Magnetic powder, magnet, method for manufacturing magnetic powder, and method for manufacturing magnet

Abstract

The present disclosure addresses the problem of providing an Sm-Fe-N-based magnetic material with excellent coercivity.　An Sm-Fe-N-based magnetic material according to the present disclosure has a main phase composed of a plurality of Sm-Fe-N-based crystal grains, and a grain boundary phase existing between adjacent Sm-Fe-N-based crystal grains and containing N, the ratio of the content of N in the main phase to the content of N in the grain boundary phase being 0.84 or more on an atomic basis.

Description

Magnetic powder, magnet, method for manufacturing magnetic powder, and method for manufacturing magnet

[0001] The present disclosure relates to magnetic powders, magnets, methods for manufacturing magnetic powders, and methods for manufacturing magnets.

[0002] Rare earth magnets have high magnetic flux density and can be made into extremely powerful permanent magnets, and are used in a variety of applications. Sm—Fe—N magnets are known as one type of rare earth magnet. Sm—Fe—N magnets are typically produced by nitriding Sm—Fe polycrystals. When N atoms dissolve in the crystal lattice of Sm—Fe polycrystals, the lattice becomes distorted, resulting in the development of uniaxial magnetic anisotropy, and the resulting Sm—Fe—N magnetic material is thought to be able to function as a hard magnetic material.

[0003] As such an Sm-Fe-N magnetic material, Patent Document 1 discloses that a flake-shaped isotropic Sm-Fe-N powder magnet material is produced by nitriding a powder of a magnet alloy obtained by a roll quenching method, and the content of the powder is, in atomic %, Sm ｘ Fe １００－ｘ－ｖ N ｖ It is described that the composition is (wherein 7≦x≦12 and 0.5≦v≦20), that the flake has a TbCu type crystal structure, and that the thickness of the flake is 10 to 30 μm.

[0004] Patent Document 2 describes a Sm—Fe—N based magnetic material whose composition expressed in atomic percent is Sm ｘ R ａ Fe100-xy-z-aM ｙ N ｚ (wherein R is at least one of Zr and Hf, M is at least one of Co, Ti, Nb, Cr, V, Mo, Si, Ga, Ni, Mn, and Al, x+a is 7% to 10%, a is 0% to 1.5%, y is 0% to 5%, and z is 10% to 14%).

[0005] JP 2002-57017 A JP 2018-157197 A

[0006] The Sm—Fe—N magnetic materials described in Patent Documents 1 and 2 are both manufactured without further heat treatment after nitriding. According to studies by the present inventors, the Sm—Fe—N magnetic materials described in Patent Documents 1 and 2 do not have sufficient coercive force, and in applications requiring heat resistance in particular, they are demagnetized and are unable to exhibit sufficient properties. One example of an application requiring heat resistance is in-vehicle use, which may require heat resistance of, for example, 120° C. or higher.

[0007] An object of the present disclosure is to provide an Sm—Fe—N based magnetic material with good coercivity, and a method for producing such an Sm—Fe—N based magnetic material.

[0008] The Sm—Fe—N magnetic material of the present disclosure includes a main phase consisting of a plurality of Sm—Fe—N crystal grains, and a grain boundary phase that is present between adjacent Sm—Fe—N crystal grains and contains N, and the ratio of the N content in the main phase to the N content in the grain boundary phase is 0.84 or more on an atomic basis.

[0009] According to the present disclosure, it is possible to provide an Sm—Fe—N based magnetic material with good coercivity, and also to provide a method for producing such an Sm—Fe—N based magnetic material.

[0010] 2 shows the results of STEM-EDX analysis of the Sm—Fe—N based magnetic material obtained in Example 1, where DF-I is a dark-field image and N is a mapping image (element distribution image) showing the concentration distribution of N atoms. FIG. 3 shows the results of STEM-EDX analysis of the Sm—Fe—N based magnetic material obtained in Comparative Example 1, where DF-I is a dark-field image and N is a mapping image (element distribution image) showing the concentration distribution of N atoms. FIG. 4 is a line profile showing the concentration distribution of N atoms in the Sm—Fe—N based magnetic material obtained in Example 1, corresponding to the arrows in FIG. 1. FIG. 5 is a line profile showing the concentration distribution of N atoms in the Sm—Fe—N based magnetic material obtained in Comparative Example 1, corresponding to the arrows in FIG.

[0011] (Embodiment 1: Sm—Fe—N-based magnetic material) Hereinafter, a Sm—Fe—N-based magnetic material in one embodiment of the present disclosure will be described in detail, but the present disclosure is not limited to this embodiment.

[0012] The Sm—Fe—N magnetic material of the present disclosure includes a main phase consisting of a plurality of Sm—Fe—N crystal grains, and a grain boundary phase that is present between adjacent Sm—Fe—N crystal grains and contains N, and the ratio of the N content in the main phase to the N content in the grain boundary phase is 0.84 or more on an atomic basis.

[0013] The Sm—Fe—N magnetic material of the present disclosure has the above-described structure and therefore has a good coercive force. Although not intended to be limited to a specific theory, the reason why the Sm—Fe—N magnetic material of the present disclosure exhibits the above-described effects is thought to be as follows.

[0014] That is, in Sm—Fe—N-based magnetic materials, it is believed that N atoms dissolve in the crystal lattice of Sm—Fe-based polycrystals, distorting the lattice and resulting in uniaxial magnetic anisotropy. In conventional Sm—Fe—N-based magnetic materials, N atoms are preferentially distributed in the grain boundary phase, with limited distribution in the main phase, so it is believed that the improvement in magnetic anisotropy does not necessarily reflect the N content. In contrast, in the Sm—Fe—N-based magnetic material of the present disclosure, the ratio of the N content in the main phase to the N content in the grain boundary phase is increased, so it is believed that the improvement in magnetic anisotropy is exerted and the coercivity of the magnetic material is improved.

