Magnetostrictive member and method for manufacturing magnetostrictive member

Abstract

[Problem] To provide a magnetostrictive member which uses a stable index that can be easily evaluated and is unaffected by the size and thickness of the magnetostrictive member in a device characteristic when a magnetostrictive vibration power generation device is manufactured, which produces a high device characteristic, and which suppresses variations in optimum magnetic field strength, and to provide a method for manufacturing the magnetostrictive member. [Solution] A plurality of magnetostrictive members are obtained from the same crystal. The magnetostrictive member comprises a crystal of an iron-based alloy having a magnetostrictive characteristic, and is a plate-shaped body having a longitudinal direction and a lateral direction. At least one surface of the front surface and the back surface of the plate-shaped body has a plurality of grooves extending in the longitudinal direction. The plurality of magnetostrictive members have, as the optimum magnetic field strength, magnetic field strength when a half-value frequency coupling coefficient (= kf1f2) obtained by electromechanical equivalent circuit analysis becomes maximum, and the ratio (standard deviation / average value) between the standard deviation of the optimum magnetic field strength and the average value of the optimum magnetic field strength is 0.2 or less.

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 attracted attention as functional materials. For example, Fe—Ga alloys, which are iron-based alloys, exhibit magnetostrictive and inverse magnetostrictive effects, exhibiting large magnetostrictions of approximately 100 to 350 ppm. Therefore, in recent years, they have attracted attention as vibration-powered energy harvesting materials in the energy harvesting field, and are expected to be applied to wearable devices and sensors. A method for growing single crystals of Fe—Ga alloys using a pulling method (Czochralski method, hereinafter abbreviated as the "Cz method") is known (see, for example, Patent Document 1). Other known manufacturing methods besides the Cz method include the vertical Bridgman method (VB method) and the vertical gradient freezing method (VGF method) (see, for example, Patent Documents 2 and 3).

[0003] An Fe—Ga alloy has an easy axis of magnetization in the <100> direction of the crystal, and can exhibit large magnetostriction in this direction. Conventionally, magnetostrictive members of Fe—Ga alloys have been manufactured by cutting a single crystal portion oriented in the <100> direction from an Fe—Ga polycrystal to the desired size (for example, Non-Patent Document 1). However, because the crystal orientation has a significant effect on the magnetostrictive properties, it is thought that a single crystal in which the direction in which magnetostriction is required and the <100> direction in which the magnetostriction of the crystal is maximized are the optimal material for magnetostrictive members.

[0004] When a magnetic field is applied parallel to the <100> direction of the Fe-Ga alloy single crystal, positive magnetostriction appears (hereinafter referred to as "parallel magnetostriction"). On the other hand, when a magnetic field is applied perpendicular to the <100> direction, negative magnetostriction appears (hereinafter referred to as "perpendicular magnetostriction"). When the strength of the applied magnetic field is gradually increased, the parallel magnetostriction or perpendicular magnetostriction becomes saturated. The magnetostriction constant (3 / 2λ １００ ) is determined by the difference between the saturated parallel magnetostriction amount and the saturated perpendicular magnetostriction amount, and is calculated by the following formula (A) (for example, Patent Document 4 and Non-Patent Document 2).

[0005] 3 / 2λ １００ = ε ( / / ) - ε (⊥) ...Formula (A) 3 / 2λ１００ : Magnetostriction constant ε ( / / ): Parallel magnetostriction amount when saturated by applying a magnetic field parallel to the <100> direction ε (⊥): Perpendicular magnetostriction amount when saturated by applying a magnetic field perpendicular to the <100> direction

[0006] The magnetostrictive properties of Fe—Ga alloys are believed to affect the magnetostrictive and inverse magnetostrictive effects and the characteristics of magnetostrictive vibration power generation devices, and are an important parameter in device design (see, for example, Non-Patent Document 4). 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% (see, for example, Non-Patent Document 2). It is 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 (see, for example, Non-Patent Document 3).

[0007] A magnetostrictive vibration power generation device, for example, is composed of an Fe—Ga magnetostrictive member wound around a coil, a yoke, and a permanent magnet for a field magnet (see, for example, Patent Document 5 and Non-Patent Document 4). In this magnetostrictive vibration power generation device, when the yoke, which is the moving part of the device, is vibrated, the Fe—Ga magnetostrictive member fixed to the center of the yoke vibrates in conjunction with it. The inverse magnetostrictive effect changes the magnetic flux density of the coil wound around the Fe—Ga magnetostrictive member, 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 Fe—Ga magnetostrictive member used in the device so that the easy axis of magnetization, <100>, is aligned longitudinally.

[0008] Japanese Patent Application Laid-Open No. 2016-28831 Japanese Patent Application Laid-Open No. 2016-138028 Japanese Patent Application Laid-Open No. 4-108699 Special Publication No. 2015-517024 International Publication No. 2011 / 158473 International Publication No. 2021 / 100467 Japanese Patent Application Laid-Open No. 2020-63997

[0009] Etrema, State of the Art of Galfenol Processing. A. E. 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). Toshiyuki Ueno, Journal of the Japan Society of Precision Engineering Vol. 79, No. 4, (2013) 305-308. Journal of the Marine Acoustics Society, Volume 24, No. 3 (1997)

[0010] Because the device characteristics of magnetostrictive vibration power generation devices and the like are affected by the magnetostrictive properties of the magnetostrictive member, 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, as described in Non-Patent Document 3, it is disclosed that device characteristics are affected not only by the magnetostrictive constant but also by the amount of parallel magnetostriction. Therefore, Patent Document 6 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.

[0011] However, to maximize the output (power generation) of the device, it is necessary to appropriately set the magnetic flux density of the magnet incorporated in the device. More specifically, the magnetic flux density (hereinafter referred to as the optimal magnetic field strength) must be approximately half of the maximum parallel magnetostriction of the magnetostrictive material incorporated in the device.

[0012] Here, in the magnetostrictive vibration power generation device using the magnetostrictive member of Patent Document 6, there is a large variation in the optimal magnetic field strength of the magnetostrictive material, and in order to improve the output of the device, it is necessary to adjust the magnet strength (magnetic flux density) for each device, which reduces productivity.

[0013] Furthermore, in the above, the device output is evaluated using a force coefficient, but since the force coefficient depends on the size and thickness of the magnetostrictive member, it was necessary to set an appropriate value for each size and thickness of the magnetostrictive member.

[0014] Therefore, the present invention aims to provide a magnetostrictive member and a method for manufacturing a magnetostrictive member that can be easily evaluated based on the device characteristics when incorporated into the magnetostrictive vibration power generation device using a magnetostrictive member that has a high amount of parallel magnetostriction and little variation in the amount of parallel magnetostriction between members, and that uses a stable index that is not affected by the size or thickness of the magnetostrictive member, and that has large device characteristics based on this index and also suppresses variation in the optimal magnetic field strength.

