JP6511844B2 - RTB based sintered magnet - Google Patents

Description

  The present invention relates to an R-T-B-based sintered magnet mainly composed of rare earth element (R), Fe or Fe and at least one iron group element (T) essentially containing Fe and Co and boron (B). It is a thing.

  The RTB-based sintered magnet has excellent magnetic properties, and has recently been applied to a drive motor of a hybrid car and the like. When used in a drive motor of a hybrid vehicle, the RTB-based sintered magnet is exposed to a relatively high temperature environment, so the RTB-based sintered magnet is difficult to thermally demagnetize in a high temperature environment. Desired. In order to suppress the thermal demagnetization of the RTB-based sintered magnet in a high temperature environment, it is necessary to increase the coercivity at a high temperature.

As a method of improving the coercivity at high temperature, for example, it is well known that a method of sufficiently increasing the coercivity (HcJ) at room temperature of an RTB-based sintered magnet is effective. As a method for enhancing the coercivity of RTB-based sintered magnets at room temperature, there is known a method of substituting a part of R of the main phase R ₂ T ₁₄ B compound with a heavy rare earth element such as Dy or Tb. ing. By substituting a part of R with a heavy rare earth element, the magnetocrystalline anisotropy is enhanced, and as a result, the coercivity of the RTB-based sintered magnet at room temperature can be sufficiently enhanced, whereby the high temperature can be achieved. The coercivity of the

  On the other hand, Patent Documents 1 and 2 disclose a method of controlling the grain boundary phase which is a fine structure of a rare earth magnet as a method of suppressing the amount of use of heavy rare earth elements to improve the coercive force. Patent Document 1 describes a transition metal rich phase in which the grain boundary phase is ferromagnetic, the R rich phase having a total atomic concentration of rare earth elements of 70 atomic% or more, and the total atomic concentration of rare earth elements being 25 to 35 atomic%. And a technique to obtain high coercivity by including. Patent Document 2 discloses a technology for suppressing the high temperature thermal demagnetization by setting the thickness of the two-grain grain boundary phase to 5 nm or more and 500 nm or less and setting it as a phase having a magnetism different from that of the ferromagnetic material.

JP, 2014-13628, A JP, 2014-209546, A

When the RTB-based sintered magnet is used in a high temperature environment of 100 ° C. to 200 ° C., it is necessary to further improve the coercivity at a high temperature. A composition in which a part of R of the main phase R ₂ T ₁₄ B compound is substituted with a heavy rare earth element such as Tb or Dy is a simple method for improving the coercive force at high temperatures, but heavy materials such as Dy and Tb Since rare earth elements are limited in production area and output, there are resource problems. With substitution, for example, reduction in residual magnetic flux density is also inevitable due to antiferromagnetic coupling between Nd and Dy.

In Patent Document 1, in addition to the R-rich phase, 40% or more of a transition metal-rich phase mainly composed of a ferromagnetic R ₆ T ₁₃ M type metal compound is formed in the grain boundaries. When the M element in this R ₆ T ₁₃ M-type metal compound is Al or Ga, the c-axis anisotropy is obtained, so that the generation of the domain inversion starting point of the R ₂ T ₁₄ B main phase is suppressed and the coercivity is It is said that the improvement effect can be obtained. However, when such a ferromagnetic transition metal-rich phase is formed in grain boundaries, adjacent main phase crystal grains tend to be magnetically coupled with each other. When adjacent main phase crystal grains are magnetically coupled to each other, if a reverse magnetic domain is generated in one main phase crystal grain, the adjacent main phase crystal grains are also affected to lower the coercivity. there were.

In Patent Document 2, by increasing the thickness of the two-grain grain boundary phase and making the grain boundary phase non-ferromagnetic, the magnetic dividing effect between adjacent main phase crystal grains is enhanced to suppress high-temperature heat demagnetization It is supposed to be possible. Furthermore, by forming a nonferromagnetic R ₆ T ₁₃ M phase at grain boundaries in addition to the R rich phase, the concentration of iron group elements in the R rich phase is reduced and the grain boundaries are demagnetized. Technology is disclosed. However, there is still room for improvement in the improvement of the magnetic separation effect due to the decrease in the concentration of iron group elements in grain boundaries.

  The present invention has been made in view of the above, and an object of the present invention is to provide an RTB-based sintered magnet excellent in coercive force at high temperature without increasing heavy rare earths such as Dy and Tb. I assume.

The inventors of the present application examined the requirements necessary for the formation of two grain boundaries having high magnetic separation effect between adjacent crystal grains. As a result, it has been considered that the inclusion of an Fe-rich phase such as the R ₂ T ₁₇ phase in the RTB-based sintered magnet has conventionally caused a reduction in the coercive force, but a certain amount of the Fe-rich phase is It has been found that the inclusion effect can increase the coercive force.

