Magnetostrictive member and method for manufacturing magnetostrictive member

Abstract

[Problem] To provide a magnetostrictive member having environment resistance and a method for manufacturing the magnetostrictive member. [Solution] The magnetostrictive member is composed of crystals of an iron-based alloy having magnetostrictive characteristics and is a plate-like body having a longitudinal direction and a shorter direction. The surface of the magnetostrictive member is covered with a single plated layer.

Description

Magnetostrictive member and method of manufacturing the same

[0001] The present invention relates to a magnetostrictive member and a method for manufacturing a magnetostrictive member.

[0002] Magnetostrictive materials have been attracting attention as functional materials. For example, Fe-Ga alloys, which are iron-based alloys, exhibit magnetostriction and inverse magnetostriction, exhibiting large magnetostriction of approximately 100 to 350 ppm. For this reason, they have recently attracted attention as vibration-powered energy harvesting materials, and are expected to be applied to wearable devices and sensors.

[0003] For example, a magnetostrictive vibration power generation device is composed of a magnetostrictive member such as an Fe—Ga alloy wound around a coil, a yoke, and a permanent magnet for a field magnet (see Patent Document 2 and Non-Patent Document 1). In this magnetostrictive vibration power generation device, when the yoke, which is the moving part of the device, is vibrated, the magnetostrictive member fixed to the center of the yoke vibrates in conjunction with the yoke. This causes the magnetic flux density of the coil wound around the magnetostrictive member to change due to the inverse magnetostrictive effect, generating an electromagnetically induced electromotive force and generating electricity. In a magnetostrictive vibration power generation device, vibration occurs when a force is applied in the longitudinal direction of the yoke, so it is desirable to process the magnetostrictive member, such as an Fe—Ga alloy, used in the device so that the easy axis of magnetization, <100>, is aligned longitudinally.

[0004] The magnetostrictive properties of Fe—Ga alloys are believed to affect the magnetostrictive and inverse magnetostrictive effects and the characteristics of magnetostrictive vibration-based power generation devices, making them an important parameter in device design (Non-Patent Document 1). In particular, the magnetostrictive constant depends on the Ga composition of the Fe—Ga alloy single crystal, and it is known that the magnetostrictive constant is maximized at Ga compositions of 18-19 at% and 27-28 at% (Non-Patent Document 2). It is therefore considered desirable to use Fe—Ga alloys with such Ga concentrations in devices. Furthermore, in recent years, it has been reported that in addition to a large magnetostrictive constant, the greater the amount of parallel magnetostriction, the better the device characteristics, such as output voltage, tend to be (Non-Patent Document 3).

[0005] International Publication No. 2021 / 100467 International Publication No. 2011 / 158473 Patent No. 7084620

[0006] Toshiyuki Ueno, Journal of the Japan Society for Precision Engineering Vol. 79, No.4, (2013) 305-308.AE Clark et al., Appl. Phys. 93(2003)8621. Jung Jin Park, Suok-Min Na, Ganesh Raghunath, and Alison B. Flatau., AIP ADVANCES 6, 056221(2016)

[0007] As described above, the device characteristics of magnetostrictive vibration power generation devices and the like are affected by the magnetostrictive properties of the magnetostrictive member. Therefore, magnetostrictive members are required to have high magnetostrictive properties and little variation in magnetostrictive properties. Under these circumstances, it was thought that if the crystal orientation of an Fe—Ga alloy single crystal was <100> and the Ga concentration was uniform, a magnetostrictive member with a uniform magnetostrictive constant could be obtained. However, device characteristics are affected not only by the magnetostrictive constant but also by the amount of parallel magnetostriction. Therefore, Patent Document 1 discloses that by adding multiple grooves, such as grinding marks, extending in the longitudinal direction of the magnetostrictive member, a magnetostrictive member with high magnetostrictive constant and amount of parallel magnetostriction and little variation in the magnetostrictive constant and amount of parallel magnetostriction between members can be obtained. When this magnetostrictive member was incorporated into the magnetostrictive vibration power generation device and the device characteristics were confirmed, it was confirmed that a predetermined device output (e.g., power generation amount such as force coefficient) was obtained and that there was little variation in device output between devices.

[0008] To measure the parallel magnetostriction of a magnetostrictive member, a strain gauge must be attached to the magnetostrictive material, which is a destructive test. On the other hand, when evaluating the force coefficient, impedance measurement can be performed by inserting and removing a measuring coil, which is a non-destructive test, so impedance measurement is preferable for product inspection.

[0009] Furthermore, prior to the present invention, the present inventors discovered that the parallel magnetostriction of a magnetostrictive member is positively correlated with the force coefficient calculated from impedance measurements. Furthermore, the force coefficient is positively correlated with device output (Patent Document 2). Prior to the present invention, the present inventors discovered that increasing device output increases not only the parallel magnetostriction but also the force coefficient (Japanese Patent Application No. 2023-037128, International Patent Application No. PCT / JP2024 / 4133).

[0010] Furthermore, to maximize the device's output (power generation), it is necessary to appropriately set the magnetic flux density of the magnet incorporated into the device. Specifically, the magnetic flux density (hereinafter referred to as the optimal magnetic field strength) must be approximately half the maximum parallel magnetostriction of the magnetostrictive material incorporated into the device. Therefore, prior to the present invention, the inventors of the present invention added an annealing treatment (heat treatment) to increase the force coefficient to increase the device's output and suppress variation in the optimal magnetic field strength (Japanese Patent Application: Patent Application No. 2023-037128, International Patent Application: PCT / JP2024 / 4133).

