JP3587158B2 - Magnetic anisotropic bonded magnet - Google Patents

Description

反応速度が０．２５〜０．５の範囲では、いずれもＮｄ_２Ｆｅ_１４Ｂの方位がＦｅ_２Ｂに転写され高い異方性が得られるが、この範囲外の相対反応速度が早い場合、転写がうまくいかず等方性の粉末しかえられない。一方、反応速度が遅い場合は反応が不均一になり高いＢｓが得られるもののＮｄＦｅＢが残留してしまい高い保磁力（ｉＨｃ）が得られない。
実施例２．
主として実施例１のＮｏ．１の水素吸蔵条件で水素吸蔵させて合金組織の順変態を行ったものを表２に示す保持温度、保持水素ガス圧力および保持時間で順変態後の加熱処理を行った（なお、Ｎｏ．５４については実施例１のＮｏ．５２の水素吸蔵条件で水素吸蔵させて合金組織の順変態を行った。）。その後逆変態相対速度０．２６となるように保持温度で水素ガス圧力を下げ、実施例１と同様に脱水素による逆変態反応を起こさせ、その後実施例１と同様に逆変態反応後の熱処理を８２０℃、真空下で３０分間保持し、その後冷却した。これにより表２に示す希土類磁石粉末を製造した。
【００３８】
得られた希土類磁石粉末の残留磁束密度、固有保磁力および（ＢＨ）ｍａｘを測定し、異方化率を求めた。
保磁力、異方化率とともに順変態相対反応速度、保持時間、保持温度、保持圧力、残留磁束密度、異方化率、固有保磁力および磁石粉末の（ＢＨ）ｍａｘを合わせて表２に示す。
表２

実施例１と同様にして順反応を終えたのち続けて保持温度で及び圧力で熱処理し順変態に伴う歪みを緩和した後、続けて脱水素（水素圧力０．０００１ＭＰａ（０．００１ａｔｍ））した結果は、実施例１同様高い異方性が維持された。そして、６０分以上保持することで、実施例１と比較して保磁力が高くなる。一方短時間の保持では異方性は失われないが、保磁力は低い。また、反応速度が早いと、異方性は失われ、続けて保持、脱水素を行っても異方性は回復しない。
実施例３．
主として実施例２のＮｏ．７の水素吸蔵条件で水素吸蔵させて合金組織の順変態を行いその後１８０分保持したものを、表３に示す試料温度、逆変態相対速度、逆変態水素ガス圧力０．０００１ＭＰａ（０．００１ａｔｍ）で逆変態を行い、その後、８２０℃、真空下で３０分加熱処理を行い、その後急冷した（なお、Ｎｏ．５６については実施例１のＮｏ．５２の水素吸蔵条件で水素吸蔵させて合金組織の順変態を行った。）。これにより表３に示す希土類磁石粉末を製造した。
【００３９】
得られた希土類磁石粉末の残留磁束密度、固有保磁力および（ＢＨ）ｍａｘを測定し、異方化率を求めた。
保磁力、異方化率とともに順変態相対反応速度、保持時間、逆変態相対速度、試料温度、残留磁束密度、異方化率、固有保磁力および磁石粉末の（ＢＨ）ｍａｘを合わせて表３に示す。
表３

逆変態反応速度が０．１〜０．４の範囲では、転写された方位が、乱れることなくＮｄ_２Ｆｅ_１４Ｂに転写され異方性が得られるが、Ｎｏ．５５に見られるように、逆変態反応速度がそれより早い場合には異方性が低くなり高い特性が得られない。
【００４０】
一方、Ｎｏ．５６に見られるように、変態の反応速度が早い場合には、その後の処理が良くても異方性は得られない。
実施例４．
主に実施例３のＮｏ．１１と同様に順変態、熱処理および逆変態を行ったものを表４に示す保持温度および保持時間で加熱処理を行った。（なお、Ｎｏ．５６については実施例３のＮｏ．５４の順変態、熱処理および逆変態を行った。）これにより表４に示す希土類磁石粉末を製造した。
【００４１】
また、得られた粉末磁石粉末を用い、熱硬化性樹脂としてフェノール樹脂を粉末磁石１００ｇに対して３ｇ使用し、型内で圧縮成形してボンド磁石を得た。また、成形時に２．０Ｔ（２０ｋＯｅ）の磁場を作用させたものと、無磁場のものとの２種類のものを得た。
得られた希土類磁石粉末の残留磁束密度、固有保磁力および（ＢＨ）ｍａｘを測定し、異方化率を求めた。また、この磁石に含まれる残留水素を求めた。残留水素の値は全体を１００重量％としたときの重量％で示した。さらにボンド磁石の最大エネルギー積（ＢＨ）ｍａｘを測定した。
この結果、１３５ｋＪ／ｍ³以上の最大エネルギー積を有する磁気異方性ボンド磁石を得ることができた。
【００４２】
保磁力、異方化率とともに順変態相対反応速度、保持時間、逆変態相対速度、逆変態後の保持温度および保持時間の処理条件を表４に、測定された磁気特性を表５に示す。
表４

