JP6693392B2 - R- (Fe, Co) -B system sintered magnet and its manufacturing method - Google Patents

Description

  The present invention relates to an R— (Fe, Co) —B system sintered magnet having a high coercive force at high temperature and a method for manufacturing the same.

  Nd-Fe-B system sintered magnets (hereinafter referred to as Nd magnets) have been expanding their application range and production year by year as functional materials indispensable for energy saving and high functionality. In these applications, since it is used in a high temperature environment, the incorporated Nd magnet is required to have high residual magnetic flux density and heat resistance. On the other hand, since the coercive force of the Nd magnet is easily lowered due to the temperature rise, it is necessary to increase the coercive force at room temperature in advance so that the coercive force is maintained at the operating temperature.

As a method of increasing the coercive force of the Nd magnet, it is effective to replace a part of Nd of the main phase Nd ₂ Fe ₁₄ B compound with Dy or Tb, but these elements not only have a small resource reserve. However, there are risks that prices are unstable and fluctuations are large because the production areas that are commercially established are limited and also include geopolitical factors. From such a background, it is necessary to develop a new method of increasing the coercive force while suppressing the addition amount of Dy or Tb as much as possible or a new magnet composition of the R- (Fe, Co) -B magnet.
From this point of view, various methods have been conventionally proposed.

That is, in Patent Document 1 (Japanese Patent No. 3997413), R of 12 to 17% in atomic percentage (R is at least two or more of rare earth elements including Y, and Nd and Pr are essential), 0.1 to 3% Si, 5 to 5.9% B, 10% or less Co, and the balance Fe (provided that Fe is a substitution amount of 3 at% or less of Al, Ti, V, Cr, Mn, Substituted with one or more elements selected from Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, In, Sn, Sb, Hf, Ta, W, Pt, Au, Hg, Pb, Bi R- (Fe, Co) -B-based firing having a coercive force of at least 10 kOe or more, which has a composition of R ₂ (Fe, (Co), Si) ₁₄ B intermetallic compound as a main phase. The binder magnet does not contain a B-rich phase and has an atomic percentage of 25 to 35% R, 2 ˜8% Si, 8% or less Co, balance R—Fe (Co) —Si grain boundary phase consisting of at least 1% or more by volume of R— (Fe, Co) —B based firing A binding magnet is disclosed. In this case, this sintered magnet is cooled at a rate of 0.1 to 5 ° C./min at least between 700 and 500 ° C. in the cooling step during sintering or during heat treatment after sintering. Alternatively, the R-Fe (Co) -Si grain boundary phase is formed in the structure by cooling by multi-stage cooling that maintains a constant temperature for at least 30 minutes during cooling.

Patent Document 2 (Japanese Patent Publication No. 2003-510467) discloses an Nd-Fe-B alloy having a low boron content. As a method for producing a permanent magnet from this alloy, after sintering raw material pieces, 300 It is described that the temperature is cooled to not higher than 0 ° C., and at that time, the average cooling rate is cooled to ΔT ₁ / Δt ₁ <5 K / min at 800 ° C. or higher.

Patent Document 3 (Japanese Patent No. 5572673) includes a main phase mainly containing R ₂ Fe ₁₄ B and a grain boundary phase containing more R than the main phase, and the grain boundary phase has a high rare earth element concentration. An R-T-B based magnet including a phase (R-rich phase) and a grain boundary phase (transition metal-rich phase) having a low rare earth element concentration and a high transition metal element concentration is described. It is described that the RTB-based rare earth sintered magnet is manufactured by performing heat treatment at 400 ° C. to 800 ° C. after performing at 800 ° C. to 1200 ° C.

  In Patent Document 4 (JP-A-2014-132628), the grain boundary phase has an R-rich phase in which the total atomic concentration of rare earth elements is 70 atomic% or more, and the total atomic concentration of the rare earth elements is 25 to 35 atomic%. And a transition metal-rich phase that is ferromagnetic, and an area ratio of the transition metal-rich phase in the grain boundary phase is 40% or more, an RTB-based rare earth sintered magnet is described. As a manufacturing method, a step of forming an RTB-based rare earth sintered magnet alloy material and sintering it at 800 ° C. to 1200 ° C., and a range of 650 ° C. to 900 ° C. after the sintering, It is described that a first heat treatment step of heating below the decomposition temperature of the metal-rich phase and a second heat treatment step of heating to 450 ° C. to 600 ° C. after cooling to 200 ° C. or lower after the first heat treatment step are described. There is.

Patent Document 5 (Japanese Unexamined Patent Publication No. 2014-146788) discloses a sintered body including a main phase composed of R ₂ Fe ₁₄ B and a grain boundary phase containing more R than the main phase, and the main phase Has a c-axis direction, the crystal grains of the main phase have an elliptical or elliptical shape extending in a direction intersecting the c-axis direction, and the grain boundary phase has a total atomic concentration of rare earth elements of 70 An R-T-B based rare earth sintered magnet is shown which contains an R rich phase of at least atomic% and a transition metal rich phase in which the total atomic concentration of the rare earth element is 25 to 35 atomic%. Moreover, it is described that the sintering is performed at 800 ° C. to 1200 ° C., and after the sintering, heat treatment is performed at 400 ° C. to 800 ° C. in an argon atmosphere.

