Method of manufacturing metal member and metal member therefrom

Abstract

A method of manufacturing a metal member, being capable of manufacturing a metal member including not only a second but also a third component. A metal material consisting of a compound, alloy, or a non-equilibrium alloy and having the second and third components, the second component being mutually insoluble with a first, the third component being mutually soluble with the first and second components. A metal bath having the first and third components, controlled at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition in which the third component in the metal material is decreased to reach an equilibrium with the bath. The metal member having the second composition and the third component is obtained by immersing the metal material into the bath to selectively elute the third component contained therein into the bath.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a method of manufacturing a metal member and the metal member therefrom.DESCRIPTION OF RELATED ART

[0002] Conventionally, by making metal materials porous, it has been widely applied to, for example, ultralightweight materials, high-specific stiffness materials, energy-absorbing materials, vibration-absorbing materials, soundproofing materials, thermal-insulator materials, electrode materials, filter materials, biomedical materials, heat-exchanger materials, and oil-impregnated bearing materials. In particular, a porous metal material with nanometer-scale minute pores less than 1 μm has a specific surface area which is orders of magnitude larger than that of a bulk metal body, and can therefore exhibit high functionality in terms of catalytic properties, electrode properties, gas storage properties, and sensing properties that can not be achieved with conventional materials.

[0003] The present inventors have developed a so-called liquid metal dealloying method as a method of manufacturing a porous metal material having nanometer-scale minute pores as described above. The liquid metal dealloying method relies on the following: a metal material, which consists of a compound, an alloy, or a non-equilibrium alloy concurrently containing a second component and a third component having positive and negative heat of mixing, respectively, with respect to a first component, and also has a melting point higher than the solidifying point of a metal bath consisting of the first component, is immersed into the metal bath controlled at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range in which the third component in the metal material is decreased until the metal material include the second component, but not the third component. Thereby, the third component is selectively eluted into the metal bath to obtain a metal member having minute pores (see, for example, Patent Literature 1).

[0004] Porous metal members such as ferrite-containing stainless steels, beta (bcc)-type titanium alloys, high-entropy alloys, and so on have been produced by the inventors and others using the liquid metal dealloying method (see, for example, Non-patent Literatures 1 to 3 or Patent Literature 2).CITATION LISTPatent LiteraturePatent Literature 1: WO2011 / 092909

[0006] Patent Literature 2: JP 2020-125523 ANon-Patent Literature

[0007] Non-patent Literature 1: Takeshi Wada, Albertus Deny Setyawan, Kunio Yubuta, Hidemi Kato, “Nano- to submicro-porous 3-Ti alloy prepared from dealloying in a metallic melt”, Scripta Mater., September 2011, Vol. 65, Issue 6, p. 532-535

[0008] Non-patent Literature 2: Takeshi Wada, Hidemi Kato, “Three-dimensional open-cell microporous iron, chromium and ferritic stainless steel”, Scripta Mater., May 2013, Vol. 68, Issue 9, p. 723-726

[0009] Non-patent Literature 3: Soo-Hyun Joo et al., “Beating Thermal Coarsening in Nanoporous Materials via High-Entropy Design”, Adv. Mater., 2020, Vol. 32, Issue 6, 1906160SUMMARY OF THE INVENTIONProblems to be Solved by the Invention

[0010] The liquid metal dealloying method described in Patent Literature 1 can produce a porous metal member having nanometer-scale minute pores by immersing a metal material in a metal bath to selectively elude a third component. However, the method suffers from the following problem: the elution reaction of the third component is rapid, and it is difficult to stop elution in the middle of the process. Therefore, almost all of the third component will be eluted into the metal bath, making it impossible to produce a metal member including the third component.

[0011] The present invention is made in view of the aforementioned problem. An object of the present invention is to provide a method of manufacturing a metal member, which can produce a metal member containing not only a second component but also a third component; and the metal member therefrom.Means for Solving the Problems

[0012] A method of manufacturing a metal member according to the present invention comprises: a metal-material preparation step of preparing a metal material consisting of a compound, an alloy, or a non-equilibrium alloy and having a second component and a third component, the second component being mutually insoluble with a first component, the third component being mutually soluble with the first component and mutually soluble with the second component; a metal-bath preparation step of preparing a metal bath having the first component and the third component; a metal-bath control step of controlling the metal bath prepared in the metal bath preparation step, at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition in which the third component in the metal material is decreased or increased to reach an equilibrium with the metal bath; and an obtaining step of obtaining a metal member having the second component and the third component by immersing the metal material prepared in the metal-material preparation step into the metal bath temperature-controlled at the metal-bath control step to selectively elute the third component contained in the metal material into the metal bath, or selectively diffusing the third component contained in the metal bath into the metal material.

[0013] The method of manufacturing a metal member according to the present invention represents a method of manufacturing a metal member via a metallurgical approach based on the liquid metal dealloying method. In the method of manufacturing a metal member according to the present invention, a metal material consisting of a compound, an alloy, or a non-equilibrium alloy and having a second component and a third component, and a metal bath having a first component and the third component are first prepared in the metal-material preparation step and in the metal-bath preparation step. When doing so, the metal material and the metal bath are preferably prepared in the metal-material preparation step and the metal-bath preparation step so that a substance having a composition with a decreased or increased third component in the metal material will be equilibrated with the metal bath. Further, the metal-material preparation step may be performed before or after the metal-bath preparation step, or may be performed simultaneously with the metal-bath preparation step.

[0014] Next, in the metal-bath control step, the metal bath is controlled at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition in which the third component in the metal material is decreased or increased to reach an equilibrium with the metal bath. The metal-bath control step may be performed after the metal-bath preparation step, or may be performed simultaneously with the metal-bath preparation step.

[0015] Next in the obtaining step, the metal material is immersed in the temperature-controlled metal bath. At this time, the second component contained in the metal material, which is mutually insoluble with the first component contained in the metal bath, does not elute into the metal bath and remains in the metal material. On the other hand, the third component contained in both the metal material and the metal bath, which is mutually soluble with the first component and mutually soluble with the second component, can move between the metal material and the metal bath depending on the conditions. This means that when the metal material is immersed into the metal bath, the third component can be selectively eluted from the metal material into the metal bath, or the third component contained in the metal bath can be selectively diffused into the metal material until a composition where an equilibrium is established with the metal bath is reached. In a case where the third component is eluted into the metal bath, for example, the remaining components in the metal material will be concentrated while self-assembling minute pores. Alternatively, in a case where the third component is diffused into the metal material, for example, the third component is gradually diffused so that the metal material has a uniform composition. In either of these cases, a metal member including not only the second component but also the third component can be manufactured by ensuring that the third component is included in a composition to be equilibrated with the metal bath.

[0016] It is preferred that the metal bath is controlled at the desired temperature in the metal-bath control step, and then the metal material is immersed thereinto in the obtaining step. However, the metal material may be immersed into the metal bath, and then the metal bath may be controlled to the desired temperature in the metal-bath control step to achieve the immersion of the metal material into a temperature-controlled metal bath.

