Double-layer composite anti-corrosion metal component suitable for supercritical carbon dioxide system and preparation method of double-layer composite anti-corrosion metal component

Abstract

The invention discloses a double-layer composite anti-corrosion metal component suitable for a supercritical carbon dioxide system and a preparation method thereof.The double-layer composite anti-corrosion metal component comprises a metal matrix, the surface of the metal matrix is sequentially provided with a first protective layer and a second protective layer, the first protective layer is a Ni-Cr alloy thermal spraying layer, the second protective layer is a SiO2 hole sealing layer, and the first protective layer is a Ni-Cr alloy thermal spraying layer. SiO2 of the second protective layer permeates into pores in the surface of the first protective layer; and a ceramic-metal interpenetrating structure is jointly formed by the porous sheet expansion structure formed by the first protective layer and the infiltration curing layer formed by the second protective layer, so that multiple blocking of supercritical carbon dioxide corrosion is realized. The first protective layer is formed on the surface of the metal matrix by adopting an HVAF or HVOF process, and the second protective layer is formed by coating the surface of the first protective layer with silica sol and performing heat treatment. The two layers of materials are stably combined in a synergistic curing mode of controlled pore interpenetration, chemical complexation and heat treatment induction.

Description

Technical Field

[0001] This invention relates to the field of materials protection technology, specifically to a double-layer composite anti-corrosion metal component suitable for supercritical carbon dioxide systems and its preparation method. Background Technology

[0002] Supercritical carbon dioxide (S-CO2) Brayton cycle is considered a key power generation technology for next-generation nuclear energy, solar thermal power generation, and clean energy bases due to its high efficiency, high power density, compact equipment size, and fast system response. Under typical operating conditions, key metal components in the S-CO2 cycle are exposed to a high-temperature (500℃~650℃) and high-pressure (18MPa~25MPa) CO2 atmosphere for extended periods, and trace amounts of O2, H2O, SO2, CO, and NO are also present. X Impurities such as carbon dioxide and carbon deposits are present. This environment has a corrosion mechanism that is significantly different from that of traditional high-temperature oxidation environments, making metallic materials susceptible to selective oxidation, carburizing hardening, pore blockage caused by carbon deposition, oxide film peeling, and chromium deficiency layer formation, which seriously affect the safety and lifespan of equipment.

[0003] Studies have shown that heat-resistant alloys exhibit good oxidation and creep resistance in conventional high-temperature steam environments, but the Cr2O3 protective film rapidly destabilizes under S-CO2 conditions due to the effects of CO2 and impurities. For example, Cr2O3 reacts with CO2 to form volatile CrO2(OH)2, causing the protective film to continuously thin and even rupture. Once the protective film fails, the exposed metal substrate will undergo further rapid oxidation and carburization. Simultaneously, CO... X The carbon produced by decomposition can be deposited on the surface and in the pores of materials, causing a vicious cycle of "carbon blockage - local oxygen enrichment - accelerated oxidation".

[0004] Previous studies have proposed various high-temperature coating schemes to improve the service performance of materials in S-CO2 environments. For example, Cr diffusion coatings and Aluminide coatings can form relatively stable oxide films by increasing the surface chromium or aluminum content. However, these processes typically require long-term diffusion heat treatment at 900℃ to 1100℃, which can easily lead to coarsening of the metal alloy structure, precipitation of unstable phases, and even performance degradation. At the same time, these coatings are costly and time-consuming, making them unsuitable for the industrial processing of large-diameter pressure components.

[0005] Ceramic SiO2, Al2O3, or ZrO2 coatings have good density and gas barrier properties in high-temperature gas environments, but their thermal expansion is not matched with that of iron-based materials, making them prone to cracking and peeling during continuous thermal cycling, and difficult to adapt to the service conditions under pressure fluctuations in S-CO2 systems.

[0006] Ni-Cr metal coatings can improve oxidation resistance to some extent due to their high-temperature oxidation resistance, but Ni-Cr layers prepared by thermal spraying usually have an inherent porous structure. These pores provide permeation channels for gases such as CO2, O2, and CO, and also become accumulation points for carbon deposition, thus accelerating carburization and oxide film peeling. This makes it impossible for a single-layer Ni-Cr coating to maintain its integrity in S-CO2 for a long period.

