AlCoFeNi series eutectic high-entropy alloy and preparation method thereof

Abstract

The invention provides an AlCoFeNi series eutectic high-entropy alloy. The AlCoFeNi series eutectic high-entropy alloy is composed of an eutectic high-entropy alloy matrix as shown in a formula of Al < x > Co < y > Fe < 100-x-y-z > Ni < z >, Y and Hf, wherein the Y and the Hf are doped in the eutectic high-entropy alloy matrix; the content of the Y is 0.04 to 0.06 weight percent of the eutectic high-entropy alloy matrix, and the content of the Hf is 0.04 to 0.06 weight percent of the eutectic high-entropy alloy matrix; wherein x, y and z are respectively atomic percentage contents of Al, Co and Ni, x is equal to 18-21, y is equal to 19-22, and z is equal to 39-42. The invention further provides a preparation method of the AlCoFeNi series eutectic high-entropy alloy. According to the AlCoFeNi-series eutectic high-entropy alloy provided by the invention, active elements Y and Hf are added, so that the structure of the alloy is not changed, the mechanical property of the alloy is not influenced, and on the basis, the eutectic high-entropy alloy has excellent high-temperature oxidation resistance and relatively good corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of high-entropy alloys, and particularly to an AlCoFeNi-based eutectic high-entropy alloy and a preparation method thereof. Background Art

[0002] The engine is the heart of aerospace equipment. The performance of the engine determines a series of performances such as the flight speed, maneuverability, and effective load of the aircraft. Among them, the turbine rotor blade is an important component that converts the thermal energy of the engine into mechanical energy and serves under harsh high-temperature conditions for a long time. Initially, benefiting from decades of development of nickel-based alloys, the working temperature of the engine has been steadily increased, and the performance and efficiency have been improved. The service temperature range of the most widely used nickel-based alloys (GH4099, GH3536) is 650°C to 900°C. With the continuous improvement of the performance and efficiency of the engine, its working temperature has also been continuously increased. So far, it has been increased to above 1000°C, which has exceeded the melting point T of nickel-based superalloys m , and nickel-based alloys usually have stable mechanical properties at a temperature of 0.6T m and it is difficult to meet the requirements at higher temperatures. Therefore, new alternative materials need to be studied.

[0003] High-entropy alloys (HEAs) are a new type of alloy containing five or more main alloying elements with equal or nearly equal atomic percentages (at%) and are prone to form solid solutions. Different from traditional alloys, high-entropy alloys also have five major effects: slow diffusion effect, high-entropy effect, lattice distortion effect, short-range order effect, and cocktail effect. The above five major effects endow high-entropy alloys with excellent specific strength, high-temperature mechanical properties, good low-temperature ductility and fracture toughness, superparamagnetism and superconductivity. Therefore, they have received extensive attention from scientists in recent years. The slow diffusion effect not only allows oxygen ions to slowly combine with metal cations to make the oxide grow slowly, but also ensures its excellent high-temperature strength and the stability of the high-temperature structure. HEAs are considered a promising high-temperature alloy, especially with high application potential in the aerospace industry.

[0004] Eutectic high-entropy alloys (EHEAs) have many excellent properties. They have a structure similar to that of superalloys (FCC + L12). The internal eutectic solidification structure has advantages such as low-energy phase boundaries, controllable microstructure, and good high-temperature creep resistance. And due to the presence of the L12 phase, which is similar to the indispensable strengthening phase γ' phase in nickel-based superalloys, it endows the eutectic high-entropy alloy with excellent high-temperature stability and strength. Therefore, EHEAs are a kind of materials with potential for application in high-temperature scenarios.

[0005] The research on the high-temperature oxidation behavior of EHEAs has attracted more and more scholars' attention. Kumar et al. studied the oxidation behavior of the near-EHEA AlCoCrFeNi2 after quenching at 1200 °C and then oxidizing at 1050 °C for 100 h, and the alloy's antioxidant performance was increased by the phase transformation from ordered to disordered inside the alloy through the quenching treatment at 1200 °C. Mondal et al. studied CoCrFeNiNb x 's oxidation behavior at 900 °C and found that with the addition of Nb, a protective CrNbO4 oxide film was formed during the oxidation process of the alloy, improving the alloy's high-temperature oxidation resistance.

