JPH02285604A - Hot-worked magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain an R-T-B hot-worked magnet on which a plastic processing can be conducted easily and having excellent magnetic crystal orientation and magnetic characteristics by a method wherein its carbon content is limited to a specific range. CONSTITUTION:In a magnetically anisotropic permanent magnet made of R-T-B-C alloy, which is mainly composed of transition metal T and containing yttrium-carrying rare-earth R and boron B, having fine crystal grains of average grain diameter of 0.2 to 1.0mum, carbon content is set at 0.01 to 0.8wt.%. Also, the permanent magnet such as above-mentioned is composed or R-content of 28 to 35wt.%, T-content of 60 to 72wt.%, B-content of 0.5 to 1.5wt.% and other inevitable impurities, and the angle dispersion from the C-axis of the degree of crystal orientation measured by X-rays is set at 30 degrees or less on the surface of the magnet. As a result, excellent self-lubricating properties can be obtained when a hot-work operation is conducted, and also a permanent magnet having a high energy product can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a permanent magnet substantially made of rare earth transition metals and boron, which is used in hard disks and floppy disks, which are external storage devices of computers, and various terminal devices. Regarding the improvement of warm-worked magnets that impart magnetic anisotropy through plastic working, permanent magnets that have improved workability by adding an appropriate amount of additive elements, are free from cracking, have improved crystal orientation, and have good magnetic properties. and,
It relates to its manufacturing method.

[Prior art] Permanent magnets (hereinafter referred to as R-
T-B magnets (called T-B magnets) are attracting attention as permanent magnets that are inexpensive and have high magnetic properties. This is because intermetallic compounds represented by R2T and 4B, which have a tetragonal crystal structure, exhibit excellent magnetic properties. This intermetallic compound has a square side of 0.878 nm at room temperature, and a C
The lattice constant in the axial direction is 1.218 nm. This intermetallic compound has strong magnetic anisotropy in the C-axis direction.

Industrial methods for manufacturing magnets using this intermetallic compound are broadly divided into sintered magnets using powder metallurgy and warm plastically worked magnets using ultra-quenching. The sintered magnet is obtained by coarsely pulverizing and finely pulverizing an ingot obtained by adjusting the composition to a desired composition, melting, and casting, and then molding, sintering, and heat-treating fine powder of 3 to 5 μm in a magnetic field. In the case of sintered magnets, the intrusion of oxygen from the atmosphere during the pulverization, subsequent sintering, and heat treatment processes is unavoidable, and the sintered body usually contains 3
000 to 8000 ppm of oxygen is contained as an impurity. This impurity oxygen is combined with the rare earth component in the alloy and exists as an oxide. This non-magnetic oxide reduces the saturation magnetic moment of the permanent magnet, and when the permanent magnet is excited with a reversal magnetic field, it acts as a nucleation site for reversal magnetic domains, which causes a decrease in coercive force. Various inventions have been proposed to solve this problem with sintered magnets.

For example, the most commonly used method is to increase the proportion of heavy rare earth components (eg, oy, Tb) in the R component. However, this method has the disadvantage that the total angular momentum of the heavy rare earth and the spin angular momentum of Fe are coupled antiparallelly, so the saturation magnetic moment of the alloy decreases as the ratio of heavy rare earth components increases. . Alternatively, trace amounts of additional elements, for example, ^42. Nb,G
Although it has been proposed to improve the coercive force by adding a, etc., the effect is smaller than when using the heavy rare earth.

Attempts have also been made to suppress the infiltration of oxygen during the process and improve the magnetic properties, but this requires large-scale equipment and increases manufacturing costs, resulting in many industrial problems.

On the other hand, in the ultra-quenching method, a ribbon or powder formed of amorphous or fine crystalline material or a mixture of both obtained by melt spinning or other ultra-quenching methods is densified by hot pressing in a warm state. After that, it is made anisotropic by plastic working and manufactured. Since this method does not include a pulverization step in the process, the amount of impurity oxygen is usually reduced to 200%.
It is possible to suppress it to 0 ppm or less, and therefore a high saturation magnetic moment can be expected. In addition, since there is no need for a sintering process at high temperatures, the final product obtained by warm plastic working has a fine crystal grain size of 0.02 to 1.0 μm, and warm working is performed in a particularly preferable temperature range. The average grain size of the magnet is 0.1 to 0.5 μm, which is close to the single domain critical dimension of the present magnet of 0.3 μm, and an essentially high coercive force can be obtained. In warm-worked magnets, a close correlation between plastic flow and magnetic crystal alignment in the orthogonal direction is important. That is, it is necessary to uniformly and sufficiently apply plastic flow to the entire workpiece in order to improve the degree of crystal orientation related to magnetic properties.

