JP2013089813A - Rare earth nitride-based isotropic sintered magnet and production method therefor - Google Patents
Rare earth nitride-based isotropic sintered magnet and production method therefor Download PDFInfo
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
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Abstract
Description
本発明は，Sm-Fe-N系磁石粉末の焼結体として，磁気特性に優れ，かつ高い密度を有する等方性磁石とその製造方法に関するものである。 The present invention relates to an isotropic magnet having excellent magnetic properties and high density as a sintered body of Sm—Fe—N magnet powder, and a method for producing the same.
Sm-Fe-N系磁石は残留磁束密度（Br）や保磁力（Hcj），最大エネルギー積（(BH)max）のいずれも大きいことから，Nd-Fe-B系磁石やSm-Co系磁石と並ぶ優れた磁石材料の一つとされている。現在工業的によく用いられるNd-Fe-B系磁石は，高温化では保磁力が著しく低下するため，高価なDyを添加することで要求される磁気特性を発現させている。また，Sm-Co系磁石はキュリー温度が高く，耐熱性には優れるものの，高価なCoを多量に用いるため，広く普及するに至っていない。これに対し，Sm-Fe-N系磁石はキュリー温度が高く，高価な原料を使用しなくとも優れた磁気特性を示す。従って，Sm-Fe-N系磁石は磁気特性に優れ，かつ高い耐熱性を有する磁石材料と言える。 Sm-Fe-N magnets have large residual magnetic flux density (B r ), coercive force (H cj ), and maximum energy product ((BH) max ), so Nd-Fe-B magnets and Sm-Co magnets It is considered as one of the excellent magnet materials along with system magnets. Nd-Fe-B magnets, which are often used industrially at present, exhibit the magnetic properties required by adding expensive Dy, because the coercive force decreases significantly at higher temperatures. Although Sm-Co magnets have a high Curie temperature and excellent heat resistance, they are not widely used because they use a large amount of expensive Co. In contrast, Sm-Fe-N magnets have a high Curie temperature and exhibit excellent magnetic properties without using expensive raw materials. Therefore, Sm-Fe-N magnets can be said to have excellent magnetic properties and high heat resistance.
一方で，等方性磁石は着磁パターンが自由に選択でき，モータ部品として使用される場合には回転がスムーズになる等の利点があることから，電気・電子部品に広く使用されている。通常，等方性磁石は磁石粉末と樹脂（エポキシやナイロン等）と混合した原料を圧縮成形あるいは射出成型などにより成形したボンド磁石である。しかしながら，ボンド磁石では磁石粉末の結合剤として樹脂を用いることから，その耐熱性や強度は樹脂の特性に依存することとなり，高耐熱性や高強度が要求される部位への使用には適さない。とりわけ，前述したようにSm-Fe-N系磁石は耐熱性に優れるが，ボンド磁石として用いるとその優位性を有効に利用できない。さらに，通常のボンド磁石では，樹脂結合剤を含むため，磁石粉末の体積比率を83％以上にすることは難しい。樹脂結合剤は磁石特性の発現に寄与しないため，焼結磁石に比べてボンド磁石の磁気特性は低い。 On the other hand, isotropic magnets are widely used in electrical and electronic parts because they have the advantage that the magnetization pattern can be freely selected and when used as motor parts, the rotation is smooth. Usually, the isotropic magnet is a bonded magnet formed by compression molding or injection molding of a raw material mixed with magnet powder and resin (epoxy, nylon, etc.). However, since a bonded magnet uses a resin as a binder for the magnetic powder, its heat resistance and strength depend on the properties of the resin, and is not suitable for use in parts that require high heat resistance or high strength. . In particular, as described above, Sm-Fe-N magnets are excellent in heat resistance, but their superiority cannot be used effectively when used as bonded magnets. Furthermore, since ordinary bonded magnets contain a resin binder, it is difficult to increase the volume ratio of the magnet powder to 83% or more. Since resin binders do not contribute to the development of magnet properties, the bonded magnets have lower magnetic properties than sintered magnets.
