JPH02119105A - Nd-fe-b system sintered magnet - Google Patents

Abstract

PURPOSE:To improve intrinsic coercive force at a room temperature by using elements wherein Dy is excluded and supply amount is large by dispersing V-T-B compound secondary phase. CONSTITUTION:In an Nd-Fe-B system sintered magnet, the temperature coefficient of intrinsic coercive force (iHc) is 0.5%/ deg.C or more. The composition is as follows; R=11-18at% (where R is a rare earth elements except Dy, and 80at% <=(Nd+Pr)/R <=100at%), B=6-12at%, V=2-6at%, residual part Fe, Co (Co is equal to or less than 25at% of the sum of Fe and Co (0% is contained)) and impurity. This V-T-B compound secondary phase (when Fe or Co is contained, T is Fe and Co) is dispersed, and has the maximum energy product larger than or equal to 20 MGOe and the intrinsic coercive force (iHc) larger than or equal to 15 kOe.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a permanent magnet, and more specifically, to a NdFeB-based sintered magnet.

Nd-Fe-B magnets include ultra-quenched magnets and sintered magnets. Ultra-quenched magnets are inherently magnetically isotropic. As a method of making the anisotropy, it has been proposed to create a powder by crushing the thin ribbon obtained by ultra-quenching, hot-pressing this, and then die-setting, but the manufacturing process is complicated and it is not suitable for industrial use. Actually, it has not been done yet.

The Nd-Fe-B sintered magnet was developed by the present inventors and has a maximum energy product (BH) of 50 MGOe on a laboratory scale and 40 MGOe on a mass production scale.
It exhibits excellent magnetic properties reaching Q 6, and the raw material cost is low because the main components are inexpensive elements such as Fe and B, and the rare earth elements are Nd (neodymium) and Pr (praseodymium), which are produced in large quantities. It has excellent features such as being much cheaper than rare earth cobalt magnets. Representative patents for this NdFeB-based sintered magnet include JP-A-59-89401, 59-46008, and 59-2.
No. 17003, US Pat. No. 4,597,938 and European Patent No. EP-Person-0101552, EP-^-0106
There is No. 948, and academic literature includes M, Sagawa et.
al'NewMaterial for per
manent magnets on a b
ase ofNd and Fe(iIlvit
ed), 'J, ppl, Phys,, 55
．． N.

6, Part If, p2083/2087 (Ma
Rch, 1984), and a textbook that explains the development history and social evaluation of Nd-Fe-B sintered magnets from the foreground technology of boat fishing is ``New Developments in Magnet Materials'' - Nouresho; Edited by Akira Higuchi, Kogyo Kenkyukai, published March 1, 1988 (see especially pages 121-140 and 230-239).

After magnetization, permanent magnets are exposed to reverse magnetic fields caused by various causes.
A permanent magnet must have a large coercive force so that irreversible demagnetization does not occur even when exposed to a strong reverse magnetic field.

Recently, as devices have become smaller and more efficient, the reverse magnetic field applied to permanent magnets has become increasingly large. For example, a motor is exposed to a strong self-demagnetizing field after magnetizing the permanent magnet and before attaching the yoke, and in the operating state after assembly, it is exposed to a demagnetizing field corresponding to the permeance of the magnetic circuit and a reverse magnetic field from the coil. The reverse magnetic field from the coil is at its maximum at the start. When the switch is turned on immediately after the motor stops due to an excessive load and the motor restarts, the permanent magnet is! ! t also places a severe burden on it. In order to withstand this and to minimize irreversible demagnetizing fields, permanent magnets must have as large a coercive force as possible.

Recent advances in equipment require permanent magnets to bear harsher loads that were unimaginable in the past. In a device called an undulator, which is attached to an accelerator and extracts strong synchrotron radiation, fully magnetized permanent magnet plates are glued together so that the N poles face each other and the S poles face each other in order to obtain a strong magnetic field. A structure has also been proposed. For such uses,
Of course, a permanent magnet with a large coercive force is required. This type of permanent magnet is likely to be used more and more in the future.

Coercive force is also related to the stability of a permanent magnet. If a permanent magnet is left unattended after being magnetized, it gradually undergoes irreversible demagnetization.9 This is called aging. In order to reduce aging, the coercive force should be as large as possible than the reverse magnetic field in use.

In this way, permanent magnets are required to have an increasingly large coercive force.

In addition, when a permanent magnet is exposed to high temperatures, its temperature characteristics become important because the coercive force decreases at high temperatures.

The temperature coefficient of coercive force, which affects the temperature characteristics of coercive force, is 0°3 to 0.4%/℃ for ultra-quenched ribbon magnets, slightly higher than this for anisotropic ultra-quenched magnets, and is slightly higher than this for ultra-quenched anisotropic magnets. Then 0.
It is 5%/°C or more.

The temperature coefficient of the coercive force of a sintered magnet changes depending on the measurement temperature range, and becomes larger at low temperatures. The temperature coefficient (β) of coercive force in the description of this application is determined by the following formula.

