Rare earth cobalt permanent magnet, its manufacturing method and device

Abstract

Provided are rare earth cobalt permanent magnets having excellent magnetic properties, a method for manufacturing such rare earth cobalt permanent magnets, and an apparatus including such rare earth cobalt permanent magnets. The rare earth cobalt permanent magnet consists of the following components: 23 to 27 mass% of a rare earth element R including Sm, 4.0 to 5.0 mass% of Cu, 22 to 27 mass% of Fe, 1.7 to 2.5 mass% of Zr, and Co as the balance and inevitable impurities, wherein the rare earth cobalt permanent magnet includes a plurality of crystal grains and grain boundary portions, and the size of the unit cell structure constituting the crystal grains is 100 nm to 600 nm.

Description

Technical Field

[0001] The present disclosure relates to rare earth cobalt permanent magnets, methods of manufacturing rare earth cobalt permanent magnets, and devices including the same. Background Art

[0002] As high-performance permanent magnets, rare earth cobalt permanent magnets such as Sm-Co magnets are known. Among such rare earth cobalt permanent magnets, rare earth cobalt permanent magnets containing, for example, Fe, Cu, Zr, etc. are well-known for having various useful characteristics such as improved magnetic properties.

[0003] For example, Japanese Unexamined Patent Application Publication No. 2015-188072 discloses a rare earth cobalt permanent magnet having a specific composition containing Sm, Cu, Fe, Zr, and Co and having a metal structure including a cell phase and a cell wall, the cell phase containing Sm2CO 17 phase, and the cell wall containing SmCo5 phase. Further, International Patent Publication No. WO2017 / 061126 discloses a rare earth cobalt permanent magnet having a specific composition containing Sm, Cu, Fe, Zr, and Co and having a metal structure including a plurality of crystal grains and a grain boundary portion, wherein the contents of Cu and Zr in the grain boundary portion are higher than those in the crystal grains. Summary of the Invention

[0004] Rare earth cobalt permanent magnets have characteristics of making the rate of change of magnetic force with respect to temperature small and making the permanent magnet rust-proof, and thus they are widely used in various devices. In order to further improve the performance of these devices, rare earth cobalt permanent magnets having more excellent magnetic properties are required.

[0005] An object of the present disclosure is to provide a rare earth cobalt permanent magnet having excellent magnetic properties, a method of manufacturing such a rare earth cobalt permanent magnet, and a device including such a rare earth cobalt permanent magnet.

[0006] A first exemplary aspect is a rare earth cobalt permanent magnet composed of the following components: 23 to 27 mass% of a rare earth element R including Sm, 4.0 to 5.0 mass% of Cu, 22 to 27 mass% of Fe, 1.7 to 2.5 mass% of Zr, and Co as the balance and inevitable impurities, wherein

[0007] the rare earth cobalt permanent magnet includes a plurality of crystal grains and a grain boundary portion, and

[0008] the size of the unit cell structure constituting the crystal grains is 100 nm to 600 nm.

[0009] In one aspect of the rare earth cobalt permanent magnet, the degree of orientation of the crystal grains is equal to or less than 60° with respect to the easy magnetization axis.

[0010] In one aspect of the rare earth cobalt permanent magnet, the relationships α < 0.045% / °C and β < 0.35% / °C are maintained in the temperature range of 20°C to 200°C, where α and β are the temperature coefficients of the residual magnetic flux density Br and the intrinsic coercivity Hcj, respectively.

[0011] In one aspect of the rare earth cobalt permanent magnet, when the intrinsic coercivity is represented by Hcj and the magnitude of the reverse magnetic field when the residual magnetic flux density Br is 90% is represented by Hk, the Hk / Hcj ratio is equal to or greater than 65% under the following conditions: the density of the rare earth cobalt permanent magnet is equal to or greater than 8.25 g / cm 3 ; its maximum energy product (BH)m is equal to or greater than 260 kJ / m 3 ; and the intrinsic coercivity Hcj is equal to or greater than 1600 kA / m.

[0012] Another exemplary aspect is a method for manufacturing a rare earth cobalt permanent magnet, which includes:

[0013] Step (I) of preparing an alloy, the alloy consisting of the following components: 23 to 27 mass% of a rare earth element R including Sm, 4.0 to 5.0 mass% of Cu, 22 to 27 mass% of Fe, 1.7 to 2.5 mass% of Zr, and Co as the balance and inevitable impurities;

[0014] Crushing step (II) of crushing the alloy into powder;

[0015] Pressing and forming step (III) of pressing the powder into a formed body;

[0016] Sintering step (IV) of heating the formed body to form a sintered body;

[0017] Step (V) of gradually cooling the sintered body at a cooling rate of 0.01°C / minute to 3°C / minute; and

[0018] Solution treatment step (VI) of heating the gradually cooled sintered body at 1120°C to 1170°C for 31 hours to 120 hours.

[0019] In one aspect of the method for manufacturing a rare earth cobalt permanent magnet, the sintering step (IV) is carried out at 1180°C to 1220°C for 20 minutes to 240 minutes.

[0020] In addition, the present disclosure also provides an apparatus including the above rare earth cobalt permanent magnet.

[0021] According to the present disclosure, it is possible to provide a rare earth cobalt permanent magnet having excellent magnetic properties, a method for manufacturing such a rare earth cobalt permanent magnet, and an apparatus including such a rare earth cobalt permanent magnet.

[0022] The above and other objects, features, and advantages of the present disclosure will be more fully understood from the following detailed description and the accompanying drawings, which are given by way of example only and thus are not to be considered as limiting the present disclosure. Description of the Drawings

[0023] Figure 1 is a schematic diagram for explaining the structure of a permanent magnet;

[0024] Figure 2 is a TEM (transmission electron microscope) image showing the unit cell structure of a rare earth cobalt permanent magnet according to Example 2;

[0025] Figure 3 is a TEM image showing the unit cell structure of a rare earth cobalt permanent magnet according to Comparative Example 1;

[0026] Figure 4 is a flowchart for explaining an embodiment of a manufacturing method; and

[0027] Figure 5 shows the measurement results of the degree of orientation of rare earth cobalt permanent magnets according to Example 2 and Comparative Example 1. Detailed Description of the Embodiments

[0028] Hereinafter, a rare earth cobalt permanent magnet, a method and an apparatus for manufacturing a rare earth cobalt permanent magnet according to the present disclosure will be described in order.