[0011] Incidentally, magnetostrictive vibration power generation devices are being considered not only for indoor use but also for outdoor use, such as vibration power generation devices that utilize vibrations from bridge piers. For this reason, the magnetostrictive members incorporated into magnetostrictive vibration power generation devices must be environmentally resistant. Corrosion resistance is particularly important for devices used outdoors.

[0012] Therefore, an object of the present invention is to provide a magnetostrictive member having environmental resistance and a method for manufacturing the magnetostrictive member.

[0013] According to an aspect of the present invention, there is provided a magnetostrictive member which is a plate-shaped body made of crystals of an iron-based alloy having magnetostrictive properties and which has a longitudinal direction and a lateral direction, and whose surface is coated with a single-layer plating layer.

[0014] At least some of the sides of the plate-like body may be chamfered. The chamfered surfaces may be curved. The plating layer of the magnetostrictive member may be a zinc plating layer.

[0015] Furthermore, according to an aspect of the present invention, there is provided a method for manufacturing a magnetostrictive member, which includes a step of preparing a magnetostrictive member cut into individual pieces, and a plating step of forming a single-layer plating layer on the surface of the prepared magnetostrictive member, wherein the plating step does not include strike plating.

[0016] The method may also include a step of chamfering the prepared magnetostrictive member. The plating step may be zinc plating. The zinc plating bath may be an alkaline plating bath. The chamfering may be barrel polishing.

[0017] According to the present invention, it is possible to provide a magnetostrictive member having environmental resistance and a method for manufacturing a magnetostrictive member.

[0018] 1A and 1B are diagrams showing an example of a magnetostrictive member according to an embodiment, in which (A) is a perspective view and (B) is a cross-sectional view taken along line AA in (A). 1B are diagrams showing examples of a single crystal and a thin plate member. 1C are diagrams showing an example of an impedance measuring device. 1D are diagrams showing an electromechanical equivalent circuit of a measuring coil. 1E are diagrams showing examples of an impedance measuring device. 1F are diagrams showing examples of an impedance measuring device. 1G are diagrams showing examples of an electromechanical equivalent circuit of a measuring coil. 1G are diagrams showing examples of an impedance measuring device. 1H are diagrams showing examples of an impedance measuring device. 1H are diagrams showing examples of an impedance measuring device. 1J are diagrams showing examples of an impedance measuring device. 1J are diagrams showing examples of an electromechanical equivalent circuit of a measuring coil. 1J are diagrams showing examples of an impedance measuring device. 1J are diagrams showing examples of an

[0019] Specific embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments, and can be modified as appropriate without departing from the spirit and scope of the present invention. In the drawings, some or all of the drawings are shown schematically and scaled accordingly. In the following description, the term "A to B" means "A or greater and B or less." The directions in the drawings may be explained using an XYZ coordinate system. In this XYZ coordinate system, the direction perpendicular to the XY plane is referred to as the Z direction. The X, Y, and Z directions will be explained assuming that the direction of the arrow in the drawing is the + direction and the direction opposite to the arrow is the - direction.

[0020] [Embodiment] Hereinafter, a magnetostrictive member and a method for manufacturing a magnetostrictive member according to this embodiment will be described.

[0021] (Magnetostrictive Member) First, the magnetostrictive member of this embodiment will be described. Figures 1(A) and 1(B) are diagrams showing an example of a magnetostrictive member according to an embodiment.

[0022] As shown in Figures 1(A) and 1(B), the magnetostrictive member 1 is a plate-like body having a longitudinal direction D1 and a lateral direction D2. The plate-like body is preferably rectangular in plan view. The plate-like body has a surface (front surface) 3 and a back surface 4. The surface 3 and the back surface 4 are preferably parallel to each other, but do not have to be parallel to each other. The magnetostrictive member 1 has a single-layer plating layer C on the surface 3, the back surface 4, and the side surfaces (XZ and YZ surfaces in the example of Figure 1(A)). The surface 3, the back surface 4, and the side surfaces of the plate-like body are covered with the single-layer plating layer C (see Figure 1(B)). In particular, in this embodiment, it is preferable that no undercoat plating layer, such as strike plating (described later), is provided between the surface 3, the back surface 4, the side surfaces, and the single-layer plating layer C.

[0023] A part of each side 5 of the magnetostrictive member 1 may optionally be provided with a chamfered surface 6. In the magnetostrictive member 1, at least a part of each side portion 5 of the plate-like body may optionally be provided with a chamfered surface 6 (chamfered portion). Furthermore, the magnetostrictive member 1 may optionally be provided with a plurality of grooves 2 extending in the longitudinal direction D1, as described in Patent Document 1, for example.

