KR20200041630A - High entropy alloy and manufacturing method of the same - Google Patents

Abstract

The present invention provides a high-entropy alloy having excellent mechanical properties due to phase transformation when deformed at an extremely low temperature, and a manufacturing method thereof. The disclosed high-entropy alloy comprises: 7 to 13 atom% of V; 7 to 13 atom% of Cr; 42 to 48 atom% of Fe; and 10 to 35 atom% of Co.

Description

HIGH ENTROPY ALLOY AND MANUFACTURING METHOD OF THE SAME

The present invention relates to a high-entropy alloy and its manufacturing method. More specifically, it relates to a high-entropy alloy having excellent mechanical properties due to phase transformation when deformed at cryogenic temperature and a method for manufacturing the same.

The definition of the existing high-entropy alloy (HEA) is a multi-element alloy obtained by alloying five or more constituent elements in similar proportions without the main constituent elements of the alloy, such as steel, aluminum alloy, and titanium alloy, which are general alloys. As, the mixed entropy in the alloy is high, so that no intermetallic compound or intermediate phase is formed, and a single phase structure such as a face-centered cubic (FCC) or a body-centered cubic (BCC) is formed. It is a metal material.

Particularly, Co-Cr-Fe-Mn-Ni-based high-entropy alloys are in the spotlight as materials that can be applied to extreme environments because they have excellent cryogenic properties, high fracture toughness, and corrosion resistance.

An important factor in designing such a high-entropy alloy is the composition ratio of elements constituting the alloy.

As a composition ratio of the high-entropy alloy, a typical high-entropy alloy should consist of at least five or more main alloying elements, and the composition ratio of each alloying element is defined as 5 to 35 at%, and the main alloying element It has been found that when other elements are added, the addition amount should be less than 5 at%. However, recently, the definition of high-entropy alloys is also expanding, such as the introduction of high-entropy Fe ₅₀ Mn ₃₀ Co ₁₀ Cr ₁₀ alloys.

The present invention provides a high-entropy alloy having excellent mechanical properties due to phase transformation when deformed at cryogenic temperatures, and a method for manufacturing the same.

The high-entropy alloy according to an embodiment of the present invention includes atomic%, V: 7 to 13%, Cr: 7 to 13%, Fe: 42 to 48%, and Co: 10 to 35%.

It may consist of a single-phase FCC.

Equations 1 and 2 below may be satisfied.

[Equation 1]

59 ≤ [Fe] + [Co] ≤ 71 (unit: atomic%)

[Equation 2]

2 ≤ [Fe] / [Co]

(In the above formulas 1 and 2, [Fe] and [Co] mean the atomic% of Fe and Co, respectively.)

After tensile strain at 25 ° C., it can be made of FCC single phase.

The tensile strength is 620MPa or more, and the elongation may be 30% or more.

The fracture toughness may be 230 kJ / m ^{2 or} more.

After tensile strain at -196 ° C, a strain twin with 0.2% Number Fraction and the balance FCC phase may be included.

The tensile strength is 990MPa or more, and the elongation may be 55% or more.

The fracture toughness may be 240 kJ / m ^{2 or} more.

The method for preparing a high-entropy alloy according to an embodiment of the present invention includes atomic percentages, V: 7 to 13%, Cr: 7 to 13%, Fe: 42 to 48%, and Co: 10 to 35%. Manufacturing; Homogenizing heat treatment of the ingot; Manufacturing a sheet material by rolling the heat-treated ingot; And annealing the plate material.

In the heat treatment step, the heat treatment temperature may be 1000 to 1200 ° C.

In the annealing step, the annealing temperature may be 800 to 1000 ° C.

The high-entropy alloy according to an embodiment of the present invention can be expected to have excellent mechanical properties such as fracture toughness, strength and elongation at room temperature and cryogenic temperature.