The present invention has been completed based on such findings. That is, the RTB-based sintered magnet according to the present invention is a RTB-based sintered magnet having R ₂ T ₁₄ B main phase crystal particles, and in addition to the main phase crystal particles, It further has a Fe-rich phase containing a high concentration of Fe and containing R as compared to the main phase crystal grains, and the area ratio of the Fe-rich phase to the cutting area of the RTB-based sintered magnet is 0. A range of 05% or more and 1.0% or less is characterized.

The mechanism by which the high temperature coercivity can be obtained by the presence of the Fe-rich phase in such a range is not completely clarified, but it is presumed that the mechanism is as follows. By the presence of the Fe-rich phase in the above-mentioned range, it is possible to consume T atoms, such as Fe atoms, which have been segregated in conventional double grain boundaries. As a result, the concentration of the iron group element in the two grain boundaries can be extremely reduced, and the two grain boundaries can be made non-ferromagnetic. Therefore, the magnetic separation effect of the two grain boundaries is improved, and as a result, it is possible to have a good high temperature coercivity. When the area ratio of the Fe-rich phase in the cut surface of the sintered magnet is less than 0.05%, the concentration of the iron group element in the two grain boundaries increases, the magnetic division effect is reduced, and the coercive force is reduced. Tend. On the other hand, when the area ratio of the Fe-rich phase in the cut surface of the sintered magnet exceeds 1.0%, the residual magnetic flux density decreases due to the reduction of the main phase volume ratio, and the nucleation of the Fe-rich phase as the reverse magnetic domain The coercivity tends to decrease because it functions as a site. The method of calculating the area ratio will be described later.

The Fe-rich phase preferably contains an M element. The M element is at least one element selected from Al and Ga. When the Fe-rich phase contains an M element, the wettability between the Fe-rich phase and the grain boundary phase tends to be improved. This facilitates formation of thick two-particle grain boundaries between the R ₂ T ₁₄ B main phase crystal particles and the Fe-rich phase, and the Fe-rich phase and the R ₂ T ₁₄ B main phase crystal particles are magnetically separated. . As a result, the reverse magnetic domain generated in the Fe-rich phase is unlikely to affect the adjacent R ₂ T ₁₄ B main phase crystal grains, and it is considered that the reduction of the coercivity due to the Fe-rich phase is easily suppressed.

The area ratio of the Fe-rich phase to the cutting area of the RTB-based sintered magnet is preferably in the range of 0.3% to 0.7%. In that case, it is possible to have even better high temperature coercivity.

  According to the present invention, an RTB-based sintered magnet excellent in coercive force at high temperature can be provided without increasing heavy rare earths such as Dy and Tb.

FIG. 1 is a schematic cross-sectional view of an RTB based sintered magnet according to the present invention. FIG. 2 is a reflection electron image of a cut surface of the RTB-based sintered magnet of Example 5.

  Hereinafter, the present invention will be described in detail with reference to the drawings. The present invention is not limited by the following embodiments (hereinafter referred to as embodiments). Further, constituent elements in the following embodiments include those which can be easily conceived by those skilled in the art, those substantially the same, and so-called equivalent ranges. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

An embodiment of the RTB based sintered magnet according to the present embodiment will be described. The RTB-based sintered magnet according to the present embodiment is a RTB-based sintered magnet having R ₂ T ₁₄ B main phase crystal particles, wherein the main phase crystal particles other than the main phase crystal particles are The Fe-rich phase further includes an Fe-rich phase containing a high concentration of Fe and containing R as compared to the phase crystal particles, and the area of the Fe-rich phase occupying the cut surface of the RTB-based sintered magnet is 0.05 It is characterized by being in the range of% or more and 1.0% or less.

The RTB-based sintered magnet according to the present embodiment is a sintered body formed using an RTB-based alloy. As shown in FIG. 1, in the RTB-based sintered magnet according to this embodiment, the composition of main phase crystal particles is R ₂ T ₁₄ B (R represents at least one of rare earth elements, and T is Fe or And a main phase crystal particle 2 containing an R ₂ T ₁₄ B compound represented by a composition formula that represents one or more iron group elements including Fe and Co and B represents B or B and C; and the main phase The Fe-rich phase 4 containing R and having a higher concentration of Fe compared to crystal grains, and the grain boundary phase 6 containing R more than the R ₂ T ₁₄ B compound are included.

The main phase of the RTB-based sintered magnet according to this embodiment is R ₂ T ₁₄ B main phase crystal particles, and the R ₂ T ₁₄ B main phase crystal particles are R ₂ T ₁₄ B-type tetragonal crystals. It has a crystal structure consisting of The R ₂ T ₁₄ B main phase crystal particles may contain other elements as long as they contain R, T, and B as main components.

  R represents one or more rare earth elements. The rare earth elements mean Sc, Y and lanthanoid elements belonging to the third group of the long period periodic table. The lanthanoid element includes, for example, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the like. The rare earth elements are classified into light rare earths and heavy rare earths, and heavy rare earth elements mean Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and light rare earth elements are other rare earth elements.

