JPWO2004029999A1 - R-T-B rare earth permanent magnet - Google Patents

Abstract

From the R2T14B phase (R is one or more rare earth elements (however, the rare earth element is a concept including Y), and T is one or more transition metal elements essential to Fe, Fe and Co) And a sintered body containing a grain boundary phase containing more R than the main phase, and a Zr-rich product is present in the R2T14B phase. The product rich in Zr has a plate-like or needle-like form. And according to the R-T-B rare earth permanent magnet in which this product exists, it is possible to suppress grain growth while minimizing deterioration of magnetic properties and to obtain a wide sintering temperature range. .

Description

  The present invention relates to R (R is one or more of rare earth elements, where the rare earth element is a concept including Y), T (T is at least one or more transition metals essentially comprising Fe or Fe and Co) Element) and an RTB-based rare earth permanent magnet mainly composed of B (boron).

Among rare earth permanent magnets, RTB rare earth permanent magnets are excellent in magnetic properties, and Nd as a main component is abundant in resources and relatively inexpensive. Yes.
Research and development for improving the magnetic properties of R-T-B rare earth permanent magnets has also been vigorously conducted. For example, in JP-A-1-219143, by adding 0.02 to 0.5 at% Cu to an RTB-based rare earth permanent magnet, the magnetic properties are improved and the heat treatment conditions are also improved. Has been reported. However, the method described in Japanese Patent Application Laid-Open No. 1-219143 is not effective for obtaining high magnetic properties as required for high performance magnets, specifically, high coercive force (HcJ) and residual magnetic flux density (Br). It was enough.
Here, the magnetic properties of the R-T-B rare earth permanent magnet obtained by sintering depend on the sintering temperature. On the other hand, on an industrial production scale, it is difficult to make the heating temperature uniform throughout the sintering furnace. Therefore, the R-T-B rare earth permanent magnet is required to obtain desired magnetic characteristics even if the sintering temperature varies. Here, the temperature range in which the desired magnetic characteristics can be obtained is referred to as a sintering temperature range.
In order to further improve the performance of the R-T-B rare earth permanent magnet, it is necessary to reduce the amount of oxygen in the alloy. However, when the amount of oxygen in the alloy is reduced, abnormal grain growth is likely to occur in the sintering process, and the squareness ratio is reduced. This is because the oxide formed by oxygen in the alloy suppresses the growth of crystal grains.
Therefore, as a means for improving the magnetic characteristics, a method of adding a new element to an RTB-based rare earth permanent magnet containing Cu has been studied. In Japanese Unexamined Patent Publication No. 2000-234151, there is a report of adding Zr and / or Cr in order to obtain a high coercive force and residual magnetic flux density.
Similarly, in JP-A-2002-75717, a fine ZrB compound, NbB compound or HfB compound (hereinafter referred to as “Rt-B” type rare earth permanent magnet containing Co, Al, Cu, and Zr, Nb or Hf) It has been reported that by uniformly dispersing and precipitating (MB compound), grain growth in the sintering process is suppressed and magnetic characteristics and sintering temperature range are improved.
According to JP 2002-75717 A, the sintering temperature range is expanded by dispersing and precipitating the MB compound. However, in Example 3-1, disclosed in JP-A-2002-75717, the sintering temperature width is as narrow as about 20 ° C. Therefore, it is desirable to further widen the sintering temperature range in order to obtain high magnetic characteristics in a mass production furnace or the like. In order to obtain a sufficiently wide sintering temperature range, it is effective to increase the amount of Zr added. However, the residual magnetic flux density decreases as the amount of Zr added increases, and the intended high characteristics cannot be obtained.
Therefore, an object of the present invention is to provide an R-T-B rare earth permanent magnet that can suppress grain growth while minimizing deterioration in magnetic properties and can further improve the sintering temperature range.

The inventor of the present invention minimizes the deterioration of magnetic properties when a Zr-rich product is present in the R ₂ T ₁₄ B phase constituting the main phase of the R-T-B system rare earth permanent magnet. It has been found that the grain growth can be suppressed and the sintering temperature range can be improved. That is, the present invention relates to an R ₂ T ₁₄ B phase (R is one or more rare earth elements (however, the rare earth element is a concept including Y), and T is one element in which Fe or Fe and Co are essential. Or a sintered body including a main phase composed of two or more transition metal elements) and a grain boundary phase containing more R than the main phase, and a Zr-rich product exists in the R ₂ T ₁₄ B phase. An R-T-B rare earth permanent magnet is provided.
In the RTB-based rare earth permanent magnet of the present invention, the Zr-rich product has a plate-like or needle-like form.
