JPH0677026A - Manufacture of rare earth element-fe-n base permanent magnet - Google Patents

Abstract

PURPOSE:To device q manufacturing method of rare earth element-Fe-N base permanent magnet notably contributing to the increase in the manufacturing capacity and the long term stability of the performance by securing sufficient coercive force even if rough particles are used. CONSTITUTION:A metallic film comprising at least one kind of element out of Sn, Zn, Pb, In, Al and Mg is formed on the surface of an alloy particles mainly comprising rare earth metal (R), Fe and N as well as the compound in Th2Zn17 or ThMn12 type crystalline structure in main phase and mean particle diameter of 20-150mum. Next, the alloy particles whereon the metallic film is formed are molded into a molded body to be heat-treated later at the temperature of 100-600 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rare earth-iron-nitrogen permanent magnet, and more specifically to a permanent magnet having improved manufacturability and long-term stability in performance by using coarse powder. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, high-performance Nd-Fe-B system permanent magnets have been widely used with the miniaturization of various electronic devices. However, since this magnet has a low Curie point of 310 ° C, its temperature characteristics are poor, making it difficult to use at temperatures above 150 ° C.

[0003] On the other hand, by entering the nitrogen alloyed with rare earth metals and iron, for example Sm -Fe -N-H alloy the main phase of a compound of the crystal structure of Th ₂ Zn ₁₇ has excellent magnetic properties And a Curie point of about 470 ° C. Further, it has been reported that Nd-Fe-Ti-N-based alloys having a compound of Th Mn ₁₂ crystal structure as a main phase also have similar magnetism.

[0004]

However, the above-mentioned rare earth-iron-nitrogen based alloy cannot obtain the coercive force required for a permanent magnet unless it is finely pulverized to a particle size of several .mu.m. However, there has been a problem that the moldability is deteriorated and high-pressure molding is required, and the mold life is unavoidably shortened. Further, this type of alloy powder is easily oxidized under high temperature and high humidity, and the fine powder used promotes the oxidation, which makes it difficult to obtain a permanent magnet having stable performance for a long time. It was

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to secure a sufficient coercive force even if a coarse powder is used, and thus, it is possible to improve the manufacturability and stabilize the performance for a long time. -It aims at providing the manufacturing method of an iron-nitrogen permanent magnet.

[0006]

In order to solve the above problems, the method for producing a rare earth magnet according to the present invention comprises a rare earth metal (R), Fe and N as main components, and Th ₂ Zn.
Sn, Zn, P on the surface of an alloy powder having an average particle size of 20 to 150 μm and a compound having a ₁₇ or Th Mn ₁₂ type crystal structure as a main phase
After forming a metal film composed of at least one of b, In, Al and Mg and performing molding using the powder having the metal film formed thereon, the resulting molded body is subjected to heat treatment at 100 to 600 ° C. It is characterized by being configured.

As the rare earth-iron-nitrogen based alloy in the present invention, a compound having a Th ₂ Zn ₁₇ type crystal structure as a main phase is an Sm ₂ Fe ₁₇ Nx composition or a compound having a Th Mn ₁₂ type crystal structure is a main phase. Nd (Fe, M) ₁₂ Nx composition and Pr
A (Fe, M) ₁₂ Nx composition is representatively represented (where M represents a transition element). In this case, the content of N is selected to be several to 20 several atomic%. Saturation magnetic flux density, crystal magnetic anisotropy and Curie point of these alloys are significantly improved by containing nitrogen, and they are excellent as permanent magnet materials. Further, in these alloys, a part of iron can be replaced with another transition metal such as Co or Ti, or two or more kinds of rare earth metals can be used as the rare earth metal. Co is particularly effective in raising the Curie point and improving the corrosion resistance. Also, good magnetic characteristics can be obtained by replacing a part of N with C.

In the present invention, any method may be used to obtain the above-mentioned alloy powder. For example, a method of obtaining a master alloy powder of a rare earth metal and iron (and optionally other metal) and injecting N into this is used. You can In this case, as a method for obtaining the mother alloy powder, a raw material in which a rare earth metal and Fe are mixed in a predetermined ratio is melted by high frequency, and the molten alloy is poured into a mold to form an alloy ingot, which is homogenized at high temperature. After that, a method of forming a desired powder using a jaw crusher, a stamp mill, a ball mill, or the like, or a rapid cooling method of directly quenching the molten alloy to obtain a powder can be used. The penetration of N into the master alloy powder can be carried out by bringing the master alloy powder into contact with a nitriding gas such as nitrogen, ammonia, or a mixed gas of nitrogen and hydrogen at a high temperature. In this case, the nitriding temperature is
If the temperature is lower than 200 ° C, the penetration of N is insufficient, and if it exceeds 600 ° C, the compound phase is easily decomposed. Therefore, it is desirable to select the range of 200 to 600 ° C. Further, by performing this nitriding treatment under a high pressure of several tens of atmospheres, it is possible to efficiently inject nitrogen into the master alloy powder. Further, it is possible to adjust the powder particle size by pulverizing again after the nitriding treatment.

