JPH04268052A - R-fe-b-c permanent magnet alloy reduced in irreversible demagnetization and excellent in heat stability - Google Patents

Abstract

PURPOSE:To reduce the irreversible demagnetization (the phenomenon of which the residual magnetic flux density reduced at a high temp. does not recover in the case the temp. is returned to an ordinary one) of an R (rare earth elements)-Fe-B-C permanent magnet and to improve the heat stability of its magnetic properties. CONSTITUTION:In an R-Fe-M-B-C alloy magnet (where R denotes at least one kind selected from Nd, Pr, Ce, La, Y, Sm, Tb, Dy, Gd, Ho, Er, Tm and Yb and M denotes at least one kind selected from Ba, Sr, Ca, Li, Mg and Be), each of the magnetic crystalline grains of the alloy is coated with a grain boundary phase contg. <=16.0wt.% (not including zero wt.%) C.

Description

Description: FIELD OF INDUSTRIAL APPLICATION The present invention relates to an R (rare earth element)-Fe-B-C based permanent magnet alloy that exhibits low irreversible demagnetization and excellent thermal stability. [0002] In recent years, since R-Fe-B magnets were announced by Sagawa et al. as next-generation permanent magnets that surpass the magnetic force of Sm-Co magnets, many reports have been made regarding these magnets. Ta. However, although this magnet has superior magnetic force compared to Sm--Co magnets, it has the disadvantage that its magnetic properties are significantly inferior in thermal stability and oxidation resistance. In particular, deficiencies related to oxidation resistance are important issues to improve.
Many of the above reports disclose methods of improvement. On the other hand, conventional R-Fe-B or R-Fe-
The residual magnetic flux density of Co-B magnets decreases as the environmental temperature rises.
(Br) and coercive force (iHc) are significantly lower than those of Sm--Co magnets. In other words, it has the disadvantage of poor thermal stability. Under these circumstances, as a means of stabilizing the magnetic properties against changes in environmental temperature, it has generally been proposed to reduce the temperature dependence coefficient of the residual magnetic flux density and to sufficiently increase the coercive force at room temperature. ing. A common method for improving the former is to increase the Curie temperature of the magnet, for example,
Publication No. 9-64733 proposes replacing part of Fe with Co to increase the Curie temperature and reduce the temperature dependence coefficient of residual magnetic flux density. On the other hand,
As already mentioned, the coercive force decreases rapidly as the environmental temperature rises, but a serious drawback of this decrease in coercive force is that it causes large irreversible demagnetization. [0004] Irreversible demagnetization is a phenomenon in which Br, which has decreased at high temperatures, does not recover to its original state when the temperature returns to room temperature, and generally, as the magnet shape becomes thinner, its deterioration becomes more noticeable. This irreversible demagnetization deterioration cannot be fundamentally improved even if some of the Fe is replaced with Co to reduce the temperature dependence coefficient of the residual magnetic flux density. For this reason, the environmental temperature and shape are severely restricted in actual use. For example, in automobiles,
Application to harsh applications such as high-speed equipment will be difficult. The current situation is that methods for improving this irreversible demagnetization rely exclusively on methods of increasing iHc at room temperature. In other words, it is a method to reduce irreversible demagnetization by sufficiently increasing iHc at room temperature in anticipation of a decrease in iHc at high temperatures.
He taught that by adding i, Ni, Bi, V, Nb, Cr, Mo, etc., the iHc at room temperature can be increased and the irreversible demagnetization rate can be reduced.
Publication No. 06 contains Dy, Tb, Ho, Gd, Er, Tm, Yb in addition to light rare earth elements as rare earth element components.
This paper specifies the addition of heavy rare earth elements, and teaches that this increases iHc and improves irreversible demagnetization rate. [0005] However, although irreversible demagnetization can certainly be improved by sufficiently increasing iHc in this way, in the conventional method, when the temperature reaches a high temperature of, for example, 160°C, even if the iHc at room temperature is sufficiently high as 15 to 20 kOe, However, there remains the problem of rapid deterioration. In this case, iHc will be further increased. On the other hand, when iHc increases in this way, a new problem of magnetization occurs. In other words, in order to maximize the magnetic force of a magnet, it is necessary to magnetize it with a sufficiently large magnetic field until the magnetic force is saturated, and a low magnetization rate will lead to instability of the magnetic properties. Since a magnetic field that is 3 to 4 times stronger than the iHc of the magnet is required for magnetization, an extreme increase in iHc as in the conventional method makes it difficult to attach and demagnetize the magnet, and also increases the size of the equipment. will be invited. Therefore, in the past, it has not been possible to avoid these problems as well as the deterioration of irreversible demagnetization at high temperatures. [0006] As described above, conventional R-Fe-B magnets have not been able to sufficiently improve irreversible demagnetization at high environmental temperatures. S
Although it has superior magnetic force compared to m-Co type,
In particular, the problems of thermal stability at high temperatures and magnetization associated with high iHc at a practical level still exist, and the above merits are greatly diminished. Generally, R-Fe-B (or R-F
e-Co-B) system magnets are R2Fe14B [or R2(Fe,Co)14B] type tetragonal and RFe4B
4[R(Fe,Co)4B4] type B-rich phase, R-rich phase and non-magnetic phase containing B2O3 phase.