[0007] Based on publicly available literature both domestically and internationally, research on composite coating systems for S-CO2 applications is still in the exploratory stage, particularly regarding the synergistic design of "porous metal substrate + ceramic sealed pore layer," for which no mature engineering solutions have yet been found. Taking Si-based coatings as an example, although SiO2 possesses excellent gas barrier properties, its adhesion to metal substrates is typically low, and it requires high-temperature diffusion (≥800℃) to form a stable Si-rich layer, which is not conducive to compatibility with the heat treatment windows of novel heat-resistant alloys such as IN740H currently used.

[0008] In summary, existing technologies all suffer from problems such as high process temperatures, insufficient interface matching, severe pore penetration, or easy coating peeling, making it difficult to simultaneously meet the comprehensive performance requirements of S-CO2 systems for resistance to carburization, oxidation, carbon deposition, thermal cycling, and industrial-scale preparation. There is an urgent need for a structurally sound, mildly processed, and scalably prepared bilayer composite corrosion-resistant coating system to provide long-term stable surface protection for components made of novel heat-resistant alloys such as IN740H in S-CO2 power generation systems. Summary of the Invention

[0009] The purpose of this invention is to address the common problems of oxidation, carburization, and impurity corrosion in metal components in S-CO2 high-temperature and high-pressure systems. It provides a double-layer composite anti-corrosion metal component suitable for supercritical carbon dioxide systems and its preparation method. The double-layer composite anti-corrosion metal component has a clear structure, stable interface, controllable process, and long-term service reliability. It consists of a Ni-Cr alloy layer formed by high-energy thermal spraying and a SiO2 ceramic layer formed by silica sol coating and medium-temperature curing. The two layers are stably bonded through controlled pore interpenetration, chemical complexation, and heat treatment-induced synergistic curing, thus forming a complete, continuous, and highly barrier composite interface structure.

[0010] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, a double-layer composite anti-corrosion metal component suitable for supercritical carbon dioxide systems is provided, comprising a metal substrate, wherein a first protective layer and a second protective layer are sequentially provided on the surface of the metal substrate, the first protective layer being a Ni-Cr alloy thermal spray coating, and the second protective layer being a SiO2 sealing layer, wherein the SiO2 of the second protective layer penetrates into the pores of the surface of the first protective layer; the porous sheet structure formed by the first protective layer and the penetration and curing layer formed by the second protective layer together constitute a ceramic-metal interpenetrating structure, thereby achieving multiple barriers against supercritical carbon dioxide corrosion.

[0011] As a preferred embodiment, the thickness of the first protective layer is 30μm~120μm, and the porosity is 2%~8%.

[0012] As a preferred embodiment, the first protective layer is formed on the surface of the metal substrate using hypersonic air fuel spraying (HVAF) or hypersonic flame spraying (HVOF) processes. During the preparation of the first protective layer, the spraying atmosphere is protected by air, nitrogen, or argon. The particle size of the sprayed powder is 10μm~30μm, the particle velocity is not less than 600m / s, the spraying distance is between 200mm~350mm, the spray gun moving speed is 400mm / s~600mm / s, the temperature of the metal substrate is kept not higher than 300℃ during the spraying process, and the porosity of the coating is adjusted to 2%~8% by controlling the gas combustion ratio.

[0013] As a preferred embodiment, the thickness of the second protective layer is 3μm~20μm; The SiO2 in the second protective layer penetrates into the pores on the surface of the first protective layer at a depth of 2μm to 8μm.

[0014] As a preferred embodiment, the second protective layer is formed by coating the surface of the first protective layer with silica sol and heat-treating at 450℃ to 600℃; the impregnation time of the second protective layer during the preparation process is 20s to 60s, the pulling speed is 20mm / min to 50mm / min, the curing temperature is 450℃ to 600℃, and the curing time is 0.5h to 3h.

[0015] As a preferred embodiment, the silica sol in the preparation process of the second protective layer is composed of tetraethyl orthosilicate (TEOS), ethanol, water, and an acidic catalyst, wherein the solid content is 10wt%~40wt% and the aging time is 12h~24h.

