JPH09118949A - Soft magnetic material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a soft magnetic material small in the componental segregation of fine crystal grains, high in density and good in magnetic properties by subjecting the gas atomizing powder of a soft magnetic material coated with a low m.p. Ni base alloy by electroless plating to compacting and sintering. SOLUTION: A soft magnetic material such as sendust is formed into powder by a gas atomizing method. This gas atomizing powder is uniformly coated with a low m.p. Ni base alloy, preferably, with an Ni-P alloy. The obtd. composite powder is compacted into a desired shape, and sintering is executed. This sintering can be executed at a temp. lower than the m.p. of sendust or the like. Thus, the material of high quality composed of a dense sendust alloy 1 as a soft magnetic material small in segregation and an Ni-P alloy 2 as a low m.p. Ni base alloy can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soft magnetic material such as sendust used as a material for a magnetic head or the like.

[0002]

2. Description of the Related Art 9.6 wt% Si called sendust
The -5.4 wt% Al-Fe alloy has some preferable properties including high magnetic flux density and high magnetic permeability when used as a soft magnetic material such as a magnetic head. However, this alloy has a problem in its structural properties and mechanical properties when it is produced by a casting method, and in particular, there is a problem that segregation of components, mixed grains occur, and ductility and workability are poor. The field of application is limited. At present, sendust can be formed into a complicated shape by an ordinary powder sintering method, but it tends to have low density and low magnetic properties. Compared with this, the one formed by the casting method has a high density and good magnetic properties, but can only have a simple shape. On the other hand, the inventors have obtained a sendust alloy with less fine grain component segregation and higher density and good magnetic characteristics as compared with the casting method, by using the hot pressing method or the injection molding sintering method. ing.

However, when this alloy is manufactured by the powder metallurgy method, it is difficult to sinter the powder because the soft magnetic material such as sendust alloy has a high melting point. Therefore, a method of applying a metal coating to the surface of these soft magnetic material powders and sintering the composite is expected. By the way, a physical method typified by vacuum deposition is generally used as a method for applying a metal coating to the surface of the soft magnetic material powder. However, it has been difficult to obtain a soft magnetic material powder having a uniform and relatively thick metal coating layer by the vacuum deposition method.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a composite powder of a soft magnetic material having a uniform and relatively thick coating layer which cannot be obtained by the conventional vacuum deposition method as described above.
It is an object of the present invention to provide a soft magnetic material having a small amount of segregation of fine crystal grain components used for a magnetic head and the like, which has a high density and good magnetic characteristics by compacting and sintering the composite powder.

[0005]

Means for Solving the Problems According to the invention of claim 1, the means for solving the above problems comprises forming and sintering a gas atomized soft magnetic material powder obtained by coating a low melting point Ni-based alloy by electroless plating. It is a soft magnetic material characterized by being obtained by

According to the invention of claim 2, the low melting point Ni-based alloy is a Ni-P alloy, and the soft magnetic material according to the means of claim 1 is characterized.

According to the third aspect of the present invention, the gas atomized powder of the soft magnetic material is coated with a low melting point Ni-based alloy by electroless plating to produce a composite powder, and the composite powder is compacted and sintered. It is a method of manufacturing a magnetic material.

According to a fourth aspect of the invention, there is provided the method for producing a soft magnetic material according to the third aspect, wherein the low melting point Ni-based alloy is a Ni-P alloy.

[0009]

[Function] In electroless plating, which is chemical plating, Cu, N
Other than i and Co, it is difficult to industrially plate a large amount. Then, Cu, N is formed on the surface of the soft magnetic material powder.
Among the soft magnetic material composite powders coated with i and Co, Cu
The soft magnetic material composite powder coated with can not increase the overall electric resistance. By the way, in a magnetic body such as a magnetic head using a soft magnetic material, the higher the electric resistance, the less the hysteresis loss. Therefore, the Cu-plated soft magnetic material is not suitable in terms of electrical resistance and mechanical properties. For the above reasons, it is preferable to electrolessly plate Ni or Co on the surface of the soft magnetic material powder. Also,
Since the electroless plating method can easily and uniformly coat the powder surface, it is adopted in the present invention as a plating method suitable for powder. On the other hand, the melting point of Ni-P alloy changes depending on the P content. The melting point of Ni is 1728K, but Ni
-The liquidus temperature decreases as P is added to Ni to the P content of 11 wt% which is the eutectic point of the P alloy, and the liquidus temperature becomes 1153K when the P content of the eutectic point is 11 wt%. . On the other hand, since the melting point of Sendust alloy is 1593K, the liquidus temperature of the Ni-P coating having a P content of 11 wt%, which is the eutectic point of the Ni-P alloy, is lower than the liquidus temperature of the Sendust alloy. means. Therefore, the composite powder coated with the Ni-P alloy can be molded into a complicated shape and sintered at a temperature lower than the melting point of the sendust alloy.

