JP6051892B2 - Method for producing RTB-based sintered magnet - Google Patents

Description

  The present invention relates to a method for producing an RTB-based sintered magnet (rare earth-based sintered magnet), and more particularly to an RTB-based sintered magnet containing neodymium as a rare earth element.

An R-T-B-based sintered magnet having an R ₂ T ₁₄ B type compound as a main phase and having an R-rich phase (rare earth element rich phase) at the grain boundary of the main phase crystal grains (R is a rare earth element (yttrium (Y )) Is a high residual magnetic flux density B _r (hereinafter, referred to as “contains”), which always includes neodymium (Nd), T means iron (Fe) or iron and cobalt (Co), and B means boron). simply referred to as "B _r" is) and high intrinsic coercive force H _{cJ (hereinafter,} simply and a may be referred to as "H _cJ"), the highest magnetic energy among the various magnets known so far In addition to showing the product, it also has the advantage of being relatively inexpensive.

  For this reason, it is used for various applications such as various motors such as voice coil motors for hard disk drives, motors for hybrid vehicles, motors for electric vehicles, and home appliances.

  For example, when used for various motors such as a motor for a hybrid vehicle and a motor for an electric vehicle, it is exposed to a high temperature such as 140 ° C to 180 ° C.

The _RTB -based sintered magnet has a problem that _HcJ decreases when the temperature becomes high, and irreversible heat demagnetization occurs.
For this reason, for example, as shown in Patent Documents 1 to 3, dysprosium which is a heavy rare earth element (hereinafter, sometimes referred to as “RH”) from the surface to the inside of the RTB-based sintered magnet (Dy) or terbium (Tb) is diffused to concentrate dysprosium (Dy) or terbium (Tb) in the vicinity of the grain boundary of the main phase crystal grains (the outer shell of the main phase crystal grains) to increase the H _cJ even at high temperatures. The method of obtaining is taken.

  Patent Documents 4 to 6 describe that a light rare earth element such as praseodymium (Pr) is diffused from the surface to the inside in addition to RH such as dysprosium (Dy) or terbium (Tb). Document 6 describes that Al is diffused together with praseodymium (Pr).

WO2007 / 102391 Publication WO2011 / 007758 WO2006 / 043348 Japanese Patent Laid-Open No. 2005-11973 JP 2007-287875 A JP 2008-263179 A

_HcJ can be improved by the methods described in Patent Documents 1 to 3. However, there is a demand for further downsizing, weight reduction, and high efficiency in many applications, and there is a strong demand for _RTB -based sintered magnets having higher _HcJ at higher temperatures.

On the other hand, with respect to the methods disclosed in Patent Documents 4 to 6, it is conventionally _{assumed that} there is an effect of improving _HcJ at room temperature by substituting part of Nd atoms with Pr atoms. It was thought that there was almost no effect of improving _HcJ at 180 ° C).
This is because, for example, an experimental result comparing the temperature dependence of the anisotropic magnetic field ( _HcJ increases as this value increases) in the case where R of R ₂ Fe ₁₄ B is Pr and Nd (for example, J Appl.Phys., Vol.59, No.3, p.873 (1986)). That is, at room temperature (300 K), when R is Pr, the value of the anisotropic magnetic field is higher than when R is Nd, but at a high temperature such as 160 ° C. (433 K), R is Nd. This shows a higher anisotropic magnetic field value than when R is Pr.
For this reason, it was thought that it was not preferable to add Pr for the purpose of improving _HcJ at high temperatures.

Therefore, the method of diffusing Dy or Tb from the surface to the inside and concentrating Dy or Tb in the vicinity of the grain boundary of the main phase crystal grain ensures higher H _cJ at a high temperature in the RTB-based sintered magnet. There were few practical methods that could be used. And the _{request |} requirement to use the _{RTB type |} system _| group sintered magnet which has higher _HcJ compared with _HcJ obtained by this method at high temperature became increasingly high.

Then, an _object of this invention is to provide the manufacturing method of the _{RTB type |} system _| group sintered magnet which can express higher intrinsic coercive force _HcJ at high temperature.

In aspect 1 of the present invention, 1) sintering containing a rare earth element containing neodymium (Nd), iron (Fe), and boron (B), and having an intermetallic compound represented by the following general formula as a main phase A body forming step, 2) a heavy rare earth element source containing at least one of dysprosium (Dy) and terbium (Tb), and the sintered body are disposed in a container, and the heavy rare earth element source, The sintered body is heated, and at least one of dysprosium (Dy) and terbium (Tb) is diffused into the sintered body from the heavy rare earth element supply source, thereby causing the outer shell portion of the crystal grains of the intermetallic compound to diffuse. A step of concentrating at least one of dysprosium (Dy) and terbium (Tb), and 3) a Pr-Al source containing praseodymium (Pr) and aluminum (Al) after step 2), A sintered body in which at least one of dimethyl (Dy) and terbium (Tb) is diffused is placed in a container, the Pr—Al supply source and the sintered body are heated, and the Pr—Al supply source By dispersing praseodymium (Pr) and aluminum (Al) in the sintered body, the rare earth contained in the metal phase present at the grain boundary multiple points of the crystal grains in at least a part of the surface layer portion of the sintered body The mass ratio of praseodymium (Pr) in the element is 75% or less and higher than the mass ratio of praseodymium (Pr) in the rare earth element contained in the crystal grains adjacent to the metal phase by 20 percentage points or more, and And increasing the mass ratio of aluminum (Al) contained in the sintered body by 0.01 percentage point to 0.05 percentage point, That is a method for producing R-T-B based sintered magnet.
General formula: R ₂ T ₁₄ B
(Here, R is one or more rare earth elements in which neodymium (Nd) is 50% or more by mass ratio, and T is iron (Fe) or iron (Fe) and cobalt (Co).)

  In the aspect 2 of the present invention, in the step 3), praseodymium (Pr) occupying the rare earth element contained in the metal phase present at the grain boundary multiple points of the crystal grains over the entire surface layer portion of the sintered body. The mass ratio is 75% or less, and the mass ratio is higher by 20 percentage points or more than the mass ratio of praseodymium (Pr) in the rare earth element contained in the crystal grains adjacent to the metal phase. It is a manufacturing method.

  Aspect 3 of the present invention is the manufacturing method according to aspect 1 or 2, wherein the mass ratio of praseodymium (Pr) in the rare earth element contained in the metal phase in the surface layer portion is 60% or less.

Aspect 4 of the present invention is characterized in that, in the step 3), the mass ratio of praseodymium (Pr) contained in the sintered body is increased by 0.4 percentage point to 1.5 percentage points. 2. The production method according to 2.

  Aspect 5 of the present invention is characterized in that, in the step 3), the mass ratio of aluminum (Al) contained in the sintered body is increased by 0.01 percentage point to 0.03 percentage point. 4. The production method according to any one of 4 above.

  Aspect 6 of the present invention is as described in any one of Aspects 1 to 5, wherein in the step 3), the Pr—Al supply source and the sintered body are heated to 600 ° C. to 850 ° C. It is a manufacturing method.

  Aspect 7 of the present invention is the manufacturing method according to aspect 6, wherein the Pr—Al supply source and the sintered body are heated to 600 ° C. to 760 ° C. in the step 3).

  Aspect 8 of the present invention is the production according to any one of aspects 1 to 7, wherein the Pr—Al supply source is a Pr—Al alloy containing 2 to 6 mass% of aluminum (Al). Is the method.

  In aspect 9 of the present invention, in the step 2), the heavy rare earth element supply source containing dysprosium (Dy) and the sintered body are disposed in a container, and the heavy rare earth element supply source and the sintered body And dysprosium (Dy) is concentrated in the outer shell of the crystal grains of the intermetallic compound by diffusing dysprosium (Dy) from the heavy rare earth element supply source into the sintered body. It is a manufacturing method as described in any one of the aspects 1-8 to do.

According to the present invention, it is possible to provide an _RTB -based sintered magnet that expresses higher _HcJ at a high temperature and a method for producing the same.

FIG. 1 (a) is a transmission electron microscope observation result (DF-STEM image) of the sintered body after the heavy rare earth element diffusion treatment, and FIG. 1 (b) is shown in FIG. 1 (a). It is an element mapping image of Dy by TEM-EDX of a field. 2 shows a sample No. 1 according to the example. It is a DF-STEM image of the surface layer part of 2 RTB system sintered magnets. FIG. 3 is an element mapping image of Fe and oxygen (O), Nd, and Pr in the same field of view as FIG. FIG. 4 is a DF-STEM image showing the metal phase and the oxide phase at the grain boundary multiple points shown in FIG. FIG. 5 is a DF-STEM image showing a point A in the metal phase in FIG. 2 and a point B in the crystal grain adjacent to the metal phase including the point A.

