Entropy-controlled BCC alloy having strong resistance to high-temperature neutron radiation damage

Abstract

Disclosed is an entropy-controlled solid solution matrix BCC alloy having strong resistance to high-temperature neutron radiation damage. The entropy-controlled solid solution matrix BCC alloy includes three or more multicomponent main elements selected from the element group consisting of Zr, Al, Nb, Mo, Cr, V, and Ti selected based on a neutron absorption cross-sectional area and a mixing enthalpy. Each of the elements is included in an amount of 5 to 35 at %, and the entropy-controlled solid solution matrix BCC alloy is a BCC-structure solid solution matrix alloy in a medium-entropy to high-entropy state. In this invention, damage caused by neutron radiation is reduced, and entropy is controlled to thus ensure a solid solution matrix BCC structure having a slow diffusion speed, and accordingly, resistance to void swelling due to radioactive rays is high.

Claims

1. A solid solution matrix BCC alloy consisting of: five elements selected from an element group consisting of Zr, Al, Nb, Mo, V, and Ti, selected based on a neutron absorption cross-sectional area and a mixing enthalpy, wherein four elements of the five elements are Zr, Al, Nb and Ti in the element group, wherein one element of the five elements is Mo or V in the element group, and wherein each of the five elements is included at an equiatomic ratio within an error tolerance limit of 10 at % and the solid solution matrix BCC alloy is a BCC-structure solid solution matrix alloy, which includes multicomponent main elements.

2. The solid solution matrix BCC alloy of claim 1, wherein the one element is Mo in the element group.

3. A fast-breeder reactor comprising: the solid solution matrix BCC alloy of claim 1 as a material for a portion on which neutrons are radiated at a temperature.

4. A method of manufacturing the solid solution matrix BCC alloy of claim 1, the method comprising: an arc-melting step of arc-melting raw materials and then cooling the molten raw materials, or a sintering step of manufacturing the raw materials in a powder form and then sintering the raw materials using spark plasma sintering or hot isostatic pressing at a temperature and a pressure.

5. The method of claim 4, wherein a T.sub.2nd/T.sub.s value, which is obtained by normalizing a precipitation temperature T.sub.2nd of a second phase competing with a solid solution using a solidification temperature T.sub.s, is used to evaluate whether or not the solid solution matrix BCC alloy is formed during preparation of the raw materials.

6. The method of claim 5, wherein whether a single BCC-phase alloy is formed or not is evaluated based on the T.sub.2nd/T.sub.s value of 0.65 or less.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a view showing selected alloy element candidates, which are considered to be easy to impart with a BCC solid solution structure, on the periodic table;

(3) FIG. 2 is a view showing selected alloy element candidates, which have a small neutron absorption cross-sectional area and are considered to be easy to impart with a BCC solid solution structure, among various elements;

(4) FIG. 3 is a table showing mixing enthalpies of the selected elements of FIG. 2;

(5) FIGS. 4A and 4B show the results of XRD analysis of (a) ZrTiMo and (b) ZrNbTi.sub.0.5, which are a ternary medium-entropy alloy, according to an Example of the present invention;

(6) FIGS. 5A to 5D show the results of XRD analysis of (a) AlNbTiV, (b) AlNbTiMo, (c) ZrNbMoV, and (d) ZrAlNbTi, which are a quaternary medium-entropy alloy, according to an Example of the present invention;

(7) FIGS. 6A to 6D show the results of XRD analysis of (a) Al.sub.0.5NbTiMoV, (b) ZrNb.sub.1.5TiMoV, (c) ZrNbTiMo.sub.0.5V, and (d) ZrNbCr.sub.0.5TiV, which are a quinary high-entropy alloy, according to an Example of the present invention;

(8) FIGS. 7A to 7C show the results of XRD analysis of (a) Zr.sub.1.5Nb.sub.1.5TiMoV, (b) Zr.sub.1.5NbTiMo.sub.0.5V, and (c) ZrNbTiMo.sub.0.33V.sub.0.66, which are the quinary high-entropy alloy, according to an Example of the present invention;

(9) FIGS. 8A to 8D show the results of XRD analysis of (a) ZrAl.sub.0.5NbTiV, (b) ZrAlNbTiV, (c) Zr.sub.0.5AlNbTiV, and (d) ZrAlNbTiMo, which are the quinary high-entropy alloy, according to an Example of the present invention;

