Helium-induced damage resistant and corrosion resistant medium-entropy alloy coating and preparation method thereof

Abstract

The invention discloses a helium-induced damage resistant and corrosion resistant medium-entropy alloy coating and a preparation method thereof. The FeCrAlN medium-entropy alloy coating which is uniform in component, compact in structure and good in combination with a matrix is successfully prepared on the surface of the matrix such as austenitic stainless steel by adopting an unbalanced magnetron sputtering technology and accurately regulating and controlling key process parameters such as nitrogen partial pressure and sputtering power. The coating comprises the following elements in percentage by weight: 20 to 30 at.% of Fe, 20 to 30 at.% of Cr, 20 to 30 at.% of Al, 10 to 35 at.% of N, and the balance of Fe and inevitable impurities. The thickness is 2-4.5 [mu] m, and the material has a nanocrystalline / amorphous composite structure. On the basis of the medium-entropy alloy design concept, the nitrogen element is introduced, the components and the structure are optimized, effective control over chemical components, phase composition and the microstructure of the coating can be achieved, the comprehensive performance of the coating in a severe service environment is remarkably improved, and the coating especially has excellent helium ion irradiation resistance and liquid lead and bismuth corrosion resistance; and the service life of key components such as the cladding pipe can be effectively prolonged, and the operation safety of a reactor is improved.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor materials technology, specifically relating to a medium-entropy alloy coating material for lead-bismuth cooled fast reactor structures, which has both excellent resistance to helium ion irradiation and resistance to corrosion of liquid lead-bismuth alloys, and its preparation method. Background Technology

[0002] In lead-bismuth eutectic cooled fast reactors, structural materials are subjected to harsh strong neutron and corrosive environments during long-term service, leading to a rapid degradation of material properties. During neutron irradiation, the structural materials undergo (n, α) nuclear transmutation reactions, producing helium. As an inert element, helium readily migrates as interstitial atoms and strongly combines with vacancies to form helium-vacancy complexes and helium bubbles, causing expansion, hardening, cracking, and embrittlement, severely degrading its mechanical properties. Furthermore, the high-temperature liquid lead-bismuth alloy coolant has a strong corrosive effect on the structural materials, with corrosion mechanisms including oxidation, dissolution, and flow erosion. Specifically, this manifests as the dissolution and mass migration of alloy components (such as Fe, Cr, Ni) into the liquid metal, the formation and destruction of surface oxide films, and the penetration of lead-bismuth along grain boundaries. The degree of corrosion is significantly affected by temperature, flow rate, oxygen concentration, and the material's structural composition. Particularly serious is the coupling effect between strong irradiation and the liquid lead-bismuth alloy; their synergistic effect can significantly accelerate the damage process, posing a serious threat to reactor operational safety. Therefore, improving the compatibility of structural materials with liquid lead-bismuth alloys and their radiation resistance has become a key challenge in the development of lead-bismuth fast reactors.

