JP2020150219A - Alloy powder for rare earth magnet and method of producing the same - Google Patents

Abstract

To provide alloy powder for a rare earth magnet that has main phase crystal grains of ThMn12 type compounds and has improved coercive force, and a method of producing the alloy powder for a rare earth magnet.SOLUTION: The alloy powder for a rare earth magnet is provided that includes main phase crystal grains of Fe-based ThMn12 type compounds, the alloy powder for a rare earth magnet includes main phase crystal grains in each of which a Zn-rich layer is formed on at least a part of the surface of the main phase crystal grain, and the Zn-rich layer includes CeCr2Al20 type R (Fe, Co, Cu)2(Ga, Zn)20 (R is at least one selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoid, which may include Zr or Hf).SELECTED DRAWING: Figure 1

Description

The present invention relates to an alloy powder for rare earth magnets having main phase crystal grains of an Fe-based ThMn _12- type compound and a method for producing the same.

In recent years, there has been a demand for the development of magnets with a reduced content of rare earth elements. As used herein, the rare earth element means at least one element selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids. Here, lanthanoid is a general term for 15 elements from lanthanum to lutetium. As a ferromagnetic alloy in which the composition ratio of rare earth elements contained is relatively small, RT ₁₂ (R is at least one rare earth element, T is Fe, Co or Ni) having a body-centered tetragonal ThMn ₁₂ type crystal structure is used. Are known. Although RT ₁₂ has a high magnetization, it has a problem that the crystal structure is thermally unstable.

Patent Document 1 discloses a rare earth permanent magnet in which a part of Fe, which is a T element, is partially replaced by Ti, which is a structural stabilizing element, to improve thermal stability in exchange for high magnetization. There is.

Patent Document 2 states that by partially substituting the R element of an RFe _12- based compound with an element such as Zr or Hf, the amount of the structural stabilizing element Ti or the like that replaces the transition metal element is reduced to achieve saturation magnetization. A rare earth permanent magnet in which the ThMn ₁₂ structure is stabilized while being maintained is disclosed.

Further, Patent Document 3 discloses an R'-Fe-Co-based ferromagnetic alloy in which Y or Gd is selected as a part of the R element of RFe ₁₂ , and this R'-Fe-Co-based ferromagnetic alloy is disclosed. It is described that the alloy has a ThMn12 type crystal structure generated by an ultra-quenching method and thus exhibits high magnetic properties.

Further, Patent Document 4 discloses a rare earth permanent magnet in which the stability of the ThMn ₁₂ structure is improved by adding Ti or the like to Patent Document 3.

Further, Patent Document 5 describes that the addition of Cu produces a phase having a non-magnetic and low melting point of 1-4 composition, which enables sintering and high coercive force.

Further, in Patent Document 6, the Sm ₅ Fe ₁₇ system phase, the SmCo ₅ system phase, the Sm ₂ O ₃ system phase, and the Sm ₇ Cu ₃ system, which are different from the ThMn ₁₂ type as the sub-phase with respect to the main phase ThMn ₁₂ , are described. It is described that a high coercive force can be achieved by including at least one of the phases. Further, Non-Patent Document 1 describes that a stable ThMn _12- type crystal structure can be obtained by structural stabilizing elements (Ti, V, Nb, Ta, Mo, W).

Japanese Unexamined Patent Publication No. 64-76703 Japanese Unexamined Patent Publication No. 4-322406 Japanese Unexamined Patent Publication No. 2015-156436 JP-A-2018-125512 Japanese Unexamined Patent Publication No. 2001-189206 JP-A-2017-112300

K. H. J. Buschou, Rep. Prog. Phys. 54 (1991) 1123-1213.

The rare earth permanent magnet described in Patent Document 1 has improved thermal stability due to element substitution of Fe by Ti, but since the amount of Fe substitution by Ti is large, the magnetization is reduced by that amount, and sufficient magnetic properties are provided. I can't get it.

On the other hand, in the rare earth permanent magnet described in Patent Document 2, although the ThMn ₁₂ structure is stabilized by substituting the transition metal element with Ti or the like, the soft magnetic bcc (Fe, Co, Ti) phase And Laves phase are easily generated, and sufficient coercive force cannot be obtained.

The R'-Fe-Co-based ferromagnetic alloy described in Patent Document 3 does not replace the Fe element with a structure-stabilizing element, so that high magnetization, large magnetic anisotropy, and high Curie temperature can be obtained. Since it is a non-equilibrium phase, the main phase compound may decompose in a densification process at high temperature such as sintering.

Unlike Patent Document 2, the rare earth magnet described in Patent Document 4 can suppress the formation of a soft magnetic phase, but it cannot be said that the coercive force is sufficient.

In the rare earth magnet described in Patent Document 5, the magnetic property value may not be high because the amount of Ti added is large.

In the rare earth magnet described in Patent Document 6, when the rare earth rich subphase Sm ₇ Cu ₃ is used, there is a concern that the equilibrium state shifts to a rare earth rich composition than the main phase during the heat treatment and the main phase ratio decreases. Will be done. Further, the coercive force of the sub-phase determines the coercive force of the entire bulk, and it cannot be said that the main phase ThMn ₁₂ itself contributes to the coercive force.

