RTB series fused magnets

Abstract

To provide an R-T-B based sintered magnet having a high Br and a high HcJ while reducing use of a heavy rare earth element RH.SOLUTION: An R-T-B based sintered magnet herein disclosed comprises: main phases composed of an R2T14B compound; and grain boundary phases each located at a grain boundary of the main phases. The grain boundary phase contains an R-T-M compound (M represents at least one kind selected from a group consisting of Ga, Cu, Zn, Al and Si) and an R-M compound. In any cross section, the sum total of an areal rate of the R-T-M compound and an areal rate of the R-M compound is 1.5% or more and 3.5% or less; the areal rate of the R-T-M compound is 0.4% or more and 2.5% or less, and the areal rate of the R-M compound is 0.4% or more and 2.5% or less.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an R-T-B sintered magnet.

Background Art

[0002] R-T-B sintered magnets (where R is at least one of rare earth elements, T is Fe or Fe and Co, and B is boron) are known as the most high-performance magnets among permanent magnets. For this reason, R-T-B sintered magnets are used in various motors in the automotive field such as electric vehicles (EV, HV, PHV), the renewable energy field such as wind power generation, the household electric appliance field, and the industrial field. R-T-B sintered magnets are indispensable materials for reducing the size and weight of these motors and improving their efficiency and energy savings (improvement of energy efficiency). In addition, R-T-B sintered magnets are used in drive motors for electric vehicles, and by replacing internal combustion engine vehicles with electric vehicles, they contribute to preventing global warming by reducing greenhouse gas emissions such as carbon dioxide (reduction of fuel and exhaust gas). Thus, R-T-B sintered magnets greatly contribute to the realization of a clean energy society.

[0003] R-T-B sintered magnets mainly consist of a main phase composed of R2T 14 B compound and a grain boundary phase located at the grain boundary portion of this main phase. The R2T 14 B compound, which is the main phase, is a ferromagnetic material having a high saturation magnetization and an anisotropy magnetic field, and influences the characteristics of the R-T-B sintered magnet.

[0004] R-T-B sintered magnets have a problem that irreversible thermal demagnetization occurs due to a decrease in the coercive force H cJ (hereinafter simply referred to as "H cJ ") at high temperatures. Therefore, particularly in R-T-B sintered magnets used for motors in electric vehicles, it is required to have a high H cJ even at high temperatures, that is, to have a higher H cJ at room temperature.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2013 / 008756 [Patent Document 2] International Publication No. 2018 / 143230 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] R2T 14 When the light rare earth elements RL (mainly Nd, Pr) in the B compound are replaced with heavy rare earth elements RH (mainly Tb, Dy), H cJ is known to improve. However, while H cJ improves, the saturation magnetization of the R2T 14 type compound decreases, resulting in a decrease in the residual magnetic flux density B r (hereinafter simply referred to as "B r "). Also, especially for Tb, there are problems such as unstable supply and price fluctuations due to its small original resource volume and limited production areas. Therefore, it is required to obtain a high H r while suppressing the decrease of B cJ by using Tb as little as possible (reducing the usage amount).

[0007] In Patent Document 1, by reducing the amount of B lower than that of a normal R-T-B alloy and containing one or more metal elements M selected from Al, Ga , Cu, a R2T 17 phase is generated, and by sufficiently ensuring the volume fraction of the transition metal-rich phase (R6T 17 M) generated using the R2T 13 phase as a raw material, it is described that an R-T-B-based rare earth sintered magnet with high coercivity can be obtained while suppressing the Dy content.

[0008] Patent Document 2 describes diffusing light rare earth elements RL and Ga along with heavy rare earth elements RH into the magnet from the surface of an RTB-based sintered body through grain boundaries. Furthermore, Patent Document 2 states that, as a preferred example, generating an RT-Ga phase (corresponding to the RTM compound in this disclosure) in the grain boundary phase of the RTB-based sintered body results in a higher H cJ It is stated that this can be obtained.

[0009] In recent years, particularly in electric vehicle motors, there has been a desire to reduce the amount of heavy rare earth elements (RH) used, while also increasing B r and high H cJ It is required to obtain this.

[0010] Various embodiments of this disclosure reduce the amount of heavy rare earth elements RH used while achieving high B r and high H cJ This invention provides a method for manufacturing RTB-type sintered magnets having the following properties. [Means for solving the problem]

[0011] The RTB-type sintered magnets disclosed herein, in non-limiting and exemplary embodiments, are R2T 14An RTB-type sintered magnet comprising a main phase made of compound B and a grain boundary phase located at the grain boundary portion of the main phase (where R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, and Ce, and T is Fe or Fe and Co), wherein the grain boundary phase contains an RTM compound (where M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si) and an RM compound, and the content of R (at%) is [R], and the content of T (at%) is [at]. When [T] is the %) and [M] is the content of M (at%), the contents of R, T, and M in the RTM compound satisfy the following relationships: 0.15 ≤ [R] / ([R] + [T] + [M]) ≤ 0.3, [T] / ([R] + [T] + [M]) ≥ 0.6, and 0.015 ≤ [M] / ([R] + [T] + [M]) ≤ 0.1. The contents of R and M in the RM compound satisfy the following relationships: 0.25 ≤ [R] / ([R] + [T] + [M]) ≤ 0.7 and 0.1 < [M]. The relationship / ([R]+[T]+[M])≦0.3 is satisfied, and in any cross-section, the sum of the area ratio of the RTM compound and the area ratio of the RM compound is 1.5% or more and 3.5% or less, and the area ratio of the RTM compound is 0.4% or more and 2.5% or less, and the area ratio of the RM compound is 0.4% or more and 2.5% or less.

