A composite hydrogen barrier coating and its preparation method and application

Abstract

The present application belongs to the technical field of coating materials, and discloses a composite hydrogen barrier coating, a preparation method and application thereof. In the composite hydrogen barrier coating, the substrate is coated with an iron-aluminum alloy transition layer, an Al2O3 hydrogen barrier layer and a phosphate protective layer from inside to outside. The preparation method is creatively introduced into the heat treatment of the aluminizing layer, the mechanical polishing process and the preparation of the phosphate protective layer by using the sol-gel technology in the traditional embedding aluminizing and low-temperature in-situ oxidation process. After the coating preparation process, the prepared composite hydrogen barrier coating makes the tensile strength change of the substrate material less than 5%, and the elongation change less than 10%. It is shown that the composite hydrogen barrier coating has less influence on the performance of the 316L stainless steel substrate material.

Description

Technical Field

[0001] This invention relates to the field of coating materials technology, specifically to a composite hydrogen barrier coating, its preparation method, and its application. Background Technology

[0002] Hydrogen atoms and their isotopes have very small radii and high permeability. Once they penetrate into the materials of reactor structural components, they can cause varying degrees of damage, resulting in severe economic losses and even serious reactor safety accidents and radioactive pollution. For example, in space reactors using zirconium hydride as a moderator, hydrogen diffusion and permeation at high temperatures continuously reduce the hydrogen content in the moderator, potentially leading to insufficient reactor reactivity, failure to reach criticality, and reduced thermoelectric conversion efficiency. Similarly, in the field of accident-tolerant fuel (ATF), although FeCrAl alloy cladding has excellent high-temperature oxidation resistance and high-temperature mechanical properties compared to traditional zirconium alloys, its deuterium permeability is tens of times higher, potentially causing tritium radioactive pollution. Furthermore, in fusion reactors using deuterium and tritium as fuels, hydrogen isotope leakage can cause severe fuel loss, radioactive pollution, and deterioration of structural component materials. The solution is to create permeation barriers along the hydrogen and its isotope permeation paths. Therefore, preparing hydrogen-barrier / deuterium / tritium coatings (hereinafter referred to as hydrogen-barrier coatings) with good thermal stability and radiation resistance on the surface of reactor structural components to prevent the penetration of hydrogen and its isotopes is crucial for the future development of nuclear reactors.

[0003] Al2O3 (especially α-Al2O3) has become a research hotspot for hydrogen barrier coatings due to its excellent tritium penetration resistance, high resistivity, high temperature resistance, and good compatibility with lithium and lead. Among these, the gradual change in composition and structure of the FeAl alloy gradient transition layer can alleviate the thermal mismatch between the substrate and the Al2O3 coating. Simultaneously, the high activity of Al atoms in the FeAl transition layer provides sufficient Al source for the self-healing of Al2O3 during use, thereby repairing microcracks in the coating and achieving its self-healing function. These excellent comprehensive properties have made Al2O3 coatings with FeAl alloy transition layers (Fe-Al / Al2O3 coatings) the preferred hydrogen barrier coating for participating countries of the International Thermonuclear Experimental Reactor (ITER).

[0004] Currently, most studies generally use high-temperature oxidation environments above 950℃, while there are few studies on oxidation below 750℃. This process 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 may cause the Al2O3 film formed at high temperature to crack due to excessive thermal stress, and the coating may contain voids, resulting in poor tritium permeation resistance.

[0005] Furthermore, the high-temperature hydrogen permeation resistance of single-layer Fe-Al / Al2O3 coatings decreases significantly (generally, the hydrogen barrier factor PRF ≤ 500 at 600℃), still failing to meet the high-temperature hydrogen barrier performance requirements of some high-temperature reactors. For example, the hydrogen barrier factor requirement for gaseous hydrogen in a space nuclear power source under vacuum at 600℃ is PRF ≥ 500, and for gaseous hydrogen in a (He+CO2) environment at 600℃, the PRF ≥ 1000. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite hydrogen barrier coating, its preparation method, and its application.

[0007] To achieve the above objectives, 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 the substrate is coated from the inside out with an iron-aluminum alloy transition layer, an Al2O3 hydrogen barrier layer and a phosphate protective layer.