In the present invention, the grain size of the alloy powder is 20 μm.
If it is less than m, it is not preferable for mass production because it requires high-pressure molding to form a bonded magnet, and it is easily oxidized in the manufacturing process. On the other hand, if the particle size exceeds 150 μm, N is not sufficiently penetrated. This was in the range of 20 to 150 μm.

In the present invention, as mentioned above, Sn, Zn, Pb, In and A which are low melting point metals are formed on the surface of the alloy powder.
It is characterized in that it forms a film consisting of at least one of l and Mg, but these low melting point metals were selected because these metals function as binders for bonded magnets and by heat treatment described later. This is because it has a function of partially reacting with the alloy powder to increase the coercive force. As a method for forming a metal film on the surface of the alloy powder, a plating method or a mechanical bonding method can be used. As a plating method, a chemical method using chemicals, or vapor deposition,
There is a physical method such as sputtering, and on the other hand, as a mechanical bonding treatment method, there is a method of applying a strong mechanical force to a vibration mill.

In the present invention, in the above-mentioned molding, the film metal coated on the alloy powder is strongly fixed to each other by the pressure, and a hard molded product can be obtained by the pressure molding of several Ton / cm ^2. . The present invention, in addition to the powder forming the metal film, a metal binder of the same kind as the film metal can be added by several wt% to perform warm forming,
After the warm molding, the molded product can be impregnated with an organic substance such as epoxy resin or varnish, and in any case, a molded product having further excellent strength can be obtained. Further, for this molding, various methods such as compression, injection and extrusion can be used.

The heat treatment after molding can be carried out by heating the powder and the molding die in an inert gas atmosphere or in a vacuum, and this heat treatment improves the magnetic properties, especially the coercive force. It is presumed that the reason for the improvement of the coercive force is that the soft magnetic iron component contained in the alloy powder in a small amount reacts with the coating metal and disappears. As for the heating temperature, if the temperature is less than 100 ° C, the above-mentioned improvement is not seen, and 600 ° C
If it exceeds, the decomposition of the compound tends to occur and the magnetic properties tend to deteriorate, so this was made the range of 100 to 600 ° C.

[0013]

In the above-described method for producing a rare earth-iron-nitrogen permanent magnet, the formation of the low melting point metal coating on the alloy powder and the subsequent warm forming increase the magnetic properties, especially the coercive force, and Allows the use of powder.

[0014]

Embodiments of the present invention will now be described with reference to the drawings.

EXAMPLE 1 Samarium having a purity of 99.9% and electrolytic iron were blended in a predetermined ratio, and high frequency melting was performed to produce an alloy ingot of Sm ₂ Fe ₁₇ composition containing a compound having a Th ₂ Zn ₁₇ type crystal structure as a main phase. did. This was homogenized at 1200 ° C. for 12 hours in an Ar gas atmosphere, and various mother alloy powders having an average particle diameter of 3 to 200 μm were obtained by a stamp mill and a ball mill. Next, this mother alloy powder was held in N gas at 5 atm at 450 ° C. for 2 to 36 hours to allow N to infiltrate to obtain a nitride powder (alloy powder). Subsequently, these nitride powders were immersed in a zinc chemical plating bath using a catalyst to form a zinc film on the powder surface.
Note that the amount of zinc adhered to the nitride powder obtained by the gravimetric method is
The average film thickness was 1.6 μm. Next, this metal-coated powder was supplied to a molding die and compression-molded at a pressure of 7 Ton / cm ² while applying a magnetic field of 15 KOe to produce a molded body.
After that, the molded body was placed in an electric furnace and subjected to heat treatment at 425 ° C. for 6 hours in an argon gas atmosphere to obtain magnet body samples, which were subjected to a magnetic characteristic measurement test by a BH tracer. The crystal structure was confirmed by X-ray diffraction.

FIG. 1 shows the effect of the average particle size of the nitride powder on the maximum magnetic energy product BHmax, the coercive force iHc and the residual magnetic flux density Br of the magnet sample.
From Fig. 1, the maximum magnetic energy product BHmax and the coercive force iH
c has a peak when the average powder particle size is about 25 μm,
High price in the range of 20 to 150 μm. on the other hand,
The coercive force iHc increases as the grain size of the nitriding powder becomes smaller according to the single domain grain theory. Therefore, it was found that the average powder particle size was required to be in the range of 20 to 150 μm in order to obtain good magnetic properties under the practical molding pressure in this example. As a result of X-ray diffraction,
It was confirmed that each of the nitride powders used here had a desired main phase of the Th ₂ Zn ₁₇ type crystal structure.

