FCC structure high-entropy alloy material for hydrogen permeation and preparation method of FCC structure high-entropy alloy material

Abstract

The invention discloses an FCC (Fluid Catalytic Cracking) structure high-entropy alloy material for hydrogen permeation and a preparation method of the FCC structure high-entropy alloy material, and relates to development and preparation of a novel FCC structure high-entropy alloy component for hydrogen permeation, and the alloy component is Co5Cr15Fe50Ni22Nb8. The preparation method of the alloy comprises the following steps: firstly, carrying out ultrasonic cleaning on the raw materials Co, Cr, Fe, Ni and Nb; accurately weighing the raw materials; and then smelting is conducted in a vacuum glove box electric arc smelting furnace according to a specific technology, and the alloy components are evenly distributed through multiple times of smelting. Compared with a traditional alloy, the prepared material is a double-phase high-entropy alloy which is uniform in phase composition, ordered in phase distribution and excellent in mechanical property, the hydrogen brittleness resistance of the double-phase high-entropy alloy exceeds that of the traditional alloy, and hydrogen is successfully generated in the middle and lower reaches of a hydrogen permeation test. The method has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of hydrogen purification, and in particular relates to a high entropy alloy material for hydrogen permeation and a preparation method thereof. Background Art

[0002] The emergence of hydrogen energy has largely solved the problems of fossil fuel depletion and environmental pollution. Today, hydrogen energy is mainly used in the aviation and transportation industries, but with the continuous breakthroughs in hydrogen production, hydrogen permeation, and hydrogen storage technologies, it has gradually expanded to other industries. However, due to technical issues, the application areas of hydrogen energy are still limited, so it is necessary to develop a more efficient production process from hydrogen energy production to use. The current commercial hydrogen production methods mainly include: fossil fuel hydrogen production, industrial by-product hydrogen production, water electrolysis hydrogen production, and biomass hydrogen production. In these hydrogen production methods, since impurity gases (such as CO, CO2, NH3, H2S) may enter the hydrogen, hydrogen purification becomes a key link. How to design a large-scale and long-term effective hydrogen separation method has become a new problem. Currently, the separation and purification of hydrogen mainly adopts methods such as low-temperature absorption, low-temperature distillation (deep cooling), low-temperature adsorption, pressure swing adsorption, and membrane separation.

[0003] Membrane separation is one of the most effective separation and purification methods for producing high-purity hydrogen due to its ease of operation, energy efficiency, space savings, high cost-effectiveness, and ease of integration into existing industrial production processes. Membrane separation utilizes specialized membranes to selectively permeate and diffuse a single component gas through a mixed gas, thereby separating and purifying a specific gas. Currently, the most commonly used membrane materials include polymer membranes (glass and rubber) and their composites, ceramic membranes, and metal membranes. Dense metal membranes for hydrogen separation offer significant advantages over other membrane materials due to their high hydrogen permeability, excellent mechanical strength, and high-temperature durability, making them a popular choice for hydrogen separation. In particular, palladium and palladium-based metal membranes, due to their virtually unrestricted selectivity for hydrogen, have been extensively studied over the past few decades and have become the most important metal membranes in the field. However, palladium, as a precious metal, is relatively expensive and scarce, and its separation performance degrades and eventually fails due to hydrogen embrittlement and high-temperature diffusion, limiting its widespread industrial application. Therefore, there is an urgent need to develop new metal membrane materials that are Pd-free or have low Pd content.

[0004] To address hydrogen embrittlement failures, economic benefits, and resource scarcity, researchers worldwide have discovered that group VB elements offer lower cost and superior hydrogen separation capabilities. Consequently, hydrogen separation alloy membranes based on group VB elements, such as Nb-, V-, and Ta-based materials, have been developed. These alloys exhibit not only excellent hydrogen permeability but also excellent resistance to hydrogen embrittlement. High-entropy alloys (HEAs), or multi-component alloys, emerged in 2004 as a new research direction in the field of metallic materials. Compared to traditional alloys, HEAs are alloys containing at least five elements, with concentrations ranging from 5 to 35 at.%. The design concept of multi-primary HEAs transcends the existing single-primary alloy theory, providing clearer evidence for the relationship between material composition, structure, and properties, and deepening the understanding of fundamental materials theory. However, single-phase solid HEAs lack mechanical advantages compared to traditional alloys. Therefore, due to the mechanical potential of dual-phase structures of solid solutions and intermetallic compounds, two-phase or multi-phase HEAs derived from these structures have been investigated. However, multiphase high-entropy alloys (HEAs) have poor casting properties, limiting their large-scale application. Eutectic alloys offer a range of advantages, including near-equilibrium microstructures, controllable microstructures, and high fracture toughness. In recent years, there have been numerous reports of HEAs containing group VB elements exhibiting dual-phase structures and excellent mechanical properties. The design of hydrogen-permeable alloys follows the principle of "dual-phase alloys, complementary functions," proposed by Professor Hashi of Japan in 2004, such as Nb-Hf-M and Nb-Zr-M. Therefore, they share common structural design and mechanical property requirements. Therefore, designing HEAs for hydrogen permeability has attracted considerable attention from scholars both domestically and internationally. However, due to the lack of phase diagrams for HEA composition design and the unpredictable but controllable composite properties resulting from the synergistic effects of multiple elements, known as the "cocktail effect," HEAs exhibit variable performance with varying composition. Consequently, the exploration of hydrogen permeability must proceed on the basis of excellent mechanical properties.

