A high-hardness high-entropy alloy, its preparation method and application

Abstract

The present invention discloses a high-hardness high-entropy alloy and its preparation method and application, which relates to the field of materials science. The high-hardness high-entropy alloy comprises Al, Co, Cr, Fe, Ni and Nb, and the microstructure of the high-hardness high-entropy alloy includes a matrix phase, an Nb-rich phase and a eutectic region; wherein, in the matrix phase, the average content of Nb is more than 20%; in the Nb-rich phase, the average content of Nb is more than 40%; in the eutectic region, the average content of Nb is less than 10%; the preparation method includes: adding metal raw materials of Al, Co, Cr, Fe, Ni and Nb with a purity greater than 99.9% into a melting furnace, evacuating the air, and filling with an inert gas; adjusting the current to 160 A - 180 A, melting and magnetic stirring; after turning the metal ingot over, evacuating the air to vacuum again and filling with an inert gas, and performing the melting step on the other side of the ingot; repeating to ensure that the total number of melting times is at least 5 times. The high-hardness high-entropy alloy of the present invention not only has a low cost, but also has extremely high hardness and good wear resistance.

Description

Technical Field

[0001] The present invention belongs to the field of materials science, and particularly relates to a high-hardness high-entropy alloy, a preparation method thereof, and an application thereof. Background Art

[0002] Hard alloys have become one of the most widely used high-hardness materials due to their high hardness, high wear resistance, good strength, heat resistance and other characteristics. Hard alloys are made of hard compounds of refractory metals (such as tungsten carbide, titanium carbide, etc.) and binder metals (such as cobalt, nickel, etc.) through powder metallurgy processes, and are widely used in cutting tools, geological and mining tools, die materials, and various wear-resistant parts, and are known as the "industrial teeth".

[0003] Hard alloys are also extremely widely used in the field of medical devices. They are not only used to manufacture artificial joints such as femoral heads and tibial plateaus to improve the success rate of surgery and the quality of life of patients, but also play a role in the manufacture of dental implants such as dental implants and dental root canals, effectively protecting teeth and periodontal tissues, while improving the aesthetics and comfort of teeth. In addition, hard alloys provide a stable and reliable cutting effect in the manufacture of surgical blades, reducing the operation difficulty and risk of doctors. In the manufacture of drug carriers such as drug coatings and drug microspheres, they can accurately deliver drugs to the lesion site, improve the curative effect and reduce adverse reactions. In the manufacture of orthopedic internal fixation devices such as steel plates and screws, hard alloys help to stably fix the fracture site, promote healing and reduce complications. In the cardiovascular field, hard alloys are used to manufacture vascular stents, especially drug-eluting stents, which can support the stenotic vascular lesion site and inhibit the occurrence of vascular restenosis, thereby improving the treatment efficiency and safety while bringing a better treatment experience and rehabilitation effect to patients.

[0004] The traditional preparation methods of hard alloys mainly include mechanical synthesis method and powder metallurgy method. The powder metallurgy method makes hard alloys by mixing WC and Co powders and through injection molding or sintering molding. Injection molding usually makes the mixture into a cylinder and then injects it into a mold, while sintering molding obtains the alloy by pressing and sintering at high temperature. The mechanical synthesis method uses mechanical milling to mix WC and Co powders and then sinters them into an alloy through high-temperature solid-phase reaction.

[0005] Regardless of the process used, it is necessary to powderize and uniformly mix the raw materials, and at the same time involves complex steps such as pressing, sintering and heat treatment. In hard alloys, the dosage of WC powder generally exceeds 50%, and the content of some hard alloys even reaches more than 90%. According to the market price, WC powder is relatively expensive, which directly increases the manufacturing cost of the alloy.

[0006] In summary, cemented carbide has a wide range of applications in the field of mechanical manufacturing and medical devices. Therefore, researching and developing new high-hardness alloys aimed at reducing material costs and simplifying production processes can not only meet the growing market demand but also contribute to the technological progress and upgrading of related industries. Summary of the Invention

[0007] An object of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide a high-hardness high-entropy alloy, a preparation method thereof, and an application thereof.

[0008] The technical solution of the present invention is as follows:

[0009] In a first aspect, the present invention provides a high-hardness high-entropy alloy.

[0010] The high-hardness high-entropy alloy includes Al, Co, Cr, Fe, Ni, and Nb. The microstructure of the high-hardness high-entropy alloy includes a matrix phase, an Nb-rich phase, and a eutectic region.

[0011] Among them, in the matrix phase, the average content of Nb is more than 20%; in the Nb-rich phase, the average content of Nb is more than 40%; in the eutectic region, the average content of Nb is less than 10% of the total amount of Nb.

[0012] Optionally, the Nb-rich phase has a polygonal shape.

