High-hardness high-entropy alloy and preparation method and application thereof

Abstract

The invention discloses a high-hardness high-entropy alloy and a preparation method and application thereof, and relates to the field of material 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 comprises a matrix phase, a 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 40% or above; in the eutectic region, the average content of Nb is less than 10%; the preparation method comprises the steps that Al, Co, Cr, Fe, Ni and Nb metal raw materials with the purity larger than 99.9% are added into a smelting furnace, vacuumizing is conducted, and inert gas is filled; the current is adjusted to 160-180 A, smelting is conducted, and magnetic stirring is conducted; after the metal cast ingot is turned over, the metal cast ingot is vacuumized and filled with inert gas again, and the other side of the cast ingot is smelted; and repeating, and ensuring that the total smelting frequency is at least five. The high-hardness high-entropy alloy disclosed by the invention is low in cost, and has extremely high hardness and good wear resistance.

Description

Technical Field

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

[0002] Cemented carbide has become one of the most widely used high-hardness materials due to its high hardness, high wear resistance, good strength and heat resistance. Cemented carbide is made of hard compounds of refractory metals (such as tungsten carbide, titanium carbide, etc.) and bonding metals (such as cobalt, nickel, etc.) through powder metallurgy. It is widely used in cutting tools, geological mining tools, mold materials and various wear-resistant parts, and is known as the "industrial teeth".

[0003] Cemented carbide is also widely used in the field of medical devices. It is not only used to manufacture artificial joints such as femoral heads and tibial platforms to improve the success rate of surgery and the quality of life of patients, but also plays a role in the manufacture of dental implants such as dental implants and root canals, effectively protecting teeth and periodontal tissues while improving the aesthetics and comfort of teeth. In addition, cemented carbide provides a stable and reliable cutting effect in the manufacture of surgical blades, reducing the difficulty and risk of doctors' operations, and in the manufacture of drug carriers such as drug coatings and drug microspheres, they can accurately deliver drugs to the lesion site, improve efficacy and reduce adverse reactions. In the manufacture of orthopedic internal fixation devices such as steel plates and screws, cemented carbide helps to stabilize and fix fracture sites, promote healing and reduce complications. In the cardiovascular field, cemented carbide is used to manufacture vascular stents, especially drug-eluting stents, which can support narrow vascular lesions and inhibit the occurrence of vascular restenosis, thereby improving treatment efficiency and safety while bringing patients a better treatment experience and rehabilitation effect.

[0004] Traditional methods for preparing cemented carbide mainly include mechanical synthesis and powder metallurgy. Powder metallurgy is to make cemented carbide by mixing WC and Co powders and then injecting or sintering them. Injection molding is usually to make the mixture into a cylinder and then inject it into a mold, while sintering molding is to press and sinter at high temperature to obtain an alloy. Mechanical synthesis is to mix WC and Co powders by mechanical grinding, and then sinter them into an alloy after high-temperature solid-phase reaction.

[0005] Regardless of the process used, the raw materials need to be powdered and evenly mixed, and complex steps such as pressing, sintering and heat treatment are involved. In cemented carbide, the amount of WC powder generally exceeds 50%, and the content of some cemented carbides is even as high as 90%. According to market prices, the cost of WC powder is relatively high, which directly increases the manufacturing cost of the alloy.

[0006] In short, cemented carbide has a wide range of applications in the fields of mechanical manufacturing and medical devices. Therefore, researching and developing new high-hardness alloys aims to reduce material costs and simplify production processes, which can not only meet the market's growth needs, but also help promote technological progress and upgrading of related industries. Summary of the invention

[0007] The purpose 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 and a preparation method and application thereof.

[0008] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a high-hardness high-entropy alloy. The high-hardness high-entropy alloy comprises Al, Co, Cr, Fe, Ni and Nb, and the microstructure of the high-hardness high-entropy alloy comprises a matrix phase, a Nb-rich phase and a eutectic region; 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 Nb amount.

[0009] Optionally, the Nb-rich phase is in a polygonal shape.

[0010] 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.