[0015] According to an aspect of the present invention, there is provided a magnetostrictive member obtained in plurality from the same crystal, which is a plate-like member made of crystals of an iron-based alloy having magnetostrictive properties and having a longitudinal direction and a lateral direction, and at least one of the front and rear surfaces of the plate-like member has a plurality of grooves extending in the longitudinal direction, and the plurality of magnetostrictive members have a half-value frequency coupling coefficient (= k ｆ１ｆ２ The optimum magnetic field strength is the strength at which the value of the standard deviation of the optimum magnetic field strength is maximized, and a magnetostrictive member is provided in which the ratio of the standard deviation of the optimum magnetic field strength to the average value of the optimum magnetic field strength (standard deviation / average value) is 0.2 or less.

[0016] Furthermore, the plurality of magnetostrictive members have a half-value frequency coupling coefficient (=k ｆ１ｆ２ ) is the standard deviation of the maximum value and the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) to the average value of the maximum value (standard deviation / average value) may be 0.3 or less. ｆ１ｆ２ ) is the standard deviation of the maximum value and the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) may be configured such that the ratio of the maximum value of the standard deviation to the average value (standard deviation / average value) is 0.1 or less.

[0017] Furthermore, there are magnetostrictive members obtained in plural from the same crystal, which are made of iron-based alloy crystals having magnetostrictive properties, and are plate-shaped bodies having a longitudinal direction and a transverse direction, and the plural magnetostrictive members have a half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is the strength at which it is maximized, and the ratio (standard deviation / mean value) of the standard deviation of the optimum magnetic field strength to the mean value of the optimum magnetic field strength is 0.2 or less, and the half-value frequency coupling coefficient (= k ｆ１ｆ２ The magnetostrictive member may have a thickness of 0.3 mm or more and 5 mm or less.

[0018] According to an aspect of the present invention, a method for manufacturing a magnetostrictive member of the above aspect can be provided, which includes forming a plurality of grooves extending in the longitudinal direction on at least one of the front and back surfaces of a plate-like body made of crystals of an iron-based alloy having magnetostrictive properties and having a longitudinal direction and a lateral direction, and heat-treating the plate-like body in which the plurality of grooves extending in the longitudinal direction have been formed.

[0019] The plurality of grooves may be formed by surface grinding. The heat treatment temperature may be 400°C or higher and 700°C or lower. The heat treatment holding time may be 5 hours or less. The heat treatment method may further include re-grooving the plurality of grooves extending in the longitudinal direction of the heat-treated plate-like body. The method may further include a cutting step of cutting the plate-like body with the plurality of grooves formed therein, and a chamfering step of chamfering the plate-like body cut by the cutting step.

[0020] According to an aspect of the present invention, it is possible to provide a magnetostrictive member and a method for manufacturing a magnetostrictive member, which have a high parallel magnetostriction amount and little variation in the parallel magnetostriction amount between members, and which can easily evaluate the device characteristics when a magnetostrictive vibration power generation device is manufactured using a magnetostrictive member that has a stable index that is not affected by the size or thickness of the magnetostrictive member, and which has high device characteristics and suppresses variation in the optimal magnetic field strength.

[0021] FIG. 1 is a diagram showing an example of a magnetostrictive member according to an embodiment. FIG. 2 is a diagram showing an example of a change in a BH curve when stress is applied to a magnetostrictive member. FIG. 3 is a diagram showing an example of an impedance measuring device. FIG. 4 is a diagram showing an electro-mechanical equivalent circuit of a measurement coil. FIG. 5 is a flowchart showing an example of a method for manufacturing a magnetostrictive member according to an embodiment. FIG. 6 is a diagram showing examples of a single crystal and a thin plate member.

[0022] The following description will be made with reference to the drawings. In each drawing, some or all of the components are shown in schematic form and scaled as appropriate.

[0023] [Embodiment] Hereinafter, a magnetostrictive member and a method for manufacturing a magnetostrictive member according to this embodiment will be described.

[0024] (Magnetostrictive Member) First, the magnetostrictive member of this embodiment will be described. Fig. 1 is a diagram showing an example of a magnetostrictive member according to an embodiment.

[0025] As shown in Fig. 1, 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 front surface 3 and a back surface 4. The front surface 3 and the back surface 4 are preferably parallel to each other, but do not have to be parallel to each other.

[0026] The magnetostrictive member 1 is made of an iron-based alloy crystal. Multiple magnetostrictive members 1 are 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 power generation materials in the energy harvesting field, 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.

[0027] The Fe—Ga alloy single crystal has a body-centered cubic lattice structure, and is based on the principle that the first to third <100> axes (see FIG. 6 ) among the directional indices in the Miller indices are equivalent, and the first to third {100} planes (see FIG. 6 ) among the plane indices in the Miller indices are equivalent (i.e., (100), (010), and (001) are equivalent). Furthermore, the 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.

[0028] 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.

[0029] 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 5 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 long side length of 10 mm or more, 30 mm or more, 60 mm or more, or 80 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 16 mm, the width (dimension) in the lateral direction D2 is 4 mm, and the thickness is 0.5 mm.

[0030] 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.

[0031] As described above, the inventors of the present invention confirmed that, as described in Patent Document 6, by adding multiple grooves (e.g., grinding marks) extending in the longitudinal direction of a magnetostrictive member, it is possible to obtain a magnetostrictive member with a high magnetostriction constant and parallel magnetostriction amount and little variation in the magnetostriction constant and parallel magnetostriction amount between members. However, in magnetostrictive vibration power generation devices using this magnetostrictive member, the optimum magnetic field strength of the magnetostrictive member varies greatly, requiring adjustment of the magnet strength for each device according to the variation in the optimum magnetic field strength, which reduces productivity. Therefore, the inventors have discovered that the variation in the optimum magnetic field strength can be reduced by heat-treating the magnetostrictive member. The present invention is based on this finding.

[0032] Since magnetostrictive materials are used in magnetostrictive vibration-based power generation devices, we will first explain the principles of magnetostrictive vibration-based power generation. The easy axis of magnetization of iron-based magnetostrictive materials is

[100] . As shown in Figure 2, when compressive stress is applied in the

[100] direction, the applied magnetic field strength required for magnetic saturation increases, and when tensile stress is applied in the

[100] direction, the applied magnetic field strength required for magnetic saturation decreases. When a bias magnetic field is applied to a magnetostrictive material to continuously generate compressive and tensile stresses, the magnetic flux density, which is the difference between the BH curves, changes. In magnetostrictive vibration power generation, this change in magnetic flux density is utilized to generate an AC current in a coil wrapped around the magnetostrictive material through Faraday's electromagnetic induction.

