KR20230067965A - Coherent-Precipitate-Hardened High-entropy Alloys with Hierarchical NiAl/Ni2TiAlPrecipitates and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a high-entropy alloy containing hierarchical NiAl/Ni_2TiAl precipitates, including 8 to 10.5 at% of Al, 5 to 25 at% of Cr, 15 to 35 at% of Mn, 5 to 30 at% of Fe, 10 to 25 at% of Co, 10 to 25 at% of Ni, and 0.5 to 4 at% of Ti. Thus, the present invention can provide the high-entropy alloy containing hierarchical NiAl/Ni_2TiAl precipitates in the alloy by adding Al and Ti together.

Description

High-entropy alloys containing hierarchical NiAl/Ni2TiAl precipitates and method for manufacturing the same

The present invention relates to a high entropy alloy including hierarchical NiAl/Ni ₂ TiAl precipitates in the alloy by adding Al and Ti together, and a method for manufacturing the same.

A high-entropy alloy (HEA) is an alloy in which four or more major elements are mixed in equal or nearly equal atomic ratios, and the configurational entropy of the alloy itself is high so that intermetallic compounds or mesophases are not formed. It is characterized by having a single phase organization of face-centered cubic (FCC) or body-centered cubic (BCC) without

However, in some high entropy alloys, for example, Cr-Mn-Fe-Co-Ni, when Al is added, the solid solution phase of BCC lattice structure is formed in the alloy base having FCC lattice structure during casting and heat treatment process. -solution phase) is characterized by precipitation.

In general, as the fraction of the FCC lattice structure in the high entropy alloy increases, the formability is excellent, but there is a disadvantage in that the mechanical strength is reduced. As the fraction of the BCC lattice structure increases, the formability decreases and brittleness increases. .

For this reason, Korean Patent Registration No. 10-1950578 introduces a method for adjusting the FCC fraction and BCC fraction to appropriate levels by controlling the composition of Al (Patent Document 1), and the inventors of the present invention also Fe-Ni-Al-Cr -A method of controlling the FCC fraction and the BCC fraction in the alloy using a Ti alloy is introduced. (Non-Patent Document 1)

However, due to the problem that the physical properties of the high entropy alloy rapidly change depending on the composition and heat treatment method, a lot of research is being conducted on a method for manufacturing a high entropy alloy that secures mechanical strength and formability at the same time.

(0001) Republic of Korea Patent Registration No. 10-1950578 (2019. 02. 14)

(0001) Microstructural evolution of single Ni2TiAl or hierarchical NiAl/Ni2TiAl precipitates in Fe-Ni-Al-Cr-Ti ferritic alloys during thermal treatment for elevated-temperature applications, GianSong et al., Acta Materialia, Volume 127, 1 April 2017, Pages 1-16)

In order to solve the above problems, an object of the present invention is to provide a high entropy alloy including hierarchical NiAl/Ni ₂ TiAl precipitates in the alloy by adding Al and Ti together.

One embodiment of the present invention for achieving the above object is Al 8 to 10.5at%, Cr 5 to 25at%, Mn 15 to 35at%, Fe 5 to 30at%, Co 10 to 25at% and Ni 10 to 25at% and It relates to a high entropy alloy comprising a hierarchical NiAl/Ni ₂ TiAl precipitate characterized in that it contains 0.5 to 4 at% of Ti.

In the above embodiment, the addition amounts of Cr, Mn, Fe, Co, and Ni may be the same in atomic %, or the content difference between each component may be provided within 20%.

In the above embodiment, the high entropy alloy is formed by growing a solid solution phase of a body-centered cubic (BCC) lattice structure on an alloy matrix having a face-centered cubic (FCC) lattice structure and a body-centered cubic (BCC) lattice structure. Any structure can be formed.

In the above embodiment, a hierarchical structure composed of two phases of NiAl and Ni ₂ TiAl may be formed inside the solid solution phase.

In the above embodiment, the phase fraction of NiAl and Ni ₂ TiAl in the high entropy alloy may satisfy the following relational expression 1.