[0011] Optionally, the molar percentage of each component in the high-hardness high-entropy alloy is: Al 5%~10%, Co 15%~25%, Cr 15%~25%, Fe 15%~25%, Ni 5%~14%, and Nb 15%~25%.

[0012] Optionally, the molar percentage of each component in the high-hardness high-entropy alloy is: Al 6%~9.5%, Co 16%~22%, Cr 16%~22%, Fe 17%~23%, Ni 8%~14%, and Nb 18%~24%.

[0013] Optionally, the molar percentage of each component in the high-hardness high-entropy alloy is: Al 7%~9%, Co 18%~21%, Cr 18%~21%, Fe 19%~22%, Ni 10%~13%, and Nb 20%~23%.

[0014] Optionally, the molar percentage of each component in the high-hardness high-entropy alloy is: Al 7.8%, Co 19.58%, Cr 19.02%, Fe 20.91%, Ni 11.25; Nb 21.44%.

[0015] In a second aspect, the present invention provides a method for preparing the above-mentioned high hardness high entropy alloy, comprising the following steps: S1. Adding Al, Co, Cr, Fe, Ni and Nb metal raw materials with a purity greater than 99.9% into a smelting furnace, evacuating the smelting furnace, and then filling the smelting furnace with inert gas; S2. Adjust the current of the smelting furnace to 160A-180A, turn on the arc gun to melt the Al, Co, Cr, Fe, Ni and Nb metal raw materials, and 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 turn; S3, turning over the metal ingot obtained in step S2 in the smelting furnace, evacuating the furnace to a vacuum, and then filling it with inert gas, and then performing the smelting step of step S2 on the other side of the ingot; Repeat step S3 at least 3 more times to ensure that the total number of smelting times is at least 5 times.

[0016] Optionally, in S1, the smelting furnace is evacuated to a vacuum of 0.5×10 -3 ~1.5×10 -3 Pa, and then Ar gas is filled into the smelting furnace until the vacuum degree in the smelting furnace is less than 5Pa.

[0017] Optionally, the preparation method specifically comprises the following steps: S1. Take Al, Co, Cr, Fe, Ni and Nb metal raw materials with a purity greater than 99.9%, use sandpaper to grind off the oxide scale of the Al, Co, Cr, Fe, Ni and Nb metal raw materials, put them into anhydrous ethanol, ultrasonically clean them for 2 min to 5 min, dry them, and store them in vacuum; A pure titanium ingot is added into a crucible of a smelting furnace, and the Al, Co, Cr, Fe, Ni and Nb metal raw materials are added into another crucible of the smelting furnace. The smelting furnace is evacuated to a vacuum of 0.5×10 -3 ~1.5×10 -3 Pa, and then fill the smelting furnace with inert gas Ar gas until the vacuum degree is less than 5Pa; S2. Adjust the current of the smelting furnace to 160A-180A, turn on the arc gun to smelt the pure metal titanium ingot first; then smelt the Al, Co, Cr, Fe, Ni and Nb metal raw materials, and 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 turn; S3, turning over the metal ingot obtained in step S2 in the smelting furnace, evacuating the furnace to a vacuum, and then filling it with inert gas, and then performing the smelting step of step S2 on the other side of the ingot; Repeat step S3 at least 3 more times to ensure that the total number of smelting times is at least 5 times.

[0018] In a third aspect, the present invention provides an application of a high-hardness high-entropy alloy in the preparation of medical materials.

[0019] Optionally, the medical material is at least one of a dental implant, a vascular stent, an intestinal stent, a tracheal stent, a urethral stent, and anastomosis staples.

[0020] Optionally, the dental implant comprises a dental implant and a root canal, and the vascular stent comprises a drug eluting stent.

[0021] The present invention has at least one of the following beneficial effects: 1. The high-hardness high-entropy alloy of the present invention is composed of Al, Co, Cr, Fe, Ni and Nb, and the microstructure of the high-hardness high-entropy alloy includes a matrix phase, a Nb-rich phase and a eutectic region; compared with the prior art, the high-hardness high-entropy alloy of the present invention has excellent performance, a Vickers hardness value of more than 1000, and extremely high hardness; and, the existing cemented carbides on the market are usually sintered and subjected to multiple heat treatment processes, 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 and materials prepared with similar or identical elements in the prior art.

