JP2006249456A - R-fe-b-based rare earth sintered magnet and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an R-Fe-B-based rare earth sintered magnet by which a sintered magnet having a high degree of orientation can be obtained using press forming. <P>SOLUTION: Fine powder of a first alloy having a composition consisting of 11-18 at.% of at least one rare earth element selected from the light rare earth elements, 4-12 at.% of an element A (boron or a boron-carbon mixture) and the balance an element T which is Fe or a mixture of Fe and another transition metal and trace additive elements M with inevitable impurities is mixed with fine powder of a second alloy having a composition consisting of 10-35 of at.% at least one rare earth element selected from the heavy rare earth elements, 0-10 at.% of the element A (boron or the boron-carbon mixture) and the balance the element T which is Fe or the mixture of Fe and another transition metal and the trace additive elements M with inevitable impurities, the resulting mixed powder is compacted while applying a reversal magnetic field as an orienting magnetic field, and then sintering is carried out. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an R—Fe—B rare earth sintered magnet and a method for producing the same.

  Rare earth alloy sintered magnets (permanent magnets) are generally produced by sintering a rare earth alloy powder compact and, if necessary, aging treatment.

  Currently, two types of samarium / cobalt magnets and neodymium / iron / boron magnets are widely used in various fields. Among these, neodymium / iron / boron magnets (hereinafter referred to as “R—Fe—B magnets”, R is a rare earth element including Y, Fe is iron, and B is boron) are various magnets. Since it has the highest maximum magnetic energy product among them and its price is relatively low, it is actively used in various electronic devices.

The R—Fe—B based sintered magnet is mainly composed of a main phase composed of a tetragonal compound of R ₂ Fe ₁₄ B, an R rich phase composed of Nd and the like, and a B rich phase. A part of Fe may be substituted with a transition metal such as Co or Ni, and a part of B may be substituted with C. R-Fe-B based sintered magnets to which the present invention is suitably applied are described, for example, in the specifications of US Pat. No. 4,770,723 and US Pat. No. 4,792,368.

  Conventionally, an ingot casting method has been used in order to produce an R—Fe—B alloy to be such a magnet. According to a general ingot casting method, a rare earth metal, electrolytic iron, and ferroboron alloy as starting materials are melted at a high frequency, and the resulting molten metal is cooled relatively slowly in a mold to produce an alloy ingot.

In recent years, the molten alloy is cooled relatively quickly by bringing it into contact with the inner surface of a single roll, twin roll, rotating disk, or rotating cylindrical mold, etc., and from the molten alloy, a solidified alloy (“alloy flake”) that is thinner than the ingot. The rapid cooling method typified by the strip casting method and the centrifugal casting method, which are used to produce the same), has attracted attention. The thickness of the alloy piece produced by such a rapid cooling method is generally in the range of about 0.03 mm to about 10 mm. According to the rapid cooling method, the molten alloy starts to solidify from the surface in contact with the cooling roll (roll contact surface), and crystals grow in a columnar shape from the roll contact surface in the thickness direction. As a result, the quenched alloy produced by the strip casting method has an R ₂ Fe ₁₄ B crystal having a minor axis size of about 0.1 μm to about 100 μm and a major axis size of about 5 μm to about 500 μm. And a structure containing an R-rich phase dispersed and present at the grain boundaries of the R ₂ Fe ₁₄ B crystal phase. The R-rich phase is a nonmagnetic phase in which the concentration of the rare earth element R is relatively high.

The quenched alloy has a relatively short time (cooling rate: 10 ² ° C / second or more and 10 ⁴ ° C / second or less) compared with an alloy (ingot alloy) produced by a conventional ingot casting method (die casting method). ), The structure is refined and the crystal grain size is small. Further, since the area of the grain boundary is wide and the R-rich phase spreads widely within the grain boundary, there is an advantage that the dispersibility of the R-rich phase is also excellent. Because of these characteristics, a magnet having excellent magnetic properties can be produced by using a quenched alloy.