[0012] In one embodiment, the RTB-type sintered magnet contains Ga and Cu, and the sum of the Ga content and Cu content is 0.25 mass% or more and 2 mass% or less.

[0013] In one embodiment, the RTB-type sintered magnet contains Ga and Cu, and the sum of the Ga content and Cu content is 0.25 mass% or more and 0.65 mass% or less.

[0014] In one embodiment, the R content of the RTB-type sintered magnet is 28.5 mass% or more and 30.0 mass% or less.

[0015] In one embodiment, the Tb content in the RTB-type sintered magnet is 0.2 mass% or less (including 0 mass%), and the Dy content is 0.4 mass% or less (including 0 mass%).

[0016] In one embodiment, the RTB-type sintered magnet includes a portion in which at least one of the Nd concentration and Pr concentration gradually decreases from the magnet surface toward the interior of the magnet.

[0017] In one embodiment, the RTB-type sintered magnet includes a region where the M concentration gradually decreases from the magnet surface toward the interior of the magnet.

[0018] In one embodiment, the RTB-type sintered magnet includes a portion in which at least one of the Tb concentration and Dy concentration gradually decreases from the magnet surface toward the interior of the magnet. [Effects of the Invention]

[0019] According to embodiments of this disclosure, while reducing the amount of heavy rare earth element RH used, high B r and high H cJ A method for manufacturing RTB-type sintered magnets can be provided. [Brief explanation of the drawing]

[0020] [Figure 1A] This is a schematic cross-sectional view showing a magnified portion of an RTB-type sintered magnet. [Figure 1B] This is a schematic cross-sectional view showing a further enlargement of the area within the dashed rectangular region in Figure 1A. [Figure 2A] This is a schematic perspective view showing the RTB-type sintered magnet 100 in an embodiment of the present disclosure. [Figure 2B] This graph shows an example of a region in an RTB-type sintered magnet 100 where at least one of the Nd concentration and Pr concentration gradually decreases from the magnet surface towards the interior of the magnet. [Figure 3] This flowchart shows an example of the process for manufacturing an RTB-type sintered magnet according to an embodiment of the present disclosure. [Modes for carrying out the invention]

[0021] First, the basic structure of the RTB-type sintered magnet according to this disclosure will be explained. The RTB-type sintered magnet has a structure in which powder particles of raw material alloy are bonded together by sintering, and is mainly R2T 14 It is composed of a main phase consisting of B compound particles and a grain boundary phase located at the grain boundaries of this main phase.

[0022] Figure 1A is a schematic cross-sectional view showing an enlarged portion of an RTB-type sintered magnet, and Figure 1B is a schematic cross-sectional view showing a further enlargement of the area within the dashed rectangular region of Figure 1A. In Figure 1A, an arrow with a length of 5 μm is included as an example to indicate the size as a reference length. As shown in Figures 1A and 1B, RTB-type sintered magnets are mainly R2T 14 The structure consists of a main phase 12 made of compound B and a grain boundary phase 14 located at the grain boundaries of the main phase 12. Furthermore, as shown in Figure 1B, the grain boundary phase 14 has two R2T 14 B compound particles (grains) are adjacent to a two-particle grain boundary phase 14a and three R2T 14 The B compound particles contain adjacent grain boundary triple points 14b. The typical main phase grain size is between 2 μm and 10 μm, based on the average equivalent diameter of the magnet cross-section. The main phase 12 is R2T. 14 Compound B is a ferromagnetic material with high saturation magnetization and anisotropic magnetic field. Therefore, in RTB-type sintered magnets, the main phase 12 is R2T. 14 By increasing the proportion of compound B, r This can improve R2T 14 To increase the proportion of B compound, the amounts of R, T, and B in the raw alloy should be R2T 14 The goal is to approximate the stoichiometric ratio of compound B (amount of R:amount of T:amount of B = 2:14:1).

[0023] However, since RTB-type sintered magnets also contain grain boundary phases 14, R, T, and B in the raw alloy are consumed not only in the main phase 12 but also in the formation of the grain boundary phases 14. The grain boundary phases 14 partially melt during the sintering process and become R2T, which is the main phase 12.14 It exhibits the function of physically bonding B compounds to each other. For this reason, conventionally, the grain boundary phase 14 has been designed to have a rare earth-rich (R-rich) composition with a relatively low melting temperature. Specifically, the amount of R is R2T 14 The composition of the raw alloy has been set so that it is greater than the stoichiometric ratio of compound B, thereby using the excess R for the formation of the grain boundary phase. On the other hand, the composition of the grain boundary phase 14, specifically the types and amounts of substances contained in the grain boundary phase 14, is H cJ It is also known to affect the size.

