JP2022100371A - Rare earth sintered magnet and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rare earth sintered magnet containing a rare earth element and iron, which has a surface layer having a nearly uniform appearance color.

SOLUTION: A rare earth sintered magnet 10 includes, on the outermost surface of the sintered magnet body 11 containing a rare earth element (excluding La) and iron, a surface layer made of an amorphous material containing a rare earth element of the same kind as the rare earth element, iron, and oxygen, and has no other layer on the outside of the surface layer 12. The surface layer 12 is chemically stable and prevents the internal sintered magnet body 11 from being oxidized. Since the surface layer 12 is easily formed such that the color of the appearance is close to uniform, a problem in which the surface layer 12 is mistakenly recognized as a defective product having cracks, scratches, etc. when the appearance is image-analyzed can be prevented from occurring.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a rare earth sintered magnet, particularly a sintered magnet containing a rare earth element (hereinafter referred to as “R”) and iron (Fe), and a method for producing the same.

The RFeB-based sintered magnet, which is a sintered magnet containing R and Fe and boron (B), was discovered by Masato Sagawa et al. In 1982, and has many magnetic properties such as residual magnetic flux density. It has the feature that it is much higher than the permanent magnets up to. Therefore, RFeB-based sintered magnets are used in various products such as automobile motors such as hybrid automobiles and electric automobiles, various motors such as industrial machine motors, speakers, headphones, and permanent magnet type magnetic resonance diagnostic devices. ..

Since the magnetic properties of RFeB-based sintered magnets deteriorate when they are oxidized by reacting with oxygen or water (water vapor) in the atmosphere, a film of metal, resin, or the like has been conventionally formed on the surface of the RFeB-based sintered magnet. As an example of such film formation, Patent Document 1 describes an RFeB-based sintered magnet in an atmosphere having an oxygen partial pressure of 1 × 10 ² Pa or more and 1 × 10 ⁵ Pa or less and a water vapor partial pressure of 0.1 Pa or more and less than 1000 Pa. It is described that a surface layer made of hematite is formed on the surface of an RFeB-based sintered magnet by heating to a temperature of 200 ° C. or higher and 600 ° C. or lower. Hematite is a trigonal crystal having a chemical composition of Fe ₂ O ₃ , and since it is chemically stable, it is possible to prevent oxidation of the RFeB-based sintered magnet inside.

International Publication WO 2009/041639 (Japanese Patent No. 4636207) Japanese Unexamined Patent Publication No. 2006-019521

In the RFeB-based sintered magnet described in Patent Document 1, so-called color unevenness may occur in which the appearance color becomes non-uniform. RFeB-based sintered magnets with such color unevenness are mistakenly recognized as defective products with cracks or scratches when the appearance is image-analyzed in order to find defective products in the final manufacturing process. It causes.

An object to be solved by the present invention is to provide a rare earth sintered magnet which is a sintered magnet containing R and Fe and has a surface layer whose appearance color is close to uniform, and a method for producing the same.

The rare earth sintered magnet according to the present invention, which has been made to solve the above problems, has a surface layer made of an amorphous substance containing iron and oxygen on the surface of the sintered magnet body containing the rare earth element and iron. It is a feature.

In the present invention, the surface layer may contain a rare earth element (R) in an amount of 5 atomic% or less. Further, a part of Fe may be replaced with cobalt (Co).

The rare earth sintered magnet according to the present invention has a surface layer made of amorphous material containing Fe and O. This amorphous surface layer is chemically stable and prevents the internal sintered magnet body from oxidizing. Then, such an amorphous surface layer is easy to be formed so that the color of the appearance is closer to uniform than the surface layer made of hematite described in Patent Document 1. Therefore, when the appearance is image-analyzed, it is possible to prevent the problem of erroneously recognizing the defective product as having cracks or scratches.

When the rare earth sintered magnet according to the present invention is manufactured by using the manufacturing method described later, the surface layer contains a rare earth element, but the rare earth element does not affect the appearance of the surface layer.

