EP4671417A1

EP4671417A1 - METHOD FOR PRODUCING A MULTI-COMPONENT ALLOY PLATING FILM AND MULTI-COMPONENT ALLOY PLATING FILM

Info

Publication number: EP4671417A1
Application number: EP24760299.8A
Authority: EP
Inventors: Kazuhiro Fukami; Yuki Murakami; Kuniaki Murase
Original assignee: Kyoto University NUC
Current assignee: Kyoto University NUC
Priority date: 2023-02-21
Filing date: 2024-02-19
Publication date: 2025-12-31
Also published as: WO2024177000A1; JPWO2024177000A1

Abstract

A method for forming a multi-component alloy plating film includes formation step of forming a multi-component alloy plating film by electrodeposition with use of a plating solution that includes a plurality of types of metal elements, an ionic liquid, and water, the multi-component alloy plating film containing the plurality of types of metal elements as principal components. The plating solution has a non-polar domain and a polar domain, the polar domain having a volume of not more than 10 when the non-polar domain has a volume of 1. With this configuration, the degree of flexibility of the types of metal elements to be used is increased and the composition is controlled, so that a multi-component alloy plating film is formed at a practical processing speed.

Description

Technical Field

The present invention relates to a multi-component alloy plating film, and a method for forming a multi-component alloy plating film.

Background Art

In recent years, attention has been given to multi-component alloys which include a plurality of types of principal metal elements, unlike conventional alloys which include a main metal as the matrix phase and a trace amount of an auxiliary metal element within the matrix phase. Due to variations in the content ratios of the constituent metal elements, multi-component alloys are expected to have physical properties and/or mechanical properties that differ from those of conventional alloys. As the multi-component alloys, for example, a medium entropy alloy (hereinafter, MEA) which includes not less than three types of principal metal elements in substantially equal ratios, and a high entropy alloy (hereinafter, HEA) which includes not less than five types of principal metal elements in substantially equal ratios.
Since the respective redox potentials of the constituent metal elements of a multi-component alloy are different from each other, it is difficult to cause all the constituent metal elements to be simultaneously deposited to form a plating film of the multi-component alloy in an intended composition. As such, although studies on methods for forming bulk materials have been mainstream regarding MEAs and HEAs until now, research on methods for forming plating films of multi-component alloys has started to be carried out in recent years.
Examples of reports on the formation of plating films of multi-component alloys include Non-Patent Literature 1. Non-Patent Literature 1 indicates that by using a water-in-oil emulsion, where water droplets are included within an oil phase, as a plating solution, a CoNiCu MEA film was formed. The water droplets included in the oil phase of the water-in-oil emulsion contain Co, Ni, and Cu.

Citation List

[Non-patent Literature]

[Non-patent Literature 1]
Y.Murakami et al., Electrochem. Commun., 128, 107057 (2021)

Summary of Invention

Technical Problem

Although indicating that a CoNiCu MEA film was formed, Non-Patent Literature 1 does not disclose a method for using other constituent metal elements to form an MEA film and an HEA film. In particular, when constituent metal elements including Cr are used, it is not easy to control the respective atomic ratios of the constituent metal elements in the resultant plating film to obtain a crystalline plating film, and it is unknown that a Cr-containing MEA film and a Cr-containing HEA film can be obtained with the method disclosed in Non-Patent Literature 1. Further, with the method disclosed in Non-Patent Literature 1, the film formation speed is insufficient, and it is therefore difficult to form an MEA film and an HEA film at a practical processing speed.
An aspect of the present invention has been made for solving the above problems, and an object thereof is to increase the degree of flexibility of the types of metal elements to be used and control the composition, thereby forming a multi-component alloy plating film at a practical processing speed.

Solution to Problem

In order to solve the above problems, a multi-component alloy plating film formation method in accordance with an aspect of the present invention includes a formation step of forming a multi-component alloy plating film by electrodeposition with use of a plating solution that includes a plurality of types of metal elements, an ionic liquid, and water, the multi-component alloy plating film containing the plurality of types of metal elements as principal components, and the plating solution has a non-polar domain and a polar domain, the polar domain having a volume of not more than 10 when the non-polar domain has a volume of 1.

Advantageous Effects of Invention

With an aspect of the present invention, it is possible to form, at a practical processing speed, a multi-component alloy plating film in which the degree of flexibility of the types of metal elements used is increased and the composition of which is controlled.

Brief Description of Drawings

Fig. 1 is a flowchart illustrating an example flow of a method for forming a multi-component alloy plating film in accordance with an aspect of the present invention.
Fig. 2 is a diagram explaining the structure of an ionic liquid used in the method for forming a multi-component alloy plating film in accordance with an aspect of the present invention.
Fig. 3 is a diagram illustrating the results of X-ray diffraction analyses of multi-component alloy plating films formed in Example 1 and Comparative Example 1 of the present invention.
Fig. 4 is a diagram illustrating an image of the surface of a multi-component alloy plating film formed in Example 2 of the present invention.
Fig. 5 is a diagram illustrating the result of an X-ray diffraction analysis of a multi-component alloy plating film formed in Example 3 of the present invention.
Fig. 6 is a diagram illustrating the results of X-ray diffraction analyses of multi-component alloy plating films formed in Example 4 and Comparative Example 2 of the present invention.
Fig. 7 is a diagram illustrating the result of an X-ray diffraction analysis of a multi-component alloy plating film formed in Example 5 of the present invention.
Fig. 8 is a diagram illustrating the result of an X-ray diffraction analysis of a multi-component alloy plating film formed in Example 6 of the present invention, and the electron diffraction image of the plating film captured via a transmission electron microscope (TEM).
Fig. 9 is a diagram schematically explaining a method and a device for forming a multi-component alloy plating film in an aspect of the present invention.
Fig. 10 is a diagram illustrating a cross-sectional scanning electron microscope image, a TEM electron diffraction image, and an X-ray photoelectron spectroscopy analysis result of a multi-component alloy plating film of Example 7 of the present invention.
Fig. 11 is a diagram illustrating the measurement results of the elastic modulus and the hardness of plating films of Example 7 and Comparative Example 3 of the present invention immediately after electrodeposition and after annealing treatment.
Fig. 12 is a diagram illustrating a TEM electron diffraction image and an X-ray photoelectron spectroscopy analysis result of the multi-component alloy plating film of Example 7 of the present invention after annealing treatment.
Fig. 13 is a diagram illustrating a TEM electron diffraction image and an X-ray diffraction analysis result of the multi-component alloy plating film of Example 7 of the present invention after annealing treatment.
Fig. 14 is a diagram illustrating cross-sectional scanning electron microscope images and an X-ray photoelectron spectroscopy analysis result of the multi-component alloy plating film of Comparative Example 4.
Fig. 15 is a diagram illustrating cross-sectional scanning electron microscope images, a TEM electron diffraction image, and an X-ray photoelectron spectroscopy analysis result of a multi-component alloy plating film of Example 8 of the present invention.
Fig. 16 is a diagram illustrating the results of X-ray diffraction analyses of the multi-component alloy plating films formed in Example 7, Example 8, and Comparative Example 4 of the present invention.
Fig. 17 is a diagram illustrating the result of measurement of the corrosion behaviors of the plating films of Example 7 and Comparative Example 3 of the present invention.
Fig. 18 is a diagram illustrating the ratios of the metal elements contained in a plating film of Example 9 of the present invention.
Fig. 19 is a diagram illustrating cross-sectional scanning electron microscope images of the plating film of Example 9 of the present invention.

