R-t-b based permanent magnet

Abstract

Provided is an R-T-B-based permanent magnet having improved residual flux density and coercive force. The R-T-B-based permanent magnet contains a rare earth element R, a transition metal element T, and B, wherein the R-T-B-based permanent magnet contains at least Nd as R, the R-T-B-based permanent magnet contains at least Fe among Fe and Co as T, and the R-T-B-based permanent magnet has a plurality of main phase particles containing a crystal of R2T 14 B, and a two-particle grain boundary between two main phase particles adjacent in the easy magnetization axis direction, the thickness of the two-particle grain boundary being 3 nm or less, the two-particle grain boundary having crystallinity and being non-oriented.

Description

Technical Field

[0001] This disclosure relates to an RTB-based permanent magnet. Background Technology

[0002] RTB-based permanent magnets contain rare earth elements such as R (Nd, etc.), transition metal elements such as T (Fe, etc.), and boron (B). RTB-based permanent magnets possess excellent magnetic properties and are widely used. RTB-based permanent magnets include sintered magnets manufactured using powder metallurgy and hot-worked magnets manufactured using thermoplastic processing. (See Patent Documents 1-3 below.)

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-96203

[0006] Patent Document 2: Japanese Patent Application Publication No. 2018-107328

[0007] Patent Document 3: Japanese Patent Application Publication No. 2016-29679 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] The remanent flux density (Br) and coercivity (HcJ) are generally used as indicators of the magnetic properties of RTB permanent magnets.

[0010] Here, alloy ribbons, used as raw materials for hot-working magnets, are obtained via ultra-rapid solidification. In ultra-rapid solidification, molten metal of an RTB-based alloy is rapidly cooled on the surface of a cooling roller. As a result, the molten metal solidifies, forming an alloy ribbon. The alloy ribbon obtained by ultra-rapid solidification contains microcrystals (and amorphous alloys). Therefore, the grains (main phase particles) constituting the hot-working magnet are finer than those of sintered magnets. As shown in Kronmuller's formula, it is known that the finer the grain size of an RTB-based permanent magnet, the greater the coercivity. Therefore, hot-working magnets should have higher coercivity than sintered magnets. However, the coercivity of existing hot-working magnets is equal to that of sintered magnets with the same composition, and the high coercivity expected from fine grain size has not been obtained.

[0011] In addition, there is room for improvement in the residual magnetic flux density of existing RTB-based permanent magnets (e.g., hot-worked magnets).

[0012] One aspect of the present invention was developed in view of the above circumstances, and its object is to provide an RTB-based permanent magnet with improved residual magnetic flux density and coercivity.

[0013] Means for solving technical problems

[0014] One aspect of the present invention provides an RTB-based permanent magnet containing rare earth element R, transition metal element T, and B.

[0015] The magnet contains at least Nd as R.

[0016] The magnet contains at least Fe as T from Fe and Co.

[0017] This magnet has the following characteristics: containing R2T 14 The crystallization of B consists of multiple principal phase particles and a two-particle grain boundary phase located between two adjacent principal phase particles along the easy magnetization axis.

[0018] The thickness of the grain boundary between the two grains is less than 3 nm.

[0019] The two grain boundaries are crystalline and non-oriented.

[0020] The R content in RTB-based permanent magnets can be 28% by mass or more and 33% by mass or less, and the B content in RTB-based permanent magnets can be 0.8% by mass or more and 1.1% by mass or less.

[0021] RTB-based permanent magnets may also contain Ga, with the grain boundaries containing R6T. 13 The phase of Ga.

[0022] RTB series permanent magnets can also be heat-processed magnets.

[0023] Invention Effects

[0024] According to one aspect of the present invention, an RTB-based permanent magnet with improved residual magnetic flux density and coercivity is provided. Attached Figure Description

[0025] Figure 1A This is a perspective view of an RTB-based permanent magnet according to one embodiment of the present invention.

[0026] Figure 1B yes Figure 1A The diagram shows a cross-sectional view of the RTB system permanent magnet (view on arrow).

[0027] Figure 2 yes Figure 1B The diagram shows a cross-section (region II) of the RTB-type permanent magnet.

[0028] Figure 3AThe image is a HAADF-STEM image obtained by observing the cross-section of an RTB-based permanent magnet according to an embodiment of the present invention using STEM.

[0029] Figure 3B It will be through the Figure 3A The bright spot in the region constituting the grain boundary of the two grains in the HAADF-STEM image shown is taken as the center of the image.

[0030] Figure 3C It will be through the Figure 3A The bright spot in the region constituting the grain boundary of the two grains in the HAADF-STEM image shown is taken as the center of the image.

[0031] Figure 4 This is a flowchart illustrating the method for manufacturing a permanent magnet according to this embodiment.

[0032] Figure 5 It is a general three-dimensional diagram showing the extrusion die used in the heat treatment process.

[0033] Figure 6 It means Figure 5 The diagram shows the inlet, plastic processing section, and outlet of the extrusion die.

[0034] Figure 7 It means Figure 5 The diagram shows the inlet, plastic processing section, and outlet of the extrusion die.

[0035] Symbol Explanation

[0036] 2……Permanent magnet, 2cs……Cross section of permanent magnet, 4……Main phase grain, 6……Multiple grain boundary points, 8……Two-grain grain boundary, 10, 30……Extrusion die, 10a……Starting end face, 10b……Ending end face, 11……Entrance, 11a, 12a, 14a……Starting end, 11b, 12b, 14b……Ending end, 12……Plastic processing section, 14……Exit section. Detailed Implementation

[0037] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. In the drawings, the same reference numerals are used to denote the same constituent elements. The present invention is not limited to the embodiments described below. The term "permanent magnet" as used below refers to an RTB-based permanent magnet. The concentrations of the elements described below are expressed in atomic percentages.

[0038] (Permanent magnet)

[0039] The permanent magnet of this embodiment contains rare earth elements (R), transition metal elements (T), and boron (B). The permanent magnet of this embodiment is a heat-worked magnet. However, the permanent magnet of the present invention can also be a sintered magnet.