表５

脱水素時間が２５分以上保持することで、十分に水素が抜け異方性が失われることなく、高い保磁力が得られることがわかる。一方保持時間が早い場合は少し水素が残り、高い保磁力は得られない。
【００４３】
また、異方化の反応速度が早い場合には、高い保磁力は得られるものの、異方性は完全に消去され、等方性の粉末しか得られない。
実施例５．
Ｎｄ：１２．５ａｔ％、Ｂ：６．２ａｔ％、残部Ｆｅよりなる合金に表６に示す微量のＧａ，Ｎｂを添加し、実施例１で説明したのと同様にボタンアーク溶解で溶製し、１１４０℃で均質化終了を行い、その後表６に示す条件で高温水素熱処理を行った。その後実施例４と同様に磁気特性を測定した。測定結果を表７に示す。
表６

表７

Ｇａ添加は逆磁区の発生を抑えるための粒界のクリーニング効果をもち高い保磁力が得られる。また、Ｎｂ添加は、転写の効果を上げる働きをもつ。その結果Ｇａ，Ｎｂの量元素の微量添加で従来得られていない、３５０ｋＪ／ｍ3（４４．０ＭＧＯｅ）の高い特性が得られる。
そして、最大エネルギー積が１６７．９〜２００．５ｋＪ／ｍ³（２１．１〜２５．０ＭＧＯｅ）の磁気異方性ボンド磁石を得ることができた。
【発明の効果】
本発明の異方性磁石粉末は、ＲＦｅ（Ｇａ＋Ｎｂ）Ｂ系合金を高温水素熱処理して得られ、異方性（Ｂｒ／Ｂｓ＝１．６Ｔ（１６ＫＧ））が０ . ８２〜０．８６である希土類磁石である。また、本発明の異方性磁石粉末は、結晶粒のアスペクト比が２．０以下である。この異方性磁石粉末を用いることにより１６７．９〜２００．５ｋＪ／ｍ³（２１．１〜２５．０ＭＧＯｅ）の優れた（ＢＨ）ｍａｘをもつ異方性ボンド磁石とすることができる。
このＲＦｅ（Ｇａ＋Ｎｂ）Ｂ系合金の前記磁気異方性磁石粉末が、残留磁束密度（Ｂｒ）が１．３２〜１．３９Ｔ（１３．２〜１．３９ｋＧ）、固有保磁力（ｉＨｃ）が７９６〜１１９３ｋＡ／ｍ（１０．０〜１５ｋＯｅ）、（ＢＨ）ｍａｘが３００〜３５０ｋＪ／ｍ³（３７．８〜４４．０ＭＧＯｅ）であることが好ましい。
【図面の簡単な説明】
【図１】希土類合金の順変態反応の合金組成と反応速度との関係を示す線図である。
【図２】希土類合金の順変態反応の反応温度と反応速度との関係を示す線図である。
【図３】希土類合金の順変態反応の水素ガス圧力と反応速度との関係を示す線図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic anisotropic bonded magnet made of a rare earth element-iron-boron alloy and having high anisotropy.
[0002]
[Prior art]
Conventionally, rare earth magnets made of an RFeB-based alloy containing yttrium (Y) containing a rare earth element (hereinafter referred to as R), iron (Fe), and boron (B) as main components have a residual magnetic flux density, a coercive force, and the like. Because of its excellent magnetic properties, it is widely used industrially. This rare earth magnet is reported, for example, in JP-A-60-257107, JP-A-62-23903, and JP-B-7-68561.
[0003]
Japanese Patent Application Laid-Open No. Sho 62-23903 discloses that a coercive force (iHc) of 5 kOe (iHc) is improved by improving a dehydrogenation treatment of a high-temperature hydrogen heat treatment for performing a forward transformation and a reverse transformation of a structure by absorbing and desorbing hydrogen in an RFeB-based alloy. A method of manufacturing a permanent magnet as high as 398 kA / m is disclosed. Here, the high-temperature hydrogen heat treatment means a heat treatment accompanied by a transformation of the structure, and is distinguished from a low-temperature hydrogen heat treatment in which only the occlusion and dehydrogenation of the hydrogen without the transformation of the structure occur.
[0004]
In Japanese Patent Publication No. 7-68561, this high-temperature hydrogen heat treatment is improved, and an RFeB-based alloy is mixed with a hydrogen gas of 10 Torr (1.3 kPa) or more or a hydrogen gas of a partial pressure of 10 Torr (13 kPa) or more and an inert gas. By performing a series of high-temperature hydrogen heat treatments such as performing heat treatment at a temperature of 500 ° C. to 1000 ° C. in a mixed gas atmosphere to absorb hydrogen in the raw material to cause forward transformation, and performing dehydrogenation again, A method for obtaining a rare-earth permanent bonded magnet having iHc of 10 kOe (795 kA / m) and high magnetic properties is disclosed.
[0005]
Further, Japanese Patent Publication No. Hei 7-68561 discloses Nd_12.0Pr_1.4Fe_80.8B_5.81atmH₂The temperature was raised to 830 ° C. in a gas, and then maintained at 830 ° C. for 5 hours.₂The gas pressure is maintained at a predetermined pressure in the range of 10 to 760 Torr (1.3 kPa to 0.1 MPa), and then at 830 ° C., 1.0 × 10 3^-5Torr (1.31 × 10^-3The pressure is reduced to a degree of vacuum of Pa) and maintained for 40 minutes, followed by rapid cooling to obtain an anisotropic bonded magnet. As a bonded magnet having the most remarkable anisotropy in the embodiment, Br is applied to a magnetic field during compression molding to bring Br from 6.1 kG (0.61 T) to 7.2 kG (0.72 T) to about 18.2. % Improved.
[0006]
Further, Japanese Patent Publication No. Hei 4-20242 discloses that a rare-earth magnet is once formed by melt spinning, and then the rare-earth magnet is hot-rolled to form a structure in which the crystal directions are aligned. A method for doing so is disclosed.
[0007]
[Problems to be solved by the invention]
The present invention is high temperature hydrogen heat treatedA rare earth magnet powder, andIt is an object of the present invention to provide a magnetic anisotropic bonded magnet having a large maximum energy product by compression molding a rare-earth magnet powder having a high anisotropy, that is, a high Br / Bs and a thermosetting resin.
The method of producing a rare-earth magnet having a structure in which the crystal directions are aligned by hot-rolling the rare-earth magnet to obtain a rare-earth magnet powder having high anisotropy requires a high production cost due to the complicated operation. Further, the crystal grains of the obtained rare earth magnet powder have a flat characteristic.
[0008]
On the other hand, high-temperature hydrogen heat treatment, which is a feature of rare earth magnets as a hydrogen storage alloy, is a forward transformation of the structure by absorbing hydrogen, and a reverse transformation of the structure by dehydrogenation, makes the crystal grains finer and reduces the crystal grains, thereby reducing the residual magnetic flux. There is a method of obtaining a rare-earth magnet powder by a high-temperature hydrogen heat treatment for improving magnetic properties such as density and coercive force. The rare-earth magnet powder obtained by the high-temperature hydrogen heat treatment has an advantage that the operation is relatively simple and the production cost is low, but there is a problem that a rare-earth magnet powder having excellent magnetic properties cannot be obtained. In particular, it is extremely difficult to provide anisotropy.
[0009]
During the high-temperature hydrogen heat treatment of the rare-earth magnet, as disclosed in the above-mentioned Japanese Patent Publication No. 7-68561, Nd_12.0Pr_1.4Fe_80.8B_5.8When a rare earth alloy having a composition is subjected to high-temperature hydrogen heat treatment, Br is improved by about 18.2% from 6.1 kG (0.61 T) to 7.2 kG (0.72 T) by applying a magnetic field during compression molding. Sex has been reported. One of the inventors of Japanese Patent Publication No. Hei 7-68561 is disclosed in J. Pat. In Alloys and Compounds 231 (1995) 51, even if a ternary rare earth alloy of NdFeB is subjected to hydrogen treatment, only an isotropic magnet powder can be obtained, but this Fe is replaced by Co, and Zr, Ga, Nb, It is described that when hydrogen treatment is performed on NdFeCoB to which elements such as Hf are added, anisotropy appears.
[0010]
The present inventor has studied the hydrogen treatment of rare earth magnets in detail, and as a result of repeated experiments, it has been found that the ternary magnet powder of NdFeB, which was conventionally considered to be able to obtain only isotropic magnet powder by high-temperature hydrogen heat treatment, It has been discovered that hydrogen heat treatment results in a magnet powder with extremely high anisotropy.AnisotropyIn terms of other magnetic characteristics, the composition of the NdFeB ternary magnet powder, which had conventionally been considered to be about 0.8 T (8.0 kG) in NdFeB ternary magnet powder by high-temperature hydrogen heat treatment, It has been found and confirmed that Br can be increased to 1.2 to 1.5 T (12 to 15 kG) without change. Further, they have found and confirmed that Br can be increased to 1.32 to 1.39 T (13.2 to 1.39 kG) by adding Ga and Nb to the ternary system of NdFeB. .
[0011]
The present inventors have found that the high anisotropy of the ternary alloy of NdFeB due to the high-temperature hydrogen heat treatment was found to cause the rare-earth alloy of NdFeB to absorb hydrogen and react with hydrogen, thereby transforming the structure of the rare-earth alloy. And Nd₂Fe₁₄B₁Is considered to be caused by the forward transformation₂B is transferred and stored, and this is transferred and stored by the reverse transformation of the alloy structure by dehydrogenation.₂Fine Nd that reproduces the crystal orientation of B₂Fe₁₄B₁Are considered to be transferred to the crystal of the above, and become a magnet powder having extremely high anisotropy. In the present invention, cobalt (Co) is not required in the composition.
[0012]
The present invention has been completed based on such a view.
[0013]
[Means for Solving the Problems]
The anisotropic magnet powder of the present invention is subjected to high-temperature hydrogen heat treatment.,A rare earth element containing 12 to 15 at% of yttrium (Y) (hereinafter referred to as R), 5.5 to 8 at% of boron (hereinafter referred to as B), and 0.01 to 1.0 at% of gallium ( Hereinafter, Ga is included), 0.01 to 0.6 at% of niobium (hereinafter, referred to as Nb), and unavoidable impurities, and the remainder is composed of iron (Fe).RFe (Ga + Nb) B-based alloy, the RFe (Ga + Nb) B-based alloy has an anisotropy (Br / Bs, where Bs is 1.6T (16 kG)) of 0.82 to 0.86, and The aspect ratio of crystal grains is 2.0 or lessIt is characterized by the following.