1 is a graph showing the FCC single phase region secured from 710 ° C to 1386 ° C thermodynamically in the composition of the high-entropy alloy according to an embodiment of the present invention.
2 is a view showing a manufacturing process of a high-entropy alloy according to an embodiment of the present invention.
3 is a view showing the results of XRD analysis of a high-entropy alloy according to an embodiment of the present invention.
4 is a view showing a microstructure photograph of the initial structure of the high-entropy alloy according to an embodiment of the present invention.
5 is a view showing a microstructure photograph after tensile deformation at room temperature and cryogenic temperature of a high-entropy alloy according to an embodiment of the present invention.
6 is a view showing tensile properties and work hardening rate after tensile deformation at room temperature and cryogenic temperature of a high-entropy alloy according to an embodiment of the present invention.
7 is a view showing the fracture toughness at room temperature and cryogenic temperature of a high-entropy alloy according to an embodiment of the present invention.
8 is a view showing a fracture surface at room temperature and cryogenic temperature of a high-entropy alloy according to an embodiment of the present invention.
9 is a view showing a wavefront at room temperature and cryogenic temperature of the high-entropy alloy according to an embodiment of the present invention.

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 only used to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is only for referring to specific embodiments and is not intended to limit the invention. The singular forms used herein include plural forms unless the phrases clearly indicate the opposite. As used herein, the meaning of “comprising” embodies a particular characteristic, region, integer, step, action, element, and / or component, and the presence or presence of another characteristic, region, integer, step, action, element, and / or component. It does not exclude addition.

When a part is said to be "on" or "on" another part, it may be directly on or on the other part, or another part may be involved therebetween. In contrast, if one part is referred to as being “just above” another part, no other part is interposed therebetween.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present invention pertains. Commonly used dictionary-defined terms are additionally interpreted as having meanings consistent with related technical documents and currently disclosed contents, and are not interpreted in an ideal or very formal meaning unless defined.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art to which the present invention pertains can easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

High Entropy  alloy

The high-entropy alloy according to an embodiment of the present invention includes atomic%, V: 7 to 13%, Cr: 7 to 13%, Fe: 42 to 48%, and Co: 10 to 35%.

Below, the reasons for limiting the content of each component element will be described.

V: 7 to 13 atomic%

When vanadium (V) is less than 7 atomic%, the solidification effect decreases, and when it exceeds 13 atomic%, the price may increase. Therefore, V is added at 5 to 15 atomic%. Specifically, it may be 8 to 12 atomic%.

Cr: 7 to 13 atomic%

When chromium (Cr) is less than 7 atomic%, corrosion resistance decreases, and when it exceeds 13 atomic%, the price may increase. Therefore, Cr is added at 7 to 13 atomic%. Specifically, it may be 8 to 12 atomic%.

Fe: 42 to 48 atomic%

When iron (Fe) is less than 42 atomic%, the price increases, and when it exceeds 48 atomic%, the FCC phase may not obtain a predominant phase. Therefore, Fe is added at 42 to 48 atomic%. Specifically, it may be 43 to 47 atomic%.

Co: 10 to 35 atomic%

When cobalt (Co) is less than 10 atomic%, the FCC phase may not obtain a predominant phase, and when it exceeds 35 atomic%, the price may increase. Therefore, Co is added at 10 to 35 atomic%. Specifically, it may be 18 to 22 atomic%.

Ni: 12 to 18 atomic%

When nickel (Ni) is less than 12 atomic%, the FCC phase may not obtain a predominant phase, and when it exceeds 18 atomic%, the price may increase. Therefore, Ni is added at 12 to 18 atomic%. Specifically, it may be 13 to 17 atomic%.

The high-entropy alloy according to an embodiment of the present invention may satisfy Equations 1 and 2 below.

[Formula 1] 59 ≤ [Fe] + [Co] ≤ 71 (unit: atomic%)

[Equation 2] 2 ≤ [Fe] / [Co]

(In the above formulas 1 and 2, [Fe] and [Co] mean the atomic% of Fe and Co, respectively.)

In a high-entropy alloy according to an embodiment of the present invention, in a situation where the sum of the content of Co and the content of Fe satisfies a certain content, the ratio of the content of Fe to the content of Co can be controlled.

According to Equation 2, the content of Co decreases, and as the content of Fe increases, Fe replaces Co, so that the ratio of the content of Fe to the content of Co can increase.

For example, in a situation where the sum of the content of Co and the content of Fe is 65 atomic%, when the content of Fe is 45 atomic% and the content of Co is 20 atomic%, the ratio value of the content of Fe to the content of Ni is Equation 2 can be satisfied by becoming 2.25. Specifically, the ratio of the content of Fe to the content of Co may be 2.2 or more.