[0013] Optionally, the microstructure of the high-hardness high-entropy alloy further includes a second phase. The second phase has the same crystal structure as the matrix phase, and the average size of the second phase is smaller than the average size of the matrix phase.

[0014] Optionally, the molar percentages of the components in the high-hardness high-entropy alloy are: Al 5% - 10%, Co 15% - 25%, Cr 15% - 25%, Fe 15% - 25%, Ni 5% - 14%, Nb 15% - 25%.

[0015] Optionally, the molar percentages of the components in the high-hardness high-entropy alloy are: Al 6% - 9.5%, Co 16% - 22%, Cr 16% - 22%, Fe 17% - 23%, Ni 8% - 14%, Nb 18% - 24%.

[0016] Optionally, the molar percentages of the components in the high-hardness high-entropy alloy are: Al 7% - 9%, Co 18% - 21%, Cr 18% - 21%, Fe 19% - 22%, Ni 10% - 13%, Nb 20% - 23%.

[0017] Optionally, the molar percentages of the components in the high-hardness high-entropy alloy are as follows: Al 7.8%, Co 19.58%, Cr 19.02%, Fe 20.91%, Ni 11.25; Nb 21.44%.

[0018] In a second aspect, the present invention provides a method for preparing the above high-hardness high-entropy alloy, comprising the following steps:

[0019] S1. Add metal raw materials of Al, Co, Cr, Fe, Ni, and Nb with a purity greater than 99.9% into a melting furnace, evacuate the inside of the melting furnace, and then fill the melting furnace with an inert gas.

[0020] S2. Adjust the current of the melting furnace to 160 A - 180 A, turn on the arc gun to melt the metal raw materials of Al, Co, Cr, Fe, Ni, and Nb. After all the metals are completely melted, turn on the magnetic stirrer, maintain the magnetic stirrer for 50 - 150 s, and then turn off the magnetic stirrer and the arc gun in sequence.

[0021] S3. After turning over the metal ingot obtained in step S2 in the melting furnace, evacuate it to vacuum again, and then fill it with an inert gas. Then, perform the melting step of step S2 on the other side of the ingot.

[0022] Repeat step S3 at least 3 times to ensure that the total number of melting times is at least 5 times.

[0023] Optionally, in S1, the inside of the melting furnace is evacuated to 0.5×10 -3 ~1.5×10 -3 Pa, and then Ar gas is filled into the melting furnace until the vacuum degree inside the melting furnace is less than 5 Pa.

[0024] Optionally, the preparation method specifically comprises the following steps:

[0025] S1. Take metal raw materials of Al, Co, Cr, Fe, Ni, and Nb with a purity greater than 99.9%, use sandpaper to polish off the oxide scale of the metal raw materials of Al, Co, Cr, Fe, Ni, and Nb, put them into absolute ethanol, ultrasonically clean for 2 min - 5 min, dry, and store them in vacuum.

[0026] Add a pure metal titanium ingot into one crucible of the melting furnace, add the metal raw materials of Al, Co, Cr, Fe, Ni, and Nb into another crucible of the melting furnace, evacuate the inside of the melting furnace to 0.5×10 -3 ~1.5×10 -3 Pa, and then fill the melting furnace with an inert gas Ar until the vacuum degree is less than 5 Pa.

[0027] S2. Adjust the current of the smelting furnace to 160A - 180A, turn on the arc gun to first smelt the pure titanium ingot; then smelt the metal raw materials of Al, Co, Cr, Fe, Ni, and Nb. After all the metals are completely melted, turn on the magnetic stirring, maintain the magnetic stirring for 50 - 150s, and then turn off the magnetic stirring and the arc gun in sequence;

[0028] S3. After turning over the metal ingot obtained in step S2 in the smelting furnace, evacuate to vacuum again, then fill with inert gas, and then perform the smelting step of step S2 on the other side of the ingot;

[0029] Repeat step S3 at least 3 more times to ensure that the total number of smelting times is at least 5 times.

[0030] Thirdly, the present invention provides an application of a high - hardness high - entropy alloy in the preparation of medical materials.

[0031] Optionally, the medical material is at least one of dental implants, vascular stents, intestinal stents, tracheal stents, urethral stents, and anastomosis nails.

[0032] Optionally, the dental implant includes a dental implant body and a dental root canal, and the vascular stent includes a drug - eluting stent.

[0033] The present invention has at least one of the following beneficial effects:

[0034] 1. The high - hardness high - entropy alloy of the present invention is composed of Al, Co, Cr, Fe, Ni, and Nb. The microstructure of the high - hardness high - entropy alloy includes a matrix phase, an Nb - rich phase, and a eutectic region; compared with the prior art, the high - hardness high - entropy alloy of the present invention has excellent properties, with a Vickers hardness value above 1000, having extremely high hardness; moreover, the existing cemented carbides on the market usually undergo multiple heat treatment processes after sintering, while the high - hardness high - entropy alloy of the present invention is smelted, and the process flow is simpler. At the same time, the hardness of the high - hardness high - entropy alloy of the present invention has exceeded the hardness of the commonly used metal materials in the prior art and the materials prepared with similar or the same elements.

