JP3522207B2 - Rare earth magnet powder and anisotropic bonded magnet for anisotropic bonded magnet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to anisotropic rare earth magnet powder consisting essentially of rare earths, transition metals and boron, and anisotropic bonded magnets.

[0002]

2. Description of the Related Art R-T-B system permanent magnets (R is at least one rare earth element including Y, and T is Fe or Fe.
And Co) are attracting attention because they are inexpensive and have high magnetic properties. RTB permanent magnets are roughly classified into bulk magnets (sintered magnets or warm-worked magnets) and bonded magnets according to the classification of the final product. Bond magnets are expected to increase in importance in the future due to their shape flexibility and price advantages. Magnetic powders for Nd-Fe-B based bonded magnets are classified into several types depending on the manufacturing method. For example, Japanese Unexamined Patent Publication (Kokai) No. 59-647393 discloses a method for producing an isotropic magnetic powder by heat-treating Nd-Fe-B-based quenched flakes obtained by the melt spinning method at an appropriate temperature. In addition, a thin piece obtained by the same melt spinning method was hot-pressed and diapset to once prepare an anisotropic bulk magnet with anisotropy in the compression direction, and then the magnet was pulverized to produce anisotropic magnetic powder. A manufacturing method is also known. In addition, as a method that has been receiving attention in recent years, Sm ₂ F
anisotropic magnetic field by entering the nitrogen element interstitially subjected to nitriding treatment e ₁₇ alloy is remarkably improved, there is a method that can be used as a result the magnetic powder for an anisotropic bonded magnet. In addition, NbFe ₁₁ Ti, N
It has been reported that a similar effect can be obtained with a ThMn ₁₂ type alloy such as dFe ₁₀ V ₂ . Furthermore, Nd-F
e-B alloy is subjected to hydrogen storage treatment and dehydrogenation treatment,
Magnetically anisotropic Nd ₂ Fe using recrystallization reaction
_A method for obtaining ₁₄ B type magnetic powder is known (Japanese Patent Application Laid-Open No. 1-132).
106 gazette, JP-A-2-4901 gazette, etc.).

[0003]

Among the magnetic powders obtained by the conventional method, the Nd-Fe-B type quenched flakes prepared by the melt spinning method are magnetically isotropic, and the maximum energy performance of the finally obtained bond magnet is obtained. Is at most 10 MGOe and there is a problem in terms of magnetic properties. Further, the anisotropic bonded magnet obtained by blending the conventional Nd-Fe-B type anisotropic magnetic powder has insufficient magnetic properties and leaves room for improvement. On the other hand, Sm ₂ Fe
_{Since 17-} type nitride magnetic powder uses Sm as a main raw material, there is concern about its future prospects in terms of resources. The ThMn ₁₂ type magnetic powder is resource-friendly because the rare earth element used is Nd, but the magnetic potential after nitriding is lower than that of Nd ₂ Fe ₁₄ B type or Sm ₂ Fe ₁₇ type. The Nd-Fe-B type anisotropic magnetic powder obtained by performing hydrogen storage treatment and dehydrogenation treatment has a feature that the manufacturing process can be considerably simplified. However, from the theoretical value of the Nd-Fe-B type bulk magnet, As a rough estimate, the magnetic properties obtained at present are not sufficient. This manufacturing method utilizes a recrystallization reaction accompanied with a phase transformation in the dehydrogenation treatment step, and finally obtains N
It is considered that the magnetic characteristics of the d-Fe-B anisotropic magnetic powder largely depend on this reaction rate. In other words, the phase transformation does not proceed even if the forced dehydrogenation is blindly performed, and the phases before the phase transformation, that is, NdH ₂ , α-T, and Fe ₂ B remain as they are or a part of them are ideal R ₂ T ₁₄ B Since no phase is obtained, the finally obtained magnetic properties are low.

[0004]

