre-treated steel plate is used as the cathode, and a graphite plate as the anode. The plate is placed in an electroplating solution for electrochemical deposition. The electroplating solution comprises the following components: nickel chloride 15 g / L; iridium chloride 5 g / L; antimony chloride 3 g / L; ethylenediaminetetraacetic acid (EDTA) 30 g / L; sodium citrate 27 g / L; citric acid 130 g / L; boric acid 43 g / L; saccharin 2 g / L; potassium chloride 16 g / L; and water as the solvent. The pH is adjusted to 2 using a 30% (w / w) NaOH aqueous solution. During the electrochemical deposition process, the two electrodes are kept parallel, and the deposition current density is controlled at 2.7 A / dm² at 25°C for a deposition time of 40 min. The sample is thoroughly rinsed with deionized water and dried for later use, forming a 10 μm thick metal bonding layer on the surface of the P91 heat-resistant steel plate.

[0041] The third step involves preparing the electrophoretic deposition ceramic layer. The sample with the attached metal binder layer is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension containing the following components: 25 g / L ceramic powder, 1 g / L elemental iodine, 0.1 g / L polyvinyl alcohol, and γ-butyrolactone as the solvent. The ceramic powder consists of 5% YSZ powder with an average particle size of 50 nm and 10% ruthenium dioxide nanoparticles with an average particle size of 60 nm. During electrophoretic deposition, the distance between the two plates is 20 mm, the deposition voltage is 30 V, and the deposition time is 120 s. The sample is thoroughly rinsed with deionized water and dried for later use, resulting in a 110 μm thick ceramic layer on the surface of the metal binder layer.

[0042] The fourth step involves placing the electrophoretically deposited sample into a heat treatment furnace with a protective atmosphere of high-purity Ar (99.995% volume purity). The temperature is raised to 1050°C at a rate of 5°C / min in the high-purity Ar protective atmosphere at a flow rate of 3.5 L / min, and then held for 220 min. The sample is then cooled to room temperature in the furnace under a continuous protective atmosphere.

[0043] like Figure 2 As shown in the image, the surface morphology of the metal-ceramic composite coating on the heat-resistant steel surface in Example 2 reveals a uniform and dense coating surface, with no cracks or peeling observed. In the backscattered electron microscope (SEM) image mode, the light-colored areas represent the ceramic matrix formed after sintering 5% YSZ powder, exhibiting a continuous distribution, as indicated by the white arrows in the image. The dark-colored areas represent the state after sintering of nano-ruthenium dioxide powder mixed with 5% yttrium oxide-doped YSZ powder, exhibiting a fine and uniform distribution, as indicated by the black arrows in the image. Pure YSZ powder, after sintering, forms a ceramic coating with high porosity, while the nano-ruthenium dioxide powder, after doping and sintering, fills these gaps, making the coating more dense. The metal-ceramic composite coating prepared in Example 2 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 coating adhesion scratch tester and found to be 56N. According to the ASTM-D3359-09 standard test method for adhesion measurement, the coating adhesion reached level 5B. In the thermal shock resistance test, after cycling at 700℃ for 20 minutes and then water-cooled to room temperature, the coating began to peel and crack after 350 cycles.

[0045] Example 3

[0046] In this embodiment, a method for preparing a metal-ceramic composite coating by electrophoretic deposition includes the following steps: The first step is to pre-treat the P91 heat-resistant steel plate by progressively polishing the surface with sandpaper ranging from coarse to fine (240 mesh → 400 mesh → 600 mesh → 800 mesh → 1000 mesh). After polishing, the steel plate is immersed in anhydrous ethanol and ultrasonically cleaned for 13 minutes to remove residual contaminants. Then, it is ultrasonically cleaned in a fume hood with acetone solution for 8 minutes to thoroughly remove grease contaminants from the steel plate surface. Next, 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. After rinsing thoroughly with deionized water, it is dried for later use.