[0015] The ratio of the N content in the main phase to the N content in the grain boundary phase is, on an atomic basis, 0.84 or more, preferably 0.85 or more, and may be, for example, less than 1, 0.99 or less. When the N content ratio is within this range, the coercive force of the Sm—Fe—N based magnetic material can be improved.

[0016] In the present disclosure, the N content in the main phase and the grain boundary phase can be measured by energy dispersive X-ray analysis (STEM-EDX) using a scanning transmission electron microscope. For example, in an Sm—Fe—N-based magnetic material, an element distribution map is obtained in a field of view including multiple main phases and grain boundary phases. Next, in an STEM dark-field image or the like, a location where a phase thought to be a grain boundary formed between crystal grains is oriented parallel to the direction of electron beam incidence is selected, and a line profile showing the N atom content is extracted along the scanning direction perpendicular to the grain boundary phase. Next, the N content is measured in a region 1 nm around the center (2 nm in total) along the scanning direction, centered on the position where the N content peaks, as the grain boundary phase, and the remaining region as the main phase. A field of view (e.g., 522 × 522 nm) that includes 50 or more main phase crystal grains is selected. ２ ) and perform such measurements at three or more different locations within the field of view, and calculate the N content in each phase by averaging the N contents in the regions corresponding to the main phase or grain boundary phase based on the N content at each measurement point. The N content in the main phase is divided by the N content in the grain boundary phase to calculate the ratio of the N content in the main phase to the N content in the grain boundary phase. A sample for STEM-EDX analysis of an Sm—Fe—N based magnetic material may be processed, for example, by a focused ion beam (FIB) device.

[0017] The method for determining the N content in the main phase and the grain boundary phase is not limited to the above. Instead of extracting a line profile from an element distribution map, a line profile may be obtained by scanning an electron beam perpendicular to the grain boundary. Alternatively, other methods may be used as long as the spatial resolution and detection accuracy satisfy the objectives, such as electron energy loss spectroscopy using a transmission electron microscope (TEM-EELS), electron energy loss spectroscopy using a scanning transmission electron microscope (STEM-EELS), or three-dimensional atom probe (3DAP). Energy dispersive X-ray analysis using a scanning transmission electron microscope (STEM-EDX) is preferred as a method for determining the N content in the main phase and the grain boundary phase, taking into account spatial resolution, detection sensitivity, quantitative accuracy, the width of the analyzable region, versatility, and the like.

[0018] In the Sm—Fe—N magnetic material, the Sm content is preferably 7.0 atomic % or more and 11.5 atomic % or less, and more preferably 7.0 atomic % or more and 11.2 atomic % or less, based on a total of 100 atomic % of the elements contained in the Sm—Fe—N magnetic material. When the Sm content in the Sm—Fe—N magnetic powder is within this range, the coercive force of the Sm—Fe—N magnetic material can be further improved.

[0019] In the Sm—Fe—N magnetic material, the Fe content is preferably 61.5 atomic % or more and 78.5 atomic % or less, more preferably 61.6 atomic % or more and 78.0 atomic % or less, and even more preferably 61.6 atomic % or more and 74.0 atomic % or less, based on a total of 100 atomic % of the elements contained in the Sm—Fe—N magnetic material. When the Fe content in the Sm—Fe—N magnetic powder is within this range, the coercive force of the Sm—Fe—N magnetic material can be improved.

[0020] In the Sm—Fe—N based magnetic material, the ratio of the Fe content to the Sm content (Fe content / Sm content), on an atomic basis, is preferably 5 or more and 11 or less, more preferably 7 or more and 10 or less, and even more preferably 8 or more and 9 or less. When the ratio of the Fe content to the Sm content in the Sm—Fe—N based magnetic material is within this range, the coercive force of the Sm—Fe—N based magnetic material can be improved.

[0021] In the Sm—Fe—N magnetic material, the total content of Sm and Fe is preferably 66.5 atomic % or more and 90.0 atomic % or less, more preferably 68.5 atomic % or more and 88.0 atomic % or less, and even more preferably 70.0 atomic % or more and 86.0 atomic % or less, based on 100 atomic % of the total Sm—Fe—N magnetic powder. When the total content of Sm and Fe in the Sm—Fe—N magnetic material is within this range, the coercive force of the Sm—Fe—N magnetic material can be improved.

[0022] In the Sm—Fe—N magnetic material, the N content is preferably 12.0 atomic % or more and 18.0 atomic % or less, and more preferably 12.5 atomic % or more and 18.0 atomic % or less, based on a total of 100 atomic % of the elements contained in the Sm—Fe—N magnetic material. When the N content in the Sm—Fe—N magnetic material is within this range, the coercive force of the Sm—Fe—N magnetic material can be improved.

[0023] The Sm—Fe—N magnetic material may further contain Co. In the Sm—Fe—N magnetic powder, the Co content is preferably 0.0 atomic % or more and 9.0 atomic % or less, and in one aspect, more preferably 1.0 atomic % or more and 9.0 atomic % or less, and even more preferably 1.5 atomic % or more and 8.7 atomic % or less, based on the total 100 atomic % of the elements contained in the main phase. When the Co content in the Sm—Fe—N magnetic material is within the above range, the coercive force of the Sm—Fe—N magnetic material can be improved. In another aspect, the Co content in the Sm—Fe—N magnetic material is more preferably 0.0 atomic % or more and 1.0 atomic % or less, and even more preferably 0.0 atomic % or more and 0.5 atomic % or less. When the Co content in the Sm—Fe—N magnetic material is within the above range, the coercive force of the Sm—Fe—N magnetic material can be improved.