As a result, the initial organization may consist of FCC single phases. Specifically, it can be made of FCC single phase, which is thermodynamically stable from 710 ° C to 1386 ° C.

After tensile strain at 25 ° C., it can be made of FCC single phase. In addition, after tensile strain at -196 ° C, a number of strain twins of 0.2% and a residual FCC phase may be included. Number Fraction is the number of lines occupied by the occurrence of strain twins as a fraction of the total number of lines forming a boundary within a unit area.

Although there is no formation of deformed twins at room temperature, deformed twins are generated at cryogenic temperatures, and twins with a number fraction of 0.2% may be formed. Fracture toughness can be increased even though the temperature is reduced from room temperature to cryogenic temperature by the formation of such twins.

Specifically, at room temperature (25 ° C), the tensile strength is 620 MPa or more, the elongation is 30% or more, and the fracture toughness may be 230 kJ / m ^{2 or} more. At extremely low temperature (-196 ° C), the tensile strength is 990 MPa or more, the elongation is 55% or more, and the fracture toughness may be 240 kJ / m ^{2 or} more.

High Entropy  Alloy manufacturing method

The method for manufacturing a high-entropy alloy according to an embodiment of the present invention, as shown in FIG. 2, is atomic%, V: 7 to 13%, Cr: 7 to 13%, Fe: 42 to 48%, and Co: 10 to 35% It includes the steps of manufacturing an ingot comprising, a step of homogenizing heat treatment of the ingot, a step of manufacturing a plate material by rolling the heat treated ingot, and annealing the plate material.

The reason for limiting the content of each component constituting the ingot is omitted because it overlaps with the description of the high-entropy alloy.

First, in the step of manufacturing the ingot, each component element is weighed and charged into a crucible, and then alloyed through a vacuum induction melting equipment, and then the ingot is cast using a mold.

Next, in the heat treatment step, the heat treatment is performed so that the microstructure of the ingot is homogenized. At this time, the heat treatment temperature may be 1000 to 1200 ℃. When the heat treatment temperature is less than 1000 ° C, the homogenization effect of the microstructure may not be sufficient. On the other hand, when it exceeds 1200 ° C, the heat treatment cost may be excessive.

In addition, the heat treatment time may be 2 to 10 hours. When the heat treatment time is less than 2 hours, the homogenization effect of the microstructure may not be sufficient. On the other hand, if it exceeds 10 hours, the heat treatment cost may be excessive.

After the heat treatment, as shown in FIG. 2, the heat treated ingot can be cooled. The cooling method and cooling rate are not particularly limited. After cooling, the oxide on the surface of the ingot can be removed by polishing.

Next, in the step of manufacturing the plate material, the heat treated ingot is rolled. Cold rolling can be performed at a reduction ratio of 60% or more.

Next, in the annealing step, the microstructure is controlled by annealing the plate material. At this time, the annealing temperature may be 800 to 1000 ℃. When the annealing temperature is less than 800 ° C, complete recrystallization may be difficult to achieve and it may be difficult to reach the FCC single phase region. On the other hand, when it exceeds 1000 ° C, coarsening of the crystal grains becomes severe, and the heat treatment cost may be excessive.

In addition, the annealing time may be 10 to 120 minutes. If the annealing time is less than 10 minutes, complete recrystallization can likewise be difficult to achieve. On the other hand, if it exceeds 120 minutes, coarsening of the crystal grains becomes severe, and the heat treatment cost may be excessive.

After annealing, as shown in FIG. 2, the plate material can be cooled. The cooling method and cooling rate are not particularly limited.

Hereinafter, specific examples of the present invention will be described. However, the following examples are only specific examples of the present invention, and the present invention is not limited to the following examples.

