JP2012234985A - Method for manufacturing neodymium-iron-boron magnet having large coercive force - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a NdFeB magnet having a large residual magnetization and a large coercive force.SOLUTION: The method for manufacturing a NdFeB magnet comprises the steps of: causing a non-magnetic phase to touch a magnetic structure including NdFeB phase; heating the non-magnetic phase to a temperature equal to or higher than its melting point; and distributing the non-magnetic phase to lie at grain boundaries in the magnetic structure. In the method, at least a part of the magnetic structure including the NdFeB phase is composed of nanocrystal grains having a grain size of 10-300 nm.

Description

  The present invention relates to a method for manufacturing an NdFeB magnet.

  The present invention relates to a method for manufacturing an NdFeB magnet having a high coercivity in a magnetization curve. In the following description, the molded body before magnetization molded into a predetermined shape is also called a magnet.

  The application of permanent magnets extends to a wide range of fields such as electronics, information communication, medical care, machine tool fields, industrial and automotive motors, and the demand for suppression of carbon dioxide emissions is increasing. In recent years, there are increasing expectations for the development of permanent magnets with even higher characteristics due to energy savings and improved power generation efficiency in the industrial field.

  At present, Nd—Fe—B type magnets, which are dominating the market as high performance magnets, are also used as magnets for drive motors for HV / EHV. In response to the recent demand for further miniaturization and higher output of motors (increase in remanent magnetization of magnets), Nd-Fe-B magnets have higher performance, especially higher coercive force. The demand for is growing.

The Nd-Fe-B magnet was invented by Sagawa et al. Over 20 years ago (Non-Patent Document 1). Since then, no magnet material exceeding the Nd ₂ Fe ₁₄ B compound has been found.

  Research on nanocomposite magnets is underway as one of the developments of materials with performance exceeding that of NdFeB magnets. The material design philosophy of the nanocomposite magnet is that the hard magnetic phase with high coercivity (Nd2Fe14B phase) and the soft magnetic phase with high saturation magnetization (α-Fe phase), both of which are fine crystal grains on the order of nm, are contained in the entire structure. By coexisting, the characteristics of both phases are expressed at the same time through exchange bonding, thereby achieving a high energy product. Nanocomposite magnets are considered promising as a concept that can achieve both high coercivity and high saturation magnetization.

  Various nanocomposite magnets using NdFeB-based materials have been proposed. For example, the following anisotropic exchange spring magnets have been proposed (Patent Document 1).

In this magnet, a melt of an alloy having a composition of Nd ₇ Fe ₈₂ Co ₅ Cu ₃ B ₃ is made into a thin film piece by a super-quenching method and then pulverized, and the obtained powder is cold-pressed into a preform. Further, the preform is manufactured by hot pressing and densification after hot pressing.

This magnet is a three-phase mixture of Nd ₂ Fe ₁₄ B phase, α-Fe phase, and Nd—Cu phase, where Nd ₂ Fe ₁₄ B phase is a hard magnetic phase and α-Fe phase is a soft magnetic phase. Yes. Among these three phases, the Nd—Cu phase is a grain boundary phase intervening in the grain boundaries of the other phases, and improves the fluidity between the phases during the upsetting process described above and increases the coercive force. It is supposed to work.

In the case of a nanocomposite magnet, the crystal grain sizes of the hard magnetic phase and the soft magnetic phase constituting the magnet are important parameters that define the magnetic characteristics, but in Patent Document 1, the Nd ₂ Fe ₁₄ B phase, α The examination of the crystal grain size of the -Fe phase and the Nd-Cu phase, and the correlation between the crystal grain size and the magnetic properties have not been conducted.

In this regard, Patent Document 2 observes an aggregate state of crystal grains of each phase in a nanocomposite magnet including three phases of an Nd ₂ Fe ₁₄ B phase, an α-Fe phase, and an Nd—Cu phase with an electron microscope. The crystal grain size of each phase is measured, and the relationship between the crystal grain size and magnetic properties is investigated. According to the survey results, it is described that the crystal grain size defines the magnetic properties. More specifically, the crystal grain size of the Nd—Cu phase defines the maximum energy product in the direction of the easy axis of magnetization, and the crystal grain size of the Nd—Cu phase is preferably 37 nm or less. Have been described.

  Moreover, in the manufacturing process of the magnet in patent document 2, the process of the plastic working performed in a 700-1100 degreeC temperature range is included as an essential process. This process guarantees the mutual fluidity of the magnetic phase, and orients the magnetic phase in a specific direction, which aligns the easy axis of magnetization of each magnetic phase, realizes a large degree of anisotropy, and consequently a high coercivity. It will be realized.

JP 2002-57015 A JP 2005-93731 A

M.M. Sagawa, S .; Fujimura, N .; Togawa, H .; Yamamoto, and Y.J. Matsuura, J. et al. Appl. Phys. 55 (1984), 2083.

The present invention relates to a method for producing an NdFeB magnet. In general, an NdFeB-based magnet is manufactured from an alloy containing Fe, Nd, and B as main components, and has a Nd ₂ Fe ₁₄ B compound as a main phase and a grain boundary phase around the main phase. The main phase Nd ₂ Fe ₁₄ B becomes a magnetic domain and causes a high remanent magnetization, and the grain boundary phase prevents the movement and generation of the domain wall and develops a high coercive force.