As a result of intensive studies, the present inventors have found that a sintered body containing a rare earth element, iron (Fe), and boron (B) and having an intermetallic compound represented by the following formula (1) as a main phase: In order to obtain high _HcJ at a high temperature, a conventional method, that is, main phase crystal grains (hereinafter simply referred to as “crystal grains” and “main phase crystal grains”) may be used. To diffuse at least one of dysprosium (Dy) and terbium (Tb) from the surface of the sintered body to the inside for the purpose of concentrating at least one of dysprosium (Dy) and terbium (Tb) in the outer shell in addition, by diffusing as detailed below praseodymium (Pr) and aluminum (Al), for example, at elevated temperatures, such as 140 ℃, R-T-B based sintered express higher H _cJ Yui磁Found that it is possible to obtain.

General formula: R ₂ T ₁₄ B (1)

  In the present invention, the mass ratio of Pr to the rare earth element contained in the metal phase present at the grain boundary multiple points of the main phase crystal grains in at least a part of the surface layer portion of the sintered body is 75% or less. And higher by 20 percentage points than the mass ratio of Pr in the rare earth elements contained in the crystal grains adjacent to the metal phase, and further the mass ratio of Al contained in the R-T-B system sintered magnet Is diffused so as to increase by 0.01 percentage point to 0.05 percentage point with respect to the mass ratio of Al after the heavy rare earth element diffusion treatment.

That is, in addition to the conventionally known means of diffusing heavy rare earth elements Dy and / or Tb from the surface of the sintered body and concentrating these heavy rare earth elements in the outer shell of the main phase crystal grains. Conventionally, it was difficult to obtain a high _HcJ improvement effect at a high temperature, and Pr was diffused together with Al from the surface of the sintered body after Dy and / or Tb was diffused, thereby increasing the number of grain boundaries. By adding Pr in an appropriate concentration range to the important metal phase (hereinafter, sometimes simply referred to as “metal phase”), and further increasing the mass ratio of Al contained in the sintered body to an appropriate range. The present _inventors have found that _HcJ at a high temperature can be further improved.

  Further, the inventors of the present application further performed a step of diffusing Pr and Al after first performing a step of diffusing at least one of Dy and Tb with respect to diffusion of at least one of Dy and Tb and diffusion of Pr and Al. By carrying out the process, it has been found that at least one of Dy and Tb, and Pr and Al can be reliably diffused into the desired state.

When a sintered body is prepared by adding Dy and / or Tb, which are heavy rare earth elements, during raw material orientation, light rare earth elements such as Nd contained in the main phase crystal grains of the sintered body are replaced by Dy and / or Tb. Therefore, the anisotropic magnetic field is improved at room temperature and at a high temperature such as 140 ° C. However, when Dy and / or Tb is added at the stage of melting the alloy material for obtaining the powder used for sintering, Dy and / or Tb diffuses relatively uniformly into the crystal grains due to heating during sintering. Therefore, at least one of Dy and Tb cannot be sufficiently concentrated in the outer shell portion of the crystal grain, and the obtained sintered body cannot have high _HcJ at a high temperature.
Therefore, Dy and / or Tb is diffused from the surface of the sintered body, and at least one of Dy and Tb is concentrated in the outer shell of the crystal grains.
Thus with a high H _cJ at a high temperature is obtained, it is possible to reliably suppress a decrease in remanence B _r.

  In the present specification, “the outer shell part of a crystal grain” is a concept including both a surface layer part of a crystal grain and a crystal grain boundary adjacent to the crystal grain. Therefore, for example, Dy is concentrated in the outer shell of a crystal grain when Dy is concentrated in at least one of the surface layer part of the crystal grain and the crystal grain boundary adjacent to the crystal grain (in the center part of the crystal grain). It means that the concentration is higher than that). Such concentration of crystal grains in the outer shell can be measured by using, for example, a transmission electron microscope and energy dispersive X-ray spectroscopy (TEM-EDX). When element mapping images of Dy and Tb are obtained by TEM-EDX, it is not clear whether Dy and Tb concentration occurs both in the surface layer of the crystal grain and in the grain boundary adjacent to the crystal grain However, even in such a case, it corresponds to “concentrated in the outer shell of the crystal grain”.

  In the present invention, in addition to the enrichment of Dy and Tb, the mass ratio of Pr in the rare earth element contained in the metal phase present at the grain boundary multiple points is 75% or less and the metal The crystal grains adjacent to the phase are characterized by being higher by 20 percentage points or more than the mass ratio of Pr in the rare earth element contained in the crystal grains. It can be confirmed by point analysis).

  Furthermore, the present invention is also characterized in that the mass ratio of Al in the sintered body in which the heavy rare earth element is diffused is increased by 0.01 percentage point to 0.05 percentage point. It can be confirmed by performing ICP emission spectroscopic analysis or line analysis on the samples before and after.

The main phase of the RTB-based sintered magnet of the present invention is an intermetallic compound represented by the general formula: R ₂ T ₁₄ B. In general, in a magnetic material such as a sintered magnet, a compound that determines the characteristics (physical properties, magnetic characteristics, etc.) of the magnetic material in a main constituent phase is defined as a “main phase”. The main phase in the present invention, that is, the intermetallic compound represented by the general formula: R ₂ T ₁₄ B is also a main constituent phase and the basic parts such as physical properties and magnetic characteristics of the R-T-B system sintered magnet of the present invention. Is decisive. In the present specification, the “main phase crystal grains” are crystal grains composed of the main phase. The main phase crystal grains are present in an area ratio of 50% or more, preferably 70% or more in the cross-sectional observation of the R-T-B system sintered magnet. The area ratio is determined by measuring a portion having an area of 0.05 mm ² or more in a cross section of a representative portion (or a non-unique portion) of the R-T-B based sintered magnet.

As described above, conventionally, when Pr is added to a sintered body containing Nd as a main rare earth element, it has been considered difficult to obtain high _HcJ at a high temperature. Pr and Al are grain boundary diffused from the surface of the sintered body, Pr is contained in the metal phase at the grain boundary in the surface layer portion of the sintered body in an appropriate concentration range, and the mass ratio of Al contained in the sintered body The present invention that increases _HcJ at a high temperature by increasing the value to an appropriate range overturns conventional common sense.

About the mechanism in which the _RTB -based sintered magnet according to the present invention in which Pr and Al are diffused from the surface of the sintered body has high _HcJ at a high temperature, there are still unclear points. The mechanism considered by the present inventors based on the knowledge obtained so far will be described below. It should be noted that the following description of the mechanism is not intended to limit the technical scope of the present invention.

In a sintered body containing Nd as a main rare earth element, when the magnetization is reversed by receiving an external magnetic field in the direction opposite to the magnetization direction, the magnetization reversal occurs in the main phase crystal grains. In the process of magnetization reversal, the magnetization reversal in a certain main phase crystal grain and the propagation of the magnetization to the adjacent main phase crystal grain is one factor in the magnetization reversal of the entire magnet. That is, the magnetic coupling between the main phase crystal grains contributes to determining _HcJ . Such propagation to the adjacent main phase crystal grains can be suppressed by the presence of a predetermined amount of Pr in the crystal grain boundary and the inclusion of a predetermined amount of Al in the crystal grain boundary. it is conceivable that. As a result, it is considered that the _HcJ of the entire sintered body can be increased.
Here, Pr and Al are arranged not only at the metal phase at the grain boundary multipoint, but also at the two-grain grain boundary (the grain boundary between the two main phase crystal grains), affecting the entire R-rich (rare earth-rich) phase. It is thought that it is exerting. However, it is not easy to accurately measure the concentrations of Pr and Al existing at or near a two-grain grain boundary whose width is extremely narrow depending on the site.
Fortunately, for Pr, if the grain boundary multiple points are wider than the two-grain grain boundary, the concentration can be measured with sufficiently high accuracy by TEM-EDX or the like with little variation depending on the part. Therefore, it is considered that characteristics reflecting the behavior of Pr in the R-rich (rare earth rich) phase of the grain boundary can be obtained by measuring the mass ratio of Pr occupying the rare earth element at the grain boundary multiple points (particularly the metal phase). . In addition, when Al is diffused from the surface, grain boundary diffusion may be dominant while the amount of diffusion is small. By measuring the amount of Al increase (diffusion amount) in the entire sintered body, It is considered that characteristics reflecting the behavior of Al in the R-rich (rare earth-rich) phase and the like can be obtained.