[0033] In Figure 2, when there is no magnetic field (magnetic field strength is 0 kA / m), the magnetic flux density is close to 0 T during both compression and tension, so there is no change in the magnetic flux density and no power generation occurs. As the magnetic field strength increases, a difference in magnetic flux density occurs between compression and tension, making it possible to generate power. When the magnetic field strength becomes very large, the magnetic field becomes saturated during both compression and tension, so there is almost no difference in magnetic field strength and no power generation occurs. Therefore, in order to generate power efficiently, it is necessary to apply an optimized magnetic field strength so that the difference in magnetic flux density between compression and tension is maximized. In this specification, the magnetic field strength at this time is referred to as the optimal magnetic field strength.

[0034] Furthermore, as a method for evaluating the power generation characteristics of a magnetostrictive vibration power generation device, there is an evaluation method based on analysis (impedance measurement) using an electromechanical equivalent circuit, as disclosed in Patent Document 7 and Non-Patent Document 5 above.

[0035] Analysis (impedance measurement) using an electromechanical equivalent circuit is explained 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 coefficient α is the degree of coupling between the mechanical system and the electrical system, and 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.

[0036]

[0037] The measured impedance loop is converted into a dynamic impedance loop by removing the electric circuit component from the measured impedance loop, and the force coefficient α is calculated using the following equations (2) and (3).

[0038] 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.

[0039] The power generation characteristics of a magnetostrictive material can be evaluated by the force coefficient αmax, but if the magnetic field strength deviates from the optimal magnetic field strength, the power generation characteristics will decrease. In other words, since the force coefficient α depends on the applied magnetic field strength, it is ideal to design a bias magnet so that the force coefficient αmax can be used within the power generation device and the magnetic field strength is the optimal magnetic field strength. Therefore, the optimal magnetic field strength is also an important characteristic indicator, and it is required that there is no variation between magnetostrictive materials. Furthermore, a smaller optimal magnetic field strength is preferable from the perspective of miniaturizing power generation devices, as it allows for the bias magnet to be incorporated into the power generation device to be smaller.

[0040] However, since the force coefficient depends on the size and thickness of the magnetostrictive member, it is necessary to set an appropriate value for each size and thickness of the magnetostrictive member.

[0041] Therefore, the inventors have studied and, as will be explained below, have determined that the half-value frequency coupling coefficient (= k ｆ１ｆ２ It has been found that the above problems can be improved by using the above-mentioned property of the magnetostrictive member.

[0042] In this embodiment, impedance is measured using an analysis (impedance measurement) using an electromechanical equivalent circuit, similar to the force coefficient, and the half-value of the resonance frequency (= f1) and the half-value of the anti-resonance frequency (= f2) obtained from the impedance measurement are used to calculate the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is calculated.

[0043] The half-frequency coupling coefficient is calculated from the impedance measurement as described above. The half-frequency coupling coefficient is measured multiple times by varying the excitation strength of the excitation coil. The excitation strength is set multiple times within a range from no magnetic field to magnetic field saturation. This magnetic field saturation can be defined as the state in which the half-frequency coupling coefficient reaches a peak, then drops and becomes almost constant. The excitation strength varies depending on the material, size, and thickness of the magnetostrictive material, so it is set appropriately. For example, for an FeGa alloy with a thickness of 2 mm and an excitation coil, a magnetic field of 0.2 to 3.6 kA / m can be set. The measurement interval should be set to a current value of 5 to 10 mA, for example, to ensure a resolution that allows the peak position to be determined. The impedance is measured in a frequency range of, for example, 10 kHz to 200 kHz. The measurement frequency range is set to the frequency range in which resonance and antiresonance occur.

[0044] In this embodiment, the half-value of the resonance frequency (= f1) and the half-value of the anti-resonance frequency (= f2) obtained from impedance measurement are used as indicators of magnetostriction characteristics. As a result, the magnetostrictive material has the maximum energy absorption at the half-value frequency, improving the correlation with the force coefficient. In addition, since the force coefficient is derived using the half-value frequency, the correlation with the half-value frequency coupling coefficient improves.

[0045] Like the force coefficient, the half-frequency coupling coefficient reaches a maximum value at a predetermined magnetic field strength. In the magnetostrictive member of this embodiment, the magnetic field strength at which this half-frequency coupling coefficient is maximized is defined as the optimal magnetic field strength. The force coefficient and the half-frequency coupling coefficient have a nearly positive correlation. Furthermore, the optimal magnetic field strength for the force coefficient and the optimal magnetic field strength for the half-frequency coupling coefficient were nearly identical. The force coefficient tends to increase as the size and thickness of the magnetostrictive member increase. In contrast, as shown in Examples 1 to 4, the half-frequency coupling coefficient is not affected by size and is nearly constant, with a high value and stable with little variation. Therefore, by using the maximum value of the half-frequency coupling coefficient as an index for a magnetostrictive member, it can be easily evaluated and can be a stable index that is not affected by the size or thickness of the magnetostrictive member.

[0046] The magnetostrictive member of this embodiment is a plate-like body made of crystals of an iron-based alloy having magnetostrictive properties, having a longitudinal direction and a lateral direction, and at least one of the front and back surfaces of the plate-like body is a magnetostrictive member having a plurality of grooves extending in the longitudinal direction, and the magnetic field strength at which the half-value frequency coupling coefficient of the plurality of magnetostrictive members is maximized is defined as the optimal magnetic field strength, and the ratio of the standard deviation of this optimal magnetic field strength to the average value of the optimal magnetic field strength (standard deviation / average value) is 0.2 or less, and the optimal magnetic field strength is calculated by electro-mechanical equivalent circuit analysis. This will be explained in detail below.

[0047] As shown in FIG. 1 , the magnetostrictive member 1 of this embodiment has a plurality of grooves 2 extending in the longitudinal direction D1 on at least one of the front surface 3 and the back surface 4 (sometimes collectively referred to as the “front and back surfaces”). The plurality of grooves 2 extending in the longitudinal direction D1 can be similar to those described in Patent Document 6, for example. As shown in Patent Document 6, by forming a plurality of grooves 2 extending in the longitudinal direction D1 on at least one of the front and back surfaces of the magnetostrictive member, it is possible to improve both the magnetostriction constant and the parallel magnetostriction amount so that they are high and have little variation between members (also referred to as “improving the magnetostriction constant and the parallel magnetostriction amount”), and in particular the parallel magnetostriction amount. In this embodiment, “the plurality of grooves 2 extending in the longitudinal direction D1” includes the plurality of grooves 2 extending in a direction parallel to the longitudinal direction D1 and the plurality of grooves 2 extending in a direction intersecting the longitudinal direction D1 at an angle of less than 40°.