[0024] The Sm—Fe—N based magnetic material may further contain M1, which is one or more elements selected from Ti, V, Cr, Mn, Zr, Nb, Hf, Ta and Si. M1 may preferably be one or more elements selected from Zr and Nb.

[0025] In the Sm—Fe—N magnetic powder, the content of the M1 is preferably 1.0 atomic % or more and 4.0 atomic % or less, more preferably 1.1 atomic % or more and 4.0 atomic % or less, and even more preferably 1.2 atomic % or more and 4.0 atomic % or less, based on a total of 100 atomic % of the elements contained in the Sm—Fe—N magnetic material. When the content of M1 in the Sm—Fe—N magnetic material is within the above range, the coercive force of the Sm—Fe—N magnetic material can be improved.

[0026] The Sm—Fe—N magnetic material may further contain M2, which is one or more elements selected from B and C. In the Sm—Fe—N magnetic powder, the content of M2 is preferably 0.0 atomic % or more and 2.5 atomic % or less, more preferably 0.1 atomic % or more and 2.3 atomic % or less, and even more preferably 0.1 atomic % or more and 2.2 atomic % or less, based on a total of 100 atomic % of the elements contained in the Sm—Fe—N magnetic material. When the content of M2 in the Sm—Fe—N magnetic material is within the above range, the coercive force of the Sm—Fe—N magnetic material can be improved.

[0027] The Sm—Fe—N magnetic material may contain O and / or Al as inevitable impurities. When the Sm—Fe—N magnetic material contains O, the O content may be, for example, 10.0 atomic % or less, or even 5.0 atomic % or less, based on 100 atomic % of the total elements contained in the Sm—Fe—N magnetic material. When the Sm—Fe—N magnetic material contains Al, the Al content may be, for example, 10.0 atomic % or less, or even 5.0 atomic % or less, based on 100 atomic % of the total elements contained in the Sm—Fe—N magnetic material.

[0028] The total content of each element in the Sm—Fe—N magnetic material does not exceed 100 atomic %. Theoretically, the total content of all elements that can be contained in the Sm—Fe—N magnetic material is 100 atomic %.

[0029] In the present disclosure, the types and contents of elements, excluding C, N, and O, that may be contained in the Sm—Fe—N-based magnetic material can be measured by X-ray fluorescence analysis (XRF) or inductively coupled plasma atomic emission spectrometry (ICP-AES), preferably X-ray fluorescence analysis (XFR). Furthermore, C can be measured by oxygen flow combustion-infrared absorption spectrometry, and N and O can be measured by inert gas fusion-thermal conductivity spectrometry (TCD).

[0030] (Main Phase) The main phase is composed of Sm—Fe—N crystal grains. The Sm—Fe—N crystal grains have a structure in which N atoms are dissolved in the crystal lattice of Sm—Fe crystals. The main phase is a region in the Sm—Fe—N magnetic material that can contribute to the exertion of magnetism, and the solid solution of N atoms applies distortion to the crystal lattice, resulting in the development of uniaxial magnetic anisotropy and enabling the material to function as a hard magnetic material.

[0031] The main phase is Th ２ Zn １７ Sm—Fe—N crystals and TbCu crystals showing the type structure ７ It is preferable that the alloy contains one or more types of crystals selected from Sm--Fe--N type crystals exhibiting a type structure.

[0032] The main phase contains at least Sm, Fe, and N.

[0033] The N content in the main phase is preferably 5.5 atomic % to 6.3 atomic % inclusive, more preferably 5.6 atomic % to 6.2 atomic % inclusive, and even more preferably 5.7 atomic % to 6.3 atomic % inclusive, based on a total of 100 atomic % of the elements contained in the main phase. When the N content in the main phase is within this range, magnetic anisotropy is enhanced, and the coercive force of the Sm—Fe—N based magnetic material can be improved.

[0034] In the present disclosure, the N content in the main phase can be measured by energy dispersive X-ray analysis (STEM-EDX) using a scanning transmission electron microscope. For example, in an Sm—Fe—N-based magnetic material, an element distribution map is obtained in a field of view that includes multiple main phases and grain boundary phases. Next, in an STEM dark-field image or the like, a location where a phase thought to be a grain boundary phase formed between crystal grains is oriented parallel to the direction of electron beam incidence is selected, and a line profile showing the N atom content is extracted along the scanning direction perpendicular to the grain boundary phase. Next, a region of 1 nm around the position where the N content peaks (total of 2 nm) along the scanning direction is defined as the grain boundary phase, and the N content is measured. A field of view (e.g., 522 × 522 nm) that includes 50 or more main phase crystal grains is selected. ２ The measurement is performed at three or more different points within the field of view of the Sm—Fe—N system. The N content in the main phase is determined by averaging the N content in the region corresponding to the main phase based on the N content at each measurement point. The observation surface of the Sm—Fe—N system magnetic material may be formed by, for example, a focused ion beam (FIB) device.

[0035] The main phase may further contain Co. The main phase may further contain M1, which is one or more elements selected from Ti, V, Cr, Mn, Zr, Nb, Hf, Ta, and Si. M1 may preferably be one or more elements selected from Zr and Nb. The main phase may further contain M2, which is one or more elements selected from B and C.

[0036] The crystallite diameter of the Sm—Fe—N crystal grains contained in the main phase is preferably 10 nm or more and 1 μm or less, more preferably 15 nm or more and 400 nm or less, and even more preferably 20 nm or more and 200 nm or less. When the crystallite diameter of the Sm—Fe—N crystal grains is within the above range, the coercive force of the Sm—Fe—N magnetic material can be improved. The Sm—Fe—N crystal grains typically exist as single crystals. In the present disclosure, the crystallite diameter can be directly measured from an image obtained by a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM).