Further, friction between particles or ribbons during warm plastic working causes non-uniform deformation and generates tensile stress, which is a factor that causes cracks. This is a big problem when trying to obtain a permanent magnet as an industrial product. Most of the working force applied during warm working is used for plastic work, but some is wasted due to friction between the die and workpiece or friction between particles within the workpiece. Therefore, various external lubricants have been proposed in order to improve the workability during warm working and to obtain a permanent magnet without a crank. For example, JP-A-60-100402 describes an example in which the surface of a die used for warm working is lined with graphite as an external lubricant. However, in this case, there is no effect of improving the non-uniform plastic flow caused by friction between particles inside the magnet body.

MO321 was developed for the purpose of improving uneven plastic flow caused by friction between particles or ribbons during warm working.
A technique has been proposed to facilitate plastic flow by adding fine powder such as CHBN to obtain a crack-free warm-worked magnet. According to this method, the magnet powder or the fine powder added between the ribbons alleviates the friction between the powders or between the ribbons, which has a remarkable effect on suppressing cracks and improving the degree of orientation. However, the effects of the above-mentioned invention have limitations because they do not reach between the solid particles that constitute the ultra-quenched magnet.

The present invention solves the above problems and provides an R-T-B which is easy to plastically work, has uniform magnetic crystal orientation, and has excellent magnetic properties.
The purpose of the present invention is to provide a system of warm-processed magnets.

[Means to solve problems]

The present invention first focuses on R containing a transition metal T as a main component, a rare earth element R containing yttrium, boron B, and carbon C.
- In a warm-worked magnet in which a molten TB-C alloy is ultra-rapidly solidified to obtain a ribbon or flake, which is crushed into powder, and then warm-worked to impart magnetic anisotropy, This is a method for manufacturing a warm-worked magnet characterized by adding a small amount of C. Regarding the magnetic properties of RT-13-C alloys, see, for example, J. Appl. Phys. 61 (8) P.
In 3574 Fe1. NdqDybBo, qCt
It has been reported that a coercive force of 8 KOe can be obtained with a composition of , z. Also, J.

Mag, and Mag, Mat, 72 (198
8) Basic magnetic properties in R2Fe+ 4C compounds have been reported for P167. However, no research has been conducted on the plastic working conditions for these alloy systems. The present invention is directed to the production of R-T-B-C system anisotropic permanent magnets obtained by warm plastic processing of amorphous or fine crystalline materials obtained by ultra-bagging, cold processing, or mixtures thereof. Regarding the method, the objective is to provide a permanent magnet alloy that has excellent self-lubricating properties during warm working and has a high energy product. Conventionally, when warm plastically deforming an R-T-B permanent magnet alloy, part of the externally applied pressure is consumed by friction between the workpiece and tool, friction between ribbons, or friction between particles. Therefore, it is difficult to apply uniform plastic strain within the workpiece, and the degree of crystal orientation, that is, the degree of anisotropy, of the resulting anisotropic permanent magnet is determined by orienting the fine powder in a magnetic field and sintering it. There was a problem that it was inferior to the obtained sintered magnet.

In order to overcome these problems, proposals have been made to improve the degree of anisotropy by applying or mixing an external lubricant or an inorganic or organic internal lubricant, but these methods
It does not improve the mechanical properties inherent to RTB alloys, and its effectiveness is limited. Furthermore, these methods have the problem that plastic deformation cannot be applied to individual particles one by one. The inventors,
In order to solve the problems of the prior art, an attempt was made to modify the mechanical properties of the R-TB alloy under warm conditions, but the present invention failed.

That is, it has been found that by adding a small amount of C to the RTB alloy, the warm plastic workability is improved and the degree of crystal orientation is greatly improved.

Here, the small amount of C added is the Nd in the alloy and some F.
It combines with the e component to form a so-called Nd-rich phase. The Nd-rich phase formed here surrounds the NdzFe+ 4B phase particles that exhibit permanent magnetic properties in this alloy, and acts as a self-lubricating agent during warm working, as well as external It becomes a medium that effectively converts the applied pressure into plastic work. If the amount of C added is 0.01% by weight or less, the viscosity of the Nd-rich phase is low, the role as a pressure medium is insufficient, and high anisotropy cannot be obtained.