While diffusing Pr and Al in this manner is effective for improving _HcJ at high temperatures, excessive Pr and Al are formed so as to form a concentrated region having a high concentration of Pr and Al at the grain boundaries. When Al is diffused from the surface of the sintered body to the inside, a part thereof cannot stay at the grain boundary, but enters the main phase crystal grain, and the concentration of Pr or Al is high near the surface of the main phase crystal grain. It is considered that the region is formed over a wide range. As described above, at a high temperature, the value of the anisotropic magnetic field is higher in the case where R of the R ₂ Fe ₁₄ B compound is Nd than in the case where R is Pr (H _cJ is higher). As can be seen from the above, it is considered that when a region having a high Pr concentration is formed in the vicinity of the surface of the main phase crystal grains over a wide range, a well-known phenomenon appears that the improvement of _HcJ at a high temperature is not observed. . Furthermore, by Al is introduced more into the main phase crystal grains, leading to decrease in B _r, it is considered more can not be almost obtained an effect of improving the H _cJ at high temperatures.

  Therefore, only when the amount of Pr and Al diffused from the surface of the sintered body into the sintered body, particularly the amount of Pr and Al diffused into the crystal grain boundary is within an appropriate range, it is concentrated at the crystal grain boundary. It is considered that the effects of Pr and Al can be brought out. That is, in the surface layer portion of the sintered body, the mass ratio of Pr in the rare earth element contained in the metal phase at the grain boundary multiple points of the main phase crystal grains is 75% or less (preferably 20% to 60%), and The amount of Pr diffused so as to be higher by 20 percentage points or more than the mass ratio of Pr in the rare earth element contained in the main phase crystal grains adjacent to the metal phase is in an appropriate range, and further, the sintering The amount of Al obtained by increasing the mass ratio of Al contained in the body by 0.01 percentage point to 0.05 percentage point (preferably 0.01 percentage point to 0.03 percentage point) is within an appropriate range. Further, the mass ratio of Pr in the rare earth element contained in the metal phase is substantially higher than the mass ratio of Pr in the rare earth element contained in the main phase crystal grains adjacent to the metal phase. 20% or more (in the case of diffusion treatment to a sintered body not containing Pr).

In the surface layer portion of the sintered body, the mass ratio of Pr in the rare earth element contained in the metal phase at the grain boundary multiple points of the main phase grains is Pr in the rare earth element contained in the main phase grains adjacent to the metal phase. If the mass ratio is less than 20 percentage points, a sufficient amount of Pr cannot be concentrated at the grain boundaries, and a sufficient effect cannot be obtained. On the other hand, when the mass ratio of Pr in the rare earth element contained in the metal phase at the grain boundary multiple points of the surface layer portion exceeds 75%, a sufficient amount of Pr is concentrated in the crystal grain boundary. A high concentration region of Pr is formed in a wide area (particularly in the vicinity of the surface of the main phase crystal grains), and the effect of improving _HcJ at a high temperature by Pr concentrated in the crystal grain boundary is near the surface of the main phase crystal grains. It is damaged by the high concentration region of Pr. As a result, the effect of improving _{HcJ at} high temperatures is reduced.

Furthermore, if the amount of increase in the mass ratio of Al contained in the sintered body is less than 0.01 percentage point, a sufficient effect cannot be obtained because a sufficient amount of Al cannot be concentrated at the grain boundaries. Absent. On the other hand, the number introduced amount of Al into the crystal grains to increase beyond 0.05 percentage points, reduces the H _cJ increased effect at high temperatures, further B _r is likely to decrease.

  In addition, although the term "surface layer part" in this specification contains the character "layer", it does not prescribe that it has a layered structure (not a layered structure is essential), In the cross section, it means the surface and its vicinity (in other words, “surface portion” or “surface vicinity portion”). Although the size and details of the RTB-based sintered magnet to be obtained depend on the conditions of Pr diffusion treatment to be described later, the amount of magnet grinding after the diffusion treatment, etc., in many cases the RT-T- of the present invention The B-based sintered magnet tends to form the “surface portion of the R-T-B-based sintered magnet” according to the present invention having the above-described characteristics more reliably between 100 μm from the surface. Note that the structure of the sintered magnet of the present invention does not greatly depend on the distance from the surface, and a substantially uniform structure can be obtained. However, the concentration of Pr tends to be lower in the central part (deep part) than in the surface part, and the coercive force of the surface part is important in motor magnets and the like that are mainly used. In the present invention, the structure represents the surface layer portion.

  Below, the manufacturing method of the RTB system sintered magnet concerning the present invention and the details of the RTB system sintered magnet obtained by it are explained.

1. Manufacturing Method As described in detail below, in the manufacturing method according to the present invention, a heavy rare earth element diffusion treatment in which at least one of Dy and Tb is diffused from the surface of the sintered body, and Pr and Al are diffused from the surface. Pr-Al diffusion treatment is performed. In this specification, even when the sintered body is subjected to either heavy rare earth element diffusion treatment or Pr—Al diffusion treatment, it may be referred to as “sintered body” (“sintered body subjected to XX treatment”). ), And a state in which the sintered body has been subjected to both heavy rare earth element diffusion treatment and Pr—Al diffusion treatment may be referred to as “magnet” (“sintered magnet” or “RT-T-”). Sometimes referred to as “B-based sintered magnet”).

1-1. Production of sintered body (1) Composition of sintered body The sintered body may have any composition known as a sintered body containing a rare earth element containing Nd, Fe, and B. The composition of a preferable sintered body is shown below.
R is a rare earth element, Nd is essential, and 50% or more of R is Nd in mass ratio. Rare earth elements other than Nd may be included.
It is preferable that Nd and other rare earth elements are contained in the entire sintered body in a total amount of 25% by mass to 35% by mass. If it is less than 25% by mass, sintering may not be possible, and if it exceeds 35% by mass, _Br may be significantly reduced.
Further, at a stage before the sintered body for performing diffusion processing, when containing a large amount of heavy rare earth elements such as Dy and Tb, finally obtained R-T-B based sintered magnet of B _r decreases Therefore, it is preferable that the total amount of heavy rare earth elements is 10% by mass or less in the entire RTB-based sintered magnet.
Rare earth elements other than Nd are often contained by using, for example, misch metal and / or didymium alloy (Nd—Pr alloy). For example, when a didymium alloy is used, the sintered body contains Pr. In this case, the diffusion treatment described later is performed in a state where the sintered body contains Pr.

T may contain iron and 50% or less thereof may be replaced with Co by mass ratio. Co is effective in improving temperature characteristics and corrosion resistance.
The T content may occupy the balance of R and boron (B) or R and B and the M element described later.

The content of boron (B) may be a known content, and for example, 0.9 mass% to 1.2 mass% is a preferable range. Is less than 0.9 wt% may high _{H cJ} can not be obtained in some cases to lower the _{B r} exceeds 1.2 mass%. A part of B can be substituted with C (carbon). Substitution with C may be able to improve the corrosion resistance of the magnet. The total content of B + C (when both B and C are included) is preferably set within the above B concentration range by converting the number of C substitution atoms by the number of B atoms.

In addition to the above elements, M element can be added to improve _HcJ at room temperature. The element M is at least one selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. . The amount of M element added is preferably 2.0% by mass or less. Inevitable impurities can also be tolerated.

The manufacturing method of the raw material alloy for RTB system sintered magnet is illustrated.
(2) Melting / Pulverizing An alloy ingot can be obtained by ingot casting method in which a metal prepared in advance so as to have a finally required composition is melted and placed in a mold.
In addition, the molten metal is brought into contact with a single roll, twin roll, rotating disk or rotating cylindrical mold, and rapidly cooled to produce a solidified alloy that is thinner than an alloy made by the ingot method. Alloy flakes can be produced by a rapid cooling method.

In the present invention, materials manufactured by either the ingot method or the rapid cooling method can be used, but those manufactured by the rapid cooling method are preferred.
The thickness of the raw material alloy for R-T-B system sintered magnet (quenched alloy) produced by the rapid cooling method is usually in the range of 0.01 mm to 3 mm and has a flake shape. The molten alloy begins to solidify from the contact surface (roll contact surface) of the cooling roll, and crystals grow in a columnar shape from the roll contact surface in the thickness direction. The quenched alloy is solidified in a short time as compared with an alloy (ingot alloy) produced by a conventional ingot casting method (die casting method), so that the structure is refined and the crystal grain size is small. By pulverizing the quenched alloy with hydrogen, the size of the hydrogen pulverized powder (coarse pulverized powder) can be set to 1.0 mm or less, for example.

