A method of defining the original interface of a material after corrosion of lead bismuth

Abstract

This invention provides a method for defining the original interface of a material after lead-bismuth corrosion. The method first subjects the material to be tested to thermal aging treatment to generate a Laves phase, then performs lead-bismuth corrosion on the material, and finally observes the material. The portion containing the Laves phase consists of the material matrix and Fe generated by oxygen diffusion inwards. 3‑x Cr x The O4 spinel oxide layer, the portion without the Laves phase, is the Fe3O4 oxide layer formed by the outward diffusion of metal. The boundary between the portion containing the Laves phase and the portion without the Laves phase is the original interface of the material after lead-bismuth corrosion. The method of this invention can clearly and effectively observe the original interface of the material after lead-bismuth corrosion, and can provide experimental evidence for studying the corrosion mechanism of liquid metals and the diffusion process of elements.

Description

Technical Field

[0001] This invention belongs to the field of functional materials, specifically relating to a method for defining the original interface of a material after lead-bismuth corrosion. Background Technology

[0002] Accelerator-Driven Subcritical Systems (ADS) are conceptual nuclear energy systems designed to address nuclear waste transmutation and energy generation. This system combines a particle accelerator and a subcritical reactor, safely converting nuclear waste to generate energy while reducing its hazardous properties. It is widely recognized as an effective technological solution for nuclear waste transmutation. The core of an ADS system consists of a subcritical reactor and a particle accelerator. The accelerator accelerates high-energy protons, which are then injected into the subcritical reactor. In the reactor, the protons interact with a target nuclide (typically lead or titanium) to produce neutrons. Lead-cooled fast reactors (LFRs), one of the six fission reactor concepts in the fourth-generation roadmap for advanced nuclear power, possess advantages such as high safety, high economic efficiency, high power density, and the ability to convert radioactive nuclides, and are considered to have broad development potential.

[0003] Lead-bismuth eutectic (LBE) alloys possess high density, low melting point, excellent radiation resistance, thermal conductivity, good neutron performance, and chemical inertness in their liquid state, making them the preferred coolant material for liquid fuel filters (LFRs) in the nuclear energy field. Candidate structural materials for LFRs must be able to operate reliably in extremely harsh environments where their performance can degrade due to radiation-induced damage, liquid metal corrosion, liquid metal embrittlement, stress, transmutation, nuclear reactions that produce helium atoms, and combinations of all these effects. Nuclear-grade structural materials are typically iron-based or nickel-based alloys. Ni's solubility in liquid LBE is approximately one hundred times that of Fe. Therefore, nickel-based alloys are unsuitable for LFRs. Candidate structural materials are primarily F / M steels (such as T91 and P92) and AuSS (such as 316L). Among these, F / M steels are more suitable for service in lead-bismuth environments due to their high thermal conductivity at high temperatures, low thermal expansion, and excellent resistance to radiation embrittlement and pore expansion. However, liquid lead-bismuth alloys cause severe liquid metal corrosion to F / M steel, which has become a key factor restricting the development and application of LFR.

[0004] On the one hand, the harsh environment of high-temperature liquid lead-bismuth makes in-situ observation of the corrosion process extremely difficult; on the other hand, there is currently a lack of effective methods to observe and define the original interface of materials after lead-bismuth corrosion. Therefore, there is still a lack of intuitive experimental support for the corrosion mechanism of liquid metals and the element diffusion process. A new method needs to be designed to clearly and effectively observe the original interface of materials after lead-bismuth corrosion, thereby obtaining experimental evidence for the corrosion mechanism of liquid metals and the element diffusion process. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. To this end, the present invention provides a method for defining the original interface of a material after lead-bismuth corrosion, which can clearly and effectively observe the original interface of the material after lead-bismuth corrosion, and can provide experimental evidence for studying the corrosion mechanism of liquid metals and the diffusion process of elements.