[0024] As mentioned above, the methods disclosed in Patent Documents 1 and 2 generate transition metal-rich phases or RT-Ga phases in the grain boundary phases of RTB-based sintered magnets, thereby H cJ This improves H cJ Although this can improve the two-particle grain boundary phase, it can make B too thick. r It was found that the value may decrease in some cases. Furthermore, the inventors found that by including an RM compound in the grain boundary phase in addition to the RTM compound, H cJ Although this can improve the situation, similarly, the two-particle grain boundary phase can become too thick, B r It was found that the amount of B may decrease. Thus, although RTM and RM compounds need to be produced, their production must be kept to a minimum. Based on these findings, further investigation revealed that by controlling the area ratio of RTM and RM compounds, high B r and high H cJ It has been found that it is possible to achieve both. Specifically, this disclosure shows that by setting the sum of the area ratio of the RTM compound and the area ratio of the RM compound to a specific range (1.5% to 3.5%), and setting the area ratio of the RTM compound to 0.4% to 2.5%, and the area ratio of the RM compound to a specific range (0.4% to 2.5%), it is possible to reduce the amount of heavy rare earth element RH used while achieving high B r and high H cJIt has been found that an R-T-B sintered magnet having the following is obtained.

[0025] Hereinafter, the R-T-B sintered magnet in the embodiment of the present disclosure will be described in detail.

[0026] <R-T-B Sintered Magnet> The R-T-B sintered magnet of the present disclosure has R2T 14 It includes a main phase composed of a B compound and a grain boundary phase located at the grain boundary portion of the main phase. The grain boundary phase contains an R-T-M compound (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si) and an R-M compound.

[0027] Regarding the R-T-B sintered magnet of this embodiment, let the content of R (at%) in the R-T-M compound and the R-M compound be [R], the content of T (at%) be [T], and the content of M (at%) be [M].

[0028] The contents of R, T, and M in the R-T-M compound of the present disclosure satisfy the relationships of 0.15 ≤ [R] / ([R] + [T] + [M]) ≤ 0.3, [T] / ([R] + [T] + [M]) ≥ 0.6, and 0.015 ≤ [M] / ([R] + [T] + [M]) ≤ 0.1. The contents of R and M in the R-M compound satisfy the relationships of 0.25 ≤ [R] / ([R] + [T] + [M]) ≤ 0.7 and 0.1 < [M] / ([R] + [T] + [M]) ≤ 0.3. The contents of R, T, and M in the R-T-M compound and the R-M compound can be measured, for example, by point analysis using FE-SEM / WDX·EDX (field emission scanning electron microscope / wavelength dispersive X-ray analysis·energy dispersive X-ray analysis). By having both the R-T-M compound and the R-M compound of the present disclosure with these composition ranges present in the grain boundary phase, a high H cJ can be obtained. These compounds can be realized, for example, by adjusting the composition of the R-T-B sintered magnet to the composition described later or by diffusing the R-M alloy described later from the magnet surface into the interior.

[0029] A distinctive feature of this disclosure is that the amounts of RTM compounds and RM compounds produced are adjusted to a specific range. Specifically, in any cross-section of the RTB-type sintered magnet, the sum of the area ratio of the RTB compound and the area ratio of the RM compound is 1.5% or more and 3.5% or less, the area ratio of the RTM compound is 0.4% or more and 2.5% or less, and the area ratio of the RM compound is 0.4% or more and 2.5% or less. By adjusting the sum of the area ratios of the RTM compound and the RM compound, and the respective area ratios of the RTM compound and the RM compound, to the above specific range, high B r and high H cJ An RTB-type sintered magnet having the following characteristics can be obtained. If the sum of the area ratios of the RTM compound and the RM compound of this disclosure, or if the lower limit of either the area ratio of the RTM compound and the RM compound falls below the lower limit, then H cJ There is a possibility that it will decrease, and if the upper limit is removed, B r It may decrease.

[0030] In this disclosure, "arbitrary cross-section" refers to a region of 90 μm × 90 μm or larger in the cross-section of an RTB-type sintered magnet obtained by cutting at an arbitrary point. By taking multiple BSE (backscattered electron) images of this region and using known image analysis software, the respective area ratios of the RTM compound and RM compound, and their sum, can be determined. Preferably, in any cross-section of the RTB-type sintered magnet, the sum of the area ratio of the RTB compound and the area ratio of the RM compound is 1.8% or more and 3.5% or less, the area ratio of the RTM compound is 0.4% or more and 2.0% or less, and the area ratio of the RM compound is 0.4% or more and 1.5% or less. r and high H cJ An RTB-type sintered magnet having the following properties can be obtained.

[0031] The RTB-type sintered magnet in this embodiment may have, for example, the following composition. R: 26.8 mass% to 33.0 mass% (must include at least one selected from the group consisting of Nd, Pr, and Ce), B: 0.85mass% or more and 1.0mass% or less, Q1: 0.05 mass% to 2.0 mass% (Q1 is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si), Q2: 0 mass% to 2.0 mass% (Q2 is at least one element selected from the group consisting of Ti, V, Cr, Mn, Ni, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi) The remainder consists of T (where T is Fe or Fe and Co) and unavoidable impurities. In the RTB-type sintered magnet of this embodiment, the atomic ratio of B to T is R2T. 14 The ratio of the number of atoms of B to T in the stoichiometric composition of compound B is lower than the ratio of atoms of T. Expressing this not in terms of the number of atoms but in terms of mass ratio (mass%), it can be represented by the following equation (1) (since T is Fe-based, the atomic weight of Fe is used). Let [[T]] be the mass ratio (mass%) of T, and [[B]] be the mass ratio (mass%) of B. [[T]] / 55.85>14×[[B]] / 10.8 (1) By satisfying formula (1) and further containing Q1, RTM compounds and RM compounds can be generated in the grain boundary phase. Therefore, the amount of RTM compounds and RM compounds generated can be adjusted by adjusting the relationship between formula (1) and Q1 (the content of T, B, and Q1), and further by adjusting manufacturing conditions such as heat treatment. Furthermore, the amount of RTM compounds and RM compounds generated can also be adjusted by the method of diffusing the RM alloy from the magnet surface into the interior, as described later.