  By finely pulverizing the coarsely pulverized powder thus obtained with a jet mill or the like, for example, an alloy powder having a D50 particle size of 3 to 7 μm by an air flow dispersion type laser analysis method can be obtained.

  The obtained alloy powder may be recovered while being dried, or may be recovered by dispersing in a dispersion medium such as oil.

  Further, a known lubricant may be used as an auxiliary agent for the coarsely pulverized powder, finely pulverized powder during jet mill pulverization and after jet mill pulverization.

(3) Press forming The obtained alloy powder is used for press forming in a magnetic field to obtain a formed body. Press forming in a magnetic field is a dry method in which a dry alloy powder is inserted into a mold cavity to which a magnetic field is applied and pressed, and a slurry is injected into the mold cavity and a slurry dispersion medium is discharged. Any known method may be used, including a wet method of pressing.

In addition, it is preferable that the molded object obtained by the wet method performs the deoiling process which removes the dispersion medium (oil etc.) which remain | survives in a molded object before sintering. The deoiling treatment is preferably performed at a temperature of 50 to 500 ° C., more preferably 50 to 250 ° C. and a pressure of 13.3 Pa (10 ⁻¹ Torr) or less for 30 minutes or more. This is because the dispersion medium remaining in the molded body can be sufficiently removed.

(4) Sintering A sintered body is obtained by sintering a formed body.
For the sintering of the molded body, a method similar to a known method for producing a sintered body can be used. In order to prevent oxidation due to the atmosphere during sintering, the atmosphere gas is preferably replaced with an inert gas such as helium or argon.

The sintered body contains a rare earth element containing Nd, Fe, and B, and has an intermetallic compound represented by the following formula (1) as a main phase.
The main phase crystal grains are present at 50% (volume ratio or cross-sectional area ratio) or more, preferably 70% (volume ratio or cross-sectional area ratio) or more in the cross-sectional observation of the sintered body.
R ₂ T ₁₄ B (1)
Here, R is one or more rare earth elements containing 50% or more of Nd by mass ratio (that is, 50% by mass or more of R as a whole is Nd), and T is Fe or Fe and Co.

1-2. Diffusion treatment Next, heavy rare earth element diffusion treatment for diffusing at least one of Dy and Tb in the sintered body and Pr-Al diffusion treatment for diffusing Pr and Al into the sintered body are performed. Note that the diffusion treatment may be performed after the sintered body is machined such as grinding.
Details of the heavy rare earth element diffusion treatment and the Pr—Al diffusion treatment are shown below.
In addition, as shown below, after performing a heavy rare earth element diffusion process, a Pr-Al diffusion process is performed. Thereby, at least one of Dy and Tb, Pr, and Al can be more easily diffused into a desired state.

1-2-1. Heavy Rare Earth Element Diffusion Treatment Any known method capable of diffusing at least one of Dy and Tb from the surface of the sintered body and concentrating at least one of Dy and Tb on the outer shell portion of the main phase crystal grains may be used. Many known diffusion methods arrange a heavy rare earth element source and a sintered body containing at least one of Dy and Tb in the same processing chamber, and heat the heavy rare earth element source and the sintered body. Heavy rare earth element diffusion treatment is performed. Examples of such treatment include the diffusion treatment described in Patent Documents 1 to 6 and the method of dispersing the metal powder shown in the examples of the present application on the surface of the sintered body.
Among these, the detail of the method of spraying the method described in patent documents 1-3 on the sintered compact surface is shown below.
In addition, by performing such heavy rare earth element diffusion treatment, the content of at least one of Dy and Tb increases as a matter of course in the entire sintered body. How much the content of at least one of Dy and Tb increases as a whole of the sintered body depends on factors such as the volume of the sintered body. However, for example, in the case of a sintered body having a general form with a minimum dimension of 10 mm or less among the vertical, horizontal, and height, in many cases, the entire sintered body is obtained by performing the diffusion treatment according to the present invention. The content of at least one of Dy and Tb increases by 0.1 percentage point to 2.0 percentage points by mass ratio. Further, it is preferable to perform an additional heat treatment (hereinafter sometimes referred to as “additional heat treatment”) after the heavy rare earth element diffusion treatment. The additional heat treatment in the present invention refers to a treatment in which only the diffusion is performed without supplying the heavy rare earth element to the sintered body. This is because the heavy rare earth element can be further diffused into the sintered body. The treatment temperature is preferably 800 ° C. or higher and 950 ° C. or lower.
Details of the diffusion process will be described below.

(1) Method described in Patent Document 1 The method described in Patent Document 1 is a method in which a sintered body and a heavy rare earth element source containing at least one of Dy and Tb are heat-resistant such as a net made of Nb or Mo. The sintered body and the heavy rare earth element supply source are heated to a predetermined temperature by being spaced apart via a mesh member made of material, and at least one of Dy and Tb is sintered from the heavy rare earth element supply source. This is a method of diffusing the inside of the sintered body while supplying it to the surface. The heating temperature of the sintered body and the heating temperature of the heavy rare earth element supply source are substantially the same.

When using the method of patent document 1, the heavy rare earth element supply source is one or more selected from Dy metal, Dy-Fe alloy, Tb metal, TbFe alloy, etc., for example. The shape of the heavy rare earth element supply source is arbitrary, for example, a plate shape, a block shape, a spherical shape, and the size is not particularly limited.
The temperatures for heating the sintered body and the heavy rare earth element supply source are preferably 850 ° C. or higher and 1000 ° C. or lower, respectively. Further, the pressure of the atmospheric gas in the processing container is preferably 10 ⁻⁵ Pa to 500 Pa. Note that “atmosphere gas” in this specification includes vacuum or an inert gas. The “inert gas” is, for example, a rare gas such as argon (Ar), but a gas that does not chemically react with the sintered body or the heavy rare earth element supply source (for example, nitrogen gas) is “inert gas”. It can be included in the “active gas”.

(2) Method described in Patent Document 2 The method described in Patent Document 2 is a method in which a sintered body and a heavy rare earth element supply source are inserted into a processing vessel so as to be relatively movable and close to or in contact with each other. By heating the sintered body and the heavy rare earth element supply source while continuously or intermittently moving the aggregate and the heavy rare earth element supply source in the processing vessel, the Dy and Tb In this method, at least one of them is diffused into the sintered body. The heating temperature of the sintered body and the heating temperature of the heavy rare earth element supply source are substantially the same.

When using the method described in Patent Document 2, the heavy rare earth element supply source is preferably an alloy containing at least one of Dy and Tb. For example, Dy-Fe alloy, Tb-Fe alloy, etc. The shape of the heavy rare earth element supply source is preferably a shape in which a curved surface is formed on the surface, such as a spherical shape, an elliptical spherical shape, or a cylindrical shape. The heavy rare earth element supply source may be in the form of particles, but preferably has a particle size of 200 μm or more. This is because if the particle size is less than 200 μm, welding with the sintered body tends to occur.
The temperature for heating the sintered body and the heavy rare earth element supply source is preferably 500 ° C. or higher and 850 ° C. or lower. Moreover, the pressure of the atmospheric gas in the processing container can be carried out at atmospheric pressure or lower, preferably 100 kPa or lower, and can be set, for example, within a range of 10 ⁻³ Pa to 10 ³ Pa.

(3) The method described in Patent Document 3 is the method described in Patent Document 3, in which the heavy rare earth element source is present on the surface of the sintered body and heated at a temperature lower than the sintering temperature. In this method, at least one of Dy and Tb is diffused into the sintered body from a heavy rare earth element supply source.

When the method described in Patent Document 3 is used, the heavy rare earth element supply source is preferably Dy-Fe, Dy-Fe-H, or the like. Furthermore, oxides, fluorides, and oxyfluorides may be included as long as the effects of the present invention are not impaired. The heavy rare earth element supply source is preferably in the form of particles, and its average particle size is 100 μm or less, preferably 10 μm or less.
Examples of the method of causing the heavy rare earth element supply source to exist on the surface of the sintered body include, for example, a method of spraying the particulate heavy rare earth element supply source directly on the surface of the sintered body, and a solution obtained by dissolving the supply source in a solvent. Examples thereof include a method of applying to the surface and a method of applying a slurry in which the supply source is dispersed in a dispersion medium to the surface of the sintered body. Examples of the dispersion medium used for the slurry include alcohol, aldehyde, ethanol, ketone, and the like.