[0006] A first aspect of the present invention provides a method for defining the original interface of a lead-bismuth material after corrosion, the method comprising the following steps:

[0007] S1: The material to be tested is subjected to thermal aging treatment to generate the Laves phase;

[0008] S2: Perform surface treatment on the material after step S1 to remove the oxide layer;

[0009] S3: Perform lead-bismuth etching on the material treated in step S2;

[0010] S4: Observe the material after step S3. The part containing the Laves phase is the material matrix and Fe generated by oxygen diffusion inward. 3-x Cr x The O4 spinel oxide layer, the part without the Laves phase is the Fe3O4 oxide layer formed by the outward diffusion of metal, and the boundary between the part containing the Laves phase and the part without the Laves phase is the original interface of the material after lead-bismuth corrosion.

[0011] Liquid metal corrosion is the most significant material degradation effect resulting from the contact between candidate structural materials and liquid liquid oxidizing agents (LBEs). Liquid metal corrosion primarily manifests through two corrosion mechanisms: dissolution and oxidation. The occurrence of these two mechanisms depends on the dissolved oxygen concentration within the liquid LBE; when the oxygen concentration in the LBE exceeds 10... -5 At wt.%, the resulting oxide film is thick and not dense, making it prone to breakage and peeling under the penetration and erosion of liquid lead-bismuth alloy, thus forming severe oxidation corrosion; while when the oxygen concentration in LBE is below 10%, the oxide film formed is relatively thick and not dense, making it prone to breakage and peeling under the penetration and erosion of liquid lead-bismuth alloy, thus forming severe oxidation corrosion; - 7At wt.%, a complete and protective oxide film cannot form on the surface of the structural material, resulting in severe dissolution corrosion. Therefore, studying the corrosion mechanism of liquid metals and the element diffusion process is of great significance for the development of lead-cooled fast reactors.

[0012] One technical solution of the present invention concerning a method for defining the original interface of a lead-bismuth material after corrosion has at least the following features:

[0013] Beneficial effects:

[0014] The oxide film formed on metallic materials after corrosion by liquid lead and bismuth has a two-layer structure: an outer layer of loose and porous Fe3O4, and an inner layer of relatively dense and protective Fe. 3-x Cr x O4 spinel layer. The method of defining the original interface of a material after lead-bismuth corrosion in this invention can clearly and effectively observe the original interface of the material after lead-bismuth corrosion, and can provide experimental evidence for studying the corrosion mechanism of liquid metals and the diffusion process of elements.

[0015] According to some embodiments of the present invention, the material to be tested includes F / M steel.

[0016] F / M steel is a high-strength, high-temperature material typically used in high-temperature, high-pressure engineering applications such as nuclear reactors, thermal power plants, chemical equipment, and aerospace technology. F stands for Ferritic stainless steel, and M stands for Martensitic stainless steel.

[0017] Ferritic stainless steel is a class of alloys composed of iron and chromium, typically containing small amounts of other alloying elements such as molybdenum, tungsten, silicon, and aluminum. These alloys are characterized by excellent high-temperature resistance and oxidation resistance. They maintain good mechanical strength and corrosion resistance under high-temperature conditions, and are therefore commonly used in high-temperature applications such as furnace tubes, boilers, and gas turbines.

[0018] Martensitic stainless steel is also an alloy composed of iron and chromium, but it undergoes a martensitic transformation during cooling, thus providing higher hardness and strength. These alloys are often used to manufacture components that require high strength and wear resistance, such as cutting tools, bearings, valves, and pumps.

[0019] F / M steel is generally known for its high-temperature and high-strength properties, making it ideal for many industrial applications. In the nuclear energy industry, F / M steel is commonly used to manufacture structural components in nuclear reactors because they need to maintain stability and strength under high temperature, high radiation, and high pressure conditions. These steels also require sophisticated heat treatment and material testing to ensure they meet stringent engineering requirements and safety standards.

[0020] According to some embodiments of the present invention, the grades of the F / M steel include T91, T92, P91 and P92.

