JP3199506B2 - Rare earth permanent magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth permanent magnet having excellent magnetic properties and useful as a material for various electric and electronic devices.

[0002]

2. Description of the Related Art With the miniaturization and high performance of motors related to electronic equipment, the demand for rare earth permanent magnets is expanding at a rate exceeding that of ferrite magnets. Among these, rare earth permanent magnets that are well known and mass-produced include Sm-Co magnets, which are widely used in speakers, motors, measuring instruments, and the like. However, since an expensive SmCo-based alloy is used, there is a problem in cost, and replacing Co with inexpensive Fe is a development issue. On the other hand, Nd-Fe-B magnets have been developed that use Nd and Fe, which are abundant in resources, as main raw materials and have higher performance than Sm-Co magnets (see JP-A-59-46008). But this Nd-F
e-B magnets are very easy to rust, require some kind of coating, and have been put into practical use for the first time by the development of inexpensive and reliable rust prevention methods such as Ni plating.

Recently, inexpensive Fe has been used as a main raw material and Sm-
Th with magnetic properties equivalent to or better than Co-based magnets
A magnet having an Mn _12- type body-centered tetragonal structure (hereinafter referred to as a 1-12-type structure) has been discovered (see JP-A-1-175205). The 1-12 type compound which is the main phase of this magnet is R-Fe-M
(R is a rare earth containing Y, M is Ti, V, Si, Cr, Mn, W,
R-Fe (Co)
Although the binary system cannot exist stably, the introduction of the third element only stabilizes the 1-12 type structure. This compound is stable even without expensive Co, and has almost the same properties as the Nd ₂ Fe ₁₄ B compound in saturation magnetization, anisotropic magnetic field, Curie temperature, etc. Despite having high corrosion resistance.

[0004]

The 1-12 type compound having excellent magnetic properties as described above is very difficult to obtain a single phase of the compound, and requires a long heat treatment for several days.
When making a nucleation type magnet using a liquid phase sintering method typified by Nd-Fe-B magnets, in addition to the main phase, a rare earth rich phase (contains a large amount of rare earth elements, melts during sintering and contributes to higher density) However, in the case of a 1-12 type magnet, if the amount of rare earth is greater than the stoichiometric composition of the compound, R ₂ , which is a reverse magnetic domain generation source,
An Fe ₁₇ type compound (2-17 type compound) is easily crystallized, which causes a decrease in coercive force. For these reasons, the 1-12 type magnet has not been industrialized yet. An object of the present invention is to solve the above-mentioned obstacles, to find a 1-12 type compound having excellent magnetic properties from the aspect of composition, and to provide a relatively easy production method.

[0005]

In order to solve the above problems, the present inventors have found that a molten ingot of a 1-12 type magnet must be solutionized in a short time to an alloy composed of a main phase and a rich phase. The present invention was completed by solving this from the aspect of magnet alloy composition, and the gist of the invention is that the composition formula is R _x Fe _100-xy (V _{1 -a} Si _a ) _y (where R includes Y One or more rare earth elements, x = 5.5-18%, y =
A rare-earth permanent magnet represented by 8 to 20% (% is an atomic percentage) and a = 0.05 to 0.7 (atomic ratio), wherein the main phase has a ThMn _12- type body-centered tetragonal structure.

Hereinafter, the present invention will be described in detail. The most important feature of the present invention is that a third element (Ti, V, Si, Cr, Mn, W, W) for realizing a body-centered tetragonal ThMn ₁₂ type structure in an R-Fe system.
Of the various combinations of Mo, Al, etc., the composite addition of two elements, especially V and Si, stabilizes the 1-12 type body-centered tetragonal structure of the main phase,
It has been found that an alloy composed of a main phase and a rare earth-rich phase can be easily obtained by a short-time heat treatment.

[0007]

In the nucleation magnet represented by the Nd-Fe-B magnet, the rare-earth-rich phase melts at a temperature lower than the melting temperature of the main phase during the sintering process in powder metallurgy, and the rare-earth-rich liquid phase Becomes dense while wrapping around the main phase. This makes it possible to obtain a uniform and fine structure without enlarging each isolated main phase. The nucleation type magnet having such a structure is characterized in that the initial magnetization curve rises steeply from the thermal demagnetization state, and the domain wall is very easy to move within the grains of the main phase. Therefore, when a reverse magnetic domain bud occurs in a crystal grain, it spreads quickly throughout the crystal grain and magnetization reversal occurs. The high coercive force of the nucleation-type magnet means that the rare earth rich phase surrounding the main phase disappears the reverse domain generation source at the grain boundary, and the domain walls generated in the phases other than the main phase are less likely to enter the main phase, and the magnetization reversal Is less likely to occur. Since the magnitude of the coercive force corresponds to the domain wall energy near the grain boundary, a large difference in the domain wall energy between the main phase and the rare earth-rich phase surrounding it causes a high coercive force. Therefore, in this type of sintered magnet, the magnitude of the coercive force is determined by how uniformly the rich phase covers the main phase.

The ingot dissolved by the composition of the above formula is heat-treated at 800 to 1,100 ° C. for 2 to 10 hours,
An alloy comprising a main phase having a 1-12 type structure and a rare earth rich phase can be easily obtained. During sintering, the rare earth-rich phase becomes dense while wrapping around the main phase 1-12 phase, as in the case of the Nd-Fe-B-based magnet described above. , A high coercive force can be obtained due to a large difference in domain wall energy.