[0009] The composite hydrogen-blocking coating of this 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 functions similarly to a metal substrate, adjusting the coefficient of thermal expansion by forming intermetallic compounds, thereby achieving the difference in the coefficient of thermal expansion between the metal substrate and the oxide, improving adhesion performance, and at the same time, this layer possesses certain hydrogen-blocking properties. An Al2O3 hydrogen-blocking layer is prepared on the surface of the iron-aluminum alloy transition layer using an in-situ oxidation method at low temperature through selective oxidation of the Fe-Al alloy transition layer. Finally, a phosphate protective layer is prepared on the outer surface of the coating using sol-gel technology. This layer has a glass structure, high-temperature fluidity, and a hydrogen-blocking capacity several tens of times higher than the substrate. This glass also has strong adhesion strength to the oxide, which can fill cracks generated in the oxide layer, and its good high-temperature strength protects the oxide layer, making the oxide layer less prone to cracking, thus stabilizing the structure and performance of the entire coating. The presence of the magnesium phosphate outer protective layer further enhances the high-temperature hydrogen permeation blocking performance of the Fe-Al / Al2O3 coating.

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

[0011] (1) Grind the substrate; embed the sample with aluminizing agent and keep it warm to aluminize; then heat-treat it in a vacuum environment to obtain the aluminized layer;

[0012] The aluminizing agent comprises, by weight parts, 20-50 parts Al powder, 2-10 parts AlCl3 powder, and 40-78 parts Al2O3 powder;

[0013] The aluminizing temperature is 500℃-750℃, and the time is 1h-10h.

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

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

[0016] (3) The iron-aluminum alloy transition layer is oxidized in situ to obtain an Al2O3 hydrogen barrier layer;

[0017] (4) Take phosphate sol to coat the Al2O3 hydrogen barrier layer and sinter it to obtain the composite hydrogen barrier coating.

[0018] This invention creatively introduces a heat treatment and mechanical polishing process for the aluminized layer into the traditional embedding aluminizing + low-temperature in-situ oxidation process. The heat treatment completely transforms the Fe2Al5-dominated aluminized layer into a FeAl-dominated aluminized layer. The aluminizing agent achieves low-temperature, high-activity aluminizing. The mechanical polishing process effectively removes the Kirkendal pore layer on the shallow surface of the coating. Furthermore, the mechanical polishing process significantly improves the uniformity of the FeAl coating thickness after heat treatment. The introduction of the heat treatment + mechanical polishing process enables the selective oxidation of the Fe-Al alloy transition layer at low temperatures to prepare a dense Al2O3 hydrogen-barrier layer. A phosphate protective layer is prepared on the outer surface of the coating using sol-gel technology. This layer has a glass structure, high-temperature fluidity, and hydrogen-barrier capacity several tens of times higher than the substrate. The glass has strong adhesion to the oxide layer, filling cracks in the oxide layer and protecting the oxide layer with its good high-temperature strength, making the oxide layer less prone to cracking, thus stabilizing the structure and performance of the entire coating. Therefore, despite the coating preparation process, the tensile strength of the substrate material changed by less than 5%, and the elongation changed by less than 10%. This indicates that the composite hydrogen barrier coating of the present invention has little impact on the properties of the 316L stainless steel substrate material.

[0019] In a preferred embodiment of the preparation method of the composite hydrogen barrier coating of the present invention, in step (1), the polishing is carried out using 600-2000 mesh sandpaper.

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

[0021] As a preferred embodiment of the preparation method of the composite hydrogen barrier coating of the present invention, in step (3), the oxidation atmosphere is 3% O2 ​​oxygen-argon mixture-pure oxygen, the temperature is 600℃-750℃, and the time is 2h-50h.

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

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

[0024] In a preferred embodiment of the preparation method of the composite hydrogen barrier coating of the present invention, in step (4), the sintering calcination temperature is 300℃-650℃ and the time is 0.5h-5h.

[0025] Thirdly, the present invention provides a composite hydrogen barrier coating prepared by the aforementioned method.

