Molten salt corrosion resistant high-entropy alloy for concentrating solar power generation system and preparation method of molten salt corrosion resistant high-entropy alloy

Abstract

The invention discloses a molten salt corrosion resistant high-entropy alloy for a concentrating solar power generation system and a preparation method of the molten salt corrosion resistant high-entropy alloy, and belongs to the field of high-temperature metal materials. The molten salt corrosion resistant high-entropy alloy for the concentrating solar power generation system comprises the following components in atomic percent: 25%-30% of Ni, 20%-25% of Co, 15%-20% of Fe, 15%-18% of Cr, 5%-8% of Al, 4%-6% of Ti, 0.5%-1.5% of Si, 0.05%-0.3% of active elements and the balance of inevitable impurities, the active element comprises at least one of Y, Lu and Hf; the atomic percent ratio of the Al element to the Ti element is 1.2-1.6; the microstructure of the high-entropy alloy comprises a face-centered cubic solid solution matrix, a B2 type intermetallic compound phase and an L12 type intermetallic compound phase, wherein the B2 type intermetallic compound phase and the L12 type intermetallic compound phase are distributed in the matrix in a dispersed mode. A layer of compact Al2O3 / Cr2O3 / SiO2 nano composite protective film is self-generated on the surface of the high-entropy alloy; the prepared high-entropy alloy has excellent molten salt corrosion resistance, excellent high-temperature strength and creep resistance and excellent thermal cycle fatigue resistance in an ultrahigh-temperature environment of 750-850 DEG C.

Description

Technical Field

[0001] This invention relates to the field of high-temperature metallic materials, specifically to high-entropy alloys resistant to molten salt corrosion for concentrated solar power generation systems and their preparation methods. Background Technology

[0002] With the continuous growth of global demand for renewable energy, concentrated solar power (CSP) technology has become a research hotspot due to its ability to efficiently utilize solar energy. CSP systems convert solar energy into heat energy through absorbers and use molten salt as a heat transfer and storage medium to achieve continuous and stable power generation. To further improve thermoelectric conversion efficiency, the operating temperature of CSP systems is gradually increasing to 750℃ and even above 800℃. However, this trend places higher performance requirements on the materials used in key hot-end components such as absorber tubes, heat exchangers, and molten salt storage tanks, including excellent long-term high-temperature strength and creep resistance, outstanding resistance to thermal cycling fatigue, and superior resistance to molten salt hot corrosion.

[0003] Currently, traditional nickel-based superalloys such as Inconel 740H and Haynes 230 are widely used in CSP systems. These materials rely on a protective Cr2O3 film formed on the surface to resist oxidation and corrosion, and are strengthened by the γ' phase. However, in practical applications, these alloys have revealed the following limitations: (1) Insufficient resistance to molten salt corrosion: In high-temperature molten salt, especially in environments containing chloride impurities or even more severe chloride molten salts, the Cr2O3 film will react with the molten salt to form soluble chromates, causing the protective film to be damaged and peeled off, thus losing its protective function. Once the protective film fails, corrosive ions such as Cl⁻ in the molten salt will rapidly erode inward along the grain boundaries, leading to rapid intergranular corrosion and failure of the alloy.

[0004] (2) High-temperature structural instability and strength decay: The core strengthening phase γ' of traditional nickel-based alloys will undergo significant coarsening, dissolution or transformation into harmful topological close-packed phases after the temperature exceeds 750~800°C, resulting in a sharp decline in its high-temperature strength and creep resistance, which cannot meet the higher requirements of the next generation of ultra-supercritical CSP systems for the material's temperature resistance.

[0005] (3) Thermal shock resistance needs to be improved: In the daily start-stop cycle of concentrated solar power, the material is subjected to severe temperature fluctuations and thermal stress. Under long-term thermal cycling, the oxide film of traditional alloys is prone to cracking and peeling due to the mismatch between the thermal expansion coefficient and the matrix. At the same time, its microstructure will gradually coarsen, eventually leading to the initiation and propagation of thermal fatigue cracks.

[0006] Given the aforementioned issues, high-entropy alloys, as an emerging material system, have shown great potential in high-temperature applications due to their unique high-entropy effect, lattice distortion, and slow diffusion. Although some CoCrFeNi-based high-entropy alloys exhibit good corrosion resistance, their high-temperature strength is often insufficient to withstand structural loads. Furthermore, high-entropy alloys strengthened by adding elements such as Al and Ti face problems such as room-temperature brittleness, processing difficulties, or poor long-term microstructural stability. More importantly, current high-entropy alloy designs still tend towards a single oxide film protection strategy, and the long-term stability, self-healing ability, and impermeability of their protective films in harsh molten salt environments remain insufficient.

[0007] Therefore, there is an urgent need to design a high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems and its preparation method, aiming to fundamentally and synergistically solve the contradiction between high-temperature strength, structural stability, thermal cycling resistance and molten salt corrosion resistance, and provide key material support for the construction and safe operation of the next generation of high-efficiency, long-life concentrated solar power plants. Summary of the Invention

[0008] The purpose of this invention is to provide a high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems and its preparation method, so as to solve the technical problems mentioned in the background art, such as insufficient corrosion resistance, poor high-temperature strength and microstructure stability, and limited resistance to thermal cycling fatigue in the ultra-high temperature molten salt environment of concentrated solar power generation.

