ODS-FeCrAl protective oxide film and its preparation method under high temperature oxygen saturated liquid lead-bismuth corrosion environment.

Abstract

This invention discloses an ODS-FeCrAl protective oxide film and its preparation method under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment. High-chromium ODS-FeCrAl alloy is used as the raw material. After the nuclear lead-bismuth eutectic alloy is melted into liquid lead-bismuth, the treated experimental sample is fixed in the liquid lead-bismuth and subjected to experiments at specified temperature and time. In a normal furnace atmosphere, the ODS-FeCrAl sample reacts with oxygen in the liquid lead-bismuth to form a protective oxide film, effectively preventing dissolution corrosion of ODS steel, avoiding the penetration and diffusion of liquid metal into the stainless steel substrate, and slowing down the oxidation rate of the material. It also avoids direct contact between the substrate and the liquid metal, effectively preventing embrittlement of the liquid metal. This provides a theoretical basis for the formation of the ODS-FeCrAl oxide film under high-temperature lead-bismuth corrosion and explores the corrosion evolution behavior of ODS steel under saturated oxygen conditions.

Description

Technical Field

[0001] This invention belongs to the field of corrosion science and protection technology, specifically relating to an ODS-FeCrAl protective oxide film and its preparation method under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment. Background Technology

[0002] With the rapid development of the nuclear power industry, the demand for improving the overall performance of nuclear reactors is becoming increasingly urgent, and the service conditions of fuel cladding materials are becoming increasingly harsh and demanding. Extending the service life of cladding materials while improving equipment stability under these stringent conditions is a hot research topic, which places higher demands on new cladding materials. Cladding materials need to improve their resistance to corrosion by liquid metal coolants under high temperature and high radiation doses. The corrosion resistance of materials at high temperatures is one of the key performance indicators affecting the safe operation of reactors; therefore, the corrosion performance and mechanisms of new cladding materials at high temperatures have become a research focus.

[0003] Oxide dispersion strengthened (ODS) alloys are alloys that achieve strengthening by introducing a large number of fine and stable oxide particles into the matrix. ODS-FeCrAl alloys contain a large number of fine and dispersed oxide particles. These hard particles can act as pinning sites to restrict the movement of dislocations, grain boundaries, and subgrain boundaries, thereby significantly improving the alloy's mechanical properties, especially its high-temperature properties. They also have many beneficial effects on radiation resistance. ODS-FeCrAl alloys have attracted widespread attention due to their excellent radiation resistance and good high-temperature performance. They possess the advantages of ferritic stainless steel, such as high melting point, good thermal conductivity, low coefficient of thermal expansion, and resistance to high-temperature corrosion, thermal fatigue, and radiation swelling, while also exhibiting good corrosion resistance at high temperatures. They are considered one of the most promising nuclear reactor cladding materials. However, there are relatively few research reports on the corrosive properties of ODS steel in liquid heavy metals, and the relevant corrosion mechanisms need further exploration. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing an ODS-FeCrAl protective oxide film and its preparation method under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment, which is used to solve the technical problem of severe corrosion of ODS-FeCrAl alloy cladding in the primary loop of lead-cooled fast reactor.

[0005] The present invention adopts the following technical solution:

[0006] Based on the method for preparing ODS-FeCrAl protective oxide film under high temperature oxygen saturated liquid lead-bismuth corrosion environment, in a vacuum environment, a nuclear lead-bismuth eutectic alloy is melted to obtain liquid lead-bismuth. The ODS-FeCrAl sample is immersed in the liquid lead-bismuth to undergo a diffusion reaction, generating a three-layer protective oxide film. The ODS-FeCrAl sample is then removed to obtain ODS-FeCrAl with a corrosion-resistant protective film.

[0007] Specifically, the melting temperature of the nuclear lead-bismuth eutectic alloy to obtain liquid lead-bismuth is 125–200℃, and the holding time is 40–50 min.