このような問題を解決するための最も有効な手段はSm-Fe-N系磁石粉末に対して焼結を行い，結合剤を含まない焼結磁石とすることである。ここで，鉄系の磁石材料粉末を焼結緻密化しようとする場合，一般には1000℃以上に加熱しなければならない。しかし，Sm-Fe-N系磁石粉末は，500℃以上に加熱すると，FeとSm-Nに分解してしまい磁石特性の失ってしまう。このような熱安定性の低いSm-Fe-N系磁石粉末を焼結する技術として，プラズマ焼結法や通電焼結法による低温焼結法がある。 The most effective means to solve such problems is to sinter the Sm-Fe-N magnet powder and make a sintered magnet that does not contain a binder. Here, in order to sinter-densify iron-based magnet material powder, generally it must be heated to 1000 ° C or higher. However, Sm-Fe-N magnet powder decomposes into Fe and Sm-N and loses its magnetic properties when heated above 500 ° C. Technologies for sintering such Sm-Fe-N magnet powders with low thermal stability include plasma sintering and low-temperature sintering using current sintering.
特許文献１は，プラズマ焼結法を用いた200℃/min以上の高速昇温によって前述の熱分解を抑制するR-Fe-N（Rは希土類元素）焼結磁石の製造法を開示している。 Patent Document 1 discloses a method for producing an R—Fe—N (R is a rare earth element) sintered magnet that suppresses the above-described thermal decomposition by high-speed heating at 200 ° C./min or higher using a plasma sintering method. Yes.
特許文献２は，プラズマ焼結法を用いた600〜1000℃/minの高速昇温，および分解温度以下の焼結温度，かつ高圧を付与したプラズマ焼結法による，高密度のSm-Fe-N系焼結磁石の製造法およびその磁石を開示している。 Patent Document 2 describes a high-density Sm-Fe- using a plasma sintering method using a plasma sintering method with a high temperature rise of 600 to 1000 ° C./min using a plasma sintering method, a sintering temperature below a decomposition temperature, and a high pressure. A method for producing an N-based sintered magnet and its magnet are disclosed.
特許文献３は，超急冷法を経て作製された等方性の磁石粉末を，4t/cm2以上の高加圧下で熱間プレスすることにより，分解温度以下の焼結温度であっても高い磁気特性を有する焼結磁石を実現する製造法を開示している。 Patent Document 3 shows that an isotropic magnet powder produced through an ultra-quenching method is hot-pressed under a high pressure of 4 t / cm 2 or higher so that the sintering temperature is high even at a decomposition temperature or lower. A manufacturing method for realizing a sintered magnet having magnetic properties is disclosed.
特許文献１に開示されている方法では，プラズマ焼結における昇温速度が高速であるため，Sm-Fe-N系磁石粉末にかかる熱負荷は抑制されることが期待できるが，この方法により達成される密度も不明である上に，結果として得られた等方性磁石の(BH)maxは8MGOe程度と低い。また，特許文献２は，焼結による熱分解なく相対密度が97%以上の磁石を作製できる技術を開示しているが，実施例として示された原料Sm-Fe-N粉末は高い磁気特性を示すTh2Zn17型の結晶相以外にFeを含む多くの副相を含有しており，実際の実用磁石に適用できるかは不明である。さらに，多くの副相を含むために(BH)maxは8MGOe以下と低い。特許文献３に開示される製造法では，Th2Zn17型よりも高い磁気特性が得られるTbCu7型結晶構造の磁石粉末を用い，これを高加圧下での熱間プレスすることで，熱分解を殆ど起こすことなく，(BH)maxが17MGOeの等方性磁石の製造を可能にする技術が開示されている。しかし，この技術がどのくらいのかさ密度を達成できるかは不明であり，従来のボンド磁石の磁石粉末体積率より数％高い程度であると考えられる。 In the method disclosed in Patent Document 1, since the heating rate in plasma sintering is high, it can be expected that the thermal load applied to the Sm-Fe-N magnet powder is suppressed. is on the density is not known is, (BH) max of the obtained isotropic magnet as a result about 8MGOe low. Patent Document 2 discloses a technique capable of producing a magnet having a relative density of 97% or more without thermal decomposition by sintering, but the raw material Sm-Fe-N powder shown as an example has high magnetic properties. In addition to the Th 2 Zn 17 type crystal phase shown, it contains many subphases containing Fe, and it is unclear whether it can be applied to actual practical magnets. In addition, (BH) max is as low as 8MGOe or less because it contains many subphases. In the manufacturing method disclosed in Patent Document 3, a magnet powder having a TbCu 7 type crystal structure that can obtain higher magnetic properties than Th 2 Zn 17 type is used, and this is hot-pressed under high pressure. A technique that enables the production of an isotropic magnet having a (BH) max of 17 MGOe with little decomposition is disclosed. However, it is unclear how much bulk density this technology can achieve, and it is thought that it is about several percent higher than the magnet powder volume fraction of conventional bonded magnets.
