Alloy component and method for manufacturing an alloy component

Abstract

This invention provides an alloy component with high specific strength and a method for manufacturing that alloy component. [Solution] At least two elements selected from Al, Ti, Si, and C, and Zr, Ni, Nb, and Mo, along with unavoidable impurities, are added to make a total elemental composition of 100 atomic percent. An alloy member containing Al, Ti, and at least two elements selected from the aforementioned selective additives in amounts of 5 to 40 atomic percent each, Si in amounts greater than 0 atomic percent and less than 10 atomic percent, and C in amounts greater than 0 atomic percent and less than 10 atomic percent.

Description

Technical Field

[0001] The present invention relates to an alloy member and a method for manufacturing the same.

Background Art

[0002] In the fields of mobility and electronic devices, lightweight and high-strength high specific strength (strength per unit density) materials are required. Conventional high specific strength materials include Al (aluminum)-based alloys and Mg (magnesium)-based alloys. However, in recent years, higher specific strength than these has been required for high specific strength materials.

[0003] On the other hand, in recent years, a high entropy alloy (HEA), which is an alloy with a new technical concept different from the design concept of conventional alloys, has been proposed. A high entropy alloy is an alloy composed of four or more main metal elements, and in the Gibbs free energy formula, the mixing entropy term (ΔS mix =R(x1ln(x1)+x2ln(x2)+…+x k ln(x k )+…+x n ln(x n ))(x k is the content of the k-th element, and R is the gas constant)) is an alloy with a value of -1.5R or less. Since a high entropy alloy consists of five or more main metal elements with different atomic radii, the distortion of the crystal lattice becomes large, resulting in higher strength than conventional alloy design. Therefore, it has also attracted attention as a high specific strength material. In addition, an alloy concept of a multi-principal element alloy (MPEA) that has multiple main metal elements and allows the existence of multiple phases has been proposed. In this application, high entropy alloys and MPEAs are treated as the same concept, and both are collectively referred to as high entropy alloys.

[0004] For example, Patent Document 1 discloses a high-entropy alloy containing Al (aluminum), Si (silicon), Ti (titanium), Zr (zirconium), and Ni (nickel) as major metallic elements. It states that such a high-entropy alloy can be used to obtain a highly hard alloy. Patent Document 2 also discloses a high-entropy alloy containing Al, Ti, Zr, and Ni as major metallic elements, and states that it can obtain the same effects as Patent Document 1. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2024-36067 [Patent Document 2] Japanese Patent Publication No. 2002-173732 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The high-entropy alloys described in Patent Documents 1 and 2 possess high strength. However, Patent Documents 1 and 2 do not consider the density of the alloy, and do not focus on alloys with high specific strength.

[0007] Therefore, the present invention provides an alloy member with high specific strength and a method for manufacturing the alloy member. [Means for solving the problem]

[0008] The first invention is an alloy member containing Al, Ti, and at least two selected additive elements from Al, Ti, Si, and C, as well as Zr, Ni, Nb, and Mo, with unavoidable impurities added, so that the total amount of constituent elements is 100 atomic percent. This includes Al, Ti, and at least two selected additive elements, each in amounts of 5 atomic percent to 40 atomic percent, Si in amounts of more than 0 atomic percent and 10 atomic percent or less, and C in amounts of more than 0 atomic percent and 10 atomic percent or less.

[0009] It is preferable that the content of at least two of the selected additive elements is greater than the content of Al and Ti.

[0010] It is preferable that the above-mentioned C is contained in an amount of 3.5 atomic% or more and 10 atomic% or less.

[0011] The second invention is a method for manufacturing an alloy member, which involves supplying a mixed powder so that, at the time of melting, the total amount of contained elements, including at least two selected from Al, Ti, Si, and C, and Zr, Ni, Nb, and Mo, plus unavoidable impurities, is 100 atomic percent, with Al, Ti, and at least two selected from the aforementioned selective additive elements each at 5 atomic percent to 40 atomic percent, Si at more than 0 atomic percent and 10 atomic percent or less, and C at more than 0 atomic percent and 10 atomic percent or less; selectively irradiating the supplied mixed powder with a light beam to melt and solidify it, and repeating the process of supplying the mixed powder and melting and solidifying it to obtain an alloy member by performing a powder melt addition manufacturing method.