Description of Embodiments

[1. Outline of method for forming multi-component alloy plating film]

The inventors of the present application found that it is possible to form an MEA plating film including Cr and even an HEA plating film including Cr, by performing electrodeposition with use of a plating solution in which a plurality of types of metal elements are dissolved in a solvent that is a mixed liquid of an ionic liquid and water. That is, the inventors of the present application found that with this method, it is possible to increase the degree of flexibility of the composition of a multi-component alloy plating film which can be formed, and completed the present invention. The meaning of the "plurality of types of metal elements" will be described later.
Specifically, the inventors of the present application found that it is possible to form a multi-component alloy plating film by adjusting the plating solution, which includes an ionic liquid, such that the volume of the polar domain is not more than 10 when the volume of the non-polar domain is 1.

(Multi-component alloy)

As used herein, the "multi-component alloy" is an alloy including a plurality of types of principal metal elements, and is different from conventional alloys including a trace amount of auxiliary metal element within the matrix phase of a single principal metal element. MEAs including not less than three types of principal metal elements in substantially equal ratios and HEAs including not less than five types of principal metal elements in substantially equal ratios are within the scope of the "multi-component alloy" in the present specification. The "multi-component alloy" in the present specification may include an auxiliary metal element together with the plurality of types of principal metal elements. In addition, the "multi-component alloy" in the present specification may further include an auxiliary element such as an additive element or an impurity element. In the present specification, when the proportion of the "plurality of types of metal elements" in a multi-component alloy plating film in a dry state is not less than 70 at%, the "plurality of types of metal elements" are regarded as the "principal components" of the multi-component alloy plating film.
In an MEA, when the total of the atomic ratios of a plurality of types of principal metal elements in the MEA in a dry state is 100, the content ratio of each of the principal metal elements is intended to be not less than 12 at% and not more than 55 at%, and is preferably not less than 28 at% and not more than 38 at%, and more preferably not less than 31 at% and not more than 35 at%. In an HEA, when the total of the atomic ratios of a plurality of types of principal metal elements in the HEA in a dry state is 100, the content ratio of each of the principal metal elements is intended to be not less than 5 at% and not more than 40 at%, and is preferably not less than 15 at% and not more than 25 at%, and more preferably not less than 18 at% and not more than 22 at%.

(Ionic liquid)

The ionic liquid is composed only of ions, and is composed of organic cations and inorganic anions. Examples of the cations of the ionic liquid include imidazolium ions, pyridinium ions, ammonium ions, and phosphonium ions. Examples of the anions of the ionic liquid include Br^-, Cl^-, NO₃ ^-, BF₄ ^-, PF₆ ^-, AlCl₄ ^-, Al₂Cl₇ ^-, CH₃CO₂ ^-, and N(SO₂CF₃)₂ ^--
Fig. 2 is a diagram explaining the structure of an ionic liquid used in the method for forming a multi-component alloy plating film in accordance with an aspect of the present invention. In Fig. 2, for convenience of explanation, a polar domain portion is indicated by extracting the polar domain portion from an ionic liquid which includes the polar domain and a non-polar domain, and a portion in which a non-polar domain is present is indicated as a cavity. The ionic liquid used in the multi-component alloy plating film formation method (hereinafter, the present formation method) in accordance with an aspect of the present invention can have a three-dimensional sponge-like structure, as illustrated in Fig. 2.
Examples of the ionic liquid used in the present formation method include an ionic liquid which includes cations that have an alkyl group having not less than 4 carbon atoms. By using an ionic liquid which includes cations that have an alkyl group having not less than 4 carbon atoms, it is possible to suitably form a multi-component alloy plating film.
An imidazolium-based ionic liquid, which is an example of the ionic liquid used in the present formation method, has a structure in which a polar domain and a non-polar domain are separated from each other. In the polar domain, polar parts such as imidazolium rings cluster together, and in the non-polar domain, alkyl groups cluster together. Since the imidazolium-based ionic liquid having a C2 ethyl group has a short alkyl chain, the volume of the non-polar domain is smaller than that of the polar domain. Thus, the imidazolium-based ionic liquid having a C2 ethyl group has a globular structure, in which the non-polar domain is surrounded by the polar domain. In the imidazolium-based ionic liquid having an alkyl chain longer than a C4 butyl group, the non-polar domain has an increased volume ratio, and therefore is not surrounded by the polar domain. Accordingly, such an imidazolium-based ionic liquid has a three-dimensional sponge-like structure, in which at least some of the non-polar domains are connected together.
The ionic liquid used in the present formation method preferably includes imidazolium ions in which the alkyl groups that constitute the non-polar domain have not less than 4 carbon atoms, and more preferably includes imidazolium ions in which an alkyl group of the non-polar domain has 4 carbon atoms. Examples of the ionic liquid that includes imidazolium ions in which the number of alkyl groups of the non-polar domain is not less than 4 include 1-butyl-3-methylimidazolium ions and 1-hexyl-3-methylimidazolium ions.

(Metal element)

As used herein, the "plurality of types of metal elements" is not less than two metal elements, and may be not less than three types, not less than four types, or not less than five types of metal elements. A combination of the "plurality of types of metal elements" is not particularly limited, but can be set as appropriate according to the purpose of plating.
The metal elements used in the present formation method are metal elements that constitute a multi-component alloy plating film, and are usable in plating at a potential of not more than -1.63 V relative to the potential of the standard hydrogen electrode. Examples of such metal elements include Cr, Co, Ni, Fe, Cu, Mn, and Zn.
In including the metal elements as described above in a plating solution, a method in which the metal elements are dissolved as metal salts may be used. The metal salts can be metal halides that contain metals as described above, and examples thereof include CrCl₃, CoCl₂, NiCl₂, FeCl₂, CuCl, MnCl₂, and ZnCl₂.

[2. Flow of multi-component alloy plating film formation method]

