Multicomponent alloy, powder, and molded body

Abstract

To provide a multicomponent alloy that exhibits a superior balance of hardness, strength, and ductility.SOLUTION: A multicomponent alloy comprising: Co: 5.00 atomic% or more and 35.00 atomic% or less, Fe: 5.00 atomic% or more and 35.00 atomic% or less, Ni: 5.00 atomic% or more and 35.00 atomic% or less, V: more than 20.00 atomic% and less than 35.00 atomic%, Cr: 20.00 atomic% or less, C: 0.05 atomic% or more and 8.74 atomic% or less, and inevitable impurities, wherein a content of O in the alloy is 630 ppmw or less, a mixing entropy ΔSmix is 1.30R or more, and a valence electron concentration VEC is 7.84 or more. The alloy has a metallographic structure including a matrix and a plurality of carbides dispersed in the matrix.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This specification discloses a multi-component alloy. This specification also discloses a powder and a compact made of this multi-component alloy. [Background technology]

[0002] Multi-component alloys with a high entropy of mixing, ΔSmix, are attracting attention. Medium-entropy alloys and high-entropy alloys are known as such alloys. The entropy, ΔSmix, of medium-entropy alloys is 1.0 times or more the gas constant, R. The entropy, ΔSmix, of high-entropy alloys is 1.5 times or more the gas constant, R. These multi-component alloys exhibit distinctive mechanical properties.

[0003] JP 2021-500469 A proposes a multi-component alloy containing Co, Cr, Fe, Ni, and V as major elements. This alloy has excellent properties at cryogenic temperatures.

[0004] JP 2019-163535 A discloses a multi-component alloy containing Cr, Fe, and V as major elements. This alloy further contains Al, Si, Mn, Mo, Ti, or Ni. This alloy has excellent corrosion resistance.

[0005] JP 2022-180747 A proposes a multi-component alloy containing Co, Cr, Fe, Ni, and V as main elements. This alloy has excellent wear resistance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special publication 2021-500469 [Patent Document 2] Patent Publication No. 2019-163535 [Patent Document 3] Patent Publication No. 2022-180747 Summary of the Invention [Problem to be solved by the invention]

[0007] The multi-component alloy disclosed in JP 2021-500469 A contains 35-48 atomic % Fe from the viewpoint of low-temperature properties. This Fe can cause low hardness. The hardness of this multi-component alloy is insufficient.

[0008] The multi-component alloy disclosed in JP 2019-163535 A contains 20-40 atomic % V from the viewpoint of corrosion resistance. This V can generate a brittle phase. The balance between strength and ductility of this multi-component alloy is insufficient.

[0009] In the multi-component alloy disclosed in JP 2022-180747 A, the content of V is suppressed from the viewpoint of ductility. This multi-component alloy has room for improvement in terms of strength.

[0010] The present applicant intends to provide a multi-component alloy that has sufficient hardness and an excellent balance between strength and ductility. [Means for solving the problem]

[0011] The multi-component alloy disclosed herein is Co: 5.00 atomic% or more and 35.00 atomic% or less, Fe: 5.00 atomic% or more and 35.00 atomic% or less, Ni: 5.00 atomic% or more and 35.00 atomic% or less, V: more than 20.00 atomic % and less than 35.00 atomic % Cr: 20.00 atomic% or less, C: 0.05 atomic% or more and 8.74 atomic% or less, and Inevitable impurities In this multi-component alloy, the O content is 630 ppmw or less on a mass basis. In this multi-component alloy, the entropy of mixing ΔSmix is ​​1.30R or more. In this multi-component alloy, the valence electron concentration VEC is 7.84 or more. This multi-component alloy has a metal structure including a matrix and a plurality of carbides dispersed in the matrix. Preferably, the maximum circle-equivalent diameter of these carbides is 10 μm or less, and the area fraction Pc of these carbides is 0.1% or more and 15.0% or less.

[0012] This multi-component alloy may further contain one or more elements selected from the group consisting of Mo, Nb, W, Ti, Zr, Al, Mn, and Si. Preferably, the total content of Mo, Nb, W, Ti, Zr, Al, Mn, and 2Si is 20.00 atomic % or less. In this specification, "2Si" means twice the actual Si content. [Effects of the Invention]

[0013] This multi-component alloy has sufficient hardness and also has an excellent balance between strength and ductility. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments are described in detail below.