△iHc: Difference in intrinsic coercive force (i Hc) at temperature change from 20°C to 120°C (KOe) iHc: Intrinsic coercive force at 20°C (KOe) ΔT: Temperature difference (100°C) Intrinsic coercive force from 20 to 120°C The temperature coefficient of magnetic force (iHc) was measured in the temperature range of 100°C.

Since the temperature coefficient of the intrinsic coercive force (iHc) of the Nd-Fe-B sintered magnet is extremely high at 0.5%/° C. or more, the intrinsic coercive force (iHc) becomes low at high temperatures, making it unusable. Specifically, when permeance coefficient = 1, Nd-Fe-B
The usage limit of the system sintered magnet is about 80°C. For this reason, the coercive force (iH
The temperature coefficient of c) was extremely large, at 0.51%/°C or more, regardless of the composition, so it could not be used at high temperatures.

(Problems to be Solved by the Invention) Various efforts have been made to increase the coercive force of Nd-Fe-B sintered magnets. Standard composition Nd+qFet
At tBll, the intrinsic coercive force (iHc) of the sintered magnet is approximately 6k.
It becomes Oe. Considering that the residual magnetization Br of this magnet exceeds 12 kG, the intrinsic coercive force (iHc) = 6 kOe
is too low and its application is limited to a very narrow range. One of the most successful methods for increasing coercive force is Nd+sFetd
This is a method in which a 3g sintered magnet is heat treated at 600℃ after sintering, and the intrinsic coercive force (iHc) has increased to 12kOe (
M, Sagawa ct at, J, ^pp1. P
h7s, vol, 55°No, 6.15. Mar
ch 1984), this was a great achievement, but in practice a larger coercive force is required.

Meanwhile, methods of increasing coercive force using additive elements were also explored, and most elements from the periodic table were tested. The most successful of these was the addition of heavy rare earth elements such as Dy.For example, N d +sF e ? 7Bs 10% of Nd [)
N d substituted with y 13. %D3's, sF
, for 77Bs, intrinsic coercive force (iHc) ≧1'7kOe
reach. Due to the discovery of the effect of increasing coercive force by adding Dy, Nd-Fe-B sintered magnets are now being used in a wide range of applications.

Various additive elements other than heavy rare earths have also been tried.

For example, JP-A-59-218704 and JP-A-59-
217305, V, Nb, Ta, Mo.

Although W, Cr, and Co were added and various heat treatments were devised, the obtained intrinsic coercive force (iHc) was low and far inferior to the effect of Dy. AQ has the effect of improving the coercive force, although it is not in the same order as Dy and Pr, but it has the disadvantage that the Curie temperature drops rapidly. Although Dy provides excellent coercive force characteristics, the amount of Dy present in the ore is 1/20 that of Sm.
It's only a matter of time, but it's extremely small. Therefore, Dy-doped NdF
If e-B sintered magnets are produced in large quantities, Dy will be used in excess of the balance of each component in the rare earth resources, which will upset the balance of rare earth resources and there is a risk that the supply of Dy will quickly become tight. There is.

Tb and HO, which are heavy rare earths like Dy, have the same effect as Dy, but Tb is much rarer than lay.
It also has many other uses, such as magneto-optical recording materials. HO has a much smaller effect of increasing the intrinsic coercive force (iHc) than ray, and is also scarcer in terms of resources than Dy, so both Tb and Ho lack practicality.

The material to which about 1.5% of [)y is added has an intrinsic coercive force (iHc) of 17 kOe or more at room temperature, and an intrinsic coercive force (iHc) of about 5 kOe at 120 to 140°C. Although the temperature coefficient of the intrinsic coercive force (iHc) is not improved by the addition of Dy, it is sufficient that the intrinsic coercive force (iHc) sufficient to overcome the reverse magnetic field can be obtained even at high temperatures. The residual magnetization Br of many rare earth magnets is about 10 kG. Therefore, under the magnet usage conditions with permeance coefficient B/H≧1, i Hc≧5
Design a magnetic circuit with the goal of kOe.

The adoption of this Dy addition method for Nd-FeB sintered magnets for AC motors is being considered (R, E, T
ompkios and T, W, Neuma ■.

General Electric Technica
l Information Series, C1as
s I Report No, 84crd312°N
1984). When Nd-Fe-B sintered magnets are used in automotive starter motors, generators, and even the highest output motors, their magnetic properties must be stable in extremely harsh environments of 180 to 200°C. Become. In this case, the amount of Dy added is as large as 4 at% or more, so Nd-Fe-B sintered magnets cannot be used for high-temperature applications such as high-output motors and automobiles due to the supply of Dy resources. Na.

Therefore, one object of the present invention is to provide a Nd-Fe-B based sintered magnet that uses an element other than Dy that is supplied in large quantities to increase the intrinsic coercive force (iHc) at room temperature. do.