Example 2 Similar to Example 1, an alloy ingot of Sm ₂ Fe ₁₇ composition was prepared from samarium and electrolytic iron as raw materials, homogenized, and then pulverized to obtain an average powder particle size of 25 μm. A mother alloy powder was obtained. Next, this mother alloy powder is 450 in N gas at 5 atm.
The temperature was kept at 12 ° C for 12 hours to obtain a nitriding powder. Then, the vapor deposition method, which is one of the physical plating treatment methods, was adopted for this nitride powder, and this was set on a rotary small plate of a vacuum vapor deposition machine, and the vacuum degree 1
Each of Zn, Sn, Pb, In, Al and Mg was vapor-deposited by resistance heating under x10 ^-5 torr. The deposition conditions were adjusted so that the amount of deposited metal was 1.5 to 2 μm as the coating film thickness. Then, using this metal-coated powder, molding was performed under the same conditions as in Example 1 to obtain a molded body, which was then placed in an electric furnace and placed in an argon gas at 100 to 7%.
Heat treatment was carried out at 00 ° C. for 1 hour to obtain magnet body samples 1 to 7, which were subjected to the same magnetic characteristic measurement test as in Example 1. Further, for comparison, a sample 8 on which Cu was vapor-deposited and a sample 9 on which no metal vapor deposition was performed were obtained, and these were also subjected to the same measurement test. The results are shown in Table 1.

[0018]

[Table 1]

As is clear from Table 1, the samples 1 to 7 according to the present invention using the powder having the low melting point metal film formed thereon,
In each case, high residual magnetic flux density Br and coercive force iHc are obtained. On the other hand, sample 8 with Cu vapor deposition has a coercive force.
Almost no improvement in iHc was observed, and the coercive force iHc of Sample 9 which was not vapor-deposited was remarkably small. Therefore, it became clear that the low melting point metals specified in the present invention are necessary for obtaining excellent magnetic properties. It was also confirmed that there is no problem even if the vapor deposition method is applied to the formation of a metal film on the nitride powder.

Example 3 The nitride powder produced in Example 2 was charged into a zinc-lined stainless steel ball mill container, the interior of the container was replaced with N gas, and the dry operation was performed for 24 hours. A zinc film was mechanically formed on the powder surface. Next, this metal-coated powder is used to perform molding under the same conditions as in Example 1, and after molding, the powder is placed in a vacuum furnace and heated in a nitrogen gas at 100 to 700 ° C. for 1 hour.
The heat treatment was performed for a time, and the magnetic characteristics of the obtained magnet body sample were measured.

FIG. 2 shows the effect of heat treatment temperature on the coercive force iHc of the magnet sample. From the figure, it is clear that the coercive force iHc has a peak near the molding temperature of 400 to 500 ° C, but has an excellent value of 2000 Oe or more in the temperature range of 100 to 600 ° C. It was also confirmed that there is no problem even if the mechanical bonding treatment method is applied to the formation of the metal film on the nitride powder.

Example 4 Sm ₂ (Fe _0.8 Co _0.2) containing samarium, cobalt, and electrolytic iron having a purity of 99.9% at a predetermined ratio and high-frequency-melted to have a compound having a Th ₂ Zn ₁₇ type crystal structure as a main phase. ) A ₁₇ composition alloy ingot was produced. This is 1150 ℃, 12 hours,
After homogenizing under Ar gas atmosphere, quenching is performed, and the average particle size is 50 μm and 3 by a stamp mill and a ball mill.
A master alloy powder of μm was obtained. Next, this mother alloy powder was charged into an electric furnace and kept at 500 ° C. for 8 hours in N gas at 5 atm to allow N to infiltrate. Then, these nitride powders were treated in the same manner as in Example 1. A 0.6 μm zinc film was formed on the powder surface by immersing in a zinc electroplating bath using a catalyst. Next, these metal-coated powders were mixed with 10% by weight of zinc powder to obtain 15KO.
While applying a magnetic field of e, compression molding is performed at a pressure of 4 to 10 Ton / cm ² to produce a molded body, which is then placed in an electric furnace and heat-treated at 450 ° C. for 8 hours in an argon gas atmosphere. I went. The maximum energy product BH m
In order to perform the measurement test of ax and compact density, and also to know the long-term stability, the above-mentioned nitriding powder was placed in a constant temperature bath at 125 ° C for 500 times.
The weight change of the powder was measured while keeping the time.

FIG. 3 shows the maximum energy product B of the magnet sample.
The effect of the average powder particle size and the molding pressure on the H max and the density is examined. From the figure, the magnet body sample using the coarse powder having the average particle diameter of 50 μm has excellent magnetic characteristics such as the maximum energy product (BH max) of 10 MGOe or more at the molding pressure of 1 Ton / cm ² or more, and the relatively low pressure. It has been clarified that it is possible to increase the density in molding.