[0009] The technical solution to achieve the objective of this invention is: In a first aspect, the present invention provides a high-entropy alloy resistant to molten salt corrosion for a concentrated solar power generation system, comprising, by atomic percentage: Ni: 25-30%, Co: 20-25%, Fe: 15-20%, Cr: 15-18%, Al: 5-8%, Ti: 4-6%, Si: 0.5-1.5%, active elements: 0.05-0.3%, with the balance being unavoidable impurities; the high-entropy alloy has a dense Al2O3 / Cr2O3 / SiO2 composite protective film naturally formed on its surface.

[0010] Furthermore, the active element includes at least one of Y, Lu, and Hf.

[0011] Furthermore, the active element is obtained by adding a compound of Y and Hf, wherein the content of Y is 0.05~0.15% and the content of Hf is 0.1~0.15%.

[0012] Furthermore, the atomic percentage ratio of Al to Ti is 1.2 to 1.6.

[0013] Furthermore, the microstructure of the high-entropy alloy includes a face-centered cubic solid solution matrix, and B2-type intermetallic compound phases and L12-type intermetallic compound phases dispersed in the solid solution matrix, wherein the B2-type intermetallic compound phase is mainly NiAl and the L12-type intermetallic compound phase is mainly Ni3Ti.

[0014] In a second aspect, the present invention provides a method for preparing a high-entropy alloy resistant to molten salt corrosion for a concentrated solar power generation system as described in the first aspect, the preparation steps including: (1) Weigh and mix the ingredients according to the atomic percentage of each component, and then prepare pre-alloyed spherical powder by vacuum melting and gas atomization. (2) The pre-alloyed spherical powder obtained in step (1) is subjected to high-energy ball milling amorphization treatment to obtain alloy powder; (3) The alloy powder obtained in step (2) is subjected to spark plasma sintering to obtain an alloy ingot; (4) The alloy ingot obtained in step (3) is subjected to solution treatment and aging treatment to obtain a high-entropy alloy.

[0015] Furthermore, the high-energy ball milling amorphization treatment is carried out at a rotation speed of 300~400 rpm, a ball milling time of 5~15 h, and a ball-to-material ratio of (10~15):1. The high-energy ball milling amorphization treatment is carried out under inert gas protection throughout the process.

[0016] Furthermore, the discharge plasma sintering is carried out in a vacuum environment with a uniaxial pressure of 30~50MPa, a heating rate of 100~200℃ / min, a sintering temperature of 1050~1150℃, and a holding sintering time of 5~15min.

[0017] Furthermore, the solution treatment temperature is 1150℃, the solution treatment time is 1h, and the solution is cooled by water quenching after the solution treatment is completed; the aging treatment adopts two-stage aging treatment, first aging treatment at 700℃ for 16h, then aging treatment at 850℃ for 4h, and finally air cooling to room temperature.

[0018] Furthermore, the high-entropy alloy is used to prepare absorber tubes, heat exchanger tubes, or molten salt tank liners in concentrated solar power generation systems.

[0019] By adopting the above technical solution, the present invention has the following beneficial effects: (1) The high-entropy alloy for molten salt corrosion resistance of the concentrated solar power generation system of the present invention comprises, by atomic percentage: Ni: 25~30%, Co: 20~25%, Fe: 15~20%, Cr: 15~18%, Al: 5~8%, Ti: 4~6%, Si: 0.5~1.5%, active element: 0.05~0.3%, and the balance being unavoidable impurities; the obtained high-entropy alloy has excellent resistance to molten salt corrosion, excellent high-temperature strength and creep resistance, as well as excellent resistance to thermal cycling fatigue under ultra-high temperature environment of 750~850℃.

[0020] (2) The microstructure of the high-entropy alloy for molten salt corrosion resistance used in the concentrated solar power generation system of the present invention includes a face-centered cubic solid solution matrix, and B2 type intermetallic compound phase and L12 type intermetallic compound phase dispersed in the solid solution matrix. Among them, the B2 type intermetallic compound phase is mainly NiAl and the L12 type intermetallic compound phase is mainly Ni3Ti. Through the synergistic effect of the multi-principal solid solution matrix and the B2+L12 biphase nano-precipitates, continuous strengthening from room temperature to ultra-high temperature is achieved. At the same time, the slow diffusion effect of the high-entropy matrix effectively inhibits the coarsening of the precipitates during long-term service, thereby ensuring that the material has excellent high-temperature strength, creep resistance and thermal cycling fatigue resistance.