The present disclosure provides an alloy powder for rare earth magnets having main phase crystal grains of a ThMn type ₁₂ compound and having an improved coercive force, and a method for producing the same.

The alloy powder for rare earth magnets of the present disclosure is an alloy powder for rare earth magnets containing main phase crystal grains of a Fe-based ThMn12 type compound, and the alloy powder for rare earth magnets is at least a part of the surface of the main phase crystal grains. Contains main phase crystal grains in which a Zn-rich layer is formed, and the Zn-rich layer is a CeCr2Al20 type R (Fe, Co, Cu) 2 (Ga, Zn) 20 (R is scandium (Sc), yttrium (Y). ), And at least one selected from the group consisting of lanthanoids, which may include Zr or Hf).

In certain embodiments, at least a part of the surface of the Zn-rich layer contains main phase crystal grains in which a Ga-rich layer is further formed, and the Ga-rich layer contains IrIn3 type (Fe, Co, Zn) Ga3. ..

In certain embodiments, the grain of the main phase contains Cu.

The method for producing an alloy powder for rare earth magnets of the present disclosure is, in an exemplary embodiment, a rare earth alloy powder of composition formula RTwMzCuα, where R is selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids. At least one element, T is Fe and / or Co, and M is at least one of the structure stabilizing elements consisting of Ti, V, Mo, W, Nb, Ta, w, z, alpha, respectively, 8 ≦ w ≦ 12,0.42 a ≦ z <0.70,0.40 ≦ α ≦ 0.70 , preparing a rare earth alloy powder, the composition formula R _beta (Fe, Co ) A Zn-Ga based alloy of _γ Ga _δ Zn _ε , where R is at least one element selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids, 0 ≦ β <0. 25, 0 ≦ γ <0.4, 0 <δ <1, 0 <ε <1, Zn—Ga-based alloy is prepared, and the rare earth alloy powder and the Zn—Ga-based alloy are mixed. A step of forming a Zn-rich layer on at least a part of the surface of the main phase crystal grains of the rare earth alloy powder by heating at 400 ° C. or higher and 800 ° C. or lower is included, and the Zn-rich layer is a CeCr2Al20 type R (Fe). , Co, Cu) 2 (Ga, Zn) 20 (R is at least one selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids, and may contain Zr or Hf. )including.

According to the embodiment of the present invention, it is possible to provide an alloy powder for a rare earth magnet which has main phase crystal grains of a ThMn ₁₂ type compound and has an improved coercive force, and a method for producing the same.

It is a figure which shows the structure and its composition in Experimental Example 1 of this disclosure. It is a figure which evaluated the structure obtained at the time of making the Zn-rich layer of Experimental Example 1 of this disclosure by SEM, and its composition. It is a figure which evaluated the structure and its composition in Experimental Example 2 of this disclosure by STEM. It is the figure which showed by enlarging the cross section of the main phase crystal grain which formed the Zn-rich layer of this disclosure. It is a figure which enlarged and schematically showed the cross section of the main phase crystal grain which formed the Zn-rich layer and the Ga-rich layer of this disclosure.

The alloy powder for rare earth magnets of the present disclosure contains main phase crystal grains of a Fe-based ThMn type ₁₂ compound. FIG. 4 is an enlarged cross section of the main phase crystal grain on which the Zn-rich layer is formed, and FIG. 5 is a diagram showing the cross section of the main phase crystal grain on which the Zn-rich layer and the Ga-rich layer are formed. It is an enlarged and experimentally shown figure. 4 and 5 are shown for reference as an example, with an arrow having a length of 5 μm as a reference length indicating the size. As shown in FIG. 4, the alloy powder for rare earth magnets of the present disclosure contains the main phase crystal grains 11 in which the Zn-rich layer 12 is formed on at least a part of the surface of the main phase crystal grains 11. The Zn-rich layer 12 is selected from the group consisting of CeCr ₂ Al ₂₀ type R (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ (R is scandium (Sc), yttrium (Y), and lanthanoid. It is a layer containing at least one (which may contain Zr or Hf). Further, the alloy powder for rare earth magnets of the present disclosure is a main phase crystal grain in which a Ga-rich layer 13 is further formed on at least a part of the surface of the Zn-rich layer 12 as shown in FIG. 5 in an exemplary embodiment. Includes 11. The Ga-rich layer 13 is a layer containing IrIn ₃ type (Fe, Co, Zn) Ga ₃ . In the present disclosure, the whole of the plurality of main phase crystal grains is simply referred to as "main phase", and the phase existing at the grain boundary of the main phase crystal grains is referred to as "grain boundary phase" as a whole. Further, the structural stabilizing element of the ThMn type ₁₂ compound (for example, Ti, V, Nb, Ta, Mo, W, etc.) is referred to as "M element".

Since the magnetization reversal starts from the end of the crystal grain, it is expected that the coercive force will be improved by covering the circumference of the crystal grain with a non-magnetic or low-magnetization low melting point alloy. As a result of diligent research, the present inventors have found that when a rare earth alloy powder containing the main phase crystal grains of a Fe-based ThMn _12- type compound and a Zn—Ga based alloy containing Zn and Ga are heat-treated together, they are Zn-rich with low magnetization. It has been found that a layer is formed on at least a part of the surface of the main phase crystal grains to increase the coercive force. In order to form a structure of such a form, it is preferable that Cu is contained in the main phase crystal grains of the alloy powder for rare earth magnets.

