KR20210143564A - Medium entropy alloys and manufacturing method thereof - Google Patents

Abstract

The present invention provides a medium entropy alloy and a manufacturing method thereof. The medium entropy alloy according to one embodiment of the present invention comprises Al, Co, Cu, and Mn and satisfies the following equation 1. The equation 1 is, 2 <= ([Co]+[Cu])/([Al]+[Mn]) <= 15, where [X] represents an atomic percentage of X. The medium entropy alloy has excellent mechanical properties such as high hardness and high strength.

Description

MEDIUM ENTROPY ALLOYS AND MANUFACTURING METHOD THEREOF

The present invention relates to a mesoentropic alloy and a method for manufacturing the same. More specifically, it relates to multiphase medium-entropy alloys (MEAs) and a method for manufacturing the same, which utilizes phase boundary reinforcement caused by multiphase formation and simultaneously forms a complex solid solution. It relates to a medium entropy alloy having excellent room temperature mechanical properties due to the solid solution strengthening effect through the solution and a method for manufacturing the same.

High-entropy alloys (HEAs) are polyelement obtained by alloying five or more constituent elements in the same or similar proportions, unlike conventional alloys consisting of a major element and other elements. As an alloy, an intermetallic compound is not formed due to high mixing entropy, and it is a metal material having a single-phase structure such as a face-centered cubic (FCC) or body-centered cubic (BCC).

Two important factors in designing a high-entropy alloy are the composition ratio of the elements constituting the alloy and the compositional entropy of the alloy system.

Among them, the first is the composition ratio of the high entropy alloy. A high-entropy alloy must consist of at least five elements or more, and the composition ratio of each alloying element is defined as 5 to 35 at%. In addition, when other elements are added in addition to the main alloy constituent elements during the manufacture of the high entropy alloy, the amount of addition should be 5 at% or less.

Generally, alloys are classified into high-entropy alloys, medium-entropy alloys (MEAs), and low-entropy alloys (LEAs) according to the constituent entropy (ΔS _conf ) of the alloy system obtained by the following Relational Equation 1. If [constituent entropy ≥ 1.5 R], it is classified as a high entropy alloy, if [1.5 R > constituent entropy ≥ 1.0 R], it is classified as a medium entropy alloy. Other alloys with [1.0 R > constituent entropy] are a low entropy alloy is divided into

[Relational Expression 1]

(R: gas constant, X _i : mole fraction of i element, n: number of constituent elements)

The initial high-entropy and medium-entropy alloys were designed to have a single-phase structure, and among them, the most actively studied FCC-based high-entropy alloys have excellent cryogenic properties, high fracture toughness and corrosion resistance, so they can be applied to extreme environments. It is gaining popularity as a material.

However, FCC-based high-entropy alloys have low room temperature yield strength and hardness compared to high elongation, which is an obstacle to commercialization. In order to solve this problem, recent studies have been made on polyphase high-entropy and multi-phase medium-entropy alloys having two or more phases, but it is difficult to design and develop various alloys due to low solubility between constituent elements.

Therefore, in order to expand the industrial field, it is essential to prepare an alloy database having excellent properties by developing a multi-phase high-entropy and multi-phase medium-entropy alloy having improved mechanical properties.

The present invention provides a mesoentropic alloy and a method for manufacturing the same. More specifically, instead of the conventional single-phase high entropy alloy, the alloy is divided into Co-rich and Cu-rich regions by using the miscibility gap of the Co-Cu binary system, as well as Al , by controlling the amount of Mn, the L2 ₁ phase is precipitated in the Co-rich region to create a microstructure having a total of two or more multi-phases, and by maximizing the phase interface strengthening effect, excellent mechanical properties with high hardness and high strength at room temperature are obtained. It provides a medium entropy alloy.

The neutral entropy alloy according to an embodiment of the present invention includes Al, Co, Cu, and Mn, and satisfies Equation 1 below.

