JP2018093201A - R-t-b based permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an R-T-B based permanent magnet showing high residual magnetic flux density Br and coercive force HcJ, and further showing the same also after a heavy rare earth element is diffused along grain boundaries.SOLUTION: There is provided an R-T-B based permanent magnet in which, R is a rare earth element, T is an element other than a rare earth element, B, C, O or N, and B is boron. T at least includes Fe, Cu, Co and Ga. A total of R content is 28.0-30.2 mass%, Cu content is 0.04-0.50 mass%, Co content is 0.5-3.0 mass%, Ga content is 0.08-0.30 mass%, and B content is 0.85-0.95 mass%, relative to 100 mass% of a total mass of R, T and B.SELECTED DRAWING: None

Description

  The present invention relates to an R-T-B permanent magnet.

  A rare earth permanent magnet having an R-T-B system composition is a magnet having excellent magnetic properties, and many studies have been made with the aim of further improving the magnetic properties. In general, the residual magnetic flux density (residual magnetization) Br and the coercive force HcJ are used as indices representing the magnetic characteristics. It can be said that magnets having these values have excellent magnetic properties.

  For example, Patent Document 1 describes an Nd—Fe—B rare earth permanent magnet having good magnetic properties.

  Patent Document 2 describes a rare earth permanent magnet in which a magnet body is immersed in a slurry in which fine powders containing various rare earth elements are dispersed in water or an organic solvent, and then heated and diffused at grain boundaries.

JP 2006-210893 A International Publication No. 2006/43348 Pamphlet

  The present invention provides an RTB-based permanent magnet having a high residual magnetic flux density Br and a coercive force HcJ, and a high residual magnetic flux density Br and a coercive force HcJ after heavy rare earth elements are diffused at grain boundaries. With the goal.

In order to achieve the above object, the RTB-based permanent magnet of the present invention is:
An R-T-B permanent magnet in which R is a rare earth element, T is an element other than rare earth elements, B, C, O and N, and B is boron,
T contains at least Fe, Cu, Co and Ga,
The total mass of R, T and B is 100% by mass,
The total content of R is 28.0% by mass to 30.2% by mass,
The Cu content is 0.04 mass% to 0.50 mass%,
Co content of 0.5 mass% to 3.0 mass%,
Ga content is 0.08 mass% to 0.30 mass%,
The B content is 0.85% by mass to 0.95% by mass.

  The RTB-based permanent magnet of the present invention can improve the residual magnetic flux density Br and the coercive force HcJ by having the above characteristics. Furthermore, the effect of diffusing heavy rare earth elements at grain boundaries can be further enhanced. Specifically, the residual magnetic flux density Br and the coercive force HcJ of the RTB-based permanent magnet obtained by diffusing heavy rare earth elements can also be improved.

  The total content of R may be 29.2 mass% to 30.2 mass%.

  R may contain at least Nd.

  R may contain at least Pr, and the Pr content may be greater than 0 and 10.0% by mass or less.

  R may contain at least Nd and Pr.

T may further contain Al,
The content of Al may be 0.15% by mass to 0.30% by mass.

T may further contain Zr,
The content of Zr may be 0.10% by mass to 0.30% by mass.

  Further, C may be contained, and the content of C may be 1100 ppm or less with respect to the total mass of the RTB-based permanent magnet.

  Further, N may be included, and the content of N may be 1000 ppm or less with respect to the total mass of the RTB-based permanent magnet.

  Furthermore, O may be contained, and the content of O may be 1000 ppm or less with respect to the total mass of the RTB-based permanent magnet.

  When the total content of R is TRE, TRE / B may be 2.2 to 2.7 in terms of atomic ratio.

  14B / (Fe + Co) may be greater than 0 and 1.01 or less in atomic ratio.

  The concentration distribution of the heavy rare earth element may decrease from the outside toward the inside.

  Hereinafter, an embodiment of the present invention will be described.

<R-T-B permanent magnet>
The RTB-based permanent magnet according to the present embodiment has particles and grain boundaries made of R ₂ T ₁₄ B crystals. And by containing several specific elements by content of a specific range, residual magnetic flux density Br, coercive force HcJ, corrosion resistance, and manufacturing stability can be improved. Furthermore, the decrease width of the residual magnetic flux density Br in grain boundary diffusion described later can be reduced, and the increase width of the coercive force HcJ can be increased. That is, the RTB-based permanent magnet according to this embodiment is an RTB-based permanent magnet that has excellent characteristics even without a grain boundary diffusion step and is suitable for grain boundary diffusion. From the viewpoint of improving the coercive force HcJ, the element diffused by grain boundary diffusion is preferably a heavy rare earth element.

  R is a rare earth element. The rare earth elements include Sc, Y, and lanthanoid elements belonging to Group 3 of the long-period periodic table. Examples of lanthanoid elements include La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and the like. R preferably contains Nd.

  In general, rare earth elements are classified into light rare earth elements and heavy rare earth elements. Lu.

