JPH0382742A - Permanent magnet alloy excellent in oxidation resistance - Google Patents

Abstract

PURPOSE:To provide superior oxidation resistance while maintaining high magnetic properties by coating respective magnetic crystalline grains in a magnet with oxidation resisting protective film having a composition which contains all of the alloying elements constituting the above magnetic crystalline grains and in which C content is specified. CONSTITUTION:In an R-Fe-B-C alloy magnet (R means at least one kind among rare earth elements including Y), respective crystalline grains in the alloy are coated with oxidation resisting protective film. The protective film has a composition which contains practically all the alloying elements constituting the magnetic crystalline grains and in which C comprises 0.1-16wt.%. It is preferable that the grain size of the crystalline grains and the thickness of the oxidation resisting protective film are regulated to about 0.5-5mum and about 0.001-15mum, respectively. Since this permanent magnet alloy has excellent oxidation resistance and hardly rusts, and further, it has superior magnetic properties, it can suitably be used for various magnet applied products.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is directed to dilute ±11(R)-iron (Fe) having excellent oxidation resistance.
)-Boron (B)-Carbon (C) permanent magnet alloy.

(Prior Art) In recent years, many reports have been made since R-Fe-B magnets were disclosed by Sayo et al. as next-generation permanent magnets that surpass the magnetic force of 5s-Co magnets. Although the magnet has superior magnetic force compared to 5s-Co magnet, its magnetic properties are significantly inferior in thermal stability and oxidation resistance.
For example, it is difficult for the permanent magnet material disclosed in JP-A-59-46008 to be durable in practical use.

In fact, many of the above-mentioned reports point out defects in oxidation resistance and disclose improvements thereto.

Methods for improving this oxidation resistance can be roughly divided into a method using nine alloy combinations and a method of covering the surface of the magnet with an oxidation-resistant protective film.

As an example of the former, for example, JP-A No. 59-64733 teaches that corrosion resistance can be imparted to a magnet by replacing part of Fe with Co;
Publication No. 9 teaches that oxidation resistance is improved by incorporating a low melting point metal element such as AI, Zn, Sn, etc. or a high melting point metal element such as Fe, Co, Ni, etc. into the matrix phase. Furthermore, in JP-A-62-133040 and JP-A-63-77103, it is stated that C in F61 stone promotes oxidation, and oxidation resistance is improved by reducing the content of C to a certain level. Teach that it will be done.

However, there is a limit to the effectiveness of methods for improving oxidation resistance using these alloy compositions alone, and it is actually difficult to put them into practical use. For this reason, in practical use, the surface of the magnet (the outermost exposed surface of the M1 stone product) is protected against oxidation through a complex and numerous process as shown in the above-mentioned Japanese Patent Application Laid-Open No. 63-114939. It is necessary to cover it with a film.

Regarding the formation of this oxidation-resistant protective film on the high surface of the magnet, it has been proposed to coat the magnet with an oxidation-resistant material by plating, sputtering, vapor deposition, organic coating, or the like. However, in either case, it is necessary to form a strong and homogeneous protective film layer of several tens of micrometers or more on the outer surface of the magnet, so the operation is complicated and requires many steps. However, it was not possible to avoid the problems of peelability, dimensional accuracy, and cost increase.

[Problems that the invention attempts to solve] In this way, the conventional R-F e-B system, R-Fe-C.

-B and R-Fe-Co-B-C magnets have not achieved a drastic improvement in oxidation resistance, and have superior magnetic properties and abundance compared to 5s-Co magnets. Despite having the great advantage of stable supply due to the availability of natural resources, at a practical level, it is necessary to form an oxidation-resistant protective film to isolate the magnet surface from the atmosphere, which increases costs and changes in dimensional accuracy. Therefore, there was a problem in that the above-mentioned advantages were greatly impaired.

Generally, R-F e-B magnets are composed of magnetic crystal grains and a non-magnetic phase including a B-rich phase and a Nd-rich phase.
Regarding the oxidation mechanism, oxidation first progresses from the B-rich phase on or near the magnet surface.

