High plasticity directional multi-stage lamellar structure eutectic high-entropy alloy and preparation method thereof

Abstract

This invention relates to a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy and its preparation method. The eutectic high-entropy alloy comprises Al, Co, Fe, and Ni, and its general formula is Al. a Co b Fe c Ni d The alloy has the following properties: 5≤a≤30, 5≤b≤30, 5≤c≤30, 10≤d≤50, and a+b+c+d=100. The preparation method includes the following steps: raw material pretreatment; alloy melting; alloy cutting and processing; directional solidification loading; and directional solidification. Compared with existing technologies, the eutectic high-entropy alloy of this invention has high yield strength and excellent plasticity. Furthermore, the preparation method is simple, safe, reliable, economical, and practical, possessing enormous application potential in engineering applications.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials technology, and in particular relates to a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy and its preparation method. Background Technology

[0002] High-entropy alloys are a newly emerging type of alloy material in recent years, exhibiting broad research value and application potential due to their unique multi-principal element design. Because early single-phase high-entropy alloys such as FCC or BCC often struggled to balance strength and plasticity, and suffered from casting problems such as segregation and shrinkage cavities, eutectic high-entropy alloys with a two-phase lamellar structure and good casting performance were proposed.

[0003] Eutectic high-entropy alloys possess the properties of both phases, offering a novel approach to high-entropy alloy design. However, most currently developed eutectic high-entropy alloy systems, even with optimized alloy composition, heavily rely on subsequent mechanical and heat treatment processes to achieve optimal strengthening effects. These processes often reduce the material's thermal stability, hindering its application at high temperatures. The preparation of high-performance as-cast high-entropy alloys will not only advance their high-temperature applications but also significantly contribute to the development of high-mechanical-performance high-entropy alloys through subsequent mechanical and heat treatment.

[0004] Directional solidification is an important technique widely used in the fabrication of high-temperature turbine blades and can also be used to improve the mechanical properties of in-situ composite materials such as eutectic high-entropy alloys. The uniaxial heat flow during directional solidification can alter the natural convection of the metal, guiding the solidification direction and producing samples without shrinkage defects. Based on this, by combining different pulling rates, different types of solid-liquid interface morphologies can be controlled, thereby producing materials with different solidification structures and mechanical properties. Furthermore, directional solidification technology can be combined with continuous casting technology to manufacture large quantities of metallic materials with excellent properties.

[0005] Previous research has largely focused on developing new high-entropy alloy systems, with limited attention paid to controlling the solidification process of eutectic high-entropy alloys to achieve synergistic optimization of microstructure and properties. Lei Wang et al. published their findings on AlCoCrFeNi in the journal *Intermetallic*. 2.1 The article discusses the directional solidification of eutectic high-entropy alloys (Microstructures and room temperature tensile properties of as-cast and directionally solidified AlCoCrFeNi). 2.1While it has been shown that directional solidification can significantly improve the plasticity of eutectic high-entropy alloys, up to twice that of arc-melted alloys, this method is only applicable to a few eutectic high-entropy alloys. Furthermore, the yield strength is not significantly improved, and in some conditions, it even decreases. These problems limit further industrial application and development.

[0006] CN111636027B discloses a eutectic high-entropy alloy exhibiting both secondary yielding and high strength and high ductility, and its preparation method. This high-entropy alloy is composed of Al, Co, Cr, Fe, and Ni, and its general formula is Al. a Co b Cr c Fe d Ni e Where 10 < a ≤ 25, 10 < b ≤ 25, 0 ≤ c < 25, 10 < d ≤ 25, 10 ≤ e < 41, and a + b + c + d + e = 100. The high-entropy alloy microstructure consists of eutectic lamellars arranged in a single direction, and the tensile curve exhibits a clear secondary yield phenomenon. However, the primary yield strength of this eutectic high-entropy alloy is only 370 MPa, and the elongation at break is only 19%, indicating that its plasticity and yield strength still need to be improved. In addition, the directional solidification rate in this preparation method is only 1-15 μm / s, which is not conducive to industrial production. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the prior art by providing a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy and its preparation method.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] This invention provides a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy, comprising Al, Co, Fe, and Ni, with the general formula Al. a Co b Fe c Ni d , where 5≤a≤30, 5≤b≤30, 5≤c≤30, 10≤d≤50, and a+b+c+d=100.