[Relationship 1]

40 ≤ B2 / L2 ₁ ≤ 50

(In the above relational expression 1, B2 is the phase fraction (%) of NiAl precipitates, and L2 ₁ is the phase fraction (%) of Ni ₂ TiAl precipitates)

In the above embodiment, the high entropy alloy may simultaneously have a yield strength of 1,000 MPa or more and a compressive strain of 20% or more at room temperature.

Another embodiment of the present invention for achieving the above object is a) preparing raw materials composed of Al, Cr, Mn, Fe, Co, and Ni and Ti, b) vacuum arc melting the raw materials to obtain an ingot manufacturing step; may include.

In the above embodiment, in the high-entropy alloy including hierarchical NiAl/Ni ₂ TiAl precipitates, body-centered cubic (BCC)-based precipitates may be precipitated on a face-centered cubic (FCC)-based alloy matrix.

The present invention is a CrMnFeCoNiAl _x high-entropy alloy in which both a face-centered cubic (FCC) lattice structure and a body-centered cubic (BCC) lattice structure are formed by growing a solid solution phase of a body-centered cubic (BCC) lattice structure on an alloy base having a face-centered cubic (FCC) lattice structure. can provide.

In addition, the present invention can provide a CrMnFeCoNiAl _0.5 Ti _x high-entropy alloy in which a hierarchical structure consisting of two phases of NiAl and Ni ₂ TiAl is formed inside the solid solution phase.

1 is a graph for explaining the phase change of the CrMnFeCoNi high entropy alloy according to the Al composition according to an embodiment of the present invention.
2 is an XRD graph of a CrMnFeCoNiAl _x high entropy alloy according to an embodiment of the present invention.
3 is an XRD graph of a CrMnFeCoNiAl _0.5 Ti _x high entropy alloy according to an embodiment of the present invention.
4 and 5 are SEM pictures of CrMnFeCoNiAl _0.5 Ti _x high entropy alloy according to an embodiment of the present invention.
6 is a tensile graph of a CrMnFeCoNiAl _0.5 Ti _x high-entropy alloy according to an embodiment of the present invention.
7 is a graph for explaining mechanical properties of a high entropy alloy according to Al and Ti compositions according to an embodiment of the present invention.

Hereinafter, a high entropy alloy including hierarchical NiAl/Ni ₂ TiAl precipitates according to the present invention will be described in detail. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Therefore, the present invention may be embodied in other forms without being limited to the drawings presented below, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, unless there is another definition in the technical terms and scientific terms used, they have meanings commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of well-known functions and configurations that may be unnecessarily obscure are omitted.

In the present specification, the CrMnFeCoNi high entropy alloy means a high entropy alloy including Cr-Mn-Fe-Co-Ni.

In the present specification, the CrMnFeCoNiAl _x high entropy alloy refers to a high entropy alloy including x at% of Al in the CrMnFeCoNi high entropy alloy.

In the present specification, the CrMnFeCoNiAl _0.5 Ti _x high entropy alloy refers to a high entropy alloy including 8 to 10.5 at% Al and x at% Ti in the CrMnFeCoNi high entropy alloy.

The present invention relates to a high entropy alloy containing hierarchical NiAl/Ni ₂ TiAl precipitates, and specifically, Al 8 to 10.5 at%, Cr 5 to 25 at%, Mn 15 to 35 at%, Fe 5 to 30 at%, Co 10 to 25 at%, 10 to 25 at% Ni, and 0.5 to 4 at% Ti, or a high entropy alloy containing unavoidable impurities in the composition.

In the present invention, a high-entropy alloy (HEA) is an alloy in which four or more major elements are mixed in an equal or almost equal atomic ratio, and the configurational entropy of the alloy itself is high, so that an intermetallic compound or mesophase It is characterized by having a single phase organization of face-centered cubic (FCC) or body-centered cubic (BCC) without formation of back.

However, when Al is added to some high-entropy alloys, for example, high-entropy alloys including Cr-Mn-Fe-Co-Ni, the solid-solution phase of the BCC lattice structure is formed in the FCC-based alloy matrix during casting and heat treatment. phase) may be precipitated. In addition, as the Al content in the high-entropy alloy increases, the solid-solution phase of the BCC lattice structure in the high-entropy alloy increases, and finally, the FCC single-phase structure changes to a BCC single-phase structure.

