High-entropy alloy and method of manufacturing the same

Abstract

To provide a high-entropy alloy having excellent mechanical properties and a method of manufacturing the same by using a metal additive manufacturing process.SOLUTION: A high-entropy alloy according to an embodiment may include: a dual-phase structure of a columnar face-centered cubic (FCC) phase and an isometric body-centered cubic (BCC) phase; a cell structure; and precipitates.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a high-entropy alloy and a method for manufacturing the same, and more particularly to a high-entropy alloy having excellent mechanical properties using a metal additive manufacturing process and a method for manufacturing the same. [Background technology]

[0002] A typical metal alloy is composed of a main element and a small amount of alloying elements, and the more alloying elements are added, the greater the possibility of forming intermetallic compounds. The intermetallic compounds can cause brittleness in the material, thereby weakening its mechanical properties. High-entropy alloys (HEA) are alloys in which five or more elements act as major elements and have a high entropy of mixing. Due to the high entropy, Gibbs free energy is low, preventing the formation of intermetallic compounds, and the alloy consists of a single phase of the highly flexible face-centered cubic (FCC), body-centered cubic (BCC), or hexagonal close-packed (HCP).

[0003] High-entropy alloys not only have high strength and elongation in a variety of fields, but also exhibit excellent properties such as high-temperature resistance and corrosion resistance, and are being actively researched as materials that can overcome the limitations of existing materials. High-entropy alloys are multi-element alloys in which multiple constituent elements are alloyed in similar proportions, deviating from the traditional concept of alloys that contain at least one major element and small amounts of impurities. High-entropy alloys have a high entropy of mixing within the alloy, preventing the formation of intermetallic compounds and resulting in a single-phase or dual-phase structure. In particular, FCC-based high-entropy alloys with a single-phase face-centered cubic structure are gaining attention as structural metal materials for cryogenic temperatures due to their excellent plastic hardening at low temperatures around 77K, as well as their excellent tensile strength and elongation. However, although the FCC-based high-entropy alloy exhibits excellent tensile properties at cryogenic temperatures, it exhibits low yield strength at room temperature, which limits the application range of the FCC-based high-entropy alloy.

[0004] To solve this problem, recent studies have been carried out to manufacture alloys by adjusting the composition of the FCC-based high-entropy alloys or adding specific alloying elements. Attempts have been made to improve the yield strength of alloys by adding specific alloying elements to adjust phase stability and induce martensitic transformation, or by precipitating a secondary phase in the FCC matrix using a heat treatment process. Although such alloys improve the yield strength of the alloy, the brittle martensite and precipitated intermetallic compounds restrict plastic deformation and reduce the excellent plastic hardening and elongation rate of existing FCC-based high-entropy alloys, which hinders workability, a problem closely related to the industrialization of high-entropy alloys.

[0005] To solve this problem, it is necessary to realize excellent mechanical properties through an entropy alloy in which the proportion of brittle martensite and intermetallic compounds is appropriately controlled through a manufacturing process that is not concerned with workability. Heterostructured materials are materials that intentionally combine two regions with different microstructural characteristics, and have attracted much attention as microstructural materials that can achieve excellent mechanical properties even when made of the same constituent materials. In this case, the two regions can be, for example, a soft domain and a hard domain. Heterogenous deformation induced strengthening accommodates the difference in deformation rate through dislocations at the boundary between two regions. In other words, the resulting geometrically necessary dislocations (GND) at the boundary can form additional back dislocations, thereby improving both strength and elongation. The heterostructure materials mentioned above have attracted much attention because it has been revealed that they can overcome the tradeoff between material strength and softness by generating a large amount of such geometrically necessary dislocations, and research into processes for manufacturing such heterostructure materials is actively being conducted.

[0006] Metal 3D printing or metal additive manufacturing is a technology that can produce 3D parts by stacking metal-based materials such as metal powder and metal filaments, and is a technology that dramatically shortens the process steps compared to existing part processing processes. Among them, the Direct Energy Deposition (DED) process is a technology that produces parts with nearly 3D shapes by supplying metal powder to a target position and melting and stacking it with a laser heat source, repeating this process.

[0007] In order to produce a high-entropy alloy that exhibits excellent plastic hardening and elongation, the present invention has been completed by researching a method for producing a high-entropy alloy as a heterostructure material through the aforementioned layer-by-layer manufacturing process. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] ES Kim et al., J. Alloys Compd., Vol. 942, 169062 (2023) Summary of the Invention [Problem to be solved by the invention]

[0009] The technical problem to be solved by the present invention is to provide a high-entropy alloy that has excellent mechanical properties at room temperature by forming a multiple heterostructure through the formation of BCC martensite and precipitation phases, thereby having excellent yield strength and elongation at room temperature, and additionally having excellent tensile strength and elongation through transformation-induced plasticity during deformation. Another technical problem that the present invention aims to solve is to provide a method for manufacturing a high-entropy alloy having the above-mentioned advantages in a single additive manufacturing process of the high-entropy alloy without the conventional heat treatment and rigid plastic processing processes. [Means for solving the problem]

[0010] The high-entropy alloy according to one embodiment may be a high-entropy alloy including a dual-phase structure of a columnar FCC (Face-Centered Cubic) phase and an equiaxed BCC (Body-Centered Cubic) phase, a cellular structure, and precipitates.

[0011] The high entropy alloy according to one embodiment may be a high entropy alloy whose cell structure satisfies the following formula 1: [Formula 1] 2≦(AB)≦10 A is the Ti content (at%) outside the cell, The above B is the Ti content (at%) inside the cell.

[0012] In one embodiment, the high entropy alloy may be a high entropy alloy in which the BCC phase is a martensite phase formed along a dendrite solidification structure within the FCC phase grains.

[0013] A high entropy alloy according to one embodiment may be a high entropy alloy containing, based on the total amount of the high entropy alloy (100 at%), Ni: 5 to 25 at%, Mn: 2.5 to 15.0 at%, Co: 2.5 to 15.0 at%, Ti: 0.25 to 5.0 at%, Si: 0.25 to 5.0 at%, and the remainder being Fe and other impurities.

[0014] The high-entropy alloy according to one embodiment may be a high-entropy alloy in which the cell structure contains, based on the entire cell structure (100 at%), Ni: 5.0 to 25.0 at%, Mn: 2.5 to 15.0 at%, Co: 2.5 to 15.0 at%, Ti: 0 to 7.5 at%, Si: 0 to 5.0 at%, and the remainder Fe and other impurities.

[0015] According to one embodiment, the high-entropy alloy may be a high-entropy alloy in which the precipitate contains, based on the total precipitate (100 at%), Ni: 10.0 to 30.0 at%, Mn: 2.5 to 15.0 at%, Co: 2.5 to 15.0 at%, Ti: 10.0 to 30.0 at%, Si: 1.0 to 15.0 at%, and the remainder Fe and other impurities.

[0016] The high entropy alloy according to one embodiment may be a high entropy alloy in which the cell structure satisfies the following formula 2: [Formula 2] 5≦(CD)≦30 where C is the Ni content (at%) outside the cell. The above D is the Ni content (at%) inside the cell.

[0017] The high entropy alloy according to one embodiment may be a high entropy alloy in which the cell structure satisfies the following formula 3: [Formula 3] 2≦(EF)≦10 E is the Co content (at%) outside the cell, The above F is the Co content (at%) inside the cell.

[0018] The high entropy alloy according to one embodiment may be a high entropy alloy in which the precipitate satisfies the following formula 4: [Formula 4] 2≦(IJ)≦10 where I is the Mn content (at%) outside the precipitate, The above J is the Mn content (at%) inside the precipitate.

[0019] The high entropy alloy according to one embodiment may be a high entropy alloy in which the precipitate satisfies the following formula 5: [Formula 5] 2≦(KL)≦10 where K is the Co content (at%) outside the precipitate, The above L is the Co content (at%) inside the precipitate.