[0017] In the method of manufacturing a metal member according to the present invention, the first component, the second component, and the third component may each consist of a single metal element, or they may each consist of a plurality of elements including metal elements. It is noted that the metal elements may include semi-metal elements such as tin, carbon, silicon, boron, germanium, and so on. Further, a metal member to be manufactured with the method of manufacturing, a metal member according to the present invention may have any compositions and any structures, such as alloys and composite members. The metal member may be, for example, a stainless steel, a high-entropy alloy, a metal having a different surface, or a composite member covered with an alloy and the like. As used herein, a plurality of components being mutually soluble means that the components are miscible and can form a homogeneous alloy while a plurality of components being mutually insoluble means that the components are immiscible to form separate phases and can not form a homogeneous alloy.

[0018] According to the method of manufacturing a metal member according to the present invention, the metal-bath control step may comprise controlling the metal bath at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition in which the third component in the metal material is decreased to reach an equilibrium with the metal bath, and the obtaining step may comprise obtaining the metal member consisting of a porous alloy having minute pores by immersing the metal material into the metal bath to selectively elute the third component contained in the metal material into the metal bath. In this case, the second and third components remaining in the metal material are repeatedly joined to form nanometer-scale particles, and these particles are further partially joined to self-assemble minute pore. In this way, the metal member according to the present invention having the second component and the third component, and consisting of a porous alloy with minute pores in which nanometer-scale particles are partially joined can be manufactured.

[0019] In a case where the third component contained in this metal material is to be selectively eluted into the metal bath, the metal member consisting of a porous alloy with minute pores can be manufactured by removing a substance derived from the metal bath which adheres to the formed minute pores. Further, by adjusting the temperature of the metal bath and the immersion time of the metal material, a metal member consisting entirely of a porous alloy and a metal member which is porous only at a surface layer can be obtained, and porous structures having various pore sizes and pore fractions can be manufactured. Thereby, for example, minute pores having nanometer-scale widths can be formed. It is noted in this case that the metal material and the metal bath are preferably prepared so that a substance having a composition in which the third component in the metal material is decreased reaches an equilibrium with metal baths. Moreover, the third component is preferably contained in the composition of a substance which is to be equilibrated with the metal bath.

[0020] According to the method of manufacturing a metal member according to the present invention, the metal-bath control step may comprise controlling the metal bath at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition where the third component in the metal material is increased to reach an equilibrium with the metal bath, and the obtaining step may comprise immersing the metal material into the metal bath to selectively diffuse the third component contained in the metal bath into the metal material, thereby obtaining the metal member. In this case, the third component will be gradually diffused into the metal material until the metal material has a uniform composition. Thereby, a metal member containing the third component can be manufactured. Further, the diffusion state of the third component into the metal material can be controlled by means of the immersion time of the metal material into the metal bath. Therefore, for example, by decreasing the immersion time into the metal bath, a metal member in which a surface of the metal material before immersion into the metal bath is covered with the third component can be manufactured as in a plating process. Moreover, a metal member with a surface layer having a high content of the third component, and a metal member having an overall uniform composition can be manufactured by increasing the immersion time into the metal bath. It is noted in this case that the metal material may have no third component but only the second component. Even in this case, the third component contained in the metal bath will be diffused into the metal material. Therefore, a metal member containing not only the second component but also the third component can be manufactured.

[0021] Alternatively, in a case where the third component contained in this metal bath is allowed to selectively diffuse into the metal material, the metal-material preparation step may comprise preparing a porous metal material as the metal material, and the obtaining step may comprise obtaining a metal member consisting of a porous alloy having minute pores as the metal member. Alternatively, the metal-material preparation step may comprise preparing a porous metal material as the metal material, and the obtaining step may comprise obtaining a metal member, in which a surface of the porous metal material is covered with the third component by immersing the metal material into the metal bath for a shorter time.

[0022] The method of manufacturing a metal member according to the present invention may comprise a removal step of selectively removing an adhered admixture adhered to the metal member, which includes the first component and the third component, after the metal member obtained in the obtaining step is lifted from the metal bath. The adhered admixture preferably consists of the components of the metal bath after the metal member is obtained. The method may also comprise a removal step of selectively removing components of the metal bath including the first component and the third component after obtaining the metal member in the obtaining step by solidifying the metal bath while the metal member remains immersed into the metal bath. In these cases, for example, the metal member can be recovered by using an acidic or alkaline aqueous solution capable of selectively eluting only the adhered admixture or the components of the metal bath. The adhered admixture and the components of the metal bath, for example, may adhere around the metal member, may partially adhere inside the minute pores, or may be filled inside the minute pores.

[0023] For the method of manufacturing a metal member and the metal member therefrom according to the present invention, the first component may include at least any one of Mg, Bi, Pb, Cu, and Ag, and the second component may include at least one of Fe, Cr, V, Co, Mo, Ni, Zr, Ta, W, Hf, Nb, and Ti, and the third component may include at least any one of Ni, Pd, Al, Ag, Cu, Mn, and Co.Advantageous Effect of the Invention

[0024] The present invention can provide a method of manufacturing a metal member and the metal member therefrom, wherein the metal member can contain not only a second component but also a third component.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows an X-ray diffraction spectrum of a metal member from Example 1 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention.

[0026] FIG. 2 shows (a) a micrograph from scanning electron microscopy (SEM); and elemental maps of (b) Fe and (c) Ni showing results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) for the metal member from Example 1 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention.

[0027] FIG. 3 shows (a) a micrograph from scanning electron microscopy (SEM); (b) a SEM micrograph of an enlarged portion of (a) showing the range of elemental analysis by energy dispersive X-ray spectroscopy (EDS); and elemental maps of (c) Fe and (d) Ni showing results from that elemental analysis, for the metal member obtained from Example 1 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention.

[0028] FIG. 4 shows a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 2 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention.

[0029] FIG. 5 shows (a) a micrograph from scanning electron microscopy (SEM) of an enlarged portion of FIG. 4 showing the range of elemental analysis by energy dispersive X-ray spectroscopy (EDS); elemental maps of (b) Fe, (c) Cr, (d) Ni, (e) Mg, and (f) Bi showing results from that elemental analysis, for the metal member obtained from Example 2 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention.

[0030] FIG. 6 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 2 after removing components of the metal bath in accordance with the method of manufacturing a metal member according to the embodiment of the present invention; and (b) a SEM micrograph of an enlarged portion of (a).

[0031] FIG. 7 shows (a) an X-ray diffraction spectrum; and (b) a spectrum from energy dispersive X-ray analysis (EDX) of the metal member obtained in Example 2 after removing components of the metal bath, for the method of manufacturing a metal member according to the embodiment of the present invention.

[0032] FIG. 8 shows an X-ray diffraction spectrum of a metal member from Example 3 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention.

[0033] FIG. 9 shows (a) a micrograph from scanning electron microscopy (SEM), showing the range of elemental analysis by energy dispersive X-ray spectroscopy (EDS); elemental maps of (b) V, (c) Fe, (d) Ni, (e) Cr, and (f) Co showing results from that elemental analysis, for the metal material from Example 3 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention.