(10) FIGS. 9A to 9D show the results of XRD analysis of (a) Zr.sub.0.5AlNbTiMoV, (b) ZrAlNbTiMoV, (c) ZrAl.sub.0.5NbTiMoV, and (d) ZrAl.sub.0.5NbTiMo.sub.0.5V, which are a senary high-entropy alloy, according to an Example of the present invention;

(11) FIGS. 10A and 10B show that T.sub.2nd and T.sub.s of (a) Zr.sub.0.5AlNbTiMoV and (b) ZrAlNbTiMoV, which are the senary high-entropy alloy of the present invention, are predicted using thermodynamic calculation (CALPHAD); and

(12) FIGS. 11A to 11D show the results of XRD analysis of (a) NbCrTiVCu, (b) ZrNbCrTiCu, (c) ZrNbTiFe, and (d) ZrAlNbTiF, which are alloys including elements (Cu and Fe) other than the constitutional elements of the present invention, as Comparative Examples of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(13) Hereinafter, a detailed description will be given of embodiments of the present invention, with reference to the appended drawings.

(14) A novel entropy-controlled BCC alloy having strong resistance to high-temperature neutron damage according to the present invention has a BCC (body-centered cubic) solid solution matrix structure using an entropy-controlled alloy design of elements having a small neutron absorption cross-sectional area even though the alloy is a multicomponent-based alloy including a plurality of main elements, thereby having a property of strong resistance to radiation damage even in a high-temperature radioactive radiation environment. Accordingly, in order to use the entropy-controlled BCC alloy as a structural material for fourth-generation nuclear power systems, which are currently being developed, the following design procedure is performed.

(15) First, Group IV, V, and VI transition elements having a body-centered cubic (BCC) structure are selected as alloy element candidates in order to reduce void swelling, which is a kind of radiation damage and forms voids in metal at high temperatures when radioactive rays are radiated, thus causing the surface of the metal to swell.

(16) FIG. 1 is a view showing alloyed element candidates, which are selected based on a BCC structure formed during alloying, on the periodic table. As can be seen from the periodic table, the Group V and VI transition elements have a stable BCC phase, and the Group IV transition element has a stable BCC phase at high temperatures. Accordingly, it is easy to form the BCC structure when the Group IV, V, and VI transition elements are cast. Further, when a Period IV transition element is added to the Group IV, V, and VI transition elements, which are easy to impart with the BCC structure, it is easy to ensure the BCC structure having high solid solubility. Al is a BCC-stabilized element and is easy to impart with the BCC structure during alloying. The element group satisfying the aforementioned conditions is represented by the thick line in FIG. 1.

(17) Next, the elements having the small neutron absorption cross-sectional area are selected as the alloy element candidates so as to prevent neutron damage caused by radiation. Generally, the size of the cross-sectional area is used to represent the probability of a reaction occurring between incident particles and an atomic nucleus in a nuclear reaction. Neutrons do not have electric charges and are thus easily brought close to other atomic nuclei, to thus cause various types of interactions. Among the interactions, a cross-sectional area to an absorption reaction of neutrons into a target atomic nucleus is referred to as a neutron absorption cross-sectional area, and is used as a standard in determining reactivity with neutron particles. The neutron absorption cross-sectional area is represented by the number of absorbed neutrons per unit time and unit area, and “barn(b)” is used as the unit of the cross-sectional area. 1 b is 10.sup.−24 cm.sup.2. Generally, the reactivity of the material to the neutron particles is reduced to thus increase resistance to neutron radiation damage as the neutron absorption cross-sectional area of the material is reduced, and accordingly, a material having the small neutron absorption cross-sectional area is suitable as a nuclear material. In the present invention, added elements are designed to be selected from element groups having the small value of 10 or less σa/barns, thereby minimizing the neutron absorption cross-sectional area of the developed material.

(18) FIG. 2 is a view showing the neutron absorption cross-sectional areas of various elements and the result of selection of candidate groups based on the neutron absorption cross-sectional areas. The element group satisfying the aforementioned condition is represented by the thick line in FIG. 2, and is compared to the alloy group that is easy to impart with the BCC structure, in FIG. 1, and common elements are represented by the thick circle.

(19) Subsequently, in order to provide the alloy in a high-entropy or medium-entropy state to thus ensure the stable BCC structure at high temperatures and improve mechanical properties at high temperatures using entropy controlling, the elements are selected so as to have a mixing enthalpy (ΔH) of ±15 kJ/mol or less. However, Al, which is the BCC-stabilized element, may have a stable BCC structure even when the mixing enthalpy is high, thus being considered as the constitutional element.