[0040] Permanent magnets contain at least neodymium (Nd) as a rare earth element R. Permanent magnets may also contain other rare earth elements R besides Nd. These other rare earth elements R may be selected from at least one of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), thallium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

[0041] Permanent magnets contain at least iron (Fe) as a transition metal element T. Permanent magnets may also contain only Fe as a transition metal element T. Permanent magnets may also contain both Fe and cobalt (Co) as transition metal elements T.

[0042] Figure 1A This is a schematic perspective view of the rectangular parallelepiped permanent magnet 2 of this embodiment. Figure 1B This is a schematic diagram of the cross-section 2cs of the permanent magnet 2. Figure 2 This is a magnified view (region II) of the cross-section 2cs of the permanent magnet 2. The cross-section 2cs of the permanent magnet 2 can also be approximately parallel to the easy magnetization axis direction C of the permanent magnet 2. The easy magnetization axis direction C can also be specified based on the measurement of the magnetic flux distribution of the permanent magnet 2. The easy magnetization axis direction C can also be specified based on the measurement of the magnetic flux distribution of the analytical sample separated from the permanent magnet 2.

[0043] In this embodiment, the permanent magnet 2 is a cuboid (plate). However, the shape of the permanent magnet 2 is not limited to a cuboid. For example, the shape of the permanent magnet 2 can also be a cube, a polygonal prism, an arc segment, an annular sector, a sphere, a circular plate, a cylinder, a tube, or a ring.

[0044] like Figure 2 As shown, the permanent magnet 2 has multiple (numerous) principal phase particles 4. The principal phase particles 4 contain at least Nd, T, and B. The principal phase particles 4 can also be referred to as grains or primary particles. The principal phase particles 4 contain R2T. 14 B crystallization (single crystal or polycrystalline). Main phase particle 4 can also be composed solely of R2T. 14 The crystalline structure of B. R2T 14 Bo can also crystallize into tetragonal crystals. That is, it can be R2T. 14 The crystallographic axes of B are the a-axis, b-axis, and c-axis, which are orthogonal to each other, and R²T 14 The lattice constant of B along the a-axis and R²T 14The lattice constants of B along the b-axis are equal, and R2T 14 The lattice constant of B along the c-axis can also differ from the lattice constants along the a-axis and b-axis. (R²T) 14 The c-axis direction of B can also be approximately parallel to the easy magnetization axis direction C of the permanent magnet 2.

[0045] The main phase particle 4 may also contain other elements besides Nd, T, and B. For example, R2T, which constitutes the main phase particle 4, 14 B can also be represented as (Nd) 1-x Pr x )2(Fe 1-y Co y ) 14 B. x can also be greater than 0 and less than 1. Y can also be greater than 0 and less than 1. The main phase particle 4 can also contain heavy rare earth elements such as Tb and Dy as R, in addition to light rare earth elements. R2T 14 A portion of the B in B can also be replaced by other elements such as gallium (Ga) or carbon (C). The composition within the main phase particle 4 can also be homogeneous. Alternatively, the composition within the main phase particle 4 can be non-homogeneous. For example, the concentration distributions of R, T, and B in the main phase particle 4 can also have gradients.

[0046] The main phase particle 4 can also be composed of a surface portion and a central portion covered by the surface portion. The surface portion can also be referred to as a shell, and the central portion can also be referred to as a core. The surface portion of the main phase particle 4 can contain at least one heavy rare earth element selected from Tb and Dy. The surface portion of each of all the main phase particles 4 can also contain at least one heavy rare earth element selected from Tb and Dy. The surface portion of a portion of all the main phase particles 4 can contain at least one heavy rare earth element selected from Tb and Dy. By containing heavy rare earth elements in the surface portion, the anisotropic magnetic field tends to increase locally near the grain boundary, making it difficult to generate a nucleus with magnetization reversal near the grain boundary. As a result, the coercivity of the permanent magnet 2 at high temperatures (e.g., 100–200 °C) increases. It is easy to obtain both the remanent magnetic flux density and coercivity of the permanent magnet 2, therefore, the total concentration of heavy rare earth elements in the surface portion can be higher than the total concentration of heavy rare earth elements in the central portion.

[0047] The major and minor axes of the main phase particles 4 are not particularly limited; for example, the major axis can be 100–1000 nm and the minor axis can be 20–200 nm. The total volume percentage of the main phase particles 4 in the permanent magnet 2 is not particularly limited; for example, it can be 80% or more but less than 100% by volume. The major and minor axes of the main phase particles 4 are, respectively, the lengths of the long and short sides of the quadrilateral with the smallest area circumscribed by the main phase particles 4 in the HAADF-STEM image obtained by observing the cross-section of the permanent magnet 2 using STEM (scanning transmission electron microscopy).

[0048] The permanent magnet 2 has multiple grain boundary multi-points 6. Each grain boundary multi-point 6 is a grain boundary phase surrounded by at least three main phase particles 4. Additionally, the permanent magnet 2 has multiple two-grain grain boundaries 8. Each two-grain grain boundary 8 is a grain boundary phase located between two adjacent main phase particles 4 along the easy magnetization axis. The grain boundaries may also contain at least Nd, and the Nd content in the grain boundaries may be greater than the Nd content in the main phase particles. That is, the grain boundaries may also contain an Nd-rich phase. In addition to Nd, the grain boundaries may also contain at least one of Fe and B.

[0049] The thickness of the two-grain boundary 8 is less than 3 nm. Coercivity and remanent flux density are further increased, and rectangularity is improved; therefore, the thickness of the two-grain boundary 8 can also be greater than 0.8 nm. The thickness of the two-grain boundary 8 is the average of the thickness measurements at any 10 or more locations in a HAADF-STEM image obtained by observing the cross-section of the permanent magnet 2 using STEM (scanning transmission electron microscopy). The magnification of the HAADF-STEM image can be set as long as the lattice image can be clearly observed. The average of the thickness measurements at any 10 or more locations in the HAADF-STEM image is the average of the following values: by grouping two adjacent main phase particles together, randomly selecting 10 or more groups from a single HAADF-STEM image, and measuring the thickness of the grain boundary phase located between the two main phase particles in each group.

