Liquid metal lead-bismuth corrosion resistant coating and method for producing the same

Abstract

The application discloses a liquid metal lead-bismuth corrosion resistant coating and a preparation method thereof. The liquid metal lead-bismuth corrosion resistant coating is a gradient coating, and from the stainless steel base body outward, the coating comprises a secondary outer layer and an outermost layer in sequence. The outermost layer is a corrosion resistant dense oxide ceramic coating, and specifically can be an aluminum oxide and chromium oxide composite ceramic phase. The secondary outer layer is a transition layer, which supports the ceramic coating of the outermost layer, connects the base body, and increases the bonding force and compatibility of the coating and the base body. FeCrAl alloy is used as the transition layer. Through experiments, it is verified that the method provided by the application can prepare a continuous, uniform and dense aluminum-chromium composite oxide / FeCrAl gradient coating on the stainless steel base body. There is no obvious interface between the coating and the base body, a metallurgical bonding transition between the coating and the base body is realized, and the coating and the base body are firmly combined. The liquid metal lead-bismuth corrosion resistant coating has a wide application prospect in the field of advanced nuclear industry.

Description

Technical Field

[0001] This invention belongs to the field of new energy, including lead-based fast reactors and lead-based cooled solar energy systems. Specifically, it relates to a coating resistant to liquid lead-bismuth corrosion and a method for preparing it on the surface of nuclear structural steel. Background Technology

[0002] Lead-cooled fast reactors (LFRs) are one of the most promising reactor types for Generation IV advanced nuclear energy systems, with broad development prospects. Lead-bismuth eutectic alloys (LBEs) possess excellent properties such as low melting point, high thermal conductivity, and high neutron yield, making them a preferred material for LFR coolants. They are also important candidate materials for coolants and spallation targets in accelerator-driven subcritical systems (ADS).

[0003] However, the compatibility of LBE with structural materials at high temperatures has become one of the major bottlenecks restricting the development of LFR. Components such as Ni, Fe, and Cr contained in reactor structural materials will dissolve and migrate in LBE, resulting in severe dissolution corrosion. When the oxygen concentration in LBE is high, it will come into contact with structural materials and undergo oxidation reactions, forming oxidative corrosion. In addition, the Pb-Bi-induced material embrittlement effect will also cause material performance degradation. These potential threats have a significant impact on the structural integrity and safety of LFR and ADS systems, and become limiting factors for system lifespan.

[0004] Therefore, developing relevant liquid metal corrosion-resistant technologies is essential to protect structural materials from corrosion. Current solutions include developing new materials, adding corrosion inhibitors, and preparing coatings on material surfaces. Among these, preparing corrosion-resistant coatings on structural material surfaces is considered a very economical and effective method, as it can maximize the preservation of the substrate's inherent superior properties.

[0005] Many types of corrosion-resistant coatings are available, such as FeCrAlY, Al2O3, TiN, Ti3SiC2, and SiC. While these coatings exhibit excellent resistance to liquid metal corrosion, many suffer from poor mechanical compatibility with the substrate. For example, they are prone to cracking or peeling under thermal shock or micro-strain in the substrate. Furthermore, most current research focuses on preparing coatings and their corrosion resistance on small-sized samples. Due to these limitations, current techniques for preparing these coatings, including pulsed laser deposition (PLD), physical vapor deposition (PVD), chemical vapor deposition (CVD), and thermal spraying, still face significant challenges in preparing coatings on the inner surfaces of large, irregularly shaped parts, such as the inner surfaces of complex-shaped containers, the impeller surfaces of liquid metal-driven pumps, and the inner walls of coolant transport pipelines. Therefore, the application of liquid metal corrosion-resistant coatings in the actual nuclear industry remains a significant challenge.

[0006] Therefore, designing new LBE corrosion-resistant coatings and developing technologies to prepare LBE corrosion-resistant coatings on the surfaces of large-sized irregular parts are key to solving the above problems. Summary of the Invention

[0007] The purpose of this invention is to study and design a new LBE corrosion resistant coating that has good compatibility with nuclear structural steel, and to find and develop technologies or methods to prepare such a coating on the surface of large-sized irregular parts (such as the inner wall of coolant transport pipes).

[0008] To address the above problems, this invention provides a coating resistant to liquid metal lead-bismuth corrosion and its preparation method.