このように，樹脂結合剤を用いることなく磁石粉末を成形する従来技術では，作製された磁石が実用性に乏しいか，ないしはボンド磁石よりわずかに高い磁石粉末体積率しか達成できない。 As described above, in the prior art in which magnet powder is formed without using a resin binder, the produced magnet has poor practicality or can achieve only a slightly higher magnet powder volume ratio than a bonded magnet.
本発明は，上記問題を解決するためになされたものであり，磁気特性に優れるとともに，高い密度を持つSm-Fe-N系等方性焼結磁石とその製造法を提供することを課題としている。 The present invention has been made to solve the above problems, and has as its object to provide an Sm—Fe—N isotropic sintered magnet having excellent magnetic properties and high density, and a method for producing the same. Yes.
本発明の希土類窒化物系等方性焼結磁石は，鱗片形状の希土類窒化物系磁石粉末の粒子が焼結により結合して形成される磁石であって，相対（かさ）密度が83体積％以上であり，前記磁石粉末はSm-Fe-N系合金であることを特徴としている。 The rare earth nitride-based isotropic sintered magnet of the present invention is a magnet formed by combining particles of scale-shaped rare earth nitride-based magnet powder by sintering, and the relative (bulk) density is 83% by volume. As described above, the magnet powder is an Sm—Fe—N alloy.
上記磁石としては，最大エネルギー積(BH)maxが13MGOeを超えること，そして相対（かさ）密度が86%体積以上で，最大エネルギー積(BH)maxが15MGOe以上であることが好ましい。 The magnet preferably has a maximum energy product (BH) max of more than 13 MGOe, a relative (bulk) density of 86% volume or more, and a maximum energy product (BH) max of 15 MGOe or more.
また，前記焼結磁石を形成する内部粒子のうち，アスペクト比（長さ／厚み）が2を超える粒子の累計分布が20個数%以上であること，さらにはこの分布が30個数%以上であって，最大エネルギー積(BH)maxが15MGOe以上であることが好ましい。 Further, among the internal particles forming the sintered magnet, the cumulative distribution of particles having an aspect ratio (length / thickness) exceeding 2 is 20% by number or more, and this distribution is 30% by number or more. Thus, the maximum energy product (BH) max is preferably 15 MGOe or more.
本発明の焼結磁石は，鱗片形状の粒子を含有するSm-Fe-N系磁石粉末を，1200MPa以上1800MPa以下の圧力で圧縮成型する工程と，350℃以上450℃以下の温度および1200MPa以上1500MPa以下の圧力で焼結する工程を含む方法により製造することができる。 The sintered magnet of the present invention comprises a step of compression molding Sm—Fe—N magnet powder containing scale-shaped particles at a pressure of 1200 MPa to 1800 MPa, a temperature of 350 ° C. to 450 ° C., and a pressure of 1200 MPa to 1500 MPa. It can be produced by a method including a step of sintering at the following pressure.
さらには，この圧縮成型する工程において，1200MPa以上1800MPa以下の任意の圧力と，その10%以下の圧力を交互に負荷し，これを2回以上100回以下繰り返すことにより圧縮成型体を形成することでより高密度な等方性焼結磁石が作製することが可能となる。 Furthermore, in this compression molding process, an arbitrary pressure of 1200 MPa to 1800 MPa and a pressure of 10% or less are alternately applied, and a compression molded body is formed by repeating this twice or more and 100 times or less. This makes it possible to produce a higher density isotropic sintered magnet.
また，前記の圧縮成型工程において，希土類窒化物系磁石粉末の全粒子うち，アスペクト比が２を超える鱗片形状粒子を30個数%以上，さらには60個数%以上含むSm-Fe-N系磁石粉末を原料粉末とすることが好適である。 In addition, in the compression molding step, Sm-Fe-N magnet powder containing 30% by number or more, more than 60% by number of scale-shaped particles having an aspect ratio exceeding 2 out of all particles of rare earth nitride magnet powder. Is preferably used as a raw material powder.
