U.S. patent application number 10/963757 was filed with the patent office on 2005-06-30 for method for producing magnetostrictive element, sintering container and magnetostrictive element.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Mori, Teruo, Suzuki, Tsuneo, Tokoro, Seigo.
Application Number | 20050142022 10/963757 |
Document ID | / |
Family ID | 34642688 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050142022 |
Kind Code |
A1 |
Mori, Teruo ; et
al. |
June 30, 2005 |
Method for producing magnetostrictive element, sintering container
and magnetostrictive element
Abstract
A setter 20 to be arranged in a sintering container 10 is
provided with holes 21 to keep a compact 100 upright. The compact
100 is not in contact with the setter 20 at a temperature level at
which the sintering reaction proceeds between them because of
contraction of the compact 100 during sintering.
Inventors: |
Mori, Teruo; (Tokyo, JP)
; Suzuki, Tsuneo; (Tokyo, JP) ; Tokoro, Seigo;
(Tokyo, JP) |
Correspondence
Address: |
HOGAN & HARTSON L.L.P.
500 S. GRAND AVENUE
SUITE 1900
LOS ANGELES
CA
90071-2611
US
|
Assignee: |
TDK CORPORATION
|
Family ID: |
34642688 |
Appl. No.: |
10/963757 |
Filed: |
October 13, 2004 |
Current U.S.
Class: |
419/38 |
Current CPC
Class: |
B22F 2998/00 20130101;
H01L 41/20 20130101; H01F 41/0273 20130101; B22F 2999/00 20130101;
B22F 2003/1042 20130101; B22F 3/10 20130101; H01F 1/0557 20130101;
B22F 2998/00 20130101; B22F 3/1208 20130101; B22F 2999/00 20130101;
B22F 3/10 20130101; B22F 2202/05 20130101 |
Class at
Publication: |
419/038 |
International
Class: |
B22F 003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2003 |
JP |
2003-363324 |
Claims
What is claimed is:
1. A method for producing a magnetostrictive element comprising the
steps of: compacting a starting material powder into a shape in a
magnetic field to prepare a compact; and sintering said compact
kept upright in a container.
2. The method for producing a magnetostrictive element according to
claim 1, wherein: said compact is kept in said container upright by
a supporting member, said supporting member is not in contact with
said compact when said compact contracts as a result of sintering
during said sintering step.
3. The method for producing a magnetostrictive element according to
claim 1, wherein: said compact contains Tb, Dy and Fe, and can be
sintered into a magnetostrictive element.
4. The method for producing a magnetostrictive element according to
claim 1, wherein: said compact is stick-shaped.
5. A sintering container, which holds an object to be sintered into
a magnetostrictive element during a sintering step, comprising: a
container body having a basal plane and an opening; a freely
detachable lid to cover said opening; and a setter arranged in said
container body and provided with a cavity, wherein: said object can
be set in said cavity in such a way that said object extends along
the direction in which a magnetostrictive element is driven after
said object is sintered into said magnetostrictive element.
6. The sintering container according to claim 5, wherein: said
object to be sintered is longitudinally shaped, and said object can
be set in said cavity in such a way that its major axis extends
almost vertically.
7. The sintering container according to claim 6, wherein: thickness
of said setter is almost the same as longitudinal length of said
object to be sintered.
8. The sintering container according to claim 5, wherein: said
setter is made of a material which reacts with said object to be
sintered at temperature higher than temperature at which said
object contracts as a result of sintering.
9. The sintering container according to claim 5, wherein: said
setter is made of a material containing Dy.sub.2O.sub.3.
10. A magnetostrictive element comprising a sintered body having a
composition represented by Formula (1) RT.sub.y (wherein, R
represents one or more rare earth elements (providing that the rare
earth elements include Y), T represents one or more transition
metal elements, and 1<y<4), wherein: spacing of lattice
planes in said magnetostrictive element as-sintered, is almost
uniform.
11. The magnetostrictive element according to claim 10, wherein:
said sintered body has a composition represented by Formula (2)
Tb.sub.aDy.sub.(1-a)T.sub.y (wherein, 0.27<a.ltoreq.0.50).
12. The magnetostrictive element according to claim 10, wherein: in
the [222] orientation in the X-ray intensity distribution, a half
width of said magnetostrictive element is between 0.05 and
0.70.