It is said that the phase then shifts to the Nd1J phase.

Therefore, in order to improve oxidation resistance, it is necessary to reduce B as much as possible and to impart oxidation resistance to the Nd-rich phase, but with conventional technology, it is difficult to obtain high magnetic properties at a practical level. The reality is that the B content has to be increased, and no significant results have been achieved in imparting oxidation resistance to the Nd-rich phase.

For example, JP-A No. 59-64733 by Maezumi proposes imparting corrosion resistance by replacing part of Fe with CO, but does not mention anything about the content of B with respect to oxidation resistance. Coercive force (i
The B content is set at 2 to 28 at% to ensure a high iHc), and in order to achieve an iHc of 3 KOe, the B content is required to be at least 4 at%. teaches that the content of B should be further increased. In this way, when ensuring high magnetic properties by containing a large amount of B, it is actually difficult to fully demonstrate oxidation resistance even if corrosion resistance is imparted by adding Co. As stated by the inventors of the publication, in order to put a magnet containing a large amount of carbon into practical use, it is essential to form a strong oxidation-resistant protective film on the magnet surface (the outermost exposed surface of a single-stone product). Become.

Furthermore, in the above-mentioned Japanese Patent Application Laid-Open No. 63-114939, active Nd For example, according to the examples described in the publication, a weather resistance test (60°C x 90% RH) of a sintered body was conducted.
) states that the standing time during which red rust was observed on the magnet surface was improved to 100 hours, compared to 25 hours in the comparative example. However, in such a state, it is difficult to use it at a practical level.

In reality, it is necessary to form a strong oxidation-resistant protective film on the magnet surface. Therefore, in this case as well, it is difficult to drastically improve the oxidation resistance of the magnet itself. Note that this publication also makes no mention of the content of B with respect to oxidation resistance, and since the content of B shown in the examples is 3.5 to 6.7 at%, the above-mentioned characteristics do not apply. It may be considered that B is intended to be contained within the range of 2 to 28 at % disclosed in JP-A-59-46008.

The purpose of the present invention is to solve the problems of such R-Fe-B-based permanent magnets, especially the problem of oxidation resistance. The object of the present invention is to provide the magnet itself with excellent oxidation resistance while maintaining high magnetic properties without the need for a protective film.

[Means for solving problems]

As a means to solve these problems, the present inventors have developed drastic oxidation resistance based on a microscopic concept, rather than the conventional macroscopic concept of coating the magnet surface with an oxidation-resistant protective film. As a result of intensive research into improving properties, we discovered a TFR standard technology that was difficult to predict using conventional technology, in which each magnetic crystal grain in the magnet is coated with an oxidation-resistant protective film.
This made it possible to provide a new permanent magnet alloy with dramatically improved oxidation resistance. Furthermore, we have newly discovered that it is possible to provide good magnetic properties that can withstand practical use even in the B content range of less than 2 at %, which was considered to be out of the practical range because high magnetic properties could no longer be obtained using conventional techniques.

That is, the present invention provides an R-Fe-B-C alloy magnet (where R is at least one rare earth element including Y) in which each of the magnetic crystal grains of the alloy has an oxidation resistance of g111! This oxidation-resistant protective film contains substantially all of the alloying elements constituting the magnetic crystal grains, and contains 0.
The present invention provides an R-Fe-B-C permanent magnet alloy with excellent oxidation resistance, characterized by containing 1 to 16% by weight of C. Here, the magnetic crystal grains preferably have a grain size of 0.
The thickness of the oxidation-resistant protective film covering each crystal grain of this grain size is in the range of 0.001 to 15 μ-.

The preferred composition of the magnet of the present invention (total composition of magnetic crystal grains and oxidation-resistant protective film) is, in atomic percentage, R (at least one rare earth element containing Y): 10 to 30%, B: less than 2%. (excluding 0%), c:o, s~20%, balance is Fe
and impurities that are unavoidable during manufacturing, and although the oxidation resistance effect is fully exhibited even with B content of 2% or more,
In particular, when the B content is as low as less than 2%, the oxidation resistance is significantly improved while exhibiting sufficient magnetic properties.

