JP2009231391A - R-t-b based sintered magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low oxygen R-T-B based sintered magnet having an ideal texture structure, having coercive force satisfying heat resistance requested of an HEV magnet in tendency to increase hereafter and reducing use of heavy rare earth elements which are rare resources as much as possible. <P>SOLUTION: The R-T-B based sintered magnet has a main phase consisting of compound having an R<SB>2</SB>T<SB>14</SB>B-type crystal structure, and a grain boundary phase. The R-T-B based sintered magnet consists of R:27.3 mass% to 29 mass%, X (X is at least one kind among Cu, Ag and Au):0.06 mass% to 0.18 mass%, B:0.92 mass% to 1 mass%, O:not more than 0.05 mass%, and a remaining part Fe or Fe, Co and inevitable impurity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an RTB-based sintered magnet having an excellent structure and having an ideal structure.

A typical RTB-based sintered magnet as a high-performance permanent magnet is a main phase composed of a compound having an R ₂ T ₁₄ B-type crystal structure that contributes to the magnetization action, and a grain boundary portion of the main phase. And a grain boundary phase. Here, R is at least one of rare earth elements, T is Fe or Fe and Co, and B is boron.

R-T-B based sintered magnets are increasing in production year by year due to their high magnetic properties, and are used in various applications such as for various motors, various actuators, and MRI apparatuses.

In recent years, new applications have been opened for energy saving and space saving, and the demand for magnets for hybrid cars (HEV) has increased, and the production amount of RTB-based sintered magnets tends to increase further in the future. The magnet for HEV is required not only to have a high maximum energy product but also to have heat resistance, and to further increase the coercive force.

For the purpose of increasing the coercive force of an R-T-B permanent magnet, an R ₂ TM ₁₄ B magnetic phase and a grain boundary phase containing an R-TM-O compound exist, and the R ₂ TM ₁₄ B magnetic phase and the grain boundary An R-TM-B permanent magnet has been proposed in which the crystal structure of the grain boundary phase in the vicinity of the phase interface is a face-centered cubic structure, and the R ₂ TM ₁₄ B magnetic phase and grain boundary phase are matched ( Patent Document 1).

In patent document 1, when the R-TM-O compound used as a grain boundary phase has a face-centered cubic structure, and the R ₂ TM ₁₄ B magnetic phase and the R-TM-O compound have a specific orientation relationship, they are particularly excellent. Although there is disclosure that it has magnetic properties, only known techniques are disclosed in the disclosed embodiments.

R11.7 to 13.5 mol%, Cu 0.01 to 0.1 mol%, B5 to 7 mol%, Co 0.8 mol for the purpose of providing an R-T-B sintered magnet having a high maximum energy product Sintered magnets having a maximum energy product of 400 kJ / m ³ or more are proposed (Patent Document 2).

However, in Patent Document 2, although a sintered magnet having a high maximum energy product is obtained, the coercive force is very low. Even the highest coercive force among the examples disclosed in Patent Document 2 is 888 kA / m (about 11 kOe), and this level of coercive force cannot be used for applications requiring heat resistance.

Conventionally, in order to improve the coercive force, it is known to contain heavy rare earth elements such as Dy and Tb. Even in the sintered magnet of Patent Document 2, it is considered that the coercive force is improved if a large amount of heavy rare earth element is contained, but this makes it impossible to obtain a characteristic maximum energy product of 400 kJ / m ³ or more.

Recently, depletion of resources has become a major problem for heavy rare earth elements such as Dy and Tb, and the price has risen abnormally, and efforts are being made to reduce the amount of heavy rare earth elements used as much as possible. .
JP 2000-49005 Japanese Patent No. 3921399

As described above, although various proposals have been made for improving the magnetic properties of the RTB-based sintered magnet, the fundamental solution has not been made. In particular, a technique for replacing the addition of heavy rare earth elements such as Dy and Tb has not been proposed for increasing the coercive force required for heat-resistant applications.

In Patent Document 1, an R-TM-O compound serving as a grain boundary phase has a face-centered cubic structure, and the R ₂ TM ₁₄ B magnetic phase and the R-TM-O compound have a specific orientation relationship. The organizational structure is mentioned. However, it cannot be said that the magnetic properties of the obtained RTB-based sintered magnet satisfy the present demand.