The rare earth sintered magnet according to the present invention includes a first intermediate layer in which an amorphous substance containing Fe and O and a microcrystal containing R, Fe and O are mixed between the surface layer and the sintered magnet body. A second intermediate layer having microcrystals containing R, Fe and O and not having an amorphous substance containing Fe and O may be provided between the first intermediate layer and the sintered magnet body. These first intermediate layer and second intermediate layer are formed between the surface layer and the sintered magnet main body when the rare earth sintered magnet according to the present invention is manufactured, for example, by the manufacturing method described later. These first intermediate layer and second intermediate layer have higher corrosion resistance than the sintered magnet body, and the grain boundary phase having a higher rare earth element content in the sintered magnet body, particularly the sintered magnet body, is oxidized. Contributes to suppression. Further, the presence of these two intermediate layers makes it possible to increase the corrosion resistance of the sintered magnet body as compared with the case where a single intermediate layer is present.

The method for manufacturing a rare earth sintered magnet according to the present invention is
A substrate made of a sintered magnet containing rare earth elements and iron, having an oxygen content of 1000 ppm or less and a carbon content of 800 ppm or less is heated in the atmosphere at a heating temperature of 100 ° C or higher and 300 ° C or lower. This is characterized by having a surface layer forming step of forming a surface layer made of amorphous material containing iron and oxygen on the surface of the base material.

According to the method for producing a rare earth sintered magnet according to the present invention, the contents of oxygen and carbon, which are impurities in a substrate composed of a sintered magnet containing R and Fe, are set to low values of 1000 ppm or less and 800 ppm or less, respectively. By heating in the atmosphere at a temperature within the above range, it has a surface layer made of amorphous material containing Fe and O (and the first intermediate layer and the second intermediate layer), and contains R and Fe. Sintered magnets can be manufactured.

Here, when the oxygen content in the substrate exceeds 1000 ppm or the carbon content exceeds 800 ppm, the surface layer cannot be formed. Further, when the heating temperature is less than 100 ° C., the surface layer cannot be formed. On the other hand, when the heating temperature exceeds 300 ° C, a surface layer made of hematite instead of amorphous is formed, and the growth rate of the surface layer becomes high, so that the structure becomes non-uniform and color unevenness occurs. It will occur.

Here, when the heating temperature exceeds 275 ° C and is 300 ° C or less, color unevenness does not occur, but the color of the entire surface becomes darker than when the heating temperature is 275 ° C or less, and image recognition becomes difficult. .. Therefore, it is desirable that the heating temperature is 100 ° C or higher and 275 ° C or lower.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to obtain a rare earth sintered magnet which is a sintered magnet containing R and Fe and has a surface layer whose appearance color is close to uniform, and a method for producing the same.

The cross-sectional view which shows the structure of one Embodiment of the rare earth sintered magnet which concerns on this invention. The cross-sectional view which shows the structure of the other embodiment of the rare earth sintered magnet which concerns on this invention. The figure for demonstrating embodiment of the rare earth sintered magnet manufacturing method which concerns on this invention. FIG. 3 is a transmission electron micrograph of a cross section near the surface of an example of a rare earth sintered magnet of the present embodiment, and is a partially enlarged photograph (a) and a photograph (b) showing a wider range than (a). An electron diffraction image of the surface layer in an example of a rare earth sintered magnet of the present embodiment. The base material (a) used in producing the rare earth sintered magnet of the present embodiment, the examples of the rare earth sintered magnet of the present embodiment ((b), (c)), and the rare earth sintered magnet of the comparative example ( d) A photograph showing the appearance of the surface. Photograph showing the appearance of the surface of the base material (a) and the examples of the rare earth sintered magnet of the present embodiment ((b), (c)) after the corrosion resistance test.

An embodiment of a rare earth sintered magnet and a method for manufacturing the same according to the present invention will be described with reference to FIGS. 1 to 7.

(1) One Embodiment of the rare earth sintered magnet according to the present invention FIG. 1 shows a cross-sectional view of the configuration of the rare earth sintered magnet of the present embodiment. In this rare earth sintered magnet 10, a surface layer 12 is formed on the surface of the sintered magnet main body 11. A first intermediate layer 131 exists between the surface layer 12 and the sintered magnet main body 11, and a second intermediate layer 132 exists between the first intermediate layer 131 and the sintered magnet main body 11. Therefore, each of these layers is arranged in the order of the second intermediate layer 132, the first intermediate layer 131, and the surface layer 12 from the sintered magnet main body 11 toward the outside.

