JP2675430B2 - Corrosion resistant rare earth-transition metal magnet and method of manufacturing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rare earth-transition metal magnet having excellent magnetic properties as well as excellent corrosion resistance and temperature characteristics, and a method for producing the same.

(Prior Art) Alnico magnets, ferrite magnets, rare earth magnets, and the like are mentioned as typical permanent magnet materials currently manufactured. Alnico magnets are historically old, but demand is declining due to the development of inexpensive ferrite magnets and rare earth magnets with even higher magnetic properties. Ferrite magnets, on the other hand, are chemically stable because they use oxides as the main raw material, and because they are low cost, they still occupy the mainstream of magnet materials, but they have the drawback of a small maximum energy product.

After that, Sm-Co based magnets that combined the magnetic anisotropy of rare earth ions and the magnetic moment of transition metal elements appeared, and the conventional maximum energy product was renewed significantly. However, the Sm-Co magnets have to be expensive magnets because they contain Sm and Co, which are scarce resources, as the main components.

Therefore, a magnetic alloy that does not contain expensive Sm and Co and that has low cost and high magnetic properties was developed.As a result, Sagawa et al. Developed a ternary stable alloy by the sintering method (Japanese Patent Publication Sho 61-3424).
2 and JP-A-59-132104), and JJC
roat et al. have alloys with high coercive force by the liquid quenching method (JP-A-59)
-64739 publication) was developed. These are magnets composed of Nd, Fe and B, and their maximum energy products exceed those of Sm-Co magnets.

However, since Nd-Fe-B magnets contain a large amount of light rare earth elements such as Nd, which has a very high activity, and Fe, which easily rusts, they are inferior in corrosion resistance and, as a result, their magnetic properties deteriorate. It has a drawback that it lacks reliability as an industrial material.

Therefore, in order to improve the corrosion resistance, for example, a sintered magnet is subjected to surface plating (Japanese Unexamined Patent Publication No. 63-77103), coating treatment (Japanese Unexamined Patent Publication No. 60-63901), etc. Although measures such as surface treatment are taken in advance before kneading the magnetic powder and resin, none of these can be said to be effective rust-prevention treatment for a long period of time, and the cost increases due to the treatment, and the protective film There were also problems such as loss of magnetic flux due to.

As a solution to the above problem, the inventors have previously proposed Nd-Fe
A rare earth-transition metal-boron-based magnet alloy in which Fe of a B-based magnet is replaced with Co and Ni to a high concentration has been proposed (JP-A-2-
4939 publication).

Since the above-mentioned magnet has excellent corrosion resistance and the Curie point is increased, the reliability as a material is significantly improved.

(Problems to be Solved by the Invention) This invention is a further development of the above magnet,
We propose a rare-earth-transition metal magnet with a two-phase structure.

As for the Nd-based magnet having a two-phase structure, a magnet based on a two-alloy method, which is a mixture of a rare-earth-rich phase and a rare-earth-poor phase mixed and liquid-phase sintered, and which has excellent magnetic properties, has been previously proposed (Japanese Patent Application Laid-Open No. 2004-242242). Akira
Nos. 63-93841 and 63-164403), the above method still has a problem with respect to corrosion resistance, although the magnetic characteristics are improved.

The present invention advantageously solves the above problems, and is a rare-earth element having a two-phase structure excellent not only in magnetic properties but also in corrosion resistance.
The aim is to propose a transition metal based magnet together with its advantageous manufacturing method.

(Means for Solving the Problems) First, the details of the invention will be described.

Now, as a result of earnestly advancing the metallurgical studies on the above magnets using a high-resolution electron microscope, etc., the inventors have found that the magnet has Nd ₂ (Fe, Co, Ni) ₁₄ having a large saturation magnetic flux density. B
Phase and Nd ₂ (Fe, Co, Ni) ₁₇ , Nd (Fe, Co, Ni) ₅ , Nd ₂ which has strong coercive force surrounding the crystal grains
(Fe, Co, Ni) ₇ , Nd (Fe, Co, Ni) ₄ B and Nd (Fe, Co, Ni)
_It was clarified that there are grain boundary phases such as ₁₂ B ₆ and Nd _1-X TM _{1 + X} (however, TM is mainly Ni _O x is between −0.2 and 0.2) which becomes CrB structure.

