JP6520337B2 - Sm-Fe-N rare earth magnet - Google Patents

Description

The present invention relates to Sm-Fe-N rare earth magnets.

As high performance rare earth magnets, Sm-Co based magnets and Nd-Fe-B based magnets are put to practical use, but in recent years, development of new rare earth magnets has been actively conducted.

For example, a Sm-Fe-N-based rare earth nitride magnet is proposed in which N is interstitially dissolved in Sm-Fe crystals. Since Sm-Fe-N based magnets have high Curie temperature and exhibit magnetic properties equivalent to Nd-Fe-B based magnets, improvements are being made as rare earth magnets excellent in high heat resistance.

Patent Document 1 proposes a two-phase separation type Re-Fe-N-H-M based magnet. Re is a rare earth element, M is Li, Na, K, Mg, Ca, Sr, Ba, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Pd, Cu, Ag, Elements of Zn, B, Al, Ga, In, C, Si, Ge, Sn, Pb, Bi and oxides of these elements and rare earth elements, fluorides, carbides, nitrides, hydrides, carbonates, sulfates And at least one of silicates, chlorides and nitrates. In the same publication, the addition of M forms a two-phase separation type microstructure as seen in Sm-Co and Nd-Fe-B, thereby forming a bulk magnet such as a sintered magnet or a bonded magnet. Sometimes the purpose is to bring out the same high magnetic properties as powder. Specifically, a bulk magnet of two-phase separation type having a phase with a high content of M at the particle boundary and a low content of M at the particle center or a phase without M It manufactures.

Further, in Patent Document 2, a nitrogen-containing rare earth magnet such as Sm ₂ Fe ₁₇ N _X in which an N atom is mixed in the R-T compound is heated to 600 ° C. or more, and the crystal structure is decomposed into RN and α-Fe. In the case of Nd-Fe-B alloys and the like, it is impossible to use conventional high temperature liquid phase sintering method and hot pressing method which require high temperature of 1000 ° C. or more for a long time. On the other hand, an RTN alloy powder (R is a rare earth element, T is a transition metal, N is a nitrogen) is formed into a predetermined shape, and then this formed body is sintered and solidified. In the manufacturing method, the above-mentioned compact is heated at a temperature rising rate of 600 to 1000 ° C./min, at a sintering temperature of 550 ° C. or less, within one minute of sintering time, at a sintering pressure of 6 to 10 ton / cm ² , current density of 0.7 to ² to plasma sintering under the conditions of .0kA / cm ² Method for producing nitrogen-containing rare earth magnet is disclosed.

Japanese Patent Application Laid-Open No. 3-16102 JP-A-7-240307

The generation mechanism of the coercivity (H _cj ), which is one of the magnetic properties in the Sm-Fe-N based magnet, is said to be a nucleation type. Therefore, the magnetic properties are easily influenced by the surface of the particles. That is, although a defect is generated on the surface of the magnet particle due to mechanical impact at the time of pulverization or oxidation of particles, a domain wall is generated due to this defect, but it is easy in the nucleation type magnet because there is no pinning site of the domain wall in the crystal grain. In this case, the coercivity is likely to deteriorate because domain wall movement occurs. In the above-mentioned prior art, since pulverization with a ball mill etc. is carried out at the time of preparation of the raw material magnet powder, high magnetic properties can be obtained even by the plasma sintering method at a low temperature for a short time due to the influence of oxidation. could not.

The present invention has been made to solve the above problems, and provides a Sm-Fe-N-based rare earth magnet with high magnetic properties and high density.

In order to suppress the deterioration of the magnetic properties of the Sm-Fe-N rare earth magnet due to oxidation, it is found that it is effective to introduce a SmFe ₃ N _x phase in addition to the main phase Sm ₂ Fe ₁₇ N ₃ phase. The present invention has been achieved.

The rare earth magnet according to the present invention is a Sm-Fe-N rare earth magnet having a relative density of 90% or more, and an area of a cross-sectional area of a SmFe ₃ N _x phase (1.0 ≦ x ≦ 2.5) as a subphase. A Sm-Fe-N-based rare earth magnet characterized in that it contains 5% or less (not including 0) in proportion.

It is possible to provide a Sm-Fe-N-based rare earth magnet having high magnetic properties and high relative density.

Hereinafter, embodiments of the present invention will be described. The embodiments of the present invention are not limited to the embodiments described later, and various modifications can be made within the scope of the technical idea thereof.

The Sm-Fe-N-based rare earth magnet in the present invention has a Sm ₂ Fe ₁₇ N ₃ phase in which N intrudes into a Th ₂ Zn ₁₇ crystal structure as a main phase. Further, it may be a TbCu ₇ type crystal structure phase. The composition ratio may be shifted if the ratio of Sm, Fe and N is close to the stoichiometric ratio of 2: 17: 3.