[0005] In summary, how to bring the excellent properties of high-entropy alloys into the field of hydrogen separation alloy films will inevitably become the focus of subsequent research by various scholars. Among them, the research and development of VB group high-entropy alloys will become the most meaningful and valuable materials for research and development. Summary of the Invention

[0006] The present invention aims to provide a new type of Co5Cr 15 Fe 50 Ni 22 A preparation method for Nb8 high entropy alloy materials is developed, and a new high entropy hydrogen-permeable alloy is developed at the same time. The high entropy alloy structure is composed of two phases, namely solid solution FCC and Nb-rich Laves phase, which has excellent resistance to hydrogen embrittlement and excellent mechanical properties at high temperatures.

[0007] The present invention provides an FCC structure high entropy alloy material for hydrogen permeation, wherein the alloy composition is Co5Cr 15 Fe 50 Ni 22 Nb8.

[0008] The present invention also provides a method for preparing an FCC structure high entropy alloy material for hydrogen permeation, comprising the following steps:

[0009] Step 1: Select uniform-sized metal raw material particles of Co, Cr, Fe, Ni, and Nb with a purity higher than 99%;

[0010] Step 2: Use a vacuum glove box arc melting furnace with an argon atmosphere. Place the raw materials from step 1 in the order of Co, Cr, Fe, Ni, and Nb in a water-cooled copper crucible in the arc melting furnace. Then, melt the raw materials weighed in step 1 in the water-cooled copper crucible. Operate the arc gun to strike an arc 3-5 mm away from the metal raw materials. After striking the arc, gradually increase the current to increase the arc power and raise the temperature to melt the material for initial melting. After the alloy is completely converted to liquid, maintain arc melting for 2 minutes, then turn off the current. After the alloy cools, flip it over.

[0011] Step 3: Place the alloy flipped in step 2 back into the water-cooled copper crucible. After the alloy is completely melted into liquid, maintain arc melting for 2 minutes. To avoid excessive cooling, slowly reduce the current to reduce the arc power and temperature. After the alloy cools, flip it over again.

[0012] Step 4: Repeat step 3 10 times to ensure the uniformity of the alloy composition. During the melting process, observe whether there are any unmelted metal particles inside the alloy. If there are any, repeat step 3.

[0013] Step 5: Cut the smelted metal ingot into standard samples suitable for hydrogen permeation molds using wire-cut electric discharge technology. The sample has a diameter of 16 mm and a thickness of 0.7 mm.

[0014] Step 6: First, the cut specimens were ultrasonically cleaned with propanol and anhydrous ethanol for 20 minutes to remove the oil layer and other impurities, and then the specimens were metallographically planed with sandpaper of 80-2000 Cw mesh. The specimens were then polished with a polishing machine. Diamond polishing agent and water were added during polishing. Polishing was continued until the specimens showed a mirror finish without obvious scratches.

[0015] Step 7: Place the polished sample into the vacuum deposition chamber of the equipment, place the metal Pd into the deposition tank, and evacuate the chamber to 10 -5 After leveling, vapor deposition is performed, and the thickness of the Pd layer on the surface of the prepared alloy is 250nm.

[0016] Preferably, the mass percentages of the raw metals Co, Cr, Fe, Ni and Nb in step one are: 5:13.22:47.32:21.88:12.6.

[0017] Preferably, in step 1, when selecting raw materials, the mass of each element is weighed on an analytical balance, and the total weight is 20 g.