The sintered magnet main body 11 is made of a sintered magnet containing R and Fe. In this embodiment, an RFeB-based sintered magnet is used for the sintered magnet main body 11.

The surface layer 12 is made of an amorphous substance containing Fe and O. The surface layer 12 may contain R in an amount of 5 atomic% or less. This R was contained in the rare earth element in the sintered magnet main body 11 when the surface layer 12 was manufactured by the manufacturing method described later.

The first intermediate layer 131 has a structure in which an amorphous substance containing Fe and O (similar to the amorphous substance of the surface layer 12) and microcrystals containing R, Fe and O are mixed. Further, the second intermediate layer 132 is composed of microcrystals containing R, Fe and O, and does not contain the same amorphous material as the surface layer 12.

According to the rare earth sintered magnet 10 of the present embodiment, the surface layer 12 is made of an amorphous substance containing chemically stable Fe and O, so that the internal sintered magnet body 11 can be prevented from being oxidized. can. Since the surface layer 12 made of such an amorphous substance is easy to be formed so that the color of the appearance is close to uniform, it is recognized that the surface layer 12 is mistakenly recognized as a defective product having cracks, scratches, etc. when analyzing the appearance. Can be prevented.

If the thickness of the surface layer 12 is too thin, the antioxidant effect cannot be sufficiently obtained, and if it is too thick, the magnetic properties of the rare earth sintered magnet 10 deteriorate. Therefore, the thickness may be set to several nm to several tens of nm. preferable. However, in the present invention, the thickness of the surface layer 12 is not limited to this range. The thickness of the first intermediate layer 131 may be, for example, several tens of nm to several hundred nm, and the thickness of the second intermediate layer 132 may be, for example, several hundred nm to several μm, but the thickness is not limited to these ranges.

The technical significance of the first intermediate layer 131 and the second intermediate layer 132 is as follows. Generally, in an RFeB-based sintered magnet, an R-rich phase having a higher R content than the composition of an RFeB-based material exists between crystal grains (grain boundaries), and this R-rich phase is easily oxidized. It has drawbacks. On the other hand, in the rare earth sintered magnet 10 of the present embodiment, the first intermediate layer 131 and the second intermediate layer 132 are present between the surface layer 12 and the sintered magnet main body 11, and the first intermediate layer 131 and the second intermediate layer 132 thereof are present. 2 Since the intermediate layer 132 itself has higher corrosion resistance than the sintered magnet main body 11, the corrosion resistance of the sintered magnet main body 11 can be increased. Further, since the intermediate layer is not only one layer but also two layers, the corrosion resistance of the sintered magnet main body 11 can be further improved.

However, in the present invention, the first intermediate layer 131 and the second intermediate layer 132 are not essential, and the surface layer 12A is formed directly on the surface of the sintered magnet body 11A as in the rare earth sintered magnet 10A shown in FIG. May be.

(2) One Embodiment of the rare earth sintered magnet manufacturing method according to the present invention Next, one embodiment of the rare earth sintered magnet manufacturing method according to the present invention will be described with reference to FIG.

First, a base material 21 made of a sintered magnet containing R and Fe, having an oxygen (O) content of 1000 ppm or less and a carbon (C) content of 800 ppm or less is prepared. The method for producing the base material 21 is not particularly limited as long as it can satisfy the above O and C contents, but is described in Patent Document 2 as a method for producing a sintered magnet having a low O content. It is preferable to use. The method described in Patent Document 2 is called a PLP (Press-less Process) method, in which an alloy powder (raw material powder) as a raw material for a sintered magnet is filled in a container and then oriented in a magnetic field, and then this method is performed. The raw material powder is sintered by heating it while it is still filled in this container. In the general method for manufacturing a sintered magnet, a step of compression molding the raw material powder is performed using a press machine, whereas the PLP method has a feature that such compression molding is not performed. Therefore, the PLP method does not require the use of a press machine and facilitates the handling of raw material powder. Therefore, the work from filling the container to carrying it into the sintering furnace in the glove box with an inert gas atmosphere inside is performed. It can be done easily. As a result, it becomes easy to prevent the raw material powder from being oxidized during the production of the base material 21, and the O content of the obtained base material 21 can be lowered.