Further, depending on the composition of the Zn—Ga based alloy, the main phase crystal grains are further formed with a Ga-rich layer on at least a part of the surface of the Zn-rich layer. It is considered that by forming the Ga-rich layer, it is possible to expand between the main phase crystal grains and break the magnetic bond between the main phase crystal grains.

<Alloy powder for rare earth magnets>
The alloy powder for rare earth magnets of the present disclosure contains main phase crystal grains of a Fe-based ThMn type ₁₂ compound. The main phase crystal grains of the TnMn ₁₂ type compound in the alloy powder for rare earth magnets of the present invention can typically exist stably even at 1000 ° C. or higher, and a high-performance magnet manufacturing process such as a sintering method is adopted. Can be suitably used for. Generally, the "ThMn _12- type crystal structure" is a tetragonal crystal, but in the embodiment of the present invention, the crystal lattice of the tetragonal crystal is slightly distorted to have orthorhombic symmetry, or in the crystal. Even if the periodicity of the atom is slightly disturbed, it is regarded as "ThMn ₁₂ type crystal structure". Further, regardless of the presence or absence of Cu, for example, in the case of Ti element, when the main phase concentration is less than 7.7 at%, a rare earth element and two Fe elements (Fe dumbbells) are irregularly replaced inside the crystal. May include. This may be generally observed in the ThMn _12- type crystal structure stabilized by using Y in an amount smaller than the substitution composition range of the structural stabilizing element described in Non-Patent Document 1.

[Composition and structure of Zn-rich layer]
The alloy powder for rare earth magnets of the present disclosure includes main phase crystal grains in which a Zn-rich layer is formed on at least a part of the surface of the main phase crystal grains. As shown in FIG. 4, the Zn-rich layer is preferably formed on the entire surface (around) of the main phase crystal grains. Further, if the Zn-rich layer does not contain CeCr ₂ Al ₂₀ type R (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ , the coercive force may decrease. Therefore, it is preferable that the Zn-rich layer is mainly CeCr ₂ Al ₂₀ type R (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ . The coercive force can be improved by including the main phase crystal grains in which the Zn-rich layer is formed in the alloy powder for rare earth magnets. Therefore, the main phase crystal grains on which the Zn-rich layer is formed are preferably 70% by mass or more, and more preferably 90% by mass or more, when the total amount of the rare earth magnet alloy powder is 100% by mass.

The Zn-rich layer may be composed of a plurality of phases. The main phase of the Zn-rich layer is a CeCr ₂ Al _20- type compound in which a selective coordination of elements occurs at a specific site in the ZrZn _22- type crystal structure, and is R (Fe, Co, Cu) ₂ (Ga, Zn). ) ₂₀ , and Fe, Ru, Co, Rh, Ni, Pd, Cu, and Ag can mainly enter the above-mentioned selective coordination site. In addition, a typical composition such as a Zn phase, a phase having a FeZn ₂ Ga ₂ composition, or a phase in which M elements such as Ti ₆ (Fe _, Co, Zn _, Ga) ₂₃ are concentrated may be included. However, "representative" is used in the sense of allowing the elements contained in the magnetic powder for rare earth magnets, including impurity elements, to dissolve in the structure in an amount less than the amount that can be dissolved.

Since R (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ , which is the main phase of the Zn-rich layer, does not contain Ti, it depends on the type of structural stabilizing element of the main phase of the alloy powder for rare earth magnets. Do not generate.

[Composition and structure of Ga-rich layer]
In an exemplary embodiment, the alloy powder for rare earth magnets of the present disclosure contains main phase crystal grains in which a Ga-rich layer is further formed on at least a part of the surface of the Zn-rich layer. The Ga-rich layer is preferably formed on the entire surface (around) of the Zn-rich layer as shown in FIG. The Ga-rich layer is a layer containing IrIn ₃ type (Fe, Co, Zn) Ga ₃ .

The Ga-rich layer contributes to the removal of the bcc (Fe, Co) phase (which may contain M element) in the rare earth magnet alloy powder when it cannot be sufficiently removed. During the densification process, it has the effect of entering between the magnetic particles for rare earth magnets and expanding the grain boundaries, contributing to the improvement of the coercive force of the bulk body.

Further, it is preferable that the main phase crystal grains in the alloy powder for rare earth magnets contain Cu. By containing Cu in the main phase crystal grains, a Zn-rich layer having a lower magnetization is easily formed on at least a part of the surface of the main phase crystal grains, and the coercive force is increased.

The alloy powder for rare earth magnets of the present disclosure has, for example, the following composition.
Formula RT _{w 'case} of the (R is at least one element of rare earth elements, T is Fe and / or Co), the composition ratio _{w''Mz' Cu α} 'Ga δ' Zn ε, z The ranges of', α', δ', and ε'are 6≤w'≤12, 0.10≤z'<0.70, 0.10≤α'≤0.70, 0 <δ'<, respectively. 2.0, 0 <ε'<2.0.

The rare earth magnet alloy powder of the present disclosure is, for example, a step of preparing a rare earth alloy powder, a step of preparing a Zn—Ga alloy, and a mixture of the rare earth alloy powder and the Zn—Ga alloy at 400 ° C. It can be obtained by heating at 800 ° C. or lower and forming a Zn-rich layer on at least a part of the surface of the main phase crystal grains of the rare earth alloy powder.

