JPH02117103A - Rare-earth permanent magnet having desirable resistance to oxidation and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve corrosion resistance of a sintered body magnet itself by substituting an Nd rich phase having extremely low corrosion resistance with a matrix phase composed of at least one of R5(Pd1-xTx)2, R3(Pd1-xTx)2 and R(Pd1-xTx) having superior corrosion resistance. CONSTITUTION:An alloy powder principally composed of Nd2Fe14B phase is mixed with an alloy powder principally composed of at least one of Nd5(Pd1-xTx)2, Nd3(Pd1-xTx)2 and Nd(Pd1-xTx) phases, and the mixture is molded and sintered to provide a sintered body having a composite texture in which Nd2Fe14B phase is dispersed in a matrix composed of at least one of Nd5(Pd1-xTx)2, Nd3(Pd1-xTx)2 and Nd(Pd1-xTx) phases. The sintered body having such composite texture scarcely contains Nd rich phase. If contained any, it is isolated from others, taking a spherical shape. So, even if the Nd rich phase is oxidized, the oxidation does not penetrate the inside of the sintered body. Thus, corrosion resistance of the sintered body itself can be improved remarkably.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides an Rx whose main component is an R2T14B intermetallic compound.
The present invention relates to TxB permanent magnets, and in particular to rare earth permanent magnets with excellent oxidation resistance and methods of manufacturing the same.

<Prior Art> R-Fe-B magnets represented by Nd-Fe-B have higher magnetic properties than S m -Co alloy permanent magnets which have been widely used. Therefore, its uses are expanding. This R-FeeB magnet has an Nd-rich phase, NdFe, B, and Nd-rich phases in addition to the magnetic Nd2Fe14B phase in its metallographic structure. In this, the Nd-rich phase acts like a binder and binds the Nd2Fe14B phase, so that a Nd-Fe-B magnet sintered body exists.

However, this Nd-rich phase is extremely easily oxidized in the atmosphere, so when it is incorporated into a device such as a magnetic circuit, the oxidation of the magnet will cause property deterioration and variations, and furthermore, the oxides generated by the magnet will scatter and damage surrounding components. It has the disadvantage of causing contamination.

As a document regarding this improvement of corrosion resistance, JP-A-60-5
Publication No. 4406 (J, P, A) and JP-A-60-6390
Publication No. 3 etc. can be mentioned. These documents aim to improve the corrosion resistance of the magnet by forming an oxidation-resistant film on the surface of the magnet by plating, chemical conversion treatment, or the like.

[Problem to be solved by the invention WJ] However, since these oxidation-resistant films use a large amount of water and aqueous solution during their formation process, oxidation progresses from the Nd-rich phase of the magnet during the treatment process. After the film is formed, oxidation progresses inside the film, causing blistering or peeling of the film, so it is not suitable for improving corrosion resistance.

In addition, as a method that does not use water, oxidation-resistant resin coating such as epoxy, sputtering, which has recently become popular,
A, 17. by methods such as vapor deposition and ion blating;
There is also a method such as dry plating in which a metal film such as Ni is formed. However, even with these coatings that do not use water, if the film deteriorates due to long-term use, or if the magnet surface comes into contact with the atmosphere due to minute chips during use or during handling such as product inspection or installation into equipment, the magnet may be damaged from this area. Since the Nd-rich phase in the structure oxidizes significantly over time and spreads throughout the inside of the magnet, it is not suitable for improving corrosion resistance.

As mentioned above, in any of the conventional corrosion resistance reforming methods, the Nd-rich phase, which is extremely active in the atmosphere, exists continuously in the sintered body of the magnet, so the above six methods are not effective. It has been extremely difficult to impart the inherent corrosion resistance properties to water-based magnets.

That is, in water-based magnets, it has been impossible to obtain sufficient corrosion resistance unless the corrosion resistance of this Nd-rich phase is fundamentally improved.

Therefore, the technical problem of the present invention is to replace the Nd-rich phase, which has extremely low corrosion resistance, with R5 (Pd, ~xTx)2°Ri (Pd+xTx)2, R(Pd+), which has even better corrosion resistance.
~ T) By substituting a matrix phase composed of at least one type or more, the corrosion resistance of the sintered magnet itself is improved, and the original corrosion resistance of plating, chemical conversion coating, etc. is imparted to the aqueous magnet. There is a particular thing.

[Means to solve the problem] As a result of various studies conducted by the inventors, Rs (Pd + - xTx) 2-phase.