[0035] 2. Compared with the prior art, the high - hardness high - entropy alloy of the present invention forms A2 and B2 phases in the eutectic region, which improves the plastic deformation ability of the material compared with the laves phase formed in the eutectic region in the existing literature.

[0036] 3. The high - hardness high - entropy alloy of the present invention has a low friction coefficient and a stable friction process, which can reduce the wear on the material surface during use and extend the service life of mechanical components. At the same time, it can reduce the vibration and noise caused by friction and improve the stability and reliability of the overall machinery.

[0037] 4. The high-hardness high-entropy alloy oxide layer of the present invention is mainly formed at the matrix phase and adheres closely to the matrix without cracks or spalling, which effectively hinders corrosive substances from reaching the surface or interior of the material to a certain extent, thereby improving the corrosion resistance of the material. Description of the Drawings

[0038] Figure 1 Original data of four points during the Vickers hardness test of the high-hardness high-entropy alloy prepared in Example 1.

[0039] Figure 2 Optical microscope image, scanning electron microscope image and corresponding EDS energy spectrum diagram of the high-hardness high-entropy alloy prepared in Example 1; among them, (a) is the optical microscope image, (b) is the scanning electron microscope image and the corresponding EDS energy spectrum diagram, and (c) is the partial enlarged view.

[0040] Figure 3 XRD diffraction peak spectrum diagram of the high-hardness high-entropy alloy prepared in Example 1.

[0041] Figure 4 Energy spectrum diagram of the matrix phase of the high-hardness high-entropy alloy prepared in Example 1.

[0042] Figure 5 Energy spectrum diagram of the Nb-rich phase of the high-hardness high-entropy alloy prepared in Example 1.

[0043] Figure 6 , Figure 7 Energy spectrum diagram of the eutectic region of the high-hardness high-entropy alloy prepared in Example 1.

[0044] Figure 8 Energy spectrum diagram of the eutectic region of the high-hardness high-entropy alloy prepared in Example 1.

[0045] Figure 9 Scanning electron microscope images of AlCoCrFeNi with different contents of Nb element added in Comparative Example 3, Comparative Examples 5-7; among them, (a) AlCoCrFeNiNb0.2, (b) AlCoCrFeNiNb0.3, (c) AlCoCrFeNiNb0.5, (d) AlCoCrFeNiNb0.75.

[0046] Figure 10 XRD diagrams of AlCoCrFeNi with different contents of Nb element added in Comparative Examples 1-2, Comparative Example 4, Comparative Examples 6-7.

[0047] Figure 11 XRD pattern of the eutectic region of the high-hardness high-entropy alloy prepared in Example 1.

[0048] Figure 12is a friction coefficient curve graph; among them, (a) is the high-hardness high-entropy alloy prepared in Example 1, and (b) are the high-hardness high-entropy alloys prepared in Comparative Examples 1-3 and Comparative Examples 5-7.

[0049] Figure 13 is the friction coefficient curve of the prior art with similar element types to the present application.

[0050] Figure 14 is the surface of the high-entropy alloy after oxidation; among them, (a) is the oxidized surface of the high-hardness high-entropy alloy prepared in Example 1, and (b) is the oxidized surface of the AlCoCrFeNi high-entropy alloy prepared in Comparative Example 1. Specific Embodiments

[0051] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0052] Example 1

[0053] This example provides a preparation method of a high-hardness high-entropy alloy, including the following steps:

[0054] (1) Weigh metal raw materials of aluminum (Al), cobalt (Co), chromium (Cr), iron (Fe), nickel (Ni), and niobium (Nb) with a purity greater than 99.9%. After using 240# sandpaper to polish off the oxide scale, weigh the required weight using an electronic balance with a precision of one ten-thousandth. Among them, the molar ratio of the metal raw materials of aluminum (Al), cobalt (Co), chromium (Cr), iron (Fe), nickel (Ni), and niobium (Nb) is 7.8:19.58:19.02:20.91:11.25:21.44. Then put the weighed raw materials into a beaker, pour in anhydrous ethanol, vibrate and clean in an ultrasonic cleaner for 3 minutes to remove impurities such as abrasives and grease on the surface of the raw materials. Finally, use a hair dryer to dry the samples, put them into a vacuum bag, and evacuate and store them for subsequent melting.

[0055] (2) Preparation work: Open the air release valve, wait for the reading of the furnace pressure gauge to become zero, and then press the green "up" button to open the furnace door. Then use a clean non-woven fabric dipped in anhydrous alcohol to clean the inside of the vacuum chamber and the crucible. Then put a pure metal titanium ingot into the middle crucible to absorb the oxygen in the furnace. Put the pretreated raw materials into the remaining crucibles in ascending order of melting point, lower the furnace lid, and prepare to evacuate.

