JPH0841502A - Production of alloy powder for rare-earth permanent magnet - Google Patents

Abstract

PURPOSE:To provide an R2Fe14B phase and to obtain the alloy powder for a rare-earth permanent magnet by applying rapid cooling with water, hydrogenation and dehydrogenation to a rare-earth element-iron-boron alloy of specified composition. CONSTITUTION:This alloy consists essentially of R (rare-earth elements including Y), T (transition metal contg. >=50 atomic % Fe) and B and contains 2-12% R, 5-20% B and the balance T. This alloy is subjected to a stage to form an amorphous or metastable crystalline structure or a structure contg. both structures, further to a stage to heat-treat the structure in an atmosphere contg. hydrogen to occlude the hydrogen and then to a stage to heat-treat the product in an atmosphere substantially free from hydrogen to discharge the hydrogen, and the alloy powder for the magnet is obtained. In this method, hydrogen is occluded in a structure not contg. R2T14B compd. phase to form the hydride of the R, and then the R2T14B compd. phase is formed in the hydrogen discharging stage.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to rare earth elements (including Y).
The present invention relates to a method for producing an alloy powder for a rare earth permanent magnet, which comprises, as a basic component, a transition metal (essentially containing Fe) and B and is used in a bond magnet.

[0002]

2. Description of the Related Art A mixture of magnet powder and resin is extruded,
It is well known to obtain a resin-bonded permanent magnet (composite magnet) by compression molding or injection molding. In particular, rare-earth bonded permanent magnets, which take advantage of the excellent magnetic properties of rare-earth alloys, have recently attracted attention. The present invention relates to a method for producing an alloy powder for a rare earth permanent magnet, which is a magnetic powder with high magnetic properties used for such a rare earth bonded permanent magnet. Known permanent magnet materials mainly composed of rare earths and transition metals include Sm-Co and Nd-Fe-B systems,
Widely used due to its excellent properties. Above all, N
Isotropic Nd- having a composition slightly finer than the stoichiometric composition of d ₂ Fe ₁₄ B and having a fine Nd ₂ Fe ₁₄ B phase of about several tens nm generated by liquid quenching and heat treatment.
The production amount of Fe-B materials is rapidly increasing due to their excellent cost performance.

In recent years, the Nd ₂ Fe ₁₄ B stoichiometric composition of the hard magnetic phase in this isotropic Nd-Fe-B system material is more than Nd.
A report on a material having a decreased amount and an increased magnetization and maximum energy product has been attracting attention as a next-generation bonded magnet material. They are roughly divided into two groups, both of which generate a fine structure of 100 nm or less by liquid quenching and heat treatment as in the conventional material. One is N
d ₂ Fe ₁₄ B Slightly less rare earth than stoichiometric composition 8
The material is about 10 at%. The coercive force is drastically reduced because α-Fe is generated only by decreasing the amount of Nd, but Z
The addition of r, Nb, and V has succeeded in suppressing the decrease in coercive force (eg, Proceeding of the 10th. Int'l. Workshop.
on RE Magnets, Kyoto Japan, 315 (1989)). Hereinafter, this type of material is referred to as a simple rare earth reduction type.

[0004] Another, Nd ₂ Fe ₁₄ B extremely low Nd than composition, At a Nd ₄ Fe ₇₇ B ₁₉ near the composition is a high B, and Nd ₂ Fe ₁₄ B phase and Fe ₃ B phase It has succeeded in producing an extremely high saturation magnetization of 1.2T by producing the following fine grain structure. (See J. de Physique, C8, 1988, P669-670).
The main phase of this material is the magnetically soft Fe ₃ B phase, which is a major difference from existing permanent magnet materials. Hereinafter, this type of material is referred to as a low Nd high B type. But the coercive force is 3 kO
Since it was about e, which was insufficient for practical use, several studies on increase in coercive force have been published since then. For example _{Nd 3 Dy 2 Fe 70. 5 Co} 5 Ga 1 coercivity 6 in composition B _18.5
It was reported that good squareness was obtained with kOe (Journal of Applied Magnetics, Japan 17,1993,185-190). Here, it is said that the magnetic field is improved by increasing the anisotropic magnetic field of the hard phase Nd ₂ Fe ₁₄ B phase by substituting a part of Nd with Dy and by refining the structure by adding Co and Ga.