[0016] As a preferred embodiment, the surface of the metal substrate is sandblasted to achieve a surface roughness of Ra 2.5μm~5μm; the metal substrate is an iron-based or nickel-based corrosion-resistant high-temperature alloy substrate.

[0017] As a preferred embodiment, the Ni-Cr alloy thermal spray coating contains 70% Ni and 30% Cr.

[0018] As a preferred embodiment, the temperature of the supercritical carbon dioxide system is 500℃~600℃ and the pressure is 20MPa~25MPa.

[0019] Secondly, a method for preparing a double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems is provided, comprising the following steps: The surface of the metal substrate is sandblasted to achieve a surface roughness of Ra 2.5μm~5μm; A first protective layer is prepared on the surface of a metal substrate using hypersonic air fuel spraying (HVAF) or hypersonic flame spraying (HVOF). The spraying atmosphere is protected by air, nitrogen, or argon. The particle size of the sprayed powder is 10μm~30μm, the particle velocity is not less than 600m / s, the spraying distance is between 200mm~350mm, the spray gun moving speed is 400mm / s~600mm / s, the temperature of the metal substrate is kept not higher than 300℃ during the spraying process, and the porosity of the coating is adjusted to 2%~8% by controlling the gas combustion ratio. A silica sol is coated on the surface of the first protective layer. The silica sol is composed of tetraethyl orthosilicate (TEOS), ethanol, water, and an acidic catalyst, with a solid content of 10wt%~40wt% and an aging time of 12h~24h. The silica sol impregnation time is 20s~60s, the pulling speed is 20mm / min~50mm / min, the curing temperature is 450℃~600℃, and the curing time is 0.5h~3h, forming a second protective layer and obtaining a double-layer composite anti-corrosion metal component.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects: The first protective layer is prepared using a high-energy thermal spraying process. Through comprehensive control of powder particle size, spray gun distance, particle velocity, and flame temperature, a micro-controllable porosity is formed on the Ni-Cr alloy surface. These pores are not defects, but rather provide "penetration channels" for the subsequent second protective layer (i.e., SiO2 sol), allowing the ceramic layer to embed into the metal micropores to form an interpenetrating interface. This structure means that the ceramic layer no longer simply remains on the surface, but is partially "interlocked" within the metal layer, increasing the interlayer bonding strength to 18MPa~24MPa, which is 2-4 times higher than that of traditional ceramic coatings.

[0021] The second protective layer is prepared using silica sol. By precisely controlling the viscosity, dipping speed, pulling speed, and heat treatment of the SiO2 sol, the sol is penetrated into the pores of the Ni-Cr alloy, where it gels, solidifies, and forms "embedded interlocking bonds," creating a continuous, glassy, ​​dense layer on the outside. The resulting dual-protective structure of "internal interlocking – external barrier" forcibly elongates and significantly obstructs the gas permeation path. The double-layer composite corrosion-resistant metal component of this invention exhibits a corrosion weight gain of only 0.28 mg / cm³ in a supercritical carbon dioxide system after 1000 hours. 2 ~0.45mg / cm 2 It is far superior to similar single-layer Ni-Cr or SiO2 coatings.

[0022] The double-layer composite anti-corrosion metal component of the present invention has the following characteristics: (1) layered interface, (2) ceramic-metal interlocking with uniform interface stress distribution, making it less prone to cracking, and (3) having a "buffering effect" in thermal cycling to avoid stress concentration. These characteristics enable the double-layer composite anti-corrosion metal component provided by the present invention to solve the problem of easy failure of the metal-ceramic interface. The composite coating showed no signs of peeling after 100 thermal cycles (20℃~550℃). Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 SEM image of the coating surface of the double-layer composite anti-corrosion metal component in an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, those skilled in the art can obtain other embodiments without creative effort.

[0026] Please see Figure 1This invention proposes a double-layer composite anti-corrosion metal component suitable for supercritical carbon dioxide systems. It not only overcomes the weakness of traditional metal coatings where "pores become CO2 permeation channels," but also avoids the cracking and peeling problems caused by the brittleness and thermal expansion coefficient differences of ceramic coatings. It constructs a composite structure that is more robust both thermodynamically and mechanically, achieving a synergistic effect of the metal layer "providing a strong and tough skeleton" and the ceramic layer "providing a tight seal." This allows it to maintain stability for more than 1000 hours under S-CO2 conditions (500-600℃, 20-25MPa, containing a small amount of H2O and SO2).