[0021] (3) The high-entropy alloy for molten salt corrosion resistance used in the concentrated solar power generation system of the present invention, through the synergistic effect of Al, Cr, and Si elements, can spontaneously form a dense, stable, and self-healing Al2O3 / Cr2O3 / SiO2 gradient composite oxide film on the alloy surface. The inner Al2O3 and Cr2O3 provide the main barrier, while the outermost amorphous SiO2 can effectively block the penetration of corrosive media such as chloride ions in molten salt. First, since Al, Cr, and Si have extremely high oxygen affinity, they provide a thermodynamic basis for the formation of the protective oxide film. Among them, the most stable Al2O3 is intended to form the inner layer that blocks diffusion; the rapidly nucleating Cr2O3 This forms an intermediate transition layer; while SiO2, which tends to form an amorphous surface layer, provides excellent impermeability. The unique properties of these three oxides together contribute to the formation conditions of the gradient composite film. In the early stage of high-temperature oxidation, Cr, with its faster diffusion rate, first forms a continuous Cr2O3 layer. As the oxidation process proceeds, the thermodynamically more stable Al diffuses and accumulates below the Cr2O3 layer, gradually replacing it partially, thus forming a dense Al2O3 inner layer. At the same time, the more reactive Si diffuses to the outermost layer and oxidizes to form an amorphous SiO2 film. This process, driven by the competition between diffusion rate and oxidation stability, naturally forms a “SiO2 top film - Cr2O3 intermediate layer -” structure. The gradient structure of the "Al2O3 inner layer" is further enhanced by the "slow diffusion effect" of the high-entropy alloy matrix, which significantly slows down the consumption rate of key elements such as Al and Cr, ensuring that the oxide film has a long-lasting self-healing ability. The sufficient reserves of Al and Cr provide a material basis for the continuous generation of protective film. Trace active elements such as Y and Hf, by segregating at the interface, act like "rivets" to enhance the bonding force between the film and the substrate and prevent it from peeling off. The design of the strengthening phase in the alloy also avoids the excessive consumption of Al elements, thereby ensuring the stable formation and maintenance of the surface oxide film.

[0022] (4) The high-entropy alloy for molten salt corrosion resistance of the concentrated solar power generation system of the present invention contains active elements such as Y and Hf, which further enhances the bonding force between the oxide film and the substrate and effectively prevents the diffusion of harmful elements into the grain boundaries, so that the alloy can still maintain an extremely low corrosion rate in molten salt above 750°C.

[0023] (5) The high-entropy alloy for molten salt corrosion resistance of the concentrated solar power generation system of the present invention adopts a composite process of "gas atomization + high-energy ball milling amorphization + discharge plasma sintering" to achieve atomic-level uniform mixing of alloy components, effectively avoid macroscopic segregation, and obtain fine grain structure, which lays the foundation for subsequent precipitation of ideal two-phase nanostructure, while ensuring the stability and reproducibility of performance during mass production. Detailed Implementation

[0024] To better understand the above technical solution, the following will provide a detailed explanation of the technical solution in conjunction with specific implementation methods.

[0025] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0026] The following embodiments are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention. Example 1 A high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems is prepared using the following steps: (1) The following atomic percentages were used to prepare a pre-alloyed spherical powder with uniform composition by vacuum melting and gas atomization: Ni: 28%, Co: 22%, Fe: 18%, Cr: 16%, Al: 6.5%, Ti: 5%, Si: 1%, Y: 0.1%, Hf: 0.15%, with the balance being unavoidable impurities; wherein, Al / Ti = 1.3; (2) High-energy ball milling: The pre-alloyed spherical powder obtained in step (1) is subjected to high-energy ball milling amorphization treatment for 10 hours, wherein the rotation speed is 350 rpm, the ball-to-material ratio is 10:1, and the process is carried out under argon protection to obtain partially or completely amorphized alloy powder. (3) The alloy powder obtained in step (2) is loaded into the spark plasma sintering mold, and under vacuum, a uniaxial pressure of 40 MPa is applied and heated to 1100°C at a rapid heating rate of 150°C / min. The temperature is held for 10 minutes to carry out rapid densification sintering and obtain a high-density alloy ingot. (4) Heat treatment: The alloy ingot obtained in step (3) is subjected to solution treatment and aging treatment, specifically: solution treatment at 1150℃ for 1h followed by water quenching; then two-stage aging treatment is performed, first aging at 700℃ for 16h, then aging at 850℃ for 4h, and finally air cooling to room temperature.

[0027] Example 2 The difference between Example 2 and Example 1 lies only in that the concentrated solar power generation system in Example 2 uses a high-entropy alloy resistant to molten salt corrosion. By atomic percentage, the composition includes: Ni: 27%, Co: 23%, Fe: 17%, Cr: 16%, Al: 7.2%, Ti: 4.8%, Si: 0.9%, Y: 0.08%, Hf: 0.12%, with the balance being unavoidable impurities; wherein, Al / Ti = 1.5.

[0028] Example 3 The difference between Example 3 and Example 1 is only that the concentrated solar power generation system in Example 3 uses a high-entropy alloy resistant to molten salt corrosion, which, by atomic percentage, comprises: Ni: 28%, Co: 22%, Fe: 18%, Cr: 16%, Al: 6.5%, Ti: 5%, Si: 1%, Y: 0.05%, Lu: 0.2%, with the balance being unavoidable impurities.

[0029] Example 4 The difference between Example 4 and Example 1 is only that the concentrated solar power generation system in Example 4 uses a high-entropy alloy resistant to molten salt corrosion, which, by atomic percentage, comprises: Ni: 25%, Co: 20%, Fe: 15%, Cr: 15%, Al: 5%, Ti: 4%, Si: 0.5%, Hf: 0.05%, with the balance being unavoidable impurities.

[0030] Example 5 The difference between Example 5 and Example 1 is only in step (3), specifically: (3) the alloy powder obtained in step (2) is loaded into the discharge plasma sintering mold, and under vacuum, a uniaxial pressure of 40 MPa is applied, and the temperature is heated to 1150°C at a rapid heating rate of 150°C / min. The temperature is held for 5 minutes to carry out rapid densification sintering and obtain a high-density alloy ingot.