[0020] The high entropy alloy according to one embodiment may be a high entropy alloy in which the precipitate satisfies the following formula 6: [Formula 6] 5≦(MN)≦35 where M is the Ti content (at%) outside the precipitate, The above N is the Ti content (at%) inside the precipitate.

[0021] The high entropy alloy according to one embodiment may be a high entropy alloy in which the precipitate satisfies the following formula 7: [Formula 7] 2≦(OP)≦20 The above O is the Si content (at%) outside the precipitate, The above P is the Si content (at%) inside the precipitate.

[0022] The high-entropy alloy according to one embodiment may be a high-entropy alloy in which the precipitates are elliptical and have a major axis length of 50 to 500 nm.

[0023] The high entropy alloy according to one embodiment may be a high entropy alloy in which the precipitate phases of said precipitates are Fe2SiTi and Ni3Ti.

[0024] The high entropy alloy according to one embodiment may be a high entropy alloy in which the FCC phase fraction is 85% or more, based on a phase fraction of 100%.

[0025] In one embodiment, the high entropy alloy has an absolute value of the difference between the geometrically necessary dislocations (GND) of the BCC phase and the FCC phase of 10 × 10 12 mm -2 The alloy may be a high-entropy alloy.

[0026] According to one embodiment, the high entropy alloy may be a high entropy alloy in which, when the high entropy alloy is subjected to tensile deformation, a deformation-induced phase transformation of the FCC phase to the BCC phase occurs.

[0027] The high entropy alloy according to one embodiment may be a high entropy alloy, wherein the yield strength of said high entropy alloy is 300 MPa or greater.

[0028] The high entropy alloy according to one embodiment may be a high entropy alloy, wherein the ultimate tensile strength of said high entropy alloy is 700 MPa or greater.

[0029] In addition, according to another embodiment, a method for manufacturing a high-entropy alloy includes the steps of manufacturing an alloy powder from raw metals, melting the alloy powder by supplying energy to the alloy powder by irradiating it with a laser beam, and stacking the molten alloy powder to manufacture an alloy. The manufactured high-entropy alloy may be a method for manufacturing a high-entropy alloy that includes a dual-phase structure of a columnar FCC (Face-Centered Cubic) phase and an equiaxed BCC (Body-Centered Cubic) phase, a cellular structure, and precipitates.

[0030] In one embodiment, the method for producing a high entropy alloy may be a method for producing a high entropy alloy, wherein the alloy powder produced in the step of producing the raw metal into alloy powder has a D50 in the range of 45 to 95 μm.

[0031] According to one embodiment, the method for producing a high entropy alloy may be a method for producing a high entropy alloy, wherein the alloy powder produced in the step of producing the raw metal into alloy powder has a volume fraction of powder particles corresponding to D40 to D60 in the powder particle size distribution of 30 volume % or more.

[0032] According to one embodiment, the method for producing a high entropy alloy may be a method for producing a high entropy alloy, wherein the laser beam has an output of 220 watts (W) or more in the step of supplying energy to the alloy powder to melt it.

[0033] According to one embodiment, the method for manufacturing a high-entropy alloy may be a method for manufacturing a high-entropy alloy, in which an FCC phase matrix grown in the opposite direction to the heat flow and a BCC martensite phase formed by thermal history are formed in the step of manufacturing the alloy by stacking the molten alloy powder. [Effects of the Invention]

[0034] According to one embodiment of the present invention, the high-entropy alloy is manufactured using a single additive manufacturing process, without the conventional processes of heat treatment and rigid-plastic processing, by inducing a multiple heterostructure through the formation of BCC martensite and precipitate phases. At the same time, high geometrically necessary dislocations are formed near the BCC martensite, resulting in excellent mechanical properties such as yield strength, tensile strength, and elongation at room temperature. In addition, the deformation-induced phase transformation that occurs during deformation provides a high-entropy alloy with excellent bake hardening properties.

[0035] According to another embodiment of the present invention, a method for manufacturing a high-entropy alloy can provide a method for manufacturing a high-entropy alloy having the above-mentioned advantages by inducing a heterostructure through the formation of BCC martensite and precipitate phases in a single additive manufacturing process without performing the existing processes of heat treatment and rigid-plastic processing. [Brief explanation of the drawings]

[0036] [Figure 1] This is a SEM-EBSD result on a 20 μm-200 μm scale of a cross section of a high-entropy alloy according to an embodiment of the present invention, taken along the stacking direction. [Figure 2] FIG. 2 is a diagram showing the particle size distribution and particle size of the alloy powder used in the examples of the present invention. [Figure 3] 1A and 1B are diagrams showing a phase map and an inverse pole figure (IPF) map observed by cross-sectional SEM-EBSD of the alloy powder used in the examples of the present invention. [Figure 4] 1 shows an equilibrium phase diagram of a high-entropy alloy according to an embodiment of the present invention. [Figure 5] This shows ECCI and phase map results observed using SEM-EBSD on a 500 nm-20 μm scale of a cross section of a high-entropy alloy according to an embodiment of the present invention, viewed along the stacking direction. [Figure 6]This is an EDS result observed using SEM-EBSD on a 500 nm-20 μm scale of a cross section of a high-entropy alloy according to an embodiment of the present invention, viewed along the stacking direction. [Figure 7] TEM, EDS, and SAED results on a 20nm-500nm scale of a cross section of a high-entropy alloy according to an embodiment of the present invention, viewed along the stacking direction. [Figure 8] This is an SEM-EBSD result on a 500 nm-20 μm scale of a cross section of a high-entropy alloy according to Comparative Example 1 of the present invention, viewed along the additive manufacturing direction. [Figure 9] This is an SEM-EBSD result on a 20 μm-200 μm scale of a cross section of a high-entropy alloy according to Comparative Example 2 of the present invention, viewed along the additive manufacturing direction. [Figure 10] This is an SEM-EBSD result on a 20 μm-200 μm scale of a cross section of a high-entropy alloy according to Comparative Example 3 of the present invention, viewed along the additive manufacturing direction. [Figure 11] TEM, EDS, and SAED results on a 500 nm-20 μm scale of a cross section of a high-entropy alloy according to Comparative Example 3 of the present invention, viewed along the additive manufacturing direction. [Figure 12] 1 is a graph showing deformation rates and stresses of high-entropy alloys according to examples and comparative examples of the present invention. [Figure 13] 1 shows DIC images of a high-entropy alloy according to an embodiment of the present invention acquired at different deformation rates and SEM-EBSD results at a scale of 500 nm-200 μm of a cross section viewed along the stacking direction. [Figure 14] This shows the results of TEM analysis of the microstructure of the example that was deformed by 25% at a nano-scale of 500 nm or less. [Figure 15] This shows the results of TEM analysis of the 25% deformed microstructure of the example at a nano-scale of 500 nm or less. [Figure 16] This shows the results of TEM analysis of the microstructure of the example that was deformed by 25% at a nano-scale of 500 nm or less. [Figure 17] This shows the results of TEM analysis of the microstructure of the example that was deformed by 25% at a nano-scale of 500 nm or less. [Figure 18] This shows the results of TEM analysis of the microstructure of the example that was deformed by 25% at a nano-scale of 500 nm or less. [Figure 19] This shows the results of TEM analysis of the microstructure of the example that was deformed by 25% at a nano-scale of 500 nm or less. [Figure 20] This is a schematic diagram of the heterostructure and deformation behavior of a high-entropy alloy drawn based on the microstructural analysis results of the example. DETAILED DESCRIPTION OF THE INVENTION

[0037] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0038] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the phrase clearly dictates otherwise. As used in the specification, the term "comprising" refers to the inclusion of particular features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components. When a part is referred to as being "on" or "above" another part, it means that it is directly on or above the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them. Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted as having an ideal or very formal meaning unless otherwise defined. Hereinafter, embodiments of the present invention will be described in detail, but these are presented as examples and should not be construed as limiting the present invention, which is defined only by the scope of the claims set forth below.

