JPH03141608A - Rare earth element-iron-nitrogen magnetic material controlled in microstructure, manufacture, and manufacture of powder which is its stock - Google Patents

Abstract

PURPOSE:To improve magnetic characteristics by controlling the particle diameter, mixture of phases, and phase splitting of Re-Fe alloys prepared initially and by classifying them by every grade before composition of Re-Fe-N or Re- Fe-N-H-O magnetic materials. CONSTITUTION:Before composition of the base alloy of rare earth element-iron- nitrogen magnetic material, to average crystal particle diameter of the base alloy is adjusted to a range of submicrons to 300mum by controlling the cooling speed of molten metal and by varying the annealing temperature over a range of 700-1300 deg.C to time annealing at a duration where a phase consisting mainly of iron can be reduced to an allowable amount as the magnetic material. After preparation of rare earth element-iron alloy or composition of rare earth element-iron-nitrogen magnetic material powder, classification is conducted to sort out the powder of an arbitrary region of particle size distribution ranging from submicrons to 300mum.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to rare earth element-iron-nitrogen (hereinafter "Re-Fe-N
The present invention relates to a magnetic material with improved characteristics by controlling the average crystal grain size in the microstructure of the magnetic material in the range of submicrons to 300 μm, a method for producing the same, and a method for producing powder of the material.

[Prior Art] Permanent magnets and magnetic recording media occupy a central position in the field of industrial applications of magnetic materials. The magnetic materials used in these have remarkable characteristics.

That is, permanent magnet materials such as Nd-Fe-B and Sm-Co are characterized by the microstructure formed during sintering or annealing. 50 to 100μ1 for Nd-Fe-B system
A sintered body having a crystal grain size above the above exhibits the highest magnetic properties, and the composition and structure of the grain boundary portion of the grains are important factors that influence the performance of the magnet. This situation also applies to Sm-Co magnets, and in particular, Sm2CO17 magnets precipitate at grain boundaries during heat treatment called multi-stage aging treatment.
The mlCo5-based composition is important for the development of magnetic properties.

On the other hand, magnetic materials for magnetic recording media, such as 7-FezO
3. Fe-Nt-Co alloys, barium, and strontium ferrite are often used by being dispersed in a coating binder with a thickness of several μm, so they are used as fine particles ranging from submicrons to 1 to 2 μm in size. used. These particles are first of all fine particles,
Furthermore, relatively high coercive force (He) and residual magnetization (Br
), it is necessary to make technical improvements to the particle shape, orientation method, etc.

Therefore, to summarize the characteristics of the magnetic materials mentioned above, in permanent magnet materials, magnetic properties are expressed by controlling the composition and microstructure of the grain boundary area at a particle size much larger than the single domain particle size, and magnetic properties for magnetic recording are achieved. In powder, magnetic properties are brought out by making the most of the fact that they are fine particles, such as particle size and particle shape magnetic anisotropy.

[Problems to be Solved by the Invention] The present invention aims to provide a magnetic material with even better magnetic properties than conventional materials by controlling the microstructure, and a method for producing its powder. .

[Means for Solving the Problems] The structure of the present invention for solving the above problems is as follows: (1) The average crystal grain size in the microstructure of the material is from submicron to 30.
When synthesizing a rare earth element-iron-nitrogen magnetic material in the range of 0 μm, (2) a master alloy of rare earth element-iron-nitrogen magnetic material, it is necessary to control the cooling rate of the molten metal and the temperature during annealing. By varying the temperature in the range of 700 to 1,300°C and setting the annealing time to a time that allows the iron-based material to be reduced to an amount acceptable as a magnetic material, the average grain size of the master alloy can be changed from submicron to 300μ. A method for producing a rare earth element-iron-nitrogen magnetic material, (3) a rare earth element-iron-nitrogen magnetic material fraction,
After preparing a rare earth element-iron alloy or after synthesizing a rare earth element-iron-nitrogen magnetic material powder, classification is applied to classify the powder in any particle size distribution range from submicron to 300μ. This is a method for producing nitrogen-based magnetic material powder.

To explain the above manufacturing method specifically, first, the Re-Fe alloy to be synthesized is crushed and then classified according to particle size, or this alloy is combined with or contains one or more of nitrogen, hydrogen, and oxygen. After that, it is crushed and classified according to particle size.

