JP2016111136A - Rare-earth magnet - Google Patents

Abstract

The present invention provides a rare earth magnet excellent in high temperature coercive force while reducing the amount of Nd. (CexNd (1-x)) yFe (100-ywzv) CowBzMv (wherein M is at least one of Ga, Al, Cu, Au, Ag, Zn, In, Mn, and 0 ≦ x ≦ 0.75, 5 ≦ y ≦ 20, 4 ≦ z ≦ 6.5, 0 ≦ w ≦ 8, 0 ≦ v ≦ 2). The shell portion 2 includes crystal grains having a higher Nd concentration in the shell portion 2 than in the core portion 1. [Selection] Figure 1

Description

  The present invention relates to a rare earth magnet having high coercivity at high temperatures.

  Rare earth magnets using rare earth elements are also called permanent magnets, and their uses are used in motors for driving hard disks and MRI, as well as drive motors for hybrid vehicles and electric vehicles.

  Residual magnetization (residual speed density) and coercive force can be cited as indicators of the magnet performance of this rare earth magnet. However, the rare earth magnets used also have increased heat generation due to miniaturization of motors and higher current density. The demand for heat resistance is further increasing, and how to maintain the coercive force of a magnet under high temperature use is one of the important research subjects in the technical field. Taking Nd-Fe-B magnets, one of the rare-earth magnets frequently used in vehicle drive motors, to refine crystal grains, use a composition alloy with a large amount of Nd, Attempts have been made to increase the coercivity by adding heavy rare earth elements such as high Dy and Tb.

  As rare earth elements, there are a general sintered magnet having a crystal grain scale of about 3 to 5 μm constituting a structure, and a nanocrystal magnet obtained by refining crystal grains to a nanoscale of 50 nm to 300 nm.

  The microstructure of a general rare earth magnet of Nd—Fe—B system is composed of Nd-rich crystal grains and grain boundaries interposed between the crystal grains. Since Nd constituting the crystal grains is an expensive rare earth element, how to reduce the amount of use while guaranteeing magnet performance is one of the important development issues in the technical field.

  Therefore, as measures for reducing the amount of Nd used, the use of light rare earth elements such as Ce and La and the use of elements such as Gd, Y, Sc, Sm, and Lu can be considered.

  However, when these elements are applied instead of Nd, it is assumed that the magnetic properties of rare earth magnets are significantly reduced even when much of Nd is replaced with these elements. The amount of these elements used must be limited, and a sufficient material cost reduction effect cannot be expected. Further, when these elements having low magnetic properties are used, there is a very strong tendency that their usage is generally limited to isotropic.

  Therefore, when attempting to anisotropy of rare earth magnets using the light rare earth elements and elements such as Gd and Y, the coercive force of the rare earth magnets is significantly reduced in a machining process such as hot plastic machining. Therefore, the deterioration of magnetic properties is inevitable.

  Here, Patent Document 1 describes Nd, R (at least one rare earth element selected from La, Ce, Pr, Dy, Ho, and Tb), Fe, and M (Al, Ti, V, Cr, In an Nd—R—Fe—MB system magnet containing at least one metal element of Mn, Co, Ni, Zr, Nb, Mo, Ta, and W) and B, the concentration of R and M Discloses a magnet characterized by being high at the periphery of the crystal grains (main phase) constituting the magnet and low at the center.

  In the magnet disclosed here, R may be Ce or La. However, a magnet using only Ce or La as R is not specifically disclosed, and such a magnet is high at a high temperature. It is not clear whether or not the coercive force is exhibited.

JP 63-127505 A

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a rare earth magnet excellent in high temperature coercive force while reducing the amount of Nd.

In order to achieve the above object, according to the present invention,
_{(Ce x Nd (1-x} )) y Fe (100-ywzv) Co w B z M v
(In the above formula, M is at least one of Ga, Al, Cu, Au, Ag, Zn, In, and Mn, and 0 ≦ x ≦ 0.75, 5 ≦ y ≦ 20, 4 ≦ z ≦ 6.5. , 0 ≦ w ≦ 8, 0 ≦ v ≦ 2)
There is provided a rare earth magnet having a crystal grain having an overall composition, and comprising a core part and a surrounding shell part, and having crystal grains having a higher Nd concentration in the shell part than in the core part.