[0003] To address this challenge, researchers have proposed a strategy of preparing high-performance protective coatings on traditional structural steel substrates using surface modification techniques. This approach preserves the mechanical properties of the substrate while constructing a stable radiation-resistant and corrosion-resistant barrier on the surface. Commonly used coating materials include ceramic coatings, monometallic coatings, multi-element alloy coatings, and medium / high entropy alloy coatings. However, ceramic coatings are prone to spalling due to their intrinsic brittleness and lack of self-healing ability, while refractory metal coatings exhibit weak resistance to LBE corrosion due to the non-dense and unstable oxides they form. Fe-Cr-Al alloy coatings, on the other hand, can form a dense structure at high temperatures. or The protective film, exhibiting excellent resistance to high-temperature oxidation and corrosion, is widely considered a highly promising candidate material for accident-tolerant fuel (ATF) cladding coatings. To further improve the neutron economy of the fuel cladding, the coating typically needs to be thinned, but this may increase the risk of damage or peeling under mechanical stress, wear, and irradiation. Therefore, how to simultaneously improve the mechanical strength and radiation resistance of FeCrAl coatings without excessively increasing the coating thickness or sacrificing other properties has become an important research direction in this field. To address these issues, various strengthening methods for FeCrAl coatings have been explored in existing technologies. Among them, the introduction of nitrogen (N) is an effective approach. Studies have shown that incorporating an appropriate amount of N into FeCrAl coatings through techniques such as magnetron sputtering can significantly improve the coating's hardness and toughness, and exhibit excellent resistance to helium ion irradiation. This is mainly because the introduction of N can cause changes in the coating's microstructure, such as grain refinement, formation of nitride nanocrystals, or induction of amorphization. However, through in-depth research, the applicant discovered that this nitrogen-doping strategy, adopted to improve mechanical and radiation resistance properties, introduces an inherent technical defect that had previously been overlooked: the corrosion resistance of nitrogen-doped FeCrAl coatings significantly decreases in high-temperature LBE corrosion environments. Analysis suggests that nitrogen readily combines with key elements in the coating that form a protective oxide film (such as Cr and Al) to form stable nitrides, excessively consuming free Cr and Al used to form a dense passivation film, leading to a deterioration in the coating's ability to resist corrosion from liquid metals such as lead and bismuth. This results in a new technical contradiction: while nitrogen doping enhances mechanical and radiation resistance properties, it may come at the cost of sacrificing crucial LBE corrosion resistance. Under certain oxygen concentrations, a dense, thin, and self-healing oxide layer can be generated, exhibiting good potential for LBE corrosion resistance. However, developing coating systems that can simultaneously withstand high temperatures, strong radiation, and strong corrosion remains challenging. Recent studies have shown that doping with nitrogen (N) in non-near-isoproportional FeCrAl coatings can significantly improve their resistance to helium ion irradiation. However, LBE corrosion experiments revealed coating delamination and the formation of a loose iron oxide layer on the surface, indicating insufficient corrosion resistance. Therefore, there is an urgent need in this field for an innovative coating design strategy that can fundamentally solve the above contradictions, simultaneously playing a dual role in blocking LBE corrosion and inhibiting irradiation damage in irradiation-corrosion coupled environments. This strategy would achieve synergistic optimization of the coating's mechanical properties, radiation resistance, and LBE corrosion resistance, providing efficient protection for next-generation lead-bismuth fast reactor structural materials. Summary of the Invention

[0004] This invention discloses a helium-damage-resistant and corrosion-resistant medium-entropy alloy coating for lead-bismuth cooled fast reactors and its preparation method. Based on the medium-entropy alloy design concept, this coating significantly improves its overall performance under harsh service environments by introducing nitrogen and optimizing its composition and structure. In particular, it exhibits excellent resistance to helium ion irradiation and resistance to liquid lead-bismuth corrosion, effectively extending the service life of key components such as cladding tubes and improving reactor operational safety. In terms of preparation method, this invention employs unbalanced magnetron sputtering technology. By precisely controlling key process parameters such as nitrogen partial pressure and sputtering power, a FeCrAlN medium-entropy alloy coating with uniform composition, dense structure, and good bonding with the substrate is successfully prepared on the surface of substrates such as 316 austenitic stainless steel. This method enables effective control over the coating's chemical composition, phase composition, and microstructure, thereby ensuring the reliability and consistency of the coating's performance.

[0005] To achieve the above objectives, the present invention includes the following technical solutions:

[0006] A method for preparing a medium-entropy alloy coating resistant to helium-induced damage and corrosion includes the following steps:

[0007] (1) Provide an austenitic stainless steel matrix and perform cleaning pretreatment;

[0008] Preferably, the austenitic stainless steel is 316 austenitic stainless steel.

[0009] (2) The cleaned substrate is placed in the vacuum chamber of the magnetron sputtering equipment and back sputtered cleaned under Ar atmosphere;

[0010] Preferably, in order to further remove impurities from the surface of the austenitic stainless steel substrate and prepare for the deposition of a FeCrAlN medium-entropy coating, the austenitic stainless steel is mounted on the sample stage inside the vacuum furnace of the vacuum magnetron sputtering equipment, and then subjected to backsputter cleaning. The backsputter cleaning conditions are: sputtering gas is Ar, sputtering pressure is 3.0 ~ 4.0 Pa, bias voltage is -1300 ~ -1700V, and time is 10 ~ 20 min;

[0011] Preferably, the backsplash cleaning conditions are: splash pressure of 3.5 Pa, splash bias of -1500 V, and splash time of 15 min.