[0012] It is preferable to supply the mixed powder during the melting process such that the content of at least two elements selected from the selective additives is greater than the content of Al and the content of Ti.

[0013] It is preferable to supply the mixed powder such that, during the melting process, the amount of C is between 3.5 atomic% and 10 atomic%. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an alloy member with high specific strength and a method for manufacturing the alloy member. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram showing an example of an additive manufacturing apparatus used in a method for manufacturing an alloy member, which is one embodiment of the present invention. [Figure 2] This figure shows the SEM observation image and EDS elemental analysis results of the alloy member of Example 1. [Figure 3] It is a figure showing the SEM observation image and EDS elemental analysis results of the alloy member of Example 2. [Figure 4] It is a figure showing the SEM observation image and EDS elemental analysis results of the alloy member of Comparative Example 1. [Figure 5] It is a graph comparing the Vickers hardness of Example 1, Example 2 and Comparative Example 1. [Figure 6] It is a figure showing the SEM observation image and EDS elemental analysis results of the alloy member of Example 3. [Figure 7] It is a figure showing the SEM observation image and EDS elemental analysis results of the alloy member of Comparative Example 2. [Figure 8] It is a graph comparing the Vickers hardness of Example 3 and Comparative Example 2.

Mode for Carrying Out the Invention

[0016] (Alloy member) Hereinafter, an alloy member according to an embodiment of the present invention will be described. In aiming to develop an alloy member having a higher specific strength than conventional high specific strength Al alloys and being easier to synthesize than Mg alloys, the inventors focused on high entropy alloys.

[0017] Unlike conventional alloy design philosophies that adjust properties by adding trace amounts of additives to 1-3 main metal elements, high-entropy alloys have an alloy composition consisting of 4-5 main metal elements. In high-entropy alloys, each main metal element is present in an amount of at least 5 atomic percent, and the content of the most abundant main metal element is set so as not to exceed 40 atomic percent, taking into account the balance with the other main metal elements. High-entropy alloys with these characteristics have the following features: (a) Stabilization of the mixed state due to the negative increase of the mixing entropy term (hereinafter also simply called the mixing entropy term) in Gibbs' free energy equation due to the presence of multiple main metal elements; (b) Improvement of mechanical properties due to increased lattice strain caused by the inclusion of multiple main metal elements with different atomic radii in the crystal lattice sites; (c) Delay in atomic diffusion due to the complex microstructure; and (d) Improved corrosion resistance and high-temperature properties due to the combined effects resulting from the coexistence of various main metal elements.

[0018] In other words, by designing a high-entropy alloy consisting of major metal elements that are low in reactivity and easy to synthesize, and which include elements among the major metal elements that impart high specific strength characteristics to high-entropy alloys, it is possible to develop alloy components that have higher specific strength than Al alloys and are easier to synthesize than Mg alloys.

[0019] Al and Ti were selected as the main metallic elements capable of imparting such high specific strength characteristics, and Zr, Ni, Nb, and Mo were selected as other main metallic elements that can be mixed with them. Zr, Ni, Nb, and Mo are selective additive elements, and at least two of them are selected and mixed with Al and Ti. Note that "mixing with each other" means that each element does not separate individually but mixes to form an alloy structure.

[0020] Furthermore, in the alloy member according to one embodiment of the present invention, in order to further bring out the characteristics of a high-entropy alloy (b), Si and C were selected and added as elements with smaller atomic radii than the main metal elements. By adding elements with even smaller atomic radii than the main metal elements and dissolving them in this way, the lattice strain can be further increased and the mechanical properties can be improved. In addition, because Si and C have low densities, they contribute to further increasing specific strength.

[0021] The major metallic elements and additive elements listed so far have low reactivity and do not undergo violent oxidation reactions involving combustion when heated in air, unlike Mg and Ca (calcium), making alloy synthesis easy.

