JP7380369B2 - Manufacturing method of RTB sintered magnet and alloy for diffusion - Google Patents

Description

The present invention relates to a method for manufacturing an RTB sintered magnet and a diffusion alloy.

RTB system sintered magnet (R is at least one rare earth element and always contains at least one of Nd and Pr; T is Fe or Fe and Co; B is boron) is a permanent magnet It is known as the highest performance magnet in the world, and is used in various motors such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV, etc.), motors for industrial equipment, and home appliances. It is used.

The RTB-based sintered magnet is composed of a main phase mainly composed of an R ₂ T ₁₄ B compound and a grain boundary phase located at the grain boundaries of this main phase. The R ₂ T ₁₄ B compound, which is the main phase, is a ferromagnetic material with high saturation magnetization and anisotropic magnetic field, and is the basis of the characteristics of RTB-based sintered magnets.

RTB-based sintered magnets have a problem in that irreversible thermal demagnetization occurs because the coercive force H _cJ (hereinafter sometimes simply referred to as "coercive force" or "H _cJ ") decreases at high temperatures. Therefore, RTB-based sintered magnets used particularly in electric vehicle motors are required to have high H _cJ even at high temperatures, that is, to have higher H _cJ at room temperature.

International Publication No. 2007/102391 International Publication No. 2016/133071 International Publication No. 2018/143230 JP2019-169695

It is known that when Nd, which is a light rare earth element RL in the R ₂ T ₁₄ B-type compound phase, is replaced with a heavy rare earth element (mainly Dy and Tb), H _cJ is improved. However, in RTB-based sintered magnets, when light rare earth elements (mainly Nd and Pr) are replaced with heavy rare earth elements, H _cJ improves, but the saturation magnetization of the R ₂ T ₁₄ B-type compound phase decreases. Therefore, there is a problem in that the residual magnetic flux density B _r (hereinafter sometimes simply referred to as "residual magnetic flux density" or "B _r ") decreases.

Patent Document 1 describes that a heavy rare earth element such as Dy is supplied to the surface of a sintered magnet made of an RTB alloy, and the heavy rare earth element is diffused into the inside of the sintered magnet. The method described in Patent Document 1 diffuses Dy from the surface of the RTB-based sintered magnet into the interior, and concentrates Dy only in the outer shell of the main phase crystal grains, which is effective for improving H _cJ . By doing so, high H _cJ can be obtained while suppressing a decrease in B _r .
However, heavy rare earth elements such as Dy in particular have problems such as unstable supply and large fluctuations in price due to the limited amount of resources and limited production areas. There is. Therefore, in recent years, it has been desired to improve H _cJ without using heavy rare earth elements as much as possible.

For example, in Patent Document 2, R-Ga-Cu of a specific composition is coated on the surface of an R-T-B based sintered body with a lower amount of B than usual (below the stoichiometric ratio of the R ₂ T ₁₄ B compound). By bringing the alloys into contact and performing heat treatment at a temperature of 450°C or higher and 600°C or lower, H _cJ can be improved by controlling the composition and thickness of the grain boundary phase in the RTB sintered magnet. Are listed.

Further, for example, Patent Document 3 describes an R1-T-B sintered magnet material with a specific composition (R1 is at least one kind of rare earth element, and always includes at least one of Nd and Pr), and R2-Ga. An alloy (R2 is at least two rare earth elements, and always includes at least one of Tb and Dy, and at least one of Pr and Nd) is prepared, and at least a portion of the surface of the sintered magnet material is coated with R2- By applying a diffusion step of bringing at least a portion of the Ga alloy into contact and performing a first heat treatment at a specific temperature, and a step of performing a second heat treatment at a specific temperature, the amount of heavy rare earth elements used can be reduced. It has been shown that it is possible to provide an RTB based sintered magnet having higher B _r and higher H _cJ while reducing the . Further, Patent Document 4 proposes forming an R--OH phase on the surface of a diffusion alloy in order to suppress metal accumulation on the surface of a sintered body during the diffusion process.

However, when the diffusion source alloy (R2-Ga alloy) described in Patent Document 3 is used, the diffusion alloy is oxidized or hydroxylated, resulting in an effective amount of heavy rare earth elements (that can be introduced into the sintered magnet material). There were cases where the value decreased. Furthermore, even when the diffusion alloy described in Patent Document 4 is used, the effective amount of heavy rare earth elements sometimes decreases due to hydroxylation of the diffusion alloy. In addition, in recent years, there has been a demand for obtaining high B _r and high H _cJ without using heavy rare earth elements as much as possible, especially in motors for electric vehicles.

_Embodiments of the present disclosure suppress the effective loss of heavy rare earth elements (which can be introduced into the sintered magnet material) due to oxidation and hydration of the diffusion alloy, and _R- A method for manufacturing a TB-based sintered magnet and a diffusion alloy are provided.

