EP0597582B1

EP0597582B1 - Rare-earth magnet powder material

Info

Publication number: EP0597582B1
Application number: EP19930307756
Authority: EP
Inventors: Ryoji C/O Chuo-Kenkyusho Nakayama; Takuo C/O Chuo-Kenkyusho Takeshita; Yoshinari C/O Chuo-Kenkyusho Ishii
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 1992-11-13
Filing date: 1993-09-30
Publication date: 1997-12-17
Anticipated expiration: 2013-09-30
Also published as: DE69315807T2; DE69315807D1; DE69315807T4; JPH06151137A; EP0597582A1

Description

The present invention relates to a rare-earth magnet powder material excellent in an isotropy, which comprises any of the rare-earth elements including Y (hereinafter referred to as "R"), Fe or a component in which part of the Fe is substituted by Co (hereinafter referred to as "T") and B as the main components, and further containing one or more of Si, Ga, Zr, Nb, Mo, Hf, Ta, W, Al, Ti and V (hereinafter referred to as "M") in an amount of from 0.001 to 5.0 atomic %, of which the main phase is an R₂T₁₄B-type intermetallic compound phase.
An R-Fe-B-M magnet material powder available by homogenizing an R-T-B-M raw material alloy, of which the main phase is an R₂T₁₄B-type intermetallic compound phase, with R, T and B as the main components, further containing M in an amount of from 0.001 to 5.0 atomic % by holding same in an Ar atmosphere at a temperature of from 600 to 1,200°C, or heating the R-T-B-M raw material alloy, without homogenizing, in H₂ gas or a mixed H₂/inert gas atmosphere from the room temperature, holding same at a temperature of from 500 to 1,000°C to cause occlusion of H₂, then dehydrogenating same by holding same at a temperature of from 500 to 1,000°C in a vacuum atmosphere or an inert gas atmosphere, then cooling and crushing same is known to have an excellent anisotropy and to have a structure comprising the recrystallized fine aggregate structure of the R₂T₁₄B-type intermetallic compound phase of an average recrystallization grain size of from 0.05 to 20 µm (See Japanese Patent Provisional Publication No. 3-129,702, Japanese Patent Provisional Publication No. 3-129,703, Japanese Patent Provisional Publication No. 4-133,406, and Japanese Patent provisional publication No. 4-133,407).
EP-A-0 304 054 describes the preparation of rare earth-iron-boron magnet powders having an average particle size of 2.0 to 500 µm and which powders contain a recrystallized grain structure containing a R₂Fe₁₄B intermetallic compound phase where R represents a rare-earth element, the average crystal grain size of the recrystallised grains being of 0.05µm to 50 µm. The powder may also further comprise elements M as described herein.
There have been reported some Dulk sinter magnets produced from R-Fe-B-M magnet powder materials having a maximum energy product exceeding 50 MGOe. Although, from the original magnetic properties of the material, a maximum energy product of about 25 MGOe is expected even in a bonded magnet available by using an R-Fe-B-M magnet powder material, bonded magnets and hot-pressed magnets (hereinafter referred to as a "full-density magnet") actually manufactured with the use of the above-mentioned anisotropic R-Fe-B-M magnet powder obtained through H₂ occlusion and dehydrogenation have shown insufficient properties. anisotropy than conventional ones with the use of this R-Fe-B-M magnet powder, and the following discoveries were made.
The grain size of anisotropic R-Fe-B-M magnet powders having the recrystallized fine aggregate structure of the R₂T₁₄B-type intermetallic compound phase of an average recrystallization grain size of from 0.05 to 20 µm obtained through conventional H₂ occlusion and dehydrogenation exerts an important effect on the magnetic properties of bonded magnets and full-density magnets made from them. Bonded magnets and full-density magnets prepared by the use of an anisotropic R-Fe-B-M magnet powder having an average grain size within a range of from 5 to 200 µm, magnetic anisotropy is remarkably improved, and furthermore, during the process of forming in a magnetic field for imparting anisotropy, the an isotropic magnet powder is given a sufficient orientation in an oriented magnetic field within 1.5 times iHc of the anisotropic magnet powder.
The present invention was developed on the basis of these discoveries and provides an ansiotropic magnet powder material having the recrystallized fine aggregate structure of an R₂T₁₄B-type intermetallic compound phase, which comprises any of the rare-earth elements including Y (herein referred to as "R"), Fe or a component in which part of the Fe is substituted by Co (herein referred to as "T"), and B as the main components and which components have an average recrystallized grain size of from 0.05 to 20 µm the powder comprising one or more of Si, Ga, Zr, Nb, Mo, Hf, Ta, W, Al, Ti and V (herein referred as "M") characterised in that the material contains a total amount of 0.001 to 5.0 atomic percent of M and the average grain size of the powder is within the range from 5 to 200 µm.
In the R-T-B-M anisotropic magnet powder material according to the invention the powder should have an average grain size of from 5 to 200 µm because an average grain size of under 5 µm is not desirable as it leads to a lower iHc of bond magnets and full-density magnets made and an average grain size of over 200 µm results on the other hand in a lower magnetic anisotropy in such magnets.
In the R-T-B-M anisotropic magnet material powder of the present invention, part of Fe may be substituted by Cr. Mn, Ni, Cu or Zn, and part of B may be substituted by C, N or O.