[0029] It should be noted that, unless otherwise specified, a numerical range such as "n - m" or "n to m" (i.e., "n to m") includes the lower limit value and the upper limit value.

[0030] In addition, the easy magnetization axis of the rare earth cobalt permanent magnet is also referred to as the c-axis.

[0031] <Rare Earth Cobalt Permanent Magnet>

[0032] The rare earth cobalt permanent magnet according to the present disclosure (hereinafter also referred to as the permanent magnet according to the present disclosure, etc., or simply as the permanent magnet) is composed of the following components: 23 to 27 mass% of a rare earth element R including Sm, 4.0 to 5.0 mass% of Cu, 22 to 27 mass% of Fe, 1.7 to 2.5 mass% of Zr, and the balance Co and inevitable impurities, where

[0033] the rare earth cobalt permanent magnet includes a plurality of crystal grains and grain boundary portions, and

[0034] the size of the unit cell structure constituting the crystal grains is 100 nm to 600 nm.

[0035] The rare earth element R is a collective term for Sc, Y, and the lanthanide elements. In addition, in the permanent magnet according to the present disclosure, the rare earth element R includes at least Sm. By containing the rare earth element in the above ratio, a permanent magnet having high magnetic anisotropy and high coercivity can be obtained. The rare earth element R may consist only of Sm, or may be a combination of Sm and other rare earth elements. Considering the magnetic properties, other rare earth elements R are preferably at least one element selected from Nd, Pr, and Ce. Considering the magnetic properties, based on all rare earth elements, the rare earth element R preferably contains 70% by mass or more than 70% by mass, more preferably 80% by mass or more than 80% by mass of Sm.

[0036] The rare earth cobalt permanent magnet contains 4.0 to 5.0% by mass of Cu. By containing 4.0% by mass or more than 4.0% by mass of Cu, the rare earth cobalt permanent magnet becomes a permanent magnet having high coercivity. In addition, by limiting the content of Cu to 5.0% by mass or less than 5.0% by mass, a decrease in magnetization intensity is prevented.

[0037] The rare earth cobalt permanent magnet contains 22 to 27% by mass of Fe. By adjusting the content of Fe to a value within this range, a cell structure with a cell size of 100 nm to 600 nm may be formed in the manufacturing method described later. In addition, by containing 22% or more than 22% of Fe, the saturation magnetization intensity is increased. In addition, by limiting the content of Fe to 27% or less than 27%, the rare earth cobalt permanent magnet becomes a permanent magnet having high coercivity.

[0038] In addition, the rare earth cobalt permanent magnet contains 1.7% to 2.5% of Zr. By containing Zr in the above range, a permanent magnet having a high maximum magnetic energy product (BH)m can be obtained, and the maximum magnetic energy product is the maximum static magnetic energy that the magnet can maintain.

[0039] In addition, the balance (i.e., 38.5% to 49.3%) of the permanent magnet consists of Co and inevitable impurities.

[0040] By containing Co, the thermal stability of the permanent magnet is improved. On the other hand, when the content of Co is too large, the content of Fe is relatively reduced, thereby increasing the possibility that magnetization may deteriorate. From these aspects, the content of Co is preferably 38.5% to 49.3%.

[0041] The permanent magnet according to the present disclosure may contain inevitable impurities within a range that does not impair the effects of the present disclosure. Inevitable impurities are elements that inevitably mix into the permanent magnet from raw materials or during the manufacturing process. Examples of inevitable impurities include, but are not limited to, C (carbon), N (nitrogen), P (phosphorus), S (sulfur), Al (aluminum), Ti (titanium), Cr (chromium), Mn (manganese), Ni (nickel), Hf (hafnium), Sn (tin), and W (tungsten).

[0042] Based on the total amount of the rare earth cobalt permanent magnet, the total content ratio of inevitable impurities is preferably 5% by mass or less than 5% by mass, more preferably 1% by mass or less than 1% by mass, still more preferably 0.1% by mass or less than 0.1% by mass.

[0043] Next, the structure of the permanent magnet will be described with reference to Figure 1 FIG. Figure 1 is a schematic cross-sectional view showing a part of the cross-section of the permanent magnet. As Figure 1 shown in the example, the permanent magnet 10 includes a plurality of crystal grains 1 (the region surrounded by the solid line in the figure), and the grain boundary portion 2 (the solid line in the figure) between the crystal grains 1. Each crystal grain 1 has a unit cell phase 3 (the region surrounded only by the dotted line or the region surrounded by the dotted line and the solid line in the figure) and a unit cell wall 4 (the dotted line in the figure). The unit cell phase 3 includes a crystal phase having a Th2Zn 17 type structure (hereinafter also referred to as "2-17 phase"). The unit cell wall 4 includes a crystal phase having an RCo5 type structure (hereinafter also referred to as "1-5 phase") and surrounds the unit cell phase. In the present disclosure, the unit cell structure is a combination of a unit cell phase 3 and a unit cell wall 4 surrounding the unit cell phase, and it is the smallest unit constituting the crystal grain. The unit cell size represents the length of the unit cell wall 4 (the length of its long side).

[0044] As described above, the permanent magnet has a unit cell phase, and the unit cell phase has a crystal phase including a Th2Zn 17 type structure as the main phase. The Th2Zn 17 type structure is a crystal structure having an R-3m type space group. In the permanent magnet according to the present disclosure, the Th portion is occupied by a rare earth element and Zr, and the Zn portion is Co, Cu, Fe, and Zr. In addition, as described above, the permanent magnet has a unit cell wall, and the unit cell wall includes a crystal phase having an RCo5 type structure. In the crystal phase having an RCo5 type structure, the R portion is a rare earth element and Zr, and the Co portion is Co, Cu, and Fe.