[0034] FIG. 10 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 3 after removing components of the metal bath in accordance with the method of manufacturing a metal member according to the embodiment of the present invention; and (b) a SEM micrograph of an enlarged portion of (a).

[0035] FIG. 11 shows an X-ray diffraction spectrum of the metal member obtained from Example 3 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention.

[0036] FIG. 12 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 4 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention; (b) a SEM micrograph of an enlarged portion of (a) showing the range of elemental analysis by energy dispersive X-ray spectroscopy (EDS); elemental maps of (c) Cr; (d) Mn, (e) Fe, (f) Co, and (f) Ni showing results from that elemental analysis.

[0037] FIG. 13 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 4 after removing components of the metal bath in accordance with the method of manufacturing a metal member according to the embodiment of the present invention; and (b) a SEM micrograph of an enlarged portion of (a).

[0038] FIG. 14 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member after removing components of the metal bath obtained from Example 4 at a temperature of the metal bath of 693 K in accordance with a method of manufacturing a metal member according to an embodiment of the present invention.

[0039] FIG. 15 shows a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 5 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention.

[0040] FIG. 16 shows (a) an enlarged portion of FIG. 15 of the micrograph from scanning electron microscopy (SEM) of the metal member obtained from Example 5 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention, showing the range of elemental analysis by energy dispersive X-ray spectroscopy (EDS); elemental maps of (b) Bi, (c) Ni, and (d) Mo showing results from that elemental analysis.

[0041] FIG. 17 shows a micrograph from scanning electron microscopy (SEM) of the metal member after removing components of the metal bath obtained from Example 5 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention.

[0042] FIG. 18 shows a micrograph from scanning electron microscopy (SEM) of the metal members (a) Mo94.4Ni5.6; (b) Mo52.4Ni47.6; (c) Mo25Ni75; and (d) Mo20.2Ni79.8 after removing components of the metal bath obtained from Example 5 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention.

[0043] FIG. 19 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 6 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention; (b) a SEM micrograph of an enlarged portion of (a); elemental maps of (c) Mg, (d) Fe, (e) Al+Fe, and (f) Al showing results from that elemental analysis by energy dispersive X-ray spectroscopy (EDS).

[0044] FIG. 20 shows a micrograph from scanning electron microscopy (SEM) of the metal member after removing components of the metal bath obtained from Example 6 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention.

[0045] FIG. 21 shows a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 7 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention.

[0046] FIG. 22 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member after removing components of the metal bath obtained from Example 8 in accordance with the method of manufacturing a metal member according to the embodiment of the present invention; (b) a SEM micrograph of an enlarged portion of (a); and (c) an X-ray diffraction spectrum.

[0047] FIG. 23 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 9 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention; and elemental maps of (b) Fe, (c) Co, and (d) Mg showing results from elemental analysis by energy dispersive X-ray spectroscopy (EDS).

[0048] FIG. 24 shows (a) a micrograph from scanning electron microscopy (SEM) of a metal member obtained from Example 10 in accordance with a method of manufacturing a metal member according to an embodiment of the present invention; and elemental maps of (b) Co, (c) Ni, and (d) Bi showing results from elemental analysis by energy dispersive X-ray spectroscopy (EDS).DETAILED DESCRIPTION OF THE INVENTIONA Method of Manufacturing a Metal Member According to a First Embodiment of the Invention

[0049] A first embodiment of the invention will be described below based on Examples and the like.

[0050] In a method of manufacturing a metal member according to the first embodiment of the present invention, a metal material consisting of a compound, an alloy, or a non-equilibrium alloy and having a second component and a third component is first prepared in a metal-material preparation step. A metal bath having a first component and the third component is prepared in a metal-bath preparation step.

[0051] Here, the first component and the second component are mutually insoluble. In contrast, the first component and the third component are mutually soluble. The second component and the third component are mutually soluble. In the metal-material preparation step and the metal-bath preparation step, a metal material and a metal bath are prepared so that a substance having a composition in which the third component in the metal material is decreased will be equilibrated with the metal bath. At this time, the composition of the substance to be equilibrated should still include the third component.

[0052] Next, in the metal-bath control step, the prepared metal bath is controlled at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the prepared metal material to a composition in which the third component in the metal material is decreased to reach an equilibrium with the metal bath. At this time, the temperature of the metal bath may be controlled after the metal bath is prepared in the metal-bath preparation step, or the temperature may be controlled while preparing the metal bath.

[0053] Next in the obtaining step, the metal material is immersed into the temperature-controlled metal bath. At this time, the second component contained in the metal material, which is mutually insoluble with the first component contained in the metal bath, does not elute into the metal bath and remains in the metal material. In contrast, the third component contained in both the metal material and the metal bath, which is mutually soluble with the first component and mutually soluble with the second component, can move between the metal material and the metal bath depending on the conditions. Here, in the method of manufacturing a metal member according to the first embodiment of the present invention, the composition to be equilibrated with the metal bath when the metal material is immersed into the metal bath corresponds to a composition in which the third component in the metal material is decreased. Therefore, the third component can be selectively eluted to the metal bath from the metal material until the composition reaches an equilibrium with the metal bath when the metal material is immersed into the metal bath.

[0054] This enables the second component and the third component remaining in the metal material to be repeatedly joined to form nanometer-scale particles, and further enables these particles to be partially joined to self-assemble minute pores having nanometer-scale widths. In this way, a metal member, having not only the second component but also the third component, and consisting of a porous alloy with minute pores in which nanometer-scale particles are partially joined, can be manufactured.

[0055] Specifically, when a porous alloy of A1-xBx is manufactured as a metal member, C1-yBy having a composition to be equilibrated with A1-xBx is determined by using a state diagram and a curve showing the relationship between activity and composition, wherein C represents the first component, and A represents the second component, and B represents the third component, and C1-yBy is used as a metal bath. A1-x′Bx′ (x′>x) with a composition having a content of B larger than that of A1-xBx is selected as a metal material. When the metal material of the selected A1-x′Bx, is immersed into the metal bath of the selected C1-yBy, the third component B in the metal material is eluted into the metal bath so as to establish an equilibrium. This enables A1-x′Bx, to approach A1-xBx. In this case, it is assumed that the amount of the metal bath is present in an amount large enough not to change the composition of the metal bath before or after the reaction. In this way, a porous alloy having the desired composition of A1-xBx or a composition close to A1-xBx can be manufactured as a metal member. It is noted that an amount of the third component B to be eluted into the metal bath relative to the amount of the third component B contained in the metal material [(x′−x) / (1−x)] is preferably determined by considering the pore fraction of the metal member to be manufactured and the retention of that pore fraction, and is preferably about 0.3 to 0.7.

[0056] It is also noted that an adhered admixture derived from the metal bath and including the first component and the third component, which is adhered around the metal member, partially adhered inside the minute pores, or filled inside the minute pores, may be selectively removed in the removal step after the metal member obtained in the obtaining step is lifted from the metal bath. Alternatively, after obtaining a metal member in the obtaining step, the metal bath may be solidified while the metal member remains immersed, and components of the metal bath including the first component and the third component may be selectively removed in the removal step. For example, acidic or alkaline aqueous solutions capable of selectively eluting only the adhered admixture or the components of the metal bath may be used into the removal step. This enables manufacture of a metal member consisting of a porous alloy having nanometer-scale minute pores.