[0009] The corrosion-resistant coating against liquid metal lead and bismuth provided by the present invention is a gradient coating, which includes a second outermost layer and an outermost layer in sequence from the stainless steel substrate outwards.

[0010] The outermost layer is a corrosion-resistant dense oxide ceramic coating; specifically, it can be an alumina and chromium oxide composite ceramic phase; more specifically, in the alumina and chromium oxide composite ceramic phase, the alumina content reaches more than 95 wt% and the chromium oxide content is less than 5 wt%.

[0011] The outermost layer is a transition layer used to support the outermost ceramic coating and connect to the substrate, increasing the adhesion and compatibility between the coating and the substrate;

[0012] Specifically, FeCrAl alloy is used as the transition layer, i.e., the outermost layer;

[0013] More specifically, the mass content range of each element in the transition layer is Fe 65-80%, Cr 3-17%, Al 5-18%, and it does not contain the Fe2Al5 alloy phase.

[0014] The outermost layer has a thickness of 0.2-3 μm, and the thickness of the second outermost layer is not less than the thickness of the outermost layer.

[0015] The above-mentioned coating resistant to liquid lead-bismuth corrosion is prepared by a method comprising the following steps:

[0016] 1) Obtain a uniform aluminum coating on the surface of a stainless steel substrate;

[0017] 2) The stainless steel substrate with an aluminum coating obtained in step 1) is heat-treated to obtain an FeCrAl alloy layer on the substrate surface.

[0018] 3) A Cr layer is formed on the FeCrAl alloy layer on the substrate surface to obtain a Cr / FeCrAl stainless steel substrate;

[0019] 4) The Cr / FeCrAl stainless steel substrate is oxidized to form an aluminum-chromium composite oxide / FeCrAl gradient coating on the substrate surface, which is a coating resistant to liquid metal lead-bismuth corrosion.

[0020] Step 1) of the above method can specifically involve using an ionic liquid to deposit aluminum onto the surface of the stainless steel substrate to obtain an aluminum coating.

[0021] The ionic liquid used is a mixture of AlCl3 and alkyl imidazole organic salts in a molar ratio of 1:2 to 1:5.

[0022] The alkyl imidazole organic salt mentioned therein can specifically be 1-methyl-3-ethylimidazolium chloride (EMIC);

[0023] The ionic liquid is used as the electrolyte, the substrate to be plated is used as the cathode, and pure aluminum is used as the anode;

[0024] The current density can be 8-18 mA / cm² 2 Specifically, it can be 10mA / cm 2 The coating time can be 10-250 min, and the thickness of the resulting aluminum layer can be 2-20 μm;

[0025] Before aluminum plating, the substrate to be plated must undergo surface cleaning treatments such as grinding, polishing, and cleaning.

[0026] After surface cleaning and before aluminum plating, the process includes an activation treatment of the substrate to be plated. Specifically, this activation treatment may involve applying 20-38 (specifically 30) mA / cm² to the substrate as the anode. 2 The current density is used for activation treatment.

[0027] In step 2) of the above method, the heat treatment is carried out in a vacuum furnace.

[0028] The heat treatment temperature can be 550-1000℃, specifically 700℃, and the time can be 1-5h, specifically 2h;

[0029] Heat treatment allows Al elements on the surface to gradually diffuse into the substrate, forming intermetallic compounds with Fe and Cr elements in the substrate, thereby obtaining an FeCrAl alloy layer on the substrate surface.

[0030] In step 3) of the above method, the thickness of the Cr layer is less than 100 nm, specifically 20 nm;

[0031] The Cr layer is formed by electroplating.

[0032] The electroplating solution is a 0.3-0.8 mol / L chromium sulfate solution; the plating temperature is 30-60℃; and the current density is 20-30 A / dm³. 2 .

[0033] In step 4) of the above method, the oxidation treatment is carried out in a flowing argon-oxygen, helium-oxygen, or nitrogen-oxygen mixed atmosphere;

[0034] The oxidation treatment temperature can be 500-1000℃, and the time can be 10-100h;

[0035] By oxidizing the Cr / FeCrAl stainless steel substrate, the Cr and Al elements on the surface react with oxygen to form a composite phase of aluminum oxide and chromium oxide, ultimately forming an Al2O3+Cr2O3 / FeCrAl gradient coating on the substrate surface.

[0036] The application of the above-mentioned corrosion-resistant coating for liquid lead and bismuth in the nuclear industry is also within the scope of protection of this invention.