[0022] 2. Compared with the prior art, the high-hardness high-entropy alloy of the present invention forms A2 and B2 phases in the eutectic zone, and compared with the existing literature, a laves phase is formed in the eutectic zone, thereby improving the plastic deformation ability of the material.

[0023] 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 of the material surface during use and extend the service life of mechanical parts. At the same time, it can reduce the vibration and noise caused by friction and improve the stability and reliability of the overall machinery.

[0024] 4. The high-hardness high-entropy alloy oxide layer of the present invention is mainly generated on the substrate and is closely attached to the substrate without cracks or peeling, which effectively prevents corrosive substances from reaching the surface or interior of the material to a certain extent, thereby improving the corrosion resistance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the original data of 4 points during the Vickers hardness test of the high-hardness high-entropy alloy prepared in Example 1.

[0026] Figure 2 The optical microscope image, scanning electron microscope image and corresponding EDS energy spectrum image of the high hardness and high entropy alloy prepared in Example 1; wherein (a) is the optical microscope image, (b) is the scanning electron microscope image and the corresponding EDS energy spectrum image, and (c) is a local magnified image.

[0027] Figure 3 This is the XRD diffraction peak spectrum of the high hardness and high entropy alloy prepared in Example 1.

[0028] Figure 4 This is the energy spectrum of the matrix phase of the high hardness and high entropy alloy prepared in Example 1.

[0029] Figure 5 This is the energy spectrum of the Nb-rich phase of the high hardness high entropy alloy prepared in Example 1.

[0030] Figure 6 , Figure 7 This is the energy spectrum of the eutectic region of the high hardness and high entropy alloy prepared in Example 1.

[0031] Figure 8 This is the energy spectrum of the eutectic region of the high hardness and high entropy alloy prepared in Example 1.

[0032] Fig. 9 These are scanning electron microscope images of AlCoCrFeNi prepared in Comparative Examples 3 and 5-7 with different contents of Nb element added thereto; among them, (a) AlCoCrFeNiNb0.2, (b) AlCoCrFeNiNb0.3, (c) AlCoCrFeNiNb0.5, and (d) AlCoCrFeNiNb0.75.

[0033] Fig.10 The XRD diagrams of AlCoCrFeNi prepared in Comparative Examples 1-2, Comparative Examples 4, and Comparative Examples 6-7 with different contents of Nb added thereto are shown.

[0034] Fig.11 This is the XRD spectrum of the eutectic region of the high hardness high entropy alloy prepared in Example 1.

[0035] Fig.12: is a friction coefficient curve diagram; wherein (a) is the high hardness high entropy alloy prepared in Example 1, and (b) is the high hardness high entropy alloy prepared in Comparative Examples 1-3 and Comparative Examples 5-7.

[0036] Fig.13 It is a friction coefficient curve in the prior art with similar element types to the present application.

[0037] Fig.14 It is the surface of the high entropy alloy after oxidation; wherein, (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. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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.

[0039] Example 1 This embodiment provides a method for preparing a high-hardness high-entropy alloy, comprising the following steps: (1) Weigh aluminum (Al), cobalt (Co), chromium (Cr), iron (Fe), nickel (Ni), and niobium (Nb) metal raw materials with a purity greater than 99.9%. Use 240# sandpaper to grind off the oxide scale and use a 1 / 10,000 electronic balance to weigh the required weight. The molar ratio of aluminum (Al), cobalt (Co), chromium (Cr), iron (Fe), nickel (Ni), and niobium (Nb) metal raw materials is 7.8:19.58:19.02:20.91:11.25:21.44. Then put the weighed raw materials into a beaker and pour in anhydrous ethanol. Vibrate and clean them in an ultrasonic cleaner for 3 minutes to remove impurities such as grinding debris and grease on the surface of the raw materials. Finally, use a hair dryer to dry the sample and put it into a vacuum bag for vacuum storage for subsequent smelting.