[0031] Comparative Example 1 Comparative Example 1 is Haynes 230, a commercial solid solution strengthened nickel-based alloy.

[0032] Comparative Example 2 Comparative Example 2 is the commercial precipitation-strengthened nickel-based alloy Inconel 740H.

[0033] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the Al / Ti ratio in Comparative Example 3 is 1.0. Specifically, the high-entropy alloy resistant to molten salt corrosion used in the concentrated solar power generation system has the following composition by atomic percentage: Ni: 28%, Co: 22%, Fe: 18%, Cr: 16%, Al: 5.2%, Ti: 5.2%, Si: 1%, Y: 0.1%, Hf: 0.15%, with the balance being unavoidable impurities.

[0034] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that the Al / Ti ratio in Comparative Example 4 is 1.1. Specifically, the high-entropy alloy resistant to molten salt corrosion used in the concentrated solar power generation system has the following composition by atomic percentage: Ni: 28%, Co: 22%, Fe: 18%, Cr: 16%, Al: 5.5%, Ti: 5%, Si: 1%, Y: 0.1%, Hf: 0.15%, with the balance being unavoidable impurities.

[0035] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that the Al / Ti ratio in Comparative Example 5 is 1.7. Specifically, the high-entropy alloy resistant to molten salt corrosion used in the concentrated solar power generation system has the following composition by atomic percentage: Ni: 28%, Co: 22%, Fe: 18%, Cr: 16%, Al: 7.3%, Ti: 4.3%, Si: 1%, Y: 0.1%, Hf: 0.15%, with the balance being unavoidable impurities.

[0036] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that the Al / Ti ratio in Comparative Example 6 is 1.8. Specifically, the high-entropy alloy resistant to molten salt corrosion used in the concentrated solar power generation system has the following composition by atomic percentage: Ni: 28%, Co: 22%, Fe: 18%, Cr: 16%, Al: 7.4%, Ti: 4.1%, Si: 1%, Y: 0.1%, Hf: 0.15%, with the balance being unavoidable impurities.

[0037] Comparative Example 7 The only difference between Comparative Example 7 and Example 1 is the preparation process. Specifically, the steps are as follows: (1) The same atomic percentage was used to prepare the pre-alloyed spherical powder with uniform composition by vacuum melting and gas atomization. (2) The pre-alloyed spherical powder obtained in step (1) was subjected to conventional hot pressing sintering at 1100℃ and 40MPa for 60min to obtain a high-density alloy ingot. (3) Heat treatment: The alloy ingot obtained in step (2) is subjected to solution treatment and aging treatment, specifically: solution treatment at 1150℃ for 1h followed by water quenching; then two-stage aging treatment is performed, first aging at 700℃ for 16h, then aging at 850℃ for 4h, and finally air cooling to room temperature.

[0038] Comparative Example 8 The only difference between Comparative Example 8 and Example 1 is the preparation process. Specifically, the steps are as follows: (1) The same atomic percentage was used to prepare the pre-alloyed spherical powder with uniform composition by vacuum melting and gas atomization. (2) The pre-alloyed spherical powder obtained in step (1) is loaded into a discharge plasma sintering mold. Under vacuum, a uniaxial pressure of 40 MPa is applied, and the temperature is heated to 1100°C at a rapid heating rate of 150°C / min. The temperature is held for 10 minutes to carry out rapid densification sintering and obtain a high-density alloy ingot. (3) Heat treatment: The alloy ingot obtained in step (2) is subjected to solution treatment and aging treatment, specifically: solution treatment at 1150℃ for 1h followed by water quenching; then two-stage aging treatment is performed, first aging at 700℃ for 16h, then aging at 850℃ for 4h, and finally air cooling to room temperature.

[0039] Comparative Example 9 The only difference between Comparative Example 9 and Example 1 is the preparation process. Specifically, the steps are as follows: (1) The same atomic percentage was used to prepare the pre-alloyed spherical powder with uniform composition by vacuum melting and gas atomization. (2) High-energy ball milling: The pre-alloyed spherical powder obtained in step (1) is subjected to high-energy ball milling amorphization treatment for 10 hours, wherein the rotation speed is 350 rpm, the ball-to-material ratio is 10:1, and the process is carried out under argon protection to obtain partially or completely amorphized alloy powder. (3) The alloy powder obtained in step (2) is subjected to conventional vacuum sintering at 1100℃ for 120 min; (4) Heat treatment: The alloy ingot obtained in step (3) is subjected to solution treatment and aging treatment, specifically: solution treatment at 1150℃ for 1h followed by water quenching; then two-stage aging treatment is performed, first aging at 700℃ for 16h, then aging at 850℃ for 4h, and finally air cooling to room temperature.

[0040] Example of effect High-temperature tensile property test standard: GB / T 4338-2006 "Metallic materials, high-temperature tensile test method"; Test conditions: The gauge length of the specimen is heated to the test temperature in an air environment at a specified heating rate and held at that temperature for a certain time, and then stretched at the strain rate specified in the standard.

[0041] Table 1 below shows the high-temperature tensile properties of the high-entropy alloys of Examples 1-3 and Comparative Examples 1-9: Table 1 Table 1 shows that the high-entropy alloys of Examples 1-5 have good high-temperature tensile properties, specifically high high-temperature yield strength and tensile strength, and good elongation after fracture.