  In the rare earth magnet of the present invention, the crystal grains are composed of a core portion and a shell portion around the core portion, and a light rare earth element of Ce or an element such as Gd or Y replaces a part of Nd in the core portion, Therefore, the material cost can be significantly reduced as compared with a rare earth magnet made of crystal grains having a core portion made of only Nd. As described above, the core portion contains an element having a low Nd concentration even though the core portion includes an inexpensive element having a low magnetic property, and the Nd concentration is higher in the shell portion than in the core portion. Thus, while suppressing the deterioration of high magnetic properties, the magnetic separation between crystal grains is achieved, and the rare earth magnet is excellent in magnetic anisotropy.

  The core part of the crystal grain becomes a semi-hard phase having a relatively low coercive force because of the relatively small amount of Nd, while the shell part of the crystal grain becomes a hard phase having a high coercive force because of the large amount of Nd. Therefore, it can be said that the crystal grains constituting the rare earth magnet have a composite structure of a semi-hard phase and a hard phase. In addition, since the crystal grains are provided with a hard phase having a high coercive force as the shell portion, magnetic separation between the crystal grains is achieved, which leads to improvement of magnetic characteristics.

  As described above, according to the rare earth magnet of the present invention, the amount of expensive Nd element, which is a composition component of crystal grains, is reduced, and instead relatively inexpensive Ce is applied, thereby reducing the material cost. Compared to conventional rare earth magnets, it can be made much cheaper. In addition, the crystal grains have a structure having a shell part rich in Nd around the core part containing Ce, and the Nd concentration is higher in the shell part than in the core part, so that the magnetic anisotropy is excellent, and the high temperature holding is performed. It becomes a rare earth magnet made of crystal grains with excellent magnetic force.

It is the schematic diagram explaining the microstructure of the rare earth magnet of the present invention. It is a figure explaining the magnetic anisotropy in each position on the II-II line | wire of FIG. 6 is a graph showing temperature dependence of coercivity of Example 1 and Comparative Example 1. 6 is a graph showing temperature dependence of coercive force of Example 2 and Comparative Example 2. 6 is a graph showing the temperature dependence of coercivity of Example 3 and Comparative Example 3.

  Embodiments of a rare earth magnet and a method for manufacturing the same according to the present invention will be described below with reference to the drawings.

(Rare earth magnet)
FIG. 1 is a schematic diagram illustrating the microstructure of the rare earth magnet of the present invention, and FIG. 2 is a diagram illustrating the magnetic anisotropy at each position on the II-II line of FIG. The illustrated rare earth magnet 100 has a microstructure in which a large number of crystal grains 10 are provided with grain boundaries 20 interposed therebetween. In addition, although the crystal grains 10 in the illustrated example have a hexagonal cross-sectional shape, the cross-sectional shapes such as a quadrangle (rectangular shape, an ellipsoidal shape) and an elliptical shape are various.

  The crystal grain 10 has a so-called core-shell structure composed of a core portion 1 and a shell portion 2 around the core portion 1.

Crystal grains _{10, (Ce x Nd (1-} x)) y Fe (100-ywzv) Co w B z M v ( where, M is Ga, Al, Cu, Au, Ag, Zn, In, Mn of At least one, and has an overall composition of 0 ≦ x ≦ 0.75, 5 ≦ y ≦ 20, 4 ≦ z ≦ 6.5, 0 ≦ w ≦ 8, 0 ≦ v ≦ 2). The crystal grains are composed of a core portion and a surrounding shell portion, and have a composition in which the Nd concentration is higher in the shell portion than in the core portion.

  Here, x in the core portion has a larger composition than x in the shell portion.

Since the core part 1 is in a state in which a part of Nd is replaced with an element whose material cost is much lower than Nd, such as Ce, rather than Nd, a magnetic material having a core part made only of Nd The material cost can be greatly reduced as compared with rare earth magnets made of, that is, general Nd ₂ Fe ₁₄ B magnets (neodymium magnets).

However, since the core part 1 constituting the crystal grains 10 substitutes a part of Nd with Ce, the magnetic characteristics are inevitably lowered as compared with a general Nd ₂ Fe ₁₄ B magnet.

  In order to suppress this decrease in magnetic characteristics, the illustrated crystal grain 10 has the shell part 2 having a high Nd concentration around the core part 1, thereby achieving magnetic separation between adjacent crystal grains 10. The magnetic anisotropy is provided, and the deterioration of magnetic properties such as coercive force and remanent magnetization is suppressed.

  This can be easily understood from the diagram showing the magnetic anisotropy for each part of the crystal grain 10 shown in FIG. As shown in the figure, the core portion 1 has a part of Nd replaced with Ce having low magnetic properties and the magnetic anisotropy is also low. On the other hand, the surrounding shell portion 2 has an Nd concentration. Is a high region, the magnetic anisotropy becomes high.