さらに望ましくは，前記の圧縮成型工程において，希土類窒化物系磁石粉末の全粒子うち，アスペクト比が10以上の鱗片形状粒子を50個数%以上含むSm-Fe-N系磁石粉末を原料粉末とすると，より高密度な等方性焼結磁石を得ることができる。 More preferably, in the compression molding step, the Sm-Fe-N magnet powder containing 50% by number or more of scaly particles having an aspect ratio of 10 or more is used as a raw material powder among all particles of the rare earth nitride magnet powder. Thus, a higher density isotropic sintered magnet can be obtained.
本発明によれば，従来技術に比べて格段に高い相対（かさ）密度83%以上が実現され，しかも優れた磁気特性，たとえば13MGOe，そして15MGOe以上の最大エネルギー積(BH)maxが実現されることになる。 According to the present invention, a remarkably high relative (bulk) density of 83% or more is realized compared to the prior art, and excellent magnetic properties such as 13 MGOe and a maximum energy product (BH) max of 15 MGOe or more are realized. It will be.
本発明では，焼結磁石が鱗片形状のSm-Fe-N磁石粉末粒子から形成され，これら粒子同士は焼結によって結合されており，かつ全体に占める磁石粉末の相対密度，つまりかさ密度としての体積比率が83体積％以上であれば，従来のボンド磁石より磁石粉末体積率が高く優れた磁気特性を示し，かつ高強度な等方性焼結磁石となる。これは，鱗片形状の粒子は規則正しく積み重なりやすいため緻密に充填配置される上，粒子同士が面で接するために焼結により接合される面積は広くなり，樹脂結合剤を用いることなく高強度な等方性焼結磁石を成形できるからである。 In the present invention, the sintered magnet is formed of scale-shaped Sm-Fe-N magnet powder particles, these particles are bonded together by sintering, and the relative density of the magnet powder occupying the whole, that is, as the bulk density If the volume ratio is 83% by volume or more, the magnetic powder volume ratio is higher than that of the conventional bonded magnet, and excellent magnetic properties are exhibited, and the isotropic sintered magnet has high strength. This is because scale-shaped particles tend to stack regularly and are densely packed and arranged, and since the particles are in contact with each other on the surface, the area to be joined by sintering is increased, and high strength without using a resin binder, etc. This is because an isotropic sintered magnet can be formed.
なお，本発明での相対密度，つまり，かさ密度は焼結磁石の全体積に占める磁性粒子の体積比率と定義され，アルキメデス法によって測定されるものである。 In the present invention, the relative density, that is, the bulk density, is defined as the volume ratio of the magnetic particles to the total volume of the sintered magnet, and is measured by the Archimedes method.
また，その上限値については特に限定的でなく，たとえば95体積％が目安として考慮される。 Further, the upper limit is not particularly limited, and for example, 95% by volume is considered as a guide.
このような焼結磁石において，その磁石を形成する粒子のうち，アスペクト比が2を超える鱗片形状粒子を20個数%以上，さらには30個数%以上含むように制御することによって，従来のボンド磁石における磁石粉末の体積比率を超え，かつ優れた磁気特性を与えることが可能となる。 In such a sintered magnet, the conventional bonded magnet is controlled by controlling the particles forming the magnet to include 20% or more, more preferably 30% or more of scaly particles with an aspect ratio exceeding 2. It is possible to exceed the volume ratio of the magnet powder and provide excellent magnetic properties.
ここでの磁石内部粒子のアスペクト比の累計分布については，実施例でも示しているように，焼結体の加圧軸に平行な断面において観察される粒子の形状を画像解析により分析することで測定される。画像解析のツール（手段）は市販の画像処理ソフトウェアとする。 Regarding the cumulative distribution of the aspect ratio of the magnet internal particles here, as shown in the examples, the shape of the particles observed in the cross section parallel to the pressure axis of the sintered body is analyzed by image analysis. Measured. The image analysis tool (means) is commercially available image processing software.
このような本発明の焼結磁石は，鱗片形状のSm-Fe-N系磁石粉末を，350℃以下の温度および1200MPa以上1800MPa以下の圧力で圧縮成型する工程により高密度に緻密化させ，さらに350℃以上450℃以下の温度および1200MPa以上1500MPa以下の圧力で焼結することによって粉末粒子間を強固に結合することで作製できる。 Such a sintered magnet of the present invention has a densified Sm-Fe-N magnet powder that is densified to a high density by a compression molding process at a temperature of 350 ° C. or lower and a pressure of 1200 MPa to 1800 MPa. It can be produced by firmly bonding powder particles by sintering at a temperature of 350 ° C. to 450 ° C. and a pressure of 1200 MPa to 1500 MPa.