[0021] F / M steels with a Cr content of 9 wt.% (such as T91, T92, P91, and P92) are considered primary candidate materials for lead-cooled fast reactors due to their excellent thermodynamic and mechanical properties, resistance to radiation embrittlement, and resistance to pore expansion at high temperatures. Taking P92 steel as an example, its main alloying composition is Cr: 8.50–9.50%, W: 1.50–2.00%, and Mo: 0.30–0.60%. A significant change in the microstructure of P92 steel during thermal aging is the formation of a large amount of Laves phase. The Laves phase is an intermetallic compound with an A2B type hexagonal structure. The main component of the Laves phase in P92 steel is (Fe, Cr)2(W, Mo) intermetallic compound, precipitating at the interfaces such as the original austenite grain boundaries and martensite lath boundaries. With increasing aging time, the particle size and content gradually increase. Laves phase precipitates in P92 steel matrix after aging at 650℃ for 500h. After aging at 650℃ for 3000h, the Laves phase becomes the largest second phase particle in P92 steel. The particle size can reach up to 1μm after 10000h. When the oxygen concentration in the high-temperature liquid lead-bismuth environment is higher than 10... -5 At wt.%, P92 steel is susceptible to corrosion by liquid lead-bismuth, which oxidizes and forms an oxide layer on the material surface. The thickness of the oxide layer on the material surface is affected by temperature, dissolved oxygen concentration in the liquid lead-bismuth, and immersion time.

[0022] According to some embodiments of the present invention, the temperature of the heat aging treatment is 500°C to 750°C.

[0023] According to some embodiments of the present invention, the heat aging treatment time is ≥500h.

[0024] According to some embodiments of the present invention, the pressure of the heat aging treatment is 0.8 atm to 1.2 atm.

[0025] According to some embodiments of the present invention, after heat aging treatment, the surface of the material is polished to remove the oxide film on the surface, thereby obtaining a material sample with Laves phase precipitated inside.

[0026] According to some embodiments of the present invention, the method of lead-bismuth corrosion is to immerse the material in a high-temperature liquid lead-bismuth alloy environment.

[0027] The melting point of lead-bismuth alloys depends on their composition. Generally, lead-bismuth alloys have relatively low melting points. Pure lead has a melting point of approximately 327.5°C, while pure bismuth has a melting point of approximately 271.3°C. Therefore, the melting point of lead-bismuth alloys is usually between these two, depending on the ratio of lead to bismuth in the alloy. Different lead-bismuth alloys have different melting points, but they typically melt between 200°C and 400°C. Due to their low melting point, good wettability, and thermal conductivity, lead-bismuth alloys are widely used in some high-temperature applications, such as nuclear reactor coolants. The properties of these alloys make them suitable for applications requiring high-temperature operating environments.

[0028] According to some embodiments of the present invention, the lead-bismuth alloy contains 44.5 wt.% lead and 55.5 wt.% bismuth.

[0029] According to some embodiments of the present invention, the high temperature is 450°C to 600°C.

[0030] According to some embodiments of the present invention, the soaking time is 500h to 2000h.

[0031] According to some embodiments of the present invention, the method of immersing the material in a high-temperature liquid lead-bismuth alloy environment can be as follows: the material with precipitated Laves phase is ground and polished, and then placed in a high-temperature liquid lead-bismuth environment for a certain period of time to form a double oxide layer structure of a certain thickness on the surface of the material.

[0032] According to some embodiments of the present invention, the method further includes immersing the material in a mixed solution of CH3CH2OH, CH3COOH and H2O2 before observing the material after step S3 to remove residual lead-bismuth alloy on the surface of the material.

[0033] According to some embodiments of the present invention, the method of immersing the material in a mixed solution of CH3CH2OH, CH3COOH and H2O2 can be as follows: immerse the sample in a mixed solution of CH3CH2OH, CH3COOH and H2O2 with a volume ratio of 1:1:1 for 24 hours to remove residual lead-bismuth alloy from the surface of the sample.

[0034] After soaking, the sample was cut open using wire cutting, and the cut surface was used as the observation surface. The material containing the observation surface was placed in an ultrasonic cleaner until the surface oil was removed, and then the observation surface was ground and polished.

[0035] In a liquid lead-bismuth corrosive environment, the lead-bismuth alloy composition can be: Pb: 44.5 wt.%, Bi: 55.5 wt.%. A P92 steel sample was immersed in liquid lead-bismuth with saturated oxygen content at 550℃ for 1000 h.

