JP2023142656A - Magnetostrictive material and method for producing the same - Google Patents

Abstract

To provide a magnetostrictive material that does not use the elements that are expensive and involve a high resource risk and can be produced at a low cost and a method for producing the same.SOLUTION: A magnetostrictive material disclosed herein contains Mn: 44 atom% or more and 53 atom% or less, Al: 46 atom% or more and 52 atom% or less, and Cu: 0.5 atom% or more and 6 atom% or less, with a stable phase with a tetragonal structure constituting 55% or more.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to magnetostrictive materials and methods of manufacturing the same.

The magnetostrictive effect is a phenomenon in which a magnetic material is deformed when an external magnetic field is applied to the material. Magnetostrictive materials are used in a wide variety of applications, including ultrasonic generators, actuators, mold clamping devices for injection molds, and vibration power generation and torque sensors that utilize the inverse magnetostriction effect in which the magnetic field changes with external force. ing. The amount of magnetostriction is determined by the amount of change in length ΔL = L - ratio of L0 to L0, where L0 is the sample length when no magnetic field is applied, and L is the sample length in the magnetic field direction (L0 direction) when a magnetic field is applied. (ΔL/L0) is often expressed in ppm.

Magnetostrictive materials that have been known for a long time include Ni, Fe--Al alloy, and Fe--Co--V alloy, and Non-Patent Document 1 reports that the saturation magnetostriction amount of each is 35 ppm, 40 ppm, and 70 ppm. In addition, as a magnetostrictive material exhibiting a large magnetostriction phenomenon, Fe-Ga alloy is disclosed in Non-Patent Document 2, and a saturation magnetostriction of 200 ppm is obtained in the case of a single crystal, and in Patent Document 1 (Dy, Tb)-Fe alloys and La-(Fe,Si)-H alloys have been disclosed, with the (Dy,Tb)-Fe alloy having a concentration of 1000 ppm or more, and the La-(Fe,Si)-H alloy having a concentration of 2000 ppm at an applied magnetic field of 10T. The above saturation magnetostriction amount was obtained.

Japanese Patent Application Publication No. 2002-69596

Kenichi Arai, Noboru Tsuya, Bulletin of the Japan Institute of Metals, 17 (1978), 963-968 A. E. Clark, J. B. Restorff, M. Wun-Fogle, T. A. Lograsso, D. L. Schlagel, IEEE Trans. Magn. , 36 (2000), 3238-3240

In conventional magnetostrictive materials, in order to obtain a larger amount of magnetostriction, it was necessary to use elements that are scarce and expensive, such as Co, Ga, and rare earth elements. In particular, the supply of rare earth elements such as Dy and Tb is unstable due to limited production areas, and there is a high risk of future resource risks and price increases.

In addition, the magnetostrictive effect of Fe-Ga alloys and (Dy,Tb)-Fe alloys is dependent on crystal orientation, and in order to obtain a larger amount of magnetostriction, it is necessary to manufacture a single crystal, which increases manufacturing costs. There was an issue. La-(Fe,Si)-H alloys tend to undergo phase separation during melting and casting, making it difficult to obtain a high proportion of the desired compound that exhibits the magnetostrictive effect, making them unsuitable for mass production and increasing manufacturing costs. There were such issues.

The present disclosure provides a magnetostrictive material that can be manufactured at low cost without using elements that are expensive and have a high resource risk, and a method for manufacturing the same.

In a non-limiting exemplary embodiment, the magnetostrictive material of the present disclosure includes Mn: 44 atomic % or more and 53 atomic % or less, Al: 46 atomic % or more and 52 atomic % or less, Cu: 0.5 atomic % or more and 6 atomic % The ratio of the stable phase having a tetragonal structure is 55% or more.

In one embodiment, the total content of Mn, Al, and Cu is 100 atomic % (however, unavoidable impurities may be included).

In one embodiment, the absolute value of the amount of magnetostriction at room temperature is 50 ppm or more and 600 ppm or less.

