Composite hydrogen-resistant coating as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of coating materials, and discloses a composite hydrogen-resistant coating as well as a preparation method and application thereof. In the composite hydrogen-resistant coating, a matrix is coated with an iron-aluminum alloy transition layer, an Al2O3 hydrogen-resistant layer and a phosphate protective layer from inside to outside. According to the preparation method disclosed by the invention, in the traditional embedding aluminizing and low-temperature in-situ oxidation processes, aluminizing layer heat treatment and mechanical polishing processes are creatively introduced, and a sol-gel technology is adopted to prepare a phosphate protective layer. After the coating preparation process, the tensile strength change of the prepared composite hydrogen-resistant coating material is less than 5%, and the elongation change of the prepared composite hydrogen-resistant coating material is less than 10%. Therefore, the composite hydrogen-resistant coating provided by the invention has small influence on the performance of the 316L stainless steel matrix material.

Description

Technical Field

[0001] The invention relates to the technical field of coating materials, and in particular to a composite hydrogen barrier coating and a preparation method and application thereof. Background Art

[0002] Hydrogen atoms and their isotopes have a very small radius and strong permeability. Once they penetrate into the materials of reactor structural components, they will cause varying degrees of damage to the materials, which will cause serious economic losses and even cause serious reactor safety accidents and radioactive pollution to the environment. For example, in space reactors using zirconium hydride as a moderator, the diffusion and penetration of hydrogen at high temperatures causes the hydrogen content in the moderator to continue to decrease, which may lead to insufficient reactivity of the entire reactor and failure to reach criticality, as well as reduced thermoelectric conversion efficiency. For another example, in the field of accident-tolerant fuel ATF, compared with traditional zirconium alloys, although the FeCrAl alloy cladding has excellent high-temperature oxidation resistance and high-temperature mechanical properties, its deuterium permeability is dozens of times higher, which may cause potential tritium radioactive contamination. For another example, in fusion reactors using deuterium and tritium as raw materials, hydrogen isotope leakage will cause serious fuel loss, radioactive contamination, and deterioration of structural component material performance. The solution is to set up a permeation barrier on the permeation path of hydrogen and its isotopes. Therefore, it is crucial for the development of future nuclear reactors to prepare hydrogen / deuterium / tritium barrier coatings (hereinafter referred to as hydrogen barrier coatings) materials with comprehensive properties such as good thermal stability and radiation resistance on the surface of reactor structural components to hinder the penetration of hydrogen and its isotopes.

[0003] Al2O3 (especially α-Al2O3) has become a hot topic in the research of hydrogen barrier coatings due to its good anti-tritium penetration performance, high resistivity, high temperature resistance, and good compatibility with lithium and lead. Among them, the gradual composition and structure of the FeAl alloy gradient transition layer can alleviate the thermal matching problem between the substrate and the Al2O3 coating. At the same time, the high activity of Al atoms in the FeAl transition layer can provide sufficient Al sources for the self-repair of Al2O3 during use, thereby repairing the microcracks of the coating and realizing its self-repair function. These good comprehensive properties make the Al2O3 coating with FeAl alloy transition layer (Fe-Al / Al2O3 coating) the preferred hydrogen barrier coating for all participating countries of the International Thermonuclear Experimental Reactor (ITER).

[0004] At present, most studies generally use high-temperature oxidation environments above 950°C, while there are few studies on oxidation below 750°C. This process route has problems: high-temperature oxidation treatment has an adverse effect on the mechanical properties of the substrate. Although the mechanical properties can be restored by heat treatment suitable for the substrate (rapid cooling + aging), the rapid cooling process is likely to cause the Al2O3 film formed at high temperature to crack due to excessive thermal stress, and there are voids in the coating, so the coating has poor tritium penetration resistance.

[0005] In addition, the high-temperature hydrogen permeation resistance of the single-layer Fe-Al / Al2O3 coating has decreased significantly (generally, the hydrogen resistance factor PRF≤500 at 600°C), and it is still difficult to meet the high-temperature hydrogen resistance performance requirements of some high-temperature reactors. For example, the gas-phase hydrogen resistance factor of the space nuclear power source at 600°C vacuum requires PRF≥500, and the gas-phase hydrogen resistance factor PRF≥1000 in the (He+CO2) environment at 600°C. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a composite hydrogen barrier coating and a preparation method and application thereof.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a composite hydrogen barrier coating, wherein a substrate is coated from the inside to the outside with an iron-aluminum alloy transition layer, an Al2O3 hydrogen barrier layer and a phosphate protective layer.