[0036] The method for detecting the Laves phase can be as follows: after lead-bismuth corrosion, the material containing the Laves phase is polished and then observed using transmission electron microscopy, EDS energy dispersive spectroscopy analysis, and selective diffraction analysis to analyze whether the Laves phase still maintains the (Fe,Cr)2(W,Mo) structure, in order to verify that the Laves phase did not dissolve or oxidize during the lead-bismuth corrosion process.

[0037] The method for defining the original interface can be as follows: After polishing the material containing the Laves phase following lead-bismuth etching, scanning electron microscopy and EDS analysis can be used to observe that the oxide layer formed on the material surface has a double-layer structure. The outer layer is a Fe3O4 layer without the Laves phase, and the inner layer is a Fe layer with dispersed Laves phase. 3-x Cr x O4 spinel layer. The Laves phase in the matrix remains in its original distribution after lead-bismuth corrosion. That is, the original interface of the material is the boundary between the Laves-containing and non-Laves-containing portions observed under a scanning electron microscope. Outside the original interface is the Fe3O4 oxide layer, and inside the original interface is the Fe... 3-x Cr x O4 spinel oxide layer and lead-bismuth etched substrate. Attached Figure Description

[0038] Figure 1 This is a SEM image of the surface morphology of the polished P92 steel material.

[0039] Figure 2 This is the surface energy spectrum of the polished P92 steel material.

[0040] Figure 3 SEM image of the contact surface between P92 steel and liquid lead-bismuth.

[0041] Figure 4 EDS surface scan of the contact surface between P92 steel and liquid lead-bismuth.

[0042] Figure 5 EDS line scan of the contact surface between P92 steel and liquid lead-bismuth.

[0043] Figure 6 The TEM morphology of the Laves phase in the inner Fe3-xCrxO4 spinel layer is shown.

[0044] Figure 7 Diffraction patterns were selected for the Laves phase in the inner Fe3-xCrxO4 spinel layer.

[0045] Figure 8 This is a diagram showing the original interface location of a P92 steel sample after corrosion by liquid lead-bismuth. Detailed Implementation

[0046] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0047] In some embodiments of the present invention, a method for defining the original interface of a lead-bismuth material after corrosion is provided, comprising the following steps:

[0048] S1: The material to be tested is subjected to thermal aging treatment to generate the Laves phase;

[0049] S2: Perform surface treatment on the material after step S1 to remove the oxide layer;

[0050] S3: Perform lead-bismuth etching on the material treated in step S2;

[0051] S4: Observe the material after step S3. The part containing the Laves phase is the material matrix and Fe generated by oxygen diffusion inward. 3-x Cr x The O4 spinel oxide layer, the part without the Laves phase is the Fe3O4 oxide layer formed by the outward diffusion of metal, and the boundary between the part containing the Laves phase and the part without the Laves phase is the original interface of the material after lead-bismuth corrosion.

[0052] Liquid metal corrosion is the most significant material degradation effect resulting from the contact between candidate structural materials and liquid liquid oxidizing agents (LBEs). Liquid metal corrosion primarily manifests through two corrosion mechanisms: dissolution and oxidation. The occurrence of these two mechanisms depends on the dissolved oxygen concentration within the liquid LBE; when the oxygen concentration in the LBE exceeds 10... -5 At wt.%, the resulting oxide film is thick and not dense, making it prone to breakage and peeling under the penetration and erosion of liquid lead-bismuth alloy, thus forming severe oxidation corrosion; while when the oxygen concentration in LBE is below 10%, the oxide film formed is relatively thick and not dense, making it prone to breakage and peeling under the penetration and erosion of liquid lead-bismuth alloy, thus forming severe oxidation corrosion; - 7 At wt.%, a complete and protective oxide film cannot form on the surface of the structural material, resulting in severe dissolution corrosion. Therefore, studying the corrosion mechanism of liquid metals and the element diffusion process is of great significance for the development of lead-cooled fast reactors.