  In this specification, a solid alloy lump is called an “alloy lump”, and a molten metal such as an alloy ingot obtained by a conventional ingot casting method and an alloy flake obtained by a rapid cooling method such as a strip cast method is cooled. The obtained solidified alloy is included.

  A compact is produced using fine powder obtained by pulverizing these alloy ingots. The fine powder used for the production of the molded body is pulverized by, for example, a hydrogenation pulverization method and / or various mechanical pulverization methods (for example, a ball mill or an attritor is used). For example, by a fine pulverization method using a dry pulverization method using a jet mill. The average particle diameter of the fine powder is preferably in the range of 1.5 μm to 7 μm from the viewpoint of magnetic properties. Note that the “average particle size” of the powder refers to a FSSS (Fisher Sub-Sieve Sizer) particle size unless otherwise specified.

  A uniaxial press molding method is widely used for the production of the molded body. In particular, when producing a sintered magnet having a high maximum magnetic energy product (abnormally sintered magnet), an orientation magnetic field is applied in the compression step. The higher the degree of orientation of the crystal grains, the larger the maximum magnetic energy product. Further, when the degree of orientation is high, the effect is obtained that Br in the lateral direction (direction orthogonal to the orientation magnetic field) is small and that there is little bias.

  Therefore, as a method for increasing the degree of orientation, conventionally, a method of applying a pulse magnetic field having a high strength as the orientation magnetic field applied in the uniaxial press molding process has been employed. However, in order to apply a strong pulse magnetic field, the magnetic circuit becomes large. Further, since the die (die) generates heat due to the eddy current accompanying application of the orientation magnetic field (for example, reaches 60 ° C. or more), it is necessary to cool the die, and continuous molding cannot be performed.

In addition, if an isotropic compression molding method such as the CIP method or the RIP method is used, a molded body having a higher degree of orientation than the uniaxial press molding method can be obtained, but the molded body obtained by the CIP method or the RIP method is Since the dimensional accuracy is low (typically, the central part of the molded body swells), it is necessary to process the sintered body to obtain a sintered magnet having a desired outer shape, and production efficiency and material yield There is a problem that is low.
JP-A-6-96928

  The present invention has been made in view of the above-described points, and a method for producing an R—Fe—B rare earth sintered magnet capable of obtaining a sintered magnet having a higher degree of orientation than conventional ones even by using press molding. The purpose is to provide.

  The method for producing a rare earth sintered magnet according to the present invention is a method for producing an R—Fe—B rare earth sintered magnet, which is a light rare earth element LR (La, Ce, Pr, 11 to 18 atomic%). At least one rare earth element selected from the group consisting of Nd, Pm, Sm, Eu and Gd, including at least one kind of Nd and Pr) and an element A (boron of 4 atomic% to 12 atomic%) Or a mixture of boron and carbon), with the balance being element T which is Fe or a mixture of Fe and other transition metals, a minor additive element M and an inevitable impurity, and D99 (cumulative volume fraction) And a step of preparing a first alloy fine powder having a particle size of 99% or less of 12 μm or less, and a heavy rare earth element HR (Y, Tb, Dy, Ho, Er, Tm, 10 atom% or more and 35 atom% or less). Yb, Lu And at least one rare earth element selected from the group consisting of element A (boron or a mixture of boron and carbon) with the balance being Fe or Fe and another transition metal. A step of preparing a second alloy fine powder having a composition which is an element T as a mixture, a trace amount of additive element M and an inevitable impurity, and D99 (particle diameter with a cumulative volume fraction of 99%) of 12 μm or less; A step of mixing the first alloy fine powder and the second alloy fine powder to prepare a mixed powder; and a step of obtaining a compact by compressing the mixed powder while applying a reversal magnetic field as an orientation magnetic field; And a step of obtaining a sintered body by sintering the molded body. The sintering temperature is, for example, in the range of 1000 ° C. to 1140 ° C., and the sintering time is, for example, in the range of 1 hour to 8 hours.

  In one embodiment, the mixed powder includes 1% by mass or more and 50% by mass of the second alloy fine powder.