The permanent magnet according to the present invention does not require coating the outermost surface of the magnet with an oxidation-resistant protective film as in the conventional case.

The magnet itself has extremely high oxidation resistance.

For example, under the constant temperature of 60℃ x 90%RH mentioned above, 504
Even if the magnet surface is left exposed for 0 hours, Br and IHc (Dfliltn are 0.3 to 10% and 0 to 1%, respectively).
Therefore, even under such an environment, it is not necessary to form a protective film to cover the surface. The oxidation resistance and demagnetization resistance of the magnet of the present invention have not been achieved with conventional magnets, and in this respect it can be said to be a completely new permanent magnet.

On the other hand, regarding the magnetic properties of the magnet of the present invention, the isotropic sintered magnet has 4000 (G) on Br, and 1llc≧4000.
(Oe).

(BH) wax≧4 M −G ・Oe, anisotropic sintered magnet has 7000 (G) on Br, iHc≧4000 (O
e), (BH)mar≧10M-G·Oe, and has a value equal to or higher than that of conventional Nd-Fe-B permanent magnets.

The second characteristic is obtained by covering each magnetic crystal grain constituting the magnet of the present invention with a nonmagnetic film having an appropriate C content.

In other words, the present inventors added the above C to the grain boundary phase, which is a non-magnetic phase.
It has been found that by containing a predetermined amount of (carbon), this nonmagnetic phase can be given a remarkable oxidation-resistant function. By coating each magnetic crystal grain with this non-magnetic film having an oxidation-resistant function, it is possible to exhibit sufficient oxidation-resistant function even with the same B content as before, and furthermore, it is possible to exhibit sufficient oxidation-resistant function even with the same B content as before. It has been found that the formation of one film makes it possible to reduce the amount of B, and as a result, even if it is less than 2 atomic %, the magnetic properties are at the same level or higher than conventional ones, and the oxidation resistance is improved over the N period.

[Detailed Description of the Invention Magnets have a major feature in the way C (carbon) is used. Conventionally, C has generally been regarded as an impurity element that is unavoidably mixed into this type of magnet, and has not been treated as an alloying element that is actively added unless there is a special case. Publication No. 59-46008 specifies the content of B in the magnet as 2 to 28 at.%, and points out that with an ungrooved B content of 2 at.%, the coercive force iHe becomes less than IKOe. It merely states that it is possible to replace a part of B with C due to the merits of down, and furthermore, JP-A-59-163803 discloses an R-FeCo-B-C magnet. , [Ishinaka no B
The content of B and C is defined as 2 to 28 atomic %, and the content of C is 4 atomic % or less, and specific combinations of B and C are disclosed.

Despite the combined use of C, the content of B must be at least 2 at.
Similar to the 08 publication, it is explained that iHc is less than IKOe. That is, as the publication points out, C
It is understood that C is an impurity that deteriorates magnetic properties.1 For example, the contamination of carbon from lubricants used during powder molding is unavoidable, and it is difficult to completely remove it because it increases costs. For up to Br4000G, which is equivalent to a ferrite magnet, the C content is 4 atomic%.
It is proposed that the following can be tolerated, and 9C has a negative effect on magnetic properties, so C
is not required. In addition, C-containing oxidation-resistant protection II
There is no suggestion whatsoever about the formation of I (non-magnetic phase).

Furthermore, in JP-A-62-13304, R-Fe-C
In o-B-C magnets, it is taught that a large amount of C is not good in order to improve oxidation resistance, and the C content is set to 0.0.
5% by weight (approximately 0.3% in terms of atomic percentage)
Publication No. 03 also proposes to reduce C to 1000 pp+w or less for the same purpose. In this way, in the past, C
was considered to be a negative element in terms of magnetic properties and oxidation resistance, and was not considered an essential additive element.

