JPH0637693B2 - Rare earth permanent magnet material excellent in mechanical properties, manufacturing method thereof and inspection method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an R ₂ T ₁₄ B-based alloy (R is a rare earth element containing Y, T
Represents a transition element. The present invention relates to an R-T-B based intermetallic compound magnet represented by (4), particularly to a rare earth magnet permanent stone material excellent in mechanical properties, a manufacturing method thereof, and an inspection method thereof.

[Conventional technology]

Conventionally, magnet materials have been generally used with almost no movement, for example, in a speaker. Therefore, the evaluation of the magnetic material was mainly based on its magnetic properties, and it was not necessary to consider its mechanical properties. Further, the mechanical properties were merely judged by the transverse rupture strength and the like as a strength measure.

However, in recent years, high-performance permanent magnets have been developed, various actuators utilizing their properties have been put into practical use, and the tendency to require movement of magnets has increased.

[Problems to be Solved by the Invention]

However, in response to the above-mentioned requirements, conventionally, the mechanical properties of the magnet material are judged by the transverse rupture force and the like, and therefore, this is merely a measure of strength, and an accurate design strength can be estimated in actual use. It was difficult. For this reason, there is a problem in that the use of the high-performance permanent magnet material is restricted because of its unclear mechanical properties.

Moreover, among the rare earth permanent magnets, the R-Fe-B based permanent magnet material has a fragile property that cracks and chips easily occur during the manufacturing process and when it is incorporated into a product, and in particular, there are many variations in mechanical strength. Despite being recognized, since mechanical properties have not been considered in the past, there was an unclear point about the factors that determine the mechanical properties in the manufacturing stage. For this reason, it was not possible to find an effective improvement for obtaining a rare earth permanent magnet material having excellent mechanical properties, and it was difficult to establish an effective manufacturing method after all.

On the other hand, among the rare earth permanent magnets, the R-Fe-B system permanent magnet material, in particular, has a composite structure composed of the Nd ₂ Fe ₁₄ B intermetallic compound and the Nd-Fe solid solution phase, and therefore has a brittleness different from that of the Sm-Co system magnet. It has been pointed out that the fracture toughness is indicated, which is why the fracture toughness value (KI
There is an attempt to judge the mechanical properties of magnet materials using C).

However, KIC is generally calculated by performing a tensile or bending fracture test on a cracked specimen and measuring the precrack size and the fracture strength.

Here, in most cases, KIC is the critical condition for initiation of crack propagation from the precrack tip and depends on the concentrated stress at the precrack tip. Since this concentrated stress depends on the curvature of the tip of the precrack, the measured value of KIC varies greatly depending on how the precrack is inserted. Therefore, in the case of KIC, which is a material with some degree of ductility, such as a steel material, mechanically notched, fatigue cracks are generated, and a specimen with a sharp pre-crack is obtained. However, in the case of brittle materials with a small KIC, it is difficult to create a stop crack due to fatigue, and the KIC measurement value varies greatly depending on how the precrack is created.

Therefore, when the mechanical properties of the magnet material are judged by the fracture toughness value (KIC), it is difficult to obtain an accurate KIC measurement value by the above-mentioned conventional method.

In view of the above drawbacks, the technical problem of the present invention is to provide a rare earth permanent magnet material having excellent mechanical properties and a method for producing the same, and a method for effectively inspecting the mechanical properties of the rare earth permanent magnet material. By doing so, it is to provide a rare earth permanent magnet material having useful mechanical properties.

[Means for Solving the Problems]

According to the present invention, there is provided a rare earth permanent magnet material having a multi-phase structure of R ₂ T ₁₄ B magnetic crystal grains (R is a rare earth element containing Y, T is a transition element) and an RT solid solution. , Atomic percentage, R of 15 to 40%, B of 0.05 to 10%, balance T, and the latent defect diameter due to the magnetic crystal grains is substantially 150 μm or less. A rare earth permanent magnet material having excellent properties can be obtained.

Further, according to the present invention, there is provided a rare earth permanent magnet material having a multi-phase structure of R ₂ T ₁₄ B magnetic crystal particles (R is a rare earth element containing Y, T is a transition element) and an RT solid solution. In the manufacturing method, an alloy powder produced from at least one of a liquid-quenched alloy powder and a liquid-quenched alloy ribbon having a composition with an R value of 32 to 100 wt% is prepared. Is added) to produce a powder compact having a composition of R15 to 40%, B0.05 to 10%, and the balance T in atomic percentage, and sintering the powder compact to obtain a sintered compact. To produce a rare earth permanent magnet material excellent in mechanical strength, characterized in that the latent defect diameter in the sintered body is 150 μm or less.