[0040] (2) Preparation: Unscrew the air valve, wait for the furnace pressure indicator to turn to zero, and then press the green "up" button to open the furnace door. Then use a clean non-woven cloth dipped in anhydrous alcohol to clean the inside of the vacuum chamber and the crucible. Then put a pure metal titanium ingot in the middle crucible to absorb the oxygen in the furnace. Put the pre-treated raw materials in the remaining crucibles from low to high melting points, and lower the furnace cover to prepare for vacuuming.

[0041] (3) Vacuum extraction: Check whether all valves and power switches on the vacuum chamber are closed. After the inspection is completed, turn on the mechanical pump, open the vacuum gauge and angle valve to start vacuum extraction, and wait until the vacuum degree reaches 1.0×10 -3After reaching Pa, close the gate valve and vacuum gauge, open the charging valve and fill in inert gas Ar until the pressure gauge shows less than 5Pa, and finally close the charging valve.

[0042] (4) Melting: When melting, adjust the electrode position to the top of the sample to be melted, press the arc-starting button, and adjust the current to 160A-180A after the arc is successfully started to melt the alloy. First, add a titanium ingot to a crucible in the melting furnace, and remove the residual oxygen inside the melting furnace by melting the Ti ingot; after the titanium ingot cools down, add the aluminum (Al), cobalt (Co), chromium (Cr), iron (Fe), nickel (Ni), and niobium (Nb) metal raw materials in step (1) to another crucible in the melting furnace, melt the sample, and after all the metal raw materials are completely melted, turn on the magnetic stirring switch, maintain the magnetic stirring for 50~150s, and then turn off the magnetic stirring and arc gun in turn. After turning the obtained metal ingot over in the melting furnace, evacuate it to vacuum again, and then fill it with inert gas, and then perform the same melting steps on the other side of the ingot; repeat the melting several times to ensure that the total number of melting times is at least 5 times.

[0043] (5) Sampling: After the smelting is completed and the alloy has cooled, open the vent valve and the furnace door, then take out the sample to obtain a high-hardness high-entropy alloy; clean the vacuum furnace, and then evacuate the vacuum furnace. Finally, turn off all power supplies and gates, and turn off the power.

[0044] Comparative Example 1 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 rest is the same as Example 1.

[0045] Comparative Example 2 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 rest is the same as Example 1.

[0046] Comparative Example 3 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 rest is the same as Example 1.

[0047] Comparative Example 4 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 rest is the same as Example 1.

[0048] Comparative Example 5 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 rest is the same as Example 1.

[0049] Comparative Example 6 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 rest is the same as Example 1.

[0050] Comparative Example 7 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 rest is the same as Example 1.

[0051] The properties of the high hardness high entropy alloys prepared in Example 1 and Comparative Examples 1 to 7 were characterized, and the results are as follows: Table 1 shows the Vickers hardness test results of the high hardness high entropy alloy of Example 1 of the present invention. In order to avoid the accidental nature of the experiment, the present invention selects multiple points at different positions of the material for testing. It can be seen from Table 1 that the Vickers hardness values ​​of the high hardness high entropy alloy materials of Example 1 of the present invention are all above 1000HV, and the average hardness is 1074.45HV. It has extremely high hardness. In order to make the present invention fully disclosed, Figure 1 The raw data of four points during the Vickers hardness test of the high-hardness high-entropy alloy of Example 1 of the present application are shown.

[0052] Table 1 In order to more intuitively reflect the superior performance of the high-hardness high-entropy alloy of the present application, the applicant has consulted relevant literature and summarized the Vickers hardness of related materials in the prior art in Table 2. Specifically including: the hardness of commonly used cemented carbide / 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 as the present invention and the hardness of high-entropy alloys in the cast state in relevant literature.

[0053] Table 2 Among them, the data of commonly used cemented carbides in Table 2 are from pages 435 and 437 of the eighth edition of the Hardware Tools Manual; the hardness of common metal materials is from the website (https: / / it.sohu.com / a / 791858574_121769585); the hardness of materials containing the same elements as the present invention and the hardness of materials with similar elements to the present invention are all from relevant papers, which are not listed specifically here. It should be noted that in the existing relevant papers, no metal has been found to have a hardness higher than that of the present application in the cast state. The hardness of high entropy alloys in the 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, we strictly followed the standard operating procedures to ensure the consistency of the test conditions, so as to facilitate the best comparison with the hardness of the materials in Table 2.