The present inventors have proposed an additive method in which C is actively included in the non-magnetic phase (grain boundaries) surrounding the 1Mi crystals, instead of simply containing C as a replacement element for B. It was discovered that, contrary to conventional wisdom, C can greatly contribute to the oxidation resistance of magnets, and it has also become clear that it can improve m-feelability. By including C in the magnetic phase, the oxidation resistance is improved compared to the conventional one even if the B content is in the known normal range, and the effect is even more improved when the B content is 2 atomic % ungrooved. For example, in the past, when the B content was less than 2 at%, iHc
However, in the present invention, even if the amount of ungrooved B is 2 atomic %, iHc is 4 KOe.
It becomes more than e. Such novel effects of the present invention are brought about by the formation of a C-containing oxidation-resistant protective film that surrounds each magnetic crystal grain, and as a result, the deterioration of oxidation resistance and deterioration of magnetic properties, which have been observed up to now, can be avoided. Completely different from conventional magnets that use C as a negative element, we were able to complete the invention of a new magnet that requires C as an essential element.

In this case, the C-containing oxidation-resistant protective film surrounding each of the magnetic crystal grains contains substantially all of the alloying elements constituting the magnetic crystal grains other than C.

Formation of such a C-containing oxidation-resistant protective film is possible by incorporating C into the grain boundary layer existing between the magnetic crystal grains in 1M1 stone. The reason for this is inferred as follows. In other words, since the protective film contains substantially all of the alloy elements constituting the magnetic crystal grains, it is believed that this is largely due to the formation of R-Fe-C intermetallic compounds.

It is generally said that rare earth elements are easily rusted and carbides of rare earth elements are easily hydrolyzed. However, in the protective film according to the present invention, it is assumed that a non-stoichiometric R-Fe-C type intermetallic compound is generated, and this is thought to suppress the above-mentioned drawbacks.

In this way, the present inventors have found that oxidation resistance is significantly increased by coating individual magnetic crystal grains with a C-containing oxidation-resistant protective film, and that this effect becomes even more significant by reducing the B content. This discovery led to the invention of a good permanent magnet, which was difficult to achieve using known techniques.

This C-containing oxidation-resistant protective film contains substantially all of the elements constituting the magnetic crystal grains as described above, and the C content is in the range of 0.1 to 16 It is necessary that the amount is % by weight. That is, C in the protective film
Since it not only imparts oxidation resistance to the magnet but also has the effect of suppressing the decrease in iHc due to the decrease in B, its content is preferably 0.1 to 1 in the composition of the protective film.
% by weight, more preferably from 0.2 to 12% by weight. If the C content is less than 0.1% by weight, oxidation resistance cannot be imparted, and jHc becomes less than 4 KOe. On the other hand, if the amount of C in the protective film exceeds 16% by weight, the Br content of the magnet will drop significantly, making it difficult to put it into practical use. still.

In the magnet of the present invention, the composition of the protective film is as follows:
In addition to C, it contains substantially all of the alloying elements that make up the magnetic crystal grains, even if their quantitative ratios differ from those of the magnetic crystal grains.
As for the thickness of this protective film, as long as it covers each magnetic crystal grain uniformly.

Although oxidation resistance is substantially maintained regardless of its thickness,
If the film thickness is less than 0.001 am, the decrease in iHc will be significant, and if it exceeds 15 μ-, B' will no longer satisfy the directivity as intended by the present invention.
It is preferable to set the thickness in the range of 0.005 μm to 12 μm. Note that the thickness of the above-mentioned RJH includes the grain boundary triple point. The thickness of this protective film can be measured using Tl (this measurement was also used in the examples described later).On the other hand, each magnetic crystal grain itself surrounded by this oxidation-resistant protective film is a well-known R-Fe film. -B-Similar to (C) series permanent magnet &
[l or may be. However, even if the amount of B is low, the magnet of the present invention can exhibit good magnetic properties.0 Composition of the alloy magnet of the present invention (total composition including magnetic crystal grains and oxidation-resistant protective film) is preferably in atomic percentage, R:1
0 to 30%, B: less than 2% (not including 0%), C1,5
~20% 1 balance: Consists of Fe and impurities unavoidable in manufacturing.