[0032] R may include, for example, Dy, Tb, Ho, La, Ce, Pr, Gd, Y, Sm, Eu, etc. Preferably, R is 28.5 mass% or more and 30.0 mass% or less. Higher B r and H cJFurthermore, the RTB-based sintered magnet of this disclosure can achieve high B while reducing the amount of heavy rare earth element RH used. r and high H cJ Preferably, the Tb content is 0.2 mass% or less (including 0 mass%) and the Dy content is 0.4 mass% or less (including 0 mass%). More preferably, the RTB-type sintered magnet does not contain Tb (excluding unavoidable impurities), more preferably, the RTB-type sintered magnet does not contain Dy (excluding unavoidable impurities), and more preferably, the RTB-type sintered magnet does not contain Tb and Dy (excluding unavoidable impurities). In addition, RTB-type sintered magnets contain unavoidable impurities such as O (oxygen), N (nitrogen), and C (carbon).

[0033] Preferably, the RTB sintered magnet contains Ga and Cu, and the sum of the Ga and Cu content is 0.25 mass% to 2 mass%. The inclusion of Ga and Cu allows for more reliable generation of RTM and RM compounds. Even more preferably, the sum of the Ga and Cu content is 0.25 mass% to 0.65 mass%. r and H cJ You can obtain this.

[0034] The RTB-type sintered magnet in this embodiment preferably includes a portion in which the concentration of at least one of Nd and Pr gradually decreases from the magnet surface toward the interior of the magnet. Because at least one of Nd and Pr is diffused from the magnet surface toward the interior of the magnet, as a result, it includes a portion in which the concentration of at least one of Nd and Pr gradually decreases from the magnet surface toward the interior of the magnet. By diffusing at least one of Nd and Pr toward the interior of the magnet, H cJ It can improve.

[0035] Figure 2A is a schematic perspective view of the RTB-type sintered magnet 100 in this embodiment. Figure 2B is a graph showing an example of a region in the RTB-type sintered magnet 100 where at least one of the Nd concentration and Pr concentration gradually decreases from the magnet surface towards the interior of the magnet. For reference, the X, Y, and Z axes, which are orthogonal to each other, are shown in Figure 2A.

[0036] In the example shown in Figure 2A, the RTB-type sintered magnet 100 has an upper surface 100T and a lower surface 100B, which correspond to a part of the magnet surface, and a side surface 100S. The size of this RTB-type sintered magnet 100 in the Z-axis direction is the thickness t. In the graph in Figure 2B, the vertical axis is the depth (Z) from the upper surface T of the RTB-type sintered magnet 100, and the horizontal axis is the concentration (D) of at least one of the Nd concentration and Pr concentration. In this example, Pr is diffused into the interior of the RTB-type sintered magnet 100 from the upper surface 100T and the lower surface 100B, respectively. As a result, as shown in Figure 2B, there are regions where the concentration of at least one of the Pr gradually decreases from the magnet surface into the interior of the magnet, on both the side of the upper surface 100T and the side of the lower surface 100B when viewed from the center of the magnet.

[0037] This section explains the significance of RTB-type sintered magnets containing a region where at least one of the Nd and Pr concentrations gradually decreases from the magnet surface into the magnet's interior. As mentioned above, the presence of a region where at least one of the Nd and Pr concentrations gradually decreases from the magnet surface into the magnet's interior in an RTB-type sintered magnet means that at least one of Nd and Pr is diffused from the magnet surface into the magnet's interior. This state can be confirmed, for example, by performing line analysis (WDX or EDX) on any cross-section of an RTB-type sintered magnet from the magnet surface to near the center of the magnet.

[0038] The concentrations of Nd and Pr are determined when the size of the measurement site is, for example, submicron, the measurement site is the main phase crystal grain (R2T). 14This can vary depending on whether the measurement site is located at a B compound particle or a grain boundary. Furthermore, if the measurement site is located at a grain boundary, the concentration of Nd or Pr may change locally or microscopically depending on the type and distribution of Nd or Pr-containing compounds that may be formed at the grain boundary. However, if Nd and Pr are diffused from the magnet surface into the magnet interior, it is clear that the average concentration of these elements at locations of equal depth from the magnet surface will gradually decrease from the magnet surface into the magnet interior. In this disclosure, an RTB-type sintered magnet is defined as containing a region in which at least one of the Nd concentration and Pr concentration gradually decreases if at least one of the average concentrations of Nd and Pr, measured as a function of depth, decreases with increasing depth in a region up to a depth of 200 μm from the magnet surface of the RTB-type sintered magnet.