(20) FIG. 3 is a table showing the mixing enthalpies of the elements, considered based on the aforementioned considerations. Based on the aforementioned considerations, Zr, Al, Nb, Mo, Cr, V, and Ti are ultimately selected as the element group used to form the entropy-controlled BCC alloy having strong resistance to high-temperature neutron radiation damage according to the present invention, and three or more elements are mixed so that the amount of each of the elements is in the range of 5 to 35 at % to thus manufacture the entropy-controlled BCC-structure solid solution matrix alloy.

(21) For a high-entropy alloy (HEA), generally, five or more alloy elements are mixed in an amount of 5 to 35 at % (entropy increases as the amount approaches the equiatomic ratio) to entail high constitutional entropy, thereby forming a unique solid solution rather than an intermetallic compound, which is typically precipitated in a multicomponent-based alloy including a single element as a main component. Further, when the number of alloy elements is 3 to 4, the alloy is in a medium-entropy state and has properties that are similar to those of the high-entropy alloy, depending on the constitutional elements. Since the elements, which are selected in the present invention, have a small mixing enthalpy and a small difference in atomic radius, even the alloys in the medium-entropy state have a stable BCC structure in the solid solution state.

(22) Meanwhile, among the elements having the small neutron absorption cross-sectional area of 10 σa/barns or less, additional elements, such as Be, C, N, O, Si, Sn, P, Fe, Cu, Ni, and Y, or oxides or nitrides thereof, may be added in a small amount of 0.01 to 5 at % to the entropy-controlled BCC solid solution matrix alloy of the present invention to thus entail solid solution hardening or promote precipitation, thereby improving the properties. Particularly, it can be confirmed that the strength of the BCC solid solution is significantly improved when related oxides or nitrides are included in the solid solution matrix.

(23) The alloys of Examples are manufactured, depending on the composition of the present invention, in order to conduct a review, described below, of the properties of the entropy-controlled BCC-structure solid solution matrix alloy having strong resistance to high-temperature neutron radiation damage according to the present invention. The alloys of Comparative Examples, other than the composition of the present invention, are manufactured to compare the present invention and the Comparative Examples to thus confirm the effect of the present invention.

(24) Table 1 shows the representative compositions (Examples) of the present invention and the Comparative Examples in order to confirm whether the entropy-controlled BCC-structure solid solution matrix alloy having strong resistance to high-temperature neutron radiation damage according to the present invention was formed. In the Table, BCC means the body-centered cubic structure, IC means the intermetallic compound, BCC+IC means the state in which the IC is partially precipitated in the BCC solid solution matrix structure, and IC (+ BCC) means a complex structure including the IC, precipitated as the main phase, and the BCC.

(25) TABLE-US-00001 TABLE 1 Sample Composition Crystal structure Comparative Example 1 NbCrTiVCu IC (+BCC) Comparative Example 2 ZrNbCrTiCu IC (+BCC) Comparative Example 3 ZrNbTiFe IC, Unknown phases Comparative Example 4 ZrAlNbTiFe IC, Unknown phases Example 1 ZrTiMo BCC Example 2 ZrNbTi.sub.0.5 BCC Example 3 AlNbTiV BCC Example 4 AlNbTiMo BCC Example 5 ZrNbMoV BCC + IC Example 6 ZrAlNbTi BCC (B2) Example 7 Al.sub.0.5NbTiMoV BCC Example 8 ZrNb.sub.1.5TiMoV BCC Example 9 ZrNbTiMo.sub.0.5V BCC Example 10 ZrNbCr.sub.0.5TiV BCC + IC Example 11 Zr.sub.1.5Nb.sub.1.5TiMoV BCC Example 12 Zr.sub.1.5NbTiMo.sub.0.5V BCC Example 13 ZrNbTiMo.sub.0.33V.sub.0.66 BCC Example 14 ZrAl.sub.0.5NbTiV BCC Example 15 ZrAlNbTiV BCC + IC Example 16 Zr.sub.0.5AlNbTiV BCC Example 17 ZrAlNbTiMo BCC (B2) Example 18 Zr.sub.0.5AlNbTiMoV BCC Example 19 ZrAlNbTiMoV BCC + IC Example 20 ZrAl.sub.0.5NbTiMoV BCC + IC Example 21 ZrAl.sub.0.5NbTiMo.sub.0.5V BCC + IC