An example flow of the present formation method is described here with reference to Fig. 1. Fig. 1 is a flowchart illustrating an example flow of the present formation method. As illustrated in Fig. 1, the present formation method can include a step (step S11) of mixing the ionic liquid and water together, a step (step S12) of preparing a plating solution, and a formation step (step S13) of forming a plating film. The example of the present formation method will be described in detail in Examples below. However, the present formation method is not limited to this example.
In the step of mixing the ionic liquid and water together, the ionic liquid and water are mixed together to form the solvent of a plating solution. The mixing ratio of the ionic liquid to water is preferably not less than 1:45 and not more than 12:45, more preferably not less than 3:45 and not more than 9:45, and even more preferably 6:45. In a case where the metal elements to be subsequently dissolved are dissolved in the form of metal salt hydrates, the mixing of the ionic liquid and water is preferably carried out such that the ratio of the ionic liquid to the water in a resultant plating solution is the ratio described above, in consideration of the crystallization water of said metal salts.
According to a molecular dynamics simulation, in the plating solution used in the present formation method, the volume of a polar domain is not more than 10 when the volume of a non-polar domain is 1. The volume of the polar domain of the plating solution is preferably not less than 2, and the volume ratio of the polar domain of the plating solution is more preferably not more than 6.
When the amount of each of the metals or metal salts that are to be dissolved in a solvent including an ionic liquid is 1, the amount of the ionic liquid is preferably not less than 2 and not more than 10, more preferably not less than 3 and not more than 9, and most preferably 6.
In the step of preparing a plating solution, a plurality of types of metal elements are dissolved in a mixed solvent of an ionic liquid and water. The plating solution may be prepared by dissolving a plurality of types of metal elements in the water of the solvent, or by mixing, with the solvent, an aqueous solution that has a plurality of types of metal elements dissolved therein. In the plating solution, the metal elements are mainly present in the form of ions in the water, not in the ionic liquid. In the formation step of forming a multi-component alloy plating film, by using a plating solution in which the solvent is a mixed liquid of an ionic liquid and water, it is possible to cause a plurality of types of metal elements, which are the solutes, to be deposited by electrodeposition and form a multi-component alloy plating film.
It is preferable to mix each of the plurality of types of metal elements into the solvent at a target composition ratio of a plating film, e.g., an equal ratio. The respective mixing ratios of the plurality of types of metal elements are such that when the maximum mixing ratio is 1, the minimum mixing ratio is preferably not less than 0.3, and when the minimum mixing ratio is 1, the maximum mixing ratio is preferably not more than 2.4.
As an example, the dissolution of the plurality of types of metal elements in the solvent can be carried out by adding metals or metal salts to the solvent and stirring the solution for not less than 1 minute while heating the solution to be at not less than 0°C and not more than 120°C.
The plating solution prepared in the step of preparing a plating solution further preferably includes boric acid. When the amount of each metal or each metal salt mixed in the plating solution is 1, the amount of boric acid mixed in the plating solution is preferably not less than 1 and not more than 2. By mixing boric acid in the plating solution, it is possible to inhibit the generation of hydrogen in the plating solution and prevent the formation of hydroxides in the resultant plating film.
In the step of forming the multi-component alloy plating film, electrodeposition is carried out using the prepared plating solution. By electrolyzing the plating solution in electrodeposition in which the plating solution is used, the metal elements are reduced and deposited on an electrolytic electrode, and a multi-component alloy plating film is formed accordingly.
The electrolysis of the plating solution may be potentiostatic electrolysis, but is preferably pulse electrolysis. With pulse electrolysis, it is possible to reduce the compositional imbalance of the constituent metal elements in a resultant multi-component alloy plating film, and to form a multi-component alloy plating film with excellent crystallinity.
In a case where the electrolysis of the plating solution is potentiostatic electrolysis, the potential to be controlled is preferably not less than -2.5 V and not more than -1.0 V, more preferably not less than -2.0 V and not more than -1.1 V, and even more preferably not less than -1.6 V and not more than -1.1 V. Compared with pulse electrolysis, potentiostatic electrolysis has the advantage in that the film formation speed is fast and the potential control is easy. In a case where the electrolysis of a plating solution is potentiostatic electrolysis, acid may be added to the plating solution as appropriate in order to inhibit the deposition of oxides and hydroxides. Examples of the acid added to the plating solution include hydrochloric acid, and the amount of said acid is preferably not less than 0.1 and not more than 1 when the amount of each metal or each metal salt mixed in the plating solution is 1.
In a case where the electrolysis of the plating solution is pulse electrolysis, the pulse electrolysis may be based on pulse current density control, and is preferably based on pulse potential control because the pulse potential control-based pulse electrolysis is more suitable for the electrodeposition of a multi-component alloy plating film. As an example, in pulse potential control, 9000 cycles are performed, where each cycle consists of 0.1 seconds at a potential of -1.7 V vs. Ag/AgCl in 3.33 M KC1 and 0.3 seconds in open circuit (current I = 0).
The electrodes used for electrodeposition are not particularly limited. The temperature for the electrodeposition may be not less than 20°C and not more than 200°C, but is not limited thereto. The electrodeposition may be carried out until a multi-component alloy plating film of a desired thickness is obtained.
In the step of forming a multi-component alloy plating film, the base that serves as the foundation for the film formation is not particularly limited. The base may undergo base pretreatment for increasing the adhesion of a film or for imparting or increasing the electrical conductivity. In a case where a film is formed for the purpose of surface treatment of a base, for example, a copper-based base, an iron-based base, a gold base, etc. can be used. In a case where the purpose is to peel off the multi-component alloy plating film formed on the base to obtain an independent sheet-shaped alloy, it is preferable to use a base made of carbon, silicone, or the like, from which a formed multi-component alloy plating film is easy to peel.
The present formation method may further include an annealing step of subjecting, to annealing treatment, the multi-component alloy plating film obtained in the formation step. The multi-component alloy plating film that is immediately after obtained by electrodeposition in the formation step has the advantage of having a low elastic modulus and reduced warping. However, the hardness of said multi-component alloy plating film can be insufficient because of its small crystal grain size. By carrying out the annealing step after the formation step, it is possible to increase the crystal grain size of the multi-component alloy plating film and improve the hardness. Further, the improvement in the hardness of the multi-component alloy plating film after the annealing step improves the wear resistance as well.
In the annealing step, as an example, a multi-component alloy plating film is annealed at not less than 350°C and not more than 700°C. The temperature in the annealing step is more preferably not less than 400°C and not more than 550°C, and even more preferably not less than 500°C and not more than 550°C. The duration of annealing of the multi-component alloy plating film in the annealing step may be not less than 5 minutes and not more than 60 minutes, and is preferably not less than 25 minutes and not more than 30 minutes. As other annealing conditions in the annealing step, conventionally known conditions can be adopted as appropriate.
The multi-component alloy plating film formed in the step of forming the multi-component alloy plating film can be confirmed by X-ray diffraction (hereinafter, XRD) analysis, by energy dispersive X-ray spectroscopy (EDS) elemental analysis, in a visual manner, by X-ray photoelectron spectroscopy (hereinafter, XPS), or any other manner. A multi-component alloy plating film formed in the step of forming a multi-component alloy plating film can be an MEA plating film or an HEA plating film, in which when the total of the atomic ratios of the plurality of types of principal metal elements in the multi-component alloy plating film in a dry state is 100, the content ratio of each of the plurality of types of metal elements is not less than 5 at%. MEA plating films or HEA plating films are expected to have physical properties and/or mechanical properties that differ from those of conventional alloys, and can have various uses, such as corrosion-resistant coating and abrasion-resistant coating.

[3. Multi-component alloy plating film]

The multi-component alloy plating film in accordance with an aspect of the present invention (hereinafter, the present multi-component alloy plating film) includes not less than three types of metal elements which each are in an amount of not less than 12 at%, the not less than three types of metal elements including Cr. The present multi-component alloy plating film can be an MEA plating film which includes not less than three types of principal metal elements including Cr in substantially equal ratios. Alternatively, the present multi-component alloy plating film includes not less than five types of metal elements which each are in an amount of not less than 5 at%. The present multi-component alloy plating film can be an HEA plating film which includes not less than five types of principal metal elements including Cr in substantially equal ratios.
The definitions of MEAs and HEAs are expressed as presented below with use of thermodynamic mixing entropy ΔS_mix. The mixing entropy ΔS_mix is given by Expression (1) below. In Expression (1), ln represents the natural logarithm, R represents the gas constant, x_i represents the atomic concentration (molar fraction) of each component, and n represents the number of components. In the single-phase solid solution state, MEAs are defined by Expression (2) presented below. In addition, in the single-phase solid solution state, HEAs are defined by Expression (3) presented below. $Δ S_{mlx} = - R \sum_{l = 1}^{n} x_{i} \ln x_{i}$ $1.0 R \leq Δ S_{mlx} \leq 1.5 R$ $Δ S_{mlx} \geq 1.5 R$
As an example, for a three-component alloy including three types of metal elements, when these metal elements are in equal ratios (X_i = 0.33), ΔS_mix = 1.099R, and such a three-component alloy is an MEA. That is, the present multi-component alloy plating film can be an MEA plating film having a solid solution phase with 1.0 R ≤ ΔS_mix ≤ 1.5 R. The present multi-component alloy plating film can be an HEA plating film having a solid solution phase with ΔS_mix ≥ 1.5R.
The thickness of the present multi-component alloy plating film can be not less than 0.1 µm and not more than 100 µm, and may be not less than 1 µm and not more than 50 µm, not less than 5 µm and not more than 30 µm, not less than 10 µm and not more than 20 µm, or the like.
Since the present multi-component alloy plating film is an MEA plating film or an HEA plating film that satisfies the above definitions, the present multi-component alloy plating film has a low elastic modulus and reduced warping. The present multi-component alloy plating film has high hardness and is excellent in wear resistance. As such, the present multi-component alloy plating film has excellent mechanical properties, and therefore can be applied to various uses.
The present multi-component alloy plating film is an aspect of a multi-component alloy plating film formed by the present formation method detailed in sections 1. and 2. above. Thus, the descriptions regarding the metal elements, the multi-component alloy, the multi-component alloy plating film, and the formation method in the above 1. and 2. are employed as appropriate in the description of the present multi-component alloy plating film.