[0056] (3) Evacuate: Check whether all valves and power switches on the vacuum chamber are closed. After the inspection, start the mechanical pump, open the vacuum gauge and the angle valve to start evacuating. When the vacuum degree reaches 1.0×10 -3After reaching [[Pa]], close the gate valve and the vacuum gauge, then open the inflation valve to fill with inert gas Ar until the reading of the pressure gauge is less than [[5]] Pa, and finally close the inflation valve.

[0057] (4)Melting: During melting, adjust the electrode position above the sample to be melted, press the arc starting button. After successful arcing, adjust the current to 160A - 180A for alloy melting. First, add titanium ingots into one crucible in the melting furnace to remove the residual oxygen inside the melting furnace by melting the Ti ingots. After the titanium ingots cool down, add the aluminum (Al), cobalt (Co), chromium (Cr), iron (Fe), nickel (Ni), and niobium (Nb) metal raw materials in step (1) into another crucible in the melting furnace to melt the sample. After all the metal raw materials are completely melted, turn on the magnetic stirring switch and keep magnetic stirring for 50 - 150 s, then turn off the magnetic stirring and the arc gun in sequence. After turning over the obtained metal ingot in the melting furnace, evacuate to vacuum again, then fill with inert gas, and then perform the same melting steps on the other side of the ingot; repeat melting multiple times to ensure that the total number of melting times is at least 5 times.

[0058] (5)Sampling: After waiting for the alloy to cool down after melting, open the deflation valve and the furnace door, then take out the sample to obtain a high - hardness high - entropy alloy; clean the vacuum furnace, evacuate the vacuum furnace after cleaning, and finally turn off each power supply and the gate, and turn off the power.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that niobium (Nb) is not added, and the molar ratio of Al, Co, Cr, Fe, and Ni elements is 1:1:1:1:1, that is, the alloy is AlCoCrFeNi, and the others are the same as Example 1.

[0061] Comparative Example 2

[0062] The difference from Example 1 is that the molar ratio of Al, Co, Cr, Fe, Ni, and Nb elements is changed to 1:1:1:1:1:0.1, that is, the alloy is AlCoCrFeNiNb0.1, and the others are the same as Example 1.

[0063] Comparative Example 3

[0064] The difference from Example 1 is that the molar ratio of Al, Co, Cr, Fe, Ni, and Nb elements is changed to 1:1:1:1:1:0.2, that is, the alloy is AlCoCrFeNiNb0.2, and the others are the same as Example 1.

[0065] Comparative Example 4

[0066] The difference from Example 1 is that the molar ratio of Al, Co, Cr, Fe, Ni, and Nb elements is changed to 1:1:1:1:1:0.25, that is, the alloy is AlCoCrFeNiNb0.25, and the others are the same as in Example 1.

[0067] Comparative Example 5

[0068] The difference from Example 1 is that the molar ratio of Al, Co, Cr, Fe, Ni, and Nb elements is changed to 1:1:1:1:1:0.3, that is, the alloy is AlCoCrFeNiNb0.3, and the others are the same as in Example 1.

[0069] Comparative Example 6

[0070] The difference from Example 1 is that the molar ratio of Al, Co, Cr, Fe, Ni, and Nb elements is changed to 1:1:1:1:1:0.5, that is, the alloy is AlCoCrFeNiNb0.5, and the others are the same as in Example 1.

[0071] Comparative Example 7

[0072] The difference from Example 1 is that the molar ratio of Al, Co, Cr, Fe, Ni, and Nb elements is changed to 1:1:1:1:1:0.75, that is, the alloy is AlCoCrFeNiNb0.75, and the others are the same as in Example 1.

[0073] The properties of the high-hardness high-entropy alloys prepared in Example 1 and Comparative Examples 1-7 were characterized, and the results are as follows:

[0074] Table 1 shows the Vickers hardness test results of the high-hardness high-entropy alloy in Example 1 of the present invention. To avoid the contingency of the experiment, multiple points were selected at different positions of the material for testing in the present invention. It can be seen from Table 1 that the Vickers hardness values of the high-hardness high-entropy alloy material in Example 1 of the present invention are all above 1000 HV, and the average hardness is 1074.45 HV. It has extremely high hardness. To fully disclose the present invention, Figure 1 The original data of 4 points during the Vickers hardness test of the high-hardness high-entropy alloy in Example 1 of the present application are shown.

[0075] Table 1

[0076]

[0077] To more intuitively reflect the excellent performance of the high-hardness high-entropy alloy of the present application, the applicant summarized the Vickers hardness of related materials in the prior art in Table 2 by referring to relevant literature. Specifically, it includes: the hardness of common cemented carbides / the hardness of common metal materials / the hardness of materials containing the same elements as the present invention / the hardness of materials containing similar elements to the present invention and the hardness of high-entropy alloys in the as-cast state in relevant literature.