[0045] In the permanent magnet according to the present disclosure, when the domain wall is pinned between two phases, that is, when the domain wall moves between the 2-17 phase and the 1-5 phase, it is inferred that coercivity is generated. In addition, the permanent magnet is characterized in that when two-phase separation occurs, the squareness ratio increases, and as Fe and Cu are respectively enriched in the 2-17 phase and the 1-5 phase, the maximum energy product (BH)m increases, so that the magnetic properties are significantly affected, and the composition ratio has a significant impact. In addition, on the entire permanent magnet, the more constant the composition ratio between the 2-17 phase and the 1-5 phase, the better the magnetic properties that the permanent magnet can exhibit. In addition, the yield can be increased when the permanent magnet is processed into small pieces.

[0046] Since the unit cell size of the permanent magnet 10 is 100 nm to 600 nm, it has excellent magnetic properties.

[0047] The structure of the permanent magnet according to the present disclosure is made uniform by heat treatment such as sintering, gradual cooling / solution treatment, and rapid cooling. Additionally, by performing aging treatment, the permanent magnet is separated into two phases, namely the 2-17 phase and the 1-5 phase. TEM (transmission electron microscopy) and EDX (energy-dispersive X-ray spectroscopy) are used to determine the unit cell size and analyze the composition. TEM is a technique for observing a thin sample by irradiating the thin sample with an electron beam and forming an image thereof from the electrons passing through the thin sample. EDX is a technique for identifying elements by detecting the energy and intensity of characteristic X-rays emitted when the sample is irradiated with an electron beam.

[0048] Figure 2 is a TEM image of the rare earth cobalt permanent magnet according to Example 2, which will be described later. Additionally, Figure 3 is a TEM image of the rare earth cobalt permanent magnet according to Comparative Example 1, which will be described later. Figure 2 and Figure 3 each show some grains 1. As Figure 2 shown, the unit cell phase 3 and the unit cell wall 4 surrounding the unit cell phase are observed. Additionally, by comparing Figure 2 and Figure 3 it can be seen that in the permanent magnet according to the example, a permanent magnet having a larger unit cell size of 100 to 600 nm is formed by the manufacturing method described later. Therefore, the permanent magnet has excellent magnetic properties.

[0049] Additionally, the inventors of the present application have noted the degree of orientation as an index for achieving excellent magnetic properties. The degree of orientation is directly related to the magnitude of the magnetization intensity and is an important factor in discussing magnetic properties. The degree of orientation is a physical quantity indicating how much of the magnetization intensity of a magnetic material is oriented (i.e., aligned) in the easy magnetization direction. In particular, when the degree of orientation of the grains is equal to or less than 60° with respect to the easy magnetization axis, the remanent flux density Br and the rectangular ratio Hk / Hcj tend to increase. In particular, the degree of orientation of the grains with respect to the easy magnetization axis is preferably equal to or less than 55°, and more preferably equal to or less than 50°. According to the manufacturing method according to the present disclosure, which will be described later, it can be seen that a permanent magnet having a degree of orientation of the grains equal to or less than 60° with respect to the easy magnetization axis can be obtained.

[0050] Examples of methods for detecting the degree of orientation include the EBSD (electron backscatter diffraction pattern) method. In the EBSD method, for example, when an electron beam is applied to the cross-section of the permanent magnet at an incident angle of about 60° to 70°, diffracted electron beams are obtained in each crystal plane in a region about 50 nm or shorter than 50 nm from the cross-section. By analyzing the electron diffraction of the backscattered electrons generated by these diffracted electron beams, information regarding the grain orientation analysis can be obtained.

[0051] Figure 5Shows the measurement results of the degree of orientation of the rare earth cobalt permanent magnets according to Example 2 (left) and Comparative Example 1 (right). In Figure 5 it, it can be evaluated (i.e., considered) that the more concentrated the diffracted electron beam is at the center of the circle, the higher the degree of orientation. As Figure 5 shown, the diffracted electron beam in Example 2 is concentrated at the center of the circle, which means that the degree of orientation of the crystal grains has been limited to a range equal to or less than 60° with respect to the easy magnetization axis. On the other hand, in Comparative Example 1, the diffracted electron beam diffuses (or scatters) to the peripheral region, and the degree of orientation is low. As described above, the permanent magnet according to the embodiment has a high degree of crystal grain orientation, and has a high remanent flux density Br and a high squareness ratio Hk / Hcj.

[0052] In addition, the inventors have noticed the temperature coefficients of the remanent flux density Br and the intrinsic coercivity Hcj. The temperature coefficient is a coefficient representing the change in the remanent flux density Br or the intrinsic coercivity Hcj under a temperature change of 1 °C. Here, α and β are used to represent the temperature coefficient of the remanent flux density Br and the temperature coefficient of the intrinsic coercivity Hcj, respectively. Then, by adjusting these temperature coefficients so that the relationship α < 0.045% / °C and β < 0.35% / °C is maintained in the temperature range of 20 °C to 200 °C, preferably α < 0.040% / °C and β < 0.30% / °C, in this temperature range, the change in the magnetic properties of the permanent magnet is reduced, and thus a permanent magnet with excellent temperature stability is obtained. According to the manufacturing method described later, it is very likely to obtain a permanent magnet that satisfies the relationship between the above temperature coefficients.