[0037] (Grain boundary phase) The grain boundary phase exists between the plurality of Sm—Fe—N crystal grains that constitute the main phase. The grain boundary phase can typically be a layer that covers the Sm—Fe—N crystal grains, and can exist as a continuous layer that separates the plurality of Sm—Fe—N crystal grains, for example. The grain boundary phase can typically be a non-magnetic phase. When the grain boundary phase is a non-magnetic phase, the magnetic domains of the main phase are separated by the grain boundary phase, which suppresses magnetic field reversal and can increase the coercive force.

[0038] The grain boundary phase contains N. The content of N in the grain boundary phase is preferably 6.0 atomic % or more and 7.5 atomic % or less, more preferably 6.3 atomic % or more and 7.3 atomic % or less, and even more preferably 6.5 atomic % or more and 7.1 atomic % or less, based on a total of 100 atomic % of the main phase. When the content of N in the grain boundary phase is within this range, magnetic anisotropy is enhanced, and the coercive force of the Sm—Fe—N based magnetic material can be improved.

[0039] In the present disclosure, the N content in the grain boundary phase can be measured by energy dispersive X-ray analysis (STEM-EDX) using a scanning transmission electron microscope. For example, in an Sm—Fe—N-based magnetic material, an element distribution map is obtained in a field of view including multiple main phases and grain boundary phases. Next, in an STEM dark-field image or the like, a location where a phase thought to be a grain boundary phase formed between crystal grains is oriented parallel to the direction of electron beam incidence is selected, and a line profile showing the N atom content is extracted along the scanning direction perpendicular to the grain boundary phase. Next, a region of 1 nm around the position where the N content peaks (total of 2 nm) along the scanning direction is defined as the grain boundary phase, and the N content is measured. A field of view (e.g., 522 × 522 nm) that includes 50 or more main phase crystal grains is selected. ２ The measurement is performed at three or more different points within the field of view of the Sm—Fe—N system. The N content in the grain boundary phase is determined by averaging the N content in the region corresponding to the grain boundary phase based on the N content at each measurement point. The observation surface of the Sm—Fe—N system magnetic material may be formed by, for example, a focused ion beam (FIB) device.

[0040] The grain boundary phase may further contain one or more elements selected from Sm, Fe, Co, Ti, V, Mn, Zr, Nb, Hf, Ta, Si, B and C.

[0041] In another aspect, the grain boundary phase may be a region in which a measured value of 2 nm or more continuously indicates a higher N content than the Sm—Fe—N system crystal grain phase in STEM-EDX analysis. In such an aspect, the thickness of the grain boundary phase is preferably 2 nm or more and 8 nm or less, more preferably 4 nm or more and 6 nm or less. When the width of the grain boundary phase is within this range, the coercive force of the Sm—Fe—N system crystal material can be improved.

[0042] The Sm—Fe—N based magnetic material of the present disclosure may contain other heterophases in addition to the main phase and grain boundary phase. The Sm—Fe—N based magnetic material may be a powder material containing the main phase, the grain boundary phase, and optionally a heterophase, and preferably a powder material consisting of the main phase, the grain boundary phase, and optionally a heterophase.

[0043] The Sm—Fe—N based magnetic material of the present disclosure may be in the form of magnetic powder, a magnet, or the like.

[0044] (Sm—Fe—N based magnetic powder) The Sm—Fe—N based magnetic material can be in the form of magnetic powder (i.e., powder). Hereinafter, the Sm—Fe—N based magnetic material in the form of powder will also be referred to as “Sm—Fe—N based magnetic powder.”

[0045] The Sm—Fe—N based magnetic powder may be a powder material containing the main phase, the grain boundary phase, and optionally a heterophase, and is preferably a powder material consisting of the main phase, the grain boundary phase, and optionally a heterophase. The Sm—Fe—N based magnetic powder contains Sm, Fe, and N.

[0046] The average particle size of the Sm-Fe-N magnetic powder is preferably 10 μm or more and 300 μm or less, more preferably 10 μm or more and 50 μm or less, and even more preferably 20 μm or more and 40 μm or less.

[0047] The average particle size of the Sm-Fe-N magnetic powder can be measured by a laser diffraction particle size distribution measurement method.

[0048] (Sm—Fe—N based magnet) The Sm—Fe—N based magnetic material can be in the form of a magnet (i.e., bulk). Hereinafter, the Sm—Fe—N based magnetic material in bulk form will also be referred to as an “Sm—Fe—N based magnet.”

[0049] In one embodiment, the Sm—Fe—N magnet preferably includes the Sm—Fe—N magnetic powder and a binder. The binder can act as a binder for the Sm—Fe—N magnetic powder and can typically include resin (plastic), rubber, or a metal such as Zn.

[0050] In this embodiment, the content of Sm—Fe—N magnetic powder contained in the Sm—Fe—N magnet may be preferably 90% by mass or more and 99.5% by mass or less, and more preferably 95% by mass or more and 99% by mass or less.

[0051] In this embodiment, examples of the resin include thermosetting resins such as epoxy resins, phenolic resins, allyl resins, and unsaturated polyester resins; and thermoplastic resins such as polyamide resins, polyphenylene sulfide resins, polyether ketone resins, polyether ether ketone resins, and polyester resins.

[0052] In this embodiment, the Sm--Fe--N magnet may contain other additives in addition to the Sm--Fe--N magnetic powder and resin.

[0053] In another aspect, the Sm—Fe—N based magnet may be a bulk magnetic material preferably including the main phase, the grain boundary phase, and optionally a heterogeneous phase, and more preferably a bulk magnetic material consisting of the main phase, the grain boundary phase, and optionally a heterogeneous phase.