In the R-T-B rare earth permanent magnet of the present invention, it is desirable that the amount of oxygen contained in the sintered body is 2000 ppm or less. The effects of suppressing grain growth and expanding the sintering temperature range due to the presence of a Zr-rich product in the R ₂ T ₁₄ B phase are as follows. The amount of oxygen contained in the sintered body is as low as 2000 ppm or less. It is because it becomes remarkable in the case.
In the R-T-B rare earth permanent magnet of the present invention, R: 28 to 33 wt%, B: 0.5 to 1.5 wt%, Al: 0.03 to 0.3 wt%, Cu: 0.3 wt% or less (Zr is not included), Zr: 0.05 to 0.2 wt%, Co: 4 wt% or less (not including 0), and the balance is preferably substantially composed of Fe.
In the R-T-B rare earth permanent magnet of the present invention, it is more desirable to contain Zr within a range of 0.1 to 0.15 wt%.

FIG. 1 is a chart showing the combination of the low R alloy and high R alloy used in the first embodiment and the composition of the obtained permanent magnet, and FIG. 2 shows the magnetic characteristics of the permanent magnet obtained in the first embodiment. FIG. 3 is a graph showing the relationship between the amount of additive element M (Zr or Ti) of the permanent magnet obtained in the first embodiment and the residual magnetic flux density (Br), and FIG. 4 is a graph showing the first embodiment. FIG. 5 is a graph showing the relationship between the amount of additive element M (Zr or Ti) of the obtained permanent magnet and the coercive force (HcJ), and FIG. 5 shows the additive element M (Zr or Ti) of the permanent magnet obtained in the first embodiment. ) Is a graph showing the relationship between the amount and the squareness ratio (Hk / HcJ), FIG. 6 is a TEM (Transmission Electron Microscope) photo of the sample of Example 1 (Zr amount is 0.10 wt%). FIG. 7 (a) shows the sample of Example 1. FIG. 7 (b) shows an EDS (Energy Dispersiveon X-ray Fluorescence Spectroscopy) profile of a product existing in a sample having a Zr content of 0.10 wt%. FIG. 8 is a diagram showing an EDS profile of the R ₂ T ₁₄ B phase in sample No. 1 (sample with a Zr content of 0.10 wt%), and FIG. 8 shows a TEM of the sample of Example 1 (sample with a Zr content of 0.10 wt%). FIG. 9 is a high-resolution photograph, FIG. 9 is a TEM photograph of the sample of Example 1 (Zr amount is 0.10 wt%), and FIG. 10 is a TEM of the sample of Example 1 (Zr amount is 0.10 wt%). FIG. 11 (a) is a photograph of EPMA (Electron Probe Micro An) of the sample of Example 1 (sample with a Zr content of 0.10 wt%). lyzer: a photograph showing the Zr mapping result (electron beam microanalyzer) (bottom), a photograph showing the composition image of the same field of view as the Zr mapping result (bottom), FIG. 11 (b) is a sample of Comparative Example 2 ( A sample showing the Zr mapping result by EPMA (a sample having a Zr amount of 0.10 wt%) (bottom) and a photo showing the composition image of the same field of view as the Zr mapping result (bottom), FIG. 12 shows the second embodiment. FIG. 13 is a graph showing the relationship between the sintering temperature and the residual magnetic flux density (Br) in the second embodiment, and FIG. 14 is the sintering temperature in the second embodiment. FIG. 15 is a graph showing the relationship between the sintering temperature and the squareness ratio (Hk / HcJ) in the second embodiment, and FIG. 16 is a graph showing the relationship between the coercive force (HcJ) and the coercivity (HcJ). To freeze temperature FIG. 17 shows the combination of the low R alloy and the high R alloy used in the third embodiment and the composition of the obtained permanent magnet. FIG. 17 is a graph corresponding to the residual magnetic flux density (Br) and the squareness ratio (Hk / HcJ). FIG. 18 is a chart showing the magnetic characteristics of the permanent magnet obtained in the third embodiment. FIG. 19 is a combination of the low R alloy and the high R alloy used in the fourth embodiment and the permanent magnet obtained. FIG. 20 is a chart showing the magnetic properties of the permanent magnets obtained in the fourth embodiment.

Embodiments of the present invention will be described below.
<Organization>
As is well known, the rare earth permanent magnet obtained by the present invention has an R ₂ T ₁₄ B phase (R is one or more rare earth elements (however, the rare earth element is a concept including Y), T Includes at least a main phase composed of Fe or one or more transition metal elements essential for Fe and Co) and a grain boundary phase containing more R than the main phase. The present invention is characterized in that a Zr-rich product is present in the R ₂ T ₁₄ B phase. The RTB-based rare earth permanent magnet in which this product is present can suppress grain growth while minimizing deterioration in magnetic properties, and can obtain a wide sintering temperature range. The product, it is necessary to be present in the R 2 _T 14 _B Aiuchi, not intended to require that present in all R _{2 T} 14 _B Aiuchi. Moreover, this product may exist in the grain boundary phase. However, when the product rich in Zr exists only in the grain boundary phase, the effect of the present invention cannot be enjoyed.