[0053] <Method for manufacturing rare earth cobalt permanent magnet>

[0054] The method for manufacturing a rare earth cobalt permanent magnet according to the present disclosure (hereinafter also referred to as the manufacturing method according to the present disclosure, etc., or simply referred to as the manufacturing method) includes:

[0055] Step (I) of preparing an alloy, the alloy consisting of the following components: 23 to 27% by mass of a rare earth element R including Sm, 4.0 to 5.0% by mass of Cu, 22 to 27% by mass of Fe, 1.7 to 2.5% by mass of Zr, and Co as the balance and inevitable impurities;

[0056] Crushing step (II) of crushing the alloy into powder;

[0057] Pressing and molding step (III) of pressing the powder into a molded body;

[0058] Sintering step (IV) of heating the molded body to form a sintered body;

[0059] Step (V) of gradually cooling the sintered body at a cooling rate of 0.01 °C / min to 3 °C / min; and

[0060] A solution treatment step (VI) of heating the gradually cooled sintered body at 1120 °C to 1170 °C for 31 hours to 120 hours.

[0061] According to the above manufacturing method, a rare earth cobalt permanent magnet including a plurality of crystal grains and grain boundary portions can be manufactured, wherein the size of the unit cell structure constituting the crystal grains is 100 nm to 600 nm. Each step in the method for manufacturing a rare earth cobalt permanent magnet according to this embodiment will be described below with reference to Figure 4 the flowchart shown.

[0062] First, an alloy composed of the following components is prepared: 23 to 27 mass% of a rare earth element R including Sm, 4.0 to 5.0 mass% of Cu, 22 to 27 mass% of Fe, 1.7 to 2.5 mass% of Zr, and Co as the balance and inevitable impurities (step S1: step (I)). The method for preparing the alloy is not limited to any specific method. For example, the alloy can be prepared from a commercially available alloy having a desired composition, or by mixing the above elements to obtain a desired composition.

[0063] Specific examples of mixing the elements will be described below, but the present disclosure is not limited to this example method.

[0064] First, each metal element of the desired rare earth element, Fe, Cu, and Co as components and a base alloy are prepared. It should be noted that an alloy having a eutectic temperature composition is preferably selected as the base alloy because it is easy to make the composition of the obtained alloy uniform. In this manufacturing method, FeZr or CuZr is preferably selected and used as the base alloy. As an example of FeZr, FeZr containing about 20% of Fe and about 80% of Zr is suitable. In addition, as an example of CuZr, CuZr containing about 50% of Cu and 50% of Zr is suitable.

[0065] A uniform alloy can be obtained by the following steps: mixing the above components to have a desired composition, placing the mixture in a crucible made of Al or the like, and melting the mixture in a vacuum of 1×10 -2 Torr or less than 1×10 -2 Torr or in an inert gas atmosphere by using a high-frequency furnace. In addition, the present disclosure may include a step of casting the molten alloy by using a mold to obtain an alloy ingot. Alternatively, as a different method, a sheet-like alloy (tape casting method) having a thickness of about 1 mm can be manufactured by dropping the molten alloy onto a copper roll.

[0066] In the case of forming an alloy ingot by the above casting, the manufacturing method preferably includes, before step (II) (to be described later), a step of heat-treating the alloy ingot at a solution treatment temperature for not less than one hour and not more than 20 hours. By this step, the composition can be made more uniform. It should be noted that the solution treatment temperature of the alloy ingot can be appropriately adjusted according to the composition of the alloy, etc.

[0067] Next, the alloy is pulverized into powder (step S2: step (II)). The method for pulverizing the alloy is not limited to any specific method and can be selected from known methods as appropriate. For example, first, the alloy ingot or sheet alloy is coarsely pulverized to a size of about 100 μm to 500 μm by a known pulverizer, and then finely pulverized by a ball mill or a jet mill. Although the average particle size of the powder is not limited to any specific value, the alloy ingot or sheet alloy can be pulverized into powder with an average particle size of not less than 1 μm and not more than 10 μm, preferably about 6 μm, so that the sintering time of the sintering step (to be described later) can be shortened, and a uniform permanent magnet can be manufactured.

[0068] Next, the obtained powder is press-molded to obtain a molded body having a desired shape (step S3: step (III)). In the manufacturing method according to the present disclosure, it is preferable to press-mold the obtained powder in a constant magnetic field to align the crystal orientations, thereby improving the magnetic properties. There is no particular limitation on the relationship between the direction of the magnetic field and the pressing direction, and the relationship can be selected as appropriate according to the shape of the product, etc. For example, when manufacturing an annular magnet or a thin plate-shaped magnet, parallel magnetic field pressing can be used, in which the magnetic field is applied in a direction parallel to the pressing direction. On the other hand, in order to obtain excellent magnetic properties, it is preferable to use right-angle magnetic field pressing, in which the magnetic field is applied at a right angle to the pressing direction.

[0069] The magnitude of the magnetic field is not limited to any specific value, and depending on the use of the product, etc., the magnetic field can be, for example, a magnetic field of 15 kOe or weaker than 15 kOe, or a magnetic field of 15 kOe or stronger than 15 kOe. However, in order to obtain excellent magnetic properties, it is preferable to perform press-molding in a magnetic field of 15 kOe or stronger than 15 kOe. In addition, the pressure in the press-molding can be appropriately adjusted according to the size, shape, etc. of the product. For example, the pressure can be 0.5 to 2.0 tons / cm 2 . That is, in the method for manufacturing a rare earth cobalt permanent magnet according to the present disclosure, in order to achieve excellent magnetic properties, it is particularly preferable to press-mold the powder under the condition of a magnetic field of 15 kOe or stronger than 15 kOe, while applying a pressure of not less than 0.5 tons / cm 2 and not higher than 2.0 tons / cm 2 perpendicular to the magnetic field.

[0070] Next, the formed body is heated to obtain a sintered body (Step S4: Step (IV)).

