Rare-earth iron-boron magnet containing cerium and lanthanum

Details Rare-earth iron-boron magnet containing cerium and lanthanum Rare-earth iron-boron magnet containing cerium and lanthanum

1999-09-24

2001-07-17

Sheehan, John (Department: 1742)

Metal treatment

Stock

Magnetic

C252S062540, C252S062550, C075S244000

Reexamination Certificate

active

06261387

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to rare-earth iron-boron based permanent magnet compositions that include cerium and/or lanthanum.
BACKGROUND OF THE INVENTION
Rare earth-iron-boron based magnets, such as the well known Nd—Fe—B magnets, are used in numerous applications, including computer hardware, automobiles, consumer electronics and household appliances. In particular, magnets using rare earth elements, such as Nd or Pr, are useful primarily because of their superior magnetic properties, as manifested by their large coercivity, remanence, magnetization and maximum energy product. The primary disadvantage of such magnets is that because of the cost of scarce rare earth metals, such as Nd or Pr, they are relatively expensive to make.
Alternative, inexpensive permanent magnets, such as the ferrite-based magnets, which have long been available, generally exhibit poor magnetic properties as compared with rare earth based magnets. Thus, they are unsuitable for many applications. For example, the remanence of a permanent magnet fabricated from sintered ferrite is typically about 4.0 kG while the remanence for a bonded Nd—Fe—B magnet is about 6.5 kG. It would be useful to fabricate a bonded permanent magnet with a remanence that is intermediate between these values, of about 5.0 to 6.0 kG, which is sufficient for many applications for which ferrite magnets are unsuitable to use. In such cases, it would be particularly useful if such magnets could be fabricated at a lower cost than what is currently required for bonded Nd—Fe—B magnets.
U.S. Pat. No. 4,765,848 (“the Mohri patent”) discloses a permanent magnet composition [(Ce
x
La
1−x
)
y
R
1−y
]
z
(Fe
1−v
B
v
)
1−z
where R is one or more rare-earth elements, excluding Ce and La. In the disclosure of this patent, restrictions have been placed on the values of x, y, z and v: 0.4≦x≦0.9; 0.2<y<1.0; 0.05≦z≦0.3; and 0.01≦v≦0.3. With such limitations, the patent discloses that the coercivity of the resulting permanent magnet is greater than 4 kOe. This coercivity is viewed as an appropriate index for providing a useful magnet, and the patent teaches that the coercivity is insufficient when the values of the various constituents fall outside the ranges specified above.
One of the principal teachings of the Mohri patent is that there is a synergistic effect when both Ce and La are used in rare-earth iron-boron magnets. According to the teaching of the Mohri patent, both Ce and La, when used alone, decrease the magnetic properties, but when used togther, the synergistic effect acts to enhance the coercivity.
SUMMARY OF THE INVENTION
The present invention provides, contrary to the teachings of the Mohri patent, useful rare-earth iron-boron magnets where the amounts of the constituent elements are outside the ranges disclosed by the Mohri patent. Such permanent magnets exhibit adequate magnetic properties to make them useful in many applications. Moreover, permanent magnets in accordance with the present invention exhibit magnetic properties that fill in the gaps currently existing with available magnets of different compositions. As used herein, the term “permanent rare-earth magnet” includes a magnetic particle or magnetic powder, a bonded magnet made from such a magnetic particle or magnetic powder, and a fully dense isotropic or anisotropic magnet. All the compositions referred to herein are in atomic percent unless otherwise specified.
The present invention is directed to a permanent rare- earth magnet comprising an alloy having a composition expressed as [(Ce
x
La
1−x
)
y
R
1−y
]
z
(F
1−v
B
v
)
1−z
. In the composition, R is one or more rare-earth elements selected from the group consisting of Y, Pr, Nd, Sm, Er, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. F is Fe or Fe and up to 20 atomic percent Co by substitution. The subscripts denote the relative atomic composition with 0.9<x≦1.0, 0.2≦y≦0.8, 0.04≦z≦0.25, and 0.01≦v≦0.30. This composition is outside the compositions disclosed in the Mohri patent. The permanent rare-earth magnet of the present invention may be a fully dense isotropic or anisotropic magnet, such as a sintered, hot-pressed, or hot-pressed and hot-worked magnet, or a bonded magnet. The process for making a sintered permanent rare earth magnet is well known and is described in, for example, U.S. Pat. Nos. 4,770,723, 4,792,368 and 5,645,651, which are incorporated herein by references. The process for making a hot-pressed magnet is also well known and is described in, for example, U.S. Pat. Nos. 4,792,367 and 4,844,754, where are incorporated herein by reference. The process for making a bonded magnet is well known and is described in, for example, U.S. Pat. No. 4,902,361, which is incorporated herein by reference. In a preferred embodiment, y is between approximately 0.35 and approximately 0.60. In another preferred embodiment, z is between approximately 0.10 and 0.18. In yet another preferred embodiment, v is between approximately 0.060 and 0.085. In one embodiment of the invention, the rare earth R is Nd. In another embodiment, R is Nd
1−w
Pr
w
, with the value of w preferably less than 0.30. In a further embodiment, R is Nd
1−t−t′
Pr
t
R′
t′
, wherein R′ is one or more elements selected from the group consisting of Nb and Ga.
The value of t is preferably less than 0.20 and the value of t, is preferably less than 0.1.
The invention is also directed to a permanent rare-earth magnet comprising an alloy having a composition expressed as [Ce
y
R
1−y
]
z
(F
1−v
B
v
)
1−z
. In this composition, R is one or more rare-earth elements selected from the group consisting of Y, Pr, Nd, Sm, Er, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. F is Fe or Fe and up to 20 percent Co by substitution. The subscripts denote the relative elemental composition with 0.0<y≦0.3, 0.04≦z≦0.25, and 0.01≦v≦0.30. This composition is outside the compositional ranges disclosed or taught by the Mohri patent because La is not present, except that it may be present as an impurity which is usually less than 0.1 atomic percent. In contradistinction, the Mohri patent teaches that La must be present in the composition in the amount greater than 0.1 atomic percent of the total amount of Ce and La. The permanent rare-earth magnet of the present invention may be a fully dense isotropic or anisotropic magnet. The permanent rare-earth magnet of the present invention may also be a bonded magnet.
In a preferred embodiment, the value of y is preferably less than approximately 0.2. In another preferred embodiment, z is preferably between approximately 0.10 and approximately 0.15. In yet another preferred embodiment, v is approximately 0.067. In another embodiment, the rare earth R is Nd. In still another embodiment, the rare earth R is Nd
1−w
Pr
w
. The value of w is preferably less than 0.30.
The invention is also directed to a permanent rare-earth magnet comprising an alloy having a composition expressed as [(Ce
x
La
1−x
)
y
R
1−y
]
z
(F
1−v
B
v
)
1−z
. In the composition, R is one or more rare-earth elements selected from the group consisting of Y, Pr, Nd, Sm, Er, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. F is Fe or Fe and up to 20 atomic percent Co by substitution. The subscripts denote the relative elemental composition with 0≦x<0.4, 0.2≦y≦0.8, 0.04≦z≦0.25, and 0.01≦v≦0.30. The permanent rare-earth magnet of the present invention may be a fully dense isotropic or anisotropic magnet, or a bonded magnet. The composition of the present invention is outside the compositional range (with x>0.4) taught or suggested by the Mohri patent that would provide a good magnet.
In a preferred embodiment, x is less than approximately 0.01. The value of y is preferably between approximately 0.45 and approximately 0.55. The value of z is preferably between approximately 0.10 and approximately 0.18. The value of v is pref

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