When used in automobile starter motors, generators, and -m high-output motors, the magnetic properties must be stable in extremely harsh environments of 180 to 200°C. In this case, the amount of Dy added is as large as 4 at % or more, so the Nd-Fe-B sintered magnet could not be used industrially from the viewpoint of supplying Dy resources. In other words, N with a temperature coefficient of intrinsic coercive force (iHc) of 0.5%/°C or more
The d-Fe-B sintered magnet has a high intrinsic coercive force (iHc) at high temperatures.
is significantly reduced, and the present invention is intended to increase its absolute value.

Furthermore, a second object of the present invention is to provide a Nd-Fe-B based sintered magnet that can increase the intrinsic coercive force (iHc) even if the amount of Dy used is reduced.

(Means for Solving the Problems) In the course of research to solve the above problems, the inventors discovered that Nd
-Constitution NWA and intrinsic coercive force of Fe-B sintered magnet (
We examined previous research on the causes of iHc). Nd-
In Fe-B based sintered magnets, the R2Fet, tB compound phase (however, R is a rare earth element such as Nd) is the matrix phase (main phase), and this phase has strong magnetic anisotropy. Therefore, it is certain that excellent magnetic properties can be obtained. In addition, in the Nd-Fe-B sintered magnet with the standard composition, in addition to the above matrix phase, a second phase of R-85 to
There is also a phase called the Nd-rich phase, which has a composition of 97 at% and the balance is Fe (however, if the sintered body contains rare earths other than Nd, they are also included). It is also certain that it plays an important role in increasing magnetic force.

Standard Nd Fe B magnets, e.g. Nd, %F
It is known that in e77Bs, in addition to these two phases, an Nd+Fe4B4 compound phase called a B-rich phase is generated. This phase does not contribute much to improving coercive force.

The above-mentioned Dy (Tb, Ho as well) increases the magnetic anisotropy of the R2Fe+aB compound phase, thereby increasing the intrinsic coercive force (i I-1c ) compared to the case without Dy, improving stability at high temperatures. The inventor studied the above-mentioned conventional knowledge and determined that R2F e 14
Depending on the method of strengthening the anisotropy of the B compound phase, in addition to using a large amount of Dy that exceeds the resource balance, N d
Since there is no way to increase the intrinsic coercive force (iHc) of a -F e -B based sintered magnet and it is not possible to increase the high temperature stability, we believe that this is not a fundamental solution.

As a result of further investigation, the present inventor found that a specific composition of
In d-Fe-B sintered magnets, Nd-rich phases such as the NdsFe4Ba phase, which do not play a very important role, are suppressed to a minimum amount, and the presence of Nd-rich phases, which have not been known to exist in addition to Nd-rich phases, is suppressed to the minimum amount. A V-Fe-B compound phase is formed, which is not
The present invention was completed based on the discovery that the absolute value of iHc) was increased and the high temperature stability was improved.

That is, the NdFe-B sintered magnet that achieves the first object of the present invention has R=11 to 18 at% (however, rare earth elements excluding R11Dy, 80 at%≦(Nd+Pr)/R≦1
00at%), B=6-12a7%, V=2-6
at%, T! It has a composition consisting of 1 part Fe, Co (however, Co is 25 at% or less (including 0%) of the total of Fe and Co) and impurities, and has a V-T-B compound secondary phase (however, T
is Fe, or if Co is contained, Fe and co. ) are dispersed and have a maximum energy product of 20 MGOe or more and an intrinsic coercive force (iHC) of 15 kOe or more.

The N d -FeB-based sintered magnet that achieves the second objective of the present invention has R=11 to 18 at% (where R is a rare earth element, R+=Nd+Pr, R2=D3/, 80 at%≦(
R, +R2)/R≦100at%), 0×R254%,
B = 6 to 12 at%, V = 2 to 6 at%, balance Fe, C
o (However, Co is less than 25 at% of the total of Fe and Co (
0%)) and impurities, and V-
The T-B compound secondary phase is dispersed, and 20 M G O
Maximum energy product greater than e and 15+3x, (where x is D
Intrinsic coercive force (iHc) of 21 kOe or more when y content (at%), 15+3x is 21 kOe or more
It is characterized by having the following.

Hereinafter, the configuration of the present invention will be explained in detail.

V-F in the structure constituting the sintered body within the above-mentioned content ranges of Nd, Pr, (Dy), B, Fe, and ■.
An e-B compound phase is formed. - On the other hand, outside these content ranges, R2Fe14B compound phase,
The Nd-rich phase and the B-rich phase are the constituent phases, and the V-T
-B compound phase is not produced, or even if it is produced, the amount is very small, or N d impairs the properties of the magnet.
2F e 17 phases are generated.

The V-Fe-B compound phase of the used sample of N011 in Table 2 below was measured by EPMA″r and found to be V29.5 at%,
It had a composition of 24.5 at% Fe, 46 at% B, and an amount of NdR. Further, when the VFe-B compound phase was measured by electron beam diffraction, it was found that the unit cell was a square structure with lattice constants a=5.6 and c=3.1.

