High-temperature-resistant low-permeability hydrogen composite coating and application thereof

Abstract

This invention belongs to the field of high-temperature protective coating technology and discloses a high-temperature resistant, low-hydrogen-permeability composite coating and its application. The composite coating includes a bonding layer, a transition layer, a functional layer, and a sealing layer arranged sequentially from bottom to top with decreasing porosity. The bonding layer is prepared by cold spraying CrAlSi alloy powder onto a metal substrate followed by vacuum annealing. The transition layer includes multiple layers of transition sub-layers stacked together, and the mass fraction of flake-shaped h-BN powder in each transition sub-layer increases linearly from 10% to 50% from the bonding layer to the functional layer. The raw materials of the functional layer include flake-shaped h-BN powder, Y2O3 powder, Al2O3 powder, and ZrO2 powder, and the mass fraction of flake-shaped h-BN powder in the functional layer is 55-60%. This invention improves the interfacial bonding strength between the coating and the metal substrate through a multi-level gradient composite design and an interface-strengthened coating preparation process.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature protective coating technology, and more specifically, relates to a high-temperature resistant and low-hydrogen-permeability composite coating and its application. Background Technology

[0002] Hydrogen, due to its clean, efficient, and zero-carbon properties, is hailed as one of the most promising green energy sources. With the continued growth of global energy demand, hydrogen energy is widely considered crucial for achieving global energy transition and addressing climate change, making its development and utilization a national strategic goal for countries worldwide. However, hydrogen energy faces a very challenging problem in its application—hydrogen embrittlement—which seriously threatens the safety and reliability of related components and application systems, greatly limiting its application. To effectively address this challenge, hydrogen-barrier coating technology has emerged, focusing on solving problems such as hydrogen embrittlement, interface failure, and process complexity.

[0003] With the rapid development of advanced nuclear energy systems, aerospace propulsion, and the hydrogen energy industry, problems such as material embrittlement and fuel leakage caused by hydrogen isotope permeation under high-temperature environments are becoming increasingly prominent. Especially under extreme conditions, coatings must simultaneously meet core requirements such as high-temperature stability, hydrogen barrier efficiency, and service life, posing a severe challenge to high-temperature hydrogen barrier coating technology. Traditional oxide (such as alumina, chromium oxide) or carbide (such as silicon carbide) based hydrogen barrier coatings suffer from significant defects and technical bottlenecks under extreme conditions, including thermal expansion mismatch, low interfacial bonding strength, and high-temperature performance degradation. Hexagonal boron nitride (h-BN), due to its unique two-dimensional layered structure and physicochemical properties, has become an ideal hydrogen barrier material. Specifically: The hexagonal lattice spacing of h-BN (0.333 nm) is smaller than the dynamic diameter of a hydrogen molecule (0.289 nm), effectively blocking hydrogen penetration. The adsorption energy of its polar BN bonds for hydrogen atoms (0.35 eV) is significantly higher than that of graphite (0.07 eV), achieving chemisorption and retention. Its coefficient of thermal expansion (0.6-1.2 × 10⁻⁶) is also significantly lower. -6 The difference between h-BN and most metal matrices is reduced by more than 70% compared to Al2O3, which can significantly alleviate interfacial thermal stress. Experiments show that h-BN can be stable up to 850℃ in an inert atmosphere, and its layered structure can still adsorb hydrogen atoms to form a stable complex at high temperatures through the polar characteristics of boron-nitrogen bonds.

[0004] However, the application of existing h-BN coatings still reveals problems such as insufficient interfacial bonding strength and insufficient adaptability to dynamic working conditions, which seriously restricts engineering applications. Technological breakthroughs are urgently needed through material system innovation and process reform. Summary of the Invention

[0005] The purpose of this invention is to address the bottlenecks in existing technologies by proposing a high-temperature resistant, low-hydrogen-permeability composite coating and its application. This invention improves the interfacial bonding strength between the coating and the metal substrate through a multi-level gradient composite design and an interface-strengthened coating preparation process, constructing a coating system with strong adaptability to dynamic operating conditions, possessing ultra-low hydrogen permeability, high-temperature stability, and thermal shock resistance.