[0042] Comparative Example 1 is the commercial solid solution strengthened nickel-based alloy Haynes 230. The Haynes 230 alloy is mainly strengthened by solid solution with Cr, W and Mo, and its surface relies on a Cr2O3 film for corrosion resistance. By comparison, the high temperature yield strength and tensile strength of Comparative Example 1 are significantly lower than those of the high entropy alloys in Examples 1 to 5.

[0043] Comparative Example 2 is the commercial precipitation-strengthened nickel-based alloy Inconel 740H. Inconel 740H alloy, strengthened by the γ' phase, is a representative of advanced high-temperature alloys. Its high-temperature yield strength and tensile strength are lower than those of the high-entropy alloys of Examples 1-3 and Example 5. However, the high-temperature yield strength and tensile strength of Comparative Example 2 are higher than those of Comparative Example 1. This indicates that the high-entropy alloy matrix of the present invention, with its B2+L12 dual-phase precipitation structure, exhibits superior high-temperature yield strength and tensile strength compared to the conventional γ'-strengthened nickel-based alloy of Comparative Example 2. Furthermore, the high-temperature yield strength and tensile strength of the conventional γ'-strengthened nickel-based alloy are superior to the solid-solution-strengthened alloy of Comparative Example 1.

[0044] The difference between Comparative Examples 3-6 and Example 1 lies in the Al / Ti atomic ratios, which are 1.0, 1.1, 1.7, and 1.8, respectively. With increasing Al / Ti ratio, the high-temperature yield strength and tensile strength of the alloy at 750°C show a trend of first increasing and then decreasing. Specifically, the Al / Ti ratio of Comparative Example 3 is 1.0, which is relatively low. The low Al content leads to insufficient driving force for the formation of the B2-NiAl phase, resulting in fewer precipitates and uneven size distribution. The alloy mainly relies on the L12-Ni3Ti phase for strengthening, thus its high-temperature yield strength and tensile strength are significantly lower than those of Example 1. The Al / Ti ratio of Comparative Example 4 is 1.1, slightly higher than Comparative Example 3, but still below the preferred range of this invention. The amount of B2 phase precipitation is relatively low. However, the Al / Ti ratio was insufficient, resulting in suboptimal high-temperature strength. In Comparative Example 5, the Al / Ti ratio was increased to 1.7, where Ti was relatively insufficient, weakening the strengthening effect of the L12 phase. At the same time, excessive Al easily formed coarse primary β-(Ni,Fe)Al brittle phases during solidification and subsequent heat treatment, leading to a significant decrease in elongation after fracture at high temperature. In Comparative Example 6, the Al / Ti ratio was further increased to 1.8, making the brittle phase problem more serious and further deteriorating the overall mechanical properties. The above results indicate that when the atomic percentage ratio of Al to Ti in this invention is controlled within the range of 1.2 to 1.6, the synergistic effect of the B2 and L12 dual-phase precipitation structure is optimal, which can maintain good plasticity while ensuring high strength and achieving the best high-temperature tensile properties.

[0045] The difference between Comparative Example 7 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization skips the "high-energy ball milling amorphization" step and is directly subjected to conventional hot pressing sintering. This makes it impossible to achieve atomic-level uniform mixing of elements, resulting in a lower sintering density of about 97.5% and coarse grains. Due to the poor uniformity of the microstructure, it is impossible to form uniform and fine two-phase nanoprecipitates, and its high-temperature strength is lower than that of Examples 1-5.

[0046] The difference between Comparative Example 8 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization skips the "high-energy ball milling amorphization" step and is directly subjected to spark plasma sintering. Although Comparative Example 8 achieved a high density of about 99.0% by using spark plasma sintering, the elements were not uniformly distributed at the microscale because the powder was not amorphized. This compositional inhomogeneity led to the dispersed and coarse size distribution of the B2 and L12 phases precipitated during subsequent aging, and the uneven composition of the oxide film, which seriously degraded the high-temperature strength of the alloy.

[0047] The difference between Comparative Example 9 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization is ball-milled with high energy and then subjected to conventional hot pressing sintering instead of spark plasma sintering. Conventional vacuum sintering has a slow heating and long holding time, and no pressure assistance, which causes abnormal grain growth in the amorphous powder during the densification process. It also cannot effectively suppress the coarsening of the precipitated phase during the sintering process, resulting in coarsening of the final microstructure and a decrease in the high-temperature strength of the alloy.

[0048] High-temperature creep and endurance strength test standard: GB / T2039-2012 "Metallic materials uniaxial tensile creep test method"; Test conditions: Under constant temperature and constant tensile load, record the time from specimen to fracture.

[0049] Table 2 below shows the creep performance test results of the high-entropy alloys of Examples 1-3 and Comparative Examples 1-9 at 750℃ / 200MPa: Table 2 Table 2 shows that the high-entropy alloys of Examples 1-5 have good high-temperature creep properties.

[0050] Comparative Example 1 is a commercial solid solution strengthened nickel-based alloy, Haynes 230; its high-temperature creep performance is weaker than that of Example 1.

[0051] Comparative Example 2 is the commercial precipitation-strengthened nickel-based alloy Inconel 740H; its high-temperature creep performance is weaker than that of Example 1.