[4. Main points]

With the present formation method, it is possible to form a multi-component alloy plating film that has a plurality of types of metal elements deposited therein, by using a plating solution in which the constituent metal elements are dissolved in a mixed solvent of an ionic liquid and water. With the present formation method, the compositional imbalance of the metal elements that constitute the multi-component alloy plating film is reduced. This makes it possible to form, for example, an MEA plating film including Cr and an HEA plating film including Cr. With the present formation method, it is possible to increase the degree of flexibility of the composition of a multi-component alloy plating film which can be formed.
With the method disclosed in Non-Patent Literature 1, metal ions contained in the water droplets in the plating solution are reduced at an electrode and deposited as an alloy, and the constituent metal elements are therefore intermittently supplied to the electrode. As such, the reaction speed is low, and the time required for forming a multi-component alloy plating film may be prolonged. In this regard, with the present formation method, by using a plating solution in which a plurality of types of metal elements are dissolved in a mixed solvent of an ionic liquid and water, it is possible to continuously supply the plurality of types of metal elements to an electrode, and to form a multi-component alloy plating film more quickly. As an example, with the method disclosed in Non-Patent Literature 1, the thickness of the film obtained in 2-hour film formation was only approximately 200 nm, whereas with the present formation method, said thickness can be approximately 10 µm.
Further, the multi-component alloy plating film formed by the present formation method has mechanical properties excellent in the balance between strength and toughness, and therefore can have various uses.
The present invention can also be expressed as follows.
A multi-component alloy plating film formation method in accordance with Aspect 1 of the present invention includes a formation step of forming a multi-component alloy plating film by electrodeposition with use of a plating solution that includes a plurality of types of metal elements, an ionic liquid, and water, the multi-component alloy plating film containing the plurality of types of metal elements as principal components, and the plating solution has a non-polar domain and a polar domain, the polar domain having a volume of not more than 10 when the non-polar domain has a volume of 1.
In a multi-component alloy plating film formation method in accordance with Aspect 2 of the present invention, in the Aspect 1, the plating solution may further include boric acid.
In a multi-component alloy plating film formation method in accordance with Aspect 3 of the present invention, in Aspect 1 or 2, in the formation step, the electrodeposition may be carried out by pulse electrolysis based on pulse potential control.
In a multi-component alloy plating film formation method in accordance with Aspect 4 of the present invention, in any one of Aspects 1 to 3, the ionic liquid may include cations that have an alkyl group having not less than 4 carbon atoms.
In a multi-component alloy plating film formation method in accordance with Aspect 5 of the present invention, in any one of Aspects 1 to 4, the multi-component alloy plating film may include the plurality of types of metal elements which each are in an amount of not less than 5 at%.
In a multi-component alloy plating film formation method in accordance with Aspect 6 of the present invention, in Aspect 1, 2, 4, or 5, in the formation step, the electrodeposition may be carried out by potentiostatic electrolysis.
A multi-component alloy plating film formation method in accordance with Aspect 7 of the present invention may further include, in any one of Aspects 1 to 6, an annealing step of subjecting, to annealing treatment, the multi-component alloy plating film obtained in the formation step.
A multi-component alloy plating film in accordance with Aspect 8 of the present invention includes not less than three types of metal elements which each are in an amount of not less than 12 at%, the not less than three types of metal elements including Cr.

[5. Additional remark]

The present invention is not limited to the embodiments, but can be altered by a skilled person in the art within the scope of the claims. Any embodiment derived by combining, as appropriate, technical means disclosed in differing embodiments is within the technical scope of the present invention.

Examples

[1. Electrodeposition of multi-component alloy plating film with use of plating solution including ionic liquid and water]

(Preparation of plating solution)

As the ionic liquid, 1-butyl-3-methylimidazolium chloride (bmimCl) was used. Ultrapure water was quickly added via a pipette to 3 g of bmimCl stored in a dry chamber such that bmimCl:H₂O = 6:45 (molar ratio). Note that in consideration of the amounts of crystallization water in the crystals of CrCl₃·6H₂O, CoCl₂·6H₂O, and NiCl₂·6H₂O, which were added afterward, H₂O was added at this point in time in an amount that resulted in bmimCl:H₂O = 6:(45 - 6 × 3) = 6:27.
Next, CrCl₃·6H₂O, CoCl₂·6H₂O, and NiCl₂·6H₂O were added to a mixed liquid of bmimCl and H₂O such that bmimCl:CrCl₃:CoCl₂:NiCl₂ = 6:1:1:1 (molar ratio).
After a vessel containing the mixed liquid was sealed with a rubber stopper in order to avoid changes in the ratio of H₂O due to volatilization, stirring was carried out at a hot plate temperature of 80°C, at 700 rpm, for not less than 30 minutes, and complexes were stabilized accordingly. A plating solution of Example 1 was thus prepared. According to a molecular dynamics simulation, in this plating, the volume of the polar domain was 4.3 when the volume of the non-polar domain was 1.
As Comparative Example 1 of the present invention, a plating solution which was an aqueous solution that did not substantially contain an ionic liquid was prepared by mixing CrCl₃, CoCl₂, NiCl₂, and H₂O in a ratio of 1:1:1:45 (molar ratio).

(Electrodeposition)

The prepared plating solution was placed in an electrolytic cell and sealed, and stirred at a temperature of 70°C, at 200 rpm, for 5 minutes. A multi-component alloy plating film was obtained by performing pulse electrolysis for a total of 1 hour, which included 9,000 cycles, where each cycle consisted of 0.1 seconds at a potential of -1.7 V vs. Ag/AgCl in 3.33 M KCl and 0.3 seconds in open circuit (current I = 0).

(Analysis method)

An EDS elemental analysis and an XRD analysis of the resultant multi-component alloy plating film were carried out. The EDS elemental analysis was carried out with use of an EDS analysis device (APEX, manufactured by EDAX) in which the acceleration voltage was set at 20 kV. The XRD analysis was carried out via an XRD analysis device (X'Pert PRO Alpha-1, manufactured by PANanalytical) in which CuKα radiation was used as X-rays, and by step-scanning in 0.133° steps.

(Results)

An EDS elemental analysis was carried out with respect to respective multi-component alloy plating films obtained using plating solutions of Example 1 and Comparative Example 1 of the present invention. The multi-component alloy plating film of Example 1 had a composition of Cr 14, Co 54, and Ni 32 in terms of the atomic ratio. The multi-component alloy plating film of Comparative Example 1 had a composition of Cr 0, Co 31, and Ni 69. The multi-component alloy plating film of Example 1 included all of Cr, Co, and Ni, and an electrodeposited film of a CrCoNi alloy was obtained. In the multi-component alloy plating film of Comparative Example 1, however, Cr was not included, and a Co-Ni alloy was deposited.
Both the multi-component alloy plating films obtained in Example 1 and Comparative Example 1 of the present invention and the multi-component alloy plating films obtained in Examples and Comparative Examples which will be described later included, as auxiliary elements, O in an amount of not less than 10 and not more than 14, C in an amount of not more than 8 and not more than 11, and Cl in an amount of not more than 1 and not more than 2, when the total of the atomic ratios of the principal metal elements was 100.
Illustrated in Fig. 3 are the results of XRD analyses of the multi-component alloy plating films of Example 1 and Comparative Example 1 of the present invention. In Fig. 3, a graph 1001 indicates the result of the XRD analysis of the multi-component alloy plating film of Example 1, a graph 1002 is an enlarged view of the graph 1001, and a graph 1003 indicates the result of the XRD analysis of the multi-component alloy plating film of Comparative Example 1. In the light of the peak intensities in each of the graphs illustrated in Fig. 3, the crystals that constituted the multi-component alloy plating film of Example 1 mainly had the face-centered cubic lattice structure (face-centered cubic (FCC) structure). Further, the hexagonal closest-packed structure (HCP) structure, which is a crystal structure, was also slightly present. The crystals that constituted the multi-component alloy plating film of Comparative Example 1 had the FCC structure.