The present invention also provides a rare earth element (hereinafter, referred to as R) containing 12 to 15 at% of yttrium (Y) which has been subjected to high-temperature hydrogen treatment, and 5.5 to 8 at% of boron (hereinafter, referred to as B). It contains 0.01 to 1.0 at% of gallium (hereinafter, referred to as Ga), 0.01 to 0.6 at% of niobium (hereinafter, referred to as Nb), and unavoidable impurities. ) And an RFe (Ga + Nb) B-based alloy composed ofAnisotropy (Br / Bs, where Bs is 1.6 T (16 kG)) is 0.82 to 0.86, and the aspect ratio of crystal grains is 2.0 or less.Magnetic anisotropic bonded magnet made by compression molding of magnetic anisotropic magnet powder and thermosetting resinIt is.
Further, the magnetic anisotropic magnet powder isThe residual magnetic flux density (Br) is 1.32 to 1.39 T (13.2 to 1.39 kG),Specific coercive force (iHc) is 796 to 1193 kA / m (10.0 to 15 kOe), and (BH) max is 300 to 350 kJ / m^Three(37.8 to 44.0 MGOe).
The magnetic anisotropic bonded magnet has a (BH) max of 167.9 to 200.5 kJ / m. ³ (21.1 to 25.0 MGOe).
[0014]
The RFeB-based alloy constituting the anisotropic magnet powder of the present invention has R₂Fe₁₄B₁  Is considered to have high anisotropy because it is composed of recrystallized grains having a tetragonal crystal structure. The anisotropic magnet powder of the present invention is obtained by high-temperature hydrogen heat treatment, and has a feature that its crystal grains are close to spherical, that is, the aspect ratio of the crystal grains is small. More specifically, the size of the crystal grains is about 0.1 to 1.0 μm, and the aspect ratio of almost all the crystal grains is 2.0 or less.
[0015]
Here, the crystal grain does not mean an alloy powder, but means individual crystal grains of many crystal grains constituting one alloy powder. The aspect ratio is a value defined by a ratio of the longest grain size to the minimum grain size of the crystal grains (longest grain size / minimum grain size). Further, the crystal grains of the hot-rolled rare earth magnet are flat, and the shape of the crystal grains is completely different from that of the rare earth magnet powder subjected to the high-temperature hydrogen heat treatment.
[0016]
In addition, since a normal BH tracer cannot be used for Br of the magnet powder, the following method was adopted as a method for measuring Br in the present invention. First, the magnet powder was classified into particles having a particle size of 74 to 105 μm and used. Then, it was shaped so that the demagnetizing field became 0.2, magnetized at 4578 kA / m (45 KOe) after orientation in the magnetic field, and measured by VSM to obtain Br.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The RFeB-based alloy constituting the anisotropic magnet powder of the present invention contains 12 to 15 at% of R, 5.5 to 8 at% of B, and unavoidable impurities, and the remainder is Fe. If R exceeds 15 at%, Br decreases, and if it does not reach 12 at%, primary crystal α-Fe remains. When B exceeds 8 at%, Br decreases, and when B does not reach 5.5 at%, Nd decreases.₂Fe₁₇A phase or the like precipitates. As R, one or more selected from Y, La, Ce, Pr, Nd, Sm, Gd, Td, Dy, Ho, Er, Tm, and Lu can be used. Among them, Nd is preferably used for reasons of cost and magnetic properties.
[0018]
The coercive force of the magnet powder obtained by mixing 0.01 to 1.0 at% of Ga with RFeB is improved. It is considered that this Ga facilitates smoothing of the crystal grain boundaries and increases iHc. The anisotropy can be increased by adding 0.01 to 0.6 at% of Nb. This Nb is Fe₂  It is considered that the transfer of B is ensured to improve Br.
[0019]
The anisotropic magnet powder of the present invention,The anisotropy (Br / Bs, where Bs is 1.6T (16 kG)) is 0.70 or more. As other magnetic characteristics, Br is 1.2 to 1.5 T (12 to 15 kG),iHc has characteristics of 636 to 1272 kA / m (8.0 to 16 kOe), and (BH) max has characteristics of 238 to 358 kJ / m3 (30 to 45 MGOe).
On the other hand, the anisotropic magnet powder of the present invention is more preferably RFe (Ga + Nb) obtained by adding 0.01 to 1.0 at% of Ga and 0.01 to 0.6 at% of Nb to an RFeB-based alloy. In B type alloy,Its anisotropy (Br / Bs, where Bs is 1.6T (16 kG)) is 0.82 to 0.86. As other magnetic properties,The residual magnetic flux density Br is 1.32 to 1.39 T (13.2 to 13.9 kG), iHc is 796 to 1193 kA / m (10.0 to 15.0 kOe), and (BH) max is 300 to 350 kJ / m3. (37.8-44.0 MGOe).
The anisotropic magnet powder of the present invention causes the RFeB-based alloy to absorb hydrogen and cause the reaction between hydrogen and the alloy to proceed within a relative reaction rate range of 0.25 to 0.50, thereby causing a forward transformation of the structure. Then, it can be produced by advancing a dehydrogenation reaction to cause reverse transformation of the structure. The method of preparing the raw materials used in this production is not particularly limited, but a high-purity rare earth, iron, and boron are used, mixed in a predetermined amount, melted in a melting furnace or the like, and cast to produce an alloy ingot. This can be used as a raw material. Further, the ingot may be pulverized into a powder form, which may be used as a raw material.
[0020]
At this time, depending on the method of preparing the raw material, there may be a bias in the composition distribution in the raw material. Such a deviation in the composition distribution is not preferable. Therefore, it is desirable to homogenize these raw materials. This homogenization treatment can reduce the occurrence of bias in the composition distribution.
Hydrogen is absorbed in the RFeB alloy of the present invention, and the reaction rate V between the alloy and hydrogen is
V = V₀・ (PH₂/P).exp(-Ea/RT)
(Where V_O: Frequency factor, PH₂: Hydrogen gas pressure (Pa), P_O: Dissociation pressure (Pa), Ea: activation energy (kJ / mol), R: gas constant (J / molK), T: temperature (K). ). Since this reaction rate is considered to be proportional to the transformation rate of the structure, the transformation rate of the structure was evaluated based on this reaction rate.
[0021]
That is, the reaction rate of the forward transformation reaction of the microstructure is the reaction rate V when the reaction temperature is 830 ° C. and the hydrogen gas pressure is 0.1 MPa._bTo V_b= 1 and a relative reaction rate V based on this reference reaction rate_rDefined. V_rCan be expressed by the following equation. V_r= (1 / 0.576) · PH₂・ Exp (-Ea / RT)
The reverse transformation of the structure was 830 ° C. and the hydrogen gas pressure was 0.001 MPa (0.01 atm) as the standard reaction rate. The relative reaction rate of the reverse transformation reaction can be similarly determined.
[0022]
The activation energy Ea is 195 to 200 kJ / mol depending on the composition as shown in FIG. The activation energy Ea is Nd and H₂Reacts with NdH₂Is determined with reference to the heat of formation.
Specifically, when the relative reaction rate of the forward transformation reaction is defined by the reaction temperature and the hydrogen gas pressure, it is shown in FIG. 2 showing the temperature dependence of the relative reaction rate and FIG. 3 showing the pressure dependence of the relative reaction rate.
[0023]
In order to keep the relative reaction rate of the normal transformation reaction within the reaction rate range of 0.25 to 0.50, the reaction temperature is in the range of 780 to 840 ° C., and the hydrogen pressure is 0.01 to 0.06 MPa (0. The range of 1 to 0.6 atm) is good. It should be noted that the reaction temperature mentioned here is a temperature at which the RFeB-based alloy absorbs hydrogen and causes a forward transformation, and is not a control temperature of the reaction furnace.
[0024]
The reaction in which the RFeB-based alloy absorbs hydrogen to cause a forward transformation is an exothermic reaction, and the start of the forward transformation causes the reaction temperature to rapidly increase. Therefore, the actual reaction temperature is significantly different from the control temperature of the reactor. It is also conceivable that the hydrogen gas pressure fluctuates significantly due to hydrogen occlusion. For example, when a mixed gas of an inert gas and a hydrogen gas is employed, hydrogen is occluded, and the hydrogen gas concentration around the RFeB-based alloy that undergoes a forward transformation may be greatly reduced. Strict control of the reaction temperature and control of the hydrogen gas pressure are required to obtain highly anisotropic magnet powder.
[0025]
When the relative reaction rate of the forward transformation is out of the reaction rate range of 0.25 to 0.50, the anisotropy decreases. It should be noted that magnet powder composed of an RFeB-based alloy is inherently anisotropic, and it is also extremely difficult to make it completely isotropic.Here, as a definition of anisotropy, when anisotropic Br / Bs (Bs = 1.6T (Bs = 16 kG)) is used, those having a value of 0.5 or less are fully isotropic, and 0.5 is Those exceeding 0.70 and below are defined as isotropic, and those exceeding 0.70 are defined as anisotropic.
