Spherical particles of Fe base metallic glass alloy, Fe base sintered alloy soft magnetic material in bulk form produced by sintering the same, and method for their production

#The present invention relates to spherical particles of Fe-based metallic glass alloy, a bulk Fe-based sintered alloy soft magnetic material of metallic glass, prepared by sintering the spherical particles, which has excellent magnetic characteristics applicable to a core of a magnetic head, a transformer or a motor, and methods for their production

#A conventional soft magnetic material applicable to a core of a magnetic head, a transformer, a motor, etc., includes a Fe—Si alloy, a Fe—Si—Al alloy (Sendust), a Ni—Fe alloy (Permalloy), and a Fe-based or Co-based amorphous alloy material. When a soft magnetic material is applied to a DC motor core etc., it is generally effective to form the soft magnetic material in a high-density bulk shape. Contrary to this need, the conventional amorphous alloy material prepared by quenching molten metal has been able to be formed only in a limited shape, such as thin strip, wire, powder or thin film.

#In the circumstances, a method comprising mechanically crushing the amorphous alloy thin strip, sintering the obtained alloy powder, and solidifying/forming the sintered alloy in a bulk shape has been developed. However, this method has a problem about difficulties in obtaining a high-density sintered body due to the need for performing the sintering process at a relatively low temperature to prevent the alloy powder from being crystallized during the sintering process.

#FIG. 1 is a schematic sectional view showing one example of a high-pressure-gas atomizing apparatus for use in producing metallic glass alloy particles to be used as a sintering material for a Fe-based sintered metal soft magnetic material of the present invention.

#FIG. 2 is a photograph showing an SEM (Scanning Electron Microscope) observation image of one example of metallic glass alloy particles to be used as a sintering material for the Fe-based sintered metal soft magnetic material of the present invention.

#FIG. 3 is a fragmentary sectional view showing one example of a spark plasma sintering apparatus to be used for implementing a method of the present invention.

#Each of Fe, Ga, Fe—C alloy, Fe—P alloy, B and Si as raw materials was weighted on a scale to be set at a given amount. These raw materials were molten in an Ar atmosphere under reduced pressure by use of a high-frequency induction heating furnace, to form plural types of alloy ingots. Each of the ingots was put in a crucible to form a molten alloy having a given composition. Then, the molten alloy was dropped from a molten alloy nozzle having a hole diameter of 0.8 mm, and subjected to a gas atomizing process using a gas injection nozzle having an injection pressure set at 9.8 MPa, to prepare a spherical alloy powder.

#The obtained alloy powder was sorted by 56 μm, 75 μm, 100 μm, 125 μm and greater than 125 μm, using a sieve. Each of the alloy powders was subjected to an X-ray diffraction analysis and a differential scanning calorimetry (DSC) to determine whether the alloy powder is crystallized. A maximum particle size in each of the alloy powders having an amorphous phase is shown in Table 1. As shown in Table 1, the maximum particle size in each of the alloy powders having an amorphous phase is in the range of 53 to 125 μm. Thus, the alloy powders having a particle size of 53 to 125 μm were selected and used as a row powder in a subsequent sintering process.

#Table 1 shows the composition and particle size of each soft magnetic metallic glass alloy particle obtained through the above gas atomizing process. In Particle Nos. 7 to 9, a particle primarily comprising an amorphous phase could not be prepared due to crystal precipitation.