KR20230029178A - High- strength and heat-resisting hierarchical high entropy alloy and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a high-strength and heat-resisting hierarchical high entropy alloy which comprises Al and any one element selected from a first element group consisting of Ti, Nb, and V and a second element group consisting of Co and Ni, wherein 10 to 30 at% of Al, 20 to 30 at% of the elements of the first element group, and 1 to 8 at% of the elements of the second element group are included.

Description

High-strength superheat-resistant hierarchical high-entropy alloy and its manufacturing method

The present invention relates to a high-strength superheat-resistant hierarchical high-entropy alloy in which strength is enhanced by uniformly precipitating a sigma phase inside the high-entropy alloy and a manufacturing method thereof.

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 has the advantage of being able to induce solid solution strengthening by causing lattice distortion and substitution depending on the size difference of the elements.

In order to further develop the characteristics of such a high entropy alloy, research is being conducted to enhance physical properties by including metal and non-metal additives in the high entropy alloy.

For example, Korean Patent Registration No. 10-1927611 discloses a method for improving synthesis yield and mechanical properties by adding a body centered cubic (BCC)-based alloying element, and Korean Patent Registration No. 10-1831056 discloses a non-metal element. It discloses a method of making a high entropy alloy with excellent hardness and corrosion resistance by adding a. Korean Patent Registration No. 10-1708763 discloses a high entropy alloy having multiple main elements.

However, even with the above method, there are still many difficulties in manufacturing a high entropy alloy having high strength and elongation at a temperature of 100 ° C or lower and maintaining sufficient strength even at 600 ° C or higher.

(0001) Republic of Korea Patent No. 10-1927611 (2018. 12. 04) (0002) Republic of Korea Patent Registration No. 10-1831056 (2018. 02. 21) (0003) Republic of Korea Patent No. 10-1708763 (2017. 02. 15)

In order to solve the above problems, an object of the present invention is to provide a superheat-resistant high-entropy alloy and a manufacturing method thereof, in which strength is greatly improved by uniformly precipitating a sigma phase inside the high-entropy alloy.

An embodiment of the present invention for achieving the above object includes any one element selected from a first element group consisting of Al, Ti, Nb, and V, and a second element group consisting of Co and Ni, wherein the Al is 10 to 30 at%, the elements of the first element group are 20 to 30 at%, respectively, and the elements of the second element group are 1 to 8 at%. will be.

In the above embodiment, the addition amount of the three elements selected from the first element group may be the same in atomic %, or the content difference between each component may be 5% or less.

In the above embodiment, the high-strength superheat-resistant hierarchical high-entropy alloy has a body-centered cubic (BCC) structure, and the element of the second element group has a tetragonal structure (Tetragonal structure), and may be precipitated within the body centered cubic (BCC) structure.

In the above embodiment, the high-strength superheat-resistant hierarchical high-entropy alloy may simultaneously have a yield strength of 1,600 MPa or more and a compressive strain of 13% or more at a temperature of 100° C. or less.

In the above embodiment, the high-strength superheat-resistant hierarchical high entropy alloy may have a yield strength of 1,000 to 1,200 MPa and a compressive strain of 20 to 30% at a temperature of 600 to 750 ° C.

According to another embodiment of the present invention, a) preparing a raw material containing any one element selected from Al, the first element group and the second element group; b) preparing an ingot by weighing the raw materials and then vacuum arc remelting (VAR); c) injecting the ingot into a quartz tube filled with titanium pieces in a vacuum state; and d) maintaining the ingot-injected quartz tube at 1,000 to 1,200° C. for a predetermined time, wherein the first element group is composed of Ti, Nb, and V, and the second element group is composed of Co and Ni. It relates to a method for producing a high-strength superheat-resistant hierarchical high-entropy alloy, characterized in that it is configured.

In the above embodiment, after melting the raw materials weighed in step b) to form a master alloy, the master alloy may be re-melted five or more times to manufacture an ingot.

In the above embodiment, the heat treatment may be performed for 30 to 120 minutes.