[0010] Furthermore, the prepared eutectic high-entropy alloy is a multi-level eutectic lamellar structure with alternating regular oriented lamellars and irregular oblique lamellars.

[0011] Another aspect of the present invention provides a method for preparing a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy, comprising the following steps:

[0012] S1: Raw material pretreatment: Remove impurities and oxide scale from the surface of the four metal elements Al, Co, Fe, and Ni, clean and dry them; generally, sandpaper is used to polish the surface of the raw materials to remove impurities and oxide scale. After calculating the required mass of each metal element according to the actual atomic ratio between each metal, the required mass of the metal raw materials is weighed using an electronic balance with an accuracy of 0.01%, so that the mass error of each raw material is controlled within ±0.05%. After accurate weighing, the raw materials are placed in a beaker containing anhydrous ethanol, ultrasonically vibrated and cleaned, dried and sealed for later use.

[0013] S2: Alloy Melting: After cleaning and drying, the metal raw materials are placed into a button-shaped copper ingot tray of a conventional electric arc furnace. The vacuum hood is closed, and a vacuum and reverse-charge gas protection system is applied. Melting of the raw materials begins, with at least four melting cycles to obtain button-shaped alloy ingots of the eutectic high-entropy alloy. In this step, the cleaned alloy raw materials are placed into the vacuum electric arc melting furnace in sequence according to their melting points, from lowest to highest. Each melting cycle uses a current of 400-600A for 60 seconds. The ingots are flipped after each melting cycle. Three button-shaped alloy ingots are placed in a plate-shaped copper mold of the conventional electric arc furnace. A vacuum and reverse-charge gas protection system is applied, and melting of the button-shaped alloy ingots begins, with at least three melting cycles to obtain eutectic high-entropy alloy plates. Each melting cycle uses a current of 400-600A for 60 seconds.

[0014] S3: Alloy cutting and processing: Cut the eutectic high-entropy alloy plate in S2 into an alloy rod with a diameter of 9.8mm, and use an angle grinder to remove the cutting marks on its surface until the surface of the alloy rod is bright. Finally, use anhydrous ethanol for ultrasonic cleaning and set aside for use.

[0015] S4: Directional solidification loading: The cut and polished alloy rod from S3 is loaded into the corundum crucible of the directional solidification device. The distance between the top of the quenching pool and the bottom of the corundum crucible is adjusted to 50-80mm. Then, an atmosphere protection cover is placed on top, and a protective atmosphere is introduced. At the same time, the bottom of the corundum crucible is connected to the pulling mechanism.

[0016] S5: Directional solidification: Turn on the induction power of the directional solidification device, first run it at low power for preheating, then slowly increase it to the specified power and hold it at that temperature for at least 3 minutes. After holding the temperature, adjust the pulling speed and distance of the pulling mechanism in S4, and start pulling down the corundum crucible for directional solidification. After directional solidification is completed, the eutectic high-entropy alloy is obtained.

[0017] During the smelting process, pretreatment is required. This involves first smelting a pre-placed pure titanium ingot to deplete the oxygen in the furnace, extinguishing the arc, and waiting for the titanium ingot to cool and observe its surface. If no colored oxidation phenomenon appears on the surface of the titanium ingot, the raw material smelting begins.

[0018] Further, in step S2, the specific operations for vacuuming and backflushing gas protection are as follows: after closing the vacuum hood of the electric arc furnace, open the valve of the mechanical pump and use the mechanical pump to evacuate the vacuum level inside the furnace to 3.0 × 10⁻⁶. 0 Once the pressure is below 2 Pa, close the valve of the mechanical pump and open the valve of the molecular pump, then use the molecular pump to evacuate the vacuum to 2.0 × 10⁻⁶ Pa. -3 The pressure is reduced to below Pa, then the evacuation is stopped, and a protective atmosphere is introduced into the melting chamber.