13. A magnetostrictive element comprising a sintered body having a
composition represented by Formula (2) Tb.sub.aDy.sub.(1-a)T.sub.y
(wherein, 0.27<a.ltoreq.0.50, T represents one or more
transition metal elements, and 1<y<4), wherein: a half width
of said magnetostrictive element is between 0.05 and 0.70, in the
[222] orientation in the X-ray intensity distribution.
14. The magnetostrictive element according to claim 13, wherein:
said T is Fe.
15. The magnetostrictive element according to claim 13, which has a
magnetostrictive value of 1100 ppm or more in a magnetic field of 1
kOe.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for producing a
magnetostrictive element, sintering container used for the same
method, and magnetostrictive element.
[0003] 2. Description of the Related Art
[0004] Magnetostrictive elements have been used for various
devices, e.g., linear actuators, vibrators, pressure torque
sensors, vibration sensors and gyro sensors.
[0005] When a magnetostrictive element is used for a linear
actuator, vibrator or the like, a driving force is generated by
changing a magnetic field applied to change the dimensions of the
magnetostrictive element. When a magnetostrictive element is used
for a pressure torque sensor, vibration sensor, gyro sensor or the
like, on the other hand, it detects permeability changing with
dimensional changes of the magnetostrictive element caused by
external pressure and thereby the pressure is detected.
[0006] These magnetostrictive elements are produced by compacting
an alloy powder of given composition into a compact in a magnetic
field and sintering it in an inert gas atmosphere (See, for
example, Japanese Patent Laid-Open No. 2003-3203, Page 4).
[0007] During the sintering step, a compact to be sintered into a
magnetostrictive element tends to be oxidized, and also discolored
by radiation heat from the heater as the heat source for sintering.
Therefore, a compact 1 is contained in a closed container 2, as
shown in FIG. 7, while it is sintered in a sintering furnace. The
container 2 is provided with a setter 3 therein, on which the
compact 1 of a stick shape is laid down while being sintered.
[0008] However, when a material containing a rare earth element
(so-called super magnetostrictive material) is processed to produce
a magnetostrictive element, the compact 1 is so active to cause
problems of producing reaction products on the side surface 1a at
which it comes into contact with the setter 3.
[0009] The reaction products, when formed on the side surface 1a,
strain the compact 1 by a mechanical stress produced while it is
sintered to contract, which causes uneven spacing of lattice planes
in the body, thereby magnetic properties of the compact 1 and hence
magnetostrictive element are deteriorated.
[0010] One of the attempts to solve these problems is to structure
the setter 3 to support the compact 1 only by both ends, in order
to decrease contact area between the compact 1 and setter 3. This
structure, however, causes thermal deformation of the compact 1
during the sintering step, and does not solve effectively the
problems.
SUMMARY OF THE INVENTION
[0011] The present invention is developed to solve these technical
problems. It is an object of the present invention to provide a
method for producing a magnetostrictive element of higher
performance. It is another object of the present invention to
provide a container used for the same method.
[0012] The method of the present invention for producing a
magnetostrictive element, developed to achieve the above objects,
comprises the steps of compacting a starting material powder into a
shape in a magnetic field to prepare a compact, and sintering the
compact kept upright in a container.
[0013] During the sintering step, it is preferable to support the
compact kept upright in the container by a supporting member that
is not in contact with the compact when the compact contracts
following sintering during the sintering step. This prevents the
compact from reacting with the supporting member to produce a
reaction product thereon.
[0014] The compact, which contains Tb, Dy and Fe, can be sintered
into a magnetostrictive element.
[0015] Shape of the compact is not limited. It may be stick-shaped,
for example.
[0016] For the method for producing a magnetostrictive element, the
sintering container of the present invention, described below, is
suitably used.
[0017] The sintering container of the present invention holds an
object to be sintered into a magnetostrictive element. It comprises
a container body having a basal plane and an opening, a freely
detachable lid to cover the opening of the container, and a setter
arranged in the container body. The setter is provided with a
cavity. The object can be set in the cavity in such a way that the
object extends along the direction in which a magnetostrictive
element is driven after the object is sintered into the
magnetostrictive element. The object, when longitudinally shaped,
can be set in the cavity in such a way that its major axis extends
almost vertically. Thickness of the setter can be designed to be
almost same as the longitudinal length of the object to be
sintered.
