KR20180041407A - Stress-induced phase transformable dual-phase high entropy alloy and manufacturing method for the same - Google Patents

Abstract

The present invention relates to a high entropy alloy having an improved mechanical property by using a composite phase fine structure capable of stress-induced phase transformation. A content ratio of (Fe, Co) vs (Ni, Mn) is controlled to be increased in a quinary (NiCoFeMnCr) compound alloy. Lamination fault energy is controlled in composition of Ni_a_Co_b_Fe_c_Mn_d_Cr_e_ (a+b+c+d+e=100, 1<=a<=15, 15<=b<=50, 15<=c<=50, 1<=d<=15, 15<=e<=25), and a composite phase fine tissue of a y phase and a ε phase and the y phase are processed by stress-induced phase transformation to the ε phase or a α′ phase under stress. So, the composite phase high entropy alloy can an excellent mechanical property in which the strength and orientation are improved at same time. According to the present invention, the high entropy alloy largely improves the mechanical property and can be used as a structure material corresponding a marine plant and a polar extreme environment requiring excellent toughness and high rigidity at a low temperature. Also, the high entropy alloy can be used as the structure material corresponding a high temperature extreme environment such as a turbine blade for high-efficiency next-generation thermal power generation, a jacket pipe, a nuclear pressure container, and a launcher propulsion unit requiring high temperature strength and an excellent high temperature creep property.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a stress-induced phase changeable complex-phase high entropy alloy and a method of manufacturing the same. BACKGROUND ART [0002]

TECHNICAL FIELD The present invention relates to a high entropy alloy, and more particularly, to a high entropy alloy having a dual-phase microstructure and a stress-induced phase transformation will be.

High entropy alloy is an alloying system in which all constituent elements added as a common element are composed of a plurality of metal elements in a similar fraction unlike an alloy of a single main element of a conventional commercial alloy system, , A high mixed entropy is generated due to a similar atom fraction and forms a stable solid solution at high temperature instead of an intermetallic compound or an intermediate compound.

Such high-entropy alloys are attracting attention as new materials for metals because they have excellent mechanical properties including high strength and ductility. Recently, they are known to exhibit excellent properties in extreme environmental properties such as high temperature properties and low temperature properties. However, since most of the studies have been conducted to confirm the mechanical properties of alloys composed of equiatomic alloys which are easy to form single solid solution entanglement alloys, Efforts to obtain improved mechanical properties are scarce.

Japanese Patent No. 04190720

Nature Vol.534 pp.227-230.

The present invention is to further improve the mechanical properties of the above-described high entropy alloy, and it is an object of the present invention to provide a dual-phase microstructure having a γ austenite phase and an ε martensite phase at the same time, the present invention is intended to provide a high entropy alloy which exhibits stress-induced phase transformation characteristics in an ε or α 'martensite phase and has excellent mechanical properties with improved strength and elongation at the same time.

In order to achieve the above object, the present invention provides a stress-induced phase changeable dual phase high entropy alloy, which is a high entropy alloy in which constituent elements serve as a common main element, and Ni _a Co _b Fe _c Mn _d Cr in that the _{e (a + b + c +} d + e = 100, 1≤a≤15, 15≤b≤50, 15≤c≤50, 1≤d≤15, 15≤e≤25) features.

In order to construct a high entropy alloy, metal elements having a similar interatomic size of 10% or less and a mixed heat relationship close to zero are selected, and similar atomic ratios with a content deviation of ± 10% or less among the elements And the like. The hyper-enthalpy alloy of the present invention is composed of five elements of Ni, Co, Fe, Mn and Cr, which are three-period transition metal elements having a similar interatomic size of 10% or less and a mixed heat relationship close to zero, The entropy alloy is Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ which is constituted by the same fraction of each constituent element. In contrast, the high entropy alloy of the present invention has a γ-austenite phase (face centered cubic, FCC phase (ΔGhcp-fcc) is small in the ε-martensite phase (Hexagonal close-packed, HCP phase), and the total composition is made into a non-equiatomic composition (Fe, Co) to (Ni, Mn) content ratio by increasing Ni and Mn to 15 at.% Or less and Fe and Co to 15 at.% Or more to increase stacking fault energy (SFE) By this means, Bit phase and ε was configured so that the combined phase (Dual-phase) microstructure with a martensite phase at the same time, and γ austenite phase may have a stress - induced phase transformation characteristics.