[0006] In recent years, more and more EHEA systems have been developed, including the initial Al-Co-Cr-Fe-Ni system, Co-Cr-Fe-Ni-Ta system, Co-Fe-Ni-V-Mo system, etc. Al 19 Co 20 Fe 20 Ni 41 is a new type of EHEA designed by Jin et al. on the basis of the Al-Fe-Co-Cr-Ni system. Through directional solidification, a fishbone-like multi-level eutectic lamellar structure was formed. The tensile elongation of this alloy reached an unprecedented 50%, and the yield strength and tensile strength were 670 MPa and 1050 MPa respectively, achieving the coexistence of high strength and high plasticity. However, this alloy is slightly lacking in high-temperature oxidation resistance. Peng et al. found that after testing the Al 19 Co 20 Fe 20 Ni 41 alloy at 800 °C for 100 h of isothermal oxidation, its oxidation performance was poor, and only a loose and porous multi-layer oxide could be formed, which could not effectively protect the alloy from oxygen erosion.

[0007] Therefore, it is of great significance to provide a method for improving the antioxidant performance of AlCoFeNi-based EHEAs. Summary of the Invention

[0008] The technical problem solved by the present invention is to provide a eutectic high-entropy alloy of the AlCoFeNi system. The eutectic high-entropy alloy provided in this application has excellent high-temperature oxidation resistance and good corrosion resistance.

[0009] In view of this, the present application provides an AlCoFeNi-based eutectic high-entropy alloy, which consists of a eutectic high-entropy alloy matrix shown in formula (Ⅰ) and Y and Hf doped in the eutectic high-entropy alloy matrix; the content of Y is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix, and the content of Hf is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix;

[0010] Al x Co y Fe 100-x-y-z Ni z (Ⅰ);

[0011] Wherein, x, y, and z are the atomic percentages of Al, Co, and Ni respectively, x = 18-21, y = 19-22, z = 39-42.

[0012] In some specific embodiments, x = 19-20, and / or, y = 20-21, and / or, z = 40-41.

[0013] In some specific embodiments, the content of Y is 0.05 wt% of the eutectic high-entropy alloy matrix.

[0014] In some specific embodiments, the content of Hf is 0.05 wt% of the eutectic high-entropy alloy matrix.

[0015] In some specific embodiments, the eutectic high-entropy alloy matrix is as shown in formula Al 19 Co 20 Fe 20 Ni 41 shown, the content of Y is 0.05 wt% of the eutectic high-entropy alloy matrix, and the content of Hf is 0.05 wt% of the eutectic high-entropy alloy matrix.

[0016] In some specific embodiments, the AlCoFeNi-based eutectic high-entropy alloy has an FCC and BCC duplex structure and is a separated eutectic structure.

[0017] In some specific embodiments, the surface oxide film of the AlCoFeNi-based eutectic high-entropy alloy includes Al2O3, (Ni, Co)Fe2O4, (Ni, Co)Al2O4, and NiCo2O4.

[0018] In some specific embodiments, the thickness of the surface oxide film is greater than 15 μm.

[0019] The present application also provides a preparation method of the AlCoFeNi-based eutectic high-entropy alloy, including the following steps:

[0020] Ingredients are proportioned according to the composition ratio of the AlCoFeNi-based eutectic high-entropy alloy, and the raw materials are mixed and then melted to obtain the AlCoFeNi-based eutectic high-entropy alloy.

[0021] In some specific embodiments, the atmosphere for the melting is high-purity argon, and the melting method is vacuum arc melting.

[0022] This application provides an AlCoFeNi-based eutectic high-entropy alloy, which is composed of a eutectic high-entropy alloy matrix as shown in the formula Al x Co y Fe 100-x-y-z Ni z and Y and Hf doped in the eutectic high-entropy alloy matrix; the content of Y is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix, and the content of Hf is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix; the AlCoFeNi-based eutectic high-entropy alloy provided by this application uniformly dopes Y and Hf in the eutectic high-entropy alloy matrix as shown in the formula Al x Co y Fe 100-x-y-z Ni z shown, which neither changes the structure of the alloy nor affects its mechanical properties, and on this basis, the alloy has excellent high-temperature oxidation resistance. Further, the AlCoFeNi-based eutectic high-entropy alloy provided by this application also has good corrosion resistance. Description of the Drawings

[0023] Figure 1 XRD results of the eutectic high-entropy alloys prepared in Comparative Example 1 and Example 1 of the present invention;

[0024] Figure 2 Backscattered electron images of the eutectic high-entropy alloys prepared in Comparative Example 1 and Example 1 of the present invention;

[0025] Figure 3 TEM photo and EDS surface scan results of the eutectic high-entropy alloy prepared in Comparative Example 1 of the present invention;

[0026] Figure 4 TEM photo and EDS surface scan results of the eutectic high-entropy alloy prepared in Example 1 of the present invention;

[0027] Figure 5 Mass gain curve of the eutectic high-entropy alloy without Y and Hf doping and with Y and Hf doping of the present invention at 1000 °C isothermal oxidation for 8 h;