[0018] Preferably, after the raw materials are selected in step 1, the raw materials are placed in anhydrous ethanol that can cover the raw materials and ultrasonically shaken and cleaned for 25 minutes.

[0019] Preferably, after ultrasonic vibration cleaning, the raw materials need to be dried with hot air before preparing the melt sample.

[0020] Preferably, the current of the initial melting in step 2 is gradually increased from 75A to 200A.

[0021] Preferably, when turning the cooled alloy in step 3, it is necessary to turn it 180° in the same direction each time.

[0022] The present invention has the following beneficial effects:

[0023] 1. This invention, a VB group low-Nb high-entropy alloy, produces a uniform dual-phase high-entropy alloy and a eutectic structure with hydrogen embrittlement resistance. Compared to previous studies, the FCC solid solution phase is relatively rare in hydrogen permeation films and shows almost no hydrogen permeability. However, this alloy generates hydrogen gas downstream of hydrogen permeation. Therefore, theoretically, it has better hydrogen embrittlement resistance and excellent mechanical properties.

[0024] 2. The raw materials used in the present invention are commercially available, the process is simple and the cost is low.

[0025] Therefore, compared with the prior art, the present invention broadens the possibilities of hydrogen permeable alloys in terms of organizational structure and successfully discovers high-entropy alloy materials with hydrogen permeability, achieving the effect of reducing costs and improving performance, and has broad application prospects in the field of hydrogen permeation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The Co5Cr of Example 1 of the present invention 15 Fe 50 Ni 22 Hydrogen solubility test curve of Nb8 alloy.

[0027] Figure 2 The Co5Cr of Example 1 of the present invention 15 Fe 50 Ni 22 Hydrogen permeation flow curve of Nb8 alloy.

[0028] Figure 3 The Co5Cr of Example 1 of the present invention 15 Fe 50 Ni 22 Graph of hydrogen permeability coefficient of Nb8 alloy.

[0029] Figure 4 The Co5Cr of Example 1 of the present invention 15 Fe 50 Ni 22 Micro-Vickers hardness values of Nb8 alloy and photos of the test patterns and samples.

[0030] Figure 5 The Co5Cr of Example 1 of the present invention 15 Fe 50 Ni 22 XRD pattern of Nb8 alloy.

[0031] Figure 6 The Co5Cr of Example 1 of the present invention 15 Fe 50 Ni 22 SEM image of Nb8 alloy.

[0032] Figure 7 The Co5Cr of Example 1 of the present invention 15 Fe 50 Ni 22 Element distribution of Nb8 alloy in EDS. DETAILED DESCRIPTION

[0033] In order to understand the technical content of the present invention, specific embodiments are given to illustrate the present invention, but the present invention is by no means limited thereto.

[0034] 1. Select Co, Cr, Fe, Ni, and Nb with a purity of more than 99% as raw materials, and weigh the mass of each element on an analytical balance according to the mass percentage of 5:13.22:47.32:21.88:12.6, with a total weight of 20g;

[0035] 2. Use a vacuum glove box arc melting furnace with an argon atmosphere. Place the raw materials from step 1 in the order of Co, Cr, Fe, Ni, and Nb in a water-cooled copper crucible in the arc melting furnace. Then, melt the raw materials weighed in step 1 in the water-cooled copper crucible. Operate the arc gun to strike an arc at a distance of 3 to 5 mm from the metal raw materials. After striking the arc, gradually increase the current to increase the arc power and raise the temperature to melt the material for initial melting. After the alloy is completely converted into liquid, maintain arc melting for 2 minutes, then turn off the current. After the alloy cools, turn it over. The melting current gradually increases from 75A to 200A.

[0036] 3. Place the alloy flipped in step 2 back into the water-cooled copper crucible. After the alloy is completely melted into liquid, maintain arc melting for 2 minutes. To avoid cooling too quickly, slowly reduce the current to reduce the arc power and temperature. Flip the alloy after it cools down.

[0037] 4. Repeat step 3 10 times to ensure the uniformity of the alloy composition. During the melting process, observe whether there are any unmelted metal particles inside the alloy. If there are any, repeat step 3.

[0038] 5. Cut the smelted metal ingot into standard specimens (Φ = 16 mm, d = 0.7 mm) suitable for hydrogen permeation molds using wire-cut electric discharge technology;

[0039] 6. First, clean the cut specimens with anhydrous ethanol and acetone by ultrasonic vibration, then use sandpaper with a mesh size of 80-2000Cw to coarsely grind the specimens, and then use a polishing machine to polish the specimens. Diamond polishing agent should be added during polishing. Continue polishing until the specimens show a mirror surface without obvious scratches.