[2. Electrodeposition of multi-component alloy plating film with use of plating solution containing boric acid]

A plating solution was prepared in the same manner as in Example 1 of the present invention, except that boric acid was added to the plating solution. As the plating solution of Example 2 of the present invention, a plating solution was prepared by mixing bmimCl, CrCl₃, CoCl₂, NiCl₂,H₂O, and H₃BO₃ in a ratio of 6:1:1:1:45:3 (molar ratio).
Using the plating solution of Example 2, a multi-component alloy plating film was obtained by potentiostatic electrolysis at a potential of -2.5 V vs. Pt. As in Example 1, an EDS elemental analysis of the obtained multi-component alloy plating film was carried out, and a scanning electron microscope(SEM) image was obtained. The SEM image was captured with use of an SEM (TM4000Plus, manufactured by Hitachi, Ltd.) in which the acceleration voltage was set at 20 kV.
The composition the multi-component alloy plating film of Example 2 obtained by EDS elemental analysis were Cr 33, Co 33, and Ni 34. An MEA plating film was obtained which had little elemental imbalance, with substantially equal atomic ratios of Cr, Co, and Ni.
Illustrated in Fig. 4 is a surface electron image of the multi-component alloy plating film of Example 2 of the present invention. In Fig. 4, an image 1004 indicates a surface electron image. As illustrated in Fig. 4, the surface morphology of the multi-component alloy plating film of Example 2 was smooth and granular. This indicates that there was not imbalance between the ratios of the constituent metal elements.

[3. Electrodeposition of multi-component alloy plating film by potentiostatic electrolysis]

A multi-component alloy plating film was formed in the same manner as in Example 2 of the present invention, except that the potential in the potentiostatic electrolysis was changed. Potentiostatic electrolysis at a potential of -1.7 V was carried out for 30 minutes, and a multi-component alloy plating film of Example 3 of the present invention was obtained accordingly. An EDS elemental analysis of the obtained multi-component alloy plating film was carried out. The multi-component alloy plating film of Example 3 had a composition of Cr 43, Co 33, and Ni 24. An MEA plating film was obtained which had substantially equal atomic ratios of Cr, Co, and Ni. An MEA plating film was obtained by potentiostatic electrolysis. However, a hydroxide was partially co-deposited, and the adhesion was worse than that of the multi-component alloy plating film of Example 1, which was obtained by pulse electrolysis.
Illustrated in Fig. 5 is the result of an XRD analysis of the multi-component alloy plating film of Example 3 of the present invention. In Fig. 5, a graph 1005 indicates the result of the XRD analysis of the multi-component alloy plating film of Example 3, and a graph 1006 is an enlarged view of the graph 1005. As illustrated in Fig. 5, although the multi-component alloy plating film of Example 3 had the FCC structure, the crystal grains were very fine.

[4. Electrodeposition of multi-component alloy plating film with use of plating solution including different ionic liquid]

A plating solution of Example 4 of the present invention was prepared in the same manner as in Example 2 of the present invention, except that 1-hexyl-3-methylimidazolium chloride (hmimCl) was used as the ionic liquid. As the plating solution of Example 4 of the present invention, a plating solution was prepared by mixing hmimCl, CrCl₃, CoCl₂, NiCl₂,H₂O, and H₃BO₃ in a ratio of 6:1:1:1:45:2 (molar ratio). According to a molecular dynamics simulation, in this plating solution, the volume of the polar domain was 2.8 relative to that of the non-polar domain, which was 1.
A plating solution of Comparative Example 2 of the present invention was prepared in the same manner as in Example 2, except that 1-ethyl-3-methylimidazolium chloride (emimCl) was used as the ionic liquid. As the plating solution of Comparative Example 2 of the present invention, a plating solution was prepared by mixing emimCl, CrCl₃, CoCl₂, NiCl₂,H₂O, and H₃BO₃ in a ratio of 6:1:1:1:45:2 (molar ratio). According to a molecular dynamics simulation, in this plating solution, the volume of the polar domain was 11 relative to the volume of the non-polar domain, which was 1.
Using the plating solutions of Example 4 and Comparative Example 2, multi-component alloy plating films were obtained by pulse electrolysis in the same manner as in Example 1. EDS elemental analyses and XRD analyses of the obtained multi-component alloy plating films were carried out in the same manner as in Example 1.
The multi-component alloy plating film of Example 4 had the composition, obtained by the EDS elemental analysis, of Cr 30, Co 27, Ni 43. An MEA plating film was obtained which had substantially equal atomic ratios, although the ratio of Ni was slightly higher. The multi-component alloy plating film of Example 4 was similar to the multi-component alloy plating film of Example 2, in which bmimCl was used as the ionic liquid. The multi-component alloy plating film of Comparative Example 2 had the composition, obtained by the EDS elemental analysis, of Cr 0, Co 36, Ni 64. The multi-component alloy plating film of Comparative Example 2 did not include Cr, and the Co-Ni alloy was deposited.
Illustrated in Fig. 6 are the results of XRD analyses of the multi-component alloy plating films of Example 4 and Comparative Example 2 of the present invention. In Fig. 6, a graph 1007 indicates the result of the XRD analysis of the multi-component alloy plating film of Example 4, a graph 1008 is an enlarged view of the graph 1007, a graph 1009 indicates the result of the XRD analysis of the multi-component alloy plating film of Comparative Example 2, and a graph 1010 is an enlarged view of the graph 1009.
As illustrated in Fig. 6, the multi-component alloy plating films of Example 4 and Comparative Example 2, which are considered to slightly have included the HCP structure in addition to the FCC structure, had less smooth surfaces and worse adhesion than the multi-component alloy plating film of Example 2, in which bmimCl was used as the ionic liquid.

[5. Electrodeposition of multi-component alloy plating film of FeCoNi]

A plating solution of Example 5 of the present invention was prepared in the same manner as in Example 2 of the present invention, except that Fe was used instead of Cr as a metal element of a multi-component alloy plating film. As the plating solution of Example 5 of the present invention, a plating solution was prepared by mixing bmimCl, FeCl₂, CoCl₂, NiCl₂,H₂O, and H₃BO₃ in a ratio of 6:1:1:1:45:2 (molar ratio).
With use of the plating solution of Example 5, a multi-component alloy plating film was obtained by pulse electrolysis in the same manner as in Example 1 of the present invention. An EDS elemental analysis and an XRD analysis of the obtained multi-component alloy plating film were carried out in the same manner as in Example 1.
The composition obtained by EDS elemental analysis in Example 5 was Fe 52, Co 22, and Ni 26. Although the Fe ratio was slightly higher, an MEA plating film was obtained. The result of the XRD analysis of the multi-component alloy plating film of Example 5 was illustrated in Fig. 7. In Fig. 7, a graph 1011 indicates the result of the XRD analysis of the multi-component alloy plating film of Example 5, and a graph 1012 is an enlarged view of the graph 1011. As illustrated in Fig. 7, the multi-component alloy plating film of Example 5 had a single phase of the FCC structure, or a HCP structure was slightly present.

