A dual-phase precipitation co-strengthened nuclear-grade FeCrNiAlTi high-entropy alloy, a preparation method and application thereof

Abstract

The application discloses a dual-phase precipitation co-strengthened nuclear-grade FeCrNiAlTi high-entropy alloy and a preparation method and application thereof, and relates to an FCC-based FeCrNiAlTi high-entropy alloy co-strengthened by coherent L12-Ni3Al and incoherent L21-Ni2AlTi phases; the high-entropy alloy comprises the following metal elements: Fe, Cr, Ni, Al and Ti. The high-entropy alloy is prepared by adopting a secondary cold rolling and heat treatment process, an L12-Ni3Al and L21-Ni2AlTi structure is simultaneously precipitated in an FCC matrix, the alloy has excellent oxidation resistance, corrosion resistance, neutron irradiation resistance, room-temperature and high-temperature mechanical properties, and also has good processing performance, and therefore provides a candidate alloy for a supercritical water-cooled reactor cladding material.

Description

Technical Field

[0001] This invention relates to the technical field of high-entropy alloys, specifically to a core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening, its preparation method, and its applications. Background Technology

[0002] High / medium entropy alloys have attracted increasing attention from researchers due to their excellent strong-plasticity combination, low-temperature fracture toughness, corrosion resistance, oxidation resistance, and functional properties. The unique "hysteresis diffusion" effect of high entropy alloys slows the diffusion of defects such as vacancies generated during irradiation, improving the alloy's resistance to radiation swelling. Therefore, high entropy alloys hold promise as materials for key components in nuclear reactors, such as fuel cladding materials and cooling water pipe loop materials. Statistical results show that over 90% of existing high entropy alloy systems contain Co. This is because Co not only improves the high-temperature strength of the alloy but also reduces its stacking fault energy, triggering deformation mechanisms such as stacking faults, twinning, and phase transformations during deformation, while simultaneously improving the material's strength and plasticity. However, Co has a large neutron absorption cross-section coefficient; its addition to nuclear materials not only reduces neutron utilization but also leads to radiation swelling and failure. Furthermore, Co is expensive, and its large-scale addition significantly increases the cost of the alloy, limiting the industrial-scale application of high entropy alloys.

[0003] FeCrNi-based high-entropy alloys have similar compositions to traditional austenitic stainless steels, but their cost is significantly lower than that of Co-containing high-entropy alloys. They also exhibit excellent corrosion resistance, oxidation resistance, and machinability. Furthermore, since they do not contain carbon, their weldability is better than stainless steel, making them a promising candidate for use as fuel cladding materials in supercritical water-cooled reactors. However, two issues remain before industrial application: 1) Supercritical water-cooled reactors typically operate at temperatures up to 650°C and pressures up to 25 MPa, which the high-temperature mechanical properties of ternary FeCrNi medium-entropy alloys cannot meet; 2) While the neutron absorption cross-sectional coefficients of the three components in the FeCrNi alloy are less than 1 / 10 that of Co, they are far greater than those of existing Zr alloys, indicating that their resistance to neutron irradiation swelling needs further improvement.

[0004] Existing research indicates that precipitating coherent nanoparticles in an alloy can significantly improve its resistance to radiation swelling. Adding Al and Ti to FeCrNi-based alloys can form coherent precipitates that enhance radiation resistance; however, the alloy's mechanical properties, such as brittleness, tensile yield strength, and tensile strength, do not meet current processing requirements. In other words, existing alloys still face the challenge of simultaneously achieving optimal high-temperature mechanical properties, processing performance, and radiation resistance. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, one objective of this invention is to provide a nuclear-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthened structure. This high-entropy alloy is an FCC-based FeCrNiAlTi high-entropy alloy co-strengthened by coherent L12-Ni3Al and incoherent L21-Ni2AlTi phases, exhibiting excellent corrosion resistance, oxidation resistance, and neutron radiation resistance, while also possessing good high-temperature mechanical properties, processing performance, and low cost. A second objective of this invention is to provide a method for preparing this nuclear-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthened structure, employing multiple cold rolling and heat treatment processes to allow the FCC matrix to undergo complete recovery and recrystallization, while L21 only recovers without recrystallization, thereby improving the alloy's strength without embrittlement. A third objective of this invention is to provide an application of this nuclear-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthened structure, which can be used as a fuel cladding material in supercritical water-cooled reactors.

