JPH03250607A - Corrosive resistant rare earth-transition metal magnet and its manufacture - Google Patents

Abstract

PURPOSE:To cause the title magnet to have both high magnetic characteristics and high corrosion resistance by mixing and pressing a powder mainly composed of an intermetallic compound having a specific RE2TM14B composition and one or more kinds of powder having, as a main phase, RE-TM interfamily compound or RE-TM-B intermetallic compound lower in the melting point than the first powder and thereafter by sintering the obtained product. CONSTITUTION:A mixed powder of a permanent magnet alloy, which consists of RE not less than 10% and not more than 25% including one or two sorts or materials selected from Y, Sc and lanthanoids, B of not less then 2% and not more than 20% and the rest TM and its constitution is in the phase od RE2TM14B composition having Nd2Fe14B structure, and a powder mainly composed of RE-TM intermetallic compound phase or RE-TM eutectic structure and/or RE-TM-B intermetallic compound phase lower in the melting point than the first phase is subjected to compression molding and sintered thereafter. For further improvement of corrosion resistance, it is effective that a grain boundary phase is electrochemically nobler than a main phase. Therefore, it is preferable to make the ratio of Ni and/or Co in TM in the RE-TM and RE-TM-B low melting point phase higher than that in the RE2TM14B phase.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a rare earth-transition metal magnet that not only has excellent magnetic properties but also excellent corrosion resistance and temperature characteristics, and a method for manufacturing the same.

(Prior art) Typical permanent magnet materials currently manufactured include:
Examples include alnico magnets, ferrite magnets, and rare earth magnets. Alnico magnets have a long history, but demand is declining due to the development of cheaper ferrite magnets or even rare earth magnets with even higher magnetic properties. On the other hand, ferrite magnets are chemically stable and low-cost because they are mainly made of oxides, so they still occupy the mainstream of magnet materials today, and they have the drawback of having a small maximum energy product.

Subsequently, SmCo-based magnets appeared that combined the magnetic anisotropy of rare earth ions and the magnetic moment of transition metal elements, significantly updating the conventional maximum energy product. However, 5lll-Co-based magnets are S
Since the main components are M and Co, the magnet has to be expensive.

Therefore, an inexpensive magnetic alloy with high magnetic properties that does not contain expensive 5IIl or Co was developed.
-34242 and JP-A-59-132104), and J, J., Croat et al. developed an alloy with high coercive force by liquid quenching method (JP-A-59-64739).
developed. These are magnets made of Nd, Fe, and B, and their maximum energy product exceeds that of Sm--Co magnets.

However, Nd-Fe-B magnets are composed of light rare earth elements such as Nd, which has very high activity, and F, which easily rusts.
Since it contains a large amount of e, it has poor corrosion resistance, resulting in deterioration of magnetic properties and lack of reliability as an industrial material.

Therefore, in order to improve the corrosion resistance, for example, sintered magnets are subjected to surface plating (Japanese Unexamined Patent Publication No. 63-77103), coating treatment (Japanese Unexamined Patent Publication No. 60-63901), etc., and resin-bonded magnets are treated with magnetic powder. Countermeasures such as pre-surface treatment before kneading the resin and resin have been taken, but none of these treatments can be said to be an effective anti-corrosion treatment over a long period of time, and the cost of treatment is high, and furthermore, the protective film is There were also problems such as loss of magnetic flux.

As a solution to the above problem, the inventors first developed an Nd-F
We have proposed a rare earth-transition metal-boron magnet alloy in which Fe in an e-B magnet is replaced with Co and Ni at a high concentration (Japanese Patent Application Laid-Open No. 2-4939).

The above-mentioned magnet has excellent corrosion resistance and has a raised Curie point, so its reliability as a material has been greatly improved.

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

Regarding Nd-based magnets with a two-phase structure, a magnet using a two-alloy method with excellent magnetic properties, in which a rare earth-rich phase and a rare earth-poor phase are mixed and liquid-phase sintered, has previously been proposed (Unexamined Japanese Patent Publication No. Publications No. 63-93841 and No. 63-164403)
However, although the above-mentioned method improves the magnetic properties, there still remains a problem in terms of corrosion resistance.

The purpose of this invention is to advantageously solve the above problems, and to propose a rare earth-transition metal magnet with a two-phase structure that has excellent not only magnetic properties but also corrosion resistance, together with an advantageous manufacturing method. do.