[0008] Specifically, in the ODS-FeCrAl samples, the mass percentage of iron is 71.45%–77.25%, the mass percentage of chromium is 18.5%–21.5%, the mass percentage of aluminum is 3.75%–5.75%, the mass percentage of yttrium oxide is 0.3%–0.7%, and the mass percentage of titanium is 0.2%–0.6%.

[0009] Specifically, the ODS-FeCrAl sample was immersed in liquid lead bismuth under oxygen saturation, with the temperature controlled at 445–455℃ for 20–100 h.

[0010] Specifically, the protective oxide film has a thickness of 0.7–5 μm and consists of a Cr2O3 spinel layer, a Fe(Cr,Al)2O4 layer, and a Fe3O4 layer from the inside out.

[0011] Furthermore, the thickness of the Cr2O3 spinel layer is 100–900 nm.

[0012] Furthermore, the thickness of the Fe(Cr,Al)2O4 layer is 0.4–1.5 μm.

[0013] Furthermore, the thickness of the Fe3O4 layer is 0.1–3 μm.

[0014] Another technical solution of the present invention is an ODS-FeCrAl protective oxide film based on a high-temperature oxygen-saturated liquid lead-bismuth corrosion environment.

[0015] Specifically, the ODS-FeCrAl protective oxide film has a melting point greater than 2266℃.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects:

[0017] Based on the preparation method of ODS-FeCrAl protective oxide film under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment, high-chromium ODS-FeCrAl alloy was used as raw material. After the nuclear lead-bismuth eutectic alloy was melted into liquid lead-bismuth, the treated experimental sample was fixed in liquid lead-bismuth and subjected to experiments at the specified temperature and time. In a normal furnace atmosphere, the ODS-FeCrAl sample reacted with oxygen in the liquid lead-bismuth to form a protective oxide film, which effectively prevented dissolution corrosion of ODS steel, avoided the penetration and diffusion of liquid metal into the stainless steel substrate, and slowed down the oxidation rate of the material. It also prevented direct contact between the substrate and the liquid metal, effectively preventing embrittlement of the liquid metal. This provides a theoretical basis for the formation of oxide film in ODS-FeCrAl alloy under high-temperature lead-bismuth corrosion conditions, and the corrosion evolution behavior of ODS steel under saturated oxygen conditions was investigated. By comparing the corrosion morphology of the partially immersed sample with that of the unimmersed sample, the corrosion evolution behavior of ODS-FeCrAl and the influence of the protective oxide layer formed during corrosion on the corrosion resistance under high-temperature corrosion conditions were obtained. Characterization tests revealed the specific thickness, composition, and morphology of the oxide film. The resulting oxide film effectively prevents the penetration of liquid metal and the dissolution of alloying elements into the liquid metal, thus preventing dissolution corrosion of the alloy and laying a theoretical foundation for the high-temperature corrosion evolution behavior of ODS-FeCrAl under oxygen saturation.

[0018] Furthermore, the oxygen concentration in liquid heavy metals is widely considered an effective means of preventing dissolution corrosion of alloys. High-chromium ODS-FeCrAl is difficult to form a protective oxide film in an oxygen-deficient environment, which easily leads to the dissolution of alloying elements and the penetration of Pb into the matrix. Under higher oxygen concentration conditions, a protective oxide layer can be formed to prevent dissolution corrosion of the matrix and Pb penetration. Therefore, under a suitable oxygen concentration atmosphere, the oxidation rate is faster in the initial stage of oxidation, and a continuous and dense protective oxide layer will quickly form on the alloy surface, slowing down the oxidation rate of the material.

[0019] Furthermore, in the chemical composition of the high-chromium ODS-FeCrAl alloy, the Cr content is 18.5%–21.5%, and the Al content reaches over 3.4%, effectively resisting static lead-bismuth corrosion. The addition of Y element slows down the oxidation rate of stainless steel; the formed Y₂O₃ hinders element diffusion and slows down oxide formation. The addition of Ti refines oxide particles and significantly improves the material's high-temperature strength. The FeCrAl alloy is developed based on the FeCr alloy. When the alloy contains a certain amount of Al, sufficient Cr element is needed to ensure the formation of a dense protective alumina; this is the role of the third element. Therefore, in this experiment, accelerating the formation of the experimental product under oxygen-saturated conditions within a short time, the resulting dense protective oxide can resist liquid lead-bismuth corrosion, prevent dissolution corrosion of the matrix and Pb penetration, and slow down the alloy's oxidation rate.