[0026] Fourthly, the composite hydrogen barrier coating described in this invention is applied to the coating materials of reactor structural components.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention creatively introduces a heat treatment and mechanical polishing process for the aluminized layer into the traditional embedding aluminizing + low-temperature in-situ oxidation process. The heat treatment completely transforms the Fe2Al5-dominated aluminized layer into a FeAl-dominated aluminized layer. The aluminizing agent achieves low-temperature, high-activity aluminizing. The mechanical polishing process effectively removes the Kirkendal pore layer on the shallow surface of the coating. Furthermore, the mechanical polishing process significantly improves the uniformity of the FeAl coating thickness after heat treatment. The introduction of the heat treatment + mechanical polishing process enables the selective oxidation of the Fe-Al alloy transition layer at low temperatures to prepare a dense Al2O3 hydrogen-barrier layer. A phosphate protective layer is prepared on the outer surface of the coating using sol-gel technology. This layer has a glass structure, high-temperature fluidity, and hydrogen-barrier capacity several tens of times higher than the substrate. The glass has strong adhesion to the oxide layer, filling cracks in the oxide layer and protecting the oxide layer with its good high-temperature strength, making the oxide layer less prone to cracking, thus stabilizing the structure and performance of the entire coating. Therefore, despite the coating preparation process, the prepared composite hydrogen barrier coating resulted in a change of less than 5% in the tensile strength of the substrate material and a change of less than 10% in the elongation. This indicates that the composite hydrogen barrier coating of the present invention has a minimal impact on the properties of the 316L stainless steel substrate material. Attached Figure Description

[0029] Figure 1 The process flow for preparing the Fe-Al / Al2O3 / magnesium phosphate coating in this invention is as follows;

[0030] Figure 2 The surface morphology of the aluminized material embedded at 600℃ for 2 hours (500×).

[0031] Figure 3 BSE cross-section (1000×) of aluminized material embedded at 600℃ for 2 hours;

[0032] Figure 4 XRD patterns of aluminizing embedded at 600℃ for 2 hours;

[0033] Figure 5 Surface morphology (500×) after heat treatment at 600℃ for 2 hours at 10℃ / min for 60 hours;

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

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

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

[0037] Figure 9 BSE cross-section (1000×) after heat treatment at 700℃ for 60h, polished with 2000-grit sandpaper for 5min, followed by polishing with 3μm polishing fluid for 5min (300r / min);

[0038] Figure 10 The XRD pattern is the result of polishing with 2000-grit sandpaper for 5 min and then polishing with 3μm polishing liquid for 5 min (300 r / min) after heat treatment at 700℃ for 60 h.

[0039] Figure 11 Surface morphology and backscattering pattern of the sample after 600℃-2h embedding-700℃-60h heat treatment-700℃-24h-O2-1kPa oxidation;

[0040] Figure 12 Surface morphology and elemental distribution of the sample after 600℃-2h embedding-700℃-60h heat treatment-700℃-24h-O2-1kPa oxidation at 1000×;

[0041] Figure 13 XPS data for the surface of the sample after 600℃-2h embedding-700℃-60h heat treatment-700℃-24h O2-1kpa oxidation;

[0042] Figure 14 TEM data of the cross-section of the sample after 600℃-2h embedding-700℃-60h heat treatment-700℃-24h O2-1kpa oxidation;

[0043] Figure 15 The surface morphology and backscattering pattern of the sample after being coated four times at spin coating speeds of 600 r / min-10s + 1500 r / min-30s;

[0044] Figure 16 Elemental distribution and content of magnesium phosphate coatings applied four times at spin coating speeds of 600 r / min-10s + 1500 r / min-30s;

[0045] Figure 17 For deuterium permeation testing;

[0046] Figure 18 This is a schematic diagram of a deuterium permeation testing device.

[0047] Figure 19 The hydrogen isotope permeation curve of the sample;

[0048] Figure 20Schematic diagram for selecting characteristic time for hydrogen permeation curves: (a) static method; (b) dynamic method;

[0049] Figure 21 Macroscopic surface morphology of Fe-Al / Al2O3 / magnesium phosphate coating samples coated four times at spin coating speeds of 600 r / min-10s + 1500 r / min-30s;

[0050] Figure 22 The permeability-temperature curve of the Fe-Al / Al2O3 / magnesium phosphate coating;

[0051] Figure 23 This is a dimensional diagram of the sheet-like sample;

[0052] Figure 24 This is a macroscopic image of a sheet sample after tensile fracture at room temperature.

[0053] Figure 25 This is a stress-strain curve diagram of a sheet-like sample.