Figure 2 shows an electron diffraction photograph used to analyze the crystal structure. The structure of this crystal was compared with the structures of known compounds in order to identify it, but at present it is most likely to be tetragonal V3B2, and it is estimated that some of the V in this phase is replaced with Fe. be done. Elements other than those listed above can be dissolved in solid solution in this phase, and depending on the composition of the sintered body, added elements, and impurities, various elements with similar properties to ① may replace V, or elements with properties similar to B may be substituted for V. Similar C etc. can make B 1m. Even in such a case, a phase (probably, (V ,-.

As long as Fe1113B2 phase) is generated in the sintered body, a good intrinsic coercive force (iHc) can be obtained. Intrinsic coercive force (
In Nd-Fe-B sintered magnets with particularly good iHc),
As shown in the EPMA image in Figure 1, the ■-F e-B compound phase is dispersed at the grain boundaries and triple junctions of the R2F c and 4B compound main phase crystal grains, and the high-resolution electronic image shows that When observed with a mirror, as shown in Figure 3, a very fine V-
It was found that the Fe-B compound phase was mainly dispersed at the grain boundaries and also partially within the grains. The characteristics of the NdFeB-based sintered magnet are better when the V-Fe-B compound phase is mainly dispersed at the grain boundaries than when it is mainly dispersed within the grains. It is desirable that almost all of the R2F e t4B crystal grains be in contact with several or more V-FeB compound phase particles at their grain boundaries.

Intrinsic coercive force (
In order to achieve the iHc) improvement effect, it is necessary to mix the raw material powders with special care to achieve uniform mixing in the conventional sintered magnet manufacturing process in which two or more types of fine powders are mixed. Even in the manufacturing method where a powder with a predetermined composition is obtained by grinding one type of intent, homogenization mixing is required to sufficiently uniformly disperse the separated powders of each phase after grinding with a jet mill. process is required. The goal for uniform mixing is 30 minutes or more with a rocking mixer.

Furthermore, when heat treatment is performed at 600 to 800°C after sintering, changes are observed in the structure of grain boundaries, and the intrinsic coercive force (iHc
) is increased by 7 to 11 kOe at room temperature and 2 to 5 kOe at 140°C.

The present invention has a temperature coefficient of intrinsic coercive force (iHc) of 0.5%/
In a Nd-Fe-B based sintered magnet having a temperature of .degree. C. or higher, it is possible to obtain a sufficient intrinsic coercive force (i Hc ) for use in various devices at high temperatures despite a significant decrease in coercive force.

The intrinsic coercive force (iHc) is 15k in the permanent magnet of claim 1.
It becomes Oe or more. In the permanent magnet (Dy added) according to claim 2, the intrinsic coercive force (iHc) is increased by 3 kOe when Dy is contained in lat%, so the intrinsic coercive force (iHc) is
iHc)≧15+3x (where x is Dy content (at%
)) becomes.

However, the maximum applied magnetic field of the electromagnet used to measure the demagnetization curve in the experiments leading to the completion of the present invention was equivalent to 21 kOe, so if the intrinsic coercive force exceeds 21 kOe, the actual value cannot be measured. Met. Therefore, the intrinsic coercive force (i
Hc) is 21kOe or more as calculated by the above formula, the intrinsic coercive force (iHc> of the permanent magnet of the present invention is 21kOe or more).
Must be Oe or higher.

When AI2 is further added to the Nd-Fe-B based sintered magnet of Nd, Pr, (Dy)Fe and B based composition of the present invention, the intrinsic coercive force (iHc) is increased. This is presumed to be because a trace amount of Aρ promotes fine dispersion of the V-T-B compound phase.

One rule of thumb for using Nd-Fe-B sintered magnets in high-temperature applications is that the intrinsic coercive force (iHc) ≥ 5 kOe.
Is required. Now consider that the temperature coefficient of the magnet increases up to 140°C. For applications such as motors,
For example, if the temperature coefficient of the intrinsic coercive force (iHc) is 0.5%/°C, the intrinsic coercive force (iHc) at room temperature must be 12.5 kOe or higher. There is. This value of intrinsic coercive force (iHc) is satisfied within the composition range of claim 1 of the present invention. For example, if the temperature coefficient of the intrinsic coercive force (iHc) is 0.6%/°C, the intrinsic coercive force (iHc) at room temperature is 17.8 kOe.
It needs to be more than that. The value of this intrinsic coercive force (iHc) is within the composition range of claim 1 of the present invention, excluding the upper and lower limits, and is satisfied by a composition in which aluminum is added. If the temperature coefficient of the intrinsic coercive force (iHc) is 0.7%/℃ or higher, the composition with Dy added will increase the intrinsic coercive force (iHc) to 5 kOe or higher at 140℃.
can be obtained. The reason for limiting the composition of each element is, in addition to the above-mentioned reasons, that if it is less than the lower limit, the intrinsic coercive force (iHc) will be low, while if it exceeds the upper limit, the residual magnetization will be reduced. Regarding Aρ, if it exceeds 3 at %, the Curie temperature becomes 300° C. or less, and adverse effects such as an increase in temperature change in residual magnetization become significant. (2) The increase in intrinsic coercive force (iHc) caused by addition only slightly lowers the Curie temperature. Furthermore, if the amount of V is too large, not only the residual magnetization but also the intrinsic coercive force (iHc) will decrease, leading to a decrease in stability at high temperatures. This is because if the amount of V is too large, an organic Nd2Fer7 phase will be generated. In this application, the rare earth elements (R) are mainly Nd and P.
r is used in Nd2Fe+aB et al. P r 2
This is because it has both a larger saturation magnetization and a larger uniaxial magnetocrystalline anisotropy than R2Fe+4B made by other clays such as F614B.