To explain a little more concretely, the manufacturing method involves controlling the cooling rate of the molten metal, varying the annealing temperature in the range of 700 to 1300°C, and reducing the annealing time to an amount that allows the iron-based phase to be used as a magnetic material. It is characterized by having the time to do so. In addition, in order to clarify the effect of controlling the average grain size, rare earth element - iron (hereinafter referred to as "Re-Fe")
The alloy or Re-Fe-N based magnetic material powder is classified, and the powder is separated in any particle size distribution range from submicron to 300 μm.

In the present invention, the Re-Fe-N magnetic material and the magnetic material of the previous application (Japanese Patent Application No. 63-228547) are characterized in that they can exhibit higher magnetic properties in the form of fine particles than conventional magnetic materials. In order to sufficiently draw out the particles, the particle size of the master alloy is controlled by changing the annealing conditions, and at the same time, after each crushing, an operation is performed to adjust the particle size by classifying. This operation made it possible to bring out the characteristics of these magnetic materials more clearly.

In addition, the present invention uses a Re-Fe-N magnetic material, the Re-Fe-N-H magnetic material of the prior application, and a rare earth element-iron-nitrogen-hydrogen-oxygen (hereinafter referred to as "Re-Fe-N-H-C"). )' (Japanese Patent Application No. 1-235822) system magnetic materials, the crystal grain size of the Re-Fe alloy master alloy that is first synthesized is controlled by changing the annealing conditions, and nitrogen, hydrogen, or oxygen is added. This is a manufacturing method for magnetic materials that is characterized by greatly improving magnetic properties by pulverizing and classifying the material, compared to the case without these processing steps.The magnetic properties here refer to magnetization. , coercive force, magnetic anisotropy, and squareness ratio.

As stated in claims (1) to (3) of the above-mentioned claims, the present invention relates to the production of a Re-Fe-N magnetic material or a Re-Fe-N-H-0 material. In the process, it is necessary to control the particle size of the master alloy synthesized first, and to classify the master alloy after crushing, or after nitriding and hydrogenating.
The present invention relates to a manufacturing method for improving magnetic properties by controlling the particle size of a magnetic material by classification, or by pulverizing and classifying a master alloy, nitriding, hydrogenating, and further classifying.

(Details of manufacturing method) Here, a method for manufacturing a magnetic material using a Re2Fei alloy as the Re-Fe alloy and containing nitrogen, hydrogen, and oxygen in the mother alloy will be described as an example.

The Re-Fe-N-H system and Re-Fe-N- of the earlier application
The manufacturing process of the H-0 magnetic material is as follows.

(1) Synthesis of Re-Fe alloys (2) Coarse pulverization (3) Nitriding and hydrogenation (4) Fine pulverization Among these, classification is performed after (2) coarse pulverization and (3) after nitridation and hydrogenation. This is an effective method for controlling the diameter. Further, the microstructure of the master alloy can be controlled mainly by the annealing conditions after the synthesis of the alloy (1).

Below, we will focus on methods for controlling the microstructure of the master alloy and effective methods for classification.

(1) Synthesis of master alloy The raw material alloy can be produced by a high frequency furnace, an arc melting furnace, or by a liquid ultra-quenching method.

The composition preferably ranges from 5 to 25 atomic % Re and from 75 to 95 atomic % Fe. If Re is less than 5 atomic %, a large amount of α-Fe phase exists in the alloy, making it impossible to obtain a high coercive force. Also,. If Re exceeds 25 atomic %, high saturation magnetic flux density cannot be obtained.

The synthesis of the master alloy is generally carried out by rapidly cooling a mixture of molten rare earth elements and iron. This is the same for any of the above methods. Figure 5 shows a part of the phase diagram of the Sm-Fe base alloy as an example ("Iron-Bin").
ary Phase DiagraLIlsOrtru
d Kubaschevskl, Sprlnger-v.
erlagq1982, from P2O3).

As is clear from this phase diagram, when producing Sm 2 Fe 17 alloy, for example, 1500
When rapidly cooling a molten alloy once melted at ~1800°C,
At around 1280-1450°C, a-Fe precipitates and 10
The S m 2 Fe 17 alloy precipitates between 10 and 1280°C, and the Sm1Fe3 phase precipitates below 1010°C. As a result, the first alloy obtained is α-Fe.

The three main constituent phases are Sm2FeI7 and Sm1Fe3. When this master alloy is annealed at, for example, 800 to 1250°C, the α-Fe and 5rrzFez phases gradually disappear, and a uniform 2-17 alloy can be produced by X-ray diffraction with the Sm2FeI7 phase as the main phase.