However, in a composition in which the content of the main phase Nd ₂ Fe ₁₄ B is increased with the aim of high magnetization, the grain boundary phase is deficient, and the fragmentability between the main phase Nd ₂ Fe ₁₄ B particles is reduced, The coercive force decreases. On the contrary, in the composition having a low content of Nd ₂ Fe ₁₄ B in the main phase (a composition having a high content of the grain boundary phase), the grain boundary phase is increased, the breakability is improved, and the coercive force is increased. When the grain boundary phase is locally unevenly distributed, the content of the main phase Nd ₂ Fe ₁₄ B is relatively lowered, leading to a decrease in magnetization.

  Also known is a nanocomposite magnet that further includes a soft magnetic phase, for example, an α-Fe phase, in order to improve the magnetization of the NdFeB magnet.

  However, in the composition of the two-phase nanocomposite magnet, the Nd-rich phase (the grain boundary phase as referred to in the nanocrystalline magnet) does not exist, and thus the NdFeB phases may be connected. When NdFeB is connected, there is a problem that it behaves like NdFeB having a large particle diameter, is not a single magnetic domain, and the coercive force decreases.

  Patent Documents 1 and 2 propose a method of adding Cu or the like to a raw material in advance. The added Cu or the like becomes a grain boundary phase surrounding the grain boundary of the Nd-Fe-B phase, and this grain boundary phase improves the fluidity of the Nd-Fe-B phase and aligns the direction of the crystal to be anisotropic. It is said that it works to increase the coercive force by increasing the coercivity.

  However, it is considered that the exchange bonding between the Nd-Fe-B phase and the α-Fe phase is established when the distance between these phases is about 5 nm to 10 nm, and between the Nd-Fe-B phase and the α-Fe phase. When a grain boundary phase (phase such as NdCu) of 10 nm or more exists, exchange junction does not occur, and an increase in residual magnetization cannot occur.

  In the method of adding Cu or the like proposed in Patent Documents 1 and 2, the film thickness of the added third phase grain boundary (Nd—Cu phase or the like) is too large, and the exchange junction with Fe is not established, and residual magnetization is not established. There is a problem that it is not possible to obtain an increase.

  An object of the present invention is to provide a method for producing an NdFeB magnet having both high magnetization remanence and high coercive force, which can solve the above-described problems of the prior art.

  As means for solving the above problems, the present invention provides the following.

(1) a step of bringing a nonmagnetic phase into contact with a magnetic structure comprising an Nd ₂ Fe ₁₄ B phase;
Heating the non-magnetic phase to a temperature equal to or higher than its melting point, and diffusing the non-magnetic phase into the magnetic structure.
Here, at least a part of the magnetic structure including the Nd ₂ Fe ₁₄ B phase is a nanocrystal particle having a particle diameter of 10 to 300 nm.

(2) The method according to (1), wherein the magnetic structure comprising the Nd ₂ Fe ₁₄ B phase is an NdFeB / Fe nanocomposite magnetic structure further comprising an α-Fe phase.

(3) It has a composition of RxFe (100-xyz) ByTz, where R is one kind or two or more kinds of rare earth elements, T is Ga, Zn, Si, Al, Nb, Zr, Ni , Cu, Cr, Hf, Mo, P, C, Mg, Hg, Ag, Au, Co, and inevitable impurities, 2 ≦ x <14, 1 ≦ y <10, 0 ≦ z <5 A step of preparing a molten alloy, and a step of rapidly cooling the molten alloy to obtain a ribbon,
The method according to (1) or (2), wherein a magnetic structure comprising the Nd ₂ Fe ₁₄ B phase is prepared.

  (4) The method according to (3), further comprising a step of sintering the ribbon to obtain a sintered body.

  (5) The method according to any one of (1) to (4), wherein a thickness of the nonmagnetic phase diffused at grain boundaries is 10 nm or less.

  (6) The nonmagnetic phase has a composition of RM, where R is one kind or two or more kinds of rare earth elements, M is Ga, Zn, Si, Al, Nb, Zr, Ni, Cu, The method according to any one of (1) to (5), wherein the method is one or more of Cr, Hf, Mo, P, C, Mg, Hg, Ag, Au.

  (7) The method according to any one of (1) to (6), wherein the nonmagnetic phase has a melting point of 700 ° C. or lower.

  (8) The method according to any one of (1) to (7), wherein the time for diffusing the nonmagnetic phase into the magnetic structure is 1 minute or longer and 30 minutes or shorter.

  (9) The method according to any one of (1) to (8), wherein the nonmagnetic phase is an NdCu alloy.

  (10) The method according to (9), wherein in the NdCu alloy, the nonmagnetic phase has an Nd content of 50 at% or more and 82 at% or less.

  (11) The method according to any one of (1) to (10), wherein the nonmagnetic phase is grain boundary diffused at a ratio of 1 wt% or more and 50 wt% or less based on the mass of the magnetic structure.