[6. Electrodeposition of multi-component alloy plating film by pulse electrolysis with use of plating solution containing boric acid]

A multi-component alloy plating film was obtained by pulse electrolysis with use of a plating solution containing boric acid. As the plating solution of Example 6 of the present invention, a plating solution was prepared by mixing bmimCl, CrCl₃, CoCl₂, NiCl₂,H₂O, and H₃BO₃ in a ratio of 6:1:1:1:45:2 (molar ratio). The method for preparing the plating solution and the conditions for pulse electrolysis were the same as those in Example 1 of the present invention.
An EDS elemental analysis and an XRD analysis of the obtained multi-component alloy plating film were carried out in the same manner as in Example 1, and an electron diffraction image of the plating film was captured via a transmission electron microscope (TEM; JEM-6500F, manufactured by JEOL).
The multi-component alloy plating film of Example 6 had the composition, obtained by the EDS elemental analysis, of Cr 30, Co 30, and Ni 40. An MEA plating film was obtained which had little elemental imbalance, with substantially equal atomic ratios of Cr, Co, and Ni.
Illustrated in Fig. 8 are the result of the XRD analysis of the multi-component alloy plating film of Example 6 of the present invention, and the TEM electron diffraction image of the plating film. In Fig. 8, a graph 1013 indicates the result of the XRD analysis of the multi-component alloy plating film of Example 6, and a graph 1014 is an enlarged view of the graph 1013. In the light of the peak intensities in the graph 1013 and the graph 1014 of Fig. 8, the multi-component alloy plating film of Example 6 had a structure in which FCC microcrystals were aggregated.
In Fig. 8, an image 1015 is illustrated which is a TEM electron diffraction image of the portion in which the microcrystals were aggregated in the multi-component alloy plating film of Example 6. In the Debye ring indicated in the image 1015, the four main concentric circles corresponded to the respective spacings of the planes of 2.07 Å, 1.82 Å, 1.25 Å, and 1.09 Å from inside to outside, and the crystal structure of the captured portion was similar to that of Ni of the FCC structure.
Further, the mechanical properties of the multi-component alloy plating film of Example 6 were evaluated. The multi-component alloy plating film of Example 6 was evaluated via a nanoindenter (TI950 TriboIndenter, manufactured by Bruker) to have a Young's modulus (elastic modulus) of approximately 120 GPa and hardness of approximately 5.5 GPa, between the surface and the depth of 180 nm from the surface.

[7. Electrodeposition of multi-component alloy plating film via potentiostatic electrolysis]

(Preparation of plating solution)

As illustrated in Fig. 9, a plating solution was prepared, and electrodeposition was carried out via potentiostatic electrolysis. Fig. 9 is a diagram schematically explaining a method and a device for forming a multi-component alloy plating film. A plating solution was prepared by mixing bmimCl, H₂O, HCl, CrCl₃, CoCl₂, NiCl₂, and H₃BO₃ in a ratio of 6:45:x:1:1:2 (molar ratio). For each of the molar ratios x of HCl, namely 0, 0.06, 0.3, and 0.6, the plating solution was prepared. In the preparation of the plating solution, as illustrated in Fig. 9, a mixed liquid of bmimCl, which was an ionic liquid represented by C₄mimCl, HCl, and H₂O was prepared first, and the remaining salts were added to the liquid. After the addition of the salts, the liquid was stirred at 80°C for not less than 30 minutes. A plating solution was thus prepared.

(Electrodeposition)

A gold plate or a copper plate was used as the working electrode, a platinum plate was used as the counter electrode, and a silver-silver chloride electrode was used as the reference electrode. In a state in which these electrodes were immersed in the plating solution, the plating solution was heated with the hot plate temperature set at 70°C, and was subjected to potentiostatic electrolysis while being stirred at 200 rpm. A set potential (constant value) was applied to the reference electrode with use of a potentiostat. Multi-component alloy plating films were obtained by carrying out potentiostatic electrolysis at the respective set potentials of - 1.1 V, -1.2 V, -1.3 V, -1.4 V, -1.5 V, and -1.6 V. The thicknesses of the multi-component alloy plating films were controlled by the plating time.

(Analysis method)

Each of the obtained multi-component alloy plating films was washed with water, and the film state thereof was visually analyzed. In addition, an XPS analysis, an XRD analysis, an SEM observation, and a TEM observation were carried out. In the TEM observation, the multi-component alloy plating film that was processed into flakes with use of a focused ion beam processing device was used. By carrying out an EDS analysis accompanying SEM or TEM, the distribution and the composition of each element were determined.

(Results)

A multi-component alloy plating film was obtained by performing potentiostatic electrolysis at any of the applied voltages. Further, the results of visual analyzes of the multi-component alloy plating films are shown in Table 1 for each of the applied voltages and each of the molar ratios of HCl.
As shown in Table 1, a multi-component alloy plating film was obtained under any of the conditions. It has been shown that by controlling the applied voltage, it is possible to obtain a multi-component alloy plating film having desired appearance. It has further been shown that by controlling the molar ratio of HCl, the appearance of the multi-component alloy plating film can vary.
Further, with respect to a multi-component alloy plating film of Example 7 obtained by potentiostatic electrolysis at a potential of -1.3 V with the molar ratio of HCl set at 0.06, an SEM observation and a TEM observation were carried out, and the composition of the multi-component alloy plating film was obtained by XPS. A cross-sectional SEM image, a TEM electron diffraction image, and an XPS analysis result of the multi-component alloy plating film of Example 7 are shown in Fig. 10.
In Fig. 10, an image 1020 indicates a cross-sectional SEM image. In Fig. 10, a graph 1021 indicates the Cr spectra for the surface of the film, and a graph 1022 indicates the Cr spectra for the interior of the film (12 minutes after Ar sputtering). In Fig. 10, a graph 1023 indicates Co spectra for the surface of the film, and a graph 1024 indicates Co spectra for the interior of the film. In Fig. 10, a graph 1025 indicates Ni spectra at the surface of the film, and a graph 1026 indicates the Ni spectra for the interior of the film. In Fig. 10, an image 1027 indicates a TEM electron diffraction image.
The multi-component alloy plating film of Example 7 that was subjected to the analysis had a thickness of 1.8 µm, and had a composition of Cr 43, Co 37, and Ni 20 (the average of the compositions at 5 measurement points, percentages by the number of atoms), and had thermodynamic mixing entropy which satisfied ΔS_mix > 1.0R. As illustrated in the image 1020 of Fig. 10, there was no contrast in the cross-sectional SEM image, and no clear phase separation or hydroxide codeposition was found. Further, as illustrated in the graphs 1021 to 1026 of Fig. 10, on the surface of the film, both the metals and the oxides were present, while in the interior of the film, for Co and Ni, only the metals were present, and even for Cr, the amount of oxide was small. Further, as illustrated in the image 1027 of Fig. 10, the multi-component alloy plating film of Example 7 had a microstructure in which the microcrystals that had the FCC structure or the HCP structure and that had a size of not more than 10 nm were densely aggregated.

[8. Annealing treatment after electrodeposition of multi-component alloy plating film via potentiostatic electrolysis]