[0047] The second step involves preparing the metal bonding layer. A pre-treated steel plate is used as the cathode, and a graphite plate as the anode. The plates are placed in an electroplating solution for electrochemical deposition. The electroplating solution comprises the following components: nickel chloride 30 g / L; iridium chloride 8 g / L; antimony chloride 1 g / L; ethylenediaminetetraacetic acid (EDTA) 60 g / L; sodium citrate 34 g / L; citric acid 160 g / L; boric acid 50 g / L; saccharin 1.2 g / L; potassium chloride 10 g / L; and water as the solvent. The pH is adjusted to 3.5 using a 30% (w / w) NaOH aqueous solution. During electrochemical deposition, the two electrodes are kept parallel, and the deposition current density is controlled at 30°C for 30 min. The sample is thoroughly rinsed with deionized water and dried for later use, forming a 5 μm thick metal bonding layer on the surface of the P91 heat-resistant steel plate.

[0048] The third step involves preparing the electrophoretic deposition ceramic layer. The sample with the attached metal binder layer is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension containing the following components: 40 g / L ceramic powder, 2 g / L elemental iodine, 0.2 g / L polyvinyl alcohol, and γ-butyrolactone as the solvent. The ceramic powder consists of 8% YSZ powder with an average particle size of 60 nm and 20% ruthenium dioxide nanoparticles with an average particle size of 50 nm. During electrophoretic deposition, the distance between the two electrodes is 10 mm, the deposition voltage is 120 V, and the deposition time is 30 s. The sample is thoroughly rinsed with deionized water and dried for later use, resulting in a ceramic layer with a thickness of 80 μm on the surface of the metal binder layer.

[0049] The fourth step involves placing the electrophoretically deposited sample into a heat treatment furnace with a protective atmosphere of high-purity Ar (99.995% volume purity). The temperature is raised to 900°C at a rate of 7°C / min in the high-purity Ar protective atmosphere at a flow rate of 2.5 L / min, and then held at that temperature for 180 min. The sample is then cooled to room temperature in the furnace under a continuous protective atmosphere.

[0050] like Figure 3 As shown in the image, the surface morphology of the metal-ceramic composite coating on the heat-resistant steel surface in Example 3 reveals a uniform and dense coating surface, with no cracks or peeling observed. In the backscattered electron microscope (SEM) image mode, the light-colored area represents the ceramic matrix formed after sintering 8% YSZ powder, exhibiting a continuous distribution, as indicated by the white arrow in the image. The dark-colored area represents the state after sintering of nano-ruthenium dioxide powder mixed with 8% yttrium oxide-doped YSZ powder, exhibiting a fine and uniform distribution, as indicated by the black arrow in the image. Pure YSZ powder, after sintering, forms a ceramic coating with high porosity, while the nano-ruthenium dioxide powder, after doping and sintering, fills these gaps, making the coating more dense. The metal-ceramic composite coating prepared in Example 3 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 50N. According to the ASTM-D3359-09 standard test method for adhesion measurement, the coating adhesion reached level 5B. In the thermal shock resistance test, after cycling at 700℃ for 20 minutes and then water-cooled to room temperature, the coating began to peel and crack after 360 cycles.

[0052] Example 4

[0053] In this embodiment, a method for preparing a metal-ceramic composite coating by electrophoretic deposition includes the following steps: The first step is to pre-treat the P91 heat-resistant steel plate by progressively polishing the surface with sandpaper ranging from coarse to fine (240 mesh → 400 mesh → 600 mesh → 800 mesh → 1000 mesh). After polishing, the steel plate is immersed in anhydrous ethanol and ultrasonically cleaned for 15 minutes to remove residual contaminants. Then, it is ultrasonically cleaned in a fume hood with acetone solution for 12 minutes to thoroughly remove grease contaminants from the steel plate surface. Next, 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 5 minutes to remove the surface oxide film and activate the surface. After rinsing thoroughly with deionized water, it is dried for later use.