During this annealing, the microstructure of the 2-17 main phase, that is, the particle size and the state of phase separation and precipitation at grain boundaries, changes, and the microstructure varies greatly depending on the annealing conditions.

For example, when a rapid cooling method such as an ultra-quenching method is used, an Sm2Ferr alloy in which the average grain size of the mother alloy after annealing is 5 μm or less can be prepared. On the other hand, when melted in a high frequency furnace and poured into a metal mold, the phase separation of the three a-Fe and SmlFe phases is large, and relatively high temperature and long annealing is required to obtain a single SmzFen phase. The 2-17 phase is 150
It has a particle size of μ or more and a high degree of crystallinity.

The composition of the master alloy is preferably Sm2Fe17 single-phase in this example, but the microstructure can vary from an average grain size of less than 5 .mu.m to an average grain size on the order of 300 .mu.m. Furthermore, these microstructural differences are deeply correlated with the mechanical properties of the master alloy, such as strength, hardness, and softness, as well as with the degree of crystallinity and reactivity with the gas phase in subsequent processes, resulting in material affects various properties including magnetism.

(2) Coarse pulverization The pulverization at this stage may be performed using a method such as a show crusher or stamp mill that prepares only coarse powder, or may be performed using a ball mill or jet mill depending on the conditions. However, this pulverization is for the purpose of uniformly performing the nitriding and hydrogenation in the next step.

There is a correlation between coarse pulverization and the microstructure of the master alloy described in (1). For example, a master alloy having a relatively fine average particle size of about 5 to 30 μm is generally hard and requires a lot of stress and time during coarse grinding. In addition, the shape of the particles after pulverization is relatively spherical, and it appears that pulverization is progressing due to so-called intergranular fracture.

On the other hand, a master alloy that has grown to an average particle size of 150 μm or more can be similarly pulverized by coarse pulverization, but many particles have sharp edges due to intragranular fractures.

After the above-mentioned coarse grinding, the average particle size is usually 50 to 100μ.
An aggregate of m particles is obtained. However, the appearance of the obtained particles varies greatly depending on the microstructure of the master alloy and the grinding method, which greatly affects the effectiveness of the treatment after coarse grinding.

(3) Classification If classification is performed after the coarse pulverization described in (2) above, the results of subsequent processing may be greatly influenced. In other words, the average particle size and particle size distribution during coarse grinding vary greatly depending on the mother alloy and the coarse grinding method, and in general, fine particles have many changes in composition due to mechanical stress, such as defects within the particles and oxidation on the surface. Can be seen. Therefore, when forming a ferromagnetic material through a solid phase-gas phase reaction, it is preferable that the inside of the crystal contains as few defects as possible and the surface of the particles is normal. , the properties of the magnetic material finally obtained through subsequent processing are improved.

In the Re-Fe-N magnetic material or Re-Fe-N-H-0 magnetic material described here as an example, (1) to
After the steps up to (3), first, nitrogen and hydrogen are mainly reacted, and then oxygen is added. Note that the amount of nitrogen and hydrogen in the material powder at this stage is about the same as that of a root ball, and the amount of oxygen is 300 to 10,000 p11100.

(4) Nitriding and Hydrogenation A method for combining or impregnating nitrogen and hydrogen into the pulverized raw material master alloy is to pressurize or heat-treat the raw material alloy powder in ammonia gas or a reducing mixed gas containing ammonia gas. The method is valid. The amount of nitrogen and hydrogen contained in the alloy can be controlled by the mixture component ratio of the ammonia gas-containing mixed gas, heating temperature, pressurizing force, and treatment time.

As the mixed gas, a mixture of hydrogen, helium, neon, nitrogen, and argon, or a mixture of two or more of them and ammonia gas is effective. Although the mixing ratio can be changed in relation to the processing conditions, it is particularly effective for the ammonia gas partial pressure to be from 0.02 to 0.75 atm, and for the processing temperature to be preferably in the range of 200 to 650°C. At low temperatures, the penetration rate is low, and at high temperatures of 650° C. or higher, iron nitrides are produced, and the magnetic properties are degraded. In the pressurized treatment, the nitrogen and hydrogen contents can be changed even at a pressure of about 1 Oatm.