The obtained base material 21 is placed on a mounting table 221 provided in the heating furnace 22. Then, the inside of the heating furnace 22 is heated to a temperature of 100 ° C. or higher and 300 ° C. or lower while being filled with the atmosphere having a partial pressure of steam of 1000 Pa or more and 3500 Pa or less (FIG. 3). Here, if the partial pressure of water vapor is less than 1000 Pa, the corrosion resistance of the rare earth sintered magnet cannot be sufficiently ensured, and if it exceeds 3500 Pa, control during manufacturing becomes difficult. Then, after maintaining this temperature for a predetermined time (for example, 0.5 to 300 minutes), the inside of the heating furnace 22 is cooled at a speed of 0.5 ° C./min or more. By this heating, R and Fe are oxidized near the surface of the base material 21. The mounting table 221 is provided with a large number of holes so that the atmosphere can pass through. By the heating and cooling operations up to this point, the second intermediate layer 132, the first intermediate layer 131, and the surface layer 12 are formed from the oxidized R and / or Fe in this order from the side closer to the base material 21.

(3) Experimental Results Next, the experimental results of actually producing the rare earth sintered magnet of the present embodiment by using the rare earth sintered magnet manufacturing method of the present embodiment will be described.

FIG. 4 shows a transmission electron micrograph of a cross section near the surface of the rare earth sintered magnet 10B (Example 1) produced by the method of the present embodiment. FIG. 4 (a) shows an enlarged part of (b). This rare earth sintered magnet was produced by heating a base material at 250 ° C. for 120 minutes in the atmosphere and then cooling it at a rate of 5 ° C./min. From FIG. 4, a light gray layer can be seen on the outermost surface of the rare earth sintered magnet 10B in contrast to the inside of the rare earth sintered magnet 10B (lower side of the figure). This layer is the surface layer 12B. Helloring can be seen in the electron diffraction image (FIG. 5) obtained by using the EDX device (JED-2300T, manufactured by JEOL Ltd.) for the surface layer 12B. This halo ring indicates that the surface layer 12B is amorphous.

Further, in FIG. 4, the first intermediate layer 131B shown in gray, which is darker than the surface layer 12B and lighter than the inner portion, can be seen inside the surface layer 12B. Further, the second intermediate layer 132B exists inside the first intermediate layer 131B. The sintered magnet body does not exist in the range photographed in the photograph of FIG. 4, but exists inside the rare earth sintered magnet 10B from this range.

The thickness of each layer is about 10 nm for the surface layer 12B, about 200 nm for the first intermediate layer 131B, and 1 μm for the second intermediate layer 132B.

The contents of R, Fe and O in the surface layer 12B, the first intermediate layer 131B and the second intermediate layer 132B shown in FIG. 4 were measured by the above-mentioned EDX device. The second intermediate layer 132B was measured at two points, a portion close to the first intermediate layer 131B and a portion close to the sintered magnet body. The measurement results are shown in Table 1.

The surface layer 12B is mainly composed of an amorphous substance containing Fe and O. The O content of the surface layer 12B is higher than the O content of Fe ₂ O ₃ constituting hematite and the like, and is almost twice that of Fe. The R content of the surface layer 12B is 2 atomic% lower than the R content of the first intermediate layer 131B and the second intermediate layer 132B. The second intermediate layer 132B is a microcrystal containing R, Fe and O, and has a higher R content and a lower O content than the surface layer 12B. Further, even in the second intermediate layer 132B, the farther from the surface of the rare earth sintered magnet 10B, the higher the R content and the lower the O content. The first intermediate layer 131B has a higher R content than the surface layer 12B, and the O content is an intermediate value between the surface layer 12B and the second intermediate layer 132B. This means that the first intermediate layer 131B is a mixture of an amorphous substance containing Fe and O similar to that of the surface layer 12B and microcrystals containing R, Fe and O similar to those of the second intermediate layer 132B. It reflects.