[0052] The difference between Comparative Examples 3-6 and Example 1 lies in the Al / Ti ratios: 1.0, 1.1, 1.7, and 1.8, respectively. With increasing Al / Ti ratio, the creep life of the alloy at 750°C showed a trend of first increasing and then decreasing. Specifically, the Al / Ti ratio of Comparative Example 3 was 1.0, which is relatively low. The low Al content resulted in insufficient driving force for the formation of the B2-NiAl phase, leading to a smaller number of precipitated phases and uneven size distribution. The alloy mainly relied on the L12-Ni3Ti phase for strengthening, thus its creep life was significantly lower than that of Example 1. The Al / Ti ratio of Comparative Example 4 was 1.1, slightly higher than Comparative Example 3, but still below the preferred range of this invention. The amount of B2 phase precipitation was still insufficient, resulting in its creep life failing to reach the optimal level. These results indicate that when the atomic percentage ratio of Al to Ti in this invention is controlled within the range of 1.2–1.6, the synergistic strengthening effect of the B2 and L12 dual-phase precipitation structure is optimal, and the alloy exhibits the longest creep life.

[0053] The difference between Comparative Example 7 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization skips the "high-energy ball milling amorphization" step and is directly subjected to conventional hot pressing sintering; its high-temperature creep performance is weaker than that of Example 1.

[0054] The difference between Comparative Example 8 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization skips the "high-energy ball milling amorphization" step and is directly subjected to discharge plasma sintering; its high-temperature creep performance is weaker than that of Example 1.

[0055] The difference between Comparative Example 9 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization is ball-milled at high energy and then subjected to conventional hot pressing sintering instead of spark plasma sintering. Conventional vacuum sintering involves slow heating, long holding time, and no pressure assistance, which leads to abnormal grain growth of amorphous powder during densification and cannot effectively suppress the coarsening of precipitates during sintering, resulting in coarsening of the final microstructure and a decrease in the high-temperature creep performance of the alloy.

[0056] High-temperature hardness test standard: GB / T4340.1-2009 "Metallic materials Vickers hardness test - Part 1: Test method" (the method is applicable to high temperature and must be carried out in a high vacuum or protective atmosphere environment); test conditions: hold at the test temperature for a sufficient time to make the overall temperature of the sample uniform before applying the load.

[0057] Table 3 below shows the test results of the high-entropy alloys of Examples 1-3 and Comparative Examples 1-9 at 750℃: Table 3 Table 3 shows that the high-entropy alloys of Examples 1-5 have high high-temperature hardness.

[0058] Comparative Example 1 is the commercial solid solution strengthened nickel-based alloy Haynes 230. The Haynes 230 alloy is mainly strengthened by solid solution with Cr, W and Mo. By comparison, the high temperature hardness of Comparative Example 1 is significantly lower than that of the high entropy alloys of Examples 1 to 5.

[0059] Comparative Example 2 is the commercial precipitation-strengthened nickel-based alloy Inconel 740H; Inconel 740H alloy is strengthened by the γ' phase and is a representative of advanced high-temperature alloys, with a high-temperature hardness lower than that of the high-entropy alloys in Examples 1-5.

[0060] The difference between Comparative Examples 3-6 and Example 1 lies in the Al / Ti atomic ratios of 1.0, 1.1, 1.7, and 1.8, respectively. With increasing Al / Ti ratio, the high-temperature hardness of the alloy exhibits a trend of first increasing and then decreasing. Specifically, the Al / Ti ratio of Comparative Example 3 is 1.0, which is relatively low. The low Al content leads to insufficient driving force for the formation of the B2-NiAl phase, resulting in fewer precipitated phases and uneven size distribution. The alloy mainly relies on the L12-Ni3Ti phase for strengthening, thus its high-temperature hardness is significantly lower than that of Example 1. The Al / Ti ratio of Comparative Example 4 is 1.1, slightly higher than Comparative Example 3, but still below the preferred range of this invention. The amount of B2 phase precipitation is still insufficient, resulting in a high-temperature hardness still lower than that of Example 1. These results indicate that when the atomic percentage ratio of Al to Ti in this invention is controlled within the range of 1.2-1.6, the synergistic effect of the B2 and L12 dual-phase precipitation structures is optimal, achieving the best high-temperature hardness.

[0061] The difference between Comparative Example 7 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization skips the "high-energy ball milling amorphization" step and is directly subjected to conventional hot pressing sintering. This makes it impossible to achieve atomic-level uniform mixing of elements, resulting in a lower sintering density of about 97.5% and coarse grains. Due to the poor uniformity of the microstructure, it is impossible to form uniform and fine two-phase nanoprecipitates, and its high-temperature hardness is lower than that of Examples 1-5.

[0062] The difference between Comparative Example 8 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization skips the "high-energy ball milling amorphization" step and is directly subjected to spark plasma sintering. Although Comparative Example 8 achieved a high density of about 99.0% by using spark plasma sintering, the elements were not uniformly distributed at the microscale because the powder was not amorphized. This compositional inhomogeneity resulted in the dispersed and coarse size distribution of the B2 and L12 phases precipitated during subsequent aging, and the oxide film composition was uneven. The high-temperature hardness of the alloy was lower than that of Example 1.