Rs (PD1xTx) 2-phase, R (pcl, -”r,
) phase has better corrosion resistance than the Nd-rich phase, and moreover, the Nd2Fe+iB
The present invention was based on the discovery that a sintered body having a composite structure in which phases are dispersed in a matrix of at least one of these phases can be obtained.

That is, according to the present invention, an alloy powder having a main phase of Nd2Fe14B phase and two Ndq (PD1xTx) phases.

Ndi (P d+xTx)2 , Nd (PD1,
NdzFe
The zB phase is Nd, (PD1xTx)2.

Ndj (PD1-T,)2, Nd (PD1-T,
) A sintered body is obtained which is characterized by having a composite structure dispersed in a matrix composed of at least one type of phase. There is almost no Nd-rich phase in the sintered body having this composite structure, and even when it does exist, it is a two-phase Nd, (Pd1-, T,).

Nd3 (Pdl-mxTx) 2-phase.

Since it exists in a spherical and isolated state in the Nd (Pd1-T,) phase, even if this Nd-rich phase oxidizes, it does not advance into the interior of the sintered body and does not affect the oxidation of the sintered body, so it does not affect the oxidation of the sintered body at all. No problem. Also, Nds (PdI-xTx) two-phase.

Nd 3 (Pd1- T irises) 2
Since the Nd (PdI-x'r,) phase has significantly better corrosion resistance than the Nd-rich phase, the corrosion resistance of the sintered body itself can be significantly improved.

Therefore, even if a conventional oxidation-resistant coating such as ordinary plating or chemical conversion treatment is applied to the magnet of the present invention in order to further improve corrosion resistance, the sintered body will not be oxidized during the first treatment step. The inherent oxidation resistance of these oxidation-resistant coatings can also be imparted to water-based magnets, which is extremely useful industrially.

Here, in the present invention, R5 (P drxTx) 2.

RJ(PdIxTx)2, R(PdI-xTx
) Phase X is set to 0 to 0.3 because in the region where X exceeds 0.3, excessive T causes Rs (
P drxTx) 2.

R3 (P dr-xTx) 2. R(P di-m
If the -s Q~0.3.

In addition, although the corrosion resistance can be sufficiently improved with the R% (P d +−−Tyo)2°Ri (P d +xTx) 2 phase in these matrix phases, in order to further improve the corrosion resistance, it is necessary to It is preferable that the abundance ratio of the R (PdI-7) phase is 50vol% or more.

Examples of the present invention will be described below.

-〈Example-1〉 27Nd-1, OB-F e b was produced by high-frequency melting in an Ar atmosphere using Nd, Fe, and B with a purity of 9596 or higher.
An ingot having a main phase of Nd2Fe14 and B phase having a composition of at (vL%) was obtained. This ingot was coarsely ground, and the resulting coarse powder was used as material (1).

Next, using Nd, Fe, Pd, and B equivalent to the above, 7g
,3Nd-18,2Pd-2,5Fe-1,OB,73
Nd-23Pd-3Fe-1, OB, 68.5Nd-2
7Pd-3,5Fe-1, OB, 64Nd-31Pd-
4Fe-1,0B 59Nd-35,5Pd-4,5
An ingot having a 5fI composition (vt%) of Fe1 and OB was obtained by the same method as above.

These ingots were coarsely ground, and the five types of powder obtained were used as materials (II)-1 to (II)-1. The metal structures in the ingots of these (II)-1 to 5 materials were analyzed using an image analyzer using E, D, and X, and the composition analysis and space factor of each phase were investigated. PdFe) 2 phase is 90
% or more, 1-2 material has approximately 50% Ndq (FePd) 2 phases and N d 3 (F e P d ) 2 phases.
(II)-3 material has two phases of Nd and (PdFe) approximately 9
0% or more, (n)-4 material has a structure of Nd* (PdFe) phase and approximately 50% Nd (PdFe) phase, (■-5 material has a structure of 90% Nd (FePn) phase). These (II)-1 to 5 materials have Ndq (P d
It was found that the powder contains at least one of Fe) 2 Flj, two phases of Ndi (FePd), and Nd (FePd) as a main component. Next, appropriate amounts of each of materials (II)-1 to 5 were added to the material (1) described above and weighed so that the Nd value was 32 wt% to obtain five types of mixed powders. These five types of mixed powder were pulverized to an average particle size of about 4 μm using a ball mill. Next, the obtained fine powder was
A green compact was obtained by molding in a magnetic field of XOe at a pressure of 1 OLon/c-.