さらに，前記の圧縮成型する工程において，1200MPa以上1800MPa以下の任意の圧力と，その10%以下の圧力を交互に負荷し，これを2回以上100回以下繰り返すことにより，鱗片形状のSm-Fe-N系磁石粉末は更に高密度な成形体とすることができ，ひいては高密度な焼結磁石につながる。 Further, in the compression molding step, an arbitrary pressure of 1200 MPa or more and 1800 MPa or less and a pressure of 10% or less are alternately applied, and this is repeated twice or more and 100 times or less to obtain a scaly Sm-Fe. -N-based magnet powder can be made into a higher density compact, which leads to a higher density sintered magnet.
前記の工程における圧力や温度条件に加えて，原料粉末として，アスペクト比が２を超える鱗片形状粒子を30個数%以上，さらには60個数%以上含むSm-Fe-N系磁石粉末を用いることで，本発明の焼結磁石を作製することができる。さらに，アスペクト比が10以上の鱗片形状粒子を50個数%以上含むSm-Fe-N系磁石粉末を原料粉末とすれば，従来のボンド磁石における磁石粉末の体積比率や磁気特性を大幅に超えた本発明の焼結磁石を作製できる。 In addition to the pressure and temperature conditions in the above process, Sm-Fe-N-based magnet powder containing scale-shaped particles with an aspect ratio of more than 2 and more than 30% by number, and further more than 60% by number, is used as the raw material powder. Thus, the sintered magnet of the present invention can be produced. Furthermore, if the raw material powder is Sm-Fe-N magnet powder containing 50% or more of scale-shaped particles with an aspect ratio of 10 or more, the volume ratio and magnetic properties of conventional bonded magnets are significantly exceeded. The sintered magnet of the present invention can be produced.
原料とする磁石粉末としては，等方性磁石としては最優れた磁石特性を有する，TbCu7型結晶構造のものが好ましい。また、その元素組成についてはSm-Fe-N以外にも、磁石性能や耐熱性の向上のために数%の添加物を入れた従来公知のものをはじめとして各種のものが考慮されてよい。 The magnet powder used as a raw material is preferably a TbCu 7- type crystal structure having the best magnetic properties as an isotropic magnet. In addition to Sm-Fe-N, various elemental compositions may be considered, including conventionally known ones containing several percent of additives in order to improve magnet performance and heat resistance.
たとえば、組成式はRxT100-x-y-zAyNzであって，Rは少なくともSmと，LaおよびCe以外の希土類元素，TはFeまたはCo，Niであり，少なくともFeを含む遷移金属元素，AはTi，Al，Si，V，Cr，Mn，Cu，Zn，Ga，Zr，Nb，Mo，Hf，Taからなる金属元素，Nは窒素であるものが考慮される。 For example, the composition formula is a R x T 100-xyz A y N z, R is at least Sm, rare earth elements, T other than La and Ce is Fe or Co, Ni, transition metal elements including at least Fe , A is a metal element composed of Ti, Al, Si, V, Cr, Mn, Cu, Zn, Ga, Zr, Nb, Mo, Hf, Ta, and N is nitrogen.
また、これら原料粉末の大きさについては、本発明では、鱗片状の粉末が緻密に充填されるために圧縮負荷により粉末が破砕されやすいことが好ましく考慮される。 Further, regarding the size of these raw material powders, in the present invention, it is preferably considered that the powder is easily crushed by a compressive load because the scaly powder is densely packed.
破砕されやすさはアスペクト比と粉末の径によるが、一般的に粉末径が小さ過ぎる場合（たとえば数μm以下）には破砕されにくくなる。一方、理論的にはより大きな径ではかなりの程度の粉末径まで有効であるが、その作製の観点等からは、実際的には最大径として１mm以下であることが好ましく考慮される。 The ease of crushing depends on the aspect ratio and the diameter of the powder, but generally it is difficult to crush when the powder diameter is too small (for example, several μm or less). On the other hand, theoretically, a larger diameter is effective up to a considerable degree of powder diameter, but from the viewpoint of production, etc., it is preferably considered that the maximum diameter is practically 1 mm or less.