[0020] Furthermore, the experiment ultimately resulted in a protective oxide layer with a thickness of 0.7–5 μm in the high-temperature liquid lead-bismuth corrosion environment. This protective layer effectively prevents the penetration of liquid metal and the dissolution of alloying elements into the liquid metal, thus preventing dissolution corrosion of the alloy material; it also avoids direct contact between the substrate and the liquid metal, effectively preventing the liquid metal from becoming brittle.

[0021] Furthermore, the inner oxide film Cr2O3 gradually increases in thickness from 100 to 900 nm, is tightly bonded to the substrate, and is not easily detached. This effectively blocks the outward diffusion of matrix elements, slows down the inward diffusion of oxygen elements, delays the corrosion process, and improves the corrosion resistance of the material.

[0022] Furthermore, the thickness of the outermost iron-chromium-aluminum spinel oxide layer is 0.4–1.5 μm. As the corrosion time increases, the porosity gradually decreases, and the oxide film gradually thickens and becomes continuous and dense. This largely blocks the diffusion and penetration of lead and bismuth into the substrate, as well as the diffusion of alloying elements into lead and bismuth, thus playing an effective anti-corrosion role and becoming a barrier layer between the liquid metal and the substrate.

[0023] Furthermore, the outermost nanocrystal oxide film, Fe3O4, has a thickness of 0.1–3 μm, gradually increasing in thickness. This outermost oxide film is dense and continuous, effectively isolating the substrate from lead and bismuth and preventing corrosion of the substrate. It also hinders the diffusion of Fe from the substrate, significantly reducing the risk of oxidation and corrosion by oxygen under high-temperature and lead-bismuth corrosive conditions. However, the thinness of the oxide film makes it prone to cracking, allowing lead and bismuth to easily penetrate.

[0024] In summary, this invention can effectively prevent dissolution corrosion of ODS steel, avoid the penetration and diffusion of liquid metal into the stainless steel matrix, and slow down the oxidation rate of the material; it also avoids direct contact between the matrix and liquid metal, effectively preventing liquid metal embrittlement. This invention contributes to the research on the corrosion behavior of ODS steel in liquid heavy metals, provides a theoretical basis for the corrosion evolution behavior of ODS steel under saturated oxygen conditions, and lays a theoretical foundation for the engineering application of ODS steel.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] Figure 1 The OM morphology diagram of the high-chromium ODS-FeCrAl alloy;

[0027] Figure 2 A macroscopic comparison image of the sample before and after heat preservation treatment;

[0028] Figure 3SEM image of the corroded surface at the lead-bismuth detachment point of the experimental sample after being kept at 455℃ for 20 hours;

[0029] Figure 4 SEM image of the cross-sectional interface of the experimental sample after removing lead and bismuth from the sample taken out after being kept at 455℃ for 20h.

[0030] Figure 5 SEM image of the cross-sectional interface of the experimental sample after removing lead and bismuth from the sample taken out after being kept at 452℃ for 40h.

[0031] Figure 6 SEM and EDS images of the cross-sectional interface of the experimental sample after removing lead and bismuth from the sample taken out after being kept at 450℃ for 60h.

[0032] Figure 7 SEM images of the corrosion surface at the lead-bismuth peeling point of the experimental sample taken after being kept at 448℃ for 80 hours.

[0033] Figure 8 SEM and EDS images of the protective film interface of the experimental sample taken after being kept at 445℃ for 100h and then removed from the lead and bismuth.

[0034] Figure 9 XRD pattern of the experimental sample after removing lead and bismuth from the sample taken out after being kept at 450℃ for 60h.