[0027] The embodiments of the present invention are applicable to the double-layer composite anti-corrosion metal components of supercritical carbon dioxide systems, which include a metal substrate. The surface of the metal substrate is provided with a first protective layer and a second protective layer in sequence. The first protective layer is a Ni-Cr alloy thermal spray coating, and the second protective layer is a SiO2 sealing layer. The SiO2 of the second protective layer penetrates into the pores of the surface of the first protective layer. The porous sheet structure formed by the first protective layer and the penetration and curing layer formed by the second protective layer together constitute a ceramic-metal interpenetrating structure, thereby achieving multiple barriers against supercritical carbon dioxide corrosion.

[0028] In one possible implementation, the thickness of the first protective layer is 30 μm to 120 μm, and the porosity is 2% to 8%.

[0029] In one possible implementation, the first protective layer is formed on the surface of the metal substrate using hypersonic air fuel spraying (HVAF) or hypersonic flame spraying (HVOF) processes. During the preparation of the first protective layer, the spraying atmosphere is protected by air, nitrogen, or argon. The particle size of the sprayed powder is 10μm~30μm, the particle velocity is not less than 600m / s, the spraying distance is between 200mm~350mm, the spray gun moving speed is 400mm / s~600mm / s, the temperature of the metal substrate is maintained not higher than 300℃ during the spraying process, and the porosity of the coating is adjusted to 2%~8% by controlling the gas combustion ratio.

[0030] In one possible implementation, the thickness of the second protective layer is 3μm to 20μm; and the SiO2 of the second protective layer penetrates into the pores of the first protective layer at a depth of 2μm to 8μm.

[0031] In one possible implementation, the second protective layer is formed by coating the surface of the first protective layer with silica sol and heat-treating it at 450°C to 600°C; the impregnation time of the second protective layer during the preparation process is 20s to 60s, the pulling speed is 20mm / min to 50mm / min, the curing temperature is 450°C to 600°C, and the curing time is 0.5h to 3h.

[0032] In one possible implementation, the silica sol used in the preparation of the second protective layer is composed of tetraethyl orthosilicate (TEOS), ethanol, water, and an acidic catalyst, wherein the solid content is 10wt%~40wt% and the aging time is 12h~24h.

[0033] In one possible implementation, the surface of the metal substrate is sandblasted to achieve a surface roughness of Ra 2.5μm~5μm; the metal substrate is an iron-based or nickel-based corrosion-resistant high-temperature alloy substrate, including novel heat-resistant alloys such as IN740H.

[0034] In one possible implementation, the NiCr alloy coating 102 has a Ni content of 70% and a Cr content of 30%.

[0035] NiCr (70% Ni, 30% Cr) alloy, also known as Cr30Ni70 high-temperature alloy, is a high-performance material with nickel and chromium as its main components. Through a reasonable composition ratio, this high-temperature alloy exhibits excellent performance in various extreme environments. The stable crystal structure of nickel-based alloys at high temperatures allows Cr30Ni70 to withstand extreme high-temperature thermal stress, while the addition of chromium enhances the material's oxidation and corrosion resistance. Cr30Ni70 high-temperature alloy has a high melting point, typically above 1350℃, and can operate for extended periods at temperatures above 1000℃ without failure. Its high-temperature creep resistance ensures stable operation of equipment at high temperatures, extending maintenance cycles. The addition of chromium enhances the material's oxidation and corrosion resistance, making Cr30Ni70 alloy perform exceptionally well in high-temperature oxidizing environments. For example, its oxidation rate at 950℃ is only 0.1 mm per year, while the oxidation rate of stainless steel under the same conditions exceeds 0.5 mm per year. Cr30Ni70 alloy maintains good mechanical strength and electrical properties at high temperatures, making it suitable for manufacturing parts that need to withstand high temperatures and complex stresses.

[0036] In one possible implementation, the supercritical carbon dioxide system described in this embodiment of the invention has a temperature of 500℃~600℃, a pressure of 20MPa~25MPa, and contains a small amount of H2O and SO2.