In general, when the CrMnFeCoNi high-entropy alloy has a single-phase structure of FCC, as shown in FIG. 1, it has a relatively low yield strength but excellent formability. On the other hand, when the high entropy alloy has a single-phase structure of BCC, yield strength is greatly increased, but formability may be reduced and brittleness of the high entropy alloy may be increased.

In the present invention, Al may be added to the CrMnFeCoNi high entropy alloy, and the Al content may be controlled to 8 to 10.5 at%. Through this, the present invention can provide a high entropy alloy having a yield strength of 400 MPa or more and a compressive strain of 15% or more at the same time by appropriately combining the fractions of the FCC lattice and the BCC lattice in the high entropy alloy.

According to an embodiment, in the present invention, by adding 8 to 10.5 at% Al in the CrMnFeCoNi high entropy alloy, NiAl having a B2 type lattice structure may be precipitated in a solid solution phase having a BCC lattice structure.

The NiAl is characterized by having a B2 type lattice structure based on a BCC lattice. This means that NiAl can maintain coherence with the solid solution phase of the BCC lattice structure. The free energy of the NiAl is minimized due to the coherence, and thus the precipitation of the NiAl may be promoted.

That is, the present invention can coherently precipitate NiAl similar to the BCC lattice structure on the solid solution to precipitate spherical NiAl having a size of several nanometers, more preferably having an average diameter of 30 to 30 on the solid solution. Spherical NiAl having a thickness of 50 nm can be deposited.

As a result, the present invention can provide a high entropy alloy having a yield strength of 400 MPa or more and a compressive strain of 30% or more at the same time by inducing more precipitation hardening in the steel.

In addition, the present invention may include 0.5 to 4 at% of titanium (Ti) in a state including 8 to 10.5 at% of Al. Hereinafter, for convenience of description, Ti is an element added to the high entropy alloy, but is not limited thereto, and any metal capable of performing the same role in the alloy may be deformable.

According to an embodiment, the present invention may further include Ti in the CrMnFeCoNiAl _x high entropy alloy, and by adjusting the content of Ti to 0.5 to 4 at%, Ni of the L2 ₁ type lattice structure in the solid solution phase of the BCC lattice structure. ₂ TiAl can be deposited.

The Ni ₂ TiAl is characterized by having an L2 ₁ type lattice structure based on a BCC lattice like the NiAl. However, unlike the above-mentioned NiAl, it is not precipitated as a spherical precipitate having a size of several nanometers in the solid solution phase, but may form a hierarchical structure (or hierarchical structure) by combining with the NiAl.

However, since the L2 ₁ type lattice structure of Ni ₂ TiAl has a slightly more strained lattice structure in BCC, unlike the B2 type lattice structure of NiAl (the L2 ₁ type lattice structure has a higher lattice constant than the B2 type lattice structure Therefore, when the Ni ₂ TiAl and the NiAl are combined, the lattice is deformed while maintaining the BCC, and lattice strain reinforcement may be performed.

When the Ni ₂ TiAl and the NiAl form a hierarchical structure due to the above-described lattice strain reinforcement, the strength of the high-entropy alloy can be increased, and in particular, the strength is improved even at a high temperature of 200 ° C. or more, and the improved strength can be maintained. there is.

The hierarchical structure is a structure in which the NiAl and the Ni ₂ TiAl are combined in a lamella structure, and unlike other structures, the strength is very strong, but it is easy to break and has reduced formability. For this reason, when the hierarchical structure of NiAl and Ni ₂ TiAl bonded inside the high entropy alloy increases, strength may increase, but formability may decrease.

According to an embodiment, the high entropy alloy including the hierarchical NiAl/Ni ₂ TiAl precipitate may provide a phase fraction of the NiAl and the Ni ₂ TiAl in the alloy to satisfy the following relational expression 1.

[Relationship 1]

40 ≤ B2 / L2 ₁ ≤ 50

(In the above relational expression 1, B2 is the phase fraction (%) of NiAl precipitates, and L2 ₁ is the phase fraction (%) of Ni ₂ TiAl precipitates)

When the phase fraction of NiAl and Ni ₂ TiAl is less than 40%, NiAl precipitated in the high-entropy alloy is insufficient, forming a hierarchical structure and remaining Ni ₂ TiAl continuously precipitates on the solid solution The high entropy alloy is changed to a single phase structure of BCC. As a result, formability of the high entropy alloy may be reduced.

