JP2011091119A - Method of manufacturing permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a permanent-magnet manufacturing method that can increase the coercive force. <P>SOLUTION: When a molding temperature (°C) exceeds a grain-boundary liquefaction temperature in hot compression molding of a step S13, integrated value of (the molding temperature-the grain boundary liquefaction temperature) (°C) and its time (min) is set as a first thermal effect. When processing temperature (°C) exceeds the grain boundary liquifaction temperature in hot plastic processing of a step S14, the integrated value of (the processing temperature-the grain boundary temperature) (°C) and its time (min) is set as a second thermal effect, the total of the first thermal effect and the second thermal effect is set at ≥1,000 (°C min). Alternatively, the total of the first thermal effect and the second thermal effect is set less than 1,000 (°C min). Then, heat treatment is applied to a permanent magnet after the hot plastic processing. By setting the thermal effects, it is possible to effectively execute diffusion, in an effective manner, through a crystal grain boundary of magnetic powder by an added rare earth element with increased coercive force. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a permanent magnet to which a rare earth element-containing material is added, and more particularly to an improvement in a heating method.

  In the manufacture of the permanent magnet, as shown in FIG. 18, a magnetic powder is prepared as a raw material powder in step S101. At this time, each powder of the magnetic powder is a single crystal having a size of about 5 to 10 μm, and the easy magnetization axis of the lump of powder that is an aggregate of the single crystals is oriented in a random direction. Next, in step S102, a compact is produced by press-molding the magnetic powder in a magnetic field. At this time, since the anisotropy is imparted to the compact, the easy axis of magnetization of the magnetic powder constituting the compact is in the same direction. Next, in step S103, the molded body is sintered at a temperature of about 1100 ° C. to produce a sintered body, and in step S104, the sintered body is machined into a desired shape. Thereby, a sintered magnet is manufactured as a permanent magnet.

  For permanent magnets used in drive motors for hybrid vehicles and electric vehicles, high coercive force is essential to improve heat resistance, so rare earth elements such as Pr, Dy, and Tb are added to magnetic materials. Thus, the coercive force is improved. However, when a rare earth element is used, in addition to an increase in cost due to its expensiveness, a decrease in magnetization due to the addition of the rare earth element is caused. For this reason, since the usage-amount of a magnetic material increases, the further cost increase is caused. In addition, the rare earth element production region is highly unevenly distributed, so rare earth elements are known as the element with the highest supply risk (see Materia, Vol. 46, No. 8, 2007). Among them, the production of heavy rare earth elements such as Dy is currently oligopolistic in one country, so the supply risk is even higher.

  From the above, in order to reduce the amount of rare earth element added for increasing the coercive force, a technique for appropriately adding a rare earth element-containing material in a predetermined process of the manufacturing method shown in FIG. 18 has been developed. . For example, there are the following methods 1 and 2.

  In Method 1 (for example, Patent Document 1), in step S101 of FIG. 18, as shown in FIG. 19A, each powder of the magnetic powder is a single crystal having a size of about 5 to 10 μm, and its magnetization is easy. A rare earth element-containing material Q1 is mixed with the magnetic powder Q2 whose axis (arrow in each powder Q1 in the figure) is oriented in a random direction in order to increase the coercive force. Then, using the mixed powder as a raw material powder, Steps S102 to S104 in FIG. 18 are performed. In this technique, as shown in FIG. 19B, the high coercive rare earth element is concentrated only in the vicinity of the grain boundary (about several μm) of the magnetic powder Q2 that requires high coercive force, so that the entire rare earth element magnet is obtained. The amount of addition to is reduced. On the other hand, in the method 2 (for example, Patent Document 2), after machining in step S104 in FIG. 18, as shown in FIG. 20A, the surface of the magnet composed of the magnetic powder Q2 is made to have a high coercive force. The rare earth element-containing material Q1 is applied and heat treatment is performed at a temperature of about 700 to 1000 ° C. In addition, the arrow in each powder Q2 in the figure is the axis of easy magnetization. In this technique, the high coercivity rare earth element in the rare earth element-containing material Q1 selectively diffuses in the magnetic powder Q2 grain boundary inside the magnet, and near the grain boundary pole on the magnet surface as shown in FIG. The concentration of rare earth elements added to the entire magnet is reduced by concentrating high coercivity rare earth elements.

JP 2000-331810 A JP 2006-303433 A

  However, in Method 1, the high coercivity rare earth element in the rare earth element-containing material Q1 is added to each particle in the permanent magnet by sintering after the addition of the rare earth element-containing material Q1 for increasing the coercive force to the magnetic powder Q2. As a result, the effect of reducing the amount of rare earth element added is small. On the other hand, in Method 2, the coercive force characteristic becomes uniform when manufacturing a micro magnet having a maximum size of several millimeters. However, when manufacturing a larger magnet, the coercive force is increased near the grain boundary pole on the magnet surface. Since the concentration of the rare earth element is performed, a concentration distribution in which the concentration of the rare earth element decreases toward the inside of the magnet occurs, and the coercive force characteristics become non-uniform.

  Therefore, the present invention provides a permanent magnet capable of achieving both reduction in the amount of rare earth element addition and high coercivity, as well as uniform coercivity even when the magnet is large. An object is to provide a manufacturing method.