[0006] One of the objectives of this invention is achieved through the following technical solution: A dual-phase precipitation-strengthened core-grade FeCrNiAlTi high-entropy alloy, wherein the high-entropy alloy is an FCC-based FeCrNiAlTi high-entropy alloy jointly strengthened by coherent L12-Ni3Al and incoherent L21-Ni2AlTi phases; the high-entropy alloy comprises the following metallic elements: Fe, Cr, Ni, Al and Ti; the atomic percentages of the metallic elements in the high-entropy alloy are as follows: Ni: 30.0~40.0%, Cr: 18.0~25.0%, Al: 5.0~8.0%, Ti: 5.0~8.0%, with the remainder being Fe and unavoidable impurity elements.

[0007] Furthermore, the high-entropy alloy also includes Nb; the atomic percentage of Nb in the high-entropy alloy is: Nb: 0.01~2.0%.

[0008] Furthermore, the high-entropy alloy also includes Ta, and the atomic percentage of Ta in the high-entropy alloy is: Ta 0.01~2.0%; Furthermore, the high-entropy alloy also includes Nb and Ta; the atomic percentages of Nb and Ta in the high-entropy alloy are: Nb: 0.01~2.0%, Ta: 0.01~2.0%; wherein 12.0%≤Al+Ti+Nb+Ta≤17.0%.

[0009] The second objective of this invention is achieved by the following technical solution: The above-mentioned method for preparing core-grade FeCrNiAlTi high-entropy alloys with dual-phase precipitation co-strength includes the following steps: 1) First, the metal raw materials used in the high-entropy alloy are melted and formed into alloy plates; 2) The alloy sheet is cold-rolled once; 3) Homogenize the cold-rolled alloy sheet; 4) The alloy sheet is then subjected to a second cold rolling process; 5) The alloy sheet after secondary cold rolling is annealed to obtain a core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening.

[0010] Furthermore, in step 1), the melting is carried out in a vacuum arc melting furnace, and the forming is performed by suction casting using a copper mold with rapid cooling; the thickness of the alloy plate is 4~6mm.

[0011] Further, in step 2), the parameters of the first cold rolling are: the reduction amount per pass is 0.1 mm, and the total rolling amount is 15~20%; in step 4), the parameters of the second cold rolling are: the reduction amount per pass is 0.1 mm, and the total rolling amount is 20~25%.

[0012] Further, in step 3), the specific steps of the homogenization treatment are as follows: the alloy plate is sealed and then heated at 1150~1200℃ for 1~2 hours.

[0013] Furthermore, in step 5), the parameters for the annealing step are: the annealing temperature is 900~1000℃, and the temperature is maintained for 0.5~1h after heating. The annealing step enables partial recrystallization of the alloy, wherein the FCC matrix undergoes complete recovery recrystallization, while the L21 phase only undergoes recovery.

[0014] The third objective of this invention is achieved by the following technical solution: The aforementioned dual-phase precipitation-strengthened nuclear-grade FeCrNiAlTi high-entropy alloy is used to prepare fuel cladding materials in supercritical water-cooled reactors.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The high-entropy alloy of the present invention is an FCC-based FeCrNiAlTi high-entropy alloy jointly strengthened by coherent L12-Ni3Al and incoherent L21-Ni2AlTi phases, comprising Fe, Cr, Ni, Al and Ti. The coherently precipitated nano-L12-Ni3Al in this alloy can improve the high-temperature strength and neutron irradiation resistance of the alloy, while the incoherently precipitated L21-Ni2AlTi phase can improve the yield strength of the alloy. By precipitating nanoscale L12-Ni3Al phase in the FCC matrix, a microstructure similar to that of nickel-based high-temperature alloys is obtained, giving the alloy excellent high-temperature mechanical properties; the nanoscale ordered L12-Ni3Al phase precipitation can undergo an ordered-disorder transformation during irradiation, thereby annihilating point defects caused by irradiation and preventing the alloy from failing due to irradiation swelling; by precipitating incoherent L21-Ni2AlTi phase in the FCC matrix, the yield strength of the alloy can be significantly improved, and by further controlling the content of the precipitated phase, the plasticity of the alloy can be prevented from decreasing significantly. The FeCrNiAlTi high-entropy alloy provided by this invention contains only inexpensive elements, which significantly reduces the cost of the alloy and enables large-scale commercial application.