[0009] The composite hydrogen barrier coating of the present invention is a coating material with a low neutron absorption cross section (thermal neutron absorption cross section: σMg<σZr<σAl<σFe). The iron-aluminum alloy transition layer mainly plays a role similar to that of the metal bottom layer. By forming intermetallic compounds to adjust the thermal expansion coefficient, the difference between the thermal expansion coefficients of the metal matrix and the oxide is achieved, the adhesion performance is improved, and the layer has a certain hydrogen barrier performance. An in-situ oxidation method is used on the surface of the iron-aluminum alloy transition layer, and the Al2O3 hydrogen barrier layer is prepared by selective oxidation of the Fe-Al alloy transition layer at low temperature. Finally, a phosphate protective layer is prepared on the outer surface of the coating by sol-gel technology. The layer belongs to a glass structure, has high-temperature fluidity and has a hydrogen barrier capacity that is about several dozen times higher than that of the substrate. The glass has a strong bonding strength relative to the oxide, can fill the cracks generated in the oxide layer, and protect the oxide layer with its good high-temperature strength, so that the oxide layer is not easy to crack, thereby stabilizing the structure and performance of the entire coating. The presence of the magnesium phosphate outer protective layer further improves the high-temperature hydrogen penetration resistance of the Fe-Al / Al2O3 coating.

[0010] In a second aspect, the present invention provides a method for preparing a composite hydrogen barrier coating, comprising the following steps:

[0011] (1) grinding the substrate; embedding the sample with an aluminizing agent, and aluminizing the sample at a temperature of 100 °C; and then heat treating the sample in a vacuum environment to obtain an aluminized layer;

[0012] In parts by mass, the aluminizing agent includes 20-50% Al powder, 2-10% AlCl3 powder, and 40-78% Al2O3 powder;

[0013] The aluminizing temperature is 500°C-750°C, and the time is 1h-10h;

[0014] The heat treatment temperature is 500°C-750°C, and the time is 10h-250h;

[0015] (2) removing the Kirkendall pore layer on the shallow surface of the aluminized layer by mechanical polishing to obtain an iron-aluminum alloy transition layer;

[0016] (3) in-situ oxidation of the iron-aluminum alloy transition layer to obtain an Al2O3 hydrogen barrier layer;

[0017] (4) Coating the Al2O3 hydrogen barrier layer with a phosphate sol and sintering to obtain a composite hydrogen barrier coating.

[0018] The preparation method of the present invention creatively introduces a heat treatment + mechanical polishing process of the aluminized layer in the traditional embedded aluminizing + low-temperature in-situ oxidation process. The heat treatment can completely transform the aluminized layer mainly composed of the Fe2Al5 phase into the aluminized layer mainly composed of the FeAl phase. The aluminizing agent can achieve low-temperature high-activity aluminizing. The mechanical polishing process can effectively remove the Kirkendall hole layer on the shallow surface of the coating. In addition, the mechanical polishing process of the coating can also significantly improve the uniformity of the thickness of the FeAl coating after heat treatment. The introduction of the heat treatment + mechanical polishing process of the aluminized layer can realize the preparation of a dense Al2O3 hydrogen barrier layer by selective oxidation of the Fe-Al alloy transition layer at low temperature. A phosphate protective layer is prepared on the outer surface of the coating by using sol-gel technology. The layer belongs to a glass structure, has high-temperature fluidity and has a hydrogen barrier capacity that is about several dozen times higher than that of the substrate. The glass has a strong bonding strength relative to the oxide, can fill the cracks generated in the oxide layer, and protect the oxide layer with its good high-temperature strength, so that the oxide layer is not easy to crack, thereby stabilizing the structure and performance of the entire coating. Therefore, despite the coating preparation process, the change in tensile strength of the base material is less than 5%, and the change in elongation is less than 10%, indicating that the composite hydrogen barrier coating of the present invention has little effect on the performance of the 316L stainless steel base material.

[0019] As a preferred embodiment of the method for preparing the composite hydrogen barrier coating of the present invention, in step (1), the grinding is performed using sandpaper with mesh sizes of 600-2000.

[0020] As a preferred embodiment of the method for preparing the composite hydrogen barrier coating of the present invention, in step (2), the mechanical polishing uses diamond polishing liquid particles with a diameter of 3 μm-9 μm, and the polishing time is 1 min-15 min.

[0021] As a preferred embodiment of the method for preparing the composite hydrogen barrier coating of the present invention, in step (3), the oxidizing atmosphere is 3% O2 ​​oxygen-argon mixed gas-pure oxygen, the temperature is 600°C-750°C, and the time is 2h-50h.

[0022] As a preferred embodiment of the method for preparing the composite hydrogen barrier coating of the present invention, in step (4), the phosphate sol includes 0.1 mol / L-2 mol / L of magnesium dihydrogen phosphate and 0.1 vol%-1 vol% of sulfur salt.

[0023] As a preferred embodiment of the method for preparing the composite hydrogen barrier coating of the present invention, in step (4), the spin coating speed of the coating is 300 r / min-4000 r / min, the time is 30 s-3 min, and the number of coatings is 1-10 times.

[0024] As a preferred embodiment of the method for preparing the composite hydrogen barrier coating of the present invention, in step (4), the sintering temperature is 300° C.-650° C., and the sintering time is 0.5 h-5 h.

[0025] In a third aspect, the present invention provides a composite hydrogen barrier coating prepared by the preparation method of the composite hydrogen barrier coating.