[0048] It has been found that by forming multiple grooves 2 on the surface of the magnetostrictive member as described above, the magnetostriction constant and parallel magnetostriction amount are stable at high levels. When the impedance measurement described above was performed using this magnetostrictive member, it was found that the force coefficient and half-value frequency coupling coefficient were also stable at high levels. This gives the magnetostrictive member 1 of this embodiment excellent magnetostriction characteristics. Furthermore, it is presumed that by forming multiple grooves 2 on the surface of the magnetostrictive member 1, stress such as residual strain in a certain direction is applied within the crystal, and the magnetic moments are uniformly rearranged, thereby improving the parallel magnetostriction amount, force coefficient, etc. to high levels.

[0049] Furthermore, the magnetostrictive member of this embodiment is modified by heat treatment, which will be described later, so that the variation in magnetostrictive properties is suppressed. For example, from the results of Example 2 (with heat treatment) and Comparative Example 2 (without heat treatment), which compare magnetostrictive members of the same size with and without heat treatment, it can be seen that heat treatment (i) reduces the variation (standard deviation) and the ratio of the standard deviation to the average value (standard deviation / average value) of the half-value frequency coupling coefficient, and (ii) reduces the average value, variation (standard deviation), and the ratio of the standard deviation to the average value (standard deviation / average value) of the optimal magnetic field strength.

[0050] In the magnetostrictive member of this embodiment, the half-value frequency coupling coefficient (= k ｆ１ｆ２ When the magnetic field strength at which the value of (1 / 2) is maximum is defined as the optimum magnetic field strength, the ratio of the standard deviation of the optimum magnetic field strength to the average value of the optimum magnetic field strength (standard deviation / average value) is 0.2 or less, and preferably 0.15 or less.

[0051] The standard deviation of the optimum magnetic field strength is preferably 0.6 or less, and more preferably 0.3 or less.

[0052] In addition, in the magnetostrictive member 1 of this embodiment, the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) and the standard deviation of the maximum value of the half-value frequency coupling coefficient (= k ｆ１ｆ２ The ratio of the maximum value of the standard deviation to the average value (standard deviation / average value) is preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less.

[0053] In addition, in the magnetostrictive member 1 of this embodiment, the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is preferably 0.7 or more.

[0054] In addition, in the magnetostrictive member 1 of this embodiment, the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is preferably 0.05 or less.

[0055] In this embodiment, the force coefficient, half-value frequency coupling coefficient, and optimal magnetic field strength are values ​​calculated by electromechanical equivalent circuit analysis as described above, and can be determined, for example, by the method described in this specification.

[0056] The above average values ​​and variations (standard deviations) may be calculated from multiple magnetostrictive members produced from the same crystal. For example, they may be calculated from multiple magnetostrictive members produced under the same manufacturing conditions from a single grown crystal, or they may be produced simultaneously under the same manufacturing conditions. Furthermore, there are no limitations on the number of magnetostrictive members produced from the same crystal, or on the number of measurements (n) used to calculate the above average values ​​and variations (standard deviations). The number n is preferably 4 to 10.

[0057] As described above, the magnetostrictive member of this embodiment is a magnetostrictive member obtained in plurality from the same crystal, and is a plate-like member made of iron-based alloy crystals having magnetostrictive properties, having a longitudinal direction and a lateral direction, at least one of the front and rear surfaces of the plate-like member has a plurality of grooves extending in the longitudinal direction, and the plurality of magnetostrictive members have a half-value frequency coupling coefficient (= k ｆ１ｆ２ The magnetic field strength at which the value of the standard deviation of the optimum magnetic field strength is maximized is defined as the optimum magnetic field strength, and the ratio of the standard deviation of the optimum magnetic field strength to the average value of the optimum magnetic field strength (standard deviation / average value) is 0.2 or less.

[0058] The magnetostrictive member 1 of this embodiment, due to the above-mentioned configuration, can easily evaluate the device characteristics when a magnetostrictive vibration power generation device is manufactured using a magnetostrictive member with a high amount of parallel magnetostriction and little variation in the amount of parallel magnetostriction between members, and uses a stable index that is not affected by the size or thickness of the magnetostrictive member, resulting in high device characteristics and reduced variation in the optimal magnetic field strength.

[0059] (Method for manufacturing a magnetostrictive member) Next, a method for manufacturing the magnetostrictive member of this embodiment will be described. The method for manufacturing the magnetostrictive member of this embodiment is the method for manufacturing the magnetostrictive member 1 of this embodiment described above. The method for manufacturing the magnetostrictive member of this embodiment is the method for manufacturing the magnetostrictive member 1 of this embodiment described above, and includes forming a plurality of grooves 2 extending in the longitudinal direction D1 on at least one of the front surface 3 and the back surface 4 of a plate-like body made of crystals of an iron-based alloy having magnetostrictive properties and having a longitudinal direction D1 and a lateral direction D2, and heat-treating the plate-like body with the plurality of grooves extending in the longitudinal direction formed therein.

[0060] In the following description, a method for manufacturing the magnetostrictive member 1 from a single crystal ingot of an Fe—Ga alloy is described as an example, but the manufacturing method of the magnetostrictive member of this embodiment is not limited to the following description. Furthermore, any description in this specification that is applicable to the manufacturing method of the magnetostrictive member of this embodiment is also applicable to the manufacturing method of the magnetostrictive member of this embodiment. Furthermore, in the manufacturing method of the magnetostrictive member of this embodiment that is applicable to the magnetostrictive member of the above-mentioned embodiment, it is also applicable to the magnetostrictive member of this embodiment.

[0061] Fig. 5 is a flowchart showing an example of a method for manufacturing a magnetostrictive member according to this embodiment. Fig. 6 is a diagram showing first to third examples (a, b, c) of a single crystal (single crystal ingot) and a thin plate member. The method for manufacturing a magnetostrictive member according to this embodiment includes, for example, a crystal preparation step (step S1), a crystal cutting step (step S2), a groove forming step (step S3), a cutting step (step S4), a heat treatment step (step S5), and a chamfering step (step 6).

[0062] In the manufacturing method of the magnetostrictive member of this embodiment, first, in the crystal preparation step (step S1), a crystal of an iron-based alloy having magnetostrictive properties is prepared. The prepared crystal may be a single crystal or a polycrystal. Furthermore, the prepared crystal may be a grown crystal or a commercially available crystal. For example, in the crystal preparation step, a single crystal of an Fe—Ga alloy is prepared. There are no particular limitations on the method for growing the single crystal of the Fe—Ga alloy. The method for growing the single crystal of the Fe—Ga alloy may be, for example, a pulling method or a unidirectional solidification method. For example, the Cz method can be used as the pulling method, and the VB method, VGF method, and micro-pulling-down method can be used as the unidirectional solidification method.