[0054] (Embodiment 2: Manufacturing method of Sm—Fe—N based magnetic material) The Sm—Fe—N based magnetic material of the present disclosure can be manufactured by a manufacturing method including: (a) preparing an Sm—Fe based crystalline material; (b) nitriding the Sm—Fe based crystalline material to obtain an Sm—Fe—N based precursor material; and (c) heat-treating the Sm—Fe—N based precursor material at 400° C. or higher and 500° C. or lower in an atmosphere in which the concentrations of N atoms and O atoms are each 100 ppm or lower, to obtain the Sm—Fe—N based magnetic material.

[0055] The manufacturing method of the present disclosure can provide an Sm—Fe—N based magnetic material with good coercivity. Although not limited to a particular theory, the reason why the manufacturing method of the present disclosure exhibits the above-described effects is thought to be as follows.

[0056] As described above, in Sm—Fe—N-based magnetic materials, it is believed that the dissolution of N atoms into the crystal lattice of the Sm—Fe-based crystalline material distorts the lattice and causes uniaxial magnetic anisotropy. Conventional Sm—Fe—N-based magnetic materials are manufactured by nitriding an Sm—Fe-based crystalline material. However, this nitriding treatment limits the dissolution of N atoms into the crystalline portion, and the N atoms are distributed mainly in the grain boundary portion. In contrast, in the manufacturing method disclosed herein, after the nitriding treatment, a further heat treatment is performed in an atmosphere in which the concentrations of N atoms and O atoms are each 100 ppm or less. This can promote the dissolution of N atoms into the main phase, and at the same time, suppresses the expulsion of N atoms from the magnetic material. As a result, it is believed that a magnetic material with high coercivity can be manufactured.

[0057] (a) Preparation of Sm—Fe—N-based crystalline material In the manufacturing method of the present disclosure, first, an Sm—Fe—N-based crystalline material is prepared. The Sm—Fe—N-based crystalline material is preferably manufactured by a manufacturing method including: (i) preparing an Sm—Fe-based alloy containing an amorphous phase; and (ii) crystallizing the Sm—Fe-based alloy containing the amorphous phase and, if necessary, pulverizing the crystallized Sm—Fe-based alloy to obtain the Sm—Fe-based crystalline material.

[0058] (i) Preparation of Sm—Fe-based alloy containing amorphous phase The Sm—Fe-based alloy is preferably prepared by a manufacturing method including preparing a metal raw material containing at least Sm and Fe, and melting the metal raw material, rapidly cooling, and solidifying the metal raw material to obtain the Sm—Fe-based alloy.

[0059] The types and proportions of elements contained in the metal raw materials are the same as those of elements constituting the Sm--Fe--N based magnetic material.

[0060] By melting the metal raw materials, each element can be uniformly distributed in the melt. The temperature when melting the metal is preferably, for example, 1,200°C or higher and 1,700°C or lower. The atmosphere when melting the metal is preferably, for example, an inert atmosphere not containing nitrogen, such as an Ar atmosphere or a He atmosphere. Such melting is not particularly limited, but is preferably performed by high-frequency melting. The metal raw materials may be mixed before being melted.

[0061] By rapidly cooling the melt, the melt can be cooled below the freezing point without crystallization while maintaining the uniformity of the composition, and a Sm--Fe alloy containing an amorphous phase can be obtained.

[0062] The quenching is not particularly limited, but is preferably carried out by roll quenching. In roll quenching, the molten material is quenched by spraying it onto a rotating metal roll. The conditions for roll quenching are not particularly limited. As the metal roll, it is preferable to use a roll made of, for example, molybdenum, copper, or an alloy material containing these as the main component. The peripheral speed of the roll can be, for example, preferably 30 m / s or more and 100 m / s or less, more preferably 50 m / s or more and 90 m / s or less.

[0063] (ii) Preparation of Sm—Fe-based crystalline material By subjecting a Sm—Fe-based alloy containing an amorphous phase to a crystallization treatment, Sm—Fe-based crystals are precipitated, and a Sm—Fe-based crystalline material is obtained. The crystallization treatment can be typically carried out by heating.

[0064] The temperature when heating the Sm—Fe-based alloy containing an amorphous phase may be, for example, preferably 690° C. or higher and 800° C. or lower, more preferably 725° C. or higher and 785° C. or lower. The heating time when heating the Sm—Fe-based alloy containing an amorphous phase may be, for example, 5 minutes or higher and 60 minutes or lower, preferably 5 minutes or higher and 30 minutes or lower. The atmosphere when heating the Sm—Fe-based alloy containing an amorphous phase may be, for example, an inert atmosphere not containing nitrogen, such as an Ar atmosphere or a He atmosphere. Heating the Sm—Fe-based alloy containing an amorphous phase under such conditions makes it easier to generate Sm—Fe-based crystals more uniformly.

[0065] The Sm—Fe-based crystalline material may be further pulverized. By pulverization, a powdered Sm—Fe-based crystalline material is obtained. The pulverization method is not particularly limited, but it can be performed using, for example, a crusher, a stamp mill, a ball mill, or the like. By such pulverization, the Sm—Fe-based crystalline material is pulverized to, for example, 10 to 300 μm, preferably 10 to 150 μm, and more preferably 30 to 80 μm.

[0066] (b) Nitriding of Sm—Fe-based crystalline material By nitriding an Sm—Fe-based crystalline material, N atoms are incorporated into the Sm—Fe-based crystalline material, and an Sm—Fe—N-based precursor material is obtained.

[0067] The nitriding treatment can be typically carried out by heat treatment in a nitrogen atmosphere, an ammonia atmosphere, a hydrogen atmosphere, or a mixture thereof.

[0068] When nitrogen gas is used in the nitriding treatment, the partial pressure of nitrogen is 10 kPa or more and 100 kPa or less, preferably 50 kPa or more and 100 kPa or less. By using such a nitrogen partial pressure, the nitriding reaction proceeds sufficiently.