[0037] Another embodiment of the present invention also proposes a method for preparing a double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems, comprising the following steps: The surface of the metal substrate is sandblasted to achieve a surface roughness of Ra 2.5μm~5μm; A first protective layer is prepared on the surface of a metal substrate using hypersonic air fuel spraying (HVAF) or hypersonic flame spraying (HVOF). The spraying atmosphere is protected by air, nitrogen, or argon. The particle size of the sprayed powder is 10μm~30μm, the particle velocity is not less than 600m / s, the spraying distance is between 200mm~350mm, the spray gun moving speed is 400mm / s~600mm / s, the temperature of the metal substrate is kept not higher than 300℃ during the spraying process, and the porosity of the coating is adjusted to 2%~8% by controlling the gas combustion ratio. A silica sol is coated on the surface of the first protective layer. The silica sol is composed of tetraethyl orthosilicate (TEOS), ethanol, water, and an acidic catalyst, with a solid content of 10wt%~40wt% and an aging time of 12h~24h. The silica sol impregnation time is 20s~60s, the pulling speed is 20mm / min~50mm / min, the curing temperature is 450℃~600℃, and the curing time is 0.5h~3h, forming a second protective layer and obtaining a double-layer composite anti-corrosion metal component.

[0038] Supercritical carbon dioxide possesses unique physicochemical properties, differing from both gases and liquids, exhibiting high density, low viscosity, and excellent diffusivity. In this state, carbon dioxide is highly corrosive to many metallic materials, especially under high temperature and pressure conditions, where the corrosion is even more pronounced. For example, at 500-600℃ and 20-25MPa, carbon dioxide reacts chemically with metal surfaces to form metal oxides or carbonates, leading to corrosion and damage. The presence of impurities in the system, such as moisture, oxygen, and sulfides, further exacerbates the corrosion process. Moisture reacts with carbon dioxide to form carbonic acid, a weak acid that causes acid corrosion of metallic materials; oxygen promotes oxidation reactions in metals, accelerating the corrosion process; and sulfides form sulfide corrosion products with metals, leading to embrittlement and failure.

[0039] Equipment operating under S-CO2 conditions, such as heat exchangers, pipes, and valves, is typically made of metal. If this equipment lacks good corrosion resistance, the metal surface will gradually corrode during long-term operation, leading to thinner walls, reduced strength, and even safety accidents such as leaks and ruptures. For example, in supercritical carbon dioxide cycle systems in the nuclear energy field, corrosion leaks could lead to the release of radioactive materials, posing serious threats to the environment and human health. Corrosion also affects the heat transfer efficiency and fluid flow performance of equipment. Corrosion products deposit on the equipment surface, forming a fouling layer that increases thermal resistance and reduces heat transfer efficiency; simultaneously, the fouling layer alters fluid flow channels, increasing flow resistance and affecting the normal operation of the system.

[0040] Under S-CO2 conditions, equipment experiences frequent start-ups and shutdowns, as well as temperature fluctuations. When the equipment starts, the temperature rises rapidly from a low temperature to a high temperature; when it stops, the temperature drops rapidly from a high temperature to a low temperature. These rapid temperature changes generate thermal stress within the equipment. If the materials have poor thermomechanical stability, this thermal stress can lead to thermal fatigue cracks. As the number of cycles increases, these cracks gradually propagate, eventually causing equipment failure. For example, in the supercritical CO2 cycle of a solar thermal power generation system, due to the intermittent nature of solar energy, the system needs to be frequently started and stopped, subjecting the equipment to significant thermal stress. If the materials have poor thermomechanical stability, the equipment is prone to thermal fatigue damage, affecting the system's reliability and service life.

[0041] Under S-CO2 conditions, equipment must withstand not only high temperature and pressure, but also mechanical loads generated by fluid flow, such as pressure loads and vibration loads. If the thermomechanical stability of the material is insufficient, plastic deformation and creep may occur under mechanical loads, leading to dimensional changes and performance degradation of the equipment. For example, in the impeller of a supercritical carbon dioxide compressor, the impeller must withstand enormous centrifugal force and fluid forces during high-speed rotation, while also being affected by the high-temperature environment. If the impeller material has poor thermomechanical stability, problems such as impeller deformation and cracks may occur during long-term operation, affecting the normal operation and efficiency of the compressor.