(Nd+Pr)/R≧80at% was set for Nd, P
This is to obtain high saturation magnetization and high coercive force by increasing the content of r (other than Dy). Also, D3'(1
The reason why the content of (2 kOe/% increase in 1llc at 40°C) is 4 at% or less is because R2 = D y is a rare resource, and because if it exceeds 4 at%, the residual magnetization decreases significantly. be.

In addition, rare earth raw materials include not only highly purified raw materials, but also didymium with unseparated layers of Nd and Pr, and even Ce.
It is possible to use a mixed raw material such as Cc didymium, which remains in an unseparated layer.

When part of Fe is replaced with Co, the Curie temperature increases and the temperature coefficient of residual magnetization Br is improved. On the other hand, Co
If the amount exceeds 25 at% of the total amount of Fe and Co, the intrinsic coercive force (iHc) decreases due to the appearance of a secondary phase, which will be described later. Therefore, the upper limit of the substitution amount is set to 25 at%. In the permanent magnet of the present invention containing Co, the N d 2F e +tB compound is converted into the Ndz(FeCo) + 4B compound, and the V-F
e-B compound changes to V-(FeCo)-B compound,
In addition, two new (Co--Fe)--Nd phases appear as secondary phases. The (Co/Fe)-Nd phase has an intrinsic coercive force (iH
c) decrease.

The present inventor added various elements to the above-mentioned Nd-Fe-B based sintered magnet and investigated the effect of this on the intrinsic coercive force (iHc). As a result, it was found that by adding the following elements, the intrinsic coercive force (iHc) was improved or not improved at all, but did not decrease.

Like V, Ml increases the intrinsic coercive force (iHc).

M2. Ml has a small effect on improving magnetic properties, but these elements may be mixed in during the refining process with rare earth elements and Fe, or during the manufacturing process of Fe-B, so M2. It is advantageous that the addition of Ml is tolerable.

M1=0 to 4 at% (However, M is Cr, M.

(one or more types of W), M2 = 0 to 3 at% (however, M2 is N
b, Ta, Ni or more), M3=0 to 2 at% (f
In this case, M is Ti, Zr, Hf, and Si.

One or more types of Mn) Among these elements, the transition element replaces a part of T in the V-T-B compound phase.

Ml, M2. When the amount of M added exceeds the upper limit, the Curie temperature decreases and the residual magnetization Br also decreases.

Components other than those mentioned above are impurities. In particular, ferroboron, which is often used as a boron raw material, inevitably contains aluminum as an impurity, and aluminum is also leached from the crucible. Therefore, even when not added as an alloy component, aluminum is 0.4% by weight (0.8 at%).
, included in NdFe-B based sintered magnets.

It has been announced that other elements may also be added to Nd-Fe-B permanent magnets. For example, it is said that when Ga is added at the same time as Co, the intrinsic coercive force (iHc) is increased.

However, in the permanent magnet of the present invention, Ga has an inherent coercive force (
It is an impurity because it does not increase iHc).

Further, although the addition of Cu was proposed in an application filed on the same date as the present application, if the amount added is less than 0.01%, there is no particular effect, and Cu is an impurity.

Furthermore, oxygen is mixed into the Nd-Fe-B sintered magnet as an impurity during the alloy pulverization process, the post-pulverization pressing process, and the sintering process. In addition, Nd-Fe-B alloy powder can be directly applied to Ca, Mg
Alternatively, in the co-reduction method obtained by Na reduction, a large amount of oxygen is mixed into the Nd-Fe-B based sintered magnet during leaching (CaOM g O, Na20 separation and cleaning step). Maximum oxygen content is 110,000 pp (weight ratio) Nd Fe
Contaminated with B-based sintered magnets. Such oxygen does not improve magnetic or other properties.

Furthermore, carbon from rare earth raw materials, Fe-B raw materials, lubricants used during the process, and carbon, phosphorus, and sulfur contained in iron are mixed into the Nd-FeB sintered magnet. With current technology, a maximum of 5000 pf)m (weight ratio) of carbon is mixed into the Nd-FeB sintered magnet. This carbon also does not improve magnetic or other properties.

For the Nd-Fe-B based sintered magnet of the present invention described above, high intrinsic coercive force (i) Ic) can be obtained by performing heat treatment in the following temperature range within the heat treatment temperature range of 500 to 1000 ° C. be able to.

(Hereafter, margin) I asked for it.