[0026] In a fourth aspect, the composite hydrogen barrier coating of the present invention is applied to coating materials of reactor structural components.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The preparation method of the present invention creatively introduces a heat treatment + mechanical polishing process of the aluminized layer in the traditional embedded aluminizing + low-temperature in-situ oxidation process. The heat treatment can completely transform the aluminized layer mainly composed of the Fe2Al5 phase into the aluminized layer mainly composed of the FeAl phase. The aluminizing agent can achieve low-temperature high-activity aluminizing. The mechanical polishing process can effectively remove the Kirkendall hole layer on the shallow surface of the coating. In addition, the mechanical polishing process of the coating can also significantly improve the uniformity of the thickness of the FeAl coating after heat treatment. The introduction of the heat treatment + mechanical polishing process of the aluminized layer can realize the preparation of a dense Al2O3 hydrogen barrier layer by selective oxidation of the Fe-Al alloy transition layer at low temperature. A phosphate protective layer is prepared on the outer surface of the coating by using sol-gel technology. The layer belongs to a glass structure, has high-temperature fluidity and has a hydrogen barrier capacity that is about several dozen times higher than that of the substrate. The glass has a strong bonding strength relative to the oxide, can fill the cracks generated in the oxide layer, and protect the oxide layer with its good high-temperature strength, so that the oxide layer is not easy to crack, thereby stabilizing the structure and performance of the entire coating. Therefore, despite the coating preparation process, the prepared composite hydrogen barrier coating changes the tensile strength of the base material by less than 5% and the elongation by less than 10%, indicating that the composite hydrogen barrier coating of the present invention has little effect on the performance of the 316L stainless steel base material. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention provides a process flow for preparing the Fe-Al / Al2O3 / magnesium phosphate coating;

[0030] Figure 2 The surface morphology of the aluminum-infiltrated film at 600℃-2h (500×);

[0031] Figure 3 BSE cross-section of 600℃-2h embedded aluminizing (1000×);

[0032] Figure 4 The XRD spectrum of aluminum embedded at 600℃-2h;

[0033] Figure 5 The surface morphology (500×) is 600℃-2h-10℃ / min-700℃-heat treated for 60h;

[0034] Figure 6 BSE cross-sectional view (1000×) of 600℃-2h-10℃ / min-700℃-heat treatment for 60h;

[0035] Figure 7 The XRD pattern is 600℃-2h-10℃ / min-700℃-heat treatment for 60h;

[0036] Figure 8The surface morphology (500×) is after heat treatment at 700℃ for 60h, polishing with 2000-grit sandpaper for 5min and polishing with 3μm polishing liquid for 5min (300r / min);

[0037] Fig. 9 BSE cross-sectional view (1000×) after 700℃-heat treatment for 60h, polishing with 2000-grit sandpaper for 5min + polishing with 3μm polishing liquid for 5min (300r / min);

[0038] Fig.10 This is the XRD spectrum after heat treatment at 700℃ for 60h, followed by polishing with 2000-grit sandpaper for 5min and polishing with 3μm polishing liquid for 5min (300r / min);

[0039] Fig.11 The surface morphology and backscattering image of the sample were 600℃-2h embedding-700℃-60h heat treatment-700℃-24h-O2-1kpa oxidation;

[0040] Fig.12 The surface morphology and element distribution of the sample at 1000× were obtained by embedding at 600℃-2h, heat treatment at 700℃-60h, oxidation at 700℃-24h, and oxidation at 1kpa;

[0041] Fig.13 The XPS data of the sample surface was obtained by 600℃-2h embedding-700℃-60h heat treatment-700℃-24h-O2-1kpa oxidation;

[0042] Fig.14 The cross-sectional TEM data of the sample was obtained by embedding at 600℃ for 2h, heat treating at 700℃ for 60h, oxidizing at 700℃ for 24h and oxidizing at 1kPa.

[0043] Fig.15 The surface morphology and backscattering image of the sample coated 4 times at a spin coating speed of 600r / min-10s+1500r / min-30s;

[0044] Fig.16 The element distribution and content of the magnesium phosphate coating coated four times at a spin coating speed of 600r / min-10s+1500r / min-30s;

[0045] Fig.17 It is a deuterium penetration test device;

[0046] Fig.18 This is the schematic diagram of the deuterium penetration test device;

[0047] Fig.19 is the hydrogen isotope permeation curve of the sample;

[0048] Fig. 20Schematic diagram of characteristic time selection of hydrogen permeation curve: (a) static method; (b) dynamic method;

[0049] Fig.21 The macroscopic surface morphology of the Fe-Al / Al2O3 / magnesium phosphate coating sample coated 4 times at a spin coating speed of 600r / min-10s+1500r / min-30s;

[0050] Fig. 22 It is the permeability-temperature curve of Fe-Al / Al2O3 / magnesium phosphate coating;

[0051] Fig.23 This is the size diagram of the sheet sample;

[0052] Fig.24 This is a macroscopic picture of the sheet sample after tensile fracture at room temperature;

[0053] Fig.25 is the stress-strain curve of the sheet sample;

[0054] Fig.26 The tensile stress and interface shear force distribution of each small piece;

[0055] Fig. 27 Provide on-site observation of the initiation and propagation of interface cracks by camera;

[0056] Fig.28 is the cross-sectional view of the coating sample;

[0057] Fig.29 This is the surface morphology of the coating near the tensile fracture of the coating sample. DETAILED DESCRIPTION

[0058] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0059] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, can be obtained from commercial channels.