[0028] Figure 6 Surface XRD pattern of the eutectic high-entropy alloy prepared in Example 1 of the present invention after oxidation at 1000 °C for 5 min;

[0029] Figure 7 Backscattered electron image and EDS results of the surface of the eutectic high-entropy alloy of the present invention after oxidation at 1000 °C for 24 h;

[0030] Figure 8 Backscattered electron image and EDS results of the oxidation cross-section of the eutectic high-entropy alloy prepared in Example 1 of the present invention after oxidation at 1000 °C for 24 h;

[0031] Figure 9 STEM image and EDS results of the eutectic high-entropy alloy prepared in Example 1 of the present invention after oxidation at 1000 °C for 30 min;

[0032] Figure 10 STEM image and selected area electron diffraction image of the eutectic high-entropy alloy prepared in Example 1 of the present invention after oxidation at 1000 °C for 30 min;

[0033] Figure 11 Schematic diagram of the oxidation mechanism of the eutectic high-entropy alloy prepared in Example 1 of the present invention at each stage;

[0034] Figure 12 Electrochemical impedance spectra (a) of the eutectic high-entropy alloys prepared in Comparative Example 1 and Example 1 of the present invention in 0.6 M NaCl and equivalent circuit diagram (b) for fitting EIS data; Detailed implementation manners

[0035] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0036] In view of the need of the AlCoFeNi-based eutectic high-entropy alloy in the prior art for high-temperature oxidation resistance, the present application provides an AlCoFeNi-based eutectic high-entropy alloy (EHEAs), which improves the high-temperature oxidation resistance and corrosion resistance of the EHEAs by adding trace amounts of Y element and Hf element to the AlCoFeNi-based eutectic high-entropy alloy. Specifically, the embodiments of the present invention disclose an AlCoFeNi-based eutectic high-entropy alloy, which is composed of a eutectic high-entropy alloy matrix shown in formula (Ⅰ) and Y and Hf doped in the eutectic high-entropy alloy matrix; the content of Y is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix, and the content of Hf is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix;

[0037] Al x Co y Fe 100-x-y-z Ni z (Ⅰ);

[0038] Among them, x, y, and z are the atomic percentage contents of Al, Co, and Ni respectively, where x = 18-21, y = 19-22, and z = 39-42.

[0039] In the AlCoFeNi-based eutectic high-entropy alloy provided by this application, the molecular formula is like Al x Co y Fe 100-x-y-z Ni z The eutectic high-entropy alloy serves as the matrix of the eutectic high-entropy alloy, in which trace amounts of Y and Hf are uniformly doped; among them, x, y, and z are the atomic percentage contents of the corresponding elements Al, Co, and Ni. x is 18-21, y is 19-22, and z is 39-42. Specifically, x is 19-20, y is 20-21, and z is 40-41; more specifically, x = 19, y = 20, and z = 41; for example, the molecular formula of the eutectic high-entropy alloy matrix is like Al 19 Co 20 Fe 20 Ni 41 .

[0040] In the AlCoFeNi-based eutectic high-entropy alloy, Y and Hf are uniformly doped in the above-mentioned eutectic high-entropy alloy matrix. Among them, the content of Y is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix, and the content of Hf is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix. Specifically, the content of Y is 0.05 wt% of the eutectic high-entropy alloy matrix, and the content of Hf is 0.05 wt% of the eutectic high-entropy alloy matrix. More specifically, in the AlCoFeNi-based eutectic high-entropy alloy, Al 19 Co 20 Fe 20 Ni 41 The eutectic high-entropy alloy matrix contains 0.05 wt% of Y and 0.05 wt% of Hf of the Al 19 Co 20 Fe 20 Ni 41 eutectic high-entropy alloy matrix.

[0041] The AlCoFeNi-based eutectic high-entropy alloy provided by this application has an FCC and BCC dual-phase structure and is a separated eutectic structure; further, the surface oxide film of the AlCoFeNi-based eutectic high-entropy alloy provided by this application includes Al2O3, (Ni, Co)Fe2O4, (Ni, Co)Al2O4, and NiCo2O4, and Al2O3 is close to the eutectic high-entropy alloy end.

[0042] This application also provides a preparation method for the AlCoFeNi-based eutectic high-entropy alloy, including the following steps:

[0043] Ingredients are prepared according to the composition ratio of the eutectic high-entropy alloy, and the prepared raw materials are mixed and melted.

[0044] In the above preparation method of the eutectic high-entropy alloy, the selection of the raw materials is carried out according to the selection well-known to those skilled in the art, and this application does not impose special restrictions on this. The implementation manner of the melting is not particularly limited in this application, and it can be carried out in the manner well-known to those skilled in the art. Specifically, the melting is carried out in a high-purity argon atmosphere, and the vacuum arc melting method is adopted for the melting. There is no special restriction on the specific implementation process in this application.