The relative density in the present invention, ie, the bulk density, is defined as the density of the sintered magnet divided by the theoretical density of the main phase, and the density of the sintered magnet is measured by the Archimedes method. The portion outside the magnetic particles may be a void, a low melting point metal binder such as Zn, or another grain boundary component. By setting the relative density to 90% or more, it is possible to obtain a magnet having excellent magnetic properties as compared to conventional bonded magnets.

SmFe-N based rare earth magnet of the present invention includes a SmFe ₃ N _x phase as the subphase. The SmFe ₃ N _x phase is easily oxidized as compared to the main phase Sm ₂ Fe ₁₇ N ₃ phase, so when oxygen and hydrocarbons attached to the particle surface are evaporated during the calcination, etc. By oxidizing the SmFe ₃ N _x phase, it is possible to prevent the oxidation of the main phase Sm ₂ Fe ₁₇ N ₃ phase and to suppress the deterioration of the magnetic properties. The SmFe ₃ N _x phase mainly has the effect of suppressing the oxidation of the main phase in the manufacturing process, but even after becoming a sintered magnet, it can prevent the oxidation of the main phase by oxygen and moisture intruding from the outside. .

Moreover, _{x of the} SmFe ₃ N _x phase contained as a subphase is 1.0 or more and 2.5 or less. When x is in this range, the SmFe ₃ N _x phase can be stably present, and can exhibit the function as an oxidation suppression phase.

The SmFe ₃ N _x phase contained as a subphase is 5% or less (not including 0) in the area ratio of the cross-sectional area. Since the SmFe ₃ N _x phase does not have high magnetic properties, when the above range is exceeded, the secondary phase becomes a cause of deterioration of the magnetic properties, and the magnetic properties of the sintered magnet as a whole deteriorate.

A part of the SmFe ₃ N _x phase contained as a secondary phase may be oxidized. When the function to suppress the oxidation of the main phase is exhibited, a part thereof is oxidized.

Hereinafter, the suitable example of the manufacturing method of the magnet of this invention is demonstrated.

Hereinafter, Examples and Comparative Examples of the present invention will be described. The method of manufacturing the magnet includes sintering method, rapid solidification method, vapor deposition method, HDDR method, etc. The method of crushing the alloy obtained by rapid solidification method and solidifying it using plasma sintering PAS (electrolytic solidification) is explained Do.

First, SmFe ₃ N _x powder of an auxiliary phase material is prepared. A Sm-Fe alloy having a desired composition ratio is prepared. The raw material alloy can be prepared by arc melting of raw materials of R and Fe in an inert gas, preferably Ar atmosphere, and other known melting methods.

The Sm-Fe alloy produced by the above method is ground in a mortar to produce a powder of several tens of micrometers or less. In addition to the mortar grinding, coarse grinding machines such as a stamp mill, a jaw crusher, and a brown mill may be used. When the crystallinity of the pulverized powder is not good, heat treatment at about 600 ° C. may be performed as crystallization treatment here. Next, the pulverized powder is subjected to a nitriding treatment. In the nitriding treatment, heat treatment may be performed at 450 to 550 ° C. for 2 hours to 16 hours in a nitriding atmosphere, ammonia gas may be used instead of nitrogen gas, or a mixed gas with hydrogen gas may be used. The obtained nitrided powder is further pulverized so as to have an average particle diameter of several μm.

For even _Sm 2 _Fe 17 _{N 3} powder as a main phase, appropriately, by adjusting the alloy blend composition is prepared in the same manner as described above SmFe ₃ N _x powder. _Next, with respect to Sm _{2 Fe} 17 _{N 3} powder, formulated to the SmFe ₃ N _x powder becomes a desired ratio, mixed powder was prepared. Furthermore, an appropriate amount of Zn powder to be used as a sintering aid is added.

The obtained mixed powder was filled in a cemented carbide die and subjected to plasma sintering PAS under a vacuum atmosphere to form a sintered body. In addition, as this electric-solidification conditions, pressure: 10 ton / cm ² or more, temperature rising rate: 20 ° C./min or more, sintering temperature 400 ° C. to 480 ° C., sintering time 1 minute or less.

After processing the obtained sintered body into a desired size, the density is measured by Archimedes method, and the magnetic property (residual flux density B _r , coercivity H _cJ ) is measured by a vibrating sample magnetometer (VSM). taking measurement. Density calculates relative density (%) at theoretical value (6.76 g / cm ³ ).

In addition, the cross section of the sintered body is observed with an energy dispersive spectroscopy (EDS) apparatus provided in a scanning transmission electron microscope (STEM) and the presence or absence of a SmFe ₃ N _x phase Evaluate the area ratio. From the elemental mapping image, a region which is R richer than the main phase and contains N is extracted, and in the quantitative analysis value near the center of the region, the ratio of the number of atoms of Sm to Fe to N is 1: 3. When the ratio is close to 1.0 to 2.5, it can be determined that the region is the SmFe ₃ N _x phase. Here, x is determined by taking an average of quantitative analysis values of 5 or more SmFe ₃ N _x phases. Further, the area ratio of SmFe ₃ N _x phase per unit area is calculated by specifying the area of Sm Fe ₃ N _x phase and obtaining the area by image analysis. The oxidation state of the SmFe ₃ N _x phase can also be evaluated here.