[0006] To achieve the above objectives, the present invention provides a high-temperature resistant and low-hydrogen-permeability composite coating, wherein the composite coating comprises a bonding layer, a transition layer, a functional layer and a sealing layer arranged sequentially from bottom to top with decreasing porosity; The bonding layer is obtained by cold spraying CrAlSi alloy powder onto a metal substrate and then vacuum annealing; the particle size of the CrAlSi alloy powder is 5-25μm. The transition layer comprises multiple transition sublayers stacked together. Each transition sublayer independently comprises flake-shaped h-BN powder with a particle size of 1-3 μm, SiC powder with a particle size of 50-100 nm, and Al powder with a particle size of 1-5 μm. Furthermore, the mass fraction of the flake-shaped h-BN powder in each transition sublayer increases linearly from 10% to 50% from the bonding layer to the functional layer. The raw materials for the functional layer include flake-shaped h-BN powder with a particle size of 1-3 μm, Y2O3 powder with a particle size of 50-100 nm, Al2O3 powder with a particle size of 0.5-1.5 μm, and ZrO2 powder with a particle size of 50-200 nm; and the mass fraction of the flake-shaped h-BN powder in the functional layer is 55-60%. The raw materials for the sealing layer include Al2O3-SiO2 biphase nanosol and binder.

[0007] The core innovation of this invention lies in the multi-level gradient structure design and interface enhancement technology, specifically as follows: (1) Multi-level gradient structure design Unlike previous gradient coatings with a single structural gradient (thickness and type), this invention employs a multi-level gradient structural design that coordinates the composition, porosity, and microstructure of sheet-like h-BN powder. Specifically: The content of flake-shaped h-BN powder: In the bonding layer → transition layer → functional layer, the h-BN content gradually increases from 0% to about 60%, thereby achieving a smooth transition of the coefficient of thermal expansion and relieving thermal stress; Porosity gradient: The coating system of this invention exhibits a layer-by-layer distribution with decreasing porosity from bottom to top, namely bonding layer (porosity < 5%) → functional layer (porosity < 2%) → sealing layer (porosity < 0.1%), which seals hydrogen permeation channels step by step. Grain size gradient composite reinforcement: The coating adopts a composite design of micron- and nano-scale particles, using nanoparticles to fill the gaps between micron-particles to form a "micron-nano-micron" grain size gradient composite structure, which improves the overall density and toughness of the coating.

[0008] (2) Interface enhancement technology

[0009] A mechanically interlocked structure between the CrAlSi alloy and the metal substrate is formed by cold spraying; then, high-temperature vacuum annealing is carried out to promote the diffusion of Cr and Al elements and form a dense Cr2O3 and Al2O3 oxide film (which has excellent oxidation resistance, and Si can enhance the thermal shock resistance of the coating), which achieves chemical bonding with the metal substrate, thereby greatly improving the interfacial bonding strength.

[0010] According to the present invention, preferably, the metal substrate is a metal substrate that has undergone sandblasting and optional chemical activation treatment (the surface roughness of the treated metal substrate Ra=3.2-4.8μm), the abrasive used in the sandblasting treatment is 80-100 mesh corundum sand, the pressure of the sandblasting treatment is 0.4-0.6MPa, and the spray distance is 100-150mm.

[0011] In this invention, the chemical activation treatment involves etching with an activation solution for 60 seconds. It should be noted that the chemical activation process can be omitted for stainless steel substrates, while easily oxidized substrates such as titanium and titanium alloys require chemical activation to etch away the surface passivation film. The ratio and concentration of the activation solution should be adjusted for different metal substrates.

[0012] According to the present invention, preferably, the metal matrix is ​​made of stainless steel or Ti-Al alloy.

[0013] According to the present invention, preferably, the porosity of the bonding layer is <5%.

[0014] According to the present invention, preferably, the porosity of the transition layer is <3%.

[0015] According to the present invention, preferably, the porosity of the functional layer is <2%.

[0016] According to the present invention, preferably, the porosity of the sealing layer is <0.1%.

[0017] According to the present invention, preferably, the thickness of the bonding layer is 15-20 μm.

[0018] According to the present invention, preferably, the thickness of the transition layer is 25-30 μm.

[0019] According to the present invention, preferably, the thickness of the functional layer is 40-50 μm.