[0039] According to one embodiment of the present invention, the high entropy alloy may be a high entropy alloy including a dual phase structure of face-centered cubic (FCC) and body-centered cubic (BCC) phases, a cellular structure, and precipitates. The high-entropy alloy may be a quinary or higher multi-element alloy, specifically an alloy containing Fe, Ni, Co, Mn, Ti, and Si elements. The dual phase structure is a structure containing two main phases. The term "two main phases" refers to a phase fraction of the two main phases of 80% or more, specifically 80-100%, 85-100%, 80-99%, or 85-99%, based on a phase fraction of 100%.

[0040] The cellular structure may refer to a structure surrounded by different phases or compositions. Specifically, the cellular structure may be composed of dual phases formed by composition separation within a grain, and may be a structure formed of a phase different from other regions in a dendrite cross section observed by enlarging a grain. The phases formed inside and outside the cells may differ in composition, or the composition of the outside and inside of the cells may be different. In this case, the inside of the cells may be a BCC phase, and the outside of the cells may be an FCC phase. The difference in composition between the inside and outside of the cells may be formed by composition separation due to supercooling. The cell structure can be confirmed using an SEM. The shape of the cell structure may be circular or elliptical, and the size of the cells may be, but is not limited to, 0.1 to 10 μm, 0.5 to 8 μm, 0.7 to 6 μm, or 1 to 4 μm.

[0041] The precipitates may be formed separately from the cell structure and may be regions with different compositions inside and outside the cell structure. They may be derived from Ti or Si, and specifically may have precipitate phases of Fe2SiTi and Ni3Ti. The precipitates can be identified through lattice structure analysis using SAED. The shape of the precipitate may be circular or elliptical, and the size of the precipitate may be, but is not limited to, 1 to 900 nm, 10 to 800 nm, 30 to 700 nm, 50 to 500 nm, or 100 to 400 nm based on the major axis length. Meanwhile, in this specification, the precipitate may be named nanoprecipitates.

[0042] In one embodiment, the FCC phase may be formed from columnar crystals, and the BCC phase may be formed from equiaxed crystals. This allows for the formation of a first heterostructure in which two regions are formed with different shapes. The first heterostructure can be observed on a 20 μm-200 μm scale. The first heterostructure provides excellent yield strength as well as ultimate tensile strength. In this case, equiaxed crystals are defined as alloy particles with an average aspect ratio of 2.0 or less, and can be formed from crystal grains of similar size in all directions. The average aspect ratio may be specifically 0.5 or more. When the temperature gradient in a specific direction is large, coarse columnar crystal grains with an average aspect ratio that does not fall within the above range can be formed. Specifically, columnar crystals refer to thin, long crystals like pillars. Here, the aspect ratio of the grains constituting the alloy can be calculated by analyzing a SEM-EBSD image of a cross section of the alloy using a known image analysis program.

[0043] In one embodiment, the cell structure may independently satisfy the following formulas 1 to 3, thereby forming a second heterostructure having heterogeneous compositions inside and outside the cell. The second heterostructure may be observed on a 500 nm to 20 μm scale. Here, the outside of the cell may refer to a region outside the cell that is 0.1 μm or more away from the cell boundary, specifically, a region outside the cell at a distance of 0.1 to 50 μm, 0.1 to 20 μm, or 1 to 20 μm.

[0044] [Formula 1] 2≦(AB)≦10 A is the Ti content (at%) outside the cell, The above B is the Ti content (at%) inside the cell.

[0045] [Formula 2] 5≦(CD)≦30 where C is the Ni content (at%) outside the cell. The above D is the Ni content (at%) inside the cell.

[0046] [Formula 3] 2.5≦(EF)≦10 E is the Co content (at%) outside the cell, The above F is the Co content (at%) inside the cell. By satisfying the above formulas 1 to 3 independently or simultaneously, a second heterostructure having heterogeneous compositions inside and outside the cell can be formed, and the second heterostructure can provide excellent yield strength as well as ultimate tensile strength.

[0047] In one embodiment, the BCC phase is a martensite phase formed along the dendrite solidification structure within the FCC phase grains, which is a non-equilibrium phase. The formation of this relatively soft FCC phase matrix within the cellular structure ensures elongation, while the formation of the BCC phase outside the cellular structure provides heterostructure strengthening, resulting in excellent yield strength and ultimate tensile strength.

[0048] In one embodiment, the absolute value of the difference between the geometrically necessary dislocations (GND) of the BCC phase and the FCC phase is 10×10 12 mm -2 It may be more than 20 × 10 12 mm -2 That's it, 10 x 10 12 ~100×10 12 mm -2 , 15×10 12 ~80×10 12 mm -2 or 20 x 10 12 ~60×10 12 mm -2 may be.

[0049] In one embodiment, the FCC phase fraction may be 85% or more, based on a 100% FCC phase fraction. Specifically, the FCC phase may be 87% or more, more specifically, the FCC phase may be 89% or more. Even more specifically, the FCC phase may be 95% or less. When the BCC phase and the FCC phase satisfy the above ranges, a soft FCC matrix is formed, ensuring the elongation of the alloy while also achieving excellent yield strength and tensile strength. If the FCC phase content is outside the lower limit of the above range, the elongation rate decreases, resulting in a brittle alloy.If the FCC phase content is outside the upper limit of the above range, the fraction of the BCC phase, which affects strength, decreases, resulting in reduced yield strength and tensile strength.

[0050] In one embodiment, the precipitates may independently satisfy the following formulas 4 to 7, thereby forming a third heterostructure in which the interior and exterior of the precipitates have heterogeneous compositions. The third heterostructure can be observed on a 20-500 nm scale. The third heterostructure provides excellent yield strength and ultimate tensile strength. In this case, the outside of the precipitate may refer to a region outside the precipitate that is 0.01 nm or more away from the precipitate boundary, and specifically may refer to a region outside the precipitate that is 0.01 to 500 nm, 0.1 to 500 nm, 1 to 500 nm, 1 to 400 nm, 10 to 400 nm, or 20 to 300 nm away.

[0051] [Formula 4] 2≦(IJ)≦10 where I is the Mn content (at%) outside the precipitate, The above J is the Mn content (at%) inside the precipitate.

[0052] [Formula 5] 2≦(KL)≦10 where K is the Co content (at%) outside the precipitate, The above L is the Co content (at%) inside the precipitate.

[0053] [Formula 6] 5≦(MN)≦35 where M is the Ti content (at%) outside the precipitate, The above N is the Ti content (at%) inside the precipitate.

[0054] [Formula 7] 2≦(OP)≦20 The above O is the Si content (at%) outside the precipitate, The above P is the Si content (at%) inside the precipitate.

[0055] In one embodiment, the precipitates may be elliptical, and the length of the major axis of the precipitates may be 50 to 500 nm, specifically 50 to 400 nm, 70 to 400 nm, 90 to 350 nm, or 100 to 300 nm. In this case, the length of the major axis of the precipitates may be measured in a horizontal plane. When the precipitates satisfy the length range, the high-entropy alloy can ensure excellent yield strength and tensile strength.

[0056] In one embodiment, the precipitate phases of the precipitates may be Fe2SiTi and Ni3Ti. The precipitates are precipitated as the two types of precipitate phases, which allows the high-entropy alloy to ensure excellent yield strength and tensile strength.