EXAMPLES

EXAMPLE 1

Using a high-frequency melting furnace, an alloy having a chemical composition comprising 11.6% Nd, 0.5% Pr, 11.8% Co, 6.5% B, 0.1% Zr and the balance Fe (atomic %) was melted in an Ar gas atmosphere, and cast into an ingot. This ingot was homogenized in an Ar atmosphere by holding it at a temperature of 1,130°C for 30 hours, and then crushed to blocks each having a side of up to 20 mm. The block was caused to occlude hydrogen by heating it from room temperature to 750° C in an hydrogen atmosphere under 1 atm. Hydrogen occlusion was caused by holding the block at 750°C for one hour while maintaining the hydrogen atmosphere of 1 atm. to accelerate phase transformation. The block was further heated to 850°C. held at 850°C for one hour, and was forcedly caused to release hydrogen until a 1 x 10^-1 vacuum atmosphere was achieved to accelerate phase transformation. The block was then cooled in Ar gas.
The ingot after hydrogen occlusion and release had a recrystallized fine aggregate structure of the R₂T₁₄B-type intermetallic compound phase having an average recrystallization grain size of 0.2 µm. By crushing this ingot to the powder grain sizes as shown in Table 1, samples of an anisotropic magnet powder material of the present invention (hereinafter referred to as "samples of the invention") Nos. 1 to 7 and comparative samples of anisotropic magnet material powder (hereinafter referred to as "comparative samples") Nos. 1 and 2 were prepared.
Each of these samples of the invention Nos. 1 to 7 and comparative samples Nos. 1 and 2 was mixed with 2.5 wt.% epoxy resin and compression-formed while adjusting the density to 6.0 g/cm³ in a magnetic field of 15 kOe to prepare pressurized powder. This pressurized powder was thermoset at 150°C for one hour to prepare an anisotropic bonded magnet. The magnetic properties of the anisotropic magnets prepared are shown in Table 1.
Furthermore, each of these samples of the invention Nos. 1 to 7 and comparative samples Nos. 1 and 2 was compression-formed in a magnetic field into pressurized powder. This pressurized powder was set on a hot press to conduct hot pressing in vacuum at 790°C for ten minutes under a pressure of 1 ton/cm² so that the direction of application of the magnetic field agreed with the direction of compression, and rapidly cooled in Ar gas to prepare an anisotropic full-density magnet. The magnetic properties of the resulting anisotropic full-density magnets are shown in Table 1.
The results shown in Table 1 reveal that the bonded magnets manufactured from the samples of the invention Nos. 1 to 7 having an average grain size within a range of from 5 to 200 µm show better magnetic properties than those of the bonded magnets manufactured from the comparative samples Nos. 1 and 2 having an average grain size outside the range of from 5 to 200 µm.