[0060] Example 1: Preparation process of iron-aluminum alloy / aluminum oxide / magnesium phosphate composite hydrogen barrier coating

[0061] 1. Aluminized layer prepared by embedding aluminizing process

[0062] The specific process steps are as follows:

[0063] The surface of the 316L substrate was polished to 2000# and ultrasonically cleaned for use. Aluminum powder, alumina powder, and aluminum chloride powder were placed in a drying oven and dried at 80°C for 60 minutes, and then the powders were put into a plastic bottle at a ratio of 40wt% aluminum powder, 56wt% alumina powder, and 4wt% aluminum chloride powder, and placed in an oscillator for 2 hours to obtain an aluminizing agent. The sample was embedded in a crucible using an aluminizing agent, and the inside was filled with carbon powder to reduce the air in the crucible, sealed with refractory mud, and placed in a muffle furnace for heat preservation and aluminizing. The aluminizing temperature was 600°C and the aluminizing time was 2 hours.

[0064] Results Figure 2-4 , Figure 2 The surface morphology shown in the figure shows that the coating formed by the aluminum embedding at 600℃-2h is dense and void-free. Figure 3 The cross-sectional view shown shows that its thickness is about 14μm, Figure 4 The displayed XRD spectrum shows that the formed coating is mostly FeAl3 phase with a small amount of Fe2Al5 peaks. This is because FeAl3 is in the outermost layer of the coating and Fe2Al5 is in the inner layer. Due to the limited penetration of X-rays, most of them hit the FeAl3 layer.

[0065] 2. Heat treatment of aluminized layer

[0066] As a high-aluminum brittle phase, Fe2Al5 has compatibility issues with structural materials and is prone to cracking of the coating. These cracks will act as fast diffusion channels to increase the penetration of tritium, seriously affecting the hydrogen permeation resistance of the oxidized sample. After heat treatment at 700℃ for 60h in a vacuum environment, the aluminized layer mainly composed of Fe2Al5 phase can be completely transformed into an aluminized layer mainly composed of FeAl phase. The FeAl phase has better mechanical properties and is not prone to cracking of the coating, which is beneficial to improving the hydrogen permeation resistance of the coating and will not deteriorate the overall mechanical properties of the material.

[0067] Results Figure 5-7 , Figure 5 This is the surface morphology of the aluminized sample at 600℃ for 2h and then heat treated at 700℃ for 60h. Since the surface of the sample is covered with aluminum oxide after heat treatment, the actual morphology cannot be observed and polishing is required to remove the aluminum oxide. Figure 6 This is a cross-sectional view of the heat treatment at 700℃ for 60h. It can be found that after heat treatment for 60h, the contrast of the coating becomes lighter, indicating that a phase change has occurred. Figure 7 XRD shows that after heat treatment at 700℃ for 60h, the phase changes completely from FeAl3 to FeAl, and the FeAl coating is about 19μm thick.

[0068] The total thickness of the coating of the 600℃-2h embedded aluminized sample is about 14μm. When the heat treatment time is 700℃ for 60h, the aluminized layer mainly composed of Fe2Al5 phase can be completely transformed into the aluminized layer mainly composed of FeAl phase.

[0069] 3. Mechanical polishing of aluminized layer

[0070] After the aluminized layer is heat treated at 700℃, the Kirkendall pores generated by the difference in diffusion coefficients of Fe and Al are mainly concentrated on the shallow surface of the coating and can be effectively removed by mechanical polishing. In addition, the mechanical polishing process of the coating can also significantly improve the uniformity of the thickness of the FeAl coating after heat treatment.

[0071] Mechanical polishing was used to remove the Kirkendall pore layer on the shallow surface of the coating and to improve the uniformity of the thickness of the FeAl coating after heat treatment. 2000-grit sandpaper was used for polishing for 5 minutes, and then diamond polishing liquid particles with a diameter of 3 μm were used for polishing at 300 r / min for 5 minutes.

[0072] During the heat treatment process, mutual diffusion of Fe and Al elements will occur. Al elements on the coating surface diffuse inward, and Fe elements in the matrix diffuse outward. However, the diffusion coefficient of Al elements is larger than that of Fe elements, resulting in more Al elements diffusing inward than Fe elements diffusing outward. Therefore, a large number of Kirkendall holes are generated on the shallow surface of the coating. Figure 8 It shows that after polishing at 300 r / min for 5 min with 2000 grit sandpaper and 300 r / min for 5 min with 3 μm polishing liquid, the number of pores is significantly reduced. Fig. 9 The coating thickness was reduced from 19 μm to 14 μm. Fig.10 The XRD pattern shows that the phase remains FeAl after polishing.