Moreover, when C is 0.8% by weight or more, C is NdzFel
Because it replaces B in the 4B phase, the excess B makes it mechanically brittle and forms a rich phase, which significantly increases the deformation resistance of the material itself, making it difficult to apply sufficient plastic deformation and making it difficult to maintain. This is not preferable because the magnetic force also decreases. In the present invention, it is extremely difficult to industrially stably obtain microcrystals with an average crystal grain size of less than 0.02 μm using current technology, and if the average crystal grain size exceeds 1.0 μm, the coercive force decreases. I don't like it. Here, the average crystal grain size is measured by a cutting method in a micrograph. In other words, when a line segment is arbitrarily drawn on a photograph, the line segment length is divided by the number of crystal grains that cut the line segment, and the grain size is defined as the grain size. do. What should be noted here is that warm-processed magnets have a flat shape in a plane perpendicular to the C-axis of the crystal, and when cutting along a plane that includes the C-axis, the direction is the thickness direction of the flat plate. Therefore, the above-mentioned average grain size refers to that on a plane perpendicular to the C-axis. Further, the alloy according to the present invention contains a transition metal as a main component, a rare earth element R including yttrium, boron, and carbon. In the present invention, the transition metals are mainly composed of iron, with some of them being Co and Ni.

Not only transition metals in the narrow sense of Ru, Rh, Pd+ Os, Ir+ Pt but also atomic numbers 21-29.39-47
．． It refers to transition metals in a broad sense, including all elements of 72 to 79.89 or more.

Furthermore, as the present inventors have already announced, the addition of Ga has the effect of significantly improving the coercive force in warm-worked magnets, so it is effective to add Ga as necessary. Furthermore, addition of known additive elements according to the purpose does not deviate from the effects of the present invention. The rare earth elements R are also Nd, Pr
As is well known, it is possible to partially substitute with Ce, didymium, etc. for the purpose of cost reduction, and to partially substitute with heavy rare earths, etc. for the purpose of improving temperature characteristics. The composition range of R according to the present invention is 28 to 40% by weight, and when the R content is less than 29% by weight, Fe-rich N
Since a d2Fe+J phase is formed and the coercive force is significantly reduced, a high energy product cannot be obtained.

Further, if R is 40% by weight or more, the proportion of the Nd-rich phase in the alloy becomes too large, and the effect of a small amount of C cannot be fully exhibited. The content of transition metal T is 60-70
Weight% is preferable; if it is less than 60% by weight, the saturation magnetic moment will decrease, and if it is 70% by weight or more, the coercive force will decrease. If the B content is less than 0.5% by weight, Nd2Fe+
If the formation of J is insufficient and exceeds 1.5% by weight, a large amount of B-rich phase will be formed, which will significantly impede plastic workability, which is not preferable. The angular dispersion value, which is an index of the degree of crystal orientation determined by X-ray diffraction according to the present invention, is defined as follows. First, measure the X-ray diffraction intensity of each diffraction surface of an isotropic sample using the diffractometer method, and then measure the X-ray diffraction intensity of each diffraction surface of a sample cut from an anisotropic warm-processed magnet. Then, the intensity is normalized by each diffraction intensity of the isotropic sample. Next, the normalized value, that is, the relative intensity, is plotted against the angle that each diffraction surface makes with the 0 plane, and the obtained fish school is approximated by a Gaussian distribution centered on the 0 plane, and its dispersion is determined. The value of this dispersion becomes an index of crystal orientation 1 tropism.

The present invention can bring about a remarkable improvement in the degree of orientation in which the angular dispersion from the C axis of the crystal is less than 30° on the magnet surface. In conventional warm-processed magnets, the angular dispersion on the magnet surface is 30° or more, so the magnetic orientation is not uniform and the magnetic properties are insufficient.

The warm-worked magnet of the present invention is obtained by warm plastic working, and plastic working such as extrusion, swaging, rolling, and upsetting is used as a means for this purpose. Upsetting is particularly effective in imparting anisotropy.

A feature of the warm-worked magnet to which carbon is added as an additive according to the present invention is that the deformation is uniform, resulting in a uniform strain distribution within the cross section.