In addition, it was also found that the smaller the amount of Nd phase, which is a generation point of corrosion, and the higher the concentration of Ni and Co in the grain boundary phase, the better the corrosion resistance.

Therefore, as a result of further studying this point, the inventors have found that the above-mentioned grain boundary phase is Nd ₂ (Fe, Co, Ni) ₁₇ except Nd 2.
-Fe-B system It is difficult to appear in the framework of the ternary phase diagram, rather
I came to think that this is a phase that can only appear in the framework of the Nd-Co-B system.

For reference, Fig. 1 shows the Nd-Fe-B ternary phase diagram (NFCh
aban, Yu.B.Kuzma, NSBilonizhko, OOKachmar and N.
U. Petrov, Akad Nauk, SSSR, SetA, Fiz.−Mat.Tekh, Nauki
No. 10 (1979) 873), and FIG. 2 shows the Nd-Co-B ternary phase diagram (NSBilonizhko and Yu.B.Kuzma, Izv.Akad.N).
auk SSSR Neorg. Mater, 19 (1983) 487) (however, in the original paper, the Nd ₂ Fe ₁₄ B phase was changed to the ~ Nd ₂ Fe ₉ B phase, and also Nd ₂ Co).
₁₄ Phase B is confused with ~ Nd ₂ Co ₉ B phase, so it is corrected in Figs. ) In Fig. 1, the phase of No. 1 is Nd ₂ Fe ₁₄ B phase, and the composition around it is NdFe ₄ B ₄ phase (phase of No. 2), Nd phase, Nd ₂
The Fe ₁₇ phase and the Fe phase will appear. But second
In the figure, the magnets prepared with the peripheral composition of the Nd ₂ Co ₁₄ B phase of No. 1 have Nd ₂ Co ₁₇ phase, NdCo ₅ phase, Nd ₂ Co ₇ phase, NdCo ₄ B phase (No. 2 phase) and NdCo. ₁₂ B ₆ phase (phase of No. 7) and the like appear, and originally the Nd phase should not appear in the equilibrium state.

As described above, the Nd phase serves as a rust generation point, but on the other hand, it has a function of surrounding the crystal grains of the main phase and exhibiting coercive force.

Therefore, the present invention has two magnetically useful phases, namely, RE ₂ TM ₁₄ B phase having a high residual magnetic flux density, and a low melting point to improve sinterability, and surrounds the main phase crystal grains with a clean interface. By producing a two-phase magnet using a RE-TM phase or a RE-TM-B phase having a composition that exhibits a coercive force and is electrochemically noble to the same extent as the main phase, as a starting material, It is intended to obtain a permanent magnet having excellent magnetic properties and corrosion resistance.

That is, the present invention includes RE: 10 at% or more and 25 at% or less, where one or two or more selected from RE: Y, Sc and lanthanoid B: 2 at% or more and 20 at% or less, and the balance is substantially TM (where TM is Fe, Co and Ni
RE ₂ T having a Nd ₂ Fe ₁₄ B structure whose structure is a permanent magnet alloy consisting of one or more selected from
M ₁₄ B (where TM is the same as above) and a RE-TM'-based intermetallic compound phase (T
M ′ is Ni or a mixture of Ni and at least one selected from Fe and Co, and the Ni content in TM ′ is 8 at.
%) Or a eutectic structure (where TM 'is the same as above) involving RE-TM' type intermetallic compound phase and / or RE
-TM'-B type intermetallic compound phase (where TM 'is the same as above) is a corrosion resistant rare earth-transition metal type permanent magnet.