[0042] Materials with excellent corrosion resistance and thermomechanical stability can operate stably for extended periods under S-CO2 conditions, reducing corrosion damage and thermal fatigue failure of equipment, thereby lowering maintenance frequency and costs. For example, in chemical production, equipment manufactured using materials with good corrosion resistance and thermomechanical stability can extend its service life and reduce production interruptions and downtime losses caused by equipment failures.

[0043] Supercritical carbon dioxide (S-CO2) systems are commonly used in fields with high safety requirements, such as nuclear energy and aerospace. In these fields, the reliability and safety of the equipment are paramount. Excellent corrosion resistance and thermomechanical stability ensure that the equipment will not experience leaks, ruptures, or other safety accidents during long-term operation, guaranteeing the safe and stable operation of the system. For example, in supercritical carbon dioxide cooling systems in the nuclear energy field, the safe operation of the equipment is directly related to the safety of the nuclear reactor; therefore, materials with high corrosion resistance and thermomechanical stability must be used.

[0044] Example 1: This embodiment uses IN740H heat-resistant alloy as the metal substrate, with dimensions of 150mm × 50mm × 4mm. First, the metal substrate is sandblasted using 24-30 mesh brown corundum, sprayed uniformly at a distance of 80-120mm under a pressure of 0.5-0.7MPa, stabilizing the surface roughness at Ra 2.5μm. This roughness ensures that the coating forms a sheet-like structure while maintaining suitable mechanical adhesion. After sandblasting, the surface is ultrasonically cleaned with anhydrous ethanol for 10 minutes to ensure it is free of oil and residual solid particles.

[0045] The Ni-Cr metal framework layer was prepared using HVAF high-energy spraying. The powder used consisted of 70wt% Ni and 30wt% Cr, with a particle size range of 15-25μm. The powder morphology was spherical atomized, which is beneficial for maintaining uniform melting of particles under high temperature and high speed. Propane was used as fuel and air as oxidant during spraying, with the fuel-to-fuel ratio controlled at 1:5-1:6.5 to stabilize the flame temperature in the range of 1950-2150℃, accelerating the particles to 700m / s. The spraying distance was controlled at 230-270mm to avoid excessive particle impact that could compact the pores. The substrate temperature was monitored in real time during spraying to ensure it did not exceed 300℃, preventing microstructural changes in IN740H.

[0046] The Ni-Cr coating obtained under the above conditions exhibits a highly regular lamellar structure with a thickness of 45-55 μm and a porosity maintained within the range of 3-5%. The pore network is uniformly distributed, providing a structural basis for the subsequent penetration and curing of SiO2 sol. If the flame temperature exceeds 2150℃, it will cause the powder to overmelt and significantly reduce the porosity; if the substrate is overheated, it will cause surface softening, affecting the coating adhesion.

[0047] The SiO2 layer was prepared by sol-coating. The sol used TEOS as a precursor, ethanol as a solvent, and nitric acid as a catalyst for hydrolysis and polycondensation. After aging for 12 hours, the viscosity remained at 6-10 mPa·s (25℃). During the impregnation process, the sample was vertically immersed in the sol for 30 seconds to ensure full penetration into the pore channels of the Ni-Cr layer. Subsequently, it was pulled up at a uniform speed of 30-50 mm / min to form a uniform and continuous liquid film. On high-roughness surfaces, to avoid localized accumulation or pinholes in the sol, the ethanol ratio was adjusted to 6 times that of TEOS to optimize wettability and surface spreading.

[0048] After sol-gel film formation, the sample was subjected to medium-temperature heat treatment in an air furnace at a heating rate of 3℃ / min, and finally held at 550℃ for 1 hour to allow SiO2 to complete the gel-glass transition and form an approximately 2-4 μm penetration layer at the contact interface, achieving an interlocking structure between the ceramic and metal. The final SiO2 layer thickness was approximately 8-12 μm, with a continuous interlayer interface and no obvious defects.