[0073] 4. In-situ oxidation of FeAl layer

[0074] First, place the aluminized layer sample in a high-temperature tube furnace, set the vacuum degree of the pressure-stabilizing exhaust system to a lower value, and evacuate the residual gas in the channel and tube. At the same time, the high-temperature tube furnace is heated to the set value at 10°C / min, start the insulation program, set the O2 and Ar mixing ratio to determine the oxidation environment, turn on the dual-channel gas flow controller, and start the in-situ oxidation of the coating sample.

[0075] The present invention adopts an in-situ selective oxidation method to prepare an Al2O3 hydrogen barrier layer at low temperature. It is intended to prepare the Al2O3 hydrogen barrier layer by oxidation of the Fe-Al alloy transition layer at low temperature (700°C). According to the selective oxidation principle of the alloy and the oxidation phase diagram theory, a systematic study is carried out from the aspects of controlling the alloy content, oxidation atmosphere, oxidation time and pretreatment to achieve selective oxidation to prepare a dense Al2O3 film.

[0076] Fig.11 and 12 The oxidation temperature of the coating sample shown is 700℃, the oxidation time is 24h, and the oxidation atmosphere is pure oxygen atmosphere (1kPa pressure). Fig.11 and 12 From the surface morphology and element distribution, it can be seen that the oxide layer coating of the sample oxidized at 700℃-24h-O2-1kpa is dense and the elements are evenly distributed.

[0077] X-ray photoelectron spectroscopy (XPS) refers to the use of photoelectron information excited by inner-shell electrons or valence electrons of atoms under X-ray irradiation to analyze the elemental composition and chemical state of the sample surface. Due to the weak penetration of photoelectrons, the XPS test depth is generally 5-10nm. Here, XPS is used to effectively analyze the elemental composition and valence state information of the sample surface after oxidation.

[0078] Fig.13 The XPS graph of the sample surface oxidized at 700℃-24h-O2-1kPa is shown. It can be seen that the sample surface is mainly composed of Al and O peaks, without obvious Fe and Cr peaks, indicating that the sample surface is mainly Al2O3 phase. Fig.14 The TEM characterization results of the cross-section of the coating sample oxidized at 700℃-24h-O2-1kpa are shown. It can be seen that the main components of Area#1 are Al and O elements, and the Al:O atomic ratio is close to 2:3, indicating that the layer is Al2O3 phase, and the thickness of the Al2O3 layer is about 131nm. The main components of Area#2 are Fe and Al elements, and the Fe:Al atomic ratio is close to 1:1, indicating that the layer is FeAl phase, and a small amount of Cr and Ni elements are caused by the diffusion of elements in the 316L stainless steel matrix into the FeAl layer.

[0079] 5. Preparation of magnesium phosphate coating on FeAl / Al2O3 substrate

[0080] There are a few pores on the surface of the aluminum oxide layer of the FeAl / Al2O3 matrix prepared by the embedding-heat treatment-polishing-in-situ oxidation process. During the preparation of the phosphate layer, it can further densify the pores on the surface of the aluminum oxide layer and protect the aluminum oxide layer. At the same time, the phosphate layer also has a certain degree of hydrogen barrier effect, which can further improve the hydrogen barrier performance.

[0081] The phosphate protective layer is prepared by a sol-gel method, specifically:

[0082] The FeAl / Al2O3 matrix sample was ultrasonically cleaned in anhydrous ethanol for 3 minutes, and then plasma cleaned for 4 minutes. The concentration of magnesium dihydrogen phosphate was set to 1 mol / L, and 0.1 vol% sulfur salt was added as a surfactant to increase wettability. The spin coating speed was 600r / min-10s+1500r / min-30s (i.e., first 600 slow spin for 10s, then 1500 fast spin for 30s), and the number of coatings was set to 4 times. When spin coating, first use a pipette to absorb 0.05mL of 1mol / L magnesium dihydrogen phosphate solution, wait for one minute after the sample surface is dripped with the solution, and then start the spin coater. After the spin coating is completed, the sample is placed in a drying oven at 80℃ and dried for 10 minutes. This is the step of coating once. If it is coated 4 times, the dried sample needs to be spin coated again → dried, and this cycle is repeated 4 times. Finally, the sample is sintered in a tubular furnace, and the vacuum degree of the tubular furnace is set to 50mttor. During sintering, the temperature was first increased to 300°C at a rate of 5°C / min and kept for 1 hour, then increased to 450°C at a rate of 1°C / min and kept for 1 hour, then increased to 600°C at a rate of 1°C / min and kept for 1 hour, and finally decreased to room temperature at a rate of 5°C / min.

[0083] from Fig.15 and Fig.16 From the surface morphology and element distribution diagram, it can be seen that when the coating times increases to 4 times, the pores on the coating surface morphology are few and shallow, and the element distribution diagram shows the uniform distribution of Mg and P elements in the pores.