[0050] The two-grain boundary 8 is crystalline. The crystalline nature of the two-grain boundary 8 can be confirmed by the following method: A HAADF-STEM image is obtained by observing the cross-section of the permanent magnet 2 using STEM (scanning transmission electron microscopy). In the obtained HAADF-STEM image, an FFT (two-dimensional Fourier transform) is performed on any five or more regions (2×2 nm) constituting the two-grain boundary 8 to obtain an image centered on a bright spot (direct point). If, in at least one of the images obtained from the five or more regions, a bright spot other than the central bright spot (direct point) is observed, it is determined that the two-grain boundary 8 is crystalline.

[0051] Figure 3A The image is a HAADF-STEM image obtained by observing the cross-section of permanent magnet 2 using STEM. Figure 3B and Figure 3C Therefore, through the Figure 3A An image centered on a bright spot obtained by performing FFT on the region (size: 2×2nm) constituting the grain boundary between two grains in a HAADF-STEM image. For example... Figure 3B As shown, in region R6, in addition to the central bright spot P1, two other bright spots P2 can be observed. Figure 3CAs shown, in regions R1 to R5, bright spots other than the central bright spot were also observed.

[0052] The two-grain boundary 8 is unoriented, meaning its orientation is random. This unoriented nature of the two-grain boundary 8 can be confirmed by the following method: STEM observation of the cross-section of the permanent magnet 2 yields a HAADF-STEM image. In the obtained HAADF-STEM image, an FFT (two-dimensional Fourier transform) is performed on any five or more regions (2×2 nm) constituting the two-grain boundary 8, resulting in an image centered on a bright spot (direct point). Comparing multiple obtained images, if the bright spots other than the central bright spot (direct point) do not overlap, the two-grain boundary 8 is determined to be unoriented.

[0053] When the permanent magnet 2 contains Ga, the two-grain boundary 8 can also contain R6T. 13 The Ga phase. When the two-grain boundary 8 contains R6T. 13 When Ga is in the phase, the Nd and Fe on the surface of the main phase particle 4 exhibit anisotropy that contributes to the increase of coercivity. As a result, the coercivity of the permanent magnet 2 is further improved.

[0054] R6T in two grain boundaries 8 13 The presence or absence of Ga can also be determined by analyzing the composition and lattice constant of the two-grain boundary 8. The composition of the two-grain boundary 8 can also be analyzed using energy-dispersive X-ray fluorescence spectroscopy (EDX). The lattice constant of the two-grain boundary 8 can be confirmed by the following method: observing the cross-section of the permanent magnet 2 using STEM and obtaining a HAADF-STEM image. In the obtained HAADF-STEM image, the periodicity (interface spacing and lattice constant) is calculated by performing a two-dimensional Fourier transform on any five or more regions (2×2 nm) constituting the two-grain boundary 8.

[0055] The compositions of the principal phase particles 4 and the grain boundary phases can also be identified by analyzing the principal phase particles 4 and the grain boundary phases exposed in the cross section 2cs of the permanent magnet 2. The principal phase particles 4 and the grain boundary phases exposed in the cross section 2cs of the permanent magnet 2 are easily identified based on the signal intensity of the backscattered electron image obtained by electron probe microscopy (EPMA). The compositions of the principal phase particles 4 and the grain boundary phases can also be analyzed by electron probe microscopy (EPMA) or energy-dispersive X-ray spectroscopy (EDS).

[0056] The following describes the overall composition of the permanent magnet 2. However, the composition of the permanent magnet 2 is not limited to the composition described below. The content of each element in the permanent magnet 2 may also deviate from the ranges described below.

[0057] The total content of rare earth element R in the permanent magnet 2 can be 25.00% by mass or more and 35.00% by mass or less, or 28.00% by mass or more and 33.00% by mass or less. When the R content is within the above range, the remanent magnetic flux density and coercivity of the permanent magnet 2 are easily increased. If the R content is too low, it is difficult to form R2T that constitutes the main phase particles 4. 14 B readily forms the soft magnetic α-Fe phase. As a result, coercivity tends to decrease. On the other hand, with excessive R content, the volume ratio of the main phase particles 4 decreases, and the remanent magnetic flux density tends to decrease. Remanent magnetic flux density and coercivity tend to increase. Therefore, the combined proportion of Nd and Pr in all rare earth element R can be 80 atomic% or more and 100 atomic% or less, or 95 atomic% or more and 100 atomic% or less.

[0058] The combined content of Tb and Dy in the permanent magnet 2 can be 0.20% by mass or more and 5.00% by mass or less. By including at least one heavy rare earth element, Tb or Dy, the magnetic properties (especially the coercivity at high temperatures) of the permanent magnet 2 are easily increased. However, the permanent magnet 2 may also not contain Tb or Dy.

[0059] The boron (B) content in the permanent magnet 2 can be 0.70% by mass or more and 1.10% by mass or less, or 0.80% by mass or more and 1.10% by mass or less. When the B content is 0.70% by mass or more, the remanent magnetic flux density tends to increase. When the B content is 1.10% by mass or less, the coercivity of the permanent magnet 2 tends to increase. When the B content is within the above range, the rectangularity ratio (Hk / HcJ) of the permanent magnet 2 tends to approach 1.0. Hk is the strength of the demagnetizing field, which is equivalent to 90% of the remanent magnetic flux density.

[0060] The permanent magnet 2 may contain gallium (Ga). The Ga content may be 0.03% by mass or more and 1.00% by mass or less, or 0.20% by mass or more and 0.80% by mass or less. When the Ga content is within the above range, the formation of secondary phases (e.g., phases containing R, T, and Ga) can be appropriately suppressed, and the remanent magnetic flux density and coercivity of the permanent magnet 2 can be easily increased. However, the permanent magnet 2 may also not contain Ga.

[0061] The permanent magnet 2 may also contain aluminum (Al). The Al content in the permanent magnet 2 may be 0.01% by mass or more and 0.2% by mass or more and 0.04% by mass or less and 0.07% by mass. By keeping the Al content within the above range, the coercivity and corrosion resistance of the permanent magnet are easily improved. However, the permanent magnet 2 may also not contain Al.