[0015] The powder according to the present invention is an aggregate of many particles. The material of these particles is a multi-component alloy. This multi-component alloy is Co: 5 atomic% or more and 35 atomic% or less, Fe: 5 atomic% or more and 35 atomic% or less, Ni: 5 atomic% or more and 35 atomic% or less, V: More than 20 atomic % and less than 35 atomic % Cr: 20 atomic% or less and C: 0.05 atomic% or more and 8.74 atomic% or less Preferably, the remainder is unavoidable impurities. This multi-component alloy may contain O. The O content is 630 ppmw or less by mass. A compact can be obtained from this powder by sintering, which will be described in detail later. In other words, this compact is a powder metallurgy compact.

[0016] This multi-component alloy contains multiple elements as a base. In this embodiment, Co, Fe, Ni, and V are base elements. In this embodiment, the Cr content can be 5.00 atomic % or more. In this case, Cr is also a base element. The atomic content (at %) of each base element is sufficiently large. Therefore, the metal structure of this multi-component alloy is clearly different from the metal structure of an alloy based on only a single element. The entropy of mixing ΔSmix of this alloy is sufficiently large.

[0017] The entropy of mixing, ΔS mix , can be calculated by the following formula:

number

[0018] The closer the atomic content of the base elements in this alloy is to equal amounts, the greater the entropy of mixing ΔSmix of this alloy. In alloys with a large entropy ΔSmix, the mixed state is stable. In alloys with a large entropy ΔSmix, a complex and fine metal structure can be obtained. This metal structure has excellent relaxation diffusion. In alloys with a large entropy ΔSmix, the lattice distortion caused by the difference in atomic radii is large. Since the large lattice distortion increases the deformation resistance, compacts obtained from this alloy have high hardness. From these perspectives, the entropy of mixing ΔSmix is ​​preferably 1.30R or more, more preferably 1.40R or more, and particularly preferably 1.50R or more. Here, R represents the gas constant. A specific value of the gas constant R is 8.314 J·K. -1 mol -1 is.

[0019] Among the base elements, the difference (Pmax-Pmin) between the atomic content Pmax of the element with the maximum atomic content and the atomic content Pmin of the element with the minimum atomic content is preferably 15 atomic % or less, more preferably 10 atomic % or less, and particularly preferably 5 atomic % or less.

[0020] The atomic content of each of Co, Fe, and Ni is adjusted to be in the range of 5.00 atomic % or more and 35.00 atomic % or less so as to obtain a large entropy ΔSmix. This content is more preferably 10.00 atomic % or more, and particularly preferably 15.00 atomic % or more. This content is more preferably 30.00 atomic % or less, and particularly preferably 25.00 atomic % or less.

[0021] V is an extremely important element in the multi-component alloy according to this embodiment. The atomic radius of V is larger than the atomic radius of each of Co, Fe, and Ni. A multi-component alloy containing V has large lattice distortion. In an alloy with large lattice distortion, dislocation movement can be hindered. V can contribute to the strength of the multi-component alloy. Furthermore, V does not inhibit the "large valence electron concentration VEC" described below. From these viewpoints, the V content is preferably more than 20.00 atomic %, more preferably 22.00 atomic % or more, and particularly preferably 23.00 atomic % or more. From the viewpoint that the multi-component alloy can sufficiently contain elements other than V, the V content is preferably less than 35.00 atomic %, more preferably 33.00 atomic % or less, and particularly preferably 30.00 atomic % or less.

[0022] The strain parameter δr of this alloy is preferably 2.65% or more. In this alloy, lattice strain is large, and therefore dislocations do not move easily. This alloy has excellent strength. From this viewpoint, the strain parameter δr is more preferably 2.75% or more, and particularly preferably 2.85% or more.