[0071] In this manufacturing method according to the present disclosure, the sintering conditions can be arbitrarily determined as long as the obtained sintered body is sufficiently densified. For example, known conditions can be used. To densify the sintered body, the sintering temperature is preferably 1180°C to 1220°C. By adjusting the temperature to 1220°C or lower than 1220°C, volatilization of rare earth elements, especially Sm, is prevented, and thus a permanent magnet having excellent magnetic properties can be manufactured. The sintering time is preferably 20 minutes to 240 minutes, more preferably 30 minutes to 180 minutes, to sufficiently densify the sintered body while preventing Sm volatilization. In addition, to prevent oxidation, it is preferable to perform the above sintering step in a vacuum or inert atmosphere of 10 Pa or lower than 10 Pa, more preferably in a vacuum of 10 Pa or lower than 10 Pa.

[0072] Next, the obtained sintered body is gradually cooled at a cooling rate of 0.01°C / minute to 3°C / minute (Step S5: Step (V)). By slowly and gradually cooling at a cooling rate of 3°C / minute or lower than 3°C / minute, a cell structure with cell walls of 100 nm to 600 nm is likely to be formed in the grains. In addition, a cooling rate of 0.01°C / minute is sufficient as the lower limit of the cooling rate, but considering the manufacturing speed, a cooling rate of 0.05°C / minute or higher than 0.05°C / minute is preferred. The temperature is lowered to the solution treatment temperature for the solution treatment step (to be described below).

[0073] Next, the gradually cooled sintered body is subjected to a solution treatment, in which the sintered body is heated at 1120°C to 1170°C for 31 hours to 120 hours (Step S6: Step (VI)). Generally, in order to improve productivity and at the same time obtain a cell size of 100 nm to 600 nm, it is preferred to perform the above steps (IV) to (VI) as a series of steps.

[0074] By heating the sintered body at 1120°C or higher than 1120°C, the composition of the formed body can be made uniform, and the aforementioned 1-7 phase can be formed in the aging treatment step (to be described later). The 1-7 phase is a precursor that makes the crystal phase of the Th2Zn 17 type structure the main phase. However, if the heating temperature exceeds 1170°C, conversely, it is less likely to form the 1-7 phase, and volatilization of rare earth elements may be promoted. Since the optimum solution treatment temperature of the sintered body varies according to the composition of the sintered body, it is preferred to appropriately adjust the heating temperature within the above temperature range.

[0075] In addition, in order to fully form the 1-7 phases and adjust the unit cell size to 100 nm to 600 nm, the solution treatment time is adjusted to 31 hours or longer than 31 hours. On the other hand, in order to prevent Sm volatilization and adjust the unit cell size to 100 nm to 600 nm, the solution treatment time is adjusted to 120 hours or shorter than 120 hours. When the solution treatment time is shorter than 31 hours or longer than 120 hours, the unit cell size tends to decrease.

[0076] Through the above steps, a rare earth cobalt permanent magnet including a plurality of grains and grain boundary portions can be manufactured, wherein the size of the unit cell structure constituting the grains is 100 nm to 600 nm. The manufacturing method may further include other steps as needed. As other steps, the manufacturing method preferably includes an aging treatment step (S7) of the rare earth cobalt permanent magnet after the solution treatment.

[0077] By performing the aging treatment, it is more likely to form the unit cell phase of the 2-17 phase and the unit cell wall of the 1-5 phase. The aging temperature is not limited to any specific temperature. However, in order to more easily obtain a rare earth cobalt permanent magnet including grains with a unit cell structure of 100 nm to 600 nm, it is preferable to hold the permanent magnet at a temperature of not less than 700 °C and not higher than 900 °C for not less than 2 hours and not more than 20 hours, and then adjust the cooling rate to 2 °C / minute or lower than 2 °C / minute until the permanent magnet is cooled to 400 °C or lower than 400 °C. Holding the permanent magnet at a temperature of not less than 700 °C and not higher than 900 °C for not less than 2 hours and not more than 20 hours can maintain the unit cell size. In particular, it is preferable to perform the aging treatment in a temperature range of not less than 800 °C and not higher than 850 °C or lower than 850 °C. In addition, in order to obtain excellent magnetic properties, the cooling rate is preferably adjusted to 2 °C / minute or lower than 2 °C / minute, more preferably 0.5 °C / minute or lower than 0.5 °C / minute. If the cooling rate is too high, the elements cannot be enriched into the 2-17 phase and the 1-5 phase, so excellent magnetic properties cannot be obtained.

[0078] Step (VI) and the aging treatment are preferably performed as a series of steps. In this case, the cooling method performed between step (VI) and the aging treatment is not limited to any specific method. However, in order to maintain the obtained unit cell size, it is preferable to rapidly cool the permanent magnet at a cooling rate of 60 °C / minute or higher than 60 °C / minute. In particular, the unit cell size can be maintained by shortening the time for the temperature of the permanent magnet to drop from the solution treatment temperature to 600 °C. The cooling rate of the rapid cooling can be 60 °C / minute or higher than 60 °C / minute, preferably 70 °C / minute or higher than 70 °C / minute, and more preferably 80 °C / minute or higher than 80 °C / minute. In addition, the upper limit of the cooling rate of the rapid cooling is preferably, for example, 250 °C or lower than 250 °C, although it depends on the shape of the compact.

[0079] According to the manufacturing method of the present application, a rare earth cobalt permanent magnet can be obtained from an ingot having a predetermined composition, wherein the size of the unit cell structure constituting the crystal grains is 100 nm to 600 nm, and the degree of orientation of the crystal grains may be equal to or less than 60° with respect to the easy magnetization axis. In addition, the permanent magnet has the following excellent magnetic properties. That is, in the permanent magnet, the relationships α < 0.045% / °C and β < 0.35% / °C may be maintained in the temperature range of 20°C to 200°C, where α and β are the temperature coefficients of the residual magnetic flux density Br and the intrinsic coercive force Hcj, respectively. In addition, when the intrinsic coercive force is represented by Hcj and the magnitude of the reverse magnetic field when the residual magnetic flux density Br is 90% is represented by Hk, the Hk / Hcj ratio is equal to or greater than 65% under the following conditions: the density of the rare earth cobalt permanent magnet is equal to or greater than 8.25 g / cm 3 ; its maximum energy product (BH)m is equal to or greater than 260 kJ / m 3 ; and the intrinsic coercive force Hcj is equal to or greater than 1600 kA / m.