[0019] Furthermore, the protective atmosphere is argon.

[0020] Further, in step S3, the eutectic high-entropy alloy plate is cut using electrical discharge wire cutting. Further, in step S4, the specific operation of introducing the protective atmosphere is as follows: place the quartz bell jar connected to the vent valve above the corundum crucible, open the protective gas valve, and continue until the flow meter reading stabilizes.

[0021] Furthermore, the protective gas is argon, and the flow rate of the protective gas is 0.1-1.0 L / min.

[0022] Furthermore, in step S5, the low power is 1-2kW, the specified power is 4-6kW, and the slow increase rate is 0.1kW / 100s.

[0023] Furthermore, in step S5, the pull-down speed of the pull rod is 100-400μm / s, and the pull-down distance is 50-80mm.

[0024] This invention constructs a multi-level eutectic lamellar microstructure with alternating regular longitudinal lamellae and irregular oblique lamellae. The synergistic strengthening between the multi-level lamellar regions gives the alloy high yield strength. During deformation, microcracks easily form within the phase and at the phase interface due to the poor deformability of one phase. As the strain increases, these microcracks are captured and suppressed by the other phase, preventing them from growing into secondary cracks, thus giving the alloy excellent plasticity.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The cast eutectic high-entropy alloy with a directional multi-level lamellar structure prepared by the present invention not only has improved yield strength compared with the alloy prepared by arc melting, but also has a strong inhibitory effect on microcrack propagation and secondary crack generation during deformation, thus achieving a significant improvement in plasticity.

[0027] (2) The eutectic high-entropy alloy prepared by the present invention has stable performance and extremely high repeatability.

[0028] (3) The preparation method of this invention is simple, easy to operate, safe, reliable, economical and practical, and applicable to a variety of eutectic high-entropy alloy systems with a two-phase lamellar structure. The directional solidification and continuous casting have a relatively fast pull-down speed, which has important production value and guiding significance for the rapid production of high-performance long bars. Moreover, it can be industrialized for continuous production, and the raw materials used are all non-toxic and harmless, inexpensive and easy to obtain. Attached Figure Description

[0029] Figure 1 A schematic diagram of the multi-level lamellar directional solidification structure prepared according to the present invention and a SEM image of the longitudinal section phase structure in Example 1.

[0030] Figure 2 The tensile stress-strain curves of the sample in Example 1 and the sample in the arc-melted state of the same alloy are compared. The longer curve is the tensile stress-strain curve of Example 1.

[0031] Figure 3 The image shows a longitudinal section SEM image of the (near) eutectic high-entropy alloy in the simulated actual production process of Example 5.

[0032] Figure 4 The tensile stress-strain curves of the sample in Example 5 are compared with those of the sample in the arc-melted state of the same alloy. The longer curve is the tensile stress-strain curve of Example 5. Detailed Implementation

[0033] The following specific embodiments further illustrate the present invention. Unless otherwise specified, the methods described are conventional methods, and the raw materials, unless otherwise specified, are all obtainable through publicly available commercial channels and are all bulk metals with a purity of not less than 99.9 wt%. These embodiments are for illustrative purposes only and are not intended to limit the invention in any way.

[0034] The equipment and testing methods used in the following embodiments are as follows:

[0035] High vacuum non-consumable arc melting furnace: DHL-1250 high vacuum non-consumable arc melting furnace manufactured by Shenyang Huiyu Vacuum Technology Co., Ltd., China;

[0036] Quasi-static tensile mechanical property testing: A quasi-static tensile test at room temperature was conducted using an MTS E44 microcomputer-controlled electronic universal testing machine, according to standard GB / T228.1-2010. The strain rate was selected as 10. -3 s -1 .

[0037] SEM testing conditions: A tungsten filament scanning electron microscope, model VEGA3Easy Probe, was used to observe the tissue at magnifications ranging from 2000x to 10000x to determine the final tissue morphology.