As the third element for stabilizing the body-centered tetragonal ThMn ₁₂ structure, which is the main phase, in addition to V and Si, Ti, Cr, Mn, W,
Although there are Mo and Al, an alloy composed of a main phase and a rare-earth-rich phase can be easily obtained particularly with a combination of V and Si. The reason for this dissolution, a structure of the alloy as-cast fine Therefore short-time heat treatment (meaning short range diffusion)
Then, disappearance of α-Fe and formation of ThMn ₁₂ type tetragonal crystal occur. In addition, since 1-12 type compounds containing V and Si are very stable and are formed preferentially in an equilibrium state, the Fe in the alloy is almost 1-12 type.
Since it is contained in the type compound, the rare earth content is higher than the 1-12 type compound, R ₂ Fe ₁₇ compound, RFe ₂ compound, etc. are not formed,
It is believed that a rare earth rich phase is formed.

[0010] In the present invention the composition formula _{R x Fe 100-xy (V} 1-a Si a) y, if x is less than 5.5 atomic%, the rare earth is 1-12
It is consumed to form the type compound, rare earth-rich phase hardly appears, and α-Fe remains even after solution treatment, and sufficient coercive force cannot be obtained. On the other hand, if it exceeds 18 atomic%, the saturation magnetization is greatly reduced. Further, when y is out of the range of 8 to 20 atomic%, the body-centered tetragonal ThMn ₁₂ structure is not stabilized.
2-17 phase and α-Fe phase are crystallized, and large coercive force cannot be expected. When the value of a is less than 0.05 (atomic ratio), α-Fe does not easily disappear, and serves as a source of a reverse magnetic domain to decrease the coercive force. In addition, complete elimination of α-Fe requires a long time for heat treatment, which is not economical. In addition, rare earth elements having a high vapor pressure are easily evaporated, and a desired composition cannot be obtained. When the value of a exceeds 0.7, the 2-17 phase is easily crystallized,
Coercive force is greatly reduced.

Although the present invention is based on the R-Fe-V-Si system,
Part of V and Si is Ti, Cr, Mn, W, Nb, Mo, Ta, Al,
It can be replaced with Sn, Zr, Hf, Ge. However, an excessively large addition causes deterioration of magnetic properties, so the replacement amount is 5%.
It is up to about atomic%. The rare earth elements to which the present invention is applied include La, Ce, Pr, Nd, Pm, Sm, Eu, Gc, Tb, Dy, H containing Y.
One, two or more of o, Er, Tm, Yb and Lu.

The permanent magnet alloy according to the present invention has excellent magnetic properties by subjecting a compound having the above alloy composition to melting, casting, solution treatment, pulverization, molding in a magnetic field, sintering, and aging by ordinary powder metallurgy. Can be realized.

[0013]

EXAMPLES Hereinafter, embodiments of the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. (Example 1 of actual machine) 99.9% by weight of Sm metal, 99.9% by weight of M = Si, V, Cr, Ti, Mo each metal and Fe, Sm 11.
0, Fe 76.0, M 15.0 Atomic% (15.0 atomic% in total when M is 2 or more), weighed so as to perform high frequency melting in inert gas, cooled the molten metal with Cu mold, 1,10
A solution was formed at 0 ° C. for 2 hours to obtain Sample No. 2. As a result of observation of this sample by X-ray diffraction and EPMA, a metal phase was identified. Containing V + Si: 1-12 phase, composed of rare earth rich phase. Others: α-Fe phase, 1-12 phase, 2-17
Phase, consisting of a rare earth rich phase. Figure 1 shows Sm 11.0, Fe 76.
0, M 15.0 (V 10.0, Si 5.0) A composition image by an electron probe X-ray microanalyzer (hereinafter abbreviated as EPMA) obtained by subjecting the compound (sample No. 2) having a composition of each atomic% to the above-mentioned heat treatment. Show. In the figure, the gray part is the ThMn _12- type body-centered tetragonal compound, and the surrounding white part is the Sm-rich phase. Table 1 shows the results of separately measuring the magnetic properties (coercive force) of the sintered body using a self-recording magnetometer.

Example 2 Sm metal having a purity of 99.9% by weight,
Ferrovanadium containing 99.9% by weight of Si and 45% of Fe
Fe was weighed as shown in Table 1 (Sample Nos. 1 to 5), subjected to high frequency melting in an inert gas, cooled with a Cu mold, and then solution-solutioned at 1,100 ° C. for 2 hours. After coarsely pulverizing the ingot, it was finely pulverized by a jet mill using N ₂ gas to an average particle diameter of 3 to 5 μm. After the fine powder is oriented in a static magnetic field of 12 kOe and press-molded at a pressure of 1 t / cm ² , the compact is sintered in an inert gas at a temperature of 1,150 ° C. for 1 hour, and subsequently heated at 600 ° C. After a heat treatment at a temperature for one hour, it was rapidly cooled. Table 1 shows the results of measuring the magnetic properties of the sintered body with a self-recording magnetometer.

Comparative Example Sample No. 6 was added without Si, and sample N was not added.
A sintered body was prepared in the same manner as in Example 1 except that V was not added to o.7, and the magnetic properties were measured.

[0016]

[Table 1]

[0017]

According to the present invention, a compound having the above composition easily forms a structure useful for a nucleation type sintered magnet by a short-time heat treatment, and is a rare earth permanent magnet having excellent magnetic properties by ordinary powder metallurgy. A magnet can be obtained, and its utility value is extremely high in industry.

[Brief description of the drawings]

FIG. 1 is a drawing showing a metal structure by EPMA of the composition of Sample No. 2 of Example 1 of the present invention.

Claims (1)

(57) [Claims] 1. A composition formula _{R x Fe 100-xy (V} 1-a Si a) y ( wherein R represents one or more rare earth elements including Y, x =
5.5-18%, y = 8-20% (% is atomic percentage), a = 0.0
A rare earth permanent magnet represented by 5 to 0.7 (atomic ratio), wherein the main phase has a ThMn _12- type body-centered tetragonal structure.