(In addition, in R-Fe-Co-B magnets, R(Fe, Co
) It is said that there is also a Laves phase represented by 2)
The principle of coercive force generation is said to be based on a reverse magnetic domain nucleation mechanism. In other words, the existence of this reverse magnetic domain determines the coercive force, and as iHc decreases as it grows, the coercive force of the nucleation type magnet becomes structure-sensitive, and the coercivity of the tetragonal and grain boundary phases
It is dominated by the R-rich phase, B-rich phase, and other impurity phases. By the way, the sprouts of the reverse magnetic domain nuclei, that is, the reverse magnetic domain nuclei, are generated in defects in the tetragonal and grain boundary phases, soft magnetic phases, and other impurity phases, and easily grow due to the presence of these defects and foreign substances. . In this way, if the structure of the magnet is inhomogeneous or contains impurities and various defects, i
Hc easily decreases, and as a result, irreversible demagnetization of residual magnetism, which is important at a practical level, increases. From the above, the following basic measures can be taken to reduce the irreversible demagnetization rate from the viewpoint of the magnet structure. (1) Homogenization of tetragonal crystals, (2) Homogenization and uniformity of grain boundary phase, (3) Removal of soft magnetic phase, (4
) Removal of other impurity phases. After these improvements have been made, it is thought that by optimizing iHc, a drastic improvement in irreversible demagnetization can be achieved. [0010] As a conventional method for improving irreversible demagnetization, for example, the above-mentioned Japanese Patent Application Laid-Open No. 59-89401 and Japanese Patent Application Laid-Open No. 6
It has already been mentioned that Publication No. 0-32306 discloses a method of improving iHc at room temperature by sufficiently increasing it, but these methods do not make any improvement to the structure of the magnet, and are simply This is a passive improvement method in which the iHc at room temperature is made extremely high by increasing the anisotropic magnetic field using additives, thereby improving irreversible demagnetization at the expense of lowering the iHc at high temperatures. Therefore, the improvement effect at higher temperatures is small;
As already mentioned, problems such as magnetization remain. On the other hand, by making the composition of the permanent magnet alloy homogeneous,
Many methods have been reported to improve iHc.
It has generally been proposed to heat treat magnet alloys. For example, in Japanese Patent Application Laid-open No. 59-217304, after sintering,
It is taught that iHc can be improved by heat treatment at a temperature of 50°C or higher. According to this method, although the homogenization of the magnet composition is improved by heat treatment, there are still impurity phases such as B-rich phase and B2O3 phase, so there is no change in the structure of the structure and the reverse magnetic domain remains. The origin of the nucleus and its growth have not been fundamentally resolved. Therefore, even if iHc is increased by this method, it is judged that the effect of improving irreversible demagnetization at high temperatures is small. [0012] As described above, in order to improve irreversible demagnetization according to the prior art, the actual situation is that no countermeasures are taken for the structure of the magnet alloy structure. [0013] Furthermore, as a method of suppressing the generation and growth of reverse magnetic domain nuclei by removing impurities, it is possible to suppress the generation of oxide phases and B-rich phases, for example. This can be suppressed by reducing the amount of oxygen. In addition, many B-rich phases exist in conventional materials, and their size is comparable to that of tetragonal crystals, so they not only cause defects as an impurity phase, but also become large magnetic spaces in some cases, causing demagnetization field formation. It can also be a factor. However, the reality is that in order to obtain higher magnetic properties at a practical level than before, it is necessary to increase the B content; for example, in JP-A-59-4
In Publication No. 6008 and Japanese Unexamined Patent Publication No. 1987-64733, in order to secure an iHc of 1 kOe or more,
The B content is specified to be 2 to 28 at%, and the iHc is 3 to 28 at%.