[0026]
The relative reaction rate of the forward transformation is within the reaction rate range of 0.25 to 0.50.An anisotropic magnet powder having a Br / Bs (Bs = 1.6T (Bs = 16 kG)) of 0.70 or more is obtained.
As described above, the NdFeB rare-earth alloy undergoes a forward transformation to cause the NdFeB rare-earth alloy to undergo hydrogen transformation to perform forward transformation.₂Fe₁₄B₁Is considered to be caused by the forward transformation₂It is thought that it will be transferred more accurately by B. When the relative reaction rate of the forward transformation is out of the reaction rate range of 0.25 to 0.50, Fe₂Transfer to B is not sufficient and the anisotropy is low. The inventor currently states that Fe₂If the transfer to B is not sufficient, it is thought that it is impossible to increase the anisotropy in a later step.
[0027]
It is impossible with a normal furnace to control the relative reaction rate of the forward transformation, which accelerates with the reaction, within the relative reaction rate range of 0.25 to 0.50. Therefore, as a new heat treatment furnace, the present inventors have developed and used a furnace having an endothermic means for canceling the heat generated during the reaction described in Japanese Patent Application No. 8-206231. This heat absorbing means arranges a hydrogen storage alloy in a tube, puts this tube in a furnace, reduces the hydrogen gas pressure in the tube in reverse to the heat generated by the reaction, advances the dehydrogenation reaction, absorbs heat, and generates heat by the reaction. Absorb and offset. Thereby, the control temperature of the furnace and the reaction temperature can be made substantially equal.
[0028]
This forward transformation reaction ideally ends in about 30 minutes, but the reaction time industrially depends on the throughput. After the completion of the forward transformation, the coercive force of the magnet powder obtained by continuing the heat treatment at a temperature at which the forward transformation has occurred for at least one hour is improved. This is thought to be related to the relaxation of the internal strain caused by the forward transformation. It is considered that if the internal strain remains, the structure becomes uneven after the reverse transformation, and the coercive force decreases.
[0029]
Thereafter, the stored hydrogen is dehydrogenated to cause reverse transformation. This reverse transformation is Fe₂Nd that generates the crystal orientation of B₂Fe₁₄B₁Is transferred to the crystal orientation.
During this reverse transformation, Fe₂In order to transfer the direction of B, it is preferable that the transfer be made within a relative reaction speed range of 0.1 to 0.4. Specifically, the reverse transformation is achieved by maintaining the hydrogen gas pressure at 1/10 to 1/100 of the hydrogen gas pressure of the forward transformation. The reverse transformation is an endothermic reaction opposite to the normal transformation, and the reaction temperature decreases at an accelerated rate due to the start of the reverse transformation. Therefore, in order to keep the actual reaction temperature in the range of 780 to 840 ° C., a furnace having the same capability as in the forward transformation is required.
[0030]
This reverse transformation theoretically ends within 10 minutes. Industrially, it depends on the throughput. After completion of the reverse transformation, the temperature of the reverse transformation is maintained for at least 25 minutes or more, and the Nd₂Fe₁₄B₁It is preferable to remove hydrogen contained in the rare earth magnet powder having crystals. This improves the coercive force. If the dissociated hydrogen remains in the alloy, the coercive force will be significantly impaired. After cooling, the anisotropic magnet of the present invention is obtained. Cooling is at least 5 ° C / min. It is desirable to carry out at a cooling rate of
[0031]
When the ingot-shaped raw material is used, the obtained ingot-shaped rare earth permanent magnet can be easily ground in a mortar or the like. When a powdery raw material is used, it may be solidified by aggregation or the like, but can be easily ground in a mortar or the like.
The rare-earth permanent bonded magnet is manufactured using the obtained rare-earth permanent magnet powder and a resin serving as a binder for the magnet powder. At this time, a thermosetting resin such as an epoxy resin can be used as the resin, and a mixture obtained by mixing the resin and the magnet powder under a predetermined magnetic field for magnetization is subjected to pressure molding or the like. Then, the resin is thermally cured by heat treatment to form an anisotropic rare earth permanent bonded magnet.
[0032]
Effect of the Invention
The anisotropic magnet powder of the present invention,RFe (Ga + Nb) B-based alloy is obtained by high-temperature hydrogen treatment, and its anisotropy (Br / Bs, where Bs is 1.6T (16 kG)) is 0.82-0.86.It has extremely large anisotropy.Other magnetic properties,The residual magnetic flux density Br is 1.32 to 1.39 T (13.2 to 13.9 kG), which is a very large anisotropy. Further, the coercive force is 796 to 1193 kA / m (10.0 to 15.0 kOe), which is excellent in magnetic properties. (BH) max has a characteristic of 300 to 350 kJ / m3 (37.8 to 44.0 MGOe). And an anisotropic bonded magnet using these magnet powders is 167.9 to 200.5 kJ / m.^ThreeIt has a high (BH) max of (21.1 to 25.0 MGOe).
[0033]
In the method for producing anisotropic magnet powder of the present invention, the relative reaction rate of the normal transformation reaction in the high-temperature hydrogen heat treatment is set to a predetermined rate. As a result, rare-earth magnet powder having large anisotropy can be easily obtained.
[0034]
【Example】
Hereinafter, specific examples will be described.
(Example 1)
An alloy consisting of Nd: 12.5 at%, B: 6.2 at%, and the balance Fe was melted by button arc melting, homogenization was completed at 1140 ° C., and then hydrogen treatment was performed under the conditions shown in Table 1.
[0035]
Specifically, the sample was placed in a quartz tube as small as about 15 g, and connected to a gas pressure control device via a conduit so that the hydrogen gas pressure in the quartz tube could be controlled. An infrared heating furnace was used as the heating furnace. The temperature was measured using a thermocouple, the temperature of the sample and the temperature of the atmosphere were measured, and the furnace was controlled based on these temperatures.
The hydrogen gas pressure shown in Table 1 was introduced into the quartz tube, and heated in that state to reach the reaction temperature in about 60 minutes. When the temperature of the sample exceeds the temperature of the atmosphere at the start of the reaction, the heating is stopped immediately, the temperature of the atmosphere is lowered by cooling by radiation, the heat generated by the reaction is absorbed, and the sample temperature is maintained within the target reaction temperature + 5 ° C. It was made to be. Since the sample amount was as small as 15 g and the infrared furnace was used, the ambient temperature in the quartz tube could be controlled relatively easily.
[0036]
Thereafter, heat treatment was performed at 820 ° C. and a hydrogen gas pressure of 0.02 MPa (0.2 atm) for 3 hours.
Thereafter, the hydrogen gas pressure in the quartz tube was released so that the reverse transformation relative velocity became 0.26, dehydrogenation was attempted, and the reverse transformation reaction was advanced. In this reverse transformation reaction by dehydrogenation, a control method in which the hydrogen gas pressure is delicately controlled, and when the temperature begins to decrease due to the endothermic reaction, the pressure reduction of the hydrogen gas pressure is stopped, and when the temperature returns to the predetermined temperature, the pressure is restarted again. The temperature was controlled within the target temperature range of −5 ° C., and was set to 0.0001 MPa (0.001 atm) which was 1/100 or less of the hydrogen gas pressure at the time of storing the hydrogen gas.
[0037]
The heat treatment at a predetermined temperature was continued until 30 minutes after the start of the reverse transformation reaction by dehydrogenation. Thereafter, the system was cooled and the hydrogen treatment was completed. This produced a rare earth magnet powder.
The residual magnetic flux density of the obtained rare earth magnet powder isIt measured and calculated the anisotropic ratio.
Residual magnetic flux density,Anisotropic rateTable 1 also shows the relative rate of normal transformation, the processing temperature, and the hydrogen gas pressure during hydrogen storage. The aspect ratio was determined as an average value of 25 samples by measuring the maximum diameter and the minimum diameter of each crystal grain with an electron microscope.
Table 1