[0024] The magnetostrictive member 1 is made of a crystal of an iron-based alloy. For example, multiple magnetostrictive members 1 can be obtained from the same crystal. The iron-based alloy is not particularly limited as long as it has magnetostrictive properties. Magnetostrictive properties refer to the property of undergoing a change in shape when a magnetic field is applied. Examples of iron-based alloys include Fe—Ga, Fe—Ni, Fe—Al, Fe—Co, Tb—Fe, Tb—Dy—Fe, Sm—Fe, and Pd—Fe. The above alloys may also be alloys to which a third component has been added. For example, an Fe—Ga alloy may be alloyed to which Ba, Cu, or the like has been added. Among these iron-based alloys, Fe—Ga alloys have greater magnetostrictive properties and are easier to process than other alloys, and therefore are used in vibration-generated energy harvesting materials, wearable devices, sensors, and the like. In the following explanation, an example of a magnetostrictive member 1 will be described in which the magnetostrictive member 1 is made of a single crystal of an Fe—Ga alloy. FIG. 2 is a diagram showing an example of a single crystal and a thin plate member.

[0025] A single crystal of an Fe—Ga alloy has a body-centered cubic lattice structure, and is based on the principle that the first to third <100> axes (see FIG. 2) among the directional indices in the Miller indices are equivalent, and the first to third {100} planes (see FIG. 2) among the plane indices in the Miller indices are equivalent (i.e., (100), (010), and (001) are equivalent). However, these do not have to be completely equivalent. Furthermore, an Fe—Ga alloy has the property of exhibiting large magnetostriction in a specific orientation of the crystal. When utilizing this property in a magnetostrictive vibration power generation device, it is desirable to align the direction in the device requiring magnetostriction of the magnetostrictive member 1 with the orientation (direction) in which the magnetostriction of the crystal is maximized. Specifically, as described above, it is desirable to set the <100> direction, which is the easy magnetization direction in the single crystal, to the longitudinal direction D1 of the magnetostrictive member 1. The <100> direction, which is the direction of easy magnetization in a single crystal, can be made the longitudinal direction D1 of the magnetostrictive member 1, for example, by calculating the crystal orientation of the single crystal using known crystal orientation analysis and cutting the single crystal based on the calculated crystal orientation of the single crystal.

[0026] The crystal that can be used for the magnetostrictive member 1 of this embodiment may be a single crystal or a polycrystal. In order to increase the degree of orientation integration in the <100> direction and improve the properties as a magnetostrictive material, it is more advantageous to use a single crystal than a polycrystal. Although polycrystals have inferior magnetostrictive properties to single crystals, they can be produced at low cost, so polycrystals may also be used.

[0027] The magnetostrictive member 1 is used, for example, as a material (component) for vibration power generation devices in the energy harvesting field, and as a material (component) for wearable terminals and sensors. For example, a magnetostrictive vibration power generation device such as that shown in Patent Document 2 above is composed of a coil, a magnetostrictive member made of an Fe—Ga alloy wound around the coil, a yoke, and a permanent magnet for a field magnet. This magnetostrictive vibration power generation device has a mechanism in which, when the yoke, which is the moving part of the device, is vibrated, the magnetostrictive member fixed to the center of the yoke vibrates in conjunction with the coil. The inverse magnetostrictive effect changes the magnetic flux density of the coil wound around the magnetostrictive member, generating electromagnetically induced electromotive force, thereby generating electricity. When used in such a mechanism, the magnetostrictive member 1 is preferably thin and rectangular in shape in a plan view. There are no particular limitations on the thickness of the magnetostrictive member 1. For example, a thickness of 0.3 mm to 5 mm is preferred. The shape and size of the magnetostrictive member 1 are appropriately set depending on the size of the intended device. For example, the magnetostrictive member 1 may have a side length of 5 mm or more, 10 mm or more, 20 mm or more, or 30 mm or more. For example, the size of the magnetostrictive member 1 may be such that the length (dimension) in the longitudinal direction D1 is 25 mm, the width (dimension) in the lateral direction D2 is 4 mm, and the thickness is 0.5 mm. Furthermore, the dimensions (longitudinal (long side), lateral (short side), and thickness) of the magnetostrictive member 1 may be in a range between two values ​​selected from the group consisting of any of the above upper limit values ​​and any of the lower limit values ​​and any of the values ​​described in the examples, within the scope of the present invention, or one value selected from this group may be the lower limit value (lower limit range), or one value selected from this group may be the upper limit value (upper limit range).

[0028] The shape and dimensions of the magnetostrictive member 1 are not particularly limited. For example, the magnetostrictive member 1 does not have to be rectangular in plan view. For example, the shape of the magnetostrictive member 1 may be elliptical, track-shaped, or irregular in plan view. When the shape of the magnetostrictive member 1 is other than rectangular in plan view, the longitudinal direction D1 is the major axis direction, long axis direction, etc., and the short direction D2 is the direction perpendicular to the longitudinal direction D1.

[0029] As mentioned above, magnetostrictive vibration power generation devices are being considered not only for indoor use but also for outdoor use, such as vibration power generation devices that utilize vibrations from bridge piers. For this reason, magnetostrictive members incorporated into magnetostrictive vibration power generation devices must have high and stable magnetostrictive properties and be environmentally resistant. Corrosion resistance is particularly important for devices used outdoors. However, as mentioned above, iron-based alloys such as Fe—Ga alloys have high magnetostrictive properties but poor corrosion resistance. While plating generally improves the corrosion resistance of some materials, the present inventors have discovered that plating can cause a problem with magnetostrictive members, where the magnetostrictive properties are reduced.