To achieve kOe, the B content must be at least 4 at%
In order to obtain iHc at a higher practical level, it is taught that the content of B should be further increased. That is, in the prior art, if the B content is reduced, α-Fe tends to precipitate, and iHc accordingly decreases rapidly. Therefore, it was not possible to suppress the formation of the B-rich phase. Therefore, in order to put into practical use conventional materials that contain a large amount of B and a large amount of B-rich phase as an impurity phase, an extremely high iHc is required as described above as a countermeasure against irreversible demagnetization at high temperatures. The purpose of the present invention is to solve the problems of R-Fe-B permanent magnets, especially the problem of irreversible demagnetization, without making the iHc extremely high as with conventional materials. The object of the present invention is to provide a permanent magnet alloy that exhibits small irreversible demagnetization even at a relatively low iHc and has excellent thermal stability. [Means for Solving the Problems] As a means to solve these problems, the inventors of the present invention have intensively studied the drastic improvement of irreversible demagnetization through the structure of the magnetic alloy. By making the magnetic crystal grains with a tetragonal structure and the R-rich grain boundary phase homogeneous, and by covering each magnetic crystal grain with the grain boundary phase, irreversible demagnetization is significantly improved compared to conventional materials. Moreover, in order to further enhance these effects, we have discovered a new technology that was difficult to even predict using the conventional technology of removing the B-rich phase. We have made it possible to provide a new permanent magnet alloy that has extremely small magnetism and a maximum energy product equal to or greater than that of the new permanent magnet alloy. In other words, we have discovered a new technology that can 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 the conventional technology could no longer provide high magnetic properties. This led to a revolutionary improvement in irreversible demagnetization. That is, according to the present invention, R-Fe-M-
B-C alloy magnet (However, R is Nd, Pr, Ce,
La, Y, Sm, Tb, Dy, Gd, Ho, Er, Tm
, Yb, M is Ba, Sr,
At least one selected from Ca, Li, Mg, Be)
In the alloy, each of the magnetic crystal grains is
It is covered with a grain boundary phase, and this grain boundary phase contains 16% by weight or less (excluding 0% by weight) of C. R-Fe- M-B
-C-based permanent magnet alloy is provided. [0018] The magnetic crystal grains preferably have a grain size in the range of 0.3 to 150 μm, and the thickness of the grain boundary phase covering each crystal grain of this grain size is in the range of 0.001 to 30 μm. It is. The preferred composition (total composition of magnetic crystal grains and grain boundary phase) of the magnet of the present invention is R (R is Nd, Pr, Ce, La, Y, Sm, Tb, Dy, Gd) in atomic percentage.
, Ho, Er, Tm, Yb): 10 to 30%, B: 7% or less, preferably less than 2% (not including 0 atomic %), C: 0.1 to 20%, M
: At least one metal element M in the following specified percentage (however, 2
When more than one species is included, the total M content is less than or equal to the largest value of M among the elements), with the remainder consisting of Fe and impurities unavoidable in manufacturing. Here, the content of M element (however, 0
(excluding atomic %) is Ba: 5% or less, Sr: 5% or less, Ca: 7% or less, Li: 4% or less, Mg: 6% or less,
Be: 4% or less. [Operation] Although the effect of reducing irreversible demagnetization in the alloy of the present invention is sufficiently exhibited even when the B content is 2% or more, irreversible demagnetization is particularly noticeable when the B content is as low as less than 2%. Furthermore, the magnetic properties are equivalent to or better than conventional materials. Furthermore, even if no M is added, irreversible demagnetization is smaller than that of conventional materials, but by containing M at the predetermined atomic % (excluding 0 atomic %) as described above, it becomes even more Can be effectively made smaller. A feature of the permanent magnet according to the present invention is that irreversible demagnetization at high temperatures is small even if the iHc of the magnet is not extremely high as in the conventional case. For example, if the permeance coefficient (PC) is 3 and the iHc is 11, .When a 3KOe magnet was left at an ambient temperature of 160℃ for 30 minutes and then returned to room temperature,
Its irreversible demagnetization rate is -9.3%. On the other hand, the irreversible demagnetization rate of the conventional material with iHc 11.9 kOe measured using PC3 using the same method as above was -27.2%.
Although the iHc is 0.6 kOe larger, it shows a large deterioration. Therefore, even in such a high-temperature environment, the irreversible demagnetization characteristics of the magnet of the present invention are extremely good even at iHc, which is sufficiently lower than that of conventional materials, 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, in an isotropic sintered magnet, Br≧4000 (G), iHc≧4
000(Oe), (BH)max≧4(MGOe),
For anisotropic sintered magnets, Br≧7000(G), iH
c≧4000 (Oe), (BH)max≧10 (MG
Oe), which is equal to or higher than that of conventional R-Fe-B permanent magnets. [0024] Such novel irreversible demagnetization characteristics were obtained by covering each magnetic crystal grain constituting the magnet of the present invention with a non-magnetic phase having an appropriate C content. . That is, the present inventors incorporated a predetermined amount of C (carbon) into the grain boundary phase, which is a non-magnetic phase.