[0063] The magnetostriction constant of an Fe—Ga alloy single crystal is maximized by adjusting the gallium content to 18.5 at% or 27.5 at%. Therefore, the Fe—Ga single crystal is preferably grown so that the gallium content is 16.0 to 20.0 at% or 25.0 to 29.0 at%, and more preferably 17.0 to 19.0 at% or 26.0 to 28.0 at%. The shape of the grown single crystal is not particularly limited, and may be, for example, cylindrical or rectangular prism. The grown single crystal may be cut into a cylindrical single crystal, if necessary, by cutting the seed crystal, the diameter-increasing portion, or the shoulder portion (the portion that increases from the seed crystal to the desired diameter of the single crystal) using a cutting device. The size of the grown single crystal is not particularly limited, as long as it is large enough to secure the magnetostrictive member in the desired direction. When growing an Fe—Ga single crystal, a seed crystal is used whose top or bottom surface is processed to a {100} plane so that the growth axis direction is <100>. The grown Fe—Ga alloy single crystal grows in a direction perpendicular to the top or bottom surface of the seed crystal, and inherits the orientation of the seed crystal.

[0064] Following the crystal preparation step (step S1), a crystal cutting step (step S2) is performed. The crystal cutting step is a step of cutting a crystal to create a thin plate member. The thin plate member is the material that will be used to make the magnetostrictive member 1 of this embodiment. The crystal cutting step is, for example, a step of cutting a single crystal of an Fe—Ga alloy having magnetostrictive properties using a cutting device to create a thin plate member having a {100} plane as its main surface. Cutting devices that can be used include wire electric discharge machines, inner diameter blade cutting devices, and wire saws. Among these, the use of a multi-wire saw is particularly preferred because it can simultaneously cut multiple thin plate members. In the case of an Fe—Ga single crystal, the cutting direction of the single crystal is <100>, and the cutting surface, i.e., the main surface of the thin plate member, is cut to be the {100} plane. The cutting direction of the single crystal is not particularly limited. For example, as shown in FIG. 6, the cutting direction of the single crystal may be perpendicular or parallel to the single crystal growth direction (the direction in which the crystal is grown).

[0065] Following the crystal cutting process (step S2), a groove forming process (step S3) is performed. In the groove forming process, multiple grooves 2 are formed on at least one of the front and back surfaces 3 and 4 of the resulting thin plate member. The multiple grooves 2 stabilize the magnetostriction constant and parallel magnetostriction at high levels and can improve the magnetostriction constant and parallel magnetostriction. In the groove forming process, multiple grooves 2 are formed in the thin plate member so that, when the thin plate member is finally cut into the magnetostrictive member 1, multiple grooves 2 extending in the longitudinal direction D1 of the magnetostrictive member 1 are formed. The multiple grooves 2 formed can be similar to those described in Patent Document 6, for example. For example, multiple grooves 2 can be formed by surface grinding on at least one of the front and back surfaces of the thin plate member obtained by the crystal cutting process. An example of performing the groove forming process by surface grinding on the thin plate member will be described below. When multiple grooves 2 are formed by surface grinding, the effects of improving the magnetostriction constant, parallel magnetostriction, force coefficient, and half-value frequency coupling coefficient can be efficiently achieved.

[0066] The surface grinding is performed using a surface grinding machine. In the surface grinding, from the viewpoint of efficiently realizing the effect of modifying the magnetostriction constant and the amount of parallel magnetostriction, it is preferable that the direction of the grinding marks formed on the thin plate member is parallel to the longitudinal direction D1 of the magnetostrictive member 1. For this reason, it is preferable that the grinding marks are linear. When making the grinding marks linear, it is preferable that the surface grinding machine is a type in which the grinding wheel or processing table moves in a linear direction, and it is preferable to use a surface grinding machine that uses a flat grinding wheel and in which the processing table moves back and forth. It is also possible to use a surface grinding machine that uses a cup grinding wheel and in which the processing table rotates, but when using such a surface grinding machine, the grinding marks will be curved, so it is preferable to set the curvature of the grinding marks to be small (the degree of curvature is small).

[0067] Furthermore, the grinding marks must be formed on the surface (surface) of the magnetostrictive member 1. For this reason, when processing a thin plate member to adjust its thickness, etc., the surface grinding process may be performed after the predetermined processing is performed using a processing machine other than a surface grinder, such as a double-sided lapping device or a surface grinder using a cup grinding wheel. Alternatively, the surface of the thin plate member (magnetostrictive member) may be polished as in the conventional method to give a mirror finish to the surface, and then the surface grinding process may be performed. From the viewpoint of efficiently achieving the effects of modifying the magnetostriction constant, parallel magnetostriction amount, force coefficient, and half-value frequency coupling coefficient, it is preferable to perform the surface grinding process on both the front and back surfaces of the thin plate member.

[0068] The grinding stone used for surface grinding preferably has a lower limit of roughness (grit) of #40 or more, more preferably #100 or more, and an upper limit of #500 or less, more preferably #400 or less, preferably a range of #40 to #500, more preferably #40 to #400 or less, more preferably #100 to #400 or less. When the roughness (grit) of the grinding stone is within the above range, the effects of improving the magnetostriction constant, parallel magnetostriction, force coefficient, and half-value frequency coupling coefficient can be more reliably exhibited. Note that using a grinding stone smaller than #40 may result in an unstable size of grinding marks. Using a grinding stone exceeding #500 may result in the surface of the magnetostrictive member being smooth, which may prevent the effects of improving the magnetostriction constant, parallel magnetostriction, force coefficient, and half-value frequency coupling coefficient from being efficiently exhibited.