[0005]

As described above, isotropic Nd-Fe- having a fine crystal grain structure by liquid quenching and heat treatment.
In the B-based material, the magnetization was increased by two completely different methods, but each has the following problems. First, in the former simple rare earth reduction type, the coercive force is 8 kO.
It is more than e and has a practical ability, but the amount of increase in magnetization is small compared to the conventional material and the superiority is poor.

On the other hand, although the latter is a low Nd high B type, it has a very large magnetization, but on the other hand, the coercive force is still insufficient at the maximum of 6 kOe, so that a further increase in coercive force is required for practical use. . The simplest method of increasing the coercive force other than increasing the anisotropic magnetic field of the hard phase and refining the structure is to increase the volume fraction of the hard phase. However, Nd ₂ Fe _{1 4}
In the composition that increases the volume ratio of the B phase, that is, in the composition in which the Nd ₂ Fe ₁₄ B phase direction approaches in the Nd-Fe-B system ternary phase diagram, the metastable Nd ₂ Fe ₂₃ B ₃ phase is Nd ₂ Fe ₁₄ It is known that the coercive force decreases because it crystallizes instead of the B phase (J.Mag.
Mag.Mat. 80 (1989) 101-104). It should be noted that when the structure composed of the Nd ₂ Fe ₂₃ B ₃ phase is sufficiently heated, mainly α-Fe and Nd Fe ₄
The structure is composed of the B ₄ phase and contains a small amount of the Nd ₂ Fe ₁₄ B phase, but the coercive force is 1 because the volume ratio of the Nd ₂ Fe ₁₄ B phase is low.
The present inventor has confirmed that it is kOe or less. This N
The composition region in which the d ₂ Fe ₂₃ B ₃ phase is crystallized and the coercive force is unlikely to be expressed is hereinafter referred to as an intermediate composition region. FIG. 1 shows the composition region of each of the above-mentioned type magnets near Fe in the Nd-Fe-B system ternary phase diagram.

[0007]

DISCLOSURE OF THE INVENTION The inventor has found that isotropic N having a fine grain structure produced by liquid quenching and heat treatment.
As a method of solving the above-mentioned lack of magnetization of the simple rare earth-reducing type and the lack of coercive force of the low Nd and high B type in the d-Fe-B system material, a composition in an intermediate composition range having an intermediate composition between the two The suitability of phases was examined. As a result, amorphous to Nd ₂
Nd ₂ Fe ₂₃ B ₃ phase disappears due to hydrogen absorption and dehydrogenation treatment in the temperature range where the Fe ₂₃ B ₃ phase crystallizes, and Nd ₂
The fact that Fe ₁₄ B phase is generated was found. The present invention has been made based on these findings. That is, the present invention uses a rare earth-iron-boron as a basic component, and in an isotropic permanent magnet material having a fine crystal grain structure produced by liquid quenching and heat treatment, a metastable rare earth compound is produced to form a hard phase. Since a certain R ₂ Fe ₁₄ B phase is not generated, it is possible to generate the R ₂ Fe ₁₄ B phase by subjecting it to hydrogen absorption and dehydrogenation treatment in a composition range where it does not function as a magnet. It has been resolved.

Next, the constitution of the present invention will be described in detail below. (1) Composition R (rare earth element including Y), T (transition metal having Fe of 50 at% or more) and B as basic components, R: 2 to 12 at% B: 5 to 20 at% T: balance. Is characterized by.