  In order to solve the above problems, the present inventor coated a rare earth element-containing material on the surface of a magnetic powder having a crystal or a mixed phase of a crystal and an amorphous phase and having a grain boundary inside. A method of manufacturing a permanent magnet using magnetic powder has been proposed (see Japanese Patent Application No. 2008-317342). As a result of intensive studies on the heating performed by such a method for producing a permanent magnet, it has been found that the coercive force can be further increased by appropriately setting the thermal effect due to the heating above the grain boundary liquidus temperature. .

  The thermal effect is defined as an integral value (° C. · min) of (heating temperature−grain boundary liquidus temperature) (° C.) and heating time (min). For example, when there is a relational expression U = F (T) between the heating time T and the heating temperature U as shown in FIG. 15, the integral value is a relational expression U when the heating temperature U is equal to or higher than the grain boundary liquidus temperature U0. = F (T) and the area (shaded area in the figure) surrounded by the straight line (U = U0) of the grain boundary liquidus temperature. When there are a plurality of such areas, the area of all these areas Total. The total heat effect is the sum of the heat effects of the processes when there are a plurality of processes considering the heat effects. The grain boundary liquidus temperature is the lowest temperature at which crystal grain boundaries become liquid phase (= the lowest temperature at which atomic diffusion occurs).

  A first method for producing a permanent magnet according to the present invention is a method for producing a hot plastic working magnet, which has a crystal or a mixed phase of a crystal and an amorphous phase, and has a grain boundary in the surface thereof. A surface-coated magnetic powder is produced by coating a rare earth element-containing material comprising at least one of a rare earth elemental metal, an alloy, and a compound, and a compact is produced by hot compression molding the surface-coated magnetic powder. Then, a permanent magnet is obtained by performing hot plastic working on the molded body, and when the molding temperature (° C) is higher than the grain boundary liquidus temperature in hot compression molding, Temperature) (° C.) and the integrated value of the time (min) as the first thermal effect, and in hot plastic working, when the processing temperature (° C.) is equal to or higher than the grain boundary liquidus temperature, (processing temperature− Between the grain boundary liquidus temperature (℃) and the time (min) When the minutes value and a second thermal effect, is characterized by setting the total of the first thermal influence and the second heat effect on 1000 (℃ · min) or more.

  In the first method for producing a permanent magnet of the present invention, since the surface-coated magnetic powder produced by coating the surface of the magnetic powder having a grain boundary inside with a rare earth element-containing material is used, By heating in the hot plastic working, the rare earth element in the rare earth element-containing material can be selectively diffused along the crystal grain boundary from the interface of the magnetic powder toward the inside thereof. The diffusion to the center of each particle due to can be suppressed. Therefore, since the concentration of the rare earth element added as described above can be performed in the vicinity of the grain boundary, it is possible to reduce both the amount of rare earth element added and increase the coercive force. Further, since the crystal grain size is slightly larger than the single magnetic domain particle diameter, the effect of increasing the coercive force can be obtained in the same manner as the above-described conventional method 2, so that the coercive force can be further increased. Furthermore, the diffusion distance of the rare earth element to the magnetic powder is about half the thickness of the magnetic powder (distance between the interfaces of the magnetic powder), so the diffusion distance is shortened. Thereby, since the heating time can be shortened, the manufacturing time can be shortened. In addition, since it is possible to prevent the occurrence of a concentration distribution in which the concentration of the rare earth element decreases toward the inside of the magnet, the coercive force characteristics can be made uniform even when the magnet is large. Furthermore, by making the coating of the rare earth element-containing material on the magnetic powder uniform, the coercive force characteristics can be further uniformed.

  Here, in the first method for producing a permanent magnet according to the present invention, the total of the first thermal effect by hot compression molding and the second thermal effect by hot plastic working is set to 1000 (° C./min) or more. Since the diffusion of rare earth elements through the grain boundary of magnetic powder can be effectively performed, the peak value of the coercive force improvement value can be obtained in the relationship between the coercive force improvement value and the thermal effect, and the high coercive force can be obtained. Can be further improved.

  The first permanent magnet manufacturing method of the present invention can employ various configurations. In the hot compression molding, the magnetic powders become dense (high density), and in the hot plastic working, the crystal grains become coarse. Here, for example, the first thermal effect is set smaller than the second thermal effect. Can do. In this aspect, when the heat effect is set to a predetermined value in a range of 1000 (° C./min) or more, the heat effect in hot compression molding is reduced by setting the first heat effect to be smaller than the second heat effect. Since it can be made small, the diffusion of rare earth elements from the interface of the magnetic powder into the inside can be suppressed. Subsequently, when hot plastic working is performed, the tendency of rare earth elements to diffuse through the grain boundaries formed after the coarsening of crystal grains by hot plastic working becomes stronger, so diffusion of rare earth elements to the center of the crystal grains As a result, it is possible to further increase the coercive force. In the first method for producing a permanent magnet of the present invention, the permanent magnet after hot plastic working may be subjected to heat treatment.