In a non-limiting exemplary embodiment, the method for producing a magnetostrictive material of the present disclosure includes Mn: 44 atomic % or more and 53 atomic % or less, Al: 46 atomic % or more and 52 atomic % or less, Cu: 0.5 atomic % or more a first step of preparing a first alloy to obtain an alloy containing 6 atomic % or less, and a second step of heat-treating the first alloy at a temperature of 300° C. or higher and 750° C. or lower to obtain a second alloy. .

In one embodiment, the first alloy is prepared such that the total content of Mn, Al, and Cu is 100 atomic % (however, unavoidable impurities may be included).

According to the present disclosure, it is possible to provide a magnetostrictive material that can be manufactured at low cost without using elements that are expensive and have a high resource risk, and a method for manufacturing the same.

FIG. 1 is a perspective view schematically showing a method for measuring the amount of magnetostriction.

The present inventors have determined that by limiting each element of Mn, Al, and Cu to an appropriate composition range and performing appropriate heat treatment, a phase with a tetragonal structure can be obtained as a stable phase at a high ratio of 55% or more. It was found that a large amount of magnetostriction of 50 ppm or more can be obtained isotropically at room temperature without depending on the crystal orientation. Note that the stable phase in the present disclosure refers to a tetragonal phase that has a tetragonal structure and exists even after isothermally maintained within a heat treatment temperature range of 500° C. or more and 750° C. or less for 24 hours or more. In addition, the amount of magnetostriction in the present disclosure is defined as the length when the room temperature is 300K, the sample length when no magnetic field is applied is L0, and the sample length in the magnetic field direction (L0 direction) when a magnetic field of 8.9T is applied is L0. The absolute value of the ratio (ΔL/L0) between the amount of change ΔL=L−L0 and L0 is expressed in ppm.

<Magnetostrictive material>
The reasons for limiting the composition of the magnetostrictive material will be explained below.
The content of Mn is 44 atomic % or more and 53 atomic % or less. When the Mn content is less than 44 atomic % or more than 53 atomic %, the ratio of different phases (γ ₂ -Mn ₅ Al ₈ phase, β-Mn phase, κ-MnAlCu phase) increases, resulting in a stable phase with a tetragonal structure. A ratio of 55% or more cannot be obtained, and a sufficient amount of magnetostriction of 50 ppm or more cannot be obtained.

The content of Al is 46 atomic % or more and 52 atomic % or less. When the Al content is less than 46 atomic % or more than 52 atomic %, the ratio of different phases (γ ₂ -Mn ₅ Al ₈ phase, β-Mn phase, κ-MnAlCu phase) increases, resulting in a stable phase with a tetragonal structure. A ratio of 55% or more cannot be obtained, and a sufficient amount of magnetostriction of 50 ppm or more cannot be obtained.

The content of Cu is 0.5 atomic % or more and 6 atomic % or less. When the Cu content is less than 0.5 atomic % or more than 6 atomic %, the ratio of different phases (γ ₂ -Mn ₅ Al ₈ phase, β-Mn phase, κ-MnAlCu phase) becomes large, resulting in a tetragonal structure. The ratio of the stable phase in the magnet cannot be obtained to be 55% or more, and a sufficient amount of magnetostriction of 50 ppm or more cannot be obtained.

Although some of Mn, Al and Cu may be replaced with other elements, the total content of Mn, Al and Cu expressed in atomic % is 100% (however, unavoidable impurities may be included) It is preferable that

The form of the magnetostrictive material is not limited to the form of a lump (bulk), but may take the form of a rod, a film, a powder particle, or the like.

<Method for manufacturing magnetostrictive material>
Embodiments of the method for manufacturing a magnetostrictive material in the present disclosure will be described below.

(First step)
In the present disclosure, obtaining a first alloy having a composition within the composition range of the magnetostrictive material described above is referred to as a first step. The composition of the first alloy is the same as that of the magnetostrictive material described above, so a description thereof will be omitted.