  In this way, by substituting a part of Nd with an inexpensive element for the core 1, the amount of Nd is reduced, and the shell portion 2 having a high Nd concentration is included, thereby suppressing a decrease in the overall magnetic characteristics. The crystal grains 10 are formed. That is, when the magnetic anisotropy of the shell portion is higher than the magnetic anisotropy of the core portion, the coercive force is improved. Therefore, in the rare earth magnet of the present invention, by taking the core-shell structure, It is considered that the magnetization of the peripheral part of the crystal is less likely to be reversed and the magnetization reversal of the entire magnet phase is suppressed as a result. Therefore, the rare earth magnet 100 made of such crystal grains 10 has magnetic anisotropy and magnetic properties while reducing the material cost of the rare earth magnet and the manufacturing cost of the rare earth magnet resulting from this. It will be excellent.

Further, in the rare earth magnet of the core-shell structure of the present invention, compared with a conventional magnet having no boundary between the core part and the shell part and in which Nd ₂ Fe ₁₄ B and Ce ₂ Fe ₁₄ B of the magnetic phase are mixed, The coercive force is improved at a temperature of 160 ° C. or lower. This is because the temperature characteristic is improved by Ce ₂ Fe ₁₄ B in the core part, and the rate of decrease in coercive force at high temperature is suppressed because the magnetization is not easily reversed by Nd ₂ Fe ₁₄ B in the shell part. it is conceivable that.

  Moreover, the average particle diameter of the crystal grain 10 shown in FIG. 1 is 1000 nm or less, Preferably it is 500 nm or less. This is because a constant demagnetization resistance, that is, a constant coercive force can be ensured by adjusting the average grain size of the crystal grains to 1000 nm or less.

  Here, the “average particle size” is, for example, the average value of the lengths t of the crystal grains 10 shown in FIG. 1 (the cross section is not circular, but this length is also included in the “particle size”). For example, the “average particle size” is obtained by defining a certain region by an SEM image, a TEM image, or the like of the rare earth magnet 100 and calculating the average value of the particle sizes t of the crystal grains in the certain region. When the cross-sectional shape of the crystal grains is elliptical, the major axis can be the grain size, and when the crystal grains are square, the length of the longer diagonal can be the grain diameter. In addition, the calculation method of the average particle diameter illustrated here is an example to the last.

  In the rare earth magnet of the present invention, the core part of the crystal grain is the center part of the crystal grain, and the shell part is the surface part of the crystal grain.

(Rare earth magnet manufacturing method)
Next, a method for manufacturing the rare earth magnet 100 shown in FIG. 1 will be described.
_{First, (Ce x Nd (1-} x)) y Fe (100-ywzv) Co w B z M v ( where, M is Ga, Al, Cu, Au, Ag, Zn, In, at least one Mn And 0 ≦ x ≦ 0.75, 5 ≦ y ≦ 20, 4 ≦ z ≦ 6.5, 0 ≦ w ≦ 8, 0 ≦ v ≦ 2). .

  For example, a method of manufacturing an isotropic magnetic powder having a nanocrystalline structure by a liquid quenching method, a method of manufacturing an isotropic or anisotropic magnetic powder by an HDDR method, or the like can be applied to this magnetic powder manufacturing method.

  An outline of the method using the liquid quenching method is as follows. For example, in a furnace (not shown) in an Ar gas atmosphere whose pressure is reduced to 50 kPa or less, an alloy ingot is melted at a high frequency by a melt spinning method using a single roll, and a molten metal having a core portion composition is made of copper It can be manufactured by jetting onto a roll to produce a quenched ribbon (quenched ribbon) and roughly pulverizing it.

  For example, magnetic powder pulverized to about 10 μm or less is magnetically oriented, and an anisotropic rare earth magnet precursor is manufactured through liquid phase sintering. Alternatively, an isotropic rare earth magnet precursor is produced by hot pressing an isotropic magnetic powder having a nanocrystalline structure produced by a liquid quenching method. Alternatively, an anisotropic rare earth magnet precursor is produced by hot pressing an isotropic magnetic powder having a nanocrystalline structure and then performing hot plastic working. Alternatively, an isotropic or anisotropic rare earth magnet precursor is produced by hot pressing an isotropic or anisotropic magnetic powder produced by the HDDR method.

  By the method as described above, an isotropic or anisotropic rare earth magnet precursor is produced (the first step of the production method is heretofore).