[0054] As can be seen from Table 2, the high-hardness high-entropy alloy material prepared in Example 1 of the present application has exceeded the hardness of commonly used metal materials and materials prepared with similar or identical elements in the prior art. For the cemented carbide materials actually used, the materials of the present application also far exceed some models.

[0055] It should be noted that the existing cemented carbides on the market are usually sintered, which is a key manufacturing process that enables the powder particles to be tightly combined, thereby giving the cemented carbide the required mechanical properties and wear resistance. The sintered cemented carbide contains almost no pores, which is crucial for it to maintain performance under high stress conditions. In order to further improve the performance of cemented carbide, the prior art will also undergo a series of heat treatment processes, such as annealing, quenching and tempering, which help to adjust the microstructure of the alloy, optimize its hardness, strength and wear resistance, and ensure the reliability and durability of cemented carbide in applications such as metal cutting, oil drilling and mold manufacturing. In contrast, the high-hardness high-entropy alloy of Example 1 of the present invention is cast, and the process flow is simple, but the hardness is higher than the prior art, which is sufficient to reflect the creativity of the material elements and molar percentage design of this application.

[0056] See also Figure 2 (a) is a light microscope image of the high hardness high entropy alloy of the present invention. Figure 2 It can be seen from (a) that the dendrite region of the high entropy alloy prepared in Example 1 of the present invention mainly includes two phases, α phase and β phase, and the nanophase with eutectic structure is formed between the dendrites. Figure 2 (b) is a scanning electron microscope image of the high hardness high entropy alloy prepared in Example 1 of the present invention and the corresponding EDS spectrum. Figure 2 (c) is a local enlarged image to illustrate the microstructure of the eutectic region. Figure 2 As can be seen in (b), the β phase is polygonal in shape. In the prior art, this phase only appears in materials rich in tungsten carbide and in the sintered state. Generally, the cross-sectional shape of the grain of the material is composed of spline curves. In addition, according to the surface scanning results, the β phase is rich in Nb elements, which plays a role in precipitation strengthening of the material.

[0057] Subsequently, nanoindentation tests were performed on the two phases using a nanoindentation 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.

[0058] Table 3 In order to further illustrate the phase composition of the high hardness high entropy alloy of the present application, the high hardness high entropy alloy prepared in Example 1 of the present application was sampled and XRD tested after polishing. The spectrum was analyzed using jade software. The results are as follows: Figure 3 As shown. Figure 3 It can be seen that the crystal structure of the most likely phase in the material of this application is similar to Ni, Fe3Co, Fe11Co5, and Fe13Co3 (it should be noted that for Jade software, such crystal structure is generally not considered when the cause factor is greater than 10. Therefore, the crystal structure of Co and Cr10Al16 is not considered in the material of this application).

[0059] Then the matrix phase ( Figure 4 )、Nb-rich phase( Figure 5 )、eutectic region( Figure 6 as well as Figure 7 ) was scanned. The results show that the matrix phase and the Nb-rich phase contain more Nb. Figure 4 The XRD results did not detect the crystal structure containing Nb phase, so it is reasonable to speculate that it may be because the lattice distortion of these two phases is large, which makes the diffraction peaks unable to align with the diffraction peaks of the standard card. Severe lattice distortion is conducive to improving the hardness of the material, which may also be a reason for the extremely high hardness of this material. Since the existing literature (doi:10.1016 / j.msea.2011.10.110) shows that laves phase appears when different contents of Nb (0.1-0.75) are added to AlCoCrFeNi, the matrix phase is likely to be a laves phase structure with large lattice distortion.