[0053] It is understandable that the oxide film formed on metallic materials after corrosion by liquid lead and bismuth has a two-layer structure: an outer layer of loose and porous Fe3O4, and an inner layer of relatively dense and protective Fe. 3-x Cr x O4 spinel layer. The method of defining the original interface of a material after lead-bismuth corrosion in this invention can clearly and effectively observe the original interface of the material after lead-bismuth corrosion, and can provide experimental evidence for studying the corrosion mechanism of liquid metals and the diffusion process of elements.

[0054] In some embodiments of the present invention, the material to be tested includes F / M steel.

[0055] F / M steel is a high-strength, high-temperature material typically used in high-temperature, high-pressure engineering applications such as nuclear reactors, thermal power plants, chemical equipment, and aerospace technology. F stands for Ferritic stainless steel, and M stands for Martensitic stainless steel.

[0056] Ferritic stainless steel is a class of alloys composed of iron and chromium, typically containing small amounts of other alloying elements such as molybdenum, tungsten, silicon, and aluminum. These alloys are characterized by excellent high-temperature resistance and oxidation resistance. They maintain good mechanical strength and corrosion resistance under high-temperature conditions, and are therefore commonly used in high-temperature applications such as furnace tubes, boilers, and gas turbines.

[0057] Martensitic stainless steel is also an alloy composed of iron and chromium, but it undergoes a martensitic transformation during cooling, thus providing higher hardness and strength. These alloys are often used to manufacture components that require high strength and wear resistance, such as cutting tools, bearings, valves, and pumps.

[0058] F / M steel is generally known for its high-temperature and high-strength properties, making it ideal for many industrial applications. In the nuclear energy industry, F / M steel is commonly used to manufacture structural components in nuclear reactors because they need to maintain stability and strength under high temperature, high radiation, and high pressure conditions. These steels also require sophisticated heat treatment and material testing to ensure they meet stringent engineering requirements and safety standards.

[0059] In some embodiments of the present invention, the grades of F / M steel include T91, T92, P91 and P92.

[0060] F / M steels with a Cr content of 9 wt.% (such as T91, T92, P91, and P92) are considered primary candidate materials for lead-cooled fast reactors due to their excellent thermodynamic and mechanical properties, resistance to radiation embrittlement, and resistance to pore expansion at high temperatures. Taking P92 steel as an example, its main alloying composition is Cr: 8.50–9.50%, W: 1.50–2.00%, and Mo: 0.30–0.60%. A significant change in the microstructure of P92 steel during thermal aging is the formation of a large amount of Laves phase. The Laves phase is an intermetallic compound with an A2B type hexagonal structure. The main component of the Laves phase in P92 steel is (Fe, Cr)2(W, Mo) intermetallic compound, precipitating at the interfaces such as the original austenite grain boundaries and martensite lath boundaries. With increasing aging time, the particle size and content gradually increase. Laves phase precipitates in P92 steel matrix after aging at 650℃ for 500h. After aging at 650℃ for 3000h, the Laves phase becomes the largest second phase particle in P92 steel, with the largest particle size reaching 1μm after 10000h. When the oxygen concentration in the high-temperature liquid lead-bismuth environment is higher than 10... -5 At wt.%, P92 steel is susceptible to corrosion by liquid lead-bismuth, which oxidizes and forms an oxide layer on the material surface. The thickness of the oxide layer on the material surface is affected by temperature, dissolved oxygen concentration in the liquid lead-bismuth, and immersion time.

[0061] In some embodiments of the present invention, the temperature of the heat aging treatment is 500°C to 750°C.

[0062] In some embodiments of the present invention, the heat aging treatment time is ≥500h.

[0063] In some embodiments of the present invention, the pressure of the heat aging treatment is 0.8 atm to 1.2 atm.

[0064] In some embodiments of the present invention, after heat aging treatment, the material surface is polished to remove the oxide film on the surface and obtain a material sample with Laves phase precipitated inside.

[0065] It should be noted that removing the oxide film on the surface refers to removing the oxide film generated during the heat aging process.

[0066] In some embodiments of the present invention, the method of lead-bismuth corrosion is to immerse the material in a high-temperature liquid lead-bismuth alloy environment.