[0045] This application provides an AlCoFeNi-based eutectic high-entropy alloy, which is obtained by uniformly doping Y and Hf in the eutectic high-entropy alloy matrix shown as follows: Al x Co y Fe 100-x-y-z Ni z As a result, the oxide film formed by the eutectic high-entropy alloy at high temperature grows slowly, and a dense Al2O3 film is formed. Moreover, Fe, Co, and Ni continue to grow in a flaky morphology. As the continuous oxidation proceeds, a large amount of Y and Hf diffuse to the matrix joints of Al2O3, ensuring the connectivity of the oxide scale. At the same time, the doping of Y and Hf can enhance the interfacial toughness. As the oxide film thickens, Y and Hf elements dynamically move towards the oxide / matrix interface, forming fine oxidation pins at the interface, effectively preventing the separation of the interface, thereby strengthening the interface bonding. The segregation of Y and Hf elements at the oxide / matrix interface can also inhibit the growth of interface voids, further improving the adhesion of the oxide film. At the same time, the AlCoFeNi-based eutectic high-entropy alloy provided by this application also has good corrosion resistance due to the addition of trace amounts of Y and Hf.

[0046] To further understand the present invention, the following examples are used to illustrate in detail the AlCoFeNi-based eutectic high-entropy alloy and its preparation method provided by the present invention. The protection scope of the present invention is not limited by the following examples.

[0047] Example 1

[0048] Using the vacuum arc melting method, high-purity (99.99 wt%) Al, Co, Fe, Ni, Y, and Hf are prepared according to the set ratio. The prepared metal raw materials are placed on a water-cooled Cu hearth, and then melted by arc melting in a high-purity argon atmosphere. The obtained alloy button ingot is remelted five times to homogenize its composition. Finally, an Al 19 Fe 20 Co 20 Ni 41 (at%) EHEA doped with 0.05 wt% Y and 0.05 wt% Hf is obtained.

[0049] Comparative Example 1

[0050] Using the vacuum arc melting method, high-purity (99.99 wt%) Al, Co, Fe, and Ni are proportioned according to the set ratio. The metal raw materials after proportioning are placed on a water-cooled Cu hearth, and then melted by arc melting under a high-purity argon atmosphere. The obtained alloy button ingots are remelted five times to homogenize the composition, and finally Al 19 Fe 20 Co 20 Ni 41 (at%) EHEA is obtained.

[0051] Example 2

[0052] The eutectic high-entropy alloy ingots prepared in Example 1 and Comparative Example 1 above are subjected to an oxidation experiment. Specifically:

[0053] Using wire cutting technology, 2 blocks of 3×3×3 mm 3 are cut from each alloy ingot. The alloy specimen blocks with different compositions are divided into one group. The two groups of specimens are ground from 400 mesh to 2000 mesh on six surfaces according to the standard metallographic method using SiC sandpaper. Before the oxidation of the specimens, the ground samples are ultrasonically cleaned to remove the Si particles on the alloy surface;

[0054] The first group of specimens are respectively placed in a laboratory electric furnace for isothermal oxidation experiments at 1000 °C for 24 h. The samples are placed in the center of the furnace. After the samples are oxidized at 1000 °C for the corresponding time, the samples are taken out of the furnace, and then the samples are air-cooled outside the furnace to room temperature for further testing;

[0055] In order to study the oxidation kinetics, the second group of specimens are subjected to thermogravimetric analysis (TGA) experiments at 1000 °C. A thermal balance is used to continuously record the function of mass gain and time, and the experiment is ended when the curve region is stable.