[0022] The alloy contains at least two elements selected from Al, Ti, Si, and C, as well as Zr, Ni, Nb, and Mo, along with unavoidable impurities, so that the total amount of each element, including unavoidable impurities, is 100 atomic percent. Of these, Al, Ti, and at least two elements selected from the selective additive elements (Zr, Ni, Nb, and Mo) are each contained in an amount of 5 atomic percent to 40 atomic percent. The major metal elements form the base of an alloy with high specific strength, and by containing at least 5 atomic percent of each, the mixing entropy term is negatively increased, stabilizing the mixing state, increasing lattice strain, and improving mechanical properties. Furthermore, each of the at least two elements selected from the selective additive elements (Al, Ti, Zr, Ni, Nb, and Mo) is contained in such a way that even the most abundant major metal element does not exceed 40 atomic percent, taking into account the content of the other elements (Al, Ti, and at least two elements selected from the selective additive elements). On the other hand, if three or more selective additive elements are chosen, the content of any element exceeding two may be less than 5 atomic percent.

[0023] Furthermore, Si and C are each contained in amounts greater than 0 atomic% and less than or equal to 10 atomic%. Si and C are included to further solidify into the main metal elements and provide solid solution strengthening. In conventional alloys, C is an interstitial element that solidifies into the crystal lattice, but in the alloy member according to one embodiment of the present invention, where the mixed state is stabilized, C also enters the sites of the crystal lattice, increasing the lattice strain. In particular, considering the difference in atomic radius with the main metal elements, C is important because it contributes more easily to solid solution strengthening. Preferably, the total amount of Si and C is 5 atomic% or more. By keeping it within this range, the mixing entropy term of the alloy member increases sufficiently negatively, so the mixed state of all constituent elements in the alloy member is stabilized, the lattice strain increases, and the mechanical properties are improved.

[0024] The mixing entropy term in Gibbs' free energy equation described above is preferably -1.5R or less. A sufficiently negative increase in the mixing entropy term fully exhibits the characteristics of a high-entropy alloy. In particular, in this embodiment, the mixing state becomes stable, lattice strain increases, and mechanical properties improve. A more preferable mixing entropy term is -1.55R or less, and even more preferably -1.6R or less.

[0025] One example of such an alloy component is a high-entropy alloy in which Si and C are dissolved in a main metallic element component consisting of Al and Ti, and at least two other elements selected from selective additive elements consisting of Zr, Ni, Nb, and Mo, which are mixed with Al and Ti. The main metallic element components are each contained in amounts of 5 atomic% to 40 atomic% and Si and C are contained in amounts of more than 0 atomic% and 10 atomic% or less.

[0026] Such alloy components can be manufactured by methods such as casting, forging, and powder melting addition (hereinafter simply referred to as addition manufacturing), with addition manufacturing being particularly preferred. Addition manufacturing is known to have a very fast cooling rate because it involves locally irradiating fine raw material powder with a light beam emitted from a heat source to melt and solidify the raw material powder. Therefore, atoms do not diffuse easily during cooling, and the atomic mixture state in the alloy component is easily stabilized.

[0027] (Method of manufacturing alloy components) Next, we will explain additive manufacturing methods for obtaining such alloy components. Additive manufacturing methods can generally be broadly classified into powder bed fusion (PBF) and directed energy deposition (DED), but alloy components can be obtained by either method. Below, we will describe one embodiment of obtaining an alloy component by DED.

[0028] Figure 1 shows a schematic diagram of an additive manufacturing apparatus for DED (hereinafter simply referred to as the additive manufacturing apparatus) as an example of this embodiment. The additive manufacturing apparatus 100 mainly comprises a light beam irradiation head section (hereinafter simply referred to as the head section) 110 connected to a powder supply device inside a chamber, and a base section 120. The head section 110 is movable in a direction parallel to the mounting surface of the additive-formed object on the base section 120. By moving the head section 110 and simultaneously supplying raw material powder and irradiating the base section 120 with a light beam, a solidified layer 130 of melted and solidified raw material powder is formed on the base section 120. By stacking multiple of these solidified layers, the alloy member of the present invention can be obtained.