Patent Document 6 (Japanese Unexamined Patent Publication No. 2014-209546) includes R ₂ T ₁₄ B main phase crystal grains and a two-particle grain boundary phase between two adjacent R ₂ T ₁₄ B main phase crystal grains, A rare earth magnet is disclosed, which has a thickness of the two-grain grain boundary phase of 5 nm or more and 500 nm or less and which has a magnetic property different from that of a ferromagnetic material. In addition, [0031] contains an element for forming a compound that does not become ferromagnetic while containing T element as a two-grain grain boundary phase. For this purpose, Al, Ge, Si, Sn, It is preferable to add an M element such as Ga, and by adding these elements in addition to Cu to the rare earth magnet, a La ₆ Co ₁₁ Ga ₃ type crystal structure having good crystallinity as a two-grain grain boundary phase is obtained. A crystal phase can be formed uniformly and widely, and an R—Cu thin layer can be formed at the interface between the La ₆ Co ₁₁ Ga ₃ type two-grain grain boundary phase and the R ₂ T ₁₄ B main-phase crystal grain, whereby the main phase is formed. It is described that the lattice strain at the interface can be suppressed and the generation of reverse magnetic domains can be suppressed. In this case, as a manufacturing method of this magnet, it is described that after sintering, heat treatment is performed in a temperature range of 500 ° C. to 900 ° C., but if the cooling rate is 100 ° C./min or more, particularly 300 ° C./min or more. It is said to be preferable.

In Patent Document 7 (International Publication No. 2014/157448) and Patent Document 8 (International Publication No. 2014/157451), an Nd ₂ Fe ₁₄ B-type compound is used as a main phase, and the main phase is between the two main phases. Disclosed is an RTB-based sintered magnet having 5 to 30 nm-thick intergranular grain boundaries that exist and grain boundary triple points that exist between three or more main phases.

Japanese Patent No. 3997413 Japanese Patent Publication No. 2003-510467 Japanese Patent No. 5572673 JP, 2014-132628, A JP, 2014-146788, A JP, 2014-209546, A International Publication No. 2014/157448 International Publication No. 2014/157451

  However, there is a demand for an R- (Fe, Co) -B system sintered magnet that exhibits a high coercive force at high temperatures even if it does not contain Dy or Tb or if the content of Dy or Tb is small.

  An object of the present invention is to provide a novel R- (Fe, Co) -B system sintered magnet having a high coercive force at room temperature and high temperature, and a method for producing the same, in response to the above-mentioned demand.

As a result of various studies to achieve such an object, the present inventors have shaped and sintered finely pulverized alloy powder for a sintered magnet, cooled it to a temperature of 400 ° C. or lower, and then 700 to 1000 ° C. a range contains the Pr 5 atomic% or more, and R ₂ as main phase (Fe, Co) ₁₄ B Pr content than the intermetallic compound is often R '- (Fe, Co) -M 1' phase and R '-(Fe, Co)-in the sintered body is heated to a temperature equal to or higher than the decomposition temperature (T _d ° C) of the compound composed of the same component, and then cooled to 400 ° C or lower at a rate of 5 to 100 ° C / min. A high temperature heat treatment step of eliminating the M ₁ 'phase to 1 volume% or less, and a temperature of 400 to 600 ° C and a temperature of T _d ° C or lower for 1 minute to 20 hours after the high temperature heat treatment step , R contained in the magnet body '- (Fe, Co) -M 1' precipitate than 80 vol% of phases And then perform a low temperature heat treatment step of cooling to 200 ° C. or lower, or cooling to 400 ° C. or lower at a rate of 5 to 100 ° C./min to obtain R ′-(Fe, Co) -M _{1 in the} sintered body. 'phase is lost less than 1% by volume, then held for 1 minute to 20 hours at and above T _d ° C. below the temperature range of 400 to 600 ° C., R included in the magnet body of the final product' - (Fe , Co) -M ₁ 'phase is deposited at 80% by volume or more, and then a low temperature heat treatment step of cooling to 200 ° C. or less is performed to form R ₂ (Fe, Co) ₁₄ B intermetallic compound as a main phase, includes M ₂ boride phase field triple point, free of R _1.1 Fe ₄ B ₄ compound phase, and the phase width of more than 50nm in mean R '- (Fe, Co) -M' phase the main phase 50 An R- (Fe, Co) -B system sintered magnet having a core / shell structure coated with at least volume% is obtained. It was found that this magnet can obtain a coercive force of 10 kOe or more, and it was found that such a sintered magnet maintains a high coercive force even at a high temperature and has excellent heat resistance. The present invention was completed by establishing the optimum composition.

In Patent Document 1, even if the cooling rate after sintering is slow and the R- (Fe, Co) -Si grain boundary phase forms a grain boundary triple point, in reality, R- (Fe, Co). The -Si grain boundary phase does not cover the main phase and does not form a two-grain grain boundary phase between adjacent main phases. Further, in Patent Document 2 as well, the cooling rate is similarly slow and the R- (Fe, Co) -M grain boundary phase does not give a structure in which the main phase is covered. Patent Document 3 does not show the cooling rate after sintering or after heat treatment, and in view of the description of the structure, the two-grain grain boundary phase is not formed. In Patent Document 4, the grain boundary phase includes an R-rich phase and a transition metal-rich phase that is a ferromagnetic phase with R of 25 to 35 atomic%, but the R- (Fe, Co) -M phase of the present invention is strong. It is an antiferromagnetic phase, not a magnetic phase. Further, while the first heat treatment of Patent Document 4 is performed at a decomposition temperature of the R- (Fe, Co) -M phase or lower, the high temperature heat treatment of the present invention is at least the decomposition temperature of the R- (Fe, Co) -M phase. This is what you do.
Patent Document 5 describes performing heat treatment at 400 to 800 ° C. in an argon atmosphere after sintering, but there is no description of the cooling rate, and from the description of the structure, R- (Fe , Co) -M phase does not have a structure covering the main phase. In Patent Document 6, it is said that the cooling rate after heat treatment is preferably 100 ° C./min or higher, particularly preferably 300 ° C./min or higher, and the R ₆ T ₁₃ M phase has crystallinity in the grain boundary phase of the obtained magnet, and It is composed of an amorphous or microcrystalline R-Cu phase. In the present invention, the R- (Fe, Co) -M phase is amorphous or microcrystalline.
Patent Document 7 has a problem that the thickness (phase width) of the first grain boundary is small and a sufficient improvement in coercive force cannot be obtained. In Patent Document 8 as well, since the method for manufacturing the sintered magnet described in the example is substantially the same as the method for manufacturing the magnet in Patent Document 7, the thickness (phase width) of the first grain boundary is similarly small. It is a thing.
Further, so far, there is no mention of the Pr content ratio and heat resistance in the R- (Fe, Co) -M phase of the present invention.