The present invention can provide a high-entropy alloy having a yield strength of 1,600 MPa or more and a compressive strain of 13% or more at a temperature of 100 ° C or less by precipitating a sigma phase of a tetragonal structure on a base material of a body centered cubic (BCC) lattice structure. .

Through this, the present invention can provide a high entropy alloy that simultaneously secures strength and elongation and maintains strength even at a high temperature of 600° C. or higher.

1 is an XRD graph of Preparation Example and Comparative Preparation Example according to an embodiment of the present invention.
2 is SEM-BSE pictures of Preparation Examples 1 and 2 according to an embodiment of the present invention.
3 is a SEM-BSE photograph of Comparative Preparation Example 1 and Comparative Preparation Example 2 according to an embodiment of the present invention.
4 is an XRD graph of Example 1 and Example 2 according to an embodiment of the present invention.
5 is SEM-BSE pictures of Examples 1 and 2 according to an embodiment of the present invention.
6 to 8 are graphs illustrating the high-temperature strength of the high-strength superheat-resistant hierarchical high-entropy alloy prepared according to Example 1 of the present invention.
9 to 11 are graphs illustrating the high-temperature strength of the high-strength superheat-resistant hierarchical high-entropy alloy prepared according to Example 2 of the present invention.

Hereinafter, the high-strength superheat-resistant hierarchical high-entropy alloy 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.

The present invention relates to a high-strength superheat-resistant hierarchical high-entropy alloy, and specifically, it may be provided as an alloy of Al and any one element selected from Ti, Nb, V, and Co or Ni.

In general, a high-entropy alloy (HEA) is an alloy in which four or more major elements are mixed in equal or almost equal atomic ratios, and the configurational entropy of the alloy itself is high, resulting in intermetallic compounds or mesophases. There are features that do not exist. In addition, the high entropy alloy has a single phase structure of face-centered cubic (FCC) or body-centered cubic (BCC), or face-centered cubic and body-centered cubic, depending on its composition and manufacturing method. It may be provided as a composite phase structure containing all.

In the present invention, the group 4, 5, 6 transition elements that can have a body-centered cubic structure, particularly Ti, Nb, which are refractory elements having a melting temperature of 1500 ° C or higher and having excellent mechanical properties even at a temperature of 1,000 ° C or higher, A high-strength superheat-resistant hierarchical high-entropy alloy having a body-centered cubic structure provided by V can be produced. Hereinafter, a group of elements provided as Ti, Nb, and V is defined as a first group of elements.

In addition, the present invention may include 1 to 8 at% of any one element selected from Co or Ni.

Elements belonging to the above-mentioned first element group have excellent mechanical properties even at a temperature of 1,000 ° C. or higher, but have a relatively reduced yield strength at a temperature of 100 ° C. or lower.

To compensate for this, the present invention includes Co or Ni, which has a relatively small atomic radius compared to Al and elements belonging to the first element group, to induce solid solution strengthening, thereby improving mechanical characteristics. can do.

Specifically, when Co or Ni is included in a high entropy alloy composed of Al and an element belonging to the first element group, Co or Ni is exchanged in a space where an element belonging to the first element group is located, causing lattice deformation. . In other words, the Co or Ni induces solid solution strengthening in the high entropy alloy to enhance mechanical properties even at room temperature.

According to an embodiment, through the above-described solid solution strengthening effect, the high-strength superheat-resistant hierarchical high-entropy alloy can be strengthened to simultaneously have a low-temperature strength of 100 ° C or less, more preferably a yield strength of 1,400 MPa or more and a compressive strain of 25% or more at room temperature. can

In addition, according to another embodiment of the present invention, the solid solution strengthening effect may be further improved by further including a process of heat-treating the high-strength superheat-resistant hierarchical high-entropy alloy at 1,000 to 1,200 ° C. for 30 to 120 minutes.

Specifically, Al(Nb,Co) ₂ or Al(Nb,Co) ₂ may be formed by combining Al and Nb of the first element group through the heat treatment. The Al(Nb,Co) ₂ or Al(Nb,Co) ₂ is evenly precipitated in the high-entropy alloy base material to cause a greater solid solution strengthening effect than when Co or Ni is simply precipitated. Hereinafter, the Al (Nb, Co) ₂ or Al (Nb, Co) ₂ precipitated phase precipitated on the high-strength superheat-resistant hierarchical high-entropy alloy base material is classified as a Sigma phase (σ) or Sigma precipitates (Sigma precipitates). can do.