[0029] In this embodiment, the raw material powder used is a mixed powder in which multiple powder materials are mixed so that, when melted, the total amount of contained elements, including at least two selected from Al, Ti, Si, and C, and Zr, Ni, Nb, and Mo, plus unavoidable impurities, is 100 atomic percent, with at least four elements from the major metal element group consisting of Al, Ti, Zr, Ni, Nb, and Mo each present in amounts of 5 atomic percent to 40 atomic percent, Si being greater than 0 atomic percent and 10 atomic percent or less, and C being greater than 0 atomic percent and 10 atomic percent or less. Methods for preparing such a mixed powder include mixing multiple powder materials using a powder mixing device and then filling it into a powder supply device, or replenishing multiple powder materials in the powder supply device and supplying the mixed powder to the head unit 110 by creating a powder mixing space between the powder supply device and the head unit 110. Regarding the method of supplying the mixed powder, it is acceptable to either fill the powder supply device with pre-mixed powder and supply it to the base section 120, or to fill the powder supply device with various material powders and then supply them onto the base section 120 while mixing them. In other words, it is sufficient that the powder is mixed at the time it is supplied onto the base section 120.

[0030] One method for manufacturing such alloy members involves obtaining an alloy member by powder melt addition using a mixed powder, in which, at the time of melting, at least two elements selected from Al, Ti, Si, and C, and Zr, Ni, Nb, and Mo, along with unavoidable impurities, make up 100 atomic percent of the total constituent elements. Specifically, Al and Ti, and at least two of Zr, Ni, Nb, and Mo, are present in concentrations of 5 to 35 atomic percent each, Si is greater than 0 atomic percent and less than 10 atomic percent, and C is greater than 0 atomic percent and less than 10 atomic percent. [Examples]

[0031] <Comparison of Al-Ti-Zr-Ni quaternary alloys and high-entropy alloys with SiC addition> As raw material powders, alloy powders with a composition of 52Ti-48Al[at.%] (particle size distribution range: 150 μm or less) manufactured by Kobelco Chemical, alloy powders with a composition of 39Zr-61Ni[at.%] (particle size distribution range: 45~150 μm) manufactured by High Purity Chemical, and silicon carbide (SiC) powder (particle size distribution range: 24~32 μm) manufactured by Shinano Electric Refining were prepared. Each raw material powder was supplied to a DED-type additive manufacturing apparatus equipped with a powder mixing space so that the composition would be as shown in Table 1 when mixed. The supply rate of each powder was adjusted so that the total amount of all powders was 14 g / min. Subsequently, alloy members with a width of approximately 25 mm, a length of approximately 25 mm, and a layer height of approximately 16 mm were obtained using the DED-type additive manufacturing apparatus under the molding conditions shown in Table 2 for Examples 1-2 and Comparative Example 1. Each alloy member was fabricated in the atmosphere while supplying argon gas as a shielding gas along with the powder from the nozzle.

[0032] [Table 1]

[0033] [Table 2]