[Equation 1]

2 ≤ ([Co]+[Cu])/([Al]+[Mn]) ≤ 15

In this case, [X] means atomic% of X.

In the mesoentropic alloy according to an embodiment of the present invention, based on atomic %, the ratio of Cu to Co may be 0.8 to 1.2, and the ratio of Mn to Al may be 0.8 to 1.2.

The neutral entropy alloy according to an embodiment of the present invention, in atomic%, Al: more than 2.5% less than 20%, Co: more than 30% less than 47.5%, Cu: more than 30% less than 47.5%, Mn: more than 2.5% 20 %, and may contain unavoidable impurities.

In the mid-entropy alloy according to an embodiment of the present invention, the alloy may include a triple phase.

The triple phase comprises a first phase mainly composed of Co; a second phase mainly composed of Cu; and a third phase rich in Al, Co, and Mn.

The area ratio of the first phase, the second phase, and the third phase may be 22:36:42 to 43:44:13.

The first phase may be a Co-rich FCC phase, and the second phase may be a Cu-rich FCC phase.

The third phase may be an _{L2 1 precipitated phase.}

The third phase is atomic%, and Co may be 52% or more.

The content ratio of Al, Co, and Mn in the third phase may be 1:1.5:1 to 1:3:1 based on atomic%.

The mid-entropy alloy according to an embodiment of the present invention may have a yield strength of 350 MPa or more at room temperature (298K), a tensile strength of 600 MPa or more, and an elongation of 7% or more.

The middle entropy alloy according to an embodiment of the present invention may have a Vickers hardness of 170 kgf/mm ^{2 or} more.

A method for manufacturing a mid-entropy alloy according to an embodiment of the present invention comprises the steps of: manufacturing an ingot by casting a mixed powder containing Al, Co, Cu, and Mn, satisfying the following Equation 1; quenching the ingot; and homogenizing heat treatment of the quenched ingot.

[Equation 1]

2 ≤ ([Co]+[Cu])/([Al]+[Mn]) ≤ 15

In this case, [X] means atomic% of X.

In the step of manufacturing the ingot by casting the mixed powder, the heat treatment temperature may be 1400 to 1700 ℃.

In the homogenization heat treatment of the quenched ingot, the heat treatment temperature may be 600 to 900 °C, and the heat treatment time may be 10 to 14 hours.

The medium entropy alloy according to an embodiment of the present invention may have a Vickers hardness of ^{183 kgf/mm 2 or more at room temperature.} In addition, depending on the content of Al and Mn, a combination of excellent mechanical properties of yield strength of 376 to 546 MPa and elongation of 9 to 36% can be obtained, thereby supplementing the low yield strength of the existing single-phase high-entropy alloy.

The medium entropy alloy according to an embodiment of the present invention forms a triple phase of the Co-rich FCC phase, Cu-rich FCC phase, and L2 ₁ phase to generate a solid solution effect as well as a phase interface strengthening effect, resulting in improved room temperature mechanical properties can get

The medium entropy alloy according to an embodiment of the present invention may have excellent hardness and strength at room temperature due to solid solution strengthening and phase interface strengthening according to multi-phase formation, thereby having excellent mechanical properties.