Therefore, the present invention provides the following R-Fe-B based sintered magnet and a method for producing the same.
[1]
12 to 17 atomic% of R (R is at least two kinds of rare earth elements including Y, and Nd and Pr are essential), 0.1 to 3 atomic% of M ₁ (M ₁ is Si, Al , Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi are two or more elements selected , and Si is essential. to), 0.05 to 0.5 atomic% of M ₂ (M ₂ is one or more elements selected Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, from W), 4.8 + 2 × m to 5.9 + 2 × m atomic% B (m is atomic% of M ₂ ), 10 atomic% or less Co, 0.5 atomic% or less carbon, 1.5 atomic% or less oxygen, 0.5 atomic % has the following composition of nitrogen and the balance Fe, an _{R 2 (Fe, Co) 14} B intermetallic compound as a main phase, at least 10k at room temperature R- (Fe, Co) having the above coercive force e a -B based sintered magnet includes M ₂ boride phase at the grain boundary triple point, and contains no R _1.1 Fe ₄ B ₄ compound phase, Further, 25 to 35 atom% of R '(requires at least 5 atom% of R's Pr, the balance is a rare earth element containing Nd and Y, and the content of Pr in R'is R ₂ as a main phase. (Fe, Co) ₁₄ B is more than Pr content in the intermetallic compound), 2 to 8 atomic% of M ₁ ′ (M ₁ ′ , Si occupies 0.5 to 50 atomic%, balance is Al , Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi), Co of 8 atomic% or less, amorphous and / or microcrystalline the balance being Fe R '- (Fe, Co ) -M 1' phase, or the R '- (Fe, Co) -M 1' phase and 'Amorphous than 50 atomic% or microcrystalline R'-M ₁ "phase (M _1" of Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn , Sb, Pt, Au, Hg, Pb, Bi) and a core / shell structure in which the main phase is covered with a grain boundary phase of R ′-(Fe, The coverage of the Co) -M ₁ 'phase with respect to the main phase is 50% by volume or more, and the width of the grain boundary phase sandwiched between the two main phase particles is 50 nm or more on average. R- (Fe, Co) -B system sintered magnet.
[ 2 ]
Ga accounts for 1.0 to 80 atomic% as M ₁ 'in the R'-(Fe, Co) -M ₁ 'phase, and the balance is Si, Al, Mn, Ni, Cu, Zn, Ge, Pd, Ag. , Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi, one or more elements selected from the R- (Fe, Co) -B system sintering described in [1]. magnet.
[ 3 ]
Al accounts for 0.5 to 50 atomic% as M ₁ 'in the R'-(Fe, Co) -M ₁ 'phase, and the balance is Si, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag. , Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi, one or more elements selected from the R- (Fe, Co) -B system sintering described in [1]. magnet.
[ 4 ]
Cu accounts for 0.5 to 50 atomic% as M ₁ 'in the R'-(Fe, Co) -M ₁ 'phase, and the balance is Si, Al, Mn, Ni, Zn, Ga, Ge, Pd, Ag. , Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi, one or more elements selected from the R- (Fe, Co) -B system sintering described in [1]. magnet.
[ 5 ]
The R-Fe-B system sintered magnet according to any one of [1] to [ 4 ], wherein the total content of Dy, Tb, and Ho is 5.5 atomic% or less.
[ 6 ]
A method for producing the R- (Fe, Co) -B system sintered magnet according to any one of [1] to [5], comprising:
12 to 17 atomic% R (R is at least two kinds of rare earth elements including Y, and Nd and Pr are essential), 0.1 to 3 atomic% M ₁ (M ₁ is Si, Al , Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi are two or more elements selected , and Si is essential. to), 0.05 to 0.5 atomic% of M ₂ (M ₂ is one or more elements selected Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, from W), 4.8 + 2 × m-5.9 + 2 × m atomic% B (m is atomic% of M ₂ ), 10 atomic% or less Co, and balance Fe composition, and finely pulverized to an average fine particle diameter of 5.0 μm or less. The alloy powder for a sintered magnet is molded, sintered at a temperature of 1000 to 1150 ° C., cooled to a temperature of 400 ° C. or lower, and then Wherein in the range of 00~1000 ℃ R '- (Fe, Co) -M 1' decomposition temperatures (T _d ° C.) of the phase and compounds having the same ingredients were heated above, then up to 400 ° C. or less 5-100 ° C. / cooled at a rate, R in the sintered body '- (Fe, Co) -M 1' and the high-temperature heat treatment step of eliminating phase below 1 vol%, 400 to 600 ° C. after this high-temperature heat treatment step 1 minute by holding to 20 hours in the range a and T _d ° C. below the temperature of, R included in the magnet body produced '- (Fe, Co) -M 1' to precipitate more than 80% by volume of phase , then 200 ° C. you and performing low temperature heat treatment step of cooling to below R - (Fe, Co) -B based sintered magnet manufacturing method of.
[ 7 ]
A method for producing the R- (Fe, Co) -B system sintered magnet according to any one of [1] to [5], comprising:
12 to 17 atomic% R (R is at least two kinds of rare earth elements including Y, and Nd and Pr are essential), 0.1 to 3 atomic% M ₁ (M ₁ is Si, Al , Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi are two or more elements selected , and Si is essential. to), 0.05 to 0.5 atomic% of M ₂ (M ₂ is one or more elements selected Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, from W), 4.8 + 2 × m-5.9 + 2 × m atomic% B (m is atomic% of M ₂ ), 10 atomic% or less Co, and balance Fe composition, and finely pulverized to an average fine particle diameter of 5.0 μm or less. The alloy powder for a sintered magnet is molded and sintered at a temperature of 1000 to 1150 ° C., and then a speed of 5 to 100 ° C./min up to 400 ° C. or less. In cooled, R '- (Fe, Co ) -M 1' content of phase to give a 1% by volume or less of the sintered body, followed by 400 to 600 in the range of ℃ and the R '- (Fe, Co ) -M ₁ 'phase and a hold for 1 minute to 20 hours at a decomposition temperature (T _d ° C.) below the temperature of the compound of the same components, R included in the magnet body produced' - (Fe, Co) - M ₁ 'is deposited over 80% by volume of phase, then 200 ° C. you and performing low temperature heat treatment step of cooling to below R - (Fe, Co) -B based sintered magnet manufacturing method of.
[ 8 ]
Content of Dy and / or Tb in the said alloy for sintered magnets is 0-5.0 atomic%, The R- (Fe, Co) -B type | system | group sintered magnet of Claim 6 or 7 characterized by the above-mentioned. Manufacturing method.