[0039] In this embodiment, the RTB-type sintered magnet may, during the manufacturing process, contain not only at least one of Nd and Pr, but preferably a metallic element M (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si) which is diffused from the magnet surface towards the magnet interior. Therefore, in a more preferred embodiment, the RTB-type sintered magnet includes a portion in which the concentration of M (M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si) gradually decreases from the magnet surface towards the magnet interior. It is possible to generate RTM compounds and RM compounds by diffusing R and M (e.g., RM alloy) from the magnet surface towards the interior, and the amount generated can be adjusted by adjusting the diffusion conditions (such as the amount of R and M introduced and the diffusion temperature). Similarly, preferably, the magnet includes a portion in which the concentration of Tb and Dy gradually decreases from the magnet surface towards the magnet interior. These also mean that Tb, Dy, etc. are diffused from the magnet surface towards the magnet interior, similar to Nd and Pr. By diffusing Tb, Dy, etc. from the magnet surface towards the magnet interior, higher H cJ You can obtain it.

[0040] The fact that there is a portion where the concentration of at least one of Nd and Pr and at least one of M, Tb, and Dy gradually decreases from the magnet surface to the magnet interior means that these elements are in a state of being diffused from the magnet surface to the magnet interior. Whether or not there is a "portion where the concentration of a predetermined element gradually decreases from the magnet surface to the magnet interior" can be confirmed, for example, by performing line analysis (line analysis) using WDX or EDX from the magnet surface to near the magnet center in any cross-section of the R-T-B sintered magnet. The concentration of these predetermined elements may locally increase or decrease depending on whether the measurement site is the main-phase crystal grains (R2T 14 B compound particles) or the grain boundary, or depending on the type and presence or absence of the R-T-B sintered magnet body before diffusion and the compounds containing R and the metal element M generated during diffusion. However, the overall concentration gradually decreases (gradually becomes lower) as it goes deeper into the magnet interior. Therefore, even if the concentration of a predetermined element locally increases or decreases, it is recognized as corresponding to "including a portion where the concentration of a predetermined element gradually decreases from the magnet surface to the magnet interior" of the present disclosure.

[0041] <Method for manufacturing R-T-B sintered magnet> Hereinafter, embodiments of the method for manufacturing the R-T-B sintered magnet of the present disclosure will be described.

[0042] The manufacturing method in the present embodiment may include, for example, as shown in FIG. 3, a step S10 of preparing an R-T-B sintered body, a step S20 of preparing an R-M alloy, a step S30 of performing a first heat treatment, and a step S40 of performing a second heat treatment. The step S30 is a step of diffusing R and M into the magnet interior by bringing at least a part of the R-M alloy into contact with at least a part of the surface of the R-T-B sintered body and performing the first heat treatment at a temperature of 700°C or higher and 950°C or lower in a vacuum or inert gas atmosphere. The step S40 is a step of performing a second heat treatment on the R-T-B sintered magnet on which the first heat treatment has been performed at a temperature of 400°C or higher and 750°C or lower and at a temperature lower than the first heat treatment temperature in a vacuum or inert gas atmosphere. By diffusing the R-M alloy from the magnet surface to the interior, higher B r and H cJYou can obtain this. It should be noted that the manufacturing method in this embodiment does not necessarily require a diffusion step. As described above, the RTB-based sintered magnet can be obtained by adjusting the composition of the RTB-based sintered magnet (contents of T, B, and Q1) and further adjusting manufacturing conditions such as heat treatment to adjust the amount of RTM compound and RM compound produced. The following explains each of these steps in more detail.

[0043] (Process for preparing RTB-based sintered bodies) First, let's explain the composition of the RTB-based sintered body.

[0044] The RTB-based sintered body prepared in this process has, for example, the following composition. R: 26.6 mass% or more and 32.8 mass% or less (R is at least one rare earth element and must include Nd), B: 0.85mass% or more and 1.0mass% or less, Q1: 0 mass% to 1.5 mass% (Q1 is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si), Q2: 0 mass% to 2.0 mass% (Q2 is at least one element selected from the group consisting of Ti, V, Cr, Mn, Ni, Zr, Nb, Mo, Ag, In, Sn, Hf, Ta, W, Pb, and Bi) The remainder consists of T (where T is Fe or Fe and Co) and unavoidable impurities.

[0045] Even in RTB-based sintered bodies, the aforementioned equation (1) is satisfied.

[0046] Next, we will explain the preparation method for RTB-based sintered bodies.

[0047] Alloy ingots can be obtained by an ingot casting method, in which a metal or alloy pre-adjusted to the above-mentioned composition is melted and solidified in a mold. Alternatively, alloys may be produced by a strip casting method, in which molten metal or alloy pre-adjusted to the above-mentioned composition is rapidly cooled by contacting it with a single roll, double roll, rotating disk, or rotating cylindrical mold to produce a rapidly solidified alloy. Flake-shaped alloys may also be produced by other rapid cooling methods, such as centrifugal casting.