Table 1 In the above, the heat treatment temperature range is the maximum specific coercive force (i
It is shown in the temperature range corresponding to the intrinsic coercive force (i Hc ) from Hc ) max to a value 1 kOe lower than this.

If the value of AQ is not entered, AQ is contained as an impurity.

As described above, the Nd-F eBB-based sintered magnet with a limited composition can increase the absolute value of the intrinsic coercive force (iHc) by dispersing the V-T-B compound secondary phase. One of the reasons for this effect is: ■ Since the T-B compound has the effect of suppressing grain growth during sintering, R2Fe+aB
This is thought to be due to the fact that the particle size of the compound main phase becomes smaller in the entire sintered body than in the case where the V-T-B compound is not present, and as a result, the absolute value of the intrinsic coercive force (iHc) becomes higher. Another reason is that N-d 2F e 1aB
This is presumed to be because the crystal grain boundaries of the phase were modified by the addition of V, making it difficult for magnetization reversal nuclei to occur.

For the standard composition of N d 19F e 77B [1], the intrinsic coercive force (iHc) when replaced with 3.5 at % of V becomes 15 kOe or more. This value is significantly higher than the intrinsic coercive force (iHc) of the above standard composition, which is about 6 kOe (without heat treatment) to about 12 kOe (with heat treatment).
% and 5 at% of V as the value of the intrinsic coercive force (iHc) of the Nd-Fe-B sintered magnet, which is 8.1 to 8.3 k.
Although the value of Oe has been announced (Japanese Patent Application Laid-Open No. 1987 = 89401
No.) The intrinsic coercive force (iHc) of the sintered magnet of the present invention is significantly higher than that of the conventional Nd-Fe-V-B magnet.

Note that Nd-Fe-B magnets having a composition other than the standard composition also have an increase in the intrinsic coercive force similar to that described above.

Further, the maximum energy product of the N d -F e -B based sintered magnet according to the present invention is 20 MGOe or more.

This value is the minimum magnetic property required for a high-performance rare earth magnet, and below this value, the rare earth magnet cannot compete with other magnets.

■The secondary phase of the V-T-B compound due to the addition has an inherent coercive force (
It not only increases iHc) but also improves edibility. Before this explanation, the background of corrosion of Nd-Fe-B based sintered magnets will be explained.

Nd-Fe-B magnets are used as parts of audio equipment and OA-FA equipment, such as motors, actuator speakers,
It is also already used in large quantities in MHI magnetic circuits. These are devices used in relatively mild environments (low temperature, low humidity).

It is known that Nd-Fe-B magnets are less prone to rust than SmCo magnets in dry air (R, Blaa
k aad E, Adler: The effect
t of surface oxidatioOoa t
he dcmagnetixatioacurve o
f5iotcrcd Nd-Fe-B perman
eot magnets.

9th Inter(rational work)
op on Rare EarthMageets a
nd Their Applications, Ba
d5odcIl.

FRG, 1987).

Therefore, it can be said that NdFe-B magnets have excellent erodibility against oxidation in dry air.

However, Nd-Fe-B magnets tend to rust in water or in high humidity environments. As a countermeasure against the tendency of Nd-Fe-B magnets to rust, various surface treatment methods such as plating and resin coating have been adopted. However, any surface treatment has defects such as pinholes and cracks, so water leaks from defects in the surface coating.
If it penetrates the surface of the magnet, it will severely oxidize the magnet. When oxidation occurs, the properties of the magnet rapidly deteriorate, and rust appears on the surface of the magnet, impeding the functionality of the device. That is, since conventional Nd-Fe-B magnets have extremely low resistance to water, countermeasures against poor corrosion resistance have been taken by surface treatment. However, this measure is not perfect, and problems such as rust often occur when used in conventional electronic equipment.

Under the above-mentioned background, attempts have been made to improve the erodibility of Nd-Fe-B magnets, specifically the problem of poor erodibility to water, by changing the composition of the magnet, rather than by surface treatment.

According to one of these, it was proposed to add AQ or Co to NdFe-B. however. The effect of Al on improving the edibility of the tea is slight, and AI also has the disadvantage of lowering the Curie temperature. Further, the addition of Co is accompanied by a decrease in iHc.

Research has also been conducted on corrosion of Nd-Fe-B based sintered magnets from the perspective of metallographic structure.

Regarding the mechanism of water corrosion of Nd-Fe-B magnets, there is a study by Zaimoku et al.
(October 1987)). According to it, the standard composition is 33.3
wt%Nd-65,0wt%Fe-1,4wt%B-0
, the following three phases at 3% AR: ■N d 2F e +aB
:■Nd-rich alloy (e.g. Nd-10wt%Fe)
;■ N d Fe 4B, which is said to be a B-rich compound phase
For a sintered alloy consisting of m, the corrosion rate in water is ■〉■〉
■〉It was found that the order was as follows.

According to the present invention, the edible property is improved by converting most or all of the DB-rich compound phase into V-T-B compounds.