The sigma phase (σ) is characterized by having a tetragonal structure, and thus may cause a larger lattice strain in a high-strength superheat-resistant hierarchical high-entropy alloy base material formed in a body centered cubic (BCC) structure.

According to an embodiment, through the above-described heat treatment, the high-strength superheat-resistant hierarchical high-entropy alloy has a low-temperature strength of 100 ° C. or less, more preferably, a yield strength of 1,600 MPa or more and a compressive strain of 13% or more at room temperature. It can be strengthened at the same time. .

In addition, the above-described Al (Nb, Co) ₂ or Al (Nb, Co) ₂ may have a yield strength of 1,000 to 1,200 MPa and a compressive strain of 20 to 30% at a high temperature of 600 ° C to 750 ° C.

That is, according to the present invention, a high entropy alloy with enhanced strength can be manufactured by including any one selected from Co or Ni in the first element group provided with Al, Ti, Nb, and V.

In addition, in the present invention, a sigma precipitation phase may be formed in the high entropy alloy by heat-treating the high entropy alloy at 1,000 to 1,200 ° C for 2 hours or less. The sigma precipitated phase may induce a larger lattice strain in the high entropy alloy base material formed in the body centered cubic (BCC) structure, and through this, the solid solution strengthening effect may be further strengthened.

Above, the high-strength superheat-resistant hierarchical high-entropy alloy according to the embodiment of the present invention has been described. Hereinafter, a composition of a high-strength superheat-resistant hierarchical high-entropy alloy according to an embodiment of the present invention will be described.

The Al is contained in an amount of 10 to 30 at%.

The Al may stabilize a body-centered cubic (BCC) structure in the high-strength superheat-resistant hierarchical high-entropy alloy, causing the high-strength superheat-resistant hierarchical high-entropy alloy to have a body-centered cubic (BCC) structure. In addition, when the Al undergoes a heat treatment process, it may be combined with Nb and an element of the second element group to be described later to precipitate a sigma phase having a tetragonal structure. When the amount of Al is less than 10 at%, the base material in the high-strength superheat-resistant hierarchical high-entropy alloy is not stabilized as a single BCC structure, and mechanical properties may be reduced.

Conversely, when the Al content exceeds 30 at%, the component ratio of Nb and the second element group is relatively reduced, so that a sufficient amount of the sigma phase cannot be precipitated after heat treatment. For this reason, the Al may be included in 10 to 30 at%, more preferably 15 to 25 at%.

The first group of elements includes Ti, Nb, and V, and may contribute to refractory properties, lifespan, strength, compression set, and the like of the high-strength superheat-resistant hierarchical high-entropy alloy.

For example, Ti of the first element group may improve resistance to high-temperature oxidation of the high-strength superheat-resistant hierarchical high-entropy alloy. Through this, it is possible to improve the refractory properties and lifespan of the high-strength superheat-resistant hierarchical high-entropy alloy.

Nb of the first element group may be combined with Al of the high-strength superheat-resistant hierarchical high-entropy alloy and an element of the second element group to form a sigma phase. The sigma phase may improve both low-temperature strength and high-temperature strength of the high-strength superheat-resistant hierarchical high-entropy alloy.

V of the first element group may contribute to maintaining strength and improving compression set of the high-strength superheat-resistant hierarchical high-entropy alloy in a high-temperature environment of 600° C. or higher.

Elements of the first element group may each be included in an amount of 20 to 30 at%. If the elements of the first element group are included in less than 20 at%, the above-described effects cannot be implemented at an appropriate level due to insufficient composition of each element. Conversely, when the content of the elements of the first element group exceeds 30 at%, the Al and the elements of the second element group are relatively reduced, so that sufficient strength cannot be secured.

According to an embodiment, Ti, Nb, and V in the first element group may include the same atomic % or a content difference between each component of 5% or less.