[0035] Figure 10 TEM image of corrosion products from an experimental sample taken after being kept at 445℃ for 60 hours. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0038] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0039] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0040] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0041] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is simply an abbreviation of these numerical combinations.

[0042] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0043] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0044] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0045] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0046] This invention provides an ODS-FeCrAl protective oxide film and its preparation method under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment. The method, conducted under saturated oxygen concentration, accelerates the formation process of experimental products and studies the interfacial microstructure and interfacial layer formation. This provides a theoretical basis for exploring the corrosion behavior of alloys and the formation mechanism of the ODS-FeCrAl protective film in liquid lead-bismuth, offering insights for effectively improving the protective film formed by ODS-FeCrAl in liquid lead-bismuth, and laying a theoretical foundation for the industrial application of ODS-FeCrAl. It effectively prevents dissolution corrosion of ODS steel materials, avoids the penetration and diffusion of liquid metal into the stainless steel substrate, and slows down the oxidation rate. It also avoids direct contact between the substrate and liquid metal, effectively preventing liquid metal embrittlement. This contributes to the research on the corrosion behavior of ODS steel in liquid heavy metals and lays a theoretical foundation for the engineering application of ODS steel materials.

[0047] The high-chromium ODS-FeCrAl alloy used in this invention contains 18.5%–21.5% chromium, 3.75%–5.75% aluminum, 0.3%–0.7% yttrium oxide, and 0.2%–0.6% titanium by mass. When the Cr content in the alloy is around 20%, a dense, well-bonded, stable, and continuous α-Al₂O₃ can be formed with an Al content greater than 2%. This continuous, dense, and stable structure avoids direct contact between the matrix and the liquid metal, and also prevents the penetration and diffusion of the liquid metal. However, when the Al content reaches a critical point, spinel with poor adhesion appears between the alumina layer and the matrix. For ODS steel, the active elements alter the growth mode of the alumina layer. The active elements and oxide particles in the alloy enhance the adhesion of the alumina layer, solving this problem while improving the corrosion resistance of the alloy material.

[0048] For the oxygen concentration selected in the experiments of this invention, high-chromium ODS-FeCrAl is difficult to form a protective oxide film in an oxygen-deficient environment, which easily leads to the dissolution of alloying elements and the penetration of lead and bismuth into the matrix. Under higher oxygen concentration conditions, a continuous and dense in-situ self-generated protective layer can be formed to prevent the matrix from dissolving and corroding. Therefore, under a suitable oxygen concentration atmosphere, the oxidation rate is relatively fast in the initial stage of oxidation, and a continuous and dense protective oxide layer will quickly form on the alloy surface, slowing down the oxidation rate of the material.

[0049] This invention discloses a method for preparing an ODS-FeCrAl protective oxide film under high-temperature, oxygen-saturated liquid lead-bismuth corrosion conditions. The method involves placing ODS-FeCrAl in liquid lead-bismuth at high temperature and under saturated oxygen conditions to generate the protective film. The specific steps are as follows:

[0050] In S1, the mass percentage of iron in the high-chromium ODS-FeCrAl alloy is 71.45%–77.25%, the mass percentage of chromium is 18.5%–21.5%, the mass percentage of aluminum is 3.75%–5.75%, the mass percentage of yttrium oxide is 0.3%–0.7%, and the mass percentage of titanium is 0.2%–0.6%. As raw materials, they are wire-cut into experimental samples of 50*6*3mm. After the experimental samples are ground and polished with sandpaper, cleaned with alcohol, and dried, they become corrosion-resistant samples.

[0051] S2. For liquid lead-bismuth: Use a 50mL alumina crucible to hold 50mL of liquid lead-bismuth. Weigh 500g of solid lead-bismuth eutectic alloy (Pb mass fraction of 44.5% and Bi mass fraction of 55.5%) and place it in the alumina crucible. Heat in a high-temperature energy-saving atmosphere furnace at a temperature of 125-200℃ for 40-60 minutes until the lead-bismuth eutectic alloy is completely melted.