  The crystal grains constituting the rare earth magnet precursor produced in the first step are crystal grains having a small amount of Nd and low magnetic properties (constructed only from the semi-hard phase described above). Nd element or Nd-M alloy (M: Ga or a part of Ga is at least selected from Al, Cu, Au, Ag, Zn, In, Mn, and Fe in order to form a shell portion serving as a hard phase in this crystal grain. A modified metal composed of one type) is diffused and infiltrated into the rare earth magnet precursor (second step of the manufacturing method).

  For example, a vapor phase method in which Nd element is vaporized in a vacuum at around 850 ° C. and enters the grain boundary of the rare earth magnet precursor is applied. Alternatively, a liquid phase method in which a melt of a low melting point Nd-M alloy is infiltrated into the grain boundary of the rare earth magnet precursor is applied. Alternatively, a solid of a compound with Nd element, Nd-M alloy, oxygen, fluorine, or the like is brought into contact with a rare earth magnet precursor and heated in a range of about 500 to 900 ° C., so that the grain boundary between crystal grains An exchange reaction between the remaining R solid solution and the Nd element is caused, and a solid phase method in which the modified metal is diffused and penetrated through the grain boundary is applied.

  Here, a heavy rare earth element such as Dy or Tb may be used as the Nd element or the Nd-M alloy, but preferably, as the M element of the Nd-M alloy without using the heavy rare earth element, Any one of Cu, Mn, In, Zn, Al, Ag, Ga, Fe and the like, which are transition metal elements or typical metal elements, may be used. Specific examples of such an Nd-M alloy include an Nd—Cu alloy (eutectic point 520 ° C.), an Nd—Al alloy (eutectic point 650 ° C.), and any eutectic point is 650. Extremely low temperature of about ℃ or less. Even when a heavy rare earth element or an alloy thereof is used as a modified alloy, it is preferable to use an alloy having an eutectic point of about 900 ° C. or lower.

  As described above, the Nd-M alloy having a low eutectic point is used to diffuse and penetrate at a low temperature. For example, when placed in a high temperature atmosphere of about 800 ° C. or higher, the coarsening of crystal grains becomes a problem. This manufacturing method is suitable for a crystal magnet (with a crystal grain size of about 50 nm to 300 nm).

Example 1
_{(Ce x Nd (1-x} )) y Fe (100-ywzv) Co w B z Ga v (x = 0.25, y = 13.5, z = 5.8, w = 4, v = 0. The alloy having the composition 5) was nanocrystallized by liquid quenching (the amorphous may be heat-treated). Here, as an implementation quenching condition, the molten metal temperature is 1450 ° C., an inert atmosphere (Ar reduced pressure atmosphere), and the peripheral speed is 20 to 40 m / s. A ribbon having this nanocrystalline structure was packed in a die and pressed and heated to produce a molded body. Here, as implementation molding conditions, the molding pressure is 400 MPa, the temperature is 650 ° C., and the holding time is 180 s. This molded body was subjected to hot plastic processing (strong processing) to obtain an oriented nanocrystal structure. Here, as the strong processing conditions, the processing temperature is 750 ° C., the strain rate is 0.1 to 10 / s, and the processing method is upsetting. The rare earth magnet precursor (core part) manufactured by this upsetting process is Ce _0.25 Nd _0.75 Fe ₁₄ B, which is in a semi-hard state where the coercive force is lower than that of Nd ₂ Fe ₁₄ B. Accordingly, a low melting point alloy of Nd ₇₀ Cu ₃₀ was brought into contact with the rare earth magnet precursor in a semi-hard state, and heat treatment was performed at a melting temperature. Here, the heat treatment conditions are a heat treatment temperature of 650 ° C., a treatment time of 165 to 360 min, and a contact alloy amount of 10 wt% (relative to the rare earth magnet precursor). The Nd ₇₀ Cu ₃₀ alloy was prepared by wetting Nd (manufactured by high purity chemical) and Cu (manufactured by high purity chemical), arc melting, and liquid quenching.

Through the above steps, the core part is Ce _0.25 Nd _0.75 Fe ₁₄ B phase, the shell part is (Nd, Ce) ₂ Fe ₁₄ B phase, and the Nd concentration of the shell part ≧ Nd concentration of the core part. A core-shell type magnet was obtained. The starting alloy contained Co and Ga, but the core and shell of the obtained magnet did not contain Co and Ga. This is because Co and Ga are included, but are neglected because they are very small. Hereinafter, the same applies to Examples 2-3 and Comparative Examples 1-3.