In an exemplary embodiment, the method for manufacturing an RTB-based sintered magnet of the present disclosure includes R1: 27.5% by mass or more and 35.0% by mass or less (R1 is at least one kind of rare earth element, B: 0.80% by mass or more and 0.99% by mass or less, Ga: 0% by mass or more and 0.8% by mass or less, M1: 0% by mass or more and 2.0% by mass Hereinafter, (M1 is at least one of Cu, Al, Nb, and Zr), T: 60% by mass or more (T is Fe or Fe and Co, and the content of Fe with respect to the entire T is 85% by mass or more), a step of preparing an R1-TB-based sintered magnet material containing R2-Y (yttrium)-M2 diffusion alloy (R2 is at least two rare earth elements (excluding Y), Tb and Dy, and at least one of Pr and Nd, and M2 always includes at least one of Cu and Ga); a diffusion step of contacting at least a portion of the R2-Y-M2 diffusion alloy and performing heat treatment at a temperature of 700° C. or higher and 950° C. or lower in a vacuum or an inert gas atmosphere; R2 in the R2-Y-M2 diffusion alloy is 75% by mass or more and 98% by mass or less, M2 is 1% by mass or more and 25% by mass or less, and O (oxygen: including inevitable impurities) is 0.2%. It is 1.0 mass% or less by mass%, and Y is 0.4 mass% or more and 0.6 mass% or less.

In one embodiment, after the diffusion step, a low-temperature heat treatment step is included in which heat treatment is performed at a temperature of 450° C. or higher and 750° C. or lower and lower than the heat treatment temperature of the diffusion step.

In one embodiment, the surface of the RTB-based sintered magnet after the diffusion step is ground, and the RTB-based sintered magnet after the grinding is heated at a temperature of 450°C or more and 750°C or less. , and a low-temperature heat treatment step in which the heat treatment is performed at a temperature lower than the heat treatment temperature of the diffusion step.

In one embodiment, the R1-TB-based sintered magnet material satisfies the following formula (1), [T]/55.85>14×[B]/10.8 (1)
([T] is the content of T expressed in % by mass, and [B] is the content of B expressed in % by mass.

In one embodiment, R2 of the R2-Y-M2 diffusion alloy always contains Pr, and the content of Pr is 50% by mass or more of the entire R2.

In one embodiment, the total content of at least one of Tb and Dy in the R2-Y-M2 diffusion alloy is 1% by mass or more and 20% by mass or less of the entire R2.

In one embodiment, M2 of the R2-Y-M2 diffusion alloy contains both Cu and Ga.

In an exemplary embodiment, the R2-Y-M2 diffusion alloy of the present disclosure includes R2 (which is at least two rare earth elements, and necessarily includes at least one of Tb and Dy, and at least one of Pr and Nd). ), Y, M2 (always including at least one of Cu and Ga) and O (oxygen), R2 is 75% by mass or more and 98% by mass or less, and the amount of M2 is 1% by mass or more and 25% by mass or less. Yes, Y is 0.4% by mass or more and 0.6% by mass or less, O (oxygen: including inevitable impurities) is 0.2% by mass or more and 1.0% by mass or less, and the average particle size is 10 μm or more and 500 μm. The powder is as follows.

In one embodiment, R2 consists of Pr and at least one of Tb and Dy.

According to an embodiment of the present disclosure, by bringing an R2-Y-M2 diffusion alloy containing a specific amount of Y into contact with an R1-T-B sintered magnet material and heat-treating it at a specific temperature, the diffusion alloy It is possible to effectively suppress the loss of heavy rare earth elements (Dy and Tb) due to oxidation and hydroxidation, and obtain an RTB based sintered magnet having high B _r and high H _cJ .

FIG. 2 is an enlarged cross-sectional view schematically showing a part of an RTB-based sintered magnet. FIG. 2B is a further enlarged cross-sectional view schematically showing the inside of the broken line rectangular area in FIG. 2A. 1 is a flowchart illustrating an example of steps in a method for manufacturing an RTB-based sintered magnet according to the present disclosure.

First, the basic structure of the RTB-based sintered magnet according to the present disclosure will be explained. RTB-based sintered magnets have a structure in which powder particles of a raw material alloy are bonded together by sintering, with a main phase mainly consisting of R ₂ T ₁₄ B compounds and grain boundaries of this main phase. It is composed of a grain boundary phase.

FIG. 1A is an enlarged schematic cross-sectional view of a part of the RTB-based sintered magnet, and FIG. 1B is a further enlarged schematic cross-sectional view of the rectangular area indicated by the broken line in FIG. 1A. It is. In FIG. 1A, as an example, an arrow having a length of 5 μm is shown as a standard length indicating the size for reference. As shown in FIGS. 1A and 1B, the RTB-based sintered magnet has a main phase 12 mainly composed of R ₂ T ₁₄ B compounds, and a grain boundary phase 14 located at the grain boundary portion of the main phase 12. It is composed of. Further, as shown in FIG. 1B, the grain boundary phase 14 includes a two-grain grain boundary phase 14a in which two R ₂ T ₁₄ B compound particles (grains) are adjacent to each other, and a two-grain boundary phase 14a in which three R ₂ T ₁₄ B compound particles are adjacent to each other. grain boundary triple point 14b. A typical main phase crystal grain size is 2 μm or more and 10 μm or less as an average value of the equivalent circle diameter of the magnet cross section. The R ₂ T ₁₄ B compound, which is the main phase 12, is a ferromagnetic material with high saturation magnetization and an anisotropic magnetic field.
Therefore, in the RTB-based sintered magnet, B _r can be improved by increasing the abundance ratio of the R ₂ T ₁₄ B compound, which is the main phase 12. In order to increase the abundance ratio of the R ₂ T ₁₄ B compound, the amount of R, the amount of T, and the amount of B in the raw material alloy are adjusted to the stoichiometric ratio of the R ₂ T ₁₄ B compound (R amount: T amount: B amount = 2:14:1).