[0040] 7. Place the polished sample in the vacuum evaporation chamber of the equipment and place Pd in the evaporation tank. After evacuating the vacuum, perform evaporation. The thickness of the Pd layer on the surface of the prepared alloy is 250nm.

[0041] The beneficial effects of the present invention are verified by the following examples:

[0042] Example 1

[0043] A method of preparing Co5Cr in this example 15 Fe 50 Ni 22 The method for high entropy hydrogenation of Nb8 alloy comprises the following steps:

[0044] (1) Raw material preparation: The alloy smelting raw materials used in this embodiment are all metals with a purity of more than 99% Co, Cr, Fe, Ni, and Nb with different melting points. The atomic percentage of the designed alloy is converted into mass percentage, and the total weight is determined to be 20g. The weight of each metal element is then weighed using an analytical balance. Then, each part of the metal raw materials is separately placed in a sample bag and marked for later use.

[0045] (2) Alloy melting: The alloy is melted in a vacuum glove box arc melting furnace. The weighed materials are placed in a water-cooled copper crucible in order from low to high melting points of the raw materials; under the protective atmosphere of argon, the arc gun is operated to keep a distance of 3 to 5 mm from the surface of the material, and then the arc is triggered. The current is gradually adjusted to increase the arc power, thereby increasing the melting temperature of the material and achieving initial melting; in view of the complexity of the composition of high entropy alloys and the differences in the cooling rates of their various parts, which may lead to serious composition segregation and difficulty in dissolution, in order to ensure the uniformity of the alloy composition, the alloy is turned over and remelted at least 10 times after the initial melting;

[0046] (3) Sample cutting: The metal ingots after melting and cooling and solidification are accurately processed into standard specimens that meet the requirements of the hydrogen permeation mold using the electric spark wire cutting technology. The dimensions are 16 mm in diameter and 0.7 mm in thickness (Φ = 16 mm, d = 0.7 mm);

[0047] (5) Sample polishing: To ensure the characterization effect and the effective adhesion of the catalytic layer palladium, the sample is required to have a high degree of surface flatness, so the sample needs to be polished and ground beforehand. The specific operation steps are as follows: First, the cut sample disc is ultrasonically cleaned with acetone and anhydrous ethanol; second, the sample is coarsely ground with sandpaper with a mesh size of 80 to 2000Cw; then, the sample is polished with a polishing machine and diamond polishing agent until its surface shows a mirror effect and there are no obvious scratches; finally, the sample is immersed in anhydrous ethanol and ultrasonically treated for 25 minutes, and then dried for subsequent use;

[0048] (6) The polished sample is placed in the evaporation chamber of a vacuum evaporation device, and palladium is then placed in the evaporation tank. After the vacuum extraction process is completed, the evaporation operation is performed, and the surface of the final alloy sample is covered with a palladium film with a thickness of 250 nanometers.

[0049] The following tests were performed on this embodiment:

[0050] (1) Hydrogen solubility test

[0051] Hydrogen solubility is a key parameter for analyzing the hydrogen transport properties of alloy membranes. This paper uses a Sieverts-type test instrument (a gas adsorption instrument from the Beijing Nonferrous Metals Research Institute). Samples were tested at four temperatures: 250°C, 300°C, 350°C, and 400°C. The PCT hydrogen pressure range at each temperature was 0.01-0.6 MPa. The sample was first ultrasonically cleaned and dried for 20 minutes, then cut into approximately 2mm thick blocks. The first activation was performed at 400°C and a hydrogen pressure of 7 MPa. The primary purpose was to reduce and remove oxides from the alloy surface. The sample was then removed and ground into a matte powder using a mortar. 2.5-3g of the sample was weighed and placed back into a sample tube for a second activation at the same temperature and hydrogen pressure as the first activation. This activation was intended to fully activate the alloy by absorbing hydrogen. After activation, the sample was vacuumed at 400°C for two hours to fully release the hydrogen from the alloy. Finally, the alloy material was subjected to a constant pressure and timed hydrogen dissolution test at four temperatures, and the test results were used to calculate the (Pressure-Composition-Temperature) PCT curve of the test alloy film in the pressure range of 0.01-0.6MPa using the Sieverts method.