In addition, the stress-inducible phase-changeable high-entropy alloy of the present invention is a combination of constituent elements in a non-identical fraction, unlike conventional representative high entropy alloys, and in particular (Fe, Co) , Mn) in the direction of increasing the content ratio of the high-entropy alloy than the existing high-entropy alloys by significantly lowering the energy level of the austenite phase and ε-martensite phase simultaneously have dual-phase microstructure And a γ austenite phase exhibits stress-induced phase transformation characteristics in an ε or α 'martensite phase under stress, and exhibits excellent mechanical properties in which strength and elongation are improved at the same time.

The inclusion of at least one element selected from the group consisting of C, N, Al, Ti, V, Cu, Zr, Nb and Mo in the high entropy alloy of the present invention at 10 at. It is possible to improve the characteristics by precipitation strengthening.

According to another aspect of the present invention, there is provided a method of manufacturing a stress-induced phase changeable dual phase high entropy alloy comprising the steps of: preparing a raw material; And a step of dissolving the raw material to prepare a high entropy alloy, wherein the raw material is at least one selected from the group consisting of Ni _a Co _b Fe _c Mn _d Cr _e (a + b + c + d + e = 100, , 15? B? 50, 15? C? 50, 1? D? 15, 15? E? 25) the energy change (ΔG _{hcp -fcc)} - characterized in that it is prepared to be 1000 J / mol or less (Calphad basis).

It can be designed on the basis of the free energy change (? G _{hcp- fcc} ) during the phase change when phase transformation from? Austenite to? Martensite phase as an index related to the stacking defect energy in the course of designing the high entropy alloy of the present invention , and a free-energy change (ΔG _{hcp- fcc} ) at the time of phase transformation from the γ-austenite phase to the ε-martensite phase is-1000 J / mol or less (Calphad calculation standard) An entropy alloy can be obtained.

Particularly, when the above-mentioned condition is satisfied and the phase change free energy change (? G _{bcc- fcc} ) is? 2500 J / mol (Calphad calculation criterion) when? Austenite is phase-transformed into? ' Phase-high entropy alloys capable of stress-induced multi-stage phase transformation on α 'martensite phase via ε-martensite phase on γ austenite during transformation.

At this time, it is preferable to perform the homogenization treatment after the step of producing the high entropy alloy, and the homogenization treatment is performed by hot rolling the produced ingot at a temperature of about 900 ± 100 ° C. to 80% Annealing at about 1200 占 폚 to about 300 占 폚 for about 48 hours, and then performing annealing.

Further, in order to control the microstructure size of the homogenized high entropy alloy, after cold rolling to 80% or less of the original thickness, annealing is performed in an Ar atmosphere at about 900 占 폚 to 200 占 폚 for about 24 hours .

The present invention having the above-described structure adjusts the ratio of the elements constituting the high entropy alloy to the non-equal proportions and particularly adjusts the ratio of (Fe, Co) to (Ni, Mn) Unlike conventional high entropy alloys, which form a single solid solution by lowering the stacking defect energy, a dual-phase microstructure having γ austenite phase and ε martensite phase simultaneously can be realized.

In addition, the γ-austenite phase in the dual-phase microstructure exhibits a stress-induced phase transformation from ε to α 'martensite phase under stress, so that the mechanical properties of the γ-austenite phase are significantly improved .

In addition, the high entropy alloy of the present invention generally has a trade-off strength and elongation at the same time, has a low thermal expansion coefficient and a relatively slow diffusion rate, It can be used as a structural material for plants and extreme environments. It also has a high-temperature environment-friendly structure such as a projectile for high temperature creep and high temperature strength, a nuclear pressure vessel, a cladding tube, and a turbine blade for high efficiency next generation thermal power generation. There is an effect that can be applied as a material.