  According to the second method for producing a permanent magnet of the present invention, a rare earth element single metal, alloy, and compound are formed on the surface of a magnetic powder having a crystal or a mixed phase of a crystal and an amorphous phase and having a grain boundary inside. Covering at least one rare earth element-containing material to produce a surface-coated magnetic powder, hot-pressing the surface-coated magnetic powder to produce a compact, and subjecting the compact to hot plastic working When the molding temperature (° C) is equal to or higher than the grain boundary liquidus temperature in hot compression molding, (molding temperature-grain boundary liquidus temperature) (° C) and its time (min) When the processing temperature (° C) is equal to or higher than the grain boundary liquidus temperature in the hot plastic working, the integrated value of (processing temperature-grain boundary liquidus temperature) (° C) and its time When the integral value with (min) is the second heat effect, the first heat shadow When the sum of the second thermal influence is set to less than 1000 (℃ · min), it is characterized by performing the heat treatment to the permanent magnet after hot plastic working.

  In the second permanent magnet manufacturing method of the present invention, the following effects can be obtained in addition to the effects of the first permanent magnet manufacturing method of the present invention. That is, since the sum total of the first heat effect by hot compression molding and the second heat effect by hot plastic working is set to less than 1000 (° C./min), magnetism in hot compression molding and hot plastic working is set. Diffusion of rare earth elements from the powder interface to the inside can be suppressed. In this case, since the second heat influence can be set small, the coarsening of the crystal grains can be suppressed. By performing a heat treatment on the permanent magnet in such a state, the rare earth element can be optimally diffused through the grain boundaries of the crystal grains, so that the coercive force can be further increased. In the second method for producing a permanent magnet of the present invention, the total of the heat effect due to the heat treatment, the first heat effect, and the second heat effect may be set to 1000 (° C./min) or more.

  The method for setting the thermal effect of the first method for producing a permanent magnet of the present invention can be applied not only to the method for producing a permanent magnet by hot plastic working as described above but also to a method for producing a permanent magnet by sintering. it can.

  The third method for producing a permanent magnet of the present invention is the surface of a magnetic powder having a crystal or a mixed phase of a crystal and an amorphous phase, a grain boundary existing inside, and each crystal grain being oriented in one direction. A surface-coated magnetic powder is prepared by coating a rare earth element-containing material comprising at least one of a rare earth elemental metal, an alloy, and a compound, and the surface-coated magnetic powder is compression-molded in a magnetic field. When a green body is prepared, sintered into the green body, and the sintering temperature (° C) is equal to or higher than the grain boundary liquidus temperature during sintering, (sintering temperature-grain boundary liquidus temperature) (° C) and its When the integrated value with time (min) is the third heat effect, the third heat effect is set to 1000 (° C./min) or more.

  In the third method for producing a permanent magnet according to the present invention, as in the first method for producing a permanent magnet according to the present invention, the surface of the magnetic powder having grain boundaries inside is coated with a rare earth element-containing material. Since the surface-coated magnetic powder is used and the thermal influence setting method of the first permanent magnet manufacturing method of the present invention is applied, the same effect as the first permanent magnet manufacturing method of the present invention can be obtained. Can do.

  Various methods can be applied to the coating of the rare earth element-containing material on the surface of the magnetic powder in the first to third permanent magnet manufacturing methods of the present invention. For example, the surface of the magnetic powder can be coated with the rare earth element-containing material by ultrasonic dispersion. Specifically, a slurry can be produced by mixing magnetic powder and a rare earth element-containing material in a liquid, and the slurry can be irradiated with ultrasonic waves. When the slurry is irradiated with ultrasonic waves, only the rare earth element-containing material can be selectively finely divided without pulverizing the magnetic powder, and the rare earth element-containing material can be uniformly dispersed in the slurry. By drying the slurry subjected to such ultrasonic dispersion, a surface-coated magnetic powder in which the finely divided rare earth element-containing material is attached to the surface of the magnetic powder can be obtained.

  In this case, since the finely divided rare earth element-containing material can adhere to the magnetic powder due to the surface tension of the liquid when the slurry is dried, it is possible to uniformly coat the surface of the magnetic powder with the rare earth element-containing material. it can. In addition, since the amount of rare earth element added can be reduced, when the surface-coated magnetic powder is applied to the method for producing a permanent magnet, the produced permanent magnet can prevent a decrease in magnetization.

  According to the first or third permanent magnet manufacturing method of the present invention, the total of the first thermal effect by hot compression molding and the second thermal effect by hot plastic working, or the third thermal effect by sintering. Is set to 1000 (° C./min) or more, so that diffusion through the crystal grain boundary of the magnetic powder with rare earth elements can be effectively performed, thereby further increasing the coercive force. An effect can be obtained.

  According to the second method for producing a permanent magnet of the present invention, the total of the first thermal effect by hot compression molding and the second thermal effect by hot plastic working is set to less than 1000 (° C./min), Since the permanent magnet after the interplastic working is heat-treated, diffusion of rare earth elements through the grain boundaries of the magnetic powder can be optimally performed, which can further increase the coercive force. Can be obtained.