In an R-T-B rare earth permanent magnet, Ti is conventionally known as an additive element for forming a product in the R ₂ T ₁₄ B phase (for example, J. Appl. Phys. 69 (1991) 6055). . The present inventor has found that if a product is formed in the R ₂ T ₁₄ B phase by adding Zr and Ti, it is effective in expanding the sintering temperature range. Here, in the case of Zr, even if an amount that sufficiently exhibits the effect of widening the sintering temperature range is added, the magnetic characteristics, specifically, the residual magnetic flux density (Br) is hardly lowered. . On the other hand, in the case of Ti, it has been clarified that the residual magnetic flux density (Br) is remarkably lowered when an amount that sufficiently exhibits the effect of widening the sintering temperature range is added, which is not preferable in practice. As described above, by making the composition of the product rich in Zr, a high-performance permanent magnet can be stably manufactured in a wide sintering temperature range.
The present inventors have confirmed that there are several manufacturing requirements for the Zr-rich product to be present in the R ₂ T ₁₄ B phase. As a series of steps of the method for manufacturing a permanent magnet according to the present invention will be described later, here, the requirements for the presence of a Zr-rich product in the R ₂ T _{1 4} B phase will be described.
As a manufacturing method of the R-T-B system rare earth permanent magnet, a method using a single alloy having a desired composition as a starting material (hereinafter referred to as a single method) and a plurality of alloys having different compositions are started. There are two methods (hereinafter referred to as mixing method) as raw materials. Typically, the mixing method uses an alloy mainly composed of the R ₂ T ₁₄ B phase (low R alloy) and an alloy containing more R than the low R alloy (high R alloy) as starting materials.
The inventor of the present invention obtained an RTB-based rare earth permanent magnet by containing Zr in either a low R alloy or a high R alloy. As a result, it was confirmed that when a permanent magnet was produced by containing Zr in a low R alloy, a Zr-rich product was present in the R ₂ T ₁₄ B phase. Meanwhile, product-rich Zr if was contained Zr, it was confirmed that does not exist in the R _{2 T} 1 _{4 B} Aiuchi to high R alloys.
Further, even when Zr is contained in the low R alloy, if a Zr-rich product is present in the R ₂ T ₁₄ B phase at the stage of the low R alloy, the Zr will be changed to Zr after sintering. A rich product exists in the R-rich phase (grain boundary phase) at the triple point in the sintered structure, but a Zr-rich product could not be confirmed in the R ₂ T ₁₄ B phase. Therefore, in order to present a product rich in Zr to R-T-beta type _R 2 _{T 14} B rare earth permanent magnet Aiuchi, the product-rich Zr in the material alloy stage _R 2 _{T 14} B Aiuchi It is important not to exist.
For that purpose, it is necessary to consider the manufacturing method of the raw material alloy. When producing a low R alloy by strip casting, it is necessary to control the peripheral speed of the cooling roll. When the peripheral speed of the cooling roll is low, α-Fe is precipitated and a Zr-rich product is generated in the R ₂ T ₁₄ B phase of the low R alloy. According to the study of the present inventors, when the peripheral speed of the cooling roll is in the range of 1.0 to 1.8 m / s, a low R alloy in which a product rich in Zr does not exist in the R ₂ T ₁₄ B phase is obtained. be able to. By using this low R alloy, a permanent magnet having high magnetic properties can be obtained.
Moreover, even if a low R alloy in which a Zr-rich product does not exist in the R ₂ T ₁₄ B phase is obtained, it is not desirable for the present invention to add heat treatment to the alloy and use it as a raw material alloy. This is because a product rich in Zr is generated in the R ₂ T ₁₄ B phase of the low R alloy by performing heat treatment in a temperature range (approximately 700 ° C. or higher) that modifies the structure of the low R alloy. .
<Chemical composition>
Next, the desirable chemical composition of the RTB-based rare earth permanent magnet according to the present invention will be described. The chemical composition here refers to the chemical composition after sintering.
The rare earth permanent magnet of the present invention contains 25 to 35 wt% of R.