[0016] (2) The high-entropy alloy of the present invention may also include Nb and / or Ta. Nb and Ta are both L12-Ni3Al phase forming elements. When a composite L12-Ni3(Al,Ti,Nb,Ta) intermetallic compound is formed, its thermal stability can be greatly improved, so that the precipitated phase will not be severely coarsened during long-term high-temperature service.

[0017] (3) The method for preparing the high-entropy alloy of the present invention includes the following steps in sequence: melting One-time cold rolling homogenization treatment Secondary cold rolling Compared to most existing alloy preparation processes, this invention employs a two-stage cold rolling and heat treatment process. The first cold rolling increases the number of defects such as dislocations in the alloy, which is beneficial for atomic diffusion during the homogenization stage. Homogenization eliminates compositional segregation during casting; annealing allows for partial recrystallization of the alloy, while FCC matrix undergoes complete recovery recrystallization, whereas L21 only recovers without recrystallization. This results in improved alloy strength without causing embrittlement.

[0018] (4) The high-entropy alloy of this invention possesses excellent high-temperature mechanical properties, processing performance, and radiation resistance. Furthermore, using FCC as a matrix, this alloy can undergo large-scale cold working and exhibits good processing capabilities. By rationally matching the alloy composition and preparation method, this invention achieves a microstructure in which L12-Ni3Al and L21-Ni2AlTi are simultaneously precipitated in the FCC matrix, giving the alloy excellent oxidation resistance, corrosion resistance, neutron radiation resistance, room temperature and high-temperature mechanical properties, and also demonstrating good processing performance, thus providing a candidate alloy for supercritical water-cooled reactor cladding materials. Attached Figure Description

[0019] Figure 1 Calculate Ni for Pandat software 35 Fe 30 Cr20Al x Ti 15-x Isothermal cross-section of the alloy at 800℃; Figure 2 The X-ray diffraction pattern of the high-entropy alloy of Example 1 after annealing at 900℃ for 0.5h is shown. Figure 3 The EBSD results are for the high-entropy alloy of Example 1 after annealing at 900℃ for 0.5h. Figure 4 The image shows the TEM microstructure of the high-entropy alloy of Example 1 after annealing at 900℃ for 0.5h. Figure 5 The room temperature tensile mechanical properties of the high-entropy alloy of Example 1 after annealing at 900℃ for 0.5h; Figure 6 This is a TEM image of the high-entropy alloy from Example 4 after annealing at 1000℃ for 0.5h. Figure 7 The room temperature tensile mechanical properties of the high-entropy alloy of Comparative Example 1 after annealing at 600℃ / 4h (a) and 800℃ / 1h (b) are shown. Detailed Implementation

[0020] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0021] The purpose of this invention is to address the problem of the inability to simultaneously achieve strength, processing performance, and neutron irradiation resistance in existing FeCrNi-based high-entropy alloys, by providing a nuclear-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strength and its preparation method. The FeCrNiAlTi high-entropy alloy prepared using this specific composition and technology has two intermetallic compounds as its strengthening phases: coherent nano-L12-Ni3Al with the FCC matrix and incoherent L21-Ni2AlTi. The nano-L12 precipitate not only improves the high-temperature strength of the alloy but also undergoes ordered precipitation during irradiation. The disordered cyclic transformation improves the alloy's resistance to neutron irradiation without reducing its processing performance; while a certain amount of incoherent L21 precipitation can significantly improve the alloy's yield strength, thereby improving the alloy's room temperature mechanical properties.

[0022] The high-entropy alloy comprises the following metallic elements: Fe, Cr, Ni, Al, and Ti; the atomic percentages of the metallic elements in the high-entropy alloy are as follows: Ni: 30.0~40.0%, Cr: 18.0~25.0%, Al: 5.0~8.0%, Ti: 5.0~8.0%, with the remainder being Fe and unavoidable impurity elements.