FIG. 1 is a diagram showing an image in which a nonmagnetic phase diffuses. FIG. 2 is a diagram showing an image in which a nonmagnetic phase diffuses when the magnetic structure is an NdFeB / Fe nanocomposite magnetic structure including an α-Fe phase. FIG. 3 is an NdCu phase diagram. FIG. 4 is a diagram showing a heating path of the quenching ribbon and the NdCu powder. FIG. 5 is a diagram showing an outline of a method for heating the quenching ribbon and the NdCu powder. 6 is a diagram showing demagnetization curves of the magnets obtained in Example 1 and Comparative Example 1. FIG. FIG. 7 is a diagram showing the temperature dependence of the coercivity of the magnets obtained in Example 1 and Comparative Example 1. FIG. 8 is a TEM image of the magnets of Example 1 and Comparative Example 1. FIG. 9 is a diagram showing a heating path of the NdFeB sintered body and NdCu. FIG. 10 is a diagram showing an outline of a method of heating the NdFeB sintered body and NdCu. FIG. 11 is a diagram showing the demagnetization curves of the magnets obtained in Example 2 and Comparative Example 2. FIG. 12 is a diagram showing the XRD measurement results of the magnets obtained in Example 2 and Comparative Example 2. FIG. 13 is a diagram showing SEM images of the magnets obtained in Example 2 and Comparative Example 2. FIG. 14 is a diagram showing a heating path of the quenching ribbon and the NdCu powder. FIG. 15 is a graph showing the rate of change of coercive force when the diffusion time of the magnets obtained in Example 3 and Comparative Example 3 is changed. FIG. 16 is a diagram showing a decreasing curve of the magnets obtained in Example 3 and Comparative Example 3. FIG. 17 is a diagram showing a heating path of the quenching ribbon and the NdCu powder. FIG. 18 is a diagram illustrating the demagnetization curves of the magnets obtained in Comparative Example 4 and Example 4. FIG. 19 shows the amount of nonmagnetic phase (NdCu) and the coercive force. FIG. 20 is a diagram showing the SEM observation results for a magnet having a nonmagnetic phase (NdCu) amount of 200 wt%.

One embodiment of the method for producing a magnet according to the present invention comprises the following steps.
(1) a step of bringing a nonmagnetic phase into contact with a magnetic structure comprising an Nd ₂ Fe ₁₄ B phase;
(2) a step of heating the nonmagnetic phase to a temperature equal to or higher than its melting point; and (3) a step of diffusing the nonmagnetic phase into the magnetic structure.

  Hereinafter, each step will be described in detail.

The magnetic structure comprising the Nd ₂ Fe ₁₄ B phase used in the step (1) is a magnetic structure that imparts high magnetization to the Nd ₂ Fe ₁₄ B phase, and the base of the magnet obtained in the present invention It will be.

Here, at least a part of the magnetic structure including the Nd ₂ Fe ₁₄ B phase is nanocrystalline particles having a particle diameter of 10 to 300 nm. When the particle diameter is within this range, the ratio of single domain particles increases. A single magnetic domain is a state in which only one magnetic domain having no domain wall exists. In a structure in which single magnetic domain particles are aggregated, a change in magnetization of each magnetic domain occurs only by a mechanism of rotation of magnetization. In contrast to a single magnetic domain, a multiple magnetic domain is a state in which a domain wall exists and a plurality of magnetic domains exist. In a structure in which multi-domain particles are aggregated, a change in magnetization of each magnetic domain also occurs due to the movement of the domain wall. Therefore, in the case of a single magnetic domain as compared with the case of multiple magnetic domains, there is no movement of the domain wall, so that the change in magnetization is difficult to occur, that is, the coercive force is increased.
When this particle diameter is larger than 300 nm, it is not a single magnetic domain, and the intrinsic coercive force is reduced. On the other hand, when the particle size is reduced to about 10 nm, the Nd ₂ Fe ₁₄ B phase starts to show isotropic magnetic properties. Therefore, at least a part of the magnetic structure including the Nd ₂ Fe ₁₄ B phase has a particle diameter of 10 to 300 nm.

The magnetic structure including the Nd ₂ Fe ₁₄ B phase may be an NdFeB / Fe nanocomposite magnetic structure further including an α-Fe phase. A nanocomposite magnet is a magnet in which a fine hard magnetic phase and soft magnetic phase of nanometer order coexist in a tissue. By including a soft magnetic phase (α-Fe phase) with high saturation magnetization, high magnetization is brought about. In addition, the α-Fe phase is inherently soft magnetic and does not have a high coercive force, but exchange bonding with the hard magnetic phase (Nd—Fe—B phase) results in a nanocomposite magnet having a high coercive force.
In general, in a nanocomposite magnet, the Nd ₂ Fe ₁₄ B phase and the α-Fe phase are each required to exist as nanometer-order particles. For _example, the particle size of the Nd 2 _{Fe 14} B phase is suitably it is in the order of 10 to 300 nm. This is because when the thickness is larger than 300 nm, a single magnetic domain is lost and a problem such as a decrease in intrinsic coercivity occurs. On the other hand, when the particle size is reduced to about 10 nm, the Nd ₂ Fe ₁₄ B phase starts to show isotropic magnetic properties. Therefore, it is usually preferable to regulate the particle size of the Nd ₂ Fe ₁₄ B phase to 10 to 300 nm.
The particle size of the α-Fe phase is preferably about 10 to 50 nm. When this is smaller than 10 nm, this α-Fe phase becomes non-magnetic, and when it is larger than 50 nm, the exchange interaction with the particles of the Nd ₂ Fe ₁₄ B phase is deteriorated and the nanocomposite is deteriorated. This is because the function as a magnet is reduced. Usually, it is preferable that the particle size of the α-Fe phase is 10 to 20 nm in order to develop a good exchange interaction.

This magnetic structure (nanocrystalline particle or nanocomposite magnetic structure) comprising the Nd ₂ Fe ₁₄ B phase can be prepared by the following steps.
_{1) R x Fe (100-} x-y-z) B y T process for preparing a melt of an alloy having a composition of _z, and 2) obtaining a ribbon by quenching a melt of the alloy.