〔Example〕

(Example 1) Nd 29 Wχ, Fe 69.5 W%', B
IWX, CO, 5H% alloy, and as comparison materials, Nd''29 Wχ, Fe 70 χ, B'1 cocoon
Those that passed the test were melted into button ingots using arc melting. The obtained button ingot was high-frequency melted in Ar and injected onto a single roll rotating at a circumferential speed of 30 m/s to produce irregularly shaped flakes with a thickness of about 30 μm. did.

Next, the flakes were crushed to a size of 500 μm or less to form a powder, which was then cold-molded at a molding pressure of 3 tons/cIII without applying a magnetic field to a density of 5.7 g/cc and a diameter of 28 mm.
A green compact with a height of 47 mm was produced.

The obtained compact was hot pressed at 700°C at 1 ton/c+fl to obtain a compact with a density of approximately 7.5 g/cc, and this compact was then heated at 700°C to reduce the compression ratio (before upsetting). The magnetic anisotropy was imparted by warm processing by upsetting so that the value obtained by dividing the height by the height after upsetting was 4.

Figure 1 shows a true/false diagram of the true car during upsetting in comparison with a comparison material. It can be seen that by adding a small amount of C, the true stress rises at a low amount of strain, but at subsequent amounts of strain, the stress remains almost constant and deformation progresses.

On the other hand, it can be seen that in the comparative material that does not contain C, the stress rises in the initial strain region is low, and the stress rises rapidly in the high strain region.

Furthermore, Table 1 shows the magnetic properties of samples cut from the material after upsetting and the angular dispersion values determined by X-ray diffraction. From Table 1, it can be seen that by adding a small amount of C, the degree of crystal orientation is improved and the magnetic properties are greatly improved.

(Example 2) N(] 30.5, Fe 67.9, in weight%
An alloy of B 2 O,9, GaO,5, and CO,2 was melted by arc melting, and then upset in the same manner as in Example 1, and its magnetic properties and degree of crystal orientation were measured. The obtained magnetic properties are B
r12.8 KG, Hci 17.5 KOe
, (BH), 40.2 MGOe, and the angular dispersion value determined by X-ray diffraction was 17°, indicating a remarkable effect due to the addition of a small amount of C.

(Example 3) By the same method as in Example 1, Nd 30.5Fe b
ai! , -B0.9-GaO,5-Cx was made anisotropic by warm upsetting, and the dependence of magnetic properties on the amount of C was investigated. The results are shown in Table 2.

Good magnetic properties are obtained when the amount of C is 0.01 to 0.8% by weight.

(Example 4) Anisotropic upsetting magnets with a constant C amount and various Nd, 'Fe, and B amounts were produced in the same manner as in Example 1, and the magnetic properties and crystal orientation were evaluated. . The results are shown in Table 3.4.

From Table 3, Nd 28~40 Wχ, Fe 60~
It can be seen that high magnetic properties can be obtained in the range of 70 WLB O,5 to 1.5-χ.

As described above, according to the present invention, it is possible to obtain a warm plastically worked magnet that has improved crystal orientation, which has conventionally been insufficient, and has a high energy product.

(Effects of the Invention) According to the present invention, it is possible to obtain an R-T-B permanent magnet that is easy to warm-work, has a uniform magnetic crystal orientation, and has excellent magnetic properties.

[Brief explanation of drawings]

FIG. 1 shows true stress/true strain diagrams during upsetting for a warm worked magnet according to the present invention and a comparative example.

Claims (3)

[Claims] (1) R-T-B-C alloy containing transition metal T as the main component, rare earth element R including yttrium, and boron B, with an average crystal grain size of 0.02 and having magnetic anisotropy.
A permanent magnet having fine crystal grains of ~1.0 μm, characterized in that the carbon content is 0.01 to 0.8% by weight or less. (2) R-T-B-C alloy containing transition metal T as a main component, rare earth element R including yttrium, and boron B, and having an average crystal grain size of 0.02 with magnetic anisotropy.
In a permanent magnet having fine crystal grains of ~1.0 μm, the R content is 28-35% by weight and the T content is 60-35% by weight.
72% by weight, a B content of 0.5 to 1.5% by weight, and other unavoidable impurities. (3) R-T-B-C alloy containing transition metal T as a main component, rare earth element R including yttrium, and boron B, and having magnetic anisotropy and an average crystal grain size of 0.0
A permanent magnet having fine crystal grains of 2 to 1.0 μm, characterized in that the angular dispersion of the degree of crystal orientation from the C axis measured by X-ray diffraction is less than 30 degrees at the magnet surface. .