Here, R is one or more selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, and Y. When the amount of R is less than 25 wt%, the generation of the R ₂ T ₁₄ B phase that is the main phase of the rare earth permanent magnet is not sufficient. For this reason, α-Fe or the like having soft magnetism is precipitated, and the coercive force is remarkably lowered. On the other hand, when the amount of R exceeds 35 wt%, the volume ratio of the R ₂ T ₁₄ B phase, which is the main phase, decreases, and the residual magnetic flux density decreases. On the other hand, when the amount of R exceeds 35 wt%, R reacts with oxygen, and the amount of oxygen contained increases, resulting in a decrease in the R-rich phase effective for generating coercive force, leading to a decrease in coercive force. Therefore, the amount of R is set to 25 to 35 wt%. A desirable amount of R is 28 to 33 wt%, and a more desirable amount of R is 29 to 32 wt%.
Since Nd is abundant in resources and relatively inexpensive, it is preferable that the main component as R is Nd. Dy is effective in increasing the anisotropic magnetic field of the R ₂ T ₁₄ B phase and improving the coercive force. Therefore, it is desirable that Nd and Dy are selected as R and the total of Nd and Dy is 25 to 33 wt%. In this range, the amount of Dy is preferably 0.1 to 8 wt%. It is desirable to determine the amount of Dy within the above range depending on which of the residual magnetic flux density and the coercive force is important. That is, when it is desired to obtain a high residual magnetic flux density, the Dy amount is preferably 0.1 to 3.5 wt%, and when a high coercive force is desired, the Dy amount is desirably 3.5 to 8 wt%.
The rare earth permanent magnet of the present invention contains 0.5 to 4.5 wt% of boron (B). When B is less than 0.5 wt%, a high coercive force cannot be obtained. However, when B exceeds 4.5 wt%, the residual magnetic flux density tends to decrease. Therefore, the upper limit is 4.5 wt%. A desirable amount of B is 0.5 to 1.5 wt%, and a more desirable amount of B is 0.8 to 1.2 wt%.
The RTB-based rare earth permanent magnet of the present invention can contain one or two of Al and Cu in a range of 0.02 to 0.6 wt%. By including one or two of Al and Cu in this range, it is possible to increase the coercive force, the corrosion resistance, and the temperature characteristics of the obtained permanent magnet. In the case of adding Al, a desirable amount of Al is 0.03 to 0.3 wt%, and a more desirable amount of Al is 0.05 to 0.25 wt%. In addition, in the case of adding Cu, the amount of Cu is 0.3 wt% or less (excluding 0), desirably 0.15 wt% or less (not including 0), and the more desirable amount of Cu is 0.03 to 0 0.08 wt%.
The RTB-based rare earth permanent magnet of the present invention preferably contains 0.03 to 0.25 wt% of Zr in order to generate a Zr-rich product in the R ₂ T ₁₄ B phase. When the oxygen content is reduced in order to improve the magnetic properties of the R-T-B rare earth permanent magnet, Zr exhibits the effect of suppressing abnormal growth of crystal grains during the sintering process. Make the tissue uniform and fine. Therefore, Zr has a remarkable effect when the amount of oxygen is low. A desirable amount of Zr is 0.05 to 0.2 wt%, and a more desirable amount is 0.1 to 0.15 wt%.
The RTB-based rare earth permanent magnet of the present invention has an oxygen content of 2000 ppm or less. When the amount of oxygen is large, the oxide phase, which is a nonmagnetic component, increases and the magnetic properties are deteriorated. Therefore, in the present invention, the amount of oxygen contained in the sintered body is set to 2000 ppm or less, desirably 1500 ppm or less, and more desirably 1000 ppm or less. However, when the oxygen amount is simply reduced, the oxide phase having the effect of suppressing grain growth decreases, and grain growth easily occurs in the process of obtaining a sufficient density increase during sintering. Therefore, in the present invention, a predetermined amount of Zr that exhibits the effect of suppressing abnormal growth of crystal grains during the sintering process is contained in the R-T-B system rare earth permanent magnet.
The R-T-B rare earth permanent magnet of the present invention contains 4 wt% or less of Co (not including 0), preferably 0.1 to 2.0 wt%, more preferably 0.3 to 1.0 wt%. . Co forms the same phase as Fe, but is effective in improving the Curie temperature and improving the corrosion resistance of the grain boundary phase.
<Manufacturing method>
Next, the suitable manufacturing method of the RTB system rare earth permanent magnet by this invention is demonstrated.
In the present embodiment, the rare earth permanent magnet according to the present invention is made using an alloy mainly composed of the R ₂ T ₁₄ B phase (low R alloy) and an alloy containing more R than the low R alloy (high R alloy). A manufacturing method will be described.
First, a low R alloy and a high R alloy are obtained by strip casting the raw metal in a vacuum or an inert gas, preferably in an Ar atmosphere. Here, as described above, in the obtained strip, particularly the low R alloy strip, care must be taken so that no Zr-rich product is generated in the R ₂ T ₁₄ B phase. Specifically, the peripheral speed of the cooling roll is set to a range of 1.0 to 1.8 m / s. A desirable peripheral speed of the cooling roll is 1.2 to 1.5 m / s.