[0023] The distortion parameter δr is calculated by the following formula:

number

[0024] The atomic radius of the alloy calculated by the following formula is substituted into the above formula.

number

[0025] Cr contributes to the corrosion resistance of multi-component alloys. From the viewpoint of corrosion resistance, the Cr content is preferably 0.20 atomic % or more, more preferably 0.40 atomic % or more, and particularly preferably 0.50 atomic % or more. In multi-component alloys, Cr is not an essential element. In other words, the Cr content may be below the detection limit.

[0026] As mentioned above, this multi-component alloy contains a large amount of V. V and Cr are elements with low valence electron concentrations. In a multi-component alloy containing a large amount of Cr in addition to V, the valence electron concentration of the alloy is too low. From the viewpoint of achieving a sufficiently high average valence electron concentration in the alloy, the Cr content is preferably 20.00 atomic % or less, more preferably 10.00 atomic % or less, and particularly preferably 5.00 atomic % or less.

[0027] From the viewpoint of achieving a sufficiently large average valence electron concentration, the total content of V and Cr is preferably 40.50 atomic % or less, more preferably 40.20 atomic % or less, and particularly preferably 39.90 atomic % or less.

[0028] Carbon combines with other elements to form carbides. In the metal structure of this multi-component alloy, numerous carbides are dispersed in the matrix. According to the findings of the present inventors, these carbides can contribute to the hardness of the multi-component alloy. Furthermore, the appropriate amount of carbides dispersed in the matrix does not impair the ductility of the alloy. From these viewpoints, the C content is preferably 0.05 atomic % or more, more preferably 1.39 atomic % or more, and particularly preferably 2.30 atomic % or more. Excessive C leads to the excessive formation of carbides. These excess carbides impair the ductility of the alloy. From the viewpoint of excellent ductility, the C content is preferably 8.74 atomic % or less, more preferably 6.67 atomic % or less, and particularly preferably 4.53 atomic % or less.

[0029] The multi-component alloy according to this embodiment may contain O as an impurity. According to the findings of the present inventors, O combines with V to form oxides. Excess O leads to the formation of excess oxides. Excess oxides impair the hot workability of the compact. From the viewpoint of hot workability, the O content in the powder is preferably 630 ppmw or less, more preferably 500 ppmw or less, and particularly preferably 400 ppmw or less.

[0030] Examples of unavoidable impurities that may be contained in this multi-component alloy include P, S, Sn, and N. The P content is preferably 0.10% by mass or less, and more preferably 0.02% by mass or less. The S content is preferably 0.10% by mass or less, and more preferably 0.002% by mass or less. The Sn content is preferably 0.10% by mass or less, and more preferably 0.02% by mass or less. The N content is preferably 0.50% by mass or less, and more preferably 0.01% by mass or less.

[0031] In this specification, the valence electron concentration (VEC) of a multi-component alloy can be calculated by the following formula.

number

[0032] The valence electron concentration (VEC) of a multi-component alloy is an index for predicting the crystal structure of the compact. In alloys with a high valence electron concentration (VEC), the FCC phase of the compact is stable. Furthermore, alloys with a valence electron concentration (VEC) of 6.88 or more but less than 7.84 are prone to forming brittle phases upon sintering (see Tsai, et al.: Materials Research Letters, 1 (2013) 207-212). From these perspectives, the valence electron concentration (VEC) is preferably 7.84 or more, more preferably 7.87 or more, and particularly preferably 7.90 or more.

[0033] As mentioned above, because the entropy ΔSmix is ​​large, the metal structure of this multi-component alloy is excellent in relaxation diffusion. Furthermore, in this metal structure, the carbides dispersed in the matrix exert a so-called pinning effect. The relaxation diffusion effect and the pinning effect suppress the growth of crystal grains in the compact. This compact has excellent softening resistance at high temperatures. From the viewpoint of softening resistance, the carbide area fraction Pc in the metal structure of the compact is preferably 0.1% or more, more preferably 1.0% or more, and particularly preferably 2.0% or more. Excess carbides impair the elongation property of the compact. From the viewpoint of elongation property, this area fraction Pc is preferably 15.0% or less, more preferably 13.0% or less, and particularly preferably 10.0% or less.

[0034] To measure the area ratio Pc, a backscattered electron image of the polished surface of the molded body is taken using a scanning electron microscope. The area of ​​each carbide present in the backscattered electron image obtained by the photograph, magnified 4000 times, is measured. The area ratio Pc is calculated based on the total area of ​​all carbides present in the image.