FIG. 1 shows the change in free energy (ΔG _hcp-fcc ) during phase change by adjusting the content ratio of (Fe, Co) to (Ni, Mn) in the NiCoFeMnCr 5-element alloy using Calphad calculation and first- FIG.
FIG. 2 is a graph showing the results of EBSD (Electron Backscattering Diffraction) measurements on a Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ high entropy alloy according to Comparative Example 2 and a Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₂₀ high entropy alloy sample according to the present invention And the phase map results obtained through.
FIG. 3 is a tensile test result at room temperature for a Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ high entropy alloy of Comparative Example 2 and a Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₂ 0 high entropy alloy specimen according to the present invention.
4 is a phase map result obtained from EBSD measurements of a 60% localized strain region after tensile testing of Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₂₀ high entropy alloy specimen of the present invention.
FIG. 5 is a graph showing the free energy change (? G _bcc-fcc ) during phase change according to adjusting the content ratio of (Fe, Co) to (Ni, Mn) in the NiCoFeMnCr 5-element alloy using Calphad .
6 is a result of X-ray diffraction analysis showing the phase change behavior (a) and (b) of the Ni ₅ Co ₃₅ Fe ₃₅ Mn ₅ Cr ₂₀ high entropy alloy specimen of Example 12 before cold rolling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, embodiments of the present invention will be described in detail.

The present invention is to further improve the mechanical properties of the above-described high entropy alloy, and it is an object of the present invention to provide a dual-phase microstructure having a γ austenite phase and an ε martensite phase at the same time, The present invention provides a high entropy alloy which exhibits stress-induced phase transformation in an ε or α 'martensite phase and has excellent mechanical properties with improved strength and elongation at the same time.

To this end, the hyperentropic alloy of the present invention is composed of five elements of Ni, Co, Fe, Mn and Cr, which are three-period transition metal elements having a mixed thermal relationship with a similar interatomic size of less than 10% However, the conventional high-entropy alloy is Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ (aka Cantor alloy) in which the constituent elements are constituted at the same fraction. Compared with the conventional high entropy alloy, the high entropy alloy of the present invention is obtained by Calphad calculation and first principle calculation (Fe, Co), the total composition is not the same fraction by predicting an alloying system having a small free energy change (? G _{hcp- fcc} ) upon phase change from? austenite (FCC)? epsilon martensite (HCP) (Ni, Mn) ratio, the laminated defect energy is greatly lowered compared to the conventional high-entropy alloy, so that the dual-phase microstructure having both γ and ε phases and the stress- Was transformed to make it happen is easy.

1 shows the free energy change (ΔG _{hcp- fcc} ) during the phase change by adjusting the content ratio of (Fe, Co) to (Ni, Mn) in the NiCoFeMnCr 5-element alloy using Calphad calculation and first- FIG. As can be seen in the figure, the same fraction of high entropy alloy Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ (aka Cantor alloy) is made not in the same fraction and the content of Ni and Mn is increased while increasing Fe and Co contents The free energy change (ΔG _{hcp- fcc} ) at the phase change gradually decreases. In particular, by adjusting non-equiatomic composition of constituent elements by adjusting Fe and Co contents to 15 at.% Or more and Ni and Mn contents to 15 at.% Or less respectively, ΔG _{hcp- fcc} ) was greatly reduced to-1000 J / mol (Calphad calculation standard). The decrease in free energy change (ΔG _{hcp- fcc} ) with respect to this phase change is closely related to the decrease of the stacking defect energy inside the material. Thus, the γ austenite phase instability due to the activation of the twin and the ε martensitic phase stability Phase microstructures with γ and ε phases at the same time, and to transform them into twin-based strain-deforming mechanisms at room temperature.

In order to investigate the effect of the free energy change (ΔG _{hcp- fcc} ) reduction upon the phase change on the deformation behavior of the material, Ni, Co, Fe, Mn and Cr constituting the alloy were prepared as parent elements with purity of 99.9% (Induction Melting) method, which had a stirring effect by stirring at a temperature of 900 ° C and a high temperature of 50%, and homogenized at 1200 ° C for 3 hours in an Ar environment. In the present invention, since casting can realize a high temperature through an arc plasma in addition to an induction melting method, an arc melting method capable of rapidly forming a bulk solid homogeneous solid solution and minimizing impurities such as oxides and pores, It is possible to manufacture through a commercial casting process utilizing a resistance heating method which is possible. In addition to this, besides the commercial casting method in which the raw material metal can be dissolved, the raw material is made into powder or the like, and the powder metallurgy method is applied to the casting at a high temperature / high pressure by spark plasma sintering or hot isostatic pressing Sintering method. In the case of the sintering method, more precise microstructure control and manufacturing of parts having a desired shape can be easily performed. The homogenization treatment of the prepared specimen is carried out by subjecting the produced ingot to high temperature rolling at a temperature of about 900 ± 100 ° C. to 80% of its original thickness and then annealing in an Ar atmosphere at about 1200 ± 300 ° C. for about 48 hours Is preferable for refining the crystal grains and removing defects.