R is 2 to 12 at%. R is 2 at%
When it is below, the volume ratio of the R ₂ Fe ₁₄ B type compound phase which is a hard phase becomes insufficient, resulting in a decrease in coercive force. On the other hand, if it is 12 at% or more, the volume ratio of the soft magnetic phase is reduced, resulting in a decrease in magnetization. R type is Nd, Pr
Or a mixture thereof is preferable. Also, if a part of it is replaced with a heavy rare earth such as Dy, the coercive force increases because the anisotropic magnetic field of the R ₂ Fe ₁₄ B phase increases. However, since the magnetization decreases at the same time, the addition amount is appropriate up to about 50% of R.
La has the effect of facilitating the formation of an amorphous or fine crystal grain structure. However, addition of La lowers the anisotropic magnetic field of the R ₂ Fe ₁₄ B phase, so excessive addition causes a decrease in coercive force. Therefore, an appropriate amount of La added is about 25% of R. The more preferable range of R is 5 to 8 at%.

B is 5 to 20 at%. B is 5 at%
When it is below, the coercive force is lowered because the volume ratio of α-Fe is increased. Further, if it is 20 at% or more, the magnetization is lowered. The balance is the transition metal T, of which 50% or more is Fe. When Fe of T is 50% or less, each magnetic property is deteriorated. Co within 30% as T other than Fe
Addition is effective for improving magnetic properties at high temperatures, and improving coercive force and squareness due to the refinement of the structure. However, addition of 30% or more of Co causes a decrease in coercive force. Other small amount of IVa, V
Addition of Group a elements, and further Cr, Cu, Si, Al, and Ga is also effective for the refinement of the structure, and the coercive force and squareness are improved.

(2) Texture before hydrogen storage treatment It is characterized in that it is an amorphous or metastable crystalline phase texture, or a texture containing both amorphous and metastable crystalline phases. The reasons for limiting the structure before the hydrogen storage treatment are as follows. In this composition region, in the equilibrium state, in addition to the R ₂ Fe ₁₄ B phase, it is mainly composed of α-Fe and RFe ₄ B ₄ phases. Then, according to a general casting solidification method, each of these phases is a crystal grain of several μm or more. Even if hydrogen storage and dehydrogenation processes described below are performed on such a structure, only rare earth compound-containing α-Fe containing only rare earth compounds is decomposed and recombined.
Since, etc. do not change, good magnetic properties cannot be expressed. In a permanent magnet material in which a hard phase and a soft phase coexist, by having a fine mixed structure, it is possible to achieve both high magnetization caused by the soft phase and high coercive force caused by the hard phase due to exchange interaction, which is a quantum mechanical magnetic interaction. Is possible. Therefore, in order to form a uniform fine mixed structure, it is necessary to start from an amorphous or single phase structure which is a compositionally uniform state. However, since there is no equilibrium phase in this composition region, it is necessary to make the structure amorphous or a metastable phase near the compounding composition, for example, the R ₂ Fe ₂₃ B ₃ phase.

A method for producing an isotropic or anisotropic magnet powder by hydrogen storage and dehydrogenation treatment of an RTB alloy similar to that of the present invention is well known (for example, Proceeding of the
11th. Int'l. Workshop on RE Magnets, 49 (1990)). However, this is due to Nd ₂ Fe ₁₄ B in the composition near Nd ₂ Fe ₁₄ B.
The structure is refined by causing the decomposition of phases and the recombination reaction. In contrast, the composition range of the present invention is R ₂ Fe
_Since it is on the side of rare earth and higher B than ₁₄ B, it must have a structure composed of a compositionally uniform amorphous phase or a metastable phase near the compounding composition as described above. When the R ₂ Fe ₁₄ B phase is included, it necessarily includes the α-Fe, RFe ₄ B ₄ phase, etc., and it is difficult to generate a structure in which the respective magnetic phases are finely mixed by hydrogen absorption and dehydrogenation treatment. is there.

(3) Method of generating texture before hydrogen storage treatment The formation of an amorphous or metastable crystal phase texture before hydrogen storage treatment, or a texture containing both amorphous and metastable crystal phases is
Liquid quenching, vapor quenching, mechanical alloying, etc. are possible. Among them, the liquid quenching method is excellent in both characteristics and cost. The vapor-phase quenching method has a high cooling rate and is most excellent in the amorphous forming ability, but the productivity is extremely poor. The mechanical alloy method has been reported to be amorphized in an alloy that cannot be amorphized by the liquid quenching method, and is a very effective method, but the alloy composition of the present invention is sufficiently amorphous by the liquid quenching method. Quality can be improved. Also, the liquid quenching method is remarkably superior in productivity.