At the time when Patent Document 1 was proposed, the technology for suppressing oxidation of raw materials during the manufacturing process was not established as in the present. Therefore, there was only recognition that a certain amount of oxygen was always contained. For example, it is described that the oxygen amount of the sintered magnet obtained in Patent Document 1 is 4.5 at% (about 10,000 ppm). In this way, it is a sintered magnet based on the ideal structure that is assumed on the premise that it contains a specific amount of oxygen and a considerably larger amount of oxygen compared to the present, so it is compared with the current sintered magnet. Thus, it cannot be said that the magnetic properties are always excellent.

In recent years, the technology for suppressing oxidation of raw materials during the manufacturing process has progressed, and compared with the time when Patent Document 1 was proposed, it has become possible to significantly reduce the oxygen content of sintered magnets. For example, Patent Document 2 includes a specific number of 3000 ppm or less. It is well known that the magnetic properties are improved if the amount of oxygen in the sintered magnet is reduced. At present, it is indispensable to reduce the amount of oxygen for high magnetic properties.

Thus, compared with the time when Patent Document 1 was proposed, reduction of the oxygen content of sintered magnets has become the mainstream, and at present when improvements have been made to the magnet composition, magnet structure, etc., the ideal according to Patent Document 1 is present. High magnetic properties cannot be obtained with a tissue structure.

The present invention finds an ideal structure in a low-oxygen RTB-based sintered magnet, which is currently mainstream, and satisfies the heat resistance required for HEV magnets that tend to increase further in the future. An object of the present invention is to provide an RTB-based sintered magnet having a coercive force capable of being used and capable of minimizing the use of heavy rare earth elements, which are rare resources.

In order to achieve the above-mentioned object, the inventors have conducted intensive research for elucidating an ideal tissue structure. As a result, a specific amount of Cu is contained in the composition region in the vicinity of the stoichiometry of R ₂ T ₁₄ B and with an ultra-low oxygen content of O (oxygen) of 0.05% by mass or less (500 ppm or less). Thus, an R—Cu—O compound having a face-centered cubic structure is formed in the grain boundary phase, and the R—Cu—O compound becomes a pool of oxygen existing in the grain boundary phase, which is unnecessary for the grain boundary phase. It discovered that the production | generation of a compound can be suppressed.

Moreover, even if Cu is replaced with Ag or Au which is the same group 1B in the above configuration, an R-Ag-O compound or an R-Au-O compound is formed, and the same effect as that of the R-Cu-O compound is obtained. I found out that

Furthermore, the R—X—O compound (X is at least one of Cu, Ag, and Au) is extremely excellent in wettability with the R ₂ T ₁₄ B main phase, and almost all R ₂ T ₁₄ B in the sintered magnet. It has been found that an ideal structure can be realized in which the periphery of the main phase can be encapsulated with an R—X—O compound and there are very few defects.

And the above-mentioned ideal organization structure greatly improves the magnetic characteristics, especially the coercive force, and the addition amount is greatly increased even when heavy rare earth elements such as Dy and Tb are not used or when heavy rare earth elements are used. It was confirmed that a high coercive force required for heat resistance could be obtained even if the amount was reduced to 1, and the present invention was proposed.

The RTB-based sintered magnet of the present invention has a main phase composed of a compound having a R ₂ T ₁₄ B (R is at least one rare earth element, T is Fe or Fe and Co) type crystal structure, An RTB-based sintered magnet having a field phase, R: 27.3 mass% to 29 mass%, X (X is at least one of Cu, Ag, Au): 0.06 mass% ~ 0.18 mass%, B: 0.92 mass% to 1 mass%, O: 0.05 mass% or less, remaining Fe or Fe and Co and unavoidable impurities.

The present invention is characterized in that, in the RTB-based sintered magnet having the above-described configuration, an R—X—O compound having a face-centered cubic structure is included in the grain boundary phase.