First, raw materials are melted and cast so that the composition of the first alloy falls within the above-mentioned composition range. In the present disclosure, since the amount of magnetostriction does not depend on the crystal orientation of the tetragonal phase, the structure of the alloy may be a polycrystalline structure that is easy to manufacture, and melting and casting can be performed by any method. For example, casting is performed by methods such as high frequency melting, arc melting, strip casting, and liquid ultra-quenching. After casting, heat treatment may be performed at a temperature of 800° C. or higher to homogenize the structure.

(Second process)
In the present disclosure, the process of heat-treating the first alloy to obtain a second alloy having a stable phase ratio of 55% or more having a tetragonal structure is referred to as a second step.

In the first alloy, foreign phases and high-temperature phases (γ-MnAl phase and ε-MnAl phase) generated during the casting process may remain, making it impossible to obtain a high proportion of stable phases having a tetragonal structure. By heat-treating the first alloy within the composition range described above, a phase change to a tetragonal structure occurs within the first alloy, and a stable phase having a tetragonal structure can be obtained in a high proportion.

The atmosphere during the heat treatment is preferably a vacuum or an inert gas such as argon gas. The heat treatment temperature is preferably 300°C or higher and 750°C or lower. If the temperature is less than 300° C., it may take a very long time to change to the tetragonal phase, making it difficult to mass produce. When the temperature exceeds 750° C., a high temperature phase is generated, and a stable phase having a tetragonal structure cannot be obtained in a high proportion.

Regarding the holding time of the heat treatment, an appropriate time may be set depending on the composition and the heat treatment temperature so that the ratio of the stable phase having a tetragonal structure is 55% or more. The holding time of the heat treatment is, for example, 1 hour to 336 hours. Note that the second alloy may be pulverized by a known method, and may be further heat-treated at 750° C. or lower to remove distortion caused by pulverization.

Whether the phase having a tetragonal structure is a stable phase can be confirmed by, for example, whether the phase remains even after long-term heat treatment (24 hours or more) in the second step. It can also be confirmed, for example, by determining whether the phase still exists after additional long-term heat treatment (24 hours or more) after the second step.

As described above, in the present disclosure, a tetragonal phase that has a tetragonal structure and exists even after isothermally maintained within a heat treatment temperature range of 500° C. to 750° C. for 24 hours or more is referred to as a stable phase.

The crystal structure of the tetragonal phase can be confirmed using X-ray diffraction or electron beam diffraction. Specifically, if the diffraction pattern obtained by X-ray diffraction or electron beam diffraction matches the diffraction pattern of a known tetragonal structure, it can be confirmed that the structure is a tetragonal structure. Similarly, it is possible to confirm whether the phase is a β-Mn phase, a γ ₂ -Mn ₅ Al ₈ phase, or a κ-MnAlCu phase other than the tetragonal phase by checking whether it matches the known diffraction pattern of each phase. can.

The ratio of the tetragonal phase can be confirmed using a scanning electron microscope or the like. Specifically, this can be confirmed by distinguishing between the tetragonal phase and phases other than the tetragonal phase based on contrast differences due to compositional differences in the cross-sectional structure, and determining the area ratio of the tetragonal phase.

Further, the ratio of the tetragonal phase can also be confirmed by Rietveld analysis of X-ray diffraction. Specifically, the diffraction pattern obtained by X-ray diffraction is fitted by the least squares method using a diffraction pattern calculated from a crystal structure model of a tetragonal phase and a phase other than the tetragonal phase. This can be confirmed by determining the phase ratio from the intensity ratio of each phase.