(Means for solving problems) First, the background to the elucidation of this invention will be explained.

Now, as a result of intensive metallographic research on the above-mentioned magnet using a high-resolution electron microscope, the inventors found that the magnet contains Ndz (Fe, Co,
N+) 14B phase and Ndz (Fe, C.

Ni)+7. Nd(Fe, Co, Ni)s, Ndz
(Fe, Co, Ni)7. Nd(Fe.

Co + N i ) a B and Nd(Fe, Co
, Ni) 12B&, and further Nd+ which becomes CrB structure
-xTMx (however, TM is mainly Ni) and other grain boundary phases were found to exist.

It was also found that the smaller the amount of Nd phase, which is a point where corrosion occurs, and the higher the concentration of Ni and Co in the grain boundary phase, the better the corrosion resistance.

Therefore, the inventors further considered this point and found that the aforementioned grain boundary phase is Ndz (Fe, Co, Ni) +
I came to realize that phases other than 7 are difficult to appear in the framework of the Nd-Fe-B ternary phase diagram, and can only appear in the framework of the Nd-Co-B system.

For reference, Figure 1 shows the Nd-Fe-B ternary phase diagram (N,
F., Chaban, Yu, B., Kuzma, N.S.
, B11onizhko, 0゜0, niachmar
and N, U, Petrov, Akad Nauk
, 5SSR.

5etA Fiz, -Mat, Tekh,
Nauki No. 10 (1979) 873
), and Figure 2 shows the Nd-C0-B ternary phase diagram (N
S B11onizhko and Yu, B, Kuz
ma, Izv, Akad, NaukSSSRNeo
rg, Mater, 19 (1983) 487)
(However, in the original paper, the NdzFe+aB phase is ~N
Since the d z F e q B phase and the NdCo5 phase were mistaken for ~Nd2Co, B phase, they have been corrected in FIGS. 1 and 2. ) In Figure 1, the phase numbered 1 is N
dzFe+aB phase, and the surrounding composition is NdFe
jL phase (phase numbered 2), Nd phase, NdJe+7 phase, and Fe phase will appear. On the other hand, in Fig. 2, the magnet manufactured with the surrounding composition of Nd2Co14B phase number 1 has Nd zCo + 7 phase, NdCo5 phase, Nd
2Co, phase, NdCo4B phase (phase with number 2) and Nd
Co4B phase (phase number 7) etc. appear, and originally the Nd phase should not appear in an equilibrium state.

As mentioned above, the Nd phase not only becomes a point of rust generation, but also has no magnetic utility, and should be eliminated.

Therefore, in this invention, we have developed two magnetically useful phases, namely RE2TM and B phases with high residual magnetic flux density, which improve sintering properties, have a main phase grain boundary cleaning action, and furthermore have an electrochemical The low melting point RE-TM phase and R
By producing a two-phase magnet using the E-TM-B phase as a starting material, it is attempted to obtain a permanent magnet with excellent magnetic properties and corrosion resistance.

That is, this invention includes RE: 10 at% or more and 25 at% or less, where one or more selected from RELY, Sc, and lanthanoids, B: 2 at% or more and 20 at% or less, and the remainder is substantially RE2TM14B is a permanent magnet alloy consisting of TM (TM4, one or more selected from Fe, Co, and Ni) and has a structure of Nd2Fe+J (here TM is the same as above).
A phase with a composition of
system intermetallic compound phase (TM is ■ or Ni and Fe
mixture with at least one selected from C0) or RE-TM-based eutectic structure (here, TM is the same as above)
The present invention is a corrosion-resistant rare earth-transition metal based permanent magnet characterized by being composed of a RE-TM-B based intermetallic compound phase (where H is the same as above).

This invention also provides RE2TM, B-based intermetallic compound phase (
However, TM consists of a powder mainly composed of one or more selected from Fe, Co, and Ni, and a RE-TM intermetallic compound phase with a lower melting point than the powder (Tatashihi means Ni or mixture of Ni and at least one selected from Fe and Co) or RE-TM system co-product structure (here, Tt'l is the same as above) and/or RE
T! Manufacture of a corrosion-resistant rare earth-transition metal magnet by compressing and molding a mixed powder with a powder mainly consisting of an I-B intermetallic compound phase (here TM is the same as above) and then sintering it. It's a method.