  In one embodiment, the average particle size of the first and second alloy fine powders is 2.0 μm or more and 5.0 μm or less.

  In one embodiment, in the sintering step, crystal grain growth is performed until the average crystal grain size of the main phase is in the range of 8 μm to 40 μm.

  In one embodiment, the strength of the reversal magnetic field is 2.5T or less. The strength of the reversal magnetic field is preferably 1.0 T or more.

  In one embodiment, the heavy rare earth element HR of the second alloy fine powder contains at least one element selected from Dy and Tb.

  In a certain embodiment, the process of producing the said molded object is performed using a uniaxial press molding method.

  The rare earth sintered magnet of the present invention is manufactured by any one of the above manufacturing methods.

In one embodiment, Bs ′ = (Br _x ² + Br _y ² + Br _z ²⁾ where Br _x is the residual magnetic flux density in the orientation magnetic field direction, and Br _y and Br _z are the residual magnetic flux densities in two directions orthogonal to the orientation magnetic field direction. ) When the ratio of Br _{x to} ^1/2 (= Br _x / Bs ′) is defined as the orientation degree parameter P, the value of the orientation degree parameter P is more than 0.990.

  According to the present invention, an R—Fe—B rare earth sintered magnet having a higher degree of orientation than that of the prior art can be produced even by using uniaxial press molding.

  Hereinafter, a method for manufacturing an R—Fe—B rare earth sintered magnet according to an embodiment of the present invention will be described with reference to the drawings.

  In the method for manufacturing an R—Fe—B rare earth sintered magnet according to the embodiment of the present invention, a heavy rare earth element HR represented by Dy is used in addition to a light rare earth element LR represented by Nd as a rare earth element. Also, a first alloy containing a light rare earth element LR and a second alloy containing a heavy rare earth element HR are prepared separately and mixed as fine powders (first alloy fine powder and second alloy fine powder), respectively. Then, a molded body is produced using the obtained mixed powder (sometimes referred to as “blend method”). At this time, both the first alloy fine powder and the second alloy fine powder have a D99 (particle diameter with a cumulative volume fraction of 99%) in the fine particle size distribution determined by FSSS of 12 μm or less.

  Here, the first alloy is a light rare earth element LR of 11 atomic% or more and 18 atomic% or less (La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd, at least one kind of rare earth element selected from the group consisting of And containing at least one of Nd and Pr) and 4 to 12 atom% of element A (boron or a mixture of boron and carbon) with the balance being Fe or Fe and another transition metal Element T, which is a mixture thereof, a trace amount of additive element M, and an inevitable impurity composition.

  On the other hand, the second alloy is a heavy rare earth element HR (at least one kind selected from the group consisting of Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu) of 10 atomic% to 35 atomic%. And element A (boron or a mixture of boron and carbon) in an amount of not less than 10 atom% and not more than 10 atom%, with the balance being Fe or a mixture of Fe and other transition metals, element T, trace additive element M, and It has a composition that is an inevitable impurity.

  Note that the transition metal element is Ti, V, Cr, Mn, Fe, Co, Ni, or the like, and the element T is preferably one in which Fe or a part of Fe is substituted with at least one of Ni and Co. Further, the trace additive element M is preferably at least one of Al, Cu, Ga, Cr, Mo, V, Nb, and Mn, and the content is preferably 5 atomic% or less.

The mixed powder of the first alloy fine powder and the second alloy fine powder preferably contains 1% by mass or more and 50% by mass of the second alloy fine powder. If the amount of the second alloy fine powder is less than the above range, the effects of the present invention described later may not be obtained. On the other hand, if the amount of the first alloy fine powder is less than the above range, the first alloy fine powder may not be obtained. The R ₂ Fe ₁₄ B type crystal phase, which is the main phase contained in the powder, may decrease, resulting in a problem that the residual magnetic flux density Br decreases.