[0012] (3) Use FeCrAl target material for pre-sputtering cleaning in Ar atmosphere;

[0013] Preferably, after the austenitic stainless steel is backsputtered and cleaned, the FeCrAl target is rapidly ignited using a DC power supply for pre-sputtering to remove oxides and adsorbed impurities from the target surface. The pre-sputtering conditions are: gas pressure 0.4 ~ 0.7 Pa, target power 280 ~ 370 W, and time 8 ~ 18 min.

[0014] Preferably, the pre-sputtering conditions are: Ar atmosphere at 0.5-0.6 Pa, target power of 300-350 W, and cleaning time of 10-15 min.

[0015] (4) FeCrAl target material was sputtered in a mixed atmosphere of Ar and N2 without heating the substrate or applying a bias voltage. The sputtering conditions were: Ar gas flow rate 35 ~ 45 sccm, N2 flow rate 4 ~ 12 sccm, sputtering gas pressure 0.5 ~ 0.9 Pa, target power 280 ~ 370 W, target-substrate distance 75 ~ 85 mm, and sputtering time 40 ~ 50 min.

[0016] This results in the formation of a FeCrAlN medium-entropy alloy coating on the surface of an austenitic stainless steel substrate, with the following elemental composition: Fe: 20–30 at.%, Cr: 20–30 at.%, Al: 20–30 at.%, N: 10–35 at.%.

[0017] Preferably, no bias voltage is applied to the austenitic stainless steel substrate, nor is heating performed. In step (4), the sputtering pressure is 0.6-0.8 Pa, the Ar gas flow rate is controlled at 40 sccm, the distance between the target and the austenitic stainless steel substrate is 80 mm, and the sputtering time is 45 min. Within the above N2 flow rate, the atomic percentages of Fe, Cr, Al, and N can be well controlled, resulting in a FeCrAlN medium-entropy coating with excellent mechanical properties, resistance to helium ion irradiation, and resistance to liquid lead-bismuth corrosion.

[0018] Furthermore, the FeCrAl target is a spliced ​​target composed of Fe, Cr, and Al metal blocks, with an area ratio of Fe, Cr, and Al of 18-22:16-20:18-22, or 9-11:8-10:9-11. This invention also discloses a helium-resistant and corrosion-resistant medium-entropy alloy coating prepared by the above method, wherein the coating has a nanocrystalline / amorphous composite structure.

[0019] Furthermore, the above-mentioned medium-entropy alloy coating has a coating thickness of 2-4.5 μm.

[0020] Furthermore, in the aforementioned medium-entropy alloy coating, the nanocrystals comprise AlN and / or CrN nitride phases.

[0021] Furthermore, the aforementioned medium-entropy alloy coating has a hardness of not less than 13 GPa before helium ion irradiation, and at a dose of 3×10⁻⁶ GPa... 16 ions / cm 2 After being irradiated with helium ions at an energy of 60 keV, the hardness is not less than 16 GPa.

[0022] Furthermore, the aforementioned medium-entropy alloy coating, after being corroded in saturated oxygen liquid lead-bismuth at 500 °C for 500 hours, can block the penetration of Pb and Bi elements, achieving a penetration depth of less than 2 μm.

[0023] The present invention also discloses a substrate material comprising a 316 austenitic stainless steel substrate and a FeCrAlN medium-entropy alloy coating formed on its surface by the preparation method described in claim 1 or 2.

[0024] Furthermore, in the aforementioned substrate material, after the coating is irradiated with helium ions, it is then etched in saturated oxygen liquid lead-bismuth at 500 °C for 500 hours, resulting in a penetration depth of Pb and Bi elements of less than 1.5 μm.

[0025] The present invention also discloses the application of the above-mentioned medium-entropy alloy coating or matrix material in the surface protection of nuclear reactor cladding materials.

[0026] The present invention also discloses a lead-bismuth cooled fast reactor cladding component, the surface of which is provided with the above-mentioned medium-entropy alloy coating.