[0056] 1) Process of microstructure observation

[0057] The phase composition of the alloys prepared in Example 1 and Comparative Example 1 and the crystal structure of the oxidation products are characterized by SmartLab SE type X-ray diffraction (XRD). Scanning is carried out in the range of 20° to 100° at a scanning speed of 2° / min. The X-ray source is Cu-K αThe target has a rated current of 40 mA and a rated voltage of 40 kV. An Apreo S HVac scanning electron microscope (SEM) was used to characterize the microstructure and the morphology after oxidation of the samples, and an Oxford Ultim Max 100 energy-dispersive X-ray spectroscopy (EDS) was used to analyze the composition of the alloy phases and the oxidized surface. The specimens after observing the oxidized surface were placed in a cold mounting mold cup, and the resin powder and the curing agent were thoroughly mixed in a ratio of 5:4 and then used to cast the samples. After complete solidification, the cold mounting of the samples was completed. The cold-mounted samples were ground from 400 mesh to 2000 mesh with SiC, using alcohol as a lubricant, and low-speed polishing was carried out with 1 μm diamond in an alcohol-based lubricant to prepare the oxidized cross-section. A Shimadzu-type electron probe microanalyzer (EPMA) was used to conduct a preliminary morphological observation and composition analysis of the oxidized cross-sections of the eutectic high-entropy alloys prepared in Example 1 and Comparative Example 1 after high-temperature oxidation for 24 h. In order to further understand the composition of the oxide layer, a method of extraction using a focused ion beam (FIB) was adopted. A thin slice was extracted from the middle of the upper surface of the oxidized sample to prepare a thin slice of the alloy oxidized cross-section with a thickness of about 80 μm. A JEM-200 (CF-HR) scanning transmission electron microscope (STEM) equipped with an EDS system was used to conduct scanning transmission electron microscopy (STEM) analysis and EDS analysis of the oxidized cross-section, and selected area electron diffraction (SAED) was carried out on different oxide layers to determine the crystal structure and material composition of each oxide layer.

[0058] To further determine the structural composition of each alloy phase, wire cutting was used to cut 8×8×0.5 mm 3 thin slices from each alloy ingot, and the alloy thin slices with a surface of 2000 mesh and a thickness of 80 μm were ground using SiC sandpaper. After punching the slices, a Struers TenuPol-5 electrolytic twin-jet instrument was used to prepare the thin slices. The working voltage was 40 V, the working temperature was -20 °C, and the electrolyte was 95% methanol + 5% perchloric acid. Similarly, a JEM-200 (CF-HR) scanning transmission electron microscope (STEM) equipped with an EDS system was used to conduct scanning transmission electron microscopy (STEM) morphological observation and EDS composition analysis of the alloy, and selected area electron diffraction (SAED) was carried out on the phase composition of different alloys to determine the alloy phase structure.

[0059] 2) Microstructure Characterization

[0060] Figure 1 (a) and (b) are the XRD patterns of the EHEA prepared in Comparative Example 1 and Example 1 respectively. It can be seen that the EHEA prepared in Comparative Example 1 is a FCC + BCC duplex structure, and the EHEA prepared in Example 1 is also a FCC + BCC duplex structure; this indicates that Al Figure 1 Co 19 Co 20Fe 20 Ni 41 After adding a small amount of Y and Hf, the EHEA still has a composition of FCC phase and BCC phase. The changes in the diffraction peak intensity and lattice parameters indicate that the lattice structures of FCC and BCC have distorted due to the addition of Y and Hf, changing the crystal phase structure of the alloy.

[0061] Figure 2 The backscattered electron images of the EHEAs prepared in Comparative Example 1 and Example 1 are shown. From Figure 2 (a), it can be seen that the Al 19 Co 20 Fe 20 Ni 41 EHEA alloy shows a fine lamellar eutectic structure. The bright and dark regions in the figure correspond to the FCC and BCC phases respectively, and its characteristic morphologies are divided into two types: one is the arrangement of slender lamellar structures, and the other is the irregular interleaved arrangement. For the eutectic high-entropy alloy prepared in Example 1, with the doping of Y and Hf, from Figure 2 (b), it can be seen that the alloy microstructure has partially transformed from the initial lamellar eutectic microstructure into a separated eutectic microstructure, showing grain coarsening and a significant reduction in the grain boundary density; however, the phase composition of the alloy is still a near-eutectic structure.

[0062] In order to more accurately identify the phase structures and chemical composition compositions of the eutectic high-entropy alloys prepared in Example 1 and Comparative Example 1, a transmission electron microscope (TEM) was used to observe the phase structures and chemical element compositions of the alloys with and without Y and Hf doping. As Figure 3 and Figure 4 shown, from Figure 3 a, 4a of HADDF-STEM, it can be observed that both EHEAs are typical eutectic lamellar structures. The widths of the two phases of the alloy are at the micron level, with a width of 2 - 3 μm. It was also observed that after adding Y and Hf elements to the alloy, the widths of the two phases increased slightly. Therefore, the addition of Y and Hf elements will accelerate the nucleation rate inside the alloy, resulting in a slight broadening of the alloy phases. Combining the corresponding SADPs ( Figure 3 b, 3c, 4b, 4c), it can be clearly seen that superlattice lattices exist in both phases, indicating that the two-phase structures of these two alloys are ordered FCC and BCC phases, namely L12 and B2 phases. The corresponding STEM-EDS spectra ( Figure 3 d~3g, Figure 4 d~4g) show that the L12 phase in all alloys is rich in Fe, Co, and Ni, and the B2 phase is rich in Al and a small amount of Ni, which is consistent with the elemental analysis results in SEM-EDS. Since the doping concentrations of Y and Hf are relatively low (0.05 wt%), they only precipitate in small amounts at some phase boundaries in some regions. Therefore, no precipitates of Y and Hf were observed in the regions selected by TEM.