[0054] Figure 26 The distribution of tensile stress and interfacial shear force for each small segment;

[0055] Figure 27 To enable on-site observation of the initiation and propagation of interface cracks using a camera;

[0056] Figure 28 This is a cross-sectional view of the coated sample;

[0057] Figure 29 The surface morphology of the coating near the tensile fracture of the coated sample is shown. Detailed Implementation

[0058] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below with reference to specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0059] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0060] Example 1: Preparation process of iron-aluminum alloy / alumina / 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 316L substrate surface was polished to 2000# and ultrasonically cleaned for later use. Aluminum powder, alumina powder, and aluminum chloride powder were dried in a drying oven at 80℃ for 60 minutes. Then, the powders were mixed in a plastic bottle at a ratio of 40wt% aluminum powder, 56wt% alumina powder, and 4wt% aluminum chloride powder, and shaken in a shaker for 2 hours to obtain the aluminizing agent. The sample was then embedded in a crucible using the aluminizing agent, with the interior filled with carbon powder to reduce air pockets. The crucible was sealed with refractory clay and placed in a muffle furnace for aluminizing at 600℃ for 2 hours.

[0064] See results Figure 2-4 , Figure 2 The surface morphology image shown indicates that the coating formed by aluminizing during embedding at 600℃ for 2 hours is dense and free of voids. Figure 3 The cross-sectional view shown indicates that its thickness is approximately 14 μm. Figure 4 The XRD pattern shows that the coating is mostly FeAl3 phase with a small number of Fe2Al5 peaks. This is because FeAl3 is on the outermost layer of the coating, while Fe2Al5 is on the inner layer. Due to the limited penetrating power of X-rays, most of them hit the FeAl3 layer.

[0065] 2. Heat treatment of the aluminized layer

[0066] Fe2Al5, as a high-alumina brittle phase, presents compatibility issues with structural materials, easily leading to coating cracking. These cracks act as rapid diffusion channels, increasing tritium permeation and severely impacting the hydrogen permeation resistance of the oxidized sample. Heat treatment at 700℃ for 60 hours in a vacuum environment can completely transform the Fe2Al5-dominated aluminized layer into a FeAl-dominated aluminized layer. The FeAl phase possesses better mechanical properties, is less prone to coating cracking, and thus improves the hydrogen permeation resistance of the coating without deteriorating the overall mechanical properties of the material.

[0067] See results Figure 5-7 , Figure 5 The surface morphology of the aluminized sample after 600℃-2h heat treatment at 700℃-60h is shown. Since the surface of the sample is covered with alumina after heat treatment, the actual morphology cannot be observed. Polishing is required to remove the alumina. Figure 6 The cross-sectional view of the coating after heat treatment at 700℃ for 60 hours shows that the contrast of the coating becomes lighter, indicating that a phase transformation has occurred. Figure 7 XRD analysis showed that after heat treatment at 700℃ for 60 h, the phase completely transformed from FeAl3 to FeAl, with the FeAl coating thickness being approximately 19 μm.

[0068] The total thickness of the coating of the aluminized sample embedded at 600℃ for 2 hours is about 14 μm. When the heat treatment time is 60 hours at 700℃, the aluminized layer with Fe2Al5 phase as the main component can be completely transformed into an aluminized layer with FeAl phase as the main component.

[0069] 3. Mechanical polishing of the aluminized layer

[0070] After heat treatment at 700℃, the Kirkendal pores resulting from the difference in diffusion coefficients between Fe and Al are mainly concentrated on the shallow surface of the coating and can be effectively removed by mechanical polishing. Furthermore, mechanical polishing can significantly improve the uniformity of the FeAl coating thickness after heat treatment.

[0071] Mechanical polishing was used to remove the Kirkendal pore layer on the shallow surface of the coating and to improve the uniformity of the FeAl coating thickness after heat treatment. Polishing was performed with 2000-grit sandpaper for 5 minutes, followed by polishing with 3μm diameter diamond polishing slurry particles at 300 rpm for 5 minutes.