These compacts were heated at 1000 to 1150°C for 0 to 4 hrA.
Sintered in r. After that, the obtained sintered body was
It was heated at ℃ and then rapidly cooled. Also, as a comparative material, 32 N d
A sintered body having a composition of -1, OB -F e L+al (wt%) of 6 was obtained by a normal powder metallurgy method.

These sintered bodies were subjected to Ni plating with Cu underplating. Magnetic properties of these samples and 60'CX 959
Table 1 shows the results of the 6 constant temperature and humidity tests. From Table 1, it can be seen that the test pieces according to the present invention all exhibited superior corrosion resistance compared to the test pieces of the comparative example, and in terms of magnetic properties, they also exhibited excellent magnetic properties as rare earth permanent magnets.

Furthermore, in the corrosion resistance test, Nd (
It can be seen that when the amount of the PdFe phase is 50% or more, the corrosion resistance is significantly improved.

<Example-2> 57Nd-42Pd1, OB,
57.8Nd-39Pd-2,3Fe-0,9B, 58
．． 4Nd-37, 2Pd-3, 4Fe-1, OB, 59
．． 6Nd-33,5Pd-5,9Fe-1,OB,60
．． 3Nd-31, 6Pd-7, lFe-1, OB, 60
．． 9Nd-29, 7Pd-8, 4Fe-1, OB (all W L% 6, Fe / P d ratio 0/1,
0.110.9, 0.1510.85, 0.210.8
゜0.2510.75, 0.310.7, 0.3510
．． 7fili coarse powder (65)
I[[)-1 to 7 materials were obtained.

Each of these coarse powders was 15 wL%, and the remaining amount was 8 wL%.
596 was mixed using material (1) of Example-1 to obtain seven types of mixed powders.

These mixed coarse powders were finely pulverized, compacted in a magnetic field, sintered, and heat treated in the same manner as in Example 1 to obtain sintered magnet samples.

Figure 1 shows the magnetic properties of these sintered bodies and (II[)-1 to 7
The relationship with the Fe/Pb ratio of the material is shown. From Figure 1 (m)
- Fe / Cu ratio of materials 1 to 6 is 0/1 to 0.31
It can be seen that high magnetic properties are exhibited between 0.7 and 0.7.

In the following margins, we mainly talked about Nd-Fe-B, but it is easy to infer that similar effects can be expected for RxTxB alloys made of rare earth elements (R) including Y, and transition metals T5 and B. It's possible.

<Effects of the Invention> As described above, according to the present invention, Nds (PdFe)2゜Nd3 (
PdFe)2, Nd A sintered magnet manufactured by a conventional powder metallurgy method by mixing powders having at least one of the (Pd, Fe) phases as a main phase is Nd, (PdFe)2. Nd3
It has a metal structure in which a Nd2Fe14B phase is dispersed in a matrix of one or more types of (PdFe)2+Nd (Pd, Fe) phases.

This sintered magnet has significantly improved corrosion resistance compared to conventional Nd-Fe-B magnets, and has
Since it is possible to impart the inherent corrosion resistance of oxidation-resistant plating of Cu, Cr, etc., chemical coating, etc., it is possible to easily obtain rare earth permanent magnets with excellent corrosion resistance, which is extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 shows Nd-(F e
xPdl-*) It is a figure showing the relationship between Fe substitution pressure and magnetic properties of a sintered body obtained by mixing powders in which the value of X of B is changed.

Claims (3)

[Claims] (1) R_5(PD_1_-_xT_x)_2, R_3
(Pd_1_-_xT_x)_2,R(PD_1_-_
xT_x) (where R is a rare earth element including Y, T is a transition metal, and x represents a number from 0 to 0.3).
A rare earth permanent magnet with excellent oxidation resistance characterized by dispersed _1_4B phase. (2) The rare earth permanent magnet according to claim 1, wherein the volumetric composition ratio of R(PD_1_-_xT_x) in the matrix is 50% or more. (3) In a method for producing a rare earth permanent magnet in which rare earth magnet alloy powder is formed in a magnetic field and liquid-phase sintered, the rare earth magnet alloy powder is mixed into an alloy powder whose main component is an R_2T_1_4B intermetallic compound, R_5(Pd_1_- _xT_x)_2, R_3(Pd_1_-_xT_x)_2, R(Pd_1
____xT_x) (where R is a rare earth element including Y, T is a transition metal, and x represents a number from 0 to 0.3). A method for manufacturing rare earth permanent magnets with excellent oxidation resistance.