In other words, by including C in the phase so that 16% by weight or less, preferably in the range of 0.05 to 16% by weight, this nonmagnetic phase becomes more homogeneous and the irreversible demagnetization characteristics are improved. I found out what I can do. Furthermore, it has been found that by containing M in the above-described predetermined atomic % (excluding 0 atomic %) in the magnet, it becomes even more effective. It is presumed that the inclusion of M promotes atomic diffusion in the magnetic crystal grain phase and the grain boundary phase, homogenizes these phases, and suppresses the formation of impurity phases. In other words, if each magnetic crystal grain is coated with such a C-containing nonmagnetic phase, irreversible demagnetization can be improved even with the same B content as in conventional materials, and furthermore, B can be reduced to less than 2 atomic percent. As a result, irreversible demagnetization has been dramatically improved while the magnetic properties are at or above the same level as conventional ones, and it has also become clear that the effect becomes even better when the above-mentioned M is included. [Detailed Description of the Invention] The magnet of the present invention is made of C (carbon)
Since there is a major feature in the way it is used, I will explain this point first. [0026] Conventionally, carbon has generally been regarded as an impurity element that is unavoidably mixed in this type of magnet, and has not been treated as an alloying element that is actively added unless there is a special case. For example, the above-mentioned Japanese Patent Application Laid-Open No. 59-46008 discloses replacing a part of B with C, but
This specifies the content of B in the magnet as 2 to 28 atomic%, and 2
If the amount of B is less than atomic %, the coercive force iHc will be less than 1 kOe, so a B amount of 2 atomic % or more is required. It is merely stated that it is possible to replace part of B with C. Furthermore, JP-A-59-
No. 163803 discloses an R-Fe-Co-B-C magnet, in which the B content in the magnet is set at 2 to 28 at%,
The content of C is specified to be 4 at% or less, and specific combinations of B and C are disclosed, but despite the combination of C, the content of B is required to be at least 2 at%, If the amount of B is less than %,
Similar to the above Japanese Patent Application Laid-Open No. 59-46008, iHc is 1.
It is explained that it is less than kOe. In other words, as the publication points out, C is understood to be an impurity that degrades magnetic properties. For example, C contamination from lubricants used during powder molding is unavoidable, and it is impossible to completely eliminate this. Because removal would increase costs, we propose that up to 4000G of Br, which is equivalent to a hard ferrite magnet, can have a C content of 4 atomic percent or less, and that C has a negative effect on magnetic properties. However, C is not necessarily required. Further, these publications do not suggest at all the formation of a C-containing grain boundary phase (non-magnetic phase). Furthermore, JP-A-62-13304 teaches that in order to improve oxidation resistance in R-Fe-Co-B-C magnets, it is not good to have a large amount of C; proposed to suppress C to below 0.05% by weight (approximately 0.3% in terms of atomic percentage), and furthermore, in JP-A-63-77103 published by another applicant, for the same purpose, C was suppressed to 100% by weight.
It is proposed to reduce the amount to 0 ppm or less. Thus, 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 developed a method of addition in which C is actively included in the non-magnetic phase (grain boundaries) surrounding magnetic crystal grains, rather than simply containing C as a replacement element for B. Therefore, contrary to conventional wisdom, we have found that C can greatly contribute to improving the irreversible demagnetization of magnets, and furthermore, by incorporating M together with C into the magnet, these effects can be made even more advantageous. We have found that this occurs. That is, by including C in such a non-magnetic phase, irreversible demagnetization is improved at a lower iHc than before even if the B content is within the known normal range.
In particular, it has been found that the effect becomes even more remarkable when the amount of B is less than 2 at %. In the past, it was thought that if the B content was less than 2 at %, the iHc would be 1 kOe or less, but in the present invention, even if the B content is less than 2 at %, the iHc is 4 kOe or more. Such novel effects of the present invention are brought about by the formation of a C-containing grain boundary phase surrounding each magnetic crystal grain and the inclusion of M in the C-containing grain boundary phase and the magnet. We were able to complete the invention of a new magnet that uses C as an essential component, which is completely different from conventional magnets that use C as a negative element, which causes deterioration of magnetic properties and deterioration of oxidation resistance. In this case, the C-containing grain boundary phase surrounding each of the magnetic crystal grains contains, in addition to C, at least one of the alloying elements constituting the magnet. The reason for this improvement in irreversible demagnetization is surmised as follows. It has already been mentioned that the C-containing grain boundary phase contains at least one of the alloying elements constituting the magnetic crystal grains, among which the transition metal elements Fe or Co are α-F.
It tends to lead to the formation of soft magnetic phases such as e and R (Fe, Co)2, and even a small amount of these phases will promote the generation and growth of reversed magnetic domain nuclei, leading to irreversible demagnetization deterioration. . On the other hand, it is estimated that a non-stoichiometric R-Fe-MC intermetallic compound is generated in the grain boundary phase of the permanent magnet alloy according to the present invention, which suppresses the formation of the above impurities. It is thought that This means that the grain boundary phase is a homogeneous non-magnetic phase, which is presumed to suppress the generation of reverse magnetic domain nuclei. Furthermore, M is estimated to promote atomic diffusion within the magnetic crystal grains, thereby making the crystal grains homogeneous and improving iHc, thereby improving the irreversible demagnetization rate. On the other hand, irreversible demagnetization is significantly improved even when the B content is less than 2 atomic %, but this is presumed to be due to the suppression of the B-rich phase that always exists in conventional materials. In other words, it is considered that in this case as well, the B-rich phase was the point of generation of the reversed magnetic domain. In the past, it has been reported that when B is less than 2%, α-Fe is easily generated and magnetic properties are significantly deteriorated, but in the permanent magnet alloy according to the present invention, α-Fe is easily generated due to the C-containing grain boundary phase. -The generation of Fe is suppressed, making it possible to achieve a level of properties equal to or higher than that of conventional materials. [0032] As described above, the present inventors coated individual magnetic crystal grains with a C-containing grain boundary phase and further contained M in the magnet, thereby achieving irreversible demagnetization even at a lower iHc than conventional materials. They found that the improvement effect was particularly large at high temperatures, and that the effect became even more significant as the B content was reduced, leading to the invention of a permanent magnet with good thermal stability, which had been difficult to achieve with known technology. Ta. As mentioned above, this C-containing grain boundary phase contains, in addition to C, at least one kind of alloying element constituting the magnet, and the C content is 16% by weight in the grain boundary phase composition. % (excluding 0% by weight). In other words, C in the grain boundary phase not only makes the grain boundary phase a homogeneous nonmagnetic phase, but also reduces iHc as B decreases.