It is process drawing showing the manufacturing method of the permanent magnet of 1st Embodiment which concerns on this invention. It is a sectional side view showing the schematic structure of the apparatus used by the coating process of the manufacturing method of the permanent magnet of 1st Embodiment which concerns on this invention. 2 represents the state of the rare earth element-containing material and the magnetic powder during the operation of the apparatus shown in FIG. 2, (A) is a conceptual diagram illustrating a state in which the rare earth element-containing material collides with the magnetic powder, It is a conceptual diagram showing the state to which a rare earth element containing material disperse | distributes. The product in each process of the manufacturing method of the permanent magnet of 1st Embodiment which concerns on this invention is represented, (A) is schematic structure sectional drawing of the state of the surface covering magnetic powder after a coating process, (B) is hot It is a schematic structure sectional view of the interface part of magnetic powder at the time of plastic working. 4A shows the surface portion of the magnetic powder after the coating treatment shown in FIG. 4A, and FIG. 4B shows the relationship between the coercive force-enhancing element amount and the coercive force for the surface-coated magnetic powder in FIG. It is a graph showing. (A) represents the interface portion of the magnetic powder after hot compression molding according to the modification of the first embodiment, and (B) represents the coercive force-enhancing element amount and the coercive force for the compact of (A). It is a graph showing a relationship. (A) shows the interface part of the magnetic powder after the hot plastic working by the modification of 1st Embodiment, (B) is the coercive force improvement element amount and coercive force about the permanent magnet of (A). It is a graph showing a relationship. It is process drawing showing the manufacturing method of the permanent magnet of 2nd Embodiment which concerns on this invention. (A) represents the interface part of the magnetic powder after the hot compression molding of the second embodiment according to the present invention, and (B) represents the coercive force-enhancing element amount and coercive force for the molded body of (A). It is a graph showing the relationship. (A) represents the interface part of the magnetic powder after the hot plastic working according to the second embodiment, and (B) represents the relationship between the coercive force improving element amount and the coercive force for the permanent magnet of (A). It is a graph. (A) represents the interface part of the magnetic powder after the heat treatment according to the second embodiment, and (B) is a graph representing the relationship between the coercive force improving element amount and the coercive force for the permanent magnet of (A). . (A) shows the interface part of the magnetic powder after the conventional hot compression molding, (B) is a graph showing the relationship between the amount of coercive force-enhancing elements and the coercive force for the molded product of (A). . (A) shows the interface part of the magnetic powder after the conventional hot plastic working, (B) is a graph showing the relationship between the coercive force improving element amount and the coercive force for the permanent magnet of (A). . It is process drawing showing the manufacturing method of the permanent magnet of 3rd Embodiment which concerns on this invention. It is a figure for demonstrating the definition of a thermal influence. It is a figure for demonstrating the definition of a coercive force improvement value. It is a graph which shows the relationship between the coercive force improvement value obtained in the Example of this invention, and the heat influence. It is process drawing showing the manufacturing method of the permanent magnet by a prior art. The product in each process of the manufacturing method of the permanent magnet by the conventional method 1 is represented, (A) is a schematic block diagram of the state after mixing with a magnetic powder and a rare earth element containing material, (B) is the rare earth in a permanent magnet. It is a schematic block diagram of the addition state of an element. The product in each process of the manufacturing method of the permanent magnet by the conventional method 2 is represented, (A) is a schematic block diagram of the state after mixing with a magnetic powder and a rare earth element containing material, (B) is the rare earth in a permanent magnet. It is a schematic block diagram of the addition state of an element.

(1) First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram showing a method for manufacturing a permanent magnet according to a first embodiment of the present invention. As shown in FIG. 1, first, in step S11, magnetic powder and a rare earth element-containing material for increasing the coercive force are prepared.

  The magnetic powder is a powder having a crystal or a mixed phase of a crystal and an amorphous phase, a grain boundary inside, and a hardness higher than that of the rare earth element-containing material. The magnetic powder has a flat shape such as a plate shape. Specifically, the magnetic powder has a cross-sectional size of, for example, a length of 200 μm and a thickness of 30 μm. Each of the powders includes a large number of fine crystal grains of, for example, several tens of nm. ing. The easy axis of crystal grains is oriented in a random direction. The magnetic powder is, for example, a rare earth magnetic powder (Nd—Fe—B magnetic powder) containing a rare earth element, an iron group element, and boron.

  Examples of the rare earth element-containing material include rare earth element powders containing at least one of rare earth elemental metals, alloys and compounds, and rare earth element sols and rare earth element liquids such as sol and liquid rare earth element compounds. It is done. Specifically, the rare earth element powder is made of an oxide containing Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, or Y, or a fluoride. Examples thereof include powders and powders composed of a mixture thereof. Moreover, as rare earth element sol and rare earth element liquid, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, or sol-like fluoride containing Y, sol-like colloidal form, etc. Examples thereof include fluorides and fluorides composed of a mixture thereof.

  Next, in step S12, for example, using the apparatus 100 shown in FIG. 2, the surface of the flat magnetic powder is coated with a rare earth element-containing material. First, in the container 104, the slurry S is prepared by mixing the rare earth element-containing material, the magnetic powder, and the liquid. For example, an organic solvent is used as the liquid. As the organic solvent, for example, ethanol, acetone, or IPA (isopropyl alcohol) is used. In the production of the slurry, it is preferable that the mixing ratio of the magnetic powder is larger than that of the rare earth element-containing material.

  Next, the container 104 is placed in the vibration liquid 103 of the vibration liquid tank 102. Subsequently, ultrasonic waves are oscillated by the ultrasonic oscillator 101, and the ultrasonic waves are applied to the slurry S in the container 104 through the vibrating liquid 103 in the vibrating liquid tank 102. The frequency of the ultrasonic wave is, for example, 100 kHz or less.