Until sintering step described below after obtaining the low R alloys having the R _{2 T} 14 _B phase is product no rich Zr, not to produce the product in R _{2 T} 14 _B Aiuchi, i.e. the R It is important for the present invention to maintain the morphology of the ₂ T ₁₄ B phase. For example, it is desirable to avoid performing a heat treatment in which the low R alloy is heated and maintained at 700 ° C. or higher before the pulverization process starting from hydrogen pulverization. This point will be further described in the first embodiment described later.
A characteristic feature of the present embodiment is that Zr is added from a low R alloy. This is because, as explained in the section of <Structure>, by adding Zr from a low R alloy in which a Zr-rich product is not generated in the R ₂ T ₁₄ B phase, the R—T—B system rare earth permanent This is because a Zr-rich product can be present in the R ₂ T ₁₄ B phase of the magnet. In addition to rare earth elements, Fe, Co and B, the low R alloy can contain Cu and Al. In addition to the rare earth elements, Fe, Co and B, the high R alloy can contain Cu and Al.
After the low R and high R alloys are made, these raw alloys are ground separately or together. The pulverization process includes a coarse pulverization process and a fine pulverization process. First, the raw material alloys are coarsely pulverized until each particle size becomes about several hundred μm. The coarse pulverization is desirably performed in an inert gas atmosphere using a stamp mill, a jaw crusher, a brown mill or the like. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen. In addition, hydrogen can be released after hydrogen storage and further coarse pulverization can be performed.
After the coarse pulverization process, the process proceeds to the fine pulverization process. In the fine pulverization, a jet mill is mainly used, and a coarsely pulverized powder having a particle diameter of about several hundreds of micrometers is pulverized until the average particle diameter becomes 3 to 5 μm. The jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, and the high-speed gas flow accelerates the coarsely pulverized powder. Or it is the method of generating and colliding with a container wall.
When the low R alloy and the high R alloy are separately pulverized in the fine pulverization step, the finely pulverized low R alloy powder and high R alloy powder are mixed in a nitrogen atmosphere. The mixing ratio of the low R alloy powder and the high R alloy powder may be about 80:20 to 97: 3 by weight. Similarly, the mixing ratio when the low R alloy and the high R alloy are pulverized together may be about 80:20 to 97: 3 by weight. By adding about 0.01 to 0.3 wt% of additives such as zinc stearate at the time of fine pulverization, fine powder having high orientation can be obtained at the time of molding.
Next, the mixed powder composed of the low R alloy powder and the high R alloy powder is filled in a mold held by an electromagnet and molded in a magnetic field with its crystal axis oriented by applying a magnetic field. The forming in the magnetic field may be performed at a pressure of about 0.7 to 1.5 t / cm ² in a magnetic field of 12.0 to 17.0 kOe.
After molding in a magnetic field, the compact is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, a difference of a particle size and a particle size distribution, what is necessary is just to sinter at 1000-1100 degreeC for about 1 to 5 hours. In the present invention, a Zr-rich product is produced in the R ₂ T ₁₄ B phase in this sintering step. The mechanism by which Zr-rich products that do not exist at the low R alloy stage are formed after sintering is not clear, but Zr that was dissolved in the R ₂ T ₁₄ B phase at the low R alloy stage is not baked. There is a possibility of precipitation in the R ₂ T ₁₄ B phase during the setting process.
After sintering, the obtained sintered body can be subjected to an aging treatment. The aging treatment is important for controlling the coercive force. In the case where the aging treatment is performed in two stages, holding for a predetermined time at around 800 ° C. and around 600 ° C. is effective. When the heat treatment at around 800 ° C. is performed after sintering, the coercive force increases, which is particularly effective in the mixing method. In addition, since the coercive force is greatly increased by heat treatment near 600 ° C., when aging treatment is performed in one stage, it is preferable to perform aging treatment near 600 ° C.

<First embodiment>
An RTB-based rare earth permanent magnet was manufactured by the following manufacturing process.
1) Raw Material Alloy A raw material alloy (strip) having the composition and thickness shown in FIG. 1 was produced by strip casting. The roll peripheral speed was 1.5 m / s for the low R alloy and 0.6 m / s for the high R alloy. However, for the low R alloy according to Comparative Example 3 in FIG. 1, the roll peripheral speed was set to 0.6 m / s. The thickness of the alloy is an average value obtained by measuring the thickness of 50 slabs (strips). In addition, in the low R alloy according to Example 1 of FIG. 1, a Zr-rich product (hereinafter referred to as an in-phase product) was not confirmed in the R ₂ T ₁₄ B phase. In such a low R alloy, it was confirmed that the in-phase product was present in the R ₂ T ₁₄ B phase.