[0072] During heat treatment, interdiffusion of Fe and Al elements occurs. Al diffuses inward from the coating surface, while Fe diffuses outward from the matrix. However, the diffusion coefficient of Al is greater than that of Fe, resulting in more Al diffusing inward than Fe diffusing outward. Therefore, a large number of Kirkendal pores are generated on the shallow surface of the coating. Figure 8 The results showed that after polishing at 300 rpm for 5 minutes on 2000-grit sandpaper and at 300 rpm for 5 minutes on 3μm polishing fluid, the number of pores was significantly reduced. Figure 9 The coating thickness was reduced from 19 μm to 14 μm. Figure 10 The XRD pattern shows that the phase remains FeAl after polishing.

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

[0074] First, the aluminized layer sample is placed in a high-temperature tube furnace. The vacuum level of the pressure stabilization and evacuation system is set to a low value to purge 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, and the heat preservation program is started. The O2 and Ar mixing ratio is set to determine the oxidation environment. The dual-channel gas flow controller is turned on to start the in-situ oxidation of the coating sample.

[0075] This invention employs an in-situ selective oxidation method to prepare an Al2O3 hydrogen barrier layer at low temperatures. The aim is to prepare the Al2O3 hydrogen barrier layer at a low temperature (700℃) through oxidation of a Fe-Al alloy transition layer. Based on the principle of selective oxidation of alloys and the theory of oxidation phase diagrams, a systematic study is conducted on controlling alloy content, oxidation atmosphere, oxidation time, and pretreatment to achieve selective oxidation preparation of a dense Al2O3 film.

[0076] Figure 11 and 12 The oxidation temperature of the coating sample shown was 700℃, the oxidation time was 24h, and the oxidation atmosphere was pure oxygen (1kPa pressure). Figure 11 and 12 The surface morphology and elemental distribution show that the oxide layer of the sample oxidized at 700℃-24h-O2-1kpa is dense and the elemental distribution is uniform.

[0077] X-ray photoelectron spectroscopy (XPS) utilizes 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 a sample surface. Due to the weak penetrating power of photoelectrons, the detection depth of XPS is typically 5-10 nm. Here, XPS was used to effectively analyze the elemental composition and valence state information of the surface of an oxidized sample.

[0078] Figure 13 XPS images of the sample surface after oxidation at 700℃-24h-O2-1kPa are shown. It can be seen that the sample surface mainly consists of Al and O peaks, with no obvious Fe and Cr peaks, indicating that the sample surface is mainly composed of the Al2O3 phase. Figure 14 The results of cross-sectional TEM characterization of the coated sample after oxidation at 700℃-24h-O2-1kPa are presented. It can be seen that the main components of Area #1 are Al and O elements, with an Al:O atomic ratio close to 2:3, indicating that this layer is the Al2O3 phase, and the thickness of the Al2O3 layer is approximately 131nm. The main components of Area #2 are Fe and Al elements, with a Fe:Al atomic ratio close to 1:1, indicating that this layer is the FeAl phase. The small amounts of Cr and Ni elements are due to the diffusion of elements from the 316L stainless steel matrix into the FeAl layer.

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

[0080] The alumina layer on the FeAl / Al2O3 matrix prepared by the embedding-heat treatment-polishing-in-situ oxidation process has a few pores on its surface. During the preparation of the phosphate layer, these pores on the alumina layer surface can be further densified, and the phosphate layer can also be protected. Simultaneously, 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 was prepared using the sol-gel method, specifically as follows:

[0082] The FeAl / Al2O3 matrix sample was ultrasonically cleaned in anhydrous ethanol for 3 min, followed by plasma cleaning for 4 min. The concentration of magnesium dihydrogen phosphate was set at 1 mol / L, and 0.1 vol% sulfur salt was added as a surfactant to increase wettability. The spin-coating speed was 600 r / min - 10 s + 1500 r / min - 30 s (i.e., first slow rotation at 600 r / min for 10 s, then rapid rotation at 1500 r / min for 30 s), and the number of coats was set to 4. During spin-coating, 0.05 mL of 1 mol / L magnesium dihydrogen phosphate solution was first pipetted onto the sample surface, and after the solution was applied, one minute was allowed to pass before starting the spin coater. After spin-coating, the sample was placed in an 80℃ drying oven for 10 min. This was one coat step. For four coats, the dried sample needed to be spin-coated again and dried, repeating this cycle 4 times. Finally, the sample was sintered in a tube furnace with a vacuum level of 50 mTtor. During sintering, the temperature is first increased to 300℃ at a rate of 5℃ / min and held for 1 hour, then increased to 450℃ at a rate of 1℃ / min and held for 1 hour, then increased to 600℃ at a rate of 1℃ / min and held for 1 hour, and finally decreased to room temperature at a rate of 5℃ / min.