The mechanical properties of the multi-component alloy plating film of Example 7 were evaluated. In addition, after subjected to annealing treatment that followed the electrodeposition via potentiostatic electrolysis, the mechanical properties of the multi-component alloy plating film of Example 7 were analyzed. As Comparative Example 3, pure chromium plating was prepared from a plating solution containing hexavalent chromium, and the mechanical properties thereof were evaluated. The elastic modulus and hardness (the quality of being hard) were measured via a nanoindenter (TI950 TriboIndenter, manufactured by Bruker) for each of the multi-component alloy plating film of Example 7 that was immediately after electrodeposition, the multi-component alloy plating film of Example 7 that was after annealing treatment at 400°C for 30 minutes, the multi-component alloy plating film of Example 7 that was after annealing treatment at 550°C for 30 minutes, and the pure chromium plating film of Comparative Example 3. The results are shown in Fig. 11.
Fig. 11 is a diagram illustrating the measurement results of the elastic modulus and the hardness of the multi-component alloy plating film of Example 7 immediately after the electrodeposition and after the annealing treatment. In Fig. 11, a graph 1030 indicates the elastic modulus of each of the multi-component alloy plating films, a graph 1031 indicates the hardness of each of the multi-component alloy plating films, and a graph 1032 indicates an index of wear resistance that is expressed by dividing the hardness of each multi-component alloy plating film by the elastic modulus. In each graph, in order from the top, the results are shown for the multi-component alloy plating film of Example 7 immediately after electrodeposition (as-deposited), said plating film after annealing treatment at 400°C for 30 minutes (400°C 30 min annealing), and said plating film after annealing treatment at 550°C for 30 minutes (550°C 30 min annealing), and the pure chromium plating film (hexavalent Cr) of Comparative Example 3.
As illustrated in Fig. 11, the elastic modulus of the multi-component alloy plating film of Example 7 immediately after electrodeposition was low. Although the hardness of the multi-component alloy plating film of Example 7 was low immediately after electrodeposition, said hardness was improved due to the annealing treatment so as to be higher than that of Comparative Example 3. The wear resistance of the multi-component alloy plating film of Example 7 was improved so as to be higher than that of Comparative Example 3 because the hardness was improved due to the annealing treatment. Further, with respect to the temperature of the annealing treatment, the hardness was improved to a greater degree for 550°C.
In addition, a TEM observation, an XPS analysis, and an XRD analysis were performed on the multi-component alloy plating film of Example 7 after annealing treatment at 400°C for 30 minutes and after annealing treatment at 550°C for 30 minutes. The results are shown in Fig. 12 and Fig. 13.
In Fig. 12, an image 1040 indicates a TEM image for an annealing temperature of 400°C, and graphs 1041 to 1043 indicate the spectra of respective metals in the interior of the film (Ar sputtering for 12 minutes) for an annealing temperature of 400°C. In Fig. 12, an image 1044 indicates a TEM image for an annealing temperature of 550°C, and graphs paragraphs 1045 to 1047 indicate the spectra of respective metals in the interior of the film (Ar sputtering for 12 minutes) for an annealing temperature of 550°C. In Fig. 13, an image 1050 indicates a TEM image for an annealing temperature of 550°C, and a graph 1051 indicates the result of an XRD analysis for an annealing temperature of 550°C.
As illustrated in the image 1040 of Fig. 12, the annealing treatment at 400°C resulted in the growth of crystal grains and the emergence of a relatively large HCP phase. The metal ratios determined from the XPS analysis shown in the graphs 1041 to 1043 of Fig. 12 were Cr:Co:Ni = 25:52:23 and O:Cr:Co:Ni = 11:23:46:20. Considering that Cr in the form of metal accounted for 81%, the metal ratio was Cr:Co:Ni = 22:54:24. The mixing entropy ΔS_mix was 1.00 R.
Further, as illustrated in the image 1044 of Fig. 12, the annealing treatment at 550°C resulted in further crystal growth and a more pronounced grain boundary. The metal ratios determined from the XPS analysis shown in the graphs 1045 to 1047 of Fig. 12 were Cr:Co:Ni = 32:45:23, O:Cr:Co:Ni = 13:28:39:20. Considering that Cr in the form of metal accounted for 78%, the metal ratio was Cr:Co:Ni = 27:49:24. The mixing entropy ΔS_mix was 1.05 R.
As illustrated in the image 1050 of Fig. 13, a large number of twinned crystals were found due to the annealing at 550°C. It has thus been shown that by annealing at 550°C, the hardness was increased due to twinning and enhanced deposition. Further, as illustrated in the graph 1051 of Fig. 13, although the principal phase of the multi-component alloy plating film immediately after electrodeposition was the FCC structure, the HCP structure emerged after the annealing.

[9. Potentiostatic electrolysis for multi-component alloy plating film with use of plating solution with different ionic liquid]

A plating solution of Example 8 was prepared in the same procedure as in Example 7 of the present invention, except that hmimCl represented by C₆mimCl was used as the ionic liquid. In the plating solution of Example 8, the volume of the polar domain was 2.8 when the volume of the non-polar domain was 1. In addition, a plating solution of Comparative Example 4 was prepared in the same manner as in Example 7 of the present invention, except that emimCl represented by C₂mimCl was used as the ionic liquid. In the plating solution of Comparative Example 4, the volume of the polar domain was 11 when the volume of the non-polar domain was 1.
With use of the prepared plating solutions, multi-component alloy plating films were obtained by carrying out potentiostatic electrolysis at respective set potentials of -1.2 V, -1.3 V, and -1.4 V, in the same manner as in Example 7, in which C₄mimCl was used. The results of visual analyses of the multi-component alloy plating films are shown in Table 2 for each of the applied voltages and each of the types of ionic liquids, together with the results of Example 7.
As shown in Table 2, a multi-component alloy plating film was obtained by potentiostatic electrolysis when any of the ionic liquids was used. For C₄mimCl and C₆mimCl as the ionic liquid, the electrolytic deposits exhibited similar potential dependence.
Further, with respect to Comparative Example 4, in which C₂mimCl was used as the ionic liquid, cross-sectional SEM images of the multi-component alloy plating films obtained at the respective applied voltages were captured and XPS analyses of said plating films were carried out. The cross-sectional SEM images and the XPS analysis results of a multi-component alloy plating film of Comparative Example 4 are shown in Fig. 14.
In Fig. 14, an image 1060 indicates a cross-sectional SEM image of the multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.2 V, and graphs 1061 to 1063 indicate the spectra of respective metals in the interior of the film. In addition, an image 1064 of Fig. 14 indicates a cross-sectional SEM image of the multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.3 V. Further, an image 1065 of Fig. 14 indicates a cross-sectional SEM image of the multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.4 V, and graphs 1066 to 1068 indicate the spectra of respective metals in the interior of the film.
The thickness of the multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.2 V was 8.8 pm. As illustrated in the image 1060 of Fig. 14, although the cross-sectional SEM image of the multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.2 V was almost uniform, hydroxides of all the metal elements were present, as shown in the graphs 1061 to 1063. The composition was Cr 16, Co 68, and Ni 16. However, considering that Cr is reduced by Ar sputtering, the components are not considered to have been deposited in the form of metal. The mixing entropy ΔS_mix was 0.85 R.
The multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.3 V had a thickness of 11.5 µm and ΔS_mix of 0.65 R. As illustrated in the image 1064 of Fig. 14, from the cross-sectional SEM image of the multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.3 V, a contrast due to voids or hydroxides was generated in the interior of the electrodeposited film. In addition, the composition was Cr 1, Co 71, and Ni 28, where Cr was almost absent.
Further, the multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.4 V had a thickness of 8.2 pm and ΔS_mix of 0.97 R. As illustrated in the image 1065 of Fig. 14, a contrast due to the hydroxides was generated in the cross-sectional SEM image of the multi-component alloy plating film of Comparative Example 4 prepared via potentiostatic electrolysis at -1.4 V. As shown in the graphs 1066 to 1068, hydroxides of all the metals were co-deposited. The composition was Cr 35, Co 52, and Ni 13 (XPS: Cr 22, Co 66, and Ni 12). In terms of the amounts of deposition in the form of metal, the ratio of Co was great, and it was not possible to obtain an MEA plating film.
Next, with respect to Example 8, in which C₆mimCl was used as the ionic liquid, cross-sectional SEM images of the multi-component alloy plating films obtained at the respective applied voltages were captured and XPS analyses and TEM observations of said plating films were carried out. A cross-sectional SEM image, a TEM electron diffraction image, and an XPS analysis result of the multi-component alloy plating film of Example 8 are shown in Fig. 15.
In Fig. 15, an image 1070 indicates a cross-sectional SEM image of the multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.2 V, and graphs 1071 to 1073 indicate the spectra of respective metals in the interior of the film. Further, an image 1074 of Fig. 15 indicates a cross-sectional SEM image of the multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.3 V, and graphs 1075 to 1077 indicate the spectra of respective metals in the interior of the film. In addition, an image 1078 of Fig. 15 indicates a TEM electron diffraction image of the multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.3 V.
The multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.2 V had a thickness of 0.4 µm, thus was thin although having a metallic luster. As illustrated in the image 1070 of Fig. 15, in the multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.2 V, there were many hydroxides as shown in the cross-sectional SEM image, and the oxygen ratio was slightly higher as shown in the graphs 1071 to 1073. Variations in composition were observed depending on the measurement points, and the average of the compositions at 3 points was Cr 39, Co 34, and Ni 27, where the ratio of Cr was slightly higher.
The multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.3 V had a thickness of 0.3 pm and ΔS_mix of 1.08 R. As shown in the images 1074 and the graphs 1075 to 1077 of Fig. 15, in the multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.3 V, there were many hydroxides and the oxygen ratio was slightly higher, as in the multi-component alloy plating film prepared via potentiostatic electrolysis at -1.2 V. The average of the compositions at 5 points was Cr 36, Co 39, and Ni 25, and it was possible to obtain an MEA plating film.
Further, as shown in the image 1078 of Fig. 15, the multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.3 V was the aggregate of nanocrystals that had the FCC structure and that had a diameter of approximately 1 nm, which were finer than those of the multi-component alloy plating film of Example 7. In the multi-component alloy plating film of Example 8 prepared via potentiostatic electrolysis at -1.3 V, the crystal portion and the grain boundary portion existed, and in the grain boundary portion, the ratios of Cr, Cl, and O were slightly higher.
Illustrated in Fig. 16 are the results of XRD analyses of the multi-component alloy plating film of Example 7 (C₄mimCl) prepared via potentiostatic electrolysis at -1.3 V, the multi-component alloy plating film of Example 8 (C₆mimCl) prepared via potentiostatic electrolysis at -1.3 V, and the multi-component alloy plating film of Comparative Example 4 (C₂mimCl) prepared via potentiostatic electrolysis at -1.4 V. As illustrated in Fig. 16, in the multi-component alloy plating film of Comparative Example 4, the half-width was wide, hydroxides were co-deposited, and the ratio of Co was great. The multi-component alloy plating film of Example 8 had a significantly smaller thickness and a smaller particle size than the multi-component alloy plating film of Example 7. It has been shown in the analyzed XRD-patterns that the effect of the length of the alkyl chain of the ionic liquid is substantial, and the C₄mimCl is suitable for the electrodeposition of MEAs.
From these results, it can be said that when C₂mimCl is used as the ionic liquid, Cr is less likely to be deposited regardless of the potential, and C₂mimCl is not suitable for the electrodeposition of MEAs. It can also be said that when C₆mimCl is used as the ionic liquid, although the ratio of Cr deposited is high, the film formation speed is slow, and a large amount of hydroxides can be generated. It can be said that when C₄mimCl is used as the ionic liquid, since each of the metals is deposited in the form of metal, and the variation in the ratio is small, C₄mimCl is suitable for the electrodeposition of MEAs.