FIG. 6 shows the rare earth sintered magnet 10B of Example 1 (FIG. 6 (b)) and the rare earth sintered magnet 10C of Example 2 having different manufacturing method conditions from those of Example 1 (FIG. 6). The photograph which took the appearance of the surface is shown. The rare earth sintered magnet 10C of Example 2 was produced by heating a substrate of the same production lot as that of Example 1 in the air at 300 ° C. for 120 minutes and then cooling at a rate of 5 ° C./min. be. FIG. 6 also shows photographs of the surface appearance of the base material (a) and the rare earth sintered magnets ((d) and (e)) of Comparative Examples 1 and 2. For the rare earth sintered magnets of Comparative Examples 1 and 2, the base material of the same production lot as that of Example 1 was used in the air at 350 ° C. (Comparative Example 1) or 400 ° C. (Comparative Example 2) for 120 minutes (Comparative Example 1, It was produced by heating (both 2) and then cooling at a rate of 5 ° C./min (both Comparative Examples 1 and 2). In Comparative Examples 1 and 2, the temperature at the time of heating does not satisfy the conditions of the manufacturing method of the rare earth sintered magnet manufacturing method according to the present invention.

From FIG. 6, it can be seen that in Examples 1 and 2, almost no color unevenness is observed on the surface, whereas in Comparative Examples 1 and 2, color unevenness is observed on the surface. Further, when Example 1 and Example 2 are compared, the surface color of Example 1 is lighter than that of Example 2. It is preferable that the surface color is light as in Example 1 because it is easy to perform image recognition. In each photograph, the left side is brighter than the right side, but this is due to the position of the lighting at the time of shooting and is not an essential matter.

Next, the results of corrosion resistance tests on the substrate, Examples 1 and 2, and Comparative Examples 1 and 2 will be described. This corrosion resistance test was carried out by accommodating each sample in a constant temperature and humidity chamber having a temperature of 85 ° C. and a humidity of 85% for 1000 hours. FIG. 7 shows a photograph of the appearance of the surface of each sample after the corrosion resistance test. Spotted rust is seen on the surface of the substrate (FIG. 7 (a)), whereas such rust is seen in Example 1 (same (b)) and Example 2 (same (c)). I can't. From this experimental result, it was confirmed that in the rare earth sintered magnets of Examples 1 and 2, the progress of oxidation (generation of rust) can be prevented by the surface layer. In Comparative Example 1 (FIG. 7 (d)) and Comparative Example 2 ((e)), the corrosion resistance was the same as in Examples 1 and 2.

Furthermore, when the heating temperature at the time of preparing the surface layer was set to 100 ° C, 150 ° C, 200 ° C and 275 ° C (other conditions are the same as in Example 1), the same experiment as above was performed, and color unevenness was observed. It was confirmed that a rare earth sintered magnet having an unprecedented appearance was obtained, and that no rust was observed in the corrosion resistance test.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist of the present invention.

10, 10A, 10B, 10C ... Rare earth sintered magnet 11, 11A ... Sintered magnet body 12, 12A, 12B ... Surface layer 131, 131B ... First intermediate layer 132, 132B ... Second intermediate layer 21 ... Base material 22 ... heating furnace

Claims (2)

The surface of the sintered magnet body containing a rare earth element (excluding La) and iron has a surface layer made of an amorphous material containing a rare earth element of the same type as the rare earth element, iron and oxygen, and is outside the surface layer. Is a rare earth sintered magnet characterized by having no other layers. A first intermediate layer in which an amorphous substance containing iron and oxygen and microcrystals containing rare earth elements, iron and oxygen are mixed is provided between the surface layer and the sintered magnet body, and the first intermediate layer is burned. The rare earth according to claim 1, wherein a second intermediate layer having microcrystals containing rare earth elements, iron and oxygen and having no amorphous material containing iron and oxygen is provided between the magnet main bodies. Sintered magnet.

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