In the RTB-based sintered magnet having the above-described configuration, the present invention is characterized in that the average crystal grain size of the main phase is 3 μm to 7 μm.

The present invention is characterized in that, in the RTB-based sintered magnet having the above-described configuration, O: 0.0135% by mass to 0.05% by mass.

In the RTB-based sintered magnet having the above-described configuration, the present invention is characterized in that the grain boundary phase has a thickness of 5 nm or more.

The present invention is characterized in that, in the RTB-based sintered magnet having the above-described configuration, the grain boundary phase does not contain an amorphous phase.

In the RTB-based sintered magnet having the above-described configuration, the present invention is characterized in that the a-axis length of the R—X—O compound is 0.55 nm.

ADVANTAGE OF THE INVENTION According to this invention, the RTB-type sintered magnet which has high coercive force which can satisfy the heat resistance requested | required of the magnet for HEV which tends to increase further in the future can be provided.

According to the present invention, the use of heavy rare earth elements such as Dy and Tb, which may be depleted in the near future, can be reduced as much as possible, protection of rare resources can be achieved, and low cost and high magnetic properties can be achieved. An RTB-based sintered magnet can be provided.

As described above, the RTB-based sintered magnet of the present invention has an R ₂ T ₁₄ B stoichiometric ratio of R: 27.3 mass% to 29 mass% and B: 0.92 mass% to 1 mass%. X is 0.06 mass% to 0.18 mass% X (X is Cu) in a composition region very close to the measurement and O: 0.05 mass% or less (500 ppm or less), an unprecedented ultralow oxygen content. , Ag, or Au). With this configuration, an R—X—O compound having a face-centered cubic structure in the grain boundary phase is formed.

Then, the R—X—O compound becomes a pool of oxygen existing in the grain boundary phase, and generation of unnecessary compounds in the grain boundary phase can be suppressed, and the R—X—O compound becomes R ₂ T _14. Since the wettability with the B main phase is extremely excellent, almost all of the R ₂ T ₁₄ B main phase in the sintered magnet can be wrapped with the R—X—O compound. As a result, an ideal structure with very few defects can be realized, and the magnetic properties, particularly the coercive force, can be improved.

Patent Document 1 discloses that an R-TM-O compound serving as a grain boundary phase has a face-centered cubic structure, and is high when the R ₂ TM ₁₄ B magnetic phase and the R-TM-O compound are in a specific orientation relationship. It is described that a coercive force can be obtained. However, in Patent Document 1, only the Nd-Fe-O compound is specifically exemplified as the R-TM-O compound, and various elements including Cu can be used instead of R. However, there is no description that Cu, Ag, or Au is used instead of TM. Furthermore, although there is a description that Cu or the like may be added as a trace addition element, there is no description about the content thereof, and there is no description about the relationship between the Nd—Fe—O compound and Cu. Thus, from Patent Document 1, the configuration of the present invention cannot be assumed.

Patent Document 2 contains R11.7 to 13.5 mol%, Cu 0.01 to 0.1 mol%, B5 to 7 mol%, Co 0.8 mol% or less, oxygen 3000 ppm or less, and the balance Fe. An RTB-based sintered magnet having an energy product of 400 kJ / m ³ or more is described. However, Patent Document 2 discloses only an example containing 0.04 mol% or less of Cu. As will be described later, when the Cu content is 0.04 mol% (= 0.04 mass%), the formation of the R—Cu—O compound becomes insufficient, and excess oxygen is combined with R to form a grain boundary phase. An R ₂ O ₃ compound is formed or combined with R of the main phase to reduce the amount of main phase generated, leading to a decrease in magnetic properties. Patent Document 2 states that “the smaller the oxygen content, the better, but since oxidation in the production process is unavoidable, the oxygen content cannot be made zero, and usually 500 ppm or more is contained.” As described above, an RTB-based sintered magnet having 0.05 mass% or less (500 ppm or less) of oxygen is not assumed at all. Therefore, from Patent Document 2, the configuration of the present invention cannot be assumed.

As represented by the description in Patent Document 2 that “the smaller the oxygen content, the better”, conventionally, it has been considered that oxygen should be as close to zero as possible in order to improve magnetic properties. In recent years, it is speculated that the ultimate magnetic properties can be obtained if the oxidation control technology of raw materials during the manufacturing process advances and the oxygen content becomes zero in the near future.