  In the present embodiment, T represents Fe or one or more iron group elements including Fe and Co. T may be Fe alone, or part of Fe may be substituted by Co. When a part of Fe is replaced by Co, the temperature characteristics can be improved without degrading the magnetic characteristics.

  In the RTB-based sintered magnet according to the present embodiment, part of B can be substituted with carbon (C). In this case, the manufacture of the magnet is facilitated, and the manufacturing cost can be reduced. Also, the substitution amount of C is an amount that does not substantially affect the magnetic properties.

In the R-T-B-based sintered magnet according to the present embodiment, the R ₂ T ₁₄ B main phase crystal particles may contain various known additive elements. Specifically, it may contain at least one element of elements such as Ti, V, Cu, Cr, Mn, Ni, Zr, Nb, Mo, Hf, Ta, W, Al, Ga, Si, Bi, Sn, etc. Good.

The Fe-rich phase is a phase containing R and having a higher concentration of Fe than R ₂ T ₁₄ B main phase crystal grains. Examples of the Fe-rich phase include an R ₂ T ₁₇ phase having a 2-17 type crystal structure. The presence of the Fe-rich phase can be confirmed by analyzing R and Fe of the cross section of the sintered magnet by an analytical method such as EPMA (Electron Probe Micro Analyzer).

As described above, the Fe-rich phase contains more Fe than R ₂ T ₁₄ B main phase crystal grains as a constituent element, and may further contain Co. The number of atoms of the iron group element T contained in the Fe-rich phase is in the range of 83.0 to 93.0% with respect to the total number of atoms of R, T, B, and M elements contained in the Fe-rich phase . Further, the number of atoms of R contained in the Fe-rich phase is in the range of 5.0 to 15.0% with respect to the total number of atoms of R, T, B, and M elements contained in the Fe-rich phase. If R and T in this range are included as main components, components other than these may be included.

  The Fe-rich phase may contain B. The number of B atoms contained in the Fe-rich phase is 1.0% or less with respect to the total number of R, T, B and M atoms contained in the Fe-rich phase.

Also, the Fe-rich phase preferably contains an M element. The M element is at least one element selected from Al and Ga. The number of atoms of M element contained in the Fe-rich phase is preferably 0.5 to 3.0% with respect to the total number of atoms of R, T, B, and M elements contained in the Fe-rich phase. When the Fe-rich phase contains the M element in such a range, the wettability between the Fe-rich phase and the grain boundary phase tends to be improved. This facilitates formation of thick two-particle grain boundaries between the R ₂ T ₁₄ B main phase crystal grains and the Fe-rich phase, and the R ₂ T ₁₄ B main phase crystal grains and the Fe-rich phase are magnetically separated. . As a result, the reverse magnetic domain generated in the Fe-rich phase is less likely to affect adjacent R ₂ T ₁₄ B main phase crystal grains. As a result, it is considered that the decrease in coercivity due to the Fe-rich phase can be suppressed.

The area ratio of the Fe rich phase can be calculated by the following procedure. First, element mapping of the R-T-B-based sintered magnet cut surface is performed by EPMA, and a place where the characteristic X-ray intensity of Fe is higher than that of R ₂ T ₁₄ B main phase crystal particles is specified. The location is then subjected to quantitative analysis by EPMA, the concentration of each element is analyzed and compared to the concentration in the R ₂ T ₁₄ B main phase crystal grains. As a result of comparison, a region including R and having an Fe concentration higher than that of the R ₂ T ₁₄ B main phase crystal particle is identified and compared with the backscattered electron image. In the backscattered electron image, an area of the same contrast including the area identified by EPMA is identified as the Fe-rich phase. The area ratio of the Fe rich phase identified after that is calculated by image processing software.

In the present embodiment, the area ratio of the Fe-rich phase to the cut area of the RTB-based sintered magnet is in the range of 0.05% to 1.0%. If the area ratio of the Fe-rich phase to the cutting area of the RTB-based sintered magnet is less than 0.05%, the concentration of the iron group element in the two grain boundaries increases, and the magnetic division effect is weakened Coercivity tends to decrease. On the other hand, when the area ratio of the Fe-rich phase to the cutting area of the RTB-based sintered magnet exceeds 1.0%, the residual magnetic flux density decreases due to the reduction of the main phase volume ratio, and the Fe-rich phase The coercivity tends to decrease because it functions as a nucleation site of reverse magnetic domain. More preferably, the area ratio of the Fe-rich phase to the cut area of the RTB-based sintered magnet is in the range of 0.3% to 0.7%. The area ratio of the Fe-rich phase can be controlled by the composition of the sintered body such as the amount of B or the amount of Zr, the composition of the second alloy in the case of using the two-alloy method, or the aging treatment condition.

The RTB-based sintered magnet according to the present embodiment includes a grain boundary phase in addition to the main phase and the Fe-rich phase. The grain boundary phase may include an R-rich phase mainly composed of R, an R ₆ T ₁₃ M phase, and the like. In addition to the R-rich phase, a B-rich phase having a high proportion of boron (B) atoms may be included.