[0027] Compared with the prior art, the present invention has the following outstanding advantages:

[0028] (1) Synergistically resolving key technical contradictions to achieve a breakthrough balance in performance. This invention creatively introduces the concept of medium-entropy alloy design and constructs a FeCrAl alloy coating matrix phase with a near-equal atomic ratio, fundamentally resolving the core technical contradiction that traditional FeCrAl coatings cannot synergistically improve mechanical properties, radiation resistance, and resistance to lead-bismuth corrosion after the introduction of nitrogen. One of the innovations of this invention is that it abandons the traditional FeCrAl alloy target with fixed composition and creatively adopts a composite target material made of high-purity Fe, Cr, and Al elemental metal strips. This design gives the coating composition of this invention flexibility, allowing for continuous and precise control of the stoichiometric ratio of Fe, Cr, and Al in the deposited coating by precisely adjusting the relative area of ​​each metal strip. This is the premise for achieving a near-equal atomic ratio medium-entropy alloy composition design and successfully resolving the contradiction between "nitrogen doping" and "corrosion resistance". Based on this composition and structural design, the coating exhibits the following synergistically optimized superior performance:

[0029] Exceptional strength-toughness balance: The coating's high hardness stems from the solid solution strengthening effect resulting from the severe lattice distortion unique to medium-entropy alloys, as well as the dispersion strengthening of nitride nanocrystals (such as AlN and CrN) formed after the introduction of nitrogen. Furthermore, the hysteretic diffusion effect of medium-entropy alloys promotes the formation of a unique nanocrystalline / amorphous composite structure, which effectively suppresses microcrack propagation, enabling the coating to maintain good toughness even at ultra-high strength.

[0030] Excellent resistance to helium ion irradiation: The numerous grain boundaries, phase boundaries and other interfaces in the coating can serve as efficient trapping points, strongly binding helium ions and inhibiting their migration and aggregation, thereby effectively preventing the formation of large-sized helium bubbles and significantly reducing the risk of irradiation swelling and embrittlement of the material.

[0031] A key breakthrough in lead-bismuth corrosion (LBE) resistance: The most unexpected effect of this invention is the successful solution to the corrosion resistance degradation problem caused by nitrogen doping. By using a near-equiatomic ratio design, the initial contents of Cr and Al are significantly increased, providing ample elemental reserves for the introduction of N. Even though some Cr and Al are used to form nitrides, sufficient free Cr and Al are still retained in the coating, ensuring rapid formation of a continuous and dense coating in high-temperature corrosive environments. Composite oxide film. The synergistic improvement of these three properties fundamentally solves the technical contradiction that traditional FeCrAlN coatings struggle to balance mechanical properties, radiation resistance, and corrosion resistance.

[0032] (2) The process is highly controllable, and the coating quality is excellent and reproducible. The magnetron sputtering technology used in this invention is combined with the splicing target design, and the reaction gas is precisely controlled. Parameters such as flow rate, sputtering pressure, and power enable effective control over the chemical composition, phase composition, and thickness of FeCrAlN medium-entropy alloy coatings. This process exhibits good repeatability and facilitates the preparation of high-performance coatings with uniform composition, dense structure, and good adhesion to the substrate.

[0033] (3) It has strong compatibility with existing technologies and significant engineering application potential. Using the magnetron sputtering technology, a dense and uniform FeCrAlN medium-entropy alloy coating with a thickness ranging from 2 to 4.5 μm can be prepared on the surface of substrate materials such as 316 austenitic stainless steel. This technical route has good compatibility with existing cladding material manufacturing processes. Through surface modification, its resistance to radiation-corrosion coupling damage can be significantly improved while retaining the excellent mechanical properties of the substrate, providing a reliable solution for the long-life and high-safety service of key components in lead-bismuth fast reactors, with significant engineering application prospects and economic benefits. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the splicing target used in an embodiment of the present invention.

[0035] Figure 2 The surface morphology and cross-sectional morphology of the coatings prepared for Comparative Example 1 and Example 2 of this invention are shown in the figures.

[0036] Figure 3 Vickers indentation patterns of the coatings prepared in Comparative Example 1 and Example 2 of this invention.

[0037] Figure 4 The surface morphology images of the coatings prepared for Comparative Example 1 and Example 2 of this invention after helium ion irradiation are shown.

[0038] Figure 5 The Vickers indentation patterns of the coatings after helium ion irradiation were prepared for Comparative Example 1 and Example 2 of this invention.

[0039] Figure 6 The cross-sectional morphology and EDS images of the coatings prepared in Comparative Examples 1, 2 and Example 2 of this invention after being etched in liquid lead bismuth at 500 °C for 500 h are shown.