In addition, this invention is based on the RE ₂ TM ₁₄ B-based intermetallic compound phase (however,
TM is a powder mainly composed of one or more selected from Fe, Co and Ni), and a melting point lower than that of the powder, RE
-TM 'type intermetallic compound phase (However, TM' is Ni or Ni
A mixture with at least one selected from Fe and Co,
And the Ni content in TM 'is 8 at% or more) or RE
Eutectic structure (here T
M'is the same as above) and / or a powder mainly composed of RE-TM'-B based intermetallic compound phase (where TM 'is the same as above) is compression-molded and then sintered. The method for producing a corrosion resistant rare earth-transition metal magnet according to claim 1.

In the present invention, in order to further improve the corrosion resistance, the intermetallic compound phase of RE-TM 'or RE-TM'-B, which is a grain boundary phase, is electrochemically applied to the same degree as the main phase. It is effective to prevent galvanic corrosion, and therefore T in the RE-TM 'system and RE-TM'-B system low melting phase.
It is preferable to increase the proportion of Ni and / or Co in M ′ than that in the RE ₂ TM ₁₄ B phase. In particular, increasing the proportion of Ni is particularly effective in improving the corrosion resistance.

As such a low melting point RE-TM 'type intermetallic compound phase,
Those having a CrB structure are particularly suitable.

In the present invention, the RE ₂ TM ₁₄ B intermetallic compound phase and RE
-TM 'type and RE-TM'-B type intermetallic compound ratio is
The formula weight unit is preferably about 95: 5 to 40:60.
This is because if the ratio of the two is out of the above range, there is a disadvantage that the coercive force and the saturation magnetic flux density are significantly deteriorated. Here, the formula unit is, for example, Nd ₂ Fe.
This corresponds to the case where ₁₄ B is regarded as one molecule (in solid, this is called formula). The particle size of each powder to be mixed is
About 0.5 to 5 μm is desirable for easy handling and homogeneous mixing.

Here, RE ₂ TM ₁₄ B has a melting point lower than that of the intermetallic compound phase RE-
Representative compositions of the TM'-based intermetallic compound phase (including a eutectic structure; the same applies hereinafter) and the RE-TM'-B-based intermetallic compound phase are as follows.

・ RE-TM 'system RE ₂ TM ₁₇ ,, RETM ₅ ,, RE ₂ TM ₇ ,, RETM ₃ ,, RETM ₂ ,, RE _1-X TM _{1 + X} , RE ₇ T
M ₃ , RE ₃ TM and TE-TM eutectic structure ・ RE-TM'-B type RETM ₄ B, RE ₃ TM ₁₁ B ₄ ,, RE ₂ TM ₅ B ₂ ,, RE ₂ TM ₇ B ₃ ,, RE ₂ TM ₅ B ₃ , RETM ₁₂
B ₆ , RETM ₂ B ₂ , RETM ₉ B ₄ , RE ₂ TMB _{3 In} addition, the above-mentioned RE ₂ TM ₁₄ B, RE-TM 'type, RE-TM'-B type intermetallic compound powders are the main phases. , Can be obtained as follows.

That is, each constituent element simple substance is weighed so as to have a predetermined composition, and an alloy ingot is produced by vacuum melting or high frequency melting in a vacuum or in an inert gas atmosphere. Then, the ingot is also kept in vacuum or in an inert gas atmosphere at a temperature of 600 to 1000 ° C. for 1 to 30 days to form a single-phase intermetallic compound. Since many intermetallic compounds generally have a solid solution range of a certain degree (up to 20%), the composition range of the starting composition is allowed accordingly.

The intermetallic compound in a single phase is coarsely crushed with a hammer mill and then crushed with a jet mill or an attritor.
Fine powder with a diameter of 5 to 5 μm. The low melting point RE-TM ', R
Among E-TM'-B, those with low hardness and difficult to crush, if crushed by hydrogen embrittlement for several hours in the temperature range of room temperature to 350 ° C before hammer crushing, Is easy.