[0037] The specific application can be: the application of the liquid lead-bismuth corrosion resistant coating in lead-based fast reactor systems, that is, the liquid lead-bismuth / lead corrosion resistant coating used as a structural material in lead-based fast reactor systems, and the corrosion resistant coating for storage containers and transport pipelines of liquid lead-bismuth / lead coolant.

[0038] The present invention has the following advantages:

[0039] The LBE corrosion resistant coating structure provided by this invention has a reasonable design. The outermost layer is an oxide ceramic, which is stable at high temperatures and can effectively prevent liquid metal from corroding the material matrix. The addition of Cr element can induce the rapid and continuous growth of the alumina layer in the fourth oxidation process. On the other hand, the chromium oxide composite formed at the same time can effectively improve the toughness of the alumina layer and increase the coating's resistance to micro-strain.

[0040] The formation of the transition layer FeCrAl layer differs from other coating or spraying methods. It is formed through metallurgical combination with the substrate, resulting in high bonding strength. Meanwhile, the outermost ceramic coating is formed by oxidation growth on the basis of the transition layer, with a smooth transition and no obvious interface. The two also have very good compatibility. The entire coating is almost integrated with the substrate, resulting in excellent overall performance.

[0041] The outermost oxide ceramic layer is designed with a moderate thickness to ensure good mechanical compatibility with the matrix material. It can also maintain good bonding under thermal shock and certain mechanical stress, avoiding cracking. If it is too thin, it will be consumed too quickly, while if it is too thick, it will easily lead to stress cracking under micro-strain.

[0042] Furthermore, once the surface alumina coating is consumed, only a small amount of oxygen needs to be added to the environment (a certain amount of oxygen also exists in liquid lead bismuth). The Al element in the FeCrAl transition layer diffuses outward and continues to react with oxygen in the environment to regenerate alumina, thus providing continuous protection for the substrate.

[0043] Experimental verification shows that the method provided by this invention can prepare a continuous, uniform, and dense aluminum-chromium composite oxide / FeCrAl gradient coating on a stainless steel substrate. There is no obvious interface between the coating and the substrate, achieving a metallurgical bonding transition between them. The coating and substrate are firmly bonded. Figure 1 As shown in Figure 2, to test the corrosion resistance to high-temperature liquid lead-bismuth, a coating was prepared on one side of the surface of martensitic stainless steel (SIMP steel), while the other side was left uncoated and only polished. After 600 hours of high-temperature liquid lead-bismuth corrosion at 600℃, the uncoated sample showed extensive corrosion, with lead-bismuth penetrating to a depth of approximately 50-60 μm below the sample surface; while the coated surface showed almost no corrosion. The coating effectively protected the substrate from the erosion of liquid lead-bismuth. Figure 3 As shown.

[0044] The coating proposed in this invention addresses specific practical problems encountered in LBE / Pb-cooled reactor systems, possessing significant engineering application potential and providing technical support for material corrosion protection in the future development of advanced lead-based reactors in my country. It can significantly extend the service life of structural materials in lead-based fast reactors, increase the replacement cycle of LBE / Pb coolant storage containers and transport pipelines, reduce material loss, lower reactor operation and maintenance costs, and simultaneously improve the reactor's safety factor, reducing safety accidents caused by material performance degradation due to corrosion, thus greatly enhancing the system's safety and economy. Furthermore, this technology can also be extended to corrosion-resistant applications in industrial pipelines in the petroleum and energy sectors. Attached Figure Description

[0045] Figure 1 The image shows a cross-sectional SEM image of the aluminum-chromium composite oxide / FeCrAl gradient coating formed on the surface of SIMP stainless steel in Example 1, where regions I, II, and III are the aluminum-chromium composite oxide layer, the iron-chromium-aluminum transition layer, and the substrate, respectively.

[0046] Figure 2 SEM image of a SIMP stainless steel cross-section without coating after corrosion at 600℃ for 600h.

[0047] Figure 3 SEM image of a SIMP stainless steel cross-section with a coating after being corroded at 600℃ for 600h.