EXAMPLE 2

Using a high-frequency melting furnace, an alloy having a chemical composition comprising 12.2% Nd, 17.2% Co, 7.0% B, 0.1% Zr, 0.5% Ga and the balance Fe (atomic %) was melted in an Ar gas atmosphere, and cast into an ingot. This ingot was homogenized in an Ar atmosphere by holding it at a temperature of 1,120°C for 40 hours, and then crushed to blocks each having a side of up to 10 mm. The block was caused to occlude hydrogen by heating it from the room temperature to 760°C in a hydrogen atmosphere under 1 atm. Hydrogen occlusion was caused by holding the block at 760°C for one hour while maintaining the hydrogen atmosphere of 1 atm. to accelereate phase transformation. The block was further heated to 820°C, held at 820°C for one hour, and was forcedly caused to release hydrogen until a 1 x 10^-1 vacuum atmosphere is achieved to accelerate phase transformation. The block was then cooled in Ar gas.
The ingot after hydrogen occlusion and release had a recrystallized fine aggregate structure of the R₂T₁₄B-type intermetallic compound phase having an average recrystallization grain size of 0.3 µm. By crushing this ingot to an average grain size of 50 µm and 150 µm, samples of the magnet powder of the present invention ion Nos. 8 and 9 were prepared. By crushing this ingot to an average grain size of 300 µm, a sample of comparative magnet powder No. 3 was prepared. The prepared samples of the invention Nos. 8 and 9 had a coercive force, iHc, of 14,2 kOe, and the comparative sample No. 3 had a coercive force, iHc , of 14.6 kOe.
Each of the samples of the invention Nos. 8 and 9 and the comparative sample No. 3 was mixed with 2.7 wt.% epoxy resin and compression-formed while making adjustment so as to give a density of 6.0 g/cm³ in an oriented magnetic field in to a pressurized powder. This pressurized powder was thermoset at 130°C for one hour to prepare an anisotropic bonded magnet. The magnetic properties of the prepared anisotropic bonded magnets are represented in a graph as shown in Fig. 1, with H_F/iHc (where H_F is the oriented magnetic field during forming in the magnetic field; and iHc is the coercive force of the powder) on the abscissa, and B_r/B_r70 (where B_r is the remanent magnetization; and B_r70 is the remanent magnetization in a magnetized field of 70 kOe) on the ordinate.
Furthermore, each of these samples of the invention Nos. 8 and 9 and the comparative sample No. 3 was compression-formed in an oriented magnetic field into pressurized powder. The pressurized powder was set on a hot press and hot-pressed under vacuum at 800°C for ten minutes under a pressure of 1 ton/cm² so that the direction of application of the magnetic field agreed with the direction of compression. The hot-pressed powder was then rapidly cooled in Ar gas to prepare an anisotropic full-density magnet. The magnetic properties of the prepared anisotropic full-density magnet are represented in a graph as shown in Fig. 2, with H^F/iHc on the abscissa and B_r/B_r70 on the ordinate.
The results shown in Figs. 1 and 2 suggest that use of the samples of the invention Nos. 8 and 9 having an average grain size of 50 µm and 150 µm, respectively, improves the degree of orientation in a low-orientation magnetic field having an iHc of up to 1.5 times and permits preparation of an anisotropic bond magnet and an anisotropic full-density magnet having sufficiently high properties, whereas use of the comparative sample No. 3 having an average grain size of 300 µm does not improve the degree of orientation in an oriented magnetic field having an iHc of up to 1.5 times, and does not give an anisotropic bonded magnet or an anisotropic full-density magnet having sufficiently high properties.
According to the rare-earth magnet material powder excellent in anisotropy of the present invention having an average grain size within a range of from 5 to 200 µm, the degree of orientation in a low-orientation magnetic field of a coercive force, iHc, of up to 1.5 times is improved, and it is possible to manufacture an anisotropic rare-earth magnet having better magnetic properties than those of conventional ones in a low magnetic field output, thus providing industrially useful effects.

Claims

An anisotropic magnet powder material having the recrystallized fine aggregate structure of an R₂T₁₄B-type intermetallic compound phase, which comprises any of the rare-earth elements including Y, herein referred to as "R", Fe or a component in which part of the Fe is substituted by Co, herein referred to as "T", and B as the main components and which components have an average recrystallized grain size of from 0.05 to 20 µm, said powder further comprising one or more of Si, Ga, Zr, Nb, Mo, Hf, Ta, W, Al, Ti and V, herein referred as "M" characterised in that the material contains a total amount of 0.001 to 5.0 atomic percent of M and the average grain size of the powder is within the range from 5 to 200 µm.
A powder material as claimed in Claim 1 wherein part of the Fe is additionally or alternatively substituted by Cr, Mn, Ni, Cu or Zn.
A powder material as claimed in Claim 1 or Claim 2 wherein part of the B is substituted by C, N or O.
Use of the powder as claimed in any one of the preceding claims in the manufacture of bonded or hot-pressed magnets.