The content of R in the RTB-based sintered magnet according to the present embodiment is 25% by mass or more and 35% by mass or less, preferably 28% by mass or more and 33% by mass or less. If the content of R is less than 25% by mass, the formation of the R ₂ T ₁₄ B compound which is the main phase of the RTB-based sintered magnet is not sufficient. For this reason, α-Fe or the like having soft magnetism may be precipitated, and the magnetic properties may be degraded. Further, in the present embodiment, in terms of cost reduction and resource risk avoidance, the amount of heavy rare earth element contained as R is preferably 1.0 mass% or less.

In the RTB-based sintered magnet according to the present embodiment, the content of B is preferably 0.70 to 0.95% by mass, and in particular 0.80 to 0.90% by mass. preferable. By setting the content of B in a specific range smaller than the stoichiometric ratio of the basic composition represented by R ₂ T ₁₄ B as described above, the formation of the Fe-rich phase can be promoted.

  T represents one or more types of iron group elements including Fe or Fe and Co. T may be Fe alone, or part of Fe may be substituted by Co. The content of Fe is a substantial remainder in the components of the RTB-based sintered magnet, and a part of Fe may be replaced by Co. When part of Fe is replaced with Co to include Co, the content of Co is preferably 4% by mass or less, more preferably 0.1% by mass or more and 2% by mass or less, and 0.3% by mass. It is further more preferable to set it as% or more and 1.5 mass% or less. When the content of Co exceeds 4% by mass, the residual magnetic flux density tends to decrease. In addition, when the content of Co is less than 0.3% by mass, the corrosion resistance tends to decrease.

  The R-T-B-based sintered magnet of the present embodiment preferably contains Zr. Although the preferable range of content of Zr in this embodiment changes also with other compositions, such as B amount, 0.05-2.0 mass% is preferable, 0.2 mass% or more and 2.0 mass% are more preferable. It is further more preferable that it is 0.45 mass% or more and 1.3 mass% or less. By controlling the content of Zr in accordance with the composition of the RTB-based sintered magnet, the area ratio of the Fe-rich phase can be controlled within a specific range. In addition, Zr can suppress abnormal growth of main phase crystal particles in the manufacturing process of the sintered magnet, and can improve the magnetic characteristics by making the structure of the sintered magnet obtained uniform and fine.

  In the RTB-based sintered magnet of the present embodiment, it is preferable to contain Ga. The content of Ga is preferably 0.05 to 1.5% by mass, and more preferably 0.3 to 1.0% by mass. When Ga is contained in the RTB-based sintered magnet, the Fe-rich phase is likely to contain Ga. Thereby, the wettability between the Fe rich phase and the grain boundary phase is improved, and the high temperature coercivity of the obtained magnet is improved. When the content of Ga exceeds 1.5% by mass, the residual magnetic flux density tends to decrease.

  In the RTB-based sintered magnet of the present embodiment, it is preferable to contain Cu. The content of Cu is preferably in the range of 0.05% by mass to 1.5% by mass, and more preferably 0.2% to 1.0% by mass. By containing Cu, it is possible to achieve high coercivity, high corrosion resistance, and temperature characteristics of the obtained magnet. When the content of Cu exceeds 1.5% by mass, the residual magnetic flux density tends to decrease. When the content of Cu is less than 0.05% by mass, the coercivity tends to decrease.

  In the RTB-based sintered magnet of the present embodiment, it is preferable to contain Al. When Al is contained in the RTB-based sintered magnet, the Fe-rich phase is likely to contain Al. Thereby, the wettability between the Fe rich phase and the grain boundary phase is improved, and the high temperature coercivity of the obtained magnet is improved. The content of Al is preferably 0.03% by mass or more and 0.4% by mass or less, and more preferably 0.05% by mass or more and 0.25% by mass or less.

  The R-T-B-based sintered magnet of the present embodiment may contain additional elements other than the above. Specifically, Ti, V, Cr, Mn, Ni, Nb, Mo, Hf, Ta, W, Si, Bi, Sn, Ca and the like can be mentioned.

  In the RTB-based sintered magnet according to the present embodiment, the content of oxygen (O) is preferably 0.05% by mass or more from the viewpoint of corrosion resistance, and 0.2% by mass from the viewpoint of magnetic characteristics It is preferable that it is the following.

  In the RTB-based sintered magnet according to the present embodiment, the content of carbon (C) is preferably 0.05% by mass or more and 0.3% by mass or less. If the amount of carbon exceeds 0.3% by mass, the magnetic properties of the resulting RTB-based sintered magnet tend to deteriorate. When the amount of carbon is 0.05% by mass or less, orientation becomes difficult at the time of magnetic field molding. Since carbon is mainly added by the lubricant at the time of molding, it can be controlled by the amount.

  Moreover, in the RTB-based sintered magnet according to the present embodiment, the content of nitrogen (N) is preferably 0.15 mass% or less. If the content of N is larger than this range, the coercivity tends to be insufficient.