The second element group may be provided with Co and Ni, and may include 1 to 8 at% of any one element selected from the second element group.

As described above, the second group of elements may be dissolved in the high-strength superheat-resistant hierarchical high-entropy alloy to form a precipitate phase having a tetragonal structure.

Specifically, a sigma phase of Al(Nb,Co) ₂ or Al(Nb,Co) ₂ may be precipitated by combining with Al in the high-strength superheat-resistant hierarchical high-entropy alloy and Nb in the first element group, through which By inducing a larger lattice strain, the mechanical strength of high-strength superheat-resistant hierarchical high-entropy alloys can be greatly improved. It is preferable that any one element selected from the second element group is included in an amount of 1 at% or more in order to realize the above-described effect. When the second element group is included in an amount of less than 1 at%, the amount of precipitation of the sigma phase decreases, so that the solid solution strengthening effect is not implemented. On the other hand, when the content of any one element selected from the second group of elements exceeds 8 at%, the sigma phase becomes coarse and the uniformity of distribution decreases, so that ductility may be excessively reduced and brittleness may increase. For this reason, any one element selected from the second element group may be included in an amount of 1 to 8 at%, more preferably 3 to 6 at%.

The composition of the high-strength superheat-resistant hierarchical high-entropy alloy according to the embodiment of the present invention has been described above. Hereinafter, a method for manufacturing a high-strength superheat-resistant hierarchical high-entropy alloy according to an embodiment of the present invention will be described.

According to an embodiment, the manufacturing method of the high-strength superheat-resistant hierarchical high-entropy alloy includes the steps of a) preparing a raw material including Al, any one element selected from the first element group and the second element group, b) After weighing the raw materials, preparing an ingot by vacuum arc remelting (VAR), c) injecting the ingot into a quartz tube containing titanium pieces in a vacuum state, and d) the ingot It may include; maintaining the injected quartz tube at 1,000 to 1,200 ° C for a certain period of time. In this case, the first element group may be provided with Ti, Nb, and V, and the second element group may be provided with Co and Ni.

In step a), the raw material may be prepared with a purity of 99.95% or more. In addition, the above raw materials can be prepared in an argon atmosphere with a purity of 99.0% or more. Through this, it is possible to improve the purity of the ingot produced in step b) to be described later.

According to an embodiment, step b) may be performed by vacuum arc remelting (VAR).

Specifically, after weighing the raw material in the above-described composition range, it may be melted in a vacuum arc melting furnace to form a master alloy. Thereafter, an ingot may be manufactured by charging the master alloy into a water-cooled copper furnace and then remelting the master alloy using an arc.

According to an embodiment, step b) may be performed in a vacuum and 99.99% pure argon atmosphere to prevent Ti from being oxidized to form an oxide layer. At this time, the vacuum state may be performed at 3x10 ^-2 Torr or less, more preferably 3x10 ^-3 Torr or less.

According to an embodiment, the re-dissolution in step b) may be repeated at least 5 times. If the process of remelting the ingot is performed less than 5 times, the first element group composed of refractory elements may not be completely dissolved and impurities may be formed in the form of slag. This prevents uniform physical properties and causes cracks. For this reason, b) re-dissolution may be performed at least 5 times, and more preferably 8 times or more. Through this, a high entropy alloy having a lattice structure of a body centered cubic (BCC) structure can be manufactured.

After step b), the ingot may be injected into a quartz tube filled with titanium pieces in a vacuum state.

According to an embodiment, step c) may be performed in a vacuum state maintained at 10 ⁻² Torr or less. In addition, it is possible to prevent the ingot from being oxidized during a heat treatment process to be described later by filling the quartz tube with titanium pieces.

According to an embodiment, the step d) may be performed at 1,000 to 1,200 ° C, more preferably maintained at 1,000 to 1,200 ° C for 30 to 120 minutes.

In step d), if the temperature of the heat treatment is less than 1,000° C., the temperature at which the sigma phase can be precipitated is not reached, and thus the amount of precipitation of the sigma phase may be reduced. This may decrease the yield strength by reducing the solid solution strengthening effect realized due to the sigma phase.