[0057] In one embodiment, the high-entropy alloy of the present invention can contain, relative to the total high-entropy alloy (100 at%), Ni: 5-25 at%, Mn: 2.5-15.0 at%, Co: 2.5-15.0 at%, Ti: 0.25-5.0 at%, Si: 0.25-5.0 at%, and the balance being Fe and other impurities. The reasons for limiting the composition of the high-entropy alloy will be explained below.

[0058] Ni: 5 to 25 at% Nickel (Ni) is an element that plays a role in stabilizing the FCC phase, and may be contained in an amount of 5 to 25 at %, specifically 7.5 to 20.0 at %. If the nickel content exceeds the upper limit, a soft FCC phase is formed, resulting in reduced yield strength and tensile strength, whereas if the nickel content exceeds the lower limit, the BCC phase is stabilized, suppressing the formation of the FCC phase, resulting in brittleness of the alloy.

[0059] Mn: 2.5 to 15 at% Manganese (Mn) is an element that stabilizes the FCC phase, and may be contained in an amount of 2.5 to 15 at %, specifically 5.0 to 12.5 at %. If the manganese content exceeds the upper limit, a soft FCC phase is formed, resulting in reduced yield strength and tensile strength, whereas if the manganese content exceeds the lower limit, the BCC phase is stabilized, suppressing the formation of the FCC phase, resulting in brittleness of the alloy.

[0060] Co: 2.5 to 15 at% Cobalt (Co) is an element that stabilizes the FCC phase, and may be contained in an amount of 2.5 to 15 at %, specifically 5.0 to 12.5 at %. If the cobalt content exceeds the upper limit, a soft FCC phase is formed, resulting in reduced yield strength and tensile strength, whereas if the cobalt content exceeds the lower limit, the BCC phase is stabilized, suppressing the formation of the FCC phase, resulting in brittleness of the alloy.

[0061] Ti: 0.25 to 5.0 at% Titanium (Ti) is an element that plays a role in forming nano-precipitates, and may be contained in an amount of 0.25 to 5.0 at %, specifically 1.0 to 4.0 at %. If the titanium content exceeds the upper limit, there is a problem that brittle intermetallic compounds other than nanoprecipitates described below are formed, and if the titanium content exceeds the lower limit, there is a problem that nanoprecipitates that improve yield strength are not formed.

[0062] Si: 0.25 to 5.0 at% Silicon (Si) is an element that constitutes nanoprecipitates, and the silicon (Si) content may be 0.25 to 5.0 at %, specifically 1.0 to 3.0 at %. If the silicon content exceeds the upper limit, there is a problem of forming brittle intermetallic compounds other than the nanoprecipitates described below, and if the silicon content exceeds the lower limit, there is a problem of not forming nanoprecipitates that improve yield strength.

[0063] Fe: 60.0 to 75.0 at% Iron (Fe) is a major element that dissolves other alloy elements to form a matrix of FCC or BCC structure and martensite. The iron content may be 60 to 75.0 at %, specifically 62.5 to 70.5 at %. If the iron content exceeds the upper limit, the BCC phase is stabilized, suppressing the formation of the FCC phase, resulting in brittleness of the alloy.If the iron content exceeds the lower limit, brittle intermetallic compounds are formed.

[0064] Furthermore, the high-entropy alloy may contain unavoidable impurities. "Avoidable impurities" refer to impurities that are inevitably mixed in during the steelmaking and manufacturing processes of the high-entropy alloy. Because unavoidable impurities are widely known, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a range that does not detract from the technical concept of the present invention. When an additional element is further included, the remaining Fe may be replaced with an additional element.

[0065] In one embodiment, the cell structure of the high-entropy alloy of the present invention may contain, based on the total cell structure (100 at%), Ni: 5.0-25.0 at%, Mn: 2.5-15.0 at%, Co: 2.5-15.0 at%, Ti: 0-7.5 at%, Si: 0-5.0 at%, and the remainder Fe and other impurities. The interior of the cell structure may have a different composition from the exterior of the cell, forming a heterostructure, and the heterostructure may enable the high-entropy alloy to ensure excellent yield strength and tensile strength. The specific reasons for limiting the cell structure composition will be explained below.

[0066] Ni: 5 to 25 at% Nickel (Ni) is an element that plays a role in stabilizing the FCC phase, and may be contained in an amount of 5 to 25 at %, specifically 7.5 to 20.0 at %. Elemental segregation that occurs during the early stages of solidification causes the interior of the cells to solidify with a deficiency of Ni, an FCC phase stabilizing element, causing the interior of the cells to rapidly transform into the BCC martensite phase with low FCC stability. Conversely, the exterior of the cells, which is rich in Ni, has higher FCC phase stability than the interior of the cell structure and solidifies as the FCC phase.

[0067] Mn: 2.5 to 15 at% Manganese (Mn) is an element that stabilizes the FCC phase, and may be contained in an amount of 2.5 to 15 at %, specifically 5.0 to 12.5 at %. Due to elemental segregation that occurs during the early stages of solidification, the interior of the cells solidifies with a shortage of Mn, an FCC phase stabilizing element, causing the interior of the cells to rapidly transform into the BCC martensite phase with low FCC stability. Conversely, the exterior of the cells, which is rich in Mn, has higher FCC phase stability than the interior of the cell structure and solidifies as the FCC phase.

[0068] Co: 2.5 to 15 at% Cobalt (Co) is an element that stabilizes the FCC phase, and may be contained in an amount of 2.5 to 15 at %, specifically 5.0 to 12.5 at %.

[0069] Ti: 0 to 7.5 at% Titanium (Ti) is an element that plays a role in forming nano-precipitates, and may be contained in an amount of 0 to 7.5 at %, specifically 0.25 to 5.0 at %, or 1.0 to 4.0 at %. Similar to the elemental separation of Ni and Mn, Ti, which has a higher melting point, is also observed to be considerably separated into elements outside the cell.

[0070] Si: 0 to 5.0 at% Silicon (Si) is an element that constitutes nanoprecipitates, and the silicon (Si) content may be 0 to 5.0 at %, specifically 1.0 to 3.0 at %. Similar to the elemental separation of Mn in the case of Ni, Si, which is a more non-metallic element, is also considerably separated into elements and observed outside the cell.

[0071] Fe: 60.0 to 75.0 at% Iron (Fe) is a major element that dissolves other alloy elements to form a matrix of FCC or BCC structure and martensite. The iron content may be 60 to 75.0 at %, specifically 62.5 to 70.5 at %.

[0072] The cell structure may also contain unavoidable impurities. "Avoidable impurities" refers to impurities that are inevitably mixed in during the steelmaking and manufacturing processes of high-entropy alloys. Because unavoidable impurities are widely known, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a range that does not detract from the technical concept of the present invention. When an additional element is further included, the remaining Fe may be replaced with an additional element.

[0073] In one embodiment, the precipitate can contain, based on the total precipitate (100 at%), 10.0 to 30.0 at% Ni, 2.5 to 15.0 at% Mn, 2.5 to 15.0 at% Co, 10.0 to 30.0 at% Ti, 1.0 to 15.0 at% Si, and the remainder being Fe and other impurities. The reasons for limiting the composition of the precipitate will be explained below.

[0074] Ni: 10.0 to 30.0 at% The precipitate may contain nickel (Ni) in an amount of 10.0 to 30.0 at %. Specifically, the nickel content may be 17.5 to 27.5 at %.

[0075] Mn: 2.5 to 15.0 at% The precipitate may contain manganese (Mn) in an amount of 2.5 to 15.0 at %. Specifically, the manganese content may be 4.5 to 12.5 at %.

[0076] Co: 2.5 to 15.0 at% The precipitate may contain 2.5 to 15.0 at % of cobalt (Co), specifically, 4.5 to 12.5 at % of cobalt (Co).

[0077] Ti: 10.0 to 30.0 at% The precipitate may contain titanium (Ti) in an amount of 10.0 to 30.0 at %. Specifically, the titanium content may be 17.5 to 27.5 at %.