  The temperature at which the sintered body and the heavy rare earth element supply source are heated is equal to or lower than the sintering temperature, and specifically, 800 ° C. or higher and 1000 ° C. or lower is preferable. When the temperature is higher than the sintering temperature, heavy rare earth elements may diffuse into the crystal grains or the structure of the sintered body may be altered and high magnetic properties may not be obtained. The lower limit of the heating temperature can be selected as appropriate, but if the temperature is too low, the treatment time becomes longer and the mass productivity deteriorates. Therefore, 800 degreeC or more is preferable. Moreover, it is preferable that the pressure of the atmospheric gas in a processing container is below atmospheric pressure.

1-2-2. Pr-Al diffusion treatment Next, the sintered body subjected to the heavy rare earth element diffusion treatment is subjected to Pr-Al diffusion treatment. Pr and Al are supplied to the inside from the surface of the sintered body, and in the surface layer portion of the sintered body, the mass ratio of Pr in the rare earth element contained in the metal phase at the grain boundary multiple points is adjacent to the metal phase. The mass ratio of Pr is 20 percentage points or more higher than the mass ratio of Pr in the rare earth element contained in the crystal grains, and the mass ratio of Pr in the rare earth element contained in the metal phase in the surface layer portion is 75% or less. Further, the mass ratio of Al contained in the sintered body is increased by 0.01 percentage point to 0.05 percentage point.
Preferably, the mass ratio of Pr in the rare earth elements contained in the metal phase in the surface layer portion of the sintered body is 20% to 60%, and the mass ratio of Al contained in the sintered body is 0.01 percentage point. Increase by 0.03 percentage points. This is _{because the} effect of improving _{HcJ at a} high temperature can be further enhanced.

  The Pr—Al diffusion treatment is not limited as long as Pr and Al can be diffused from the Pr—Al supply source into the sintered body.

By performing such a Pr—Al diffusion treatment, the content of Pr is naturally increased in the entire sintered body. The extent to which the Pr content increases as a whole of the sintered body depends on factors such as the volume of the sintered body. However, for example, in the case of a sintered body having a general form with a minimum dimension of 6 mm or less among the vertical, horizontal, and height, the entire sintered body is often obtained by performing the diffusion treatment according to the present invention. The Pr content increases by 0.4 to 1.5 percentage points by mass ratio.
Details of the diffusion process will be described below.

(1) Pr—Al supply source As the Pr—Al supply source, an arbitrary form of Pr—Al supply source such as a solid or slurry containing Pr and Al may be used.
A preferred Pr—Al source is an alloy containing Pr and Al. When using an alloy, the Pr content is preferably 30% by mass or more and the Al content is preferably 2 to 10% by mass or less, and more preferably the Al content is 2 to 6% by mass or less.
The shape and size of the Pr—Al supply source may be appropriately selected depending on the diffusion treatment method, and may be a thin film, a powder or a bulk such as a plate.

(2) Diffusion treatment method The Pr-Al diffusion treatment is preferably a method in which a Pr-Al supply source and a sintered body are brought into contact with each other and Pr or Al is diffused from the Pr-Al supply source into the sintered body at grain boundaries.

  The Pr—Al supply source may have an arbitrary shape as described above, but is preferably spherical or particulate (powder). This is because the contact area between the Pr—Al supply source and the sintered body can be increased. In the case of particles, the preferred particle diameter is 100 μm or less, more preferably 10 μm or less. This is because the contact area can be increased more reliably. However, since fine particles are easily oxidized, it is preferable to use a dispersion medium that suppresses oxidation.

  When a particulate Pr—Al supply source is used, the Pr—Al supply source and the sintered body may be brought into contact with each other by spraying or spraying the Pr—Al supply source directly on the surface of the sintered body. After applying the slurry in which the supply source is dispersed in the dispersion medium to the surface of the sintered body, the Pr-Al supply source and the sintered body may be contacted by evaporating the dispersion medium. In addition, alcohol (ethanol etc.), an aldehyde, and a ketone can be illustrated as a dispersion medium.

  The Pr—Al supply source and the sintered body are heated to 600 ° C. to 850 ° C., preferably 600 ° C. to 760 ° C. When heated to a temperature higher than 850 ° C., the structure obtained by the heavy rare earth element diffusion treatment may be adversely affected. On the other hand, if the temperature is lower than 600 ° C., Pr and Al do not diffuse sufficiently at the grain boundaries, and the present invention is effective. This is because such a surface layer portion may not be formed.

  The temperature at which the sintered body is heated during the Pr—Al diffusion treatment is, for example, a heavy rare earth element when the temperature at which the sintered body is heated during the heavy rare earth element diffusion treatment as in Patent Documents 1 and 3 is high. The temperature is preferably lower than the temperature at which the sintered body is heated during the diffusion treatment. When the heating temperature in the subsequent Pr—Al diffusion treatment is high, at least one of Dy and Tb diffused to a desired state is diffused into the main phase crystal grains. There is a risk that it cannot be maintained. In this case, the temperature for heating the sintered body during the Pr—Al diffusion treatment is more preferably 50 ° C. to 350 ° C. lower than the temperature for heating the sintered body during the heavy rare earth element diffusion treatment.

  Further, the pressure of the atmospheric gas (that is, the pressure of the atmospheric gas for performing the diffusion treatment) in the processing container (the container in the present invention may be a furnace or a container may be placed in the furnace). ) Is not particularly limited as long as it is an inert gas atmosphere (for example, a rare gas such as argon (Ar)), and may be a vacuum pressure or an atmospheric pressure or higher.

In the surface layer portion of the sintered body, the mass ratio of Pr occupying the rare earth element contained in the metal phase present at the grain boundary multiple points is the mass ratio of Pr occupying the rare earth element contained in the crystal grains adjacent to the metal phase. The mass ratio of Pr in the rare earth element contained in the metal phase present at the grain boundary multiple points of the surface layer portion is 75% or less, and the mass of Al contained in the sintered body In order to increase the ratio from 0.01 percentage point to 0.05 percentage point, depending on the size of the sintered body and the type of Pr—Al source used, the heating temperature during processing, the Pr—Al source Various conditions such as the amount, the particle diameter (when the Pr—Al supply source is in the form of particles), and the treatment time may be adjusted. Among these, the introduction amount (increase amount) of Pr and Al can be controlled relatively easily by adjusting the heating temperature during the treatment, the amount of the Pr—Al supply source, or the treatment time.
As just mentioned, in the present specification, “higher than 20 percentage points” means that the numerical value is 20 or more larger in the content expressed in percentage (mass%). For example, when the Pr content in the rare earth element of the object A is 10% by mass, the Pr content in the object B is 20 percentage points higher than the object A. It means that the content of Pr is 30% by mass or more.

When using a method in which the sintered body is disposed in the container apart from the Pr-Al supply source, that is, once vapor of Pr and Al (gas phase) is formed, this vapor phase reaches the surface of the sintered body, When Pr and Al are diffused from the surface of the sintered body to the inside, Pr is hardly vaporized, so the Pr—Al supply source is heated to 1100 ° C. to 1200 ° C. in a high vacuum (10 ⁻³ to 10 ⁻⁴ Pa). It is preferable to do. Even in this case, it is preferable to maintain the temperature of the sintered body at 600 ° C. to 850 ° C., more preferably 600 ° C. to 760 ° C. for the reasons described above, so that the sintered body and the Pr—Al supply source are separately provided. It is preferable to control at the temperature.

  Multiple points (grain boundary multiple points) of crystal grain boundaries are so-called R-rich phases (rare earth element rich phases), and have a metal phase containing rare earth elements. The grain boundary multiple points can be observed as a region surrounded by three or more crystal grains by, for example, observing a cross section of the RTB-based sintered magnet with a transmission electron microscope (TEM). The mass ratio of Pr in the rare earth elements contained in the metal phase located at the grain boundary multiple points and the mass ratio of Pr in the rare earth elements contained in the crystal grains adjacent to the metal phase are, for example, a transmission electron microscope and energy It can obtain | require by performing a compositional analysis using a dispersion | distribution X-ray spectroscopy (TEM-EDX).

  Note that a sintered body obtained using a didymium alloy (mainly a mixture of Nd and Pr) as a raw material contains, for example, about 5 to 7% by mass of Pr. Even before the diffusion treatment, the crystal grain boundary including multiple grain boundary points tends to have a higher mass ratio of Pr in the contained rare earth element than in the crystal grain. However, the difference between the mass ratio of Pr in the rare earth element contained in the metal phase located at the grain boundary multiple points of the crystal grain and the mass ratio of Pr in the rare earth element contained in the crystal grain adjacent to the metal phase is Much smaller than 20 percentage points.