[0054] The second step involves preparing the metal bonding layer. A pre-treated steel plate is used as the cathode, and a graphite plate as the anode. The plate is placed in an electroplating solution for electrochemical deposition. The electroplating solution comprises the following components: nickel chloride 25 g / L; iridium chloride 10 g / L; antimony chloride 5 g / L; ethylenediaminetetraacetic acid (EDTA) 50 g / L; sodium citrate 40 g / L; citric acid 80 g / L; boric acid 25 g / L; saccharin 1.7 g / L; potassium chloride 20 g / L; and water as the solvent. The pH is adjusted to 4 using a 30% (w / w) NaOH aqueous solution. During the electrochemical deposition process, the two electrodes are kept parallel, and the deposition current density is controlled at 1 A / dm² at 40°C for 60 min. The sample is thoroughly rinsed with deionized water and dried for later use, forming a 15 μm thick metal bonding layer on the surface of the P91 heat-resistant steel plate.

[0055] The third step involves preparing the electrophoretic deposition ceramic layer. The sample with the attached metal binder layer is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension containing the following components: 15 g / L ceramic powder, 0.2 g / L elemental iodine, 0.18 g / L polyvinyl alcohol, and γ-butyrolactone as the solvent. The ceramic powder consists of 7% YSZ powder with an average particle size of 50 nm and 5% ruthenium dioxide nanoparticles with an average particle size of 40 nm. During electrophoretic deposition, the distance between the two electrodes is 18 mm, the deposition voltage is 90 V, and the deposition time is 60 s. The sample is thoroughly rinsed with deionized water and dried for later use, resulting in a 90 μm thick ceramic layer on the surface of the metal binder layer.

[0056] The fourth step involves placing the electrophoretically deposited sample into a heat treatment furnace with a protective atmosphere of high-purity Ar (99.995% volume purity). The temperature is raised to 1100°C at a rate of 9°C / min in the high-purity Ar protective atmosphere at a flow rate of 2L / min, and then held for 60 minutes. The sample is then cooled to room temperature in the furnace under a continuous protective atmosphere.

[0057] like Figure 4As shown in the image, the surface morphology of the metal-ceramic composite coating on the heat-resistant steel surface in Example 4 reveals a uniform and dense coating surface, with no cracks or peeling observed. In the backscattered electron microscope (SEM) image mode, the light-colored area represents the ceramic matrix formed after sintering 7% YSZ powder, exhibiting a continuous distribution, as indicated by the white arrow in the image. The dark-colored area represents the state after sintering of nano-ruthenium dioxide powder mixed with 7% yttrium oxide-doped YSZ powder, exhibiting a fine and uniform distribution, as indicated by the black arrow in the image. Pure YSZ powder, after sintering, forms a ceramic coating with high porosity, while the nano-ruthenium dioxide powder, after doping and sintering, fills these gaps, making the coating more dense. The metal-ceramic composite coating prepared in Example 4 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 coating adhesion scratch tester and found to be 59N. According to the ASTM-D3359-09 standard test method for adhesion measurement, the coating adhesion reached level 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 358 cycles.

[0059] The results show that this invention improves the interfacial bonding strength within the coating by adding iridium chloride and antimony chloride to the electroplating solution to construct a nickel-iridium-antimony composite adhesive layer. Using γ-butyrolactone as the suspension solvent significantly enhances the dispersion uniformity and suspension stability of YSZ and nano-ruthenium dioxide powder, ensuring consistent ceramic coating thickness and a dense structure. Doping modification of the YSZ ceramic layer with nano-ruthenium dioxide powder achieves synergistic optimization of the coating's thermal insulation and thermal shock resistance. The metal-ceramic composite coating prepared by this invention possesses both strong interfacial bonding and excellent thermal insulation performance, effectively blocking high-temperature heat transfer and resisting thermal shock. It significantly reduces the operating temperature of the heat-resistant steel component substrate, extending its service life under harsh conditions. Through the synergistic design of the "adhesive layer-ceramic layer" and multi-dimensional composition and process innovation, it simultaneously solves the problems of poor bonding and insufficient thermal insulation performance in traditional composite coatings, significantly improving the high-temperature performance of heat-resistant steel. The process is highly controllable and suitable for industrial mass production, providing reliable technical support for the application of heat-resistant steel in high-parameter thermal power generation, aerospace, and other fields, and has significant industrial application value.