[0038] Example 1

[0039] In this embodiment, the highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy Al is presented. 19 Co 20 Fe 20 Ni 41 The preparation steps are as follows:

[0040] S1: Raw material pretreatment: Select Al 19 Co 20 Fe 20 Ni 41 For the eutectic high-entropy alloy system, four metallic elements (Al, Co, Fe, and Ni) with a purity of no less than 99.9 wt% were cut into small pieces for subsequent processing. These pieces were then cleaned with sandpaper to remove impurities and oxide scale from their surfaces. The required masses of each metallic element were calculated: Al 8.8478 g, Co 20.3426 g, Fe 19.2766 g, and Ni 41.5327 g. The required masses of the metallic elements were weighed using an electronic balance with an accuracy of 0.001 g, ensuring that the mass error of each element was controlled within ±0.003 g. After precise weighing, the materials were placed in a beaker containing anhydrous ethanol, ultrasonically cleaned, and then dried before being sealed in plastic for later use.

[0041] S2: Alloy Melting: The cleaned metal raw materials are placed into the plate-shaped groove of the water-cooled copper crucible in the vacuum electric arc furnace, arranged from lowest to highest melting point. After closing the vacuum hood of the electric arc furnace, the valve of the mechanical pump is opened, and the vacuum level inside the furnace is evacuated to 3.0 × 10⁻⁶. 0 Once the pressure is below 2.0 Pa, close the valve of the mechanical pump. Open the valve of the molecular pump and use the molecular pump to evacuate the vacuum to a level less than or equal to 2.0 × 10⁻⁶ Pa. -3 Pa. Then stop evacuation and introduce 99.999 wt% high-purity argon into the melting chamber. During melting, first melt a pre-placed pure titanium ingot to deplete the oxygen in the furnace, extinguish the arc, wait for the titanium ingot to cool, and observe its surface. If no colored oxidation phenomenon appears on the surface of the titanium ingot, start melting the raw material. The alloy is melted at least 4 times in an argon atmosphere. After each melting, the alloy ingot is turned over to ensure uniform composition. The current for each melting is 500A, and the time is 60s, finally obtaining a plate-shaped alloy with dimensions of 40mm × 110mm × 10mm.

[0042] S3: Alloy Cutting Process: The eutectic high-entropy alloy plate in S2 is cut into metal rods with a diameter of 9.8 mm and a length of 110 mm using an electrical discharge wire EDM machine. Then, the cutting marks on the surface are removed using an angle grinder until the surface of the alloy rod is bright. Finally, it is ultrasonically cleaned with anhydrous ethanol for later use.

[0043] S4: Directional solidification loading: The cut and polished alloy rod from S3 is loaded into the corundum crucible of the directional solidification device. The distance between the top of the quenching pool and the bottom of the corundum crucible is adjusted to 60mm. Then, an atmosphere protection cover is placed on top, argon gas is introduced, and the bottom of the corundum crucible is connected to the pulling mechanism.

[0044] S5: Directional solidification: Turn on the induction power of the directional solidification device, first run it at low power for preheating, then slowly increase it to the specified power and hold it at that temperature for at least 3 minutes. After holding the temperature, adjust the pulling speed and distance of the pulling mechanism in S4, and start pulling down the corundum crucible for directional solidification. After directional solidification is completed, the eutectic high-entropy alloy is obtained.

[0045] Test preparation:

[0046] The alloy was prepared by wire EDM, and its metallographic structure was observed after grinding and polishing. A dog-bone-shaped tensile specimen with a thickness of 1.0 mm, a gauge length of 13 mm, a width of 3.2 mm, and a total length of 35 mm was obtained from the directional solidification stable growth portion. The specimen was then polished sequentially with 120#, 400#, 800#, 1200#, and 2000# sandpaper, followed by mechanical property testing. The test results are as follows: Figures 1 to 4 As shown:

[0047] The schematic diagram of the alloy is shown below. Figure 1 As shown, the directional solidification proposed in this invention forms a directional multi-level eutectic lamellar structure. Furthermore, SEM characterization revealed that the directional solidification method preserved the typical two-phase eutectic lamellar structure of FCC+B2, successfully constructing a directionally arranged fishbone-like multi-level eutectic lamellar structure.