[0060] After scanning the two phases in the eutectic region of this application, it was found that ( Figure 6 , Figure 7:Due to the small size of the nanophase in the eutectic area, in order to eliminate the error caused by point scanning, two zone points were taken for each phase) The content of the three elements of Fe, Cr, and Ni is approximately three times that of the Co element. The three elements of Fe, Cr, and Ni have similar properties and similar electronegativity. Combined with the XRD results, the diffraction peak (BCC) of Fe3Co is the eutectic phase structure, which is expected to be A2 and B2 eutectics. At the same time, the Nb content of the two phases in the eutectic area is only about 5%, and it can be considered that the Nb element in the eutectic area has been dissolved into the crystal structure of the eutectic phase.

[0061] To further explore the eutectic region, an energy spectrometer was used to perform surface scanning of the eutectic region. Figure 8 As shown. It can be clearly seen that the eutectic structure contains almost no Nb element, but contains more Fe / Co / Cr / Ni elements. This also means that the eutectic structure does not contain laves phase structure. This is completely different from the phase structure formed by the AlCoCrFeNiNb series of high entropy alloys in the prior art. Fig. 9 It shows that adding different contents of Nb element into AlCoCrFeNi, Fig.10 is the corresponding XRD diagram. Combined with XRD, it can be seen that its microstructure changes from hypoeutectic to hypereutectic, but no matter how much the Nb content is, the eutectic area is bcc and laves phase. This is completely different from the element ratio of the eutectic area and the formed phase structure of the present application. It is known to those skilled in the art that the Laves phase is a high hardness phase, but the plasticity is very low. For the present application, the matrix phase provides high hardness, and the eutectic area does not contain the laves phase, which can provide the material with a certain plastic deformation ability.

[0062] A comprehensive analysis of the XRD and point scanning results shows that the matrix phase and the Nb-rich phase have undergone severe lattice distortion, which hinders the movement of material dislocations and thus strengthens the hardness of the material. In addition, the A2 and B2 phases formed in the eutectic region, compared with the laves phase formed in the eutectic region in the existing literature, improve the plastic deformation ability of the material.

[0063] Through further observation of the organization, it was found that there was another phase in the eutectic region ( Fig.11 The second phase is shown in Figure 1. The point scanning shows that the element ratio is similar to that of the matrix phase, so it can be inferred that it has the same crystal structure as the matrix phase, but is smaller in size than the matrix phase. This second phase particle can increase the yield strength of the material by hindering the movement of dislocations.

[0064] The present invention is further subjected to friction experiments to characterize the performance of the present invention. In this experiment, Si3N4 is selected as the counter-grinding material, and the wear is carried out for 30 minutes at room temperature with a motor frequency of 40Hz, a load of 500g, and a wear radius of 5mm. The mass of the sample before the experiment is 6.1872g, and the mass after the experiment is 6.1848g. The experimental shape is a cuboid of 15*20*2.6mm.

[0065] The wear rate is calculated by 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 material of the present application is 2.86967*10 -5 mm 3 / (N*m), with extremely low wear rate.

[0066] Get as Fig.12 (a) is a graph showing the friction coefficient of the high hardness high entropy alloy of the present application. Fig.12 (b) is the friction coefficient curve of the materials containing 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 material of the present application is quite low, and the whole process is quite stable. This can reduce the wear of the material surface during use and extend the service life of mechanical parts. At the same time, it can reduce the vibration and noise caused by friction and improve the stability and reliability of the overall machinery.

[0067] Fig.13 The friction coefficient curves of the materials prepared in the prior art and in Example 1 of the present application are shown. Fig.13 It can be clearly seen that the prior art materials are significantly different from the present application in terms of the value of the friction coefficient and the stability of the overall friction fluctuation. Specifically, the material prepared in the present application shows obvious advantages in friction performance. Not only is the friction coefficient low, but also its friction fluctuation is smaller and more stable during long-term use. This shows that the material of the present application has more excellent tribological properties and can better meet the high requirements of high-hardness alloys in practical applications.

[0068] It should be noted that the higher the hardness of a material, the better its wear resistance. This is because hardness is the ability of a material to resist external objects pressing into its surface, while wear resistance refers to the ability of a material to resist wear. When a hard object slides or impacts the surface of a material, a material with a higher hardness is more able to resist this mechanical force, thereby reducing the wear of the material. However, wear resistance is not only determined by hardness, but is also affected by many factors.