On the other hand, if the phase fraction of the NiAl and the Ni ₂ TiAl exceeds 50%, the NiAl is precipitated in an excessive amount compared to the Ni ₂ TiAl, so that the effect of strengthening the strength cannot be implemented.

For this reason, in the high entropy alloy, the phase fraction of NiAl and Ni ₂ TiAl in the alloy may satisfy the above relational expression 1, and more preferably satisfy the following relational expression 2.

[Relationship 2]

43 ≤ B2 / L2 ₁ ≤ 48

(In the above relational expression 2, B2 is the phase fraction (%) of NiAl precipitates, and L2 ₁ is the phase fraction (%) of Ni ₂ TiAl precipitates)

The high entropy alloy including the hierarchical NiAl/Ni2TiAl precipitate according to an embodiment of the present invention has been described above. Hereinafter, a composition of a high entropy alloy including hierarchical NiAl/Ni ₂ TiAl precipitates according to an embodiment of the present invention will be described.

The Al is included in an amount of 8 to 10.5 at%.

The Al may precipitate a solid solution phase having a BCC lattice structure in the high entropy alloy. In addition, precipitation hardening may be induced by precipitating NiAl of B2 type lattice structure in the solid solution phase of the BCC lattice structure in the solid solution phase. If the amount of Al is less than 8 at%, a sufficient amount of solid solution phase and NiAl are not formed, so that a yield strength of 400 MPa or more cannot be realized.

Conversely, when the Al content exceeds 10.5%, the high entropy alloy is changed into a BCC single phase, and a compressive strain of 30% or more cannot be secured. For this reason, the Al may be included in 8 to 10.5 at%, more preferably 8.5 to 9.5 at%.

The Ti is included in an amount of 0.5 to 4 at%.

The Ti may form a hierarchical structure by precipitating Ni ₂ TiAl in the solid solution phase. Through this, it is possible to improve the yield strength of the high entropy alloy. If Ti is less than 0.5 at%, yield strength of 1,000 MPa or more cannot be achieved. On the other hand, when Ti exceeds 4 at%, the high entropy alloy changes to a single phase of BCC, and a compressive strain of 20% or more cannot be secured. For this reason, Ti is preferably included in an amount of 0.5 to 4 at%.

In addition, the high entropy alloy according to an embodiment of the present invention contains Cr 5 to 25 at%, Mn 15 to 35 at%, Fe 5 to 30 at%, It may include 10 to 25 at% of Co and 10 to 25 at% of Ni.

When the amount of Cr is less than 5 at%, the FCC lattice is stabilized, and when it exceeds 25 at%, the BCC lattice is stabilized, so it is preferably 5 to 25 at%. When the Mn content is less than 15 at%, the FCC lattice is stabilized, and when it exceeds 35 at%, the BCC lattice is stabilized, so it is preferably 1 to 35 at%. When Fe is less than 5 at%, the FCC lattice is stabilized, and when Fe is greater than 30 at%, the BCC lattice is stabilized, so it is preferably 5 to 30 at%. When the Co is less than 10 at%, the FCC lattice is stabilized, and when it exceeds 25 at%, the BCC lattice is stabilized, so it is preferably 10 to 25 at%. When Ni is less than 10 at%, the FCC lattice is stabilized, and when Ni is greater than 25 at%, the BCC lattice is stabilized, so it is preferably 10 to 25 at%.

According to an embodiment, the addition amounts of Cr, Mn, Fe, Co, and Ni may be provided so that each component has the same atomic % after preparing the high entropy alloy, but is not limited thereto, and the Cr, Mn, Fe, Co And Ni may be provided so that any one component selected from Ni and the other component are included within 20 atomic%.

According to an embodiment, the high entropy alloy including the hierarchical NiAl/Ni ₂ TiAl precipitate comprises a) preparing a raw material made of Al, Cr, Mn, Fe, Co, Ni, and Ti, b) the raw material It can be manufactured through the step of vacuum arc melting them to produce an ingot.