なお，加熱焼結では，放電プラズマ焼結法やホットプレス焼結法も可能であるが、高速加熱および短時間焼結により低熱負荷焼結が実現できる，通電焼結法を採用することが好ましい。 In addition, although the discharge plasma sintering method and the hot press sintering method can be used for the heating sintering, it is preferable to adopt an electric current sintering method that can realize low thermal load sintering by high-speed heating and short-time sintering. .
以下，本発明の実施例および比較例を詳述する。 Examples of the present invention and comparative examples will be described in detail below.
実験には超急冷法を経て作製された厚み25μmの鱗片状の原料Sm-Fe-N粉末を準備した。なお，原料粉末はTbCu7型結晶構造の磁石粉末である。この粉末を分級処理することにより，表1に示すような異なるアスペクト比（長さ／厚さ）の分布を持つ粉末A〜Dを供試粉末とした．また，同じ原料を分級処理することにより，2以上のアスペクト比を持つ粒子を殆ど含まない，つまり鱗片状粉末ではなく多角形粒状粉末といえる粉末Eも準備した。 For the experiment, a scaly raw material Sm—Fe—N powder having a thickness of 25 μm prepared through a rapid quenching method was prepared. The raw material powder is a TbCu 7- type crystal structure magnet powder. By classifying the powder, powders A to D having different aspect ratio (length / thickness) distributions as shown in Table 1 were used as test powders. In addition, by classifying the same raw material, we prepared powder E, which contains almost no particles with an aspect ratio of 2 or more, that is, it is not a scaly powder but a polygonal granular powder.
＜実施例Ｉ＞
表１の粉末Ａ，Ｄ，Ｅの各々から1gを秤量し，内径6mmの超硬合金製円筒形ダイセットに充填し，サーボ制御型プレス装置による加圧機構を備えたパルス通電焼結機に設置した。焼結室内を10Pa以下の真空雰囲気としたのち，粉末に1200MPaの圧縮圧力を負荷し，直ちに除荷した。再び粉末に1200MPaの圧縮圧力を印加し，この圧力を保持したまま400℃の温度にて１分間の通電焼結を行った。こうして得られた焼結体のかさ密度，最大エネルギー積（(BH)max），および焼結体内部粒子のアスペクト比の累計分布を評価した。アスペクト比の測定は，焼結体の加圧軸に平行な断面において観察される粒子の形状を，画像解析により分析することによって得た。また，最大エネルギー積はパルスB-Hトレーサー装置を用いて測定した。結果を次の表２に示した。
<Example I>
Weigh 1 g of each of powders A, D, and E in Table 1 and fill them into a cemented carbide cylindrical die set with an inner diameter of 6 mm. installed. After the sintering chamber was evacuated to 10 Pa or less, the powder was loaded with a compression pressure of 1200 MPa and unloaded immediately. A compression pressure of 1200 MPa was applied again to the powder, and current sintering was performed for 1 minute at a temperature of 400 ° C. while maintaining this pressure. The cumulative distribution of bulk density, maximum energy product ((BH) max ), and aspect ratio of the internal particles of the sintered body was evaluated. The measurement of the aspect ratio was obtained by analyzing the shape of the particles observed in the cross section parallel to the pressure axis of the sintered body by image analysis. The maximum energy product was measured using a pulsed BH tracer device. The results are shown in Table 2 below.