[0057] In the method of manufacturing a metal member according to the first embodiment of the invention, a metal member consisting entirely of a porous alloy or a metal member in which only a surface layer is porous can be obtained, and the pore size and the pore fraction of a porous structure to be manufactured can also be varied by adjusting the temperature of the metal bath and / or the immersion time of the metal material.Example 1

[0058] A porous alloys having a composition close to Fe75Ni25 (the numbers in the subscript represent a composition ratio. The same shall apply hereafter.) was manufactured as a metal member. A metal bath having a composition of (Mg0.5Bi0.5)98.5Ni1.5 was prepared as a metal bath having a composition to be equilibrated with Fe75Ni25. An alloy consisting of (Fe0.75Ni0.25)50Ni50=Fe37.5Ni62.5 and having a composition with a content of Ni larger than that of Fe75Ni25 was prepared as a metal material. In this case, the first components are Mg and Bi, and the second component is Fe, and the third component is Ni.

[0059] It is noted that the metal material was manufactured under an atmosphere of pure argon gas by the arc melting method using Fe and Ni as raw materials to achieve a composition of Fe37.5Ni62.5. The metal bath was manufactured by placing Mg, Bi, and Ni in a crucible so as to give a composition of (Mg0.5Bi0.5)98.5Ni1.5 under an atmosphere of pure argon gas, and heating it to 1023 K. Results from X-ray diffraction analysis of the metal material are shown in FIG. 1, and a micrograph from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the metal material are shown in FIG. 2.

[0060] The metal material was immersed into the metal bath maintained at 1023 K for 30 minutes. In this case, the metal bath was controlled below the lowest value (1440° C.) of liquidus-line temperatures within a compositional variation range from the composition Fe37.5Ni62.5 of the metal material to the composition Fe75Ni25 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. A micrograph from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the resulting metal member are shown in FIG. 3.

[0061] The dark portions shown in FIGS. 3(a) and 3(b) correspond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in FIGS. 3(a) and 3(b), the resulting metal member was a porous metal with ligament widths ranging between several μm and 1 μm or less, and had minute pores with widths of less than several μm, and especially had many minute pores with nanometer-scale widths of less than 1 μm, in which the components of the metal bath were filled in the minute pores. As shown in FIGS. 3(c) and 3(d), the resulting metal member was a porous alloy consisting of Fe and Ni.

[0062] Compositional analysis by EDS performed on the ligaments of the resulting metal member showed that they included 67.8% to 73.7% (at %; The same shall apply hereafter.) of Fe with an average of 70.7%, and 26.3% to 32.2% of Ni with an average of 29.3%. These results demonstrated that the resulting metal member was a porous alloy with a composition of Fe70.7Ni29.3 which was closer to the target composition Fe75Ni25 than the composition Fe37.5Ni62.5 of the pre-reacted metal material. These suggest that Ni (the third component) was selectively eluted from the metal material into the metal bath when the metal material was immersed into the metal bath.Example 2

[0063] A porous stainless steel having a composition close to the composition Fe65.8Cr19.4Mo1.5Ni13.4 of an austenitic stainless steel SUS316L was manufactured as a metal member. A metal bath having a composition of (Mg0.75Bi0.25)92Ni7Cr1 was prepared as a metal bath having a composition to be equilibrated with Fe65.8Cr19.4Mo1.5Ni13.4. As a metal material, an alloy consisting of (Fe0.658Cr0.194Mo0.015Ni0.134)30Ni70=Fe19.73Cr5.82Mo0.44Ni74.01 was prepared, which had a composition with a content of Ni larger than that of Fe65.8Cr19.4Mo1.5Ni13.4. In this case, the first component is Mg, and the second components are Fe, Cr, and Mo, and the third component is Ni.

[0064] It is noted that the metal material was manufactured under an atmosphere of pure argon gas by the arc melting method using Fe, Cr, Mo, and Ni as raw materials to achieve a composition of Fe19.73Cr5.82Mo0.44Ni74.01. The metal bath was manufactured by placing Mg, Bi, Ni, and Cr in a crucible to give a composition of (Mg0.75Bi0.25)92Ni7Cr1 under an atmosphere of pure argon gas, and heating it to 1023 K.

[0065] The metal material was immersed into the metal bath maintained at 1023 K for 10 minutes. In this case, the metal bath was controlled below the lowest value of liquidus-line temperatures within a compositional variation range from a composition Fe19.73Cr5.82Mo0.44Ni74.01 of the metal material to a composition Fe65.8Cr19.4Mo1.5Ni13.4 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. A micrograph from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the resulting metal member is shown in FIGS. 4 and 5.

[0066] The dark portions shown in FIGS. 4 and 5(a) correspond to the resulting metal member, and the white portions correspond to the components from the solidified metal bath. As shown in FIGS. 4 and 5(a), the resulting metal member was a porous metal with ligament widths of less than 1 μm, and had many minute pores with nanometer-scale widths of less than 1 μm, in which the components of the metal bath such as Mg and Bi were filled in the minute pores as shown in FIGS. 5(e) and 5(f). As shown in FIGS. 5(b) to 5(d), the resulting metal member was a porous alloy consisting of Fe, Cr, Ni, and Mo.

[0067] The resulting metal member was immersed into an aqueous solution of nitric acid to remove the components of the metal bath. Micrographs from scanning electron microscopy of the metal member after removing the components of the metal bath are shown in FIGS. 6(a) and 6(b), and results from X-ray diffraction and results from energy dispersive X-ray analysis (EDX) are shown in FIGS. 7(a) and 7(b), respectively. As shown in FIGS. 6(a) and 6(b), an adhered admixture derived from the metal bath and adhered around the metal member or filled inside the minute pores was able to be selectively removed by immersion into an aqueous solution of nitric acid. As shown in FIG. 7(a), the metal member had an austenite structure of face-centered cubic lattice (fcc). The results in FIG. 7(b) also showed that the composition of the metal member had 64.7% of Fe, 20.1% of Cr, 13.6% of Ni, and 1.4% of Mo, which was almost consistent with that of an austenitic stainless steel SUS316L. The above results indicate that the present inventors were able to manufacture a porous austenitic stainless steel SUS316L as a metal member.Example 3

[0068] As a metal member, a porous high-entropy alloy with a composition close to that of a high-entropy alloy V15Cr15Fe20Co25Ni25 was manufactured. A metal bath with a composition of (Bi0.5Mg0.5)98.2Ni1.5Cr0.3 was prepared as a metal bath with a composition to be equilibrated with V15Cr15Fe20Co25Ni25. An alloy consisting of (V0.15Cr0.15Fe0.2Co0.25Ni0.25)50Ni50=V7.5Cr7.5Fe10Co12.5Ni62.5 having a composition with a content of Ni larger than that of V15Cr15Fe20Co25Ni25 was prepared as a metal material. In this case, the first component is Mg, and the second components are V, Cr, Fe, and Co, and the third component is Ni.