[0063] 3) Oxidation Kinetics

[0064] Figure 5 Al without Y and Hf doping and doped with different amounts of Y and Hf 19 Co 20 Fe 20 Ni 41 The isothermal oxidation kinetic curves of EHEA oxidized in air at 1000 °C for 6 h show that, as can be seen from Figure 5 it, in the initial stage of oxidation, the oxidation weight gain trend of all alloys is rapid increase at the beginning, and then the oxidation rate (curve slope) gradually levels off. Especially for Al 19 Co 20 Fe 20 Ni 41 EHEA doped with Y and Hf, the curve has leveled off after 2 h. After 6 h of oxidation, the oxidation weight gain of Al 19 Co 20 Fe 20 Ni 41 EHEA doped with 0.05 wt% Y and Hf is significantly lower than that of Al 19 Co 20 Fe 20 Ni 41 EHEA without Y and Hf doping, about 0.15 mg·cm -2 . According to the classical oxidation theory, for the high-temperature oxidation process of metals, the oxidation kinetic relationship between the mass gain per unit area Δm / A and the oxidation time t can usually be described by the power function model:

[0065] Δm / A = k p t n (1);

[0066] where Δm / A is the gain per unit area, k p is the parabolic rate constant, n is the kinetic exponent, and t is the oxidation time. After fitting, it is found that n = 2, and the curve conforms to the parabolic law. The k 19 Co 20 Fe 20 Ni 41 values of EHEA for Al without Y and Hf doping and doped with 0.05 wt% Y and Hf are 1.73×10 p mg cm -4 h -2 and 1.31×10 -1 mg cm -4 h -2 respectively. -1, which indicates that after doping Y and Hf in the EHEA alloy, the oxidation weight gain rate slows down, indicating that the oxidation rate of the EHEA after doping Y and Hf decreases, and its oxidation resistance is improved.

[0067] 4) Surface characterization of the oxide layer

[0068] Figure 6 is the XRD pattern of the EHEA prepared in Example 1 after oxidation for 5 min. For the EHEA prepared in Comparative Example 1, since the surface oxide film severely peeled off due to the absence of Y and Hf addition, XRD detection was not performed on it. It can be seen from the XRD pattern that the oxides formed on the surface of the EHEA prepared in Example 1 are all Al2O3, (Ni, Co)Fe2O4, (Ni, Co)Al2O4, and NiCo2O4.

[0069] Figure 7 is Al after oxidation at 1000 °C for 5 min 19 Co 20 Fe 20 Ni 41 Backscattered electron image (BSE) and EDS surface scan results of the EHEA surface, where Figure 7 (a, b) are for Al without Y and Hf 19 Co 20 Fe 20 Ni 41 BSE image and EDS surface scan results of the EHEA surface; (c, d) are for Al doped with 0.05 wt% Y and Hf 19 Co 20 Fe 20 Ni 41 BSE image and EDS surface scan results of the EHEA surface; it can be seen from the figure that when the alloy is not doped with Y and Hf elements, from the EDS surface scan results, there are a large amount of Al2O3 on its surface, and there are also a small amount of complex oxides of Fe, Co, and Ni. When the alloy is added with Y and Hf, its surface morphology changes, and a large amount of complex oxides of Fe, Co, and Ni are distributed on the surface, and it contains a small amount of Al2O3. It can be seen that the addition of Y and Hf elements promotes the selective oxidation of the alloy, accelerates the oxidation of Fe, Co, and Ni elements in the alloy, and makes a large amount of oxides generated on the surface.

[0070] 5) Cross-section characterization of the oxide layer

[0071] The morphology of the oxide film on the cross-section of the EHEA prepared in Example 1 is as Figure 8 shown, by Figure 8It can be seen that the overall thickness of the oxide film is above 15 μm, and the oxide film is relatively dense. Since the growth rate of the spinel oxide is relatively fast, a relatively thick spinel oxide is observed to adhere to the Al2O3. At the same time, a small amount of Y element and Hf are observed to be enriched under the Al2O3 or distributed in the upper oxide scale, ensuring the adhesion of the alloy oxide scale and reducing defects such as pores and cracks formed in the upper layer of oxidation. Moreover, the layered L12 and B2 phases can still be observed in the alloy added with Y element and Hf element, which proves the high-temperature stability of the alloy. By observing the oxide morphology on the surface and cross-section of the EHEA, it can be seen that the addition of Y element and Hf effectively improves the high-temperature oxidation resistance of the EHEA.