V forms a very stable compound with B and N daF
Prevents the generation of e and B. The phagocytosis of T-B compound is ■
It is higher than the B-rich compound phase and higher than both the ■ and ■ phases. By these actions, the B-rich compound phase of the Nd-Fe-B magnet can be reduced or eliminated, and the cause of poor water-chocotability can be eliminated. The corrosion resistance of Nd-Fe-B sintered magnets having such a structure is determined by the oxidation weight gain (1
20 hour test), the edibility is 2.
If the oxidation property is improved by more than twice as much (oxidation weight gain is 1/2 or less), it is thought that the problem of rust that occurs when used in conventional equipment will be extremely reduced.

(Example) Hereinafter, the present invention will be explained in more detail using experimental examples.

Example 1 An alloy was high-frequency melted and IA-molded into an iron pot shape. As starting materials, electrolytic iron with a purity of 99.9 wt% as Fe,
B is a ferroboron alloy and boron with a purity of 99 wt%, Nd is 99 wt%, Pr is 99 wt%, and Dy is 99 wt%.
wt% is used, ■ is ferrovanadium containing 50wt% of V, and Aff is 99.9wt.
% purity was used. During melt casting, the molten metal is sufficiently stirred so that the amount of V is uniform in the alloy, and the ingot is quickly cooled by reducing the thickness to 10 mm or less, so that the V-Fe-B compound phase is finely dispersed in the ingot. The obtained ingot was ground into 35 meshes using a stamp mill, and then finely ground using a jet mill using nitrogen gas to obtain a powder having a particle size of 2.5 to 3.5 μm. 10 pieces of this powder
Molding was carried out at a pressure of 1.5 L/cm2 in a magnetic field of kOe.

In addition, during the powder treatment, the powder was sufficiently stirred after jet milling so that the V-Fe-B compound phase was finely dispersed in the sintered body. The obtained pressure specimen was 1050-11
Sintering was performed at 20° C. in an argon atmosphere for 1 to 5 hours. The sintered body was heat-treated at 800° C. for 1 hour, then quenched by blowing argon gas, then heat-treated at 600 to 700° C. for 1 hour, and quenched by blowing Ar.

The composition and magnetic properties of the sample are shown in Table 2.

(Left below) Table 2 2 (Continued) Example 2 Nd14Fe tBa■8 was prepared using the same method as in Example 1.
A plate of OxlOx 1 mm was prepared. This board was heated to 80℃, 9
It was heated in air at 0% RH for up to 120 hours and the oxidation weight gain was measured. The results are shown in Figure 4. From this figure, it can be seen that the addition of ■ greatly improves the edibility of the drink.

Example 3 Table 3 shows the results of measuring oxidation weight gain using the same method as in Example 2 for the compositions shown in Table 3.

(Margin below) Table (ml) Table 3 (w2) (Effects of the invention) As explained above, according to the invention set forth in claim 1 of the present application, the Nd-FeB sintered magnet does not contain Dy at all. , it is possible to obtain an intrinsic coercive force (iHc) that far exceeds the characteristics achieved with conventional NdFe-B based sintered magnets of the same composition. Therefore, the sintered magnet of the present invention can be used as a high-performance magnet in applications where conventional magnets could not be used, and even when used in the same applications as conventional magnets, stable magnetic characteristics with little aging can be obtained. Conventionally, in order to obtain a high intrinsic coercive force (iHc) as in the present application, it was necessary to add a large amount of ])y far exceeding the balance of rare earth resources, but the present invention improves the balance of rare earth resources. The above magnetic properties can be achieved without deteriorating the magnetic properties.

According to the invention described in claim 2, Nd containing a small amount of Dy
- Fe-B based sintered magnet, which is a conventional Nd-Fe-B
This type of sintered magnet has far superior properties than those with the same amount of -Dy. Therefore, the sintered magnet of the present invention can be used as a high-performance magnet in applications where conventional magnets could not be used, and even when used in the same applications as conventional magnets, stable magnetic characteristics with little aging can be obtained.

According to the third aspect of the invention, in addition to the above effects, the intrinsic coercive force (iHc) can be further increased.

In addition to the above-mentioned effects, the invention described in claim 4 can further increase the intrinsic coercive force (iHc) a little (when the additive element is M8). Further, restrictions on raw material impurities are reduced (when the additive elements are M2 and M3).

In addition to the above-mentioned effects of claim 4, the invention as claimed in claim 5 provides N
It becomes possible to use d-Fe-B based sintered magnets.

In the invention set forth in claim 6, in addition to the above effects of claim 5, the intrinsic coercive force (iHc) can be further increased.

In the seventh aspect of the invention, when the additive element is M, the intrinsic coercive force (iHc) is slightly increased.

Furthermore, when the additive elements are M2 and M3, restrictions on raw material impurities are reduced.

In the invention described in claim 8.9, in addition to the above-mentioned effects of claim 2, the Nd-Fe-B based sintered magnet is also used in the bIi device whose temperature during use increases to about 140°C and 200'C, respectively. be able to use it.

According to the tenth aspect of the invention, in addition to the above effects of the eighth aspect, the intrinsic coercive force (iHc) can be further increased.