[0078] Table 2

[0079]

[0080] Among them, the data of common cemented carbides in Table 2 are from pages 435 and 437 of the eighth edition of the "Hardware Tools Handbook"; the hardness of common metal materials is from the website (https: / / it.sohu.com / a / 791858574_121769585); the hardness data of materials containing the same elements as the present invention and materials with elements similar to the present invention are all from relevant papers, which are not specifically listed here. It should be noted that in the existing relevant papers, in the as-cast state, no metal with a hardness higher than this application has been found. The hardness of high-entropy alloys in the as-cast state in the relevant literature is from page 151 of the book "Advanced High-Entropy Alloy Technology" edited by Zhang Yong. It should be noted that in order to ensure the accuracy and repeatability of the data, the Vickers hardness test mentioned in the present invention adopts the international standard test method, and the equipment is a micro-Vickers hardness tester. During the test process, we strictly follow the standard operating procedures to ensure the consistency of the test conditions for easy comparison with the hardness of the materials in Table 2.

[0081] As can be seen from Table 2, the high-hardness high-entropy alloy material prepared in Example 1 of this application has exceeded the hardness of common metal materials and materials prepared with similar or the same elements in the prior art in terms of hardness. For the cemented carbide materials actually used, the materials of this application also far exceed some models.

[0082] It should be noted that the existing cemented carbides on the market usually undergo sintering treatment, which is a key manufacturing process that can tightly bind powder particles, thereby endowing the cemented carbide with the required mechanical properties and wear resistance. The sintered cemented carbide contains almost no pores, and this characteristic is crucial for maintaining its performance under working conditions with high stress. In order to further improve the performance of cemented carbides, the prior art also undergoes a series of heat treatment processes such as annealing, quenching, and tempering. These processes help to adjust the microstructure of the alloy, optimize its hardness, strength, and wear resistance, and ensure the reliability and durability of cemented carbides in applications such as metal cutting, oil drilling, and die manufacturing. In contrast, the high-hardness high-entropy alloy of Example 1 of the present invention is cast, with a simple process flow, but its hardness is higher than that of the prior art, which fully demonstrates the creativity of the material elements and molar percentage design of this application.

[0083] Please refer to Figure 2 Figure (a) is the optical microscope image of the high-hardness high-entropy alloy of the present invention. As can be seen from Figure 2 Figure (a), the dendrite region of the high-entropy alloy prepared in Example 1 of the present invention mainly contains two phases, the α phase and the β phase, and the interdendritic region is a nanophase that forms a eutectic structure. Figure 2(b) Scanning electron microscope image and corresponding EDS spectrum of the high-hardness high-entropy alloy prepared in Example 1 of the present invention, Figure 2 (c) is a partial enlarged view to illustrate the microstructure morphology of the eutectic region. From Figure 2 (b), it can be seen that the β phase presents a polygonal shape. In the prior art, this shape of the phase only appears in materials rich in tungsten carbide and in the sintered state. Generally, the cross-sectional shape of the grains of the material consists of spline curves. In addition, according to the surface scanning results, the β phase is rich in Nb element, which plays a role in precipitation strengthening of the material.

[0084] Subsequently, a nanoindentation test was carried out on the two phases using a nanoindentation constant device, and the results are shown in Table 3. It can be seen that the average hardness of the α phase is as high as 1166.75 HV, while the hardness of the β phase is as high as 1861 HV. This further shows that the high-entropy alloy prepared in Example 1 of the present application has extremely high hardness.

[0085] Table 3

[0086]

[0087] In order to further elaborate on the phase composition of the high-hardness high-entropy alloy of the present application, a sample of the high-hardness high-entropy alloy prepared in Example 1 of the present application was taken, polished, and then subjected to XRD testing. And the spectrum was analyzed using Jade software, and the results are as Figure 3 shown. From Figure 3 it can be seen that. The crystal structures of the phases most likely to exist in the material of the present application are the same as those of Ni, Fe3Co, Fe11Co5, Fe13Co3 (it should be noted that for the Jade software, when the figure of merit is greater than 10, this crystal structure is generally not considered to exist. Therefore, the crystal structures of Co and Cr10Al16 are not considered in the material of the present application).