  The R- (Fe, Co) -B system sintered magnet of the present invention gives a coercive force of 10 kOe or more even if it does not contain Dy and Tb or has a small content of Dy and Tb.

3 is a view (magnification: 3000 times) of the cross section of the sintered magnet produced in Example 1, observed by an electron probe microanalyzer (EPMA). FIG. FIG. 3 is a diagram in which a grain boundary phase of the sintered magnet manufactured in Example 1 is observed with a transmission electron microscope.

Hereinafter, the present invention will be described in more detail.
First, the magnet composition of the present invention will be described. In terms of atomic percentage, R of 12 to 17 atom%, preferably 13 to 16 atom% of R, 0.1 to 3 atom% of M ₁ , and preferably 0.5 to 2 are used. 0.5 atomic% M ₁ , 0.05 to 0.5 atomic% M ₂ , preferably 0.07 to 0.4 atomic% M ₂ , 4.8 + 2 × m to 5.9 + 2 × m atomic%. B, preferably 4.9 + 2 × m to 5.7 + 2 × m atomic% B (m is atomic% of M ₂ ), 10 atomic% or less Co, and the balance Fe.

  Here, R is at least two kinds of rare earth elements including Y, and Nd and Pr are essential. The total ratio of Nd and Pr is preferably 80 to 100 atom%. When the atomic percentage of R is less than 12 atomic%, the coercive force of the magnet is extremely reduced, and when it exceeds 17 atomic%, the residual magnetic flux density Br is reduced. It should be noted that R may not contain Dy and Tb, and when it is contained, the total amount of Dy and Tb is 5.0 atomic% or less (0 to 5.0 atomic%), preferably 2.0 atomic% or less. (0 to 2.0 atom%), particularly 1.5 atom% or less (0 to 1.5 atom%).

M ₁ is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi. And is added as an element that constitutes the R ′-(Fe, Co) -M ₁ ′ phase and the R′-M ₁ ″ phase. When M ₁ is less than 0.1 atomic%, the amount of R ′-(Fe, Co) -M ₁ ′ phase generated in the sintered body is small and the main phase R ₂ (Fe, Co) ₁₄ B phase is sufficiently contained. Since it cannot be covered, the squareness deteriorates. Further, the width of the grain boundary phase is reduced, and the expected effect of improving the coercive force cannot be obtained, which is not preferable. Further, when M ₁ exceeds 3 atomic%, the residual magnetic flux density Br decreases, which is not preferable.

M ₂ is composed of one or more elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W, and is the main phase R ₂ (Fe, Co) ₁₄ B phase in the sintered magnet. It is added as an element that forms a more thermodynamically stable boride (for example, TiB ₂ , ZrB ₂ , NbB _2, etc.). This boride is generated at the grain boundary triple points in the sintered magnet, and has an effect of suppressing abnormal grain growth of main phase crystal grains during sintering. An effect of suppressing the squareness, which is exacerbated by the occurrence of abnormal grain growth, can be expected. Further, with the B content of this system composition, the primary crystal α-Fe tends to remain excessively in the raw material alloy, and as a result, the squareness of the sintered magnet deteriorates. As a result of suppressing the precipitation of the α-Fe phase by adding M ₂ , there is an effect of improving the squareness of the sintered magnet. When M ₂ is less than 0.05 atomic%, the amount of boride formed in the magnet is small and the effect of improving the squareness is small, which is not preferable. If it exceeds 0.5 atom%, the residual magnetic flux density Br decreases, which is not preferable.
The amount of B is in the range of 4.8 + 2 × m to 5.9 + 2 × m at%, and when the amount of B is more than 5.9 + 2 × m at%, an R ′-(Fe, Co) -M ₁ ′ phase is produced. If not, the coercive force will decrease. When it is less than 4.8 + 2 × m atom%, the residual magnetic flux density Br is significantly reduced, which is not preferable.

  Co may not be contained, but 10 atom% or less, preferably 5 atom% or less may be added for the purpose of improving the Curie temperature and corrosion resistance. This is not preferable because it causes a significant decrease in

  The magnet of the present invention preferably has a low content of oxygen, carbon, and nitrogen, but it is inevitable to mix in the manufacturing process, and the oxygen content is 1.5 atomic% or less, particularly 1.2 atomic% or less. A carbon content of up to 0.5 atom%, especially up to 0.4 atom%, and a nitrogen content of up to 0.5 atom%, especially up to 0.3 atom%, are acceptable. In addition, as impurities, elements such as H, F, Mg, P, S, Cl and Ca are allowed to be contained in an amount of 0.1% by mass or less, but it is preferable that these elements are also small.

  Although the amount of Fe is the balance, it is preferably 70 to 80 atom%, particularly preferably 75 to 80 atom%.