[0069] In the groove forming step, for example, the plurality of grooves 2 are preferably formed so that the surface roughness Ra in the longitudinal direction D1 of the surface on which the plurality of grooves 2 are formed in the magnetostrictive member 1 is within a predetermined range. For example, the plurality of grooves 2 are preferably formed so that the lower limit of the surface roughness Ra in the longitudinal direction D1 of the surface on which the plurality of grooves 2 are formed is preferably 0.3 μm or more, and the upper limit is preferably 1.5 μm or less, in the range of 0.3 μm to 1.5 μm. Furthermore, the plurality of grooves 2 are preferably formed so that the surface roughness Ra in the lateral direction D2 of the surface on which the plurality of grooves 2 are formed in the magnetostrictive member 1 is preferably 0.6 μm or more, more preferably 0.7 μm or more, and the lower limit is preferably 4.5 μm or less, in the range of 0.6 μm to 4.5 μm. Furthermore, the plurality of grooves 2 are preferably formed so that the magnetostriction constant and the parallel magnetostriction amount of the magnetostrictive member 1 and the magnetostrictive material from which the magnetostrictive member 1 is made are within predetermined ranges. For example, the multiple grooves 2 are preferably formed so that the magnetostrictive member 1 (magnetostrictive material) has a magnetostriction constant of 200 ppm or more and a parallel magnetostriction of 200 ppm or more. The multiple grooves 2 that fall within the above-mentioned preferred ranges of surface roughness Ra, magnetostriction constant, parallel magnetostriction, force coefficient, and half-value frequency coupling coefficient can be formed by the above-mentioned surface grinding process. The groove forming process may be performed by a method other than surface grinding, as long as it is possible to form multiple grooves 2 on at least one of the front surface 3 and the back surface 4 of the obtained thin plate member. For example, the thin plate member may be fabricated so that the multiple grooves 2 are formed using a fixed abrasive wire saw. In other words, the multiple grooves 2 may be grooves formed when slicing a crystal to create a thin plate member using a fixed abrasive wire saw. There are two types of cutting using a wire saw: the free abrasive method, in which the workpiece is pressed against a row of multiple parallel, ultra-fine wires arranged at a constant pitch, and the wires are fed in the linear direction while a machining liquid containing abrasive grains (also called a slurry) is supplied between the workpiece and the wires to perform the cutting; and the fixed abrasive method, in which the workpiece is cut by feeding a wire in the linear direction with abrasive grains such as diamonds fixed to it by electroplating or adhesive.The cut surface produced by the free abrasive grain method has a non-directional matte finish, which does not achieve the present effect. However, when cutting with a fixed abrasive grain wire saw, grinding marks are generated in the wire feed direction, making it possible to form multiple grooves 2 similar to those formed by the surface grinding process. When cutting with a fixed abrasive grain wire saw, the crystal cutting process (step S2) and the groove forming process (step S3) can be performed simultaneously, allowing for efficient production of thin plate members. Alternatively, multiple grooves 2 may be formed by applying a certain amount of pressure using sandpaper or the like. In the groove forming process, by appropriately adjusting the configuration of the multiple grooves 2 formed in the magnetostrictive member, a magnetostrictive member material having the optimal magnetic field strength of the present embodiment can be obtained. For example, as described above, in this embodiment, the magnetostrictive characteristics, including the force coefficient, are affected by the width, length, and thickness of the magnetostrictive member. However, by appropriately adjusting the configuration of the multiple grooves 2 formed in the magnetostrictive member in the groove forming process according to the width, length, and thickness of the magnetostrictive member, the magnetostrictive characteristics can be adjusted (modified) to obtain a magnetostrictive member having the characteristics of this embodiment. The configuration (conditions) of the plurality of grooves 2 formed in the magnetostrictive member of this embodiment can be determined through preliminary experiments.

[0070] Following the groove forming step (step S3), a cutting step (step S4) is carried out. In the cutting step, the thin plate member in which the plurality of grooves 2 have been formed in the groove forming step is cut to obtain a magnetostrictive material. This magnetostrictive material is the material for the magnetostrictive member 1 of this embodiment. The magnetostrictive material is subjected to a heat treatment in a heat treatment step described below, thereby obtaining the magnetostrictive member 1 of this embodiment.

[0071] In the cutting process, when cutting the thin plate member having a plurality of grooves 2 formed therein, the thin plate member is cut so that a plurality of grooves 2 extending in the longitudinal direction D1 are formed in the magnetostrictive member 1 to be finally manufactured. In the cutting process, the thin plate member is cut to a predetermined size. In the cutting process, the thin plate member is cut as a magnetostrictive material so that, for example, the magnetostrictive member 1 becomes a rectangular plate-like body in a planar view. In the cutting process, the thin plate member is cut using a cutting device. The cutting device used in the cutting process is not particularly limited, and for example, a peripheral blade cutting device, a wire electric discharge machine, a wire saw, etc. can be used. The direction in which the magnetostrictive material is extracted from the thin plate member is not particularly limited, and it may be set to a direction that allows for efficient extraction depending on, for example, the size of the magnetostrictive member.

[0072] Next, a heat treatment process (step S5) is carried out. By heat-treating the material, the heat treatment process lowers the optimal magnetic field strength of the magnetostrictive member and reduces variation while maintaining the force coefficient and half-value frequency coupling coefficient at high levels. This is presumably because the heat treatment relieves internal stress on the front and back surfaces of the magnetostrictive member. For example, in the heat treatment process, multiple grooves 2 extending in the longitudinal direction D1 are formed on the front and back surfaces of the magnetostrictive material obtained in the cutting process, and this magnetostrictive material is heat-treated at a predetermined temperature and time. This heat treatment modifies the ratio (standard deviation / average value) of the standard deviation of the optimal magnetic field strength determined by electro-mechanical equivalent circuit analysis of the magnetostrictive member to the average value of the optimal magnetic field strength so that it is 0.2 or less, as shown in the examples. The magnetostrictive member 1 of this embodiment can be obtained by this heat treatment. Furthermore, the effect of heat treatment in lowering the optimum magnetic field strength of the magnetostrictive member and reducing variation while maintaining the force coefficient and half-value frequency coupling coefficient at a high level is also effective for materials that do not have multiple grooves 2.

[0073] The heat treatment method is not particularly limited. For example, a box-shaped or tubular electric furnace can be used. The heating temperature is not particularly limited as long as the heat treatment produces the desired effect. The heat treatment conditions (temperature, time) can be determined through preliminary experiments. The heat treatment temperature (heat treatment temperature) is preferably 400°C or higher and 700°C or lower, and more preferably 600°C or higher and 650°C or lower. If the heat treatment temperature is lower than 400°C, the internal stress is not alleviated by the heat treatment, and the optimal magnetic field strength may not change. If the heat treatment temperature exceeds 700°C, the temperature is too high, weakening the grinding effect, reducing the parallel magnetostriction amount and the force coefficient and half-value frequency coupling coefficient. If the heat treatment temperature is within the above temperature range, the average value of the optimal magnetic field strength of the magnetostrictive member can be lowered and its variation reduced.

[0074] The holding time of the heat treatment is preferably 5 hours or less, more preferably 30 minutes to 5 hours, and even more preferably 30 minutes to 1 hour. Within the above range, the effect of suppressing variations in the magnetostrictive member can be more reliably exhibited.

[0075] Furthermore, it is preferable that the heat treatment be carried out in an inert gas atmosphere. For example, argon gas or nitrogen gas can be used. By using an inert gas atmosphere, oxidation of the surface of the magnetostrictive member can be prevented. The inert gas may be continuously supplied to the heat treatment furnace. The flow rate depends on the heat treatment furnace, but when the inert gas is argon gas, it is preferably 0.5 to 5 L / h.