However, the present inventors have found that an R—X—O compound is indispensable for an ideal structure of an R—T—B system sintered magnet. That is, it has been concluded that oxygen is an indispensable element for an R-T-B sintered magnet. Although the reason for limitation will be described later, the oxygen indispensable in the present invention is 0.05% by mass or less, preferably 0.0135% by mass to 0.05% by mass. And in order to make this oxygen act most effectively, 0.06 mass%-0.18 mass% 1B group element X (Cu, Ag, Au) is indispensable, and this oxygen and X element are The ideal tissue structure can be realized for the first time when it exists in a composition region very close to stoichiometry. Patent Documents 1 and 2 do not have these technical ideas at all.

Hereinafter, the reasons for limiting the composition of the RTB-based sintered magnet in the present invention will be described in detail.

The RTB-based sintered magnet according to the present invention has a main phase composed of a compound having a R ₂ T ₁₄ B (R is at least one rare earth element, T is Fe or Fe and Co) type crystal structure, Has a phase. This configuration is the same as a conventionally known R-T-B permanent magnet. However, as will be described later, the RTB-based sintered magnet according to the present invention is formed with an R—X—O compound having a face-centered cubic structure in the grain boundary phase. It differs from the conventional one in that it has a typical organizational structure.

R can be selected from at least one of rare earth elements, and it is desirable that R contains any one of Nd and Pr. More preferably, a combination of rare earth elements represented by Nd-Pr, Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, and Nd-Pr-Dy-Tb is used. . However, as described above, heavy rare earth elements such as Dy and Tb are rare resources and are very expensive, so it is preferable to use them as little as possible. In addition to the above elements, a small amount of other rare earth elements such as Ce and La may be contained, and misch metal or didymium can also be used. Further, R may not be a pure element, and may contain impurities that are unavoidable in the manufacturing process within a commercially available range.

R forms a main phase composed of a compound having an R ₂ T ₁₄ B type crystal structure with T (T is Fe or Fe and Co) and B, and also serves as a source of R in the R—X—O compound. The content thereof is _R 2 _{T 14} very close to stoichiometry B 27.3 wt% to 29 wt% is preferred. When R is less than 27.3% by mass, the main phase is not sufficiently formed, and the R—X—O compound is not formed. When it exceeds 29.0% by mass, excess R is collected in the grain boundary phase, This is not preferable because an unnecessary compound is formed in the boundary phase or the size of the grain boundary phase is increased.

B and R form a main phase composed of a compound having an R ₂ T ₁₄ B type crystal structure. The content is preferably 0.92% by mass to 1% by mass, and more preferably 0.94% by mass to 0.98% by mass, which is very close to the stoichiometry of R ₂ T ₁₄ B. If it is less than 0.92% by mass, the coercive force is lowered, and if it exceeds 1% by mass, the residual magnetic flux density is lowered.
The lower limit is preferably 0.94% by mass when the composition is composed of only main components such as R, T, and B, and the lower limit can be 0.92% by mass when Ga is added as an additive element. When Ga is added, the B content can be reduced to the utmost limit, so that B is used only to form a main phase composed of a compound having an R ₂ T ₁₄ B type crystal structure, and excess B is not present. Since a necessary compound such as R _1.1 T ₄ B ₄ compound is not formed, an extremely excellent residual magnetic flux density can be obtained together with an excellent coercive force.

T occupies the rest of R and B, and R and B form a main phase composed of a compound having an R ₂ T ₁₄ B type crystal structure. T always contains Fe, and 50% or less of it can be substituted with Co. Moreover, a small amount of transition metal elements other than Fe and Co can be contained. Co is effective in improving temperature characteristics and corrosion resistance, and is usually used in a combination of 10 mass% or less of Co and the balance Fe.