The structure of the magnet of the present invention has the R ₂ (Fe, Co) ₁₄ B phase as the main phase, and the grain boundary phase essentially contains 25 to 35 atomic% of R ′ (5 atomic% or more of Pr of R ′ is essential). The balance is a rare earth element containing Nd and Y, and the Pr content in R ′ is higher than the Pr content in the R ₂ (Fe, Co) ₁₄ B intermetallic compound as the main phase), 2 to 8 Atomic% M ₁ '(M ₁ ' is selected from Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi. At least one element), 8 atomic% or less of Co, the balance Fe and an amorphous and / or microcrystalline R ′-(Fe, Co) -M ₁ ′ phase, and R ′ of 50 atomic% or more. R'-M ₁ '' phase (M ₁ 'amorphous or microcrystalline' is Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Consists d, In, Sn, Sb, Pt, Au, Hg, Pb, 1 or more elements selected from Bi) and. At the grain boundary triple point, the R oxide phase of the high melting point compound, or the R carbide phase, the R nitride phase, the R oxyfluoride phase and their mixed phase, and the M ₂ boride phase (for example, TiB ₂ , ZrB ₂ , NbB ₂ ) are formed. On the other hand, the R ₂ (Fe, Co) ₁₇ phase and the R _1.1 Fe ₄ B ₄ compound phase do not exist.

The R '- (Fe, Co) -M 1' grain boundary phase is a compound containing Fe, or Fe and Co, it is considered to be an intermetallic compound phase having I4 / mcm becomes crystal structure, for example R ₆ such as Fe ₁₃ Ga ₁ can be mentioned. When quantitative analysis using an analytical technique such as electron probe microanalyzer (EPMA), 25 to 35 atomic%, including the measurement error R ', 2 to 8 atom% of M _1', 0 to 8 atomic% of Co , The balance is Fe. In some cases, the magnet composition does not include Co, but at this time, the main phase and the R ′-(Fe, Co) -M ₁ ′ grain boundary phase naturally do not include Co. By distributing the same phase in a grain boundary phase such as a two-grain grain boundary phase so as to cover the main phase, the adjacent main phases are magnetically separated, so that the coercive force can be improved.

R '- (Fe, Co) -M 1' grain boundary phase, the main phase R ₂ (Fe, Co) ₁₄ becomes a liquid phase in the B phase and the high temperature R'-M ₁ peritectic reaction with '' It is thought to be generated by. That is, R ′-(Fe, Co) -M ₁ ′ forms a stable phase below this peritectic point. R - peritectic point of _{'(Fe, Co) -M 1} ' depends on the type of additive element M ₁ '. For example, when R ′ = 100% Nd, 640 ° C. when M ₁ ′ = Cu, 750 to 820 ° C. when M ₁ ′ = Al, 850 ° C. when M ₁ ′ = Ga, 890 ° C. when M ₁ ′ = Si ℃, when M ₁ '= Sn is 1080 ℃.

R ′-(Fe, Co) -M ₁ ′ It is preferable that Pr of 5 atom% or more is contained in R ′ constituting the grain boundary phase. Generally, Pr is added from the viewpoint of improving the coercive force in order to improve the anisotropic magnetic field of the R ₂ Fe ₁₄ B compound of the main phase, but the temperature coefficient of coercive force (β [% / ° C.]) decreases. , The coercive force decreases at high temperature. On the other hand, in the R ′-(Fe, Co) -M ₁ ′ phase formed in the present magnet, Pr is more stable than Nd, so that the R ′-(Fe, Co) -M ₁ ′ medium Has a higher concentration than the Pr content of the main phase, and the Pr content of the R ₂ (Fe, Co) ₁₄ B phase of the main phase relatively decreases. It has been found that this compositional distribution of Pr enhances the coercive force at room temperature and at the same time maintains a high coercive force even at high temperature. Moreover R '- (Fe, Co) -M 1' by Pr amount increases in, R '- (Fe, Co) -M 1' peritectic point of phase is lowered, cover the main phase described below The R ′-(Fe, Co) -M ₁ ′ phase precipitation conditions for the purpose can be relaxed. For example, in the case of R ′ = 78 atomic% Nd + 22 atomic% Pr, the temperature becomes 810 ° C. when M ₁ ′ = Ga.

When the R ′-(Fe, Co) -M ₁ ′ phase is distributed in the grain boundary between two particles, the average phase width is preferably 50 nm or more. The average value is more preferably 50 to 500 nm, still more preferably the average value is 100 to 500 nm. If the phase width is narrower than 50 nm on average, sufficient effect of improving coercive force due to magnetic separation cannot be obtained.

The R ′-(Fe, Co) -M ₁ ′ phase is present as a two-grain grain boundary phase between the adjacent main phases as described above, and exists so as to cover the main phase, so to speak, it is a core. / Form a shell structure. The coverage of the main phase with the R ′-(Fe, Co) -M ₁ ′ grain boundary phase is 50% by volume or more, preferably 60% by volume or more, more preferably 70% by volume or more, and the entire main phase is coated. You may. Note that the remainder of the second grain grain boundary phase that covers the main phase R 'is R'-M 1 of 50 _atom%' is' phase.

The R ′-(Fe, Co) -M ₁ ′ phase is amorphous or microcrystalline, or microcrystalline containing amorphous, and the R′-M ₁ ″ phase is amorphous or microcrystalline. In the present invention, microcrystalline refers to a group of crystals oriented in a plurality of directions within an electron irradiation diameter range observed by a transmission electron microscope, the size of the crystal is approximately 10 nm or less, and crystalline refers to an electron irradiation diameter range. It is defined as a single crystal body oriented in one direction and having a crystal size of more than about 10 nm.