1 shows the X-ray diffraction (XRD) results of the Al-Co-Cu-Mn-based medium entropy alloy of Comparative Examples 1 and 2 and Examples 1 and 2 of the present invention.
Figure 2a shows the result of analyzing the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Comparative Example 1 of the present invention by Scanning Electron Microscopy (SEM).
Figure 2b shows the result of analyzing the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Example 1 of the present invention by Scanning Electron Microscopy (SEM).
Figure 2c shows the result of analyzing the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Example 2 of the present invention by Scanning Electron Microscopy (SEM).
Figure 2d shows the results of analyzing the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Comparative Example 2 of the present invention by Scanning Electron Microscopy (SEM).
Figure 3a shows the result of analyzing the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Comparative Example 1 of the present invention by Energy Dispersive Spectroscopy (EDS).
Figure 3b shows the result of analyzing the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Example 1 of the present invention by Energy Dispersive Spectroscopy (EDS).
Figure 3c shows the results of analyzing the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Example 2 of the present invention by Energy Dispersive Spectroscopy (EDS).
Figure 3d shows the results of analyzing the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Comparative Example 2 of the present invention by Energy Dispersive Spectroscopy (EDS).
4 shows the results of a room temperature (298K) tensile test of the Al-Co-Cu-Mn-based medium entropy alloy of Comparative Examples 1 and 2 and Examples 1 and 2 of the present invention.

In this specification, terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

In this specification, the terminology used is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising," as used herein, specifies a particular characteristic, region, integer, step, operation, element and/or component, and includes the presence or absence of another characteristic, region, integer, step, operation, element and/or component. It does not exclude additions.

In the present specification, the term "combination of these" included in the expression of the Markush form means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Markush form, and the components It means to include one or more selected from the group consisting of.

In this specification, when a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be accompanied in between. In contrast, when a part refers to being "directly above" another part, the other part is not interposed therebetween.

Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related art literature and the presently disclosed content, and unless defined, are not interpreted in an ideal or very formal meaning.

In addition, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

The present inventors studied to supplement the low yield strength of the conventional FCC series high entropy alloy. As a result, a medium entropy alloy having multiple phases was designed, and the excellent room temperature mechanical properties of high hardness, yield strength and tensile strength of the alloy can be expressed by the three properties of this alloy. (1) solid solution strengthening due to solid solution of Al and Mn, (2) phase interface strengthening due to separation into Co-rich and Cu-rich phases due to immiscibility of Co-Cu, (3) L2 due to addition of Al and Mn Precipitation strengthening of phase _1.

mesoentropic alloy

The neutral entropy alloy according to an embodiment of the present invention includes Al, Co, Cu, and Mn, and satisfies Equation 1 below.

[Equation 1]

2 ≤ ([Co]+[Cu])/([Al]+[Mn]) ≤ 15

In this case, [X] means atomic% of X.

In addition, based on atomic %, the ratio of Cu to Co may be 0.8 to 1.2, and the ratio of Mn to Al may be 0.8 to 1.2.

In addition, in atomic%, Al: more than 2.5% and less than 20%, Co: more than 30% less than 47.5%, Cu: more than 30% and less than 47.5%, Mn: more than 2.5% and less than 20%, and unavoidable impurities. have. More specifically, in atomic%, Al: 10 to 15%, Co: 35 to 40%, Cu: 35 to 40%, Mn: 10 to 15%, and unavoidable impurities may be included.

The alloy may include a triple phase.

The triple phase may include a first phase containing Co as a main component; a second phase mainly composed of Cu; and a third phase rich in Al, Co, and Mn.

The area ratio of the first phase, the second phase, and the third phase may be 22:36:42 to 43:44:13.

The first phase may be a Co-rich FCC phase, and the second phase may be a Cu-rich FCC phase.

The third phase may be an _{L2 1 precipitated phase.}

The third phase is atomic%, and Co may be 52% or more. More specifically, it may be 53% or more. More specifically, it may be 53% to 60%.

The content ratio of Al, Co, and Mn in the third phase may be 1:1.5:1 to 1:3:1 based on atomic%. More specifically, it may be 1:1.5:1 to 2:4:1. More specifically, it may be 1:1.5:1 to 1:2:1.

The alloy may have a yield strength of 350 MPa or more at room temperature (298K), a tensile strength of 600 MPa or more, and an elongation of 7% or more. More specifically, the yield strength may be 350 to 550 MPa, the tensile strength may be 600 to 800 MPa, and the elongation may be 7 to 45%. More specifically, the yield strength may be 376 to 546 MPa, the tensile strength may be 611 to 761 MPa, and the elongation may be 9 to 36%.