For the above reasons, in the present invention, the Ni-P alloy film is formed on the surface of the soft magnetic material powder by electroless plating. Other alloys considered to have the same effect as the Ni-P alloy include Ni-Co-P and Ni-B. By the way, heretofore, almost no example of applying a coating technique to powder in a functional material such as Sendust alloy has been found.

By the way, in the electroless plating method, if powder is used as the base material, bath decomposition easily occurs. Selection of the plating bath is extremely important in determining the film properties. As a result of various studies, it was found that a mixed complex plating bath using a mixed complex of DL-malic acid (C ₆ H ₅ O ₄ ) and disodium succinate (Na ₂ C ₄ H ₄ O ₄ ) is suitable. It was Further, the deposition behavior of electroless plating, particularly the deposition rate and its alloy composition, depend on the plating conditions.

Therefore, the effect of the pH of the plating bath on the coating speed of the plating bath and the P content of the film was investigated, and the results are shown in FIG. The coating rate corresponds to the deposition rate in FIG. The precipitation rate increased as the pH increased in the range of pH 4.0 to 6.0. Plating will not start below pH 4.0,
Bath decomposition occurred above pH 6.0. As a result of investigating by plating on a copper plate, the deposition rate was 2.9 mass% / 20 min to 17.4 mass with increasing pH.
% / 20min. It is considered that this increase in speed is due to an increase in driving force of the reducing agent (sodium hypophosphite). The P content in the film decreases with increasing pH,
It decreased from 12.8 mass% to 9.2 mass%. For the above reasons, the pH of the plating bath is set to 4.0 to 6.0.

Next, in order to investigate the effects of the P content of the Ni-P coating and the sintering temperature on the sintered density, Ni was investigated.
-P alloy plated powder 1323K to 156
Sintered at 3K, the results are shown in FIG. From the figure, it can be seen that the Ni—P plating improves the sinterability. Ni-P
The plated powder is 1 compared to the unplated powder
It can be seen that the sintering can be performed at a low temperature of 00K to 200K.
The Ni-P coating physically changes during the sintering process. That is, at room temperature, it is a fine crystal and P is finely scattered, but Ni ₃ P precipitates at 620 K or higher, and a liquid phase occurs at 1168 K or higher.

In the sintering of Sendust alloy powder, the crystal grains are smaller in the sintered powder powder than in the gas atomized powder powder. Ni-
It is considered that the increase in sintered density due to P plating is due to the low melting point of Ni-P on the powder surface. It is considered that the improvement of the sinterability of the Ni-P plated powder was made through the reorganization, melting and precipitation of the composite powder.

[0015]

BEST MODE _FOR CARRYING OUT THE INVENTION Spherical powder of a sendust alloy having a composition of Fe _85.0 Si _9.6 Al _{5.4 is} produced by a gas atomizing method. Using this spherical powder having a particle size of 38 μm or less, a Ni—P coating is applied by electroless plating under the plating bath composition and plating conditions shown in Table 1. In plating, first-grade reagent and distilled water are used. When plating, plating is performed without pretreatment.

[0016]

[Table 1]

That is, the sendust alloy powder produced by the inert gas atomizing method was immersed in a stirred plating bath at a rate of 5 g per liter under the plating bath composition and plating conditions shown in Table 1, and the treatment time was 20 minutes. Apply electroless plating. The plating film obtained on the surface of the Sendust alloy powder is uniformly coated with a thickness of 1 μm when observed with an optical microscope.

Α-camphor (camellia C ₁₀ H ₁₆ O) is mixed as a binder with the composite powder of the Sendust alloy powder that has been subjected to electroless plating, and the powder is compacted into a green compact. Next, after holding this green molded body at 473K in vacuum to sublimate α-camphor, the temperature was maintained at a predetermined temperature of 1323K to 1563K and sintered,
After that, the furnace is cooled to 1073K and held, and then cooled to room temperature to obtain a sintered soft magnetic substance of Sendust.

A magnetic material such as a magnetic head manufactured from these composite powders having Ni as a coating layer has a small hysteresis loss and excellent high-frequency magnetic characteristics equivalent to or better than those of excellent electrical and mechanical characteristics. It is a soft magnetic material.

The alloy components of this plating deposit are measured by ICP spectroscopy, and the deposition rate is calculated from the weight increase of the powder after plating for 1 hour.

[0021]

Example A mixed complex of C ₄ H ₆ O ₅ (DL-malic acid) and Na ₂ C ₄ H ₄ O ₄ (disodium succinate) was used as a plating bath, and the bath composition and plating conditions are shown in Table 1 above. Shown in.
A powder of 38 μm or less of a spherical powder of Sendust alloy produced by the gas atomization method was immersed in a stirred plating bath at a rate of 5 g per liter, and electroless plating was performed for a treatment time of 20 minutes.