[0062] The permanent magnet 2 may also contain copper (Cu). The Cu content in the permanent magnet 2 may be 0.01% by mass or more and 1.50% by mass or less, or 0.04% by mass or more and 0.50% by mass or less. By keeping the Cu content within the above range, the coercivity, corrosion resistance, and temperature characteristics of the permanent magnet 2 are easily improved. However, the permanent magnet 2 may also not contain Cu.

[0063] The permanent magnet 2 may also contain cobalt (Co). The Co content in the permanent magnet can be 0.30% by mass or more and 6.00% by mass or less, or 0.30% by mass or more and 4.00% by mass or less. The presence of Co in the permanent magnet 2 easily increases its Curie temperature. Furthermore, the presence of Co in the permanent magnet 2 easily improves its corrosion resistance. However, the permanent magnet 2 may also not contain Co.

[0064] The remainder after removing the aforementioned elements from the permanent magnet 2 may consist only of Fe, or Fe and other elements. In order for the permanent magnet 2 to possess sufficient magnetic properties, the total content of elements other than Fe in the remainder may also be less than 5% by mass relative to the total mass of the permanent magnet 2.

[0065] The permanent magnet 2 may also contain at least one element selected from silicon (Si), titanium (Ti), manganese (Mn), zirconium (Zr), vanadium (V), chromium (Cr), nickel (Ni), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), bismuth (Bi), tin (Sn), calcium (Ca), carbon (C), nitrogen (N), oxygen (O), chlorine (Cl), sulfur (S), and fluorine (F) as other elements (e.g., unavoidable impurities). The total content of other elements in the permanent magnet 2 may also be 0.001% by mass or more and 0.50% by mass or less.

[0066] The overall composition of the permanent magnet 2 can also be analyzed by methods such as fluorescence X-ray (XRF) analysis, high-frequency inductively coupled plasma (ICP) luminescence analysis, inert gas melting-nondispersive infrared absorption (NDIR) method, combustion in oxygen flow-infrared absorption method, and inert gas melting-thermal conductivity method.

[0067] Permanent magnet 2 can also be used in motors, generators, or actuators. For example, permanent magnet 2 can be used in a variety of fields such as hybrid vehicles, electric vehicles, hard disk drives, magnetic resonance imaging (MRI) devices, smartphones, digital cameras, slim TVs, scanners, air conditioners, heat pumps, refrigerators, vacuum cleaners, washer-dryers, elevators, and wind turbines.

[0068] [Effects]

[0069] In permanent magnets, magnetization reversal propagates between multiple principal phase particles (i.e., domain walls cross grain boundaries). Regarding the propagation of magnetization reversal, the presence of bigrained grain boundaries between adjacent principal phase particles magnetically separates them. Therefore, it is believed that the thicker the bigrained grain boundary, the better it suppresses the propagation of magnetization reversal. However, with thick bigrained grain boundaries, the remanent magnetic flux density decreases. This decrease in remanent magnetic flux density caused by thick bigrained grain boundaries is particularly pronounced when the permanent magnet is a hot-worked magnet. This is because, compared to sintered magnets, hot-worked magnets have smaller major and minor axes of principal phase particles, resulting in a larger specific surface area. Consequently, the thickness of the bigrained grain boundary has a greater impact on the remanent magnetic flux density.

[0070] However, the permanent magnet 2 is crystalline through the grain boundary 8, which is non-oriented and has a thickness of less than 3 nm. This also suppresses the propagation of magnetization reversal between the main phase particles. Therefore, the remanent magnetic flux density and coercivity of the permanent magnet 2 are improved.

[0071] (Manufacturing method of permanent magnets)

[0072] <First Implementation>

[0073] In this embodiment, a method for manufacturing a heat-processed magnet will be described as a method for manufacturing a permanent magnet.

[0074] The method for manufacturing a hot-working magnet according to this embodiment uses an extrusion die. The extrusion die includes a plastic processing section having a starting end face and a terminal end face facing each other, and an exit section having a starting end face and a terminal end face, which are sequentially connected towards the starting end face and the terminal end face. The method includes a hot-working step of hot-extruded a molded body obtained by molding magnetic powder from the starting end face of the extrusion die through the plastic processing section and the exit section to the terminal end face. The area of ​​the end face at the terminal end of the plastic processing section is smaller than the area of ​​the end face at the starting end face. The area of ​​the end face at the terminal end of the exit section is approximately the same as the area of ​​the end face at the starting end face. The temperature difference (T1-T2) between the molded body at the starting end face of the exit section and the molded body at the starting end face is 30°C or more.

[0075] The hot-working magnet manufacturing method of this embodiment achieves an unloading rate exceeding 0 by having such a structure. As a result, the two grain boundaries 8 of the obtained permanent magnet 2 become non-oriented.

[0076] Weigh the starting material in a manner consistent with the composition of the desired permanent magnet 2. The starting material may also be, for example, a metal, alloy, or oxide.

[0077] Raw material alloys can be produced, for example, using starting materials via ultracrystallization. To suppress oxidation of the raw material alloy, ultracrystallization can also be carried out in an argon atmosphere (or a nitrogen atmosphere).

[0078] The raw material alloy obtained above is pulverized into magnetic powder. Figure 4 The process flow is as follows (step S1). The pulverization can be carried out, for example, by a cutting pulverizer or a propeller mill, in an argon atmosphere (or a nitrogen atmosphere). The particle size of the magnetic powder obtained by pulverization is, for example, about 100–300 μm. The magnetic powder is not finely pulverized to the size scale of a single crystal of the permanent magnet 2 (about 40 nm), and has a polycrystalline structure composed of multiple single crystals.

[0079] The magnetic powder obtained in step S1 is formed by compression molding machine to obtain a molded body. Figure 4 Step S2 of the flowchart. Molding is performed in an argon atmosphere (or nitrogen atmosphere) at a high temperature below 800°C (750°C for example) and under a stamping pressure below 100 MPa for tens of seconds. Through molding, the magnetic powder grows into plate-like grains, resulting in a dense molded body. However, in this molded body state, the magnetic particles that have grown into plate-like grains are randomly oriented, and the orientation of their easy magnetization axes is inconsistent.