First, step 1) will be described.
Here, R is one kind or two or more kinds of rare earth elements. For example, for example, one or more of Nd, Pr, Gd, Tb, Dy, Ce, Pm, Sm, Eu, Ho, Er, Tm, Yb, and Lu can be used.
T is one or more kinds of Ga, Zn, Si, Al, Nb, Zr, Ni, Cu, Cr, Hf, Mo, P, C, Mg, Hg, Ag, Au, and Co, and inevitable impurities. Since it is an alloy material, it is unavoidable that a small amount of impurities are mixed in, but a smaller amount of impurities is more preferable.
In the composition formula, 2 ≦ x <14, 1 ≦ y <10, and 0 ≦ z <5.
R x _Fe fusion type for the alloy melt having a composition of _(100-x-y-z ) B y T z is not particularly limited as long as it can be heated above the melting point of the alloy having the composition . For example, the melting method includes melting by an arc, melting by a heater, melting by high frequency induction heating, and the like.

Next, step 2) will be described.
As a method for rapidly cooling a molten metal of this alloy to obtain a ribbon, there are melt spinning, atomizing, single roll method and the like. Here, a description will be given using a single roll furnace. An alloy ingot having the above composition is set in a single roll furnace and melted by high frequency induction heating, and then the molten alloy is sprayed onto a rotating roll and rapidly cooled on the roll to obtain a quenched ribbon. The molten alloy is usually injected from an injection nozzle using an inert gas such as argon or nitrogen. The molten metal temperature, injection pressure, injection nozzle diameter, and the like are adjusted as appropriate.

  In using the rapid cooling method, the type, the material of the roll, the size of the roll, etc. are not particularly limited. For example, as the roll, a copper roll plated with Cr can be used. The size of the roll is preferably determined according to the production scale.

  A step of sintering the ribbon obtained by this rapid cooling to obtain a sintered body may be added. In the sintering step, means used in a known method for producing a sintered magnet can be employed. As a magnet sintering / heat treatment facility, a batch-type vacuum / atmosphere sintering furnace or heat treatment furnace can be used for small-scale production. The batch furnace can be heated and cooled in the same chamber according to the temperature pattern. By increasing the density of the sintered body by sintering, effects such as (i) an increase in residual magnetic flux density Br, (ii) an increase in mechanical strength, and (iii) resistance to corrosion such as oxidation are produced. .

The nonmagnetic phase will be described.
The nonmagnetic phase can be a grain boundary phase in the finally obtained magnet. The grain boundary phase _is to separate the exists between the magnetic structure comprising Nd 2 _{Fe 14} B _phase, the magnetic structure each other comprising Nd 2 _{Fe 14} B phase. The coercive force of the magnet can change depending on the situation of the grain boundary phase. For example, when two magnetic structures including an Nd ₂ Fe ₁₄ B phase exist with a grain boundary phase in between, even if there is a change in magnetization in one magnetic structure, This magnetic structure is less affected by the change in magnetization, and as a result, the coercive force is increased.

In order to obtain this grain boundary phase, first, in step (1), a nonmagnetic phase is brought into contact with a magnetic structure comprising an Nd ₂ Fe ₁₄ B phase. Next, in step (2), the nonmagnetic phase is heated to a temperature equal to or higher than its melting point. The heated nonmagnetic phase melts. Next, in step (3), the nonmagnetic phase is diffused into the magnetic structure at the grain boundaries. That is, the molten nonmagnetic phase permeates from the contact surface with the magnetic structure and diffuses as a grain boundary phase between the magnetic structures.

  When the nonmagnetic phase is diffused between the magnetic structures by this method, the grain boundary phase uniformly surrounds the magnetic structure without forming an uneven grain boundary phase, and the coercive force can be improved. Moreover, the fact that the grain boundary phase is not unevenly distributed leads to suppression of the amount of grain boundary phase (volume fraction in the magnet), which in turn increases the amount of magnetic structure (volume fraction in the magnet). Can result in high magnetization of the magnet.

An image in which the nonmagnetic phase diffuses will be described with reference to FIG. Before diffusion in FIG. 1, there are many magnetic structures (main phases) including the Nd ₂ Fe ₁₄ B phase, and high magnetization is brought about. There is also a grain boundary phase, but the amount thereof is small and the magnetic structure (main phase) is in contact with each other, so the coercive force is not high. From this state, a nonmagnetic phase (for example, NdCu) is diffused at grain boundaries. The amount of the nonmagnetic phase to be diffused does not reduce the amount (volume fraction) of the magnetic structure (main phase) as much as possible, and the nonmagnetic phase becomes the grain boundary phase and the nonmagnetic phase becomes the grain boundary phase. The phase can be adjusted appropriately so that it is sufficiently divided. After the magnetic phase diffuses as the grain boundary phase, the grain boundary phase divides the magnetic structure (main phase). As an effect, the coercive force is improved. In addition, since the amount (volume fraction) of the magnetic structure is not reduced as much as possible, high magnetization is maintained.