(Working) According to the present invention, a pre-prepared RE-TM'-based powder having a composition of RE ₂ TM ₁₄ B as a main component and having a lower melting point than that of the pre-prepared RE-TM 'system is used. Both high magnet characteristics and high corrosion resistance can be obtained by mixing and pressing one or more powders containing an intermetallic compound or RE-TM'-B type intermetallic compound as the main phase, followed by sintering. Can be combined.

The reason is that the powder having a lower melting point than the powder mainly composed of RE ₂ TM ₁₄ B intermetallic compound phase promotes sintering and
It is considered that this is because the grain boundary phase is formed between the RE ₂ TM ₁₄ B crystal grains to improve the coercive force.

Now, in RE ₂ TM ₁₄ B phase, Nd and Pr are preferable as RE in terms of the magnitude of the magnetic moment and the magnetic coupling with the TM atom, and also in terms of cost.
It goes without saying that other REs, or a combination of these with Nd and Pr may be used.

The TM may be one or more selected from Fe, Co and Ni, and in particular, it is desirable to increase the proportion of Ni from the viewpoint of high corrosion resistance of the magnet. Also, since this RE ₂ TM ₁₄ B phase is responsible for the saturation magnetic flux density of the magnet, the proportion of Fe, Co and Ni present in TM is 10 at% or more and less than 73 at% for Fe and 7 at% or more for Co and 50 at% for Co. % Or less, Ni is 5 at
% Or more and 30 at% or less is preferable, but the corrosion resistance of the permanent magnet according to the present invention is the same as that of the conventional RE-TM- even when the RE ₂ TM ₁₄ B phase with 100% Fe as TM is the main phase. It is superior to B magnets and can therefore be used as the main phase, depending on the application of the magnet.

Next, as RE in the RE-TM 'type and RE-TM'-B type low melting point phases, when cost is important, La, Ce, Pr, Nd
For light rare earth elements such as, if you want to further improve the corrosion resistance, medium heavy rare earth elements up to Lu after the atomic number Sm or Y, Sc
Etc. fits advantageously.

For TM ', Ni and / or Co, especially Ni
Since it is effective to improve the corrosion resistance in the present invention, Ni is always included as TM 'in the present invention, and the content is limited to 8 at% or more from the viewpoint of the corrosion resistance.

 The effects of adding Ni are as follows.

i) The melting points of the RE-TM 'system and RE-TM'-B system are lowered, the infiltration of the liquid phase during the liquid phase sintering is promoted, the sintering density is increased, and the residual magnetic flux density is improved.

ii) For the same reason as the above i), the effect of cleaning the grain boundary of the liquid phase during the liquid phase sintering is enhanced, and the coercive force is further improved.

iii) It is more effective in improving the corrosion resistance than Co and is also inexpensive.

Furthermore, the ratio of Ni and / or Co in the low melting point phase is set to RE ₂ TM
Corrosion resistance can be further improved by increasing it higher than that of the ₁₄ B phase because the RE / TM 'ratio is generally higher in the low melting point phase than in the RE ₂ TM ₁₄ B phase. Therefore, in order to make the electrochemical corrosion potentials almost the same in the main phase and the grain boundary phase so that galvanic corrosion does not occur, it is desirable to increase the ratio of Ni in the low melting point phase that becomes the grain boundary phase. . Furthermore, since magnetically unnecessary Nd phases can be eliminated, the residual magnetic flux density increases, and as a result, the maximum energy product (BH) _max also improves.

In this respect, as a method of enriching the grain boundary phase with Ni, the alloy is first melted with the average composition of the entire magnet as in the conventional case,
It is also possible to pulverize, press, and sinter to utilize the fact that the solid solution limit of Ni in RE ₂ TM ₁₄ B of the main phase is small, and consequently the grain boundary phase can be enriched with Ni.