[0018] The setter cavity can be directed perpendicular to the basal
plane of the container body.
[0019] It is also preferable that the setter is made of a material
which reacts with the object to be sintered at temperature higher
than temperature at which the object contracts as a result of
sintering. This makes the object non-contacting with the cavity
surface when it contracts as the sintering proceeds, allowing the
object kept upright while coming into contact with the setter or
container body only at the basal plane. Therefore, the object is
not in contact with the cavity surface when temperature reaches a
level at which the sintering reaction occurs, preventing formation
of a reaction product by the sintering reaction between them.
[0020] The cavity may be a closed or through hole so long as it is
concave upward to hold the object to be sintered. When it is a
through-hole, the object to be sintered stands on the basal plane
of the container body.
[0021] When the object to be sintered has a composition represented
by Formula (2) Tb.sub.aDy.sub.(1-a)T.sub.y (wherein,
0.27<a.ltoreq.0.50, T is one or more transition metal elements,
and 1<y<4), it is preferable that the setter is made of a
material which reacts with the object to be sintered at temperature
higher than temperature at which the object contracts as a result
of sintering. Dy.sub.2O.sub.3 is a suitable material for the
setter, because it is inert to the object to be sintered. The
setter may be totally made of Dy.sub.2O.sub.3, or partly only for
the cavity portion which may be in contact with the object to be
sintered.
[0022] In the magnetostrictive element produced by employing the
above method and the above sintering container, the spacing of
lattice planes is almost uniform, because formation of a product by
its reaction with the setter is prevented.
[0023] The magnetostrictive element of the present invention can be
regarded as the one comprising a sintered body having a composition
represented by Formula (1) RT.sub.y (wherein, R represents one or
more rare earth elements (providing that the rare earth elements
include Y), T represents one or more transition metal elements, and
1<y<4), spacing of lattice planes in the magnetostrictive
element as-sintered, is almost uniform. T may be at least one of
Fe, Co and Ni.
[0024] The magnetostrictive element may be also regarded as the
one, wherein in the [222] orientation in the X-ray intensity
distribution, a half width of the magnetostrictive element is
between 0.05 and 0.70.
[0025] When the magnetostrictive element of the present invention
is composed of a sintered body having a composition represented by
Formula (2) Tb.sub.aDy.sub.(1-a)T.sub.y (wherein,
0.27<a.ltoreq.0.50, T is one or more transition metal elements
and 1<y<4), it may be regarded as the one having a half width
of 0.05 to 0.70, inclusive, in the [222] orientation in the X-ray
intensity distribution. It can exhibit a magnetostrictive value of
1100 ppm or more in a magnetic field of 1 kOe.
[0026] Fe is a preferable choice as T.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is an oblique view showing an exterior of a sintering
container in one embodiment of the present invention;
[0028] FIG. 2A is a cross-sectional view of a sintering container,
holding compacts, and FIG. 2B is a top view of a setter arranged in
the container body of a sintering container;
[0029] FIG. 3 is a cross-sectional view showing that compacts
contract in a sintering container;
[0030] FIG. 4 shows the degree of orientation, determined by X-ray
analysis, of the sintered body obtained;
[0031] FIG. 5 shows a relationship between half width in the X-ray
intensity distribution and magnetostrictive value;
[0032] FIG. 6 shows a relationship between half width in the X-ray
intensity distribution and magnetostrictive value; and
[0033] FIG. 7 is a cross-sectional view of a conventional sintering
container.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] The present invention is described in detail, based on the
embodiments illustrated in the attached drawings.
[0035] First, the method for producing a magnetostrictive element
of one embodiment is described.
[0036] In this embodiment, an alloy powder having a composition
represented by Formula (1) RT.sub.y (wherein, R is one or more rare
earth elements, T is one or more transition metal elements and
1<y<4) is sintered to prepare a magnetostrictive element.
[0037] R is at least one selected from rare earth elements of
lanthanoids and actinoids, where the rare earth elements represents
a concept including Y. Of these elements, Nd, Pr, Sm, Tb, Dy and Ho
are particularly preferable as R, and Tb and Dy are more
preferable. They may be used in combination. T is at least one
selected from transition metal elements. Of these, transition metal
elements of Fe, Co, Ni, Mn, Cr and Mo are particularly preferable
as T, and Fe, Co and Ni are more preferable. Fe, Co and Ni may be
used in combination.