FIG. 2 shows an image in which the nonmagnetic phase diffuses when the magnetic structure is an NdFeB / Fe nanocomposite magnetic structure that also includes an α-Fe phase. Before diffusion (lower right) in FIG. 2, a magnetic structure (main phase) including an Nd ₂ Fe ₁₄ B phase and an NdFeB / Fe nanocomposite magnetic structure including only an α-Fe phase are shown. From this state, a nonmagnetic phase (for example, NdCu) is diffused at grain boundaries. The nonmagnetic phase begins to diffuse between the main phases, between the main phase and the α-Fe phase, or between the α-Fe phases (right middle in FIG. 2), and finally the main phase and the α- Each of the Fe phases is divided (upper right in FIG. 2).
The effect of this division will be described. First, the coercive force is improved by separating the main phases. In addition, the main phase and the α-Fe phase are also separated, but the exchange junction between the main phase and the α-Fe phase can be maintained. That is, the effect of high magnetization due to the soft magnetic phase (α-Fe phase), which is a feature of the nanocomposite magnet, can be maintained. That is, the distance between the divided main phase and the α-Fe phase, that is, the thickness of the grain boundary phase can be appropriately adjusted, and as a result, an exchange junction is established between the main phase and the α-Fe phase. Can be adjusted within range.

  In the NdFeB / Fe nanocomposite magnetic structure, the distance at which the exchange junction between NdFeB / Fe is established is said to be about 5 nm to 10 nm, and the thickness of the grain boundary phase (nonmagnetic phase) existing between NdFeB / Fe is 10 nm. The following is preferable. This is because when the thickness of the grain boundary phase (nonmagnetic phase) exceeds 10 nm, the exchange junction between NdFeB / Fe is not established and high magnetization cannot be expected. The thickness of the grain boundary phase (nonmagnetic phase) is preferably 0.5 nm or more. This is because if the thickness of the grain boundary phase (nonmagnetic phase) is less than 0.5 nm, it is not possible to cut the exchange junction between NdFeB / NdFeB and sufficiently improve the magnetic separation property.

  The non-magnetic phase can have a composition of R-M, where R is one or more rare earth elements, M is Ga, Zn, Si, Al, Nb, Zr, Ni, Cu, Cr, One or more kinds of Hf, Mo, P, C, Mg, Hg, Ag, Au.

  These RM compositions generally have a low melting point and may be up to 700 ° C. Table 1 shows the melting points of typical RM compositions.

In the step (2), the nonmagnetic phase is heated to a temperature equal to or higher than its melting point, and at the same time, the magnetic phase including the Nd ₂ Fe ₁₄ B phase is also heated. When the magnetic phase comprising the Nd ₂ Fe ₁₄ B phase is heated at a temperature exceeding 700 ° C., the particles become coarse and the intrinsic coercive force may be lowered. In the present invention, since the melting point of the RM composition is generally low, it is not necessary to heat above 700 ° C. Accordingly, it is possible to prevent the magnetic phase including the Nd ₂ Fe ₁₄ B phase from becoming coarse and thus reducing the intrinsic coercive force.

Also, the time for diffusing the nonmagnetic phase into the magnetic structure may be short. The time for grain boundary diffusion may be appropriately adjusted according to the type and properties (melting point, particle size, density, etc.) of the magnetic phase and nonmagnetic phase. For example, the lower limit of the grain boundary diffusion time may be 10 minutes or more, 30 minutes or more, and the upper limit of the grain boundary diffusion time is 30 minutes or less, 40 minutes or less, 50 minutes or less, 60 minutes or less, etc. May be. If the diffusion time is too short, for example, if it is less than 5 minutes, the grain boundary diffusion is not sufficient, and the magnetic phase containing the Nd ₂ Fe ₁₄ B phase cannot be sufficiently separated, resulting in high coercivity. It may not be possible. If the diffusion time is too long, for example, if it exceeds 60 minutes, the particles are coarsened and the intrinsic coercive force may be lowered.

The nonmagnetic phase, RM, may be an NdCu alloy. The reason is as follows. In many cases, a grain boundary phase containing Nd exists around the magnetic phase containing the Nd ₂ Fe ₁₄ B phase. Therefore, when the NdCu alloy is diffused as the grain boundary phase, the affinity with the existing grain boundary phase containing Nd is high. The melting point of the NdCu alloy is as low as 520 ° C.

Furthermore, the Nd content of the NdCu alloy can be adjusted. In that case, the Nd content in the NdCu alloy can be 50 at% or more and 82 at% or less. According to the NdCu phase diagram of FIG. 3, the NdCu alloy in that range has a melting point of 700 ° C. or less, and the Nd ₂ Fe ₁₄ B phase (magnetic phase) that is heated at the same time becomes coarse, and as a result, the intrinsic coercive force decreases. Can be prevented.

The mass ratio of the nonmagnetic phase diffused at the grain boundary (based on the mass of the magnetic structure) can be appropriately adjusted. The lower limit of the mass ratio of the nonmagnetic phase may be 1 wt% or more, 2 wt% or more, 3 wt% or more, 5 wt% or more, 10 wt% or more, 20 wt% or more, or the like. The upper limit value of the mass ratio of the nonmagnetic phase may be 100 wt% or less, 80 wt% or less, 70 wt% or less, 60 wt% or less, 50 wt% or less, or the like. If the mass ratio of the nonmagnetic phase is too low, for example, if it is less than 1 wt%, the grain boundary diffusion is not sufficient, and the magnetic phase containing the Nd ₂ Fe ₁₄ B phase cannot be sufficiently separated, and as a result, the high coercive force May not be obtained. If the mass ratio of the nonmagnetic phase is too high, for example, if it exceeds 100 wt%, the mass ratio of the magnetic phase including the Nd ₂ Fe ₁₄ B phase is relatively low, and high magnetization cannot be obtained.

  Examples of the present invention will be described below.