[0076] Furthermore, when the thickness of the magnetostrictive member exceeds 2 mm, the effect of forming multiple grooves 2 extending in the longitudinal direction D1 on the front and back surfaces of the magnetostrictive member on improving the magnetostriction constant, parallel magnetostriction, force coefficient, and half-value frequency coupling coefficient is smaller than when the thickness is 2 mm or less. However, it has been found that by forming multiple grooves 2 extending in the longitudinal direction D1 on the front and back surfaces of the magnetostrictive member and then performing a heat treatment, it is possible to obtain almost the same improvement effect as when the thickness is 2 mm or less. Therefore, even with a magnetostrictive member with a thickness exceeding 2 mm, a stable force coefficient and half-value frequency coupling coefficient can be obtained. For example, a stable force coefficient and half-value frequency coupling coefficient can be obtained even with a thickness of 3 mm or more.

[0077] If the heat treatment process (step S5) is performed without the groove formation process (step S3), the internal stress is alleviated and the variation in the optimal magnetic field strength is reduced, but the force coefficient and half-value frequency coupling coefficient do not change, and the average value remains low and the variation remains large.

[0078] In the above example, in the cutting step (step S4), the magnetostrictive member is cut into the shape and then the heat treatment step (step S5) is performed. However, in the present invention, the heat treatment step (step S5) may be performed after the groove forming step (step S3), and then the cutting step (step S4) may be performed.

[0079] Next, the chamfering process (step S6) is performed. The chamfering process (step S6) is a process of chamfering the plate-shaped body (magnetostrictive member) cut in the cutting process. In the chamfering process, for example, each edge of the magnetostrictive member is chamfered. The magnetostrictive member is made of an Fe-based alloy material and has high ductility. Therefore, when the magnetostrictive member is cut into a predetermined shape in the cutting process, burrs may occur on each edge of the magnetostrictive member. If the magnetostrictive properties are measured while burrs remain on the magnetostrictive member, the magnetostrictive properties may change. This has been a factor in increasing the variability in the magnetostrictive properties. In this embodiment, adding the chamfering process reduces the variability in the magnetostrictive properties and stabilizes the measured values ​​of the magnetostrictive properties. In the chamfering process, the means for chamfering is not particularly limited. For example, beveling may be performed using a beveling device, or if the amount is small, processing using a file or the like may be performed. The chamfering process may be performed after the cutting process.

[0080] The present invention will be specifically explained below using examples, but the present invention is not limited to these examples.

[0081] Example 1 A magnetostrictive member was manufactured based on the manufacturing method of this embodiment described above. Raw materials were prepared with a stoichiometric iron-to-gallium ratio of 81:19, and a cylindrical Fe—Ga alloy single crystal was grown by the vertical Bridgman (VB) method. The growth axis direction of the single crystal was set to <100>. The orientation of the {100} plane on the top or bottom surface of the single crystal, which was perpendicular to the crystal growth axis direction, was confirmed by X-ray diffraction. Measurement of the top and bottom surface samples of the crystal using a Shimadzu sequential plasma emission spectrometer (ICPS-8100) revealed that the gallium content of the single crystal was 17.2 to 19.8 at%.

[0082] Magnetostrictive members were manufactured from the grown single crystals as follows. First, a loose abrasive wire saw was used to cut the single crystal parallel to the single crystal growth direction (parallel to the <100> orientation) to produce thin plate members with cut surfaces, i.e., main surfaces, in the {100} direction (crystal cutting process). Next, the resulting thin plate members were subjected to surface grinding using a #170 flat grinding wheel on a surface grinder to adjust the thickness of the thin plate members and form multiple grooves (grinding marks) on the front and back surfaces to obtain the magnetostrictive member of the present embodiment (groove forming process). 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 magnetostrictive material (magnetostrictive material before heat treatment) measuring 16 mm in the longitudinal direction, 4 mm in the lateral direction, and 0.5 mm in thickness was cut using a peripheral blade cutting device (cutting process). The 10 magnetostrictive material pieces cut as described above were then heat-treated. A tubular electric furnace was used as the heat treatment furnace. Argon gas was flowed through the furnace at 1 L / min. The heat treatment was performed at a heat treatment temperature of 600°C for a holding time of 60 minutes (heat treatment step). After the heat treatment, chamfering was performed using a file to chamfer each side of the magnetostrictive member (chamfering step).

[0083] Next, the magnetostrictive properties of the manufactured magnetostrictive members were measured. The magnetostrictive properties were measured using the characteristic evaluation device shown in Figure 4 described above. The impedance of the prepared magnetostrictive members was measured using the method described above under conditions of a magnetic field strength (applied magnetic field) of 1.1 kA / m to 8.8 kA / m and a measurement frequency of 10 kA / m to 200 kHz, and the force factor and half-value frequency coupling coefficient were calculated from the measurement results. Ten magnetostrictive materials were prepared, and the maximum values ​​of the force factor and half-value frequency coupling coefficient, as well as the optimal magnetic field strength at which the half-value frequency coupling coefficient was maximized, were determined using the same method, and the average values ​​and variations (standard deviations) for each were calculated. The results are shown in Table 1.

[0084] [Example 2] In Example 2, the grinding wheel used in the grinding process was a #100 flat grinding wheel, the size of the magnetostrictive member cut out in the cutting process was 32 mm in the longitudinal direction, 8 mm in the lateral direction, and 1 mm in thickness, and the holding time of the heat treatment was 120 minutes. Other than the above, the same as Example 1 was used. The manufacturing conditions and evaluation results are shown in Table 1.

[0085] [Example 3] In Example 2, the grinding wheel used in the grinding process was a #40 flat grinding wheel, the size of the magnetostrictive member cut out in the cutting process was 64 mm in the longitudinal direction, 16 mm in the lateral direction, and 2 mm in thickness, and the holding time of the heat treatment was 120 minutes. Other than the above, the same as Example 1 was used. The manufacturing conditions and evaluation results are shown in Table 1.

[0086] [Example 4] In Example 2, the grinding wheel used in the grinding process was a #40 flat grinding wheel, the size of the magnetostrictive member cut out in the cutting process was 96 mm in the longitudinal direction, 24 mm in the lateral direction, and 3 mm in thickness, and the holding time of the heat treatment was 120 minutes. Other than the above, the same as in Example 1 was used. The manufacturing conditions and evaluation results are shown in Table 1.

[0087] In Comparative Example 1, the surface of the magnetostrictive material was a processed surface (wire saw processed surface) cut with a wire saw device of the free abrasive type, which cuts by supplying a processing liquid containing abrasive grains, and no heat treatment was performed. Other than that, the same as in Example 1. The manufacturing conditions and evaluation results are shown in Table 1.