(26) An arc-melting process is applied to a method of manufacturing the alloy. Alloy raw materials are melted at high temperatures using Arc plasma and then cooled to manufacture the alloy. The reasons why the arc-melting process is applied in the Examples and the Comparative Examples are that it is easy to form a bulk-type homogeneous solid solution and that the generation of contaminant elements, such as oxides and voids, is minimized, which can be compared to a sintering process. Further, the arc-melting process has a merit in that the ductility-brittleness transition temperature (DBTT) of the composition is relatively lower in the arc-melting process than in the sintering process, thus increasing the rupture time. However, the method of manufacturing the alloy according to the present invention is not limited to the arc-melting process, but the alloy may be manufactured using a commercial casting process, in which raw material metal having a high melting point is melted, and also using high temperature/high pressure sintering, including spark plasma sintering or hot isostatic pressing of raw materials, which are manufactured in a powder form. The sintering process has a merit in that it is easy to control the fine structure and manufacture parts having a desired shape.

(27) FIGS. 4A and 4B show the results of XRD analysis of ternary medium-entropy alloys according to an Example of the present invention. It can be confirmed that both alloy compositions of (a) ZrTiMo and (b) ZrNbTi.sub.0.5 according to the present invention have a favorable BCC structure. Particularly, from FIGS. 4A and 4B, it can be confirmed that when the composition is controlled so as to approach the equiatomic ratio, constitutional entropy is increased in the system using even the ternary alloy to thus manufacture the alloy having the BCC structure in the solid-solution state, which is similar to that of the high-entropy alloy. This constitution is also applied to the multicomponent alloy system having three or more components according to the present invention.

(28) FIGS. 5A to 5D show the results of XRD analysis of quaternary medium-entropy alloys according to an Example of the present invention. It can be confirmed that the single BCC phase is precipitated in the case of (a) AlNbTiV, (b) AlNbTiMo, and (d) ZrAlNbTi according to the present invention. It can be confirmed that some intermetallic compounds are precipitated in addition to the BCC phase in the case of the (c) ZrNbMoV composition, but the BCC-structure solid solution matrix is ensured. Accordingly, it can be confirmed that a favorable BCC solid solution matrix structure, which is similar to the high-entropy alloy, is obtained using even the quaternary alloy.

(29) FIGS. 6A to 6D show the results of XRD analysis of (a) Al.sub.0.5NbTiMoV, (b) ZrNb.sub.1.5TiMoV, (c) ZrNbTiMo.sub.0.5V, and (d) ZrNbCr.sub.0.5TiV, which are quinary high-entropy alloys, according to an Example of the present invention, and include the case where any one element has an atomic ratio that is different from those of other constitutional elements. Additionally, in the alloys of FIGS. 6A to 6D, two elements are selected from among Zr, Al, and Nb, having small neutron absorption cross-sectional areas, one or more elements are selected from Cr and Ti, which help to improve the lifespan of the material in the high-temperature corrosive environment, and one or more elements are selected from Mo and V, which are the elements controlling the mechanical properties of the solid solution at high temperatures. Further, any one element of the constitutional elements has an atomic ratio that is different from those of the other elements. From FIGS. 6A to 6D, it is confirmed that a favorable solid solution matrix BCC alloy was manufactured in all cases. As for (d), the alloy to which both Ti and Cr were added, since Ti and Cr easily form the intermetallic compound, some intermetallic compounds are generated, but the matrix mostly has the BCC-structure in the high-entropy state. Accordingly, it can be confirmed that a high-entropy solid solution matrix BCC alloy is manufactured even when the atomic ratio of the constitutional elements is changed within the range of the present invention.

(30) FIGS. 7A to 7C show the results of XRD analysis of (a) Zr.sub.1.5Nb.sub.1.5TiMoV, (b) Zr.sub.1.5NbTiMo.sub.0.5V, and (c) ZrNbTiMo.sub.0.33V.sub.0.66, which are the quinary high-entropy alloy, according to an Example of the present invention. The alloys shown in FIGS. 8A to 8D are designed to be the quinary high-entropy alloy, which includes two or more elements selected from Zr, Al, and Nb, one or more elements selected from Cr and Ti, and one or more elements selected from Mo and V, as in FIGS. 6A to 6D, and two elements of the constitutional components have atomic ratios that are different from those of the three other elements.