In this invention, in order to further improve corrosion resistance, it is effective to make the grain boundary phase more electrochemically responsible than the main phase. It is preferable that the proportion of Ni and/or Co in the TM is higher than that in the RE2TM and 4B phases. In particular, increasing the Ni ratio is particularly effective in improving corrosion resistance and reducing costs.

Further, in this invention, the ratio of the RE2TM, JB intermetallic compound phase and the RE-TM series, RE-TM-B series intermetallic compound phase is from 95=5 to 40:60 in substitution units.
It is preferable to set it as approximately. This is because if the ratio of both is out of the above range, there will be a disadvantage that the coercive force and saturation magnetic flux density will be significantly deteriorated. substitute here
la unit) corresponds to the case where, for example, Nd2Fe14B is regarded as one molecule (in the case of a solid, this is called a formula). The particle size of each powder to be mixed is
A thickness of about 0.5 to 5 μm is desirable for ease of handling and homogeneous mixing.

Here, the typical compositions of the RE-TM intermetallic compound phase (including eutectic structure, hereinafter) and the RE-TM-B intermetallic compound phase, which have a lower melting point than the RE2TMI4B intermetallic compound phase, are as follows. It is as follows.

・RE-TM system REzTM+t, RETM5. REZTM7. R
ETM:l, RETMZREITMI-X, REt
Tl'h, RE3TM and RE-TMM crystal structure/RE-phylum-B system RETM4B, RE3TMII8-1RE2TMSBZ
, RE2TM7BllRE2TM5B3. RETM, 2
B6. RETM□B2. RETM,B.

REzTMBi In addition, the above-mentioned RE2TM, B, RE-TM series, RE-
T! A powder having an I-B intermetallic compound phase as a main phase can be obtained as follows.

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

The intermetallic compound made into a single phase is coarsely ground with a hammer mill, and then pulverized with a jet mill or an attritor.
Finely powder with a diameter of 5 to 5 μm. In addition, the low melting point phase RE-T
Among M and RE-B, those with low hardness and difficult to grind should be heated at room temperature to 35°C before being crushed in a hammer mill.
Hydrogen embrittlement at a temperature of about 0°C for several hours facilitates subsequent crushing.

(Function) According to this invention, I? E2TM, 4
Powder mainly composed of an intermetallic compound having the composition B, with a pre-prepared RE-TM intersystem compound or RE-TM-B intermetallic compound having a lower melting point as the main phase. By mixing and pressing the powder with one or more of the following powders and then sintering the mixture, it is possible to have both high magnetic properties and high corrosion resistance.

The reason for this is that the powder, which has a lower melting point than the RE2TM14B powder mainly consisting of an intermetallic compound phase, has the effect of promoting sintering and forming a grain boundary phase between the crystal grains of RE2TM, B, and improving the coercive force. This is thought to be because it has

Now, in the RE2TM, B phase, it is desirable to use Nd or Pr as the RE from the viewpoint of the magnitude of its magnetic moment and magnetic coupling with heavy atoms, as well as from the viewpoint of cost. and Nd,
Needless to say, it may be used in combination with Pr.

Regarding TM, one or more selected from Fe, Co, and Ni may be used (and (). From the viewpoint of high corrosion resistance of the magnet, it is desirable to increase the proportion of Ni. Also, this RE2TM , 4B phase is responsible for the saturation magnetic flux density of the magnet, so Fe, Co and Ni in TM
The abundance ratio of Fe is 10at% or more and less than 73at%, Co is 7at% or more and 50at% or less, and Ni is 5at% or more.
It is desirable that the corrosion resistance of the permanent magnet of the present invention is about 30 at% or more and 30 at% or less, but even when RE2TM with 100% Fe as TM and B phase is used as the main phase, the corrosion resistance of the permanent magnet of this invention is equal to that of conventional Ra-TM. -B [It is superior to stone, so it can of course be used as the main phase depending on the purpose of the magnet.

Next, as the RE in the low melting point phase of the RE-TM system and RE-TM-B system, if cost is important, La is the preferred RE.

Light rare earth elements such as Ce, Pr, and Nd are advantageously suitable, and when it is desired to improve the corrosion resistance of the layer, medium rare earth elements having an atomic number from Sm to Lu, Y, Sc, etc. are suitable.