[0038] In the alloy represented by the Formula (1) RT.sub.y,
1<y<4. RT.sub.2 (RT.sub.y with y=2) as a laves type
intermetallic compound is suitable for a magnetostrictive element
because of its high Curie temperature and high magnetostrictive
value. When y is 1 or less, the R-rich phase deposits in the alloy
during heat treatment which follows sintering and leads to decrease
its magnetostrictive value. When y is 4 or more, on the other hand,
the RT.sub.3 or RT.sub.5 phase increases also leads to decrease a
magnetostrictive value of the alloy. It is therefore preferable to
keep the relationship 1<y<4 to increase the RT.sub.2 phase,
more preferably 1.5.ltoreq.y.ltoreq.2.0, still more preferably
1.8.ltoreq.y.ltoreq.1.95.
[0039] R may be a mixture of rare earth elements, in particular, a
mixture of Tb and Dy is preferable. In the alloy represented by
Formula (3) Tb.sub.aDy.sub.(1-a), a further preferably satisfies
the relationship 0.27<a.ltoreq.0.50. This ensures a high
saturation magnetostrictive coefficient and hence a high
magnetostrictive value of the alloy represented by Formula (2)
Tb.sub.aDy.sub.(1-a)T.sub.y. When a is 0.27 or less, the alloy may
not have a sufficient magnetostrictive value at room temperature or
lower. When a is above 0.50, on the other hand, the alloy may not
have a sufficient magnetostrictive value at around room
temperature. It is more preferably 0.27.ltoreq.a.ltoreq.0.40, still
more preferably 0.28.ltoreq.a.ltoreq.0.34.
[0040] As T, particularly Fe is prefereable, which forms with Tb or
Dy an intermetallic compound ((Tb, Dy) Fe.sub.2) having a high
magnetostrictive value and high other magnetostrictive properties.
Fe may be partly substituted by Co or Ni. In this case, however, Fe
preferably accounts for 70% by weight or more, more preferably 80%
or more, because Co decreases permeability although increasing
magnetic anisotropy, while Ni decreases Curie temperature to
decrease magnetostrictive value at room temperature and in a high
magnetic field.
[0041] The alloy powder as a starting material is preferably
treated to absorb hydrogen partially or totally. The alloy powder,
when absorbs hydrogen, produces a strain in the particles that
constitute the powder, the resulting internal stress cracking the
particles. The particles in the mixture are cracked into fractions,
when exposed to pressure during the compacting step, and the
resulting compact can be sintered more densely. Rare earth
elements, e.g., Tb and Dy, are easily oxidated, and coated with an
oxide film of high melting point in the presence of oxygen even in
a trace quantity, to retard sintering. They are more resistance to
oxidation, when absorb hydrogen. Therefore, the alloy powder can be
sintered more densely, when treated to absorb hydrogen partially or
totally.
[0042] The hydrogen-absorbing starting material preferably has a
composition represented by Formula (4) Dy.sub.bT.sub.(1-b) with b
satisfying the relationship of 0.37.ltoreq.b.ltoreq.1.00. T may be
Fe itself or Fe partly substituted by Co or Ni. This allows the
starting alloy powder to be sintered more densely.
[0043] In this embodiment, the starting material powder is sintered
in a mixed hydrogen/inert gas atmosphere with the relationship of
hydrogen gas: argon (Ar) gas=X: 100-X (Formula 5) with X (vol %)
satisfying 0<X<50. The mixed hydrogen/inert gas atmosphere is
provided in a heating-up period in a range of 650.degree. C. or
higher or/and in a stable temperature range of 1150 to 1230.degree.
C., inclusive.
[0044] For the alloy represented by Formula (1) RT.sub.y, the
starting material powder is placed in the mixed hydrogen/inert gas
atmosphere at least in a heating-up period at 650.degree. C. or
higher.
[0045] The compact of the starting material powder is heated at 3
to 20.degree. C./minute in a furnace for sintering. At below
3.degree. C./minute, productivity will go down. At above 20.degree.
C./minute, on the other hand, the compacted powder may not be
heat-treated uniformly in the furnace to cause problems, e.g.,
segregation or production of a dissimilar phase. The reason to set
the temperature range for the above mixed hydrogen/inert gas
atmosphere at 650.degree. C. or higher is to avoid oxidation of the
rare earth element by oxygen remaining in a very small
quantity.