[0048] In the embodiments of this disclosure, alloys manufactured by either the ingot method or the rapid quenching method can be used, but it is preferable to use alloys manufactured by a rapid quenching method such as the strip casting method. The thickness of alloys manufactured by the rapid quenching method is usually in the range of 0.03 mm to 1 mm and is in flake shape. The molten alloy begins to solidify from the surface in contact with the cooling roll (roll contact surface), and crystals grow columnar in the thickness direction from the roll contact surface. Compared to alloys manufactured by the conventional ingot casting method (die casting method) (ingot alloys), the rapid quenched alloy is cooled in a shorter time, resulting in a finer structure and smaller grain size. It also has a larger grain boundary area. Since the R-rich phase spreads widely within the grain boundaries, the rapid quenching method offers excellent dispersibility of the R-rich phase. For this reason, it is easy to fracture at the grain boundaries by the hydrogen pulverization method. By hydrogen pulverizing the rapid quenched alloy, the size of the hydrogen pulverized powder (coarse pulverized powder) can be reduced to, for example, 1.0 mm or less. The coarse pulverized powder obtained in this way is then pulverized with a jet mill.

[0049] Jet mill grinding is performed in an inert atmosphere such as nitrogen. Grinding may also be performed in a jet mill in a humid atmosphere, for example. Preferably, the powder particles are made small (average particle size of 2.0 μm or more and 10.0 μm or less, more preferably an average particle size of 2.0 μm or more and 8.0 μm or less, more preferably an average particle size of 2.0 μm or more and 4.5 μm or less, and still more preferably an average particle size of 2.0 μm or more and 3.5 μm or less). By making the powder particles small, high H cJ You can obtain this.

[0050] The fine powder used in the production of RTB-type sintered bodies may be produced from a single raw material alloy (single raw material alloy) or by a method of mixing two or more raw material alloys (blending method), provided that the above conditions are met.

[0051] In a preferred embodiment, a powder molded body is produced from the above-mentioned fine powder by pressing in a magnetic field, and then this powder molded body is sintered. In pressing in a magnetic field, it is preferable to form the powder molded body by pressing in an inert gas atmosphere or by wet pressing from the viewpoint of suppressing oxidation. In particular, with wet pressing, the surface of the particles constituting the powder molded body is coated with a dispersant such as an oil, and contact with oxygen and water vapor in the atmosphere is suppressed. Therefore, oxidation of the particles by the atmosphere before, during, or after the pressing process can be prevented or suppressed. For this reason, it is easy to control the oxygen content within a predetermined range. When performing wet pressing in a magnetic field, a slurry is prepared by mixing fine powder with a dispersion medium, and it is supplied to the cavity of the mold of the wet pressing apparatus and pressed in a magnetic field. Note that RTB-type sintered bodies may be prepared using known methods such as the PLP (Press-Less Process) method described in, for example, Japanese Patent Application Publication No. 2006-19521, without molding.

[0052] Next, the molded body is sintered to obtain an RTB-type sintered body. The sintering of the molded body is preferably carried out under a pressure of 1300 Pa (10 Torr) or less, more preferably 700 Pa (5 Torr) or less, at a temperature in the range of 950°C to 1150°C. To prevent oxidation due to sintering, residual gas in the atmosphere may be replaced with an inert gas such as helium or argon. The obtained sintered body may be subjected to heat treatment. Known conditions can be used for heat treatment conditions such as heat treatment temperature and heat treatment time.

[0053] (Process for preparing RM alloy) R or an alloy containing R and M is diffused from the surface to the interior of the RTB-based sintered body. For this purpose, an RM alloy containing the elements to be diffused is prepared.

[0054] First, let's describe the composition of the RM alloy. In the RM alloy, R is a rare earth element and must contain at least one selected from the group consisting of Nd, Pr, and Ce. Preferably, R is 65 mass% to 100 mass% of the total RM alloy, and M is 0 mass% to 35 mass% of the total RM alloy. In addition, R preferably contains Pr, and the Pr content in R is preferably 65 mass% to 86 mass% of the total RM alloy. Preferably, the Pr content of the RM alloy is 50 mass% or more of the total R, and more preferably, the Pr content of the RM alloy is 65 mass% or more of the total R. The inclusion of Pr facilitates diffusion in the grain boundary phase, thus promoting grain boundary diffusion and enabling higher H cJ You can obtain this.

[0055] The shape and size of the RM alloy are not particularly limited and are arbitrary. The RM alloy can take the form of films, foils, powders, blocks, particles, etc.

[0056] Next, we will explain the method for manufacturing RM alloy.

[0057] RM alloys can be prepared using raw material alloy manufacturing methods employed in general RTB-type sintered magnet manufacturing methods, such as die casting, strip casting, single-roll ultra-rapid cooling (melt spinning), or atomization. Alternatively, the RM alloy may be obtained by grinding the alloy obtained by the above methods using known grinding means such as a pin mill.

[0058] (The first heat treatment process) A diffusion process is performed in which R and M are diffused into the magnet by bringing at least a portion of the RM alloy into contact with at least a portion of the surface of the RTB-based sintered body prepared by the method described above, and carrying out a first heat treatment at a temperature of 700°C to 950°C in a vacuum or inert gas atmosphere. As a result, a liquid phase containing R and M is generated from the RM alloy, and this liquid phase is diffused into the interior of the RTB-based sintered body from the surface through the grain boundaries.

[0059] If the first heat treatment temperature is below 700°C, for example, the amount of liquid phase containing R and M is too small, resulting in a high H cJ It is not possible to obtain this. On the other hand, if the temperature exceeds 950℃, H cJ The temperature may decrease. Preferably, it is between 850°C and 950°C. cJ This can be obtained. Furthermore, it is preferable to cool the RTB-type sintered magnet that has undergone the first heat treatment (700°C to 950°C) down to 300°C at a cooling rate of 5°C / min or more from the temperature at which the first heat treatment was performed. cJ This can be obtained. More preferably, the cooling rate up to 300°C is 15°C / min or more.