[0048] like Figure 2 As shown, the mechanical properties of the material prepared by this invention are significantly improved compared to the alloys melted by electric arc furnace, with a yield strength of 650 MPa and a uniform elongation of 50.3%, which is a great improvement over ordinary electric arc melting.

[0049] like Figure 3 As shown, for (near) eutectic high-entropy alloy systems that inevitably arise in actual production due to compositional deviations or process variations, such as in Example 5, the microstructure can still be controlled to obtain a fishbone-like multi-level eutectic lamellar structure.

[0050] like Figure 4 As shown, the mechanical properties of the material prepared by this invention are improved compared to the alloys melted by electric arc furnace, with a yield strength of 660 MPa and a uniform elongation of 26%. For (near) eutectic high-entropy alloy systems under extreme conditions, it is a significant improvement over ordinary electric arc melting.

[0051] Example 2

[0052] The two embodiments are largely the same as in Example 1, except that the pull-down speed of the pull rod in S5 is 200 μm / s.

[0053] Example 3

[0054] The two embodiments are largely the same as in Example 1, except that the pull-down speed of the pull rod in S5 is 350 μm / s.

[0055] Example 4

[0056] The majority of the components are the same as in Example 1, except that the eutectic high-entropy alloy system selected in S1 is Al. 19 Co 19 Fe 19 Ni 43 .

[0057] Example 5

[0058] The majority of the components are the same as in Example 1, except that the eutectic high-entropy alloy system selected in S1 is Al. 16 Co 20 Fe 20 Ni 44 .

[0059] Example 6

[0060] The majority of the components are the same as in Example 1, except that the eutectic high-entropy alloy system selected in S1 is Al. 16 Co 20 Fe 23 Ni 41 .

[0061] Example 7

[0062] Compared with Example 1, most of the contents are the same, except that in S4 the distance between the top of the quenching pool and the corundum crucible is adjusted to 5 cm.

[0063] Example 8

[0064] Compared with Example 1, it is mostly the same, except that in S4 the distance between the top of the quenching pool and the corundum crucible is adjusted to 8cm.

[0065] Example 9

[0066] The two embodiments are largely the same as in Example 1, except that the power of the low-power operation in S5 starts at 1kW.

[0067] Example 10

[0068] The two embodiments are largely the same as in Example 1, except that the power specified in S5 is 4kW.

[0069] Example 11

[0070] The two embodiments are largely the same as in Example 1, except that the power specified in S5 is 6kW.

[0071] Comparative Example 1

[0072] Compared with Example 1, most of the results are the same, except that in S5, ordinary electric arc melting is used for heating, that is, a DHL-1250 vacuum non-consumable electric arc melting furnace is used, and the melting current is 500A.

[0073] Comparative Example 2

[0074] Compared with Example 4, most of the results are the same, except that in S5, ordinary electric arc melting is used for heating, that is, a DHL-1250 vacuum non-consumable electric arc melting furnace is used, and the melting current is 500A.

[0075] Comparative Example 3

[0076] Compared with Example 5, most of the results are the same, except that in S5, ordinary electric arc melting is used for heating, that is, a DHL-1250 vacuum non-consumable electric arc melting furnace is used, and the melting current is 500A.

[0077] Comparative Example 4

[0078] Compared with Example 6, most of the results are the same, except that in S5, ordinary electric arc melting is used for heating, that is, a DHL-1250 vacuum non-consumable electric arc melting furnace is used, and the melting current is 500A.

[0079] Comparative Example 5

[0080] Compared with Example 1, most of the results are the same, except that the induction directional solidification heating method in S5 directly uses a specified power of 5kW for heating.

[0081] Example 12

[0082] The majority of the components are the same as in Example 1, except that the (near) eutectic high-entropy alloy system selected in S1 is Al5Co. 30 Fe 30 Ni 35 .

[0083] Example 13

[0084] The majority of the components are the same as in Example 1, except that the (near) eutectic high-entropy alloy system selected in S1 is Al. 30 Co5Fe 15 Ni 50 .