The alloy may have a Vickers hardness of 170 kgf/mm ^{2 or} more. More specifically, it may be ^{183 kgf/mm 2 or more.} More specifically, it may be 184 to 250 kgf/mm ^{2 .}

Hereinafter, the reason for limiting the content of each component element, the range of Equation 1, and the interatomic ratio will be described.

Al: more than 2.5 atomic % and less than 20 atomic %

When aluminum (Al) is added appropriately, the Co-rich region _{precipitates the L2 1} phase in the FCC phase. However, when aluminum (Al) is added too little, the Co-rich region forms an FCC single phase. Conversely, when too much aluminum (Al) is added, the L2 ₁ phase is stabilized and the Co-rich region can form an _{L2 1 single phase.} Therefore, it can be added within the above range for interfacial strengthening through multi-phase formation. More specifically, 3 to 17 atomic % may be added. More specifically, 5 to 16 atomic % may be added. More specifically, 10 to 15 atomic % may be added.

Mn: greater than 2.5 atomic % and less than 20 atomic %

Manganese (Mn) is preferably added in an appropriate amount in order to maximize the solid solution strengthening effect, but if too much is added, it may not be dissolved in solution and Mn phase may be precipitated. More specifically, 3 to 17 atomic % may be added. More specifically, 5 to 16 atomic % may be added. More specifically, 10 to 15 atomic % may be added.

In this case, for aluminum (Al) and manganese (Mn), the ratio of Mn to Al may be 0.8 to 1.2, based on atomic %. This is to stably form the third phase because the atomic ratio in one lattice structure is expected to be 2:1:1 in the third phase to be formed by cobalt, aluminum, and manganese. That is, Mn and Al can be added in an equal proportion. More specifically, the ratio may be 1.

Co: More than 30 atomic% and less than 47.5 atomic%

When too little cobalt (Co) is added, the intermetallic compound β-Mn phase may be stabilized by the relatively high content of Mn. Conversely, when too much is added, the solid solution strengthening effect is lowered and the third phase is not precipitated, so that the precipitation strengthening effect is also lowered. In addition, there are also disadvantages in that the alloy price increases and the alloy density increases to lower the specific strength. More specifically, 32 to 45 atomic % may be added. More specifically, 35 to 40 atomic % may be added.

Cu: more than 30 atomic % and less than 47.5 atomic %

When copper (Cu) is added too little, the intermetallic β-Mn phase may be stabilized due to the relatively high content of Mn. Conversely, when too much is added, there is a disadvantage in that the solid solution strengthening effect is lowered. More specifically, 32 to 45 atomic % may be added. More specifically, 35 to 40 atomic % may be added.

In this case, in the case of cobalt (Co) and copper (Cu), the ratio of Cu to Co may be 0.8 to 1.2 based on atomic %. This is to maximize the interfacial strengthening effect between the Co-rich and Cu-rich phases by adding close to the same fraction. That is, Co and Cu can be added in an equal proportion. More specifically, the ratio may be 1.

Other unavoidable impurities may be included. Other unavoidable impurities are components other than the above alloying elements, and are unavoidable components that are unavoidably incorporated into raw materials or manufacturing processes.

[Equation 1] 2 ≤ ([Co]+[Cu])/([Al]+[Mn]) ≤ 15

In order to maximize solid solution strengthening, phase interface strengthening, and precipitation strengthening, the content of atoms in the alloy is as described above. When the ratio of the amount of the sum of Co and Cu to the amount of the sum of Mn and Al is too small based on atomic percent, not only solid solution strengthening is lowered, but also precipitation strengthening does not occur because the third phase does not precipitate, the price of the alloy increases, and the density There is a disadvantage in that the specific strength decreases due to the increase (in the case of Comparative Example 2). Conversely, when the ratio is too large, Al and Mn form an intermetallic compound, or the Co-rich _{phase forms an L2 1} single phase that is vulnerable to fracture, thereby reducing elongation (in the case of Comparative Example 1). More specifically, the ratio may be 2 or more and 14 or less. More specifically, the ratio may be 2 or more and 10 or less. More specifically, the ratio may be 2 or more and 4.5 or less.