[0049] After exposure to S-CO2 (containing 50ppm SO2 and 300ppm H2O) at 550℃ and 20MPa for 1000 h, the sample showed a corrosion weight gain of only 0.41 mg / cm³. 2 Cross-sectional observation showed that the Ni-Cr layer pores were completely sealed, with no signs of carbon deposition and an intact interface structure. In the same corrosive environment, the corrosion weight gain of the IN740H matrix was 2.3 mg / cm³. 2 The surface formed multiple layers of oxides and carbon deposits, with localized peeling; the corrosion weight gain of a single Ni-Cr coating was 1.20 mg / cm³. 2 The interconnected pores become CO2 permeation channels, leading to carburization; the corrosion weight gain of a single SiO2 coating is 1.10 mg / cm³. 2 Cracking occurred after thermal cycling, and the lack of metal support led to localized detachment. It is evident that the double-layer composite coating prepared in this embodiment provides the best protective effect, significantly reducing corrosion-induced weight gain and inhibiting the penetration of corrosive atmosphere into the substrate. The interface between the substrate and the coating, as well as between the double-layer coating, exhibits good bonding, with no delamination or detachment observed.

[0050] Example 2: In this embodiment, the Ni-Cr layer was prepared using HVOF. The particle velocity was maintained at 680 m / s, resulting in a higher coating density. By adjusting the oxygen / kerosene ratio (0.85–1.10), a Ni-Cr layer with a thickness of 70–80 μm was obtained, with a porosity controlled at approximately 3–4%.

[0051] In the SiO2 preparation, a two-stage dip-coating process was employed. After sol-gel film formation, the sample was placed in an air furnace for medium-temperature heat treatment at a heating rate of 3℃ / min, and finally held at 550℃ for 1 hour. Each dip-coating resulted in a thickness of 6-8 μm. After curing, the total thickness reached 14-16 μm. The thicker SiO2 layer not only provides stronger barrier properties but also forms an enhanced interlocking interface through the infiltration of the Ni-Cr layer.

[0052] After exposure to S-CO2 (containing 50 ppm SO2 and 300 ppm H2O) at 550℃ and 20 MPa for 1000 h, the sample showed a corrosion weight gain of 0.27 mg / cm³. 2 No continuous carburization was observed on the surface, and the interface was intact without cracks.

[0053] Example 3: In this embodiment, the Ni-Cr layer was prepared using HVOF. The particle velocity was maintained at 680 m / s, resulting in a higher coating density. By adjusting the oxygen / kerosene ratio (0.85-1.10), a Ni-Cr layer with a thickness of 70-80 μm was obtained, with a porosity controlled at approximately 3-4%.

[0054] The SiO2 layer was prepared by sol-coating. The sol used TEOS as a precursor, ethanol as a solvent, and nitric acid as a catalyst for hydrolysis and polycondensation. After aging for 12 hours, the viscosity remained at 6-10 mPa·s (25℃). During the impregnation process, the sample was vertically immersed in the sol for 30 seconds to ensure full penetration into the pore channels of the Ni-Cr layer. Subsequently, it was pulled up at a uniform speed of 30-50 mm / min to form a uniform and continuous liquid film. After sol film formation, the sample was subjected to medium-temperature heat treatment in an air furnace at a heating rate of 3℃ / min, and finally held at 500℃ for 2 hours. The resulting SiO2 had a slightly lower density, but its bonding with the metal layer remained stable. After exposure to a 540℃, 20MPa S-CO2 environment for 800 hours, the corrosion weight gain was 0.53 mg / cm³. 2 Although the temperature was slightly higher than in Example 1, there was still no peeling, which verified the process tolerance of the system of the present invention.

[0055] This invention discloses a double-layer composite anti-corrosion metal component suitable for supercritical carbon dioxide systems and its preparation method. The double-layer composite anti-corrosion metal component sequentially comprises a Ni-Cr alloy thermal spray coating deposited on the surface of a metal substrate and a SiO2 sealing pore layer covering its outer surface. The Ni-Cr layer is prepared using a high-energy thermal spraying method, exhibiting a controlled porous structure, providing interface conditions for the subsequent penetration, sealing, and mechanical interlocking of the SiO2 layer. The SiO2 layer is prepared by silica sol coating and low-temperature heat treatment at 450-600℃, which can partially penetrate and seal the pores of the Ni-Cr layer, obtaining a stable and dense gas barrier film. This invention has advantages such as substrate friendliness, energy-saving process, and excellent coating corrosion resistance, and can be widely used for the protection of high-temperature pressure metal components in supercritical carbon dioxide circulation systems, reheaters, coolers, and heat exchanger systems.