Hereinafter, the contents of the present invention will be described in detail using examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
First, Sm metal and Fe metal were blended in a ratio of 1: 3, and melted and alloyed in a vacuum melting furnace substituted with Ar. Analysis of the composition of this alloy confirmed SmFe ₃ phase. Next, the alloy was ground in a mortar to form a powder having an average particle size of 32 μm or less. Then, the powder was placed in a stainless steel vat, this performed 10 hours nitriding treatment while heating to 500 ° C. with flowing _{N 2} gas containing _{H 2,} to prepare a SmFe ₃ N _x powder. The nitrided powder was further ground by a ball mill to an average particle diameter of 1.7 μm.

Further, with regard to Sm ₂ Fe ₁₇ N ₃ powder serving as the main phase, the alloy composition was appropriately adjusted, and the same preparation as the above-described SmFe ₃ N _x powder was made. The obtained powder was confirmed by XRD to be a single phase of Sm ₂ Fe ₁₇ N ₃ phase. The average particle size was 1.1 μm.

Sm Fe ₃ N _x powder was mixed with Sm ₂ Fe ₁₇ N ₃ powder so that the area ratio of the cross section was about 5%, to prepare a mixed powder. Furthermore, 5 wt% of Zn powder was added.

2 g of the obtained mixed powder was filled in a 10 .phi. Cemented carbide die, and plasma sintering PAS was performed under a vacuum atmosphere to form two solid bodies. Sintering was performed at a pressure of 12 ton / cm ² , a temperature rising rate of 50 ° C./min, a sintering temperature of 450 ° C., and a sintering time of 1 minute.

The relative density and magnetic properties of the obtained sintered body were measured. Further, the cross section of the sintered body was observed to evaluate the value of x and the area ratio of SmFe ₃ N _x phase. The results are shown in Table 1.

Comparative Example 1
A sintered body was produced and evaluated in the same manner as in Example 1 except that SmFe ₃ N _x powder was not added. The results are shown in Table 1.

Example 2, Comparative Example 3, Comparative Example 2
A sintered body was prepared and evaluated in the same manner as in Example 1 except that the addition amount of SmFe ₃ N _x powder was made to be 0.1%, 1%, and 10% in area ratio. The results are shown in Table 1.

Comparative Example 3, Example 4, Example 5>
A sintered body was produced and evaluated in the same manner as in Example 1 except that the nitriding treatment time for producing the SmFe ₃ N _x powder was set to 1 hour, 3 hours, and 15 hours. The results are shown in Table 1.

Example 6
The sintered body was prepared and evaluated in the same manner as in Example 1 except that sintering was performed by changing the temperature rising rate to 1000 ° C./min and the sintering time to 0 minutes as the current flow solidification conditions. It is shown in Table 1.

Comparative Example 4
A sintered body was produced in the same manner as in Example 1 except that sintering was carried out by changing the sintering temperature to 350 ° C. as the current flow solidification conditions, and the results of evaluation are shown in Table 1.

From Table 1, the presence 5% 0.1% SmFe ₃ N _x phase in area ratio of the cross-sectional area, as compared with Comparative Example 1 was not added SmFe ₃ N _x phase, the coercivity _{H cJ} Improvement was seen. Most of the SmFe ₃ N _x phases in these sintered bodies are oxidized, and the main phase particles of Comparative Example 1 in which no SmFe ₃ N _x phase is added are more oxidized than the main phase particles of the example. It is inferred that the SmFe ₃ N _x phase functioned as the oxidation suppression phase of the main phase because there were a lot of regions. However, some of the SmFe ₃ N _x phase in the sintered body of the example had a non-oxidized region. Also, as in Comparative Example 2, if there are many SmFe ₃ N _x phase, decrease in remanence _{B r} and coercivity _{H cJ} was observed. It is considered that the added SmFe ₃ N _x phase itself is the cause of the deterioration of the characteristics. Furthermore, when _x in the SmFe ₃ N _x phase was small, the coercivity decreased. In the vicinity of the SmFe ₃ N _x phase of this sintered body, α-Fe is scattered, and it is inferred that the soft magnetic phase generated by the decomposition of the SmFe ₃ N _x phase is a cause of the deterioration of the magnetic characteristics. On the other hand, when the relative density was low, it was found that the magnetic properties were low regardless of the state of the SmFe ₃ N _x phase.

Claims (1)

Sm-Fe-N rare earth magnet with a relative density of 90% or more, and SmFe ₃ N _x phase (1.0 ≦ x ≦ 2.5) in area ratio of cross section not more than 5% (not including 0) A Sm-Fe-N based rare earth magnet characterized by including.