[0069] The metal material was manufactured under an atmosphere of pure argon gas by the arc melting method using V15Cr15Fe20Co25Ni25 and Ni as raw materials to achieve a composition of V7.5Cr7.5Fe10Co12.5Ni62.5. Further, the metal bath was manufactured by placing Mg, Bi, Ni, and Cr in a crucible so as to give a composition of (Bi0.5Mg0.5)98.2Ni1.5Cr0.3 under an atmosphere of pure argon gas, and heating it to 1023 K. Results from X-ray diffraction of the metal material are shown in FIG. 8, and a micrograph from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the metal material are shown in FIG. 9.

[0070] The metal material was immersed into the metal bath maintained at 1023 K for 30 minutes. In this case, the metal bath was controlled below the lowest value of liquidus-line temperatures within a compositional variation range from the composition V7.5Cr7.5Fe10Co12.5Ni62.5 of the metal material to the composition V15Cr15Fe20Co25Ni25 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. In addition, the metal member after cooled was immersed into an aqueous solution of nitric acid to remove the components of the metal bath. Micrographs from scanning electron microscopy of the metal member after removing the components of the metal bath are shown in FIGS. 10(a) and 10(b), and results from X-ray diffraction are shown in FIG. 11.

[0071] As shown in FIGS. 10(a) and 10(b), an adhered admixture derived from the metal bath and adhered around the metal member or filled inside the minute pores was able to be selectively removed by immersion into the aqueous solution of nitric acid. Further, the resulting metal member was a porous metal with ligament widths of 1 μm or less, and had many minute pores with nanometer-scale widths of less than 1 μm. As shown in FIG. 11, the metal member had an austenite structure of face-centered cubic lattice (fcc).

[0072] Energy dispersive X-ray analysis (EDX) performed on the resulting metal member showed that the composition of the metal member had 14.9% of V, 11.9% of Cr, 18.8% of Fe, 21.3% of Co, and 33.2% of Ni. These results demonstrated that the resulting metal member was a porous high-entropy alloy having a composition of V14.9Cr11.9Fe18.8Co21.3Ni33.2, which is closer to the target composition of V15Cr15Fe20Co25Ni25 than the composition V7.5Cr7.5Fe10Co12.5Ni62.5 of the metal material before the reaction.Example 4

[0073] As a metal member, a porous high-entropy alloy having a composition close to that of a high-entropy alloy V20Cr20Fe20Co20Ni20 was manufactured. A metal bath having a composition Bi95.2Ni1.3Mn3.5 was prepared as a metal bath having a composition to be equilibrated with Cr20Mn20Fe20Co20Ni20. An alloy consisting of (Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)50Ni50=Cr10Mn10Fe10Co10Ni60 having a composition with a content of Ni larger than that of Cr20Mn20Fe20Co20Ni20 was prepared as a metal material. In this case, the first component is Bi, and the second components are Cr, Fe, and Co, and the third component is Ni.

[0074] The metal material was manufactured by the arc melting method under an atmosphere of pure argon gas using Cr20Mn20Fe20Co20Ni20 and Ni as raw materials to achieve a composition of Cr10Mn10Fe10Co10Ni60, and then further cold rolled to a thickness of about 100 microns, and then subjected to homogenization treatment at 1273 K for 12 hours. The metal bath was manufactured under an atmosphere of pure argon gas by inserting Bi, Ni, and Mn, which were pre-weighed so as to give a composition of Bi95.2Ni1.3Mn3.5, into a crucible, and heating it at 1373 K or above to assure that all the metals were dissolved, and then lowering the temperature to 823 K.

[0075] The metal material was immersed into the metal bath maintained at 823 K for 30 minutes. In this case, the metal bath was controlled below the lowest value of liquidus-line temperatures within a compositional variation range from the composition Cr10Mn10Fe10Co10Ni60 of the metal material to the composition Cr20Mn20Fe20Co20Ni20 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. A micrograph from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the metal member after cooling are shown in FIG. 12.

[0076] The dark portions shown in FIGS. 12(a) and 12(b) correspond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in FIGS. 10(c) to 10(g), Cr, Mn, Fe, Co, and Ni were uniformly distributed in the ligament portions of the resulting metal member.

[0077] The metal member after cooled as shown in FIG. 12 was immersed into an aqueous solution of nitric acid to remove the components of the metal bath. Micrographs from scanning electron microscopy of the metal member after removal of the components of the metal bath is shown in FIG. 13. As shown in FIG. 13, an adhered admixture derived from the metal bath and adhered around the metal member or filled inside the minute pores was able to be selectively removed by immersion into the aqueous solution of nitric acid. Further, the resulting metal member was a porous metal with ligament widths of about 0.3 to 0.5 μm, and had many minute pores with nanometer-scale widths of less than 1 μm.

[0078] Energy dispersive X-ray analysis (EDX) performed on the resulting metal member indicated that the resulting metal member had Cr13.4Mn16.5Fe26.6Co19.7Ni23.8. These results demonstrated that the resulting metal member was a porous high-entropy alloy having a composition closer to the target composition Cr20Mn20Fe20Co20Ni20 than the composition Cr10Mn10Fe10Co10Ni60 of the metal material before the reaction.

[0079] Next, a porous high-entropy alloy having a composition close to Cr20Mn20Fe20Co20Ni20 was manufactured as in FIGS. 12 and 13 except that the metal material had the same composition, but the metal baths had different compositions and different temperatures. The manufacturing conditions are summarized and shown in Table 1. A micrograph from scanning electron microscopy of the resulting metal member when the temperature of the metal bath in Table 1 was 693 K is shown in FIG. 14. It is noted that Table 1 also shows results of FIGS. 12 and 13.TABLE 1Temper-ImmersionaturetimeComposition ofExamples of composition of(K)(min.)metal bathresulting porous metal69330Bi98.5Ni0.5Mn1.0Cr17.4Mn12.6Fe29.2Co22.2Ni18.672330Bi98.0Ni0.5Mn1.5Cr17.9Mn14.0Fe25.3Co22.0Ni20.877330Bi96.4Ni1.1Mn2.5Cr15.0Mn15.8Fe26.2Co20.3Ni22.782330Bi95.2Ni1.3Mn3.5Cr13.4Mn16.5Fe26.6Co19.7Ni23.8

[0080] As shown in FIG. 14, a porous high-entropy alloy was obtained even when the temperature of the metal bath was the lowest as shown in Table 1. Considering the results shown in FIGS. 12 to 14, it can be said that porous high-entropy alloys having compositions close to the target composition of Cr20Mn20Fe20Co20Ni20 were obtained in all the cases of Table 1. Further, as comparing FIG. 13(b) with FIG. 14, the metal member has narrower ligaments and finer structures in FIG. 14. This suggests that a lower temperature of the metal bath may result in a finer porous metal and a larger surface area.Example 5

[0081] As a metal member, a porous body of a Mo—Ni binary alloy used as a catalyst for hydrogen generation was manufactured. The Mo—Ni binary alloy, which may be present as an Ni solid solution phase, a MoNi4 phase, a MoNi3 phase, a MoNi phase, or an Mo solid solution phase, is likely to show improved catalytic performance by making it a porous body.