<Manufacturing method of alloy powder for rare earth magnets>
[Step A: Step of preparing rare earth alloy powder]
(Composition of rare earth alloy powder)
The rare earth alloy powder of the present disclosure is represented by the composition formula of RT _w M _z Cu _α . In the exemplary embodiment, non-limiting, represented by a composition formula of _RT w Ti _z Cu _α.

In the rare earth alloy powder of the composition formula RT _w M _z Cu _α , R is at least one element of the rare earth element, and T is Fe and / or Co. The ranges of the composition ratios w, z, and α are 8 ≦ w ≦ 12, 0.42 ≦ z <0.70, and 0.40 ≦ α ≦ 0.70, respectively. Hereinafter, this alloy may be referred to as "R-Fe-Co-M-Cu based rare earth alloy powder". Further, the R-Fe-Co-M-Cu based rare earth alloy bulk body obtained by densifying this alloy powder may be simply referred to as "bulk body".

For example, R-Fe-Co-Ti -Cu -based rare earth alloy powder composition formula _{R1 1-x R2 x (Fe} 1-y Co y) is described by w _Ti z Cu _α. R1 has at least Y and may further have Gd. R2 has at least Sm and may further contain at least one rare earth element selected from the group consisting of La, Ce, Nd and Pr excluding Gd. x, y, z, w are 0.5 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.4, 8 ≦ w ≦ 12, 0.42 ≦ z <0.70, 0.40 ≦ α, respectively. The composition ratio may satisfy ≦ 0.70.

In this case, the composition ratio of R1, R2 and Ti determines the magnetic property value and high temperature stability of the main phase. From the viewpoint of magnetic anisotropy, it is desirable that the composition ratio (x) of R2 is equal to or greater than the composition ratio (1-x) of R1, that is, 0.5 ≦ x ≦ 1.0. Further, it is desirable that Ti is as small as possible from the viewpoint of saturation magnetization, but it is desirable that Ti be as large as possible from the viewpoint of high temperature stability. As a result of studies by the present inventors, a range of 0.42 ≦ z <0.70 is desirable. In addition to Ti, structural stabilizing elements such as V, Nb, Ta, Mo, and W may be used, or a combination thereof may be used. In the case of V and / or Mo, 0.42 ≦ z <0.90.

From the viewpoint of improving the magnetization and magnetic anisotropy at the practical temperature accompanying the increase in the magnetic moment and the increase in the Curie temperature, it is preferable to replace a part of Fe with Co. However, if the amount of substitution is too large, it is not desirable because it causes a decrease in magnetization and magnetic anisotropy. Specifically, the Co substitution amount y is preferably 0 ≦ y ≦ 0.4, more preferably 0.1 ≦ y ≦ 0.3, and preferably 0.15 ≦ y ≦ 0.20.

By adding Cu, a rare earth-rich grain boundary phase (R-Cu-based grain boundary phase) coexisting with the main phase is generated. The following effects can be obtained by forming this rare earth-rich grain boundary phase.
-The heat treatment facilitates the progress of crystal growth of the main phase.
-It is possible to reduce the formation of different phases during dissolution and solidification.
-Since the rare earth-rich grain boundary phase absorbs and releases hydrogen, cracks occur between the main phase and the grain boundary phase, and the particles can be efficiently pulverized into single crystal particles.
-The Zn-rich layer makes it easier to surround the grains of the main phase crystal, improving the coercive force.

The amount of Cu determines the amount of grain boundary phase formed in the rare earth alloy. If the amount of grain boundary phase is small, bcc (Fe, Co) phase (may contain M element) and Nd ₃ (Fe, Ti) ₂₉ type crystal structure phase (hereinafter, 3-29) during dissolution and solidification. Not only can the different phases such as (phase), Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and the phase of the crystal structure having an irregular substitution part inside (hereinafter referred to as 2-17 phase) not disappear, but also anisotropic firing. It is not easy to grow crystals to a size sufficient to obtain a magnetized powder. As a result of examination by the present inventors, a range of 0.40 ≦ α ≦ 0.70 is desirable.

The grain boundary phase produced is a Cu group. The grain boundary phase is primarily the phase of the crystal structure of KHG ₂ type (hereinafter, 1-2 phase), and other R and Cu, Fe, the ratio of Co 1: Composition of 4 (hereinafter, 1-4 Composition) phase is also included. The molar ratio of R2 / (R1 + R2) of the R element constituting the grain boundary phase is higher than that of the main phase in both the 1-2 phase and the 1-4 composition phase. In addition, Fe and Co are slightly dissolved, and the amount of the solid solution is larger in the phase having a 1-4 composition than in the phase 1-2. Ti hardly dissolves in both phases. Most of the other M elements do not dissolve in solid solution.

The appropriate amount of w varies depending on the amount of Cu added, but is 8 ≦ w ≦ 12. This is because if w is too large, a soft magnetic bcc (Fe, Co) phase (which may contain M element) is formed, and if w is too small, a 2-17 phase or a 3-29 phase is formed.