[0083] from Figure 15 and Figure 16 The surface morphology and elemental distribution diagram show that when the number of coatings is increased to 4, the surface morphology of the coating has fewer and shallower pores, and the elemental distribution diagram shows that the Mg and P elements in the pores are evenly distributed.

[0084] Example 2: Performance of the iron-aluminum alloy / alumina / magnesium phosphate composite hydrogen barrier coating

[0085] 1. Introduction to Hydrogen Isotope Permeation Testing Apparatus

[0086] Construct a hydrogen isotope permeation testing device, such as Figure 17 As shown, it can test sheet-like samples with a thickness of approximately 0.5 mm, as well as tubular samples with a diameter of less than 10 mm, a thickness of approximately 0.5 mm, and a length ranging from 10 cm to 50 cm, fully meeting the requirements for coating hydrogen isotope permeability testing in this project. The schematic diagram is shown below. Figure 18As shown. To ensure cleanliness and prevent contamination of the pipeline, 1 / 4” stainless steel pipes were electrolytically polished and heated externally. The vacuum chamber was heated and temperature-controlled to reduce background interference. A heating furnace was used, with a heating temperature range of 25℃-1200℃ and stable temperature control of ±2℃. An imported German Pfeiffer Vacuum molecular pump was selected to achieve the required vacuum level. A dry pump was used as the backing pump to achieve an oil-free vacuum system. A German Pfeiffer Vacuum mass spectrometer was used to analyze and detect permeation data, with a fastest response time of 2ms. The piping used double compression fittings and VCR connectors. The vacuum section of the low-pressure side detection chamber used CF flange interfaces to ensure a good vacuum level. The quadrupole mass spectrometer was a German Pfeiffer Vacuum QMG220M1. The vacuum system used a dry pump as the backing pump and a German Pfeiffer Vacuum Hipace80 molecular pump.

[0087] According to molecular dynamics, the rates at which hydrogen, deuterium, and tritium participate in chemical reactions are inversely proportional to the square root of their masses. Therefore, any one of them can be used to represent a hydrogen isotope in permeability testing (the irradiation effect of tritium is not considered here). Because tritium is radioactive and its handling is limited, while hydrogen has a high environmental background, deuterium is often used for permeability testing. All permeability tests in this project will be conducted using deuterium gas.

[0088] The permeation sample system is divided into high-pressure and low-pressure sections. The high-pressure section, upstream of the permeation, introduces deuterium gas, and a pressure stabilizing tank is designed at the upstream inlet to maintain stable deuterium pressure during the permeation test. In the low-pressure section, downstream of the permeation, a spherical stainless steel cavity with a diameter of approximately 200 mm is designed to contain the permeated deuterium. The inner surface of the cavity is polished and degassed, and the background vacuum level is better than 10 during testing. -7 Pa. Under high vacuum conditions, pure D2 is introduced into the sample to be tested. On the other side of the sample, the gas permeability of D2 through the sample is analyzed by quadrupole mass spectrometry to evaluate the gas permeability performance of the sample.

[0089] The ion current-time curve directly acquired using a hydrogen isotope permeation testing system is shown below. Figure 19 As shown, the leakage rate-ion current intensity calibration curve obtained through standard leak calibration yields 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, guide the design and preparation process of hydrogen barrier coatings, and further optimize the coating preparation parameters.

[0091] Under constant deuterium pressure, deuterium permeation tests were conducted on the coating samples at temperatures ranging from 360℃ to 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 permeation temperature.

[0092] 2. Data Processing and Analysis Principles

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

[0094]

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

[0096] S represents solubility;

[0097] L — the thickness of the sample (m);

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

[0099] The permeability Ф is generally defined as:

[0100] φ=DS mol / [m·s·(MPa)] 12 (2)

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

[0102]

[0103] Under certain conditions, J∞ can be measured and then calculated. Furthermore, whether J∞ and p satisfy the square root relationship is usually a criterion for whether the permeation process is controlled by the bulk diffusion process.