[0020] According to the present invention, preferably, the thickness of the sealing layer is 5-10 μm.

[0021] According to the present invention, preferably, based on the total mass of the CrAlSi alloy powder, the mass fraction of Cr is 50-55%, the mass fraction of Al is 40-45%, and the mass fraction of Si is 5%.

[0022] According to the present invention, preferably, the cold spraying (CS) uses nitrogen as the working gas. When performing the cold spraying, the working gas pressure is 4.0-4.5 MPa, the working gas is heated to 400-450°C, the metal substrate needs to be preheated to 100-150°C, the spraying distance is 15-20 mm, and the powder feeding rate is 6-8 g / min.

[0023] According to the present invention, preferably, when preparing the bonding layer, the vacuum annealing conditions include: heating to 550-650°C at a heating rate of 4.5-5.5°C / min and holding at that temperature for 1.5-2.5 hours.

[0024] According to the present invention, preferably, the mass fraction of SiC powder in each transition sublayer from the bonding layer to the functional layer is linearly reduced from 22.5% to 20%, and the mass fraction of Al powder is linearly reduced from 67.5% to 30%. In the present invention, the mass fractions of Al powder and SiC powder in each transition sublayer are adjusted in reverse gradient according to the mass fraction of lamellar h-BN powder in each transition sublayer. The SiC / Al composite phase can enhance interlayer toughness and prevent high-temperature cracking of the coating.

[0025] According to the present invention, preferably, the transition layer is obtained by spraying each transition sublayer material layer by layer with atmospheric plasma spraying (APS), and after the previous transition sublayer is sprayed, the part to be sprayed needs to be cooled to <150°C before the next transition sublayer is sprayed to prevent the accumulation of interlayer thermal stress.

[0026] According to the present invention, preferably, the process parameters of the atmospheric plasma spraying include: plasma power of 32-38kW, a mixture of Ar and H2 as the working gas, a volume ratio of Ar to H2 of (2.5-3.5):1, a spraying distance of 120-150mm, and a powder feeding rate of 18-20g / min.

[0027] According to the present invention, preferably, the multilayer transition sublayer has 3-5 layers.

[0028] According to the present invention, preferably, based on the total mass of the raw materials of the functional layer, the mass fraction of the flake-shaped h-BN powder is 55-60%, the mass fraction of Y2O3 powder is 2-4%, the mass fraction of Al2O3 powder is 16-18%, and the mass fraction of ZrO2 powder is 20-25%.

[0029] According to the present invention, preferably, the functional layer is obtained by high-speed flame spraying of the raw material of the functional layer onto the transition layer and then vacuum annealing.

[0030] In this invention, the functional layer is the main barrier layer for hydrogen blocking.

[0031] According to the present invention, preferably, the high-speed flame spraying gun uses propylene as fuel and oxygen as combustion-supporting gas, and the flow ratio of propylene to oxygen is (250-350):(800-900); the internal combustion chamber pressure of the high-speed flame spraying gun is 0.5-0.6MPa; the spraying distance of the high-speed flame spraying is 200-250mm, the powder feeding rate is 25-30g / min, and the spraying is performed in 4-5 passes.

[0032] According to the present invention, preferably, when preparing the functional layer, the vacuum annealing conditions include: heating to 750-850°C at a heating rate of 4.5-5.5°C / min and holding at that temperature for 1.5-2.5 hours to improve the density of the functional layer.

[0033] According to the present invention, preferably, the adhesive has a mass fraction of 1-3% based on the total mass of the raw materials of the sealing layer. The adhesive is preferably polyvinyl alcohol (PVA).

[0034] According to the present invention, preferably, the sealing layer is obtained by spin-coating the raw material of the sealing layer onto the functional layer and then drying, sintering and curing it.

[0035] In this invention, as a preferred embodiment, the raw material of the sealing layer is spin-coated onto the functional layer, and the spin-coating is repeated 3 times. After each spin-coating, the material is dried at 120°C for 30 minutes before the next spin-coating is performed. After all spin-coatings are completed, sintering and curing are carried out.

[0036] According to the present invention, preferably, the sintering and solidification conditions include: first heating to 550-650°C at a heating rate of 4.5-5.5°C / min, holding at that temperature for 0.5-1.5h, and then continuing to heat to 800-900°C at a heating rate of 4.5-5.5°C / min, holding at that temperature for 0.5-1.5h.