[0030] Therefore, the present inventors, after studying plating methods, etc., discovered that the magnetostrictive properties of magnetostrictive members are disadvantageously reduced by the properties of the plating, and further discovered that they are affected by strike plating and other plating processes, leading to the completion of an embodiment of the present invention. A method for manufacturing a magnetostrictive member according to an embodiment of the present invention is a method for manufacturing a magnetostrictive member, comprising the steps of preparing magnetostrictive members cut into individual pieces and forming a single-layer plating layer on the surface of the prepared magnetostrictive members, wherein the plating step does not include strike plating. Furthermore, a magnetostrictive member according to an embodiment of the present invention is a magnetostrictive member that is a plate-shaped member made of crystals of an iron-based alloy having magnetostrictive properties, has a longitudinal direction and a lateral direction, and is characterized in that the surface of the magnetostrictive member is covered with a single-layer plating layer. This will be explained in detail below.

[0031] The magnetostrictive member 1 is formed by, for example, processing a single crystal grown by the Cz method, VB method, or the like into a thin plate-like member by cutting the crystal using discharge wire cutting or the like, and then cutting the thin plate member into a predetermined shape using a cutting device or the like to produce individual magnetostrictive members. Burrs may be generated during this cutting process, and the magnetostrictive properties may vary due to the burrs. For this reason, the magnetostrictive member 1 may be provided with chamfered surfaces 6 on at least some of the edges of the plate-like body, and the provision of the chamfered surfaces 6 suppresses the variation in magnetostrictive properties due to the burrs generated during cutting.

[0032] The plating layer C of the magnetostrictive member 1 is formed to improve corrosion resistance, so it is preferable to coat the entire surface of the magnetostrictive member 1. Therefore, it is important that the plating layer C is formed on the magnetostrictive member 1 after it has been cut into individual pieces. Plating the magnetostrictive member before it has been cut into individual pieces is undesirable, as the cut portions are not plated and corrosion may occur from these portions. There are no particular limitations on the plating method, but barrel plating or rack plating is preferred, given that the magnetostrictive member 1 is an individual piece. Barrel plating is a method in which the magnetostrictive member is placed in a container called a barrel and plated while the barrel itself is rotated. Barrel plating is preferred because it allows for the simultaneous plating of a large number of individual pieces, making it efficient and possible to process a large number of individual pieces.

[0033] The type of plating (layer) in the plating layer C is not particularly limited as long as it is a corrosion-resistant plating (layer). For example, zinc plating (layer), tin plating (layer), nickel plating (layer), etc. are preferred.

[0034] In plating, strike plating is typically performed as a base plating to improve adhesion between the plated material and the plated layer. Strike plating, for example, can be performed with a higher current and in a shorter time than when forming the main plating, resulting in a denser plating and improved adhesion. Nickel strike plating is often used for iron-based alloys. However, as shown in the comparative example described below, when plating magnetostrictive members with nickel strike plating followed by zinc plating, the magnetostrictive properties before plating, such as the force coefficient, decrease or the optimal magnetic field strength fluctuates. This is thought to be due to the plating stress generated by strike plating on the front and back surfaces, which are the main surfaces of the magnetostrictive member, affecting the main surfaces and changing the magnetostrictive properties. In particular, it has been found that the fluctuations in magnetostrictive properties due to strike plating are significant for magnetostrictive members obtained by stabilizing the magnetostrictive properties by forming multiple grooves 2 extending in the longitudinal direction of the magnetostrictive member, such as grinding marks, as shown in Patent Document 1. For this reason, an embodiment of the present invention is characterized by a manufacturing process flow for magnetostrictive members that does not involve strike plating. That is, in the magnetostrictive member 1 of this embodiment, the plating layer C is a single layer without being strike-plated. The plating layer C is, for example, a main plating layer. Note that the causes of changes in magnetostrictive properties due to plating are not limited to those described above and may include other causes.

[0035] When plating the magnetostrictive member 1, it is important not to change the stress or surface roughness on both main surfaces of the magnetostrictive member. For example, magnetostrictive characteristics are also affected by the plating thickness and the type of plating solution. Plating baths include acidic baths (acidic plating baths) and alkaline baths (alkaline plating baths). In this embodiment, as shown in the examples, it was found that acidic baths are more likely to etch the surface of the magnetostrictive member than alkaline baths, making the magnetostrictive characteristics more likely to change. From this perspective, it is preferable that the plating bath be an alkaline bath. As the plating thickness increases, the plating stress tends to increase and the magnetostrictive characteristics tend to change. The thickness of the plating layer C is preferably, for example, 1 μm or more and 10 μm or less, and more preferably 2 μm or more and 8 μm or less. When the thickness of the plating layer C is within the above range, changes in the magnetostrictive characteristics due to plating can be more reliably suppressed and corrosion resistance can be more reliably imparted. For example, by setting the thickness of the plating layer C within the above range, fluctuations in magnetostriction characteristics can be suppressed, as shown in the examples. When compared to the reference values, the force coefficient can fluctuate within ±10% and the optimal magnetic field strength can fluctuate within ±20%. Preferably, the force coefficient can fluctuate within ±5% and the optimal magnetic field strength can fluctuate within ±5%. The force coefficient and optimal magnetic field strength can be evaluated using methods similar to those described in Japanese Patent Application No. 2023-037128 and International Patent Application No. PCT / JP2024 / 4133, as described in detail in the examples. The thickness, force coefficient, and optimal magnetic field strength of the plating layer C may be within a range between two values ​​selected from the group consisting of any of the above upper and lower limits and any of the values ​​described in the examples, as long as they do not deviate from the spirit of the present invention. Alternatively, one value selected from this group may be used as the lower limit (lower limit range), or one value selected from this group may be used as the upper limit (upper limit range).