[0080] <Device>

[0081] The present disclosure also provides a device including the above permanent magnet. Examples of such a device include a clock (watch), a motor, various instruments, a communication device, a computer terminal, a speaker, a video disc, and a sensor. In addition, since the magnetic force of the rare earth cobalt permanent magnet according to the present disclosure is unlikely to deteriorate even at a high ambient temperature, it can be applied to an angle sensor, an ignition coil, a drive motor (e.g., a drive motor for an HEV (hybrid electric vehicle)) in a motor vehicle compartment, etc.

[0082] [Examples]

[0083] Hereinafter, the present disclosure will be described in a specific manner with reference to examples and comparative examples. It should be noted that the present disclosure is not limited by the description of the following examples.

[0084] <Examples 1 to 5>

[0085] Base alloys each containing 20% of Fe and 80% of Zr and various components were prepared to obtain the compositions of Examples 1 to 5 shown in Table 1. Then, they were melted by a high-frequency furnace, and the melt was cast into alloy ingots.

[0086] Next, the obtained base alloy was coarsely pulverized in an inert gas so that the average diameter was about 100 μm to 500 μm, and then finely pulverized into powder in an inert gas using a ball mill so that the average diameter was about 6 μm. The powder was pressed at a pressure of 1 ton / cm in a magnetic field of 15 kOe to obtain a molded body. 2 of pressure.

[0087] In a vacuum of 10 Pa or less than 10 Pa, these green compacts were heated from the degassing temperature to the sintering temperature at a rate of 5 °C per minute, and then sintered at 1210 °C for 100 minutes. After sintering, the temperature was then lowered to the solution treatment temperature of 1140 °C at a cooling rate of 0.5 °C per minute, and solution treatment was carried out at the solution treatment temperature for 35 hours. After solution treatment, the sintered body was held at 850 °C for 12 hours, and aging treatment was carried out under the condition that the sintered body was gradually cooled to 350 °C at a cooling rate of 0.5 °C per minute. Through these steps, the rare earth cobalt permanent magnets according to Examples 1 to 5 were obtained.

[0088] <Comparative Examples 1 and 2>

[0089] Except that the composition of the ingot was changed to the compositions of Comparative Examples 1 and 2 shown in Table 1, the rare earth cobalt permanent magnets according to Comparative Examples 1 and 2 were obtained in the same manner as in Example 1 above.

[0090] <Examples 6 to 11>

[0091] Base alloys each containing 20% Fe and 80% Zr and various components were prepared to obtain the compositions of Examples 6 to 11 shown in Table 2. Then, they were melted by a high-frequency furnace, and the melt was cast into alloy ingots.

[0092] Next, the obtained base alloy was coarsely crushed in an inert gas so that the average diameter was about 100 μm to 500 μm, and then finely crushed into powder in an inert gas using a ball mill so that the average diameter was about 6 μm. By pressing this powder in a magnetic field of 15 kOe at a pressure of 1 ton / cm 2 a green compact was obtained.

[0093] In a vacuum of 10 Pa or less than 10 Pa, these green compacts were heated from the degassing temperature to the sintering temperature at a rate of 4 °C per minute, and then sintered at the sintering temperature shown in Table 2 for the sintering time shown in Table 2. After sintering, the temperature was then lowered to the solution treatment temperature at the cooling rate shown in Table 2, and solution treatment was carried out at the solution treatment temperature shown in Table 2 for the solution treatment time shown in Table 2. After solution treatment, the sintered body was held at 850 °C for 10 hours, and aging treatment was carried out under the condition that the sintered body was gradually cooled to 350 °C at a cooling rate of 0.5 °C per minute. Through these steps, the rare earth cobalt permanent magnets according to Examples 6 to 11 were obtained.

[0094] <Examples 12 to 16>

[0095] Base alloys each containing 20% Fe and 80% Zr and various components were prepared to obtain the compositions of Examples 12 to 16 shown in Table 3. Then, they were melted by a high-frequency furnace and the melt was cast into alloy ingots.

[0096] Next, the obtained base alloys were coarsely pulverized in an inert gas so that the average diameter was about 100 μm to 500 μm, and then finely pulverized into powders in an inert gas using a ball mill so that the average diameter was about 6 μm. The powders were pressed under a pressure of 1 ton / cm 2 in a magnetic field of 15 kOe to obtain compacts.

[0097] In a vacuum of 10 Pa or less than 10 Pa, these compacts were heated from the degassing temperature to the sintering temperature at a rate of 3 °C / minute, and then sintered at the sintering temperature shown in Table 3 for the sintering time shown in Table 3. After sintering, the temperature was then lowered to the solution treatment temperature at the cooling rate shown in Table 3, and solution treatment was carried out at the solution treatment temperature shown in Table 3 for the solution treatment time shown in Table 3. After solution treatment, the sintered body was held at 850 °C for 10 hours, and aging treatment was carried out under the condition that the sintered body was gradually cooled to 350 °C at a cooling rate of 0.5 °C / minute. Through these steps, rare earth cobalt permanent magnets according to Examples 12 to 16 were obtained.

[0098] <Examples 17 to 20>

[0099] Base alloys each containing 20% Fe and 80% Zr and various components were prepared to obtain the compositions of Examples 17 to 20 shown in Table 4. Then, they were melted by a high-frequency furnace and the melt was cast into alloy ingots.

[0100] Next, the obtained base alloys were coarsely pulverized in an inert gas so that the average diameter was about 100 μm to 500 μm, and then finely pulverized into powders in an inert gas using a ball mill so that the average diameter was about 6 μm. The powders were pressed under a pressure of 1 ton / cm 2 in a magnetic field of 15 kOe to obtain compacts.