The R-Fe-Co-M-Cu based rare earth alloy powder thus obtained contains main phase crystal grains having a ThMn _12- type crystal structure. The main phase crystal grains of the TnMn ₁₂ type compound in the rare earth alloy powder of the present invention can typically exist stably even at 1000 ° C. or higher, and are suitable for adopting a high-performance magnet manufacturing process such as a sintering method. Can be used for. Generally, the "ThMn _12- type crystal structure" is a tetragonal crystal, but in the embodiment of the present invention, the crystal lattice of the tetragonal crystal is slightly distorted to have orthorhombic symmetry, or in the crystal. Even if the periodicity of the atom is slightly disturbed, it is regarded as "ThMn ₁₂ type crystal structure". Further, regardless of the presence or absence of Cu, for example, in the case of Ti element, when the main phase concentration is less than 7.7 at%, a rare earth element and two Fe elements (Fe dumbbells) are irregularly replaced inside the crystal. May include. This may be generally observed in the ThMn _12- type crystal structure stabilized by using Y in an amount smaller than the substitution composition range of the structural stabilizing element described in Non-Patent Document 1.

The rare earth alloy powder may further contain Zn and Sn. The melting point of the grain boundary phase may be lowered and a uniform two-grain grain boundary may be formed, and the encircling of the main phase crystal grains in the rare earth alloy powder by the Zn-rich layer may proceed more smoothly.

(Method of producing rare earth alloy powder)
Rare earth alloy powder (R-Fe-Co-M-Cu based rare earth alloy powder) is produced by known methods such as mold casting method, centrifugal casting method, strip casting method, and liquid ultra-quenching method. A method of crushing can be adopted. When the formation of a phase that is not preferable as a rare earth alloy, such as the (Fe, Co) phase of bcc (which may contain M element) during solidification of the molten alloy, is suppressed as much as possible, the strip casting method, which has a relatively high cooling rate, or The liquid ultra-quenching method can be adopted. When the cooling rate at the time of solidification is slow, the grain size of the precipitated different phase becomes large, so that the different phase is unlikely to disappear in the next heat treatment step. Even nanocrystals produced by the liquid ultra-quenching method can be easily grown into crystal grains of 10 μm or more suitable for obtaining anisotropic magnetic powder by undergoing the following heat treatment process, so that rare earth alloys have the fastest cooling rate possible. It is better to solidify with. It is better that the coagulated structure has less macrosegregation and is as uniform as possible. For example, when produced by the liquid ultra-quenching method, the roll peripheral speed is preferably 1 to 40 m / s in an inert atmosphere.

Further, by applying heat treatment to the rare earth alloy, it is possible to reduce the heterogeneous phase generated in the solidification process and to easily obtain a powder composed of single crystal-like particles useful as a raw material for anisotropic sintered magnets by a pulverization method. Crystal grains can be coarsened. Although it depends on the composition, the eutectic temperature of the 1-2 phase and the 1-4 composition phase is around 820 ° C, the melting point of the 1-2 phase is around 860 ° C, and the melting point of the 1-4 phase is around 880 ° C. is there. Therefore, the heat treatment temperature is preferably 900 ° C. or higher and 1250 ° C. or lower, and more preferably 1000 ° C. or higher and 1100 ° C. or lower. The heat treatment time depends on the temperature, but is preferably 5 minutes or more and 50 hours or less. If the time is too short, a sufficient reaction will not occur to eliminate the heterogeneous phase or the grain growth will be insufficient, and if the time is too long, the rare earth elements will evaporate and oxidize, and the operational efficiency will be poor. In this temperature range, the grain boundary phase becomes a liquid phase and a part of the main phase is dissolved and reprecipitated. Therefore, in the main phase, crystal grains grow dramatically and solidify due to a rapid chemical reaction via the liquid phase. The different phase of time can be easily eliminated if the grain size is not large. The amount of grain boundary phase is preferably 3 wt% or more and 20 wt% or less. If the amount of grain boundary phase is small, not only the heterogeneous phase during dissolution and solidification cannot be eliminated, but also it is not easy to grow the crystal to a size sufficient to obtain anisotropic sintered magnetic powder, and the amount of grain boundary phase. This is because the ratio of the main phase decreases when the amount is large, so that the magnetization as a magnet body decreases. The bcc (Fe, Co) phase (which may contain M element) that could not be completely eliminated in this step can be eliminated in step C if the amount is small.

The grain boundary phase contained in the rare earth alloy causes hydrogen absorption and release phenomena reflecting the rare earth rich composition, and is particularly remarkable by heat treatment in hydrogen. By absorbing and releasing hydrogen, the rare earth rich phase undergoes volume expansion and contraction, and cracks occur between the main phase crystal grains and the subphase. For example, a rare earth alloy is heated to 400 ° C. or higher in hydrogen to absorb hydrogen, and then switched to a vacuum atmosphere to sufficiently release hydrogen at 700 ° C. or lower. This increases the probability that the magnetic powder will crack at the cracks during the crushing process using a jet mill, stamp mill, ball mill, etc., making it possible to obtain highly orientable anisotropic magnetic powder containing a large amount of fine powder in single crystal units. Become.

In this way, a rare earth alloy powder can be produced.