The total C content in the magnet of the present invention is preferably 0.5 to 20 at.%. When the total C content in the magnet exceeds 20 at%, the Br decreases significantly.1 Br≧4KG as an isotropic sintered magnet and Br≧7KG as an anisotropic sintered magnet, which is the objective of the present invention. The value of is no longer satisfied. On the other hand, 0.5
If it is less than atomic %, it becomes difficult to impart oxidation resistance. in this way.

The MC content in the magnet is preferably 0.5 to 2 at%, but the C in the oxidation-resistant protective film described above not only provides oxidation resistance, but also reduces the amount of B (1) This is because it has the effect of suppressing the decrease in 1c.

Its content is 0.1 in IjlF'Ii of the protective film.
-16% by weight, preferably 0.2-12% by weight. As the raw material for C, carbon black, high purity carbon, or alloys such as Nd-C and Fe-C can be used.

R is a rare earth element such as Y, La, Ce, Nd, or Pr.

T b+ D y, H01E r, S m, G +j
+One or more of Eu, Pm, Tm, Yb, and Lu are used. still.

Mixtures of two or more of them, such as mitshu metal and didim, can also be used. The reason why R is preferably set to 10 to 30 atomic % here is because Br is practically excellent within this range.

As B, pure boron or ferroboron can be used, and even if its content exceeds the known range of 2 at. However, preferably B is 2
Even greater effects are obtained when the content is less than atomic %, more preferably 1.8 atomic % or less. On the other hand, if no B is added, although the oxidation resistance is good, the iHc is extremely reduced, making it impossible to achieve the object of the present invention. As ferroboron, AI, Si
It is also possible to use materials containing impurities such as.

As mentioned above, the permanent magnet alloy of the present invention preferably has a thickness of 0.001 to 15 μII + more preferably o
Each magnetic crystal grain is covered with a C-containing oxidation-resistant protective film in the range of . ~30μ-. When the grain size of the magnetic crystal grains is less than 0.5 μ-, 1 llc becomes less than 4 KOe, and when it exceeds 50 tt m, the iHc decreases significantly and the characteristics of the magnet of the present invention are impaired. The grain size of this crystal grain was measured by SEH, and the Mi precept analysis was performed by l! This can be performed accurately using PMA (these measurements were also carried out in Examples described later).

When the permanent magnet alloy of the present invention is a sintered body, the method for producing the permanent magnet of the present invention includes melting, casting, crushing, shaping, and sintering, or melting, casting, crushing, shaping, sintering, and heat treatment. Although it can be produced by a conventional method consisting of a series of steps, it is preferable to introduce a step of heat-treating the cast alloy after casting in the above manufacturing process, or to introduce a step of heat-treating the cast alloy after casting, or to reduce part or all of the C raw material during or after pulverization. It can be advantageously produced by introducing a step of secondarily adding , or by introducing a combination of these two steps. On the other hand, when the permanent magnet alloy is a cast alloy, a good permanent magnet alloy of the present invention that exhibits the above-mentioned effects can be produced by using a hot plastic working method.

Examples are given below to clarify the characteristics of the magnet of the present invention.

[Example 1] Electrolytic iron with a purity of 99.9% as a raw material, boron content of 19
．． Using 32% ferroporon alloy, 99.5% pure carbon black and 98.5% pure neodymium metal (contains other rare earth metals as impurities), the composition ratio (atomic ratio) of 9 is 18Nd 71Fe IB 3C. After weighing and blending in the following manner and melting in a high frequency induction furnace in a vacuum, alloy 9 ingots were cast into a water-cooled copper mold. The alloy ingot obtained in this way was crushed by a show crusher for 10 to 1
It was crushed into pieces of 5 mm, held at 700'C for 5 hours, and then cooled at a rate of 50'C/min.