[0069] In the above nitriding treatment, when a mixed gas of ammonia and hydrogen is used, the partial pressure of ammonia is 20 kPa or more and 40 kPa or less, preferably 25 kPa or more and 33 kPa or less, when the total pressure of the mixed gas is 0.1 MPa. By using such a partial pressure of ammonia, the nitriding reaction proceeds sufficiently.

[0070] In the nitriding treatment, the heating temperature is preferably 350° C. or higher and 500° C. or lower, more preferably 400° C. or higher and 500° C. or lower. By using this heating temperature, it is possible to prevent decomposition into SmN and Fe, which may occur when the nitriding reaction is carried out at a higher temperature, and it is possible to allow the reaction to proceed more sufficiently compared to when the nitriding reaction is carried out at a lower temperature.

[0071] The nitriding treatment can typically be carried out under atmospheric pressure, for example, preferably under a pressure of 900 hPa or more and 1,100 hPa or less, more preferably 950 hPa or more and 1,050 hPa or less.

[0072] When nitrogen gas is used in the nitriding treatment, the heating time is preferably 2 to 30 hours, more preferably 8 to 25 hours. This heating time can prevent grain growth and decomposition into SmN and Fe, which may occur with a longer heating time, and allows the reaction to proceed more efficiently than with a shorter heating time. By adjusting this heating time, the amount of nitrogen incorporated into the Sm—Fe crystalline material can be adjusted.

[0073] When a mixed gas of ammonia and hydrogen is used in the nitriding treatment, the heating time is preferably 10 to 90 minutes, more preferably 20 to 60 minutes. This heating time can prevent grain growth and decomposition into SmN and Fe, which may occur with a longer heating time, and allows the reaction to proceed more fully than with a shorter heating time. By adjusting this heating time, the amount of nitrogen incorporated into the Sm—Fe crystalline material can be adjusted.

[0074] (c) Heat Treatment of Sm—Fe—N Precursor Material The Sm—Fe—N precursor material is heat-treated at 400° C. or higher and 500° C. or lower in an atmosphere in which the concentrations of N atoms and O atoms are each 100 ppm or lower, thereby diffusing the N atoms into the main phase and obtaining the Sm—Fe—N magnetic material of the present disclosure. Hereinafter, the heat treatment of the Sm—Fe—N precursor material is also referred to as “continuous heat treatment.”

[0075] It is preferable that the step of cooling the Sm—Fe—N-based precursor material is not included between the nitriding treatment and the continuous heat treatment, and it is preferable that the continuous heat treatment is carried out directly following the nitriding treatment.

[0076] In the continuous heat treatment, the atmosphere in which the N atom concentration and the O atom concentration are each 100 ppm or less is H ２ Gas atmosphere; Ar atmosphere; He atmosphere; and H ２ An example of the atmosphere is a mixture of a gas and Ar or He.

[0077] In the continuous heat treatment, the heating temperature is preferably 350° C. or higher and 500° C. or lower, more preferably 400° C. or higher and 500° C. or lower. By using this heating temperature, it is possible to prevent decomposition into SmN and Fe, which may occur when heat treatment is performed at a higher temperature, and it is possible to sufficiently promote the solid solution of N atoms into the main phase, compared to when heat treatment is performed at a lower temperature.

[0078] The continuous heat treatment can typically be carried out under atmospheric pressure, for example, preferably under a pressure of 900 hPa or more and 1,100 hPa or less, more preferably 950 hPa or more and 1,050 hPa or less.

[0079] In the continuous heat treatment, the heating time is preferably 30 to 600 minutes, more preferably 30 to 240 minutes. By using this heating time, it is possible to prevent grain growth and decomposition into SmN and Fe, which may occur when the heating time is longer, and it is possible to more sufficiently promote the solid solution of N atoms into the main phase than when the heating time is shorter.

[0080] After the continuous heat treatment, the product may be naturally cooled.

[0081] The above-described (a) preparation of a Sm—Fe—N crystalline material, (b) nitriding of the Sm—Fe crystalline material, and (c) heat treatment of the Sm—Fe—N precursor material typically result in a powdered Sm—Fe—N magnetic material (i.e., Sm—Fe—N magnetic powder).

[0082] In one embodiment, the Sm—Fe—N magnet can be produced by a manufacturing method including mixing Sm—Fe—N magnetic powder and binder raw materials to obtain a mixture, and molding the mixture to obtain the Sm—Fe—N magnet. Methods for molding the mixture include compression molding, injection molding, and the like. For example, molding can be performed by heating and melting the resin raw materials in the mixture or dissolving them in a solvent to form a liquid, and then subjecting the liquid mixture to compression molding or injection molding. The liquid mixture can be hardened by cooling, crosslinking the binder raw materials, removing the solvent, or the like. Alternatively, the Sm—Fe—N magnet can be produced by sintering the Sm—Fe—N magnetic powder.

[0083] The Sm—Fe—N based magnetic material of the present disclosure has a good coercive force and can be suitably used in various applications such as electromagnetic actuators (motors), etc. The Sm—Fe—N based magnetic material of the present disclosure is resistant to demagnetization even at high temperatures, and can therefore be suitably used in applications requiring reliability in high-temperature environments, such as in-vehicle applications.

[0084] The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited thereto.

[0085] (Examples 1 to 19) Elements having the compositions shown in Table 1 were charged and subjected to high-frequency melting to prepare master alloys. The obtained master alloys were melted in an Ar atmosphere and sprayed onto a Mo roll rotating at a peripheral speed of 70 m / s to obtain quenched ribbons (Sm—Fe-based amorphous material). The quenched ribbons were heat-treated in an Ar gas atmosphere at a treatment temperature of 755°C to obtain Sm—Fe-based crystalline material, which was then pulverized until it passed through a 150 μm mesh. The compositions shown in Table 1 are based on atomic percent.