[0078] Si: 1.0 to 15.0 at% The precipitate may contain silicon (Si) in an amount of 1.0 to 15.0 at %. Specifically, the precipitate may contain silicon (Si) in an amount of 2.5 to 12.5 at %.

[0079] Fe: 10.0 to 60.0 at% The precipitate may contain 10.0 to 60.0 at % of iron (Fe). Specifically, the iron (Fe) may be contained in an amount of 20.0 to 50.0 at %.

[0080] The precipitates may also contain unavoidable impurities. "Avoidable impurities" refer to impurities that are inevitably mixed in during steelmaking and the manufacturing process of high-entropy alloys. Because unavoidable impurities are widely known, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the above-described alloy components is not excluded, and various elements may be included within a range that does not detract from the technical concept of the present invention. When an additional element is further included, the remaining Fe may be replaced with an additional element.

[0081] In one embodiment, when the high-entropy alloy is subjected to tensile deformation, the FCC phase undergoes a deformation-induced phase transformation to the BCC phase. Specifically, when the high-entropy alloy is subjected to tensile deformation, the strain hardening rate is improved due to the transformation-induced plasticity (TRIP) effect, thereby ensuring excellent tensile strength and elongation.

[0082] In one embodiment, the high-entropy alloy is an alloy that has excellent yield strength and tensile strength at room temperature, 290 to 310K, specifically, 295 to 300K.

[0083] In one embodiment, the yield strength may be 300 MPa or more. Specifically, the yield strength may be 320 MPa, 340 MPa, 360 MPa, 380 MPa, or 400 MPa or more.

[0084] In one embodiment, the high-entropy alloy may have an ultimate tensile strength of 700 MPa or more, specifically, 800 MPa, 900 MPa, 1000 MPa, 1010 MPa, or 1020 MPa or more.

[0085] In one embodiment, the uniform stretching ratio may be 20% or more. Specifically, the uniform stretching ratio may be 22% or more, 24% or more, 26% or more, 28% or more, or 30% or more.

[0086] In one embodiment, the total stretch ratio may be 30% or more. Specifically, the total stretch ratio may be 32% or more, 34% or more, 36% or more, 38% or more, 40% or more, 42% or more, 44% or more, or 46% to 100%.

[0087] According to another embodiment of the present invention, a method for manufacturing a high-entropy alloy may include the steps of manufacturing an alloy powder from a raw metal, supplying energy to the alloy powder to melt the alloy powder, and stacking the molten alloy powder to manufacture an alloy. In this case, the manufactured high-entropy alloy may have the configuration and characteristics of the high-entropy alloy described above. The step of preparing the alloy powder from the raw metal may include charging the prepared raw metal. The raw metal has been described in detail in the high-entropy alloy section above, and reference may be made to the high-entropy alloy section above to the extent that it is not inconsistent. The step of preparing the alloy powder from the raw metal can be performed by one of gas atomization, ultrasonic wave, and plasma, and the alloy powder can be formed with a size and particle size distribution suitable for the metal additive manufacturing process. The gas atomization can use an inert gas known to those of ordinary skill in the art, specifically, but not limited to, helium, neon, argon, krypton, or xenon.

[0088] The appropriate powder particle size distribution can be appropriately changed depending on the metal additive manufacturing process. Specifically, in the direct energy deposition (DED) process of metal additive manufacturing, the volume fraction of powder particles corresponding to D40 to D60 in the powder particle size distribution is 30% by volume or more, specifically 30 to 70% by volume or 35 to 60% by volume. This can mean that the powder particle size distribution is not irregular, but the particle sizes are concentrated around the average. In this case, the particle size of the powder may be such that D10 is in the range of 30 to 50 μm, D50 is in the range of 45 to 95 μm, and D90 is in the range of 130 to 170 μm. If the powder particle size distribution range and the powder particle size range are not satisfied, problems such as clogging of the nozzle due to the powder, cracks, and voids may occur during alloy manufacturing using a metal additive manufacturing process.

[0089] In one embodiment, the energy used in the step of supplying energy to the alloy powder to melt it may be one or more selected from the group consisting of a laser beam, an electron beam, and plasma, but is not limited thereto. Any energy supply source that can supply energy to melt a material in the art may be used. The step of supplying energy to the alloy powder to melt it can be specifically performed by irradiating it with a laser beam. The output of the laser beam may be 220 watts (W) or more. If the laser beam output satisfies this range, the raw material metal can be completely melted, resulting in solidification without porous defects. On the other hand, if the laser beam output is less than 220 watts (W), the raw material metal may not be completely melted, resulting in an alloy having porous defects.

[0090] In one embodiment, the step of layering the molten alloy powder to form the alloy is performed sequentially.

[0091] In one embodiment, the step of manufacturing an alloy by layering the molten alloy powder can be performed in real time by simultaneously supplying metal powder and irradiating the high-power laser beam. Specifically, using a direct energy deposition (DED) process, metal powder is supplied to a target position and melted and layered by a laser heat source, and this process can be repeated to manufacture an alloy.

[0092] In one embodiment, in the step of manufacturing the alloy by layering the molten alloy powder, an FCC phase matrix grown in the opposite direction to the heat flow and a BCC martensite phase formed by the thermal history may be formed. The high entropy alloy manufactured by the above-described method for manufacturing a high entropy alloy can exhibit the above-described excellent effects, including the structure and composition of the high entropy alloy.

[0093] Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples. [Example]

[0094] High-entropy alloy and method for producing the same <Example> Fe, Ni, Co, Mn, Ti, and Si metals with a purity of 99.95% or higher were prepared and weighed in a mixture ratio of Fe: 65 at%, Ni: 15 at%, Co: 8 at%, Mn: 8 at%, Ti: 3 at%, and Si: 1 at%, and alloy powder was produced by gas atomization under an argon atmosphere. The prepared alloy powder was then loaded into a Direct Energy Deposition (DED) device (MX-LAB, InssTek), and an alloy block measuring 7 mm x 30 mm x 10 mm in width, length, and height was fabricated using a laser power of 220 W, a feed rate of 2.75 g / min, a laser scanning speed of 850 mm / min, and a hatch spacing of 0.3 mm.

[0095] <Comparative Example 1> Fe, Ni, Co, Mn, Ti, and Si metals with a purity of 99.95% or higher were prepared and weighed in the following mixing ratios: Fe: 65 at%, Ni: 15 at%, Co: 8 at%, Mn: 8 at%, Ti: 3 at%, and Si: 1 at%. The prepared raw metals were then placed in a zirconia crucible and melted at 1,550°C. A rectangular hexahedron-shaped alloy ingot measuring 7.8 mm thick, 150 g, 33 mm wide, and 80 mm long was cast using a mold, and annealed at 900°C for 10 minutes for homogenization and recrystallization.

[0096] <Comparative Example 2> An alloy was produced using the same process as in Comparative Example 1, except that Co, Cr, Fe, Mn, and Ni metals with a purity of 99.95% or higher were prepared and weighed out in a mixing ratio of Co: 20 at%, Cr: 20 at%, Fe: 20 at%, Mn: 20 at%, and Ni: 20 at%.

[0097] <Comparative Example 3> An alloy was manufactured using the same process as in the examples, except that Co, Cr, Fe, Mn, and Ni metals with a purity of 99.95% or higher were prepared and weighed out in a mixing ratio of Co: 20 at%, Cr: 20 at%, Fe: 20 at%, Mn: 20 at%, and Ni: 20 at%.