Example 2
In the formula shown in Example 1, x = 0.5 in which alloy _{((Ce x Nd (1-} x)) y Fe (100-ywzv) Co w B z Ga v (x = 0.5, y = 13 .5, z = 5.8, w = 4, v = 0.5)) was used as a starting material, and a core-shell type magnet was obtained in the same manner as in Example 1.

Example 3
In the formula shown in Example 1, x = 0.75 at a alloy _{((Ce x Nd (1-} x)) y Fe (100-ywzv) Co w B z Ga v (x = 0.75, y = 13 .5, z = 5.8, w = 4, v = 0.5)) was used as a starting material, and a core-shell type magnet was obtained in the same manner as in Example 1.

Comparative Example 1
In the formula shown in Example 1, x = 0 and is an alloy _{((Ce x Nd (1-} x)) y Fe (100-ywzv) Co w B z Ga v (x = 0, y = 13.5, z = 5.8, w = 4, v = 0.5)) as a starting material, a bulk magnet (grains) without a boundary between the core part and the shell part, which was crushed finely after strong processing and sintered while applying a magnetic field In the same manner as in Example 1, Nd ₇₀ Cu ₃₀ was contacted with a diameter of about 800 nm, and heat treatment was performed to produce a magnet.

Comparative Example 2
In the formula shown in Example 1, x = 0 and is an alloy _{((Ce x Nd (1-} x)) y Fe (100-ywzv) Co w B z Ga v (x = 0, y = 13.5, z = 5.8, w = 4, v = 0.5)) were used as starting materials, and a magnet was prepared in the same manner as in Example 1 except that the heat treatment step in which Nd ₇₀ Cu ₃₀ was contacted was omitted after strong processing.

Comparative Example 3
In the formula shown in Example 1, x = 0.5 in which alloy _{((Ce x Nd (1-} x)) y Fe (100-ywzv) Co w B z Ga v (x = 0, y = 13.5 Z = 5.8, w = 4, v = 0.5)) as a starting material, and an alloy with x = 0.25 ((Nd _0.75 Ce _0.25 ) _13.5 Fe _76.2 Co ₄ B _5.8 Ga _0.5 ) A magnet was manufactured in the same manner as in Example 1 except that the heat treatment step for contacting Nd ₇₀ Cu ₃₀ as a material was omitted after the strong processing.

  The above results are summarized in Table 1 below.

  About the obtained magnet, the coercive force was measured by VSM (LakeShore) at room temperature after 10T pulse magnetization. Subsequently, a hysteresis curve at each temperature from room temperature to 200 ° C. (room temperature, 60, 80, 100, 140, 160, 180, 200 ° C.) was measured to obtain a coercive force. The measurement results of the coercive force at 160 ° C. are shown in Table 2 below.

  The temperature characteristics of the coercive force are shown in FIGS. 3 to 5, and the measurement results of the core portion Nd concentration, the shell portion Nd concentration, and the overall Nd concentration in Example 3 and Comparative Example 3 are shown in Table 3 below. Show.

磁石粒子の全体のＮｄ濃度が同程度であるにもかかわらず、コアシェル構造をとることにより、温度特性が向上している。

The temperature characteristics are improved by adopting the core-shell structure despite the fact that the Nd concentration of the whole magnet particles is approximately the same.

  From the above results, it can be seen that the coercive force at high temperature is higher than that of the comparative example for all the examples, although the coercive force at the normal temperature is similar. This is because by using a core-shell structure double-phase magnet, the magnetic anisotropy of the core portion ≦ the magnetic anisotropy of the shell portion, and the magnetization reversal at the periphery of the magnet particle is suppressed. As a result, the coercive force at high temperature Is assumed to be higher than the coercive force of single-phase magnets at high temperatures.

DESCRIPTION OF SYMBOLS 1 Core part 2 Shell part 10 Crystal grain 20 Grain boundary 100 Rare earth magnet

Claims (1)

_{(Ce x Nd (1-x} )) y Fe (100-ywzv) Co w B z M v
(In the above formula, M is at least one of Ga, Al, Cu, Au, Ag, Zn, In, and Mn,
0 ≦ x ≦ 0.75,
5 ≦ y ≦ 20,
4 ≦ z ≦ 6.5,
0 ≦ w ≦ 8,
0 ≦ v ≦ 2)
A rare-earth magnet comprising crystal grains having the overall composition, and comprising a core part and a surrounding shell part, and having crystal grains having a higher Nd concentration in the shell part than in the core part.

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