  T represents an element other than rare earth elements, B, C, O and N. In the RTB-based permanent magnet according to the present embodiment, T includes at least Fe, Co, Cu, and Ga. Further, for example, one or more elements among elements such as Al, Mn, Zr, Ti, V, Cr, Ni, Nb, Mo, Ag, Hf, Ta, W, Si, P, Bi, and Sn are defined as T. Further, it may be included.

  B is boron.

  The total content of R is 28.0% by mass or more and 30.2% by mass or less, where the total mass of R, T and B is 100% by mass. When the total content of R is too small, the coercive force HcJ decreases. When the total content of R is too large, the residual magnetic flux density Br decreases. Moreover, 29.2 mass% or more and 30.2 mass% or less may be sufficient as total content of R. By setting the total content of R to 29.2% by mass or more, the amount of deformation during sintering is reduced, which improves manufacturing stability.

  Furthermore, the content of Nd is arbitrary in the RTB-based permanent magnet of the present embodiment. Further, the content of Nd may be 0% by mass to 30.2% by mass, or 0% by mass to 29.7% by mass, where the total mass of R, T, and B is 100% by mass. It may be 19.7% by mass to 29.7% by mass, 19.7% by mass to 24.7% by mass, and 19.7% by mass to 22.6% by mass. The Pr content may be 0.0 mass% to 10.0 mass%. That is, it is not necessary to contain Pr. The RTB-based permanent magnet of this embodiment may contain at least Nd and Pr as R. Further, the Pr content may be 5.0 mass% or more and 10.0 mass% or less. Furthermore, 5.0 mass% or more and 7.6 mass% or less may be sufficient. Further, when the Pr content is 10.0% by mass or less, the temperature change rate of the coercive force HcJ is excellent. In particular, from the viewpoint of increasing the coercive force HcJ at high temperatures, the Pr content is preferably 0.0 mass% to 7.6 mass%.

  In addition, the RTB-based permanent magnet of the present embodiment may include Tb and / or Dy as R in a total amount of 0.5% by mass or less. When the content of Tb and / or Dy is 0.5% by mass or less in total, the residual magnetic flux density can be easily kept good.

  The Cu content is 0.04 mass% or more and 0.50 mass% or less, where the total mass of R, T, and B is 100 mass%. If the Cu content is less than 0.04% by mass, the coercive force HcJ tends to decrease. Further, the improvement width ΔHcJ of the coercive force HcJ by heavy rare earth diffusion (application of the so-called grain boundary diffusion method) becomes insufficient, and the coercive force HcJ after heavy rare earth diffusion also tends to decrease. When the Cu content exceeds 0.50 mass%, the coercive force HcJ tends to decrease, and the residual magnetic flux density Br tends to decrease. Further, the improvement width ΔHcJ of the coercive force HcJ due to heavy rare earth diffusion tends to be saturated and the residual magnetic flux density Br tends to decrease. Moreover, 0.10 mass% or more and 0.50 mass% or less may be sufficient as content of Cu, and 0.10 mass% or more and 0.30 mass% or less may be sufficient. Corrosion resistance tends to be improved by containing 0.10% by mass or more of Cu.

  The Ga content is 0.08 mass% or more and 0.30 mass% or less, where the total mass of R, T, and B is 100 mass%. By containing 0.08% by mass or more of Ga, the coercive force HcJ is sufficiently improved. If it exceeds 0.30% by mass, a secondary phase (for example, an R—T—Ga phase) is easily generated, and the residual magnetic flux density Br decreases. Moreover, 0.10 mass% or more and 0.25 mass% or less may be sufficient as content of Ga.

  The Co content is 0.5% by mass or more and 3.0% by mass or less, where the total mass of R, T, and B is 100% by mass. Corrosion resistance is improved by containing Co. If the Co content is less than 0.5% by mass, the corrosion resistance of the finally obtained R—T—B system permanent magnet deteriorates. If the Co content exceeds 3.0% by mass, the effect of improving the corrosion resistance reaches its peak and the cost is increased. Moreover, 1.0 mass% or more and 3.0 mass% or less may be sufficient as content of Co.

  Moreover, 0.15 mass% or more and 0.30 mass% or less may be sufficient as content of Al by making the total mass of R, T, and B into 100 mass%. The coercive force HcJ before heavy rare earth diffusion and after heavy rare earth diffusion can be improved by setting the Al content to 0.15 mass% or more. Furthermore, the change in the magnetic characteristics (particularly the coercive force HcJ) with respect to the change in the aging temperature and / or the heat treatment temperature after heavy rare earth diffusion is reduced, and the variation in characteristics during mass production is reduced. That is, manufacturing stability is improved. When the Al content is 0.30% by mass or less, the residual magnetic flux density Br before and after heavy rare earth diffusion can be improved. Furthermore, the temperature change rate of the coercive force HcJ can be improved. Moreover, 0.15 mass% or more and 0.25 mass% or less may be sufficient as content of Al. By making the Al content 0.15 mass% or more and 0.25 mass% or less, the change in magnetic properties (particularly the coercive force HcJ) with respect to the change in the aging temperature and / or the heat treatment temperature after heavy rare earth diffusion is further reduced. Become.