[Means for Solving the Problem] The inventors have found that the ideal Nd
-Fe-B system anisotropic magnetic powder, by controlling the phase transformation reaction rate (recrystallization reaction rate) by the degree of vacuum in the dehydrogenation process, excellent magnetic anisotropy and an average grain size of 0.02 It was found that an Nd-Fe-B anisotropic magnetic powder substantially consisting of aggregates of fine recrystallized grains of ~ 5 µm and having higher magnetic properties than the conventional one can be obtained. The rare earth magnet powder for anisotropic bonded magnets of the present invention, which has solved the above problems, is obtained by subjecting a mother alloy to hydrogen storage treatment and dehydrogenation treatment, and has an average crystal grain size of 0.02 to 5 μm and R ₂
The dehydrogenation substantially consists of an aggregate of fine recrystallized grains having a T ₁₄ B phase (R is at least one kind of rare earth element including Y and T is Fe or Fe and Co) as a main phase. In processing
The degree of vacuum (Torr) is y, and the dehydrogenation processing time ( seconds ) is x.
The dehydrogenation condition is within the range of x = 60 to 1000 seconds.
And y = Ax ^z (where -0.70 ≤ z ≤ -0.30 )
It is, with the residual hydrogen quantity is characterized in that it is a twenty-eight to two hundred forty ppm. Further, the anisotropic bonded magnet of the present invention is obtained by binding a rare earth magnet powder obtained by subjecting a mother alloy to a hydrogen storage treatment and a dehydrogenation treatment to cause a recrystallization reaction accompanied by a phase transformation with a binder. Rare earth magnet powder
R ₂ T ₁₄ B phase (R is Y
Which is at least one of rare earth elements including T, and T is Fe or Fe and Co) as a main phase, and is substantially composed of an aggregate of fine recrystallized grains, and the degree of vacuum in the dehydrogenation treatment (Torr)
Is y and the dehydrogenation treatment time ( sec ) is x, dehydrogenation
When the processing condition is within the range of x = 60 to 1000 seconds, y = Ax ^z
(However, - 0.70 ≦ z ≦ - 0.30 ) represented by, with the residual hydrogen quantity is characterized in that it is a twenty-eight to two hundred and forty ppm. The rare earth magnet powder has an R content of 25 to 35 wt% and a B content of 0.5 to 1.5 wt%.
%, Co of 3 to 20 wt%, at least one selected from the group of Ga, Zr, Nb, Hf, Ta, Al, Si and V in total.
Those having a composition of 0.05 to 5 wt% and the balance Fe and inevitable impurities are preferable. This rare earth magnet powder is produced by applying hydrogen storage treatment and dehydrogenation treatment to the mother alloy to produce NdH ₂ , α-
It is obtained by a recrystallization reaction involving a phase transformation in the dehydrogenation process, which changes the three phases of T and Fe ₂ B into fine recrystallized grains of the R ₂ T ₁₄ B phase, and has magnetic anisotropy.

The present inventors considered that the phase transformation rate during dehydrogenation treatment affects the degree of magnetic anisotropy and repeated the experiment under various dehydrogenation treatment conditions. As a result, they have found that the dehydrogenation process has a certain regularity. That is, it comprises a primary dehydrogenation treatment step and a subsequent secondary dehydrogenation treatment step within about 60 to 1000 seconds after the start of dehydrogenation.
In particular, it was found that the primary anisotropic dehydrogenation rate determines the magnetic anisotropy potential that affects the magnetic properties. The secondary dehydrogenation treatment is a dehydrogenation treatment for releasing excess hydrogen remaining in the lattice after the completion of the primary dehydrogenation treatment, and although it is unavoidable, it has a great influence that decisively affects the magnetic properties. Absent. Degree of vacuum in primary dehydrogenation (Torr)
Is y and the dehydrogenation treatment time (seconds) is x, x = 60 to 10
Within the range of 00 seconds, it can be approximated to a straight line on a logarithmic graph.
y = Ax ^z (where A is an approximation on a logarithmic graph
It is the value of the intercept of the straight line, and z is the slope of the approximate straight line.
Ri is expressed by an exponential function of -0.70 is ≦ z ≦ -0.30), were found to increase rapidly vacuum degree in the secondary dehydrogenation. The reason why the value of x is limited here is that when x is 60 seconds or less, dehydrogenation for degassing the hydrogen atmosphere in the furnace other than the sample is included, so the phase transformation equilibrium for net R ₂ T ₁₄ B phase formation is formed. Because it is not in a state. This is because the upper limit of 1000 seconds varies slightly depending on the mass of the sample and the performance of the apparatus, but up to this range is an approximate guideline for the primary dehydrogenation treatment. When the z value was intentionally changed by adjusting the throughput of the sample or the pump capacity during dehydrogenation, the z value was -0.
If it is less than 70, the amount of magnetization and the coercive force are extremely low. This phenomenon will be described in detail. Since the primary dehydrogenation treatment is performed at a high speed, the nucleation directions necessary for recrystallization and growth occur in random directions, and the nucleation direction is magnetically isotropic because it grows in this state. Furthermore, since the equilibrium state of the reaction is disrupted, each phase decomposed during hydrogen absorption is left as it is, or a part thereof remains to reduce the substantial amount of R ₂ T ₁₄ B phase produced. Therefore, a large amount of hydrogen remains in the finally obtained magnetic powder, and the magnetic properties such as coercive force and magnetization amount also deteriorate. On the other hand, when the z value exceeds -0.30, the phase transformation proceeds, but it takes a long time to reach the final target vacuum degree (for example, about 0.1 Torr) for releasing excess hydrogen, and the recrystallized grains are coarse. As a result, the coercive force is reduced. Therefore, by setting the dehydrogenation rate to a velocity gradient within the range of −0.70 ≦ z ≦ −0.30, the phase transformation also proceeds at an appropriate rate, so that it is possible to obtain a rare earth magnet powder having high magnetic properties.