[0046] It is preferable to sinter the compact for a period in which
temperature is essentially kept at a constant level. The stable
temperature is preferably in a range of 1150 to 1230.degree. C. At
below 1150.degree. C., the sintering step needs a longer time to
remove the internal strain and hence is not effective. At above
1230.degree. C., on the other hand, which is near a melting point
of the alloy represented by RT.sub.y, problems, e.g., melting of
the sintered body or precipitation of another phase, e.g., RT.sub.3
occur.
[0047] Moreover, it is preferable to carry out the sintering in a
non-oxidative atmosphere, more specifically in a hydrogen gas
atmosphere or mixed hydrogen/inert gas atmosphere with the
relationship of hydrogen gas: argon (Ar) gas=X: 100-X (Formula 5)
with X (vol %) satisfying 0<X<50.
[0048] R readily reacts with oxygen to form a stable rare earth
oxide, which little exhibits magnetic properties for a practical
magnetic material. Oxygen, although present at a very low content
in a sintering atmosphere, can greatly deteriorate magnetic
properties of the sintered body prepared at high temperature.
Therefore, heat treatment such as sintering is carried out
preferably in a hydrogen-containing atmosphere. Oxidation is also
controlled in an inert gas atmosphere, but an inert gas alone is
difficult to completely remove oxygen, allowing it to react with a
rare earth element, which is highly reactive with oxygen, to form
the oxide. Therefore, the sintering atmosphere is preferably of a
hydrogen/inert gas mixture to prevent the oxidation of rare earth
element.
[0049] For a hydrogen gas-containing reducing atmosphere, X (vol %)
preferably satisfies 0<X<50 in Formula 5 of hydrogen gas:
argon (Ar) gas=X: 100-X. An Ar gas is inert and does not oxidize R.
Therefore, it can form a reducing atmosphere when mixed with
hydrogen gas. In order to obtain a reducing atmosphere, X (vol %)
preferably satisfies 0<X. At 50.ltoreq.X, the reducing
atmosphere is saturated. Therefore, X<50 is preferable. It is
preferable to keep a mixed hydrogen/Ar gas atmosphere during the
heating-up step carried out at 650.degree. C. or higher. It is more
preferable to keep the mixed hydrogen/Ar gas atmosphere in the
stable temperature range.
[0050] Flow of the magnetostrictive element production process will
be described in detail below.
[0051] First, Tb, Dy and Fe are weighed and then melted in an inert
gas atmosphere of Ar to prepare the alloy (hereinafter referred to
as Starting Material A) as one of starting materials. Starting
Material A has a composition of Tb.sub.0.4Dy.sub.0.6Fe.sub.1.94,
for example. The Starting Materials A is annealed in order to make
concentration distribution of the elements uniform and remove a
dissimilar phase when it deposits, and is then milled by, e.g., an
atomizer.
[0052] Then, Dy and Fe are weighed and then melted in an inert gas
atmosphere of Ar to prepare the alloy (hereinafter referred to as
Starting Material B) as one of starting materials. Starting
Material B has a composition of Dy.sub.2.0Fe, for example. It is
similarly milled by, e.g., an atomizer.
[0053] Fe, as one of starting materials, is reduced in a hydrogen
gas atmosphere to remove oxygen, and is then milled by, e.g., an
atomizer (hereinafter referred to as Starting Material C).
[0054] Starting Materials A, B and C are weighed, milled and mixed
with each other to prepare the alloy powder (starting material
powder) having a composition of Tb.sub.0.3Dy.sub.0.7Fe.sub.1.88,
for example.
[0055] The alloy powder thus obtained is compacted in a mold in a
magnetic field of a given intensity, e.g., 8 kOe, to produce the
compact.
[0056] The compact is heated in a furnace to produce a sintered
body, where temperature in the furnace is programmed to have a
given profile. For example, it is sintered in a mixed
hydrogen/argon gas atmosphere (35/65% by volume) in a stable
temperature range of 1150 to 1230.degree. C. to produce a sintered
body.
[0057] The sintered body is aging-treated and then divided into
pieces of given size to produce magnetostrictive elements.