2) Hydrogen pulverization step After occluding hydrogen at room temperature, a hydrogen pulverization treatment was performed in which dehydrogenation was performed at 600 ° C. for 1 hour in an Ar atmosphere.
In order to obtain high magnetic properties, in this experiment, the atmosphere of each process from hydrogen crushing (recovery after the crushing process) to sintering (put into the sintering furnace) was controlled in order to keep the sintered body oxygen amount to 2000 ppm or less. The oxygen concentration is less than 100 ppm.
3) Mixing / Pulverizing Step Usually, two-stage pulverization by coarse pulverization and fine pulverization is performed.
Before the pulverization, 0.05 wt% of zinc stearate is added, and a low R alloy and a high R alloy are combined with a Nauta mixer in the combination of Example 1 and Comparative Examples 1 to 3 shown in FIG. Mixed for minutes. In all of Example 1 and Comparative Examples 1 to 3, the mixing ratio of the low R alloy to the high R alloy is 90:10.
Then, it was finely pulverized to an average particle size of 4.8 to 5.1 μm with a jet mill.
4) Molding step The obtained fine powder was molded at a pressure of 1.2 t / cm ^{2 in} a magnetic field of 15.0 kOe to obtain a molded body.
5) Sintering and aging process This molded body was sintered in a vacuum at 1070 ° C for 4 hours and then rapidly cooled. Next, the obtained sintered body was subjected to a two-stage aging treatment of 800 ° C. × 1 hour and 550 ° C. × 2.5 hours (both in an Ar atmosphere).
Magnetic properties of the obtained permanent magnet were measured with a BH tracer. The results are shown in FIGS. 2 to 5, Br is the residual magnetic flux density, HcJ is the coercive force, and "Hk / HcJ" is the squareness ratio. The squareness ratio (Hk / HcJ) is an index of magnet performance and represents the degree of angularity in the second quadrant of the magnetic hysteresis loop. Hk is the external magnetic field strength when the magnetic flux density is 90% of the residual magnetic flux density in the second quadrant of the magnetic hysteresis loop. In FIG. 2 to FIG. 5, “O” is given to those in which the in-phase product is confirmed, and “X” is given to those not confirmed. The confirmation of the in-phase product is based on observation with a TEM (Transmission Electron Microscope: JEM-3010 manufactured by JEOL Ltd.). The observation sample was prepared by an ion milling method, and the C plane of the R ₂ T ₁₄ B phase was observed. The chemical composition of the obtained sintered body is shown in the column of “sintered body composition” in FIG. In Comparative Example 3, no in-phase product was confirmed, but a Zr-rich product was confirmed in the grain boundary phase.
From FIG. 2 and FIG. 5, in the R-T-B system rare earth permanent magnet (Example 1, Comparative Example 1) in which the in-phase product was confirmed, abnormal grain growth was suppressed, and a small amount It can be seen that the squareness ratio (Hk / HcJ) is improved by the additive element M (Zr or Ti). However, when Ti is selected as the additive element M as shown in FIG. 3, the residual magnetic flux density (Br) is significantly reduced. In addition, in the R-T-B system rare earth permanent magnets (Comparative Example 2 and Comparative Example 3) in which no in-phase product was confirmed, the squareness ratio (Hk / HcJ) was increased by adding a large amount of 0.2 wt% Zr. However, the residual magnetic flux density (Br) is greatly reduced (see FIG. 3). As described above, the RTB-based rare earth permanent magnet in which the in-phase product is confirmed can obtain a high squareness ratio (Hk / HcJ) while suppressing a decrease in the residual magnetic flux density (Br). .
Regarding Comparative Example 3 in which an in-phase product is confirmed in the R ₂ T ₁₄ B phase at the stage of the low R alloy, the reason why the in-phase product does not exist in the RTB-based rare earth permanent magnet is as follows. Presumed as follows. The Zr-rich product (intra-phase product) produced in the R ₂ T ₁₄ B phase at the low R alloy stage is growing very large. It is presumed that this product does not cause volume expansion even by the hydrogen pulverization treatment. Therefore, it is understood that cracks occur at the interface between the R ₂ T ₁₄ B phase and the product during hydrogen pulverization. When subjected to a milling process in this state, the product results to be separated from the _R 2 _{T 14} B phase, the product is a _R 2 _{T 14} B phase without being included in the _R 2 _{T 14} B Aiuchi It exists independently. Therefore, it is considered that the RTB-based rare earth permanent magnet according to Comparative Example 3 has a Zr-rich product only in the grain boundary phase even after the sintering process.