[0052] like Figure 1 The hydrogen solubility test results show that the hydrogen solubility of the high-entropy alloy shows a gradual increase trend with increasing temperature, while the typical hydrogen dissolution platform phenomenon in traditional hydrogen-permeable alloy materials is not observed. This indicates that there is no large amount of hydride generated inside the metal. Compared with traditional Nb-based hydrogen-permeable alloy materials, the hydrogen solubility of the high-entropy alloy with this composition is lower (one order of magnitude lower). The above results show that the hydrogen solubility coefficient of this series of high-entropy alloys is small and has good resistance to hydrogen embrittlement. This may be related to the FCC crystal structure of the Nb-containing phase. The gap between Fe2Nb and Ni2Nb is much smaller than the octahedral gap of pure Nb, which reduces the solubility of hydrogen. In addition, Nb exists in the phase in the form of an intermetallic compound, rather than a Nb-based solid solution phase, which is also the reason for the low hydrogen solubility coefficient of the alloy.

[0053] (2) Hydrogen permeation test

[0054] Hydrogen permeation performance testing was conducted using a hydrogen permeation testing system based on the differential pressure method. Alloy specimens were prepared as thin sheets with a diameter of 16 mm and a diameter of 0.07 mm. A Pd film with a thickness of approximately 300 nm was vacuum-deposited on the alloy surface. Oxygen-free copper washers were clamped on both sides of the sheet and the specimen was secured and sealed with bolts. The fixture was placed in a heating apparatus and the hydrogen permeation flow rate was measured at four temperatures: 250°C, 300°C, 350°C, and 400°C. The gas line was first tested for leaks using high-purity argon. The argon was then pumped out and purged for at least five cycles, with the final vacuum cycle held for 20 minutes. After reaching the preset temperature, the hydrogen pressure was set to 1.5 MPa as the starting pressure and then increased by 0.5 MPa every 10 minutes until it reached 4 MPa. The flow rate change was recorded until all four temperature tests were completed. The hydrogen pressure was then set to 4 MPa and the temperature was 400°C for durability testing. The test was terminated after a sudden increase in the hydrogen separation alloy membrane rupture indication.

[0055]

[0056] like Figure 2 The figure shows the hydrogen permeation flow rate diagram of sample B alloy at four temperatures of 523K-673K. As shown in the above formula, J is the hydrogen permeation flow rate; L is the thickness of the metal film material; ΔP 0.5 is the difference in the square root of the hydrogen pressure. 0.5 By performing a linear fit, the slope can be used to calculate the hydrogen diffusion coefficient φ of the alloy material. The fitting result shows the square of the correlation coefficient R 2 The results are all greater than 99%, indicating that the fitting results are reliable and the data show a good linear relationship. Figure 3 As shown in Figure 2, the hydrogen permeability coefficient of high entropy alloys gradually increases with increasing temperature. However, it reaches a maximum of 7.7644×10 -10 mol H2m -1 s -1 Pa -1 / 2 The hydrogen diffusion coefficient decreases after the value is increased, which may be due to the failure of the Pd layer on the surface of the metal film material, resulting in the deterioration of the hydrogen dissociation effect and the decrease of the hydrogen diffusion coefficient.

[0057] (3) Hardness test

[0058] Mechanical properties are important indicators of alloy mechanical properties and directly affect hydrogen permeation test. To characterize and analyze the mechanical properties of the alloy film, the Vickers hardness under cast conditions was measured using an HVS-1000 microhardness tester. The instrument parameters selected during the measurement process were HV0.3 (range 100-3000) and a dwell time of 15-20s. The hardness values of the alloy samples were measured 6-7 times at different stress points, and the average value was used as the characterization hardness value.

[0059] Figure 4 Co5Cr shown 15 Fe 50 Ni 22 Microhardness values of Nb8 alloy.

[0060] (4)XRD

[0061] The sample obtained by wire cutting was carefully sanded and polished with sandpaper. The sample was then ultrasonically cleaned in anhydrous ethanol. The phase composition of the sample was analyzed using an X-ray diffractometer. The experiment used a Cu-Kα radiation source with a power of 40 kV, 40 mA, a scanning angle of 20°≤2θ≤90°, a step size of 0.02°, and a time of 0.01 s.

[0062] like Figure 5 The X-ray diffraction results show that Co5Cr 15 Fe 50 Ni 22 The phases of Nb8 alloy are mainly composed of FCC and Nb-rich Laves phase, and the Laves phase is mainly composed of Fe2Nb phase and Ni2Nb phase.