By carrying out the diffusion treatment as described above, the surface layer portion according to the present invention, that is, crystal grains, is usually applied to the entire surface of the obtained RTB-based sintered magnet (or the entire portion immediately below the surface). The mass ratio of Pr in the rare earth element contained in the metal phase at the boundary multiple point is 20 percentage points higher than the mass ratio of Pr in the rare earth element contained in crystal grains adjacent to the metal phase, and the metal phase contains A surface layer portion in which the mass ratio of Pr in the rare earth element to be formed is 75% or less can be formed.
However, the present invention is not limited to this, for example, by masking a part of the sintered body and / or by cooling a part of the sintered body and lowering the temperature below other parts. In addition, an embodiment in which the surface layer portion according to the present invention is formed only on a part of the surface of the obtained R-T-B system sintered magnet (or a part directly under the surface) is also included.
For example, the mass of Pr occupying the rare earth element contained in the metal phase at the grain boundary multiple points of the crystal grains only in a part (or part of the part immediately below the surface), not the entire surface of the R-T-B sintered magnet. An embodiment in which the ratio is 20 percentage points or more higher than the mass ratio of Pr in the rare earth element contained in the crystal grains adjacent to the metal phase, and the mass ratio of Pr in the rare earth element contained in the metal phase is 75% or less. It is included in the present invention.
Further, in the sintered magnet containing Co, there is a metal phase containing Co, but the effect of the present invention is obtained in the Pr concentration range defined in the metal phase not containing Co.

  The surface of the sintered magnet after the heavy rare earth element diffusion treatment or Pr—Al diffusion treatment may be roughened. In many cases, Nd and the like, which are interdiffused with heavy rare earth elements and Pr during the diffusion treatment, ooze out on the surface of the sintered magnet and are solidified and easily oxidized. In such a case, it is preferable that the surface is subjected to machining (surface machining) such as cutting and polishing.

(3) Heat treatment The sintered magnet after the Pr—Al diffusion treatment is preferably subjected to a heat treatment for the purpose of improving the magnetic properties. As the heat treatment conditions such as the heat treatment temperature and the heat treatment time, known conditions (for example, at 500 ° C. for 3 hours) can be adopted as the heat treatment conditions after sintering the sintered body. Note that final magnet dimension adjustment may be performed by machining such as grinding. In this case, it may be performed before or after the heat treatment.

2. Characteristics of the obtained R-T-B system sintered magnet The R-T-B system sintered magnet obtained by the manufacturing method described above exhibits several characteristics.

As a result of the above-mentioned heavy rare earth element diffusion treatment, in the finally obtained RTB-based sintered magnet, at least one of Dy and Tb is concentrated in the outer shell portion of the crystal grains. Here, “concentration” means that there is a portion having a higher concentration than others, and a region where the concentration of at least one of Dy and Tb is high (for example, compared with the central portion of the crystal grains). Exists in the outer shell of the crystal grain (at least a part of the outer shell of the crystal grain).
In the heavy rare earth element diffusion treatment, since at least one of Dy and Tb is diffused from the surface of the sintered body as described above, depending on the conditions of the diffusion treatment, such a concentrated portion is obtained in the obtained R There is a tendency that the surface layer portion is more present than the central portion of the -TB sintered magnet.
In addition, the RTB-based sintered magnet obtained by diffusing Pr and Al from the surface of the sintered body after the heavy rare earth element diffusion treatment has a concentration of Pr in the surface layer than in the center. Tends to be slightly higher. However, Al has almost no difference in concentration between the surface layer portion and the central portion. For example, for a sintered body having a thickness of 5 mm, a difference in Al concentration between the surface layer portion and the center portion when the Pr—Al diffusion treatment is performed in a predetermined range of the present invention from both sides in the thickness direction can hardly be confirmed. That is, if the mass ratio of Al is increased by 0.01 percentage point to 0.05 percentage points by diffusion treatment in the entire sintered body, many areas of the sintered body (not all of the sintered body, Therefore, the obtained RTB-based sintered magnet exhibits the effects of the present application.

For example, when R (rare earth element) is supplied by a didymium alloy in the sintered body before the Pr—Al diffusion treatment, the mass ratio of Pr in the rare earth element originally contained in the crystal grains is about 20%.
In the diffusion treatment, Pr diffuses mainly from the surface of the sintered body to the grain boundary and does not diffuse so much into the crystal grains. That is, as in the case where the sintered body before the Pr diffusion treatment does not substantially contain Pr, by diffusing Pr from the surface of the sintered body to the inside, the crystal grains in the surface layer portion of the sintered body The mass ratio of Pr in the rare earth element contained in the metal phase at the boundary multiple points is 20 percentage points or more higher than the mass ratio of Pr in the rare earth element contained in the crystal grains adjacent to the crystal grains, and the metal phase in the surface layer portion The mass ratio of Pr occupying the rare earth element contained is 75% or less.
On the other hand, even in such a case, the mass ratio of Pr in the rare earth element contained in the crystal grains adjacent to the metal phase is about 20%, which is almost the same as that before the diffusion treatment.

Example 1
A slab having a thickness of 0.3 to 0.4 mm is produced by the strip casting method, and this is roughly pulverized into a powder having a size of about 500 μm or less by hydrogen pulverization, and then finely pulverized by a jet mill to obtain an average powder. A fine powder having a particle size (D50) of 4.9 μm was produced.

The obtained fine powder was recovered in oil to form a slurry, and a molded body was produced from this slurry by a wet method. Specifically, compression molding was performed in a state where the powder particles were magnetically oriented in an applied magnetic field. And after performing the deoiling process, it sintered on the conditions for 4 hours at 1010 degreeC with the vacuum furnace.
The composition of the sintered body was Nd: 28.8 mass%, Pr: 0.14 mass%, Dy: 1.5 mass%, B: 0.97 mass%, Co: 2.0 mass%, Cu: 0 10% by mass, Al: 0.23% by mass, Ga: 0.06% by mass, and Fe: balance. This sintered body was ground to obtain a sintered body having a thickness of 4.0 × width of 15.0 × length of 23.0 (unit: mm).

  The obtained sintered body was subjected to heavy rare earth element (Dy) diffusion treatment. In the heavy rare earth element (Dy) diffusion treatment, two Dy metals having a thickness of 3 mm and an area of 35 mm × 150 mm are prepared as a heavy rare earth element supply source, and both sides of the sintered body are 15 mm × 23 mm in a processing container. It was carried out by heating in a state where the Dy metal was laminated via a mesh made of Mo so that the Dy metal was spaced apart from each other (two faces of 15 mm × 23 mm). By supplying Dy vapor to the entire surface of the sintered body by heating at 880 ° C. for 5 hours under a pressure of 0.05 Pa, and then carrying out diffusion treatment, then flowing Ar gas and maintaining it at atmospheric pressure A heat treatment was performed at 880 ° C. for 5 hours without supplying Dy. A plurality of sintered bodies subjected to such heavy rare earth element (Dy) diffusion treatment were prepared.

  FIG. 1A is a transmission electron microscope observation result (DF-STEM image) of the sintered body after the heavy rare earth element diffusion treatment is performed, and includes six crystal grains. FIG. 1B is an element mapping image of Dy by TEM-EDX in the region shown in FIG. Here, the brighter color region indicates that there is more Dy. For the element mapping shown in Fig. 1 (b), submit an element mapping original drawing that can identify the difference in concentration by color as a property submission form at the same time as this application so that the qualitative concentration can be understood in more detail. Yes. Please refer to this original drawing if necessary. As is apparent from FIG. 1B, Dy is concentrated in the outer shell of the crystal grains.

Next, after melting Pr metal and Al metal in a high-frequency melting furnace (after obtaining the molten metal), the molten metal is brought into contact with a copper water-cooled roll rotating at a roll surface speed of 20 m / sec to form a rapidly solidified alloy ribbon. Produced. Next, the rapidly solidified alloy ribbon was pulverized by a ball mill to obtain a Pr—Al supply source made of Pr—Al alloy powder. Among the obtained alloy powders, those having a sieve mesh of 100 μm or less were used as the Pr—Al supply source.
Then, after applying a 2% aqueous solution of hydroxypropylcellulose as a binder to the 15.0 mm × 23.0 mm surface of the sintered body, the Pr—Al alloy powder is sprayed and dried with warm air to thereby form the sintered body. Pr and Al sources were deposited on the surface. After performing this on both sides (two sides of the sintered body of 15.0 mm × 23.0 mm), it was placed in a processing vessel and heated in an Ar atmosphere to perform Pr—Al diffusion. Table 1 shows the conditions of Pr—Al diffusion treatment (supply source (composition of the supply source), total amount of application, heating temperature / time). The total amount of spraying is the total amount of each sample coated with the same amount of Pr-Al alloy powder on one side (spraying amount on two surfaces). For example, sample no. 3, the total spray amount is 120 mg. In this case, 60 mg is sprayed on one side.