表２に示すように，実施例１および２は高い(BH)maxを示し，これは従来のボンド磁石の値（13MGOe）を超える。また，実施例１においては，かさ密度についてもボンド磁石が達成できる最大体積比率を上回った。一方で，比較例１では，かさ密度および(BH)maxともにボンド磁石と同程度であった。ここで，この焼結体の内部における粒子のアスペクト比の分布をみると，比較例１の焼結磁石はアスペクト比が２以下の粒状粒子から形成されていた。実施例１および２では，焼結磁石を形成する粒子としてアスペクト比が２を超える鱗片状粒子が多く含まれている。特に，実施例１ではアスペクト比が２を超える粒子の比率が３０個数％を超えており，実施例２と大きく異なる。つまり，鱗片状の粒子からなる焼結磁石は優れた磁気特性を有し，特にアスペクト比が２を超える粒子の比率が３０個数％を超える場合には高密度かつ優れた磁気特性を発揮した。
＜実施例II＞
次に，前述の粉末Aを用いた焼結磁石作製における焼結工程に対して，焼結温度を変化させて焼結磁石の作製を行った。焼結温度とかさ密度およびダイアメトラル引張り強さ（DTS）の関係を図１に示す。かさ密度は焼結温度が300℃以上になると増加する。しかし，DTSは350℃以上にならないと増加せず，これは350℃以上から磁性粉末の粒子間が焼結により結合されることを意味している。図２に焼結温度と(BH)maxの関係を示す。焼結温度が500以上になると(BH)maxは急激に減少した。これはSm-Fe-N粉末が加熱によって分解したためと考えられる。従って，焼結温度を350〜450℃とすることで高密度，高強度，かつ優れた(BH)maxの等方性磁石の作製が可能となる。
＜実施例III＞
さらに，上記の粉末Aを用いた実験おいて，焼結温度を400℃に固定して，圧縮成形圧力条件および焼結圧力条件を表３に示す範囲で変化させて焼結磁石を作製した。実施例３および４から分かるように，圧縮成形圧力が1200〜1800MPaの範囲では高密度かつ優れた(BH)maxの焼結磁石の作製が可能である。これ以下の圧力においては比較例１に示すように密度および(BH)maxともに従来ボンド磁石程度となる。一方で，1800MPaより大きな圧力にて成形を行うと，比較例３に示すように過負荷による焼結磁石の破壊が離形時に頻繁に生じた。
As shown in Table 2, Examples 1 and 2 show high (BH) max , which exceeds the value of a conventional bonded magnet (13 MGOe). Further, in Example 1, the bulk density also exceeded the maximum volume ratio that can be achieved by the bonded magnet. On the other hand, in Comparative Example 1, both the bulk density and (BH) max were comparable to those of the bonded magnet. Here, looking at the distribution of the aspect ratio of the particles inside the sintered body, the sintered magnet of Comparative Example 1 was formed of granular particles having an aspect ratio of 2 or less. In Examples 1 and 2, many scaly particles having an aspect ratio exceeding 2 are contained as particles forming the sintered magnet. In particular, in Example 1, the ratio of particles having an aspect ratio exceeding 2 exceeds 30% by number, which is greatly different from Example 2. In other words, the sintered magnet composed of scale-like particles has excellent magnetic properties, and particularly when the ratio of particles having an aspect ratio exceeding 2 exceeds 30% by number, it exhibits high density and excellent magnetic properties.
<Example II>
Next, the sintered magnet was produced by changing the sintering temperature in comparison with the sintering process in the production of the sintered magnet using the powder A described above. The relationship between the sintering temperature, the bulk density and the diametral tensile strength (DTS) is shown in FIG. The bulk density increases when the sintering temperature exceeds 300 ° C. However, DTS does not increase unless it exceeds 350 ° C, which means that the particles of magnetic powder are bonded by sintering from 350 ° C or higher. FIG. 2 shows the relationship between the sintering temperature and (BH) max . When the sintering temperature was over 500, (BH) max decreased rapidly. This is probably because the Sm-Fe-N powder was decomposed by heating. Therefore, by setting the sintering temperature to 350 to 450 ° C., it is possible to produce a high density, high strength, and excellent (BH) max isotropic magnet.
<Example III>
Further, in the experiment using the above powder A, the sintering temperature was fixed at 400 ° C., and the compression molding pressure condition and the sintering pressure condition were changed within the ranges shown in Table 3 to produce a sintered magnet. As can be seen from Examples 3 and 4, a sintered magnet having a high density and excellent (BH) max can be produced when the compression molding pressure is in the range of 1200 to 1800 MPa. At pressures lower than this, as shown in Comparative Example 1, both the density and (BH) max are about the same as those of conventional bonded magnets. On the other hand, when molding was performed at a pressure higher than 1800 MPa, as shown in Comparative Example 3, destruction of the sintered magnet due to overload frequently occurred during demolding.
加えて，実施例６および７に示すように，上記の好適な圧力範囲において，任意の圧力への加圧と，その10%以下の圧力までの除荷を100回繰り返したことによって，１回の圧力負荷に比べて，さらに高い密度および(BH)maxを持つ焼結磁石を作製できた。実施例６の繰返し加圧工程および焼結工程における密度の履歴を図３に示す。100回以下の繰返しにおいても密度増加の効果が得られることが分かる。 In addition, as shown in Examples 6 and 7, in the above-described preferred pressure range, pressurization to an arbitrary pressure and unloading up to a pressure of 10% or less were repeated 100 times. Sintered magnets with higher density and (BH) max were produced compared to the pressure load of. FIG. 3 shows the history of density in the repeated pressing process and the sintering process of Example 6. It can be seen that the effect of increasing the density can be obtained even when it is repeated 100 times or less.