  The content of Zr may be not less than 0.10% by mass and not more than 0.30% by mass, where the total mass of R, T and B is 100% by mass. By containing Zr, abnormal grain growth during sintering is suppressed, and the squareness ratio Hk / HcJ and the magnetization rate under a low magnetic field are improved. By setting the Zr content to 0.10% by mass or more, the effect of suppressing abnormal grain growth during sintering due to the Zr content increases, and the squareness ratio Hk / HcJ and the magnetization rate under a low magnetic field are improved. . By setting it to 0.30 mass% or less, the residual magnetic flux density Br can be improved. Moreover, 0.15 mass% or more and 0.30 mass% or less may be sufficient as content of Zr, and 0.15 mass% or more and 0.25 mass% or less may be sufficient. By setting the content of Zr to 0.15% by mass or more, the sintering stable temperature range is widened. That is, the effect of suppressing abnormal grain growth is further increased during sintering. And the dispersion | variation in a characteristic becomes small and manufacturing stability improves.

  Further, the RTB-based permanent magnet according to this embodiment may include Mn. When Mn is contained, the content of Mn may be 0.02% by mass to 0.10% by mass with the total mass of R, T, and B being 100% by mass. When the Mn content is 0.02% by mass or more, the residual magnetic flux density Br tends to be improved, and the improvement width ΔHcJ of the coercive force HcJ after the diffusion of the heavy rare earth element tends to be improved. When the content of Mn is 0.10% by mass or less, the coercive force HcJ tends to be improved, and the improvement width ΔHcJ of the coercive force HcJ after the diffusion of the heavy rare earth element tends to be improved. Moreover, 0.02 mass% or more and 0.06 mass% or less may be sufficient as content of Mn.

  The content of B in the RTB-based permanent magnet according to the present embodiment is 0.85% by mass or more and 0.95% by mass or less, where the total mass of R, T, and B is 100% by mass. When B is less than 0.85% by mass, it is difficult to achieve high squareness. That is, it becomes difficult to improve the squareness ratio Hk / HcJ. When B is more than 0.95% by mass, the squareness ratio Hk / HcJ after grain boundary diffusion decreases. Moreover, 0.88 mass% or more and 0.94 mass% or less may be sufficient as content of B. By setting the B content to 0.88 mass% or more, the residual magnetic flux density Br tends to be further improved. By setting the B content to 0.94 mass% or less, the coercive force HcJ tends to be further improved.

  Further, when the total content of R elements is TRE, TRE / B may be 2.2 or more and 2.7 or less in atomic ratio. Moreover, 2.29 or more and 2.63 or less, 2.32 or more and 2.63 or less, 2.34 or more and 2.59 or less, 2.34 or more and 2.54 or less, 2.36 or more and 2.54 or less Good. When TRE / B is within the above range, the residual magnetic flux density and the coercive force HcJ are improved.

  Further, 14B / (Fe + Co) may be greater than 0 and 1.01 or less in terms of the atomic ratio. When 14B / (Fe + Co) is 1.01 or less, the squareness ratio after grain boundary diffusion tends to be improved. 14B / (Fe + Co) may be 1.00 or less.

  The content of carbon (C) in the RTB-based permanent magnet according to the present embodiment may be 1100 ppm or less, 1000 ppm or less, or 900 ppm or less with respect to the total mass of the RTB-based permanent magnet. It may be. Further, it may be 600 ppm to 1100 ppm, 600 ppm to 1000 ppm, or 600 ppm to 900 ppm. By setting the carbon content to 1100 ppm or less, the coercive force HcJ before and after heavy rare earth diffusion tends to be improved. In particular, from the viewpoint of improving the coercive force HcJ after heavy rare earth diffusion, the carbon content can be 900 ppm or less. In addition, producing an R—T—B system permanent magnet having a carbon content of less than 600 ppm places a heavy load on the process and causes an increase in cost.

  In particular, from the viewpoint of improving the squareness ratio after diffusion of heavy rare earth, the carbon content may be 800 ppm to 1100 ppm.

  In the RTB-based permanent magnet according to this embodiment, the content of nitrogen (N) may be 1000 ppm or less, 700 ppm or less, or 600 ppm with respect to the total mass of the RTB-based permanent magnet. It may be the following. Moreover, 250 ppm-1000 ppm, 250 ppm-700 ppm, or 250 ppm-600 ppm may be sufficient. The smaller the nitrogen content, the easier the coercive force HcJ improves. In addition, producing an R—T—B system permanent magnet having a nitrogen content of less than 250 ppm places a large load on the process, which increases costs.