Regarding TM, containing Ni and/or Co, especially Ni, is effective in improving corrosion resistance.
In this invention, Ni must be included as TI'l, and its content in the TM is preferably approximately 2% or more.

The effects of adding Ni are as follows.

1) Lowering the melting point of the RE-T1 system and the RE-TM-B system, promoting liquid phase infiltration during liquid phase sintering, increasing the sintered density, and improving the residual magnetic flux density.

ii) For the same reason as i) above, it is effective in enhancing the grain boundary cleaning effect of the liquid phase during liquid phase sintering and further improving the coercive force.

1ii) It is more effective than Co in improving corrosion resistance and is also cheaper.

Furthermore, the ratio of Ni and/or Co in the low melting point phase is RE
Corrosion resistance can be further improved by increasing the corrosion resistance higher than that of the 2TM144B phase, and the reason for this is
The phases of these powders, if the TM composition is the same,
This is because in a sintered body, corrosion tends to occur preferentially at the grain boundaries rather than at the RE2TM14 4B phase, so it is advantageous to electrochemically attack the grain boundaries in advance.

Furthermore, since the magnetically useless Nd phase can be eliminated, the residual magnetic flux density increases, resulting in the maximum energy product (BH).
,,, will also improve.

In this regard, even if the alloy is melted at the average composition of the entire magnet from the beginning and then crushed, pressed, and sintered to bring it close to an equilibrium state, as in the past, the Nd phase cannot be formed. The drawback was that it required heating at high temperatures for a long time, during which time abnormal growth of crystal grains occurred, resulting in a significant decrease in coercive force.

Note that the RE of the main phase and the RE of the low melting point phase do not need to be the same element. In addition, in the above-mentioned two-phase magnet, a part of RE and TM is replaced by Mg, AI, 5iT.
i, V Cr, Mn, Cu, Ag, Au
, Cd, Rh, Pd, Ir.

Pt Zn Ga, Ge, Zr, Nb, M
Even if up to 8 at % of the entire magnet is replaced with at least one selected from O, In, Sn, Hf, Ta, and W, the effects of the present invention will not be lost.

Furthermore, regarding the manufacturing method, as mentioned above, RE, T
A method in which a mixed powder of powders having compositions M, B and powders mainly consisting of RE-TM and/or RE-TM-B intermetallic compound phases with low melting points is compression molded and then sintered. Another possible method for manufacturing large magnets is to vacuum seal the mixed powder in an iron pipe and then sinter it while hot rolling, although the magnetic properties are sacrificed to some extent.

(Example) Example 1 The atomic ratio of neodymium, transition metal and boron is 2+14:
1) to produce an alloy button, homogenize it in a vacuum furnace at 950°C for 7 days, and then coarsely and finely crush it to a diameter of several microns. A fine powder was obtained. At this time, Fe, Co, N in the transition metal
A plurality of types of alloy powders were manufactured by varying the ratio of i.

In the same manner, a powder was prepared in which the ratio of neodymium or (dysprosium) to nickel was 1=1.

The homogenization treatment conditions at that time were 680°C for 5 days.

Next, one type was selected from each of the above two groups, mixed in various proportions shown in Table 1, pressed while applying a magnetic field of 15 koe, and then heated at 100 koe in a vacuum atmosphere.
It was sintered at 0°C for 2 hours, and then cooled to room temperature.

Table 1 shows the results of investigating the magnetic properties and corrosion properties of the samples thus obtained. The corrosion characteristics were evaluated by the rusted area ratio on the surface of the sample after the sample was exposed to an environment with a temperature of 70'' C1 and humidity of 95% for 48 hours.

For comparison, Table 1 also shows the investigation results of a sample manufactured by a conventional method consisting of melting the entire composition of a sintered magnet from the beginning, coarse grinding, thorough grinding, and breath sintering in a magnetic field.

As is clear from the table, the rare earth-transition metal magnet with the two-phase structure according to the present invention has significantly improved magnetic properties and corrosion resistance compared to conventional magnets whose entire composition is melted from the beginning. are doing.

Example 2 Atomic ratio of neodymium, transition metal and boron is 2:14:
Arc melting is performed so that the alloy button becomes 1, and an alloy button is produced.
After homogenizing in a vacuum furnace at 950°C for 7 days, the mixture was coarsely pulverized and finely pulverized to obtain a fine powder with a diameter of several microns. At this time, Fe, Co, Ni in the transition metal
Multiple types of alloy powders were produced by varying the ratio of .