[0067] The melting point of lead-bismuth alloys depends on their composition. Generally, lead-bismuth alloys have relatively low melting points. Pure lead has a melting point of approximately 327.5°C, while pure bismuth has a melting point of approximately 271.3°C. Therefore, the melting point of lead-bismuth alloys is usually between these two, depending on the ratio of lead to bismuth in the alloy. Different lead-bismuth alloys have different melting points, but they typically melt between 200°C and 400°C. Due to their low melting point, good wettability, and thermal conductivity, lead-bismuth alloys are widely used in some high-temperature applications, such as nuclear reactor coolants. The properties of these alloys make them suitable for applications requiring high-temperature operating environments.

[0068] In some embodiments of the present invention, the lead-bismuth alloy contains 44.5 wt.% lead and 55.5 wt.% bismuth.

[0069] In some embodiments of the present invention, the high temperature is 500°C to 600°C.

[0070] In some embodiments of the present invention, the soaking time is 500h to 2000h.

[0071] In some embodiments of the present invention, the method of immersing the material in a high-temperature liquid lead-bismuth alloy environment may be as follows: the material with precipitated Laves phase is ground and polished, and then placed in a high-temperature liquid lead-bismuth environment for a certain period of time to form a double oxide layer structure of a certain thickness on the surface of the material.

[0072] In some embodiments of the present invention, the method further includes immersing the material in a mixed solution of CH3CH2OH, CH3COOH and H2O2 before observing the material after step S3 to remove residual lead-bismuth alloy on the surface of the material.

[0073] In some embodiments of the present invention, the method of immersing the material in a mixed solution of CH3CH2OH, CH3COOH and H2O2 can be as follows: immerse the sample in a mixed solution of CH3CH2OH, CH3COOH and H2O2 with a volume ratio of 1:1:1 for 24 hours to remove residual lead-bismuth alloy from the surface of the sample.

[0074] After soaking, the sample was cut open using wire cutting, and the cut surface was used as the observation surface. The material containing the observation surface was placed in an ultrasonic cleaner until the surface oil was removed, and then the observation surface was ground and polished.

[0075] In a liquid lead-bismuth corrosive environment, the lead-bismuth alloy composition can be: Pb: 44.5 wt.%, Bi: 55.5 wt.%. A P92 steel sample was immersed in liquid lead-bismuth with saturated oxygen content at 550℃ for 1000 h.

[0076] The method for detecting the Laves phase can be as follows: after lead-bismuth corrosion, the material containing the Laves phase is polished and then observed using transmission electron microscopy, EDS energy dispersive spectroscopy analysis, and selective diffraction analysis to analyze whether the Laves phase still maintains the (Fe,Cr)2(W,Mo) structure, in order to verify that the Laves phase did not dissolve or oxidize during the lead-bismuth corrosion process.

[0077] The method for defining the original interface can be as follows: After polishing the material containing the Laves phase following lead-bismuth etching, scanning electron microscopy and EDS analysis can be used to observe that the oxide layer formed on the material surface has a double-layer structure. The outer layer is a Fe3O4 layer without the Laves phase, and the inner layer is a Fe layer with dispersed Laves phase. 3-x Cr x O4 spinel layer. The Laves phase in the matrix remains in its original distribution after lead-bismuth corrosion. That is, the original interface of the material is the boundary between the Laves-containing and non-Laves-containing portions observed under a scanning electron microscope. Outside the original interface is the Fe3O4 oxide layer, and inside the original interface is the Fe... 3-x Cr x O4 spinel oxide layer and lead-bismuth etched substrate.

[0078] The following specific embodiment will further illustrate the method of the present invention.

[0079] Taking P92 steel as an example, the main alloy composition of P92 steel by weight percentage is as follows: Cr: 8.50~9.50%, W: 1.50~2.00%, Mo: 0.30~0.60%.

[0080] The lead-bismuth alloy composition in a liquid lead-bismuth corrosive environment is: Pb: 44.5 wt.%, Bi: 55.5 wt.%.