[0063] (5) SEM and EDS

[0064] Ultrasonic cleaning was used to remove contaminants from the surface of the sample obtained by wire cutting. The sample was then adhered to the SEM sample stage using conductive adhesive to ensure stable contact and a flat bottom surface. The SEM tester was tested in the backscatter imaging scanning mode.

[0065] like Figure 6 The SEM results show that the alloy structure is basically composed of two phases, which are consistent with the XRD diffraction pattern analysis results: FCC and Nb-rich Laves phase.

[0066] like Figure 7 The EDS results show the element distribution in FCC and Nb-rich Laves phase. Cr, Co, and Ni elements are evenly distributed in the two phases of the alloy. Nb in the Nb-rich Laves phase mainly exists in the form of a large amount of Ni2Nb and Fe2Nb alloy compounds.

[0067] From the above, it can be seen that the present invention successfully prepared Co5Cr 15 Fe 50 Ni 22 Nb8 high entropy hydrogen separation alloy, the alloy of this composition can ensure that it has a sufficiently high resistance to hydrogen embrittlement, has good hardness and realizes hydrogen permeation of the FCC structure alloy.

[0068] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Those skilled in the art will appreciate that various modifications and variations can be made without departing from the spirit and scope of the present invention.

Claims

1. An FCC structure high entropy alloy material for hydrogen permeation, characterized by: The alloy composition is Co5Cr 15 Fe 50 Ni 22 Nb8.

2. A method for preparing a FCC structure high entropy alloy material for hydrogen permeation, characterized in that: The following steps are involved: Step 1: Select uniform-sized metal raw material particles of Co, Cr, Fe, Ni, and Nb with a purity higher than 99%; Step 2: Using a vacuum glove box arc melting furnace with an argon atmosphere, the raw materials of step 1 are placed in a water-cooled copper crucible of the arc melting furnace in the order of Co, Cr, Fe, Ni, and Nb, and then the raw materials weighed in step 1 are melted in the water-cooled copper crucible. The arc gun is operated to strike an arc at a distance of 3 to 5 mm from the metal raw materials. After the arc is struck, the current is gradually increased to increase the arc power and increase the temperature to melt the material for initial melting. After the alloy is completely converted into liquid, the arc melting is maintained for 2 minutes, and then the current is turned off. After the alloy is cooled, it is turned over; Step 3: Place the alloy flipped in step 2 back into the water-cooled copper crucible. After the alloy is completely melted into liquid, maintain arc melting for 2 minutes. To avoid excessive cooling, slowly reduce the current to reduce the arc power and temperature. Flip the alloy after it cools down. Step 4: Repeat step 3 10 times to ensure the uniformity of the alloy composition. During the melting process, observe whether there are any unmelted metal particles inside the alloy. If there are any, repeat step 3. Step 5: Cut the smelted metal ingot into standard samples suitable for hydrogen permeation molds using wire-cut electric discharge technology. The sample has a diameter of 16 mm and a thickness of 0.7 mm. Step 6: First, the cut specimens were ultrasonically cleaned with propanol and anhydrous ethanol for 20 minutes to remove the oil layer and other impurities, and then the specimens were metallographically planed with sandpaper of 80-2000 Cw mesh. The specimens were then polished with a polishing machine. Diamond polishing agent and water were added during polishing. Polishing was continued until the specimens showed a mirror finish without obvious scratches. Step 7: Place the polished sample into the vacuum deposition chamber of the equipment, place the metal Pd into the deposition tank, and evacuate the chamber to 10 -5 After leveling, vapor deposition is performed, and the thickness of the Pd layer on the surface of the prepared alloy is 250nm.

3. The preparation method according to claim 2, characterized in that The mass percentages of the raw metals Co, Cr, Fe, Ni, and Nb in step one are: 5:13.22:47.32:21.88:12.

6.

4. The preparation method according to claim 2, characterized in that When selecting raw materials in step 1, the mass of each element is weighed on an analytical balance, and the total weight is 20 g.

5. The preparation method according to claim 2, characterized in that After the raw materials are selected in step 1, the raw materials need to be placed in anhydrous ethanol that can cover the raw materials and ultrasonically vibrate and clean for 25 minutes.

6. The preparation method according to claim 5, characterized in that After ultrasonic cleaning, the raw materials need to be dried with hot air before melting sample preparation.

7. The preparation method according to claim 2, characterized in that The current of the initial melting in step 2 is gradually increased from 75A to 200A.

8. The preparation method according to claim 2, characterized in that When turning the cooled alloy in step 3, it is important to turn it 180 degrees in the same direction each time.

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