[0048] Figure 4 Photographs of the inner surface of a 304 stainless steel pipe after being coated with an aluminum-chromium composite oxide / FeCrAl gradient coating: (a) photograph of the pipe after coating; (b) cross-sectional photograph of the coated pipe; (c) SEM photograph of the coating section on the inner wall of the pipe. Detailed Implementation

[0049] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0050] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0051] Example 1: Preparation of an aluminum-chromium composite oxide / FeCrAl gradient coating on the surface of martensitic SIMP stainless steel

[0052] Take a stainless steel SIMP steel sample (composition: ) 35mm×15mm×2mm, grind and polish the surface, and then perform surface cleaning treatment, including pickling, alcohol, acetone, etc.; place the stainless steel sample in a glove box and perform aluminum plating in a solution containing Al ions. First, apply 30mA / cm to the substrate as the anode. 2 The SIMP steel was activated using a current density of 10 mA / cm³, and then an ionic liquid, AlCl₃-EMIC (molar ratio 1:2), was used as the electrolyte. SIMP steel was used as the cathode, and pure aluminum as the anode. Al was deposited on the surface of the SIMP steel. 2 The coating time is 10 minutes, and the resulting aluminum layer thickness is 2 μm (the coating time is determined according to the required coating thickness; generally, the coating time is 10-250 minutes, which can form an aluminum layer of about 2-20 μm thickness).

[0053] The coated sample was placed in a vacuum furnace for heat treatment at 700℃ for 2 hours to obtain an FeCrAl alloy layer on the stainless steel surface. If the surface aluminum layer is thick, the heat treatment time can be appropriately extended.

[0054] After cleaning the surface of the heat-treated sample, Cr was electroplated onto the sample surface using a 0.4 mol / L chromium sulfate solution at a plating temperature of 60℃ and a current density of 22 A / dm³. 2 The Cr layer is approximately 20 nm thick.

[0055] After cleaning the Cr-plated sample with alcohol, it was oxidized in a flowing argon-oxygen mixed gas at 720°C for approximately 80 hours. The final result was an aluminum-chromium composite oxide / FeCrAl gradient coating on a SIMP steel substrate, as shown in Figure 1. Figure 1 The thickness of the aluminum-chromium composite oxide layer is approximately 0.3 μm, and the thickness of the FeCrAl transition layer is approximately 0.8 μm.

[0056] Table 1. Component analysis results at different locations

[0057]

[0058] A sample with one side coated and the other uncoated was immersed in a liquid lead-bismuth (LBE) etching apparatus at 600°C under saturated oxygen conditions and sealed. After etching for 600 hours, the sample was removed, and the lead-bismuth adhering to the sample surface was cleaned off using glycerol and alcohol. The sample was then cut and polished to prepare cross-sectional samples with and without coating. The samples were observed under a scanning electron microscope (SEM). Figure 2 and Figure 3 .

[0059] Example 2: Preparation of an aluminum-chromium composite oxide / FeCrAl gradient coating on the inner wall of an austenitic 304 stainless steel pipe.

[0060] Take a 304 stainless steel pipe sample: Φ30mm×150mm×3mm. After polishing the inner surface of the pipe, perform surface cleaning treatment, including pickling, alcohol, acetone, etc. Place the pipe sample in a glove box, and use AlCl3-EMIC ionic liquid with a molar ratio of 1:2 as the electrolyte. Apply an electrolysis solution of 30mA / cm with the substrate to be plated as the anode. 2 The activation treatment was performed using a current density of 10 mA / cm². Then, using the pipe as the cathode and pure aluminum as the anode, Al was deposited on the inner surface of the pipe at a current density of 10 mA / cm². 2 The coating time was 60 minutes, and the resulting aluminum layer thickness was approximately 10 μm.

[0061] The coated pipe sample was placed in a vacuum furnace for heat treatment at 650℃ for 10 hours to obtain an FeCrAl alloy layer on the stainless steel surface.

[0062] After cleaning the inner surface of the heat-treated pipe sample, Cr was electroplated onto the sample surface using a 0.4 mol / L chromium sulfate electroplating solution at a plating temperature of 60℃ and a current density of 22 A / dm³. 2 The Cr layer is approximately 20 nm thick.

[0063] The pipe sample was oxidized in a flowing argon-oxygen mixed gas at 720℃ for approximately 70 hours. This resulted in an aluminum-chromium composite oxide / FeCrAl gradient coating on the inner surface of the pipe substrate, such as... Figure 4 As shown.

[0064] The overall thickness of the aluminum-chromium composite oxide / FeCrAl coating is approximately 6 μm.