Further, according to the present invention, in a method for inspecting mechanical strength of a rare earth permanent magnet material having a multi-phase structure of R ₂ T ₁₄ B magnetic crystal particles and an RT solid solution phase, the rare earth permanent magnet is destroyed. A strength test is performed, the magnetic crystal particles are identified on the crack surface generated by the fracture strength test, and the identified magnetic crystal particles are approximated with a predetermined equivalent circular disk having a simple shape to form a latent defect diameter, A method of inspecting a rare earth permanent magnet material having excellent mechanical properties, which is characterized in that a fracture toughness value is obtained based on the diameter of the latent defect.

That is, the present invention clarifies the cause of variation in mechanical strength by fracture mechanics, and when an alloy powder containing R, Fe, and B as main components is formed and sintered, defects inside the sintered body, such as coarse grains, By reducing the size of defects such as inclusions and surface cracks, it is possible to improve the mechanical strength and provide a permanent magnet material with outstanding mechanical properties.

Note that the R-Fe-B diameter magnet represented by Nd-Fe-B has a composite structure consisting of the Nd ₂ Fe ₁₄ B intermetallic compound and the Nd-Fe solid solution phase, so it is different from the Sm-Co magnet. It is considered that the fracture behavior is shown. In general, rare earth magnets that exhibit brittle fracture, in many cases, generate cracks from latent defects.
It always leads to fracture without stopping.

In the sintered material, it is possible to identify the defect that is the starting point of crack initiation, and this defect is approximated by an equivalent defect of a simple shape (elliptical plate) to obtain a latent defect diameter a, which acts on the defect. Breaking stress λn and If (Y is the shape factor of the defect) is plotted, there is a linear relationship within a certain defect diameter range, and K _IC can be obtained from the following equation. In other words, a material with a small K _IC will break even with defects with low stress,
On the other hand, a material with a large K _IC does not easily break even if it has a large defect. That is, K _IC means the crack sensitivity of the material strength and shows the chipping resistance industrially.

Based on the above, we attempted to apply K _IC as a measure of the fracture strength of brittle rare earth magnets.

Observing the fracture surface of the Nd-Fe-B magnet implemented in the present invention,
As shown in FIG. 1, it is possible to find the defect that is the starting point of the destruction. Therefore, when the K _IC of the Nd-Fe-B magnet was measured, the fracture strength λn and the defect diameter It can be seen that a linear relationship is obtained with the relationship with, and thus the strength depends on the size of the defect. That is, when the defect diameter is large, the fracture stress λn is small, and conversely, when the defect diameter is small, the fracture stress λn tends to be large.

According to the present invention, when a defect having a large defect is present, the fracture strength is deteriorated and the mechanical properties are deteriorated. It has become possible to obtain a magnet that is extremely useful in practical use with excellent physical properties.

The defects that cause destruction are mainly coarse grains, and Nd ₂ Fe ₁₄ B
The particles grew during sintering and the defect size was 150
If it is less than μm, the fracture stress λn is more than 200MPa,
A magnetic material having excellent mechanical properties can be obtained. Therefore,
As a condition of excellent mechanical properties, the breaking strength λn is 200M.
If it is Pa or more, there is practically no limitation on the use due to destruction, and for that purpose the size of the defect system must be 150 μm or less.

As a composition range, when R is below 15% in atomic percentage, the number Nd ₂ Fe ₁₄ B magnetic phase of brittle fracture, since the amount of Nd-Fe solid solution phase showing ductile fracture is reduced, Nd ₂ Fe ₁₄ B
Grains grow and become coarse and become latent defects that cause fracture, mainly brittle fracture, and fracture strength λn becomes small.
Therefore, R needs to be 15 at% or more. On the other hand, R is 40at%
The above causes deterioration of magnet characteristics and is unsuitable as a magnet material.

As a manufacturing method for obtaining a latent defect diameter of 150 μm or less, a liquid quenched alloy powder or an alloy powder obtained from ribbons (amorphous and microcrystalline) and a powder obtained by crushing an ingot by melting are mixed, shaped, and compared. There is a method of suppressing grain growth and sintering at an extremely low sintering temperature.

This manufacturing method is only an example and does not define the present invention.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

(Example-1) Using Nd, Fe, and B having a purity of 99 wt% or more, an ingot of 31.0, 35.0 wt% Nd-1.1B-Febal was obtained by high frequency heating in an Ar atmosphere. Each ingot was roughly crushed using a disc mill and finally 31.0, 33.0, 35.0wt% Nd-1.1B-Febal
Weigh and mix to obtain the composition
A mill was used to obtain a fine powder having an average particle size of 3.0 (μm). Next, the obtained fine powder was molded in a magnetic field of 20 kVe at a pressure of 1.0 Ton / cm ² to obtain a green compact. Ar sintering these green compacts at a temperature of 1100 ° C for 2 hours, A sintered body of (wherein the magnetic field application direction during pressing) was obtained. The sintered body was machined to obtain a test piece of 4 × 7 × 25 (mm). During the bending test, to remove the cracks on the surface and the side where tensile stress is applied and the residual stress, it was ground with # 600 to # 1500 sandpaper.