  Moreover, it is preferable that the ratio of the heavy rare earth elements in the rare earth elements in the finally obtained mixed powder or sintered body is in the range of 0.1 atomic% to 10 atomic%. When the ratio of the heavy rare earth element is lower than the above range, the effects of the present invention described later may not be obtained. On the other hand, when the ratio of the heavy rare earth element is higher than the above range, the magnetic characteristics such as the residual magnetic flux density Br. There may be a problem of lowering.

  The first and second alloy fine powders are prepared by the known method described above. However, from the viewpoint of magnetic properties, it is preferable to use alloy flakes produced by a rapid cooling method typified by a strip casting method (see, for example, US Pat. No. 5,666,635). In addition, it is preferable to apply a lubricant to the surface of the mixed powder finally used for producing a molded body, if necessary, in order to suppress oxidation and / or improve fluidity and moldability.

  The compression molding step for obtaining a mixed powder compact is performed while applying a reversal magnetic field as an orientation magnetic field. By applying a reversal magnetic field as the orientation magnetic field, it is possible to obtain a higher degree of orientation than before. Further, this effect obtained by applying a reversal magnetic field is obtained with a magnetic field intensity of 2.5 T or less, and it is not necessary to apply a pulse magnetic field, and a static alternating reversal magnetic field may be applied. Therefore, the temperature rise of the die due to the application of the reversal magnetic field does not occur. Note that if the intensity of the reversal magnetic field is less than 1.0 T, the above-described effect may not be obtained.

The compression molding of the mixed powder is preferably performed using a uniaxial press molding method from the viewpoint of productivity. Uniaxial press molding is performed, for example, using an electric press at a pressure of 0.2 ton / cm ^{2 to} 2.0 ton / cm ² (1.96 × 10 ⁴ kPa to 1.96 × 10 ⁵ kPa).

  When the molded body is sintered, the heavy rare earth element HR and the light rare earth element LR undergo mutual diffusion in the sintering process, and the main phase (R-Fe-B crystal phase) mainly containing the light rare earth element HR as the rare earth element. Heavy rare earth element HR is introduced in the vicinity of Since it has such a structure, a decrease in coercive force at room temperature is suppressed as compared with a structure in which heavy rare earth elements HR are uniformly distributed throughout the main phase.

  Further, as shown in an experimental example later, when the second alloy fine powder containing the heavy rare earth element HR is mixed, crystal grains (main phase) grow (coarse) specifically in the sintering process. From this, it is considered that the decrease in the number of fine crystal grains that cause the degree of orientation to decrease contributes to the increase in the degree of orientation.

  In order to obtain such an effect, the average particle diameters of the first alloy fine powder and the second alloy fine powder are both preferably 2.0 μm or more and 5.0 μm or less. If it is smaller than this range, the powder is easily oxidized and difficult to handle. Conversely, if it is larger, it may become difficult to densify during sintering, or the coercive force may be lowered.

In the sintering step, it is preferable to grow the crystal grains until the average crystal grain size of the main phase is in the range of 8 μm to 40 μm. When the final average grain size is less than 8 μm, the effect of improving the degree of orientation due to the coarsening of the crystal grains may not be sufficiently obtained. Conversely, when the average grain size of the crystal grains exceeds 40 μm, the magnetic properties (for example, residual magnetic flux density B _r ) may deteriorate. The sintering conditions are, for example, in the range of 1000 ° C. to 1140 ° C., for example, in the range of 1 hour to 8 hours. What is necessary is just to set so that a crystal grain may be grown to the above-mentioned average particle diameter. The sintering atmosphere may be, for example, a reduced pressure inert gas atmosphere. In addition, the average particle diameter of the main phase (crystal) in the sintered magnet is obtained by drawing a line segment on the structure photograph and dividing the length of the line segment by the number of intersections with the grain boundary (constant direction diameter). Moreover, you may age the obtained sintered compact for about 1 hour to about 8 hours at the temperature of about 450 degreeC-about 800 degreeC as needed, for example.