X is an essential element for forming the R—X—O compound. X can be selected from at least one of the group 1B elements Cu, Ag, and Au, and the content is preferably in the range of 0.06% by mass to 0.18% by mass. If it is less than 0.06% by mass, the formation of the R—X—O compound is insufficient, the wettability between the grain boundary phase and the R ₂ T ₁₄ B main phase is reduced, and the R around the R ₂ T ₁₄ B main phase is R. It becomes impossible to wrap with the -X-O compound, and the coercive force is lowered. Further, excess R and O (oxygen) are not preferable because R ₂ O ₃ compounds are formed in the grain boundary phase, and the magnetic properties are deteriorated. If it exceeds 0.18% by mass, excess Cu forms an unnecessary R—X compound or the like in the grain boundary phase, which is not preferable.

O (oxygen) is an essential element for forming the R—X—O compound. The content is preferably 0.05% by mass or less. More preferably, it is 0.0135 mass%-0.05 mass%. Exceeding 0.05% by mass is not preferable because excess oxygen is preferentially combined with R to form an R ₂ O ₃ compound, resulting in a decrease in magnetic properties. At this time, the excess of oxygen ties also R of R _{2 T} 14 _B main phase, to reduce the generation amount of R 2 _T 14 _B main phase, the magnetic properties, especially not preferable to reduce the residual magnetic flux density.

As described above, oxygen is an indispensable element for the RTB-based sintered magnet according to the present invention. The lower limit of oxygen is preferably 0.0135% by mass. Since the lower limit value varies depending on the average crystal grain size of the sintered magnet, the average crystal grain size is 7 μm at which the oxygen content is the smallest in 3 μm to 7 μm, which is a preferable range of the average crystal grain size described later, Further, it was limited by the oxygen content when the thickness of the grain boundary phase required to form the R—X—O compound was 5 nm. The thickness of the grain boundary phase is the crystal grain boundary where the main phase and the main phase are adjacent to each other, that is, the thickness of the grain boundary phase at a so-called two-grain grain boundary. This is because a quality phase is formed and the magnetic properties are extremely deteriorated.

In the present invention, it is as described above that oxygen is an essential element, but unfortunately, it is impossible to make oxygen zero with the current technology, so what is the magnetic property when oxygen is zero? It is not certain that it will be. However, according to the inventors' model experiment, when oxygen is zero, that is, when only R metal is present in the grain boundary phase, the obtained R-T-B system sintered magnet does not exhibit coercive force. It was confirmed.

In the model experiment described above, an R metal (which uses Nd metal in the experiment) containing almost no oxygen is formed on the surface of a mirror-polished RTB-based sintered magnet by a vapor deposition method, and oxygen In order to cut off the supply source, the coercive force of the R-T-B system sintered magnet and the crystal group in contact with the R metal when a tantalum film is formed on the R metal by a vapor deposition method is measured. However, at this time, the crystal grain group in which the magnet surface of the obtained sintered magnet and the R metal layer were in contact had almost no coercive force. On the other hand, in the case where the tantalum film is not provided, that is, when an oxygen supply source is provided, a coercive force that is the same as that of a normal sintered magnet is obtained. From this, it is considered that the coercive force does not appear when the oxygen content in the sintered magnet is zero.

From the above model experiment, it is considered that the following phenomenon occurs in the present invention. That is, the presence of oxygen at the interface between the grain boundary phase and the R ₂ T ₁₄ B main phase lowers the interface energy, and a phase containing oxygen and X is formed in the grain boundary phase in the vicinity of the interface. It changes to an R—X—O compound having a face-centered cubic structure.

According to the present invention, a specific amount of oxygen is indispensable for the RTB-based sintered magnet based on the above experimental results, and the most ideal structure can be obtained by making the oxygen exist as an R—X—O compound. It has been found that a structure can be obtained and extremely excellent magnetic properties, particularly a high coercive force can be obtained.

Here, the ideal structure in the present invention means that the content ratio of the main phase in the sintered magnet is extremely high, and an R—X—O compound having a face-centered cubic structure in the grain boundary phase is formed. A compound in which almost all R ₂ T ₁₄ B main phase in the sintered magnet is encapsulated by the —X—O compound and is unnecessary for the grain boundary phase, for example, R ₂ O ₃ , R _1.1 T ₄ This refers to an organizational structure in which B ₄ , R ₂ T _{17 and the} like do not exist. Therefore, the main component compositions such as R and B have a content very close to that of stoichiometry, and a specific amount of X element and oxygen are specified in order to prevent formation of unnecessary compounds.