  Here, in the first embodiment, in the slurry S, the flat magnetic powder functions as a fine particle medium for the rare earth element-containing material. As shown in FIG. 3A, the rare earth element-containing material P1, which is an aggregate of primary particles (that is, composed of secondary particles) in an initial state, is converted into a flat magnetic powder P2 by vibration caused by ultrasonic irradiation. The collision not only breaks the agglomeration, but also leads to the primary particles being crushed. In addition, the primary particle here is a particle recognized as a single crystal by observation with an electron microscope such as TEM. The pulverization is crushing of primary particles.

  In this case, the collision is also caused by the burst energy of cavitation (small bubbles) formed in the liquid by irradiation with ultrasonic waves. On the other hand, in the slurry S, as shown in FIG. 3B, the rare earth element-containing material P1 is dispersed in the liquid by the action of diffusion. Such pulverization / dispersion of the rare earth element-containing material P1 is locally repeated in all regions on the surface of the magnetic powder P2, so that the rare earth element-containing material P1 can be uniformly dispersed in the slurry S. In FIGS. 3A and 3B, the liquid is not shown.

  In the apparatus 100, only the rare earth element-containing material P1 can be selectively finely divided without pulverizing the magnetic powder P2 as described above, and the rare earth element-containing material P1 is uniformly dispersed in the slurry S. be able to. Next, the liquid is dried under reduced pressure while irradiating with ultrasonic waves. As a result, the finely divided rare earth element-containing material P1 is maintained in a uniformly dispersed state in the liquid, and therefore does not aggregate and adheres to the surface of the magnetic powder P2 by the surface tension of the liquid during drying. As a result, the finely divided rare earth element-containing material P1 is uniformly coated on the surface of the magnetic powder P2, as shown in FIG. In addition, in the coating process of step S12, when a liquid rare earth element-containing material is used, the liquid used in the preparation of the slurry is not required, and ultrasonic irradiation to the slurry is not required. In this case, the surface of the magnetic powder containing the rare earth element-containing material is uniformly applied without performing ultrasonic irradiation on the slurry.

  Subsequently, in step S13, the surface-coated magnetic powder obtained by attaching the rare earth element-containing material P1 to the surface of the magnetic powder P2 is subjected to hot compression molding, thereby crystallization and true densification of the surface-coated magnetic powder. Do. Thereby, a molded object is produced. At this time, the distance between the interfaces of the magnetic powder P2 constituting the compact is, for example, 30 μm. The easy magnetization axes of the crystal grains in the magnetic powder are oriented in random directions.

  Next, in step S14, anisotropy is imparted to the molded body by performing hot plastic working on the molded body. Thereby, the magnetization easy axis (the arrow direction in each particle in the figure) of the crystal grains in the magnetic powder P2 constituting the compact is oriented in the same direction. Further, as shown in FIG. 4B, the rare earth element in the rare earth element-containing material P1 moves along the crystal grain boundary (arrow direction I) from the interface of the flat magnetic powder P2 toward the inside thereof. By selectively diffusing, the rare earth element is concentrated in the vicinity of the grain boundary. At this time, the diffusion of the rare earth element into the flat magnetic powder P2 is performed from all the interfaces to the inside of the flat magnetic powder P2, and therefore the diffusion distance is determined by the thickness of the magnetic powder P2 (of the magnetic powder). It is about half of the distance between the interfaces. In this case, the distance between the interfaces of the magnetic powder constituting the compact is, for example, 10 μm. In FIG. 4B, the portion where the rare earth element-containing material P1 is illustrated is the powder interface of the magnetic powder P2.

  Here, in the manufacturing method of the permanent magnet of this embodiment, the time and temperature in hot compression molding and hot plastic working are set as follows. When the molding temperature (° C.) is equal to or higher than the grain boundary liquidus temperature in the hot compression molding of step S13, the integration of (molding temperature−grain boundary liquidus temperature) (° C.) and the time (min) is integrated. When the processing temperature (° C.) is equal to or higher than the grain boundary liquidus temperature in the hot plastic working in step S14, the value is set as (the processing temperature−the grain boundary liquidus temperature) (° C.) and its value When the integrated value with time (min) is the second heat effect, the total of the first heat effect and the second heat effect is set to 1000 (° C./min) or more. Thereby, since the diffusion through the grain boundary of the magnetic powder P2 by the rare earth element can be effectively performed, the peak value of the coercive force improvement value can be obtained in the relationship between the coercive force improvement value and the thermal effect. .

In this case, it is preferable to set the first thermal effect by hot compression molding to be smaller than the second thermal effect by hot plastic working. This will be described with reference to FIGS.
In addition, about the interface part of the magnetic powder shown to FIG. 6, 7, 12, 13 only one side of the magnetic powder adjacent in an interface part is shown in figure. About the graph showing the relationship between the coercive force improving element amount and the coercive force, the coercive force improving element amount is the weight of the rare earth element added using the rare earth element-containing material P1 (= contributing to improving the coercive force). is there. In the surface-coated magnetic powder shown in FIG. 5A, the magnetic powder P2 has a plurality of crystal grains P21, and an amorphous phase P23 exists between the grain boundaries P22. In the surface-coated magnetic powder, as shown in FIG. 5B, the coercive force is constant regardless of the weight of the added rare earth element. Next, hot compression molding is performed on the surface-coated magnetic powder to produce a molded body. In this case, the magnetic powders P2 become dense (densification), and the amorphous phase P23 between the grain boundaries P22 is crystallized in the magnetic powder P2, and all but the grain boundaries 22 become crystal grains P21.