Here, Sample No. No. 1 is a sample that has not been subjected to Pr—Al diffusion treatment after heavy rare earth element (Dy) diffusion treatment. No. 14 is a sample that gave a thermal history equivalent to that of Pr—Al diffusion treatment without using a Pr—Al supply source (that is, without Pr—Al diffusion treatment). 12 is a sample using Pr metal powder instead of Pr-Al alloy powder.
Next, the obtained sintered magnet was heat-treated at 500 ° C. for 3 hours for the purpose of improving the magnetic properties, then cut out from the central portion in the length direction, and the thickness and width were set on one side. A sintered magnet having a thickness of 3.6 mm, a width of 14.6 mm, and a length of 7.0 mm was obtained by grinding 0.2 mm (0.4 mm on both sides). These sintered magnets were subjected to ICP emission spectroscopic analysis. Sample No. 1 and sample no. In any of the compositions of No. 14, Nd: 28.4 mass%, Pr: 0.14 mass%, Dy: 2.0 mass%, B: 0.97 mass%, Co: 2.0 mass%, Cu: 0 10% by mass, Al: 0.23% by mass, Ga: 0.06% by mass, and Fe: balance. The oxygen and nitrogen concentrations contained in the sintered body were measured with an oxygen gas analyzer for nitrogen and the carbon concentration was measured with a gas analyzer for carbon. The measurement results were oxygen: 800 ppm, nitrogen: 300 ppm, and carbon: 900 ppm.
The other samples were also subjected to ICP emission spectroscopic analysis to determine the amount of increase in Pr and the amount of increase in Al. Here, the Pr increase amount is the amount of Pr increased by the Pr—Al diffusion treatment, and from the Pr content after the Pr—Al diffusion treatment, the Pr content of the sintered body after the heavy rare earth element diffusion treatment. It can be determined by subtracting (0.14% by mass). Similarly, the amount of increase in Al is the amount of Al increased by the Pr—Al diffusion treatment. From the Al content after the Pr—Al diffusion treatment, the content of Al in the sintered body after the heavy rare earth element diffusion treatment. It can be determined by subtracting (0.23% by mass).

  Table 1 shows the Pr increase amount and the Al increase amount of the RTB-based sintered magnet after the Pr—Al diffusion treatment. The total rare earth amount (Nd + Dy + Pr mass%) was in the range of 30.5 mass% to 30.7 mass%, and there was no difference that affected the magnetic properties.

  The result of having performed TEM observation of the sample (R-T-B system sintered magnet) after a Pr-Al diffusion process is shown. FIG. 2 shows a DF-STEM image of a surface layer portion (depth of 100 μm from the surface) of the RTB-based sintered magnet of No. 2; FIG. 2 shows two crystal grains 20 and a grain boundary multiple point 10. Furthermore, FIG. 3 shows element mapping images of Fe, oxygen (O), Nd, and Pr in the visual field of FIG. Here, the brighter color region indicates that more elements exist. In FIG. 3, the grain boundary multipoint is a so-called rare earth rich phase in which almost no Fe is present. As is clear from FIG. 3, the oxide phase in which oxygen (O) is abundant at the grain boundary multipoints and the metal phase in which oxygen (O) is hardly present (from the grain boundary multipoints in FIG. 2 to the oxides). (Excluding the phase). Further, as is apparent from the Pr mapping image of FIG. 3, Pr is concentrated in the metal phase at the grain boundary multiple points, but partly exists in the oxide phase (the brightest color region in the Pr mapping image). That is, as shown in FIG. 4, the metal phase 12 and the oxide phase 14 exist at the grain boundary multiple points. As for Al, since the introduction amount is very small, it is difficult to confirm the location where it is clearly concentrated. However, as is clear from the above-mentioned ICP emission spectroscopic analysis, Al is sintered by diffusion treatment. Therefore, it is considered that Al is also concentrated at grain boundaries and multiple grain boundary points.

  As described above, as shown in the result of TEM observation, the RTB-based sintered magnet has multiple grain boundary points, and further has a metal phase and an oxide phase at the multiple grain boundary points. These can be identified.

  Next, as shown in FIG. 5, the point A in the metal phase and the point B in the crystal grain adjacent to the metal phase including the point A are quantitatively analyzed by TEM-EDX, and occupy the rare earth elements contained in the metal phase. The mass ratio of Pr and the mass ratio of Pr in the rare earth elements in the crystal grains adjacent to the metal phase were determined. Here, as for the metal phase, the presence of a metal phase containing Co and a metal phase containing no Co at the grain boundary multiple points was confirmed, but the metal phase containing no Co was measured. Table 2 shows the results of quantitative analysis of the measured samples.

  As shown in Table 2, sample No. 1 in which Pr was introduced by Pr—Al diffusion treatment. In Nos. 2 to 13, the mass ratio of Pr in the rare earth element contained in the metal phase tends to increase as the amount of increase in Pr increases. (4% -79%). On the other hand, sample No. In Nos. 1 and 14, no Pr—Al diffusion treatment was performed, so Pr was not detected in either case. In addition, the sample No. 1 in which Pr—Al diffusion treatment was performed at a low temperature. In No. 13, Pr was slightly present in the metal phase.

Table 4 shows the measurement results of the magnetic properties of the obtained sintered magnet. In Table 4, _"H cJ (140 ℃)", _"B r (140 ° C.)" is a value obtained by measuring the _{H cJ} and _{B r} at 140 ° C. by hot BH tracer.

  For comparison, a sample to which a large amount of Pr or Al was added at the time of melting when preparing a flake of a raw material alloy for an R-T-B magnet was prepared by a melting method, and was fired by the same method as the above-described example samples. After producing the bonded body, it was processed into the same dimensions by performing heavy rare earth element diffusion treatment and heat treatment for the purpose of improving magnetic properties under the same conditions as in the above-described example samples. Table 3 shows the composition of the obtained sintered magnet, and Table 4 shows the measurement results of the magnetic properties.

As shown in Table 4, by performing the Pr—Al diffusion treatment, the mass ratio of Pr in the rare earth element contained in the metal phase in the surface layer portion is 75% or less, and the crystal grains adjacent to the metal phase are Sample No. which is a sample of the present invention, which is higher by 20 percentage points or more than the mass ratio of Pr in the rare earth element contained, and further, the Al content is increased by 0.01 to 0.05 percentage points by mass ratio . _Nos. 2 to 8 are _samples in which _{HcJ at} a high temperature such as 140 ° C. is 700 kA / m or more, and the Pr-Al diffusion treatment is not performed after the heavy rare earth element diffusion treatment (Sample No. 1 and Sample No. compared with .14), no decrease in _{B r,} it was possible to obtain a high _{H cJ} improvement. Among these samples according to the present invention, No. Sample 8 has a relatively large amount of Pr contained in the metal phase. The effect of improving _{HcJ at} 140 ° C. is slightly smaller than 2-6. In addition, No. 1 was subjected to Pr—Al diffusion treatment by heating to a temperature higher than 800 ° C. close to the treatment temperature subjected to heavy rare earth element diffusion. In the sample _No. 7 (850 ° C.), although the amount of increase in Pr and Al and the Pr content in the metal phase are both within the scope of the present invention, the effect of improving _{HcJ at} 140 ° C. is slightly reduced. This indicates that the Pr—Al diffusion treatment is preferably 600 ° C. to 760 ° C.

Sample No. 9 is that the mass ratio of Pr in the rare earth element contained in the metal phase is 75% or less, and 20 percentage points or more than the mass ratio of Pr in the rare earth element contained in the crystal grains adjacent to the metal phase. Although it is high, the increase in the Al content by the Pr—Al diffusion treatment exceeds 0.05 percentage point (increase of 0.07 percentage point) by mass ratio, so that the sample not subjected to the Pr—Al diffusion treatment (Sample No.) The effect of improving _{HcJ at} 140 ° C. is not as great as that of the sample according to the present invention compared to .1). Furthermore, sample no. 9, a decrease of _{B r} is observed. Sample No. No. 10 increases the mass ratio of Al contained in the sintered body in the range of 0.01 percentage point to 0.05 percentage point, but the mass ratio of Pr in the rare earth element contained in the metal phase is 75. %, The _HcJ improvement effect at 140 ° C. is not as good as that of the sample according to the present invention compared to the sample not subjected to the Pr—Al diffusion treatment (Sample No. 1).