[0060] The first heat treatment can be performed by placing an RM alloy of any shape on the surface of the RTB-based sintered body and using a known heat treatment apparatus. For example, the surface of the RTB-based sintered body can be covered with a powder layer of RM alloy and the first heat treatment can be performed. For example, a slurry in which RM alloy is dispersed in a dispersion medium may be applied to the surface of the RTB-based sintered body, and then the dispersion medium may be evaporated to bring the RM alloy into contact with the RTB-based sintered body. Examples of dispersion mediums include alcohols (ethanol, etc.), aldehydes, and ketones. Furthermore, heavy rare earth elements RH may be introduced not only from the RM alloy, but also by placing fluorides, oxides, acid fluorides, etc. of heavy rare earth elements RH on the surface of the RTB-based sintered magnet together with the RM alloy. Examples of fluorides, oxides, and acid fluorides of heavy rare earth elements RH include TbF3, DyF3, Tb2O3, Dy2O3, TbOF, and DyOF.

[0061] Furthermore, the placement of the RM alloy is not particularly important, as long as at least a portion of the RM alloy is in contact with at least a portion of the RTB-based sintered body.

[0062] (The second heat treatment process) The RTB-based sintered body that has undergone the first heat treatment is subjected to a second heat treatment in a vacuum or inert gas atmosphere at a temperature of 400°C to 750°C, and at a temperature lower than the temperature at which the first heat treatment was performed. In this disclosure, this heat treatment is referred to as the second heat treatment. By performing the second heat treatment, high H cJ This can be obtained. If the second heat treatment is at a higher temperature than the first heat treatment, or if the temperature of the second heat treatment is below 400°C or above 750°C, high H cJ There is a possibility that you will not be able to obtain it. [Examples]

[0063] Embodiments of this disclosure will be described in further detail by reference to examples, but will not be limited to these examples.

[0064] Electrolytic iron, Nd metal, Pr metal, Dy metal, ferroboron alloy, electrolytic Co, Al metal, Cu metal, Ga metal, and Zr metal were blended to achieve the desired composition. These raw materials were melted and cast by strip casting to obtain flake-shaped raw material alloys. The obtained flake-shaped raw material alloys were hydrogen-embrittled in a hydrogen-pressurized atmosphere, then subjected to dehydrogenation treatment by heating to 550°C in a vacuum and cooling to obtain coarse pulverized powder. Next, phosphite ester was added to the obtained coarse pulverized powder as a lubricant and mixed. Then, using an air-flow pulverizer (jet mill device), dry pulverization was performed in a nitrogen-flow gas to obtain fine pulverized powder (alloy powder) with a particle size D50 of approximately 3 μm. In this experimental example, the amount of water in the nitrogen gas during pulverization was adjusted so that the oxygen content of the final sintered magnet was 0.1 to 0.2 mass%. The particle size D50 is a value obtained by laser diffraction using the air-flow dispersion method (volume-based median diameter). After adding a lubricant to the aforementioned finely ground powder, a slurry was prepared by immersing it in mineral oil. The obtained slurry was molded in a magnetic field (wet molding) to obtain a molded body. A so-called right-angle magnetic field molding apparatus (or horizontal magnetic field molding apparatus), in which the direction of magnetic field application and the direction of pressure are perpendicular, was used as the molding apparatus. The obtained molded body was sintered by holding it in a vacuum at 1020 to 1050°C (a temperature selected to ensure sufficient densification by sintering) for approximately 5 hours to obtain a sintered body material. The density of the sintered body material was 7.5 Mg / m3 or higher in all cases. The obtained sintered body material was machined to produce a rectangular parallelepiped sample with dimensions of 7.5 mm in length, 7.5 mm in width, and 7.2 mm in height. The height direction was the direction of magnetic field application during molding.

[0065] Pr metal, Tb metal, Cu metal, and Ga metal were blended to achieve the desired composition, and these raw materials were dissolved to obtain a powder alloy (diffusion source) by disk atomization. Compositional analysis of this powder by ICP (inductively coupled plasma) emission spectroscopy revealed that it was 0.5Nd-76.5Pr-13.4Tb-4.6Cu-5.1Ga (mass%).

[0066] For a rectangular sintered material, a 5% polyvinyl alcohol solution was applied to two sides, the vertical and horizontal, and then a diffusion source powder was applied on top. 1.5% of the diffusion source powder (by weight relative to the sintered material) was applied to each side, for a total of 3%. After coating, the sample was held in a vacuum at 900°C for 10 hours, then cooled to room temperature, and then held in a vacuum at 500°C for 1 hour, before cooling to room temperature. The heat-treated sample was then machined to form a rectangular prism with dimensions of 4.0 mm (length), 4.0 mm (width), and 7.0 mm (height), and BH tracer was used to determine the BH tracer. r H with pulse BH tracer cJ Each of these was measured. Furthermore, after the magnetization measurement, the samples were demagnetized at 350°C, and the content of Nd, Pr, Dy, Tb, B, Co, Al, Cu, Ga, and Zr in the magnet was measured by ICP emission spectrometry with total dissolution. In addition, the scrap material from which the diffusion source had been removed was crushed in a mortar, and the content was measured by gas analysis using gas fusion-infrared absorption for O (oxygen), gas fusion-thermal conduction for N (nitrogen), and combustion-infrared absorption for C (carbon). The results are shown in Table 1. Comparative Example 1 was relatively B r Although H cJ The current was less than 2000 kA / m. Examples 2 and 3 were B r The level is high at 1.4T or more, and H cJ The levels were also high, exceeding 2000 kA / m.