In step a), Al, Co, Fe, Ni, and Ti having a purity of 99.99% or more may be prepared, and Cr or Mn having a purity of 99.5% or more may be prepared.

In step b), an ingot may be manufactured by vacuum arc melting the raw materials prepared in step a).

According to an embodiment, step b) may be performed in an argon atmosphere with a purity of 99.0% or more, more preferably in an argon atmosphere with a purity of 99.9% or more, and even more preferably in an argon atmosphere with a purity of 99.99% or more. there is. By using high-purity argon within the above range, the strength of the alloy can be increased by reducing the amount of impurities included in the ingot.

Hereinafter, the high entropy alloy including the hierarchical NiAl/Ni ₂ TiAl precipitate according to the present invention will be described in more detail through examples. However, the following examples are only references for explaining the present invention in detail, but the present invention is not limited thereto, and may be implemented in various forms.

Also, unless defined otherwise, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description herein is merely to effectively describe specific embodiments and is not intended to limit the present invention. In addition, the unit of additives not specifically described in the specification may be at%.

go. CrMnFeCoNiAl _x Optimization of Al at% included in high entropy alloy

[Production Example 1]

Al, Cr, Mn, Fe, Co, and Ni were prepared so that the CrMnFeCoNiAl _x high-entropy alloy contained 9.09 at% of Al. Ingots were prepared by vacuum arc melting of the metals in a 99.99% high purity argon (Ar) atmosphere.

Next, the melting and cooling of the ingot was repeated 5 times in a water-cooled copper hearth to improve uniformity and compactness of the alloy.

Finally, a high entropy alloy was prepared by air-cooling the prepared high entropy alloy.

[Production Example 2]

In the CrMnFeCoNiAl _x high entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 10.31 at% of Al was included.

[Comparative Manufacturing Example 1]

In the high entropy alloy manufacturing process, all processes except for Al were prepared in the same manner as in Example 1.

[Comparative Manufacturing Example 2]

In the CrMnFeCoNiAl _x high entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 3.85 at% of Al was included.

[Comparative Manufacturing Example 3]

In the CrMnFeCoNiAl _x high-entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 7.41 at% of Al was included.

[Comparative Manufacturing Example 4]

In the CrMnFeCoNiAl _x high entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 13.79 at% of Al was included.

[Comparative Manufacturing Example 5]

In the CrMnFeCoNiAl _x high-entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 16.67 at% of Al was included.

Cr
(at%) Mn
(at%) Fe
(at%) Co
(at%) Ni
(at%) Al
(at%) Preparation Example 1 18.18 18.18 18.18 18.18 18.18 9.09 Preparation Example 2 17.86 17.86 17.86 17.86 17.86 10.31 Comparative Preparation Example 1 20.00 20.00 20.00 20.00 20.00 - Comparative Preparation Example 2 19.23 19.23 19.23 19.23 19.23 3.85 Comparative Preparation Example 3 18.52 18.52 18.52 18.52 18.52 7.41 Comparative Preparation Example 4 17.24 17.24 17.24 17.24 17.24 13.79 Comparative Preparation Example 5 16.67 16.67 16.67 16.67 16.67 16.67

[Characteristic evaluation method]

A. XRD Analysis

The XRD patterns of Preparation Example 1, Preparation Example 2 and Comparative Preparation Examples 1 to 5 are analyzed and shown in FIG. 2 . As the source of the XRD, Cu-K _α was used.

Referring to FIG. 2, Comparative Preparation Example 1 containing no Al and Comparative Preparation Example 2, Comparative Preparation Example 3, Preparation Example 1 and Preparation Example 2 containing 3.85, 7.41, 9.09 and 10.31 at% of Al, respectively. A peak for the (111) plane at the 2θ value of 43 to 50, a peak for the (200) plane at the point of 50 to 53 were observed, and a peak for the (220) plane at the 2θ value of 73 to 80 peak was observed. The peaks described above mean that an FCC lattice structure was formed inside the high entropy alloy.