[0069] For example, when a material is too hard and brittle, it may break easily when impacted, or peeling may occur on the surface of the material. The peeled-off material further wears the parent material, making the wear resistance of the material worse. However, since the eutectic region of the material of the present application is a BCC phase (A2 and B2 phase), compared with the laves phase in the eutectic region in the prior art, it has good deformation ability and can maintain surface integrity while absorbing impact energy, thereby improving wear resistance.

[0070] The material was further subjected to high temperature oxidation for 100 hours. Fig.14 As shown in (a), the results show that the oxide layer of the high-hardness high-entropy alloy of the present application is mainly generated on the substrate and is close to the substrate without cracks or peeling. This effectively prevents corrosive substances from reaching the surface or inside of the material to a certain extent, thereby improving the corrosion resistance of the material. It is particularly important to note that the oxidation resistance between the dendrites on the surface of the material is good, and almost no obvious oxide layer is produced. The surface of the material was scanned using an energy spectrometer equipped with a scanning electron microscope and found that ( Fig.14 (a) upper right corner), further verifying that oxides are almost only generated in the matrix phase. From the surface scanning results, it can be seen that the oxygen content in the interdendritic region is dark (close to black), indicating that there are very few oxides in the interdendritic region compared to the dendrite region.

[0071] In a system with cations as migrating substances, metal atoms diffuse outward through the oxide film and the metal interface in the form of cations and electrons. In order to maintain adhesion to the alloy matrix, the oxide film must relax. However, at the corners of the sample, the geometry of the oxide film is fixed, and relaxation cannot be carried out simultaneously in multiple directions. Therefore, since thermal stress cannot be effectively released, the oxide film is eventually ruptured. However, in the present application, since the interdendritic oxide layer is very thin, space is given to relax the dendrite region, and therefore, the oxide layer does not peel off.

[0072] Fig.14 (b) is the surface of the material of comparative example 1 after oxidation of AlCoCrFeNi high entropy alloy. It can be seen that after 100 hours of high-temperature oxidation, the surface oxide scale of the material is broken and severely peeled off. This is mainly because AlCoCrFeNi high entropy alloy is a single-phase BCC, and the generated 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 be carried out simultaneously in multiple directions. During the cyclic oxidation process, thermal stress cannot be released, resulting in the peeling of the oxide film, which further reflects the advantages of the material of the present application in terms of oxidation resistance.

[0073] For the application prospects of materials, cost is also an important part that needs to be considered. Therefore, this application is based on the authoritative metal consulting portal-"Shanghai Nonferrous Network", and the cost of relevant materials in the recent period is queried, and the price of one kilogram of raw materials is calculated, as shown in Table 4. From Table 4, it can be calculated that the price of the high hardness high entropy alloy of this application (287.91 / kg). Due to the difference in the mass fraction of WC in cemented carbide, this application is calculated based on the raw material content that can be used to prepare the commonly used cemented carbide in Table 2. The "Practical Hardware Tools Manual" also indicates that the WC content is 70-90%, and the remaining content is calculated based on the Co binder commonly used in cemented carbide. It is calculated that the price of traditional WC-based cemented carbide is (300.8-321.6 / kg). 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 hardness alloys, so there is an obvious raw material cost advantage.

[0074] Table 4 In summary, the high-hardness high-entropy alloy of the present application has the following advantages compared with the prior art: 1. The high-hardness high-entropy alloy of the present 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 of similar compositions, the hardness has outstanding advantages. Compared with the cemented carbide currently being used in the prior art, the high-entropy alloy of the present application is also superior to many models. Although slightly lower than some models of cemented carbide, however, the high-entropy alloy of the present application is only in a cast state, the process is simple, and no post-processing has been performed. The existing cemented carbide is in a sintered state, and is bound to undergo a series of post-processing processes to improve performance. Therefore, the high-entropy alloy of the present application has outstanding characteristics and significant progress in hardness.