Claims

1. A method for preparing a metal-ceramic composite coating by electrophoretic deposition, characterized in that, Includes the following steps: The first step involves pre-treating the P91 heat-resistant steel plate by progressively polishing its surface with sandpaper ranging from 240 grit to 1000 grit. After polishing, the 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 5–15 minutes to thoroughly remove grease contaminants. Next, the surface is rinsed with anhydrous ethanol and dried to remove any acetone residue. Finally, the 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 involves preparing a metal bonding layer. A pretreated P91 heat-resistant steel plate is used as the cathode, and a graphite plate as the anode. The plate is placed in an electroplating solution for electrochemical deposition. The electroplating solution comprises the following components: nickel chloride 15–30 g / L, iridium chloride 5–10 g / L, antimony chloride 1–5 g / L, ethylenediaminetetraacetic acid 30–60 g / L, sodium citrate 20–40 g / L, citric acid 80–160 g / L, boric acid 25–50 g / L, saccharin 0.5–2 g / L, potassium chloride 10–20 g / L, and water as the solvent. The pH is adjusted to 2.0–4.0 using a 30% NaOH aqueous solution. During electrochemical deposition, the two electrodes are kept parallel, and the deposition current density is controlled at 1–3 A / dm² at 20–40°C. The deposition time is 30–60 min. After thorough rinsing with deionized water, the plate is dried for later use. The third step involves preparing an electrophoretic ceramic layer. A component with a metal bonding layer is used as the cathode, and a graphite plate as the anode. Electrophoretic deposition is performed in a suspension containing the following components: 5–40 g / L ceramic powder, 0.2–2 g / L elemental iodine, 0.1–0.2 g / L polyvinyl alcohol, and γ-butyrolactone as the solvent. The ceramic powder is a mixture of 5%–20% by mass of nano-ruthenium dioxide powder and the remaining yttrium oxide-stabilized zirconium oxide powder. During electrophoretic deposition, 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. The plates are thoroughly rinsed with deionized water and then dried for later use. The fourth step is to place the electrophoretically deposited part into a heat treatment furnace with a high-purity Ar protective atmosphere. The part is heated to 900-1100°C at a heating 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 at that temperature 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 metal-ceramic composite coating by electrophoretic deposition according to claim 1, characterized in that, In the second step, the concentration of iridium chloride is 7–8 g / L, and the concentration of antimony chloride is 2–4 g / L.

3. The method for preparing a metal-ceramic composite coating by electrophoretic deposition according to claim 1, characterized in that, In the second step, a metal bonding layer with a thickness of 5 to 20 μm is formed on the surface of the P91 heat-resistant steel plate.

4. The method for preparing a metal-ceramic composite coating by electrophoretic deposition according to claim 1, characterized in that, In the third step, yttrium oxide stabilizes the yttrium oxide doping in zirconium oxide at a concentration of 5 wt% to 8 wt%.

5. A method for preparing a metal-ceramic composite coating by electrophoretic deposition according to claim 1, characterized in that, In the third step, the mass fraction of nano-ruthenium dioxide in the ceramic powder is 10-15%.

6. A method for preparing a metal-ceramic composite coating by electrophoretic deposition according to claim 1, characterized in that, In the third step, a ceramic layer with a thickness of 80–110 μm is obtained on the surface of the metal bonding layer.

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