[0098] Experimental Example 1: Particle size distribution and cross-section confirmation of alloy powder The Fe used in the above examples 65 Ni 15 The particle size distribution and cross section of Co8Mn8Ti3Si (at%, constitutional entropy ΔS=1.12R, R: gas constant) alloy powder were confirmed. (1) Checking the particle size distribution of alloy powder A laser particle size analyzer (Mastersizer3000) was used to measure the size and particle size distribution of the powder particles, and the particle size distribution and particle size are shown in Figure 2. Referring to Figure 2, D10, D50, and D90 were confirmed to be 44.7μm, 66.5μm, and 96.5μm, respectively, and the average particle size was confirmed to be 66μm or less. In addition, the volume fraction of powder particles corresponding to D40 to D60 was confirmed to be 40% by volume. This corresponds to the particle size and particle size distribution suitable for the direct energy deposition metal additive manufacturing process.

[0099] (2) Cross-section confirmation of alloy powder The cross-sectional microstructure of the alloy powder was observed using EBSD (Electron Backscatter Diffraction; Philips, XL30S, 25 kV, step size = 50 nm) analysis. Raw EBSD data were evaluated using Orientation Imaging Microscope (OIM) software (TSL-OIM analysis, version 7). Figure 3 shows the phase map and inverse pole figure (IPF) map of the cross-sectional SEM-EBSD (scanning electron microscope-electron backscatter diffraction) results of the high-entropy alloy powder. Referring to Figure 3, Fe 65 Ni 15 It can be seen that the Co8Mn8Ti3Si alloy powder has a single phase face-centered cubic (FCC) structure and is produced in a spherical shape without cracks or voids.

[0100] Experimental Example 2: Equilibrium Phase Diagram Analysis of High-Entropy Alloys 4 shows an equilibrium diagram of a high-entropy alloy according to an embodiment of the present invention. The equilibrium diagram was calculated using Thermo-Calc software, a thermodynamic calculation program. In FIG. 4, α means BCC phase, γ means FCC phase, and L means liquid. This confirmed that the FCC phase of the present invention exists as a metastable phase at high temperatures, and that a considerable proportion of the BCC phase exists as a stable phase at temperatures below approximately 700°C. It was also confirmed that Fe2SiTi and Ni3Ti type phases precipitated.

[0101] Experimental Example 3: Microstructural analysis of high-entropy alloys First, the samples were cross-sectioned and metallurgically polished using 0.25 μm colloidal silica. The phase composition of the high-entropy alloys was confirmed using a synchrotron X-ray diffractometer (XRD, 1.5402 Å wavelength, scan rate 0.6° / min, 2θ 30°-100°, step size 0.02, Si(111) double crystal monochromator). Diffraction patterns were detected using an Oxford X2000 scintillation detector. Microstructural observations were performed using a field emission scanning electron microscope (FE-SEM, JEOL JSM-7100 F, 20 kV), electron channeling contrast imaging (ECCI), electron backscatter diffraction (EBSD, Philips, XL30S, 25 kV, step size = 50 nm), and transmission Kikuchi diffraction (TKD, JEOL JSM-7900 F, 20 keV, step size = 15 nm) analysis. Raw EBSD data were evaluated using orientation imaging microscope (OIM) software (TSL-OIM analysis, version 7). High-resolution TEM characterization of samples fabricated with a focused ion beam (FIB, FEI Helios Nanolab 650i) was performed using a high-resolution transmission electron microscope (JEOL2100 F, Japan) at an accelerating voltage of 200 keV. The elemental distribution was further characterized through FE-SEM and TEM equipped with energy-dispersive X-ray spectroscopy (EDS). 1 and 5 to 12 show the results of SEM-EBSD observation of the microstructures of the high-entropy alloys manufactured according to the examples and comparative examples of the present invention, which will be described in detail below.

[0102] (1) Microstructural analysis on a 20μm-200μm scale FIG. 1 shows the results of SEM-EBSD on a 20 μm-200 μm scale of a cross section of the example viewed along the stacking direction. Referring to Figure 1, it can be seen that the material has a dual phase structure of FCC and BCC (martensite) phases. Specifically, it can be seen that the first heterostructure is composed of a columnar FCC phase and small, uniformly dispersed BCC phases. The IPF map results showed that the FCC phase grew into columnar grains along the stacking direction, opposite the maximum heat flow, while BCC martensite formed into equiaxed grains along the dendrite solidification structure within the FCC phase grains, not at the grain boundaries. The alloy is defined as having an equiaxed grain when the average aspect ratio of the alloy grains is within 2.0, and when the average aspect ratio is outside this range, it is considered to have formed into columnar grains. The aspect ratio of the alloy grains can be calculated by analyzing images of the cross section of the alloy using a known image analysis program.

[0103] The KAM value is a value that relatively indicates the degree of deviation in orientation within a metal material, and can be used to compare deformation levels. Looking at the KAM map, a high KAM value is observed along the solidification direction because a thermal deformation of about 2% is induced due to the fast solidification rate in the MAM process. In particular, a martensite phase transformation that causes crystal lattice distortion occurs, so there is a relative deformation near the BCC martensite. Looking at the geometrically necessary dislocation (GND) map of each phase, FCC has a high GND (22.9 × 10 12 mm -2 ) were observed, which are dislocations associated with the formation of BCC martensite during the metal additive manufacturing process. Similarly, BCC martensite formed from the metastable FCC phase due to the thermal gradient created during the process is highly deformed and exhibits a very high GND (44.2 × 10 12 mm -2 ) In other words, in the examples, it was confirmed that FCC and BCC have different phase shapes formed from columnar crystals and equiaxed crystals, have different degrees of phase deformation, and have different GNDs, resulting in the existence of heterostructures on a 20 μm-200 μm scale.

[0104] <Comparative Example> On the other hand, when the cross sections of the alloys prepared in Comparative Examples 2 and 3 of the present invention were observed, no heterostructure was found. Figure 9 shows the SEM-EBSD results of Comparative Example 2 on a 20 μm-200 μm scale. Referring to Figure 9, it can be seen that Comparative Example 2 is formed from a single FCC phase, and no regions with different compositions are found.

[0105] Figure 10 shows the SEM-EBSD results for Comparative Example 3 on a 20 μm-200 μm scale. Referring to Figure 10, it can be seen that Comparative Example 3 is formed from a single FCC phase, and no regions of different composition are found. Due to the complex thermal history, it is composed of a structure consisting of large crystal grains (arrows positioned relatively lower than the other arrows) and small crystal grains (arrows positioned relatively higher than the other arrows), but both crystal grains are formed from the same phase and the same composition. That is, it was confirmed that the comparative example did not have a heterostructure like the example.

[0106] (2) Microstructural analysis on the 500nm-20μm scale <Example> 5 and 6 show EDS, ECCI, and phase map results at a 500 nm-20 μm scale of a cross section along the stacking direction of a high-entropy alloy fabricated by the direct energy deposition process according to an embodiment of the present invention. Heterogeneity of the composition and phases can be confirmed. Referring to Figure 5, the results of ECCI (Electron Channeling Contrast Images) show a striking contrast. A cell structure is formed inside the crystal grains due to the fast solidification rate of the metal additive manufacturing process. The phase map confirms the existence of a sub-microscale dual phase structure, specifically, the inside of the cell structure is formed of BCC and the outside of the cell is formed of FCC.

[0107] Referring to Figure 6, EDS analysis of the heterogeneous dual-phase structure shows that elemental segregation occurred during the early stages of solidification, resulting in a lack of FCC phase stabilizing elements Mn and Ni inside the cells. As a result, the inside of the cells rapidly transformed into the BCC martensite phase with low FCC stability. Conversely, the outside of the cells, which is rich in Mn and Ni, had higher FCC phase stability than the inside of the cell structure and solidified as the FCC phase. Additionally, Ti, which has a higher melting point, was observed to be significantly segregated outside the cells. Furthermore, Si was mainly observed in the precipitated phase. The specific composition is shown in Table I below.