[0084] Example 2: Performance of Fe-Al alloy / aluminum oxide / magnesium phosphate composite hydrogen barrier coating

[0085] 1. Introduction of hydrogen isotope permeation test device

[0086] Build a hydrogen isotope permeation test device, such as Fig.17 As shown, it can test sheet samples with a thickness of about 0.5mm and tubular samples with a diameter of less than 10mm, a thickness of about 0.5mm, and a length of 10cm-50cm, which fully meets the needs of the coating hydrogen isotope permeability test in this project. Fig.18As shown. In order to ensure the cleanliness and pollution-free of the pipeline, electrolytically polished 1 / 4" stainless steel pipeline is used, and the pipeline is heated outside; the vacuum chamber has heating temperature control to reduce background interference; a heating furnace is used, the heating temperature range is 25℃-1200℃, and the temperature control is stable at ±2℃; the imported molecular pump of German Pfeiffer Vacuum is selected to achieve the required vacuum degree; a dry pump is used as the front pump to realize an oil-free vacuum system; a mass spectrometer of German Pfeiffer Vacuum is used to analyze and detect the penetration data, and the fastest response time is 2ms. The pipeline adopts double ferrules and VCR connectors. The vacuum part of the low-pressure side detection chamber adopts CF flange interface to ensure good vacuum degree. The quadrupole mass spectrometer adopts QMG220M1 of German PFEIFFERVACUUM. The front pump of the vacuum system adopts a dry pump, and the molecular pump adopts Hipace80 of German Pfeiffer Vacuum.

[0087] The rate at which hydrogen, deuterium, and tritium participate in chemical reactions is inversely proportional to the square root of their mass according to the principle of molecular dynamics. Therefore, any of them can be used to represent hydrogen isotopes in permeability experiments (ignoring the irradiation effect of tritium). Since tritium is radioactive and its operation is limited, and hydrogen has a high environmental background, deuterium is often used for permeability experiments. All permeability tests in this project will be conducted using deuterium gas.

[0088] The permeation sample divides the system into two parts: high pressure and low pressure. In the high pressure part, i.e. the upstream of the permeation, deuterium gas is introduced. A pressure regulator is designed at the upstream air inlet to maintain the upstream deuterium pressure stable during the permeation test. In the low pressure part, i.e. the downstream of the permeation, a spherical stainless steel cavity is designed to accommodate the permeated deuterium. The cavity diameter is about 200mm, and the inner surface is polished and degassed. The back vacuum degree is better than 10 during the test. -7 Under high vacuum conditions, pure D2 is filled into the sample to be tested. On the other side of the sample to be tested, the gas permeability of D2 penetrating the sample is analyzed by a quadrupole mass spectrometer to evaluate the gas permeability of the sample.

[0089] The ion current intensity-time curve directly collected by the hydrogen isotope penetration test system is as follows: Fig.19 The leakage rate-ion current intensity calibration curve obtained by calibration with a standard leak hole is used to obtain the permeation rate-time curve.

[0090] The hydrogen permeation behavior of hydrogen barrier coatings prepared under different parameters was studied to obtain the hydrogen permeation law and mechanism of the hydrogen barrier coatings, to guide the design and preparation process of the hydrogen barrier coatings, and then to feedback and optimize the coating preparation parameters.

[0091] Under constant deuterium pressure, deuterium permeation tests of coating samples were carried out at 360℃-650℃ to obtain the permeability and diffusion coefficient of the coating, and to study the evolution of the permeation behavior of the hydrogen barrier coating with the permeation temperature.

[0092] 2. Data processing and analysis principles

[0093] Gas-phase hydrogen permeation refers to the process in which hydrogen on the hydrogen-filled side of a thin-film sample permeates to the low-pressure side driven by a pressure difference. This process includes complex processes such as adsorption, decomposition, dissolution, diffusion, recombination, and desorption. Assuming that the surface process is fast enough, the hydrogen permeation rate is controlled by the bulk diffusion process, and when the ratio of the sample surface area to the thickness is very large, only one-dimensional diffusion in the normal direction of the sample can be considered. According to Fick's first law and Sievert's law, when the hydrogen partial pressure p on the hydrogen-filled side is much greater than the hydrogen partial pressure on the hydrogen-permeated side, the steady-state permeation rate of hydrogen through a unit area of ​​the sample per unit time is:

[0094]

[0095] D——Diffusion coefficient (m 2 / s);

[0096] S——solubility;

[0097] L——specimen thickness (m);

[0098] P——Hydrogen partial pressure on the hydrogen charging side (MPa)

[0099] The permeability Φ is generally defined as:

[0100] φ=DS mol / [m·s·(ΜPa) 12 ] (2)

[0101] Therefore, the basic relationship for hydrogen permeation experiment is obtained:

[0102]

[0103] Under certain conditions, we can calculate J∞ by measuring it. Moreover, whether J∞ and p satisfy the square root relationship is usually the criterion for whether the permeation process is controlled by the bulk diffusion process.