Since the rare earth magnet powder of the present invention has a magnetically high degree of anisotropy, a high performance anisotropic bonded magnet can be obtained by binding with a binder and then molding in a magnetic field. Controlling the dehydrogenation rate is not very difficult.
For example, if the volume inside the furnace and the exhaust capacity of the rotary pump are fixed, the throughput of the sample may be adjusted.If this condition is not applicable, a procedure such as installing a pressure controller in the pipe connecting the inside of the furnace and the rotary pump is taken. Can be considered. Further, it suffices that dehydrogenation is performed stepwise by opening and closing the valve, and the average dehydrogenation rate falls within a predetermined range.

[0007]

Example (Example 1) Rare earth element Nd, transition metal F
e, Co, and boron B as main components, and Ga as another element
Alternatively, Zr was added and vacuum melted to a predetermined composition to obtain a cast alloy. Then, the alloy was homogenized at 1100 ° C. for 20 hours to prepare a sample for hydrotreating. As the heat treatment furnace, a constant volume furnace equipped with a rotary pump having an exhaust capacity of 6401 / min was used, and samples of 65 g, 200 g, 1 kg, 2 kg, 3 kg and 10 kg were used.
The hydrogen treatment was carried out under the same conditions by dividing the treatment amount into 6 stages. As the hydrogen treatment conditions, first, hydrogen was sufficiently absorbed at room temperature and then heated to 840 ° C. at a temperature rising rate of 10 ° C./min while maintaining a hydrogen atmosphere at 1 atm. Then, after holding at the same temperature for 3 hours, dehydrogenation treatment was performed for 45 minutes. After completion of dehydrogenation, the inside of the furnace was replaced with an argon atmosphere and cooled. FIG. 1 shows the results of measuring the degree of vacuum in the furnace for 45 minutes from the time point 1 minute after the start of dehydrogenation of the sample to which Ga was added and plotting it on a logarithmic graph. As shown in the figure, it can be seen that until about 1000 seconds after the start of dehydrogenation, each of them is approximated to a straight line, and thereafter the vacuum degree rapidly increases. This tendency becomes remarkable as the processing amount decreases. Furthermore, the gradient (z value) calculated from this approximate straight line
Means that the higher the throughput, the slower the dehydrogenation rate. The obtained hydrogen-treated sample was pulverized, and then classified to have a particle size of 425 μm or less, and adjusted to have the same particle size distribution. The classified powder and the epoxy resin were mixed, and the obtained mixture was compression-molded in a magnetic field to obtain an anisotropic bonded magnet. Table 1 shows the ultimate vacuum after 45 minutes of dehydrogenation, the amount of hydrogen remaining in the sample after hydrogenation, the z value when the linear part of Fig. 1 was expressed by an exponential function, and the magnetism of the anisotropic bonded magnet. Show the characteristics. From this result, z value is -0.70
When it is smaller (that is, the dehydrogenation rate is faster), a large amount of hydrogen remains in the sample and the magnetic properties are low even though the ultimate vacuum is increased. On the other hand, the amount of residual hydrogen is large even in the sample having a high z value of the treated amount of 10 kg, and the residual magnetic flux density of the anisotropic bonded magnet is high, but the coercive force is low.

[0008]

[Table 1]

(Example 2) With respect to the Ga-added material, the treatment amount was set to 1 kg, and the dehydrogenation time was 0 seconds, 1000 seconds, 2000 seconds, 2700 seconds,
Hydrogen treatment was carried out in exactly the same manner as in Example 1 except that 6 steps of 3500 seconds and 4000 seconds were used. The relationship between the dehydrogenation time and the degree of vacuum in the furnace is shown in FIG. Then, the powder was pulverized and classified in the same manner as in Example 1 to adjust the particle size distribution, and the obtained powder was used to produce an anisotropic bonded magnet. Table 2 shows the ultimate vacuum, the amount of residual hydrogen, and the magnetic properties of the bonded magnet. From this result, it is found that the magnetic characteristics of the bonded magnet are almost determined by the dehydrogenation time up to about 1000 seconds. Further, dehydrogenation for a long time has the effect of reducing the amount of residual hydrogen and improving the residual magnetic flux density, but causes a significant decrease in coercive force. In addition, it was confirmed that all plots in FIG. 2 can be expressed by y = 53 ^{× −0.50} , and reproducibility was confirmed.