[0058] FIGS. 1 and 2 structurally illustrate a sintering container
10 used in the method for producing a magnetostrictive element,
where FIG. 1 is an oblique view showing the container 10 exterior,
and FIG. 2A is a cross-sectional view of the container 10 holding
compacts 100 and FIG. 2B is a top view of a setter 20 arrnged in a
container body 11 of the sintering container 10.
[0059] In this embodiment, the compact 100 to be sintered into a
magnetostrictive element is sintered while being held in the
sintering container 10.
[0060] As illustrated in FIG. 1, the container 10 comprises the
container body 11 and a lid 12.
[0061] As illustrated in FIG. 2, the setter (supporting member) 20
is arranged in the container body 11 to support the compact 100
during the sintering step.
[0062] The setter 20 is provided with a plurality of holes
(cavities) 21 extending in the direction perpendicular to a basal
plane of the container body 11, that is, extending almost
vertically. Each hole 21 has an inner diameter slightly larger than
the outer diameter of the compact 100 before sintering. In this
embodiment, thickness of the setter 20, i.e., depth of the hole 21,
is designed to be almost same as the longitudinal length of the
compact 100.
[0063] It is preferable that the setter 20 is made of a material
hardly reactive with the compact 100. It is also preferable that
the setter 20 is made of a material which reacts with the compact
100 at temperature (sintering reaction temperature) higher than
temperature at which the compact 100 contracts as a result of
sintering. These materials include CaO and Dy.sub.2O.sub.3, of
which the latter is particularly preferable for the setter 20.
[0064] A given number of the compacts 100 are set in the
corresponding holes 21, when they are sintered in the sintering
container 10 provided with the setters 20. This allows each of the
compacts 100 to be supported by the corresponding setter 20 in such
a way that its major axis extends almost vertically. In this
position, the compact 100 comes into contact with the setter 20
only partly. Dy.sub.2O.sub.3 constituting the setter 20 differs in
linear expansion coefficient from the compact 100. The hole
diameter of the setter 20 is designed to be larger by around 1%
than the outer diameter of the compact 100.
[0065] The sintering container 10 is heated in a furnace, where
temperature is programmed to have a given profile, to sinter each
of the compacts 100 held in the sintering container 10 into a
magnetostrictive element. The compact to be sintered into a
magnetostrictive element can be designed to have dimensions of 2 to
20 mm in diameter and 20 to 40 mm in length.
[0066] The compact 100 contracts while being sintered in a furnace
to form a gap between the contracted compact 100 and the holes 21,
as shown in FIG. 3, and leads to secure the compact 100 to be
non-contacting with the setter 20. Contraction of the compact 100
starts at, e.g., around 800 to 850.degree. C. On the other hand,
the sintering reaction of the compact 100 with the setter 20 starts
at, e.g., around 1150.degree. C. Therefore, they are kept away from
each other at a temperature level at which the sintering reaction
starts between them. Even when they are in contact with each other,
extent is limited to a mere point contact.
[0067] As discussed above, each setter 20 in the sintering
container 10 is provided with the holes 21 to keep each compact 100
kept upright. During sintering, this keeps the compact 100 and
setter 20 away from each other at a temperature level at which the
sintering reaction starts between them because of contraction of
the compact 100. This prevents deposition of the sintering reaction
product on the compact 100 due to the sintering reaction between
the compact 100 and setter 20. There ensures that no mechanical
stress (internal stress) is produced by the reaction product to act
on the compact 100 and secures that the spacing of lattice planes
in the sintered body obtained is almost uniform. Therefore, the
resulting sintered body has better magnetic properties than the one
sintered while being laid down. Moreover, the setter 20 can be
simply structured only to have the holes 21, producing a
significant effect at a minimum cost.
[0068] In the above embodiment, depth of the hole 21 is set at
almost the same as longitudinal length of the compact 100. However,
depth of the hole 21 may be shorter than length of the compact 100
to project the latter over the former. It is however preferable
that they have dimensions in such a way that the compacts 100 are
firmly held by the setters 20 not to fall down when the sintering
container 10 is moved after the compacts 100 contract, e.g., after
the sintering treatment is completed.
[0069] In this embodiment, each compact 100 is kept upright on the
basal plane of the container body 11, where each hole 21 in the
setter 20 may not be a through-hole but a closed one.