  According to the manufacturing method of the embodiment of the present invention, the degree of orientation is improved by the effect of applying a reversal magnetic field as the orientation magnetic field and the effect of coarsening of crystal grains in the sintering process. Both of these two effects can be obtained specifically when the second alloy fine powder containing the heavy rare earth element HR is mixed. When a single alloy fine powder containing heavy rare earth element HR and light rare earth element LR is used (sometimes referred to as “single alloy method”), these effects cannot be obtained. From the viewpoint of magnetic properties and price, the light rare earth element LR is preferably Nd or Pr, and the heavy rare earth element HR is preferably Dy or Tb.

  According to the manufacturing method described above, a sufficiently high degree of orientation can be obtained even if the step of producing a molded body is performed using a uniaxial press molding method, so that the degree of orientation can be improved without sacrificing production efficiency. it can. Of course, the effect of improving the degree of orientation can be obtained even by using the CIP method or the RIP method.

  As shown in the experimental examples exemplified below, an orientation degree parameter P defined as follows was introduced in order to quantitatively evaluate the orientation degree.

With the residual magnetic flux density in the orientation magnetic field direction (x-axis direction) of the obtained sintered magnet compact being Br _x and the residual magnetic flux densities in two directions orthogonal to the orientation magnetic field direction being Br _y and Br _z , Bs ′ = ^{_{(Br x 2 + Br y 2}} + Br z 2) the ratio of Br _x for ^1/2 is defined as the degree of orientation parameter _{P (P = Br x / Bs} '). This orientation parameter P is experimentally determined by processing a sintered body into a cube composed of planes orthogonal to the x, y, and z axes (for example, cutting out), and using a flux meter, the residual magnetic flux in each direction. It is obtained by measuring the density Br. For example, the press direction is the z-axis direction, and the direction orthogonal to the x-axis and the z-axis is the y-axis direction.

  At present, the value of the orientation degree parameter P of R-Fe-B rare earth sintered magnets (including Dy as heavy rare earths) that are mass-produced using the press molding method is in the range of 0.980 to 0.990. On the other hand, the value of the orientation degree parameter P of the R—Fe—B rare earth sintered magnet obtained by the manufacturing method of the embodiment according to the present invention exceeds 0.990.

In Patent Document 1, by replacing a part of Nd in the vicinity of the surface of the Nd ₂ Fe ₁₄ B crystal phase that is the main phase with Dy and / or Tb, coercive force is improved and demagnetization is suppressed. It is described. However, as a result of investigation by the present inventors, a sintered magnet having an orientation degree parameter P value exceeding 0.990 cannot be obtained by the method described in Patent Document 1.

  Hereinafter, although the example is given and demonstrated about the manufacturing method of the rare earth sintered magnet by this invention, this invention is not limited at all by the following example.

  As the first alloy fine powder, the composition is LR (Nd): 12.2 atomic%, B: 7.5 atomic%, Co: 1.2 atomic%, Al: 0.6 atomic%, Cu: 0.1 atomic %, Balance: Fe and alloy fine powder with inevitable impurities were prepared.

  As the second alloy fine powder, the composition was HR (Dy): 11.1 atomic%, LR (Nd): 12.2 atomic%, the balance: Fe and fine powder of inevitable impurities (second alloy fine powder for Examples) Powder 1) and an alloy fine powder (second alloy fine powder 2 for Examples) having a composition of HR (Dy) 22.3 atomic%, the balance: Fe and inevitable impurities were prepared.

  Moreover, as a single alloy fine powder for comparison, the composition was LR (Nd): 12.1 atomic%, HR (Dy): 2.0 atomic%, B: 6.1 atomic%, Co: 1.0 Atomic%, Al: 0.5 atomic%, Cu: 0.1 atomic%, balance: Fe and fine powder of alloy with inevitable impurities (Comparative Alloy Fine Powder 1), and composition is LR (Nd): 9. 9 atomic%, HR (Dy): 4.0 atomic%, B: atomic%, Co: 1.0 atomic%, Al: 0.49 atomic%, Cu: 0.1 atomic%, balance: Fe and inevitable impurities An alloy fine powder (Comparative Example Alloy Fine Powder 2) was prepared.