[0036] The plating process is performed after the magnetostrictive member is singulated, but a chamfering process may be performed before the plating process. The magnetostrictive member 1 is singulated, for example, using a peripheral blade or a dicing device. When singulating using both of the above devices, burrs of up to approximately 60 μm are generated on the cutting exit side (sometimes referred to as the burr side). Even if the processing conditions for the singulation are changed, the size of the burrs decreases, but burrs will always occur. In the magnetostrictive member 1, it is preferable to create a chamfered surface 6 (C-surface or curved surface) by chamfering to remove these burrs. Although the chamfering process can be performed after the plating process, the chamfered portion 6 is exposed without the plating layer C, making it prone to corrosion, so it is preferable to perform the plating process after the chamfering process.

[0037] The chamfering method is not particularly limited as long as it allows for chamfering of the edges (edge ​​portions) of the magnetostrictive member 1. For example, the chamfering method may involve using a bevel polishing machine with a chamfered grinding stone, or may involve processing with a cutter, grinder, abrasive paper, or the like using a jig. Each edge (all edges) may also be chamfered by barrel polishing using a barrel polishing machine or the like. Chamfering is preferably performed on portions where burrs are likely to occur when the magnetostrictive member 1 is singulated. For example, chamfering is preferably performed on the cutting exit side where burrs are likely to occur when the magnetostrictive member 1 is singulated. It is preferable to perform chamfering on at least four edges, namely, two longitudinal edges and two lateral edges on the cutting exit side of the side of the magnetostrictive member 1. Alternatively, all edges of the magnetostrictive member 1 may be chamfered. For example, the magnetostrictive member 1 according to one embodiment of the present invention includes removing at least a portion of the burrs. In one embodiment of the present invention, the magnetostrictive member 1 is a plate-like body, and at least some of the edges of the plate-like body may be configured as chamfered surfaces (chamfered portions). That is, the magnetostrictive member 1 may be a plate-like body, and may be configured to have chamfered surfaces 6 on at least some of the sides of the plate-like body. In the example shown in Fig. 1, the side portions include the portions of each side (12 sides in total) of the rectangular parallelepiped and the portions in the vicinity of the sides. Note that in this specification, "side portions" may also be abbreviated to "sides." The amount of chamfering by chamfering is not particularly limited as long as it does not deviate from the spirit of the present invention.

[0038] In particular, chamfering using barrel polishing is preferred because it can be performed continuously with barrel plating, resulting in high efficiency. Furthermore, barrel polishing and barrel plating are also preferred because they offer high production efficiency, allowing multiple magnetostrictive members to be placed in a container and processed at once. Barrel polishing involves placing magnetostrictive members in a container called a barrel, adding abrasive stones, compound, and water, and then moving or vibrating the container to bring the abrasive stones into contact with the magnetostrictive members inside the container, resulting in polishing. This results in curved chamfered surfaces on all sides of the magnetostrictive member. Furthermore, the main surfaces of the magnetostrictive member also come into contact with the abrasive stones, resulting in a smaller amount of polishing compared to the individual sides. Therefore, when a plating process is performed after barrel polishing, it is possible to remove deposits from the surface of the magnetostrictive member and improve the adhesion of the plating. For this reason, it is more preferable to perform a plating process after barrel polishing.

[0039] The characteristics of the magnetostrictive member 1 of this embodiment will be further described. For example, as shown in the examples, the magnetostrictive member 1 of this embodiment has good plating adhesion, with no peeling of the plating, when evaluated using the tape test method (15.1) of the plating adhesion test (JIS H8504) specified in the Japanese Industrial Standards. Furthermore, the magnetostrictive member 1 of this embodiment has good corrosion resistance, with no visible corrosion in a five-day water immersion test at room temperature.

[0040] As described above, the magnetostrictive member according to this embodiment is a plate-shaped member made of iron-based alloy crystals having magnetostrictive properties, having a longitudinal direction and a lateral direction, and the surface of the magnetostrictive member is coated with a single plating layer. The magnetostrictive member according to this embodiment suppresses the problem of deterioration of magnetostrictive properties due to plating, and has excellent environmental resistance.

[0041] (Method for manufacturing a magnetostrictive member) Next, a method for manufacturing a magnetostrictive member of this embodiment will be described. The method for manufacturing a magnetostrictive member of this embodiment is the method for manufacturing the magnetostrictive member 1 of this embodiment described above. In the following description, a method for manufacturing the magnetostrictive member 1 from a single crystal ingot of an Fe—Ga alloy will be described as an example, but the method for manufacturing the magnetostrictive member of this embodiment is not limited to the following description. Furthermore, any description in this specification that is applicable to the method for manufacturing the magnetostrictive member of this embodiment will also be applied to the method for manufacturing the magnetostrictive member of this embodiment. Furthermore, in the method for manufacturing a magnetostrictive member of this embodiment described below, any description that is applicable to the magnetostrictive member of the above embodiment will also be applied to the magnetostrictive member of this embodiment.