  The RTB-based sintered magnet according to the present embodiment is generally processed into an arbitrary shape and used. The shape of the RTB-based sintered magnet according to the present embodiment is not particularly limited. For example, rectangular parallelepiped, hexahedron, flat plate, columnar such as square pole, RTB-based sintered magnet It can be made into arbitrary shapes, such as cylindrical shape of a C-shaped cross-sectional shape. As a quadrangular prism, for example, a quadrangular prism whose bottom is a rectangular or a quadrangular prism whose bottom is a square may be used.

In addition, the RTB-based sintered magnet according to the present embodiment includes both a magnet product obtained by processing and magnetizing the magnet and a magnet product not having the magnet magnetized.
<Method of Manufacturing RTB-Based Sintered Magnet>

  An example of the manufacturing method of the RTB type | system | group sintered magnet which concerns on this embodiment is demonstrated. The RTB-based sintered magnet according to the present embodiment can be manufactured by the usual powder metallurgy method, and in the powder metallurgy method, a preparation step of preparing a raw material alloy, and pulverizing the raw material alloy to obtain a raw material fine powder The process of obtaining a powder, the process of forming the raw material fine powder to form a compact, the process of sintering the compact to obtain a sintered body, and the heat treatment process of subjecting the sintered body to an aging treatment.

  The preparation step is a step of preparing a raw material alloy having each element contained in the RTB-based sintered magnet according to the present embodiment. In the present embodiment, a two-alloy material is prepared by mixing two alloys of a first alloy mainly for the formation of the main phase and a second alloy mainly for the formation of grain boundaries. Although the case of the method will be described, it is also possible to use a single alloy method using a single alloy without dividing the first alloy and the second alloy.

First, a raw material metal having a predetermined element is prepared, and a strip casting method or the like is performed using these. A raw material alloy can be prepared by this. As a raw material metal, for example, rare earth metals, rare earth alloys, pure iron, pure cobalt, ferroboron, or alloys of these may be mentioned. Using these raw material metals, a raw material alloy is prepared such that an RTB-based sintered magnet having a desired composition can be obtained.

  In the case of using the 2-alloy method, it is preferable to set the alloy composition such that the amount of R contained in the second alloy is lower than that of the first alloy and the amount of T is the balance. With such an alloy composition, the second alloy can have an alloy structure containing a large amount of Fe-rich phase, thereby promoting the formation of the Fe-rich phase in the RTB-based sintered magnet. it can. The amount of R of the second alloy is preferably 20 to 28% by mass.

  The grinding step is a step of grinding the raw material alloy obtained in the preparation step to obtain a raw material fine powder. This step is preferably performed in two steps of a coarse grinding step and a fine grinding step, but may be performed in one step. The coarse grinding process can be carried out in an inert gas atmosphere using, for example, a stamp mill, a jaw crusher, a brown mill or the like. After storing hydrogen, it is also possible to carry out pulverization and hydrogen storage pulverization. In the coarse pulverizing step, the raw material alloy is pulverized until the particle size becomes about several hundred μm to several mm.

Further, in order to obtain high magnetic properties, it is preferable to set the atmosphere in each process from the pulverizing process to the sintering process to a low oxygen concentration. The oxygen concentration is adjusted by controlling the atmosphere in each manufacturing process. When the oxygen concentration in each manufacturing process is high, the rare earth elements in the powder of the alloy are oxidized to form an R oxide, which is not reduced during sintering and precipitates as it is at the grain boundary in the form of an R oxide. Of the sintered R-T-B sintered magnet is lowered. Therefore, for example, the oxygen concentration in each step is preferably 100 ppm or less.

  In the fine pulverizing step, the coarse powder obtained in the coarse pulverizing step is finely pulverized to prepare a raw material fine powder having an average particle diameter of about several μm. The average particle diameter of the raw material fine powder may be set in consideration of the degree of growth of crystal grains after sintering. Milling can be performed, for example, using a jet mill.

 When it is intended to obtain a finely divided powder of fine particle size using a jet mill, reagglomeration of the pulverized powder and adhesion to the container wall are likely to occur because the surface of the pulverized powder is very active. The yield tends to be low. Therefore, when pulverizing the coarsely pulverized powder of the alloy, a grinding aid such as zinc stearate or oleic acid amide is added to prevent reagglomeration of the powders and adhesion to the container wall, thereby achieving high yield. Pulverized powder can be obtained at a rate. In addition, it is possible to obtain a pulverized powder with high orientation at the time of molding by adding a grinding aid as described above. The amount of addition of the grinding aid varies depending on the particle size of the pulverized powder and the type of the grinding aid to be added, but is preferably about 0.1% to 1% by mass%.

  The molding step is a step of molding the raw material fine powder in a magnetic field to produce a molded body. Specifically, after the raw material fine powder is filled in a mold arranged in an electromagnet, a magnetic field is applied by an electromagnet to orientate the crystal axis of the raw material fine powder, and the raw material fine powder is pressurized by pressing I do. The molding in the magnetic field may be performed, for example, in a magnetic field of 1000 to 1600 kA / m at a pressure of about 30 to 300 MPa.