Further, as an ideal structure, the grain boundary phase at the grain boundary where the main phase and the main phase are adjacent to each other has a thickness of 5 nm or more, preferably close to 5 nm, and the grain boundary phase contains amorphous. Not good state. At this time, even if the grain boundary phase contains some amorphous material, it can be eliminated by the heat treatment step described later.

The R—X—O compound, which is a feature of the present invention, is at least one of an excess of R used for forming the main phase, 0.05% by mass or less of oxygen, and a group 1B element such as Cu, Ag, and Au. It is composed of In each case of Cu, Ag, and Au, it has been confirmed that an R—Cu—O compound, an R—Ag—O compound, and an R—Au—O compound are formed. In the claims, the content of X is defined as 0.06% by mass to 0.18% by mass, but this range is based on the case where X is Cu, and Cu has an atomic weight. When different Ag and Au are used, for example, the addition amount can be determined in a range of about 1.7 times Cu for Ag and about 3.1 times Cu for Au.

The R—X—O compound has a face-centered cubic structure and is confirmed to have an a-axis length of 0.55 nm. The R—X—O compound becomes a pool of oxygen existing in the grain boundary phase, and can suppress the generation of compounds unnecessary for the grain boundary phase. As a result, the coercive force is improved. Further, the R—X—O compound is extremely excellent in wettability with the R ₂ T ₁₄ B main phase, and by adjusting the composition of the sintered magnet to the above-described preferred composition range, almost all R in the sintered magnet is obtained. _{The 2} T ₁₄ B main phase can be surrounded by the R—X—O compound, and an ideal structure with very few defects can be realized. This greatly improves the magnetic characteristics.

In the RTB-based sintered magnet according to the present invention, the average crystal grain size is preferably 3 μm to 7 μm. In order to make the average crystal grain size less than 3 μm, it is necessary to make the powder 2.0 μm or less at the time of fine pulverization. When the fine powder becomes 2.0 μm or less, the amount of oxygen increases. The amount of oxygen will exceed 0.05% by mass. Accordingly, the average crystal grain size is preferably 3 μm or more. On the other hand, when the average crystal grain size exceeds 7 μm, it is possible to reduce the amount of oxygen in the sintered body, but this is not preferable because the magnetic properties are reduced.

In the RTB-based sintered magnet according to the present invention, in addition to the above-described composition, an M element can be added to further improve the coercive force. The element M is at least one of Al, Si, Ti, V, Cr, Mn, Ni, Zn, Zr, Nb, Mo, In, Ga, Sn, Hf, Ta, and W. The addition amount is preferably 2.0% by mass or less. If it exceeds 2.0% by mass, the residual magnetic flux density decreases, which is not preferable.

  Inevitable impurities can be allowed in addition to the above elements. For example, Mn and Cr mixed from Fe, and Al and Si mixed from Fe-B (ferroboron).

Furthermore, impurities such as hydrogen, nitrogen, and carbon can be allowed in the RTB-based sintered magnet of the present invention. When hydrogen embrittlement is used for rough pulverization, nitrogen is mixed from the lubricant during molding when nitrogen is used throughout the process, particularly when jet mill pulverization is used for fine pulverization. When hydrogen is contained as an impurity, the content is preferably controlled to 10 ppm to 100 ppm. Hydrogen has the effect of improving the magnetic properties when contained in a small amount. Therefore, the content of 10 ppm or more is acceptable. However, if it exceeds 100 ppm, the magnetic properties are adversely deteriorated. The hydrogen content can be controlled by a heat treatment pattern during sintering, particularly a holding time in the vicinity of 800 ° C.

  Below, the manufacturing method of the RTB system sintered magnet by this invention is explained in full detail. The RTB-based sintered magnet according to the present invention is characterized by its composition, and since the ideal tissue structure that is the basis of the magnetic property improvement effect is mostly determined by the composition, There is no particular limitation, and a known production method can be employed. An example of efficiently producing the RTB-based sintered magnet of the present invention will be described in detail below.