[Step B: Step of preparing Zn-Ga alloy]
(Composition of Zn-Ga alloy)
As a result of diligent research by the present inventors, the composition of the Zn—Ga based alloy according to the embodiment of the present invention always contains Zn and Ga at least. When Cu is not contained in the rare earth alloy powder, it is necessary to put it in the Zn—Ga based alloy. The composition of the Zn—Ga based alloy is described by R _β (Fe, Co) _γ Ga _δ Zn _ε . R is at least one element of a rare earth element (selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids), 0≤β <0.25, 0≤γ <0.4, 0 <. The composition ratio satisfies δ <1, 0 <ε <1. Further, in the Zn—Ga based alloy, Cu may be further added at 5 at% or less, and at least one or more of Ti, V, Nb, Ta, Mo, W and the like may be added at 5 at% or less. Absent.

The R element may be omitted because it can be procured from the rare earth alloy powder, but it is preferable to add it in advance because it is a constituent element of the main phase of the Zn-rich layer. The R element is at least one selected from the elements constituting the main phase. If the amount of the R element introduced is too large, the reaction with the main phase becomes remarkable and the 3-29 phase and the 2-17 phase are generated, and the magnetization of the magnetic particle for rare earth magnets is lowered. More preferably, 0 ≦ β ≦ 0.10.

Since Fe and Co are constituent elements of the main phase of the Zn-rich layer, they are elements necessary for forming the Zn-rich layer. However, since it can be procured from rare earth alloy powder, it does not necessarily have to be contained in the Zn—Ga based alloy. In particular, when the (Fe, Co) phase of bcc (which may contain M element) in the rare earth alloy powder has not been sufficiently removed, it is better not to add Fe and Co to the Zn—Ga based alloy. There is. On the other hand, when it is put into a Zn—Ga based alloy, the bcc (Fe, Co) phase (which may contain M element) is generated and retained unless the amount is less than the solid solution limit amount in the generated Zn-rich layer. The magnetic force decreases. More preferably, 0 ≦ γ ≦ 0.15. Since Zn and Ga are constituent elements of the main phase of the Zn-rich layer, they must be contained. Without Ga, the Zn-rich layer may not be formed on the surface of the main phase crystal grains. On the other hand, in the absence of Zn, Fe—Ga alloys and 2-17 phases are formed.

(Method for producing Zn-Ga alloy)
The Zn—Ga based alloy may be amorphous or composed of a plurality of phases, but it is preferable that the Zn-Ga alloy is not extremely segregated. Extreme segregation may hinder smooth encircling of rare earth alloy powders. Therefore, it is appropriate to adopt the strip casting method, the liquid ultra-quenching method, the gas atomizing method, the disc atomizing method, or the arc melting method, which have a relatively high cooling rate. Further, a homogeneous alloy may be prepared by a ball mill, a planetary ball mill, or the like. In addition, a nanoparticle synthesis method using a chemical liquid phase method such as a chemical reaction precipitation method, an inverse micelle method, a hydrothermal synthesis method, or a sol-gel method may be used.

[Step C: Step of forming a Zn-rich layer on at least a part of the surface of the main phase crystal grains of the rare earth alloy powder]
Using the Zn—Ga based alloy produced in step B, a heat treatment is performed to form a Zn-rich layer on the surface of the main phase crystal grains of the rare earth alloy powder produced in step A. Since the Zn-Ga alloy has a slight reaction with the rare earth alloy powder, it may be difficult to form this Zn-rich layer by diffusion along the grain boundaries of an already densified bulk body such as a sintered body. Therefore, in this step, the rare earth alloy powder produced in step A and the Zn—Ga based alloy produced in step B are mixed and then heat-treated to obtain an alloy powder for rare earth magnets having a high coercive force. By orienting the obtained alloy powder for rare earth magnets in a magnetic field and densifying it by sintering or hot forming, it is possible to obtain a magnet body having high magnetization and coercive force. The present invention is not limited to the steps after <step C>.

It is sufficient that the degree of mixing is uniform enough to dissolve the Zn—Ga based alloy and cover the periphery of the rare earth alloy powder. Various mixers and mixers such as mortars, ball mills and locking mixers can be used. The amount of Zn—Ga based alloy introduced is preferably 1 wt% to 100 wt% with respect to the rare earth alloy powder. If the amount of introduction is small, the effect of improving the coercive force cannot be sufficiently obtained, and if the amount of introduction is too large, the magnetization of the magnet body is lowered when it is densified.

Since the Zn—Ga alloy is soft, the productivity may decrease due to adhesion in the mixing device or the like. Therefore, the Zn—Ga based alloy may be put into a gas state or a plasma state and adhered to the surface of the main phase crystal grains of the rare earth alloy powder. Mass productivity may be improved by utilizing the high vapor pressure of Zn. Alternatively, a molten Zn—Ga based alloy may be injected to adhere to the surface of the main phase crystal grains of the rare earth alloy powder. When these methods are adopted, step B is included in step C.

The heat treatment temperature is preferably 400 ° C. or higher and 800 ° C. or lower. This is because if the temperature is less than 400 ° C., the Zn—Ga based alloy does not melt, and if it exceeds 800 ° C., the grain boundary phase dissolves and grain growth of the main phase occurs due to dissolution and reprecipitation. In addition, it may be desirable that the heat treatment does not also serve as a densification step. This is because in the mixing of powders, voids are generated inside the bulk body due to the dissolution of the Zn—Ga alloy, and the voids remain inside the compacted bulk body even after sintering or hot forming, and the magnet body. This is because it may cause a decrease in magnetization.