As a result of study, the present inventors found that when using a rare earth alloy such as the R2-Ga alloy described in Patent Document 3, since rare earth elements are active, it is necessary to During heat treatment after coating, the alloy inevitably reacts with O (oxygen) in the atmosphere, and some of the rare earth elements become oxides or hydroxides. In the rare earth oxides and hydroxides formed at this time, heavy rare earths such as Dy and Tb are taken in preferentially over light rare earths such as Nd and Pr, and as a result, R1-T-B sintering occurs. It has been found that the effective amount of heavy rare earths that can be diffused and introduced into the solid magnet material may be reduced. Similarly, Patent Document 4 also shows that the R-OH layer formed on the surface of the diffusion source may reduce the effective amount of heavy rare earths that can be diffused and introduced into the R1-TB sintered magnet material. I found out something.
As a result of further studies, the present inventors found that by containing Y in a specific narrow range in the diffusion alloy, Y is preferentially contained in the formed rare earth oxides and hydroxides over heavy rare earths such as Dy and Tb. It has been found that it is possible to incorporate Y into the RTB sintered magnet, and furthermore, it is possible to suppress the deterioration of the magnetic properties due to the introduction of Y into the RTB sintered magnet. This makes it possible to effectively suppress the loss of heavy rare earth elements due to oxidation and hydroxidation of the diffusion alloy, and the method for producing and diffusing RTB-based sintered magnets having high _Br and high H _cJ . can provide alloys for

As shown in FIG. 2, the method for manufacturing an RTB-based sintered magnet according to the present disclosure includes a step S10 of preparing an R1-T-B-based sintered magnet material, and a step S10 of preparing an R2-Y-M2 diffusion alloy. Step S20 of doing so. The order of the step S10 of preparing the R1-TB-based sintered magnet material and the step S20 of preparing the R2-Y-M2 diffusion alloy is arbitrary.

As shown in FIG. 2, the method for manufacturing an RTB-based sintered magnet according to the present disclosure further includes at least a portion of the surface of the R1-T-B-based sintered magnet material for the R2-Y-M2 diffusion. The method includes a diffusion step S30 of bringing at least a portion of the alloy into contact with each other and performing heat treatment at a temperature of 700° C. or more and 950° C. or less in a vacuum or an inert gas atmosphere. Preferably, after the diffusion step, a low-temperature heat treatment step S40 is included in which heat treatment is performed at a temperature of 450° C. or higher and 750° C. or lower and lower than the heat treatment temperature of the diffusion step. Furthermore, more preferably, a grinding step for processing the surface of the RTB-based sintered magnet is included between the diffusion step S30 and the low-temperature heat treatment step S40. That is, the surface of the RTB-based sintered magnet after the diffusion step is ground, and the low-temperature heat treatment step is performed on the RTB-based sintered magnet after the grinding.

(R1-T-B series sintered magnet material and RTB series sintered magnet)
In the present disclosure, the RTB-based sintered magnet before and during the diffusion process is referred to as "R1-T-B-based sintered magnet material," and the RTB-based sintered magnet after the diffusion process is referred to as "R1-T-B-based sintered magnet material." is simply referred to as "RTB-based sintered magnet."
(RT-Ga phase)
The RT-Ga phase is a compound containing R, T, and Ga, and a typical example thereof is an R ₆ T ₁₃ Ga compound. Further, the R ₆ T ₁₃ Ga compound has a La ₆ Co ₁₁ Ga ₃ type crystal structure. The R ₆ T ₁₃ Ga compound may be in the form of an R ₆ T _13-δ Ga _1+δ compound. When Cu, Al, and Si are contained in the RTB-based sintered magnet, the RT-Ga phase is R ₆ T _13-δ (Ga _1-xy-z Cu _x Al _y Si _z ) can be _1+δ .