[0080] The molded body obtained in step S2 is subjected to thermal processing by front extrusion to obtain a thermally processed magnet. Figure 4 Step S3 of the flowchart. The heat treatment is performed for tens of seconds in an argon atmosphere (or a nitrogen atmosphere, in the atmosphere), at a high temperature below 800°C (750°C for example), by a stamping pressure below 100 MPa. In the heat treatment of this embodiment, using... Figure 5 and 6 The extrusion die shown.

[0081] The extrusion die 10 has a starting end face 10a and a ending end face 10b that face each other. In this embodiment, the extrusion die 10 has a cylindrical shape, and both the starting end face 10a and the ending end face 10b are circular. In this embodiment, the starting end face 10a and the ending end face 10b are parallel to each other. There are no particular limitations on the material constituting the extrusion die 10, as long as it is a material with excellent mechanical strength at high temperatures. Examples of such materials include molybdenum alloys and nickel alloys.

[0082] The extrusion die 10 has an inlet 11, a plastic processing section 12, and an outlet 14. The inlet 11, the plastic processing section 12, and the outlet 14 are connected sequentially from the starting end face 10a to the ending end face 10b.

[0083] like Figure 5As shown, in the extrusion die 10, a punch 20 with the same dimensions (or, very short) of the end face shape of the starting end 11a of the inlet portion 11 is used to extrude the aforementioned molded body disposed on the starting end face 10a toward the terminal face 10b along the Z direction. This results in a strip-shaped heat-working magnet with the same cross-sectional shape as the end face shape of the terminal portion 14b of the outlet portion 14. The strip-shaped heat-working magnet is appropriately cut to a predetermined width.

[0084] The inlet portion 11 has a starting end portion 11a at a starting end face 10a and a terminal portion 11b. The area of ​​the end face at the terminal portion 11b of the inlet portion 11 is approximately the same as the area of ​​the end face at the starting end portion 11a. Viewed from the face-to-face direction of the starting end face 10a and the terminal face 10b, the starting end portion 11a and the terminal portion 11b have end face shapes extending in one direction. In this embodiment, the end face shapes of the starting end portion 11a and the terminal portion 11b are rectangular. The cross-sectional area in a section perpendicular to the face-to-face direction of the starting end face 10a and the terminal face 10b of the inlet portion 11 can also be approximately constant from the starting end portion 11a toward the terminal portion 11b.

[0085] For ease of explanation, the face-to-face direction of the starting end face 10a and the ending end face 10b is defined as the Z direction, the direction in which the end face shapes of the starting end 11a and the ending part 11b extend is defined as the X direction, and the direction orthogonal to the Z direction and the X direction is defined as the Y direction.

[0086] The plastic forming section 12 has a starting end portion 12a and a terminal portion 12b connected to the terminal portion 11b. The area of ​​the end face at the terminal portion 12b of the plastic forming section 12 is smaller than the area of ​​the end face at the starting end portion 12a. Viewed from the face-to-face direction of the starting end face 10a and the terminal face 10b, the starting end portion 12a and the terminal portion 12b of the plastic forming section 12 have end face shapes extending in one direction. The end face shapes of the starting end portion 12a and the terminal portion 12b are rectangular. The end face shape of the starting end portion 12a extends in the X direction (i.e., the long side is along the X-axis), and in contrast, the end face shape of the terminal portion 12b extends in the Y direction (i.e., the long side is along the Y-axis). When viewed from the face-to-face direction of the starting end face 10a and the terminal face 10b, the X direction (first direction) in which the end face shape of the starting end portion 12a extends and the Y direction (second direction) in which the end face shape of the terminal portion 12b extends intersect, or more specifically, are orthogonal. The plastic forming section 12 can also exhibit interchangeable major and minor axes during its journey from the rectangular end face of the starting end 12a to the rectangular end face of the ending end 12b. The end faces of the starting end 12a and the ending end 12b are in a torsional positional relationship.

[0087] like Figure 6As shown, the outline of the plastic forming section 12 can be composed of straight lines or curves. The cross-sectional area in the section orthogonal to the face-to-face direction of the starting end face 10a and the ending end face 10b of the plastic forming section 12 can gradually decrease from the starting end face 12a to the ending end face 12b, or it can temporarily increase and then gradually decrease. Since gradually decreasing the cross-sectional area can effectively suppress the generation of cracks in the obtained permanent magnet 2, this is more preferable.

[0088] Furthermore, by setting the ratio (area reduction rate) of the area of ​​the terminal portion 12b of the plastic processing portion 12 to the area of ​​the starting end portion 12a to 60-90% (85% as an example), it is possible to obtain a hot-processed magnet with high magnetic properties (e.g., remanent magnetic flux density).

[0089] Furthermore, the end faces of the starting end 12a and the ending end 12b of the plastic forming section 12 may not be in a torsional position, but rather in a parallel position (e.g., both extending along the X direction). When the end faces of the starting end 12a and the ending end 12b of the plastic forming section 12 are in a torsional position, a large plastic deformation can be generated when the molded body passes through the plastic forming section 12, thereby obtaining a hot-working magnet with high magnetic properties (e.g., remanent magnetic flux density).

[0090] The outlet section 14 has a starting end 14a connected to the terminal section 12b and a terminal section 14b at the terminal surface 10b. The area of ​​the end face at the terminal section 14b of the outlet section 14 is approximately the same as the area of ​​the end face at the starting end 14a.

[0091] Viewed from the face-to-face direction of the starting end face 10a and the ending end face 10b, the starting end face 14a and the ending end face 14b of the outlet portion 14 have end face shapes extending in one direction. The end face shapes of the starting end face 14a and the ending end face 14b are rectangular. The area of ​​the end face at the ending end face 14b is approximately the same as the area of ​​the end face at the starting end face 14a. The cross-sectional area of ​​the section orthogonal to the face-to-face direction of the starting end face 10a and the ending end face 10b of the outlet portion 14 can also be approximately constant from the starting end face 14a to the ending end face 14b.