[0052] Calculate the mass of solid lead-bismuth eutectic alloy: MLBE =ρ LBE ·V LBE , where ρ LBE =110961.3236T, where T is temperature and ρ LBE The unit is kg / m³ 3 50 mL is required, which yields 500 g of the desired lead-bismuth eutectic alloy.

[0053] S3. For the experimental sample processed in step S1, a specific clamp is used to fix it to ensure that the sample is immersed in the molten liquid lead bismuth, so that it can be easily removed after the corrosion is completed. Static corrosion is carried out in a high-temperature energy-saving atmosphere furnace with the experimental temperature controlled at 445-455℃. In the normal furnace atmosphere, the corrosion time is 20-100h. The sample undergoes static corrosion in liquid lead bismuth to form a protective oxide film.

[0054] The protective oxide film has a thickness of 0.7–5 μm and consists of a Cr2O3 spinel layer, a Fe(Cr,Al)2O4 layer, and a Fe3O4 layer from the inside out. The inner oxide film is a nanocrystalline layer that is serratedly bonded to the substrate. The next outer oxide film is also a nano-scale dense crystalline layer, but the grains are larger than those of the outer oxide film. The outer oxide film forms a nano-scale oxide layer.

[0055] The thickness of the Cr2O3 spinel layer is 100–900 nm, the thickness of the Fe(Cr,Al)2O4 layer is 0.4–1.5 μm, and the thickness of the Fe3O4 layer is 0.1–3 μm.

[0056] S4. The experiment is over, and the experimental sample is removed.

[0057] S5. The corrosion test sample is cold-mounted with epoxy resin. After the epoxy resin cools and solidifies, it is gently ground and polished with sandpaper to ensure that the protective film is not damaged and can be observed and detected. Then, the morphology, composition and specific substances of the protective film are characterized by SEM, XRD and electron probe.

[0058] S6. Through characterization and detection, the specific oxide film thickness, morphology, composition and specific substances are obtained.

[0059] Optical microscopy (OM) was used to observe the microstructure of the original high-chromium ODS-FeCrAl alloy; field emission scanning electron microscopy (SEM) was used to observe the morphology of the protective film on the corroded sample and the cross-sectional shape of the corroded sample; energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electron probe microanalysis (EPMA) were used to detect the composition of the protective film and analyze the specific material composition of the protective film.

[0060] This invention discloses an ODS-FeCrAl protective oxide film based on a high-temperature oxygen-saturated liquid lead-bismuth corrosion environment. This film effectively prevents ODS steel from undergoing dissolution corrosion, avoids the penetration and diffusion of liquid metal into the stainless steel substrate, and slows down the oxidation rate. It also prevents direct contact between the substrate and the liquid metal, effectively preventing liquid metal embrittlement. This invention contributes to the study of the corrosion behavior of ODS steel in liquid heavy metals and provides a theoretical basis for the corrosion evolution behavior of ODS steel.

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0062] Example 1

[0063] Experimental preparation of protective film formation of ODS-FeCrAl under high temperature oxygen saturated liquid lead-bismuth corrosion environment:

[0064] In high-chromium ODS-FeCrAl alloys, the mass fraction of iron is 71.45%–77.25%, the mass fraction of chromium is 18.5%–21.5%, the mass fraction of aluminum is 3.75%–5.75%, the mass fraction of yttrium oxide is 0.3%–0.7%, and the mass fraction of titanium is 0.2%–0.6%. The original microstructure is as follows: Figure 1 As shown.

[0065] S1. Using high-chromium ODS-FeCrAl alloy as raw material, the experimental sample was wire-cut into 50*6*3mm pieces. After grinding and polishing the experimental sample with sandpaper, it was cleaned with alcohol and dried to remove surface oil stains and oxidation marks.

[0066] S2. Weigh 500g of solid lead-bismuth eutectic alloy (Pb 44.5%, Bi 55.5%), put it into a 50mL alumina crucible, place it in a high-temperature energy-saving atmosphere furnace, and heat it to 125-200℃ for 40-60min to completely melt the solid lead-bismuth eutectic.