As a liquid quenching method, a roll method, an atomizing method, a splat quench method, etc. are generally well known. Among them, the roll method is excellent in all of the cooling rate, throughput, and uniformity, and is the most suitable method for the present invention. Among the roll methods, the single roll method is superior to the twin roll method in terms of cooling rate and workability. The splat quench method achieves the highest cooling rate and has a high ability to generate an amorphous or metastable phase structure, but the throughput is extremely small and the difference in cooling rate within the same sample is large, so Since it lacks uniformity, it is not suitable for practical production. The atomization method is excellent in throughput and uniformity, but is inferior in cooling rate, so that it is difficult to generate the structure constituting the present invention.

(4) Hydrogen storage and dehydrogenation treatment The process comprises the steps of heat-treating the above alloy in a hydrogen-containing atmosphere to store hydrogen, and further heat-treating in a substantially hydrogen-free atmosphere to release hydrogen. Is characterized by. Each step will be described below.

(A) Hydrogen Storage The atmosphere containing hydrogen is pure hydrogen or a mixed atmosphere of hydrogen and an inert gas, and the appropriate treatment conditions change depending on the hydrogen partial pressure. The treatment temperature is preferably a low temperature within the range of producing R hydride by hydrogen absorption. The increase in the treatment temperature leads to the coarsening of the structure, which leads to the coarsening of the structure after dehydrogenation and the deterioration of the magnetic properties. Similarly, the treatment time is preferably as short as possible within the range in which R hydride is produced. Specifically, the temperature is preferably 600 to 750 ° C. and within 30 minutes. Since the hydrogen storage reaction is an exothermic reaction, it is important to quickly remove the reaction heat, especially when the amount of treatment increases, for the preparation of a stable sample, and the use of a heat storage material is effective. Also,
Increasing the atmospheric pressure and increasing the thermal conductivity of the gas by mixing with He are also effective.

By this hydrogen storage reaction, for example, R ₂ Fe
_In the composition near ₂₃ B ₃ , the amorphous phase (Am) changes as follows. Am → (Am-H) → (R ₂ Fe ₂₃ B ₃ ) → (R ₂ Fe ₂₃
B ₃ -H) → RH + α-Fe + Fe ₂ B Here, it is estimated that the presence or absence of the state in parentheses changes depending on the composition. In addition, "-H" shows a hydrogen solid solution state, respectively.

(B) Dehydrogenation In order to release hydrogen from the hydrogen storage state, heating is performed in an atmosphere having a hydrogen partial pressure sufficiently low. Specifically, antioxidant,
A vacuum of 0.1 Torr or less is preferable for the purpose of rapid hydrogen release. The treatment temperature is preferably low as long as dehydrogenation is possible. As in the hydrogen storage treatment, the increase in the treatment temperature leads to the coarsening of the structure, and the magnetic properties deteriorate. Similarly, the treatment time is preferably short within a range where dehydrogenation is possible. Specifically, the temperature is preferably 600 to 750 ° C. and within 30 minutes.

By this dehydrogenation reaction, the above R ₂ Fe ₂₃
The hydrogen storage state of the composition near B ₃ changes as follows. R−H + α−Fe + Fe ₂ B → R ₂ Fe ₁₄ B + α−F
e + Fe ₂ B As described above, the hydrogen adsorption / desorption treatment allows the R ₂ Fe ₂₃ B ₃ phase to disappear, and the hard magnetic phase R ₂ Fe ₁₄ B phase to be generated, whereby magnetization becomes possible. On the other hand, as I mentioned earlier, R ₂ Fe ₂₃ B ₃
The changes when the amorphous material having the near composition is simply heated are as follows. Am → R ₂ Fe ₂₃ B ₃ → α-Fe + RFe ₄ B ₄ + R
₂ Fe ₁₄ B As described above, the amount of R ₂ Fe ₁₄ B phase generated is extremely small, and most of R is spent for RFe ₄ B ₄ phase generation. Therefore, as compared with the hydrogen absorption / desorption treatment, R ₂ Fe ₁₄ B
Since the volume fraction of the phase is low, the coercive force is reduced, and the RFe ₄ B ₄ phase is non-magnetic, so the magnetization is also reduced.