The average crystal grain size of the magnet of the present invention is 6 μm or less, preferably 1.5 to 5.5 μm, more preferably 2.0 to 5.0 μm from the viewpoint of improving coercive force, and the degree of C-axis orientation of the main phase is It is preferably at least 98%. The average crystal grain size is measured by the following procedure. First, the cross section of the sintered magnet is polished to a mirror surface, and then the surface where the grain boundaries are selectively etched using, for example, a villera solution (mixed solution of glycerin: nitric acid: hydrochloric acid at a mixing ratio of 3: 1: 2) is prepared. Observe with a laser microscope. Based on the obtained observation image, the cross-sectional area of each particle is measured by image analysis, and the diameter as an equivalent circle is calculated. The average particle size is calculated based on the data of the area fraction occupied by each particle size.
The average grain size of the sintered body is controlled by lowering the average grain size of the sintered magnet alloy powder during fine pulverization.

  The magnetization rate of the sintered magnet of the present invention is 96% or more, and particularly 97% or more. The magnetic susceptibility is defined as the magnetic polarization at Pc = 1 when a magnetic field of 640 kA / m is applied parallel to the magnetization orientation direction from the thermal demagnetization state, and a magnetic field of 1590 kA / m from the thermal demagnetization state parallel to the magnetization orientation direction. It is standardized and calculated by the magnetic polarization at Pc = 1 when applied.

In order to obtain the R- (Fe, Co) -B system sintered magnet having the above structure of the present invention, the mother alloy is first coarsely pulverized, finely pulverized, molded and sintered according to a conventional method.
The mother alloy can be obtained by melting a raw material metal or alloy in a vacuum or an inert gas, preferably Ar atmosphere, and then casting it into a flat mold or a book mold, or casting by strip casting. Further, a mother alloy having a composition close to that of the main phase R _2- (Fe, Co) ₁₄ -B ₁ phase and a sintering aid alloy having an R-rich composition as a liquid phase at the sintering temperature are separately prepared. However, a so-called two-alloy method in which coarse pulverization is followed by weighing and mixing is also applicable to the present invention. In this case, in the cast alloy, α-Fe tends to remain depending on the cooling rate at the time of casting. Therefore, in order to increase the amount of the R ₂ — (Fe, Co) ₁₄ —B ₁ phase, if necessary, A homogenization treatment is performed by performing heat treatment at 700 to 1200 ° C. for 1 hour or more in a vacuum or an Ar atmosphere. For the sintering aid alloy, a so-called liquid quenching method can be applied in addition to the casting method.

  The above alloy is generally crushed to a size of 0.05 to 3 mm, especially 0.05 to 1.5 mm. A brown mill, hydrogen crushing or the like is used in the coarse crushing step, and hydrogen crushing is preferable in the case of an alloy produced by strip casting. The coarse powder is usually finely pulverized to 5 μm or less by, for example, a jet mill using high pressure nitrogen. The oxygen concentration is controlled by lowering the oxygen concentration and water content during fine pulverization. If necessary, an additive such as a lubricant can be added in any of the steps of coarse crushing, mixing, and fine crushing of the alloy.

In this case, the alloy composition is 12 to 17 atomic% R (R is at least two kinds of rare earth elements including Y, and Nd and Pr are essential), 0.1 to 3 atomic% M ₁ (M ₁ is one or more elements selected from Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi). , 0.05 to 0.5 atomic% M ₂ (M ₂ is one or more elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W), 4.8 + 2 × m The composition is 5.9 + 2 × m atomic% B (m is atomic% of M ₂ ), 10 atomic% or less Co, and the balance Fe.

  The above-mentioned finely pulverized R- (Fe, Co) -B based alloy for sintered magnet is molded in a magnetic field compression molding machine and sintered. Sintering is preferably performed at 900 to 1250 ° C., particularly at 1000 to 1150 ° C. in a vacuum or an inert gas atmosphere for 0.5 to 5 hours.

In the present invention, the first method of obtaining a sintered magnet having the above-mentioned texture is to sinter the molded body as described above and then cool it to 400 ° C or lower, particularly 300 ° C or lower (usually room temperature). The cooling rate in this case is not particularly limited. Next, it is heated in the range of 700 to 1000 ° C. to the decomposition temperature (Td ° C.) or higher of the compound composed of the same components as the R ′-(Fe, Co) -M ₁ ′ phase. The heating rate in this case is also not particularly limited, but is preferably 1 to 20 ° C./min, and particularly 2 to 10 ° C./min. As described above, the decomposition temperature depends on the type of the additional element M. The holding time at the above temperature is preferably 1 hour or longer, more preferably 1 to 10 hours, further preferably 1 to 5 hours. The heat treatment atmosphere is preferably vacuum or an inert gas atmosphere such as Ar gas.

After the above high temperature heat treatment, it is cooled to 400 ° C. or lower, particularly 300 ° C. or lower. In this case, the cooling rate up to at least 400 ° C. is 5 to 100 ° C./min, preferably 5 to 80 ° C./min, and more preferably 5 to 50 ° C./min. In the structure after cooling, the R ′-(Fe, Co) -M ₁ ′ phase disappeared to 1 volume% or less, and the R ₂ (Fe, Co) ₁₄ B phase and the R′-M ₁ ″ phase were mainly contained. , R oxide phase, and M ₂ boride phase, and may simultaneously include R carbide phase, R nitride phase, R oxyfluoride phase, or a mixed phase thereof. If the cooling rate is less than 5 ° C./min, the R ′-(Fe, Co) -M ₁ ′ phase excessively precipitates and segregates largely at the grain boundary triple points, resulting in a large decrease in magnetic properties. Will end up. On the other hand, a cooling rate of more than 100 ° C./min can suppress the precipitation of the R ′-(Fe, Co) -M ₁ ′ phase in the cooling process, but after cooling, the R′-M ₁ ″ phase becomes grain boundary. Since it segregates into three points, the R ′-(Fe, Co) -M ₁ ′ phase and the R′-M ₁ ″ phase are continuously and uniformly precipitated in the intergranular grain boundary phase in the subsequent low temperature heat treatment, Cannot be distributed.