  Here, when the first thermal effect is set as usual, the rare earth element in the rare earth element-containing material P1 diffuses through the grain boundary P22 as shown in FIG. In this case, as shown in FIG. 12B, as the weight of the added rare earth element increases, the coercive force is improved, and the effect of adding the rare earth element is obtained. However, in the prior art, the magnitude of the first thermal effect and the second thermal effect are not considered, and when the first thermal effect is set to be large, the diffusion of the added rare earth element proceeds excessively. Subsequently, when the second heat effect is set as usual and hot plastic working is performed, the crystal grains become coarse. In this case, when the second heat effect is set to be large, the added rare earth element is taken into the crystal grain P21 in accordance with the coarsening of the crystal grain P21, and as shown in FIG. Diffuses to the center of the crystal grain P21. For this reason, as shown in FIG. 13B, the effect obtained by adding the rare earth element cannot be obtained.

  On the other hand, by setting the first thermal effect to be smaller than the second thermal effect (for example, performing hot compression molding at a high speed), the thermal effect in the hot compression molding is reduced, and FIG. As shown in FIG. 4, the diffusion of the added rare earth element is suppressed, and most of the rare earth element-containing material P1 remains on the surface of the magnetic powder P2. In this case, as shown in FIG. 6B, the coercive force is constant regardless of the weight of the added rare earth element, as before hot compression molding. Next, when hot plastic working is performed, the coarsening of the crystal grains P21 starts. However, in the aspect of this embodiment, most of the rare earth element-containing material P1 is present on the surface of the magnetic powder P2 before the hot plastic working. Since it remains, the tendency for rare earth elements to diffuse through the grain boundary P22 formed after the crystal grain P21 is coarsened by hot plastic working becomes stronger. As a result, as shown in FIG. 7A, the diffusion of rare earth elements into the central portion of the crystal grains P21 can be suppressed. Therefore, as shown in FIG. As it increases, the coercive force improves, and the effect of adding rare earth elements can be obtained.

  Subsequently, in step S15, the molded body provided with anisotropy is machined to be processed into a desired shape. Next, if necessary, the molded body processed into a desired shape is subjected to heat treatment.

  As described above, in the first embodiment, since the surface-coated magnetic powder produced by coating the surface of the magnetic powder P2 having grain boundaries inside with the rare earth element-containing material P1 is used, the concentration of the added rare earth element is increased. Therefore, it is possible to reduce both the amount of rare earth element added and increase the coercive force. Further, since the crystal grain size is slightly larger than the single domain particle diameter, the effect of increasing the coercive force can be obtained in the same manner as in the conventional method 2, so that the coercive force can be further increased. Furthermore, since the diffusion distance of the added rare earth element to the magnetic powder is shortened, the heating time can be shortened, and as a result, the manufacturing time can be shortened. In addition, since it is possible to prevent the occurrence of a concentration distribution in which the concentration of the rare earth element decreases toward the inside of the magnet, the coercive force characteristics can be made uniform even when the magnet is large.

  Here, in the first embodiment, since the total of the first thermal effect by hot compression molding and the second thermal effect by hot plastic working is set to 1000 (° C./min) or more, it depends on the added rare earth element. Since the diffusion through the crystal grain boundary of the magnetic powder P1 can be performed effectively, the coercive force can be further increased.

  In particular, by setting the first thermal effect to be smaller than the second thermal effect, it is possible to suppress the diffusion of the added rare earth element into the central portion of the crystal grains P21, and thus it is possible to further increase the coercive force. . Furthermore, the coating of the rare earth element-containing material P1 on the surface of the magnetic powder P2 can be performed uniformly by performing ultrasonic dispersion. Moreover, since the addition amount of rare earth elements can be reduced, when the surface-coated magnetic powder is applied to the method for producing a permanent magnet, the produced permanent magnet can prevent a decrease in magnetization.

(2) Second Embodiment In the second embodiment, the total of the first thermal effect by the hot compression molding S13 and the second thermal effect by the hot plastic working S14 is less than 1000 (° C./min), and FIG. As shown, the heat treatment S21 performed after the hot plastic working S14 is essential, which is different from the first embodiment. In the second embodiment, components similar to those in the first embodiment are denoted by the same reference numerals, and descriptions of components having the same functions as those in the first embodiment are omitted.

  In the second embodiment, since the total of the first thermal effect by the hot compression molding S13 and the second thermal effect by the hot plastic working S14 is set to less than 1000 (° C./min), the first thermal effect is It can be set small (for example, hot compression molding is performed at a high speed), and as a result, most of the rare earth element-containing material P1 remains on the surface of the magnetic powder P2, as shown in FIG. 9A. In this case, as shown in FIG. 9B, the coercive force is constant regardless of the weight of the added rare earth element.