[0035] From the viewpoint of ductility, the maximum size Dmax of carbides in the metal structure of the compact is preferably 10.0 μm or less, more preferably 7.0 μm or less, and particularly preferably 5.0 μm or less. The maximum size Dmax is preferably 0.1 μm or more.

[0036] To measure the maximum size Dmax, a backscattered electron image of the polished surface of the compact is taken using a scanning electron microscope. The circle-equivalent diameter D of each carbide present in the backscattered electron image obtained by the image at a magnification of 4000 times is calculated. The maximum size Dmax is the maximum circle-equivalent diameter D of all carbides present in the image. In other words, the maximum size Dmax is the maximum circle-equivalent diameter D of the carbides in the compact. The circle-equivalent diameter D of a carbide is the diameter of a perfect circle having the same area as the area S of the carbide. The circle-equivalent diameter D can be calculated using the following formula. D = (4 × S / π) 0.5

[0037] By selecting appropriate atomizing conditions, the area ratio Pc and maximum size Dmax of carbides can be adjusted. By adjusting the rapid solidification conditions of atomizing, the size of carbides can be adjusted.

[0038] This compact can be produced by powder metallurgy. In other words, the compact according to the present invention is a powder metallurgy compact. The powder used in the powder metallurgy process is preferably obtained by atomization. Gas atomization, disk atomization, water atomization, single-roll quenching, twin-roll quenching, and centrifugal atomization are employed. Preferred atomization methods are gas atomization and disk atomization. The powder obtained by atomization may be subjected to mechanical milling or the like. Rapid solidification in atomization can produce fine carbides. The effect of these carbides in pinning the crystal grains is significant. A compact containing this carbide has excellent softening resistance. Rapid solidification in atomization further contributes to the refinement of the carbides. A compact containing fine carbides has excellent elongation.

[0039] A typical method for solidifying this powder is sintering. In this sintering, the powder is subjected to a pressure treatment. A typical pressure treatment is hot isostatic pressing. The sintered body obtained by sintering is subjected to plastic processing such as hot forging to obtain the molded body according to the present invention.

[0040] According to another preferred embodiment, the multi-component alloy comprises one or more elements selected from the group consisting of Mo, Nb, W, Ti, Zr, Al, Mn and Si. Co: 5.00 atomic% or more and 35.00 atomic% or less, Fe: 5.00 atomic% or more and 35.00 atomic% or less, Ni: 5.00 atomic% or more and 35.00 atomic% or less, V: more than 20.00 atomic % and less than 35.00 atomic % Cr: 20.00 atomic% or less, and C: 0.05 atomic% or more and 8.74 atomic% or less, The alloy further contains one or more elements selected from the group consisting of Mo, Nb, W, Ti, Zr, Al, Mn, and Si. Preferably, the balance is unavoidable impurities. The total content of Mo, Nb, W, Ti, Zr, Al, Mn, and 2Si is 20.00 atomic % or less. In this multi-component alloy, the O content is 630 ppmw or less on a mass basis. In this multi-component alloy, the entropy of mixing ΔSmix is ​​1.30R or more. In this multi-component alloy, the valence electron concentration VEC is 7.84 or more. This multi-component alloy has a metal structure including a matrix and a plurality of carbides dispersed in the matrix. The maximum equivalent circle diameter of these carbides is 10 μm or less. The area fraction Pc of these carbides is 0.1% or more and 15.0% or less.

[0041] In this multi-component alloy, fine compounds containing Mo, Nb, W, Ti, Zr, Al, Mn, or Si may precipitate. Typical fine compounds are oxides. These fine compounds pin the crystal grains. This pinning can result in a fine metal structure. A multi-component alloy having this metal structure has excellent softening resistance. From the viewpoint of softening resistance, the total atomic content of Mo, Nb, W, Ti, Zr, Al, Mn, and 2Si is preferably 0.10 atomic % or more, more preferably 0.15 atomic % or more, and particularly preferably 0.20 atomic % or more. From the viewpoint of suppressing the formation of brittle phases and achieving excellent hot workability, this atomic content is preferably 20.00 atomic % or less, more preferably 15.00 atomic % or less, and particularly preferably 10.00 atomic % or less. In this specification, "2Si" means twice the actual Si content. [Example]

[0042] The effects of powder metallurgy compacts according to the examples will be explained below, but the scope of the present disclosure should not be construed as being limited based on the descriptions of these examples.