Hereinafter, experimental examples of the present invention will be specifically described, but the present invention is not limited to these experimental examples.

[Example 1]
<Step A> Step of preparing rare earth alloy powder Rare earth alloy powder (R-Fe-Co-M-Cu based rare earth alloy powder) was prepared as follows.

The raw material metals of Y, Sm, Fe, Co, Ti, and Cu having a purity of 99.9% or more were weighed step by step in consideration of evaporation of rare earth elements at the time of dissolution. After being sufficiently dissolved in the alumina crucible, the molten metal was discharged on a roll made of Cu rotating at a peripheral speed of 15 m / s. The prepared ultra-quenching thin band was included in the Nb foil, and heat treatment was performed at 1050 ° C. for 1 hour in Ar flow. It was pulverized with a jet mill to obtain magnetic powder having an average particle size of 10 μm or less. The composition of the rare earth alloy powder evaluated using the inductively coupled plasma optical spectrum spectroscopy (ICP-OES) method is Y _0.37 Sm _0.63 (Fe _0.83 Co _0.17 ) _{9 It was .65} Ti _0.52 Cu _0.54 . The composition of the main phase was Y _0.37 Sm _{0.63 (} Fe _0.83 Co _0.17 ) _11.08 Al _0.07 Si _0.02 Ti _0.57 Cu _0.26 . The composition of the grain boundary phase is Y _0.20 Sm _0.80 (Fe _0.06 Co _0.03 Cu _0.91 ) ₂ and Y _0.25 Sm _0.75 (Fe _0.14 Co _0.07 Cu _{0). .79} ) It was ₄ . Al and Si are derived from the crucible used in this step.

<Step B> Step of preparing a Zn-Ga alloy The Zn-Ga alloy was produced using an ultra-quenching device (NEV-A30023 manufactured by Nissin Giken Co., Ltd.). A raw material with a purity of 99.9% or higher, which is weighed in consideration of the evaporation of rare earth elements, is sufficiently dissolved in a quartz hot water pipe, and then the hot water is discharged on a Cu roll rotating at 20 m / s to form a ribbon. Zn—Ga based alloy was prepared. Specifically, a Zn—Ga based alloy having the composition shown in Table 1 below was prepared.

<Step C> Step of forming a Zn-rich layer on at least a part of the surface of the main phase crystal grains of the rare earth alloy powder Add 50 wt% of the Zn-Ga alloy obtained in step B to the rare earth alloy powder obtained in step A. Then, they were mixed using a dairy pot in a glove box filled with Ar. This mixed powder was placed in an Nb container to maintain a state in which oxidation was suppressed, and then put into a furnace. The alloy powders for rare earth magnets of Experimental Examples 1 to 10 were prepared by heat-treating at 500 ° C. for 1 hour in Ar flow.

After binding the rare earth alloy powder and the rare earth magnet alloy powder with paraffin and magnetizing them with a pulsed magnetic field, the change in coercive force at room temperature was evaluated using VSM. Table 1 rare earth alloy powder coercivity _(H cJ _b) (before mixing with Zn-Ga-based alloy of a rare earth alloy powder coercivity) of the alloy powder for rare earth magnet for the coercivity _(H cJ _a) (after mixing The ratio of the coercive force of the alloy powder for rare earth magnets) is indicated by "H _cJ _a / H _{cJ _b} ". The same applies to Table 2. As shown in Table 1, the coercive force could be improved by using Zn—Ga based alloys (Experimental Examples 1 to 10) within the claimed composition range.

The composition analysis of the alloy powder for rare earth magnets is performed by a desktop scanning electron microscope (JCM-6000Plus manufactured by JEOL Ltd., hereinafter referred to as desktop SEM) equipped with an energy dispersive X-ray spectroscope (EX-37001 manufactured by JEOL Ltd.). An electric field emission scanning electron microscope (JSM-7001F manufactured by JEOL Ltd., hereinafter referred to as FE-SEM) attached with an energy dispersive X-ray spectroscope (JED-2300F manufactured by JEOL Ltd.) was used.

A more detailed microstructure evaluation of the alloy powder for rare earth magnets was performed using an atomic resolution analysis electron microscope (STEM, JEM-ARM200F manufactured by JEOL Ltd.).

As the constituent phase of the Zn-rich layer, a wide-angle X-ray diffraction (XRD) apparatus (D8 ADVANCED / TXS manufactured by Bruker AX Co., Ltd.) having a CuK _α radiation source was used.

The coercive force was evaluated at room temperature with a vibrating sample magnetometer (VSM, VSM-5-20 manufactured by Toei Kogyo Co., Ltd.) after performing pulse magnetization of 6T.