Since it has the effect of suppressing a decrease in , its content is preferably 0.05 to 16% by weight, more preferably 0.1 to 16% by weight in the composition of the grain boundary phase. If the C content is less than 0.05% by weight, it is insufficient to make the grain boundary phase a homogeneous nonmagnetic phase, and iHc may be less than 4 KOe. On the other hand, if the amount of C in the grain boundary phase exceeds 16% by weight, the Br content of the magnet decreases significantly, making it difficult to put it into practical use. Regarding this grain boundary phase, it is important to uniformly cover each magnetic crystal grain, but the thickness is 0.0
Below 01μm, iHc decreases significantly, and below 30μm
If it exceeds Br, it no longer satisfies the value intended in the present invention, so it is preferably in the range of 0.001 .mu.m to 30 .mu.m, preferably in the range of 0.005 .mu.m to 15 .mu.m. Note that this thickness also includes grain boundary triple points. This thickness can be measured using a TEM (this measurement was also used in the Examples described later). On the other hand, each magnetic crystal itself surrounded by this grain boundary phase may have the same composition as the well-known R-Fe-B-(C) system permanent magnet. However, even if the amount of B is low, the magnet of the present invention can exhibit good magnetic properties. The composition of the alloy magnet of the present invention (total composition including magnetic crystal grains and grain boundary phase) is preferably R: 10 to 30 in atomic percentage.
%, B: 7% or less, preferably less than 2% (not including 0 at. Below the largest value of M among the elements (excluding 0 atomic %), C: 0.1 to 20%, the remainder consisting of Fe and impurities unavoidable in manufacturing. Content of M element (0
(excluding atomic %) is Ba: 5% or less, Sr: 5% or less, Ca: 7% or less, Li: 4% or less, Mg: 6% or less,
Be: 4% or less. In the present invention, the total C content in the magnet is preferably 0.1 to 20 atomic %. When the total C content in the magnet exceeds 20 at%, the Br decreases significantly, and Br≧4KG, which is the purpose of the present invention as an isotropic sintered magnet.
In addition, the value of Br≧7KG as an anisotropic sintered magnet is no longer satisfied. On the other hand, if it is less than 0.1 atomic %, it becomes difficult to improve irreversible demagnetization. In this way, the total C content in the magnet is preferably 0.1 to 20 at%.
However, as mentioned above, C in the grain boundary phase not only improves irreversible demagnetization but also has the effect of suppressing the decrease in iHc due to the decrease in B, so its content is determined by the composition of the grain boundary phase. 16% by weight or less (not including 0% by weight), preferably 0.05 to 16% by weight, more preferably 0.1 to 16% by weight
16% by weight is required. Raw materials for C include carbon black, high purity carbon, Nd-C, Fe-C
Alloys such as the following can be used. [0037] R is Y, La, Ce, Nd, Pr, S
One or more of m, Tb, Dy, Gd, Ho, Er, Tm, and Yb are used. Note that a mixture of two or more types of mischmetal, didyme, etc. 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. [0038] As B, pure boron or ferroboron can be used, and even if its content is within the known range of 2 atomic % or more, irreversible demagnetization is improved compared to conventional materials.
For example, the object of the present invention can be achieved even if B is contained up to about 7%, but as mentioned above, B is preferably less than 2 atomic %, more preferably 1.8 atomic % or less. effective. On the other hand, without B addition, iHc
is extremely reduced, making it impossible to achieve the object of the present invention. Ferroboron containing impurities such as Al and Si can also be used. M is Ba, Sr, Ca, Li, Mg, Be
One or more of these may be used. M in the magnet is 0
Although the irreversible demagnetization rate is improved compared to conventional products even at atomic%,
By containing M in the predetermined amount, the improvement can be more effectively achieved. On the other hand, when the M content exceeds the predetermined content, the decrease in Br and iHc becomes significant.
The characteristics of the magnet of the present invention are no longer satisfied. As mentioned above, the permanent magnet alloy of the present invention has a thickness of 0.001 to 30 μm, preferably 0.001 to 30 μm.