[0072] In order to more finely characterize the oxide film of the EHEA prepared in Example 1, FIB was used to extract the region from the oxide film to the substrate interface and make a TEM specimen. Figure 9 Al doped with 0.05 wt% Y and 0.05 wt% Hf 19 Co 20 Fe 20 Ni 41 STEM image and EDS area scan results of the cross-section of the oxide film of the EHEA oxidized at 1000 °C for 30 min in Example 1, where Figure 9 (a) is the STEM image of the oxide film interface, Figure 9 (b)–(h) are the EDS area scan images of the oxide film interface. As can be seen from the figure, for the Al 19 Co 20 Fe 20 Ni 41 oxide film of the EHEA consists of four parts. The uppermost layer is enriched with Co and Ni elements, the upper-middle layer is enriched with Fe, Co, and Ni elements, the lower-middle layer is enriched with Co, Ni, and Al elements, and the lowermost layer is enriched with Al elements.

[0073] Figure 10 STEM image (a) and selected area electron diffraction patterns (b)–(e) of the cross-section of the oxide film of the EHEA prepared in Example 1 oxidized at 1000 °C for 30 min. According to the selected area electron diffraction patterns of each region, Figure 9 the Fe, Co, Ni composite oxide in it consists of NiCo2O4 in the upper layer and (Ni, Co)Fe2O4 and (Ni, Co)Al2O4 in the middle layer. The lowermost layer is further confirmed to be continuous Al2O3, and a small amount of Y oxide is also found to appear in the oxide film.

[0074] 6) Principle of Y and Hf improving the oxidation resistance of the alloy

[0075] To better illustrate the oxidation process of the eutectic high-entropy alloy prepared in Example 1, an oxidation schematic diagram is provided.Figure 11 is the oxidation mechanism diagram of the eutectic high-entropy alloy. Like other alloys, the oxidation process of the eutectic high-entropy alloy is completed by the diffusion of oxygen atoms into the alloy interior and the diffusion of metal cations from the alloy interior to the outside. Among the four elements in Al 19 Co 20 Fe 20 Ni 41 , the diffusion order of the four elements from front to back is Al, Fe, Co, Ni. Al has the largest driving force for oxide formation thermodynamically, and the elements that diffuse out first will preferentially form oxides on the alloy surface. Therefore, Al2O3 is formed on the alloy surface first, so Al2O3 is the bottommost oxide; when oxidation continues, a dense oxide film has formed on the alloy surface, and the amount of oxygen ions diffusing into the metal interior has decreased significantly. The oxidation process of the alloy is dominated by the diffusion of metal cations from the alloy interior to the outside; the oxides of Fe, Co, and Ni formed later are non-protective oxides, and oxygen ions will penetrate into them and combine with Fe, Co, and Ni diffusing out from Al2O3 to form oxides. For Al doped with Y and Hf 19 Co 20 Fe 20 Ni 41 , similarly, with the progress of oxidation, a large amount of Y and Hf diffuse to the junction of Al2O3 and the matrix (as shown in Figure 11 ), ensuring the adhesion of the oxide scale to the matrix; the doping of Y and Hf enhances the interfacial toughness. As the oxide film thickens, Y and Hf will dynamically move towards the oxide / matrix interface, forming fine oxidation pins at the interface, effectively preventing the separation of the interface, thereby strengthening the interface bonding. In this process, Y and Hf diffuse out along the grain boundaries, hindering the diffusion of Al elements from the alloy interior to the outside, thereby slowing down the oxidation rate. At the same time, the segregation of Y and Hf at the oxide / matrix interface can inhibit the growth of interface voids, thereby further improving the adhesion of the oxide film.

[0076] Example 3

[0077] An electrochemical workstation (Biologic VMP3) with a three-electrode setup was used to conduct EIS tests and analyses on the eutectic high-entropy alloy EHEAs in 0.6 M NaCl; in the three-electrode system, the EHEA sample was the working electrode, the saturated calomel electrode was the reference electrode (SCE), and the platinum plate was the counter electrode; before each test, the sample surface was polished to 2000 grit, and each alloy was tested at least three times. The test medium was 0.6 M NaCl solution; the eutectic high-entropy alloy was the eutectic high-entropy alloy prepared in Example 1 and Comparative Example 1;

[0078] The electrochemical impedance spectroscopy (EIS) test was carried out in the frequency range of 100 kHz to 5 mHz. Before the test, ensure that the open-circuit potential (OCP) of the sample is stable in the solution for 30 min, and the potential perturbation amplitude is within 5 mV.