[0088] Subsequently, point scanning was carried out on the matrix phase ( Figure 4 ), Nb-rich phase ( Figure 5 ), eutectic region ( Figure 6 and Figure 7 ) of the material of the present application. The results show that the matrix phase and the Nb-rich phase contain a relatively large amount of Nb. However Figure 4The XRD results did not detect the crystal structure of the Nb-containing phase. Therefore, it can be reasonably speculated that it may be because the lattice distortions of these two phases are relatively large, resulting in the diffraction peaks not being able to align with those of the standard card. Severe lattice distortion is beneficial to improving the hardness of the material, which may also be one of the reasons for the extremely high hardness of this material. Since in the existing literature (doi:10.1016 / j.msea.2011.10.110), laves phases appeared when different contents of Nb (0.1 - 0.75) were added to AlCoCrFeNi, the matrix phase is very likely to be the laves phase structure with relatively large lattice distortion.

[0089] After point scanning the two phases in the eutectic region of this application, it was found that ( Figure 6 、 Figure 7 : Due to the relatively small size of the nano-phase in the eutectic region, in order to exclude the errors caused by point scanning, two areas of each phase were scanned), the contents of the three elements Fe, Cr, and Ni are approximately equal to three times that of the Co element. And the three elements Fe, Cr, and Ni have similar properties and similar electronegativities. Combining with the XRD results, the diffraction peak of Fe3Co (BCC) is the phase structure of the eutectic region, which is expected to be the A2 and B2 eutectics. At the same time, the Nb content of the two phases in the eutectic region is only about 5%, and it can be considered that the Nb element in the eutectic region is solid-solved into the crystal structure of the eutectic region phase.

[0090] Further exploring the eutectic region, the energy spectrometer was used to perform area scanning on the eutectic region as shown in Figure 8 . It can be clearly seen that the eutectic structure hardly contains the Nb element, but contains relatively more Fe / Co / Cr / Ni elements. That is to say, the eutectic structure does not contain the laves phase structure. This is completely different from the phase structure formed by the high-entropy alloy of the AlCoCrFeNiNb series in the prior art. Figure 9 shows the addition of different contents of Nb elements to AlCoCrFeNi, Figure 10 and the corresponding XRD patterns. Combining with the XRD, its microstructure changes from hypoeutectic to hypereutectic. However, regardless of the Nb content, the eutectic region is composed of bcc and laves phases. This is completely different from the element ratio and the formed phase structure of the eutectic region of this application. Those skilled in the art know that the Laves phase is a high-hardness phase with very low plasticity. For this application, the matrix phase provides high hardness, while the eutectic region does not contain the laves phase, which can provide a certain plastic deformation ability to the material.

[0091] Through comprehensive analysis of the XRD and point scanning / area scanning results, it can be summarized that: severe lattice distortions occurred in the matrix phase and the Nb-rich phase, which hindered the movement of dislocations in the material, thereby strengthening the hardness of the material. In addition, the A2 and B2 phases formed in the eutectic region improve the plastic deformation ability of the material compared with the laves phase formed in the eutectic region in the existing literature.

[0092] Upon further observation of the microstructure, it was found that there was also a phase in the eutectic region ( Figure 11 as shown, namely the second phase). Point scanning of it revealed that the elemental ratio was similar to that of the matrix phase. Therefore, it can be speculated that it has the same crystal structure as the matrix phase, but is smaller in size than the matrix phase. These second-phase particles can increase the yield strength of the material by hindering the movement of dislocations.

[0093] Friction experiments were further conducted on this application to characterize the properties of the materials of this application. In this experiment, Si3N4 was selected as the counter-material, and the wear test was carried out at room temperature for 30 minutes with a motor frequency of 40 Hz, a load of 500 g, and a wear radius of 5 mm. The mass of the specimen before the experiment was 6.1872 g, and the mass after the experiment was 6.1848 g. The shape of the specimen was a cuboid with dimensions of 15*20*2.6 mm.

[0094] The wear rate was calculated using the formula: W = V / (S×L), where W is the wear rate, V is the wear volume, S is the sliding distance, and L is the applied load. After calculation, the wear rate of the materials of this application was 2.86967*10 -5 mm 3 / (N*m), indicating an extremely low wear rate.

[0095] The friction coefficient curve of the high-hardness high-entropy alloy of this application as shown in Figure 12 (a) was obtained. Figure 12 (b) shows the friction coefficient curves of the materials with the same elements in the prior art (Comparative Examples 1-3, Comparative Examples 5-7). By comparison, it can be seen that the friction coefficient of the materials of this application is quite low and the whole process is quite stable. This enables the material to reduce the wear on the surface of the material during use and extend the service life of mechanical components. At the same time, it can reduce the vibration and noise caused by friction and improve the stability and reliability of the overall machinery.

[0096] Figure 13 The friction coefficient curves of materials with similar elemental types to those prepared in Example 1 of this application in the prior art are shown. It can be clearly seen from Figure 13 that there are significant differences between the materials in the prior art and this application in terms of the numerical value of the friction coefficient and the stability of the overall friction fluctuation. Specifically, the materials prepared in this application show obvious advantages in friction performance, not only having a low friction coefficient, but also having smaller friction fluctuations and being more stable during long-term use. This indicates that the materials of this application have more excellent tribological properties and can better meet the high requirements of high-hardness alloys in practical applications.