  First, the raw metal or alloy is melted and cast to obtain an alloy slab. For the melting and casting, known means can be employed, and the strip casting method is particularly preferred.

  Next, the alloy slab is pulverized to obtain a coarsely pulverized powder. For coarse pulverization, known means can be employed. The hydrogen embrittlement method is one of the preferred means.

  Next, finely pulverized powder is obtained by jet mill pulverizing the coarsely pulverized powder in an inert gas atmosphere. Nitrogen, argon, etc. can be used as the inert gas. Moreover, a well-known apparatus can be used about a jet mill.

  The average particle size of the finely pulverized powder is F.R. S. S. It is preferable that the average particle size is 2 μm to 5 μm by S measurement. If it is less than 2 μm, the oxygen concentration of the finely pulverized powder increases, and if it exceeds 5 μm, the coercive force decreases, which is not preferable.

  Next, the obtained finely pulverized product is molded in a magnetic field. As the applied magnetic field, it is preferable to use a pulse magnetic field having a magnetic field strength of 2.0 T or more. Thereby, Br of a rare earth sintered magnet can be improved.

  It is also a preferable method to perform the forming step by filling and sealing the finely pulverized powder in the mold and performing cold isostatic pressing after magnetic field orientation. Thereby, the residual magnetic flux density of the rare earth sintered magnet is further improved. Furthermore, the residual magnetic flux density is further improved by performing the magnetic field orientation in a pulse magnetic field of 2.0 T or more.

  Powder before pulverizing liquid lubricants such as fatty acid esters and solid lubricants such as zinc stearate in order to improve powder feeding efficiency during molding, uniformity of molding density, releasability during molding, etc. And / or is preferably added to the finely pulverized powder. The addition amount is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the powder.

  The sintering temperature is preferably 950 ° C. to 1180 ° C., and the sintering time is preferably about 1 to 10 hours. The sintered body after sintering is preferably subjected to a predetermined heat treatment. The heat treatment conditions are a temperature of 400 ° C. to 900 ° C. and a time of about 1 to 10 hours.

As a particularly preferable heat treatment condition, when the sintering temperature is T1 and the heat treatment temperature is T2, after cooling from T1 to 50 ° C./min or less, heat treatment is subsequently performed at T2, or after sintering is completed, a temperature higher than T2 ( It is preferable to reheat to T3), cool at 50 ° C./min or less from T3, and then heat-treat at T2. By adopting this heat treatment, even when amorphous exists in the grain boundary phase, the amorphous can be crystallized to be close to an ideal structure.

Example 1
Each raw material having a purity of 99.5% or more is blended and dissolved so that the composition after sintering becomes the composition shown in Table 1, and cast by a strip cast method, and a slab having a thickness of 0.1 mm to 0.3 mm A shaped alloy was obtained. At this time, in order to reduce the amount of oxygen in the alloy, the melting chamber was made an oxygen-free atmosphere, and in order to prevent contamination with impurities containing oxygen, the inside was melted in an alumina crucible coated with boron nitride. This alloy was hydrogen embrittled in a hydrogen-pressurized atmosphere, and then heated and cooled in vacuum to 600 ° C. for dehydrogenation treatment to obtain a coarsely pulverized powder.

  The obtained coarsely pulverized powder was finely pulverized by a jet mill apparatus in a nitrogen atmosphere. S. S. The finely pulverized powder having an average particle size of 2 μm to 5 μm was obtained by S measurement. The obtained finely pulverized powder was molded in a magnetic field in a nitrogen atmosphere while securing a nitrogen atmosphere so as not to oxidize, thereby producing a molded body. The magnetic field at the time of molding was a static magnetic field of 1.2 MA / m, and the applied pressure was 147 MPa.

  Furthermore, while securing a nitrogen atmosphere so as not to oxidize the obtained molded body, it was put into a sintering furnace and sintered at 1040 ° C. to 1080 ° C. for 6 hours in vacuum according to the composition. After sintering, it was cooled to 630 ° C. at 1.25 ° C./min and heat-treated at 630 ° C. for 8 hours. After the heat treatment, it was cooled to room temperature at 80 ° C./min.