    All of the above alloy fine powders were produced by the following method.

  First, alloy flakes having respective compositions were produced by a strip casting method. The alloy flakes were pulverized by a hydrogenation pulverization method to obtain a coarse alloy powder. The alloy coarse powder was finely pulverized in a nitrogen gas atmosphere using a jet mill apparatus to obtain an alloy powder having a D99 of 11 μm and an average particle size of 4.0 μm.

  Example mixed powder 1: The above first alloy fine powder and the second alloy fine powder 1 were mixed in a mass ratio of 78:22, and mixed using a rocking mixer, and mixed for example. Powder 1 was obtained. The content of Dy in all rare earth elements is 5% by mass (2.0 atomic%).

  Example mixed powder 2: The above first alloy fine powder and the second alloy fine powder 2 were mixed in a mass ratio of 78:22 and mixed using a rocking mixer. Powder 2 was obtained. The content of Dy in all rare earth elements is 10% by mass (4.0 atomic%).

  Comparative Example Alloy Powder 1: The single alloy fine powder for Comparative Example 1 was used. The content of Dy in all rare earth elements is 5% by mass (2.0 atomic%).

  Comparative Example Alloy Powder 2: The single alloy fine powder for Comparative Example 2 was used. The content of Dy in all rare earth elements is 10% by mass (4.0 atomic%).

  A powder material obtained by adding and mixing 0.4% by mass of a liquid lubricant to the above mixed powder or single alloy fine powder was subjected to a pressing step.

The powder material is uniaxially press-molded (pressing pressure 0.8 ton / cm ² (7.84 × 10 ⁴ kPa) while applying an orientation magnetic field using an electric press device, thereby forming a compact (length 40 mm × width 30 mm). × Height 20 mm) The direction of the orientation magnetic field is perpendicular to the pressing direction.

  Moreover, when producing the sintered magnet of an Example, the alternating inversion magnetic field of 1.7T was applied as an orientation magnetic field. For comparison, a 1.7 T static magnetic field was applied as the orientation magnetic field.

  The obtained molded body was sintered at 1080 ° C. for 8 hours in a reduced pressure Ar atmosphere, and then subjected to aging treatment at 500 ° C. for 1 hour.

A cube having a side of 7 mm was cut out from the obtained sintered body, and the residual magnetic flux densities Br _x , Br _y and Br _z in each direction of the cube were measured using a flux meter. The magnetizing magnetic field was 10T.

The orientation parameter P = Br _x / Bs ′ was determined from the residual magnetic flux densities Br _x , Br _y and Br _z . Here, Bs ′ = (Br _x ² + Br _y ² + Br _z ² ) ^1/2 .

  Moreover, the cross section of the obtained sintered magnet was observed using SEM and EPMA. The average crystal grain size was determined from a polarizing microscope photograph.

  FIGS. 1A to 1D show polarized micrographs of a rare earth sintered magnet containing 5% by mass of Dy. FIG. 1 (a) is a cross-sectional polarization micrograph of a sintered magnet (sample a) formed from a molded body produced while applying an alternating reversal magnetic field using the mixed powder 1 for Example. FIG. 1 (b) FIG. 1 is a polarizing micrograph of a sintered magnet (sample b) formed from a molded body produced while applying a static magnetic field using the mixed powder 1 for an example, and FIG. 1C is an alloy powder 1 for a comparative example. Is a cross-sectional polarization micrograph of a sintered magnet (sample c) formed from a molded body produced while applying an alternating reversal magnetic field using (a), (d) is a static magnetic field using the alloy powder for comparative example 1 It is a cross-sectional polarizing microscope photograph of the sintered magnet (sample d) formed from the molded object produced while applying.