[0037] In this invention, the sealing layer is prepared by a sol-gel spin coating + sintering curing process, which achieves a surface porosity of <0.1% while significantly enhancing the high-temperature stability and hydrogen barrier properties of the coating.

[0038] Another aspect of the present invention provides the application of the aforementioned high-temperature resistant and low-hydrogen-permeability composite coating in hydrogen energy equipment.

[0039] According to the present invention, preferably, the hydrogen energy equipment includes a high-temperature hydrogen storage container and a hydrogen delivery pipeline.

[0040] The beneficial effects of the technical solution of the present invention are as follows: Based on the unique advantages of h-BN, this invention overcomes the intrinsic defects of a single h-BN coating through a multi-level gradient composite design and interface-strengthened coating preparation process. This improves the interfacial bonding strength between the coating and the metal substrate (the bonding layer design combines mechanical interlocking and chemical bonding, increasing the interfacial bonding strength to >30MPa), enhances the coating's oxidation resistance in high-temperature, oxygen-rich environments (Y2O3 exhibits a self-healing effect at high temperatures, allowing the coating to maintain structural integrity at 1000℃, improving coating stability), and optimizes mechanical properties (hardness, wear resistance) and thermal shock resistance. It constructs a coating system with ultra-low hydrogen permeability (the synergistic effect of h-BN's physical barrier and chemical adsorption reduces hydrogen permeability by two orders of magnitude compared to the bare substrate), high-temperature stability, and strong adaptability to dynamic operating conditions. This solves the technical bottlenecks of existing h-BN coatings, such as low interfacial bonding strength, insufficient high-temperature oxidation and thermal shock resistance, and poor adaptability to dynamic operating conditions.

[0041] The coating of this invention adopts a multi-layer gradient composite hydrogen barrier structure with hexagonal boron nitride (h-BN) as the core reinforcing phase. Through the synergistic gradient design of h-BN composition content, porosity and microstructure, and combined with the interface strengthening coating preparation process, the thermal stress between the coating and the metal substrate is effectively relieved, and the interfacial bonding strength and thermal shock resistance are significantly improved.

[0042] The coating preparation of this invention integrates multiple processes, achieving optimized deposition and densification sealing of each layer.

[0043] The coating of this invention exhibits extremely low hydrogen permeability, excellent high-temperature oxidation resistance, and long-term service stability at high temperatures. It is particularly suitable for applications with stringent requirements for hydrogen barrier and heat resistance, such as hydrogen energy equipment (e.g., high-temperature hydrogen storage containers). It is applicable to various substrate surfaces such as stainless steel and Ti-Al alloys, providing an innovative solution for hydrogen barrier protection in extreme high-temperature environments.

[0044] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0045] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0046] Figure 1 A schematic diagram of a high-temperature resistant and low-hydrogen-permeability composite coating provided in Embodiment 1 of the present invention is shown.

[0047] Figure 2A schematic diagram of the preparation process of a high-temperature resistant and low-hydrogen-permeability composite coating provided in Embodiment 1 of the present invention is shown.

[0048] Figure 3 The electrochemical hydrogen permeation curve of a high-temperature resistant and low-hydrogen-permeability composite coating provided in Embodiment 1 of the present invention is shown.

[0049] The annotations in the attached figures are explained as follows: Bonding layer 1, transition layer 2, functional layer 3, sealing layer 4, metal substrate 5. Detailed Implementation

[0050] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0051] Example 1

[0052] This embodiment provides a high-temperature resistant and low-hydrogen-permeability composite coating, such as... Figure 1 As shown, the composite coating includes a bonding layer 1, a transition layer 2, a functional layer 3, and a sealing layer 4 arranged sequentially from bottom to top with decreasing porosity.

[0053] (1) Coating design

[0054] The raw material for the bonding layer is CrAlSi alloy powder. Based on the total mass of the CrAlSi alloy powder, the mass fraction of Cr is 55%, the mass fraction of Al is 40%, and the mass fraction of Si is 5%. The particle size of the CrAlSi alloy powder is 5-25 μm. The thickness of the bonding layer is 17-18 μm, and the porosity is <5%.