[Process of preparing R1-T-B sintered magnet material]
Composition of R1-T-B sintered magnet material (R1)
The content of R1 is 27.5% by mass or more and 35.0% by mass or less. R1 is at least one kind of rare earth element and always includes at least one of Nd and Pr. If R1 is less than 27.5% by mass, a sufficient liquid phase will not be generated during the sintering process, making it difficult to sufficiently densify the sintered body. On the other hand, when R exceeds 35.0% by mass, grain growth occurs during sintering and H _cJ decreases. R1 is preferably 28% by mass or more and 33% by mass or less, more preferably 29% by mass or more and 33% by mass or less.
(B)
The content of B is 0.80% by mass or more and 0.99% by mass or less. If the B content is less than 0.80% by mass, B _r may decrease, and if it exceeds 0.99% by mass, H _cJ may decrease. Further, a part of B can be replaced with C.
(Ga)
The Ga content in the R1-T-B series sintered magnet material is 0% by mass or more and 0.8% by mass or less. When the Ga content exceeds 0.8% by mass, the magnetization of the main phase decreases due to the presence of Ga in the main phase, and there is a possibility that high _Br cannot be obtained. Preferably, the Ga content is 0.5% by mass or less. Higher B _r can be obtained.
(M1)
The content of M1 is 0% by mass or more and 2.0% by mass or less. M1 is at least one of Cu, Al, Nb, and Zr, and even if it is 0% by mass, the effects of the present disclosure can be achieved, but the total content of Cu, Al, Nb, and Zr is 2.0% by mass or less. can do. By containing Cu and Al, H _cJ can be improved. Cu and Al may be actively added, or they may be introduced unavoidably in the raw materials used or in the manufacturing process of alloy powder (using raw materials containing Cu and Al as impurities). good). Further, by containing Nb and Zr, abnormal grain growth of crystal grains during sintering can be suppressed. Preferably, M1 always includes Cu, and contains Cu of 0.05% by mass or more and 0.30% by mass or less. This is because by containing Cu from 0.05% by mass to 0.30% by mass, H _cJ can be further improved.
(T)
The content of T is 60% by mass or more. If the T content is less than 60% by mass, B _r and H _cJ may decrease significantly. T is Fe or Fe and Co, and the content of Fe with respect to the entire T is 85% by mass or more. If the Fe content is less than 85% by mass, B _r and H _cJ may decrease. Here, "the content of Fe with respect to the entire T is 85% by mass or more" means, for example, when the content of T in the R1-TB series sintered magnet material is 75% by mass, the R1-TB series This means that 63.7% by mass or more of the sintered magnet material is Fe. Preferably, the Fe content based on the entire T is 90% by mass or more. This is because higher B _r and higher H _cJ can be obtained. Further, a part of Fe can be replaced with Co. However, if the amount of Co substitution exceeds 10% of the total T in terms of mass ratio, it is not preferable because _Br decreases. Furthermore, in addition to the above-mentioned elements, the R1-TB-based sintered magnet material of the present disclosure also contains Ag, Zn, In, Sn, Ti, Ni, Hf, Ta, W, Ge, Mo, V, Y, La, It may contain Ce, Sm, Ca, Mg, Cr, H, F, P, S, Cl, O, N, C, etc. The content is 0.5 mass% or less for each of Ni, Ag, Zn, In, Sn, and Ti, and 0.5 mass% or less for Hf, Ta, W, Ge, Mo, V, Y, La, Ce, Sm, Ca, Mg, and Cr. It is preferable that each of them is 0.2 mass% or less, H, F, P, S, and Cl are 500 ppm or less, O is 6000 ppm or less, N is 1000 ppm or less, and C is 1500 ppm or less. The total content of these elements is preferably 5% by mass or less of the entire R1-TB sintered magnet material. If the total content of these elements exceeds 5% by mass of the entire R1-T-B sintered material, it may not be possible to obtain high B _r and high H _cJ .

(Formula (1))
[T]/55.85>14×[B]/10.8 (1)
Here, [T] is the content of T (% by mass), and [B] is the content of B (% by mass).
Preferably, the composition of the R1-TB-based sintered magnet material satisfies formula (1). By satisfying formula (1), an RT-Ga phase is generated at the grain boundaries of the finally obtained RTB-based sintered magnet, and a high H _cJ can be obtained. By satisfying formula (1), the B content is lower than that of a general RTB-based sintered magnet. Typical RTB system sintered magnets are manufactured using [T]/55.85 (atomic weight of Fe) to prevent the formation of Fe phase or R ₂ T ₁₇ phase other than the main phase R ₂ T ₁₄ B phase. is less than 14×[B]/10.8 (atomic weight of B) ([T] is the content of T expressed in mass%, [B] is the content of B expressed in mass% amount). The R1-T-B based sintered magnet material in a preferred embodiment of the present disclosure differs from a general RTB based sintered magnet in that [T]/55.85 (atomic weight of Fe) is 14×[ B]/10.8 (atomic weight of B) is defined by inequality (1). Note that since Fe is the main component of T in the R1-T-B series sintered magnet material of the present disclosure, the atomic weight of Fe was used.

The R1-T-B sintered magnet material can be prepared using a common method for manufacturing R-T-B sintered magnets, typified by Nd-Fe-B sintered magnets. For example, a raw material alloy produced by a strip casting method or the like is pulverized to 2 μm or more and 10 μm or less using a jet mill, etc., then molded in a magnetic field, and sintered at a temperature of 900° C. or more and 1100° C. or less. It can be prepared by
If the pulverized particle size of the raw material alloy (volume center value obtained by measurement using air dispersion laser diffraction method = D ₅₀ ) is less than 2 μm, it is extremely difficult to produce pulverized powder, and production efficiency will decrease significantly. Undesirable. On the other hand, if the pulverized particle size exceeds 10 μm, the crystal grain size of the finally obtained RTB sintered magnet becomes too large, making it difficult to obtain a high H _cJ , which is not preferable. R1-T-B series sintered magnet material may be produced from one type of raw material alloy (single raw material alloy), as long as it satisfies each of the above conditions, or it may be produced using two or more types of raw material alloy. It may also be produced by a method of mixing them (blending method).