[0043] [Example 1] The raw metal was melted to obtain a molten metal. This molten metal was poured into an alumina crucible. The molten metal was discharged from the nozzle of the crucible and sprayed with high-pressure argon to obtain a powder. This powder was classified to adjust the particle size to 300 μm or less. This powder was filled into a capsule and the capsule was sealed. This powder was subjected to hot isostatic pressing (HIP) at 1170°C to obtain a sintered body. This sintered body was heated to 1100°C. This compact was forged and air-cooled to obtain the compact of Example 1.

[0044] [Examples 2-20 and Comparative Examples 1-14] Molded bodies of Examples 2-20 and Comparative Examples 1-14 were obtained in the same manner as in Example 1 except that raw materials with different compositions were used.

[0045] [Comparative Example 15] The raw metal was subjected to an arc melting method to obtain an ingot, which was then heated to 1100°C, forged, and air-cooled to obtain a compact.

[0046] [Dmax, Pc] A test specimen was cut out from the compact. The size of this test specimen was 10 mm × 10 mm × 10 mm. This test specimen was observed with a scanning electron microscope (SEM) to obtain a backscattered electron image at 4000x magnification. From this electron image, the maximum size Dmax of the circle-equivalent diameter of the carbide was calculated using the method described above. Furthermore, from this electron image, the area ratio Pc of the carbide was calculated using the method described above. The results are shown in Tables 3 and 4 below.

[0047] [Rockwell hardness (HRC)] The hardness of the compacts was measured using Rockwell Hardness Scale C. The results are shown in Tables 3 and 4 below. A compact having a hardness of 40 HRC or more is preferred.

[0048] [Room temperature tensile test] A JIS No. 14A φ5 test piece (φ5 × GL 25 mm) was cut out from the molded body. This test piece was subjected to a tensile test at room temperature to measure the tensile strength and elongation. The results are shown in Tables 3 and 4 below. A molded body having a tensile strength of 750 MPa or more is preferred. A molded body having an elongation of 10% or more is preferred.

[0049] [Specific wear rate] A test piece was cut out from the molded body. The size of this test piece was 19 mm x 41 mm x 6 mm. This test piece was set in an Ohkoshi type abrasion tester, and the specific wear rate was measured. The measurement conditions were as follows: Ring: SCM420 Wear speed: 2.38 m / sec Wear distance: 200m Final load: 20.6N Lubrication: None Temperature: room temperature The results are shown in Tables 3 and 4 below. The specific wear rate was 6.0 x 10-6 mm 2 A molded article having a molecular weight of 1 / kg or less is preferred.

[0050] [High temperature tensile test] A test piece measuring 10 mm in diameter and 80 mm in length was cut out from the compact. This test piece was subjected to a tensile test at 1100°C to measure the reduction in area. The results are shown in Tables 3 and 4 below. A compact having a reduction in area of ​​50% or more is preferred.

[0051] [Table 1]

[0052] [Table 2]

[0053] [Table 3]

[0054] [Table 4]

[0055] Tables 1 and 2 show the compositions at the powder stage. However, the composition at the ingot stage is shown for the compact of Comparative Example 15. Each alloy contains inevitable impurities in addition to the elements shown in Tables 1 and 2.

[0056] The alloys of Comparative Examples 1 and 3 had low entropy of mixing and did not achieve sufficient hardness. The alloy of Comparative Example 2 had an insufficient amount of V and therefore did not achieve sufficient hardness. The alloy of Comparative Example 4 had a high oxygen value and therefore did not achieve sufficient hot workability. The alloy of Comparative Example 5 had an excessive amount of carbides and therefore did not achieve sufficient elongation. The alloys of Comparative Examples 6-14 had a low VEC, which resulted in the formation of a brittle phase and therefore did not achieve sufficient elongation. The alloy of Comparative Example 15 was obtained by a casting method, and therefore coarse reticulate carbides precipitated, and therefore did not achieve sufficient elongation.