[0023] As an example, the high-entropy alloy further includes Nb; the atomic percentage of Nb in the high-entropy alloy is: Nb: 0.01~2.0%.

[0024] As an example, the high-entropy alloy further includes Ta, and the atomic percentage of Ta in the high-entropy alloy is: Ta 0.01~2.0%; As an example, the high-entropy alloy further includes Nb and Ta; the atomic percentages of Nb and Ta in the high-entropy alloy are: Nb: 0.01~2.0%, Ta: 0.01~2.0%; wherein 12.0%≤Al+Ti+Nb+Ta≤17.0%.

[0025] The following describes the roles of various alloying elements in FeCrNiAlTi high-entropy alloys.

[0026] (1) Cr: Cr is the main element that provides corrosion resistance in high-entropy alloys. Tammann's law states that when Cr is added to Fe to form a solid solution, its electrode potential changes abruptly with the increase of Cr content (n / 8 rule). That is, when the atomic percentage of Cr (at.%) reaches 12.5%, 25%, etc., the electrode potential of iron will suddenly increase, and corrosion will decrease in a jump. However, too high Cr content can easily induce σ-(FeCr) and deteriorate the mechanical properties of the alloy. Therefore, considering both the corrosion resistance and mechanical properties of the alloy, the Cr content in this invention is 18.0-25.0 at.%.

[0027] (2) Ni: Ni is an essential element for the formation of FCC solid solution. Ni also participates in the formation of L12-Ni3Al and L21-Ni2AlTi precipitates. Based on the Pandat thermodynamic calculation software, the content of Ni is determined to be 30-40 at.

[0028] (3) Al: The addition of Al can form a dense and continuous Al2O3 oxide film on the alloy surface, which improves the high temperature oxidation resistance of the alloy. The higher the content, the better the oxidation resistance. At the same time, Al also participates in the formation of L12-Ni3Al and L21-Ni2AlTi phases. However, Al is a strong BCC forming element. Excessive addition will cause the alloy to change from FCC to BCC, making the alloy severely brittle. Considering all factors, the Al addition content is 5.0-8.0 at.

[0029] (4) Ti: Ti is an essential element for the formation of the L21-Ni2AlTi phase and can also promote the formation of L12-Ni3Al. Considering its distribution relationship in the two phases, its content is determined to be 5.0-8.0 at..

[0030] (5) Nb and Ta: Both Nb and Ta are L12-Ni3Al phase-forming elements. When a composite L12-Ni3(Al,Ti,Nb,Ta) intermetallic compound is formed, its thermal stability can be greatly improved, preventing the precipitated phase from becoming severely coarsened during long-term high-temperature service. However, excessive addition of Nb or Ta will promote γ -Ni3(Nb,Ta) precipitation, therefore the content of both Nb and Ta added is less than 2 at.%.

[0031] A method for preparing a nuclear-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening includes the following steps in sequence: 1) melting and suction casting; 2) primary cold rolling; 3) homogenization treatment; 4) secondary cold rolling; and 5) annealing treatment.

[0032] Step 1) specifically involves: first converting the atomic percentage into a mass percentage according to the alloy composition, then using high-purity metal raw materials to prepare the batch according to the mass percentage, smelting the sample in a vacuum arc melting furnace, and casting the alloy plate with a thickness of 4-6mm using a copper mold rapid cooling method, preferably with a thickness of 5mm. Step 2) specifically involves cold rolling the alloy sheet obtained in step 1), with a reduction of 0.1 mm per pass and a total rolling amount of 15-20%. This process can increase defects such as dislocations in the alloy, which is beneficial for atomic diffusion during the homogenization stage.

[0033] Step 3) specifically involves sealing the alloy plate obtained in step 2) into a quartz tube and performing a homogenization treatment at 1150~1200℃ for 1-2 hours to eliminate component segregation during the casting process. Step 4) specifically involves: cold rolling the alloy obtained in step 3) again, with a reduction of 0.1 mm per pass and a total rolling amount of 20-25%.