[Process of preparing R2-Y (yttrium)-M2 diffusion alloy]
Composition of R2-Y-M2 diffusion alloy R2 in the R2-Y-M2 diffusion alloy is at least two rare earth elements (excluding Y), at least one of Tb and Dy, and Pr and Nd. Must include at least one. R2 is 75 to 98% by mass of the entire R2-Y-M2 diffusion alloy. If the R2 content is less than 75% by mass, the R2 content may be too small and the H _cJ of the finally obtained RTB-based sintered magnet may decrease, and the R2 content may be lower than 98% by mass. %, the contents of Y and M2 may decrease, and the H _cJ of the finally obtained RTB-based sintered magnet may decrease. In order to obtain higher B _r and higher H _cJ , preferably, R2 of the R2-Y-M2 diffusion alloy always contains Pr, and the content of Pr is 50% by mass or more of the entire R2, and R2 The total content of at least one of Tb and Dy in the -Y-M2 diffusion alloy is 1% by mass or more and 20% by mass or less of the entire R2. Preferably, R2 consists of Pr and at least one of Tb and Dy.
One of the most characteristic features of the present disclosure is that the diffusion alloy contains 0.4% by mass or more and 0.6% by mass or less of Y (yttrium). By containing Y in a specific narrow range, Y can be preferentially incorporated into rare earth oxides and hydroxides formed by oxidation of the diffusion alloy over heavy rare earths such as Dy and Tb. Furthermore, it is possible to suppress the deterioration of magnetic properties due to the introduction of Y into the RTB sintered magnet. As a result, effective loss of heavy rare earth elements (Dy and Tb) due to oxidation and hydration of the diffusion alloy is suppressed, and an RTB-based sintered magnet with high B _r and high H _cJ is obtained. be able to. If the Y content is less than 0.4% by mass, it will not be possible to effectively suppress the loss of heavy rare earth elements (Dy and Tb) due to oxidation and hydration of the diffusion alloy, resulting in a decrease in H _cJ . If it exceeds 0.6% by mass, Y contained in the RTB sintered magnet may lower B _r and H _cJ .
M2 in the R2-Y-M2 diffusion alloy always contains at least one of Cu and Ga. M2 is 1% to 25% by mass of the entire R2-Y-M2 diffusion alloy. If the M2 content is less than 1% by mass, H _cJ may decrease, and if it exceeds 25% by mass, B _r may decrease. In order to obtain higher H _cJ , M2 of the R2-Y-M2 diffusion alloy preferably contains both Cu and Ga.
The R2-Y-M2 diffusion alloy contains O (oxygen: including inevitable impurities), and the content of O is 0.2% by mass or more and 1.0% by mass or less. When the content of O is less than 0.2% by mass, oxides and hydroxides of Y and O are difficult to form, and the content of Y in the RTB sintered magnet increases. H _cJ may decrease, and if it exceeds 1.0 mass %, the content of O in the R1-T-B sintered magnet may increase and B _r and H _cJ may decrease.

The R2-Y-M2 diffusion alloy is a powder with an average particle size of 10 μm or more and 500 μm or less. If the average particle size is less than 10 μm, the oxidation and hydroxylation of the diffusion alloy may progress too much, resulting in a decrease in B _r and H _cJ , and if it exceeds 500 μm, the R1-T-B sintered magnet Diffusion into the material may become insufficient and high H _cJ may not be obtained. Preferably, the average particle size of the R2-Y-M2 diffusion alloy is 100 μm or more and 300 μm or less.
The average particle size in the present disclosure may be adjusted by classification using a standard sieve according to JIS Z 8801. In addition to classification using a standard sieve as described in JIS Z8801, the average particle size in the present disclosure may be determined by, for example, microscopic observation, a commercially available particle size distribution measuring device (for example, Microtrac Bell's laser diffraction/scattering type It can be measured using a particle size distribution measuring device, etc.).

The R2-Y-M2 diffusion alloy is manufactured using the raw material alloy manufacturing methods that are used in general RTB sintered magnet manufacturing methods, such as die casting, strip casting, and single-roll casting. It can be prepared using a rapid cooling method (melt spinning method), an atomization method, or the like. Further, the R2-Y-M2 diffusion alloy may be obtained by pulverizing the alloy obtained above using a known pulverizing means such as a pin mill.

As described in Patent Document 4, an R-OH layer having an average thickness of 0.5 μm or more and 3 μm or less may be formed on the surface of the powder particles of the R2-T-M2 diffusion alloy. By forming the R-OH layer, it is possible to suppress the occurrence of metal accumulation on the surface of the RTB-based sintered magnet after diffusion. It also becomes possible to make the powder less flammable and easier to handle. The R-OH layer can be formed, for example, by exposing the R2-T-M2 diffusion alloy to an atmosphere with a temperature of 20° C. or more and 150° C. or less and a relative humidity of 60% or more and 100% or less.