A three-point bending jig with a span length of 20 mm was used to perform a destructive test with an Amsler universal testing machine to obtain the transverse rupture strength λ _TRS . First
The table shows the average transverse strength λ _TRS of each alloy. 31Nd-1.1B
-The average bending strength of Febal is lower than other alloys (,). There are two The distribution of the transverse rupture strength of the alloy and the distribution of the size of the defect which is the starting point of the fracture are shown in FIGS. 2 (a) and (b). The bending strength of the 31 wt% Nd alloy is lower than that of 35 wt% Nd. Moreover, the size of the defects at that time is clearly distributed in the larger diameter, and the distribution range is wide. This also shows that the fracture strength of the alloy depends on the size of the defects.

(Example-2) A fracture surface was observed using the fracture test piece obtained in Example-1, and as shown in Fig. 3, the distance x between the fracture origin and the outer fulcrum was measured.
The distance y from the neutral axis and the minor axis length 2a and major axis length 2b of the inscribed ellipse of the defect were obtained.

In the case of three-point bending, since there is a stress gradient in the specimen, it is assumed that the specimen is in an elastically deformed state and the fracture stress λ that acts on the defect is
n was obtained by the following formula.

Here, 1 is the distance between outer fulcrums, and t is the height of the test piece. Since the stress intensity factor around the ellipse of an elliptical plate-shaped defect takes a maximum at the short axis end, K _IC was obtained from Eq. (1) with the short axis length as the defect diameter.

The relationship between the fracture strength and the defect diameter in each alloy was investigated by fracture fracture. In Fig. 4, λn in alloy and A linear relationship was obtained by plotting the relationship with and the K _IC of each alloy obtained from the slope of the straight line is shown in Table 2.

K _IC increases with increasing Nd content of the alloy. By observing the fracture surface, the Nd ₂ Fe ₁₄ B magnetic particle phase was brittle fractured and solid solution of Nd-Fe was observed. Since the body phase fractures ductilely, the increase in K _IC due to the increase in Nd content is due to the increase in the amount of Nd-Fe solid solution phase in ductility.

Therefore, when K _IC is plotted against the volume fraction of Nd-Fe solid solution phase obtained by microstructural analysis of the alloy cross section, as shown in Fig. 5, it is almost linearly proportional to the volume fraction of Nd-Fe solid solution phase. To do.

〔The invention's effect〕

As described above, according to the present invention, attention is paid to the fact that the fracture strength depends on the size of the latent defect. Therefore, by making a magnet alloy having a defect diameter of 150 μm or less, mechanical properties are improved as compared with the conventional one. It has become possible to obtain excellent magnet alloys.

So far, only Nd-Fe-B magnet alloys have been described.
It can be easily inferred that similar effects can be expected for the rare earth element (R) -Fe-B system including yttrium.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph showing the grain structure of the fracture origin region of the Nd-Fe-B magnet. Fig.2- (a) and (b) are the distribution map of transverse rupture strength λ _TRS and defect diameter a, respectively.
The distribution chart of is shown. FIG. 3 is a diagram showing the position of the defect which is the starting point of the destruction. Figure 4 shows the fracture stress λn and It is a figure showing the relation with. FIG. 5 is a diagram showing the relationship between the fracture toughness value K _IC and the Nd—Fe solid solution phase volume ratio.

Claims (3)

[Claims] 1. A rare earth permanent magnet material having a multi-phase structure of R ₂ T ₁₄ B magnetic crystal particles (R is a rare earth element containing Y, T is a transition element) and an RT solid solution, In atomic percentage, 15-40% R, 0.05-10% B, balance T
And the latent defect diameter due to the magnetic crystal grains is substantially
A rare earth permanent magnet material excellent in mechanical properties characterized by having a thickness of 150 μm or less. 2. A method for producing a rare earth permanent magnet material having a multi-phase structure of R ₂ T ₁₄ B magnetic crystal grains (R is a rare earth element containing Y, T is a transition element) and an RT solid solution. ，
An alloy powder produced from at least one of a liquid-quenched alloy powder and a liquid-quenched alloy ribbon having a composition with an R value of 32 to 100 wt% is prepared.
l% (not including O) is added to obtain R15 in atomic percentage.
A latent defect in the sintered body is produced by producing a powder compact having a composition of -40%, B0.05-10%, and the balance T, and sintering the powder compact to produce a sintered body. Diameter is 150 μm
A method for producing a rare earth permanent magnet material excellent in mechanical properties, characterized by the following. 3. A method for inspecting the mechanical strength of a rare earth permanent magnet material having a multi-phase structure of R ₂ T ₁₄ B magnetic crystal particles and an RT solid solution phase, wherein a fracture strength test is performed on the rare earth permanent magnet. The magnetic crystal particles are identified on the crack surface when generated by the fracture strength test, and the fixed magnetic crystal particles are approximated by a predetermined equivalent circular disk having a simple shape to obtain a latent defect diameter. A method for inspecting a rare earth permanent magnet material having excellent mechanical properties, which comprises determining a fracture toughness value based on a diameter.