[0034] (Cross-sectional observation and elemental distribution analysis) For the alloy members of Examples 1 and 2, and Comparative Example 1, test specimens measuring 5 mm in width, 10-15 mm in length, and 15 mm in height were cut out, and cross-sectional observation and elemental distribution analysis were performed using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS), with the cross-section horizontal to the lamination direction as the observation plane. Figure 2 shows the cross-sectional observation image and the elemental distribution analysis results within the imaging range of the cross-sectional observation image for Example 1. Figure 3 shows the cross-sectional observation image and the elemental distribution analysis results within the imaging range of the cross-sectional observation image for Example 2, and Figure 4 shows the cross-sectional observation image and the elemental distribution analysis results within the imaging range of the cross-sectional observation image for Comparative Example 1. The microstructures of Examples 1 and 2 and Comparative Example 1 all consist of multiple phases. The microstructures of Examples 1 and 2 contained a phase containing all constituent elements, a phase enriched with Al and Ni, a phase enriched with Ti, Zr, and Ni, a phase enriched with Ti, Zr, and Si, and a phase enriched with Zr and C, respectively. On the other hand, the microstructure of Comparative Example 1 contained a phase with all constituent elements, a phase concentrated with Al and Ni, a phase concentrated with Ti, Zr, and Ni, and a phase concentrated with Al, Zr, and Ni. Although the microstructure characteristics did not change significantly, the addition of SiC resulted in the formation of a new phase that is thought to be a carbide phase concentrated with Zr and C. Furthermore, Example 2 had a finer microstructure compared to Example 1. It is presumed that the red-hot time of the molded body of Example 2 immediately after molding was shorter than that of Example 1, and that the cooling rate increased due to the higher content of Si and C, which have good thermal conductivity, resulting in a finer, more dispersed microstructure. In addition, although the content of Zr and Ni was higher than that of Al and Ti in all of Examples 1, Example 2, and Comparative Example 1, it is thought that even if this relationship of content were reversed and the content of Al and Ti was higher than that of Zr and Ni, a similar alloy microstructure with mixed elements would be formed.

[0035] (Vickers hardness) Vickers hardness tests were performed on the alloy members of Examples 1-2 and Comparative Example 1 using a test force of 0.5 kgf, with the test surface perpendicular to the lamination direction, to compare their hardness. Figure 5 shows the Vickers hardness test results for Examples 1-2 and Comparative Example 1. From Figure 5, a tendency was observed for Vickers hardness to improve as the SiC content increased. The reason why the Vickers hardness of Examples 1 and 2, which had SiC added, improved compared to Comparative Example 1, which did not have SiC added, is thought to be partly due to the formation of a carbide phase concentrated with Zr and C, based on the aforementioned microstructure characteristics. However, the reason why the Vickers hardness improved by increasing the amount of SiC added even after the carbide phase had formed cannot be explained by the presence of the carbide phase alone. This improvement in hardness is thought to be due to an increase in lattice strain caused by the solid solution of Si and C into the alloy structure. Therefore, it was found that not only does adding SiC change the structural characteristics, but by dissolving elements with smaller atomic radii compared to metallic elements, such as Si and C, into high-entropy alloys, the lattice strain of each phase can be increased, thereby improving hardness.

[0036] From the above, it was found that when SiC was added to the Al-Ti-Zr-Ni quaternary alloy, the microstructure did not change significantly, and the structure remained the same with multiple phases. However, by adding SiC, solid solution occurred in each phase, increasing the lattice strain in each phase, and consequently improving the Vickers hardness. Furthermore, comparing Comparative Example 1, which did not contain SiC, with Examples 1 and 2, which contained SiC, it was found that the addition of SiC led to the formation of a carbide phase concentrated with Zr and C. It is thought that the formation of this carbide phase also improved the Vickers hardness.

[0037] <Comparison between Al-Ti-Nb-Mo quaternary alloys and high-entropy alloys with SiC addition> As raw material powders, we prepared alloy powder with a composition of 50Ti-50Al[at.%] manufactured by Kobelco Chemical (particle size distribution range: 45~150μm), pure Nb powder (particle size distribution range: 75~150μm) and pure Mo powder (particle size distribution range: 45~150μm) manufactured by High Purity Chemicals, and silicon carbide (SiC) powder (particle size distribution range: 24~32μm) manufactured by Shinano Electric Refining. Each raw material powder was supplied to a DED-type additive manufacturing apparatus equipped with a powder mixing space so that the composition would be as shown in Table 3 when mixed. Subsequently, alloy members with a width of approximately 25 mm, a length of approximately 25 mm, and a layer height of approximately 8 mm were obtained using the DED-type additive manufacturing apparatus under the molding conditions shown in Table 4 for Example 3 and Comparative Example 2. Each alloy member was fabricated in the atmosphere while supplying argon gas as a shielding gas along with the powder from the nozzle.

