Method of Manufacturing Metal Member and Metal Member Therefrom

The present invention relates to a method of manufacturing a metal member and the metal member therefrom.

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.

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).

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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.

Specifically, when a porous alloy of ABis manufactured as a metal member, CBhaving a composition to be equilibrated with ABis 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 CBis used as a metal bath. AB(x′>x) with a composition having a content of B larger than that of ABis selected as a metal material. When the metal material of the selected AB, is immersed into the metal bath of the selected CB, the third component B in the metal material is eluted into the metal bath so as to establish an equilibrium. This enables AB, to approach AB. 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 ABor a composition close to ABcan 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.

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.

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.

A porous alloys having a composition close to FeNi(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 (MgBi)Niwas prepared as a metal bath having a composition to be equilibrated with FeNi. An alloy consisting of (FeNi)Ni=FeNiand having a composition with a content of Ni larger than that of FeNiwas 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.

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 FeNi. The metal bath was manufactured by placing Mg, Bi, and Ni in a crucible so as to give a composition of (MgBi)Niunder 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, 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.

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 FeNiof the metal material to the composition FeNito 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.

The dark portions shown incorrespond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in, 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, the resulting metal member was a porous alloy consisting of Fe and Ni.

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 FeNiwhich was closer to the target composition FeNithan the composition FeNiof 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.

A porous stainless steel having a composition close to the composition FeCrMoNiof an austenitic stainless steel SUS316L was manufactured as a metal member. A metal bath having a composition of (MgBi)NiCrwas prepared as a metal bath having a composition to be equilibrated with FeCrMoNi. As a metal material, an alloy consisting of (FeCrMoNi)Ni=FeCrMoNiwas prepared, which had a composition with a content of Ni larger than that of FeCrMoNi. In this case, the first component is Mg, and the second components are Fe, Cr, and Mo, and the third component is Ni.

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 FeCrMoNi. The metal bath was manufactured by placing Mg, Bi, Ni, and Cr in a crucible to give a composition of (MgBi)NiCrunder an atmosphere of pure argon gas, and heating it to 1023 K.

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 FeCrMoNiof the metal material to a composition FeCrMoNito 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.

The dark portions shown in() correspond to the resulting metal member, and the white portions correspond to the components from the solidified metal bath. As shown in(), 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. As shown in, the resulting metal member was a porous alloy consisting of Fe, Cr, Ni, and Mo.

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, and results from X-ray diffraction and results from energy dispersive X-ray analysis (EDX) are shown in, respectively. As shown in, 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, the metal member had an austenite structure of face-centered cubic lattice (fcc). The results inalso 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.

As a metal member, a porous high-entropy alloy with a composition close to that of a high-entropy alloy VCrFeCoNiwas manufactured. A metal bath with a composition of (BiMg)NiCrwas prepared as a metal bath with a composition to be equilibrated with VCrFeCoNi. An alloy consisting of (VCrFeCoNi)Ni=VCrFeCoNihaving a composition with a content of Ni larger than that of VCrFeCoNiwas 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.

The metal material was manufactured under an atmosphere of pure argon gas by the arc melting method using VCrFeCoNiand Ni as raw materials to achieve a composition of VCrFeCoNi. Further, the metal bath was manufactured by placing Mg, Bi, Ni, and Cr in a crucible so as to give a composition of (BiMg)NiCrunder an atmosphere of pure argon gas, and heating it to 1023 K. Results from X-ray diffraction of the metal material are shown in, 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.

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 VCrFeCoNiof the metal material to the composition VCrFeCoNito 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, and results from X-ray diffraction are shown in.

As shown in, 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, the metal member had an austenite structure of face-centered cubic lattice (fcc).

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 VCrFeCoNi, which is closer to the target composition of VCrFeCoNithan the composition VCrFeCoNiof the metal material before the reaction.

As a metal member, a porous high-entropy alloy having a composition close to that of a high-entropy alloy VCrFeCoNiwas manufactured. A metal bath having a composition BiNiMnwas prepared as a metal bath having a composition to be equilibrated with CrMnFeCoNi. An alloy consisting of (CrMnFeCoNi)Ni=CrMnFeCoNihaving a composition with a content of Ni larger than that of CrMnFeCoNiwas 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.

The metal material was manufactured by the arc melting method under an atmosphere of pure argon gas using CrMnFeCoNiand Ni as raw materials to achieve a composition of CrMnFeCoNi, 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 BiNiMn, 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.

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 CrMnFeCoNiof the metal material to the composition CrMnFeCoNito 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.

The dark portions shown incorrespond to the resulting metal member, and the white portions correspond to the solidified components of the metal bath. As shown in, Cr, Mn, Fe, Co, and Ni were uniformly distributed in the ligament portions of the resulting metal member.

The metal member after cooled as shown inwas 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. As shown in, 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.