As the forming method, in addition to dry forming in which the raw material fine powder is formed as it is as described above, wet forming in which a slurry in which the raw material fine powder is dispersed in a solvent such as oil can be applied.

  The shape of the molded body obtained by molding the finely pulverized powder is not particularly limited. For example, according to the shape of the desired RTB-based sintered magnet, such as rectangular parallelepiped, flat plate, column, ring, etc. Can have any shape.

  The sintering step is a step of sintering a formed body to obtain a sintered body. After compacting in a magnetic field, the compact can be sintered in vacuum or in an inert gas atmosphere to obtain a sintered body. Sintering conditions are preferably set appropriately depending on conditions such as the composition of the compact, the method of pulverizing the raw material fine powder, and the particle size, but for example, it may be performed at 1000 ° C. to 1100 ° C. for about 1 to 48 hours.

  After sintering the molded body, the RTB-based sintered magnet is subjected to aging treatment. After sintering, the R-T-B-based sintered magnet is subjected to an aging treatment by holding the obtained RTB-based sintered magnet at a temperature lower than that during sintering. The aging treatment may be performed in a temperature range of 500 ° C. to 900 ° C. However, after heat treatment at around 900 ° C., heat treatment at around 600 ° C. may be performed in two steps. Treatment conditions are adjusted appropriately according to the number of times of aging treatment. Such an aging treatment can improve the magnetic properties of the RTB-based sintered magnet.

  When the aging treatment is performed in two stages, the aging treatment time in the second stage is preferably in the range of 10 to 30 minutes. When the second stage treatment time is 10 minutes or less, the reaction tends to be insufficient and the Fe rich phase amount tends to be large. If the treatment time is 30 minutes or more, the reaction between the Fe-rich phase and the M element proceeds, and it tends to be impossible to obtain a sufficient amount of Fe-rich phase to obtain characteristics.

  After the aging treatment is performed on the RTB-based sintered magnet, the RTB-based sintered magnet is rapidly cooled in an Ar gas atmosphere. Thereby, the RTB based sintered magnet according to the present embodiment can be obtained. The cooling rate is not particularly limited, and is preferably 30 ° C./min or more.

  The obtained RTB-based sintered magnet may be processed into a desired shape as needed. Examples of the processing method include shape processing such as cutting and grinding, and chamfering processing such as barrel polishing.

  The method may further include the step of diffusing the heavy rare earth element into the grain boundaries of the processed RTB-based sintered magnet. In grain boundary diffusion, a compound containing a heavy rare earth element is attached to the surface of an RTB-based sintered magnet by coating or evaporation, and then heat treatment is performed, or in an atmosphere containing heavy rare earth element vapor. It can implement by heat-processing with respect to a RTB type | system | group sintered magnet. Thereby, the coercivity of the RTB-based sintered magnet can be further improved.

  The R-T-B-based sintered magnet obtained by the above steps may be subjected to surface treatment such as plating, resin coating, oxidation treatment, chemical conversion treatment and the like. This can further improve the corrosion resistance.

  In the present embodiment, although the processing step, the grain boundary diffusion step, and the surface treatment step are performed, these steps are not necessarily performed.

  Although the RTB-based sintered magnet according to the present embodiment can be obtained by the above method, the method of producing the RTB-based sintered magnet is not limited to the above, and may be changed as appropriate.

  Next, the present invention will be described in more detail based on specific examples, but the present invention is not limited to the following examples.

(Experimental examples 1 to 9)
First, a raw material metal of a sintered magnet was prepared, and a first alloy and a second alloy were prepared by the strip casting method with the composition shown in Table 1. The sintered body composition shown in Table 1 is a target composition as an RTB-based sintered magnet, and is a composition in which the first alloy and the second alloy are mixed in a ratio of 95: 5, respectively. The amount of R of the second alloy was 25% by mass. In Experimental Examples 1 to 8, the final composition is manufactured by changing the amount of Zr, and the amount of Fe-rich phase in the RTB-based sintered magnet is controlled. In Experimental Example 9, it is the level which changed the aging treatment time of the 2nd step by the composition of Experimental example 5.

  After hydrogen was absorbed into the obtained raw material alloy, a hydrogen pulverizing treatment was performed to carry out dehydrogenation at 500 ° C. for 1 hour in an Ar atmosphere. Then, the obtained pulverized material was cooled to room temperature under Ar atmosphere.

The ground product of the first and second alloys obtained was mixed at a compounding ratio of 95: 5, 0.3% by mass of oleic acid amide was added as a grinding aid, and mixed, and then using a jet mill. Fine grinding was performed to obtain a raw material powder having an average particle diameter of 2 to 3 μm.

  The obtained raw material powder was compacted under a low oxygen atmosphere under the conditions of an orientation magnetic field of 1200 kA / m and a compacting pressure of 120 MPa to obtain a compact.