In addition, in Preparation Example 1, Preparation Example 2, Comparative Preparation Example 4, and Comparative Preparation Example 5 containing 9.09, 10.31, 13.79, and 16.67 at% of Al, respectively, the peak for the above-described (111) plane disappears, and (110 ) The peak for the plane gradually increased. In addition, (200) peaks were formed at 2θ values of 60 to 68. This confirms that the lattice structure changes from FCC to BCC as the at% of Al increases. The two peaks of the lattice structure mean that an FCC lattice structure was formed inside the high-entropy alloy.

That is, while Preparation Examples 1 and 2 had both an FCC lattice and a BCC lattice, it was confirmed that Comparative Preparation Examples 1 to 3 had an FCC single-phase structure and Comparative Preparation Examples 4 to 5 had a BCC single-phase structure. can

B. Yield strength and compressive strain analysis

A compressive stress test was performed at room temperature (= 20 to 30 ° C.) on the CrMnFeCoNiAl _x high entropy alloys prepared in Preparation Example 1, Preparation Example 2 and Comparative Preparation Examples 1 to 5, and the results are shown in the table. 2 and FIG. 1 above.

Al (at%) Yield strength (MPa) Compressive strain (%) Preparation Example 1 9.09 454 33.2 Preparation Example 2 10.31 1,331 17.1 Comparative Preparation Example 1 - 273 70 Comparative Preparation Example 2 3.85 281 70 Comparative Preparation Example 3 7.41 266 70 Comparative Preparation Example 4 13.79 1,331 7.6 Comparative Preparation Example 5 16.67 1,152 3.6

According to Table 2, it can be seen that Preparation Examples 1 and 2 simultaneously have a yield strength of 400 MPa or more and a compressive strain of 15% or more. Specifically, Preparation Example 1 containing 9.09 at% of al had a yield strength of 400 MPa or more and a compressive strain of 30% or more, and Preparation Example 2 containing 10.31 at% of al had a yield strength of 1300 MPa or more and a compressive strain of 15% or more. can have at the same time.

This is because, as described above, spherical NiAl having an average diameter of 10 to 50 nm is coherently precipitated inside the BCC solid solution phase, and strength is increased through precipitation hardening while maintaining a compressive strain of 15% or more.

On the other hand, Comparative Preparation Examples 1 to 3 have an FCC single-phase structure and have excellent compressive strain but insufficient strength. In addition, Comparative Preparation Examples 4 to 5 have disadvantages in that the compressive strain is low and the brittleness is high due to the BCC single-phase structure.

That is, the present invention can manufacture a high entropy alloy having an FCC and BCC composite structure by adding 8 to 10.5 at% of Al to the high entropy alloy composed of Cr, Mn, Fe, Co and Ni, and the BCC lattice A high entropy alloy having a yield strength of 400 MPa or more and a compressive strain of 15% or more can be produced by precipitating an appropriate amount of NiAl in the structure.

me. CrMnFeCoNiAl _0.5 Ti _x Optimization of Ti at% in high-entropy alloys

In order to analyze the physical properties that change when Ti is added to the high entropy alloy prepared according to the above-described Preparation Example, Examples and Comparative Examples were prepared according to Table 3 below.

[Example 1]

In the CrMnFeCoNiAl _0.5 Ti _x high entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 1.79 at% of Ti was included.

[Example 2]

In the CrMnFeCoNiAl _0.5 Ti _x high-entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 3.51 at% of Ti was included.

[Comparative Example 1]

In the CrMnFeCoNiAl _0.5 Ti _x high entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 5.17 at% of Ti was included.

[Comparative Example 2]

It was prepared with the same composition as in Preparation Example 1 without adding Ti.

[Comparative Example 3]

It was prepared with the same composition as in Preparation Example 2 without adding Ti.

[Comparative Example 3]

In the CrMnFeCoNiAl _0.5 Ti _x high entropy alloy, all processes were prepared in the same manner as in Example 1 except for preparing the raw material so that 5.17 at% of Ti was included.