[0042] A method for manufacturing a magnetostrictive member according to an aspect of the present invention includes a step of preparing a magnetostrictive member cut into individual pieces, and a plating step of forming a single-layer plating layer on the surface of the prepared magnetostrictive member, the plating step not including strike plating. One aspect of the method for manufacturing a magnetostrictive member according to the present invention includes forming a single-layer plating layer to coat the surface of a magnetostrictive member that is a plate-shaped body made of crystals of an iron-based alloy having magnetostrictive properties and that has a longitudinal direction and a lateral direction.

[0043] In the process of preparing the singulated magnetostrictive members, for example, singulated magnetostrictive members manufactured by a conventional method are prepared. Magnetostrictive members are generally produced by processing a single crystal grown by a Cz method, VB method, or the like into a thin plate-like member by discharge wire cutting or the like, and then cutting the thin plate member into a predetermined shape using a cutting device or the like to produce the individual magnetostrictive members. Furthermore, as shown in Patent Document 1, a magnetostrictive member may have grinding marks (ground surfaces) added to it, such as multiple grooves 2 extending in the longitudinal direction D1 of the magnetostrictive member, such as grinding marks (e.g., grinding marks produced by surface grinding), to obtain a magnetostrictive member with a high magnetostriction constant and parallel magnetostriction and little variation in the magnetostriction constant and parallel magnetostriction between members. "Extending in the longitudinal direction D1" includes an angle of 45° or less between the magnetostrictive member and the longitudinal direction D1. Note that the magnetostrictive member does not necessarily have the grooves 2.

[0044] Next, the magnetostrictive member that has been cut into individual pieces is subjected to a chamfering process. As described above, large and small burrs are generated at the cut portions of the magnetostrictive member that has been cut into individual pieces. The chamfering process is a process for removing burrs. As described above, the chamfering process involves chamfering at least some of the edges of the plate-like body. The edges (sides) of the plate-like body that are subjected to the chamfering process are as described above. Furthermore, in the chamfering process, the shape of the chamfered surface 6 may be any of various chamfered shapes, as described above. In the chamfering process, the shape of the chamfered surface 6 may be, for example, a C-surface, a curved surface (e.g., an R-surface or a barrel-polished surface), or a lightly chamfered surface. The chamfering process can be performed by, for example, a known method. As described above, the chamfering process is preferably barrel polishing. Note that the chamfering process is an optional process.

[0045] The next step is a plating step in which a single plating layer is formed on the chamfered surface of the magnetostrictive member. This plating step does not include strike plating, as described above. The plating step is carried out, for example, using the plating method, type of plating bath, and thickness of the plating layer, as described above. For example, the type (material) of plating used in the plating step is not particularly limited as long as it is corrosion-resistant, and zinc plating, tin plating, nickel plating, etc. are preferred. Furthermore, the plating bath used in the plating step may be an acid bath (acid plating bath) or an alkaline bath (alkaline plating bath), with an alkaline bath being more preferred, as described above. The thickness of the plating layer C is preferably, for example, 1 μm or more and 10 μm or less, and more preferably 2 μm or more and 8 μm or less. When the thickness of the plating layer C is within the above range, changes in magnetostrictive properties due to plating can be more reliably suppressed, and corrosion resistance can be more reliably imparted.

[0046] In the manufacturing method of a magnetostrictive member according to an embodiment of the present invention, as described above, it is more preferable that the chamfering is performed by barrel polishing, and the plating step is barrel plating. Barrel polishing is preferable because it can be performed continuously with barrel plating, which is efficient. Furthermore, barrel polishing and barrel plating are preferable because they provide good production efficiency, as many magnetostrictive members can be placed in a container and processed at once. Furthermore, if the plating step is performed after barrel polishing, it is preferable because, as described above, it is possible to remove deposits from the surface of the magnetostrictive member and improve the adhesion of the plating.

[0047] EXAMPLES The present invention will be specifically explained below using examples, but the present invention is not limited to these examples in any way.

[0048] Example 1 A magnetostrictive member was manufactured based on the manufacturing method of the present embodiment described above. The magnetostrictive member was prepared by processing and dividing a cylindrical Fe—Ga alloy single crystal grown by the vertical Bridgman (VB) method and having a gallium content of 17.2 to 19.8 at%.

[0049] The single crystal was divided into individual pieces using the following procedure. First, a loose abrasive wire saw was used to cut the single crystal parallel to the single crystal growth direction to produce a thin plate member. Next, the resulting thin plate member was subjected to surface grinding using a #100 flat grinding wheel on a surface grinder to adjust the thickness of the thin plate member and form multiple grooves (grinding marks) on the front and back surfaces. The cutting position was then set so that the longitudinal direction of the magnetostrictive member was the same as the grinding direction during surface grinding, i.e., the grinding mark direction, and a magnetostrictive material measuring 25 mm in the longitudinal direction, 4 mm in the lateral direction, and 0.5 mm in thickness was cut out using a peripheral blade cutting device.