  Thereafter, the molded body was sintered at 1060 ° C. for 4 hours in vacuum, and then quenched to obtain a sintered body. The obtained sintered body was subjected to two-stage aging in an Ar gas atmosphere, and was subjected to an aging treatment at 850 ° C. for one hour in the first stage and at 530 ° C. in the second stage. The aging treatment time in the second stage was 15 minutes in Experimental Examples 1 to 8 and 90 minutes in Experimental Example 9, respectively.

  The structure and magnetic properties of the RTB-based sintered magnet of the present embodiment were measured and evaluated by the following methods. As a structure | tissue, the area ratio of the Fe rich phase in arbitrary cut surfaces of a RTB type | system | group sintered magnet was calculated | required. As a magnetic characteristic, residual magnetic flux density Br and coercive force HcJ at 180 ° C. of the RTB-based sintered magnet were measured.

The surface of the cross section of the obtained RTB-based sintered magnet is scraped by ion milling to remove the influence of oxidation and the like on the outermost surface, and then the cross section of the RTB-based sintered magnet is subjected to EPMA (electron beam The element distribution was observed with a microanalyzer. The structure of the R-T-B sintered magnet of each experimental example was observed by EPMA and the element mapping by EPMA was performed in the region of 50 μm square. From the mapping data, a place where the Fe concentration was higher than that in R ₂ T ₁₄ B main phase crystal particles was identified, and a quantitative analysis was performed on the place. As a comparison, quantitative analysis of the center of adjacent R ₂ T ₁₄ B main phase crystal particles was also performed. Table 2 shows the results of the quantitative analysis of Experimental Example 3. The composition ratio in the table is the ratio of each element when the total number of atoms of Nd, Pr, Fe, Co, B, Al, and Ga is 100. Measurement 1 and 2 are the results of quantitative analysis of R ₂ T ₁₄ B main phase crystal particles, and measurement points 3 and 4 are the results of quantitative analysis of a place where the Fe concentration is higher than that of R ₂ T ₁₄ B main phase crystal particles. As compared with R ₂ T ₁₄ B main phase crystal particles at measurement points 1 and ₂ , Fe concentration is high at measurement points 3 and 4 and R is included, so measurement points 3 and 4 are Fe-rich It was confirmed that it was a phase.

  After that, the range of the Fe rich phase was identified by comparing with the backscattered electron image. Thereafter, by repeating the above procedure, the range of the Fe rich phase was identified in the 500 μm square area, and the area ratio of the identified Fe rich phase was calculated by the image processing software. The reflection electron image of Experimental example 5 is shown in FIG. The part shown by the arrow is the Fe-rich phase specified.

Table 3 shows the results of calculating the area ratio of the Fe-rich phase of the RTB-based sintered magnet for each of the experimental examples. The area ratio of the Fe-rich phase of each RTB-based sintered magnet of the experimental example was 0 to 1.23%. The area ratio of the Fe-rich phase was in the range of 0.05% to 1.0% in each of Experimental Examples 3 to 6, which are examples of the present invention. In the experimental examples 1 and 2 which are comparative examples of the present invention, the area ratio of the Fe rich phase was more than 1.0%, and in the experimental examples 7 to 9, the area ratio of the Fe rich phase was less than 0.05%.

The resulting RTB-based sintered magnet was compositionally analyzed by fluorescent X-ray analysis and inductively coupled plasma mass spectrometry (ICP-MS). As a result, it could be confirmed that any RTB-based sintered magnet substantially matches the target composition (composition shown in Table 1). In addition, the oxygen content is an inert gas melting-non-dispersive infrared absorption method, the nitrogen content is a nitrogen content, the inert gas melting-thermal conductivity method is a carbon content, and the oxygen content is a combustion-infrared absorption method. Measured. The results of the amounts of oxygen, nitrogen and carbon are shown in Table 3.

  The magnetic properties of each RTB based sintered magnet of Experimental Examples 1 to 9 were measured using a BH tracer. The measurement sample was heated to 180 ° C. by a heater, and the residual magnetic flux density Br and the coercivity HcJ at 180 ° C. were measured as magnetic characteristics. Table 3 shows the measurement results of the residual magnetic flux density Br and the coercivity HcJ of each R-T-B sintered magnet. Further, in each of Experimental Examples 1 to 9, the difference in HcJ between Experimental Example 8 in which the area ratio of the Fe-rich phase is zero and each experimental example is also shown in Table 3 as an HcJ improvement value. When HcJ improved by 10% or more, it was judged that there was an HcJ improvement effect.