When the reaction rate is in the range of 0.25 to 0.5, Nd₂Fe₁₄The direction of B is Fe₂B is transferred to B and high anisotropy is obtained, but when the relative reaction rate is out of this range, the transfer is not successful and only an isotropic powder is obtained. On the other hand, when the reaction rate is low, the reaction becomes nonuniform and high Bs is obtained, but NdFeB remains and high coercive force (iHc) cannot be obtained.
Embodiment 2. FIG.
No. 1 of Example 1 was mainly used. 1 was subjected to a forward transformation of the alloy structure by storing hydrogen under the hydrogen storage conditions, and was subjected to a heat treatment after the forward transformation at a holding temperature, a holding hydrogen gas pressure and a holding time shown in Table 2 (No. 54). Was subjected to hydrogen storage under the hydrogen storage conditions of No. 52 in Example 1 to perform a normal transformation of the alloy structure.) After that, the hydrogen gas pressure was lowered at the holding temperature so that the reverse transformation relative velocity became 0.26, and the reverse transformation reaction by dehydrogenation was caused as in Example 1, and then the heat treatment after the reverse transformation reaction was performed as in Example Was kept at 820 ° C. under vacuum for 30 minutes and then cooled. Thus, the rare earth magnet powder shown in Table 2 was produced.
[0038]
The residual magnetic flux density, intrinsic coercive force and (BH) max of the obtained rare earth magnet powder were measured.Find the anisotropic rateWas.
With coercive force and anisotropic ratioForward transformation relative reaction rate, holding time, holding temperature, holding pressure, residual magnetic flux density,Anisotropic rate,Table 2 shows the specific coercive force and the (BH) max of the magnet powder.
Table 2