[0086] The heat-treated powder (powdered Sm—Fe-based crystalline material) was then nitrided in an atmosphere, at a temperature, and for a time period shown in Table 1 to obtain a Sm—Fe—N-based precursor material. After the nitriding treatment, a continuous heat treatment was carried out in an atmosphere shown in Table 1 to obtain a Sm—Fe—N-based magnetic material. The temperature and time of the continuous heat treatment were as shown in Table 1.

[0087] (Comparative Examples 1 to 4) For Comparative Examples 1 and 2, Sm—Fe—N-based materials were obtained in the same manner as in Examples 1 to 19, except that continuous heat treatment was not performed after nitriding treatment. For Comparative Examples 3 and 4, continuous heat treatment was performed, but the high temperature of the continuous heat treatment caused some deep decomposition into SmN and Fe, resulting in a decrease in coercive force.

[0088]

[0089] (STEM-EDX analysis: acquisition of dark-field images and element distribution images) The materials obtained in the above examples and comparative examples were processed using a focused ion beam device and an Ar milling device, and observation images (dark-field images) were obtained using a transmission electron microscope (acceleration voltage 200 kV) equipped with a spherical aberration corrector manufactured by FEI, and element distribution maps were obtained using energy dispersive X-ray analysis (EDX). The field of view length of each image was 522 nm × 522 nm, and the number of pixels when collecting EDX data was 512 × 512 px.

[0090] Fig. 1 shows the analysis results of the Sm—Fe—N magnetic material obtained in Example 1, and Fig. 2 shows the analysis results of the material obtained in Comparative Example 1. In Fig. 1 and Fig. 2, the image indicated by DF-I is a dark-field image obtained by STEM, and the image indicated by N is an element distribution image of N atoms.

[0091] In the material of Comparative Example 1 shown in Figure 2, a comparison of the STEM dark-field image and the element distribution image of N atoms shows that regions with a high concentration of N atoms are present along the grain boundaries, and that N atoms are distributed concentratedly in the grain boundary phase. In contrast, in the Sm-Fe-N magnetic material of Example 1 shown in Figure 1, the difference in N atom distribution between the grain boundary phase and the main phase is smaller than in Comparative Example 1. This is thought to be because in Example 1, continuous heat treatment was performed after the nitriding treatment, and as a result of this treatment, the N atom content in the main phase and the grain boundary phase became closer to uniform.

[0092] (STEM-EDX Analysis: Acquisition of Line Profile) From the element distribution map, a location where a phase thought to be a grain boundary formed between crystal grains was oriented parallel to the electron beam incidence direction was selected, and a line profile showing the content of N atoms in a direction perpendicular to the grain boundary was extracted. For Example 1, the width of the region from which the line profile was extracted was 20 nm, the length was 41 nm, and the distance between sampling points was 1 nm. For Comparative Example 1, the width of the region from which the line profile was extracted was 20 nm, the length was 61 nm, and the distance between sampling points was 1 nm. However, the region from which the line profile was extracted is not limited to the above ranges. Generally, if the extraction width is narrow, the S / N ratio of the line profile deteriorates, and if the width is wide, the orthogonality to the curvature of the grain boundary decreases. Furthermore, if the extraction length is too short, information on the N content in the main phase and the grain boundary phase will be insufficient, and if it is too long, there is a concern that information on a grain boundary phase other than the one being focused on will affect the line profile. Taking these circumstances into consideration, it is desirable to adopt conditions appropriate for the structure to be analyzed.

[0093] In the obtained line profile, the region 1 nm before and after the center (2 m in total) along the scanning direction, centered on the position where the N atom content peaks, was designated as the grain boundary phase, and the remaining region was designated as the main phase. Based on the N atom content at each measurement point, the N atom content in the main phase and the N atom content in the grain boundary phase were calculated. For each of the examples and comparative examples, the above measurement was performed three or more times, and the N atom content in the main phase and the N atom content in the grain boundary phase were averaged to determine the N atom content in the main phase or grain boundary phase for each example or comparative example. The N atom content in the main phase was divided by the N atom content in the grain boundary phase to calculate the ratio of the N atom content in the main phase to the N atom content in the grain boundary phase.

[0094] FIG. 3 is an example showing the N atom content at the position where the line profile was extracted for the Sm—Fe—N magnetic material obtained in Example 1. The solid line represents the line profile showing the N atom content extracted in the direction, width, and length indicated by the arrow in FIG. 1 . The dashed line represents the average value of the N atom content in the grain boundary phase and the main phase. The average value of the N atom content in the main phase was calculated independently for the left and right sides of the grain boundary phase on the line profile. In the Sm—Fe—N magnetic material obtained in Example 1, the N atom content in the grain boundary phase was 6.86 atomic %, and the N atom content in the main phase was 5.92 atomic % on the left side of the grain boundary phase and 5.96 atomic % on the right side of the grain boundary phase on the line profile, resulting in an average value of 5.94 atomic % for the entire grain boundary phase. From this, it can be said that in the Sm—Fe—N based magnetic material obtained in Example 1, the ratio of the content of N atoms in the main phase to the content of N atoms in the grain boundary phase is 0.87 on the left side of the main phase and 0.86 on the right side of the main phase on an atomic basis, and the average value for the main phase as a whole is 0.87.