[0056] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems, characterized in that, The device includes a metal substrate, on the surface of which a first protective layer and a second protective layer are sequentially provided. The first protective layer is a Ni-Cr alloy thermal spray coating, and the second protective layer is a SiO2 sealing layer. The SiO2 in the second protective layer penetrates into the pores on the surface of the first protective layer. The porous sheet structure formed by the first protective layer and the penetrating and curing layer formed by the second protective layer together constitute a ceramic-metal interpenetrating structure, thereby achieving multiple barriers against supercritical carbon dioxide corrosion.

2. The double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems according to claim 1, characterized in that, The thickness of the first protective layer is 30μm~120μm, and the porosity is 2%~8%.

3. The double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems according to claim 1 or 2, characterized in that, The first protective layer is formed on the surface of the metal substrate using hypersonic air fuel spraying (HVAF) or hypersonic flame spraying (HVOF) processes. During the preparation of the first protective layer, the spraying atmosphere is protected by air, nitrogen, or argon. The particle size of the sprayed powder is 10μm~30μm, the particle velocity is not less than 600m / s, the spraying distance is between 200mm~350mm, the spray gun moving speed is 400mm / s~600mm / s, the temperature of the metal substrate is kept not higher than 300℃ during the spraying process, and the porosity of the coating is adjusted to 2%~8% by controlling the gas combustion ratio.

4. The double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems according to claim 2, characterized in that, The thickness of the second protective layer is 3μm~20μm; The SiO2 in the second protective layer penetrates into the pores on the surface of the first protective layer at a depth of 2μm to 8μm.

5. The double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems according to claim 1 or 4, characterized in that, The second protective layer is formed by coating the surface of the first protective layer with silica sol and heat-treating at 450℃ to 600℃; the impregnation time of the second protective layer during the preparation process is 20s to 60s, the pulling speed is 20mm / min to 50mm / min, the curing temperature is 450℃ to 600℃, and the curing time is 0.5h to 3h.

6. The double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems according to claim 5, characterized in that, The silica sol used in the preparation of the second protective layer is composed of tetraethyl orthosilicate (TEOS), ethanol, water, and an acidic catalyst, with a solid content of 10wt% to 40wt% and an aging time of 12h to 24h.

7. The double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems according to claim 1, characterized in that, The surface of the metal substrate is sandblasted to achieve a surface roughness of Ra 2.5μm~5μm; The metal matrix is ​​an iron-based or nickel-based corrosion-resistant high-temperature alloy matrix.

8. The double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems according to claim 1, characterized in that, The Ni-Cr alloy thermal spray coating contains 70% Ni and 30% Cr.

9. The double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems according to claim 1, characterized in that, The temperature of the supercritical carbon dioxide system is 500℃~600℃, and the pressure is 20MPa~25MPa.

10. A method for preparing a double-layer composite corrosion-resistant metal component suitable for supercritical carbon dioxide systems, characterized in that, Includes the following steps: The surface of the metal substrate is sandblasted to achieve a surface roughness of Ra 2.5μm~5μm; A first protective layer is prepared on the surface of a metal substrate using hypersonic air fuel spraying (HVAF) or hypersonic flame spraying (HVOF). The spraying atmosphere is protected by air, nitrogen, or argon. The particle size of the sprayed powder is 10μm~30μm, the particle velocity is not less than 600m / s, the spraying distance is between 200mm~350mm, the spray gun moving speed is 400mm / s~600mm / s, the temperature of the metal substrate is kept not higher than 300℃ during the spraying process, and the porosity of the coating is adjusted to 2%~8% by controlling the gas combustion ratio. A silica sol is coated on the surface of the first protective layer. The silica sol is composed of tetraethyl orthosilicate (TEOS), ethanol, water, and an acidic catalyst, with a solid content of 10wt%~40wt% and an aging time of 12h~24h. The silica sol impregnation time is 20s~60s, the pulling speed is 20mm / min~50mm / min, the curing temperature is 450℃~600℃, and the curing time is 0.5h~3h, forming a second protective layer and obtaining a double-layer composite anti-corrosion metal component.

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