[0010]

[Table 2]

(Example 3) As shown in Table 1 of Example 1, when the treatment amount was 10 kg, a large amount of hydrogen remained in the sample although the sample had a high residual magnetic flux density. Therefore, an experiment was conducted to reduce the amount of residual hydrogen by increasing the dehydrogenation efficiency using rotary pumps with different exhaust capacities. The rotary pump used is 640 l / min, 900 l / min, 15 displacement
There are four types, 00l / min and 2000l / min. The experimental conditions were exactly the same as in Example 1 except that the rotary pump was changed. The relationship between the dehydrogenation time and the degree of vacuum in the furnace is shown in FIG.
From the figure, it was confirmed that the vacuum degree was gradually improved and the ultimate vacuum degree after 45 minutes could be improved by increasing the exhaust capacity. Furthermore, it can be seen that the z value up to 1000 seconds after the start of dehydrogenation gradually decreases, and the dehydrogenation rate increases slightly. Table 3 shows the results obtained by conducting the same evaluations as in Example 1 on the obtained hydrogen-treated sample. As shown in Table 3, by increasing the evacuation capacity of the rotary pump, the z value was kept within an appropriate range and the amount of residual hydrogen was reduced, and finally a high-performance anisotropic bonded magnet was obtained.

[0012]

[Table 3]

Nd ₂ T of the rare earth magnet powder of the above embodiment
The average recrystallized grain size of _{14 B} phase was not within 0.02~5μm both.

[0014]

According to the present invention, by controlling the dehydrogenation treatment rate within a specific range, an Nd-Fe-B type anisotropic magnet powder having improved magnetic characteristics as compared with the conventional one and the same are used. A high performance anisotropic bonded magnet can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing an example of the relationship between dehydrogenation treatment time and furnace vacuum degree.

FIG. 2 is a graph showing another example of the relationship between the dehydrogenation processing time and the degree of vacuum in the furnace.

FIG. 3 is a graph showing still another example of the relationship between the dehydrogenation treatment time and the degree of vacuum in the furnace.

Continuation of the front page (56) Reference JP-A-3-14203 (JP, A) JP-A-4-198410 (JP, A) JP-A-5-156320 (JP, A) JP-A-1-99201 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01F 1/00-1/117 B22F 1/00-9/00

Claims (2)

(57) [Claims] 1. A rare earth magnet powder for anisotropic bonded magnets, which is obtained by subjecting a mother alloy to a hydrogen storage treatment and a dehydrogenation treatment to cause a recrystallization reaction accompanied by a phase transformation, and having an average crystal grain size. 0.02-5 μm, R ₂ T ₁₄ B phase (R
Is at least one rare earth element including Y, and T is Fe
Or Fe and Co) as the main phase and consists essentially of aggregates of fine recrystallized grains, and the degree of vacuum (T
orr) is y and dehydrogenation treatment time ( seconds ) is x
When the hydrogen treatment condition is within the range of x = 60 to 1000 seconds, y = A
x ^z (however, - 0.70 ≦ z ≦ - 0.30 ) represented by, has been rare earth magnet powder for an anisotropic bonded magnet, wherein the residual hydrogen amount is twenty-eight to two hundred and forty ppm. 2. An anisotropic bonded magnet in which a rare earth magnet powder obtained by subjecting a mother alloy to a hydrogen storage treatment and a dehydrogenation treatment to cause a recrystallization reaction accompanied by a phase transformation is bound with a binder, Rare earth magnet powder is 0.02-5
R ₂ T ₁₄ B phase (R is at least one rare earth element including Y, T is Fe or Fe and Co)
Is a main phase, and the degree of vacuum (Torr) in the dehydrogenation treatment is y.
And the dehydrogenation treatment time ( sec ) is x, dehydrogenation treatment conditions
Within the range of x = 60 to 1000 seconds, y = Ax ^z (only
And, - 0.70 ≦ z ≦ - 0.30 ) represented by the anisotropic bonded magnet with the residual hydrogen quantity is characterized in that it is a twenty-eight to two hundred and forty ppm.