On the other hand, when the heat treatment temperature exceeds 1,200° C., the sigma phase becomes coarse and the uniformity of distribution decreases, so that ductility may be excessively reduced and brittleness may increase. In order to prevent this, step d) is preferably performed at 1,000 to 1,200 ° C.

Hereinafter, a high-strength superheat-resistant hierarchical high-entropy alloy and a manufacturing method thereof 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. Changes in the microstructure of high-strength superheat-resistant hierarchical high-entropy alloys according to the precipitation of sigma phase (σ)

In order to explain in detail the process of precipitation of the sigma phase in the high-strength superheat-resistant hierarchical high-entropy alloy, the microstructures of the high-strength superheat-resistant hierarchical high-entropy alloy were compared before and after heat treatment.

First, in order to compare the change in physical properties of high-strength superheat-resistant hierarchical high-entropy alloys according to the addition of any one element (Co or Ni) selected from the second element group without performing heat treatment, examples and comparison are as follows. made up an example.

[Production Example 1]

Al, Ti, Nb, V, Co, and Ni with a purity of 99.95% were prepared in the composition shown in Table 1 below. Ingots were prepared by vacuum arc melting of the metals in a 99.99% high purity argon (Ar) atmosphere.

Next, the steps of dissolving and cooling the ingot were repeated 8 times. At this time, the cooling was performed using a water-cooled copper hearth.

Next, for the physical property test, the alloy was processed into a cylindrical rod having a diameter of 3 mm and a length of 50 mm by vacuum suction casting.

[Production Example 2]

It was prepared in the same manner as in Preparation Example 1 except that the composition of the metal used was changed as shown in Table 1 below.

[Comparative Manufacturing Example 1]

It was prepared in the same manner as in Preparation Example 1 except that the composition of the metal used was changed as shown in Table 1 below.

[Comparative Manufacturing Example 2]

It was prepared in the same manner as in Preparation Example 1 except that the composition of the metal used was changed as shown in Table 1 below.

Al
(at%) Ti
(at%) Nb
(at%) V
(at%) Co
(at%) Ni
(at%) Preparation Example 1 20 25 25 25 5 - Preparation Example 2 20 25 25 25 - 5 Comparative Preparation Example 1 25 25 25 25 - - Comparative Preparation Example 2 21.1 26.3 26.3 26.3 - -

In order to analyze the lattice structure of the high-strength superheat-resistant hierarchical high-entropy alloy prepared in Preparation Examples 1 to 2 and Comparative Preparation Examples 1 to 2, XRD and SEM-BSE information of the Preparation Examples and Preparation Examples were obtained. The XRD was measured by irradiating Cu-Kα rays (λ = 1.54187 Å) using a diffractometer from RIGAKU, Japan. It was photographed with a detector attached.

XRD graphs of the Preparation Example and Comparative Preparation Example are shown in Figure 1, SEM-BSE pictures of Preparation Example 1 and Preparation Example 2 without performing the heat treatment are shown in Figure 2, Comparative Preparation Example 1 and Comparative Preparation Example 2 The SEM-BSE picture of is shown in Figure 3.

Referring to FIG. 1, Preparation Examples 1 and 2 selectively including any one of Co and Ni defined as the second element group and Comparative Preparation Example 1 not including the second element group and Comparative Preparation Example 2, it can be confirmed that picks peculiar to the body centered cubic (BCC) structure occur. That is, it can be confirmed that both Preparation Examples 1 and 2 and Comparative Preparation Examples 1 and 2 have a body centered cubic (BCC) structure.

In fact, even when comparing the SEM-BSE pictures of Production Examples 1 and 2 (FIG. 2) and the SEM-BSE pictures of Comparative Production Examples 1 and 2 (FIG. 3), the dendrite areas developed in a branch shape and It can be seen that inter-dendrite areas are formed, and there is no significant difference in their shapes and areas.

That is, it can be seen from the above results that no lattice deformation occurs in the high-strength superheat-resistant hierarchical high-entropy alloy simply by adding the second element group (Co or Ni).

Thereafter, in order to observe how the microstructure of the high-strength superheat-resistant hierarchical high-entropy alloy changes according to heat treatment, heat treatment was performed on the high-strength superheat-resistant hierarchical high-entropy alloy according to an embodiment to be described later.