[0067] [Table 1]

[0068] Surface analysis was performed on the cross-section (the cross-section formed by the length and height) of scrap material containing the diffusion source using FE-SEM / WDX-EDX (Field Emission Scanning Electron Microscope / Wavelength Dispersive X-ray Analysis / Energy Dispersive X-ray Analysis). The analysis was conducted from 500 μm away from the interface between the diffusion source and the sintered material. Al, Ni, Zr, B, O, N, and C were analyzed using WDX, while Fe and Nd were analyzed using EDX. Table 2 shows the point analysis results for RTM compounds, and Table 3 shows the point analysis results for RM compounds. In the tables, R represents Nd+Pr+Dy+Tb, T represents Fe+Co, and M represents Cu+Ga+Al. No RTM compounds were observed in any part of Comparative Example 1. Furthermore, by performing line analysis (WDX) from the magnet surface to near the center of the magnet in any cross-section of the RTB-type sintered magnet, it was confirmed that the RTB-type sintered magnet contains a region where the concentration of Pr, M (Ga and Cu), and Tb gradually decreases from the magnet surface to the interior of the magnet.

[0069] [Table 2]

[0070] [Table 3]

[0071] Four BSE (backscattered electron) images of a 120 μm × 90 μm region were taken at each depth. The acquired BSE images were analyzed to calculate the area ratio of each phase. Scandium (manufactured by Seika Digital Image Co., Ltd.) was used for image analysis, assigning 256 brightness levels to each phase, counting the number of pixels, and averaging the four fields of view to calculate the area ratio of each phase. The calculation results are shown in Table 4. As mentioned above, no RTM compound was observed in Comparative Example 1, and the sum of the area ratios of RTM and RM compounds was low, less than 1.5%. In contrast, in Examples 2 and 3, the area ratio of the RTM compound was between 0.4% and 2.5%, and the sum of the area ratios of RTM and RM compounds was between 1.5% and 3.5%, which was neither too high nor too low. These appropriate phase ratios are found to be indicative of high B r and high H cJ This is thought to have led to the achievement of both.

[0072] [Table 4] [Explanation of symbols]

[0073] 12. Main phase consisting of R2T14B compound, 14. Grain boundary phase, 14a. Two-particle grain boundary phase, 14b. Grain boundary triple point

Claims

1. R ２ T １４ An R-T-B sintered magnet comprising a main phase made of compound B and a grain boundary phase located at the grain boundary portion of the main phase (where R is a rare earth element and always contains Nd or Pr, and T is Fe or Fe and Co), The R content is between 28.5 mass% and 30.0 mass%. The content of B is 0.85 mass% or more and less than 0.910 mass%, It contains Ga and Cu, The sum of the Ga content and Cu content is between 0.25 mass% and 2 mass%, The Tb content is 0.2 mass% or less (including 0 mass%), and the Dy content is 0.4 mass% or less (including 0 mass%). The grain boundary phase contains an R-T-M compound (where M is at least one selected from the group consisting of Ga, Cu, Zn, Al, and Si) and an R-M compound. The R content (at%) is denoted as [R]. [T] represents the T content (at%). When the content (at%) of M is [M], The content of R, T, and M in the R-T-M compound is: 0.15≦[R] / ([R]+[T]+[M])≦0.3, The relationships [T] / ([R]+[T]+[M])≧0.6 and 0.015≦[M] / ([R]+[T]+[M])≦0.1 are satisfied, The content of R and M in the aforementioned R-M compound is The relationships 0.25 ≤ [R] / ([R] + [T] + [M]) ≤ 0.7 and 0.1 < [M] / ([R] + [T] + [M]) ≤ 0.3 are satisfied. An R-T-B sintered magnet in which, in any cross-section, the sum of the area ratio of the R-T-M compound and the area ratio of the R-M compound is 1.8% or more and 3.5% or less, and the area ratio of the R-T-M compound is 0.4% or more and 2.0% or less, and the area ratio of the R-M compound is 0.4% or more and 1.5% or less.

2. The R-T-B sintered magnet contains Ga and Cu, The R-T-B sintered magnet according to claim 1, wherein the sum of the Ga content and Cu content is 0.25 mass% or more and 0.65 mass% or less.

3. The R-T-B sintered magnet according to claim 1 or 2, wherein the R-T-B sintered magnet includes a portion in which at least one of the Nd concentration and Pr concentration gradually decreases from the magnet surface toward the interior of the magnet.

4. The R-T-B sintered magnet according to any one of claims 1 to 3, wherein the R-T-B sintered magnet includes a portion in which the M concentration gradually decreases from the magnet surface toward the interior of the magnet.

5. The R-T-B sintered magnet according to any one of claims 1 to 4, wherein the R-T-B sintered magnet includes a portion in which at least one of the Tb concentration and Dy concentration gradually decreases from the magnet surface toward the interior of the magnet.

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