  Next, in the hot plastic working S14, since the total of the heat effects with the first heat influence is less than 1000 (° C./min), the second heat influence is set to be small (for example, hot plastic working is performed). As a result, as shown in FIG. 10A, diffusion of rare earth elements is suppressed, and most of the rare earth element-containing material P1 remains on the surface of the magnetic powder P2. In this case, since the second heat effect is set small, the coarsening of the crystal grains P21 is suppressed. In this case, as shown in FIG. 10B, the coercive force is constant regardless of the weight of the added rare earth element. Next, by performing heat treatment S21, the added rare earth element can optimally diffuse through the grain boundary P22. As a result, as shown in FIG. 11 (A), the diffusion of rare earth elements into the central portion of the crystal grains P21 can be suppressed. Therefore, as shown in FIG. 11 (B), the weight of the added rare earth elements is reduced. As it increases, the coercive force improves, and the effect of adding rare earth elements can be obtained.

  As described above, in the second embodiment, in addition to obtaining the effects of the first embodiment, the rare earth element can optimally diffuse through the grain boundary P22 of the crystal grain P21, so that the coercive force can be further increased. Can be planned.

(3) Third Embodiment The third embodiment is different from the first embodiment in that steps S31 and S32 are performed between step S12 and step S15. In the third embodiment, components similar to those in the first embodiment are denoted by the same reference numerals, and descriptions of components having the same functions as those in the first embodiment are omitted. In this case, it is preferable to use HDDR powder (Hydrogenation-Decomposition-Desorption-Recombination powder) as the magnetic powder. HDDR powder has a large number of crystal grains in one powder, and each crystal grain is oriented in one direction.

  In the third embodiment, the HDDR powder and the rare earth element-containing material are prepared in step S11, and in step S12, the surface of the HDDR powder P2 is coated with the rare earth element-containing material P1 by the same method as in the second embodiment. Process. In this case, in the HDDR powder P2, the easy magnetization axes of the crystals are oriented in the same direction in advance. Subsequently, in step S31, the surface-coated magnetic powder in which the rare earth element-containing material P1 is attached to the surface of the HDDR powder P2 is compression-molded in a magnetic field. Thereby, a molded body having anisotropy is produced.

  Subsequently, in step S32, the molded body is sintered to obtain a sintered body. In step S32, the added rare earth element is selectively diffused along the crystal grain boundary (arrow direction I) from the interface of the magnetic powder P2 to the inside thereof, as in the first embodiment, thereby enriching the rare earth element. Is performed near the grain boundary. In such sintering, when the sintering temperature (° C.) is equal to or higher than the grain boundary liquidus temperature, the integral value of (sintering temperature−grain boundary liquidus temperature) (° C.) and the time (min) is expressed as a third value. When the heat effect is considered, the third heat effect is set to 1000 (° C./min) or more.

  Next, as in the first embodiment, in step S15, the sintered body is processed into a desired shape by machining. Next, if necessary, heat treatment is performed on the molded body or sintered body processed into a desired shape.

  As described above, in the third embodiment, since the third heat influence is set to 1000 (° C./min) or more, the same operation and effect as in the first embodiment can be obtained.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to specific examples. In the examples, the amount of added Dy was changed and the relationship between the coercive force improvement value of the permanent magnet and the thermal effect was examined.

In sample preparation, DyF ₃ powder was prepared as a rare earth element-containing material, and Nd—Fe—B magnetic powder was prepared as a flat magnetic powder having a hardness higher than that of the rare earth element-containing material. Next, the surface of the magnetic powder was coated with a rare earth element-containing material. In the coating treatment, a slurry was prepared by mixing the magnetic powder and the rare earth element-containing material with an organic solvent using the same method as in the embodiment. By irradiating the slurry with ultrasonic waves, the rare earth element-containing material was finely divided and uniformly dispersed in the slurry. And the surface of the magnetic powder was coated with the finely divided rare earth element-containing material by drying the slurry. In this case, surface-coated magnetic powders having Dy addition amounts of 0.5 wt.%, 1.0 wt.%, 3.0 wt.%, And 5.0 wt.% Converted from the coated rare earth element-containing material were prepared. In addition, the analysis of the addition amount of Dy used ICP (high frequency inductively coupled plasma) analysis.

  Subsequently, after such a coating treatment, a compact was produced by performing hot compression molding on a magnetic powder having a surface coated with a rare earth element-containing material. Next, anisotropy was imparted to the molded body by subjecting the molded body to hot plastic working.

  The applied pressure at the time of hot compression molding and hot plastic working was 50 MPa. In each heating during hot compression molding and hot plastic working, a temperature rising region that raises the temperature to the holding temperature at a predetermined temperature rising rate, a holding temperature region that holds the holding temperature for a predetermined time, and a holding temperature at a predetermined cooling rate The cooling area to be cooled is set. In the hot compression molding, the holding temperature is set to 600 to 850 ° C., the temperature rising rate is set to 20 to 100 ° C./min, the holding time is set to 0 to 60 min, and the cooling rate is appropriately set within the range of 20 to 100 ° C./min. 1 Heat effect (° C / min) was changed. In the hot plastic working, the holding temperature is set to 700 to 900 ° C., the temperature rising rate is set to 20 to 100 ° C./min, the holding time is set to 0 to 20 min, and the cooling rate is appropriately set within the range of 20 to 100 ° C./min. 2 The heat effect (° C · min) was changed. Regarding the first heat effect and the second heat effect, the grain boundary liquidus temperature was set to 600 ° C., and the total of the first heat effect and the second heat effect was calculated by the method described with reference to FIG.