[0040] Figure 7 The cross-sectional morphology and EDS image of the coatings prepared for Comparative Example 1 and Example 2 of this invention after being irradiated with helium ions and etched in liquid lead-bismuth at 500 °C for 500 h are shown. Detailed Implementation

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0042] Example 1:

[0043] This embodiment employs unbalanced magnetron sputtering technology to deposit a FeCrAlN medium-entropy coating on the surface of a 316 austenitic stainless steel substrate. Iron (Fe), chromium (Cr), and aluminum (Al) elemental metal strips (134 mm × 3 mm × 3 mm) with a purity of 99.9% or higher were selected and deposited accordingly. Figure 1 The structure shown is spliced ​​to obtain a splicing target. There are 20 iron (Fe), 17 chromium (Cr), and 20 aluminum (Al) elemental metal strips, with an area ratio of 20:17:20 for Fe, Cr, and Al, and a total of 57 strips. The reaction gas is 99.999% pure N2, and the working gas is 99.999% pure Ar.

[0044] (1) Pretreatment of matrix material

[0045] 316 austenitic stainless steel is machined into 10 mm × 10 mm × 1 mm square pieces, polished smooth, and then ultrasonically cleaned with acetone and anhydrous ethanol for 15 min in sequence, and then dried for later use.

[0046] (2) Backsplash cleaning of substrate material

[0047] The pretreated 316 austenitic stainless steel matrix material was placed on the sample stage inside the vacuum chamber of the magnetron sputtering equipment, and the vacuum level inside the chamber was maintained at less than 2 × 10⁻⁶. -3 Pa, adjust the baffle between the target and the substrate, then introduce Ar gas, maintain the sputtering pressure at 3.5 Pa, control the bias voltage at -1500 V, and perform reverse sputtering cleaning on the 316 austenitic stainless steel substrate for 15 min.

[0048] (3) Pre-sputtering cleaning of target material

[0049] Continuing with Ar gas as the working gas, the sputtering pressure was adjusted to 0.45 Pa, and the FeCrAl metal target was rapidly ignited at a power of 350 W, followed by 10 minutes of pre-sputtering.

[0050] (4) Sputtered FeCrAlN medium-entropy coating

[0051] Ar gas was used as the working gas with a flow rate of 40 sccm. No bias voltage was applied, the substrate was not heated, the target-substrate distance was 80 mm, the sputtering pressure was adjusted to 0.55-0.65 Pa, the target power was 350 W, and the reactive gas N2 was introduced with a flow rate of 4 sccm. The baffle was removed and sputtering was carried out for 45 min, thus obtaining the FeCrAlN medium-entropy coating.

[0052] Example 2:

[0053] In this embodiment, an FeCrAlN coating is deposited on the surface of a 316 austenitic stainless steel substrate using unbalanced magnetron sputtering technology. The sputtering metal target and gas used are the same as in Example 1.

[0054] (1) Pretreatment of matrix material

[0055] Same as Example 1.

[0056] (2) Backsplash cleaning of substrate material

[0057] Same as Example 1.

[0058] (3) Pre-sputtering cleaning of target material

[0059] Same as Example 1.

[0060] (4) Sputtered FeCrAlN medium-entropy coating

[0061] Ar gas was used as the working gas at a flow rate of 40 sccm. No bias was applied, the 316 austenitic stainless steel substrate was not heated, the target-substrate distance was 80 mm, the sputtering pressure was adjusted to 0.55-0.65 Pa, the target power was 350 W, and the reactive gas N2 was introduced at a flow rate of 8 sccm. The baffle was removed and sputtering was carried out for 45 min, thus obtaining the FeCrAlN medium-entropy coating.

[0062] Example 3:

[0063] In this embodiment, an FeCrAlN coating is deposited on the surface of a 316 austenitic stainless steel substrate using unbalanced magnetron sputtering technology. The sputtering metal target and gas used are the same as in Example 1.

[0064] (1) Pretreatment of matrix material

[0065] Same as Example 1.

[0066] (2) Backsplash cleaning of substrate material

[0067] Same as Example 1.

[0068] (3) Pre-sputtering cleaning of target material

[0069] Same as Example 1.

[0070] (4) Sputtered FeCrAlN medium-entropy coating

[0071] Ar gas was used as the working gas at a flow rate of 40 sccm. No bias was applied, the 316 austenitic stainless steel substrate was not heated, the target-substrate distance was 80 mm, the sputtering pressure was adjusted to 0.55-0.65 Pa, the target power was 350 W, and the reactive gas N2 was introduced at a flow rate of 12 sccm. The baffle was removed and sputtering was carried out for 45 min, thus obtaining the FeCrAlN medium-entropy coating.