[0108] [Table 1]

[0109] As can be seen from Table I above, the Ni content is 15 at% inside the cell, which is lower than the 20 at% outside the cell, and the Mn content is 7.5 at% inside the cell, which is lower than the 10.5 at% outside the cell. The Co content is also 7.5 at% inside the cell, which is lower than the 10.5 at% outside the cell. Meanwhile, the Ti content is 2.5 at% inside the cell, which is lower than the 5.5 at% outside the cell. The Si content is lower than 1 at% both inside and outside the cell, with most of the Si contributing to precipitate formation. Specifically, the following was confirmed: (AB)=3.0 A is the Ti content (at%) outside the cell, The above B is the Ti content (at%) inside the cell. (CD)=5.0 where C is the Ni content (at%) outside the cell. The above D is the Ni content (at%) inside the cell. (EF)=3.0 E is the Co content (at%) outside the cell, The above F is the Co content (at%) inside the cell. In other words, it was confirmed that the composition inside and outside of the cell differs, and a heterostructure exists on the 500nm-20μm scale.

[0110] <Comparative Example> On the other hand, when the cross sections of the alloys according to Comparative Examples 1 and 3 of the present invention were observed, no heterostructure was found. Figure 8 shows the SEM-EBSD results for Comparative Example 1 on a 500nm-20μm scale. Heat treatment was performed at 900°C for 10 minutes to complete recrystallization. Referring to Figure 8, it can be seen that all phases of the grains were formed from equiaxed crystals, and HCP martensite and BCC martensite were formed at the grain boundaries, not within the FCC matrix. No difference in composition between the inside and outside of the cells was observed. Figure 11 shows TEM, EDS, and SAED results on a 500 nm-20 μm scale of a cross section of a high-entropy alloy according to Comparative Example 3 of the present invention, taken along the additive manufacturing direction. Manufactured using the same manufacturing process as the Example, a specific structure was formed due to the fast cooling rate characteristic of metal additive manufacturing. However, the alloy was made from the same phase, and only slight compositional separation was observed. The degree of compositional separation is shown in Table II below.

[0111] [Table 2]

[0112] (C*-D*)=2.0 C* is the Ni content (at%) outside the specific structure, The above D* is the Ni content (at%) inside the specific structure. (E*-F*)=2.0 E* is the Co content (at%) outside the specific structure, The above F* is the Co content (at %) within the specific structure. That is, in the comparative example, a heterostructure composed of different phases as in the example was not present, and no significant composition separation as in the example was observed.

[0113] (3) Microstructural analysis on the 20nm-500nm scale Figure 7 shows the TEM, EDS, and SAED results for a cross section of the example taken along the stacking direction on a 20-500 nm scale. Heterogeneity in the composition phase, which is difficult to observe on a 20 μm-200 μm scale and a 500 nm-20 μm scale, can be confirmed. Areas with high Ti and Si composition, i.e., nano-precipitates (ellipse major axis length: 100~300nm), are regularly observed outside the cell. This is because the residual thermal history induced when stacking each layer during the metal additive manufacturing process induces a significant heat treatment effect, which can be the driving force behind the precipitation of compositionally separated Ti and Si as a secondary phase. The EDS results in Figure 7 show that the precipitated secondary phase has an increased amount of Ni, Ti, and Si elements compared to the outside of the precipitate. The lattice structure analysis through SAED confirmed that it was P63 / mmc, a=4.79Å, and c=8.12Å. 24 It can be seen that the phase was precipitated in nano-size.

[0114] Specifically, the composition difference between the inside and outside of the nanoprecipitates in the examples is shown in Table III below. As can be seen from Table III below, the Mn nanoprecipitates have a 7.5 at% Mn content, which is lower than the 10.5 at% outside the precipitates. Similarly, the Co nanoprecipitates have a 7.5 at% Co content, which is lower than the 10.5 at% outside the precipitates. Meanwhile, the Ti nanoprecipitates have a 20 at% Ti content, which is significantly higher than the 5.5 at% outside the precipitates. The Si nanoprecipitates have a 7.5 at% Si content, which is higher than the 0.5 at% outside the precipitates.

[0115] [Table 3]

[0116] That is, a different type of precipitate phase from the forged material was precipitated in nano-sized particles evenly along the cell exterior within the matrix, which means that a heterostructure different from the previously mentioned heterostructure was formed on a 20-500 nm scale. On the other hand, in Comparative Examples 1 to 3, no precipitate phase was observed on a scale of 20 nm to 500 nm. As such, it was confirmed that the high-entropy alloys produced in the above-mentioned Examples have three types of heterostructures, while the alloys produced in Comparative Examples 1 to 3 do not have the heterostructures seen in the Examples.

[0117] Experimental Example 4: Analysis of Tensile Test Results Table IV below shows the results of tensile tests at room temperature (298 K) for the high-entropy alloys prepared according to the examples and comparative examples of the present invention. The tensile tests were conducted using a general-purpose tensile testing machine (Instron, Instron 1361) under liquid nitrogen conditions.

[0118] [Table 4]

[0119] 12 is a graph showing the deformation rate and stress of high-entropy alloys according to examples and comparative examples of the present invention. Data indicated by circular labels represent data for the examples, data indicated by solid lines represent data for Comparative Example 1, data indicated by square labels represent data for Comparative Example 2, and data indicated by triangle labels represent data for Comparative Example 3. 12 and Table IV, it can be seen that the Examples having three heterostructures exhibit superior yield strength and tensile strength without the need for additional strength-enhancing processes (e.g., age-hardening heat treatment, rigid-plastic processing) compared to Comparative Examples 1 to 3. Furthermore, while higher metal strength generally leads to lower elongation (a trade-off), the high-entropy alloys of the present invention exhibit superior uniform elongation and total elongation despite their high strength. This confirms that the hetero-strengthening effect is manifested multiple times, resulting in superior mechanical property combinations compared to the comparative examples. Specifically, as can be seen from the relative comparison indices for mechanical property combinations, "yield strength × uniform elongation (MPa%)" and "ultimate tensile strength × total elongation (MPa%)," in Table IV, the Examples have a yield strength × uniform elongation of 12,896 MPa%, an increase of approximately 16.0% over Comparative Example 1, and an ultimate tensile strength × total elongation of 46,966 MPa%, an increase of approximately 11.8% over Comparative Example 1.

[0120] Experimental Example 5: Deformation behavior analysis Figure 13 shows SEM-EBSD results of the microstructure of the example taken at different deformation rates from 500 nm to 200 μm using DIC images. Tensile tests were performed at a quasi-static deformation rate at 25°C. TWIP / TRIP (transformation / twinning-induced plasticity) behavior, which mainly occurs in alloys with metastable phases, effectively improves ultimate tensile strength. TWIP / TRIP behavior refers to twinning-induced plasticity and deformation-induced plasticity, respectively. Looking at the room temperature tensile test results of the example in FIG. 12, it can be seen that TRIP is generated due to deformation, and not only the yield strength but also the ultimate tensile strength is considerably excellent.

[0121] In Figure 13a, location c in the DIC image is the region deformed by approximately 15%. Figures c1-c5 show SEM-EBSD results acquired at location c in the DIC image a. Compared to location b, the size of the BCC martensite has increased significantly, and in the FCC, GND rapidly accumulated around the BCC martensite. In other words, deformation causes FCC->BCC martensite TRIP, resulting in an increase in strength. This result corresponds to the deformation rate point where the engineering stress begins to increase in the example shown in Figure 12. The phase map and IPF map show that the metastable FCC phase in the region outside the cell was transformed into BCC martensite during deformation. As the deformation rate increased after point c, more TRIP occurred, increasing the fraction of BCC martensite. This led to a similar increase in additional GND accumulation, resulting in improved mechanical strength at all deformation rates.