[0085] Example 14

[0086] The majority of the components are the same as in Example 1, except that the (near) eutectic high-entropy alloy system selected in S1 is Al. 20 Co 30 Fe5Ni 45 .

[0087]

[0088]

[0089] According to the table above, comparing Example 1 with Comparative Example 1, Example 4 with Comparative Example 2, Example 5 with Comparative Example 3, and Example 6 with Comparative Example 4 reveals that the induction-directed solidification heating method of the present invention significantly improves yield strength and plasticity. Furthermore, plasticity is greatly improved without sacrificing strength, and the yield strength or tensile strength in the examples is also improved, achieving a synergistic improvement in strength and plasticity. This demonstrates that the present invention has a significant performance improvement effect on various systems, and can still provide strengthening effects for complex high-entropy alloy systems that are (near)eutectic or even non-eutectic in extreme cases due to compositional deviations or process variations unavoidable in actual production.

[0090] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy, characterized in that, Includes the following steps: S1: Raw material pretreatment: Remove impurities and oxide scale from the surface of the four metal elemental raw materials Al, Co, Fe and Ni, clean and dry them; S2: Alloy smelting: Place the cleaned and dried metal raw materials into the water-cooled copper crucible of the vacuum arc furnace, then close the vacuum hood and evacuate the vacuum. After the vacuum is completed, backfill with gas for protection, and then start smelting the raw materials. Smelt at least 4 times to finally obtain a eutectic high-entropy alloy plate. The current for electric arc melting is 400-600 A, and the time is greater than 60 s; S3: Alloy cutting and processing: Cut the eutectic high-entropy alloy plate in S2 into an alloy rod of a specified size, and grind and clean it for later use; S4: Directional solidification loading: The cut and polished alloy rod from S3 is loaded into the corundum crucible of the directional solidification device. The distance between the top of the quenching pool and the bottom of the corundum crucible is adjusted to 50-80 mm. Then, an atmosphere protection cover is placed on top, and a protective atmosphere is introduced. At the same time, the bottom of the corundum crucible is connected to the pulling mechanism. S5: Directional solidification: Turn on the induction power of the directional solidification device, first run it at low power for preheating, then slowly increase it to the specified power and hold it at the temperature for at least 3 minutes. After the holding time is over, adjust the pulling speed and distance of the pulling mechanism in S4, and start pulling the corundum crucible down to the quenching pool for directional solidification. After the directional solidification is over, the eutectic high-entropy alloy is obtained. The heating method of the directional solidification device is to use a copper induction coil to induction heat the crucible; The low power is 0.5-1 kW, the specified power is 4-6 kW, and the power increases slowly at a rate of 0.1 kW / 100s-0.5 kW / 100s. The pull-down speed of the lever is 100-400 μm / s, and the pull-down distance is 50-80 mm; The obtained eutectic high-entropy alloy is a multi-level eutectic lamellar structure with alternating regularly oriented and irregularly oblique lamellar layers, and its general formula is Al. a Co b Fe c Ni d , where 5≤a≤30, 5≤b≤30, 5≤c≤30, 10≤d≤50, and a+b+c+d=100.

2. The method for preparing a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy according to claim 1, characterized in that, In step S2, the specific operation for reverse gas protection after vacuuming is completed is as follows: After closing the vacuum hood of the electric arc furnace, open the valve of the mechanical pump and use the mechanical pump to evacuate the vacuum level inside the furnace to 3.0 × 10⁻⁶. 0 Below Pa, then close the mechanical pump valve and open the molecular pump valve, using the molecular pump to evacuate to a vacuum level of 5.0 × 10⁻⁶. -3 When the pressure drops below Pa, stop pumping and introduce protective gas into the melting chamber.

3. The method for preparing a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy according to claim 1, wherein in step S3, the eutectic high-entropy alloy plate is cut using electrical discharge wire cutting.

4. The method for preparing a highly ductile, oriented, multi-level lamellar eutectic high-entropy alloy according to claim 1, characterized in that, In step S4, the protective atmosphere is argon, and the flow rate of the protective atmosphere is 0.1-1.0 L / min.

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