[0081] First, a P92 steel sample with Laves phase precipitate was prepared. The specific preparation steps are as follows:

[0082] P92 steel was cut into 10mm×10mm×5mm blocks using wire cutting.

[0083] The cut P92 steel material is placed in a box furnace at 600℃ and 1 atm pressure for 80,000 hours of heat aging treatment to generate a large volume of Laves phase inside the material, thus preparing P92 steel material with Laves phase precipitation.

[0084] The P92 steel material with Laves phase precipitation was ground and polished to remove the oxide layer generated on the material surface due to heat treatment, so as to prevent interference with the subsequent liquid lead bismuth corrosion process.

[0085] like Figure 1 and Figure 2 As shown, the surface morphology of polished P92 steel was observed using a scanning electron microscope, and combined with EDS point scanning analysis, it was determined that the brighter areas in the morphology were the precipitated Laves phase.

[0086] A high-temperature liquid lead-bismuth corrosion experiment was conducted on the P92 steel sample with Laves phase precipitation. The specific experimental steps are as follows:

[0087] The P92 steel material with Laves phase precipitated after grinding and polishing was immersed in a static lead-bismuth experimental apparatus.

[0088] The temperature of the high-temperature reactor was set at 550℃, the pressure was controlled at 1 atm, and the internal oxygen concentration was controlled to saturate the oxygen content in the liquid lead bismuth.

[0089] The P92 steel sample was continuously immersed in the above heating conditions for 1000 hours, and then cooled down and removed.

[0090] The sample was then immersed in a mixed solution of CH3CH2OH, CH3COOH and H2O2 in a volume ratio of 1:1:1 for 24 hours to remove residual lead-bismuth alloy from the sample surface.

[0091] The sample was cut into two blocks, 10mm×8mm×5mm and 10mm×2mm×5mm, using wire cutting. The cut interface of the larger block was selected as the observation surface. The larger block was then placed in an ultrasonic cleaner until surface oil was removed, and its observation surface was subsequently ground and polished.

[0092] Then, the observation surfaces of the material after lead-bismuth corrosion were inspected and analyzed. The specific steps are as follows:

[0093] like Figure 3 As shown, analysis of the observed surface using a scanning electron microscope revealed that an oxide layer formed on the surface of P92 steel in contact with liquid lead-bismuth due to corrosion and oxidation by the liquid metal.

[0094] like Figure 4 As shown, EDS surface scanning analysis and combined with the scanning electron microscopy morphology obtained in step 2 revealed a large amount of Laves phase dispersed in the matrix and part of the oxide layer, indicating that the Laves phase did not dissolve during the lead-bismuth corrosion process.

[0095] like Figure 5 As shown, EDS line scanning analysis combined with scanning electron microscopy morphology images revealed that the oxide layer has a bilayer structure: the outer layer is a Fe3O4 layer without the Laves phase, and the inner layer is a Fe layer with a dispersed Laves phase. 3-x Cr xO4 spinel layer. The Laves phase does not undergo oxidation or dissolution corrosion in the high-temperature liquid lead-bismuth environment, and its interior remains a hexagonal (Fe,Cr)2(W,Mo) intermetallic compound.

[0096] like Figure 6 as well as Figure 7 As shown, the inner Fe layer was examined using a transmission electron microscope. 3-x Cr x Selective diffraction analysis of the Laves phase in the O4 spinel layer revealed that the Laves phase is a hexagonal (Fe,Cr)2(W,Mo) intermetallic compound, indicating that the Laves phase did not undergo oxidation during lead-bismuth corrosion.

[0097] like Figure 8 As shown, the test results indicate that after the material is corroded by liquid lead-bismuth, the matrix and Fe... 3-x Cr x The presence of Laves phase dispersed within the O4 spinel layer indicates that Fe 3-x Cr x The O4 spinel layer was formed by the oxidation of the original matrix due to lead-bismuth corrosion. The absence of the Laves phase in the Fe3O4 layer indicates that it was formed by outward oxidation growth due to lead-bismuth corrosion. The boundary between the Laves-containing and non-Laves-containing portions, observed under a scanning electron microscope, represents the original interface of the material. Outside this interface is the Fe3O4 oxide layer, and inside is the Fe... 3-x Cr x O4 spinel oxide layer and lead-bismuth etched substrate.