The R-T-B rare earth permanent magnet having a Zr content of 0.10 wt% according to Example 1 was observed by TEM in the same manner as described above. The observation results are shown in FIGS. 6 is a TEM photograph of a sample having a Zr amount of 0.10 wt%, and FIG. 7 is a product present in the sample and an R ₂ T ₁₄ B phase EDS (Energy Dispersive X-ray Fluorescence Spectroscopymeter in the sample). : Energy dispersive X-ray analyzer spectroscopy) profile, FIG. 8 is a TEM high resolution photograph of the sample.
As shown in FIG. 6, an in-phase product having a large axial ratio can be confirmed in the R ₂ T ₁₄ B phase. This product has a plate-like or needle-like form. Since FIG. 6 is an observation of the cross section of the sample, it is difficult to specify whether the in-phase product is plate-shaped or needle-shaped. Considering the observation results of other samples and FIG. 8, the in-phase product has a length of several hundred nm and a width of several nm to 15 nm. Although the detailed chemical composition of the in-phase product is unclear, it can be confirmed from FIG. 7A that the in-phase product is at least rich in Zr. Further, in the observation results of other samples, in addition to the in-phase product having a large axial ratio, as shown in FIG. 9 and FIG. 10, it is also possible to observe indefinite and circular in-phase products. In Example 1, 20 crystal grains (R ₂ T ₁₄ B phase) were observed. As a result, in-phase products could be observed in 6 crystal grains. In contrast, in Comparative Example 2, no in-phase product was observed for all 20 crystal grains (R ₂ T ₁₄ B phase).
The lower part of FIG. 11 (a) shows the Zr mapping result by EPMA (Electron Probe Micro Analyzer) of the sample having the Zr amount of 0.10 wt% in Example 1. The upper part of FIG. 11 (a) shows a composition image having the same field of view as the Zr mapping result shown in the lower part of FIG. 11 (a). The lower part of FIG. 11 (b) shows the Zr mapping result by EPMA of the sample of Comparative Example 2 having a Zr amount of 0.10 wt%. The upper part of FIG. 11B shows a composition image having the same field of view as the Zr mapping result shown in the lower part of FIG. 11B.
Similar to the observation result by TEM, FIG. 11 (a) shows that in Example 1, the R ₂ T ₁₄ B phase rich in Zr is present, and that Zr is also present in the grain boundary phase. On the other hand, from FIG. 11B, Zr-rich R ₂ T ₁₄ B phase is not confirmed in Comparative Example 2, and Zr exists only in the grain boundary phase.
<Second embodiment>
A sample in which the amount of additive element M (Zr or Ti) in the sintered body composition was set to 0.10 wt% was the same as in the first example except that each sample was sintered at a temperature range of 1010 ° C. to 1090 ° C. for 4 hours. A T-B rare earth permanent magnet was obtained. The magnetic properties of the obtained permanent magnet were measured in the same manner as in the first example. The results are shown in FIG. Moreover, the change of the magnetic characteristic with respect to sintering temperature is shown in FIGS. FIG. 16 shows a plot of the magnetic characteristics at each sintering temperature as a squareness ratio (Hk / HcJ) with respect to the residual magnetic flux density (Br).
As shown in FIGS. 12 to 16, when an in-phase product is obtained by adding Zr as the additive element M, high magnetic properties can be stably obtained over a wide sintering temperature range. Recognize. Specifically, in Example 2 according to the present invention, in a sintering temperature range of 1030 to 1090 ° C., a residual magnetic flux density (Br) of 13.9 kG or more, a coercive force (HcJ) of 13.0 kOe or more, and 95% or more. The squareness ratio (Hk / HcJ) can be obtained. When Ti is added as the additive element M, the residual magnetic flux density (Br) is reduced (Comparative Example 4), and when there is no in-phase product, the squareness ratio (Hk / HcJ) is poor and the sintering temperature range is narrow. (Comparative Example 5).
<Third embodiment>
Four kinds of low R alloys and two kinds of high R alloys having the composition and thickness shown in FIG. 17 were prepared by strip casting at a roll peripheral speed of 0.6 to 1.8 m / s. And four types of RTB system rare earth permanent magnets were obtained by the combination shown in FIG. In any of samples A to D, the mixing ratio of the low R alloy and the high R alloy is 90:10. The low R alloy and high R alloy shown in FIG. 17 were hydrogen crushed in the same manner as in the first example. After the hydrogen pulverization treatment, 0.05 wt% butyl oleate was added, and the low R alloy and the high R alloy were mixed for 30 minutes with a Nauta mixer according to the combination shown in FIG. Thereafter, it was pulverized to an average particle size of 4.1 μm by a jet mill. The obtained fine powder was molded in a magnetic field under the same conditions as in Example 1, and then sintered at 1010 to 1090 ° C. for 4 hours. Next, a two-stage aging treatment was performed at 800 ° C. for 1 hour and 550 ° C. for 2.5 hours. The composition, oxygen content, and nitrogen content of the obtained sintered body are shown in FIG. 17, and the magnetic properties are shown in FIG.