Hereinafter, the microstructure of the mid-entropy alloy according to an embodiment of the present invention will be described.

The mid-entropy alloy according to an embodiment of the present invention may include multiple phases. More specifically, it may include a triple phase.

The triple phase comprises a first phase mainly composed of Co; a second phase mainly composed of Cu; and a third phase rich in Al, Co, and Mn.

In this case, the first phase may be a Co-rich FCC phase, and the second phase may be a Cu-rich FCC phase. The co-rich FCC phase and the Cu-rich FCC phase can be separated by a miscibility gap. In addition, the interfacial strengthening effect of the mid-entropy alloy can be maximized by the interface between the Co-rich FCC phase and the Cu-rich FCC phase.

Meanwhile, the first phase may include, in atomic%, Al: 4 to 8%, Co: 50 to 70%, Cu: 15 to 20%, Mn: 10 to 25%, and unavoidable impurities. More specifically, Al: 5 to 7%, Co: 52 to 65%, Cu: 16 to 19%, Mn: 12 to 22%, and unavoidable impurities may be included.

Meanwhile, the second phase may include, in atomic%, Al: 2 to 5%, Co: 5 to 20%, Cu: 60 to 85%, Mn: 5 to 15%, and unavoidable impurities. More specifically, Al: 3 to 4%, Co: 8 to 15%, Cu: 67 to 80%, Mn: 7 to 14%, and unavoidable impurities may be included.

Meanwhile, the third _{phase may be an L2 1} precipitation phase, and may be rich in Al, Co, and Mn. In this case, the content of Co in the third phase may be 52 atomic% or more. More specifically, it may be 53 atomic% or more. More specifically, it may be 53 atomic% to 60 atomic%.

Meanwhile, the third phase, in atomic%, may include Al: 10 to 30%, Co: 45 to 65%, Cu: 2 to 7%, Mn: 10 to 30%, and unavoidable impurities. More specifically, Al: 20 to 27%, Co: 50 to 60%, Cu: 3 to 6%, Mn: 12 to 20%, and unavoidable impurities may be included.

Meanwhile, the content ratio of Al, Co, and Mn in the third phase may be 1:1.5:1 to 1:3:1 based on atomic%. More specifically, it may be 1:1.5:1 to 2:4:1. More specifically, it may be 1:1.5:1 to 1:2:1.

Meanwhile, the area ratio of the first phase, the second phase, and the third phase may be 22:36:42 to 43:44:13.

Medium entropy alloy manufacturing method

A method for manufacturing a mid-entropy alloy according to an embodiment of the present invention comprises the steps of: manufacturing an ingot by casting a mixed powder containing Al, Co, Cu, and Mn, satisfying the following Equation 1; quenching the ingot; and homogenizing heat treatment of the quenched ingot.

[Equation 1]

2 ≤ ([Co]+[Cu])/([Al]+[Mn]) ≤ 15

In this case, [X] means atomic% of X.

The content of each component constituting the mixed powder and the reason for limiting Equation 1 are omitted because they overlap with the description of the above-described central entropy alloy.

First, the mixed powder was charged into a crucible, melted by heating, and poured into a mold to cast an ingot. In this case, the heating temperature may be 1400 to 1700 °C. If the heating temperature is too low, the element may not be sufficiently melted and thus an ingot having a uniform composition may not be obtained. On the other hand, when it is too high, there is a disadvantage that Mn evaporates and the Mn content is lowered. Next, the ingot is quenched. It can be rapidly cooled to room temperature. The cooling method and cooling rate are not particularly limited.