  In this way, permanent magnets having Dy addition amounts of 0.5 wt.%, 1.0 wt.%, 3.0 wt.%, And 5.0 wt.% Were produced as samples, and VSM ( The coercive force is measured using a vibrating sample magnetometer, and as shown in FIG. 17, the coercivity improvement value (kOe) of the permanent magnet and the thermal effect (= total of the first thermal effect and the second thermal effect). The relationship of (° C./min) was obtained. The data indicated by the plot ● in FIG. 17 is the data for the permanent magnet with the Dy addition amount of 0.5 wt.%, And the data indicated by the plot ▲ is the permanent with the Dy addition amount of 1.0 wt. Data for magnets, data indicated by plot ■ are for permanent magnets with Dy addition of 3.0 wt.%, Data for plot ◆ are for Dy addition of 5.0 wt.% It is data about a certain permanent magnet.

The coercive force improvement value was calculated as follows. The coercive force increases due to the effect of Dy diffusion due to heat, and decreases due to the effect of grain coarsening. In the example, in order to evaluate only the effect of Dy diffusion due to heat, the coercive force improvement value of each sample of the example is as shown in the following formula, and the sample has the same coercive force and no Dy addition prepared under the same conditions. Obtained as a difference from the coercive force of a comparative sample (= a comparative sample in which Dy addition using a rare earth element-containing material was not performed). Then, in the relationship between the coercive force improvement value and the thermal effect, as shown in FIG. 16, the range of the thermal effect in which the peak value of the coercive force improvement value is obtained is determined as the range necessary for increasing the coercive force.
Coercivity improvement value = coercivity of Dy-added sample−coercivity of Dy-free sample

  As shown in FIG. 17, for the permanent magnets with Dy addition amounts of 0.5 wt.%, 1.0 wt.%, 3.0 wt.%, 5.0 wt. As for the peak value of the coercive force improvement value, it was confirmed that the sum total of the first heat effect and the second heat effect was positioned at 1000 (° C./min) or more for any peak. Thus, it was found that a high coercive force can be achieved by setting the total of the first heat effect and the second heat effect to 1000 (° C./min) or more.

  P1 ... Rare earth element-containing material, P2 ... Magnetic powder, P21 ... Crystal grain, P22 ... Grain boundary, P23 ... Amorphous phase, S ... Slurry

Claims (6)

A surface of a magnetic powder having a crystal or a mixed phase of a crystal and an amorphous phase and having a grain boundary inside is coated with a rare earth element-containing material composed of at least one of a rare earth elemental metal, an alloy, and a compound. Create surface-coated magnetic powder,
A compact is produced by performing hot compression molding on the surface-coated magnetic powder,
A permanent magnet is obtained by performing hot plastic working on the molded body,
Integration of (the molding temperature−the grain boundary liquidus temperature) (° C.) and the time (min) when the molding temperature (° C.) is equal to or higher than the grain boundary liquidus temperature in the hot compression molding. When the processing temperature (° C.) is equal to or higher than the grain boundary liquidus temperature in the hot plastic working when the value is the first thermal effect, (the processing temperature−the grain boundary liquidus temperature) (° C.) and its When the integral value with time (min) is the second heat effect,
A method for producing a permanent magnet, characterized in that a total of the first heat effect and the second heat effect is set to 1000 (° C. · min) or more.   The method for manufacturing a permanent magnet according to claim 1, wherein the first thermal effect is smaller than the second thermal effect.   The method of manufacturing a permanent magnet according to claim 1, wherein heat treatment is performed on the permanent magnet after the hot plastic working. A surface of a magnetic powder having a crystal or a mixed phase of a crystal and an amorphous phase and having a grain boundary inside is coated with a rare earth element-containing material composed of at least one of a rare earth elemental metal, an alloy, and a compound. Create surface-coated magnetic powder,
A compact is produced by performing hot compression molding on the surface-coated magnetic powder,
A permanent magnet is obtained by performing hot plastic working on the molded body,
In the hot compression molding, when the molding temperature (° C.) is equal to or higher than the grain boundary liquidus temperature, the integrated value of (the molding temperature−the grain boundary liquidus temperature) (° C.) and the time (min) When the processing temperature (° C.) is equal to or higher than the grain boundary liquidus temperature in the hot plastic working, (the processing temperature−the grain boundary liquidus temperature) (° C.) and its When the integral value with time (min) is the second heat effect,
The total of the first heat effect and the second heat effect is set to less than 1000 (° C./min),
A method of manufacturing a permanent magnet, comprising performing a heat treatment on the permanent magnet after the hot plastic working. A rare earth element simple metal, alloy, and compound on the surface of a magnetic powder having a crystal or a mixed phase of a crystal and an amorphous phase and having grain boundaries inside, and each crystal grain being oriented in one direction A surface-coated magnetic powder is produced by coating a rare earth element-containing material comprising at least one of
The surface-coated magnetic powder is formed by compression molding in a magnetic field,
Sintering the molded body,
When the sintering temperature (° C.) is equal to or higher than the grain boundary liquidus temperature in the sintering, the integrated value of (the sintering temperature−the grain boundary liquidus temperature) (° C.) and the time (min) is expressed as a third value. A method for producing a permanent magnet, characterized in that the third heat effect is set to 1000 (° C./min) or more when the heat effect is considered.   6. The method of manufacturing a permanent magnet according to claim 1, wherein the rare earth element-containing material is coated on the surface of the magnetic powder by ultrasonic dispersion.

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