[0072] Comparative Example 1:

[0073] In this comparative example, the FeCrAl coating was deposited on the surface of a 316 austenitic stainless steel substrate using unbalanced magnetron sputtering technology. The sputtering metal target used was the same as in Example 1, and the working gas Ar purity was 99.999%. The specific preparation process included the following steps:

[0074] (1) Pretreatment of matrix material

[0075] Same as Example 1.

[0076] (2) Backsplash cleaning of substrate material

[0077] Same as Example 1.

[0078] (3) Pre-sputtering cleaning of target material

[0079] Same as Example 1.

[0080] (4) Sputtered FeCrAl coating

[0081] Ar gas was continued as the working gas with a flow rate of 40 sccm. No bias voltage was applied, the 316 austenitic stainless steel substrate was not heated, the target-substrate distance was 80 mm, the sputtering pressure was adjusted to 0.55-0.65 Pa, the target power was 350 W, the baffle was removed and sputtering was carried out for 45 min. This resulted in a near-isotropic FeCrAl coating, i.e., a FeCrAl medium-entropy coating, on the surface of the 316 austenitic stainless steel.

[0082] Comparative Example 2:

[0083] This comparative example demonstrates the deposition of a FeCrAlN coating on a 316 austenitic stainless steel substrate using unbalanced magnetron sputtering. The sputtering target was a FeCrAl alloy target with a mass percentage of 75 wt.% Fe, 15 wt.% Cr, and 10 wt.% Al (equivalent to an atomic ratio of Fe:Cr:Al ≈ 67.1 at.%:14.4 at.%:18.5 at.%). The working gas, Ar, had a purity of 99.999%. The specific preparation process included the following steps:

[0084] (1) Pretreatment of matrix material

[0085] Same as Example 1.

[0086] (2) Backsplash cleaning of substrate material

[0087] Same as Example 1.

[0088] (3) Pre-sputtering cleaning of target material

[0089] Same as Example 1.

[0090] (4) Sputtering of non-uniform FeCrAlN coating

[0091] Ar gas was continued as the working gas at a flow rate of 40 sccm. N2 was introduced as the reactive gas at a flow rate of 8 sccm. No bias voltage was applied, the substrate was not heated, and the target-substrate distance was 80 mm. The sputtering pressure was adjusted to 0.55-0.65 Pa, and the target power was 350 W. The baffle was removed, and sputtering was performed for 45 minutes, resulting in a non-uniform FeCrAlN coating on the surface of 316 austenitic stainless steel. The coating prepared in this comparative example was obtained by introducing 8 sccm of N2 based on a non-uniform Fe, Cr, and Al elemental content.

[0092] Test example:

[0093] Characterization of the structure, mechanical properties, and helium ion irradiation resistance of the FeCrAlN medium-entropy coatings deposited on the 316 austenitic stainless steel substrates of the Examples and Comparative Examples:

[0094] (1) Structural and morphological characteristics

[0095] The coatings prepared in the comparative example and the coatings prepared in Example 2 were analyzed by scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown in the figure, it can be clearly seen that the coating prepared in Example 2 is defect-free, has a dense and continuous surface, and has a uniform coating thickness of about 3.4 μm.

[0096] (2) Mechanical properties

[0097] Hardness analysis was performed on the coatings prepared in the comparative example and the examples using a nanoindenter, as shown in Table 1. The coating obtained in Example 2 had a hardness of approximately 13.9 GPa. This indicates that the coating can significantly improve the surface hardness of 316 austenitic stainless steel. Furthermore, the toughness of the coatings prepared in the comparative example and the examples was tested using a Vickers indenter under a load of 5 N. The test results are shown below. Figure 2 As shown, obvious radial and circumferential cracks appeared in the coating of Comparative Example 1, while no radial cracks appeared in the coating of Example 2, with only a small number of circumferential cracks around the indentation. This is mainly because the large number of phase interfaces in the coating of Example 2 significantly hindered the initiation and propagation of cracks, and the soft alloy phase released the strain energy at the crack tip, blunting the crack tip and significantly reducing the crack propagation ability, ultimately resulting in a significant improvement in its toughness.