If a gas other than ammonia gas is used as the main component of the nitriding or hydrogenation atmosphere, the reaction efficiency will be significantly reduced. However, it is possible to introduce nitrogen and hydrogen, for example, by carrying out a long reaction using a mixed gas of hydrogen gas and nitrogen gas.

(5) Magnetic materials that combine or contain nitrogen and hydrogen through annealing and nitriding or hydrogenation have deteriorated magnetic properties due to compositional non-uniformity and defects within the crystal due to strain. Therefore, magnetic properties are improved by annealing. The atmosphere is preferably a gas species that does not contain nitrogen or hydrogen, such as argon or helium.

(8) After the annealing of classification (5) is completed, the distribution of the particle system expands due to so-called gas absorption and pulverization or thermal shock pulverization, and differences in magnetic properties occur depending on the particle size. Classification is effective in clarifying this difference in magnetic properties. Classification using a general mechanical mesh is also sufficiently effective. However, classification using a jet mill or the like is also effective.

(7) The coarse powder after finely pulverized nitriding and hydrogenation has a saturation magnetization of 13KG as it is.
, has a coercive force of 500 to 7000e, but by grinding it with a vibrating ball mill, a planetary ball mill, and even a rotary ordinary pot-type ball mill, the coercive force can be reduced to lo
It is possible to improve it to KOe or higher. Normally, the magnetization decreases to some extent, but powder having the required magnetization and coercive force can be obtained by setting these pulverization conditions.

In this pulverization process, the amount of oxygen contained in the substance is changed by controlling the oxygen partial pressure in the atmosphere, such as during operation in a glove box or in air. Further, the amount of oxygen contained in the substance and its state of existence vary depending on the amount of water and oxygen in the organic solvent of the solvent used for pulverization, such as ethanol and water. At this stage, the amount of oxygen is set to 350, for example.
It can be controlled at a level of 0 ppm or higher.

The magnetic powder produced as described above can be formed into sintered or bonded permanent magnets, coating films for magnetic recording, and the like.

[Example code] The present invention will be explained in detail below using examples.

Example 1 Sm-Fe-N-H-0 using Sm as the rare earth element
The method for preparing the system magnetic powder will be described. Introduction Sm-
The composition of Fe is Sm2Fe+5. Sm and Fe ingots each having a purity of 3N are weighed so that s is obtained.

First, Fe metal is placed in a ceramic mold placed in a high frequency furnace and melted under reduced pressure of about 10' aim.

Next, argon gas is introduced, and Sm metal is mixed into the Fe melt under somewhat reduced pressure, followed by high frequency melting at around 1600° C. for several minutes. This mixed melt was heated to 1500 to 1600℃.
The mixture was poured into a steel mold with a width of about 3 mm and cooled. After the mold is cooled to room temperature, the alloy is taken out from the apparatus, coarsely ground into pieces of several crA square, transferred to a tube furnace, and then annealed at a temperature in the range of 850 to 1250°C for 2 to 48 hours. However, at this time, high-purity argon gas is flowed through the tube furnace.

FIG. 1 shows an example of the results of the above annealing. The annealing temperature was 940°C, 1095°C, and 1255°C, and the annealing time was varied within a range of 45 minutes to 32 hours.

In that case, the average crystal grain size of the master alloy finally obtained changes for each condition.

The average crystal grain size was measured by the Jel'['ry] method after taking a differential electron micrograph. In addition, the α-Fe phase disappears from the alloy after annealing, and the 5tr
The annealing conditions that result in a mixed phase of only the zFez orange and Sm2FeI7 phases are in the upper right region of the broken line in the figure. As is clear from Figure 1, the master alloy in which the αFe phase has disappeared has a thickness of about 30 μI to 150 μI within the experimental conditions of this example.
It has an average grain size of up to . Further, when the same treatment is performed except that the width of the mold is narrowed to about 1 la Ill, the α-Fe phase disappears after annealing at 950° C. for about 24 hours, and the average crystal grain size becomes about 6 μm.

The master alloy prepared as described above was coarsely ground using a coffee mill to have an average crystal grain size of 50 to 100 μm, and the mixture was heated at 465°C in a mixed gas with an ammonia-hydrogen molar ratio of 0.35 to 0.65. for 2 hours, and then heat treated at 465° C. for 2.5 hours in argon gas. Furthermore, the treated powder was classified into eight stages using a sieve of 20 to 108 μm, and the physical properties of each particle size were measured using a vibrating magnetometer (VSM).
The results shown in FIGS. 2 and 3 were obtained using the following.