[0079] Figure 12 Electrochemical impedance spectra (a) of the high-entropy alloys prepared in Comparative Example 1 and Example 1 of the present invention in 0.6 M NaCl and the equivalent circuit diagram (b) used to fit the EIS data; as Figure 12 (a) shows the electrochemical impedance spectra (EIS) of the two alloys. It can be seen from the figure that the arc radius of the Nyquist plot of the eutectic high-entropy alloy prepared in Example 1 is significantly larger than that of the eutectic high-entropy alloy prepared in Comparative Example 1.

[0080] Adopt as Figure 12 (b) The equivalent circuit shown is used to Figure 12 fit the curve in e (a), and a series of electrochemical parameters shown in Table 1 are obtained. Let R f be the solution resistance, and R f be the passive film resistance. The higher the value of R fit , the higher the passive film resistance of the alloy and the better the corrosion resistance. From the Z 19 Co 20 Fe 20 Ni 41 eutectic high-entropy alloy prepared in Example 1 has an R f value (61405 Ω·cm 2 ) significantly higher than that of the Al 19 Co 20 Fe 20 Ni 41 eutectic high-entropy alloy prepared in Comparative Example 1 (37262 Ω·cm 2 ), indicating that the eutectic high-entropy alloy doped with Y and Hf shows better corrosion resistance in 0.6 M NaCl.

[0081] Table 1 Data table of electrochemical parameters obtained from electrochemical impedance spectra

[0082] Sample <![CDATA[R e (ohm·cm 2 )]]> <![CDATA[Q f (μF s a-1 ·cm -2 )]]> <![CDATA[R f (ohm·cm 2 )]]> Comparative Example 1 12.58 <![CDATA[43.05×10 -6 > 37262 Example 1 11.63 <![CDATA[22.34×10 -6 > 61405

[0083] From the Z fit fitting data, it can be seen that the Al 19 Co 20 Fe 20 Ni 41 eutectic high-entropy alloy prepared in Example 1 has an R f value (61405 Ω·cm 2 ) significantly higher than that of the Al 19 Co 20 Fe20 Ni 41 The eutectic high-entropy alloy (37262 Ω·cm 2 ), indicating that the eutectic high-entropy alloy after doping with Y and Hf exhibits higher corrosion resistance.

[0084] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0085] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An AlCoFeNi-based eutectic high-entropy alloy is composed of a eutectic high-entropy alloy matrix shown in formula (Ⅰ) and Y and Hf doped in the eutectic high-entropy alloy matrix; the content of Y is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix, and the content of Hf is 0.04-0.06 wt% of the eutectic high-entropy alloy matrix; Al x Co y Fe 100-x-y-z Ni z (Ⅰ); Among them, x, y, and z are the atomic percentage contents of Al, Co, and Ni respectively, x = 18-21, y = 19-22, z = 39-42.

2. The AlCoFeNi-based eutectic high-entropy alloy according to claim 1, wherein x = 19-20, and / or, y = 20-21, and / or, z = 40-41.

3. The AlCoFeNi-based eutectic high-entropy alloy according to claim 1 or 2, characterized in that, The content of Y is 0.05 wt% of the eutectic high-entropy alloy matrix.

4. The AlCoFeNi-based eutectic high-entropy alloy according to claim 1 or 2, characterized in that, The content of Hf is 0.05 wt% of the eutectic high-entropy alloy matrix.

5. The AlCoFeNi-based eutectic high-entropy alloy according to claim 1, characterized in that, The eutectic high-entropy alloy matrix is as follows: Al 19 Co 20 Fe 20 Ni 41 As shown, the content of Y is 0.05 wt% of the eutectic high-entropy alloy matrix, and the content of Hf is 0.05 wt% of the eutectic high-entropy alloy matrix.

6. The AlCoFeNi-based eutectic high-entropy alloy according to claim 1, wherein The AlCoFeNi-based eutectic high-entropy alloy is a FCC and BCC duplex structure and is a separated eutectic microstructure.

7. The AlCoFeNi-based eutectic high-entropy alloy according to claim 1, characterized in that, The surface oxide film of the AlCoFeNi-based eutectic high-entropy alloy includes Al2O3, (Ni, Co)Fe2O4, (Ni, Co)Al2O4, and NiCo2O4.

8. The AlCoFeNi-based eutectic high-entropy alloy according to claim 7, characterized in that, The thickness of the surface oxide film is greater than 15 μm.

9. The preparation method of the AlCoFeNi-based eutectic high-entropy alloy according to any one of claims 1-8, comprising the following steps: Weigh the raw materials according to the composition ratio of the AlCoFeNi-based eutectic high-entropy alloy, mix the raw materials and then melt them to obtain the AlCoFeNi-based eutectic high-entropy alloy.

10. The preparation method according to claim 9, characterized in that, The atmosphere for the melting is high-purity argon, and the melting method is vacuum arc melting.

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