From Table 3, HcJ has a low value in Experimental Examples 7 to 9, which are comparative examples in which the area ratio of the Fe-rich phase is less than 0.05%. In Experimental Examples 3 to 6, which are Examples in which the area ratio of the Fe-rich phase is 0.05 to 1.0%, higher HcJ was obtained as compared to Comparative Examples. On the other hand, in Experimental Examples 1 and 2 in which the area ratio of the Fe rich phase is 1.0% or more, it was confirmed that both Br and HcJ decreased. In addition, in Experimental Examples 4 and 5 in which the area ratio of the Fe rich phase is in the range of 0.3% to 0.7%, a particularly high HcJ improvement effect is confirmed. The HcJ improvement was up to 156 kA / m.

(Experimental examples 10 to 13)
Experimental Examples 10 to 10 are the same as Experimental Examples 1 to 9 except that a raw material alloy is prepared by a strip casting method so that RTB-based sintered magnets having the composition shown in Table 4 can be obtained, respectively. Thirteen RTB based sinterings were prepared.

About each RTB-based sintered magnet obtained in Experimental Examples 10 to 13, in the same manner as in Experimental Examples 1 to 9, the place where the Fe concentration is higher than that of R2T14B main phase crystal particles, and the adjacent R2T14B main phase Quantitative analysis of the central part of the crystal particles was performed. The results of quantitative analysis for Experimental Example 11 are shown in Table 5. It was confirmed that the measurement point 6 is the Fe-rich phase because the Fe concentration is high at the measurement point 6 and contains R as compared with the R2T14B main phase crystal particles at the measurement point 5. In addition, from the result of measurement point 6, it was confirmed that an Fe-rich phase containing neither Al nor Ga was generated.

The area ratio of the Fe-rich phase of the R-T-B-based sintered magnet was calculated for each RTB-based sintered magnet obtained in Experimental Examples 10 to 13 in the same manner as in Experimental Examples 1 to 9. The results are shown in Table 6. In Experimental Examples 11 and 12, the area ratio of the Fe rich phase was in the range of 0.05% to 1.0%. In Experimental Example 10, the range of the Fe-rich phase was more than 1.0%, and in Experimental Example 13, the area ratio of the Fe-rich phase was less than 0.05%.

  The compositional analysis of each of the RTB-based sintered magnets obtained in Experimental Examples 10 to 13 was carried out in the same manner as in Experimental Examples 1 to 9. As a result, any RTB-based sintered magnet was also aimed. It was confirmed that the composition substantially matches the composition (each composition shown in Table 4). Moreover, it carries out similarly to Experimental example 1-9, and it shows according to Table 6 about the result of having analyzed the amount of oxygen, the amount of nitrogen, and the amount of carbon.

  The magnetic properties of the RTB-based sintered magnets obtained in Experimental Examples 10 to 13 were evaluated in the same manner as in Experimental Examples 1 to 9. The results are shown in Table 6. Similarly, in each of Experimental Examples 10 to 13, the difference in coercive force between Experimental Example 13 in which the area ratio of the Fe-rich phase is zero and each experimental example is also shown in Table 6 as an HcJ improvement value. When HcJ improved by 10% or more, it was judged that there was an HcJ improvement effect. In Experimental Example 10 in which the area ratio of the Fe-rich phase is 1.0% or more and in Experimental Example 13 in which the area ratio of the Fe-rich phase is less than 0.05%, HcJ has a low value. In Experimental Examples 11 and 12 in which the area ratio of the Fe rich phase is 0.05% to 1.0%, the HcJ improving effect was obtained. The improvement value of HcJ was up to 84 kA / m.

  According to the magnetic characteristic results of each of the RTB-based sintered magnets of Experimental Examples 1 to 9 and Experimental Examples 10 to 13, better HcJ improvement is obtained when Al and Ga are contained in the Fe-rich phase. It was confirmed that the effect could be obtained.

  The present invention has been described above based on the embodiments. It will be understood by those skilled in the art that the embodiments are illustrative and that various modifications and changes are possible within the scope of the present invention, and such modifications and changes are within the scope of the present invention. It is a place. Accordingly, the descriptions and drawings herein are to be considered as illustrative and not restrictive.

  According to the present invention, an RTB-based sintered magnet having good high-temperature coercivity even when the use amount of heavy rare earth elements such as Dy and Tb is significantly reduced compared to the conventional case, or even when not used. Can be provided.

2 R ₂ T ₁₄ B main phase crystal particle 4 Fe rich phase 6 grain boundary phase

Claims (3)

An R-T-B-based sintered magnet having R ₂ T ₁₄ B main phase crystal particles, wherein in addition to the main phase crystal particles, the concentration of Fe is higher than that of the main phase crystal particles, and R further comprising a Fe-rich phase containing the R-T-B based sintered the Fe-rich phase area ratio range der of 1.0% less than 0.05% relative to the cutting area of the magnet is, at 180 ° C. R-T-B based sintered magnet coercivity is characterized der Rukoto than 444kA / m. The R-T-B-based sintered magnet according to claim 1, wherein the Fe-rich phase contains an M element (M is at least one selected from Al and Ga). The area ratio of the Fe-rich phase to the cutting area of the RTB-based sintered magnet is in the range of 0.3% or more and 0.7% or less. RTB based sintered magnet of