(31) From the drawings, it can be confirmed that the high-entropy BCC alloy, which does not include the intermetallic compound, was formed in all compositions. Accordingly, it can be confirmed that the high-entropy BCC-structure solid solution matrix alloy is manufactured even when the composition of the constitutional element is variously changed within the composition range of 5 to 35%.

(32) FIGS. 8A to 8D show the results of XRD analysis of (a) ZrAl.sub.0.5NbTiV, (b) ZrAlNbTiV, (c) Zr.sub.0.5AlNbTiV, and (d) ZrAlNbTiMo, which are the quinary high-entropy alloy, according to an Example of the present invention. The alloys shown in FIGS. 8A to 8D are designed to be the quinary high-entropy alloy which includes Zr, Al, and Nb, and also includes one or more elements selected from Cr and Ti or one or more elements selected from Mo and V. From FIGS. 8A to 8D, it can be confirmed that in the alloy system including ZrAlNbTiV, the favorable BCC structure is formed in both cases of (a) ZrAl.sub.0.5NbTiV and (c) Zr.sub.0.5AlNbTiV, which includes any one element at the atomic ratio that is different from those of the remaining elements, but some intermetallic compounds are generated despite the matrix mostly having the BCC structure in the high-entropy state in the case of (b) ZrAlNbTiV, having the equiatomic ratio. For the aforementioned composition group, the amount of the intermetallic compound, which is formed in the solid solution matrix, is changed depending on changes in the relative content of Zr and Al. Accordingly, the ratio of the constitutional element (or the composition of the constitutional element) may be changed to adjust the amount of the intermetallic compound, which is generated in the high-entropy solid solution matrix. Further, in the case of (d) ZrAlNbTiMo alloy, which is obtained by substituting V with Mo in the (b) ZrAlNbTiV alloy, a favorable BCC structure is obtained. Accordingly, it can be seen that the generation of the intermetallic compound and the amount of the intermetallic compound are controlled depending on the type of constitutional element, in addition to the ratio of the constitutional element.

(33) FIGS. 9A to 9D show the results of XRD analysis of (a) Zr.sub.0.5AlNbTiMoV, (b) ZrAlNbTiMoV, (c) ZrAl.sub.0.5NbTiMoV, and (d) ZrAl.sub.0.5NbTiMo.sub.0.5V, which are a senary high-entropy alloy, according to an Example of the present invention. The alloys shown in FIGS. 9A to 9D are designed to be a senary high-entropy alloy which includes Zr, Al, and Nb, one or more elements selected from Cr and Ti, and one or more elements selected from Mo and V. From FIGS. 9A to 9D, it can be confirmed that a favorable BCC structure is formed in the case of (a) Zr.sub.0.5AlNbTiMoV, which includes the Zr element at an atomic ratio that is different from those of the remaining elements, but some intermetallic compounds are generated but the matrix mostly has the BCC structure in the high-entropy state in the case of (b) ZrAlNbTiMoV having the equiatomic ratio, (c) ZrAl.sub.0.5NbTiMoV, in which only Al is present at a different atomic ratio, and (d) ZrAl.sub.0.5NbTiMo.sub.0.5V, in which the atomic ratios of Al and Mo are different from those of the remaining elements. Accordingly, the present invention may be applied to the design of a multicomponent alloy having five or more components, thereby manufacturing a high-entropy BCC-structure solid solution matrix alloy. Further, the amount of the intermetallic compound that is generated in the high-entropy solid solution matrix may be adjusted depending on the type of the constitutional element that is added in an amount that is different from those of the remaining elements, in addition to the atomic ratio of the constitutional elements.

(34) As described above, the entropy-controlled solid solution matrix BCC alloy of the present invention includes an alloy having the entropy-controlled single BCC phase, and additionally includes an alloy that includes a plurality of main elements and the second phase such as the intermetallic compound present in a small amount in the solid solution matrix. Therefore, in the present invention, a T.sub.2nd/T.sub.s value is provided as a forming performance prediction factor for determining the fine structural properties. The T.sub.2nd/T.sub.s value is obtained by normalizing the precipitation temperature T.sub.2nd of the second phase, that is, the intermetallic compound, using a solidification temperature T.sub.s.