As is apparent from a comparison of FIGS. 1 (a) and 1 (b) with FIGS. 1 (c) and 1 (d), the crystal grains of the sintered magnet (sample a and sample b) using the mixed powder for Example. The diameter is larger than the crystal grain size of the sintered magnet (sample c and sample d) using the alloy powder for comparative example (single alloy). The average crystal grain size determined from the polarizing microscope photograph was 10.5 μm for sample a, 11.2 μm for sample b, 4.8 μm for sample c, and 4.9 μm for sample d. The residual magnetic flux density Br _x was 1.307 T for sample a, 1.302 T for sample b, 1.290 T for sample c, and 1.284 T for sample d.

  FIGS. 2A to 2D show polarization micrographs of a rare earth sintered magnet containing 10% by mass of Dy. FIG. 2A is a cross-sectional polarization micrograph of a sintered magnet (sample e) formed from a molded body produced while applying an alternating inversion magnetic field using the mixed powder 2 for the example. Fig. 2 is a polarizing micrograph of a sintered magnet (sample f) formed from a molded body produced while applying a static magnetic field using the mixed powder 2 for Example, and Fig. 2 (c) is an alloy powder 2 for comparative example. FIG. 2D is a cross-sectional polarization micrograph of a sintered magnet (sample g) formed from a molded body produced while applying an alternating reversal magnetic field using FIG. 2. FIG. 2D is a static magnetic field using the alloy powder 2 for comparative example. It is a cross-sectional polarized light microscope photograph of the sintered magnet (sample h) formed from the molded object produced while applying A.

  As is apparent from a comparison between FIGS. 2 (a) and 2 (b) and FIGS. 2 (c) and 2 (d), the crystal grains of the sintered magnet (sample e and sample f) using the mixed powder for Example. The diameter is larger than the crystal grain size of the sintered magnet (sample g and sample h) using the alloy powder for comparative example (single alloy). The average crystal grain size determined from the polarizing microscope photograph was 17.9 μm for sample e, 18.5 μm for sample f, 4.8 μm for sample g, and 4.8 μm for sample h. The residual magnetic flux density Br was 1.190 T for sample e, 1.181 T for sample f, 1.159 T for sample g and 1.161 T for sample h.

  In addition, when the sintering conditions of the molded body using the mixed powder for Examples were set to sintering temperature: 1040 ° C. and sintering time: 16 hours, the average crystal grain size of the obtained sintered magnet was 8 μm. The sintered body density was not sufficient. Therefore, it is preferable to sinter so that the average particle diameter is 8 μm or more. Moreover, since a residual magnetic flux density will fall when an average particle diameter exceeds 40 micrometers, it is preferable that an average particle diameter exists in the range of 8 micrometers or more and 40 micrometers or less.

  FIG. 3 shows the value of the orientation degree parameter of each sample.

  As can be seen from FIG. 3, the sintered magnet using the alloy powder for the comparative example has a low degree of orientation, and when an alternating inversion magnetic field is applied as the orientation magnetic field, the degree of orientation is further reduced than when a static magnetic field is applied. Yes. On the other hand, when the mixed powder for the example is used, the degree of orientation is higher than that of the sintered magnet using the alloy powder for the comparative example. Furthermore, the sintered magnets (sample a and sample e) to which an alternating reversal magnetic field is applied are higher than the sintered magnets (sample b and sample f) to which a static magnetic field is applied, and the orientation degree parameter exceeds 0.990. The reason is considered as follows.

  Since the concentration gradient of the element is large, the crystal grains become coarse during the sintering process. In this process, fine crystal grains that cause the disorder of orientation are absorbed by the large particles and disappear. As a result, since the number of fine crystal grains in the sintered body is reduced, a high degree of orientation can be obtained.

  As described above, according to the present invention, an R—Fe—B rare earth sintered magnet having a higher degree of orientation than the conventional one and a method for manufacturing the same are provided. The R—Fe—B rare earth sintered magnet according to the present invention is suitably used for a small motor.