In addition, these Re-Fe-N-H-0 based magnetic materials are:
The average composition is expressed as a composition formula: S m2 F 617N3
．． 7-3. g Ho, 0+00,5 ◎The variation in composition correlates with the magnetic properties, but the change is not large enough to override what is being discussed here.

In Figure 2, the magnetic anisotropy is σ1/σ' (15kOe)
This was measured in the magnetic field orientation direction of the 4πI-H curve (
σ−) and the magnetization in the 90° C. direction (σ1). The smaller the value, the better the magnetic anisotropy. Three groups are present in these samples, 50-150μ11
27.31μ■ and 88m have very different numerical values. However, what is most noteworthy about these data is that particles ground to a size close to the average grain size of the master alloy exhibit the best magnetic anisotropy. Note that samples with a master alloy average grain size of 150 μm show almost the same magnetic anisotropy in this grain size region.

FIG. 3 shows the correlation between the average classified particle size and the saturation magnetization for each mother alloy average crystal grain size of the sample shown in FIG. 2. Here, similarly to the magnetic anisotropy, the 50.150 μm sample shows the highest magnetization, and the 6 μm sample shows the lowest magnetization. Although it is not clear, there is a tendency for saturation magnetization to be high when the average crystal grain size of the mother alloy and the crushed crystal grain size are close to each other.

The above shows that the average grain size of the synthesized master alloy is related to the magnetic properties, namely saturation magnetization, coercive force, magnetic anisotropy, and squareness ratio.

Next, each mother alloy particle was classified according to its particle size, and only a portion with a diameter of 20 to 38 μm was taken out and pulverized using an ordinary rotary ball mill. This powder is molded using a uniaxial pressure die at a pressure of 10 to
Molded with n/ca+, 2, 10+nmX5IIlffl
A powder compact of X2I11 was obtained, and the magnetic coating properties were 7111.
Figure 4 shows the results. Figure 4 shows 30.50.
A case where the starting sample had a master alloy average crystal grain size of 80.150 μI was also shown as a representative example. In addition, the fine powder after being pulverized with a rotary ball mill was pulverized to 5 μm or less in all samples.

From Figure 4, the maximum magnetic energy product (B11) □1 value is 3
It is clear that the sample with a mother alloy average crystal grain size of 0 μm has the largest value. The above shows that controlling the average grain size of the master alloy affects the magnetic properties of the powder after pulverization.

[Effect of the invention] As described above, Re-Fe-N magnetic material or Re
-Fe-N-H-0-based magnetic materials need to be synthesized by controlling the microstructure of the initially produced Re-Fe alloy, especially the particle size and the mixing and phase separation state of each phase, and at each stage. Classification is effective for improving magnetic properties.

[Brief explanation of the drawing]

Figure 1 is a graph showing the correlation between annealing conditions and the average grain size after annealing. Figure 2 is a graph showing the correlation between the average grain size of the master alloy and the magnetic anisotropy of each particle system after crushing it. Graph showing. Figure 3 shows the correlation between the average crystal grain size of the master alloy and the saturation magnetization for each grain size after crushing it. Figure 4 shows the magnetic properties of the bonded magnet and the master alloy under the same pulverization conditions. FIG. 5 is a graph showing the interrelationship of average grain size of the alloy. FIG. 5 is a phase diagram showing a part of the Sm-Fe system phase diagram.

Claims (3)

[Claims] (1) A rare earth element-iron-nitrogen magnetic material characterized in that the average crystal grain size in the material's microstructure is in the range of submicrons to 300 μm. (2) When synthesizing a master alloy of rare earth element-iron-nitrogen magnetic material, it is necessary to control the cooling rate of the molten metal, vary the temperature during annealing in the range of 700 to 1300°C, and set the annealing time to A rare earth element-iron-nitrogen system characterized by adjusting the average crystal grain size of the master alloy to a range from submicron to 300 μm by allowing the phase as the main component to decrease to an amount acceptable as a magnetic material. Method of manufacturing magnetic materials. (3) In the method for producing rare earth element-iron-nitrogen magnetic material powder, classification is performed after preparing the rare earth element-iron alloy or after synthesizing the rare earth element-iron-nitrogen magnetic material powder in the range from submicron to 300 μm. 1. A method for producing rare earth-iron-nitrogen magnetic material powder, which comprises separating powder having an arbitrary particle size distribution region.