[0055] The transition layer (total thickness 26-28 μm, porosity <3%) comprises four stacked transition sublayers. Each transition sublayer independently comprises flake-shaped h-BN powder with a particle size of 1-3 μm, SiC powder with a particle size of 50-100 nm, and Al powder with a particle size of 1-5 μm. The mass fraction of flake-shaped h-BN powder in each transition sublayer increases linearly from 10% to 50% from the bonding layer to the functional layer, as shown in Table 1.

[0056] Table 1

[0057] The raw materials for the functional layer include flake-shaped h-BN powder with a particle size of 1-3 μm, Y2O3 powder with a particle size of 50-100 nm, Al2O3 powder with a particle size of 0.5-1.5 μm, and ZrO2 powder with a particle size of 50-200 nm; and based on the total mass of the raw materials for the functional layer, the mass fraction of flake-shaped h-BN powder is 55%, the mass fraction of Y2O3 powder is 3%, the mass fraction of Al2O3 powder is 17%, and the mass fraction of ZrO2 powder is 25%; the thickness of the functional layer is 44-46 μm, and the porosity is <2%.

[0058] Based on the total mass of the raw materials of the sealing layer, the raw materials of the sealing layer include 98% Al2O3-SiO2 biphase nanosol (Al / Si molar ratio 1:1.2) and 2% PVA binder; the thickness of the sealing layer is 6-7 μm and the porosity is <0.1%.

[0059] (2) Coating preparation

[0060] Substrate pretreatment: 80-100 mesh corundum sand, 0.5MPa compressed air, and a spray distance of 120mm were used to sandblast the 316L stainless steel D metal substrate 5 (a structural material for high-temperature hydrogen storage containers) to obtain a rough surface with Ra=4.2μm.

[0061] Bonding layer deposition (cold spraying): CrAlSi alloy powder is cold sprayed onto a metal substrate and then vacuum annealed to obtain a bonding layer; wherein, nitrogen is used as the working gas for cold spraying, and the working gas pressure is 4.25 MPa, the working gas is heated to 420°C, the metal substrate needs to be preheated to 135°C, the spraying distance is 15-19 mm, and the powder feeding rate is 7 g / min; the vacuum annealing conditions for preparing the bonding layer include: heating to 600°C at a heating rate of 5°C / min and holding at that temperature for 2 hours.

[0062] Transition layer preparation (APS spraying): The transition layer is prepared by spraying each transition sub-layer with atmospheric plasma layer by layer. After the previous transition sub-layer is sprayed, the part to be sprayed needs to be cooled to <150℃ before the next transition sub-layer is sprayed. The process parameters of the atmospheric plasma spraying include: plasma power 32-38kW, Ar and H2 mixed gas as working gas, Ar and H2 volume ratio of 3:1, spraying distance of 130mm, and powder feeding rate of 20g / min.

[0063] Functional layer coating (HVOF spraying): The functional layer is obtained by high-speed flame spraying the raw material of the functional layer onto the transition layer and then vacuum annealing; wherein, the high-speed flame spraying gun uses propylene as fuel and oxygen as combustion-supporting gas, the flow rate of propylene is 300L / min and the flow rate of oxygen is 850L / min; the internal combustion chamber pressure of the high-speed flame spraying gun is 0.5MPa; the spraying distance of the high-speed flame spraying is 220mm, the powder feeding rate is 25g / min, and the spraying is done in 4-5 passes; when preparing the functional layer, the vacuum annealing conditions include: heating to 800℃ at a heating rate of 5℃ / min and holding at that temperature for 2h.

[0064] Sealing layer treatment (sol-gel method): The raw material of the sealing layer is spin-coated onto the functional layer. The spin-coating is repeated 3 times. After each spin-coating, the material is dried at 120°C for 30 minutes before the next spin-coating is performed. After all spin-coatings are completed, sintering and curing are performed. The sintering and curing conditions include: first heating to 600°C at a heating rate of 5°C / min and holding at that temperature for 1 hour, then continuing to heat to 850°C at a heating rate of 5°C / min and holding at that temperature for 1 hour.

[0065] Test case

[0066] This test case examines the coating of Example 1. The test methods and results are shown in Table 2. Figure 3 .