Next, the homogenization heat treatment of the quenched ingot is performed. Homogenization heat treatment is heat treatment so that the microstructure of the ingot is homogenized and dissolved. In this case, the heat treatment temperature may be 600 to 900 °C. If the heat treatment temperature is too low, the homogenization effect of the microstructure may not be sufficient in the homogenization heat treatment step. On the other hand, if the homogenization heat treatment temperature is too high, heat treatment cost may become excessive and partial dissolution may occur. In addition, the heat treatment time may be 10 hours to 14 hours. If the heat treatment time is too short, the effect of homogenizing the microstructure may not be sufficient. On the other hand, if the heat treatment time is too long, the heat treatment cost may become excessive.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for illustrating the present invention, and the present invention is not limited thereto.

[Production Example]

Examples 1 and 2

Preparation of mesoentropic alloys

First, Al, Co, Cu, Mn metals having a purity of 99.9% or more were prepared.

The metal prepared in this way was weighed so as to have a mixing ratio as shown in Table 1 below. In addition, for classification of alloys, they were named as 2.5Al, 10Al, 15Al, and 20Al according to the Al content.

Table 1 below shows the alloy element composition ratio.

Raw material mixing ratio (at%) Al Co Cu Mn (Co+Cu)/(Al+Mn) 10Al
(Example 1) 10.00 40.00 40.00 10.00 4 15Al
(Example 2) 15.00 35.00 35.00 15.00 2.33

After the raw metal prepared in the above ratio is charged into the crucible, it is melted by heating to 1550 ° C. Using a mold, an alloy ingot of 100 g having a cuboid shape with a thickness of 7.8 mm, a width of 33 mm, and a length of 40 mm. ) was cast.

Immediately after casting, the quenched ingot was subjected to homogenization at a temperature of 800° C. for 12 hours, and then rapidly cooled to room temperature again.

Comparative Example 1 and Comparative Example 2

Preparation of low-entropy alloys

An alloy for Comparative Example was prepared according to the composition of Table 2 below in the same manner as in Example 1.

Raw material mixing ratio (at%) Al Co Cu Mn (Co+Cu)/(Al+Mn) 2.5Al
(Comparative Example 1) 2.50 47.50 47.50 2.50 19 20Al
(Comparative Example 2) 20.00 30.00 30.00 20.00 1.5

An alloy ingot was cast in the same manner as in Example 1, and solution heat treatment was performed at a temperature of 800° C. for 12 hours in the same manner as in Example 1, followed by rapid cooling to room temperature (298K).

[result]

Initial microstructure analysis

1 shows the results of X-ray diffraction of the prepared comparative example, the example alloy.

In the XRD measurement result of FIG. 1, as the amount of Al and Mn increased, the double phase of the Co-rich FCC phase and the Cu-rich FCC phase changed to a triple phase of _{the Co-rich FCC phase, Cu-rich FCC phase, and L2 1 phase, again} It can be seen that the configuration of the phase changes to the double phase of Cu-rich FCC and L2 _{1 phase.}

In addition, in FIG. 2a, Comparative Example 1, FIG. 2b is Example 1, FIG. 2c is Example 2, and in FIG. 2d, the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Comparative Example 2 is scanned by Scanning Electron Microscopy (SEM). ) and the analysis results are shown.

It can be seen that in each alloy, a light gray Cu-rich FCC phase, a gray Co-rich FCC phase, and a dark gray Co-rich L2 ₁ phase are divided according to the composition.