    In the RTB-based permanent magnet according to the present embodiment, the content of oxygen (O) may be 1000 ppm or less and 800 ppm or less with respect to the total mass of the RTB-based permanent magnet. It may be 700 ppm or less, or 500 ppm or less. Moreover, 350 ppm-500 ppm may be sufficient. The smaller the oxygen content, the easier it is to improve the coercive force HcJ before heavy rare earth diffusion. In addition, producing an R—T—B system permanent magnet having an oxygen content of less than 350 ppm places a heavy load on the process and causes an increase in cost.

  Furthermore, deformation during sintering can be suppressed by reducing the oxygen content to 1000 ppm or less, 800 ppm or less, 700 ppm or less, or 500 ppm or less while keeping the total content of R at 29.2% by mass or more. Can be improved.

  The reason why the deformation during sintering can be suppressed by reducing the oxygen content while keeping the total content of R at or above a predetermined amount is considered to be as follows. The sintering mechanism of the R-T-B system permanent magnet is liquid phase sintering, and a grain boundary phase component called an R-rich phase generates a liquid phase during sintering and promotes densification. On the other hand, O easily reacts with the R-rich phase, and when the amount of O increases, a rare earth oxide phase is formed and the amount of R-rich phase decreases. Generally, a very small amount of oxidizing impurity gas exists in the sintering furnace. For this reason, in the sintering process, the R-rich phase may be oxidized in the vicinity of the surface of the molded body, and the amount of R-rich phase may locally decrease. A composition with a large total content of R and a small amount of O has a large amount of R-rich phase, and the effect of oxidation on the shrinkage behavior during sintering is small. In a composition having a small total R content and / or a large amount of O, the amount of R-rich phase is small, so that oxidation during the sintering process affects the shrinkage behavior during sintering. As a result, deformation of the sintered body occurs due to partial shrinkage, that is, changes in dimensions. Therefore, deformation during sintering can be suppressed by reducing the oxygen content while keeping the total content of R at or above a predetermined amount.

  In addition, the method generally known conventionally can be used for the measuring method of the various components contained in the RTB system permanent magnet which concerns on this embodiment. The amount of various elements is measured by, for example, fluorescent X-ray analysis and inductively coupled plasma emission spectroscopy (ICP analysis). The oxygen content is measured, for example, by an inert gas melting-non-dispersive infrared absorption method. The carbon content is measured by, for example, combustion in an oxygen stream-infrared absorption method. The nitrogen content is measured, for example, by an inert gas melting-thermal conductivity method.

  The RTB-based permanent magnet according to the present embodiment has an arbitrary shape. For example, a shape such as a rectangular parallelepiped can be mentioned.

  Hereinafter, although the manufacturing method of a R-T-B type | system | group permanent magnet is demonstrated in detail, it will not restrict | limit to this and you may use another well-known method.

[Preparation process of raw material powder]
The raw material powder can be produced by a known method. In the present embodiment, the case of the one alloy method using a single alloy will be described, but a so-called two alloy method in which a raw material powder is prepared by mixing first and second alloys having different compositions may be used.

  First, a raw material alloy of an R-T-B system permanent magnet is prepared (alloy preparation step). In the alloy preparation process, a raw material alloy having a desired composition is prepared by melting a raw material metal corresponding to the composition of the R-T-B system permanent magnet according to the present embodiment by a known method and then casting the raw material metal.

  As a raw material metal, for example, a rare earth metal or a rare earth alloy, pure iron, ferroboron, a metal such as Co or Cu, or an alloy or compound thereof can be used. The casting method for casting the raw material alloy from the raw metal may be any method. In order to obtain an R-T-B permanent magnet having high magnetic properties, a strip casting method may be used. The obtained raw material alloy may be homogenized by a known method as necessary.

  After producing the raw material alloy, it is pulverized (pulverization step). In addition, the atmosphere of each process from a grinding | pulverization process to a sintering process can be made into a low oxygen concentration from a viewpoint of obtaining a high magnetic characteristic. For example, the oxygen concentration in each step may be 200 ppm or less. By controlling the oxygen concentration in each step, the amount of oxygen contained in the RTB-based permanent magnet can be controlled.

  Hereinafter, the pulverization step is performed in two stages: a coarse pulverization step of pulverizing until the particle size is about several hundred μm to several mm, and a fine pulverization step of pulverizing until the particle size is about several μm. As will be described below, it may be carried out in one stage only with the fine grinding process.

  In the coarse pulverization step, coarse pulverization is performed until the particle size becomes approximately several hundred μm to several mm. Thereby, coarsely pulverized powder is obtained. The method of coarse pulverization may be performed by any method, and can be performed by a known method such as a method of performing hydrogen occlusion and a method of using a coarse pulverizer. When performing hydrogen occlusion and pulverization, the amount of nitrogen contained in the RTB-based permanent magnet can be controlled by controlling the nitrogen gas concentration in the atmosphere during the dehydrogenation treatment.

  Next, the obtained coarsely pulverized powder is finely pulverized until the average particle diameter becomes about several μm (a fine pulverization step). Thereby, finely pulverized powder (raw material powder) is obtained. The average particle size of the finely pulverized powder may be 1 μm to 10 μm, 2 μm to 6 μm, or 3 μm to 5 μm. By controlling the nitrogen gas concentration in the atmosphere of the fine pulverization step, the amount of nitrogen contained in the RTB-based permanent magnet can be controlled.