Example 1
(1) Preparation of quenched ribbon (magnetic structure) The atomic ratio of Nd, Fe, B, Ga, Al and Cu is 13.3: 80.2: 5.9: 0.3: 0.2: 0.1 The raw material was weighed in a predetermined amount so that the ratio was as follows, and an alloy ingot was produced in an arc melting furnace. Next, the alloy ingot was melted at a high frequency in a single roll furnace shown in Table 2, and sprayed onto a copper roll under the single roll furnace use conditions shown in Table 2, and Nd _13.3 Fe _80.2 B _5.9 Ga _0. A quenched ribbon having a composition of ₃ Al _0.2 Cu _0.1 was prepared.

(2) Grain boundary diffusion of nonmagnetic phase The obtained Nd _13.3 Fe _80.2 B _5.9 Ga _0.3 Al _0.2 Cu _0.1 quenching ribbon was treated with NdCu powder (Nd ₇₀ Cu ₃₀ (at %)) And heated. Heating was performed according to the heating path of FIG. FIG. 5 shows an outline of a method for heating the quenching ribbon and the NdCu powder. Through heating, the NdCu powder (nonmagnetic phase) was melted and diffused into the quenching ribbon (magnetic structure) to obtain the magnet of Example 1.

(3) Magnetic property evaluation and electron microscope observation The obtained magnets were collected, and their magnetic properties were evaluated by VSM (manufactured by Lake Shorc). VSM is a vibrating sample magnetometer, which vibrates a sample in a uniform magnetic field with a certain frequency and amplitude, and locks the electromotive force induced in the detection coil placed near the sample. It is an apparatus that measures the magnetization characteristics of a sample by detecting using an in-amplifier. Moreover, the obtained magnetic structure observation was also implemented with the electron microscope (SEM and / or TEM).

(4) Comparative Example 1
A quenched ribbon similar to that of Example 1 was prepared. The difference from Example 1 is that NdCu powder (nonmagnetic phase) was not diffused. The obtained quenched ribbon was subjected to magnetic property evaluation (VSM analysis) and electron microscope observation in the same manner as in Example 1.

(5) Results and magnetic property evaluation (VSM analysis)
The magnetic property evaluation results of Example 1 and Comparative Example 1 are shown in FIGS. FIG. 6 is a graph of demagnetization curves of the magnets obtained in Example 1 and Comparative Example 1 at room temperature (25 ° C.). The coercive force at room temperature (25 ° C.) was 16.7 kOe in the magnet that was not subjected to the diffusion treatment of the nonmagnetic phase of Comparative Example 1, but 23.3 kOe in the magnet that was subjected to the diffusion treatment of the nonmagnetic phase of Example 1. Increased to. FIG. 7 is a graph showing the temperature dependence of the coercivity of the magnets obtained in Example 1 and Comparative Example 1. In the range of room temperature (25 ° C.) to 170 ° C., the magnet of Example 1 showed higher coercivity than the magnet of Comparative Example 1.
-Electron microscope observation In FIG. 8, the TEM image of the magnet of Example 1 and the comparative example 1 was shown. From FIG. 8, it is possible to observe the state before and after the diffusion of the nonmagnetic phase (NdCu). It was observed that the main phase (NdFeB magnetic structure) was directly bonded before diffusion. On the other hand, after diffusion, it was observed that a grain boundary phase (NdCu rich phase) having a thickness of several nanometers existed uniformly at the main phase interface, and the main phases were separated from each other. It is considered that the coercive force has been improved by the improvement of the division property.

Example 2
(1) Preparation of quenched ribbon (magnetic structure) A predetermined amount of raw material was weighed so that the atomic ratio of Nd, Fe, B and Ga was 10.4: 83.4: 5.2: 1.0. An alloy ingot was produced in an arc melting furnace. Next, the alloy ingot was melted at a high frequency in the single roll furnace shown in Table 2, and sprayed onto the copper roll under the single roll furnace use conditions shown in Table 2, and Nd _10.4 Fe _83.4 B _5.2 Ga _{1. A zero-} quenched ribbon was prepared.

(2) Preparation of sintered body Except the portion of the quenched ribbon that has been columnarly crystallized by visual inspection and magnetic separation from the recovered rapidly cooled ribbon, the remaining portion is filled with vinyl and pulverized by hand, and used as a carbon die for an electric heating and sintering apparatus. Filled. Subsequently, the sintered compact was produced on the conditions of Table 3.

The obtained Nd _10.4 Fe _83.4 B _5.2 Ga _1.0 sintered body was recovered and cut into a predetermined dimension (approximately 2 × 2 × 2 mm).

(3) Grain boundary diffusion of non-magnetic phase The cut Nd _10.4 Fe _83.4 B _5.2 Ga _1.0 sintered body was heated together with NdCu powder (Nd ₇₀ Cu ₃₀ (at%)). Heating was performed according to the heating path of FIG. FIG. 10 shows an outline of a method for heating the sintered body and the NdCu powder. Through heating, the NdCu powder (nonmagnetic phase) was melted and diffused at the grain boundaries in the sintered body (magnetic structure) to obtain the magnet of Example 2.

(4) Magnetic property evaluation, XRD analysis, electron microscope observation The obtained magnets were collected, and their magnetic properties were evaluated by VSM (manufactured by Lake Shorc). Moreover, the XRD analysis of the obtained magnet was also performed. Moreover, the obtained magnetic structure observation was also implemented with the electron microscope (SEM and / or TEM).

(5) Comparative Example 2
A sintered body similar to that of Example 2 was prepared. The difference from Example 2 is that the NdCu powder (nonmagnetic phase) was not diffused. About the obtained magnet of the comparative example 2, similarly to Example 2, magnetic property evaluation (VSM analysis), XRD analysis, and electron microscope observation were implemented.