As shown in FIG. 18, sample A has a residual magnetic flux density (Br) of 14.0 kG or more in a temperature range of 1030 to 1070 ° C., a coercive force (HcJ) of 13.0 kOe or more, and a squareness ratio of 95% or more. (Hk / HcJ) can be obtained.
In Sample B and Sample C, which have a lower Nd content than Sample A, the residual magnetic flux density (Br) of 14.0 kG or higher and the coercive force (HcJ) of 95 or higher in the temperature range of 1030 to 1090 ° C. and 95 % Or more squareness ratio (Hk / HcJ) can be obtained.
In the sample D having a larger Dy amount than the sample A, the residual magnetic flux density (Br) of 13.5 kG or more, the coercive force (HcJ) of 15.5 kOe or more, and the square of 95% or more in the temperature range of 1030 to 1070 ° C. A ratio (Hk / HcJ) can be obtained.
As a result of TEM observation of the samples sintered at 1050 ° C., in-phase products were observed in all the samples.
From the above results, when the in-phase product is present, high magnetic properties can be stably obtained with a wide sintering temperature range of 40 ° C. or more.
<Fourth embodiment>
Two types of low R alloys and two types of high R alloys were produced by strip casting, and two types of RTB-based rare earth permanent magnets were obtained by the combination shown in FIG. For sample E, the mixing ratio of the low R alloy to the high R alloy is 90:10. On the other hand, for sample F, the mixing ratio of the low R alloy and the high R alloy is 80:20. The low R alloy and high R alloy shown in FIG. 19 were hydrogen crushed in the same manner as in the first example. After the hydrogen pulverization treatment, 0.05 wt% butyl oleate was added, and the low R alloy and the high R alloy were mixed for 30 minutes with a Nauta mixer according to the combination shown in FIG. Thereafter, it was pulverized to a mean particle size of 4.0 μm by a jet mill. The obtained fine powder was molded in a magnetic field under the same conditions as in Example 1, and then sintered for 10 hours at 1070 ° C. for sample E and 4 hours at 1020 ° C. for sample F. Next, two-stage aging treatment was performed for each of Sample E and Sample F at 800 ° C. for 1 hour and 550 ° C. for 2.5 hours. The composition, oxygen content, and nitrogen content of the obtained sintered body are shown in FIG. 19, and the magnetic properties are shown in FIG. For convenience of comparison, the magnetic characteristics of samples A to D produced in the third example are also shown in FIG.
Even if the constituent elements are changed as in Samples A to F, the residual magnetic flux density (Br) of 13.8 kG or more, the coercive force (HcJ) of 13.0 kOe or more, and the squareness ratio (Hk / HcJ) of 95% or more. I was able to get it.

As described above in detail, the presence of a Zr-rich product in the R ₂ T ₁₄ B phase constituting the main phase of the R-T-B rare earth permanent magnet minimizes the deterioration of the magnetic properties. In addition, grain growth can be suppressed. In addition, according to the present invention, since a sintering temperature range of 40 ° C. or more can be secured, even when a large-sized sintering furnace in which uneven heating temperature is likely to occur is used, R- having stable and high magnetic properties. A TB rare earth permanent magnet can be easily obtained.

Claims (5)

R ₂ T ₁₄ B phase (R is one or more rare earth elements (however, the rare earth element is a concept including Y), T is one or two or more transitions essentially comprising Fe, Fe and Co) A main phase composed of a metal element),
A sintered body containing a grain boundary phase containing more R than the main phase,
An RTB-based rare earth permanent magnet characterized in that a product rich in Zr is present in the R ₂ T ₁₄ B phase. The RTB rare earth permanent magnet according to claim 1, wherein the product is plate-shaped or needle-shaped. The RTB rare earth permanent magnet according to claim 1, wherein the amount of oxygen contained in the sintered body is 2000 ppm or less. The sintered body contains R: 28 to 33 wt%, B: 0.5 to 1.5 wt%, Al: 0.03 to 0.3 wt%, Cu: 0.3 wt% or less (not including 0), Zr The R-T-B system rare earth according to claim 1, having a composition of 0.05 to 0.2 wt%, Co: 4 wt% or less (excluding 0), and the balance substantially consisting of Fe permanent magnet. 5. The RTB-based rare earth permanent magnet according to claim 4, wherein in the sintered body, Zr is 0.1 to 0.15 wt%.

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