In the invention according to claim 11, the additional element is M.

In this case, the intrinsic coercive force (iHc) is slightly increased. Furthermore, when the additive elements are M2 and M3, restrictions on raw material impurities are reduced.

In addition to the above-mentioned effects, the invention according to claim 12 can reduce troubles caused by poor edibility such as rust.

The present invention has solved the serious problems of Nd-Fe-B magnets that have been pointed out from the beginning of the first invention. The present invention has made it possible to provide a high-performance magnet, which was originally expected for Nd-Fe-B magnets but could not be realized, so the industrial value of the present invention is extremely large.

[Brief explanation of drawings]

Figure 1 shows the EPMA of the Nd-Fe-B sintered magnet of the present invention.
Figures 2 (A) and (B) are photographs showing the crystal structure of the VFe-B compound obtained by electron beam diffraction. Figure 3 is a similar metal structure photograph taken using a transmission electron microscope. Figure 4 is a graph showing oxidation weight gain.

Claims (12)

[Claims] 1. In a Nd-Fe-B sintered magnet with a temperature coefficient of intrinsic coercive force (iHc) of 0.5%/°C or more, R = 11 to 1.
8at% (However, R is a rare earth element excluding Dy, 80at%
%≦(Nd+Pr)/R≦100at%), B=
6 to 12 at%, V = 2 to 6 at%, balance Fe, Co (
However, Co has a composition consisting of 25 at% or less (including 0%) of the total of Fe and Co and impurities, and V-T-B
A compound secondary phase (where T is Fe, or if Co is contained, Fe and Co) is dispersed, and 2
Nd-F characterized by having a maximum energy product of 0 MGOe or more and an intrinsic coercive force (iHc) of 15 kOe or more
e-B series sintered magnet. 2. In Nd-Fe-B sintered magnets with a temperature coefficient of intrinsic coercive force (iHc) of 0.5%/℃ or more, R = 11% ~
18at% (R is a rare earth element, R_1=Nd+Pr
, R_2=Dy, 80at%≦(R_1+R_2)/R
≦100at%), 0<R_2≦4at%, B=6-1
2 at%, V = 2 to 6 at%, balance Fe, Co (however, C
o is 25 at% or less (including 0%) of the total of Fe and Co
) and impurities, a V-T-B compound secondary phase is dispersed, a maximum energy product of 20 MGOe or more, and an intrinsic coercive force (iHc) y≧15+3x (however,
x is Dy content (at%), and when y is 21 kOe or more, y=21 kOe). 3. The Nd-Fe-B based sintered magnet according to claim 1 or 2, further comprising Al≦3 at%. 4. M_1=0 to 4at% (However, M_1 is Cr, Mo
, W), M_2=0 to 3 at% (however, M_
2 is one or more of Nb, Ta, Ni) and M_3=0~
2at% or more (However, M_3 is Ti, Zr, Hf, Si
, Mn), and T in the secondary phase of the V-T-B compound is Fe, or if Co is contained, a transition element mainly consisting of Fe and Co. The Nd-Fe-B based sintered magnet according to any one of claims 1 to 3. 5. The Nd- according to claim 1 or 4, which has an intrinsic coercive force (iHc) at 140°C of 5 kOe or more.
Fe-B based sintered magnet. 6. The Nd-Fe-B based sintered magnet according to claim 5, further containing Al≦3 at%. 7. M_1=0 to 4at% (However, M_1 is Cr, Mo
, W), M_2=0 to 3 at% (however, M_
2 is one or more of Nb, Ta, Ni) and M_3=0~
2at% or more (However, M_3 is Ti, Zr, Hf, Si
, Mn), and T in the secondary phase of the V-T-B compound is Fe, or if Co is contained, a transition element mainly consisting of Fe and Co. The Nd-Fe-B based sintered magnet according to claim 5 or 6. 8. The intrinsic coercive force (iHc) at 140℃ is 5+2x(K
3. The Nd-Fe-B based sintered magnet according to claim 2, wherein the Nd-Fe-B based sintered magnet is equal to or higher than Oe) (where x is Dy content (at%)). 9. The Nd-Fe-B according to claim 8, which has an intrinsic coercive force (iHc) at 200°C of 5 kOe or more.
system sintered magnet. 10. The Nd-Fe-B based sintered magnet according to claim 8 or 9, further comprising Al≦3 at%. 11. M_1=0 to 4 at% (However, M_1 is Cr, M
o, W), M_2=0 to 3 at% (however, M
_2 is one or more of Nb, Ta, Ni) and M_3=0
~2 at% or more (however, M_3 is Ti, Zr, Hf, S
i, Mn), and T in the secondary phase of the V-T-B compound is Fe, or if Co is contained, a transition element mainly consisting of Fe and Co. Nd-Fe according to any one of claims 8 to 10,
--B-based sintered magnet. 12. Most or all of the B-rich phase is the V-T-B
The Nd-Fe-B based sintered magnet according to any one of claims 1 to 11, characterized in that it is substituted with a secondary compound phase and has excellent edibility.