[0034] Step 5) specifically involves annealing the alloy sheet obtained in step 4) at 900~1000℃. After the furnace temperature reaches the required temperature, the sample is placed in the furnace and held for 0.5~1h to allow partial recrystallization of the alloy. Specifically, the FCC matrix undergoes complete recovery recrystallization, while the L21 phase only undergoes recovery.

[0035] Example 1 The FeCrNiAlTi high-entropy alloy in this embodiment has the following composition: Ni 35 Fe 30 Cr 20 Al 7.5 Ti 7.5 (at. %), wherein the high-entropy alloy is a core-grade FeCrNiAlTi high-entropy alloy jointly strengthened by L12-Ni3Al and L21-Ni2AlTi dual-phase precipitation. Its preparation method specifically includes the following steps: 1) The effects of the content of each component on the microstructure of the alloy were predicted using Pandat thermodynamic calculation software. Typical results are as follows: Figure 1 As shown, this determines the addition range of each element in the alloy designed in this invention; 2) Select typical Ni components with the expected microstructure from the calculated phase diagram. 35 Fe 30 Cr 20 Al 7.5 Ti 7.5 (at. %), the atomic percentage is converted into mass percentage according to the alloy composition, and the metal raw materials with a purity of 99.95% are batched according to the mass percentage. The sample is melted in a vacuum electric arc melting furnace, and the alloy plate with a thickness of 5mm is cast by rapid cooling of copper mold. 3) The sheet obtained in step 2) is subjected to cold rolling once, with a reduction of 0.1 mm per pass and a total rolling amount of 20%. The sheet thickness is reduced from 5 mm to 4 mm. This process can increase the dislocation density in the alloy, which is beneficial to atomic diffusion in the homogenization stage. 4) The alloy obtained in step (3) is uniformly treated, specifically by sealing the alloy plate into a quartz tube and heating it at 1150°C for 2 hours to eliminate component segregation during the casting process. 5) The alloy sheet obtained in step 4) is subjected to a second cold rolling process, with a reduction of 0.1 mm per pass and a total rolling amount of 25%, reducing the sheet thickness from 4 mm to 3 mm. 6) Anneal the alloy sheet obtained in step 5) at 900℃. After the furnace temperature reaches the required temperature, place the sample in the furnace and hold it for 0.5h. This allows the FCC matrix in the alloy to fully recover and recrystallize, while the L21 phase only recovers, thus coordinating subsequent plastic deformation. To verify the effectiveness of the composition and preparation method of the FeCrNiAlTi high-entropy alloy proposed in this invention, systematic microstructure characterization and performance testing were performed on the samples after annealing at 900℃ for 0.5h, including XRD, EBSD, TEM microstructure characterization and room temperature tensile mechanical property characterization. The results are as follows: Figures 2-5 As shown.

[0036] from Figure 2 The XRD results show that the alloy exhibits three different microstructures after annealing at 900℃ for 0.5h: FCC, BCC, and L21-Ni2AlTi. FCC is the matrix phase, while BCC and L21 have relatively low volume fractions. Figure 3 The EBSD results also show that the alloy is mainly composed of two phases with FCC and BCC structures, with FCC accounting for 90% of the volume and BCC (including L21) accounting for 10%. The alloy uses FCC as the matrix, which can ensure the alloy's plasticity and processing performance.

[0037] from Figure 4 TEM results show that high-density L12-Ni3Al particles with a size of ~10 nm precipitated in the FCC matrix of this alloy. The presence of this precipitate can effectively improve the high-temperature mechanical properties of the alloy, and is expected to meet the mechanical performance requirements of the cladding material for long-term operation at high temperatures. Moreover, due to the small mismatch between these nanoparticles and the matrix, their nucleation energy is very low, and they can undergo a rapid order-to-disorder transition during irradiation, annihilating the vacancies generated by irradiation and improving the alloy's resistance to neutron irradiation swelling, which is expected to meet the irradiation performance requirements of high Ni content alloys. In addition, the alloy contains Ti-rich L21-Ni2AlTi with a size ranging from nanometer to micrometer, and nanoscale Cr-rich BCC phase precipitation can also be observed in the matrix. Both L21-Ni2AlTi and α-Cr, which are incoherent with the FCC matrix, can effectively improve the yield strength of the alloy.