FIG. 4 shows the effect of holding time on the rate of weight increase. From the figure, it is clear that the coarse powder having an average particle size of 50 μm has a significantly smaller weight increase rate due to oxidation than the fine powder having an average particle size of 3 μm, and is suitable for manufacturing a magnet having excellent long-term stability. is there.

Example 5 Neodymium having a purity of 99% or more, electrolytic iron, cobalt, and ferrotitanium were mixed in a predetermined ratio, and the mixture was melted at a high frequency to obtain T.
NdFe ₈ Co ₃ having a compound of h Mn ₁₂ type crystal structure as the main phase
An alloy ingot having a Ti composition was produced, and this was held in an argon gas atmosphere at 1100 ° C. for 24 hours for homogenization treatment, and then this alloy ingot was crushed by a stamp mill and a ball mill to have a grain size of 3 to 180 μm. A mother alloy powder was obtained. Next, this mother alloy powder is heated in N gas at 5 atm for 350
Hold at ℃ for 1 to 24 hours to infiltrate N and obtain nitride powder.
Then, this was immersed in a tin chemical plating bath using a nickel catalyst to form a tin film of about 0.6 μm on the powder surface.
Next, 10% by weight of tin powder was added to and mixed with the obtained powder, and compression-molded at a pressure of 7 Ton / cm ² while applying a magnetic field of 15 KOe. Measured by tracer.

FIG. 5 shows the effect of the average particle size of the nitride powder on the maximum magnetic energy product BHmax, the coercive force iHc and the residual magnetic flux density Br of the magnet sample.
From Fig. 5, the maximum magnetic energy product BHmax and the coercive force iH
c has a peak at an average powder particle size of about 25 μm as in Example 1, but has a high value in the range of 20 to 150 μm, and the coercive force iHc is a nitride powder particle size according to the single domain particle theory. Is increasing as is smaller.

Example 6 A molded body produced by using the nitride powder having a particle diameter of 25 μm in Example 1 was dipped in an epoxy resin having a viscosity of 150 CPS and held under a reduced pressure of about 10 Torr for 1 hour to form an epoxy resin on the molded body. It was impregnated with resin and cured at 120 ° C. for 2 hours.
As for the magnetic properties of the sample obtained, the maximum magnetic energy product BHmax was 11.5 MGOe, which was the same as that of the sample without impregnation, but the compressive strength of the sample was 60 kgf / mm ² , which is 1.6 times that of the sample without impregnation. It was found that it greatly contributes to the improvement of strength.

[0028]

As described in detail above, according to the method for producing a rare earth-iron-nitrogen permanent magnet of the present invention,
Magnets with excellent magnetic properties can be manufactured even with coarse powder having an average powder particle size of 20 to 150 μm, and the use of this coarse powder eliminates the need for molding at high pressure, extending the mold life, and manufacturing Sex is greatly improved. Further, by using the coarse powder, the oxidation of the powder is suppressed in the manufacturing process, and the performance of the obtained magnet is stable for a long period of time.

[Brief description of drawings]

FIG. 1 is a graph showing the influence of the average powder particle size of alloy powder on the magnetic properties of rare earth-iron-nitrogen based magnet samples obtained by the method of the present invention.

FIG. 2 is a graph showing the effect of heat treatment temperature on the magnetic properties of a magnet body sample obtained by the method of the present invention.

FIG. 3 is a graph showing the influence of the average powder particle size and molding pressure on the magnetic properties and density of the magnet sample obtained by the method of the present invention.

FIG. 4 is a graph showing the influence of the average powder particle size and the holding time on the increase in oxidized weight of the powder used in the present invention.

FIG. 5 is a graph showing the influence of the average powder particle size of the alloy powder on the magnetic properties of the rare earth-iron-cobalt-nitrogen based magnet sample obtained by the method of the present invention.

Claims (3)

[Claims] 1. An alloy powder having an average particle size of 20 to 150 μm, which contains a rare earth metal (R), Fe and N as main components and a compound having a Th ₂ Zn ₁₇ or Th Mn ₁₂ type crystal structure as a main phase, A metal film made of at least one of Sn, Zn, Pb, In, Al and Mg is formed, and molding is performed using the powder having the metal film formed thereon.
Rare earths characterized by heat treatment at 100-600 ℃
Method for manufacturing iron-nitrogen permanent magnet. 2. The method for producing a rare earth-iron-nitrogen permanent magnet according to claim 1, wherein the powder having a metal coating is added with a metal binder of the same kind as the coating metal to carry out molding. 3. The method for producing a rare earth-iron-nitrogen permanent magnet according to claim 1, wherein the molded body is heat-treated and then the molded body is impregnated with an organic binder.