[0104] The diffusion coefficient D and the permeation lag time t1 can be obtained from the approximate solution of Fick's second law, and the following relationship exists:

[0105]

[0106] The simplified method used by Devanathan et al. is typically employed, determining t1, i.e., the time corresponding to a transient permeation rate of 0.629 J∞, based on the hydrogen permeation kinetic curve. This method of determining D using equation (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∞, the latter is selected for this project, such as Figure 20 As shown. In summary, the hydrogen permeation kinetics curve can be used to determine... And D, by relation S can be calculated.

[0107] The high-temperature hydrogen barrier properties of hydrogen barrier coatings are mainly evaluated using the deuterium barrier factor (PRF) of the coating.

[0108]

[0109] Figure 21 The figure shows a comparison of the permeability of the Fe-Al / Al2O3 / magnesium phosphate coating in this invention with that of Fe-Al / Al2O3 reported in the literature. The deuterium barrier factor of the sample coated with the magnesium phosphate coating four times was significantly improved at a high temperature of 600℃ under in-situ oxidation, especially at the process of 600 r / min⁻¹⁰s + 1500 r / min⁻³⁰s, where the deuterium barrier factor reached 33479. This indicates that the magnesium phosphate coating can increase the high-temperature deuterium barrier performance of FeAl / Al2O3. Figure 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 values ​​reported in the literature.

[0110] Table 1. Deuterium blocking factor (PRF) of Fe-Al / Al2O3 / magnesium phosphate coating

[0111] <![CDATA[700℃-O2-24h oxidized sample]]> 10821 11031 7834 5645 <![CDATA[Magnesium phosphate sample oxidized at 700°C in O2 for 24 hours]]> 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 the Mechanical Properties of the Substrate

[0113] To explore the influence of coating preparation process on the mechanical properties of the substrate material, uniaxial tensile tests were conducted on coated samples to obtain the yield strength, tensile strength, elongation, and other mechanical properties of the coated substrate material. The preparation process and sample number of the coated samples are as follows:

[0114] Sample #1: A 316L sheet-like matrix sample;

[0115] Sample #2: Aluminizing at 600℃ for 2 hours, heat treatment at 700℃ for 60 hours, oxidation at 650℃-O2-1kPa for 10 hours, coating at 600r / min for 10 seconds + 1500r / min for 30 seconds, the coating was applied 4 times, which is the Fe-Al / Al2O3 / magnesium phosphate coating-substrate sample prepared in Example 1;

[0116] According to GB / T 228.1-201 Metallic materials, tensile testing—Part 1: Test methods at room temperature, a room temperature tensile test was conducted. The sample dimensions are as follows. Figure 23As shown, the original gauge length was 30 mm, the parallel length was 40 mm, the total length of the tensile sample was 139.7 mm, and the thickness was 2 mm. Room temperature tensile tests were conducted using an MTS universal tensile testing machine at a tensile rate of 1.2 mm / min. Two samples were repeatedly stretched for each coating process to eliminate the influence of random experimental errors.

[0117] Figure 24 The image shows a macroscopic view of the tensile fracture surface of the coated substrate sample. It can be seen that all fracture surfaces are within the gauge length. The uniform dimensional variation of the parallel sections indicates that significant uniform plastic deformation occurred in the coated substrate sample before necking fracture. The crack propagation direction is nearly perpendicular to the tensile direction, suggesting a possible microscopic fracture mechanism of micropore aggregation.

[0118] Tensile stress-strain curves of the coated substrate sample are as follows: Figure 25 As shown, the stress-strain curves of samples with the same coating process exhibit good repeatability in two tests. All samples initially show a significant deformation hardening trend, while the curves tend to flatten out just before fracture due to the reduction in effective load-bearing area, which is typical of austenitic steel tensile curves.

[0119] The tensile strength, yield strength, elongation, and their variations for each coated substrate sample are shown in Table 2. It can be seen that despite the coating preparation process, the tensile strength of the substrate material changed by less than 2%, and the elongation changed by less than 5%. This indicates that the coating preparation process has a relatively small impact on the properties of the 316L stainless steel substrate material.