[0101] In a vacuum of 10 Pa or less than 10 Pa, these formed bodies are heated from the degassing temperature to the sintering temperature at a rate of 2 °C per minute, and then sintered at the sintering temperature shown in Table 4 for the sintering time shown in Table 4. After sintering, the temperature is then lowered to the solution treatment temperature at the cooling rate shown in Table 4, and solution treatment is carried out at the solution treatment temperature shown in Table 4 for the solution treatment time shown in Table 4. After solution treatment, the sintered body is held at 850 °C for 10 hours and age treatment is carried out under the condition that the sintered body is gradually cooled to 350 °C at a cooling rate of 0.5 °C per minute. Through these steps, rare earth cobalt permanent magnets according to Examples 17 to 20 are obtained.

[0102] <Comparative Example 3>

[0103] A rare earth cobalt permanent magnet according to Comparative Example 3 is obtained in the same manner as in Example 17, except that the solution treatment temperature is changed to 1110 °C.

[0104] <Examples 21 to 23>

[0105] Base alloys each containing 20% Fe and 80% Zr and various components are prepared to obtain the compositions of Examples 21 to 23 shown in Table 5. Then, they are melted by a high-frequency furnace and the melt is cast into alloy ingots.

[0106] Next, the obtained base alloy is coarsely pulverized in an inert gas so that the average diameter is about 100 μm to 500 μm, and then finely pulverized into powder in an inert gas by using a ball mill so that the average diameter is about 6 μm. By pressing this powder in a magnetic field of 15 kOe at a pressure of 1 ton / cm 2 the formed body is obtained.

[0107] In a vacuum of 10 Pa or less than 10 Pa, these formed bodies are heated from the degassing temperature to the sintering temperature at a rate of 5 °C per minute, and then sintered at the sintering temperature shown in Table 5 for the sintering time shown in Table 5. After sintering, the temperature is then lowered to the solution treatment temperature at the cooling rate shown in Table 5, and solution treatment is carried out at the solution treatment temperature shown in Table 5 for the solution treatment time shown in Table 5. After solution treatment, the sintered body is held at 850 °C for 10 hours and age treatment is carried out under the condition that the sintered body is gradually cooled to 350 °C at a cooling rate of 0.5 °C per minute. Through these steps, rare earth cobalt permanent magnets according to Examples 21 to 23 are obtained.

[0108] <Comparative Examples 4 to 5>

[0109] Rare earth cobalt permanent magnets of Comparative Examples 4 and 5 are obtained in the same manner as in Example 21, except that the sintering time, solution treatment time, and cooling rate are changed as shown in Table 5.

[0110] <Examples 24 to 33>

[0111] Examples 24 to 33 of rare earth cobalt permanent magnets were obtained in the same manner as in Example 1, except that the composition of the ingot, sintering conditions, solution treatment conditions, and cooling rate were changed as shown in Table 6.

[0112] <Comparative Examples 6 to 14>

[0113] Comparative Examples 6 to 14 of rare earth cobalt permanent magnets were obtained in the same manner as in Example 1, except that the composition of the ingot, sintering conditions, solution treatment conditions, and cooling rate were changed as shown in Table 6.

[0114] <Evaluation of rare earth cobalt permanent magnets>

[0115] The magnetic properties of the rare earth cobalt permanent magnets (which were kept as shaped bodies) obtained in the above Examples and Comparative Examples were measured. The magnetic properties were measured using a B-H tracer. The measured magnetic properties were the maximum magnetic energy product (BH)m, coercivity (Hcj), and rectangular ratio expressed as the ratio of the magnetic field (Hk) to the coercivity (Hcj) (Hk / Hcj). Tables 1 to 6 show the results. In addition, samples having the same composition as the rare earth cobalt permanent magnets according to the Examples and Comparative Examples were appropriately processed while manufacturing the rare earth cobalt permanent magnets according to the Examples and Comparative Examples. Then, they were observed using a transmission electron microscope (TEM) and their composition was analyzed. In addition, their degree of orientation, temperature coefficient, and density were also measured. Tables 1 to 6 show the results.

[0116]

[0117]

[0118]

[0119]

[0120]

[0121]

[0122] [Summary of results]

[0123] In the embodiments shown in Table 1, except for changing the content of Fe and the composition of rare earth elements, the manufacturing conditions are the same for each other. As shown in Table 1, for the permanent magnets according to Embodiments 1 to 5, in each of which the content of Fe is 22 to 27 mass%, all the permanent magnets are manufactured by the manufacturing method according to the present disclosure, and their unit cell sizes are 100 nm to 600 nm; the degree of grain orientation with respect to the easy magnetization axis is equal to or less than 60°; in the temperature range of 20°C to 200°C, the temperature coefficient α of the remanent flux density is less than 0.045% / °C (α < 0.045% / °C); the temperature coefficient β of the intrinsic coercivity is less than 0.35% / °C (β < 0.35% / °C). It has been found that in all the permanent magnets according to Embodiments 1 to 5, the density is equal to or higher than 8.25 g / cm 3 : the maximum energy product (BH)m is equal to or greater than 260 kJ / m 3 ; the coercivity Hcj is equal to or greater than 1600 kA / m; the squareness ratio Hk / Hcj is equal to or higher than 65%. That is, it has been found that these permanent magnets have excellent magnetic properties.

[0124] On the other hand, in Comparative Example 1 with a Fe content of 20 mass% and Comparative Example 2 with a Fe content of 29 mass%, even when they are manufactured under the same manufacturing conditions, the unit cell size is less than 100 nm. That is, none of them obtain a permanent magnet with excellent magnetic properties.