In FIG. 3, the actual composition of the alloy of Comparative Example and Example was confirmed by Energy Dispersive Spectroscopy (EDS) mapping image. Specifically, the microstructure of the Al-Co-Cu-Mn-based medium entropy alloy of Comparative Example 1 in FIG. 3a, Example 1 in FIG. 3b, Example 2 in FIG. 3c, and Comparative Example 2 in FIG. 3D was analyzed by Energy Dispersive Spectroscopy ( EDS) analysis results are shown. In 2.5Al, Cu-rich region and Co-rich region exist, and as Al and Mn were added, Al, Co, and Mn-rich regions were created and the region expanded. Comparing this with the XRD result of FIG. 1, it was found that Cu-rich FCC and Co-rich FCC were present when Al and Mn were small, but as Al and Mn were added, Al, Co, Mn-rich L2 ₁ phase was formed. can Finally, in 20Al, it was confirmed that the Co-rich FCC phase disappeared and only the Al, Co, Mn-rich L2 ₁ phase and Cu-rich FCC phase remained.

In addition, the actual components of the phase constituting each alloy were measured and shown in Table 3. At this time, since _{the ratio of Co:Al:Mn of Co-rich L2 1 is similar to 2:1:1} , it can be confirmed that the peak of the Al, Co, Mn-rich region generated in FIG. 1 is L2 1, not B2. have.

EDS　 Analysis composition (at%) Al Co Cu Mn 2.5Al
(Comparative Example 1) Total 2.99 48.22 45.97 2.82 Cu-rich FCC 1.55 6.62 89.60 2.24 Co-rich FCC 2.77 71.74 20.49 5.02 10Al
(Example 1) Total 11.53 39.70 38.17 10.60 Cu-rich FCC 3.51 10.98 78.42 7.11 Co-rich FCC 6.83 61.81 17.50 13.87 Al, Co, Mn-rich 25.76 56.18 3.89 14.66 15Al
(Example 2) Total 16.75 35.31 32.52 15.42 Cu-rich FCC 3.64 14.21 69.87 12.30 Co-rich FCC 5.98 54.80 18.29 20.94 Al, Co, Mn-rich 22.94 53.82 4.26 18.99 20Al
(Comparative Example 2) Total 19.03 33.32 26.32 21.32 Cu-rich FCC 3.12 9.78 70.16 16.94 Al, Co, Mn-rich 22.58 51.66 4.03 21.75

Although there are some errors due to impurities inevitably mixed in the raw material or the manufacturing process, it can be seen that both the compositions of the comparative examples and the example alloys show almost the same values as the theoretical mixing ratios of Tables 1 and 2 above.

Hardness measurement result

Table 4 below shows the Vickers hardness analysis results of the alloys of Comparative Examples and Examples of the present invention.

Raw material mixing ratio (at%) Comparative Example 1 Example 1 Example 2 Comparative Example 2 Vickers hardness
(H _v , kgf/mm ² ) 117 184 248 236

As shown in Table 4, in Comparative Example 1 and Examples 1 and 2, as the Al and Mn fractions increased, the hardness increased, but it was confirmed that the hardness decreased slightly in Comparative Example 2.

Tensile test result

4 and Table 5 below show the tensile test results at room temperature (298K) for the comparative example and the example alloy according to the present invention.

Raw material mixing ratio (at%) Comparative Example 1 Example 1 Example 2 Comparative Example 2 yield strength
(MPa) 253 376 546 518 tensile strength
(MPa) 438 611 761 677 elongation
(%) 66 36 9 5

As shown in Figures 4 and 5, the intermediate entropy alloy prepared according to the embodiment of the present invention exhibited tensile properties of yield strength of 376 ~ 546 MPa, tensile strength of 611 ~ 761 MPa, and elongation of 9 ~ 36%.

In particular, in the case of Example 2, 15Al, despite being a cast material, it has excellent room temperature tensile properties of yield strength of 546 MPa, tensile strength of 761 MPa, and elongation of 9%.

Yield strength and tensile strength increased as Al and Mn were added, but decreased in Comparative Example 2, 20Al.

On the other hand, as Al and Mn were added, the elongation steadily decreased, but it was confirmed that 15Al, which had the highest strength and superior elongation than 20Al, had the best mechanical properties.