  The pulverization is performed by an arbitrary method. For example, it is carried out by a method using various pulverizers.

  When the coarsely pulverized powder is finely pulverized, by adding various pulverization aids such as lauric acid amide and oleic acid amide, a finely pulverized powder with high orientation can be obtained during molding. Further, the amount of carbon contained in the RTB-based permanent magnet can be controlled by changing the amount of the grinding aid added.

[Molding process]
In the forming step, the finely pulverized powder is formed into a desired shape. Molding may be performed by any method. In this embodiment, the finely pulverized powder is filled in a mold and pressed in a magnetic field. Since the main phase crystal is oriented in a specific direction in the obtained compact, an RTB permanent magnet having a higher residual magnetic flux density can be obtained.

  The pressurization at the time of molding can be performed at 20 MPa to 300 MPa. The applied magnetic field can be 950 kA / m or more, and can be 950 kA / m to 1600 kA / m. The magnetic field to be applied is not limited to a static magnetic field, and may be a pulsed magnetic field. A static magnetic field and a pulsed magnetic field can also be used in combination.

  In addition, as a shaping | molding method, the wet shaping | molding which shape | molds the slurry which disperse | distributed finely pulverized powder in solvent, such as oil other than the dry type | molding which shape | molds finely pulverized powder as it is as mentioned above can also be applied.

The shape of the molded body obtained by molding the finely pulverized powder can be any shape. The density of the molded body at this point can be ^{4.0Mg / m 3 ~4.3Mg / m 3} .

[Sintering process]
A sintering process is a process of sintering a molded object in a vacuum or inert gas atmosphere, and obtaining a sintered compact. The sintering temperature needs to be adjusted depending on various conditions such as composition, pulverization method, difference in particle size and particle size distribution, etc., but for the molded body, for example, 1000 ° C. or higher and 1200 ° C. in vacuum or in the presence of an inert gas. Baking is performed by performing a heating process at a temperature of 1 ° C. or less and 1 hour or more and 20 hours or less. Thereby, a high-density sintered compact is obtained. In the present embodiment, a sintered body having a density of at least 7.45 Mg / m ³ or more is obtained. The density of the sintered body may be 7.50 Mg / m ³ or more.

[Aging process]
The aging treatment step is a step of heat-treating the sintered body at a temperature lower than the sintering temperature. There is no particular limitation on whether or not to perform the aging treatment, and the number of aging treatments is not particularly limited, and is appropriately performed according to desired magnetic characteristics. Moreover, the grain-boundary-diffusion process mentioned later may serve as the aging treatment process. In the R-T-B system permanent magnet according to the present embodiment, aging treatment is performed twice. Hereinafter, an embodiment in which the aging process is performed twice will be described.

  The first aging process is the first aging process, the second aging process is the second aging process, the aging temperature of the first aging process is T1, and the aging temperature of the second aging process is T2.

  There is no restriction | limiting in particular in temperature T1 and aging time in a 1st temporary effect process. It can be 1 hour-10 hours at 700 degreeC or more and 900 degrees C or less.

  There is no restriction | limiting in particular in temperature T2 and aging time in a 2nd aging process. It can be 1 hour-10 hours at 450 degreeC or more and 700 degrees C or less.

  By such an aging treatment, it is possible to improve the magnetic properties of the RTB permanent magnet finally obtained, particularly the coercive force HcJ.

  Further, the production stability of the R-T-B system permanent magnet according to the present embodiment can be confirmed by the magnitude of the change in magnetic characteristics with respect to the change in aging temperature. For example, if the amount of change in magnetic characteristics relative to the change in aging temperature is large, the magnetic characteristics will change with a slight change in aging temperature. For this reason, the range of the aging temperature allowable in an aging process becomes narrow, and manufacturing stability becomes low. Conversely, if the amount of change in magnetic characteristics with respect to the change in aging temperature is small, the magnetic characteristics will hardly change even if the aging temperature changes. For this reason, the range of the aging temperature allowable in an aging process becomes wide, and manufacturing stability becomes high.

  The RTB system permanent magnet according to the present embodiment obtained in this way has desired characteristics. Specifically, the residual magnetic flux density and the coercive force HcJ are high, and the corrosion resistance and manufacturing stability are also excellent. Furthermore, when the grain boundary diffusion process described later is performed, the reduction width of the residual magnetic flux density when the heavy rare earth element is diffused at the grain boundary is small, and the improvement width of the coercive force HcJ is large. That is, the R-T-B system permanent magnet according to the present embodiment is a magnet suitable for grain boundary diffusion.

  In addition, the RTB system permanent magnet which concerns on this embodiment obtained by the above method becomes an RTB system permanent magnet product by magnetizing.

  The R-T-B system permanent magnet according to the present embodiment is suitably used for applications such as motors and generators.