[Example 1]

The high-strength superheat-resistant hierarchical high-entropy alloy prepared according to Preparation Example 1 was charged into a quartz tube in a vacuum state of 10 ⁻² Torr, and then heat-treated by maintaining at 1,100° C. for 60 minutes.

After heat treatment, the quartz tube was air-cooled, and then a high-strength superheat-resistant hierarchical high-entropy alloy was separated from the inside of the quartz tube.

[Example 2]

The same heat treatment as in Example 1 was performed on the high-strength superheat-resistant hierarchical high-entropy alloy prepared according to Preparation Example 2.

XRD graphs of Examples 1 and 2 are shown in FIG. 4, and SEM-BSE pictures of Examples 1 and 2 are shown in FIG.

Referring to FIG. 4, in Example 1 and Example 2, in which heat treatment was performed, it can be confirmed that a sigma phase having a tetragonal structure was formed, unlike the XRD graph of FIG. 1 in which heat treatment was not performed in the same composition. can In addition, the lattice constant (a) of the sigma phase in Example 1 was 0.9638 nm, and the lattice constant (a) of the sigma phase in Example 2 was measured to be 0.9582 nm.

Referring to FIG. 5, in Examples 1 and 2 in which heat treatment was performed, unlike FIGS. 2 and 3, which were divided into dendrite areas and inter-dendrite areas, they were not dendrite areas. It can be seen that the sigma phase is precipitated in a relatively circular shape and is uniformly distributed in the base material.

More specifically, Examples 1 and 2 can be divided into areas measured as relatively bright and areas measured as relatively dark among the sigma phases precipitated in the base material as a result of SEM-EDS measurement. Hereinafter, a relatively bright region is defined as a first region, and a relatively dark region is defined as a second region.

As a result of analyzing the composition of the first region and the second region using EDS, it was confirmed that relatively more Nb was present than the base material in the first region, and relatively more Co than the base material in the second region. Alternatively, it was confirmed that a large amount of Ni was present. The specific composition of the base material, the first region, and the second region in Examples 1 and 2 is shown in Table 2 below.

Al
(at%) Ti
(at%) Nb
(at%) V
(at%) Co
(at%) Ni
(at%) Example 1 parent material 17.4 ±0.5 28.4±1.0 23.0 ±0.7 26.3 ±0.4 4.9±0.5 - Area 1 22.0 ±0.3 20.5 ±0.4 36.6 ±0.4 15.7 ±0.2 5.2±0.2 - area 2 19.8±0.4 20.1 ±0.7 20.2 ±0.3 20.2±0.7 19.7 ±1.1 - Example 2 parent material 17.0 ±0.5 29.0±1.0 23.1 ±1.0 27.0 ±0.3 - 3.9±1.0 Area 1 21.2 ±0.6 22.2 ±0.4 34.5 ±0.5 16.3 ±0.4 - 5.7±0.4 area 2 23.2 ±0.3 23.1 ±0.2 22.1 ±0.8 12.0 ±0.3 - 19.6 ±1.1

That is, in the present invention, when the second element group composed of Co and Ni is simply included in the high-strength superheat-resistant hierarchical high-entropy alloy, the high-strength superheat-resistant hierarchical high-entropy alloy is body-centered cubic (BCC) as shown in FIGS. ) structure was maintained, and it was confirmed that no phase change occurred.

However, when the high-strength superheat-resistant hierarchical high-entropy alloy containing the second element group is subjected to heat treatment at 1,000 to 1,200 ° C, the Co or Ni is combined with Al and Nb of the base material to form a sigma phase having a tetragonal structure. Precipitated, It was confirmed that the sigma phase was uniformly distributed in the base material.

me. Changes in mechanical properties of high-strength superheat-resistant hierarchical high-entropy alloys according to the precipitation of sigma phase (σ)

In order to compare the mechanical strength of high-strength superheat-resistant hierarchical high-entropy alloys according to the presence or absence of sigma phase precipitation and to optimize heat treatment and composition conditions, experiments were conducted by adding the above-described Examples 1 and 2 and the following comparative examples. performed.