However, as a more advantageous method, a method has been proposed in which the powders of the main phase and the grain boundary phase are separately produced in advance, and the powders are mixed, pressed and sintered. According to this so-called two-phase powder mixing method, not only is it easy to produce a magnet that is rich in Ni in the grain boundary phase, but elements such as Dy and Ga that are advantageous for improving the coercive force are added to the grain boundary phase. It can also be charged to enhance its effect.

The main phase RE and the low melting point RE do not have to be the same element. In addition, in the above-mentioned magnet mainly composed of two phases, RE, TM, and a part of TM ′ are replaced with Mg, Al, Si, Ti, V, Cr, and M.
n, Cu, Ag, Au, Cd, Rh, Pd, Ir, Pt, Zn, Ga, Ge, Zr, Nb, Mo, In, Sn,
At least one selected from Hf, Ta and W does not lose the effect of the present invention even if it is replaced up to 8 at% of the whole magnet.

Furthermore, regarding the manufacturing method, as described above, RE ₂ TM
A powder of ₁₄ B composition, after a mixed powder of powder consisting mainly of low RE-TM 'system and / or RE-TM'-B based intermetallic compound phases having a melting point, and compression molding, the method of sintering In addition, although the magnet characteristics are somewhat sacrificed, as a method for manufacturing a large-sized magnet, a method in which the above mixed powder is vacuum-sealed in an iron pipe and then sintered while hot rolling is possible.

(Example) Example 1 Arc melting was carried out so that the atomic ratio of neodymium, transition metal, and boron was 2: 14: 1 to prepare an alloy button, which was homogenized in a vacuum furnace at 950 ° C for 7 days. After that, coarse pulverization and fine pulverization were performed to obtain fine powder having a diameter of several microns. At this time, various kinds of alloy powders were manufactured by changing the ratio of Fe, Co, and Ni in the transition metal variously.

Similarly, a powder having a ratio of neodymium or (neodymium + dysprosium) to nickel of 1: 1 was produced.
The homogenization treatment conditions at that time were 680 ° C. and 5 days.

Next, select one type from each of the above two groups, mix them at various ratios shown in Table 1, press while applying a magnetic field of 15 kOe, and then press at 1000 ° C. for 2 hours in a vacuum atmosphere.
Sintered for hours and then quenched to room temperature.

Table 1 shows the results of examining the magnetic properties and corrosion properties of the samples thus obtained. The corrosion characteristics were evaluated by the rusting area ratio of the sample surface after exposing the sample to an environment of a temperature of 70 ° C. and a humidity of 95% for 48 hours without forming any film on the surface.

In addition, for comparison, Table 1 also shows the results of investigation of the sample prepared by the conventional method, which comprises the steps of coarse pulverization-fine pulverization-pressing in a magnetic field-sintering step in which the entire composition of the sintered magnet is dissolved.

As is clear from the table, the two-phase rare earth-transition metal magnet according to the present invention has much improved corrosion resistance as well as magnetic characteristics as compared with the conventional one in which the entire composition is dissolved. doing.

Example 2 After arc melting was performed so that the atomic ratio of neodymium, transition metal and boron was 2: 14: 1, an alloy button was produced and homogenized at 950 ° C. for 7 days in a vacuum furnace. Coarse pulverization and fine pulverization were performed to obtain a fine powder having a diameter of several microns. At this time, various kinds of alloy powders were manufactured by changing the ratio of Fe, Co, and Ni in the transition metal variously.

Similarly, with neodymium and / or dysprosium or praseodymium, nickel or (nickel +
A powder having an atomic ratio with cobalt of 3: 1 was prepared. At that time, the homogenizing treatment conditions were 485 ° C. and 5 days.

Table 2 shows the results of investigations on the magnetic properties and corrosion properties of the samples thus obtained.

For reference, Table 2 also shows the results of examining the characteristics of the magnet disclosed in JP-A-63-164403.