[Diffusion process]
At least a part of the R2-Y-M2 diffusion alloy is brought into contact with at least a part of the surface of the R1-T-B sintered magnet material, and the temperature is set at 700°C or more and 950°C or less in a vacuum or an inert gas atmosphere. Heat treatment is carried out at temperature. As a result, a liquid phase containing R2, Y, and M2 is generated from the R2-Y-M2 diffusion alloy, and the liquid phase passes through the grain boundaries in the R1-T-B sintered magnet material to the sintered material. It is diffused into the interior from the surface. If the heat treatment temperature is less than 700°C, the amount of liquid phase containing R2, Y and M2 may be too small to obtain high H _cJ , and if it exceeds 950°C, H _cJ may decrease. There is. Preferably, in the diffusion step, the R1-T-B sintered magnet material, which has been heat-treated at a temperature of 700°C or more and 950°C or less, is cooled at a cooling rate of 5°C/min or more from the temperature at which the heat treatment was performed. It includes a step of cooling to 300°C. Higher H _cJ can be obtained. More preferably, the cooling rate to 300°C is 15°C/min or more.

The diffusion step can be performed by placing an R2-Y-M2 diffusion alloy on the surface of the R1-TB sintered magnet material and using a known heat treatment device. For example, the surface of the R1-TB sintered magnet material can be covered with a powder layer of an R2-Y-M2 diffusion alloy and subjected to heat treatment. For example, after applying a slurry in which the R2-Y-M2 diffusion alloy is dispersed in a dispersion medium to the surface of the R1-T-B sintered magnet material, the dispersion medium is evaporated to form the R2-Y-M2 diffusion alloy. It may also be brought into contact with an R1-T-B series sintered magnet material. In addition, alcohol (ethanol etc.), an aldehyde, and a ketone can be illustrated as a dispersion medium. In addition, RH is not only obtained from the R2-Y-M2 diffusion alloy, but also fluorides, oxides, oxyfluorides, etc. of RH are added to the surface of the R1-T-B sintered magnet together with the R2-Y-M2 diffusion alloy. A heavy rare earth element may be introduced by placing it in That is, as long as R2 (at least one of Dy and Tb and at least one of Nd and Pr), Y and M2 can be diffused at the same time, the method is not particularly limited. Examples of fluorides, oxides, and oxyfluorides of heavy rare earth elements include TbF ₃ , DyF ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Tb ₄ OF, and Dy ₄ OF.
In addition, as long as at least a part of the R2-Y-M2 diffusion alloy is in contact with at least a part of the R1-T-B sintered magnet material, the placement position of the R2-Y-M2 diffusion alloy is particularly limited. No question.
[Low temperature heat treatment process]
Preferably, after the diffusion step, a low-temperature heat treatment step is performed in which heat treatment is performed at a temperature of 450° C. or higher and 750° C. or lower and lower than the heat treatment temperature of the diffusion step. Thereby, even higher H _cJ can be obtained. If the temperature is lower than 450°C or higher than 750°C, it may not be possible to obtain high H _cJ . More preferably, the surface of the RTB sintered magnet after the diffusion process is ground, and the ground RTB sintered magnet is subjected to a low temperature heat treatment process. This can be carried out by performing a grinding process to process the surface of the RTB based sintered magnet between the diffusion process and the low temperature heat treatment process. Y-containing oxides and hydroxides are present on the magnet surface of the RTB-based sintered magnet after the diffusion process. By grinding the magnet surface, oxides and hydroxides containing Y can be removed from the magnet, which more reliably prevents the deterioration of magnetic properties due to the introduction of Y into the RTB sintered magnet. It can be suppressed.

Embodiments of the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the examples.

An R1-T-B sintered magnet material was produced to have the target composition shown in Table 1. Each element was weighed and cast by a strip casting method to obtain a flaky alloy with a thickness of 0.2 to 0.4 mm. The resulting flaky alloy was hydrogen-pulverized and then subjected to a dehydrogenation treatment in which it was heated to 550° C. in vacuum and then cooled to obtain coarsely pulverized powder. Next, 0.04 mass% of zinc stearate was added as a lubricant to the obtained coarsely pulverized powder based on 100 mass% of the coarsely pulverized powder, and the mixture was mixed. Dry pulverization was performed in an air stream to obtain a fine alloy powder. The particle size of the obtained fine powder was measured by a laser diffraction method using an air flow dispersion method, and as a result, the D ₅₀ (volume-based median diameter) was 4.6 μm. The obtained alloy fine powder was mixed with an organic dispersion medium and a mold release agent to prepare a slurry. The produced slurry was molded in a magnetic field to obtain a molded body. The magnetic field during molding was 1.3 MA/m, and the pressing force was 5 MPa. The forming apparatus used was a so-called right-angle magnetic field forming apparatus (transverse magnetic field forming apparatus) in which the magnetic field application direction and the pressing direction were perpendicular to each other. The obtained molded body was sintered at 1040° C. for 4 hours in a reduced pressure of argon controlled at 200 Pa to obtain an R1-TB series sintered magnet material. A part of the obtained R1-T-B type sintered magnet material was crushed in a mortar and classified using a 425 μm mesh and a 75 μm mesh. Using pulverized powder with a particle size of 75 to 425 μm, component analysis of Nd, Fe, Pr, B, Al, Cu, Ga, Tb, Mn, and Si was performed using ICP emission spectrometry and combustion/infrared absorption method. The carbon content was analyzed. Furthermore, using pulverized powder with a particle size of 425 μm or more, the amount of oxygen and nitrogen was analyzed using an inert gas melting/thermal conduction method. Table 1 shows the composition of the R1-TB series sintered magnet material.