[0097] It should be noted that the higher the hardness of the material, the better its wear resistance. This is because hardness is the ability of the material to resist the penetration of foreign objects into its surface, while wear resistance refers to the ability of the material to resist wear. When a hard object slides or impacts on the surface of the material, the material with higher hardness is more capable of resisting this mechanical force, thereby reducing the wear of the material. However, wear resistance does not solely depend on hardness and is also affected by many factors.

[0098] For example, materials that are too hard and brittle may be prone to fracture when subjected to impact, or spalling may occur on the material surface. After spalling, the material further wears against the base material, resulting in poor wear resistance of the material. However, due to the eutectic region of the material in this application being the BCC phase (A2 and B2 phases), compared with the laves phase in the eutectic region of the prior art, it has good deformation ability and can maintain surface integrity while absorbing impact energy, thereby improving wear resistance.

[0099] The material was further subjected to high-temperature oxidation for 100 hours, and the results are as Figure 14 shown in (a). The results indicate that the oxide layer of the high-hardness high-entropy alloy in this application is mainly formed at the matrix phase and adheres tightly to the matrix without cracks or spalling. This effectively hinders corrosive substances from reaching the surface or interior of the material to a certain extent, thereby improving the corrosion resistance of the material. In particular, it should be noted that the antioxidant performance at the inter-dendrite regions on the material surface is good, and almost no obvious oxide layer is generated. Using an energy spectrometer equipped with a scanning electron microscope to perform a surface scan on the material surface ( Figure 14 at the upper right corner of (a)), it is further verified that the oxide is almost only formed at the matrix phase. From the surface scan results, it can be seen that the oxygen content in the inter-dendrite region shows a dark color (close to black), indicating that there are very few oxides in the inter-dendrite region compared to the dendrite region.

[0100] In a system with cations as the migrating substances, metal atoms diffuse outward through the oxide film and the metal interface in the form of cations and electrons. To maintain adhesion to the alloy matrix, the oxide film must undergo relaxation. However, at the corners of the sample, the geometric shape of the oxide film is fixed, and relaxation cannot occur simultaneously in multiple directions. Therefore, due to the ineffective release of thermal stress, the oxide film eventually ruptures. However, in this application, since the inter-dendrite oxide layer is very thin, there is space for relaxation in the dendrite region, and thus, the oxide layer does not spall.

[0101] Figure 14(b) shows the surface of the AlCoCrFeNi high-entropy alloy, which is the material of Comparative Example 1, after oxidation. It can be seen that after 100 hours of high-temperature oxidation, the surface oxide scale of this material cracked and peeled off severely. This is mainly because the AlCoCrFeNi high-entropy alloy is a single-phase BCC, and the formed oxide film is a layer distributed on the metal surface. Therefore, at the corners of the sample, the geometry of the oxide film is fixed, and relaxation cannot occur simultaneously in multiple directions. During the cyclic oxidation process, the thermal stress cannot be released, resulting in the peeling of the oxide film, which further demonstrates the advantage of the material of this application in terms of oxidation resistance.

[0102] For the application prospect of the material, cost is also an important part to be considered. Therefore, based on the authoritative metal consulting portal - "Shanghai Nonferrous Network", this application queried the costs of relevant materials recently and calculated them at the price of one kilogram of raw materials, as shown in Table 4 specifically. It can be calculated from Table 4 that the price of the high-hardness high-entropy alloy of this application is 287.91 yuan per kilogram. Since the WC mass fraction in cemented carbide varies, this application calculates according to the raw material content that can prepare the common cemented carbides in Table 2. The "Practical Hardware Tools Handbook" also indicates that the WC content is 70 - 90%, and the remaining content is calculated with the commonly used Co binder in cemented carbide. It is calculated that the price of traditional WC-based cemented carbide is 300.8 - 321.6 yuan per kilogram. Therefore, the price per kilogram of the high-hardness high-entropy alloy of this application is about 12.89 - 33.69 yuan lower than that of traditional hard alloys, so there is an obvious advantage in raw material cost.

[0103] Table 4

[0104]

[0105] In summary, compared with the prior art, the high-hardness high-entropy alloy of this application has the following advantages:

[0106] 1. The high-hardness high-entropy alloy of this application has been tested, and the results show that it has extremely high hardness. Compared with common metals, high-entropy alloys containing the same elements, and high-entropy alloys with similar compositions, it has outstanding hardness advantages. Compared with the cemented carbides currently in use in the prior art, the high-entropy alloy of this application is also superior to many models. Although it is slightly lower than some models of cemented carbides, however, the high-entropy alloy of this application is only in the as-cast state, with a simple process and no post-treatment. While the currently used cemented carbides are in the sintered state and will inevitably go through a series of post-treatment processes to improve performance. Therefore, the high-entropy alloy of this application has outstanding characteristics and significant progress in terms of hardness.