[0067] S3. For the experimental sample prepared in step S1, fix it in an alumina crucible and vertically immerse it in liquid lead-bismuth to prevent the sample from tilting during the experiment. Under oxygen saturation, raise the furnace temperature to 455℃ and hold for 20 hours. The sample is etched in liquid lead-bismuth to form an oxide film. The obtained etched experimental sample is shown below. Figure 2 As shown.

[0068] S4. Cold mount the corrosion test specimen with epoxy resin. After the epoxy resin cools and solidifies, gently grind and polish it with sandpaper to ensure that the protective film is not damaged while still allowing it to be observed and detected. The surface of the test specimen should look like this. Figure 3 As shown, the cross-section is as follows Figure 4 As shown, the thickness of the protective film of corrosion products is 0.7–1 μm.

[0069] Example 2

[0070] Following the above experimental procedure, the sample was immersed in lead-bismuth at 452℃ for 40 hours and then removed. Using the same sample interface preparation method as described above, the cross-section of the experimental sample was obtained as shown below. Figure 5 As shown, the thickness of the protective corrosion product layer is 0.9–1.5 μm.

[0071] Example 3

[0072] Following the above experimental procedure, the sample was immersed in lead-bismuth at 450℃ for 60 hours and then removed. The sample interface was prepared using the same method described above. Figure 6 As shown, the thickness of the protective corrosion product layer is 1–2 μm.

[0073] Example 4

[0074] Following the above experimental procedure, the sample was immersed in lead-bismuth at 448℃ for 80 hours and then removed. The sample interface was prepared using the same method described above. The oxide film on the surface of the experimental sample was as follows: Figure 7 As shown, the thickness of the protective corrosion product layer is 2–3 μm. Under the same time conditions, there is no significant difference in the corrosion product system after corrosion.

[0075] Example 5

[0076] Following the above experimental procedure, the sample was immersed in lead-bismuth at 445℃ for 100 hours and then removed. The cross-section of the experimental sample was prepared using the same sample interface preparation method described above. Figure 8 As shown, the thickness of the protective corrosion product layer is 4–5 μm.

[0077] Verification Example 1

[0078] The composition of the protective oxide film, and the specific substance analysis, detection, and characterization:

[0079] After 100 hours of corrosion, the corrosion of the experimental sample was still not very obvious. Further examination of the lead-bismuth detachment area of ​​the lead-bismuth corrosion sample revealed... Figure 6 The image shows the surface morphology of liquid lead-bismuth in a high-temperature oxygen-saturated environment at 450℃ for 60 hours. Observation of the protective film morphology under high magnification revealed that the oxide film consists of three layers. The outermost layer is thin but continuous, while the next outermost and inner oxide films are dense, and the inner oxide film is tightly bonded to the substrate. EDS analysis showed that the main distributed element in this region is enriched with O, and the oxide layer is preliminarily determined to be an oxide film containing Fe, Cr, and Al.

[0080] After removing the surface lead and bismuth from the 60-hour corrosion test samples, XRD analysis was performed. Figure 9 As shown, it contains Fe3O4 and Fe(Cr,Al)2O4, according to Figure 10 TEM results showed that the nanometer-thick oxide film near the substrate was Cr2O3. Under the high-temperature static liquid lead-bismuth corrosion environment of 450℃, the outermost oxide film was Fe3O4, the next outermost oxide film was Fe(Cr,Al)2O4, and the inner oxide film was Cr2O3.

[0081] Positive effects of protective oxide films:

[0082] 1. Effectively prevents ODS steel materials from undergoing dissolution corrosion, avoids the penetration and diffusion of liquid metal into the stainless steel matrix, and slows down the oxidation rate of the material;

[0083] Second, the matrix is ​​in direct contact with the liquid metal, effectively preventing the liquid metal from becoming brittle.

