JPH0613210A - Manufacture of r-fe-b base permanent magnet - Google Patents

Abstract

PURPOSE:To manufacture the R-Fe-B base permanent magnet in small crystalline particle diameter having minimal magnetic impurity phase by a method wherein Fe is crystallized as the primary crystal during the crystalline separating step within an R-Fe-B base alloy for making the foundry structure fine or adjusting the liquid B quantity in the temperature region during the heat treatment step. CONSTITUTION:An alloy material comprising R: (rare earth metal): 12-17% (atomic%), B: 4-6%, remaining part: substantially Fe is used to form a fine foundry structure by crystallizing Fe as the primary crystal during melting.foundry steps. Next, the fine structure comprising R2Fe14B crystalline particles in crystalline particle diameter not exceeding 6mum amounting to exceeding 70% of the whole body is formed by adjusting the B content in liquid phase at the temperature of 600-1100 deg.C during the heat treatment step and 1-5 atomic% for suppressing the crystalline particle growth. Finally, two phase structure comprising R2Fe14B and a grain boundry phase not including such magnetic impurity phase as RFe4B4 or R2F17, etc., at all is to be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an R--Fe--B system permanent magnet having excellent magnetic properties, which magnet is useful as various household electric appliances, electric / electronic materials for computers and the like. Is.

[0002]

2. Description of the Related Art Permanent magnets are materials that generate a magnetic field without being supplied with electrical energy from the outside, and the demand for them is ever increasing mainly based on the electric and electronic materials described above. By the way, typical permanent magnets currently used are an alnico-based cast magnet and a rare earth-transition metal-based magnet, among which R-Fe-B belonging to the latter.
The system permanent magnet is expected as a permanent magnet having a high coercive force and energy product, and the following method has been proposed as a method for producing the R—Fe—B system permanent magnet.

(1) Japanese Patent Laid-Open No. 59-46008 and M.K.
Sagawa, etc. J .; Appl. Phys. V
ol. 55 (6) 15 March 1984, p2083
And the like, and the atomic ratio of R is 8 to 30%.
(However, R is at least 1 of rare earth elements including Y.
Species: the same applies hereinafter), a method of obtaining a permanent magnet made of a magnetic anisotropic sintered body consisting of 2 to 28% B and the balance Fe by a sintering method based on powder metallurgy.

In this method, an alloy ingot is produced by melting and casting, crushed to an appropriate particle size, kneaded with a binder, press-formed into an arbitrary shape in a magnetic field, and then sintered in argon. To get a permanent magnet.
It has also been clarified that the coercive force can be further increased by performing heat treatment at a temperature of around 600 ° C. after sintering.

(2) JP-A-59-211549, JP-A-60-100402, R.I. W. Lee; App
l. Phys. Lett. Vol. 46 (8), Apr
il, 1985, p790 and the like,
After using a quenching ribbon manufacturing apparatus used for manufacturing an amorphous alloy to produce a quenching thin piece having a thickness of about 30 μm,
It is a method of enhancing magnetic properties by performing mechanical orientation by a resin bonding method or a two-step hot pressing method.

(3) According to the method disclosed in Japanese Patent Laid-Open No. 62-276803, a cast ingot is hot-worked at a temperature of 500 ° C. or higher to refine the crystal grains,
This is a method in which the crystal axis is oriented in a specific direction to make it magnetically anisotropic.

(4) E. Otsuki, etc. ; Pro
c. 11th Int. Workshop on Ra
re EarthMagnets and Their
Application, Pittsburgh, 1
990, vol. 1, p328, etc., and the composition is adjusted (main phase component and grain boundary component).
This is a method of enhancing the magnetic properties by reducing the magnetic impurity phase as much as possible by sintering a kind of ultra-quenched powder. Among the above methods, the most commonly used method is the sintering method (1).

[0008]

In order to obtain a high-performance permanent magnet, it goes without saying that the magnetic moment of the ferromagnetic phase and the anisotropic magnetic field are large, but in addition to this, the crystal grain size is small and magnetic impurities are present. It is also very important not to include phases. When the crystal grain size becomes large, a reversal magnetic field easily occurs in the crystal grain due to energy, and as a result, the coercive force decreases. Further, as the magnetic impurity phase increases, the volume ratio of the ferromagnetic phase decreases correspondingly, so that the magnetization that can be extracted per unit volume of the magnet naturally decreases.