[0098] Table 1 shows the nitrogen flow rate, elemental content, and hardness and elastic modulus values ​​before and after helium ion irradiation for the coatings prepared in Comparative Examples 1, 2, and Examples 1, 2, and 3 of this invention.

[0099] Nitrogen flow rate Fe element content (at.%) Cr content (at.%) Al content (at.%) Ni element content (at.%) Hardness (GPa) Elastic modulus (GPa) Hardness after irradiation (GPa) Elastic modulus after irradiation (GPa) Comparative Example 1 0 sccm 32.8 32.0 35.2 0 13.8 237.2 22.4 661.9 Comparative Example 2 8 sccm 49.9 11.3 13.6 25.2 11.2 187.2 9.6 207.7 Example 1 4 sccm 27.9 27.9 30.3 13.9 20.7 312.8 29.1 444.4 Example 2 8 sccm 23.5 23.4 25.8 27.3 13.9 205.3 27.7 341.9 Example 3 12 sccm 21.6 21.1 23.0 34.3 15.8 204.9 16.0 256.6

[0100] (3) Resistance to helium ion irradiation

[0101] The coating prepared in Comparative Example 1 and the 316 austenitic stainless steel with FeCrAlN medium-entropy coating prepared in Example 2 were placed at room temperature under a vacuum of 7.5 × 10⁻⁶. -4 In the Pa ion implanter, through a dose of 3×10 16 ions / cm 2 Helium ions with an energy of 60 keV are irradiated at an angle of 20°.

[0102] Then, SEM analysis was performed on the coatings prepared in Comparative Example 1 and Example 2 after helium ion irradiation. The analysis results are as follows: Figure 3As shown, the coating of Comparative Example 1 exhibits obvious swelling and protrusions, as well as numerous pores left by helium release. In contrast, the coating surface of Example 2 does not show obvious swelling and protrusions or pores. Due to the lattice distortion effect of the medium-entropy alloy, atoms are more difficult to displace during helium ion bombardment, resulting in a more stable structure, and therefore no obvious defects were observed. Furthermore, the nitride nanocrystals present in Example 2 have grain boundaries that can act as traps to control helium nucleation and growth, suppressing the diffusion rate of helium in the coating, making helium aggregation difficult, and preventing the formation of large helium bubbles that damage the coating. The results indicate that the coating prepared in Example 2 has good resistance to helium ion irradiation.

[0103] The changes in mechanical properties of the coatings prepared in Comparative Example 1 and Example 2 after helium ion irradiation were investigated. After helium ion irradiation, the hardness of the coating in Example 2 was 27.7 GPa, while that of the coating prepared in Comparative Example 1 was 22.4 GPa. Furthermore, the toughness of the coatings in Comparative Example 1 and Example 2 after irradiation was tested, such as... Figure 4 As shown, after irradiation, neither the coating of Comparative Example 1 nor the coating of Example 2 exhibited radial cracks on their surfaces under a load of 5 N. The coating of Example 2 maintained excellent toughness while possessing high hardness.