The present disclosure will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

Examples 1 to 9 and Comparative Examples 1 to 3
Each element of Mn, Al, and Cu was weighed and melted and cast using a high frequency induction melting furnace to obtain an ingot having the composition shown in Table 1. The obtained ingot was sealed in a quartz tube in an argon gas atmosphere, and subjected to homogenization treatment in which it was maintained at 900° C. for 24 hours in a heating furnace to obtain a first alloy (first step). Subsequently, the obtained first alloy was heat treated at 600° C. for 168 hours to obtain a second alloy (second step).

The crystal structure of the second alloy ingot obtained after the second step was measured using an X-ray diffraction device. The main peaks appearing in the diffraction patterns of the second alloys of Examples 1 to 9 matched the diffraction patterns of known tetragonal structures. It was confirmed that the tetragonal phase remained even after being held at 600° C. for 168 hours, and that it was a stable phase. On the other hand, in Comparative Examples 1 to 3, no tetragonal structure diffraction pattern could be observed. The cross-sectional structure of a portion of the remaining second alloy ingot was observed using a scanning electron microscope. The tetragonal phase and phases other than the tetragonal phase were distinguished from the compositional contrast difference in the backscattered electron images, and the area ratio of the tetragonal phase was determined. there were. On the other hand, in Comparative Examples 1 to 3, the phase corresponding to the tetragonal phase was not observed or was very small.

Samples for measuring the amount of magnetostriction were cut out from the remaining ingots of the second alloy using an electrical discharge machine. The surface of the cut sample was polished with No. 600 abrasive paper to create a plate-shaped sample with length (L0) of 7 to 12 mm, width (L1) of 4 to 10 mm, and thickness (L2) of 1 to 2.5 mm. The surface of the prepared sample was cleaned with acetone, and a strain gauge was attached to the L0-L1 plane as shown in FIG. At this time, a strain gauge was attached so that the strain measurement direction was in the L0 direction. In the measurement, a magnetic field was applied in the L0 direction of the sample using a physical property measurement system (PPMS) manufactured by Quantum Design, and the amount of magnetostriction was measured. Note that the measurement was carried out by a two-gauge active dummy method using pure Cu as a dummy gauge formed in the same size range of L0 to L2 as the sample and attached with the same strain gauge as the sample. In addition, the temperature is 300K, the maximum applied magnetic field is 8.9T, and the amount of magnetostriction is the displacement amount ΔL of the length L0 when no magnetic field is applied and the length L in the magnetic field direction (L0 direction) when a magnetic field of 8.9T is applied. It was determined from the absolute value of the ratio between L-L0 and L0 (ΔL/L0). As shown in Table 1, in Examples 1 to 9, magnetostriction amounts of 50 ppm or more were obtained. On the other hand, in Comparative Examples 1 to 3, a sufficient amount of magnetostriction was not obtained.

The magnetostrictive material obtained according to the present disclosure may be suitably used for ultrasonic vibrators, actuators, mold clamping devices for injection molds, vibration power generation, torque sensors, and the like.

Claims (5)

Mn: 44 at% or more and 53 at% or less,
Al: 46 at% or more and 52 at% or less,
Cu: 0.5 at% or more and 6 at% or less,
A magnetostrictive material containing 55% or more of a stable phase having a tetragonal structure. The magnetostrictive material according to claim 1, wherein the total content of Mn, Al, and Cu is 100 atomic % (however, unavoidable impurities may be included). The magnetostrictive material according to claim 1 or 2, wherein the absolute value of magnetostriction amount at room temperature is 50 ppm or more and 600 ppm or less. Mn: 44 at% or more and 53 at% or less,
Al: 46 at% or more and 52 at% or less,
Cu: 0.5 at% or more and 6 at% or less,
a first step of preparing a first alloy to become an alloy containing;
a second step of heat-treating the first alloy at a temperature of 300° C. or higher and 750° C. or lower to obtain a second alloy;
A method of manufacturing a magnetostrictive material, including: The magnetostrictive material according to claim 4, wherein the first alloy is prepared so that the total content of Mn, Al, and Cu is 100 atomic % (however, unavoidable impurities may be included). Production method.

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