[0125] Embodiments 6 to 11 shown in Table 2 are embodiments in which the sintering temperature is changed. In all the permanent magnets obtained in Embodiments 6 to 11, the unit cell size is 100 nm to 600 nm, and they have excellent magnetic properties. Among them, in Embodiments 6 to 10 with a sintering temperature of 1180°C to 1220°C, the degree of orientation is equal to or less than 60°C; in the temperature range of 20°C to 200°C, the temperature coefficient α of the remanent flux density is less than 0.045% / °C (α < 0.045% / °C); the temperature coefficient β of the intrinsic coercivity is less than 0.35% / °C (β < 0.35% / °C). In addition, they have excellent magnetic properties. Embodiments 12 to 16 shown in Table 3 are embodiments in which the sintering time is changed. In all the permanent magnets obtained in Embodiments 12 to 16, the unit cell size is 100 nm to 600 nm, and they have excellent magnetic properties. Among them, in Embodiments 12 to 15 with a sintering time of 20 minutes to 240 minutes, the degree of orientation is equal to or less than 60°C; in the temperature range of 20°C to 200°C, the temperature coefficient α of the remanent flux density is less than 0.045% / °C (α < 0.045% / °C); the temperature coefficient β of the intrinsic coercivity is less than 0.35% / °C (β < 0.35% / °C). In addition, they have excellent magnetic properties.

[0126] The examples shown in Table 4 are examples mainly changing the solution treatment temperature. In the permanent magnet according to Comparative Example 3 in which the solution treatment temperature is lowered to 1110 °C, a cell structure with a cell size of 100 nm or larger than 100 nm is not formed, and the degree of orientation exceeds 60°. In addition, the magnetic properties of the permanent magnet according to Comparative Example 3 are poor.

[0127] The examples in Table 5 are examples mainly changing the solution treatment time and the cooling rate. In Comparative Example 4 with an increased cooling rate and Comparative Example 5 with a shortened solution treatment time, a cell structure with a cell size of 100 nm or larger than 100 nm is not formed, and the degree of orientation exceeds 60°. In addition, the magnetic properties of the permanent magnets according to Comparative Examples 4 and 5 are poor.

[0128] Table 6 shows examples manufactured under the same conditions except for the solution treatment time and the cooling rate. As shown in Table 6, it has been found that by the manufacturing method according to the present disclosure, in which the cooling rate after sintering is adjusted to 0.01 °C / minute to 0.3 °C / minute and solution treatment is performed at a predetermined solution treatment temperature for 21 hours to 120 hours, a permanent magnet with a cell size of 100 nm to 600 nm can be obtained; the degree of orientation is 60° or less than 60°; the temperature coefficient α of the residual magnetic flux density in the temperature range of 20 °C to 200 °C is less than 0.045% / °C (α < 0.045% / °C); the temperature coefficient β of the intrinsic coercivity is less than 0.35% / °C (β < 0.35% / °C). It has been found that in all the permanent magnets according to Examples 24 to 33 prepared as described above, the density is equal to or higher than 8.25 g / cm 3 : the maximum magnetic energy product (BH)m is equal to or greater than 260 kJ / m 3 ; the coercivity Hcj is equal to or greater than 1600 kA / m; the squareness ratio Hk / Hcj is equal to or greater than 65%. That is, it has been found that these permanent magnets have excellent magnetic properties.

[0129] It is apparent in the present disclosure thus described that the embodiments of the present disclosure can be varied in many ways. Such variations are not regarded as departing from the spirit and scope of the present disclosure, and all such modifications that would be apparent to those skilled in the art are intended to be included within the scope equal to or less than the appended claims.

Claims

1. A rare earth cobalt permanent magnet, which consists of the following components: 23 to 27 mass% of rare earth elements R including Sm, 4.0 to 5.0 mass% of Cu, 22 to 27 mass% of Fe, 1.7 to 2.5 mass% of Zr, and the balance Co and inevitable impurities, wherein the rare earth cobalt permanent magnet includes a plurality of crystal grains and grain boundary portions, the size of the unit cell structure constituting the crystal grains is 100 nm to 600 nm; and When the intrinsic coercivity is represented by Hcj and the magnitude of the reverse magnetic field when the residual magnetic flux density Br is 90% is represented by Hk, the Hk / Hcj ratio is equal to or greater than 65% under the following conditions: the density of the rare earth cobalt permanent magnet is equal to or greater than 8.25 g / cm 3 ; its maximum energy product (BH)m is equal to or greater than 260 kJ / m 3 ; and the intrinsic coercivity Hcj is equal to or greater than 1600 kA / m; wherein the method for manufacturing the rare earth cobalt permanent magnet includes: a step of gradually cooling the sintered body at a cooling rate of 0.01 °C / min to 3 °C / min; and a solution treatment step of heating the gradually cooled sintered body at 1120 °C to 1170 °C for 31 hours to 120 hours.

2. The rare earth cobalt permanent magnet according to claim 1, wherein the degree of orientation of the crystal grains is equal to or less than 60° with respect to the easy magnetization axis.

3. The rare earth cobalt permanent magnet according to claim 1 or 2, wherein the relationships α < 0.045% / °C and β < 0.35% / °C are maintained in the temperature range of 20 °C to 200 °C, where α and β are the temperature coefficients of the remanent flux density Br and the intrinsic coercivity Hcj, respectively.

4. A method for manufacturing a rare earth cobalt permanent magnet, which includes: a step (I) of preparing an alloy composed of the following components: 23 to 27 mass% of rare earth elements R including Sm, 4.0 to 5.0 mass% of Cu, 22 to 27 mass% of Fe, 1.7 to 2.5 mass% of Zr, and the balance Co and inevitable impurities; a pulverizing step (II) of pulverizing the alloy into powder; a pressure molding step (III) of pressure molding the powder into a molded body; a sintering step (IV) of heating the molded body to form a sintered body; a step (V) of gradually cooling the sintered body at a cooling rate of 0.01 °C / min to 3 °C / min; and a solution treatment step (VI) of heating the gradually cooled sintered body at 1120 °C to 1170 °C for 31 hours to 120 hours.

5. The method for manufacturing a rare earth cobalt permanent magnet according to claim 4, wherein the sintering step (IV) is carried out at 1180 °C to 1220 °C for 20 minutes to 240 minutes.

6. An apparatus including the rare earth cobalt permanent magnet according to any one of claims 1 to 3.

Images