[0088] Comparative Example 2 In Comparative Example 2, no heat treatment was performed. The rest was the same as in Example 2. The production conditions and evaluation results are shown in Table 1.

[0089]

[0090] [Summary] The magnetostrictive members of Examples 1 to 4 exhibited high average values ​​for the force coefficient and half-value frequency coupling coefficient, which were favorable. Furthermore, the magnetostrictive members of Examples 1 to 4 exhibited low values ​​for the variation (standard deviation) and ratio of the standard deviation to the average value (standard deviation / average value) for the half-value frequency coupling coefficient, and also exhibited low values ​​for the ratio of the standard deviation to the average value (standard deviation / average value) for the optimal magnetic field strength. Furthermore, the magnetostrictive members of Examples 1 to 4 exhibited values ​​for the force coefficient that increased with increasing size, but no such tendency was observed for the half-value frequency coupling coefficient and the optimal magnetic field strength, with stable values.

[0091] On the other hand, the magnetostrictive member of Comparative Example 1 had lower force coefficients and half-value frequency coupling coefficients, and a larger ratio of the standard deviation to the average value of the half-value frequency coupling coefficients (standard deviation / average value) than the same-sized member of Example 1. The magnetostrictive member of Comparative Example 2 had a larger variation in optimal magnetic field strength, and a larger ratio of the standard deviation to the average value of the optimal magnetic field strength (standard deviation / average value) than the same-sized member of Example 2.

[0092] From the above, it is confirmed that the magnetostrictive member of this embodiment has a high parallel magnetostriction amount and little variation in the parallel magnetostriction amount between members, and when a magnetostrictive vibration power generation device is manufactured using such a magnetostrictive member, the device characteristics can be easily evaluated using a stable indicator that is not affected by the size or thickness of the magnetostrictive member, and the device characteristics are large and the variation in the optimal magnetic field strength is also suppressed.

[0093] 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. 2024-018141 and all documents cited in the above-mentioned embodiments are incorporated by reference or incorporated herein as part of the present description.

[0094] For example, in the above description, an example of a magnetostrictive member has been described in which at least one of the front and back surfaces of the plate-like body has a plurality of grooves 2 extending in the longitudinal direction, but the plurality of grooves 2 may be omitted. For example, the magnetostrictive member is a plurality of magnetostrictive members obtained from the same crystal, made of crystals of an iron-based alloy having magnetostrictive properties, and is a plate-like body having a longitudinal direction and a lateral direction, and the plurality of magnetostrictive members have a half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is the strength at which the optimum magnetic field strength is maximized, and the ratio of the standard deviation of the optimum magnetic field strength to the average value of the optimum magnetic field strength (standard deviation / average value) is 0.2 or less, and the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) and the standard deviation of the maximum value of the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) to the average value of the parallel magnetostriction (standard deviation / average value) may be 0.3 or less. This configuration also achieves the effect of the present application described above, in which the device characteristics of a magnetostrictive vibration power generation device manufactured using a magnetostrictive member with a high parallel magnetostriction and little variation in the parallel magnetostriction between members can be easily evaluated using a stable index that is not affected by the size or thickness of the magnetostrictive member, resulting in high device characteristics and reduced variation in the optimal magnetic field strength. This magnetostrictive member can be obtained, for example, by modifying the magnetostrictive member by the heat treatment described above, thereby reducing the characteristics and variation.

[0095] 1: Magnetostrictive member 2: Groove 3: Front surface 4: Back surface D1: Longitudinal direction D2: Lateral direction S1: Crystal preparation process S2: Crystal cutting process S3: Groove forming process S4: Cutting process S5: Heat treatment process S6: Chamfering process

Claims

1. A magnetostrictive member obtained from the same crystal, which is a plate-shaped member made of an iron-based alloy crystal having magnetostrictive properties and having a longitudinal direction and a lateral direction, at least one of the front and rear surfaces of the plate-shaped member has a plurality of grooves extending in the longitudinal direction, and the plurality of magnetostrictive members have a half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is maximized, the magnetic field strength is defined as the optimum magnetic field strength, and the ratio of the standard deviation of the optimum magnetic field strength to the average value of the optimum magnetic field strength (standard deviation / average value) is 0.2 or less.

2. The plurality of magnetostrictive members have the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) and the standard deviation of the maximum value of the half-value frequency coupling coefficient (= k ｆ１ｆ２ 2. The magnetostrictive member according to claim 1, wherein the ratio of the maximum value of the magnetostrictive coefficients (standard deviation) to the average value (standard deviation / average value) is 0.3 or less.

3. The plurality of magnetostrictive members have the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) and the standard deviation of the maximum value of the half-value frequency coupling coefficient (= k ｆ１ｆ２ 2. The magnetostrictive member according to claim 1, wherein the ratio of the maximum value of said magnetostrictive coefficients to the average value (standard deviation / average value) is 0.1 or less.

4. A magnetostrictive member obtained from the same crystal, which is a plate-shaped member made of an iron-based alloy crystal having magnetostrictive properties and having a longitudinal direction and a transverse direction, and the plurality of magnetostrictive members have a half-value frequency coupling coefficient (= k ｆ１ｆ２ ) is the strength at which the optimum magnetic field strength is maximized, and the ratio of the standard deviation of the optimum magnetic field strength to the average value of the optimum magnetic field strength (standard deviation / average value) is 0.2 or less, and the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) and the standard deviation of the maximum value of the half-value frequency coupling coefficient (= k ｆ１ｆ２ ) the ratio of the maximum value of the magnetostrictive coefficients to the average value (standard deviation / average value) is 0.3 or less.

5. A magnetostrictive member according to any one of claims 1 to 4, wherein the thickness of the plate-like body is 0.3 mm or more and 5 mm or less.

6. A method for manufacturing a magnetostrictive member according to any one of claims 1 to 4, comprising forming a plurality of grooves extending in the longitudinal direction on at least one of the front and rear surfaces of a plate-like body made of crystals of an iron-based alloy having magnetostrictive properties and having longitudinal and lateral directions, and heat treating the plate-like body with the plurality of grooves extending in the longitudinal direction formed therein.

7. A method for manufacturing a magnetostrictive member according to claim 6, which includes forming the plurality of grooves by surface grinding.

8. The method for manufacturing a magnetostrictive member according to claim 6, wherein the heat treatment temperature is 400°C or higher and 700°C or lower.

9. The method for manufacturing a magnetostrictive member according to claim 6, wherein the heat treatment is held for 5 hours or less.

10. A method for manufacturing a magnetostrictive member as described in claim 6, comprising: a cutting step of cutting the plate-like body having the plurality of grooves formed therein; and a chamfering step of chamfering the plate-like body cut by the cutting step.

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