Next, R in the range of 400 to 600 ° C. after the high-temperature heat treatment step '- (Fe, Co) -M 1' holds the decomposition temperature below the temperature of the phase R '- (Fe, Co) -M 1' A low temperature heat treatment step of precipitating the phase and then cooling to 200 ° C. or lower is performed. In this case, the heating rate to the temperature range of 400 to 600 ° C. is not particularly limited. This low temperature heat treatment is carried out at 400 to 600 ° C., more preferably 400 to 550 ° C., further preferably 450 to 550 ° C. for 1 to 50 hours, more preferably 1 to 20 hours in a vacuum or an inert gas atmosphere. desirable. Previously mentioned R '- (Fe, Co) -M 1' below the decomposition temperature of the grain boundary phase, the low-temperature R - By _{'(Fe, Co) -M 1} ' precipitating a grain boundary phase, the main phase the R '- (Fe, Co) -M 1' coated with the grain boundary phase structure is obtained. If it is less than 400 ° C, the reaction rate is too slow to be practical. On the other hand, when the temperature exceeds 600 ° C., the reaction rate is fast, and the R ′-(Fe, Co) -M ₁ ′ grain boundary phase is excessively precipitated and largely segregated at the grain boundary triple point, resulting in the magnetic properties being reduced. Will greatly reduce.

A second method of obtaining a sintered magnet having the above-mentioned structure is to cool the sintered magnet to 400 ° C. or lower, particularly 300 ° C. or lower after sintering as described above. In this case, the cooling rate is important. Then, the cooling rate up to at least 400 ° C. is 5 to 100 ° C./min, preferably 5 to 80 ° C./min, and more preferably 5 to 50 ° C./min. The problems when the cooling rate is too slow or too fast are the same as in the case of the cooling rate after the high temperature heat treatment of the first method. By cooling to 400 ° C. or less, a structure having a volume fraction of the R ′-(Fe, Co) -M ₁ ′ phase of 1 vol% or less can be obtained.

Next, after cooling as described above, the same heat treatment as the low temperature heat treatment in the first method is performed. I.e., R in the range of 400~600 ℃ '- (Fe, Co ) -M 1' holds the decomposition temperature below the temperature of the phase R '- (Fe, Co) -M 1' phase is precipitated. The method, conditions, etc. are the same as those in the case of the low temperature heat treatment of the first method, and therefore the description thereof will be omitted.

  Examples and comparative examples for the present invention will be specifically described below, but the present invention is not limited to the following examples.

[Examples 1 to 3, Reference Example 1 , Comparative Examples 1 to 3]
R metal (R is Nd and Pr, or didymium), electrolytic iron, Co, other metals and ferroboron, which are weighed so as to have a predetermined composition, are used. An alloy ribbon having a thickness of 2 to 0.3 mm was produced. Next, the produced alloy ribbon was subjected to hydrogen absorption treatment at room temperature, and then heated at 600 ° C. in vacuum for dehydrogenation. 0.07% by mass of stearic acid as a lubricant was added to and mixed with the obtained alloy powder. Next, the obtained coarse powder was finely pulverized with a jet mill in a nitrogen stream to produce fine powder having an average particle size of about 3 μm. Then, these fine powders were filled in a mold of a molding apparatus in an inert gas atmosphere, and pressure-molded in a direction perpendicular to the magnetic field while orienting in a magnetic field of 15 kOe. The compact was sintered in vacuum at 1050-1100 ° C. for 3 hours. The obtained sintered body was cooled to 400 ° C. or lower, subjected to high temperature heat treatment of 900 ° C. for 1 hour, cooled to 200 ° C., further low temperature heat treatment for 2 hours, and cooled to 200 ° C. or lower. Table 1 shows the composition of the magnet, and Table 2 shows the cooling rate up to 200 ° C. after the high temperature heat treatment at 900 ° C., the low temperature heat treatment temperature, the magnetic properties and the structure morphology after the low temperature heat treatment.
When the cross section of the sintered magnet produced in Example 1 was observed with an electron probe microanalyzer (EPMA), as shown in FIG. 1, the structure of Example 1 had a grain boundary phase richer in Pr than the main phase. A structure covering the main phase was observed (note that in FIG. 1, TRE represents the total rare earth content). In addition, in the figure showing Pr / (total rare earth content), Pr is darker on the black side. When the structure of Example 1 was observed with a transmission electron microscope (TEM), the thickness of the grain boundary phase was about 50 to 130 nm as shown in FIG. In Table 3, semi-quantitative values by EDX of the R′-M ₁ ″ phase and R ′-(Fe, Co) -M ₁ ′ phase and the main phase of Examples 1 to 3, Reference Example 1 and Comparative Examples 1 to 3 are shown. Indicates. As a result, Examples 1 to 3, R'-M ₁ 'in Reference Example 1' phase and R '- (Fe, Co) content of Pr in -M _1' phase was higher than that of the main phase.

Claims (8)