[0067] Table 2

[0068] As shown in Table 1, this invention overcomes the technical bottleneck of a single h-BN coating through multi-level gradient composite design and interface strengthening technology. Specifically: This invention utilizes the self-healing mechanism of Y2O3 to ensure that the coating maintains its structural integrity even at 1000℃; This invention improves the interfacial bonding strength to >30MPa through a bonding layer design that combines mechanical interlocking and chemical bonding.

[0069] Figure 3 The electrochemical hydrogen permeation curves of the high-temperature hydrogen storage container coating sample in Example 1 are shown. According to GB / T 30074, hydrogen permeation tests were conducted using a Devanathan-Stachurski dual electrolytic cell, with the sample sandwiched between the two cells. The anode cell served as the detection cell, and the cathode cell as the hydrogen charging cell. A Gamry electrochemical workstation was used to apply polarization to the sample and collect the hydrogen permeation current density. A constant current source was used to charge the sample with hydrogen at a current density of 1 mA / cm². 2 The hydrogen escape side potential is 300mV vs SCE. When the hydrogen escape side current density reaches the maximum steady-state value I... ∞ Stop the test when the time is right; Effective diffusion coefficient of hydrogen ; in: The effective diffusion coefficient of D-hydrogen atoms, in cm⁻¹ 2 ·s -1 ; L - Total thickness of the sample (sum of metal substrate and coating), in cm; t 0.63 -Hydrogen permeation current I( t ) reaches its steady-state value I ∞ The time corresponding to 63% of the time, in seconds; I ∞ —Steady-state hydrogen permeation current density, in A·cm 2 (This can be read from the electrochemical hydrogen permeation curve); according to Figure 3 Read the steady-state hydrogen permeation current I of the coated sample ∞ 0.10 μA·cm 2 , t 0.63 Given a sample thickness L of 702387 s and a total sample thickness L of 0.5 mm, calculate the effective diffusion coefficient of hydrogen. D =5.93×10 -10 cm 2 ·s -1 ; Under the same experimental conditions: the steady-state hydrogen permeation current I of the bare metal substrate sample ∞ ′ is 0.14 μA·cm 2 , t 0.63 Given that L′ is 7157 s and the sample thickness L′ is 0.5 mm, calculate the effective diffusion coefficient of hydrogen. D =3.92×10 -8 cm 2 ·s -1 ; The comparison shows that the effective hydrogen diffusion coefficient D of the coated sample is about 1 / 66 of that of the bare metal substrate sample D′. This indicates that the composite coating prepared in this invention has a significant barrier effect on hydrogen permeation, and the hydrogen barrier performance is improved by nearly two orders of magnitude.

[0070] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A high-temperature resistant and low-hydrogen-permeability composite coating, characterized in that, The composite coating comprises, from bottom to top, a bonding layer, a transition layer, a functional layer, and a sealing layer, with decreasing porosity in the order of bottom to top; The bonding layer is obtained by cold spraying CrAlSi alloy powder onto a metal substrate and then vacuum annealing; the particle size of the CrAlSi alloy powder is 5-25μm. The transition layer comprises multiple transition sublayers stacked together. Each transition sublayer independently comprises flake-shaped h-BN powder with a particle size of 1-3 μm, SiC powder with a particle size of 50-100 nm, and Al powder with a particle size of 1-5 μm. Furthermore, the mass fraction of the flake-shaped h-BN powder in each transition sublayer increases linearly from 10% to 50% from the bonding layer to the functional layer. The raw materials for the functional layer include flake-shaped h-BN powder with a particle size of 1-3 μm, Y2O3 powder with a particle size of 50-100 nm, Al2O3 powder with a particle size of 0.5-1.5 μm, and ZrO2 powder with a particle size of 50-200 nm; and the mass fraction of the flake-shaped h-BN powder in the functional layer is 55-60%. The raw materials for the sealing layer include Al2O3-SiO2 biphase nanosol and binder.

2. The high-temperature resistant and low-hydrogen-permeability composite coating according to claim 1, wherein, The metal substrate is a metal substrate that has undergone sandblasting and optional chemical activation treatment. The abrasive used in the sandblasting treatment is 80-100 mesh corundum sand, the sandblasting pressure is 0.4-0.6 MPa, and the spray distance is 100-150 mm. The metal matrix is ​​made of stainless steel or Ti-Al alloy.