From this point of view, when the conventional method shown in the above (1) to (4) is examined, in the sintered magnet of (1), the ingot is once finely pulverized to about 3 μm. Crystal grains grow in the subsequent sintering process and heat treatment process, and the final crystal grain size becomes about 10 μm. Moreover, the basic composition of the alloy is Nd ₂ Fe ₁₄ B (Nd) which is a ferromagnetic phase.
_Since it is Nd ₁₅ Fe ₇₇ B ₈ which is deviated from the stoichiometry of _11.8 Fe _82.4 B _5.9 ), it contains a considerable amount of NdFe ₄ B ₄ phase as a magnetic impurity phase, which also causes a decrease in magnetic characteristics. ing.

The magnets (2), (3), and (4) each have a composition close to the stoichiometry of R ₂ Fe ₁₄ B, and have a small amount of magnetic impurity phase. Although it can be said that it is superior to the magnet of (1), coarsening of crystal grains is inevitable during hot working during manufacturing and heat treatment.

The present invention has been made by paying attention to the problems of the prior art as described above, and an object thereof is a ferromagnetic R having a small crystal grain size and a magnetic impurity phase reduced as much as possible.
It is intended to establish a manufacturing method of a —Fe—B system permanent magnet.

[0012]

The structure of the manufacturing method according to the present invention, which has been capable of solving the above-mentioned problems, is mainly composed of R (R represents one or more rare earth elements including Y), Fe and B as main components. In the method for producing a rare earth-based permanent magnet by melting / casting the alloy, hot-working and heat-treating, R:
12 to 17% (representing atomic percentage, the same applies hereinafter), B:
4-6%, balance: Using an alloy raw material consisting essentially of Fe, a fine cast structure is formed by crystallizing iron as a primary crystal in the melting / casting process, and 600-1100 during heat treatment. By controlling the B content in the liquid phase at a temperature of ℃ to 1 to 5% in terms of atomic percentage to suppress the growth of crystal grains, R having a crystal grain size of 6 μm or less can be obtained.
₂ Fe ₁₄ B crystal grains have a fine structure occupying 70% or more of the whole, and do not contain a magnetic impurity phase such as RFe ₄ B ₄ or R ₂ F ₁₇ and consist of R ₂ Fe ₁₄ B and a grain boundary phase. The gist is to obtain a magnet having a phase structure.

[0013]

The present inventors investigated the relationship between the magnetic properties and the metal structure of various R-Fe-B type alloys and analyzed the structure formation process of the magnet alloy in detail. As a result, in the R-Fe-B system alloy, by crystallizing Fe as a primary crystal at the time of crystal precipitation, the cast structure can be remarkably finer than in the case where R ₂ Fe ₁₄ B is a primary crystal.
Further, it was found that when the B content of the liquid phase in the temperature range of 600 to 1100 ° C. during the heat treatment is in the range of 1 to 5% in atomic ratio, the growth of crystal grains is significantly suppressed.

As a phase diagram of a ternary system containing R-Fe-B as a main component, when R is Nd and Pr, Y. Matura, etc. Jap. J.
Appl. Phys. , 24 (1985), L635, Katsuhisa Nagayama, et al .; The 14th Annual Meeting of the Applied Magnetics Society of Japan, 493 (1990) is known, and as is clear from these phase diagrams, it contains B. The amount is 4-6%
(Unless otherwise specified, it means atomic percentage), R
Of Fe is crystallized as a primary crystal in the region of 12 to 17% (the balance is Fe), and 600 to 1100 ° C. in the solidification process during manufacturing.
In the temperature range of 1, the B content in the liquid phase is 1 to 5%.

On the other hand, when the conventional R-Fe-B system sintered magnet is obtained, the primary crystal formed in the sintering and heat treatment process is Nd _2.
It is Fe ₁₄ B, and the B content in the liquid phase in the temperature range of 600 to 1100 ° C. is in the range of 10 to 20%.

The reason why the degree of refinement of the alloy structure remarkably changes depending on the difference in the phase of the primary crystal during casting and solidification is considered as follows. That is, comparing Fe and R ₂ Fe ₁₄ B, the former is a simple cubic crystal, while the latter is a cubic crystal having a complicated crystal structure.