No. shown in Table 2. A1 to A4 were produced. Using Pr, Tb, Y, Ga, and Cu raw materials with a purity of 99% or more, taking into account the evaporation of rare earth elements during melting, Sample No. The alloys A1 to A4 were weighed so that the alloy compositions were at the target values. Thereafter, the molten metal was sufficiently melted in a quartz tapping pipe of a liquid super-quenching device (melt spinning device) to form a molten alloy, and then the molten metal was tapped onto a Cu roll rotating at a roll circumferential speed of 20 m/s. The ribbon-shaped alloy thus produced was ground in a nitrogen flow chamber. The alloy powder obtained by pulverization was classified using a 300 μm mesh and a 106 μm mesh. The obtained alloy powders with a particle size of 106 to 300 μm were designated as samples A1 to A4 (that is, the average particle size of samples A1 to A4 was within the range of the present disclosure (10 μm or more and 500 μm or less)). Samples A1 to A4 were analyzed for Nd, Pr, Dy, Al, Cu, Ga, Tb, Y, and Si using ICP (inductively coupled plasma) emission spectroscopy. Table 2 shows the compositions of samples A1 to A4.

A process of forming an R-OH layer on the surface of the powder particles of the R2-T-M2 diffusion alloy by exposing the prepared samples A1 to A4 to an atmosphere with a temperature of 80° C. and a humidity of 90% (the process described in Patent Document 4) ) to obtain diffusion alloys B1 to B4. Using some of the diffusion alloys B1 to B4, the amount of carbon was analyzed by combustion and infrared absorption method, and the amount of oxygen and nitrogen was analyzed by inert gas melting and heat conduction method. Table 3 shows the oxygen content, nitrogen content, and carbon content of the diffusion alloy.

The R1-T-B series sintered magnet material was cut and machined into a rectangular parallelepiped of 4.4 mm x 10 mm x 11 mm. Cutting was performed so that the length in the magnetic field application direction during molding was 4.4 mm, and the length in the pressure application direction during molding was 10 mm. After applying a 5% PVA (polyvinyl alcohol) aqueous solution as an adhesive to the 10 mm x 11 mm surfaces (two sides) of the sintered magnet material after cutting, 1 mass% (1 mass%) per surface was applied to 100 mass% of the sintered magnet material. Diffusion alloys B1 to B4 (2 mass % in total) were deposited on each of the two sides. Then, heat treatment was performed at 900° C. for 10 hours in a reduced pressure argon atmosphere controlled at 200 Pa using a vacuum heat treatment furnace. After the heat treatment, the two sides of the sample to which the diffusion alloy was attached were ground and processed into a 4 mm x 10 mm x 11 mm rectangular parallelepiped, and then each was cut to form a 4 mm x 4 mm x 4 mm cubic sample No. Two pieces of each of Nos. 1 to 4 were made. Each of these 4 mm square samples has B _r , H _cJ and H _k (J (magnetization strength) - H (magnetic field strength) curve) with J of 0. The H-axis reading value at the position where the value of 9B _r was obtained) was measured. In addition, the components of Fe, Nd, Pr, B, Al, Cu, Ga, Tb, Y, Mn, and Si were analyzed for each remaining one by ICP emission spectrometry by dissolving the entire sample. . Furthermore, based on the results of this component analysis and the amount of the diffusion alloy applied, the introduction rate of each element contained in the diffusion alloy was calculated. This indicates that the higher the Tb introduction rate (%), the more effectively the loss of heavy rare earth elements in the diffusion alloy is suppressed. Table 4 shows the diffusion alloy used, the ICP analysis results of the 4 mm square sample, the introduction rate, and the magnetic properties (B _r , H _cJ , H _k ).

No. 2 with a relatively small amount of Y in the diffusion alloy. Compared to No. 1 and No. 2, the amount of Y in the diffusion alloy is relatively large. Samples 3 and 4 had a higher amount of Tb in the 4 mm square sample, resulting in a higher Tb introduction rate. Also, No. Only in sample No. 4, Y above the lower detection limit was detected in the 4 mm square sample. H _cJ and H _k are diffusion source No. No. using B3. Sample No. 3 had the highest result. It is thought that when the amount of Y in the diffusion alloy increases, the amount of Tb distributed to the oxide phase in the diffusion alloy decreases, and the amount of Tb diffused into the sintered magnet material increases. However, if the amount of Y in the diffusion alloy is too large, Y will diffuse too much into the sintered magnet material, reducing the magnetic properties of the main phase. No. It is considered that sample No. 3 achieved high H _cJ and H _k as a result of a good balance between the two.

4mm square sample No. after measuring magnetic properties. Samples 1 to 4 were heat treated. After wrapping a 4 mm square sample in Nb foil, it was heat treated at 500°C for 3 hours in a vacuum heat treatment furnace controlled at 200 Pa in argon. 5-8 samples were obtained. Then, using the BH tracer, sample No. Measurements of B _r and H _cJ of 5 to 8 were performed. Table 5 shows sample No. before heat treatment. The results of the magnetic properties (B _r , H _cJ , H _k ) of Nos. 1 to 4 are shown below.