[0104] From the approximate solution of Fick's second law, it can be found that the diffusion coefficient D and the penetration lag time t1 have the following relationship:

[0105]

[0106] The simplified method of Devanathan et al. is usually used to determine t1 based on the hydrogen permeation kinetic curve, that is, the time corresponding to the transient permeation rate of 0.629J∞. This method of determining D by formula (4) is called the time lag method. In the improved time lag method, more accurate calculations show that the transient permeation rate J corresponding to t1 is t =0.6l7 J∞, this project uses the latter, such as Fig. 20 In summary, the hydrogen permeation kinetics curve can be used to determine and D, by the relation S can be calculated.

[0107] The evaluation of high temperature hydrogen barrier properties of hydrogen barrier coatings is mainly based on the size of the coating deuterium barrier factor PRF.

[0108]

[0109] Fig.21 The figure shows the permeability comparison of the Fe-Al / Al2O3 / magnesium phosphate coating in the present invention and the Fe-Al / Al2O3 reported in the literature. The deuterium blocking factor of the sample coated with the magnesium phosphate coating 4 times at a high temperature of 600°C significantly improves the deuterium blocking factor under in-situ oxidation, especially under the process of 600r / min-10s+1500r / min-30s, its deuterium blocking factor reaches 33479, which shows that the magnesium phosphate coating can increase the high temperature deuterium blocking performance of FeAl / Al2O3. Fig. 22 As shown in Table 1, the deuterium barrier performance of the Fe-Al / Al2O3 / magnesium phosphate coating prepared by this process is significantly better than the value reported in the literature.

[0110] Table 1 Deuterium rejection factor PRF of Fe-Al / Al2O3 / magnesium phosphate coating

[0111] PRF / Test Temperature 600℃ 550℃ 500℃ 450℃ <![CDATA[700℃-O2-24h oxidized sample]]> 10821 11031 7834 5645 <![CDATA[Magnesium phosphate sample oxidized at 700°C in O2 for 24 h]]> 33479 19905 23549 15161 [Ceram.Int.50(2024)20367-20375] 1678 4289 8781 11914 [Fusion Eng.Des.209(2024)114735] 1553 1772 4217 - [Surf.Coat.Tech.440(2022)128491] 124 127 90 -

[0112] Example 3: Effect of Fe-Al / Al2O3 / magnesium phosphate coating process on mechanical properties of substrate

[0113] In order to explore the influence of coating preparation process on the mechanical properties of the base material, uniaxial tensile performance tests of coated samples were carried out to obtain the yield strength, tensile strength, elongation and other mechanical performance indicators of the coated base material. The preparation process and sample number of the coating sample are as follows:

[0114] Sample #1: 316L flake matrix sample;

[0115] Sample #2: 600°C-2h aluminizing, 700°C-60h heat treatment, 650°C-O2-1kPa-10h oxidation, 600r / min-10s+1500r / min-30s coating times 4 times, i.e. the Fe-Al / Al2O3 / magnesium phosphate coating-substrate sample prepared in Example 1;

[0116] According to GB / T 228.1-201 Tensile test of metallic materials Part 1: Room temperature test method, a room temperature tensile test is carried out. The sample size is as follows: Fig.23As shown, the original gauge length is 30mm, the parallel length is 40mm, the total length of the tensile sample is 139.7mm, and the thickness is 2mm. The room temperature tensile test was carried out using an MTS universal material tensile machine with a tensile rate of 1.2mm / min. Two samples were repeatedly stretched for each coating process to eliminate the influence of accidental experimental errors.

[0117] Fig.24 The figure shows the macroscopic image of the tensile fracture of the coating substrate sample. It can be seen that all fractures are within the gauge length segment. The cross-sectional dimensions of the parallel segments change evenly, indicating that a large uniform plastic deformation occurred before the coating substrate sample necked and fractured. The crack propagation direction of the fracture is nearly perpendicular to the tensile direction, and the possible microscopic fracture mechanism is microporous aggregation fracture.

[0118] The tensile stress-strain curve of the coating substrate sample is shown in Fig.25 As shown in the figure, the stress-strain curves of the samples with the same coating process tested twice have good repeatability. All samples showed a significant deformation strengthening trend in the early stage, and before breaking, the curves tended to be flat due to the reduction of the effective bearing area, which is a typical austenitic steel tensile curve.

[0119] The tensile strength, yield strength, elongation and change values ​​of each coating substrate sample are shown in Table 2. It can be seen that despite the coating preparation process, the tensile strength of the substrate material changes by less than 2%, and the elongation changes by less than 5%. This shows that the coating preparation process has little effect on the performance of the 316L stainless steel substrate material.

[0120] Table 2 Tensile results of sheet samples

[0121]

[0122] Example 4: Bonding strength of Fe-Al / Al2O3 / magnesium phosphate coating to substrate

[0123] Whether the interface bonding between the coating material and the substrate material is good or not determines the service life of the coating to a large extent. Under the same external load, the higher the strength of the interface bonding, the stronger the ability to resist the generation and expansion of interface cracks, thereby delaying the peeling of the coating from the substrate. Therefore, it is very important to characterize and evaluate the interface bonding strength of the coating / substrate material.