EXAMPLE 1
[0070] In EXAMPLE 1, the compact was sintered in the sintering
container 10 to confirm how nests were produced in the
magnetostrictive element. The results are described below.
[0071] As for Starting Material A, Tb, Dy and Fe were weighed and
then melted in an inert gas atmosphere of Ar to prepare the alloy
having a composition Tb.sub.0.4Dy.sub.0.6Fe.sub.1.94. It was
annealed to secure an even concentration distribution of each metal
element of the prepared alloy and remove a dissimilar phase when it
deposits, and was then milled by a Brown mill. Next, as for
Starting Material B, Dy and Fe were weighed and then melted in an
inert gas atmosphere of Ar to prepare the alloy having a
composition Dy.sub.2.0Fe, which was treated in a hydrogen gas
atmosphere at 150.degree. C. for 1 hour to absorb hydrogen. Then,
as for Starting Material C, Fe is reduction-treated in a hydrogen
gas atmosphere to remove oxygen.
[0072] Starting Materials A, B and C were weighed, milled and mixed
with each other by an atomizer to prepare the alloy powder having a
composition of Tb.sub.0.3Dy.sub.0.7Fe.sub.1.9.
[0073] The alloy powder was compacted in a mold in a magnetic field
of 8 kOe, to prepare the compact 100. It had a stick shape, 7 mm in
diameter and 100 mm in length.
[0074] The compacts 100 put in the sintering container 10 were
heated in a mixed hydrogen/argon (35/65% by volume) atmosphere in a
stable temperature range of 1150 to 1230.degree. C. to prepare the
sintered bodies.
EXAMPLE
[0075] Each of the compacts 100 was kept upright by the setter 20
in the sintering container 10 during the sintering process.
Comparative Example
[0076] Each of the compacts 100 was laid down (arranged
horizontally) during the sintering process, following the
conventional manner.
[0077] A total of 10 compacts 100 were sintered in each of EXAMPLE
and COMPARATIVE EXAMPLE, to measure their magnetic properties
(magnetostrictive value) for the sintered bodies obtained.
[0078] The results are given in FIGS. 4 to 6.
[0079] FIG. 4 shows the measurement result of the X-ray-analyzed
degree of orientation, and magnetostrictive value of each sintered
body was evaluated in the [222] orientation shown in FIG. 4.
[0080] FIGS. 5 and 6 show the relationship between half width of
the X-ray intensity distribution and magnetostrictive value, where
the half width of the X-ray means a width of spread of the X-ray
intensity peak in the [222] orientation at half of the peak height,
and magnetostrictive value .lambda..sub.1.0 means the value in a
magnetic field of 1 kOe.
[0081] As shown in FIG. 6, the sintered bodies laid down in
COMPARATIVE EXAMPLE had a half width of the X-ray intensity
distribution in a range from 0.74 to 1.15, whereas those kept
upright in EXAMPLE had a half width of the X-ray intensity
distribution in a range from 0.35 to 0.70, which means that the
sintered bodies prepared in EXAMPLE had a sharper X-ray intensity
peak and hence the quantity of contaminants smaller than that of
COMPARATIVE EXAMPLE.
[0082] It was also observed that the sintered bodies laid down in
COMPARATIVE EXAMPLE had a magnetostrictive value of 1030 to 1122
ppm, whereas those kept upright in EXAMPLE had a value of 1132 to
1231 ppm, at least 10% higher.
[0083] As discussed above, it is apparent that keeping the compact
100 upright during the sintering process suppresses formation of a
contaminant, i.e., product by the reaction between the compact 100
and setter 20, and greatly improves magnetostrictive value of the
sintered body.
[0084] The sintered bodies prepared in EXAMPLE and COMPARATIVE
EXAMPLE were analyzed for element dispersion conditions by an
electron probe X-ray micro analyzer (EPMA). The results indicate
that the carbides and oxides are produced less and dispersed more
uniformly in the sinter prepared in EXAMPLE than in the sintered
body prepared in COMPARATIVE EXAMPLE, and that Dy and Fe are
dispersed more uniformly in the sintered body prepared in
EXAMPLE.
[0085] It is thus confirmed that keeping the compact 100 upright
during the sintering process produces carbides and oxides less and
gives a more uniform composition with Dy and Fe dispersed more
uniformly.
* * * * *