The effects of the present invention have been confirmed outside the intermediate composition range. Increasing the coercive force by substituting Dy for Nd is a very effective method for low Nd and high B composition, but the phase relation changes with more than half the substitution, resulting in metastable R ₃ Fe.
₆₂ B ₁₄ phase was caused to crystallize and the R ₂ Fe ₁₄ B phase became unstable, resulting in a decrease in coercive force (J. Magn. Magn. Mat. 83, 1990,
228-230). However, according to the present invention, R ₃
Since the Fe ₆₂ B ₁₄ phase disappears and the R ₂ Fe ₁₄ B phase is generated, magnetization becomes possible. Conventional method: Am → Fe ₃ B + Am → Fe ₃ B + R ₃ Fe ₆₂
B ₁₄ Present invention: Am → Fe ₃ B + Am → Fe ₃ B + R−H + α
-Fe + Fe ₂ B → Fe ₃ B + R ₂ Fe ₁₄ B

[0021]

In the present invention, the basic component is rare earth-iron-boron,
In an isotropic permanent magnet material having a fine crystal grain structure formed by liquid quenching and heat treatment, a hard phase R ₂ Fe ₁₄ B phase is not generated due to the formation of a metastable rare earth compound, so that it is a magnet. In the composition range which did not exist, the hydrogen absorption and dehydrogenation treatments were performed to enable the formation of the R ₂ Fe ₁₄ B phase.

[0022]

The present invention will be described in more detail with reference to the following examples. Table 1 shows the heat treatment conditions and magnetic properties of each example and comparative example. Example 1 An alloy lump was obtained by using an arc melting furnace so that the composition of the alloy was Nd ₇ Fe _79.38 B _{13.62 in} atomic%. The liquid quench was carried out in a single roll type apparatus having a Cu-Be alloy roll having a diameter of 30 cm. The alloy cut into about 7 mm square was put into a quartz tube having a hole (orifice) with a diameter of 0.5 mm at the bottom with an inner diameter of 10 mm, melted by high frequency heating in an Ar atmosphere at 1 atm, and then 0.2 kgf / With a blowing pressure of cm ² , the roll rotation speed is 3000 rpm, and the distance between the nozzle and the roll is 0.
The sample was discharged at 5 mm to obtain a ribbon-shaped sample having a width of about 2 mm and a thickness of about 20 μm. It was confirmed by XRD that the obtained ribbon-shaped sample was amorphous. This ribbon-shaped sample was placed in a vacuum furnace, heated to 725 ° C. at a temperature rising rate of 10 ° C./min. Then, evacuate the furnace with a rotary pump and an oil diffusion pump, and
The temperature was maintained for about 30 minutes until a vacuum of 10 ⁻⁴ Torr was reached, then cooled to room temperature and taken out of the furnace.
When the magnetic characteristics of the sample taken out were measured by VSM, the residual magnetization was 110 emu / g and the coercive force was 2.5 kOe. In addition, from the XRD measurement result of the same sample after heat treatment, R
It was confirmed to consist of ₂ Fe _{1 4} B type compound phase, α-Fe and Fe ₂ B phase.

[0023]

[Table 1]

Examples 2 to 8 Alloy lumps were obtained by using an arc melting furnace so that the alloy compositions shown in Table 1 were obtained. Next, when the same treatment as in Example 1 was carried out using each of the alloys, the characteristics shown in Table 1 were exhibited.

Comparative Examples 1 to 4 Alloy lumps were obtained by using an arc melting furnace so that the alloy compositions shown in Table 1 were obtained. Next, when the same treatment as in Example 1 was carried out using each of the alloys, the characteristics shown in Table 1 were exhibited.