Due to this difference in crystal structure, R ₂ Fe ₁₄ B has a larger energy at the solid solution interface when crystallized from the melt state as crystals and further grown, as compared with Fe. So the Gibbs-Thomson effect

[0018]

[Equation 1]

Thus, the radius of the dendrite tip of R ₂ Fe ₁₄ B is necessarily larger than that of Fe. That is, R ₂ Fe
_Since σ of ₁₄ B is large, ΔTr becomes too large when γ is made small, and γ cannot be made small because the liquid phase is stabilized at the tip of the dendrite rather than the solid phase. During the crystal growth of the alloy, a solute diffusion field is formed in the liquid phase around the solid phase. The dendrite arm spacing (DAS) is greatly affected by this diffusion field, and the dendrites are mutually diffused. Are formed so that they do not overlap with each other, the radius of curvature of the dendrite tip is large R ₂
With Fe ₁₄ B, it is considered that a large DAS must be taken in order to prevent the diffusion fields of the solutes from overlapping, and as a result, the crystal structure becomes coarse.

The reason why the growth of crystal grains is suppressed by setting the B content of the liquid phase generated in the temperature range of 600 to 1100 ° C. during the heat treatment to 1 to 5% is not clear at present. Generally, the degree of crystal grain growth is governed by the material diffusion mechanism, and the grain size is almost determined by the heat treatment temperature and the heat treatment time. However, in the above-described component system according to the present invention, rather than such grain growth dominated by the diffusion mechanism, the kinetics of the growth interface dominates the grain growth, so that the B content has a significant influence. It seems that there is.

From the above-mentioned reason and from the viewpoint of being closer to the stoichiometry of R ₂ Fe ₁₄ B and containing no magnetic impurities, the content of R and B is 1 in the present invention.
It is set to 2 to 17% and 4 to 6%. By specifying the component composition of the magnet alloy in this way, a fine cast structure with Fe as the primary crystal can be obtained, and in the subsequent heat treatment step, B content in the liquid phase in the temperature range of 600 to 1100 ° C. As a result of the amount falling within the suitable range of 1 to 5%, the growth of crystals during the heat treatment is suppressed, and the magnetic impure phase such as RFe ₄ B ₄ or R ₂ F ₁₇ is not contained and R ₂ Fe ₁₄ B is substantially contained. It is possible to obtain a magnet having a fine two-phase structure composed of a grain boundary phase.

In the present invention, R (rare earth metal) includes Y, La, Ce, Pr, Nd, Sm, Eu, Gd,
Examples thereof include Tb, Dy, Ho, Er, Tm, Yb and Lu, and these may be used alone or in combination of two or more kinds. The highest magnetic properties are obtained with Pr and Nd, so practically,
Pr, Nd, Pr-Nd, Ce-Pr-Nd alloy or the like is used.

In the present invention, the permanent magnet is obtained by subjecting an alloy satisfying the prescribed requirements of the above-mentioned composition to hot working such as melting / casting, rolling, forging and the like, followed by heat treatment. Or dissolution
After casting, finely pulverize with a jet mill etc. to an average particle size of about 5 μm or less, further orient in a magnetic field, compression-mold, then heat-sinter in an inert gas atmosphere, and then heat-treat Also obtains a permanent magnet.

In this heat treatment step, the heat treatment temperature is set to 600.
By setting the temperature to about 1 to 100 ° C, the B content in the liquid phase in the heat treatment becomes 1 to 5%, and the crystal grain growth hardly progresses during the heat treatment, and the crystal grain size is 6%.
R ₂ Fe ₁₄ B crystal grains with a size of μm or less occupy 70% or more of the whole, and the permanent particles are fine and have excellent magnetic properties and substantially do not contain a magnetic impurity phase such as R ₂ Fe ₄ B ₄ or R ₂ Fe _17. You can get a magnet.

Next, the constitution and operational effects of the present invention will be described more specifically with reference to examples, but the present invention is not limited by the following examples.