[0038] Furthermore, the room temperature tensile mechanical properties of the high-entropy alloy of Example 1 were tested, and the results are shown in the appendix. Figure 5As shown, the alloy exhibits a high room temperature yield strength of 1.4 GPa, a tensile strength approaching 1.6 GPa, and a uniform elongation of 8%. Comparisons show that the alloy prepared using the composition and processing techniques of this invention has significantly higher strength than existing Co-free high-entropy alloys, while also achieving a plasticity of 8%, meeting the requirements for alloy plasticity in engineering materials. Furthermore, this alloy can be deformed using multiple cold rolling and annealing processes, potentially meeting the processing performance requirements of cladding materials.

[0039] In summary, through the composition and preparation process of the high-entropy alloy of the present invention, a FeCrNiAlTi high-entropy alloy jointly strengthened by coherent L12-Ni3Al and incoherent L21-Ni2AlTi phases can be obtained. This alloy has excellent oxidation resistance, corrosion resistance, neutron irradiation resistance, room temperature and high temperature mechanical properties, and also exhibits good processing performance. It is expected to meet the performance requirements of supercritical water-cooled reactor fuel cladding materials and is a highly promising candidate material.

[0040] Example 2 The FeCrNiAlTi high-entropy alloy in this embodiment has the following composition: Ni 35 Fe 30 Cr 20 Al7Ti7Nb1 (at. %), wherein the high-entropy alloy is a core-grade FeCrNiAlTi high-entropy alloy jointly strengthened by L12-Ni3Al and L21-Ni2AlTi dual-phase precipitation. Its preparation method specifically includes the following steps: Its preparation method specifically includes the following steps: 1) Convert the atomic percentage to mass percentage according to the alloy composition, use metal raw materials with a purity of 99.95% to make the batch according to the mass percentage, use a vacuum electric arc melting furnace to melt the sample, and use a copper mold rapid cooling method to cast the alloy plate with a thickness of 5mm. 2) The sheet obtained in step 1) is subjected to cold rolling once, with a reduction of 0.1 mm per pass and a total rolling amount of 25%. The sheet thickness is reduced from 5 mm to 3.7 mm. This process can increase the dislocation density in the alloy, which is beneficial to atomic diffusion in the homogenization stage. 3) The alloy obtained in step 2) is subjected to homogenization treatment, specifically: the alloy plate is sealed in a quartz tube and heated at 1200℃ for 1 hour to eliminate component segregation during the casting process; 4) The alloy sheet obtained in step 3) is subjected to a second cold rolling process, with a reduction of 0.1 mm per pass and a total rolling amount of 20%, reducing the sheet thickness from 3.7 mm to 2.2 mm. 6) Anneal the alloy sheet obtained in step 5) at 950℃. After the furnace temperature reaches the required temperature, place the sample in the furnace and hold it for 1 hour. This allows the FCC matrix in the alloy to fully recover and recrystallize, while the L21 phase only recovers, thus coordinating subsequent plastic deformation. Example 3 The FeCrNiAlTi high-entropy alloy in this embodiment has the following composition: Ni 35 Fe 30 Cr 20 Al7Ti7Ta1 (at. %), wherein the high-entropy alloy is a core-grade FeCrNiAlTi high-entropy alloy jointly strengthened by L12-Ni3Al and L21-Ni2AlTi dual-phase precipitation. The alloy sheet was annealed at 950℃ for 1 hour, and other preparation methods were the same as in Example 1.

[0041] Example 4 The FeCrNiAlTi high-entropy alloy in this embodiment has the following composition: Ni 35 Fe 30 Cr 20 Al 6.5 Ti 6.5 Nb1Ta1 (at. %), wherein the high-entropy alloy is a core-grade FeCrNiAlTi high-entropy alloy jointly strengthened by L12-Ni3Al and L21-Ni2AlTi dual-phase precipitation. The alloy sheet was annealed at 1000℃ for 1 hour, and other preparation methods were the same as in Example 1.