[0124] Since the Fe-Al / Al2O3 coating is prepared by in-situ growth, the Fe-Al coating is an intermetallic compound and has a high bonding strength with the substrate. At the same time, the deformation capacity of the Fe-Al coating is less than that of the 316L stainless steel substrate, which is a brittle coating / tough substrate, and is suitable for the conditions of the transverse tensile method to determine the bonding strength of the coating. Therefore, the transverse tensile method is used to determine the bonding strength of the coating and the substrate. The main principle of the transverse tensile method for determining the bonding strength of the coating is as follows: Fig.26 shown.

[0125] Under the action of tensile load, the tensile stress and interface shear force distribution of each small piece of coating broken is as follows: Fig.26 The theoretical basis of this method is based on the shear lag model in fiber reinforced composite materials, that is, any stress on the coating must be transmitted through the interface between the coating and the substrate, and the expression is:

[0126]

[0127] Where: h is the thickness of the coating, τ(x) is the shear stress at the interface, σ is the normal stress in the coating, and a is the half length of the small coating bonded to the substrate after being broken.

[0128] Under the action of tensile load, when the cracks reach saturation, that is, the number of cracks no longer increases with the increase of tensile strain, the interface shear strength between the coating and the substrate can be calculated as follows:

[0129]

[0130] Among them, δ max is the maximum crack spacing, σ b is the fracture strength of the coating at which cracks are generated, and h is the thickness of the coating.

[0131] The coating was peeled off and failed by uniaxial tensile test. The time of tensile fracture of the coating was recorded by video during the tensile test and compared with the tensile stress at that time. The tensile stress at that time was used as the fracture strength σ of the coating at which the crack occurred. b The thickness of the sample coating and the maximum crack spacing of the coating after tensile fracture were determined by scanning electron microscopy. Fig. 27 .

[0132] The results are as follows Fig.28 and 29 As shown in Table 3, the average bonding strength between the Fe-Al coating and the substrate is 136.97 and 135.74 MPa, which is much greater than the bonding strength of the cold-sprayed FeAl coating annealed at 650°C for 5 hours reported in the literature (38 MPa (Surface and Coatings Technology, 2011, 205: 5502-5509). This is determined by the embedded aluminizing process. The mutual diffusion of Fe and Al leads to the formation of different Fe-Al phases in the coating. A metallurgical bond is formed between the coating and the substrate instead of a simple mechanical bond.

[0133] Table 3 Binding strength between coating and substrate of different samples

[0134]

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A composite hydrogen barrier coating, characterized in that: The substrate is coated with an iron-aluminum alloy transition layer, an Al2O3 hydrogen barrier layer and a phosphate protective layer from the inside to the outside.

2. A method for preparing a composite hydrogen barrier coating, characterized in that: The following steps are involved: (1) grinding the substrate; embedding the sample with an aluminizing agent, and aluminizing the sample at a temperature of 100 °C; and then heat treating the sample in a vacuum environment to obtain an aluminized layer; In parts by mass, the aluminizing agent includes 20-50% Al powder, 2-10% AlCl3 powder, and 40-78% Al2O3 powder; The aluminizing temperature is 500°C-750°C, and the time is 1h-10h; The heat treatment temperature is 500°C-750°C, and the time is 10h-250h; (2) removing the Kirkendall pore layer on the shallow surface of the aluminized layer by mechanical polishing to obtain an iron-aluminum alloy transition layer; (3) in-situ oxidation of the iron-aluminum alloy transition layer to obtain an Al2O3 hydrogen barrier layer; (4) Coating the Al2O3 hydrogen barrier layer with a phosphate sol and sintering to obtain a composite hydrogen barrier coating.

3. The method for preparing the composite hydrogen barrier coating according to claim 2, characterized in that: In step (1), the grinding is performed using sandpaper with mesh sizes of 600-2000.

4. The method for preparing the composite hydrogen barrier coating according to claim 2, characterized in that: In step (2), the mechanical polishing uses diamond polishing liquid particles with a diameter of 3 μm-9 μm, and the polishing time is 1 min-15 min.

5. The method for preparing the composite hydrogen barrier coating according to claim 2, characterized in that: In step (3), the oxidizing atmosphere is 3% O2 ​​oxygen-argon mixed gas-pure oxygen, the temperature is 600°C-750°C, and the time is 2h-50h.

6. The method for preparing the composite hydrogen barrier coating according to claim 2, characterized in that: In step (4), the phosphate sol includes 0.1 mol / L-2 mol / L of magnesium dihydrogen phosphate and 0.1 vol%-1 vol% of sulfur salt.

7. The method for preparing the composite hydrogen barrier coating according to claim 2, characterized in that: In step (4), the spin coating speed is 300 r / min-4000 r / min, the time is 30 s-3 min, and the number of coating times is 1-10 times.

8. The method for preparing the composite hydrogen barrier coating according to claim 2, characterized in that: In step (4), the sintering temperature is 300°C-650°C, and the sintering time is 0.5h-5h.

9. A composite hydrogen barrier coating prepared by the preparation method according to any one of claims 2 to 8.

10. Use of the composite hydrogen barrier coating according to claim 1 or the composite hydrogen barrier coating according to claim 9 in coating materials for reactor structural components.

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