[10. Corrosion resistance evaluation of multi-component alloy plating film including Cr]

In order to compare the corrosion resistance between the Cr-containing multi-component alloy plating film of Example 7 and the pure chromium plating film of Comparative Example 3, corrosion potentials were measured. The results are shown in Fig. 17. In the measurement method, the plating films were immersed in a 0.1 mol/L aqueous solution of NaCl to be used as the working electrodes, and an Ag|AgCl electrode using saturated KCl was used as the reference electrode, and a platinum electrode was used as the counter electrode. With use of a potentiostat (SP-50, manufactured by Biologic), the potential scanning was carried out at a rate of 1 mVs^-1, and the corrosion potential was measured by a method for measuring a current density. The corrosion potential of the plating film of Example 7 was shifted in the noble direction as compared with the pure chromium plating film of Comparative Example 3, and was further remarkably shifted in the noble direction when undergoing annealing treatment. Since no significant difference was found due to the difference in the annealing temperature, only the case of the 400°C annealing condition is illustrated in Fig. 17. With the results, the multi-component alloy plating film of the present invention is expected to have more excellent corrosion resistance than conventional Cr plating films.

[11. Electrodeposition of multi-component alloy plating film of CrFeCoNiCu]

A multi-component alloy plating film of Example 9 was obtained with use of a plating solution that contained five types of metal elements including Cr. The plating solution of Example 9 was prepared as follows: to a liquid prepared by mixing bmimCl, H₂O, HCl, CrCl₃, CoCl₂, NiCl₂, and H₃BO₃ in a ratio of 6:45:0.06:1:1:1:2 (molar ratio), FeCl₂·4H₂O and CuCl₂/2H₂O were added such that the molar ratios thereof were each 0.2. With use of the obtained plating solution, electrodeposition was carried out via potentiostatic electrolysis. Multi-component alloy plating films of Example 9 were obtained by carrying out potentiostatic electrolysis at the respective set potentials of -1.2 V, -1.3 V, and -1.4 V. Preparation and electrodeposition of the plating solution were carried out in the same manner as in Example 7.
For each of the multi-component alloy plating films obtained at the respective applied voltages, the ratios of the metal elements were determined via EDS elemental analysis and a cross-sectional SEM image was obtained. The ratios of the metal elements contained in the multi-component alloy plating film are illustrated in Fig. 18, and the cross-sectional SEM images of the multi-component alloy plating films prepared via potentiostatic electrolysis at -1.2 V or -1.4 V are illustrated in Fig. 19. In Fig. 19, an image 1090 indicates the cross-sectional SEM image of the multi-component alloy plating film prepared via potentiostatic electrolysis at -1.2 V, and an image 1091 indicates the cross-sectional SEM image of the multi-component alloy plating film prepared via potentiostatic electrolysis at -1.4 V.
As illustrated in Fig. 18, for the multi-component alloy plating film prepared via potentiostatic electrolysis at -1.2 V or -1.3 V, the ratio of Co was high and the ratio of Cr was low, while for the multi-component alloy plating film prepared via potentiostatic electrolysis at -1.4 V, the ratios of respective metal elements were substantially equal to each other. The multi-component alloy plating film prepared via potentiostatic electrolysis at -1.4 V had ΔS_mix of 1.52 R, and therefore can be judged to be an HEA plating film.
As illustrated in Fig. 19, the multi-component alloy plating film prepared via potentiostatic electrolysis at -1.4 V included a more uniform portion than the multi-component alloy plating film prepared via potentiostatic electrolysis at - 1.2 V.

Industrial Applicability

The present invention can be used in the field of surface treatment including plating and the field of metal foil production.

Claims

A method for forming a multi-component alloy plating film, the method comprising
a formation step of forming a multi-component alloy plating film by electrodeposition with use of a plating solution that includes a plurality of types of metal elements, an ionic liquid, and water, the multi-component alloy plating film containing the plurality of types of metal elements as principal components,

the plating solution having a non-polar domain and a polar domain, the polar domain having a volume of not more than 10 when the non-polar domain has a volume of 1.
The method according to claim 1, wherein
the plating solution further includes boric acid.
The method according to claim 1 or 2, wherein
in the formation step, the electrodeposition is carried out by pulse electrolysis based on pulse potential control.
The method according to claim 1 or 2, wherein
the ionic liquid includes cations that have an alkyl group having not less than 4 carbon atoms.
The method according to claim 1 or 2, wherein
the multi-component alloy plating film includes the plurality of types of metal elements which each are in an amount of not less than 5 at%.
The method according to claim 1 or 2, wherein
in the formation step, the electrodeposition is carried out by potentiostatic electrolysis.
The method according to claim 1 or 2, further comprising
an annealing step of subjecting, to annealing treatment, the multi-component alloy plating film obtained in the formation step.
A multi-component alloy plating film, comprising
not less than three types of metal elements which each are in an amount of not less than 12 at%, the not less than three types of metal elements including Cr.
A multi-component alloy plating film, comprising
not less than five types of metal elements which each are in an amount of not less than 5 at%.