After completion of the forward reaction in the same manner as in Example 1, heat treatment was continuously performed at the holding temperature and pressure to alleviate the strain associated with the forward transformation, followed by dehydrogenation (hydrogen pressure 0.0001 MPa (0.001 atm)). As a result, high anisotropy was maintained as in Example 1. Then, by holding for 60 minutes or more, the coercive force becomes higher as compared with the first embodiment. On the other hand, the anisotropy is not lost by holding for a short time, but the coercive force is low. When the reaction rate is high, the anisotropy is lost, and the anisotropy does not recover even if the retention and dehydrogenation are performed continuously.
Embodiment 3 FIG.
No. 2 of Example 2 was mainly used. The alloy structure was subjected to normal transformation by hydrogen absorption under the hydrogen storage conditions of 7, and then maintained for 180 minutes. The specimen temperature, reverse transformation relative speed, and reverse transformation hydrogen gas pressure shown in Table 3 were 0.0001 MPa (0.001 atm). , And then heat-treated at 820 ° C. under vacuum for 30 minutes, and then quenched (for No. 56, hydrogen absorption was performed under the hydrogen storage conditions of No. 52 of Example 1 to form an alloy structure. Was performed.) Thus, the rare earth magnet powder shown in Table 3 was produced.
[0039]
The residual magnetic flux density, intrinsic coercive force and (BH) max of the obtained rare earth magnet powder were measured.Find the anisotropic rateWas.
With coercive force and anisotropic ratioForward transformation relative reaction rate, retention time, reverse transformation relative velocity, sample temperature, residual magnetic flux density,Anisotropic rate,Table 3 shows the specific coercive force and (BH) max of the magnet powder together.
Table 3