[0098] That is, after corrosion by liquid lead and bismuth, the material forms a double oxide film, with the upper layer being an Fe3O4 oxide layer and the lower layer being Fe... 3-x Cr x An O4 spinel oxide layer forms, and the boundary between the two is precisely the original material interface. This phenomenon indicates that during the corrosion of liquid lead-bismuth, iron first dissolves from the matrix into the liquid lead-bismuth. Since the oxygen concentration in the liquid lead-bismuth is greater than the dissolved oxygen concentration required for the formation of Fe3O4 at this temperature, the dissolved iron immediately combines with oxygen to form a Fe3O4 oxide layer outside the original material interface. Simultaneously, oxygen rapidly diffuses inward through the vacancies created by the iron and reacts with iron and chromium in the matrix within the original material interface to form Fe3O4. 3-x Cr x O4 spinel.

[0099] The method for defining the original interface of lead-bismuth alloys after corrosion provided by this invention can be used to define the original interface of the material using scanning electron microscopy. This overcomes the previous lack of more reliable experimental support for studying the corrosion mechanism and element diffusion process of liquid lead-bismuth alloys, and is of great significance for further extending the service life of structural materials in lead-cooled fast reactors.

[0100] It should also be noted that for materials where the technical solution can precipitate a hexagonal (Fe, Cr)₂ (W, Mo) intermetallic compound Laves phase, in addition to P92, T91, T92, P91, and F / M steel with a Cr content of 9 wt.% containing W and / or Mo can also be used as substitutes. The experimental conditions for heat-treating these materials to precipitate the Laves phase are not unique. P92 and T92, due to their higher W content, can precipitate the Laves phase after heat treatment at 600℃ for approximately 500 hours; while T91 and P91, lacking W, require approximately 8000 hours of heat treatment at 600℃ to precipitate the Laves phase; for other 9 wt.% F / M steels, higher W and Mo contents result in faster Laves phase precipitation. During lead-bismuth etching of materials with precipitated Laves phases, the experimental conditions will affect the thickness of the double oxide layer, but will not affect the definition and observation of the original material interface. A double oxide layer structure of a certain thickness can be formed when the reaction temperature is between 400 and 600℃ and the soaking time is more than 500 hours.

[0101] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method of defining the original interface of a material after lead bismuth corrosion, characterized in that, The method includes the following steps: S1: The material to be tested is subjected to thermal aging treatment to generate the Laves phase; S2: Perform surface treatment on the material after step S1 to remove the oxide layer; S3: Perform lead-bismuth etching on the material treated in step S2; S4: observing the material after step S3, the part containing Laves phase is the material matrix and Fe generated by inward diffusion of oxygen 3-x Cr x O4 spinel oxide layer, the part not containing Laves phase is Fe3O4 oxide layer generated by outward diffusion of metal, and the boundary between the part containing Laves phase and the part not containing Laves phase is the original interface of the material after lead-bismuth corrosion.

2. The method of claim 1, wherein, The material to be tested includes F / M steel.

3. The method of claim 1, wherein, The temperature for the heat aging treatment is 500℃~750℃.

4. The method of claim 1, wherein, The heat aging treatment time is ≥500h.

5. The method of claim 1, wherein, The pressure of the heat aging treatment is 0.8 atm to 1.2 atm.

6. The method of claim 1, wherein, The method for lead-bismuth corrosion is to immerse the material in a high-temperature liquid lead-bismuth alloy environment.

7. The method of claim 6, wherein, The lead-bismuth alloy contains 44.5 wt.% lead and 55.5 wt.% bismuth.

8. The method of claim 6, wherein, The high temperature is 450℃~600℃.

9. The method of claim 6, wherein, The soaking time is 500h to 2000h.

10. The method of claim 1, wherein, The method further includes immersing the material in a mixed solution of CH3CH2OH, CH3COOH and H2O2 before observing the material after step S3 to remove residual lead-bismuth alloy on the material surface.

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