[0050] Next, chamfering was performed. For the chamfering, each side (all sides) was chamfered using a barrel polishing machine. A magnetic bench-top barrel polishing machine was used for the barrel polishing. Stainless steel pins were used as polishing stones, and liquid compound and pure water were added. The rotation speed was 350 rpm, and the processing time was 30 minutes. In this example, the corners of the magnetostrictive member, the sides parallel to the short direction D2, and the sides parallel to the long direction D1 were polished in that order. The amount of polishing near the center of the long direction D1 was the smallest. The chamfer width at the center of the long direction D1 was measured and found to be 30 to 50 μm. The chamfer width was determined by measuring five arbitrary points on an image obtained by observation with an optical microscope.

[0051] Next, zinc plating was performed using a barrel plating device. Pre- and post-plating treatments were performed using conventional techniques. However, nickel strike plating, which is performed before the main plating, was not performed. The plating bath was an acidic Zn plating bath. The plating thickness was 3 μm. Using the above method, 10 magnetostrictive members of the present embodiment were produced (manufactured).

[0052] Next, the manufactured magnetostrictive members were evaluated. First, a water immersion test was conducted to evaluate the corrosion resistance of the magnetostrictive members. The water immersion test was conducted for 5 days at room temperature, and the appearance of the magnetostrictive members was observed after the water immersion test. If there was no corrosion after 5 days of testing under the above conditions, the members were deemed good and marked with a circle. If corrosion occurred after 5 days, the members were deemed bad and marked with a cross.

[0053] The plating adhesion was evaluated using the tape test method (15.1) of the plating adhesion test (JIS H8504) specified in the Japanese Industrial Standards. When there was no peeling of the plating, it was rated as good with a "◯" and when there was peeling of the plating, it was rated as bad with a "X".

[0054] The magnetostriction characteristics were evaluated using the same method as that described in Japanese Patent Application No. 2023-037128 and International Patent Application No. PCT / JP2024 / 4133, in terms of the maximum force coefficient (force coefficient) and the maximum optimum magnetic field strength (optimum magnetic field strength). For comparison, the force coefficients of 10 magnetostrictive members that were not chamfered and had burrs of 20 μm or less when cut were compared with the average values ​​of the optimum magnetic field strength at that time.

[0055] The following describes the evaluation of the maximum force coefficient (force factor) and the maximum optimal magnetic field strength (optimum magnetic field strength), using a method similar to that described in Japanese Patent Application No. 2023-037128 and International Patent Application No. PCT / JP2024 / 4133. The maximum force coefficient (force factor) and the maximum optimal magnetic field strength (optimum magnetic field strength) were evaluated using an evaluation method based on analysis (impedance measurement) using an electromechanical equivalent circuit. Analysis (impedance measurement) using an electromechanical equivalent circuit is described below. Figure 3 shows an overview of the impedance measurement device. A bias magnetic field is generated by an excitation coil using a DC (direct current) power supply, magnetizing the magnetostrictive material. The impedance of the measurement coil is measured with the magnetostrictive material placed inside the measurement coil. The equivalent circuit of the measurement coil is shown in Figure 4, and the equivalent impedance of this circuit can be expressed by the following equation (1). The force factor α is the degree of coupling between the mechanical system and the electrical system, is an index of the energy conversion efficiency from mechanical energy to electrical energy, and is positively correlated with the power generation output of the vibration power generation device.

[0056]

[0057] The measured impedance loop is converted into a dynamic impedance loop by removing the electric circuit component, and the force coefficient α is calculated using the following equations (2) and (3).

[0058] The impedance measurement is performed multiple times while changing the bias magnetic field generated by the excitation coil by changing the current of the DC power supply. When the force factor α is measured while changing the magnetic field strength from 0 kA / m to the saturation magnetic field, the force factor α is maximized near half the saturation magnetic field strength and decreases elsewhere. The magnetic field strength at which the force factor α is maximized is the optimal magnetic field strength. The force factor α at the optimal magnetic field strength is defined as the force factor αmax (note that the force factor αmax may also be abbreviated as force factor). That is, a bias magnetic field is generated to magnetize the magnetostrictive material, and the impedance of the measurement coil is measured with the magnetostrictive material placed in the measurement coil multiple times while changing the bias magnetic field up to the saturation magnetic field strength. Based on the measurement results of the impedance of the measurement coil obtained, the optimal magnetic field strength, which is the magnetic field strength at which the force factor α is maximized, and the characteristics of the magnetostrictive member, including the force factor αmax at the optimal magnetic field strength, can be determined.

[0059] In each example of this example and this comparative example, the magnetostrictive properties were measured using an impedance measurement device as shown in Figure 3, and the force factor and optimal magnetic field strength were determined. The impedance measurement was performed as follows. A measurement coil was created so that the manufactured magnetostrictive member would fit inside, and impedance measurements equivalent to those described in Patent Document 3 (Japanese Patent Publication No. 7084620) were performed. The excitation current was 10 to 70 mA, and current was applied at 5 mA intervals. Converted to magnetic field strength, 1 mA = 78.4 A / m, and a bias magnetic field was applied at 0.392 kA / m intervals in the range of 0.784 to 5.488 kA / m. An impedance analyzer was used to perform impedance measurements at frequencies of 50 to 150 kHz, and the force factor α at each magnetic field strength was calculated. The optimal magnetic field strength at which the force factor α was maximized and the force factor αmax at that time were calculated.