12 to 17 atomic% of R (R is at least two kinds of rare earth elements including Y, and Nd and Pr are essential), 0.1 to 3 atomic% of M ₁ (M ₁ is Si, Al , Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi are two or more elements selected , and Si is essential. to), 0.05 to 0.5 atomic% of M ₂ (M ₂ is one or more elements selected Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, from W), 4.8 + 2 × m to 5.9 + 2 × m atomic% B (m is atomic% of M ₂ ), 10 atomic% or less Co, 0.5 atomic% or less carbon, 1.5 atomic% or less oxygen, 0.5 atomic % has the following composition of nitrogen and the balance Fe, an _{R 2 (Fe, Co) 14} B intermetallic compound as a main phase, at least 10k at room temperature R- (Fe, Co) having the above coercive force e a -B based sintered magnet includes M ₂ boride phase at the grain boundary triple point, and contains no R _1.1 Fe ₄ B ₄ compound phase, Further, 25 to 35 atom% of R '(requires at least 5 atom% of R's Pr, the balance is a rare earth element containing Nd and Y, and the content of Pr in R'is R ₂ as a main phase. (Fe, Co) ₁₄ B is more than Pr content in the intermetallic compound), 2 to 8 atomic% of M ₁ ′ (M ₁ ′ , Si occupies 0.5 to 50 atomic%, balance is Al , Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi), Co of 8 atomic% or less, amorphous and / or microcrystalline the balance being Fe R '- (Fe, Co ) -M 1' phase, or the R '- (Fe, Co) -M 1' phase and 'Amorphous than 50 atomic% or microcrystalline R'-M ₁ "phase (M _1" of Si, Al, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn , Sb, Pt, Au, Hg, Pb, Bi) and a core / shell structure in which the main phase is covered with a grain boundary phase of R ′-(Fe, The coverage of the Co) -M ₁ 'phase with respect to the main phase is 50% by volume or more, and the width of the grain boundary phase sandwiched between the two main phase particles is 50 nm or more on average. R- (Fe, Co) -B system sintered magnet. Ga accounts for 1.0 to 80 atomic% as M ₁ 'in the R'-(Fe, Co) -M ₁ 'phase, and the balance is Si, Al, Mn, Ni, Cu, Zn, Ge, Pd, Ag. 2. The R- (Fe, Co) -B based sintering according to claim 1, wherein the R- (Fe, Co) -B system is one or more kinds of elements selected from Cd, In, Sn, Sb, Pt, Au, Hg, Pb and Bi. magnet. Al accounts for 0.5 to 50 atomic% as M ₁ 'in the R'-(Fe, Co) -M ₁ 'phase, and the balance is Si, Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag. 2. The R- (Fe, Co) -B based sintering according to claim 1, wherein the R- (Fe, Co) -B system is one or more kinds of elements selected from Cd, In, Sn, Sb, Pt, Au, Hg, Pb and Bi. magnet. Cu accounts for 0.5 to 50 atomic% as M ₁ 'in the R'-(Fe, Co) -M ₁ 'phase, and the balance is Si, Al, Mn, Ni, Zn, Ga, Ge, Pd, Ag. 2. The R- (Fe, Co) -B based sintering according to claim 1, wherein the R- (Fe, Co) -B system is one or more kinds of elements selected from Cd, In, Sn, Sb, Pt, Au, Hg, Pb and Bi. magnet. Dy and / or Tb claim 1 or one of claims R- (Fe, Co) of 4 content characterized in that it is a 0 to 5.0 atomic% of -B based sintered magnet. A method for producing the R- (Fe, Co) -B system sintered magnet according to claim 1.
12 to 17 atomic% R (R is at least two kinds of rare earth elements including Y, and Nd and Pr are essential), 0.1 to 3 atomic% M ₁ (M ₁ is Si, Al , Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi are two or more elements selected , and Si is essential. to), 0.05 to 0.5 atomic% of M ₂ (M ₂ is one or more elements selected Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, from W), 4.8 + 2 × m-5.9 + 2 × m atomic% B (m is atomic% of M ₂ ), 10 atomic% or less Co, and balance Fe composition, and finely pulverized to an average fine particle diameter of 5.0 μm or less. The alloy powder for a sintered magnet is molded, sintered at a temperature of 1000 to 1150 ° C., cooled to a temperature of 400 ° C. or lower, and then Wherein in the range of 00~1000 ℃ R '- (Fe, Co) -M 1' decomposition temperatures (T _d ° C.) of the phase and compounds having the same ingredients were heated above, then up to 400 ° C. or less 5-100 ° C. / cooled at a rate, R in the sintered body '- (Fe, Co) -M 1' and the high-temperature heat treatment step of eliminating phase below 1 vol%, 400 to 600 ° C. after this high-temperature heat treatment step 1 minute by holding to 20 hours in the range a and T _d ° C. below the temperature of, R included in the magnet body produced '- (Fe, Co) -M 1' to precipitate more than 80% by volume of phase , then 200 ° C. you and performing low temperature heat treatment step of cooling to below R - (Fe, Co) -B based sintered magnet manufacturing method of. A method for producing the R- (Fe, Co) -B system sintered magnet according to claim 1.
12 to 17 atomic% R (R is at least two kinds of rare earth elements including Y, and Nd and Pr are essential), 0.1 to 3 atomic% M ₁ (M ₁ is Si, Al , Mn, Ni, Cu, Zn, Ga, Ge, Pd, Ag, Cd, In, Sn, Sb, Pt, Au, Hg, Pb, Bi are two or more elements selected , and Si is essential. to), 0.05 to 0.5 atomic% of M ₂ (M ₂ is one or more elements selected Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, from W), 4.8 + 2 × m-5.9 + 2 × m atomic% B (m is atomic% of M ₂ ), 10 atomic% or less Co, and balance Fe composition, and finely pulverized to an average fine particle diameter of 5.0 μm or less. The alloy powder for a sintered magnet is molded and sintered at a temperature of 1000 to 1150 ° C., and then a speed of 5 to 100 ° C./min up to 400 ° C. or less. In cooled, R '- (Fe, Co ) -M 1' content of phase to give a 1% by volume or less of the sintered body, followed by 400 to 600 in the range of ℃ and the R '- (Fe, Co ) -M ₁ 'phase and a hold for 1 minute to 20 hours at a decomposition temperature (T _d ° C.) below the temperature of the compound of the same components, R included in the magnet body produced' - (Fe, Co) - M ₁ 'is deposited over 80% by volume of phase, then 200 ° C. you and performing low temperature heat treatment step of cooling to below R - (Fe, Co) -B based sintered magnet manufacturing method of. Content of Dy and / or Tb in the said alloy for sintered magnets is 0-5.0 atomic%, The R- (Fe, Co) -B type | system | group sintered magnet of Claim 6 or 7 characterized by the above-mentioned. Manufacturing method.