Each magnetic crystal grain is covered with a C-containing grain boundary phase in the range of 15 μm, but the grain size of the magnetic crystal grain is 0.
．． It is in the range of 3 to 150 μm, preferably 0.5 to 50 μm. When the grain size of magnetic crystal grains is less than 0.3 μm, i
When Hc is less than 4 KOe and exceeds 150 μm, iHc decreases significantly and the characteristics of the magnet of the present invention are impaired. Note that the grain size of the crystal grains can be accurately measured using SEM, and the composition analysis can be performed accurately using EPMA (these measurements were also performed in the examples described later). [0041] In order to manufacture the permanent magnet of the present invention, when the permanent magnet alloy is a sintered body, melting, casting, crushing, shaping, sintering, or melting, casting, crushing, shaping, sintering, Although it can be produced by a conventional method consisting of a series of heat treatment steps, it is preferable to introduce a step of heat treating the cast alloy after casting in the above manufacturing process, or to add a part of the C raw material during or after crushing. Alternatively, it can be advantageously produced by introducing a step of secondary addition of the entire amount, or by introducing a combination of these two steps. On the other hand, if the permanent magnet alloy is a cast alloy, by using a hot plastic working method,
A favorable permanent magnet alloy of the present invention that exhibits the above-mentioned effects can be produced. Although the permanent magnet alloy of the present invention has excellent thermal stability, it also has dramatically improved oxidation resistance compared to conventional materials. Even if the outermost surface of the magnet is not coated with an oxidation-resistant protective coating, the magnet itself has extremely excellent oxidation resistance, so the formation of the protective coating may be unnecessary in some cases. The alloy powder prepared from the permanent magnet alloy according to the present invention can provide a bonded magnet with better thermal stability and oxidation resistance than conventional materials. [0043] As described above, the permanent magnet alloy according to the present invention is
It has significantly superior thermal stability and oxidation resistance compared to conventional products, and also has good magnetic properties, making it suitable for use in a variety of magnet-applied products. Examples of magnet application products include the following products. DC brushless motor,
Various motors such as servo motors; various actuators such as drive actuators and F/T actuators for optical pickup; various audio equipment such as speakers, headphones, and earphones; various sensors such as rotation sensors and magnetic sensors; electromagnet substitutes for MRI, etc. Products: Various relays such as reed relays and polarized relays; Various magnetic couplings such as brakes and clutches; Buzzers,
Various vibration oscillators such as chimes; various adsorption devices such as magnetic separators and magnetic chucks; various opening/closing control devices such as electromagnetic switches, microswitches, and rodless air cylinders; various microwave devices such as optical isolators, klystrons, and magnetrons. ; magnetic generator; health equipment, toys, etc. Note that such magnet-applied products are merely examples, and the present invention is not limited to these. [0044] Furthermore, the permanent magnet alloy according to the present invention has excellent thermal stability and is resistant to rust, and even when used at high environmental temperatures, there is less deterioration in properties than conventional materials, and it does not deteriorate like conventional materials. Since the magnet itself has excellent oxidation resistance while maintaining high magnetic properties without forming an oxidation-resistant protective coating on the outermost exposed surface of the magnet, no protective coating is required. In addition, even if a protective coating is required for use in a special environment, there is no rust from inside the magnet, so the adhesion when forming the protective coating is good, and there is no problem with peeling of the coating or thinning of the coating. This solves problems such as dimensional accuracy due to fluctuations in . From this point of view as well, it is possible to provide a permanent magnet that is optimal for applications that require thermal stability and oxidation resistance. 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, ferroboron alloy with a boron content of 19.32%, calcium (Ca) with a purity of 99% as the additive metal M, and further with a purity of 98% as the R element. 5% neodymium metal (contains other rare earth elements as impurities) is used, and the composition ratio (atomic ratio) is 18Nd-72Fe-1B-
The materials were weighed and mixed to give 2Ca, melted in a high-frequency induction furnace in a vacuum, and then cast into a water-cooled copper mold to obtain an alloy ingot. The alloy ingot thus obtained was crushed with a jaw crusher and then coarsely crushed to -100 mesh using a stamp mill in argon gas, and the composition ratio (atomic ratio) was 18Nd-72Fe-1B-7C-2Ca. Further, carbon black with a purity of 99.5% was added to the coarsely ground powder, and then it was ground to an average particle size of 5 μm using a vibration mill. The alloy powder thus obtained was compacted under a pressure of 1 ton/cm2 in a magnetic field of 10 KOe, held at 1120°C for 1 hour in argon gas, and then rapidly cooled to obtain a sintered body. As Comparative Example 1, a sintered body was obtained in the same manner as in Example 1, except that calcium as a raw material was omitted and the composition ratio was 18Nd-74Fe-1B-7C. In addition, as Comparative Example 2, the raw materials were the same as in Example 1 except for carbon black, and the composition ratio was 18Nd-74Fe-6B.