Furthermore, after crushing the alloy ingot to 1100 mesh using a stamp mill in argon gas, the U* ratio (atomic ratio)
So that it becomes 18Nd 71Fe IB IOC,
Furthermore, carbon black with a purity of 99.5% was added to the crushed material, and then it was pulverized to an average particle size of 5 μm using a vibration mill. 20KO of the alloy powder thus obtained
A sintered body was obtained by forming the sintered body at a pressure of 1 ton/c- in a magnetic field of 300° C., then holding it at 1100° C. for 1 hour in argon gas, and then rapidly cooling it.

Comparative Example 1 was the same as the above example except that carbon black was not used. 1 composition ratio (atomic ratio)
Weigh and mix so that 18Nd 76Fe 6B becomes 18Nd 76Fe 6B, and do the same as in the example process (however, no carbon blank is added).
After melting, the mixture was crushed by II, crushed @, and formed in a magnetic field, followed by sintering and quenching to obtain a sintered body.

As an evaluation of the oxidation resistance (weather resistance property M) of the sintered body thus obtained, the Br1Hc demagnetization rate when left at a constant temperature of 60°C and 90% humidity for 6 months (5040 hours) is shown. 1 and FIG.

As is clear from FIG. 1, in the sintered body of Example 1 (the sintered body in which each magnetic crystal grain is coated with a C-containing protective film), the fIjim ratio after 6 months is Br (solid line): -0 ,36%
, Hfc (broken line) was extremely small at 0.1%, and it was recognized that the oxidation resistance was extremely good. On the other hand, in the sintered body of Comparative Example 1 which does not have the C-containing protective film, the Km ratio after only one month (720 hours) was 9.8%.
%, 1) lc: 3.0%, and if left for any longer than this, rust would be severe and measurement would be impossible.

In addition, the results of observing the structure of the sintered body of Example 1 with an SEM are shown in the photograph in Figure 2, and furthermore, C and N using EPHA are shown.
The line analysis results for element d are shown in the photograph in FIG. Note that FIG. 4 shows the lines of each element obtained by copying the line analysis lines in the photograph of FIG. 3. These photographs show that the magnetic crystal grains are covered with an oxidation-resistant protective film containing C, and that most of the C is present in the N d U protective film. Note that the C content in the protective film was 6.1% by weight. Furthermore, when the grain size of 100 magnetic crystal grains was measured from a 58M photograph of the sintered structure, the range was 0.7 to 25 μm. On the other hand, the thickness of the W1 film measured by TEM was 0.01 to 5.6 μm. These values are shown in Table 1 below. In addition, the magnetic properties of Br, +Na and (B H
) The values of max are shown in Table 1.

As described above, the permanent magnet alloy according to the present invention has significantly better oxidation resistance than the known one of Comparative Example 1.

It can also be seen that the magnetic properties are the same or better.

[Examples 2 to 6] A sintered body was obtained by carrying out the same operations as in Example 1 except that the raw materials were measured and blended so that the boron (B) it as shown in Table 1 was obtained when melting the raw materials.

In addition, Comparative Example 2 is an example in which the amount of poron is O atomic %,
A sintered body was obtained in the same manner as above except that boron was not blended.

Oxidation resistance of each obtained sintered body, CI in the protective film, (
The i-type crystal grain size and the thickness of the protective film were evaluated in the same manner as in Example 1, and the results are shown in Table 1. Further, the oxidation resistance evaluation results of Examples 5 and 6 are also shown in FIG.

From these results, it can be seen that the sintered body having the C-containing protective film of the present invention has an extremely low demagnetization rate over a long period of time and has excellent oxidation resistance. Although this effect is sufficient in Example 6 where B is 3 atomic %, it is particularly noticeable in examples where B is 2 atomic % (for example, Examples 1 and 5 in FIG. 1).

[Example 7 to IO] A sintered body was obtained by carrying out the same operation as in Example 1, except that carbon black was additionally twisted during pulverization so that the amount of carbon became the Mi ratio shown in Table 2. In addition.

In Example 7, carbon black was not added during melting, but only during pulverization.