  Note that the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

Although the RTB-based permanent magnet is obtained by the above method, the manufacturing method of the RTB-based permanent magnet is not limited to the above method and may be changed as appropriate. For example, the RTB-based permanent magnet according to the present embodiment may be manufactured by hot working. The method for producing an RTB-based permanent magnet by hot working includes the following steps.
(A) Melting and quenching step of dissolving raw metal and quenching the obtained bath water to obtain a ribbon (b) Grinding step of pulverizing the ribbon to obtain a flaky raw powder (c) Crushed raw material powder (D) Preheating step for preheating the cold formed body (e) Hot forming step for hot forming the preheated cold formed body (f) Hot forming body A hot plastic working process in which plastic deformation is performed into a predetermined shape.
(G) An aging treatment step of aging the R-T-B permanent magnet

  Hereinafter, a method of diffusing heavy rare earth elements in grain boundaries in the RTB-based permanent magnet according to the present embodiment will be described.

[Processing process (before grain boundary diffusion)]
As needed, you may have the process of processing the RTB type | system | group permanent magnet which concerns on this embodiment into a desired shape. Examples of the processing method include shape processing such as cutting and grinding, and chamfering processing such as barrel polishing.

[Grain boundary diffusion process]
Grain boundary diffusion is carried out by attaching a heavy rare earth metal, a compound or alloy containing heavy rare earth elements, etc. to the surface of an R-T-B permanent magnet by coating or vapor deposition, and then performing a heat treatment. be able to. The coercive force HcJ of the RTB-based permanent magnet finally obtained can be further improved by the grain boundary diffusion of the heavy rare earth element.

  The heavy rare earth element may be Dy or Tb, with Tb being preferred.

  In the embodiment described below, a paint containing a heavy rare earth element is prepared, and the paint is applied to the surface of the RTB-based permanent magnet.

  The aspect of the paint is arbitrary. What is used as a metal of a heavy rare earth element, a compound or alloy containing the heavy rare earth element, and what is used as a solvent or a dispersion medium are also arbitrary. Further, the concentration of heavy rare earth elements in the coating is arbitrary.

  The diffusion treatment temperature in the grain boundary diffusion step according to this embodiment can be set to 800 ° C. to 950 ° C. The diffusion treatment time can be 1 hour to 50 hours. Note that the grain boundary diffusion step may also serve as the aging treatment step described above.

  Further, after the diffusion treatment, a heat treatment may be further performed. In this case, the heat treatment temperature can be 450 ° C. to 600 ° C. The heat treatment time can be 1 hour to 10 hours. Such heat treatment can improve the magnetic properties of the finally obtained RTB-based permanent magnet, particularly the coercive force HcJ.

  In addition, the production stability of the R-T-B system permanent magnet according to the present embodiment is such that the amount of change in magnetic properties with respect to the change in the diffusion treatment temperature in the grain boundary diffusion step and / or the heat treatment temperature after heavy rare earth diffusion is large. You can check with Hereinafter, the diffusion treatment temperature in the heavy rare earth diffusion step will be described, but the same applies to the heat treatment temperature after heavy rare earth diffusion. For example, if the amount of change in the magnetic characteristics with respect to the change in the diffusion treatment temperature is large, the magnetic characteristics change with a slight change in the diffusion treatment temperature. For this reason, the range of the diffusion treatment temperature allowed in the grain boundary diffusion step is narrowed, and the production stability is lowered. On the other hand, if the amount of change in the magnetic characteristics with respect to the change in the diffusion treatment temperature is small, the magnetic characteristics will hardly change even if the diffusion treatment temperature changes. For this reason, the range of the diffusion treatment temperature allowed in the grain boundary diffusion step is widened, and the production stability is increased.

[Processing process (after grain boundary diffusion)]
After the grain boundary diffusion step, various types of processing of the RTB-based permanent magnet may be performed. There is no restriction | limiting in particular in the kind of processing to implement. For example, shape processing such as cutting and grinding, and surface processing such as chamfering processing such as barrel polishing may be performed.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not restrict | limited to these Examples.

(Experimental example 1)
(Production of RTB-based sintered magnet)
As raw materials, Nd, Pr, electrolytic iron, and a low carbon ferroboron alloy were prepared. Furthermore, Al, Ga, Cu, Co, Mn, and Zr were prepared in the form of a pure metal or an alloy with Fe.

  Using the raw metal, a raw material alloy was prepared by strip casting so that the finally obtained magnet composition had the composition of each sample shown in Tables 1 and 3 to be described later. The contents (ppm) of C, N, and O shown in Tables 1 and 3 represent contents relative to the total mass of the magnet. Although Fe is not shown in Table 3, the content (% by mass) of each element other than C, N, and O shown in Table 1 and Table 3 is Nd, Pr, B, Al, Ga, Cu, Co , Mn, Zr and Fe are the total content of 100% by mass. The alloy thickness of the raw material alloy was 0.2 mm to 0.4 mm.