[0057] The molded articles according to each example had an excellent balance of hardness, strength, ductility, and wear resistance.

[0058] These evaluation results clearly demonstrate the superiority of the present invention. [Industrial Applicability]

[0059] The multi-component alloys described above are suitable for a variety of applications requiring high strength and toughness.

Claims

1. Co: 5.00 atomic% or more and 35.00 atomic% or less, Fe: 5.00 atomic% or more and 35.00 atomic% or less, Ni: 5.00 at% or more and 35.00 at% or less, V: more than 20.00 atomic % and less than 35.00 atomic %; Cr: 20.00 at% or less, C: 0.05 atomic% or more and 8.74 atomic% or less, and Inevitable impurities It contains The O content is 630 ppmw or less by mass, The entropy of mixing ΔSmix is ​​1.30R or more, The valence electron concentration VEC is 7.84 or more, A multi-component alloy having a metal structure including a matrix and a plurality of carbides dispersed in the matrix.

2. The maximum circle equivalent diameter of the carbide is 10 μm or less, 2. The multi-component alloy according to claim 1, wherein the area fraction Pc of these carbides is 0.1% or more and 15.0% or less.

3. Further containing one or more elements selected from the group consisting of Mo, Nb, W, Ti, Zr, Al, Mn and Si, 3. The multi-component alloy according to claim 1, wherein the total content of Mo, Nb, W, Ti, Zr, Al, Mn, and 2Si is 20.00 atomic % or less.

4. The powder is made of a multi-component alloy, The multi-component alloy is Co: 5.00 atomic% or more and 35.00 atomic% or less, Fe: 5.00 atomic% or more and 35.00 atomic% or less, Ni: 5.00 at% or more and 35.00 at% or less, V: more than 20.00 atomic % and less than 35.00 atomic %; Cr: 20.00 at% or less, C: 0.05 atomic% or more and 8.74 atomic% or less, and Inevitable impurities It contains The content of O in the multi-component alloy is 630 ppmw or less by mass, The entropy of mixing ΔSmix of the multi-component alloy is 1.30R or more, The valence electron concentration VEC of the multi-component alloy is 7.84 or more, The powder, wherein the multi-component alloy has a metal structure including a matrix and a plurality of carbides dispersed in the matrix.

5. The maximum circle equivalent diameter of the carbide is 10 μm or less, The powder according to claim 4, wherein the area ratio Pc of these carbides is 0.1% or more and 15.0% or less.

6. The multi-component alloy further contains one or more elements selected from the group consisting of Mo, Nb, W, Ti, Zr, Al, Mn, and Si; 6. The powder according to claim 4 or 5, wherein the total content of Mo, Nb, W, Ti, Zr, Al, Mn and 2Si is 20.00 atomic % or less.

7. A compact whose material is a multi-component alloy, The multi-component alloy is Co: 5.00 atomic% or more and 35.00 atomic% or less, Fe: 5.00 atomic% or more and 35.00 atomic% or less, Ni: 5.00 at% or more and 35.00 at% or less, V: more than 20.00 atomic % and less than 35.00 atomic %; Cr: 20.00 at% or less, C: 0.05 atomic% or more and 8.74 atomic% or less, and Inevitable impurities It contains The content of O in the multi-component alloy is 630 ppmw or less by mass, The entropy of mixing ΔSmix of the multi-component alloy is 1.30R or more, The valence electron concentration VEC of the multi-component alloy is 7.84 or more, A compact, wherein the multi-component alloy has a metal structure including a matrix and a plurality of carbides dispersed in the matrix.

8. The maximum circle equivalent diameter of the carbide is 10 μm or less, The compact according to claim 7, wherein the area ratio Pc of these carbides is 0.1% or more and 15.0% or less.

9. The multi-component alloy further contains one or more elements selected from the group consisting of Mo, Nb, W, Ti, Zr, Al, Mn, and Si; 9. The molded body according to claim 7 or 8, wherein the total content of Mo, Nb, W, Ti, Zr, Al, Mn, and 2Si is 20.00 atomic % or less.

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