From the table, it is understood that the two-phase structure rare earth-transition metal magnet according to the present invention is excellent in magnetic characteristics and corrosion resistance. Further, as is clear from comparison between the conforming example 8 and the conforming example 13, particularly in RE ₃ (Ni, Co) ₁ , the higher the Ni ratio, the higher the corrosion resistance. Further, in the conventional example, although the magnet characteristics are good, the corrosion resistance is inferior because it does not contain Ni.

Example 3 In the same manner as in Example 1, fine alloy powder having a RE ₂ TM ₁₄ B composition was produced. Also, as a powder raw material for mixing this, RE ₂ TM
Sintered magnets were manufactured in the same manner as in Example 1 after making alloy fine powders in which the proportion of Ni and Co in TM was higher than that of _14B powders and mixing them.

The characteristics of the sintered magnet thus obtained are shown in Table 3 in comparison with those of the sintered magnet obtained by the conventional method.

As is clear from the table, as a mixed powder, RE ₂ TM ₁₄ B
Further improvement in corrosion resistance has been achieved when using alloy fine powder in which the proportion of Ni or Co in TM is higher than that of powder.

(Effect of the Invention) Thus, according to the present invention, compared with the conventional manufacturing method,
It is possible to manufacture a rare earth-transition metal magnet having improved corrosion resistance and improved magnetic properties. In particular, the improved corrosion resistance realizes a marked improvement in reliability as an industrial material.

[Brief description of the drawings]

 FIG. 1 is an Nd-Fe-B ternary phase diagram, and FIG. 2 is an Nd-Co-B ternary phase diagram.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Akira Fujita Inventor 1 Kawasaki-cho, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Yoko Kitano 1 Kawasaki-cho, Chiba City Chiba Prefecture Kawasaki Steel Co., Ltd. Corporate Technology Research Headquarters (72) Inventor Junichi Shimomura 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Corporate Technology Research Headquarters (56) References JP-A-63-127505 (JP, A)

Claims (4)

(57) [Claims] 1. RE: 10 at% or more and 25 at% or less, where one or two or more selected from RE: Y, Sc and lanthanoid B: 2 at% or more and 20 at% or less, and the balance substantially TM (where TM is Fe, Co and Ni
RE ₂ T having a Nd ₂ Fe ₁₄ B structure whose structure is a permanent magnet alloy consisting of one or more selected from
M ₁₄ B (where TM is the same as above) and a RE-TM'-based intermetallic compound phase (T
M ′ is Ni or a mixture of Ni and at least one selected from Fe and Co, and the Ni content in TM ′ is 8 at.
%) Or a eutectic structure (where TM 'is the same as above) involving RE-TM' type intermetallic compound phase and / or RE
A corrosion-resistant rare earth-transition metal permanent magnet, characterized in that it is composed of a -TM'-B based intermetallic compound phase (where TM 'is the same as above). 2. The corrosion-resistant rare earth-transition metal permanent magnet according to claim 1, wherein the RE-TM'-based intermetallic compound phase having a low melting point has a CrB structure. 3. A RE ₂ TM ₁₄ B-based intermetallic compound phase (where TM is F
powder mainly composed of one or more selected from e, Co and Ni), and RE-TM 'having a lower melting point than the powder.
Intermetallic compound phase (However, TM 'is Ni or Ni and Fe, Co
A mixture of at least one of the
Ni content in M'is 8 at% or more) or RE-TM '
A powder mainly composed of a eutectic structure (where TM 'is the same as above) and / or RE-TM'-B based intermetallic phase (where TM' is the same as above) in which the intermetallic compound phase is involved. The method for producing a corrosion-resistant rare earth-transition metal magnet according to claim 1, which comprises compressing and mixing the mixed powder with and. 4. The method for producing a corrosion-resistant rare earth-transition metal permanent magnet according to claim 3, wherein the RE-TM ′ intermetallic compound phase having a low melting point has a CrB structure.