In the same manner, a powder was prepared in which the atomic ratio of neodymium and/or dysprosium or praseodymium and nickel or nickel+cobalt was 3:1. The homogenization treatment conditions at that time were 485° C. for 35 days.

Table 2 shows the investigation results regarding the magnetic properties and corrosion properties of the samples thus obtained.

For reference, Table 2 includes Japanese Patent Application Laid-Open No. 63-164403.
The results of investigating the characteristics of the magnet disclosed in the publication are also listed.

/ / / From the same table, it can be seen that the rare earth transition metal magnet with the two-phase structure according to the present invention has excellent magnetic properties and corrosion resistance. Moreover, as is clear from comparing Compatible Example 8 and Compatible Example I3, especially RE+ (Ni, Co).

The Ni ratio is high (indeed, the corrosion resistance is improved).Although the conventional example has good magnetic properties, it is inferior in corrosion resistance because it does not contain Ni.

Example 3 In the same manner as in Example 1, an alloy fine powder having a composition of REzTM+-B was produced. In addition, as a powder raw material to be mixed with this,
Ni and G occupy more in TM than REZTMI4B powder.
.

After preparing fine alloy powders with a high ratio of and mixing them, a sintered magnet was manufactured in the same manner as in Example 1.

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.

O- As is clear from the same table, as a mixed powder, RE, TM
When a fine alloy powder with a higher proportion of Ni and Co in TI'I than 4B powder is used, further improvement in corrosion resistance is achieved.

(Effects of the Invention) Thus, according to the present invention, it is possible to manufacture a rare earth-transition metal magnet with improved corrosion resistance and improved magnetic properties compared to conventional manufacturing methods. These improvements have resulted in a significant improvement in reliability as an industrial material.

[Brief explanation of drawings]

Figure 1 is a ternary phase diagram of Nd-Fe-B, and Figure 2 is a Nd-Fe-B ternary phase diagram.
-Go-B ternary phase diagram. Figure 1 1 ・-Nd2FeHa B 2- Nd Fea Ba 3 --- Nd Z Fe 8J Amendment to manual punishment December 20, 1990

Claims (4)

[Claims] 1. RE: 10 at% or more and 25 at% or less, where R
E: One or more selected from Y, Sc, and lanthanoids B: Contains 2 at% or more and 20 at% or less, and the remainder is substantially TM (however, TM is Fe, Co
and Ni), the structure of which is Nd_2Fe
A phase with a composition of RE_2TM_1_4B (here, TM is the same as above) having a structure of _1_4B, and a RE-TM intermetallic compound phase with a lower melting point than that phase (however, TM is N
i or a mixture of Ni and at least one selected from Fe and Co), RE-TM-based eutectic structure (here TM is the same as above) and/or RE-TM-B-based intermetallic compound phase (here and TM is the same as above). 2. R
The corrosion-resistant rare earth-transition metal permanent magnet according to claim 1, which has a higher corrosion resistance than that of the E_2TM_1_4B phase. 3. A powder mainly composed of a RE_2TM_1_4B intermetallic compound phase (TM is one or more selected from Fe, Co, and Ni) and a RE-TM intermetallic compound phase with a lower melting point than the powder (however, TM is one or more selected from Fe, Co, and Ni). TM is Ni
or a mixture of Ni and at least one selected from Fe and Co), RE-TM eutectic structure (here TM is the same as above) and/or RE-TM-B intermetallic compound phase (here 2. The method for producing a corrosion-resistant rare earth-transition metal magnet according to claim 1, comprising compression molding a mixed powder with a powder mainly consisting of TM (same as above) and then sintering the mixture. 4. A powder mainly composed of a RE_2TM_1_4B intermetallic compound phase (TM is one or more selected from Fe, Co, and Ni) and a RE-TM intermetallic compound phase with a lower melting point than the powder (however, TM is one or more selected from Fe, Co, and Ni). TM is Ni
or a mixture of Ni and at least one selected from Fe and Co), RE-TM eutectic structure (here TM is the same as above) and/or RE-TM-B intermetallic compound phase (here 3. The method for producing a corrosion-resistant rare earth-transition metal magnet according to claim 2, comprising compressing and molding a mixed powder with a powder mainly consisting of TM (same as above), and then sintering the mixture.