[0104] (4) Resistance of the coating to lead-bismuth alloy corrosion

[0105] The corrosion resistance of the coatings in a liquid lead-bismuth alloy at 500 °C was investigated. First, 316 austenitic stainless steels with coatings prepared in Comparative Examples 1 and 2 and those prepared in Example 2 were placed in a liquid lead-bismuth alloy saturated with oxygen at 500 °C for 500 h for corrosion. Figure 5 As shown, after 500 h of corrosion, the coating in Comparative Example 2 exhibited obvious delamination, with Fe elements significantly diffusing outwards to form a loose iron oxide layer on the coating surface. Lead and bismuth were also clearly observed to penetrate into the iron oxide layer, indicating that the coating lacked resistance to lead and bismuth corrosion. In contrast, the coatings prepared in Comparative Example 1 and Example 2 showed intact structures, with no obvious element diffusion observed. Lead, bismuth, and oxygen elements did not penetrate into the coating interior, indicating that the coatings possessed excellent resistance to lead and bismuth corrosion. Since the coupling effect of liquid lead and bismuth corrosion and irradiation damage in an actual reactor would accelerate coating failure, to further verify the overall performance of the coatings, the coatings prepared in Comparative Example 1 and Example 2 were subjected to 3 × 10⁻⁶ h of corrosion. 16 ions / cm 2 After irradiation with helium ions at an energy of 60 keV, the alloy was corroded in a liquid lead-bismuth alloy saturated with oxygen at 500 °C for 500 h. The results showed that... Figure 6As shown, lead and bismuth penetrated to a depth of approximately 2.5 μm into the coating prepared in Comparative Example 1, while significant enrichment of Cr was observed. Furthermore, Al diffused into the 316 austenitic stainless steel substrate. The coating prepared in Example 2 maintained its structural integrity, without the enrichment or diffusion of Cr and Al, and lead and bismuth only penetrated to a depth of approximately 1 μm. This indicates that the coating of Example 2 maintained excellent resistance to liquid lead and bismuth corrosion even after helium ion irradiation. This is mainly due to two factors: firstly, the strong lattice distortion and abundant nitride nanocrystals in the coating of Example 2 suppressed interstitial diffusion of helium ions, effectively dispersing helium ions and inhibiting their aggregation ability; secondly, compared to Comparative Example 2, the coating prepared in Example 2 contained more Cr and Al, resulting in sufficient inert elements to form a thin and dense oxide layer on the coating surface after nitride formation, preventing corrosion by liquid lead and bismuth. The combined effect of these two factors enabled the coating prepared in Example 2 to maintain its structural integrity under the coupled effects of helium ion irradiation damage and liquid lead and bismuth corrosion, exhibiting excellent overall performance.

[0106] The above are merely a few preferred embodiments of the present invention, described in a relatively specific and detailed manner, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method of producing a helium damage resistant and corrosion resistant medium entropy alloy coating, characterized by, The method comprises the following steps: (1) providing an austenitic stainless steel substrate and performing cleaning pretreatment; (2) placing the cleaned substrate in a vacuum chamber of a magnetron sputtering device and performing reverse sputtering cleaning in an Ar gas atmosphere; (3) performing pre-sputtering cleaning using an FeCrAl target in an Ar gas atmosphere; (4) sputtering the FeCrAl target in an Ar and N2 mixed gas atmosphere without heating the substrate and without applying a bias voltage, and the sputtering conditions are as follows: Ar gas flow rate 35-45 sccm, N2 flow rate 4-12 sccm, sputtering gas pressure 0.5-0.9 Pa, target power 280-370 W, target-substrate distance 75-85 mm, and sputtering time 40-50 min. Thus, an FeCrAlN medium-entropy alloy coating is formed on the surface of the austenitic stainless steel substrate, and the element composition of the coating is as follows: Fe: 20-30 at.%, Cr: 20-30 at.%, Al: 20-30 at.%, and N: 10-35 at.%.

2. The production method according to claim 1, characterized by, The FeCrAl target is a spliced target composed of Fe, Cr and Al metal blocks, and the area ratio of Fe, Cr and Al is 9-11:8-10:9-11.

3. The anti-helium damage resistant and corrosion resistant medium entropy alloy coating produced by the method of claim 1 or 2, wherein, The coating has a nanocrystalline / amorphous composite structure, and the thickness of the coating is 2-4.5 μm.

4. The medium-entropy alloy coating of claim 3, wherein, The nanocrystals include AlN and / or CrN nitride phases.

5. The medium-entropy alloy coating of claim 3, wherein, The hardness of the coating before helium ion irradiation is not less than 13 GPa, and after irradiation with a dose of 3x10 16 ions / cm 2 and an energy of 60 keV, the hardness is not less than 16 GPa.

6. The medium-entropy alloy coating of claim 3, wherein, After the coating is corroded in saturated oxygen liquid lead bismuth at 500 ℃ for 500 hours, the coating can block the penetration of Pb and Bi elements, and the penetration depth is less than 2 μm.

7. A base material, characterized by The method comprises the following steps:

8. The base material according to claim 7, characterized by After the coating is subjected to helium ion irradiation and then corroded in saturated oxygen liquid lead bismuth at 500 ℃ for 500 hours, the penetration depth of Pb and Bi elements is less than 1.5 μm.

9. Use of the medium-entropy alloy coating according to any one of claims 3-6 or the substrate material according to any one of claims 7-8 in the surface protection of a nuclear reactor cladding material.

10. A lead-bismuth cooled fast reactor cladding component, characterized by, The surface of the substrate is provided with the medium-entropy alloy coating according to any one of claims 3-6.

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