Example

[ High Entropy  Preparation of alloy]

First, V, Cr, Fe, Co, and Ni raw material metals having a purity of 99.9% or more were prepared. The raw metal prepared in this way was weighed to a mixing ratio as shown in Table 1 below.

division Raw material mixing ratio (atomic%) Equation 1 Equation 2 V Cr Fe Co Ni [Fe] + [Co] [Fe] / [Co] Example 1 10 10 45 35 0 80 1.29 Example 2 10 10 45 30 5 75 1.5 Example 3 10 10 45 20 15 65 2.25 Example 4 10 10 45 10 25 55 4.5

(1) Preparation of small specimens

After loading the raw material metals according to Examples 1 to 4 prepared in the same ratio as in Table 1 in the crucible, dissolved using a vacuum induction melting equipment, and using a mold, a cuboid with a thickness of 7.8 mm, width of 33 mm, and length of 80 mm. Shaped alloy ingots were cast.

As shown in FIG. 2, the cast ingot was subjected to a homogenization heat treatment at a temperature of 1100 ° C. for 6 hours, followed by water quenching.

In order to remove the oxide formed on the surface of the homogenized alloy, surface grinding was performed, and cold rolling was performed to a thickness of 7 mm.

In addition, for each cold-rolled alloy plate material, it was annealed to maintain the FCC phase by heating at 900 ° C. for 10 minutes, followed by water quenching.

(2) Preparation of large specimens

After loading the raw material metal according to Example 3 prepared in the ratio shown in Table 1 above into a crucible, and dissolving it using a vacuum induction melting equipment, using a mold, a 58 mm thick, 80 mm wide, 108 mm long cube-shaped alloy An ingot was cast.

The cast ingot having a thickness of 58 mm was subjected to homogenization heat treatment for 6 hours at a temperature of 1100 ° C., followed by water quenching.

In order to remove the oxide formed on the surface of the homogenized alloy, surface grinding was performed, and cold rolling was performed from a thickness of 58 mm to 16 mmm.

In addition, for each cold-rolled alloy plate material, it was annealed to maintain the FCC phase by heating at 900 ° C. for 1 hour, followed by water quenching.

[ XRD  And microstructure analysis results]

Figure 3 shows the XRD measurement results at room temperature of the alloy according to Example 3 prepared by a large specimen through the above-described process.

XRD measurement was performed after polishing in the order of sandpaper 600, 800, 1200, and 2000 in order to minimize phase transformation due to deformation during polishing of the specimen, and then electrolytic etching in 8% perchloric acid.

Figure 4 shows the results of the EBSD analysis of the initial structure of the alloy according to Example 3 prepared through the above-described process. Figure 5 shows the results of EBSD analysis after tensile strain at room temperature (25 ° C) and cryogenic temperature (-196 ° C) of Example 3, respectively.

As can be seen through FIGS. 3 to 5, FCC single phase was observed in the initial tissue, and FCC single phase was observed even after tensile deformation at room temperature (25 ° C.), and few strain twins were found.

After tensile strain at cryogenic temperatures (-196 ° C), large amounts of strain twins with a number fraction of 0.2% were found.

[Results of tensile test]

Table 2 below shows the tensile test results at room temperature (25 ° C) and cryogenic temperature (-196 ° C) of Examples 1 to 4, which were prepared as small specimens. And Figure 6 and Table 3 below shows the tensile test results at room temperature (25 ° C) and cryogenic temperature (-196 ° C) of Example 3 made of large specimens. At present, the elongation cannot be attached at cryogenic temperatures, so the elongation was obtained by directly measuring the length change before and after tensile with an optical microscope.

division Room temperature (25 ℃) Cryogenic (-196 ℃) Yield strength
(Mpa) The tensile strength
(MPa) Elongation
(%) Yield strength
(MPa) The tensile strength
(MPa) Elongation
(%) Example 1 427 745 70.1 653 1623 65.0 Example 2 348 714 62.0 601 1291 81.7 Example 3 345 689 52.6 533 1092 76.3 Example 4 339 684 47.0 468 996 69.4

As shown in Table 2, in the case of Examples 1 to 4, the yield strength at room temperature (25 ° C) was 330 MPa or higher, the tensile strength was 680 MPa or higher, and the elongation was 45% or higher. After tensile deformation at room temperature, it showed high strength and good elongation.