In Experimental Example 1, Y _0.01 Sm _0.02 Ti _0.02 Fe _0.10 Co _0.01 Zn _0.61 Ga _0.23 , which is a Zn-rich layer composition, was used as the Zn—Ga based alloy. FIG. 1 shows a BSE image and a composition map of an alloy powder for rare earth magnets evaluated by a tabletop SEM. Rare earths in which a Zn-rich layer having a composition of Y _0.01 Sm _0.03 Fe _0.09 Co _0.02 Cu _0.03 Zn _0.66 Ga _0.16 was formed around at least a part of the rare earth alloy powder. Shows alloy powder for magnets. The coercive force increased by 2.80 in comparison with the unmixed rare earth alloy powder. FIG. 2 shows the BSE image of the used Zn—Ga based alloy evaluated by FE-SEM and the result of composition analysis. When the wide-angle X-ray diffraction is also analyzed, there are mainly three types of constituent phases, and the typical compositions are (Y, Sm) (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ , and (Fe,). Co) Zn ₂ Ga ₂ and Zn are shown. From these results, it is shown that (Y, Sm) (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ is the main layer of the Zn-rich layer.

In Experimental Example 2, Sm _0.08 Zn _0.38 Ga _0.54 was used as the Zn—Ga based alloy. Similar to Experimental Example 1, an alloy powder for a rare earth magnet having a Zn-rich layer formed on at least a part of the rare earth alloy powder was obtained. The coercive force increased by 3.00 in proportion. FIG. 3 shows the tissue evaluated by STEM and the composition analysis result thereof. It is shown that the Ti-rich phase in which Ti is concentrated is unevenly distributed in the Zn-rich layer that can be seen as a single color by SEM. It is shown that the Zn-rich layer contains a Ti-rich phase. It is also shown that Ti is an element that is not always necessary to form (Y, Sm) (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ , which is the main phase of the Zn-rich layer. It is also shown that a Ga-rich layer of (Fe, Co, Zn) Ga ₃ is mainly formed on the surface of the Zn-rich layer. The distance between alloy powders for rare earth magnets can be extended.

In Experimental Examples 3 to 10, the types and compositions of the constituent elements of the Zn—Ga based alloy are changed. When evaluated by a tabletop SEM, a material structure as seen in Experimental Example 1 and Experimental Example 2 was obtained. The coercive force of the rare earth magnet alloy powder in which at least a part of the rare earth alloy powder was formed was increased as compared with the rare earth alloy powder in which the Zn-rich layer was not formed.

[Example 2]
Rare earth alloy powders were prepared in the same manner as in Example 1 so as to have the composition of the main phase of the rare earth alloy powders shown in Experimental Examples 11 to 21 in Table 2 (step A). Further, the Zn—Ga based alloy of Experimental Example 1 was prepared (step B), mixed in the same manner as in Example 1 and heat-treated (step C) to obtain an alloy powder for rare earth magnets.

Although there are differences in the solid solution type and its amount depending on the R type and its composition ratio, when Examples 11 to 21 were confirmed by a tabletop SEM, a Zn-rich layer was formed on at least a part of the surface of the main phase crystal grains. The material structure was obtained. As shown in Table 2, the coercive force was increased in all of the alloy powders for rare earth magnets of Examples 11 to 21. It was shown that the coercive force improving effect can be obtained regardless of the M element species and the R element species.

The embodiments of the present disclosure can be used in the production of rare earth magnets having main phase crystal grains of ThMn type ₁₂ compounds. Since such rare earth magnets can be suitably used for motors, actuators, and the like, they have various industrial uses.

Claims (4)

An alloy powder for rare earth magnets containing main phase crystal grains of a Fe-based ThMn _12- type compound.
The alloy powder for rare earth magnets contains main phase crystal grains in which a Zn-rich layer is formed on at least a part of the surface of the main phase crystal grains.
The Zn-rich layer is a CeCr ₂ Al ₂₀ type R (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ (R is at least selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids. An alloy powder for rare earth magnets, which is one and may contain Zr or Hf). Main phase crystal grains in which a Ga-rich layer is further formed are contained in at least a part of the surface of the Zn-rich layer.
The alloy powder for rare earth magnets according to claim 1, wherein the Ga-rich layer contains IrIn ₃ type (Fe, Co, Zn) Ga ₃ . The alloy powder for rare earth magnets according to claim 1 or 2, wherein the main phase crystal grains contain Cu. A rare earth alloy powder of composition formula RT _w M _z Cu _α , where R is at least one element selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanides, and T is Fe and /. Or Co, M is at least one of the structure stabilizing elements composed of Ti, V, Mo, W, Nb, and Ta, and w, z, and α are 8 ≦ w ≦ 12, 0.42 ≦, respectively. A step of preparing a rare earth alloy powder in which z <0.70 and 0.40 ≦ α ≦ 0.70, and
Composition Formula R _β (Fe, Co) _γ Ga _δ Zn _ε Zn-Ga alloy, R is at least one element selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids. Yes, there is a step of preparing a Zn—Ga based alloy in which 0 ≦ β <0.25, 0 ≦ γ <0.4, 0 <δ <1, 0 <ε <1, and
A step of mixing the rare earth alloy powder and the Zn—Ga based alloy and heating at 400 ° C. or higher and 800 ° C. or lower to form a Zn-rich layer on at least a part of the surface of the main phase crystal grains of the rare earth alloy powder. , Including
The Zn-rich layer is a CeCr ₂ Al ₂₀ type R (Fe, Co, Cu) ₂ (Ga, Zn) ₂₀ (R is at least selected from the group consisting of scandium (Sc), yttrium (Y), and lanthanoids. A method for producing an alloy powder for a rare earth magnet, which is one and may contain Zr or Hf).