  Next, hydrogen was occluded by flowing hydrogen gas to the raw material alloy at room temperature for 1 hour. Next, the atmosphere was switched to Ar gas, dehydrogenation treatment was performed at 600 ° C. for 1 hour, and the raw material alloy was occluded by hydrogen. For sample numbers 74 to 76, the nitrogen gas concentration in the atmosphere during the dehydrogenation treatment was adjusted so that the nitrogen content was a predetermined amount. Furthermore, after cooling, a sieve having a particle size of 425 μm or less was obtained using a sieve. In addition, from the hydrogen occlusion pulverization to the sintering step described later, a low oxygen atmosphere with an oxygen concentration of less than 200 ppm was always used. For sample numbers 67 to 71, the oxygen concentration in the atmosphere was adjusted so that the oxygen content would be a predetermined amount.

  Subsequently, 0.1% oleic amide by mass ratio was added as a grinding aid to the raw alloy powder after using hydrogen storage and sieving, and mixed. In addition, about sample numbers 63-66, the addition amount of the grinding | pulverization adjuvant was adjusted so that carbon content might become predetermined amount.

  Subsequently, it was pulverized in a nitrogen stream using a collision plate type jet mill device to obtain fine powder (raw material powder) having an average particle diameter of 3.9 μm to 4.2 μm. Sample numbers 72 and 73 were finely pulverized in a mixed gas stream of Ar and nitrogen, and the nitrogen gas concentration was adjusted so that the nitrogen content was a predetermined amount. The average particle diameter is an average particle diameter D50 measured with a laser diffraction particle size distribution meter.

The obtained fine powder was molded in a magnetic field to produce a molded body. The applied magnetic field at this time is a static magnetic field of 1200 kA / m. The pressing force during molding was 98 MPa. The magnetic field application direction and the pressurizing direction were orthogonal to each other. When the density of the molded body at this time was measured, the density of all the molded bodies was within the range of 4.10 Mg / m ^{3 to} 4.25 Mg / m ³ .

Next, the molded body was sintered to obtain a sintered body. The optimum sintering conditions differed depending on the composition and the like, but were held for 4 hours within the range of 1040 ° C to 1100 ° C. The sintering atmosphere was in a vacuum. At this time, the sintered density was in the range of 7.45 Mg / m ^{3 to} 7.55 Mg / m ³ . Thereafter, in the Ar atmosphere and atmospheric pressure, the first temporary effect treatment was performed for 1 hour at the first temporary effect temperature T1 = 850 ° C., and further the second aging treatment was performed for 1 hour at the second aging temperature T2 = 520 ° C. . From the above, RTB-based sintered magnets of the samples shown in Tables 1 and 3 were obtained.

  The composition of the obtained RTB-based sintered magnet was evaluated by fluorescent X-ray analysis. B (boron) was evaluated by ICP. The oxygen content was measured by an inert gas melting-non-dispersive infrared absorption method, the carbon content was measured by combustion in an oxygen stream-infrared absorption method, and the nitrogen content was measured by an inert gas melting-thermal conductivity method. . It was confirmed that the composition of each sample was as shown in Tables 1 and 3.

  The RTB-based sintered magnet was processed into a vertical size of 14 mm × 10 mm × 11 mm (magnetization easy axis direction is 11 mm), and the magnetic properties were evaluated with a BH tracer. In addition, before the measurement, magnetization was performed with a 4000 kA / m pulsed magnetic field.

In general, the residual magnetic flux density and the coercive force HcJ are in a trade-off relationship. That is, the higher the residual magnetic flux density, the lower the coercive force HcJ, and the higher the coercive force HcJ, the lower the residual magnetic flux density. Therefore, in this embodiment, a performance index PI (Potential Index) for comprehensively evaluating the residual magnetic flux density and the coercive force HcJ is set. When the magnitude of the residual magnetic flux density measured in mT units is Br (mT) and the coercive force magnitude measured in kA / m units is HcJ (kA / m),
PI = Br + 25 × HcJ × 4π / 2000
It was. In this example, when PI ≧ 1635 before Tb diffusion, which will be described later, the residual magnetic flux density and coercive force HcJ before Tb diffusion are good. Also, the squareness ratio Hk / HcJ before Tb diffusion was 97% or more. In this embodiment, the squareness ratio Hk / HcJ is the magnetic field when the magnetization is 90% of Br in the second quadrant (JH demagnetization curve) of the magnetization J-magnetic field H curve. m) is calculated as Hk / HcJ × 100 (%).

  The case where PI before Tb diffusion was 1635 or more and the squareness ratio before Tb diffusion was 97% or more was evaluated as ◯, and the case where any of the characteristics was not good was evaluated as ×.