[0082] First, the present inventors manufactured a porous intermetallic compound having a composition close to that of the intermetallic compound MoNi4. A metal bath having a composition of Bi82Ni18 was prepared as a metal bath having a composition to be equilibrated with MoNi4. An alloy consisting of (Mo0.2Ni0.8)50Ni50=Mo10Ni90, having a composition with a content of Ni larger than that of MoNi4 was prepared as a metal material. In this case, the first component is Bi, and the second component is Mo, and the third component is Ni.

[0083] The metal material was manufactured by the arc melting method under an atmosphere of pure argon gas using Ni and Mo as raw materials to achieve a composition of Mo10Ni90. The metal bath was manufactured under an atmosphere of pure argon gas by inserting Bi and Ni, which were pre-weighed so as to give a composition of Bi82Ni18, into a crucible, and heating it at 1373 K or above to assure that all the metals were dissolved, and then lowering the temperature to 1073 K.

[0084] The metal material was immersed into the metal bath maintained at 1073 K for 10 minutes. In this case, the metal bath is controlled below the lowest value (about 1400° C.) of liquidus-line temperatures within a compositional variation range from the composition Mo10Ni90 of the metal material to the composition MoNi4 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. A micrograph from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the resulting metal member are shown in FIGS. 15 and 16.

[0085] The dark portions shown in FIGS. 15 and 16(a) correspond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in FIGS. 15 and 16(a), the resulting metal member was a porous metal with ligament widths of less than 1 μm, and had many minute pores with nanometer-scale widths of less than 1 μm, in which the components of the metal bath such as Bi and Ni were filled in the minute pores as shown in FIGS. 16(b) and 16(c). Further, as shown in FIGS. 16(c) and 16(d), the resulting metal member was a porous alloy consisting of Ni and Mo.

[0086] The resulting metal member was immersed in a mixed aqueous solution of hydrochloric acid (HCl) and hydrogen peroxide (H2O2) to remove the components of the metal bath. A micrograph from scanning electron microscopy of the metal member after removing the components of the metal bath is shown in FIG. 17. As shown in FIG. 17, an adhered admixture derived from the metal bath and adhered around the metal member or filled inside the minute pores was able to be selectively removed by immersion into aqueous hydrochloric acid (HCl) and hydrogen peroxide (H2O2). The results from elemental analysis by EDS indicated that the metal member shown in FIG. 17 had 74% of Ni and 26% of Mo.

[0087] Next, porous bodies of Mo—Ni binary alloys were manufactured as in FIGS. 15 to 17 except that the composition of the metal material, the composition of the metal bath, the temperature of the metal bath, and the immersion time into the metal bath were varied. The manufacturing conditions are summarized and shown in Table 2. Micrographs from scanning electron microscopy of the metal members (the resulting porous metals) manufactured as in Table 2 are shown in FIGS. 18(a) to 18(d). It is noted that the constituent phases of each manufactured metal members were determined from the results of X-ray diffraction or elemental analysis by EDS.TABLE 2BathImmersionPrecursorBathtemperaturetimeResultingalloycomposition(K)(min.)porous metalMo20Ni80Bi99.5Ni0.5102310Mo94.4Ni5.6(Mo solidsolution phase)Mo20Ni80Bi85.4Ni14.6107360Mo52.4Ni47.6(MoNi phase)Mo10Ni90Bi83Ni17107360Mo25Ni75(MoNi3 phase)Mo10Ni90Bi81.5Ni18.5107360Mo20.2Ni79.8(MoNi4 phase)

[0088] As shown in Table 2 and FIG. 18, respective porous metals having compositions close to the corresponding target compositions of the Mo solid solution phase, the MoNi phase, the MoNi3 phase, or the MoNi4 phase were obtained in all of the cases.Example 6

[0089] A porous Fe—Al intermetallic compound having a composition close to Fe70Al30 was manufactured as a metal member. A metal bath having a composition of Mg99Ali was prepared as a metal bath having a composition to be equilibrated with Fe70Al30. An alloy consisting of Fe25Al75 having a composition with a content of Al larger than that of Fe70Al30 was prepared as a metal material. In this case, the first component is Mg, and the second component is Fe, and the third component is Al.

[0090] The metal material was manufactured by the arc melting method under an atmosphere of pure argon gas using Fe and Al as raw materials to achieve a composition of Fe25Al75. The metal bath was manufactured by placing Mg and Al in a crucible so as to give a composition of Mg99Al1 under an atmosphere of pure argon gas, and heating it to 1073 K.

[0091] The metal material was immersed into the metal bath maintained at 1073 K for 10 minutes. In this case, the metal bath is controlled below the lowest value (about 1170° C.) of liquidus-line temperatures within a compositional variation range from the composition Fe25Al75 of the metal material to the composition Fe70Al30 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. Micrographs from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the resulting metal member are shown in FIGS. 19(a) to 19(f).

[0092] The dark portions shown in FIGS. 19(a) and 19(b) correspond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in FIG. 15, the resulting metal member was a porous metal with ligament widths of less than 3 μm, and had many minute pores with widths of less than 3 μm, in which the component Mg of the metal bath was filled in the minute pores as shown in FIG. 19(c). Further, as shown in FIGS. 19(d) to 19(f), the resulting metal member was a porous alloy consisting of Fe and Al.

[0093] The resulting metal member was immersed into concentrated nitric acid (HNO3) to remove the components of the metal bath. A micrograph from scanning electron microscopy of the metal member after removing the components of the metal bath is shown in FIG. 20. As shown in FIG. 20, an adhered admixture derived from the metal bath and adhered around the metal member or filled inside the minute pores was able to be selectively removed by immersion into concentrated nitric acid (HNO3). The results from elemental analysis by EDS indicated that the metal member shown in FIG. 20 had 70% of Fe and 30% of Al.Example 7

[0094] A porous alloy having a composition close to Fe70Ni30 was manufactured as a metal member. A metal bath having a composition of Bi97Ni3 was prepared as a metal bath having a composition to be equilibrated with Fe70Ni30. An alloy consisting of (Fe0.70Ni0.30)30Ni70=Fe21Ni79 and having a composition with a content of Ni larger than that of Fe70Ni30 was prepared as a metal material. In this case, the first component is Bi, and the second component is Fe, and the third component is Ni.

[0095] The metal material was manufactured by the arc melting method under an atmosphere of pure argon gas using Fe and Ni as raw materials so as to give a composition of Fe21Al79. The metal bath was manufactured by placing Bi in a crucible under an atmosphere of pure argon gas, and heating it to 1023 K.

[0096] The metal material was immersed into the metal bath maintained at 1023 K for 60 minutes. In this case, the metal bath was controlled below the lowest value (about 1440° C.) of liquidus-line temperatures within a compositional variation range from the composition Fe21Ni79 of the metal material to the composition Fe70Ni30 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. A micrograph from scanning electron microscopy of the resulting metal member is shown in FIG. 21.