また，実施例１および３から分かるように，焼結時の圧力が1200〜1500MPaの範囲では高密度かつ優れた(BH)maxの焼結磁石の作製が可能である。これ以下の圧力においては比較例４に示すように密度および(BH)maxともに低い。一方で，1500MPaより高い圧力下で焼結すると，比較例３と同様に離形時の破壊が頻繁に起こった。 As can be seen from Examples 1 and 3, a sintered magnet having a high density and excellent (BH) max can be produced when the pressure during sintering is in the range of 1200 to 1500 MPa. At pressures below this, both density and (BH) max are low as shown in Comparative Example 4. On the other hand, when sintered under a pressure higher than 1500 MPa, as in Comparative Example 3, breakage occurred frequently during demolding.
＜実施例IV＞
圧縮成形時の圧力を1200MPaとし，また焼結時の温度および圧力を400℃および1200MPaに固定して，粉末A〜Eを用いた焼結を実施した。表１に示したように，粉末Aはアスペクト比が2から12までの広い分布をもつ鱗片状粒子から構成されており，いくらかの粒状粒子（アスペクト比＜２）を含む。粉末Bは粉末Aに比べてアスペクト比が４以下の粒子の含有量が多く，また8以上の粒子を殆ど含まない。粉末Cは，50個数%以上の粒子がアスペクト比10以上であり完全な鱗片状の粗大粉末である。粉末Dは，粒子の半分以上が粒状粒子であり，鱗片状粒子の含有率が低い。また粉末Eは殆どが粒状粒子からなる。
<Example IV>
The pressure during compression molding was 1200 MPa, and the sintering temperature and pressure were fixed at 400 ° C. and 1200 MPa, and sintering using powders A to E was performed. As shown in Table 1, powder A is composed of scaly particles having a wide distribution with an aspect ratio of 2 to 12, and includes some granular particles (aspect ratio <2). Compared to powder A, powder B has a higher content of particles with an aspect ratio of 4 or less and almost no particles with an aspect ratio of 8 or more. Powder C is a complete scale-like coarse powder with an aspect ratio of 10 or more with particles of 50% by number or more. In powder D, more than half of the particles are granular particles, and the content of scaly particles is low. The powder E is mostly composed of granular particles.
各粉末から得られた焼結磁石のかさ密度を表４に示す。この結果を見ると，鱗片状粒子を多く含む粉末から作製された焼結磁石ほど高いかさ密度が達成されており，さらにはアスペクト比の大きい粒子を多く含む粉末ほど高密度の焼結磁石をしている。このことは，鱗片状粒子は圧縮によって積み重なるように緻密に充填されやすいこと，さらにはアスペクト比の高い粒子は圧縮によって破砕されやすく，破砕された細かい粒子が隙間に充填されたことに起因する。表１のアスペクト比の分布と表２のかさ密度の結果を詳細に比べると，アスペクト比が２以上の鱗片状粒子が60個数%以上含まれる粉末を用いることにより，密度の高い焼結磁石の作製が可能であることが分かる。さらには，アスペクト比が10以上の鱗片状粒子を50個数%以上含む粒子を用いれば非常に高密度な等方性焼結磁石の作製が達成できることが分かる。 Table 4 shows the bulk density of the sintered magnet obtained from each powder. As can be seen from the results, a sintered magnet made from a powder containing a large amount of scaly particles achieves a higher bulk density, and a powder containing a large amount of particles having a large aspect ratio produces a sintered magnet with a higher density. ing. This is because the scaly particles are easily packed densely so as to be stacked by compression, and the particles having a high aspect ratio are easily crushed by compression, and the crushed fine particles are filled in the gaps. Comparing the distribution of the aspect ratios in Table 1 and the bulk density results in Table 2 in detail, by using a powder containing more than 60% by weight of scaly particles with an aspect ratio of 2 or more, It can be seen that the fabrication is possible. Furthermore, it can be seen that if particles containing 50% by number or more of scaly particles having an aspect ratio of 10 or more are used, it is possible to produce a very high density isotropic sintered magnet.
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