[0092] The temperature difference (T1-T2) between the molded body at the starting end 14a of the outlet 14 and the temperature T2 of the molded body at the terminal end 14b is 30°C or more. As a result, the orientation of the two-grained grain boundaries 8 of the obtained hot-worked magnet becomes unoriented. The inventors believe the reason for this unoriented orientation of the two-grained grain boundaries 8 of the obtained hot-worked magnet is as follows: Because the temperature difference (T1-T2) between the molded body at the starting end 14a of the outlet 14 and the temperature T2 of the molded body at the terminal end 14b is 30°C or more, shrinkage occurs in the molded body. This shrinkage reduces the stress on the molded body from the inner wall of the extrusion die 10. Consequently, disturbance occurs in the orientation of the two-grained grain boundaries 8.

[0093] Considering the excellent coercivity and remanent flux density of the obtained hot-worked magnet, the temperature difference (T1-T2) between the molded body at the starting end 14a of the exit portion 14 and the molded body at the terminal portion 14b is preferably 30°C or more, more preferably 50°C or more. T1-T2 may also be 200°C or less. The temperature T1 of the molded body at the starting end 14a of the exit portion 14 and the temperature T2 of the molded body at the terminal portion 14b can be calculated by simulation.

[0094] The unloading rate is preferably 0.1% or more, and more preferably 0.2% or more. In this application specification, the unloading rate is a value calculated based on the temperature of the molded body at each part of the mold, using the dimensions of the molded body calculated from the coefficient of linear expansion and the dimensions of each part of the mold. Specifically, it is calculated as follows. That is, ΔT, α, X2, L1, and L2 are defined as follows.

[0095] ΔT: The temperature difference (T2-T1) between the molded body at the end portion 14b and the molded body at the starting end portion 14a.

[0096] α: The coefficient of linear expansion along the easy magnetization axis of the desired hot-worked magnet.

[0097] X2: The length of the mold at the end part 14b in the direction parallel to the easy magnetization axis of the molded body.

[0098] L1: The length of the molded body at the starting end 14a in the direction parallel to the easy magnetization axis of the molded body.

[0099] L2: The length of the molded body in the direction parallel to the easy magnetization axis of the molded body at the terminal part 14b. It is calculated using the following formula (a).

[0100] L2=(αΔT+1)×L1...Formula (a)

[0101] The unloading rate is calculated using the following formula (b).

[0102] Unloading rate = -{(L2-X2) / X2}×100……Equation (b)

[0103] <Second Implementation>

[0104] The method for manufacturing a hot-working magnet according to this embodiment uses an extrusion die. The extrusion die includes a plastic processing section having a starting end face and a terminal face facing each other, and an exit section having a starting end face and a terminal face, which are sequentially connected towards the starting end face and the terminal face. The method includes a hot-working step of hot-extruding a molded body obtained by molding magnetic powder from the starting end face of the extrusion die through the plastic processing section and the exit section to the terminal face. The area of ​​the end face at the terminal face of the plastic processing section is smaller than the area of ​​the end face at the starting end face. The area of ​​the end face at the terminal face of the exit section is larger than the area of ​​the end face at the starting end face.

[0105] The hot-working magnet manufacturing method of this embodiment achieves an unloading rate exceeding 0 by having this structure. As a result, the two-grain boundaries 8 of the obtained permanent magnet 2 become non-oriented. The unloading rate is preferably 0.1% or more, more preferably 0.2% or more.

[0106] Steps S1 and S2 of the method for manufacturing a hot-working magnet in the second embodiment can be the same as those in the method for manufacturing a hot-working magnet in the first embodiment. In step S3 of the method for manufacturing a hot-working magnet in the second embodiment, the atmosphere, pressure, and time for hot working can also be the same as in the first embodiment. In the hot working of this embodiment, the following is used: Figure 7 The extrusion die 30 shown.

[0107] The extrusion die 30 is the same as the extrusion die 10, except for the shape of the outlet portion 14. The area of ​​the end face at the terminal portion 14b of the outlet portion 14 of the extrusion die 30 is larger than the area of ​​the end face at the starting end portion 14a. As a result, the orientation of the two grain boundaries 8 in the obtained hot-working magnet becomes unoriented. The inventors believe that the reason for the unoriented orientation of the two grain boundaries 8 in the obtained hot-working magnet is as follows: Because the area of ​​the end face at the terminal portion 14b is larger than the area of ​​the end face at the starting end portion 14a, the stress on the molded body from the inner wall of the extrusion die 30 is reduced. This causes disturbance in the orientation of the two grain boundaries 8.

[0108] Viewed from the face-to-face direction of the starting end face 10a and the ending end face 10b, the extrusion die 30 has an end face shape in which the starting end 14a and the ending end 14b of the outlet portion 14 extend in one direction. Compared to the starting end 14a, the short side of the ending end 14b is longer, and the length of its long side is the same. Alternatively, compared to the starting end 14a, the length of the long side and the length of the short side of the ending end 14b may be the same, or both the long and short sides of the ending end 14b may be longer than the starting end 14a. The starting end 14a and the ending end 14b may not be similar in shape, or they may be similar in shape. The extrusion die 30 has a region A, in which the cross-sectional area of ​​a section orthogonal to the face-to-face direction of the starting end face 10a and the ending end face 10b of the outlet portion 14 gradually increases from the starting end 14a toward the ending end 14b, and a region B, in which the cross-sectional area is approximately constant. Figure 7 As shown, the extrusion die 10 may or may not have a region B with a substantially constant cross-sectional area. The contour of region A of the outlet portion 14 may be as follows: Figure 7 The diagram shown can be composed of straight lines, but it can also be composed of curves.

[0109] Considering the excellent coercivity and residual magnetic flux density of the obtained hot-worked magnet, the ratio (area increase rate) of the area of ​​the terminal portion 14b of the outlet portion 14 to the area of ​​the starting end portion 14a is preferably 100.05 to 100.50%.

[0110] The temperature of the molded body at the starting end 14a of the outlet section 14 can be the same as the temperature of the molded body at the terminal section 14b, and the temperature of the molded body at the starting end 14a of the outlet section 14 can also be lower than the temperature of the molded body at the terminal section 14b. When the temperature of the molded body at the starting end 14a of the outlet section 14 is lower than the temperature of the molded body at the terminal section 14b, the difference (T1-T2) between the temperature T1 of the molded body at the starting end 14a of the outlet section 14 and the temperature T2 of the molded body at the terminal section 14b can be 10°C or more. From the perspective of excellent coercivity and remanent flux density of the obtained hot-worked magnet, it is preferable to be 30°C or more, more preferably 50°C or more. T1-T2 can also be 200°C or less.