Observation with an optical microscope revealed that the plating film produced in this example was uniformly coated on the surface of the powder to a thickness of 1 μm.

1 mass% of α-camphor (Shoujo C ₁₀ H ₁₆ O) was mixed as a binder to the composite powder of the Sendust alloy powder subjected to the electroless plating, and the mixture was kept at room temperature for 2 minutes.
A green compact was obtained by compacting at 94 MPa. The obtained green molded body was held at 473K in vacuum for 1 hour to sublimate α-camphor, and then the temperature was raised to a predetermined value of 1323K to 1563K at a speed of 20K / min and held for 2 hours for sintering. The furnace was cooled to 1073K and held for 1 hour, and then cooled to room temperature to obtain a sendust sintered soft magnetic material. A schematic diagram of the microstructure of the obtained sintered soft magnetic material is shown in FIG. In the figure, 1 is a sendust alloy,
2 is a Ni-P alloy.

The obtained sintered body is processed and polished to a thickness of 0.2 mm, and also for removing the internal stress introduced during machining, in vacuum at 10 ^-4 torr at 1073 K for 1 hour. It heat-processed and cooled to room temperature after that at a cooling rate of 60 K / hr. The microstructure of the obtained sample was examined using an optical microscope and a high resolution SEM.

FIG. 4 shows the effect of the P content of the Ni-P plating film on the hardness of the soft magnetic material sintered body. For the hardness measurement, a micro Vickers hardness meter was used under the conditions of a load of 200 gf (1.96 N) and a time of 30 seconds. The Ni-P plated Sendust alloy sintered material has a slightly higher hardness than the non-plated Sendust alloy sintered material.
This is considered to be due to the precipitation of Ni ₃ P. Further, the sintering temperature at which the Ni-P plated Sendust alloy sintered body reaches the maximum hardness was 100 to 200 K lower than that of the non-plated Sendust alloy sintered body. This is considered to be due to the low melting point of the Ni-P plating film applied to the surface of the Sendust alloy powder.

FIG. 5 shows the frequency characteristics of the effective magnetic permeability of the Sendust alloy and the Ni-P plated Sendust alloy. The magnetic characteristics were measured using the impedance method. The Ni-P plating film applied to the powder surface did not particularly affect the magnetic flux density of the alloy, but the coercive force was considerably increased. This is probably due to the mixing of Ni and P. For high frequency characteristics,
The Ni-P plated one showed a slightly lower magnetic permeability up to 5 kHz than the non-plated one. It is considered that this is because the Ni-P plated portion became the impedance (resistance) of the domain wall movement. Further, when the sintering temperature was in the range of 1273K to 1523K, the magnetic properties were not particularly affected.

[0027]

As described above, according to the present invention, since a metal coating layer having a uniform composition and a relatively large thickness is formed on the surface of the soft magnetic material powder, the surface of the soft magnetic material powder is coated with these metal coatings. The composite powder having the composition can reduce the sintering temperature at the time of sintering by 100 to 200 degrees, increase the electric resistance of the entire magnetic body to reduce the hysteresis loss, improve the magnetic characteristics at high frequency, and mechanically. A soft magnetic material having excellent effects such as favorable characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a microstructure of a soft magnetic material sintered body.

FIG. 2 is a graph showing the influence of the pH of the plating bath on the deposition rate of the plating bath and the P content of the coating.

FIG. 3 shows the effect of Ni- on the sintered density of the soft magnetic material sintered body.
It is a graph which shows the P content rate of P alloy plating, and the influence of sintering temperature.

FIG. 4 is a graph showing the effect of the P content of Ni—P alloy plating on the hardness of a soft magnetic material sintered body.

FIG. 5 is a graph showing frequency characteristics of effective magnetic permeability in a soft magnetic material sintered body and a Ni—P plated powder soft magnetic material sintered body.

[Explanation of symbols]

 1 Sendust alloy 2 Ni-P alloy

Claims (4)

[Claims] 1. A soft magnetic material obtained by compacting and sintering a gas atomized powder of a soft magnetic material obtained by coating a low melting point Ni-based alloy by electroless plating. 2. The soft magnetic material according to claim 1, wherein the low melting point Ni-based alloy is a Ni-P alloy. 3. A method for producing a soft magnetic material, characterized in that a gas atomized powder of a soft magnetic material is coated with a low melting point Ni-based alloy by electroless plating to produce a composite powder, and the composite powder is compacted and sintered. . 4. The method for producing a soft magnetic material according to claim 3, wherein the low melting point Ni-based alloy is a Ni—P alloy.