As in the case where the heat treatment at 500°C for 3 hours was not performed, diffusion alloy No. Sample No. using B3. 7 had the highest H _cJ and H _k . H _cJ and H _k are for sample No. after treatment at 900°C for 10 hours. Sample No. 1 was heat-treated at 500°C for 3 hours more than samples 1 to 4. Scores 5 to 8 are higher overall. This is thought to be due to the heat treatment at 500°C for 3 hours, which resulted in the expansion of the two-grain boundaries of the main phase grains and the lowering of the magnetization of the two-grain boundary phase, resulting in progress in magnetic separation between the main phase grains. I can see it. However, the reason why the magnitude relationship of H _cJ and H _k does not change with or without heat treatment at 500° C. for 3 hours is considered to be due to the magnitude relationship of the anisotropic magnetic field of the main phase that is the base. By balancing the improvement in anisotropy due to Tb substitution in the main phase and the decrease in anisotropy due to Y substitution, diffusion source No. It is considered that the anisotropic magnetic field of the main phase became the highest when B3 was used.

Claims (10)

R1: 27.5% by mass or more and 35.0% by mass or less (R1 is at least one type of rare earth element and always includes at least one of Nd and Pr),
B: 0.80% by mass or more and 0.99% by mass or less,
Ga: 0% by mass or more and 0.8% by mass or less,
M1: 0% by mass or more and 2.0% by mass or less, (M1 is at least one of Cu, Al, Nb, and Zr),
T: 60% by mass or more (T is Fe or Fe and Co, and the content of Fe with respect to the entire T is 85% by mass or more),
A step of preparing an R1-TB-based sintered magnet material containing
R2-Y (yttrium)-M2 diffusion alloy (R2 is at least two rare earth elements (excluding Y), always includes at least one of Tb and Dy, and at least one of Pr and Nd, M2 (always includes at least one of Cu and Ga);
At least a part of the R2-Y-M2 diffusion alloy is brought into contact with at least a part of the surface of the R1-T-B sintered magnet material, and the temperature is set at 700°C or more and 950°C or less in a vacuum or an inert gas atmosphere. a diffusion step of carrying out a heat treatment at a temperature;
R2 in the R2-Y-M2 diffusion alloy is 75% by mass or more and 98% by mass or less, M2 is 1% by mass or more and 25% by mass or less, and O (oxygen: including inevitable impurities) is 0.2%. A method for producing an RTB-based sintered magnet, wherein Y is from 0.4% by mass to 0.6% by mass, and Y is from 0.4% by mass to 0.6% by mass. The RTB-based sintered magnet according to claim 1, further comprising a low-temperature heat treatment step in which, after the diffusion step, heat treatment is performed at a temperature of 450° C. or higher and 750° C. or lower and lower than the heat treatment temperature of the diffusion step. manufacturing method. The surface of the RTB-based sintered magnet after the diffusion process is ground, and the RTB-based sintered magnet after the grinding process is heated to a temperature of 450°C or more and 750°C or less, and during the diffusion process. The method for manufacturing an RTB based sintered magnet according to claim 1 or 2, wherein a low temperature heat treatment step is performed in which the heat treatment is performed at a temperature lower than the heat treatment temperature. The R1-TB-based sintered magnet material satisfies the following formula (1),
[T]/55.85>14×[B]/10.8 (1)
([T] is the content of T expressed in mass %, [B] is the content of B expressed in mass %), Method of manufacturing a condensed magnet. The R-T-B system according to any one of claims 1 to 4, wherein R2 of the R2-Y-M2 diffusion alloy always contains Pr, and the content of Pr is 50% by mass or more of the entire R2. Method of manufacturing sintered magnets. R- according to any one of claims 1 to 5, wherein the content of at least one of Tb and Dy in the R2-Y-M2 diffusion alloy is 1% by mass or more and 20% by mass or less of the entire R2. A method for manufacturing a TB-based sintered magnet. The method for manufacturing an RTB based sintered magnet according to any one of claims 1 to 6, wherein M2 of the R2-Y-M2 based diffusion alloy contains both Cu and Ga. R2 (at least two of the rare earth elements, always containing at least one of Tb and Dy, and at least one of Pr and Nd), Y, M2 (necessarily containing at least one of Cu and Ga), and O (oxygen ), R2 is 75% by mass or more and 98% by mass or less, M2 amount is 1% by mass or more and 25% by mass or less, Y is 0.4% by mass or more and 0.6% by mass or less, O (Oxygen: including unavoidable impurities) is 0.2% by mass or more and 1.0% by mass or less, and the average particle size is 10 μm or more and 500 μm or less. The R2-Y-M2 diffusion alloy according to claim 7, wherein the R2 comprises Pr and at least one of Tb and Dy. The R2-Y-M2 diffusion alloy according to claim 7 or 8, wherein the total content of at least one of Tb and Dy is 1% by mass or more and 20% by mass or less of the entire R2.

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