U.S. patent application number 10/615939 was filed with the patent office on 2004-01-22 for green compact and process for compacting the same, metallic sintered body and process for producing the same, worked component part and method of working.
This patent application is currently assigned to Kabushiki Kaisha Toyota Chuo Kenkyusho. Invention is credited to Kondoh, Mikio, Saito, Takashi, Takamiya, Hiroyuki.
Application Number | 20040013558 10/615939 |
Document ID | / |
Family ID | 30447649 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040013558 |
Kind Code |
A1 |
Kondoh, Mikio ; et
al. |
January 22, 2004 |
Green compact and process for compacting the same, metallic
sintered body and process for producing the same, worked component
part and method of working
Abstract
A process for compacting a green compact includes the steps of
applying a higher fatty acid-based lubricant to an inner surface of
a die, filling a raw material powder whose major component is an
active metallic element into the die, compacting the raw material
powder by warm pressurizing to make a green compact, and ejecting
the green compact from the die, whereby the resulting green compact
has a high density. It is possible to form active metallic powders
including an active metallic element such as Ti and Al by
pressurizing by high pressures, and to produce high-density green
compacts which have not been available conventionally.
Inventors: |
Kondoh, Mikio; (Toyoake-shi,
JP) ; Saito, Takashi; (Nagoya-shi, JP) ;
Takamiya, Hiroyuki; (Tajimi-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Kabushiki Kaisha Toyota Chuo
Kenkyusho
Aichi-gun
JP
|
Family ID: |
30447649 |
Appl. No.: |
10/615939 |
Filed: |
July 10, 2003 |
Current U.S.
Class: |
419/36 |
Current CPC
Class: |
B22F 2003/145 20130101;
B22F 2003/026 20130101; B22F 3/02 20130101 |
Class at
Publication: |
419/36 |
International
Class: |
B22F 003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 17, 2002 |
JP |
2002-208092 |
Jun 11, 2003 |
JP |
2003-166642 |
Claims
What is claimed is:
1. A process for compacting a green compact, comprising the steps
of: applying a higher fatty acid-based lubricant to an inner
surface of a die; filling a raw material powder whose major
component is an active metallic element into the die; compacting
the raw material powder by warm pressurizing to make a green
compact; and ejecting the green compact from the die; whereby the
resulting green compact has a high density.
2. The process set forth in claim 1, wherein the active metallic
element is titanium (Ti).
3. The process set forth in claim 2, wherein the raw material
powder further comprises at least one element selected from the
group consisting of aluminum (Al), zirconium (Zr), hafnium (Hf),
vanadium (V), niobium (Nb), tantalum (Ta), scandium (Sc), chromium
(Cr), iron (Fe), molybdenum (Mo), tin (Sn), tungsten (W), manganese
(Mn), nickel (Ni), copper (Cu), silicon (Si), carbon (C), boron
(B), nitrogen (N) and oxygen (O).
4. The process set forth in claim 2, wherein the raw material
powder comprises at least one member selected from the group
consisting of pure titanium powders, titanium alloy powders and
titanium compound powders.
5. The process set forth in claim 1, wherein the active metallic
element is Al.
6. The process set forth in claim 5, wherein the raw material
powder further comprises at least one element selected from the
group consisting of Cu, magnesium (Mg), Mn, Zr, strontium (Sr), Ni,
Cr, Fe, Mo, Sn, Si, C, B, N and O.
7. The process set forth in claim 5, wherein the raw material
powder comprises at least one member selected from the group
consisting of pure aluminum powders, aluminum alloy powders and
aluminum compound powders.
8. The process set forth in claim 1, wherein the raw material
powder is a mixture powder in which a hard-particle powder
comprising at least one member selected from carbides, borides,
nitrides and oxides is mixed.
9. The process set forth in claim 1, wherein the active metallic
element is Ti; and a green density being an apparent density of the
green compact is 85% or more of a true density determined by a
composition of the raw material powder.
10. The process set forth in claim 1, wherein the active metallic
element is Al; and a green density being an apparent density of the
green compact is 90% or more of a true density determined by a
composition of the raw material powder.
11. The process set forth in claim 1, wherein, in the compacting
step, the raw material powder is formed by warm pressurizing by a
compacting pressure of 392 MPa or more while holding a warm state
by controlling at least a contact-area temperature in a range of
from 100 to 225.degree. C., the contact-area temperature being a
temperature of an area where the inner surface of the die contacts
with the raw material powder.
12. The process set forth in claim 11, wherein the active metallic
element is Ti; and the contact-area temperature falls in a range of
from 100 to 225.degree. C., and the compacting pressure falls in a
range of from 500 to 2,500 MPa.
13. The process set forth in claim 11, wherein the active metallic
element is Al; and the contact-area temperature falls in a range of
from 100 to 225.degree. C., and the compacting pressure falls in a
range of from 392 to 2,500 MPa.
14. The process set forth in claim 1, wherein an ejection force is
10 MPa or less in the ejecting step when a compacting pressure is
784 MPa or more in the compacting step.
15. The process set forth in claim 14, wherein the active metallic
element is Ti; and the ejection force is 10 MPa or less when the
compacting pressure is 784 MPa or more.
16. The process set forth in claim 14, wherein the active metallic
element is Al; and the ejection force is 5 MPa or less when the
compacting pressure is 392 MPa or more.
17. The process set forth in claim 14, wherein a pressure ratio of
the ejection force with respect to the compacting pressure shows a
decreasing tendency when the compacting pressure increases.