[0065] The present invention has been described in detail above. For those skilled in the art, the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. Although specific embodiments have been given, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein. Some of the essential features can be applied within the scope of the following appended claims.

Claims

1. A coating resistant to liquid lead and bismuth corrosion, which is a gradient coating comprising, from the stainless steel substrate outwards, a second outermost layer and an outermost layer; in, The outermost layer is a corrosion-resistant, dense oxide ceramic coating; The outermost layer is a transition layer used to support the outermost ceramic coating and connect to the substrate, increasing the adhesion and compatibility between the coating and the substrate; The outermost layer is a composite ceramic phase of alumina and chromium oxide; FeCrAl alloy is used as the transition layer, i.e., the second outer layer; The method for obtaining a coating resistant to liquid lead and bismuth corrosion includes the following steps: 1) Obtain a uniform aluminum coating on the surface of a stainless steel substrate; 2) The stainless steel substrate with an aluminum coating obtained in step 1) is heat-treated to obtain an FeCrAl alloy layer on the substrate surface. 3) A Cr layer is formed on the FeCrAl alloy layer on the substrate surface to obtain a Cr / FeCrAl stainless steel substrate; 4) The Cr / FeCrAl stainless steel substrate is oxidized to form an aluminum-chromium composite oxide / FeCrAl gradient coating on the substrate surface, which is a coating resistant to liquid metal lead-bismuth corrosion.

2. The coating resistant to liquid metal lead and bismuth corrosion according to claim 1, characterized in that: In the alumina and chromium oxide composite ceramic phase, the alumina content reaches more than 95 wt%, and the chromium oxide content is less than 5 wt%. The transition layer contains Fe 65-80%, Cr 3-17%, and Al 5-18% by mass, but does not contain the Fe2Al5 alloy phase. The outermost layer has a thickness of 0.2-3 μm, and the thickness of the second outermost layer is not less than the thickness of the outermost layer.

3. A method for preparing the liquid metal lead-bismuth resistant coating as described in claim 1 or 2, comprising the following steps: 1) Obtain a uniform aluminum coating on the surface of a stainless steel substrate; 2) The stainless steel substrate with an aluminum coating obtained in step 1) is heat-treated to obtain an FeCrAl alloy layer on the substrate surface. 3) A Cr layer is formed on the FeCrAl alloy layer on the substrate surface to obtain a Cr / FeCrAl stainless steel substrate; 4) The Cr / FeCrAl stainless steel substrate is oxidized to form an aluminum-chromium composite oxide / FeCrAl gradient coating on the substrate surface, which is a coating resistant to liquid metal lead-bismuth corrosion.

4. The method according to claim 3, characterized in that: Step 1) involves using an ionic liquid to deposit an aluminum coating on the surface of a stainless steel substrate. The ionic liquid used is a mixture of AlCl3 and alkyl imidazole organic salts in a molar ratio of 1:2 to 1:

5. The alkylimidazolium organic salt is 1-methyl-3-ethylimidazolium chloride; The ionic liquid is used as the electrolyte, the substrate to be plated is used as the cathode, and pure aluminum is used as the anode; Current density is 8-18 mA / cm 2 The coating time is 10-250 min, and the thickness of the resulting aluminum layer is 2-20 µm.

5. The method according to claim 3 or 4, characterized in that: In step 2), the heat treatment is carried out in a vacuum furnace; The heat treatment is performed at a temperature of 550-1000℃ for 1-5 hours.

6. The method according to claim 3 or 4, characterized in that: In step 3), the thickness of the Cr layer is less than 100 nm; The Cr layer is formed by electroplating.

7. The method according to claim 3 or 4, characterized in that: In step 4), the oxidation treatment is carried out in a flowing argon-oxygen, helium-oxygen, or nitrogen-oxygen mixed atmosphere; The oxidation treatment is carried out at a temperature of 500-1000℃ for a time of 10-100h.

8. The application of the liquid metal lead-bismuth corrosion resistant coating as described in claim 1 or 2 in the nuclear industry.

9. The application according to claim 8, characterized in that: The application is as follows: the application of the corrosion-resistant coating for liquid lead-bismuth in lead-based fast reactor systems, that is, corrosion-resistant coatings used as structural materials in lead-based fast reactor systems, and corrosion-resistant coatings used as storage containers and transport pipelines for liquid lead-bismuth / lead coolant.

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