Then, to obtain a grain size of an appropriate size, cold rolling was performed so as to have 50% of the original thickness, and the crystal grains were refined by heat treatment at 800 ° C for 1 hour in an Ar environment. It is preferable that the microstructure size control method of the homogenized high entropy alloy specimen is in the category of cold rolling after annealing in an Ar atmosphere to about 900 ± 200 ° C. within 12 hours so as to be 80% or less of the original thickness.

Table 1 shows the elemental mixing ratios and constitutional kinds of Comparative Examples 1 to 4 and Examples 1 to 17 of the present invention.

Psalter Composition (at%) Type of construction Comparative Example 1 Ni ₀ Co ₄₀ Fe ₄₀ Mn ₀ Cr ₂₀ ? (? ') Comparative Example 2 Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ gamma Comparative Example 3 Ni ₂₆ Co ₁₄ Fe ₁₄ Mn ₂₆ Cr ₂₀ gamma Comparative Example 4 Ni ₁₄ Co ₂₁ Fe ₂₁ Mn ₁₄ Cr ₃₀ gamma Example 1 Ni ₁₀ Co ₃₀ Fe ₃₀ Mn ₁₀ Cr ₂₀ γ + ε Example 2 Ni ₈ Co ₁₉ Fe ₄₅ Mn ₈ Cr ₂₀ γ + ε Example 3 Ni ₈ Co ₃₄ Fe ₃₄ Mn ₈ Cr ₁₆ γ + ε Example 4 Ni ₈ Co ₃₀ Fe ₃₀ Mn ₈ Cr ₂₄ γ + ε Example 5 Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₂₀ γ + ε Example 6 Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₁₈ C ₂ γ + ε Example 7 Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₁₈ Al ₂ γ + ε Example 8 Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₁₈ Ti ₂ γ + ε Example 9 Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₁₈ Nb ₂ γ + ε Example 10 Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₁₈ Cu ₂ γ + ε Example 11 Ni ₆ Co ₃₄ Fe ₃₄ Mn ₆ Cr ₂₀ ? +? (? ') Example 12 Ni ₅ Co ₃₅ Fe ₃₅ Mn ₅ Cr ₂₀ ? +? (? ') Example 13 Ni ₄ Co ₃₅ Fe ₃₅ Mn ₄ Cr ₂₀ N ₂ ? +? (? ') Example 14 Ni ₄ Co ₃₅ Fe ₃₅ Mn ₄ Cr ₂₀ V ₂ ? +? (? ') Example 15 Ni ₄ Co ₃₅ Fe ₃₅ Mn ₄ Cr ₂₀ Zr ₂ ? +? (? ') Example 16 Ni ₄ Co ₃₅ Fe ₃₅ Mn ₄ Cr ₂₀ Mo ₂ ? +? (? ') Example 17 Ni ₂ Co ₃₈ Fe ₃₈ Mn ₂ Cr ₂₀ ? +? (? ')

The alloys of Comparative Examples 1 to 4 exhibit a single phase of? Or? (? '), Whereas in Examples 1 to 17 of the present invention,? And? (Or?') phase microstructure.

As shown in Table 1, the high entropy alloy of the present invention contains 10 at.% Or less of at least one element selected from among C, N, Al, Ti, V, Cu, Zr, Nb and Mo, , It is possible to improve the properties by strengthening solid solution or precipitation while maintaining the existing dual phase structure.

FIG. 2 is a graph showing the results of EBSD (Electron Backscattering Diffraction) measurements on a Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ high entropy alloy according to Comparative Example 2 and a Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₂₀ high entropy alloy sample according to the present invention And the phase map results obtained through.