[0075] 2. The niobium-rich phase hinders the movement of dislocations and plays a role in precipitation strengthening of the material. In addition, the nanopressure constant test found that its hardness is above 1500HV, which is rarely reported in relevant literature.

[0076] 3. The matrix phase and Nb-rich phase have strong lattice distortion, which hinders the movement of material dislocations and thus strengthens the hardness of the material. In addition, the A2 and B2 phases formed in the eutectic region provide the material with a certain plastic deformation ability compared to the laves phase formed in the eutectic region in the existing literature.

[0077] 4. The second phase particles dispersed in the eutectic region can increase the yield strength of the material by hindering the movement of dislocations.

[0078] 5. The friction coefficient of the material of the present application is quite low, and the whole process is quite smooth. This can reduce the wear of the material surface during use and extend the service life of mechanical parts. At the same time, it can reduce the vibration and noise caused by friction and improve the stability and reliability of the overall machinery.

[0079] 6. The high-hardness high-entropy alloy oxide layer of the present application is mainly generated on the substrate and is closely attached to the substrate without cracks or peeling. ( Fig.14 a) This effectively prevents corrosive substances from reaching the surface or interior of the material to a certain extent, thereby improving the corrosion resistance of the material. In the present application, the dendrites provide space for relaxation of the dendrite region, so that the material can release thermal stress during oxidation, so the oxide layer does not peel off. Compared with the cemented carbide in the prior art, at high temperatures, the carbide particles in the cemented carbide are not easy to melt or decompose, but a layer of oxide film will form on its surface, which will reduce the oxidation resistance of the alloy.

[0080] 7. After price comparison on authoritative metal price inquiry websites, the price per kilogram of the high-hardness high-entropy alloy in this application is about 12.89-33.69 yuan lower than that of traditional hardness alloys, so there is a clear advantage in raw material cost.

[0081] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by 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 microstructure of the high-hardness high-entropy alloy comprises a matrix phase, a Nb-rich phase and a eutectic region; 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%.

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

3. The high-hardness high-entropy alloy according to claim 1, characterized in that: The microstructure of the high-hardness high-entropy alloy also 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.

4. The high-hardness high-entropy alloy according to claim 1, characterized in that: The molar percentage of each component in the high-hardness high-entropy alloy is: Al 5%-10%, Co 15%-25%, Cr 15%-25%, Fe 15%-25%, Ni 5%-14%, and Nb 15%-25%.

5. The high-hardness high-entropy alloy according to claim 1, characterized in that: The molar percentage of each component in the high-hardness high-entropy alloy is: Al 6%~9.5%, Co 16%~22%, Cr 16%~22%, Fe 17%~23%, Ni 8%~14%, and Nb 18%~24%.

6. The high-hardness high-entropy alloy according to claim 1, characterized in that: The molar percentage of each component in the high-hardness high-entropy alloy is: Al 7%-9%, Co 18%-21%, Cr 18%-21%, Fe 19%-22%, Ni 10%-13%, and Nb 20%-23%.

7. 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: Al 7.8%, Co 19.58%, Cr 19.02%, Fe 20.91%, Ni 11.25; and Nb 21.44%.

8. A method for preparing the high hardness high entropy alloy according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Adding Al, Co, Cr, Fe, Ni and Nb metal raw materials with a purity greater than 99.9% into a smelting furnace, evacuating the smelting furnace, and then filling the smelting furnace with inert gas; S2. Adjust the current of the smelting furnace to 160A-180A, turn on the arc gun to melt the Al, Co, Cr, Fe, Ni and Nb metal raw materials, and 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 turn; S3, turning over the metal ingot obtained in step S2 in the smelting furnace, evacuating the furnace to a vacuum, and then filling it with inert gas, and then performing the smelting step of step S2 on the other side of the ingot; Repeat step S3 at least 3 more times to ensure that the total number of smelting times is at least 5 times.

9. The preparation method according to claim 8, characterized in that: In S1, the smelting furnace is evacuated to a vacuum of 0.5×10 -3 ~1.5×10 -3 Pa, and then Ar gas is filled into the smelting furnace until the vacuum degree in the smelting furnace is less than 5Pa.

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

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