[0042] Experimental results show that the alloys in Examples 2-4 are all FCC matrices, containing coherent L12-Ni3Al and incoherent L21-Ni2AlTi precipitates. The typical TEM microstructure of Example 4 is as follows: Figure 6 As shown. Although the annealing temperatures of Examples 2-4 are higher than those of Example 1, the alloy in Example 4 has higher thermal stability due to the addition of Nb and Ta alloying elements, and the size after annealing is still around 10 nm.

[0043] Comparative Example 1 The high-entropy alloy of Comparative Example 1 had the same composition as that of Example 1, but the specific preparation method was different. The high-entropy alloy of Comparative Example 1 still underwent melting, primary cold rolling, homogenization treatment, secondary cold rolling, and annealing, but the annealing temperatures were reduced to below 900°C, specifically 600°C / 4h and 800°C / 1h. The mechanical properties of the prepared alloy are as follows: Figure 7 As shown, due to insufficient annealing temperature, it is difficult for both the matrix and the L21 phase to recover and recrystallize. The alloy does not exhibit any plastic deformation and fractures prematurely during the elastic deformation stage, which fails to meet the performance requirements of the fuel cladding material for supercritical water-cooled reactors.

[0044] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening, characterized in that, The high-entropy alloy is an FCC-based FeCrNiAlTi high-entropy alloy jointly strengthened by coherent L12-Ni3Al and incoherent L21-Ni2AlTi phases; the high-entropy alloy includes the following metallic elements: Fe, Cr, Ni, Al, Ti; the atomic percentages of the metallic elements in the high-entropy alloy are as follows: Ni: 30.0~40.0%, Cr: 18.0~25.0%, Al: 5.0~8.0%, Ti: 5.0~8.0%, with the remainder being Fe and unavoidable impurity elements.

2. The core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening as described in claim 1, characterized in that, The high-entropy alloy also includes Nb; the atomic percentage of Nb in the high-entropy alloy is: Nb: 0.01~2.0%.

3. The core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening as described in claim 1, characterized in that, The high-entropy alloy also includes Ta, and the atomic percentage of Ta in the high-entropy alloy is: Ta 0.01~2.0%.

4. The core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening as described in claim 1, characterized in that, The high-entropy alloy also includes Nb and Ta; the atomic percentages of Nb and Ta in the high-entropy alloy are: Nb: 0.01~2.0%, Ta: 0.01~2.0%; wherein 12.0%≤Al+Ti+Nb+Ta≤17.0%.

5. The method for preparing the core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening as described in any one of claims 1 to 4, characterized in that, Includes the following steps: 1) First, the metal raw materials used in the high-entropy alloy are melted and formed into alloy plates; 2) The alloy sheet is cold-rolled once; 3) Homogenize the cold-rolled alloy sheet; 4) The alloy sheet is then subjected to a second cold rolling process; 5) The alloy sheet after secondary cold rolling is annealed to obtain a core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening.

6. The method for preparing a core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening as described in claim 5, characterized in that, In step 1), the melting is carried out in a vacuum arc melting furnace, and the forming is performed by suction casting using a copper mold with rapid cooling; the thickness of the alloy plate is 4~6mm.

7. The method for preparing a core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening as described in claim 5, characterized in that, In step 2), the parameters for the first cold rolling are: a reduction of 0.1 mm per pass and a total rolling amount of 15-20%; in step 4), the parameters for the second cold rolling are: a reduction of 0.1 mm per pass and a total rolling amount of 20-25%.

8. The method for preparing a core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strengthening as described in claim 5, characterized in that, In step 3), the specific steps of the homogenization treatment are as follows: seal the alloy plate and then heat it at 1150~1200℃ for 1~2 hours.

9. The method for preparing a core-grade FeCrNiAlTi high-entropy alloy with dual-phase precipitation co-strength as described in claim 5, characterized in that, In step 5), the parameters for the annealing step are: the annealing temperature is 900~1000℃, and the temperature is maintained for 0.5~1h after heating.

10. The application of the dual-phase precipitation co-strengthened core-grade FeCrNiAlTi high-entropy alloy according to any one of claims 1 to 4, characterized in that, The nuclear-grade FeCrNiAlTi high-entropy alloy, which is jointly strengthened by dual-phase precipitation, is used to prepare fuel cladding materials for supercritical water-cooled reactors.

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