2 (a) Comparative Example 2 The phase map of the Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ high entropy alloy showed that the specimen was a single γ-austenite phase (blue), but FIG. 2 (b) Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr _{20 The} high-entropy alloy specimen shows a dual-phase microstructure in which the γ austenite phase (red) and the ε martensite phase (green) are simultaneously precipitated . In Fig. 2 (b), the phase fractions of the γ-austenite phase and the ε-martensite phase were measured to be 87.5% and 12.5%, respectively.

FIG. 3 is a tensile test result of room temperature tensile test for a Ni ₂₀ Co ₂₀ Fe ₂₀ Mn ₂₀ Cr ₂₀ high entropy alloy of Comparative Example 2 and a Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₂₀ high entropy alloy specimen according to the present invention. The high entropy alloy (black) of Comparative Example 2 in which the constituent elements are contained in the same fraction exhibits a tensile strength of 690 MPa and an elongation of about 50%, which shows that the mechanical properties are excellent due to the basic characteristics of the high entropy alloy.

However, it can be confirmed that the high entropy alloy (red) of Example 6 according to the present invention is improved in strength and elongation at the same time as the high entropy alloy of Comparative Example 2, thereby further improving the mechanical properties. Specifically, the high entropy alloy of Example 6 greatly increased the tensile strength to about 980 MPa and the elongation to about 60%.

As described above, the mechanical properties of the dual-phase high entropy alloy according to the present embodiment were further improved as compared with the typical high-entropy alloy (Comparative Example 2), which is known to have excellent mechanical properties. The reason why the mechanical properties of the high entropy alloy according to the examples are improved is as follows.

FIG. 4 is a phase map result obtained from EBSD measurement of a 60% local strain region after tensile test of Example 6 Ni ₈ Co ₃₂ Fe ₃₂ Mn ₈ Cr ₂₀ high entropy alloy specimen of the present invention. As can be seen in the figure, in the region subjected to 60% of large deformation, the twin generated during deformation was activated, and the phase fraction of γ austenite phase and ε-martensite phase was 87.5% and 12.5% ) And 41.6% and 58.4%, respectively. In addition, if twinning is generated during the deformation of the metastable γ austenite having a low stacking defect energy, dislocation of the dislocation and propagation of cracks are prevented to improve the work hardening ability and elongation of the material. Finally, The austenite phase is phase-changed into? -Martensite phase.

FIG. 5 is a graph showing the change in free energy (ΔG _bcc-1) during phase change by controlling the content ratio of (Fe, Co) to (Ni, Mn) in Ni ₁₀ Co ₃₀ Fe ₃₀ Mn ₁₀ Cr ₂₀ alloy using _{Calphad. fcc} ). As can be seen from the figure, the free energy change (? G _hcp-fcc ) of the present invention when transformed into? -Martensite phase on? -Ustenite is? 1000 J / mol (Calphad calculation standard) phase) When the free energy change (ΔG _{bcc- fcc} ) during the phase change in the phase transition from γ-octene to α '-martensite phase in the high entropy alloy is less than 2500 J / mol (Calphad calculation) A composite phase capable of stress-induced multi-stage phase transformation to the α 'martensite phase by shear deformation through the ε-martensite phase through the ε-martensite phase through phase change on the stable γ-austenite phase A dual-phase high entropy alloy can be obtained.

However, when the free energy change (ΔG _{bcc- fcc} ) during the phase change when phase transformation from γ austenite to α 'martensite phase becomes too low to -5000 J / mol (Calphad calculation) The stability of the kneaded phase is greatly lowered and the pre-strain microstructure becomes ε (α ') martensite phase, so that the dual phase high entropy alloy of the present invention can not be produced.

6 is a result of X-ray diffraction analysis showing the phase change behavior (a) and (b) of the Ni ₅ Co ₃₅ Fe ₃₅ Mn ₅ Cr ₂₀ high entropy alloy specimen of Example 12 before cold rolling. As can be seen from the figure, Ni ₅ Co ₃₅ Fe ₃₅ Mn ₅ Cr ₂₀ high-entropy alloy before cold rolling has a microstructure in which the γ phase is the main phase in the dual phase of γ and ε (α '). Phase structure in which the ε-phase and the α 'phase fraction are increased after cold rolling. These results indicate that the metastable γ-austenite phase undergoes a multi-stage phase transformation to α 'martensite phase through the ε-martensite phase during deformation as the stacking defect energy in the material becomes lower, It can contribute more to the improvement of the strength and elongation. In addition, when a phase change occurs in the martensite phase during deformation, a twist effect occurs in the material due to the formed martensite phase, thereby increasing the strength of the material, and hindering the dislocation movement due to the new interface, And the mechanical characteristics are further improved when a multi-stage phase transformation process is performed.