This trend is consistent with the results of hardness analysis for each Example and Comparative Example, because Example 2 having three phases has a higher phase interface strengthening effect than Comparative Example 2 having two phases.

In addition, as can be seen in Table 3, in Comparative Example 2, a _{large amount of Al, Co, and Mn-rich L2 1} phases were precipitated, and Al and Co were absorbed, so that the Al and Co solid solutions of Cu-rich FCC decreased. The constitutive entropy value of Cu-rich FCC calculated by Equation 1 has 0.906R in Example 2 and 0.885R in Comparative Example 2.

In the mid-entropy alloy of the present invention, the tendency to change the mechanical properties as described above may have the following three reasons depending on the alloy composition, microstructure, and interfacial properties.

(1) Employment strengthening effect due to Al, Mn high-capacity increase

(2) Interfacial strengthening effect due to phase separation

(3) Precipitation strengthening effect due to Al, Co, Mn-rich L2 _{1 precipitation phase}

The present invention is not limited to the embodiments, but may be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains may develop other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that this may be practiced. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (15)

Al, Co, Cu, and Mn;
Satisfying Equation 1 below,
mesoentropic alloy.
[Equation 1]
2 ≤ ([Co]+[Cu])/([Al]+[Mn]) ≤ 15
(In this case, [X] means atomic% of X.)
According to claim 1,
based on atomic percent,
The ratio of Cu to Co is 0.8 to 1.2,
the ratio of Mn to Al is 0.8 to 1.2,
mesoentropic alloy.
According to claim 1,
Al: more than 2.5% less than 20%, Co: more than 30% less than 47.5%, Cu: more than 30% less than 47.5%, Mn: more than 2.5% less than 20%, and unavoidable impurities, in atomic %,
mesoentropic alloy.
According to claim 1,
wherein the alloy comprises a triple phase,
mesoentropic alloy.
5. The method of claim 4,
The triple phase may include a first phase containing Co as a main component; a second phase mainly composed of Cu; And Al, Co, Mn-rich third phase; Containing,
mesoentropic alloy.
6. The method of claim 5,
The area ratio of the first phase, the second phase, and the third phase is 22:36:42 to 43:44:13,
mesoentropic alloy.
6. The method of claim 5,
The first phase is a Co-rich FCC phase,
wherein the second phase is a Cu-rich FCC phase,
mesoentropic alloy.
6. The method of claim 5,
The third phase is the L2 ₁ precipitation phase,
mesoentropic alloy.
6. The method of claim 5,
The third phase is atomic%, Co is 52% or more,
mesoentropic alloy.
6. The method of claim 5,
The content ratio of Al, Co, and Mn in the third phase is 1:1.5:1 to 1:3:1 based on atomic%,
mesoentropic alloy.
According to claim 1,
The alloy has a yield strength of 350 MPa or more at room temperature (298K),
Tensile strength of 600 MPa or more,
elongation of more than 7%,
mesoentropic alloy.
According to claim 1,
The alloy has a Vickers hardness of 170 kgf / mm ² or more,
mesoentropic alloy.
manufacturing an ingot by casting a mixed powder containing Al, Co, Cu, and Mn, satisfying the following Equation 1;
rapidly cooling the ingot; and
Including; homogenizing heat treatment of the quenched ingot
A method for manufacturing a mesoentropic alloy.
[Equation 1]
2 ≤ ([Co]+[Cu])/([Al]+[Mn]) ≤ 15
(In this case, [X] means atomic% of X.)
14. The method of claim 13,
In the step of manufacturing the ingot by casting the mixed powder,
The heat treatment temperature is 1400 to 1700 ℃,
A method for manufacturing a mesoentropic alloy.
14. The method of claim 13,
In the homogenization heat treatment of the quenched ingot,
The heat treatment temperature is 600 to 900 ℃,
The heat treatment time is 10 to 14 hours,
A method for manufacturing a mesoentropic alloy.

Images