(6) Results and magnetic property evaluation (VSM analysis)
The magnetic property evaluation results of Example 2 and Comparative Example 2 are shown in FIG. FIG. 11 is a graph of the demagnetization curve of the magnet obtained in Comparative Example 2 and Example 2, that is, the magnet before and after the grain boundary phase is diffused. The magnet after diffusion (Example 2) had an improved coercive force (5.17 kOe → 8.16 kOe) compared to the magnet before diffusion (Comparative Example 2). This is presumably because the nonmagnetic phase (NdCu) diffused at the grain boundaries and effectively divided the main phase (NdFeB / Fe nanocomposite structure).
Regarding magnetization, the residual magnetic susceptibility (Mr / Ms) did not change between Example 2 and Comparative Example 2. This is because the nonmagnetic phase (NdCu) does not exist between the hard magnetic phase (NdFeB system structure) and the soft magnetic phase (Fe system structure), or if it exists, it is sufficiently thin, and the soft magnetic phase (Fe system structure) It is thought that the exchange junction that can support the magnetic spin of the tissue is maintained.
-XRD analysis In FIG. 12, the XRD measurement result of the magnet after diffusion (Example 2) and the magnet before diffusion (Comparative Example 2) is shown. A crystalline Nd peak that was not seen before diffusion was observed after diffusion. That is, it was found that the magnet after diffusion has a three-phase structure of NdFeB structure, Fe structure, and Nd-rich phase.
-Electron microscope observation In FIG. 13, the SEM image of the magnet of Example 2 and the comparative example 2 was shown. From FIG. 13, it is possible to observe the state before and after the diffusion of the nonmagnetic phase (NdCu). Before diffusion, a two-phase structure of NdFeB structure (gray part) and Fe system structure (black part) was observed. On the other hand, after the diffusion, a grain boundary phase (white part) considered to be Nd was confirmed.

Example 3
(1) Preparation of quenching ribbon (magnetic structure) A predetermined amount of raw material is weighed so that the atomic ratio of Nd, Fe, B and Al is 14.76: 78.55: 5.69: 1.0. An alloy ingot was produced in an arc melting furnace. Next, the alloy ingot was melted at a high frequency in a single roll furnace shown in Table 2, and injected into a copper roll under the single roll furnace use conditions shown in Table 2. Nd _14.76 Fe _78.55 B _5.69 Al _{1. A zero-} quenched ribbon was prepared.

(2) Grain boundary diffusion of nonmagnetic phase (effect of diffusion time on coercivity)
The resulting Nd _14.76 Fe _78.55 B _5.69 Al _1.0 quench ribbon was heated with NdCu powder (Nd ₇₀ Cu ₃₀ (at%)). Heating was performed according to the heating path of FIG. Except that the heating time was changed between 0 and 60 minutes, the method of heating the quenched ribbon and NdCu powder was the same as in Example 1 (see FIG. 5). Through heating, the NdCu powder (nonmagnetic phase) was melted and diffused into the quenching ribbon (magnetic structure) to obtain a magnet of Example 3.

(3) Magnetic property evaluation The obtained magnet was collect | recovered and the magnetic property was evaluated by VSM (made by Lake Shorc).

(4) Comparative Example 3
A quench ribbon similar to that of Example 3 was prepared. The difference from Example 3 is that NdCu powder (nonmagnetic phase) was not diffused. That is, the magnet of Comparative Example 3 is a magnet having a diffusion time of 0 minutes. The obtained magnet (quenched ribbon) was evaluated for magnetic properties (VSM analysis) in the same manner as in Example 3.

(5) Results and magnetic property evaluation (VSM analysis)
The magnetic property evaluation results of Example 3 and Comparative Example 3 are shown in FIGS. FIG. 15 shows the change rate of the coercive force when the diffusion time is changed. With respect to the change rate of the coercive force in FIG. 15, the diffusion time of 0 minutes was set as a reference, that is, 100%. When the magnetic structure for diffusing the nonmagnetic phase (NdCu) is a hot plastic processed body (strongly processed body), it has been considered that it takes about 60 minutes to diffuse the nonmagnetic phase (NdCu). However, when the magnetic structure is a quenching ribbon, the quenching ribbon has a thin thickness of 20 to 100 μm, and thus it has been found that the time required for diffusion of the nonmagnetic phase (NdCu) may be 10 minutes. Long-time diffusion (heating) treatment may lead to coarsening of the magnetic structure, but such short-time diffusion (heating) treatment can avoid coarsening, which helps maintain an improved coercivity. Connected. If the diffusion time is short, for example, 5 minutes or less, the nonmagnetic phase (NdCu) cannot be uniformly and sufficiently diffused, that is, the magnetic structure cannot be homogeneously and sufficiently divided, and the coercive force is not improved. It is done.
FIG. 16 is a graph of demagnetization curves of the magnet of Example 3 that performed diffusion for 30 minutes and the magnet of Comparative Example 3 that did not perform diffusion. It was found that the coercive force of the magnet of Example 3 in which the nonmagnetic phase was diffusion-treated for 30 minutes was clearly increased as compared with the magnet of Comparative Example 3 in which the nonmagnetic phase was not diffused.