[0084] In the static corrosion of oxygen-saturated liquid lead-bismuth at 445–455 °C, ODS-FeCrAl first generates Fe3O4. Then, oxygen diffuses, and Fe, Cr, and Al elements undergo a series of complex reactions with the diffused oxygen to generate Fe(Cr,Al)2O4. The oxygen continues to diffuse inward, and after passing through the Fe3O4 and Fe(Cr,Al)2O4 layers, it reacts with the Cr elements enriched in the matrix to generate Cr2O3, which has a melting point higher than 2266 °C.

[0085] In summary, this invention provides an ODS-FeCrAl protective oxide film and its preparation method under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment. ODS-FeCrAl undergoes interfacial and diffusion reactions with oxygen in liquid lead-bismuth. Under oxygen-saturated conditions, a corrosion-resistant protective film is generated in the high-temperature liquid lead-bismuth corrosion environment, effectively preventing dissolution corrosion of ODS steel, avoiding the penetration and diffusion of liquid metal into the stainless steel substrate, and slowing down the oxidation rate of the material. It also avoids direct contact between the substrate and the liquid metal, effectively preventing liquid metal embrittlement. This provides a theoretical basis for the formation of the ODS-FeCrAl oxide film under oxygen-saturated conditions and explores the corrosion evolution behavior of ODS steel under saturated oxygen conditions.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an ODS-FeCrAl protective oxide film under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment, characterized in that, In a vacuum environment, a nuclear lead-bismuth eutectic alloy was melted to obtain liquid lead-bismuth. An ODS-FeCrAl sample was immersed in the liquid lead-bismuth. Under oxygen saturation, the temperature was controlled at 445~455℃ for 20~100h, and a diffusion reaction occurred to generate a three-layer protective oxide film with a thickness of 0.7~5µm. From the inside out, the protective oxide film consists of a Cr2O3 spinel layer, a Fe(Cr,Al)2O4 layer, and a Fe3O4 layer. The inner oxide film is a nanocrystalline layer that is serratedly bonded to the substrate. The next outermost oxide film is also a nano-scale dense crystalline layer, but the grains are larger than those of the outer oxide film. The outer oxide film forms a nano-scale oxide layer. The ODS-FeCrAl sample was then removed to obtain ODS-FeCrAl with a corrosion-resistant protective film.

2. The method for preparing an ODS-FeCrAl protective oxide film under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment according to claim 1, characterized in that, The melting temperature of the nuclear lead-bismuth eutectic alloy to obtain liquid lead-bismuth is 125~200℃, and the holding time is 40~50min.

3. The method for preparing an ODS-FeCrAl protective oxide film under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment according to claim 1, characterized in that, In the ODS-FeCrAl samples, the mass percentage of iron is 71.45%~77.25%, the mass percentage of chromium is 18.5%~21.5%, the mass percentage of aluminum is 3.75%~5.75%, the mass percentage of yttrium oxide is 0.3%~0.7%, and the mass percentage of titanium is 0.2%~0.6%.

4. The method for preparing an ODS-FeCrAl protective oxide film under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment according to claim 1, characterized in that, The thickness of the Cr2O3 spinel layer is 100~900nm.

5. The method for preparing an ODS-FeCrAl protective oxide film under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment according to claim 1, characterized in that, The thickness of the Fe(Cr,Al)2O4 layer is 0.4~1.5µm.

6. The method for preparing an ODS-FeCrAl protective oxide film under high-temperature oxygen-saturated liquid lead-bismuth corrosion environment according to claim 1, characterized in that, The thickness of the Fe3O4 layer is 0.1~3µm.

7. The ODS-FeCrAl protective oxide film prepared by the method according to any one of claims 1 to 6 under high temperature oxygen saturated liquid lead bismuth corrosion environment.

8. The ODS-FeCrAl protective oxide film based on a high-temperature oxygen-saturated liquid lead-bismuth corrosion environment according to claim 7, characterized in that, The ODS-FeCrAl protective oxide film has a melting point greater than 2266℃.

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