[0107] 2. The niobium-rich phase hinders the movement of dislocations and plays a role in precipitation strengthening of the material. In addition, through nano-indentation constant testing, it is found that its hardness is above 1500 HV, which is rarely reported in relevant literature.

[0108] 3. The matrix phase and the Nb-rich phase have strong lattice distortions, which hinder the movement of dislocations in the material, thereby strengthening the hardness of the material. In addition, the A2 and B2 phases formed in the eutectic region provide a certain plastic deformation ability to the material compared with the laves phase formed in the eutectic region in the existing literature.

[0109] 4. The dispersed second-phase particles in the eutectic region can improve the yield strength of the material by hindering the movement of dislocations.

[0110] 5. The friction coefficient of the material of this application is quite low, and the whole process is quite stable. This enables the material to reduce the wear on the material surface during use and extend the service life of mechanical components. At the same time, it can reduce the vibration and noise caused by friction and improve the stability and reliability of the overall machinery.

[0111] 6. The oxide layer of the high-hardness high-entropy alloy of this application is mainly formed at the matrix phase and is closely attached to the matrix, without cracks or spalling. ( Figure 14 a) This effectively hinders corrosive substances from reaching the surface or interior of the material to a certain extent, thereby improving the corrosion resistance of the material. In this application, the inter-dendritic region gives the dendritic region relaxation space, enabling the material to release thermal stress during the oxidation process. Therefore, the oxide layer does not spall. Compared with the cemented carbide of the prior art, at high temperatures, the carbide particles in the cemented carbide are not easily melted or decomposed, but an oxide film will form on its surface, and this oxide film will reduce the oxidation resistance of the alloy.

[0112] 7. After price comparison on the authoritative metal inquiry website, the price per kilogram of the high-hardness high-entropy alloy of this application is about 12.89 - 33.69 yuan lower than that of the traditional hardness alloy. Therefore, there is an obvious raw material cost advantage.

[0113] As described above, it is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A high-hardness high-entropy alloy, characterized in that the high-hardness high-entropy alloy comprises Al, Co, Cr, Fe, Ni and Nb, and the molar percentages of the components in the high-hardness high-entropy alloy are as follows: Al 6% - 9.5%, Co 16% - 22%, Cr 16% - 22%, Fe 17% - 23%, Ni 8% - 14%, Nb 18% - 24%; the microstructure of the high-hardness high-entropy alloy comprises a matrix phase, an Nb-rich phase and a eutectic region; wherein, in the matrix phase, the average content of Nb is more than 20%; in the Nb-rich phase, the average content of Nb is more than 40%; in the eutectic region, the average content of Nb is less than 10%.

2. The high-hardness high-entropy alloy according to claim 1, characterized in that the Nb-rich phase is in a polygonal shape.

3. The high-hardness high-entropy alloy according to claim 1, characterized in that, the molar percentages of the components in the high-hardness high-entropy alloy are as follows: Al 7% - 9%, Co 18% - 21%, Cr 18% - 21%, Fe 19% - 22%, Ni 10% - 13%, Nb 20% - 23%.

4. The high-hardness high-entropy alloy according to claim 1, wherein the molar percentages of the components in the high-hardness high-entropy alloy are as follows: Al 7.8%, Co 19.58%, Cr 19.02%, Fe 20.91%, Ni 11.25; Nb 21.44%.

5. A method for preparing the high-hardness high-entropy alloy according to any one of claims 1 to 4, characterized in that, comprising the following steps: S1. Add metal raw materials of Al, Co, Cr, Fe, Ni and Nb with a purity greater than 99.9% into a melting furnace, evacuate the inside of the melting furnace, and then fill the inside of the melting furnace with an inert gas; S2. Adjust the current of the melting furnace to 160A - 180A, turn on the arc gun to melt the metal raw materials of Al, Co, Cr, Fe, Ni and Nb. After all the metals are completely melted, turn on the magnetic stirrer, keep the magnetic stirrer running for 50 - 150s, and then turn off the magnetic stirrer and the arc gun in sequence; S3. After turning over the metal ingot obtained in step S2 in the melting furnace, evacuate it to vacuum again, and then fill it with an inert gas, and then perform the melting step of step S2 on the other side of the ingot; Repeat step S3 at least 3 times to ensure that the total number of melting times is at least 5 times.

6. The preparation method according to claim 5, characterized in that, In S1, the melting furnace is evacuated to 0.5×10 -3 ~1.5×10 -3 Pa, and then Ar gas is filled into the melting furnace until the vacuum degree in the melting furnace is less than 5 Pa.

7. Use of a high-hardness high-entropy alloy according to any one of claims 1 - 4 in the preparation of medical materials.

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