  Table 1 shows the composition of the obtained sintered magnet. Moreover, after machining the obtained sintered magnet, the coercive force, residual magnetic flux density, and maximum energy product at room temperature were measured with a BH tracer. The measurement results are shown in Table 1. Furthermore, the cross section of the obtained sintered magnet was mirror-polished, observed with an optical microscope, and the image data was taken into analysis software to determine the average crystal grain size. Table 1 shows the average crystal grain size. Sample No. 1 to 29 are sample Nos. 30 to 39 are comparative examples. In Table 1, those indicated by horizontal bar lines could not obtain a sufficient sintered density, and the magnetic properties could not be measured.

  As is apparent from the results in Table 1, it can be seen that the RTB-based sintered magnet according to the present invention exhibits excellent magnetic properties. In particular, a coercive force of 880 kA / m (about 11 kOe) or more can be obtained without containing a heavy rare earth element such as Dy or Tb, and a preferable composition can obtain 1000 kA / m (about 12.5 kOe) or more, and heat resistance. High coercivity required for the property can be obtained.

Example 2
Sample No. in Table 1 The cross section of the sintered magnet 2 was mirror-polished and observed by TEM-EELS. The result is shown in FIG. In FIG. 1, the upper left is a composition image, the upper middle is Nd, the upper right is Cu, the lower left is Fe, the lower middle is O (oxygen), and the lower right is a mapping image of B. In FIG. 1, a portion displayed in white indicates a portion where the concentration of each element is high, and a portion displayed in black indicates a portion where the concentration of each element is low.

As shown in the composition image shown in the upper left of FIG. 1, there are Nd ₂ Fe ₁₄ B main phases in the upper right and lower left of each mapping image, and there are grain boundary phases from the lower right to the upper left so as to cross it. As apparent from each mapping image, it can be seen that the grain boundary phase contains a large amount of Nd, Cu, and O, and hardly contains Fe and B. From this result, it can be seen that an Nd—Cu—O compound is formed in the grain boundary phase.

  Although not shown in the figure, when limited-field electron diffraction was performed using the same sample, the Nd—Cu—O compound formed in the grain boundary phase had a face-centered cubic structure, and a The axial length was confirmed to be 0.55 nm. Further, in FIG. 1, the crystal grain boundary where the main phase and the main phase are adjacent to each other, that is, a so-called two-grain grain boundary, is observed, but the Nd—Cu—O compound is also present in the triple point portion of the grain boundary and the relatively large grain boundary phase. Confirmed that it exists.

Since the RTB-based sintered magnet according to the present invention has a high coercive force, it is optimal as a magnet for HEV or the like that requires heat resistance.

It is a figure which shows the result of the TEM-EELS mapping of the RTB system sintered magnet of this invention.

Claims (7)

R ₂ T ₁₄ B (R is at least one of rare earth elements, T is Fe or Fe and Co) R-T-B system sintered magnet having a main phase composed of a compound having a crystal structure and a grain boundary phase Because
R: 27.3 mass% to 29 mass%, X (X is at least one of Cu, Ag, and Au): 0.06 mass% to 0.18 mass%, B: 0.92 mass% to 1 mass% , O: 0.05% by mass or less, the balance being an RTB-based sintered magnet made of Fe or Fe and Co and unavoidable impurities. The RTB-based sintered magnet according to claim 1, wherein the grain boundary phase includes an R-X-O compound having a face-centered cubic structure. The RTB-based sintered magnet according to claim 1, wherein an average crystal grain size of the main phase is 3 µm to 7 µm. The RTB-based sintered magnet according to claim 1, wherein O: 0.0135% by mass to 0.05% by mass. The RTB-based sintered magnet according to claim 1, wherein the grain boundary phase has a thickness of 5 nm or more. The RTB-based sintered magnet according to claim 1, wherein the grain boundary phase does not contain an amorphous phase. The RTB-based sintered magnet according to claim 1, wherein the a-axis length of the R-X-O compound is 0.55 nm.