-2Ca, melted in the same manner as in Example 1 (however, without adding carbon black), coarsely crushed, finely crushed, magnetically formed, then sintered and rapidly cooled to obtain a sintered body. Ta. The irreversible demagnetization rate of the sintered body thus obtained was measured using a flux meter according to the following procedure. (1) After magnetizing the above sintered sample whose shape has been adjusted so that the permeance coefficient (Pc) is 3 at 50 KOe, the flux is measured at room temperature (25°C). Let the flux value at this time be A0. (2) Next, heat-treat the sample at 160°C for 120 minutes, cool it to room temperature, and measure the flux again. Let the flux value at this time be At. (3) Calculate the value of irreversible demagnetization rate using the following formula. Table 1 shows the evaluation of the irreversible demagnetization rate of the sintered body based on the above measurement method.
It was shown to. In Table 1, "Ratio 1" is an abbreviation for Comparative Example 1 (the same applies hereinafter). As is clear from Table 1, the irreversible demagnetization rate of the sintered body of Example 1 was -9.3%, while that of Comparative Example 1 was -17.9%, which is the same as that of the present invention. This is inferior to Example 1. Furthermore, the sintered body of Example 1 according to the present invention (a sintered body in which each magnetic crystal grain is coated with a C-containing grain boundary phase) is different from the sintered body of Comparative Example 2 (a sintered body having no C-containing grain boundary phase). body)
Coercive force (iHc) at room temperature (25℃) compared to
Despite the 0.6 KOe lower irreversible demagnetization rate, the irreversible demagnetization rate was -9.3, which was smaller than -27.2% in Comparative Example 2 (sintered body without C-containing grain boundary phase). There is. Further, the C content in the grain boundary phase of the sintered body of Example 1 was measured using EPMA and was found to be 4.1% by weight. Furthermore, the grain size of the magnetic crystal grains is determined by the SE of the sintered structure.
When 100 pieces were measured through observation by M, the range was 0.8 to 32 μm. On the other hand, the thickness of the grain boundary phase measured by TEM was 0.013 to 5.2 μm. These values are shown in Table 1. In addition, Br, iHc measured using VSM as magnetic properties at room temperature (25°C)
The values of and (BH)max are also shown in Table 1. in this way,
It is clear that the permanent magnet alloy according to the present invention has better thermal stability than those of Comparative Examples 1 and 2. [0050] As an evaluation of the oxidation resistance (weather resistance test) of the above-mentioned sintered body, the Br,
When the reduction rate of iHc was measured, Br: -1.0
5%, iHc: -0.91, which is extremely small, and almost no rust was observed upon external observation, indicating that the oxidation resistance was significantly improved. On the other hand, in the case of the sintered compact of Comparative Example 2, the reduction rate after only one month (720 hours) was -8.7% for Br and -3.8% for iHc, and if left for longer than this, the original shape would be lost. It was so rusted that it was impossible to measure it. Thus, it can be seen that the permanent magnet alloy according to the present invention is also superior in oxidation resistance compared to that of Comparative Example 2. [Examples 2 to 5] A sintered body was produced in the same manner as in Example 1, except that carbon black was added during pulverization so that the amount of carbon became the composition ratio shown in Table 1. Obtained. Furthermore,
As Comparative Example 3, 18Nd-79Fe-1B-2Ca
After weighing and blending so that In addition, as comparative examples 4 to 7,
A sintered body was obtained by performing the same operations as in the above example, except that calcium was removed from the raw material and the amount of carbon was adjusted to the composition shown in Table 1. The irreversible demagnetization rate at 160°C, the amount of C in the grain boundary phase, the magnetic crystal grain size, the thickness of the grain boundary phase, and the magnetic properties of the sintered body thus obtained were evaluated using the same method as in Example 1. The results are shown in Table 1. As is clear from Table 1, the irreversible demagnetization rate of the sintered bodies according to the present invention to which calcium is added is lower than that of Comparative Examples 4 to 7 in which no calcium is added. In addition, in Comparative Example 3, C was not contained in the grain boundary phase, and the magnetic properties were low values. [Table 1] [Examples 6 to 10] All procedures were carried out except that when melting the raw materials, the amounts of boron (B) and barium (Ba) were measured and mixed so that the amounts of boron (B) and barium (Ba) were as shown in Table 2. The same operation as in Example 1 was performed to obtain sintered bodies of Examples 6 to 10. Further, as Comparative Examples 8 to 11, sintered bodies were obtained by omitting the raw material barium, measuring and blending the boron contents so that the compositions were as shown in Table 2, and performing the same operations. In Comparative Example 12, the amount of boron (B) was 0 at%.
This is an example in which a sintered body was obtained by performing the same operations as in the above example except that boron was not blended. [0054] The temperature of the sintered body thus obtained is 160°C.