[0095] 4 is an example showing the N atom content at the position where the line profile was extracted for the material obtained in Comparative Example 1. The solid line indicates the line profile showing the N content extracted in the direction, width, and length indicated by the arrow in FIG. 2. The dashed line indicates the average value of the N atom content in the grain boundary phase and the main phase. The N atom content in the grain boundary phase of the Sm—Fe—N based magnetic material obtained in Comparative Example 1 was 8.31 atomic %, and the N atom content in the main phase was 6.71 atomic % on the left side of the grain boundary phase and 6.90 atomic % on the right side of the grain boundary phase on the line profile, with the average value for the entire grain boundary phase being 6.85 atomic %. From this, it can be said that in the Sm—Fe—N based magnetic material obtained in Comparative Example 1, the ratio of the content of N atoms in the main phase to the content of N atoms in the grain boundary phase, on an atomic basis, is 0.81 on the left side of the grain boundary phase and 0.83 on the right side of the grain boundary phase, and the average value for the main phase as a whole is 0.82.

[0096] (Magnetic Measurement) Magnetic measurements were carried out using a VSM (vibrating sample magnetometer).

[0097]

[0098] It was confirmed that the difference in the N atom content between the grain boundary phase and the main phase was small in the Sm—Fe—N magnetic materials of the examples, compared to the materials of the comparative examples. For example, in the Sm—Fe—N magnetic material of Example 1 shown in Figure 3, the ratio of the N atom content in the main phase to the N atom content in the grain boundary phase was 0.86 or more, whereas in the material of Comparative Example 1 shown in Figure 4, this ratio was 0.81. This confirms that by performing continuous heat treatment after nitriding treatment, the distribution of N atoms in the main phase and the grain boundary phase became more uniform.

[0099] From the examples and comparative examples, it was confirmed that a Sm—Fe—N-based magnetic material with high coercivity can be obtained by performing a continuous heat treatment in an inert atmosphere containing no N atoms after the nitriding treatment. For example, in Example 1, the coercivity was 1,500 kA / m, which is higher than the 930 kA / m of Comparative Example 1, which was not subjected to a continuous heat treatment.

[0100] Thus, even though the constituent elements and compositions of the materials are similar between the Examples and Comparative Examples, a large difference in coercivity can occur. This is thought to be because the N atoms are dissolved deep into the main phase by the continuous heat treatment after the nitriding treatment, and the main phase and the grain boundary phase are distributed more uniformly.

[0101] The present disclosure provides the following aspects: [1] A Sm—Fe—N based magnetic material comprising: a main phase consisting of a plurality of Sm—Fe—N based crystal grains; and a grain boundary phase containing N that exists between adjacent Sm—Fe—N based crystal grains, wherein the ratio of the N content in the main phase to the N content in the grain boundary phase is 0.84 or more on an atomic basis. [2] The Sm—Fe—N based magnetic material according to [1], having an Sm content of 7.0 atomic % or more and 11.5 atomic % or less, an Fe content of 61.5 atomic % or more and 78.5 atomic % or less, a Co content of 0 atomic % or more and 9.0 atomic % or less, a content of M1 which is one or more elements selected from Ti, V, Cr, Mn, Zr, Nb, Hf, Ta and Si which is 1.0 atomic % or more and 4.0 atomic % or less, a content of M2 which is one or more elements selected from B and C which is 0 atomic % or more and 2.5 atomic % or less, and a N content of 12.0 atomic % or more and 18.0 atomic % or less. [3] The Sm—Fe—N based magnetic material according to [1] or [2], in the form of magnetic powder or a magnet. [4] An Sm—Fe—N based magnet comprising the Sm—Fe—N based magnetic material according to any one of [1] to [3] and a binder. [5] A method for producing an Sm—Fe—N based magnetic material, comprising: preparing an Sm—Fe based crystalline material; nitriding the Sm—Fe based crystalline material to obtain an Sm—Fe—N based precursor material; and heat-treating the Sm—Fe—N based precursor material at 400° C. or higher and 500° C. or lower in an atmosphere in which the concentrations of N atoms and O atoms are each 100 ppm or lower, to obtain the Sm—Fe—N based magnetic material. [6] A method for producing an Sm—Fe—N based magnet, further comprising: preparing an Sm—Fe based crystalline material; nitriding the Sm—Fe based crystalline material to obtain an Sm—Fe—N based precursor material; heat-treating the Sm—Fe—N based precursor material at 400° C. or higher and 500° C. or lower in an atmosphere in which the concentrations of N atoms and O atoms are each 100 ppm or lower, to obtain an Sm—Fe—N based magnetic material; mixing the Sm—Fe—N based magnetic material with a binder to obtain a mixture; and molding the mixture to obtain an Sm—Fe—N based magnet.

[0102] The Sm—Fe—N based magnetic material of the present disclosure has a good coercive force and can be suitably used in a variety of applications.

Claims

1. A main phase consisting of a plurality of Sm—Fe—N crystal grains that are Sm—Fe—N crystals exhibiting a TbCu 7 type structure; a grain boundary phase that is present between adjacent Sm—Fe—N-based crystal grains and contains N, a ratio of the N content in the main phase to the N content in the grain boundary phase is 0.84 or more on an atomic basis; The Sm content is 7.0 atomic % or more and 11.5 atomic % or less, The Fe content is 61.5 atomic % or more and 78.5 atomic % or less, The Co content is 0 atomic % or more and 9.0 atomic % or less, the content of M1, which is one or more elements selected from Ti, V, Cr, Mn, Zr, Nb, Hf, Ta, and Si, is 1.0 atomic % or more and 4.0 atomic % or less; The content of M2, which is one or more elements selected from B and C, is 0.1 atomic % or more and 2.5 atomic % or less, and A Sm—Fe—N-based magnetic material having an N content of 12.0 atomic % or more and 18.0 atomic % or less.

2. 2. The Sm-Fe-N based magnetic material according to claim 1, which is in the form of magnetic powder or a magnet.

3. A Sm-Fe-N magnet comprising the Sm-Fe-N magnetic powder according to claim 2 and a binder.