Moreover, the corrosion resistance test was done with respect to each sample. The corrosion resistance test was carried out by a PCT test (pressure cooker test) under saturated vapor pressure. Specifically, the R-T-B system sintered magnet was placed in an environment of 2 atm and 100% RH for 1000 hours, and the mass change before and after the test was measured. It was judged that the corrosion resistance was good when the mass reduction per surface area of the magnet was 3 mg / cm ² or less. It was judged that the corrosion resistance was particularly good when the mass loss was 2 mg / cm ² or less. When the corrosion resistance is particularly good, ◎, when the corrosion resistance is good, 食, and when the corrosion resistance is not good, ×. However, none of the samples subjected to the corrosion resistance test this time had poor corrosion resistance.

(Tb diffusion)
Further, the RTB-based sintered magnet obtained in the above process was processed into 14 mm × 10 mm × 4.2 mm (thickness in the easy axis direction of 4.2 mm). Then, an etching treatment was performed by immersing in a mixed solution of nitric acid and ethanol in which nitric acid was 3% by mass with respect to 100% by mass of ethanol, and then immersing in ethanol for 1 minute. The etching process of immersing in the mixed solution for 3 minutes and then immersing in ethanol for 1 minute was performed twice. Next, a slurry in which TbH ₂ particles (average particle diameter D50 = 10.0 μm) are dispersed in ethanol is applied to the entire surface of the sintered magnet after the etching treatment, and the mass ratio of Tb to the mass of the sintered magnet is 0.6. It apply | coated so that it might become mass%.

  After the slurry was applied and dried, diffusion treatment was performed at 930 ° C. for 18 hours while flowing Ar at atmospheric pressure (1 atm), followed by heat treatment at 520 ° C. for 4 hours.

  After the surface of the sintered magnet after the heat treatment was scraped off by 0.1 mm for each surface, the magnetic properties were evaluated with a BH tracer. Magnetic properties were evaluated after magnetizing with a 4000 kA / m pulsed magnetic field. Since the sintered magnet was thin, three of the sintered magnets were stacked and evaluated. In this embodiment, the amount of change in residual magnetic flux density due to Tb diffusion is ΔBr, and the amount of change in coercive force due to Tb diffusion is ΔHcJ. That is, ΔBr = (Br after Tb diffusion) − (Br before Tb diffusion). Similarly, ΔHcJ = (HcJ after Tb diffusion) − (HcJ before Tb diffusion). The PI after Tb diffusion was 1745 or more, and 1765 or more was even better. The squareness ratio after Tb diffusion was 90% or more.

  A case where PI after Tb diffusion was 1745 or more and a squareness ratio after Tb diffusion was 90% or more was evaluated as ◯, and a case where any of the characteristics was not good was evaluated as ×.

  In Table 1, TRE and B were varied. Further, Nd and Pr were contained so that the mass ratio of Nd and Pr was approximately 3: 1. The results are shown in Table 2. In Table 3, the content of each component other than TRE and B was changed. In Sample Nos. 77 to 80, TRE was fixed and the contents of Nd and Pr were changed. The results are shown in Table 4.

  From Tables 1 to 4, all Examples were good in PI before Tb diffusion, squareness ratio, and corrosion resistance. Furthermore, all the examples also had good PI and squareness ratio after Tb diffusion. On the other hand, in all the comparative examples, one or more of PI before Tb diffusion, squareness ratio before Tb diffusion, PI after Tb diffusion, and squareness ratio after Tb diffusion were not good.

  Moreover, Tb density | concentration distribution was measured using the electron probe microanalyzer (EPMA) about the RTB type | system | group sintered magnet after Tb spreading | diffusion described in Table 1-4. As a result, the RTB-based sintered magnet after Tb diffusion confirmed that the concentration distribution of Tb is a concentration distribution that decreases from the outside to the inside of the RTB-based sintered magnet. did.

Claims (7)

An R-T-B permanent magnet in which R is a rare earth element, T is an element other than rare earth elements, B, C, O and N, and B is boron,
T contains at least Fe, Cu, Co and Ga,
The total mass of R, T and B is 100% by mass,
The total content of R is 28.0% by mass to 30.2% by mass,
The Cu content is 0.04 mass% to 0.50 mass%,
Co content of 0.5 mass% to 3.0 mass%,
Ga content is 0.08 mass% to 0.30 mass%,
An R-T-B permanent magnet having a B content of 0.85% by mass to 0.95% by mass.   The RTB-based permanent sintered magnet according to claim 1, wherein the total content of R is 29.2 mass% to 30.2 mass%.   The RTB-based permanent magnet according to claim 1 or 2, which contains at least Nd as R.   The RTB-based permanent magnet according to any one of claims 1 to 3, wherein at least Pr is contained as R, and the content of Pr is greater than 0 and 10.0% by mass or less.   5. The RTB-based permanent magnet according to claim 1, wherein TRE / B is 2.2 to 2.7 in terms of atomic ratio when the total content of R is TRE.   The RTB-based permanent magnet according to claim 1, wherein 14B / (Fe + Co) is greater than 0 and 1.01 or less in atomic ratio.   The RTB-based permanent magnet according to claim 1, wherein the concentration distribution of the heavy rare earth element is a concentration distribution that decreases from the outside toward the inside.