[0111] The above describes the manufacturing methods of the hot-working magnets according to the first and second embodiments. However, the present invention is not limited to the above embodiments and various modifications can be made without departing from its spirit.

[0112] In addition, the end face shapes of the starting and ending points of the inlet, the plastic forming part, and the outlet are not limited to rectangular shapes. They can be elliptical shapes extending in one direction, or they can be circular, U-shaped, or V-shaped.

[0113] Example

[0114] The present invention will now be described in more detail by way of examples, but the present invention is not limited to any of the examples described below.

[0115] (Examples 1-3, 6 and Comparative Examples 1-3, 5)

[0116] <Preparation of Alloy Sheets>

[0117] Nd, Pr, Dy, Fe, FeB, Co, Ga, and Al were selected as starting materials for the permanent magnet. The starting materials were weighed and mixed to achieve the composition of the permanent magnet as shown in Table 1, and the mixture was adjusted. Using the mixed materials, thin sheets of the raw material alloy were obtained by ultra-rapid solidification. Specifically, firstly, the mixed materials were stored in a chamber. The stored raw material alloy was heated to 1300°C to obtain molten metal. The heating rate was set to 100°C / second. The molten metal was then injected from a nozzle into a roller using ultra-rapid solidification to obtain thin sheets of the alloy. The nozzle orifice diameter was set to 0.6 mm, the pressure in the nozzle orifice was set to 240 kPa, the pressure inside the chamber was set to 200 kPa, the roller circumferential speed was set to 40 m / s, and the atmosphere was set to argon.

[0118] <Step S1>

[0119] Magnetic powder is obtained by pulverizing the raw alloy into thin sheets using a cutting pulverizer. The pulverization is carried out in an argon atmosphere with an oxygen concentration of 20 ppm. Next, the obtained magnetic powder is classified to remove particles other than those with a particle size of 50–200 μm. That is, the particle size of the magnetic powder is adjusted to 50–200 μm. The classification atmosphere is an argon atmosphere with an oxygen concentration of 20 ppm.

[0120] <Step S2>

[0121] The obtained magnetic powder was molded using a compression molding machine to obtain a rectangular prism-shaped body (22mm×11mm×80mm). The molding pressure was set to 100MPa, the temperature to 750℃, the atmosphere to be argon, the oxygen concentration to be 20ppm, and the compression time to be 300 minutes.

[0122] <Step S3>

[0123] The resulting molded part is fed into an extrusion die through a punch to obtain a permanent magnet. The extrusion die uses... Figure 6The extrusion die has the shape shown. The end face shape of the starting end and the ending end (the entrance of the plastic processing section) of the inlet is a rectangular shape extending along the X-axis. The length of the long side is 30.000 mm, and the length of the short side is 7.000 mm. The end face shape of the starting end (the starting end of the exit section) and the ending end of the exit section is a rectangular shape extending along the Y-axis. The length of the long side is 30.000 mm, and the length of the short side is 7.000 mm. The temperature of the molded body at the starting end of the inlet and the starting end of the exit section is set to 750°C, and the temperature of the molded body at the ending end of the exit section is set to the values ​​shown in Table 1. The extrusion speed is set to 1 mm / s. The pressure at the ending end of the exit section is the value shown in Table 1. The unloading rate is the value shown in Table 1. The unloading rate is a value calculated based on the temperature of the molded body at each part of the die, according to the dimensions of the molded body calculated by the coefficient of linear expansion, and the dimensions of each part of the die. Specifically, it is calculated as follows. That is, ΔT, α, X2, L1, and L2 are defined as follows.

[0124] ΔT: The temperature difference (T2-T1) between the molded body temperature T2 at the end of the outlet and the temperature T1 (750°C) at the beginning of the inlet and the beginning of the outlet.

[0125] α: Coefficient of linear expansion along the easy magnetization axis of the permanent magnet (6.5 × 10⁻⁶) -6 / ℃).

[0126] X2: 7.000mm.

[0127] L1: 7.000mm.

[0128] L2: The length of the molded body at the end of the outlet section, in a direction parallel to the easy magnetization axis of the molded body. It is calculated using the following formula (a).

[0129] L2=(αΔT+1)×L1...Formula (a)

[0130] The unloading rate is calculated using the following formula (b).

[0131] Unloading rate = -{(L2-X2) / X2}×100……Equation (b)

[0132] (Examples 4, 5, 7, and Comparative Example 4)

[0133] In step S3, besides using Figure 7 The extrusion die of the shape shown is used instead Figure 6Except for the extrusion die of the shape shown, the process is the same as in Example 1 to obtain a permanent magnet. The extrusion die used in this example is the same as the one used in Example 1, except for the shape of the outlet portion. Regarding the extrusion die used in this example, the end face shape of the outlet portion is a rectangular shape extending along the Y-axis. The lengths of the long and short sides are the values ​​shown in Table 1.

[0134] (Examples 1-7, and Comparative Examples 1-5)

[0135] <Determination of Magnetic Properties>

[0136] The magnetic properties of the permanent magnets were measured using a BH tracer. As magnetic properties, the remanent magnetic flux density (Br) at 23°C, the coercivity (HcJ) at 23°C and 150°C, and the rectangularity ratio (Hk / HcJ) at 23°C were measured. The results are shown in Table 2.

[0137] <Calculation of Coercivity Temperature Coefficient>

[0138] Based on the measured coercivity, the temperature coefficient of coercivity (β) is calculated using the following formula (1). The results are presented in Table 2.

[0139] (coercivity at 150℃ - coercivity at 23℃) / {(150-23) × coercivity at 23℃} × 100……Equation (1)

[0140] <Determination of the thickness of the grain boundary between two grains>

[0141] Thin film samples for measurement were prepared using a focused ion beam (FIB) with a permanent magnet. HAADF-STEM images of the thin film samples were captured using a STEM scanner. The STEM scanner used was a Titan-G2 (trade name) manufactured by FEI Corporation. Thicknesses were measured at 10 locations representing two grain boundaries in the HAADF-STEM images. The average of the measured thicknesses was calculated and set as the thickness of the two grain boundaries. The results are presented in Table 2.