(35) Additionally, the entropy-controlled solid solution matrix BCC alloy of the present invention is a kind of high-entropy alloy, which has a thermodynamically meta-stable phase because a high-temperature stable phase is maintained at room temperature, and whether or not the high-entropy solid solution matrix BCC alloy is formed cannot be predicted using a known thermodynamic calculation. However, from the alloy development process, it is confirmed that the temperature range at which the high-entropy solid solution matrix BCC phase is stable is wider in the alloy group having the entropy-controlled single BCC phase than in the solid solution matrix BCC alloy that includes a plurality of main elements and the precipitated second phase, such as the intermetallic compound. This is because the diffusion speed of the atom is increased in the alloy to thus easily precipitate the second phase as the precipitation temperature of the second phase approaches the solidification temperature. Based on the aforementioned description, the T.sub.2nd/T.sub.s value, which is obtained by normalizing the precipitation temperature T.sub.2nd of the second phase using the solidification temperature T.sub.s, is developed as an index of the formation condition of the entropy-controlled solid solution matrix BCC alloy. Particularly, according to the result of measurement of the fine structure in the Examples of the present invention, with regard to the formation performance of the single BCC-phase alloy, the single BCC-phase alloy is formed when the T.sub.2nd/T.sub.s value, which is measured using thermal analysis instruments or is predicted based on thermodynamic calculations and which is obtained by normalizing the precipitation temperature T.sub.2nd of the second phase, such as the intermetallic compound, using the solidification temperature T.sub.s, is 0.65 or less.

(36) FIGS. 10A and 10B show predictions of phase ratios of (a) Zr.sub.0.5AlNbTiMoV and (b) ZrAlNbTiMoV, which are the senary high-entropy alloy of the present invention, based on temperature using thermodynamic calculation (CALPHAD). As shown in FIGS. 10A and 10B, the (b) ZrAlNbMoVTi alloy is a senary alloy, but the interval between T.sub.2nd and T.sub.s is relatively small, and accordingly, the T.sub.2nd/T.sub.s value is more than 0.65 when measured. FIGS. 9A to 9D show the BCC+IC, in which some intermetallic compounds are precipitated in the solid solution BCC matrix that includes a plurality of main elements. On the other hand, in the (a) Zr.sub.0.5AlNbMoVTi alloy having the adjusted Zr composition, the interval between T.sub.2nd and T.sub.s is relatively large, and accordingly, the T.sub.2nd/T.sub.s value is less than 0.55. From the XRD analysis, it can be confirmed that a single BCC phase solid solution is formed.

(37) FIGS. 11A to 11D show the results of XRD analysis of (a) NbCrTiVCu, (b) ZrNbCrTiCu, (c) ZrNbTiFe, and (d) ZrAlNbTiF, which are alloys including Cu and Fe as elements other than the constitutional elements of the present invention, as Comparative Examples of the present invention.

(38) In FIGS. 11A to 11D, (a) NbCrTiVCu and (b) ZrNbCrTiCu are constituted by a five-component system which includes four elements, including one or more elements selected from Zr, Al, and Nb, one or more elements selected from Cr and Ti, and one or more elements selected from Mo and V as in the present invention, and further includes Cu as the remaining element, unlike the present invention. From FIGS. 11A to 11D, it can be confirmed that the BCC phase, which is represented by the inverted triangle, is present in a small amount, but the intermetallic compound phase is precipitated in a large amount.

(39) Similarly, (c) ZrNbTiFe and (d) ZrAlNbTiFe of FIGS. 11A to 11D are constituted by a five-component system which includes four elements including two or more elements selected from Zr, Al, and Nb, and one or more elements selected from Cr and Ti or one or more elements selected from Mo and V, and further includes a balance of Fe other than the constitutional elements of the present invention. From FIGS. 11A to 11D, it can be confirmed that the BCC structure, which is represented by the inverted triangle, is not precipitated, but the intermetallic compound and unconfirmed phases are precipitated.

(40) Four or five components are mixed at the equiatomic ratio to manufacture the alloy in the Comparative Examples, which are shown in FIGS. 11A to 11D, as in the present invention. However, it can be confirmed that the intermetallic compound is formed in a large amount due to the presence of Fe and Cu, other than the constitutional elements included in the present invention, and accordingly, the BCC-structure solid solution matrix state is not ensured.

(41) Accordingly, even though the multicomponent system includes four or more constitutional elements having large atomic ratios that are similar to each other, the stable BCC-structure solid solution matrix alloy is not formed in all types of multicomponent systems, but is formed based on the basic premise that the mixing enthalpy difference is small (ΔH.sub.mix=±15 kJ/mol or less).

(42) Therefore, it can be confirmed that the ternary to senary alloys of the present invention have the stable single-phase BCC structure.

(43) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.