Cr
(at%) Mn
(at%) Fe
(at%) Co
(at%) Ni
(at%) Al
(at%) Ti
(at%) Example 1 17.86 17.86 17.86 17.86 17.86 8.93 1.79 Example 2 17.54 17.54 17.54 17.54 17.54 8.77 3.51 Comparative Example 1 17.24 17.24 17.24 17.24 17.24 8.62 5.17 Comparative Example 2 18.18 18.18 18.18 18.18 18.18 9.09 - Comparative Example 3 17.86 17.86 17.86 17.86 17.86 10.31 -

[Characteristic evaluation method]

A. XRD, SEM analysis

3 shows Example 1 (Al0.5-Ti0.1 in FIG. 3), Example 2 (Al0.5-Ti0.2 in FIG. 3), Comparative Example 1 (Al0.5-Ti0.3 in FIG. 3) And Comparative Example 2 (Al0.5 in FIG. 3) XRD graph, Figure 4 is Comparative Example 2 (Fig. 4 (a), (b)) Example 1 (Fig. 4 (c), (d) ) is a photograph taken by SEM of a cross section, and FIG. 5 is a cross section of Example 2 (Fig. 5 (e), (f)) and Comparative Example 1 (Fig. 5 (g), (f)) by SEM. this is a picture taken

Referring to FIG. 3 , it can be seen that the fraction of the phase having the FCC lattice structure decreases and the fraction of the phase having the BCC lattice structure increases as Ti is added to the high entropy alloy. That is, the Ti may promote the growth of the BCC phase in the high entropy alloy.

Specifically, referring to (a) and (b) of FIG. 4 , in Comparative Example 1 in which Ti was not added, dendrites of the FCC structure were distributed throughout, and BCC was formed at some interfaces of the FCC. can However, in Comparative Example 1, a hierarchical structure in which NiAl and Ni ₂ TiAl were layered was not observed because Ti was not added.

Referring to (c) and (d) of FIG. 4 , in Example 1 including 8.93 at% of Al and 1.79 at% of Ti, the BCC region increased, and the NiAl in some BCC regions due to the Ti. It can be seen that a hierarchical structure in which Ni ₂ TiAl and Ni 2 TiAl are layered is formed.

Referring to (e) and (f) of FIG. 5 , in Example 2 including 8.77 at% of Al and 3.51 at% of Ti, a hierarchical structure was formed in most of the BCC region, and the NiAl/Ni ₂ It can be seen that TiAl extends to the FCC and BCC interfaces.

Finally, referring to (g) and (h) of FIG. 5, in Comparative Example 1 including 8.62 at% of Al and 5.17 at% of Ti, it can be seen that all FCC regions are converted to NiAl/Ni ₂ TiAl. there is.

That is, as a result of the above, as Ti in the high entropy alloy increases, the NiAl/Ni ₂ TiAl region expands, but when Ti exceeds 4at%, all FCC lattice arrangements of the high entropy alloy are converted to BCC, and the high entropy alloy It can be seen that the entropic alloy changes to the BCC single phase.

B. Analysis of yield strength and compressive strain

For the CrMnFeCoNiAl _0.5 Ti _x high entropy alloy, a compressive stress test was performed in the same manner as the CrMnFeCoNiAl _x high entropy alloy, and the results are shown in Table 4 and FIG. 6.

Al (at%) Ti (at%) Yield strength (MPa) Compressive strain (%) Example 1 8.93 1.79 1,104 34 Example 2 8.77 3.51 1,516 22.2 Comparative Example 1 8.62 5.17 2,081 1.1 Comparative Example 2 9.09 - 454 33.2 Comparative Example 3 10.31 - 1,331 17.1

Referring to Table 2 and FIG. 6, it can be seen that Examples 1 and 2 containing 0.5 to 4 at% of Ti simultaneously have a yield strength of 1,000 MPa or more and a compressive strain of 20% or more. Specifically, Example 1 containing 8.93 at% of Al and 1.79 at% of Ti has a yield strength of 1,000 MPa or more and a compressive strain of 30% or more, and includes 8.77 at% of Al and 3.51 at% of Ti. 2 has a yield strength of 1,500 MPa or more and a compressive strain of 20% or more. This means that the yield strength is increased by 650 to 1062 MPa when compared to Example 1 having the same Al composition.