(A) is a cross-sectional polarization micrograph of a sintered magnet (sample a) formed from a molded body produced while applying an alternating inversion magnetic field using the mixed powder 1 for the example, and (b) is for the example. It is a polarizing microscope photograph of the sintered magnet (sample b) formed from the compact | molding | casting produced while applying a static magnetic field using the mixed powder 1, (c) is an alternating inversion magnetic field using the alloy powder 1 for a comparative example. FIG. 4 is a cross-sectional polarization micrograph of a sintered magnet (sample c) formed from a molded body produced while applying, and (d) is a molded body produced using a comparative example alloy powder 1 while applying a static magnetic field. 2 is a cross-sectional polarization micrograph of a sintered magnet (sample d) formed from (A) is a cross-sectional polarization micrograph of a sintered magnet (sample e) formed from a molded body produced while applying an alternating inversion magnetic field using the mixed powder 2 for the example, and (b) is for the example. It is a polarizing microscope photograph of the sintered magnet (sample f) formed from the compact | molding | casting produced while applying a static magnetic field using the mixed powder 2, (c) is an alternating inversion magnetic field using the alloy powder 2 for a comparative example. It is a cross-sectional polarized light microscope photograph of the sintered magnet (sample g) formed from the molded object produced while applying (A), (d) is from the molded object produced using the comparative example alloy powder 2 while applying a static magnetic field. It is a cross-sectional polarized light microscope photograph of the formed sintered magnet (sample h). It is a graph which shows the orientation degree parameter P of each sample.

Claims (9)

A method for producing an R—Fe—B rare earth sintered magnet,
11 to 18 atomic% light rare earth element LR (La, Ce, Pr, Nd, Pm, Sm, Eu and Gd is at least one rare earth element selected from the group consisting of at least Nd and Pr. Element T (including one kind) and element A (boron or a mixture of boron and carbon) of 4 atomic% to 12 atomic%, with the balance being Fe or a mixture of Fe and other transition metals, A step of preparing a first alloy fine powder having a composition that is a trace amount of additive element M and inevitable impurities and having a D99 (particle size with a cumulative volume fraction of 99%) of 12 μm or less;
10 to 35 atomic percent heavy rare earth element HR (at least one rare earth element selected from the group consisting of Y, Tb, Dy, Ho, Er, Tm, Yb and Lu), and 0 to 10 atomic percent Containing element A (boron or a mixture of boron and carbon) in an atomic percent or less, with the balance being element T, which is a mixture of Fe or Fe and other transition metals, trace additive element M, and inevitable impurities. And a step of preparing a second alloy fine powder having a D99 (particle size with a cumulative volume fraction of 99%) of 12 μm or less,
Mixing the first alloy fine powder and the second alloy fine powder to prepare a mixed powder;
A step of obtaining a molded body by compression molding the mixed powder while applying a reversal magnetic field as an orientation magnetic field;
Obtaining a sintered body by sintering the molded body;
A method for producing a rare earth sintered magnet.   2. The method for producing a rare earth sintered magnet according to claim 1, wherein the mixed powder includes 1% by mass or more and 50% by mass of the second alloy fine powder.   The method for producing a rare earth sintered magnet according to claim 1 or 2, wherein an average particle size of the first and second alloy fine powders is 2.0 µm or more and 5.0 µm or less.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 3, wherein in the sintering step, crystal grains are grown until the average crystal grain size of the main phase is in the range of 8 µm to 40 µm.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 4, wherein the strength of the reversal magnetic field is 2.5T or less.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 5, wherein the heavy rare earth element HR of the second alloy fine powder contains at least one element selected from Dy and Tb.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 6, wherein the step of producing the compact is performed using a uniaxial press molding method.   A rare earth sintered magnet manufactured by the manufacturing method according to claim 1. With respect to Bs ′ = (Br _x ² + Br _y ² + Br _z ² ) ^{1/2, where} the residual magnetic flux density in the orientation magnetic field direction is Br _x , and the residual magnetic flux densities in two directions orthogonal to the orientation magnetic field direction are Br _y and Br _z . when defining the ratio of Br _x orientation parameter _{P (= Br x / Bs'} ) and the value of the orientation degree parameter P is 0.990 greater, rare-earth sintered magnet according to claim 8.