[0120] Table 2 Tensile results of sheet samples

[0121]

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

[0123] The quality of the interfacial bonding between the coating material and the substrate material largely determines the service life of the coating. Under the same external load, a higher interfacial bonding strength means a stronger ability to resist the initiation and propagation of interfacial cracks, thus delaying the coating from peeling off from the substrate. Therefore, characterizing and evaluating the interfacial bonding strength between the coating and the substrate is of great significance.

[0124] Since the Fe-Al / Al2O3 coating is prepared through in-situ growth, and the Fe-Al coating is an intermetallic compound with high bonding strength to the substrate, while its deformation capacity is less than that of the 316L stainless steel substrate (classifying it as a brittle coating / ductile substrate), it is suitable for determining the coating adhesion strength using the transverse tensile method. Therefore, the transverse tensile method is used to determine the coating-substrate adhesion strength. The main principle of the transverse tensile method for determining coating adhesion strength is as follows: Figure 26 As shown.

[0125] Under tensile load, the tensile stress and interfacial shear force distribution of each small section of the broken coating are as follows: Figure 26 As shown. The theoretical basis of this method is the shear lag model in fiber-reinforced composites, which states that any stress on the coating must be transmitted through the interface between the coating and the matrix, expressed as:

[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 half the length of the small piece of coating that is bonded to the substrate after being broken.

[0128] Under tensile load, when the crack saturation point is reached, meaning the number of cracks no longer increases with increasing tensile strain, the interfacial shear strength between the coating and the substrate can be calculated using the following formula:

[0129]

[0130] Where, δ max For the maximum crack spacing, σ b h represents the fracture strength of the coating that produces the crack, and h represents the thickness of the coating.

[0131] The coating was induced to peel off during a uniaxial tensile test. The time of tensile fracture during the test was recorded video, and the tensile stress at that point was compared with the recorded video. 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 coating and the maximum crack spacing after tensile fracture were determined by scanning electron microscopy. (See figure) Figure 27 .

[0132] The results are as follows Figure 28 and 29 As shown in Table 3, the average adhesion between the Fe-Al coating and the substrate is 136.97 and 135.74 MPa, respectively, which is significantly higher than the 38 MPa adhesion value reported in the literature for cold-sprayed FeAl coatings annealed at 650℃ for 5 hours (Surface and Coatings Technology, 2011, 205: 5502-5509). This is determined by the embedding aluminizing process, where the interdiffusion of Fe and Al leads to the formation of different Fe-Al phases in the coating. A metallurgical bond, rather than a simple mechanical bond, is formed between the coating and the substrate.

[0133] Table 3. Adhesion 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 solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a composite hydrogen-barrier coating, characterized in that, Includes the following steps: (1) Grind the substrate; embed the sample with aluminizing agent and keep it warm to aluminize; then heat treat it in a vacuum environment to obtain an aluminized layer; The aluminizing agent comprises, by weight percentage, 40% Al powder, 4% AlCl3 powder, and 56% Al2O3 powder; The aluminizing temperature was 600℃ and the time was 2 hours. The heat treatment was performed at a temperature of 700°C for 60 hours. (2) The Kirkendal pore layer on the shallow surface of the aluminized layer is removed by mechanical polishing to obtain an iron-aluminum alloy transition layer. The polishing is first done with 2000-grit sandpaper for 5 minutes, and then with diamond polishing liquid particles with a diameter of 3μm at 300r / min for 5 minutes. (3) The iron-aluminum alloy transition layer is oxidized in situ to obtain an Al2O3 hydrogen barrier layer; The in-situ oxidation was carried out at a temperature of 700°C for 24 hours, and the oxidation atmosphere was a pure oxygen atmosphere with a pressure of 1 kPa. (4) Take phosphate sol to coat the Al2O3 hydrogen barrier layer and sinter it to obtain the composite hydrogen barrier coating.

2. The method for preparing the composite hydrogen barrier coating according to claim 1, characterized in that, In step (1), the polishing is done using 600-2000 grit sandpaper.

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

4. The method for preparing the composite hydrogen barrier coating according to claim 1, characterized in that, In step (4), the sintering temperature is 300℃-650℃ and the time is 0.5h-5h.

5. A composite hydrogen barrier coating prepared by the preparation method according to any one of claims 1-4.

6. The application of the composite hydrogen barrier coating of claim 5 in the coating materials of reactor structural components.

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