Sample No. No. 11 is a Pr—Al diffusion treatment because the mass ratio of Pr in the rare earth element contained in the metal phase is only 20 percentage points higher than the mass ratio of Pr in the rare earth element adjacent to the metal phase. The effect of improving _{HcJ at} 140 ° C. is not as good as that of the sample according to the present invention compared to the sample (Sample No. 1) that is not. In addition, sample No. 1 was subjected to diffusion treatment using Pr metal powder instead of Pr—Al powder. 12 and Sample No. No. 12 in which the mass ratio of Pr in the rare earth element contained in the metal phase was as small as 4% by mass and no increase in the Al content was observed even when the Pr—Al diffusion treatment was performed. No. 13 is not as effective in improving _{HcJ at} 140 ° C. as the sample according to the present invention compared to the sample not subjected to the Pr—Al diffusion treatment (sample No. 1).
In addition, Sample No. which gave a thermal history equivalent to that of the Pr—Al diffusion treatment without using the Pr—Al supply source (that is, without performing the Pr—Al diffusion treatment). 14 is Sample No. Compared to 1, H _{cJ at} 140 ° C. is decreased.

Furthermore, sample No. 1 to which Pr or Al was added during dissolution was used. 15-20, the _HcJ improvement effect in 140 _degreeC is not acquired as much as the sample which _{concerns on} this invention compared with the sample (sample No. 1) which has not carried out the Pr-Al diffusion process. In addition, Sample No. with a large amount of Pr added during dissolution. Sample No. 16 with a large amount of addition of 16 or Al. 18 and 19, _{B r} is reduced at 140 ° C..

As described above, the manufacturing method of the RTB-based sintered magnet of the present invention accounts for the rare earth elements contained in the metal phase in the surface layer portion by performing the Pr—Al diffusion treatment after the heavy rare earth element diffusion treatment. The mass ratio of Pr is 75% or less, and is higher by 20 percentage points than the mass ratio of Pr in the rare earth elements contained in the crystal grains adjacent to the metal phase, and is further contained in the sintered body. By increasing the mass ratio of Al by 0.01 percentage point to 0.05 percentage point, a high _HcJ improvement effect at a high temperature such as 140 ° C. can be obtained as in the present invention. On the other hand, with either Pr or Al, the sample no. Sample Nos. 9 to 13 and Pr and Al added at the time of melting when preparing flakes of the raw material alloy for RTB-based magnets instead of diffusion treatment. 15-20 cannot obtain the high _HcJ improvement effect in high temperature like 140 _degreeC unlike the sample of this invention.

Example 2
A sintered body having the same composition and dimensions as in Example 1 and having a thickness of 4.0 mm, a width of 15.0 mm, and a length of 23.0 mm was prepared. And after apply | coating the hydroxypropyl cellulose 2% aqueous solution used as a binder to the 15.0 mm x 23.0 mm surface of the said sintered compact, sample No. Dy metal powder for sample No. 21, sample no. A Dy-Pr-Al alloy powder was sprayed for 22 and dried with warm air to attach a supply source to the surface of the sintered body. After performing this on both sides, it is placed in a processing vessel and heated in an Ar atmosphere, and Dy diffusion treatment (heavy rare earth element diffusion treatment) and Dy-Pr-Al diffusion treatment (heavy rare earth diffusion treatment and Pr-Al diffusion treatment). (Equivalent to performing simultaneously). These sintered bodies and sintered magnets were heat-treated at 500 ° C. for 3 hours for the purpose of improving magnetic properties. The obtained sintered magnet was processed in the same manner as in Example 1 and finished to 3.6 mm × width 14.6 mm × length 7.0 mm, and then subjected to ICP emission spectroscopic analysis. Table 5 shows the results of these diffusion treatment conditions (total supply amount and spray amount, heating temperature / time), Pr increase amount, and Al increase amount. Sample No. The amount of Dy contained in the sintered magnets 21 and 22 was 2.0% by mass.
Furthermore, sample no. 23, sample no. Pr-Al alloy powder was applied to 21 (sintered body subjected to Dy diffusion treatment), and Pr-Al diffusion treatment was performed. Note that the total amount of spraying is the total amount of each sample coated with the same amount of diffusion source alloy powder on each of the two surfaces. For example, sample no. No. 21 has a total application amount of the alloy powder of the supply source of 100 mg. In this case, 50 mg is applied to each side. Furthermore, Table 6 shows the magnetic property measurement results of the obtained sintered magnet. In Table 6, _"H cJ (140 ℃)", _"B r (140 ° C.)" is a value obtained by measuring the _{H cJ} and _{B r} at 140 ° C. by hot BH tracer.

As shown in Table 6, sample No. No. 23 was able to obtain a high _HcJ improvement effect at 140 ° C. as compared with the sample not subjected to the Pr—Al diffusion treatment (Sample No. 21). In contrast, sample No. 1 in which Dy and Pr—Al were simultaneously diffused. No. 22 is not as effective in improving _{HcJ at} 140 ° C. as the sample according to the present invention compared to the sample not subjected to the Pr—Al diffusion treatment (sample No. 21). This is considered to be because Pr and Al were introduced into the crystal grains without sufficiently concentrating at the grain boundaries by performing the Pr—Al diffusion treatment simultaneously with the Dy diffusion treatment.

10 Grain boundary multiple points 12 Metal phase 14 Oxide phase 20 Crystal grain

Claims (9)

1) forming a sintered body containing a rare earth element containing neodymium (Nd), iron (Fe), and boron (B) and having an intermetallic compound represented by the following general formula as a main phase;
2) A heavy rare earth element supply source containing at least one of dysprosium (Dy) and terbium (Tb) and the sintered body are disposed in a container, and the heavy rare earth element supply source and the sintered body are heated. , By diffusing at least one of dysprosium (Dy) and terbium (Tb) from the heavy rare earth element source into the sintered body, dysprosium (Dy) and terbium ( Enriching at least one of Tb);
3) After the step 2), a Pr—Al supply source containing praseodymium (Pr) and aluminum (Al), and a sintered body in which at least one of dysprosium (Dy) and terbium (Tb) is diffused are contained in the container. The Pr—Al supply source and the sintered body are heated, and praseodymium (Pr) and aluminum (Al) are diffused from the Pr—Al supply source into the sintered body, thereby the sintering. In at least a part of the surface layer of the body, the mass ratio of praseodymium (Pr) in the rare earth element contained in the metal phase present at the grain boundary multiple points of the crystal grains is 75% or less and adjacent to the metal phase 20 mass points or more higher than the mass ratio of praseodymium (Pr) in the rare earth elements contained in the crystal grains, and further, aluminum (Al) contained in the sintered body The mass ratio and process increasing 0.01 percentage points and 0.05 percentage points,
The manufacturing method of the RTB type | system | group sintered magnet characterized by including.

General formula: R ₂ T ₁₄ B
(Here, R is one or more rare earth elements in which neodymium (Nd) is 50% or more by mass ratio, and T is iron (Fe) or iron (Fe) and cobalt (Co).)   In the step 3), the mass ratio of praseodymium (Pr) in the rare earth element contained in the metal phase present at the grain boundary multiple points of the crystal grains is 75% or less over the entire surface layer portion of the sintered body. 2. The production method according to claim 1, wherein a mass ratio of praseodymium (Pr) in the rare earth element contained in the crystal grains adjacent to the metal phase is higher by 20 percentage points or more.   The manufacturing method according to claim 1 or 2, wherein a mass ratio of praseodymium (Pr) in a rare earth element contained in the metal phase in the surface layer portion is 60% or less.   3. The method according to claim 1, wherein in step 3), the mass ratio of praseodymium (Pr) contained in the sintered body is increased by 0.4 percentage point to 1.5 percentage points. .   In the step 3), a mass ratio of aluminum (Al) contained in the sintered body is increased by 0.01 percentage point to 0.03 percentage point. The manufacturing method as described.   The manufacturing method according to any one of claims 1 to 5, wherein in the step 3), the Pr-Al supply source and the sintered body are heated to 600 ° C to 850 ° C.   The manufacturing method according to claim 6, wherein in the step 3), the Pr—Al supply source and the sintered body are heated to 600 ° C. to 760 ° C.   The said Pr-Al supply source is a Pr-Al alloy whose aluminum (Al) is 2-6 mass%, The manufacturing method as described in any one of Claims 1-7 characterized by the above-mentioned.   In the step 2), the heavy rare earth element supply source containing dysprosium (Dy) and the sintered body are disposed in a container, the heavy rare earth element supply source and the sintered body are heated, and the heavy rare earth element is heated. The dysprosium (Dy) is concentrated in the outer shell of the crystal grain of the intermetallic compound by diffusing dysprosium (Dy) from the element supply source into the sintered body. The manufacturing method as described in any one.

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