[Comparative Example 1]

No heat treatment was performed on the high-strength superheat-resistant hierarchical high-entropy alloy prepared according to Preparation Example 1.

[Comparative Example 2]

No heat treatment was performed on the high-strength superheat-resistant hierarchical high-entropy alloy prepared according to Preparation Example 2.

A compression test piece was prepared by processing the high-strength superheat-resistant hierarchical high-entropy alloy prepared according to Examples 1 and 2 and Comparative Examples 1 and 2 into a diameter of 3 mm and a length of 6 mm (aspect ratio 2: 1). and a compressive stress test was conducted at room temperature with UTM equipment under the MINOS-F model name of MTDI, Korea. The results are summarized in Table 3.

heat treatment condition Yield strength (MPa) Compressive strain (%) etc Example 1 1,100℃ / 60min 1645 ±60 14.1 ±0.8 Contains 5at% of Co Example 2 1,100℃ / 60min 1723 ±14 17.7 ±2.4 Contains Ni 5at% Comparative Example 1 - 1473 ±109 30% or more Same as Example 1 Comparative Example 2 - 1510 ±13 30% or more Same as Example 2

Referring to Table 3, it can be seen that Examples 1 and 2 in which the sigma phase was precipitated simultaneously had a yield strength of 1,600 MPa or more and a compressive strain of 13% or more. Specifically, Example 1 containing 5 at% Co has a yield strength of 1,585 to 1,705 MPa and a compressive strain of 14.9% in 13.3, and Example 2 containing 5 at% Ni has a yield strength of 1,710 to 1,737 MPa and 15.3 20.1 It has a compressive strain of %. This means that the yield strength was improved by up to 25% when compared to Comparative Examples 1 and 2 in which heat treatment was not performed.

That is, it can be seen that the sigma phase was precipitated through the heat treatment, and the lattice deformation of the sigma phase occurred between the base materials of the body centered cubic (BCC) structure, thereby increasing the strength.

6 is a graph illustrating the high-temperature strength of a high-strength superheat-resistant hierarchical high-entropy alloy manufactured according to Example 1 of the present invention, and FIG. 7 is a high-strength superheat-resistant hierarchical high-entropy alloy manufactured according to Example 2 of the present invention. A graph illustrating the high temperature strength of an alloy.

In order to compare the high-temperature strength of the high-strength superheat-resistant hierarchical high-entropy alloy prepared according to the embodiment of the present invention, the yield strength (σ _0.2 ) and compressive strain (ε _p ) at 700 ° C and 800 ° C were measured. The results are disclosed in Table 4 and FIG. 6 below.

100℃ or less 700℃ 800℃ σ _0.2
(MPa) _εp
(%) σ _0.2
(MPa) _εp
(%) σ _0.2
(MPa) _εp
(%) Example 1 1,645 14.1 1,198 21 507 over 28 Example 2 1,723 17.1 1,028 over 25 378 over 28

Referring to Table 4 and FIGS. 6 to 8, the high-strength superheat-resistant hierarchical high-entropy alloy prepared in Example 1 of the present invention has a yield of 1,600 MPa or more at 1,645 MPa at a temperature (RT) of 100 ° C or less (FIG. 6) It can be seen that the strength is maintained, and the yield strength of 1,000 MPa or more is maintained even at a temperature of 600 to 750 ° C (FIG. 7). In addition, it can be seen that the yield strength of 500 MPa or more can be maintained even at 750 ° C or higher (FIG. 8), for example, 800 ° C.

This is because, as described above, a sigma precipitated phase is formed in the high-strength superheat-resistant hierarchical high-entropy alloy, and the precipitated phase is uniformly distributed in the base material to realize a very high solid solution strengthening effect.

Referring to Table 4 and FIGS. 9 to 11, the high-strength superheat-resistant hierarchical high-entropy alloy prepared in Example 2 of the present invention is 1,723 MPa at a temperature (RT) of 100 ° C or less (FIG. 9), similar to Example 1. It is more excellent in strength, and it can be seen that it has a yield strength equivalent to that of Example 1 at 1,028 MPa even at 600 to 750 ° C (FIG. 10). At 800 ° C (Fig. 11), the strength is lower than that of Example 1, but it can be seen that the strength is maintained at 378 MPa.