[0097] The dark portions shown in FIG. 21 correspond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in FIG. 21, the resulting metal member was a porous metal with ligament widths of less than 3 μm, and had many minute pores with widths of less than 3 μm, in which the components of the metal bath were filled in the minute pores. The results from elemental analysis by EDS indicated that the metal member shown in FIG. 21 had 73% of Fe and 27% of Ni.Example 8

[0098] A porous alloy having a composition close to a composition Ti50Ni50 of a shape memory alloy nickel-titanium was manufactured as a metal member. A metal bath having a composition of Mg97Ni3 was prepared as a metal bath having a composition to be equilibrated with Ti50Ni50. An alloy consisting of (Ti0.5Ni0.5)50Ni50=Ti25Ni75 and having a composition with a content of Ni larger than that of Ti50Ni50 was prepared as a metal material. In this case, the first component is Mg, and the second component is Ti, and the third component is Ni.

[0099] The metal material was manufactured by alloying Ti and Ni as raw materials under an atmosphere of pure argon gas using the arc melting method so as to give a composition of Ti25Ni75, and performing homogenization in an electric furnace at 1473 K for 1 hour under an atmosphere of pure argon gas. The metal bath was manufactured by placing Mg and Ni in a crucible so as to give a composition of Mg97Al3 under an atmosphere of pure argon gas, and heating it to 1023 K.

[0100] The metal material was immersed into the metal bath maintained at 1023 K for 30 minutes. In this case, the metal bath was controlled below the lowest value of liquidus-line temperatures within a compositional variation range from the composition Ti25Ni75 of the metal material to the composition Ti50Ni50 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. After cooling, the resulting metal members were immersed in an aqueous solution of nitric acid to remove the components of the metal bath.

[0101] Micrographs from scanning electron microscopy of the metal member after removing the components of the metal bath are shown in FIGS. 22(a) and 22(b), and results from X-ray diffraction are shown in FIG. 22(c). As shown in FIGS. 22(a) and 22(b), the resulting metal member was a porous metal with ligament widths of several 100 nm. As shown in FIG. 22(c), the B2 austenite phase was observed, indicating that the resulting metal member was a shape memory alloy. The results from elemental analysis by EDS showed that the resulting metal member had 52.5 at % of Ti and 47.5 at % of Ni.Example 9

[0102] A co-continuous composite material of an Fe—Co alloy having a composition of Fe50Co50 and Mg was manufactured as a metal member. A metal bath having a composition of Mg99Co1 was prepared as a metal bath having a composition to be equilibrated with Fe50Co50. An alloy consisting of (Fe0.5Co0.5)40Co60=Fe20Co80 and having a composition with a content of Co larger than that of Fe50Co5 was prepared as a metal material. In this case, the first component is Mg, and the second component is Fe, and the third component is Co.

[0103] The metal material was manufactured by the arc melting method under an atmosphere of pure argon gas using Fe and Co as raw materials so as to give a composition of Fe20Co80. The metal bath was manufactured by placing Mg and Co in a crucible so as to give a composition of Mg99Co1 under an atmosphere of pure argon gas, and heating it to 1073 K.

[0104] The metal material was immersed into the metal bath maintained at 1073 K for 10 minutes. In this case, the metal bath was controlled below the lowest value of liquidus-line temperatures within a compositional variation range from the composition Fe20Co80 of the metal material to the composition Fe50Co50 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. A micrograph from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the resulting metal member are shown in FIG. 23.

[0105] The dark portions shown in FIG. 23 correspond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in FIG. 23, the resulting metal member was a porous metal with ligament widths of several m, and had many minute pores with widths of less than several μm. The components of the metal bath, mainly Mg, were found to be filled in the minute pores, showing that the whole material was a composite material of an Fe—Co alloy and Mg. The results from elemental analysis by EDS shown in FIGS. 23(b) and 23(c) indicated that the ligament portions of the metal member had 44.5 at % of Fe and 55.5 at % of Co.Example 10

[0106] A co-continuous composite material of a Co—Ni alloy having a composition of Co50Ni50 and a Bi alloy was manufactured as a metal member. A metal bath having a composition of Bi88.8Ni11Co0.2 was prepared as a metal bath having a composition to be equilibrated with Co50Ni50. An alloy consisting of (Co0.5Ni0.5)50Ni50=Co25Ni75 and having a composition with a content of Ni larger than that of Co50Ni50 was prepared as a metal material. In this case, the first component is Bi, and the second component is Co, and the third component is Ni.

[0107] The metal material was manufactured by alloying Co and Ni as raw materials under an atmosphere of pure argon gas using the arc melting method so as to give a composition of Co25Ni75, and cold-rolled to a thickness of about 100 m, and then subjected to homogenization treatment in an electric furnace at 1273 K for 12 hours under an atmosphere of pure argon gas. The metal bath was manufactured under an atmosphere of pure argon gas by inserting Bi, Ni, and Co, which were pre-weighed to give a composition of Bi88.8Ni11Co0.2, into a crucible, and heating it at 1373 K or above to assure that all the metals were dissolved, and then lowering the temperature to 873 K.

[0108] The metal material was immersed into the metal bath maintained at 873 K for 30 minutes. In this case, the metal bath was controlled below the lowest value of liquidus-line temperatures within a compositional variation range from the composition Co25Ni75 of the metal material to the composition Co50Ni50 to be equilibrated with the metal bath. After immersing the metal material into the metal bath, the resulting metal member was removed from the metal bath and cooled. A micrograph from scanning electron microscopy and results from elemental analysis by energy dispersive X-ray spectroscopy (EDS) of the resulting metal member are shown in FIG. 24.

[0109] The dark portions shown in FIG. 24 correspond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in FIG. 24, the resulting metal member was a porous metal with ligament widths of 755 nm on average, and had many minute pores with widths of less than several μm. Further, the minute pores were found to be filled mainly with the component Bi of the metal bath, showing that the whole material was a composite material of a Co—Ni alloy and a Bi alloy. The results from elemental analysis by EDS shown in FIGS. 24(b) and 24(c) indicated that the ligament portions of the metal member had 49.0 at % of Co and 51.0 at % of Ni.A Method of Manufacturing a Metal Member According to a Second Embodiment of the Invention

[0110] A method of manufacturing a metal member according to a second embodiment of the invention comprises a metal-material preparation step, a metal-bath preparation step, a metal-bath control step, and an obtaining step, as in the method of manufacturing a metal member according to the first embodiment of the invention. It may further comprise a removal step.

[0111] In the following descriptions, the present inventors will mainly describe the configurations which differ from the method of manufacturing a metal member according to the first embodiment of the present invention, and omit those for the configurations, effects, and the like which overlap with the method of manufacturing a metal member according to the first embodiment of the present invention.

[0112] In the method of manufacturing a metal member according to the second embodiment of the invention, the metal-material preparation step and the metal-bath preparation step comprise: preparing a metal material and a metal bath so that a substance having a composition in which a third component is increased in the metal material is equilibrated with the metal bath. Further, the metal-bath control step comprises: controlling the prepared metal bath at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the prepared metal material to a composition in which the third component in the metal material is increased to reach an equilibrium with the metal bath.