3. The high-temperature resistant and low-hydrogen-permeability composite coating according to claim 1, wherein, The porosity of the bonding layer is <5%; The porosity of the transition layer is <3%; The porosity of the functional layer is <2%; The porosity of the sealing layer is <0.1%.

4. The high-temperature resistant and low-hydrogen-permeability composite coating according to claim 1, wherein, The thickness of the bonding layer is 15-20 μm; The thickness of the transition layer is 25-30 μm; The thickness of the functional layer is 40-50 μm; The thickness of the sealing layer is 5-10 μm.

5. The high-temperature resistant and low-hydrogen-permeability composite coating according to claim 1, wherein, Based on the total mass of the CrAlSi alloy powder, the mass fraction of Cr is 50-55%, the mass fraction of Al is 40-45%, and the mass fraction of Si is 5%. The cold spraying uses nitrogen as the working gas. When performing the cold spraying, the working gas pressure is 4.0-4.5MPa, the working gas is heated to 400-450℃, the metal substrate needs to be preheated to 100-150℃, the spraying distance is 15-20mm, and the powder feeding rate is 6-8g / min. When preparing the bonding layer, the vacuum annealing conditions include: heating to 550-650°C at a heating rate of 4.5-5.5°C / min and holding at that temperature for 1.5-2.5 hours.

6. The high-temperature resistant and low-hydrogen-permeability composite coating according to claim 1, wherein, The mass fraction of SiC powder in each transition sublayer from the bonding layer to the functional layer decreases linearly from 22.5% to 20%, and the mass fraction of Al powder decreases linearly from 67.5% to 30%. The transition layer is made by spraying each transition sub-layer with atmospheric plasma layer by layer. After the previous transition sub-layer is sprayed, the part to be sprayed needs to be cooled to <150°C before the next transition sub-layer is sprayed. The process parameters for atmospheric plasma spraying include: plasma power of 32-38kW, a mixture of Ar and H2 as the working gas, a volume ratio of Ar to H2 of (2.5-3.5):1, a spraying distance of 120-150mm, and a powder feeding rate of 18-20g / min. The multi-layer transition sublayer consists of 3-5 layers.

7. The high-temperature resistant and low-hydrogen-permeability composite coating according to claim 1, wherein, Based on the total mass of the raw materials of the functional layer, the mass fraction of flake h-BN powder is 55-60%, the mass fraction of Y2O3 powder is 2-4%, the mass fraction of Al2O3 powder is 16-18%, and the mass fraction of ZrO2 powder is 20-25%. The functional layer is obtained by high-speed flame spraying of the raw material of the functional layer onto the transition layer and then vacuum annealing. The high-speed flame spraying gun uses propylene as fuel and oxygen as combustion-supporting gas, with a flow ratio of propylene to oxygen of (250-350):(800-900); the internal combustion chamber pressure of the high-speed flame spraying gun is 0.5-0.6 MPa; the spraying distance of the high-speed flame spraying is 200-250 mm, the powder feeding rate is 25-30 g / min, and the spraying is performed in 4-5 passes. When preparing the functional layer, the vacuum annealing conditions include: heating to 750-850℃ at a heating rate of 4.5-5.5℃ / min and holding at that temperature for 1.5-2.5h.

8. The high-temperature resistant and low-hydrogen-permeability composite coating according to claim 1, wherein, The adhesive has a mass fraction of 1-3% based on the total mass of the raw materials used in the sealing layer. The sealing layer is obtained by spin-coating the raw material of the sealing layer onto the functional layer, followed by drying, sintering and curing. The sintering and solidification conditions include: first, heating to 550-650℃ at a heating rate of 4.5-5.5℃ / min, holding at that temperature for 0.5-1.5h, and then continuing to heat to 800-900℃ at a heating rate of 4.5-5.5℃ / min, holding at that temperature for 0.5-1.5h.

9. The application of the high-temperature resistant and low-hydrogen-permeability composite coating according to any one of claims 1-8 in hydrogen energy equipment.

10. The application according to claim 9, wherein, The hydrogen energy equipment includes a high-temperature hydrogen storage container and a hydrogen delivery pipeline.

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