[0063] The difference between Comparative Example 9 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization is ball-milled at high energy and then subjected to conventional hot pressing sintering instead of spark plasma sintering. Conventional vacuum sintering involves slow heating, long holding time, and no pressure assistance, which leads to abnormal grain growth of amorphous powder during densification and cannot effectively suppress the coarsening of precipitates during sintering, resulting in coarsening of the final microstructure and a decrease in the high-temperature hardness of the alloy.

[0064] Static molten salt corrosion test standard: Referencing the principle of GB / T10124-1988 "Metallic Materials Uniform Corrosion Full Immersion Test Method", the test is conducted in a laboratory molten salt apparatus; Test conditions: The sample is completely immersed in static molten salt (Solar Salt or chloride molten salt) at 750℃ for 1000 hours, and the corrosion rate is calculated by the weight change before and after corrosion.

[0065] Table 4 below shows the test results of corrosion of the high-entropy alloys of Examples 1-3 and Comparative Examples 1-9 in Solar Salt at 750°C for 1000 hours: Table 4 Table 4 shows that the high-entropy alloys of Examples 1-5 have good resistance to molten salt corrosion.

[0066] Comparative Example 1 is the commercial solid solution strengthened nickel-based alloy Haynes 230. The Haynes 230 alloy is mainly strengthened by solid solution with Cr, W and Mo, and its surface relies on a Cr2O3 film for corrosion resistance. In comparison, the molten salt corrosion resistance of Comparative Example 1 is significantly lower than that of the high entropy alloys in Examples 1 to 5.

[0067] Comparative Example 2 is the commercial precipitation-strengthened nickel-based alloy Inconel 740H; Inconel 740H alloy is strengthened by the γ' phase and is a representative of advanced high-temperature alloys. Its resistance to molten salt corrosion is lower than that of the high-entropy alloys in Examples 1-5.

[0068] The difference between Comparative Examples 3-6 and Example 1 lies in the Al / Ti atomic ratios, which are 1.0, 1.1, 1.7, and 1.8, respectively. With the increase of the Al / Ti ratio, the average corrosion rate of the alloy shows a trend of first decreasing and then increasing. Specifically, the Al / Ti ratio of Comparative Example 3 is 1.0, which is relatively low. The low Al content leads to insufficient driving force for the formation of the B2-NiAl phase, resulting in fewer precipitated phases and uneven size distribution. The alumina layer in the surface oxide film is discontinuous, thus the average corrosion rate is significantly higher than that of Example 1. In Comparative Example 5, the Al / Ti ratio increases to 1.7. At this point, Ti is relatively insufficient, weakening the strengthening effect of the L12 phase, while the excessive Al content... During solidification and subsequent heat treatment, Al readily forms coarse primary β-(Ni,Fe)Al brittle phases. These phases are incoherent with the matrix, impairing the material's toughness and potentially becoming crack initiators during thermal cycling. They also affect oxide film adhesion, leading to an increased corrosion rate. In Comparative Example 6, the Al / Ti ratio was further increased to 1.8, exacerbating the brittle phase problem. The alloy's reduced toughness resulted in easier peeling of the surface oxide film under thermal stress, significantly reducing its protective effectiveness and drastically deteriorating its resistance to molten salt corrosion. These results indicate that optimal molten salt corrosion resistance is achieved when the atomic percentage ratio of Al to Ti is controlled within the range of 1.2–1.6 in this invention.

[0069] The difference between Comparative Example 7 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization skips the "high-energy ball milling amorphization" step and is directly subjected to conventional hot pressing sintering. This makes it impossible to achieve atomic-level uniform mixing of elements, resulting in a low sintering density of about 97.5% and coarse grains. Due to the poor uniformity of the microstructure, it is impossible to form uniform and fine two-phase nanoprecipitates, and its resistance to molten salt corrosion is seriously insufficient.

[0070] The difference between Comparative Example 8 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization skips the "high-energy ball milling amorphization" step and is directly subjected to spark plasma sintering. Although Comparative Example 8 achieved a high density of about 99.0% by using spark plasma sintering, the elements were not uniformly distributed at the microscale because the powder was not amorphized. This compositional inhomogeneity led to the dispersed and coarse size distribution of the B2 and L12 phases precipitated during subsequent aging, and the oxide film composition was uneven, resulting in a serious deterioration of the alloy's resistance to molten salt corrosion.

[0071] The difference between Comparative Example 9 and Example 1 lies in the preparation process. Specifically, the pre-alloyed spherical powder obtained by gas atomization is ball-milled at high energy and then subjected to conventional hot pressing sintering instead of spark plasma sintering. Conventional vacuum sintering involves slow heating, long holding time, and no pressure assistance, which leads to abnormal grain growth of amorphous powder during densification and cannot effectively suppress the coarsening of precipitates during sintering, resulting in coarsening of the final microstructure and a decrease in the alloy's resistance to molten salt corrosion.

[0072] Thermal fatigue performance testing standard: Refer to the core concept of GB / T26076-2010 "Metallic Materials Welds and Heat Affected Zone Thermal Fatigue Test Method", or General Technical Conditions HB6660-1992 "Metallic Sheets Thermal Fatigue Test Method"; Test conditions: Perform rapid thermal cycling on constrained specimens or notched specimens between room temperature and 800°C, and record the number of cycles in which a crack of a specified length appears.