[0113] In the method of manufacturing a metal member according to the second embodiment of the present invention, a composition to be equilibrated with the metal bath corresponds to a composition in which a third component in the metal material is increased when a metal material is immersed into the metal bath. Therefore, the third component contained in the metal bath can be selectively diffused into the metal material until the composition of the metal material reaches an equilibrium with the metal bath when the metal material is immersed into the metal bath. In this case, the third component will be gradually diffused into the metal material until the metal material has a uniform composition. In this way, a metal member containing not only the second component but also the third component can be manufactured.

[0114] In the method of manufacturing a metal member according to the second embodiment of the invention, the diffusion state of the third component into the metal material can be controlled by the time for the metal material to be immersed into the metal bath. Therefore, a metal member in which a surface of the metal material before immersion into the metal bath is covered with the third component can be manufactured as in a plating process, for example, by decreasing the immersion time into the metal bath. Moreover, a metal member having a surface layer with a high content of the third component and a metal member having an overall uniform composition can be manufactured by increasing the immersion time into the metal bath.

[0115] Specifically, when a porous alloy of A1-xBx is manufactured as a metal member, C1-yBy having a composition to be equilibrated with A1-xBx is determined by using a state diagram and a curve showing the relationship between activity and composition, wherein C represents the first component, and A represents the second component, and B represents the third component, and C1-yBy is used as a metal bath. A1-x′Bx′ (x′>x) with a composition having a content of B larger than that of A1-xBx is selected as a metal material. When the metal material of the selected A1-x′Bx, is immersed into the metal bath of the selected C1-yBy, the third component B in the metal bath is diffused into the metal material to reach an equilibrium state. This enables A1-x′Bx, to approach A1-xBx. In this case, it is assumed that the amount of the metal bath is present in an amount large enough not to change the composition of the metal bath before or after the reaction. In this way, a porous alloy having the desired composition of A1-xBx or a composition close to A1-xBx can be manufactured as a metal member.

[0116] In the method of manufacturing a metal member according to the second embodiment of the invention, the metal material may have no third component, but only a second component. Even in this case, the third component contained in the metal bath will be diffused into the metal material. Therefore, a metal member containing not only the second component but also the third component can be manufactured. Specifically, an alloy having a composition of A1-xBx or a composition close to A1-xBx can be manufactured as a metal member by using A as a metal material and immersing it in a metal bath of C1-yBy.

[0117] In the method of manufacturing a metal member according to the second embodiment of the invention, a metal material prepared in the metal-material preparation step may be an ingot or a porous material with minute pores. When the metal material is porous, a metal member consisting of a porous alloy having an overall uniform composition and minute pores can be manufactured by increasing the immersion time into the metal bath. Alternatively, a metal member in which a surface of the metal material before immersion into the metal bath is covered with the third component can be manufactured as in a plating process by decreasing the immersion time into the metal bath.

[0118] Further, the metal material may have cracks on a surface thereof. In this case, the cracks on the surface of the metal material can be filled with the third component by decreasing the immersion time into the metal bath to manufacture a metal member with cracks thereof filled with the third component.

Claims

1. A method of manufacturing a metal member, the method comprising:a metal-material preparation step of preparing a metal material consisting of a compound, an alloy, or a non-equilibrium alloy and having a second component and a third component, the second component being mutually insoluble with a first component, the third component being mutually soluble with the first component and mutually soluble with the second component;a metal-bath preparation step of preparing a metal bath having the first component and the third component;a metal-bath control step of controlling the metal bath at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition in which the third component in the metal material is decreased or increased to reach an equilibrium with the metal bath; andan obtaining step of obtaining a metal member having the second component and the third component by immersing the metal material prepared in the metal-material preparation step into the metal bath temperature-controlled at the metal-bath control step to selectively elute the third component contained in the metal material into the metal bath, or selectively diffusing the third component contained in the metal bath into the metal material.

2. The method of manufacturing a metal member according to claim 1, whereinthe metal-bath control step comprises controlling the metal bath at a temperature lower than the lowest value of the liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition in which the third component in the metal material is decreased to reach an equilibrium with the metal bath, andthe obtaining step comprises obtaining the metal member consisting of a porous alloy having minute pores by immersing the metal material into the metal bath to selectively elute the third component contained in the metal material into the metal bath.

3. The method of manufacturing a metal member according to claim 2, wherein the porous alloy consists of partially joined nanometer-scale particles.

4. The method of manufacturing a metal member according to claim 1, whereinthe metal-bath control step comprises controlling the metal bath at a temperature lower than the lowest value of the liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition in which the third component in the metal material is increased to reach an equilibrium with the metal bath, andthe obtaining step comprises obtaining the metal member by immersing the metal material into the metal bath to selectively diffuse the third component contained in the metal bath into the metal material.

5. A method of manufacturing a metal member, the method comprising:a metal-material preparation step of preparing a metal material having a second component mutually insoluble with a first component;a metal-bath preparation step of preparing a metal bath having the first component and a third component, the third component being mutually soluble with the first component and mutually soluble with the second component;a metal-bath control step of controlling the metal bath prepared in the metal-bath preparation step at a temperature lower than the lowest value of liquidus-line temperatures within a compositional variation range from the composition of the metal material to a composition in which the third component in the metal material is increased to reach an equilibrium with the metal bath; andan obtaining step of obtaining a metal member having the second component and the third component by immersing the metal material prepared in the metal-material preparation step into the metal bath temperature-controlled at the metal-bath control step to selectively diffuse the third component contained in the metal bath into the metal material.

6. The method of manufacturing a metal member according to claim 4, whereinthe metal-material preparation step comprises preparing the metal material which is porous;the obtaining step comprises obtaining the metal member consisting of a porous alloy having minute pores.

7. The method of manufacturing a metal member according to claim 1, whereinthe metal-material preparation step and the metal-bath preparation step comprise preparing the metal material and the metal bath so that a substance having a composition in which a third component is decreased or increased in the metal material is equilibrated with the metal bath.

8. The method of manufacturing a metal member according to claim 1, comprising:a removal step of selectively removing an adhered admixture adhered to the metal member and including the first component and the third component, after the metal member obtained in the obtaining step is lifted from the metal bath.

9. The method of manufacturing a metal member according to claim 8, wherein the removal step comprises selectively removing only the adhered admixture with an acidic or alkaline aqueous solution.

10. The method of manufacturing a metal member according to claim 1, whereinthe first component includes at least any one of Mg, Bi, Pb, Cu, and Ag;the second component includes at least one of Fe, Cr, V, Co, Mo, Ni, Zr, Ta, W, Hf, Nb, and Ti; andthe third component includes at least any one of Ni, Pd, Al, Ag, Cu, Mn, and Co.

11. A metal member,having:a second component mutually insoluble with a first component, anda third component mutually soluble with the first component and mutually soluble with the second component; andconsisting of a porous alloy with minute pores in which nanometer-scale particles are partially joined.

12. The metal member according to claim 11, whereinthe first component includes at least any one of Mg, Bi, Pb, Cu, and Ag;the second component includes at least one of Fe, Cr, V, Co, Mo, Ni, Zr, Ta, W, Hf, Nb, and Ti; andthe third component includes at least any one of Ni, Pd, Al, Ag, Cu, Mn, and Co.

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