The irreversible demagnetization rate, C content in the grain boundary phase, magnetic crystal grain size, thickness of the magnetic field phase, and magnetic properties were evaluated using the same method as in Example 1, and the results are shown in Table 2. As is clear from Table 2, the sintered bodies of Examples 6 to 10 to which barium was added had a smaller irreversible demagnetization rate than the corresponding Comparative Examples 8 to 11, which did not contain barium. I understand. Furthermore, in Example 8 where the B content is less than 2 atomic %, the irreversible demagnetization rate is smaller even though the iHc is 0.3 KOe lower than in Example 9 where the B content is 2 atomic % or more. . Furthermore, the same can be said about Example 10, in which the B content is 2 atomic % or more, when compared with Example 4, and in Example 4, in which the B content is less than 2 atomic %, iHc is 0.4 KOe lower. Regardless, the irreversible demagnetization rate is smaller than that of Example 10, and especially when the B content is less than 2 at%, the irreversible demagnetization rate is smaller than when B≧2 at%. In addition, in Comparative Example 12 without boron addition (B
H) max was 0. [Table 2] [Examples 11 to 19] As raw materials, electrolytic iron with a purity of 99.9%, feroboron alloy with a boron content of 19.32%, carbon black with a purity of 99.5%, Table Using the various additive metals M and rare earth elements shown in Table 3, they were weighed and mixed to give the composition ratio shown in Table 3, melted in a high-frequency induction furnace in a vacuum, and then cast into a water-cooled copper mold to form an alloy ingot. I got it. The alloy ingot thus obtained was heated to 680°C for 1
After heating for 5 hours, it was allowed to cool inside the furnace. Next, after crushing the alloy ingot with a jaw crusher,
-100mes using a stamp mill in argon gas
The particles were coarsely crushed to a particle diameter of 5 μm, and then crushed to an average particle size of 5 μm using a vibration mill. The alloy powder thus obtained was subjected to the same operation as in Example 1, and Examples 11 to 19 were obtained.
A sintered body was obtained. Further, as Comparative Examples 13 to 21, sintered bodies were obtained by carrying out the same operations as in the above Examples, except that the M metal as a raw material was excluded and the compositions were measured and blended so as to have the compositions shown in Table 3. [0058] The temperature of the sintered body thus obtained is 160°C.
The irreversible demagnetization rate, the amount of C in the grain boundary phase, the magnetic crystal grain size, the thickness of the grain boundary phase, and the magnetic properties were evaluated using the same method as in Example 1, and the results are shown in Table 3. As is clear from Table 3, Example 11 in which the additive element (M) was added
The sintered bodies of ~19 are Comparative Examples 13~21 without M element addition.
It can be seen that the irreversible demagnetization rate is smaller than that of [Table 3] [Example 20] The same operations as in Example 1 were carried out except that the fine alloy powder having the same composition as in Example 1 was molded in the absence of a magnetic field. A sintered body with the same composition was obtained. As Comparative Example 22, a sintered body having the same composition as Comparative Example 1 was obtained by performing the same operation as Comparative Example 1 except that the alloy fine powder was molded in the absence of a magnetic field. The irreversible demagnetization rate at 160℃ of the sintered body thus obtained, the amount of C in the grain boundary phase, the magnetic crystal grain size,
The thickness of the grain boundary phase and magnetic properties were evaluated using the same method as in Example 1, and the results are shown in Table 4. As is clear from Table 4, the irreversible demagnetization rate of the sintered body to which calcium is added is smaller than that of Comparative Example 22, which does not contain calcium. [Table 4]

Claims (5)

[Claims] [Claim 1] R-Fe-M-B-C alloy magnet (
However, R is Nd, Pr, Ce, La, Y, Sm, Tb
, Dy, Gd, Ho, Er, Tm, Yb, M is Ba, Sr, Ca, Li, Mg,
At least one type selected from Be), each of the magnetic crystal grains of the alloy is covered with a grain boundary phase containing 16% by weight or less (excluding 0% by weight) of C. Permanent magnetic alloy with excellent thermal stability and low demagnetization. [Claim 2] The magnetic crystal grains have a grain size of 0.3 to 150
The thickness of the grain boundary phase is in the range of 0.001 to 30 μm.
Permanent magnet alloy according to claim 1, in the μm range. [Claim 3] 0.05 to 16% by weight of the grain boundary phase is
The permanent magnet alloy according to claim 1 or 2, which is C. 4. The composition of the magnetic alloy (total composition including magnetic crystal grains and grain boundary phase) is R: 10 to 10 in atomic percentage.
30%, B: 7% or less (not including 0 atom%), C: 0
．． 1 to 20%, M: At least one or more of the elements M in the specified percentage below (however, if two or more types are included, the total amount of M is less than or equal to the value of the largest M among the elements), the remainder is Fe and unavoidable in manufacturing. The permanent magnet alloy according to claim 1, 2 or 3, comprising impurities, the content of element M (however, 0 atomic %
) is Ba: 5% or less, Sr: 5% or less, Ca
: 7% or less, Li: 4% or less, Mg: 6% or less, Be:
It is less than 4%. 5. The permanent magnet alloy according to claim 4, wherein B is less than 2% (not including 0 atomic %).