On the other hand, Comparative Example 1 containing 8.62 at% of Al and 5.17 at% of Ti had a yield strength of 1,000 MPa or more, but it could be seen that the compressive strain decreased sharply to 1.1%. This is because the high-entropy alloy was changed to a BCC single phase due to the Ti, and the compressive strain decreased rapidly.

On the other hand, in Comparative Examples 2 and 3, the yield strength was lower than that of Examples 1 and 2 because a hierarchical structure in which NiAl and Ni ₂ TiAl were layered was not formed on the BCC solid solution. It was confirmed.

As described above, the present invention includes 8 to 10.5 at% of Al in the CrMnFeCoNi high entropy alloy containing Cr-Mn-Fe-Co-Ni, so that the high entropy alloy is an appropriate amount of BCC solid solution phase and An appropriate amount of NiAl can be deposited.

In addition, the present invention includes 0.5 to 4 at% of Ti in the CrMnFeCoNiAl _x high entropy alloy to precipitate a hierarchical structure in which NiAl and Ni ₂ TiAl are combined in a layered structure.

Through this, the present invention can provide a high entropy alloy having a yield strength of 400 MPa or more and a compressive strain of 15% or more at the same time by including 8 to 10.5 at% of Al in the CrMnFeCoNi high entropy alloy as shown in FIG. 7, and also CrMnFeCoNiAl _x A high entropy alloy having a yield strength of 1,000 MPa or more and a compressive strain of 20% or more at the same time may be provided by further including 0.5 to 4 at% of Ti in the high entropy alloy.

Although the present invention has been described through specific details and limited examples as described above, this is only provided to help a more general understanding of the present invention, the present invention is not limited to the above examples, and the present invention belongs Various modifications and variations from these descriptions are possible to those skilled in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and it will be said that not only the claims to be described later, but also all modifications equivalent or equivalent to these claims belong to the scope of the present invention. .

Claims (8)

8 to 10.5 at% of Al, 5 to 25 at% of Cr, 15 to 35 at% of Mn, 5 to 30 at% of Fe, 10 to 25 at% of Co, 10 to 25 at% of Ni, and 0.5 to 4 at% of Ti, A high-entropy alloy containing hierarchical NiAl/Ni ₂ TiAl precipitates. According to claim 1,
The addition amounts of Cr, Mn, Fe, Co, and Ni are the same in atomic percent, or the content difference between each component is within ₂₀ %. According to claim 1,
The high entropy alloy is a high entropy alloy containing hierarchical NiAl / Ni ₂ TiAl precipitates, characterized in that body-centered cubic (BCC)-based precipitates are precipitated on a face-centered cubic (FCC)-based alloy matrix. According to claim 3,
A high entropy alloy containing hierarchical NiAl/Ni ₂ TiAl precipitates, characterized in that a hierarchical structure consisting of two phases of NiAl and Ni ₂ TiAl is formed inside the solid solution phase. According to claim 4,
The high entropy alloy is a high entropy alloy including hierarchical NiAl/Ni ₂ TiAl precipitates, characterized in that the phase fraction of NiAl and Ni ₂ TiAl satisfies the following relational expression 1.
[Relationship 1]
40 ≤ B2 / L2 ₁ ≤ 50
(In the above relational expression 1, B2 is the phase fraction (%) of NiAl precipitates, and L2 ₁ is the phase fraction (%) of Ni ₂ TiAl precipitates) According to claim 1,
The high entropy alloy is a high entropy alloy containing hierarchical NiAl / Ni ₂ TiAl precipitates, characterized in that it simultaneously has a yield strength of 1,000 MPa or more and a compressive strain of 20% or more at room temperature. a) preparing any one raw material selected from among Al, Cr, Mn, Fe, Co, Ni, and Ti or Ta; and
b) preparing an ingot by vacuum arc melting the raw materials;
The ingot contains 8 to 10.5 at% Al, 5 to 25 at% Cr, 15 to 35 at% Mn, 5 to 30 at% Fe, 10 to 25 at% Co, 10 to 25 at% Ni, and 0.5 to 4 at% Ti Characterized in, a method for producing a high entropy alloy with addition of Al. According to claim 7,
The Al-added high-entropy alloy is characterized in that body-centered cubic (BCC)-based precipitates are precipitated on the face-centered cubic (FCC)-based alloy matrix.

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