Furthermore, as Comparative Example 3, 18 N d-81F e-I B
After weighing and blending so that the following results were obtained, the same operations as in Comparative Example 1 were performed to obtain a sintered body. In addition, as Comparative Example 4, the composition ratio was 18
A sintered body was obtained in the same manner as in the above example except that N d-56F e-I B-25C was used.

The oxidation resistance, measurement in the protective film, magnetic crystal grain size, thickness of the protective film, and magnetic properties of the sintered body thus obtained were evaluated in the same manner as in Example 1. The results are shown in Table 2.

As shown in the results of Table 2, the three alloy compositions according to the present invention (
All sintered bodies that meet the requirements for a protective film (atomic percentage) and a protective film have a low demagnetization rate and exhibit excellent oxidation resistance.In Comparative Example 3, the protective film does not contain C, so the oxidation resistance is low. Rust developed to an extent that was impossible to measure.

In Comparative Example 4, the C content of the fI-retaining film was The Br value is low because it is too large.

[Examples 11 to 13] A sintered body was obtained by carrying out all the same operations as in Example 1, except that the amount of neodymium was measured and blended so as to have the composition ratio shown in Table 3.

The oxidation resistance, Cl in the protective film, magnetic crystal grain size, thickness of the protective film, and magnetic properties of the sintered body thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 3. Ta.

As seen from the results in Table 3, it can be seen that the sintered body of the present invention has excellent magnetic properties and extremely good oxidation resistance.

[Examples 14 to 22] Sintered bodies were obtained by carrying out all the same operations as in Example 1, except that rare earth elements shown in Table 4 were added in place of neodymium during melting of the raw materials.

The oxidation resistance, C content in the protective film, magnetic crystal grain size, thickness of the protective film, and magnetic properties of the sintered body thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 4. Indicated.

From the results in Table 4, it is clear that all the sintered magnets according to the present invention have excellent magnetic properties and also have extremely good oxidation resistance.

[Example 23] Everything was the same as Example 1 except that the alloy fine powder was shaped in the absence of a magnetic field.
A sintered body was obtained by performing the same operation as above.

The oxidation resistance, C content in the protective film, magnetic crystal grain size, thickness of the protective film, and magnetic properties of the sintered body thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 5. Indicated.

[Brief explanation of drawings]

FIG. 1 shows a sintered body magnet (Example 1°5.6) of the present invention in which each magnetic crystal grain is coated with a C-containing oxidation-resistant protective film.
60'CX RH90% with the magnet surface exposed
The leaving time and B r when left in an atmosphere of 1)
FIG. 3 is a diagram showing the relationship between Ic and demagnetization rate in comparison with that of a comparative example that does not have a C-containing oxidation-resistant protective film. FIG. 2 is a photograph showing the metal structure of the magnet of the present invention of Example 1. FIG. 3 is a photograph showing the line analysis results of Nd and FeC elements in the metal m weave of FIG. 2. FIG. 4 is a diagram showing the line analysis lines of FIG. 3, and is used to display the elemental core of each line.

Claims (3)

[Claims] (1) In an R-Fe-B-C alloy magnet (where R is at least one rare earth element including Y), each of the magnetic crystal grains of the alloy is covered with an oxidation-resistant protective film, This oxidation-resistant protective film contains substantially all of the alloying elements constituting the magnetic crystal grains, and has 0.1 to 16% by weight of C. Fe-B-
C-based permanent magnet alloy. (2) The permanent magnet alloy according to claim 1, wherein the magnetic crystal grains have a particle size in the range of 0.5 to 50 μm, and the oxidation-resistant protective film has a thickness in the range of 0.001 to 15 μm. (3) The composition of the magnet alloy (total composition including magnetic crystal grains and oxidation-resistant protective film) is R: 10 to 10 in atomic percentage.
30%, B: less than 2% (not including 0 atomic %), C: 0.
3. The permanent magnet alloy according to claim 1, wherein the permanent magnet alloy comprises 5 to 20%, and the remainder is Fe and impurities unavoidable in manufacturing.