[0060] The manufacturing conditions and evaluation results are shown in Table 1. In Example 1, both the corrosion resistance and the plating adhesion were good. In addition, the force coefficient and the optimum magnetic field strength were within ±5% of the standard, and there was little change in the magnetostriction characteristics, which was good.

[0061] [Example 2] In Example 2, the plating thickness was 6 μm. Other conditions were the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1. In Example 2, both corrosion resistance and plating adhesion were good. Furthermore, the force coefficient was good, within ±10% of the standard, but the optimal magnetic field strength tended to be slightly higher, ranging from 0% to +15% of the standard.

[0062] [Example 3] In Example 3, the plating bath for Zn plating was an alkaline bath. Other conditions were the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1. In Example 3, both corrosion resistance and plating adhesion were good. In addition, the force coefficient was good, being within ±3% of the standard, and the optimum magnetic field strength was also good, being within ±5% of the standard.

[0063] In Example 4, the Zn plating bath was an alkaline bath, and the plating thickness was 6 μm. Other conditions were the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1. In Example 4, both the corrosion resistance and the plating adhesion were good. In addition, the force coefficient was good, being within ±6% of the standard, and the optimum magnetic field strength was also good, being within ±5% of the standard.

[0064] [Comparative Example 1] In Comparative Example 1, nickel strike plating was performed before Zn plating. The nickel strike plating was performed for 10 minutes. Other conditions were the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1. In Comparative Example 1, the plating layer consisted of two layers: a strike plating layer and a Zn plating layer. In Comparative Example 1, both the corrosion resistance and plating adhesion were good. In addition, the force coefficient was within ±10% of the reference, and the optimal magnetic field strength tended to be 0% to +35% greater than the reference.

[0065] [Comparative Example 2] For Comparative Example 2, a magnetostrictive member was prepared by cutting into individual pieces similar to those in Example 1 and barrel polishing. However, no plating was performed. Comparative Example 2 was the same as Example 1 except that no plating was performed. The manufacturing conditions, evaluation results, etc. are shown in Table 1. For Comparative Example 2, in the corrosion resistance evaluation, corrosion occurred over the entire surface after 24 hours of immersion in water.

[0066]

[0067] (Summary) The results of Examples 1 to 4 and Comparative Example 1 indicate that when strike plating is performed as in Comparative Example 1, the variation in magnetostrictive properties is greater than when strike plating is not performed as in Examples 1 to 4. The results of Examples 1 to 4 and Comparative Examples 1 and 2 confirm that the magnetostrictive member and method for manufacturing the magnetostrictive member of this embodiment suppress the problem of magnetostrictive property degradation due to plating and have environmental resistance. As shown in the examples, the magnetostrictive member 1 can suppress the variation in magnetostrictive properties. When compared with a reference value, the force coefficient can vary within ±3%, ±5%, ±6%, or ±10%, preferably within ±10%, more preferably within ±6%, even more preferably within ±5%, and particularly preferably within ±3%. Furthermore, the optimal magnetic field intensity can vary within ±5%, 0% to 15%, preferably within ±5%. Furthermore, the corrosion resistance of the magnetostrictive member 1 can be measured by the water immersion test, as shown in the examples, in which no corrosion is observed after the water immersion test. Furthermore, as shown in the examples, the adhesion can be determined as a state in which no peeling of the plating occurs in the above plating adhesion evaluation test.

[0068] The technical scope of the present invention is not limited to the aspects described in the above-mentioned embodiments. One or more of the requirements described in the above-mentioned embodiments may be omitted. Furthermore, the requirements described in the above-mentioned embodiments may be combined as appropriate. Furthermore, to the extent permitted by law, the disclosures of Japanese Patent Application No. 2024-153101 and all documents cited in the above-mentioned embodiments are incorporated by reference into this specification.

[0069] 1: Magnetostrictive member 2: Groove 3: Surface 4: Back surface 5: Side (side portion) 6: Chamfered surface (chamfered portion) C: Plating layer D1: Longitudinal direction D2: Shortitudinal direction

Claims

1. A magnetostrictive member that is a plate-shaped body made of crystals of an iron-based alloy having magnetostrictive properties and has a longitudinal direction and a lateral direction, the surface of which is coated with a single plating layer.

2. The magnetostrictive member according to claim 1, wherein at least some of the sides of said plate-like body are chamfered.

3. The magnetostrictive member according to claim 2, wherein the chamfered surface is a curved surface.

4. The magnetostrictive member according to claim 1, wherein the plating layer of the magnetostrictive member is a zinc plating layer.

5. A method for manufacturing a magnetostrictive member, comprising: a step of preparing a magnetostrictive member cut into individual pieces; and a plating step of forming a single plating layer on the surface of the prepared magnetostrictive member, wherein the plating step does not include strike plating.

6. A method for manufacturing a magnetostrictive member according to claim 5, further comprising a step of chamfering the prepared magnetostrictive member.

7. A method for manufacturing a magnetostrictive member according to claim 5, wherein the plating step is zinc plating.

8. A method for producing a magnetostrictive member according to claim 7, wherein the plating bath for the zinc plating is an alkaline plating bath.

9. The method for manufacturing a magnetostrictive member according to claim 6, wherein the chamfering is barrel polishing.

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