When the reverse transformation reaction rate is in the range of 0.1 to 0.4, the transferred orientation is Nd without being disturbed.₂Fe₁₄No. B is transferred to B to obtain anisotropy. As can be seen from FIG. 55, when the reverse transformation reaction rate is higher than that, the anisotropy becomes low and high characteristics cannot be obtained.
[0040]
On the other hand, No. As shown in 56, when the reaction rate of transformation is high, anisotropy cannot be obtained even if the subsequent treatment is good.
Embodiment 4. FIG.
No. 3 of Example 3 was mainly used. In the same manner as in No. 11, those subjected to the forward transformation, the heat treatment, and the reverse transformation were subjected to heat treatment at the holding temperature and holding time shown in Table 4. (For No. 56, forward transformation, heat treatment and reverse transformation of No. 54 of Example 3 were performed.) In this way, rare earth magnet powders shown in Table 4 were produced.
[0041]
Further, using the obtained powder magnet powder, 3 g of a phenol resin was used as a thermosetting resin per 100 g of the powder magnet, and compression-molded in a mold to obtain a bonded magnet. In addition, two types, one in which a magnetic field of 2.0 T (20 kOe) was applied at the time of molding and one without a magnetic field, were obtained.
The residual magnetic flux density, intrinsic coercive force and (BH) max of the obtained rare earth magnet powder were measured.Find the anisotropic rateWas. Further, residual hydrogen contained in the magnet was determined. The value of the residual hydrogen was shown in terms of% by weight when the whole was taken as 100% by weight. Further, the maximum energy product (BH) max of the bonded magnet was measured.
As a result, 135 kJ / m^ThreeA magnetic anisotropic bonded magnet having the above maximum energy product was obtained.
[0042]
With coercive force and anisotropic ratioTable 4 shows the processing conditions of the forward transformation relative reaction rate, the holding time, the reverse transformation relative rate, the holding temperature and the holding time after the reverse transformation, and Table 5 shows the measured magnetic properties.
Table 4