Example 4
(1) Preparation of quenching ribbon (magnetic structure) A predetermined amount of raw materials are weighed so that the atomic ratio of Nd, Fe, and B is 10.6: 84.1: 5.3, and the resultant is put into an arc melting furnace. An alloy ingot was prepared. Next, the alloy ingot was melted at a high frequency in the single roll furnace shown in Table 2, and sprayed onto the copper roll under the single roll furnace use conditions shown in Table 2, to rapidly cool the Nd _10.6 Fe _84.1 B _5.3 composition. A ribbon was made.

(2) Grain boundary diffusion of nonmagnetic phase (effect of diffusion amount on coercive force)
The obtained Nd _10.6 Fe _84.1 B _5.3 quenched ribbon was heated at 550 ° C. for 0.5 hour together with an alloy powder having a Nd ₇₀ Cu ₃₀ (at%) composition. Heating was performed according to the heating path of FIG. Except for changing the amount of NdCu powder, the method of heating the sintered body and the NdCu powder was the same as in Example 1 (see FIG. 5). The amount of NdCu powder was varied from 1 wt% to 50 wt% based on the mass of the sintered body (magnetic body). Through heating, the NdCu powder (non-magnetic phase) melted and diffused at the grain boundaries in the sintered body (magnetic structure) to obtain the magnet of Example 4.

(3) Magnetic property evaluation and electron microscope observation The obtained magnets were collected, and their magnetic properties were evaluated by VSM (manufactured by Lake Shorc). Moreover, the obtained magnetic structure observation was also implemented with the electron microscope (SEM and / or TEM).

(4) Comparative Example 4
A sintered body similar to that of Example 4 was prepared. The difference from Example 4 is that the amount of NdCu powder (non-magnetic phase) is outside the range of 1 wt% to 50 wt%. About the obtained magnet of the comparative example 4, similarly to Example 4, magnetic characteristic evaluation (VSM analysis) and electron microscope observation were implemented.

(5) Results / Magnetic Characteristic Evaluation (VSM Analysis) / Electron Microscope Observation The magnetic characteristic evaluation results of Example 4 and Comparative Example 4 are shown in FIGS. FIG. 18 is a graph of a demagnetization curve of the magnet obtained in Comparative Example 4 and Example 4, that is, a magnet in which the amount of the nonmagnetic phase (NdCu) is changed. As the amount of the nonmagnetic phase (NdCu) increased, the coercive force also improved. FIG. 19 shows a graph of the amount of nonmagnetic phase (NdCu) and the coercive force. However, when the amount of the nonmagnetic phase (NdCu) is 100 wt% or more, the demagnetization curve is stepped (see FIG. 18). In this regard, FIG. 20 shows SEM observation results for a magnet having a nonmagnetic phase (NdCu) amount of 200 wt%. From FIG. 20, it is observed that the rapidly cooled ribbon structure (magnetic structure) of the nanocomposite composition is released in the diffused NdCu alloy. As a result, it is considered that a step-like unique demagnetization curve appeared. Further, when the amount of the nonmagnetic phase (NdCu) is increased, the amount of the magnetic phase is relatively decreased and the magnetization is lowered. Considering these points, the amount of the nonmagnetic phase (NdCu) may be 50 wt% or less.

Claims (11)

Contacting a non-magnetic phase with a magnetic structure comprising an Nd ₂ Fe ₁₄ B phase;
Heating the non-magnetic phase to a temperature equal to or higher than its melting point, and diffusing the non-magnetic phase into the magnetic structure.
Here, at least a part of the magnetic structure including the Nd ₂ Fe ₁₄ B phase is a nanocrystal particle having a particle diameter of 10 to 300 nm. The method according to claim 1, wherein the magnetic structure comprising the Nd ₂ Fe ₁₄ B phase is an NdFeB / Fe nanocomposite magnetic structure further comprising an α-Fe phase. RxFe (100-xyz) ByTz, where R is one type or two or more types of rare earth elements, T is Ga, Zn, Si, Al, Nb, Zr, Ni, Cu, One or more kinds of Cr, Hf, Mo, P, C, Mg, Hg, Ag, Au, Co, and inevitable impurities, 2 ≦ x <14, 1 ≦ y <10, 0 ≦ z <5. Preparing a molten alloy, and rapidly cooling the molten alloy to obtain a ribbon;
The method according to claim 1, wherein a magnetic structure comprising the Nd ₂ Fe ₁₄ B phase is prepared by.   The method according to claim 3, further comprising the step of sintering the ribbon to obtain a sintered body.   The method according to any one of claims 1 to 4, wherein a thickness of the nonmagnetic phase diffused at grain boundaries is 10 nm or less.   The nonmagnetic phase has a composition of R-M, where R is one kind or two or more kinds of rare earth elements, M is Ga, Zn, Si, Al, Nb, Zr, Ni, Cu, Cr, Hf. The method of any one of Claims 1-5 which is 1 or more types which consist of Mo, P, C, Mg, Hg, Ag, Au.   The method according to claim 1, wherein the nonmagnetic phase has a melting point of 700 ° C. or lower.   The method according to any one of claims 1 to 7, wherein a time during which the nonmagnetic phase is diffused into the magnetic structure is 10 minutes or more and 60 minutes or less.   The method according to claim 1, wherein the nonmagnetic phase is an NdCu alloy.   The method according to claim 9, wherein the nonmagnetic phase has an Nd content of 50 at% or more and 82 at% or less in an NdCu alloy.   The method according to any one of claims 1 to 10, wherein the nonmagnetic phase is grain boundary diffused at a ratio of 1 wt% or more and 50 wt% or less based on the mass of the magnetic structure.