[0073] Table 5 below shows the test results of the thermal fatigue properties of the high-entropy alloys of Examples 1-3 and Comparative Examples 1-9: Table 5 Table 5 shows that the high-entropy alloys of Examples 1-5 have good thermal fatigue properties.

[0074] The standard for impact toughness testing after long-term aging is GB / T229-2007 "Charpy Pendulum Impact Test Method for Metallic Materials"; test conditions: the sample after long-term heat exposure at 800°C / 2000h is processed into a standard Charpy V-notch impact specimen and tested at room temperature.

[0075] Table 6 below shows the test results of the long-term aging impact toughness of the high-entropy alloys of Examples 1-3 and Comparative Examples 2-6, 8, and 9: Table 6 Table 6 shows that the high-entropy alloys of Examples 1-5 have good impact toughness after long-term aging. Among them, Comparative Example 1 is a solid solution strengthened alloy, and its toughness decay mechanism is different from that of the precipitation strengthened alloy of the present invention, so it is not comparable. Comparative Example 7 has a low density of about 97.5% due to sintering, and the internal pores will greatly interfere with the impact test results, so the data is not of reference value. In order to ensure the rigor and comparability of the data, neither of them was included in this test.

[0076] Comparative Example 2 is the commercial precipitation-strengthened nickel-based alloy Inconel 740H; its impact toughness after long-term aging is much lower than that of Examples 1-5.

[0077] The difference between Comparative Examples 3-6 and Example 1 is that the Al / Ti ratios are 1.0, 1.1, 1.7, and 1.8, respectively. They show a trend of first increasing and then decreasing impact toughness after long-term aging. The impact toughness of Comparative Examples 5-6 after long-term aging is significantly lower than that of Comparative Examples 3-4. This may be because the Al / Ti ratio of Comparative Examples 5-6 is increased, and Ti is relatively insufficient. Excess Al is prone to forming coarse primary β-(Ni,Fe)Al brittle phases during alloy solidification and heat treatment, which significantly reduces the toughness of the alloy.

[0078] In summary, the high-entropy alloys prepared in Examples 1-5 exhibit excellent resistance to molten salt corrosion, superior high-temperature tensile properties, creep resistance, impact toughness after long-term aging, and outstanding resistance to thermal cycling fatigue under ultra-high temperature conditions of 750-850℃.

[0079] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-entropy alloy resistant to molten salt corrosion for a concentrated solar power generation system, characterized in that, The composition, by atomic percentage, includes: Ni: 25~30%, Co: 20~25%, Fe: 15~20%, Cr: 15~18%, Al: 5~8%, Ti: 4~6%, Si: 0.5~1.5%, active elements: 0.05~0.3%, with the balance being unavoidable impurities; the surface of the high-entropy alloy is covered with a dense Al2O3 / Cr2O3 / SiO2 composite protective film.

2. The high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems according to claim 1, characterized in that, The active element includes at least one of Y, Lu, and Hf.

3. The high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems according to claim 2, characterized in that, The active element is obtained by adding a compound of Y and Hf, with the content of Y being 0.05~0.15% and the content of Hf being 0.1~0.15%.

4. The high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems according to claim 1, characterized in that, The atomic percentage ratio of Al to Ti is 1.2 to 1.

6.

5. The high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems according to claim 1, characterized in that, The microstructure of the high-entropy alloy includes a face-centered cubic solid solution matrix, and B2-type and L12-type intermetallic compound phases dispersed in the solid solution matrix.

6. A method for preparing a high-entropy alloy resistant to molten salt corrosion for a concentrated solar power generation system as described in any one of claims 1 to 5, characterized in that, The preparation steps include: (1) Weigh and mix the ingredients according to the atomic percentage of each component, and then prepare pre-alloyed spherical powder by vacuum melting and gas atomization. (2) The pre-alloyed spherical powder obtained in step (1) is subjected to high-energy ball milling amorphization treatment to obtain alloy powder; (3) The alloy powder obtained in step (2) is subjected to spark plasma sintering to obtain an alloy ingot; (4) The alloy ingot obtained in step (3) is subjected to solution treatment and aging treatment to obtain a high-entropy alloy.

7. The method for preparing the high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems according to claim 6, characterized in that, The high-energy ball milling amorphization treatment is carried out at a rotation speed of 300~400 rpm, a ball milling time of 5~15 h, and a ball-to-material ratio of (10~15):

1. The high-energy ball milling amorphization treatment is carried out under inert gas protection throughout the process.

8. The method for preparing the high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems according to claim 6, characterized in that, The discharge plasma sintering is carried out in a vacuum environment with a uniaxial pressure of 30~50MPa, a heating rate of 100~200℃ / min, a sintering temperature of 1050~1150℃, and a holding time of 5~15min.

9. The method for preparing the high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems according to claim 6, characterized in that, The solution treatment temperature is 1150℃ and the solution treatment time is 1 hour. After the solution treatment is completed, the solution is cooled by water quenching. The aging treatment is a two-stage aging treatment, first aging at 700℃ for 16 hours, then aging at 850℃ for 4 hours, and finally air-cooled to room temperature.

10. The method for preparing the high-entropy alloy resistant to molten salt corrosion for concentrated solar power generation systems according to claim 6, characterized in that, The high-entropy alloy is used to prepare absorber tubes, heat exchanger tubes, or molten salt tank liners in concentrated solar power generation systems.

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