[0038] [Table 3]

[0039] [Table 4]

[0040] (Cross-sectional observation and elemental distribution analysis) For the alloy members of Example 3 and Comparative Example 2, test specimens measuring 5 mm in width, 10 mm in length, and 8 mm in height were cut out, and cross-sectional observation and elemental distribution analysis were performed using a scanning electron microscope (SEM) and EDS, with the cross-section horizontal to the lamination direction as the observation surface. Figure 6 shows the cross-sectional observation image and the results of the elemental distribution analysis within the imaging range of Example 3. Figure 7 shows the cross-sectional observation image and the results of the elemental distribution analysis within the imaging range of Comparative Example 2. Comparative Example 2 resulted in a dendrite structure containing all constituent elements. On the other hand, the structure of Example 3 consisted of a phase containing all constituent elements, an intermetallic compound phase containing Si, and a carbide phase. Furthermore, Example 3 had a finer structure compared to Comparative Example 2. In both Example 3 and Comparative Example 2, the content of Nb and Mo was higher than that of Al and Ti. However, it is believed that even if this content ratio were reversed, and the content of Al and Ti were higher than that of Nb and Mo, a similar alloy structure with mixed elements would be formed.

[0041] (Vickers hardness) Vickers hardness tests were performed on the alloy members of Example 3 and Comparative Example 2 using a test force of 0.5 kgf, and their hardness was compared. Figure 8 shows the Vickers hardness test results for Example 3 and Comparative Example 2. From Figure 8, it was observed that the Vickers hardness tended to improve with the addition of SiC. This is thought to be due to the increase in lattice strain caused by the solid solution of SiC into the alloy structure and the formation of a carbide phase within the alloy structure.

[0042] From the above measurement results, it was found that high-entropy alloys, in which elements with smaller atomic radii compared to metallic elements such as Si and C are dissolved in Al-Ti-Zr-Ni or Al-Ti-Nb-Mo quaternary alloys, can improve hardness compared to quaternary alloys without Si or C. In this study, the combinations of metallic elements other than Al and Ti were Zr and Ni, and Nb and Mo, but the combinations are not limited to these. The same effect of hardness improvement due to SiC addition can be obtained with combinations such as Zr and Nb, Zr and Mo, Ni and Nb, and Ni and Mo. [Explanation of symbols]

[0043] 100: Additive manufacturing equipment 110: Head unit for light beam irradiation 120: Base 130: Solidified layer

Claims

1. At least two elements selected from Al, Ti, Si, and C, and Zr, Ni, Nb, and Mo, along with unavoidable impurities, are added to the total elemental composition so that it reaches 100 atomic percent. An alloy member containing Al, Ti, and at least two elements selected from the aforementioned selective additives in amounts of 5 atomic% to 40 atomic% each, Si in amounts of more than 0 atomic% and 10 atomic% or less, and C in amounts of more than 0 atomic% and 10 atomic% or less.

2. The alloy member according to claim 1, characterized in that the content of at least two elements selected from the selected additive elements is greater than the content of Al and Ti.

3. The alloy member according to claim 1, characterized in that it contains 3.5 atomic% or more and 10 atomic% or less of the aforementioned C.

4. During melting, a mixed powder is supplied such that the total amount of elements, including at least two selected from Al, Ti, Si, and C, and Zr, Ni, Nb, and Mo, plus unavoidable impurities, is 100 atomic percent, with Al, Ti, and at least two selected from the aforementioned selective additive elements each present in amounts of 5 atomic percent to 40 atomic percent, Si in amounts greater than 0 atomic percent and 10 atomic percent or less, and C in amounts greater than 0 atomic percent and 10 atomic percent or less. The supplied mixed powder is selectively irradiated with a light beam to melt and solidify it. A method for producing an alloy member, comprising obtaining an alloy member by performing a powder melt addition manufacturing method that repeatedly involves supplying the mixed powder and melting and solidifying it.

5. The method for producing an alloy member according to claim 4, characterized in that, at the time of melting, the mixed powder is supplied such that the content of at least two elements selected from the selective additive elements is greater than the content of Al and the content of Ti.

6. The method for manufacturing an alloy member according to claim 4, characterized in that the mixed powder is supplied such that the amount of C is 3.5 atomic% or more and 10 atomic% or less during the melting process.

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