Table 5

It can be seen that by holding the dehydrogenation time for 25 minutes or more, a high coercive force can be obtained without sufficient loss of hydrogen and loss of anisotropy. On the other hand, when the retention time is short, a little hydrogen remains, and a high coercive force cannot be obtained.
[0043]
When the reaction rate of the anisotropic reaction is high, a high coercive force can be obtained, but the anisotropy is completely eliminated and only an isotropic powder can be obtained.
Embodiment 5 FIG.
Trace amounts of Ga and Nb shown in Table 6 were added to an alloy consisting of Nd: 12.5 at%, B: 6.2 at%, and the balance Fe, and melted by button arc melting as described in Example 1. After completion of homogenization at 1140 ° C., high-temperature hydrogen heat treatment was performed under the conditions shown in Table 6. Thereafter, the magnetic characteristics were measured in the same manner as in Example 4. Table 7 shows the measurement results.
Table 6

Table 7

The addition of Ga has a cleaning effect on grain boundaries for suppressing the generation of reverse magnetic domains, and provides a high coercive force. Further, the addition of Nb has a function of improving the transfer effect. As a result, a high characteristic of 350 kJ / m3 (44.0 MGOe), which has not been obtained conventionally by adding a small amount of Ga and Nb, is obtained.
And the maximum energy product is 167.9 to 200.5 kJ / m.^Three(21.1 to 25.0 MGOe) magnetically anisotropic bonded magnet could be obtained.
【The invention's effect】
The anisotropic magnet powder of the present invention is an RFe (Ga + Nb) B-based alloyIs subjected to high-temperature hydrogen heat treatment, and has anisotropy (Br / Bs = 1.6T (16KG)) of 0 . 82-0.86Is a rare earth magnet.The anisotropic magnet powder of the present invention has an aspect ratio of crystal grains of 2.0 or less.By using this anisotropic magnet powder, 167.9 to 200.5 kJ / m^ThreeAn anisotropic bonded magnet having an excellent (BH) max of (21.1 to 25.0 MGOe) can be obtained.
The magnetic anisotropic magnet powder of this RFe (Ga + Nb) B-based alloy isThe residual magnetic flux density (Br) is 1.32 to 1.39 T (13.2 to 1.39 kG);Specific coercive force (iHc) is 796 to 1193 kA / m (10.0 to 15 kOe), and (BH) max is 300 to 350 kJ / m^Three(37.8-44.0 MGOe).
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between an alloy composition and a reaction rate of a forward transformation reaction of a rare earth alloy.
FIG. 2 is a diagram showing a relationship between a reaction temperature and a reaction rate of a normal transformation reaction of a rare earth alloy.
FIG. 3 is a diagram showing a relationship between a hydrogen gas pressure and a reaction rate in a forward transformation reaction of a rare earth alloy.

Claims (3)

A rare earth element (hereinafter, referred to as R) containing high-temperature hydrogen and containing 12 to 15 at% of yttrium (Y), 5.5 to 8 at% of boron (hereinafter, referred to as B), and 0.01 to 1. It contains 0 at% gallium (hereinafter referred to as Ga), 0.01 to 0.6 at% niobium (hereinafter referred to as Nb), and unavoidable impurities, and the remainder is composed of iron (Fe). The RFe (Ga + Nb) B-based alloy has an anisotropy (Br / Bs, where Bs is 1.6T (16 kG)) of 0.82-0.86. A magnetic anisotropic bonded magnet obtained by compression molding magnetic anisotropic magnet powder having a crystal grain aspect ratio of 2.0 or less and a thermosetting resin. The magnetic anisotropic magnet powder has a residual magnetic flux density (Br) of 1.32 to 1.39 T (13.2 to 1.39 kG), and an intrinsic coercive force (iHc) of 796 to 1193 kA / m (10.0 to 13.0 kG). 15 kOe), the magnetic anisotropy bonded magnet according to claim 1 which is (BH) max is 300~350kJ / m ³ (37.8~44.0MGOe). The magnetic anisotropic bonded magnet has a (BH) max of 167.9 to 200.5 kJ / m. ³ (21.1 to 25.0 MGOe).

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