Example 9 An alloy ingot having the same composition as in Example 1 was prepared in an arc melting furnace. The alloy ingot was processed at a roll rotation speed of 1000 rpm, and the other conditions were processed in the same manner as in Example 1 to obtain a width of about 2 mm and a thickness of about 3
A 5 μm ribbon-shaped sample was obtained. It was confirmed by XRD that the obtained ribbon-shaped sample was composed of the R ₂ Fe ₂₃ B ₃ type compound phase. Next, the same treatment as in Example 1 was performed using each of the alloys, and the magnetic characteristics were measured by VSM. The residual magnetization was 103 emu / g and the coercive force was 1.9 kOe.

Comparative Example 5 The ribbon-shaped sample prepared by quenching the amorphous liquid prepared in Example 1 was heat-treated in vacuum only under the same temperature rising and holding conditions as in Example 1. The coercive force was 0.1 kOe. It was below.
Further, it was confirmed by XRD that the sample consisted of an R ₂ Fe ₂₃ B ₃ type compound phase.

Comparative Example 6 A ribbon-shaped sample prepared by quenching the amorphous liquid prepared in Example 1 was heat-treated in hydrogen in the same manner as in Example 1 and then cooled and taken out. Is 0.
It was less than 1 kOe. Further, it was confirmed by XRD that the sample consisted of R hydride, α-Fe and Fe ₂ B type compound phase.

Comparative Example 7 An alloy ingot having the same composition as in Example 1 was prepared in an arc melting furnace. From XRD, it was confirmed that the alloy ingot consisted of α-Fe, RFe ₄ B ₄ type compound phase and some R ₂ Fe ₁₄ B type compound phase. The alloy ingot was crushed to several mm with a jaw crusher and then subjected to the same hydrogen adsorption / desorption treatment as in Example 1, and the coercive force was 0.1 kOe or less. Also, XRD
From the same sample, α-Fe, Fe ₂ B type compound phase, RFe ₄ B ₄
It was confirmed that it consisted of the type compound phase and some R ₂ Fe ₁₄ B type compound phase.

[0030]

According to the present invention, the basic component is a rare earth-iron-
In an isotropic permanent magnet material, which is made of boron and has a fine crystal grain structure formed by liquid quenching and heat treatment, a hard phase R ₂ F is generated due to the formation of a metastable rare earth compound.
Since e ₁₄ B phase is not generated, R ₂ F can be obtained by subjecting it to hydrogen absorption and dehydrogenation in the composition range where it did not become a magnet.
e ₁₄ B phase is generated, and it is possible to achieve both high magnetization and coercive force.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing composition regions of an isotropic permanent magnet material of the present invention and a conventional isotropic phase diagram of Nd-Fe-B system.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01F 1/053 1/06 (72) Inventor Hiroshi Hasegawa 1505 Shimokagemori, Chichibu-shi, Saitama Showaden Kochi Co., Ltd. (72) Inventor Yoichi Hirose, 1505 Shimokagemori, Chichibu, Saitama Prefecture Showa Denko Co., Ltd., Chichibu Research Institute (72) Inventor, Masato Sagawa 1 of 22 Matsumuroage-cho, Nishikyo-ku, Kyoto Prefecture Intermetallics Co., Ltd.

Claims (3)

[Claims] 1. R (a rare earth element including Y), T (a transition metal having Fe of 50 at% or more) and B as basic components, and R: 2 to 12 at% B: 5 to 20 at% T: the balance. A step of producing an amorphous or metastable crystalline phase structure of the alloy, or a structure containing both an amorphous and metastable crystalline phase; and a step of heat treating this in an atmosphere containing hydrogen to occlude hydrogen, A method for producing an alloy powder for a rare earth permanent magnet, which comprises a step of releasing hydrogen by heat treatment in an atmosphere containing substantially no hydrogen. 2. A tissue containing an R ₂ T ₁₄ B-type compound phase in the step of occluding hydrogen in a tissue substantially not containing the R ₂ T ₁₄ B-type compound phase to generate a hydride of R and releasing hydrogen. The method for producing an alloy powder for rare earth permanent magnets according to claim 1, wherein 3. The method according to claim 1, wherein the step of producing an amorphous or metastable crystalline phase structure or a structure containing both an amorphous and metastable crystalline phase is a liquid quenching method. The method for producing an alloy powder for rare earth permanent magnets according to item 1.