On the other hand, at a very low temperature (-196 ° C), the yield strength was 460 MPa or more, the tensile strength was 990 MPa or more, and the elongation was 60% or more. Likewise, after tensile deformation at cryogenic temperature, it showed high strength and good elongation.

division Room temperature (25 ℃) Cryogenic (-196 ℃) Yield strength
(Mpa) The tensile strength
(MPa) Elongation
(%) Yield strength
(MPa) The tensile strength
(MPa) Elongation
(%) Example 3 294 626 36 470 1000 61.8

As shown in Table 3, in the case of Example 3, the yield strength at room temperature (25 ° C) was 290 MPa or more, the tensile strength was 620 MPa or more, and the elongation was 35% or more. After tensile deformation at room temperature, it showed high strength and good elongation.

On the other hand, at a very low temperature (-196 ° C), the yield strength was 460 MPa or more, the tensile strength was 990 MPa or more, and the elongation was 61% or more. Likewise, after tensile deformation at cryogenic temperature, it showed high strength and good elongation.

As shown in FIG. 6, it was found that both strength and elongation increased as the temperature decreased from room temperature to cryogenic temperature, and a high work hardening rate was observed at cryogenic temperature.

[ Fracture toughness  Test result]

Fracture toughness test was performed on Example 3 prepared from large specimens. The fracture toughness test was conducted under the plane strain condition with a standard specimen according to ASTM E1820, and the results were shown in FIG. 7 and Table 4 below.

Room temperature (25 ℃) Cryogenic (-196 ℃) J _lc (kJ / m ² ) K _JlC (MPa * m ^1/2 ) J _lc (kJ / m ² ) K _JlC (MPa * m ^1/2 ) Example 3 233 219 248 232

As shown in FIG. 7 and Table 4, as the temperature goes from room temperature to cryogenic temperature, it can be seen that the fracture toughness is increased, which can be seen to be due to the formation of strain twins generated during the fracture toughness test at cryogenic temperature.

[ Fracture toughness  after Fracture  analysis]

After fracture toughness, the fracture surface and fracture surface were observed through EBSD and SEM, which can be confirmed through FIGS. 8 and 9.

As shown in FIG. 8, it was found that there was no formation of strain twins at the fracture surface during the fracture test at room temperature, but formation of strain twins at the fracture surface during the fracture test at cryogenic temperature.

On the other hand, as shown in FIG. 9, it can be seen that ductile fracture was confirmed in both the fracture surface at the fracture test at room temperature and the fracture surface at the cryogenic fracture test based on SEM observation of the fracture surface.

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

Claims (12)

A high entropy alloy comprising atomic percentages, V: 7-13%, Cr: 7-13%, Fe: 42-48% and Co: 10-35%. According to claim 1,
High-entropy alloy consisting of single-phase FCC. According to claim 1,
A high-entropy alloy satisfying the following expressions 1 and 2.
[Equation 1]
59 ≤ [Fe] + [Co] ≤ 71 (unit: atomic%)
[Equation 2]
2 ≤ [Fe] / [Co]
(In the above formulas 1 and 2, [Fe] and [Co] mean the atomic% of Fe and Co, respectively.) According to claim 1,
High-entropy alloy consisting of FCC single phase after tensile strain at 25 ° C. According to claim 4,
High-entropy alloy with a tensile strength of 620 MPa or more and an elongation of 30% or more. According to claim 4,
High-entropy alloy with a fracture toughness of 230 kJ / m ² or higher. According to claim 1,
A high-entropy alloy comprising, after tensile strain at -196 ° C, 0.2% Number Fraction strain twins and the balance FCC phase. The method of claim 7,
High-entropy alloy with a tensile strength of 990 MPa or higher and an elongation of 55% or higher. The method of claim 7,
High-entropy alloy with a fracture toughness of 240 kJ / m ² or higher. Preparing an ingot comprising atomic%, V: 7-13%, Cr: 7-13%, Fe: 42-48%, Co: 16-23% and Ni: 12% -18%;
Homogenizing heat treatment of the ingot;
Manufacturing a sheet material by rolling the heat-treated ingot; And
Annealing the plate material; High entropy alloy manufacturing method comprising a. The method of claim 10,
In the heat treatment step, the heat treatment temperature is 1000 to 1200 ° C. The method of claim 10,
In the annealing step, an annealing temperature of 800 to 1000 ° C is a high-entropy alloy manufacturing method.

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