As described above, the present invention provides a high entropy alloy composed of five elements of Ni, Co, Fe, Mn, and Cr, and is adjusted to increase the content ratio of (Fe, Co) to (Ni, Mn) By lowering the stacking defect energy significantly compared to the entropy alloy, the composite phase microstructure and the stress - induced phase transformation can occur simultaneously in the γ and ε phase. The dual-phase high entropy alloy capable of stress organic phase transformation according to the present invention has a composite structure of ε phase which contributes to γ-phase and high strength contributing to high stretching, ε (α ' ), The strength and elongation were greatly improved at the same time as compared with the same fraction of the high entropy alloy having the single phase of γ phase. As a result, it was found that the offshore plant requiring high toughness and high strength at low temperature, The present invention can be applied not only to high temperature creep characteristics and high temperature strength but also to high temperature and environment friendly structural materials such as a propulsion unit, a nuclear pressure vessel, a cladding tube and a turbine blade for a high efficiency next generation thermal power generation.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Those skilled in the art will understand. Therefore, the scope of protection of the present invention should be construed not only in the specific embodiments but also in the scope of claims, and all technical ideas within the scope of the same shall be construed as being included in the scope of the present invention.

Claims (9)

The NiCoFeMnCr 5 -type high-entropy alloy is composed of a dual-phase microstructure having both a γ-austenite phase and an ε-martensite phase, and a γ-austenite phase is stress-induced phase transformation of the phase transition material. Claim 1
The high entropy alloy,
_{Ni a Co b Fe c Mn d} Cr e (a + b + c + d + e = 100, 1≤a≤15, 15≤b≤50, 15≤c≤50, 1≤d≤15, 15≤e &Lt; / = 25). &Lt; / RTI &gt; Claim 2
Wherein the high entropy alloy further comprises at least 10 atomic percent of at least one element selected from the group consisting of C, N, Al, Ti, V, Cu, Zr, Nb and Mo. High entropy alloy. Claim 1
Wherein the γ-austenite phase in the high-entropy alloy is subjected to multi-stage phase transformation to α 'martensite phase through the ε-martensite phase during deformation. Claim 4
Wherein the high entropy alloy is Ni _a Co _b Fe _c Mn _d Cr _e (a + b + c + d + e = 100, 1 a 7, 32 b 50, 32 c 50, 7, 15? E? 25). Preparing a raw material; And
And dissolving the raw material to produce a high entropy alloy,
The raw material _{Ni a Co b Fe c Mn d} Cr e (a + b + c + d + e = 100, 1≤a≤15, 15≤b≤50, 15≤c≤50, 1≤d≤15 , 15 &amp;le; e &amp;le; 25)
And a free energy change (ΔG _{hcp- fcc} ) at the time of phase transformation from the γ-austenite phase to the ε-martensite phase through the Calphad calculation in the composition range is-1000 J / mol or less (Calphad calculation standard) A method for producing a stress - induced phase changeable composite phase high entropy alloy. The method of claim 6,
The free energy change (ΔG _{bcc- fcc} ) during phase transformation when phase transformation from the γ austenite phase to the α 'martensite phase is calculated to be less than 2500 J / mol - more than 5000 J / mol (Calphad calculation (????? ') Capable of forming a multiphase stress organic phase (????? The method of claim 6,
After the step of producing the high entropy alloy, the produced ingot is hot-rolled at a temperature of about 900 ± 100 ° C. to 80% or less of the original thickness and then annealed in an Ar atmosphere at about 1200 ± 300 ° C. for about 48 hours Wherein the homogenization treatment is performed at a temperature higher than the melting point of the high-entropy alloy. The method of claim 6,
In order to control the microstructure size of the homogenized high entropy alloy, the alloy is cold-rolled to 80% or less of the original thickness, annealed in an Ar atmosphere at about 900 ± 200 ° C for about 12 hours, &Lt; / RTI &gt; wherein the stress-inducible phase-changeable high-entropy alloy is produced by the method.

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