[0142] <Observation on the crystallinity of two grain boundaries>

[0143] The presence or absence of crystallinity in the two-grain boundary was confirmed. Specifically, in the HAADF-STEM images obtained from the measurement of the two-grain boundary thickness, an FFT (two-dimensional Fourier transform) was performed on any five or more regions (2×2 nm) constituting the two-grain boundary to obtain an image centered on a bright spot (direct point). If a bright spot other than the central bright spot (direct point) was observed in at least one of the images obtained from the five or more regions, the two-grain boundary was determined to be crystalline. The results are shown in Table 2.

[0144] <Determination of the orientation of two grain boundaries>

[0145] The orientation of the two-grain grain boundaries was determined using the obtained permanent magnets. Specifically, in the HAADF-STEM images obtained from the thickness measurement of the two-grain grain boundaries, FFT (two-dimensional Fourier transform) was performed on any five or more regions (2×2 nm) constituting the two-grain grain boundaries to obtain images centered on bright spots (direct points). By comparing multiple images, if the bright spots other than the central bright spot (direct point) did not overlap, the two-grain grain boundaries were determined to be unoriented. The results are shown in Table 2.

[0146] Table 1

[0147]

[0148] Table 2

[0149]

[0150] <R6T at two grain boundaries 13 Confirmation of the presence or absence of Ga >

[0151] For the permanent magnet obtained in Example 5, R6T in the two-grain grain boundary was confirmed by analyzing the composition and lattice constant of the grain boundary. 13 The presence or absence of Ga was determined. The composition of the grain boundaries was analyzed by energy-dispersive X-ray fluorescence (EDX) spectroscopy in HAADF-STEM images obtained from the thickness determination of the grain boundaries. The results are presented in Table 3. Table 3 also records the content ratio of R, the ratio of R to Ga (R / Ga), and the ratio of T to Ga (T / Ga).

[0152] Regarding the lattice constant of the two-grain boundary, the periodicity (interplanar spacing and lattice constant) was calculated by performing a two-dimensional Fourier transform on any six regions (2×2 nm) constituting the two-grain boundary in the HAADF-STEM image obtained from the thickness measurement of the two-grain boundary. The calculated lattice constants were 0.8034 nm along the a-axis and b-axis, and 2.278 nm along the c-axis. These measured values ​​are roughly consistent with reference values ​​(lattice constants along the a-axis and b-axis: 0.8072 nm, lattice constant along the c-axis: 2.295 nm, see CHde Groot, et al., Phys. Rev. B57 (1998) 11472). Based on the composition and lattice constant, it can be seen that the two-grain boundary contains R6T. 13 Ga.

[0153] Table 3

[0154]

[0155] Industrial availability

[0156] For example, the RTB-type permanent magnets of the present invention are suitable for use in electric motors of hybrid vehicles or electric vehicles.

Claims

1. A method for producing a hot worked magnet, wherein the hot worked magnet is an R-T-B based hot worked magnet containing a rare earth element R, a transition metal element T, and B, the R-T-B based hot worked magnet contains at least Nd as R, the R-T-B based hot worked magnet contains at least Fe as T, a thickness of a two-particle grain boundary is 3 nm or less, the two-particle grain boundary has crystallinity and is non-oriented, and the method for producing the hot worked magnet uses an extrusion die having a start end face and a terminal end face facing each other, the extrusion die is provided with a plastic working section and an exit section connected in this order toward the start end face and the terminal end face, the plastic working section has a start end portion and a terminal end portion, and the exit section has a start end portion and a terminal end portion, the method for producing the hot worked magnet includes a hot working step of performing hot extrusion of a molded body obtained by molding a magnetic powder from the start end face of the extrusion die through the plastic working section and the exit section up to the terminal end face, an area of an end face at the terminal end portion of the plastic working section is smaller than an area of an end face at the start end portion of the plastic working section, and a difference Tl-T2 between a temperature Tl of the molded body at the start end portion of the exit section and a temperature T2 of the molded body at the terminal end portion of the exit section is 30°C or more and 200°C or less.

2. A method for producing a hot worked magnet, wherein the hot worked magnet is an R-T-B based hot worked magnet containing a rare earth element R, a transition metal element T, and B, the R-T-B based hot worked magnet contains at least Nd as R, the R-T-B based hot worked magnet contains at least Fe as T, a thickness of a two-particle grain boundary is 3 nm or less, the two-particle grain boundary has crystallinity and is non-oriented, and the method for producing the hot worked magnet uses an extrusion die having a start end face and a terminal end face facing each other, the extrusion die is provided with a plastic working section and an exit section connected in this order toward the start end face and the terminal end face, the plastic working section has a start end portion and a terminal end portion, and the exit section has a start end portion and a terminal end portion, the method for producing the hot worked magnet includes a hot working step of performing hot extrusion of a molded body obtained by molding a magnetic powder from the start end face of the extrusion die through the plastic working section and the exit section up to the terminal end face, an area of an end face at the terminal end portion of the plastic working section is smaller than an area of an end face at the start end portion of the plastic working section, and a ratio of an area of the terminal end portion of the exit section with respect to an area of the start end portion of the exit section is 100.05 to 100.50%.

3. The method for producing a hot worked magnet according to claim 1 or 2, wherein a content of R in the R-T-B based hot worked magnet is 28 mass% or more and 33 mass% or less, and a content of B in the R-T-B based hot worked magnet is 0.8 mass% or more and 1.1 mass% or less.

4. The method for producing a hot worked magnet according to claim 1 or 2, wherein the R-T-B based hot worked magnet further contains Ga. The R-T-B based hot worked magnet includes: a plurality of main phase particles of a crystal containing R2T 14 B, and a two-particle grain boundary between two main phase particles adjacent in the easy magnetization axis direction. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The R-T-B based hot worked magnet includes: a plurality of main phase particles of a crystal containing R2T 14 B, and a two-particle grain boundary between two main phase particles adjacent in the easy magnetization axis direction. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The two-particle grain boundary is a phase comprising R6T 13 Ga.

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