According to the above results, the user can selectively use the high-entry alloy containing Co and the high-entry alloy containing Ni according to the use temperature and target strength. For example, in fields where the use environment is 750°C or less and high strength is required, a high-entropy alloy containing Ni can be used. A choice of alloys can be used.

As described above, the present invention is a high-strength superheat-resistant hierarchical high-entropy alloy containing any one element selected from the first element group consisting of Al, Ti, Nb, and V, and the second element group consisting of Co and Ni. It can manufacture, more specifically, high-strength ultra-heat-resistant hierarchical structure containing 10 to 30 at% of Al, 20 to 30 at% of each element of the first element group, and 1 to 8 at% of the element of the second element group. High entropy alloys can be produced.

In the process, the present invention heat-treats the high-strength superheat-resistant hierarchical high-entropy alloy at 1,000 to 1,200 ° C. to obtain the sigma of Al(Nb,Co) ₂ or Al(Nb,Co) ₂ in the high-strength superheat-resistant hierarchical high-entropy alloy. The prize can be precipitated. The sigma phase is characterized by having a tetragonal structure, unlike the parent material having a body centered cubic (BCC) structure.

That is, the heat treatment forms a precipitate phase having a different lattice structure in the high-strength superheat-resistant hierarchical high-entropy alloy, and the precipitate phase may be uniformly distributed in the base material. This may cause lattice deformation of the high-strength superheat-resistant hierarchical high-entropy alloy to further enhance the solid solution strengthening effect.

As a result, the high-strength superheat-resistant hierarchical high-entropy alloy according to an embodiment of the present invention can simultaneously realize a yield strength of 1,600 MPa or more and a compressive strain of 13% or more at a temperature of 100 ° C or less, preferably room temperature, and at 600 to 750 ° C. It is possible to implement a yield strength of 1,000 to 1,200 MPa and a compressive strain of 20 to 30% at a temperature.

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 (7)

Al and
A first group of elements consisting of Ti, Nb and V; and
Including any one element selected from the second element group consisting of Co and Ni,
The Al is 10 to 30 at%, the elements of the first element group are 20 to 30 at%, respectively, and the elements of the second element group are 1 to 8 at%. . According to claim 1,
A high-strength superheat-resistant hierarchical high-entropy alloy, characterized in that the addition amount of the three elements selected from the first element group is the same in atomic percent, or the content difference between each component is 5% or less. According to claim 1,
The high-strength superheat-resistant hierarchical high-entropy alloy has a body centered cubic (BCC) structure,
The elements of the second element group form a precipitate phase of a tetragonal structure in the high-strength superheat-resistant hierarchical high-entropy alloy,
Characterized in that it is precipitated in the body centered cubic (BCC) structure, high-strength superheat-resistant hierarchical high-entropy alloy. According to claim 3,
The high-strength superheat-resistant hierarchical high-entropy alloy is characterized by simultaneously having a yield strength of 1,600 MPa or more and a compressive strain of 13% or more at a temperature of 100 ° C or less. According to claim 3,
The high-strength superheat-resistant hierarchical high-entropy alloy is characterized by having a yield strength of 1,000 to 1,200 MPa and a compressive strain of 20 to 30% at a temperature of 600 to 750 ° C., high-strength superheat-resistant hierarchical high-entropy alloy. a) preparing a raw material containing Al, any one element selected from the first element group and the second element group;
b) preparing an ingot by vacuum arc melting the raw materials;
c) remelting the ingot and then water-cooling the melted alloy; and
d) heat-treating the cooled alloy at 1,000 to 1,200 ° C; includes,
The first element group is composed of Ti, Nb and V,
The second element group is a method for producing a high-strength superheat-resistant hierarchical high-entropy alloy, characterized in that composed of Co and Ni. According to claim 6,
Characterized in that the heat treatment is performed for 30 to 120 minutes, a method for producing a high-strength superheat-resistant hierarchical high-entropy alloy.

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