[0122] 14 to 19 show the results of TEM analysis of the microstructure of the example deformed by 25% at a nano-scale of 500 nm or less. During deformation, the FCC phase accepts the majority of the deformation, and when many dislocations are accommodated and a certain critical stress is exceeded, TRIP occurs in the deformed BCC martensite phase. Figure 14 shows a BF image, and Figure 15 shows an HR-TEM image. It was confirmed that stacking faults (SFs) caused by low phase stability were generated during deformation in the high-entropy alloy of the example, and that the generated SFs accepted localized deformation mismatch (arrows).

[0123] 16, the TEM image of the initial microstructure of the example shows that a nano-sized eta-Do24 phase precipitated in the outer cell region of the element-separated FCC phase. Precipitate phases are generally classified as either penetrable or non-penetrable by interacting with dislocations during deformation, depending on their size and interface coherency. Penetration means that dislocations moving due to deformation cross the precipitate phase. The eta-Do24 precipitated in the examples is nano-sized and is a non-shear precipitate phase that is difficult to penetrate, which can block dislocation movement during deformation and contribute to strengthening the strength. Referring to Figure 16, it can be seen that dislocations accommodated in the FCC phase around the eta-Do24 phase due to significant deformation accumulate along the periphery of the eta-Do24 phase, and the locally increased strength and sintering deformation mismatch partially generate dislocations inside the eta-Do24 phase (circles).

[0124] Figures 17 to 19 show HR-TEM images of the eta-Do24 phase with further magnification. Similar to the FCC phase, SFs formed in various directions within the eta-Do24 phase accepted deformation and contributed to strengthening. As a non-shear precipitate, SFs effectively blocked dislocation movement within the FCC phase, contributing to strengthening.

[0125] FIG. 20 is a schematic diagram of the heterostructure and deformation behavior of a high-entropy alloy, drawn based on the microstructural analysis results of the example. In the early stages of deformation, a significant amount of dislocations are randomly accommodated in the FCC phase in the outer cell region, increasing strength. Furthermore, when the critical stress is exceeded in more deformation stages, TRIP behavior is observed in the BCC martensite phase, contributing to increased strength. As deformation progresses, the non-shear nano-precipitate phase eta-Do24 hinders the movement of dislocations around it, increasing strength, and as dislocations accumulate at more deformation stages, they form SFs, contributing to localized strength enhancement. Therefore, through a comparison between the Examples and Comparative Examples and an analysis of the deformation behavior, it can be confirmed that the alloy according to the Examples has excellent yield strength and ultimate tensile strength through the three heterostructures without performing any additional processes.

[0126] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not limiting.

Claims

1. A dual phase structure of a columnar FCC (Face-Centered Cubic) phase and an equiaxed BCC (Body-Centered Cubic) phase; A cell structure; and precipitates.

2. The high-entropy alloy of claim 1 , wherein the cell structure satisfies the following formula 1: [Formula 1] 2≦(A-B)≦10 A is the Ti content (at%) outside the cell, The above B is the Ti content (at %) inside the cell.

3. 2. The high-entropy alloy according to claim 1, wherein the BCC phase is a martensite phase formed along a dendritic solidification structure within an FCC phase grain.

4. The high-entropy alloy according to claim 1, wherein the high-entropy alloy contains, based on 100 at% of the high-entropy alloy, 5 to 25 at% Ni, 2.5 to 15.0 at% Mn, 2.5 to 15.0 at% Co, 0.25 to 5.0 at% Ti, 0.25 to 5.0 at% Si, the balance being Fe and other impurities.

5. The high-entropy alloy of claim 1, wherein the cell structure contains, in 100 at% of the entire cell structure, Ni: 5.0 to 25.0 at%, Mn: 2.5 to 15.0 at%, Co: 2.5 to 15.0 at%, Ti: 0 to 7.5 at%, Si: 0 to 5.0 at%, the balance being Fe and other impurities.

6. The precipitate contains, based on 100 at% of the entire precipitate, Ni: 10.0 to 30.0 at%, Mn: 2.5 to 15.0 at%, Co: 2.5 to 15.0 at%, Ti: 10.0 to 30.0 at%, Si: 1.0 to 15.0 at%, the balance being Fe and other impurities. The high-entropy alloy described in claim 1.

7. The high entropy alloy of claim 1, wherein the cell structure satisfies the following formula 2: [Formula 2] 5≦(CD)≦30 C is the Ni content (at%) outside the cell, The above D is the Ni content (at %) inside the cell.

8. The high-entropy alloy of claim 1, wherein the cell structure satisfies the following formula 3: [Formula 3] 2≦(E-F)≦10 E is the Co content (at%) outside the cell, The above F is the Co content (at %) inside the cell.

9. The high-entropy alloy of claim 1, wherein the precipitate satisfies the following formula 4: [Formula 4] 2≦(I-J)≦10 I is the Mn content (at%) outside the precipitate, The above J is the Mn content (at %) inside the precipitate.

10. The high-entropy alloy of claim 1, wherein the precipitate satisfies the following formula 5: [Formula 5] 2≦(K-L)≦10 K is the Co content (at%) outside the precipitate, The above L is the Co content (at %) inside the precipitate.

11. The high-entropy alloy of claim 1, wherein the precipitate satisfies the following formula 6: [Formula 6] 5≦(M−N)≦35 M is the Ti content (at%) outside the precipitate, The above N is the Ti content (at %) inside the precipitate.

12. The high-entropy alloy of claim 1, wherein the precipitate satisfies the following formula 7: [Formula 7] 2≦(OP)≦20 The O is the Si content (at%) outside the precipitate, The above P is the Si content (at %) inside the precipitate.

13. 2. The high-entropy alloy according to claim 1, wherein the precipitates are elliptical and the major axis length of the precipitates is 50 to 500 nm.

14. The precipitate phase of the precipitate is Fe ２ SiTi and Ni ３ The high entropy alloy of claim 1 , which is Ti.

15. 2. The high-entropy alloy according to claim 1, wherein the FCC phase fraction is 85% or more, based on a phase fraction of 100%.

16. The absolute value of the difference between the geometrically necessary dislocations (GND) of the BCC phase and the FCC phase is 10 × 10 １２ mm －２ The high entropy alloy according to claim 1 .

17. When the high-entropy alloy is subjected to tensile deformation, The high-entropy alloy according to claim 1, wherein the FCC phase undergoes a deformation-induced phase transformation to the BCC phase.

18. The high entropy alloy according to claim 1, wherein the yield strength of the high entropy alloy is 300 MPa or more.

19. 2. The high entropy alloy of claim 1, wherein the high entropy alloy has an ultimate tensile strength of 700 MPa or greater.

20. manufacturing raw metals into alloy powder; supplying energy to the alloy powder by irradiating it with a laser beam to melt it; and laminating the molten alloy powder to produce the alloy. The high-entropy alloy produced includes a dual-phase structure of a columnar FCC (Face-Centered Cubic) phase and an equiaxed BCC (Body-Centered Cubic) phase, a cellular structure, and precipitates.

21. 21. The method of claim 20, wherein the alloy powder produced in the step of producing the raw metal into alloy powder has a D50 in the range of 45 to 95 μm.

22. 21. The method for producing a high-entropy alloy according to claim 20, wherein the alloy powder produced in the step of producing the raw metal into alloy powder has a volume fraction of powder particles corresponding to D40 to D60 in the powder particle size distribution of 30 volume% or more.

23. 21. The method of claim 20, wherein the step of supplying energy to the alloy powder to melt it has an output of the laser beam of 220 watts (W) or more.

24. 21. The method for producing a high entropy alloy according to claim 20, wherein an FCC phase matrix grown in the opposite direction to the heat flow and a BCC martensite phase formed by thermal history are formed in the step of producing the alloy by stacking the molten alloy powder.

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