[0026]

EXAMPLES Example 1 An alloy having a composition of Nd ₁₅ Fe _85-X B _X (x = 3.5 to 7.5%) was melted and cast in a high-purity argon atmosphere using a high frequency induction heating furnace, An ingot with well-developed columnar crystals was obtained.

FIG. 1 shows the B content dependency of the average crystal grain size in the obtained cast alloy. The crystal grain size was measured from the cross section of the columnar crystal. As is clear from this figure, the crystal grain size suddenly changes between 5% B and 5.5% B, where the primary crystal changes from iron to Nd ₂ Fe ₁₄ B, and the primary crystal is 5%. The crystal grain size of B or less is 1/3 to 1/4 or less of the case where B is more than 5%.

Example 2 An Nd-Fe-B ternary alloy ingot produced in the same manner as in Example 1 was crushed by a jet mill to an average particle size of about 3 μm, and then hot-pressed at 1050 ° C. for 6 hours. , And pressure-sintered. Fig. 2 shows the dependence of the average grain size of this alloy on the amount of B.
Shown in. As is clear from this figure, the B content of the liquid phase composition during heat treatment is low B side (1 to 4% B) and high B side (10 to 10% B).
The grain size changes greatly between 5% B and 5.5% B, which is the boundary at which the grain size is divided into 20%). It can be seen that the value can be suppressed to 1/3 to 1/4 or less of the case larger than that.

Example 3 An alloy of Nb ₁₅ Fe ₇₇ B ₈ and Nb _13.5 Fe _81.7 B _4.8 was melted and cast by high frequency heating in an argon atmosphere. This cast alloy was pulverized by a jet mill to an average particle size of about 3 μm, and the obtained powder was oriented in a magnetic field of 10 kOe and compression-molded in a direction perpendicular to the orientation direction at a pressure of 200 MPa. Molded body in argon atmosphere 1080
Sintering for 1 hour at ℃, and after sintering at 600 ℃ for 1 hour
Heat treated for hours. When the crystal structure of the heat-treated product made of Nd _13.5 F _81.7 B _4.8 alloy was observed by a scanning electron microscope, it had a two-phase structure consisting essentially of Nd ₂ F ₁₄ B and a grain boundary phase and a grain size of 6 μm or less. Nd ₂ Fe ₁₄ B crystal grains accounted for 70% of the whole. On the other hand, Nd ₁₅ Fe ₇₇
Heat-treated products made of B ₈ alloy are Nd ₂ Fe ₁₄ B and NdFe
Nd ₂ Fe ₁₄ B crystal grains composed of ₄ B ₄ and Nd-rich phase which is a grain boundary phase and having a grain size of 6 μm or less are 5
It was about 0%.

Table 1 is a comparison of the magnetic properties of the two alloys, and it can be seen that the example magnets according to the present invention have better magnetic properties than the conventional sintered magnet (comparative example). .

[0031]

[Table 1]

[0032]

As described above, the present invention can provide an R-Fe-B system permanent magnet having a small crystal grain size and a very small magnetic impurity phase and excellent magnetic properties. became.

[Brief description of drawings]

FIG. 1 is a diagram showing the B content dependency of the average crystal grain size in a cast alloy (as cast).

FIG. 2 is a diagram showing the B amount dependency of the average crystal grain size in the alloy after pressure sintering.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Hanaki 1-5-5 Takatsukadai, Nishi-ku, Kobe City Kobe Steel Research Institute, Kobe Steel Research Institute

Claims (1)

[Claims] 1. R (where R represents one or more rare earth elements including Y) and an alloy containing Fe and B as main components are melted.
In a method for producing a rare earth permanent magnet by casting, hot working and heat treatment, R: 12 to 17% (representing atomic percentage, the same applies hereinafter), B: 4 to 6%, balance: substantially Fe B is used in the liquid phase formed at a temperature of 600 to 1100 ° C. during the heat treatment by using an alloy raw material consisting of By suppressing the growth of crystal grains by adjusting the content to be 1 to 5% in atomic percentage, a fine structure in which R ₂ Fe ₁₄ B crystal grains having a crystal grain size of 6 μm or less occupy 70% or more of the whole is formed. R-characterized in that it has a two-phase structure of R ₂ Fe ₁₄ B and a grain boundary phase, and has no magnetic impurity phase.
Manufacturing method of Fe-B system permanent magnet.