18. The process set forth in claim 11, wherein, in the applying
step, a powdery higher fatty acid-based lubricant which is
dispersed in a dispersion comprising a surfactant is sprayed onto
the inner surface of the die, which is heated.
19. The process set forth in claim 18, wherein the dispersion
comprises at least one member selected from the group consisting of
water and alcohol-based solvents.
20. The process set forth in claim 18, wherein the dispersion
comprises a mixture liquid in which water is mixed with an
alcohol-based solvent in an amount of from 1 to 50% by volume.
21. The process set forth in claim 18, wherein the temperature of
the heated die is a boiling point of the dispersion or more, and is
less than a melting point of the higher fatty acid-based
lubricant.
22. The process set forth in claim 1, wherein the higher fatty
acid-based lubricant comprises a metallic salt whose major
component is at least one member selected from the group consisting
of lithium salts, calcium salts and zinc salts of higher fatty
acids.
23. The process set forth in claim 18, wherein the higher fatty
acid-based lubricant has a maximum particle diameter of 30 .mu.m or
less.
24. The process set forth in claim 1, wherein, in the compacting
step, a new metallic soap film being different from the higher
fatty acid-based lubricant and comprising the active metallic
element is formed on a surface of the green compact.
25. The process set forth in claim 24, wherein the active metallic
element is Ti; and the metallic soap film comprises a Ti salt of a
higher fatty acid.
26. The process set forth in claim 24, wherein the active metallic
element is Al; and the metallic soap film comprises an Al salt of a
higher fatty acid.
27. A green compact produced by a process, comprising the steps of:
applying a higher fatty acid-based lubricant to an inner surface of
a die; filling a raw material powder whose major component is an
active metallic element into the die; compacting the raw material
powder by warm pressurizing to make a green compact; and ejecting
the green compact from the die; wherein the active metallic element
is Ti; and a green density being an apparent density of the green
compact is 85% or more of a true density determined by a
composition of the raw material powder.
28. A green compact produced by a process, comprising the steps of:
applying a higher fatty acid-based lubricant to an inner surface of
a die; filling a raw material powder whose major component is an
active metallic element into the die; compacting the raw material
powder by warm pressurizing to make a green compact; and ejecting
the green compact from the die; wherein the active metallic element
is Al; and a green density being an apparent density of the green
compact is 90% or more of a true density determined by a
composition of the raw material powder.
29. A process for producing a metallic sintered body, comprising
the steps of: applying a higher fatty acid-based lubricant to an
inner surface of a die; filling a raw material powder whose major
component is an active metallic element into the die; compacting
the raw material powder by warm pressurizing to make a green
compact; ejecting the green compact from the die; and sintering the
green compact by heating to make a metallic sintered body; whereby
the resulting metallic sintered body has a high density.
30. A metallic sintered body produced by a process, comprising the
steps of: applying a higher fatty acid-based lubricant to an inner
surface of a die; filling a raw material powder whose major
component is an active metallic element into the die; compacting
the raw material powder by warm pressurizing to make a green
compact; ejecting the green compact from the die; and sintering the
green compact by heating to make a metallic sintered body; wherein
the active metallic element is Ti; and a sintered-body density
being an apparent density of the metallic sintered body is 85% or
more of a true density determined by a composition of the raw
material powder.
31. A metallic sintered body produced by a process, comprising the
steps of: applying a higher fatty acid-based lubricant to an inner
surface of a die; filling a raw material powder whose major
component is an active metallic element into the die; compacting
the raw material powder by warm pressurizing to make a green
compact; ejecting the green compact from the die; and sintering the
green compact by heating to make a metallic sintered body; wherein
the active metallic element is Al; and a sintered-body density
being an apparent density of the metallic sintered body is 90% or
more of a true density determined by a composition of the raw
material powder.
32. A method of working, comprising the steps of: applying a higher
fatty acid-based lubricant to at least one surface selected from
the group consisting of a surface of a metallic workpiece whose
major component is an active metallic element and a working surface
of a die; and warm working the metallic workpiece with the die.
33. The method set forth in claim 32, wherein the applying step is
carried out by at least one method selected from the group
consisting of dipping methods in which the workpiece, which is
heated, is immersed into a dispersion, in which the higher fatty
acid-based lubricant is dispersed, and spraying methods in which a
dispersion, in which the higher fatty acid-based lubricant is
dispersed, is sprayed onto the metallic workpiece or the die, which
is heated.
34. The method set forth in claim 32, wherein the working step is
carried out by at least one working method selected from the group
consisting of forging, rolling, extruding, drawing, component
rolling, coining, sizing and re-compressing.
35. A worked component part, produced by a process comprising the
steps of: applying a higher fatty acid-based lubricant to at least
one surface selected from the group consisting of a surface of a
metallic workpiece whose major component is an active metallic
element and a working surface of a die; and warm working the
metallic workpiece.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a high-density green
compact comprising a raw material powder whose major component is
an active metallic element such as Ti and Al (hereinafter referred
to as an active metallic powder wherever appropriate), a process
for compacting the same, a high-density metallic sintered body
which is made by sintering the green compact, and a process for
producing the same.
[0002] Moreover, the present invention relates to a worked
component part which is made by working a metallic workpiece whose
major component is an active metallic element, and a method of
working the same.
DESCRIPTION OF THE RELATED ART
[0003] In order to reduce the manufacturing cost of component parts
by reducing the expensive working cost, or in order to obtain
characteristics which are not available in bulky cast materials,
green compacts which are formed by pressurizing raw material
powders have been used conventionally. The green compacts are often
turned into sintered bodies subsequently, but are used as they are
like powder magnetic cores.
[0004] In order to utilize the characteristics of green compacts,
green compacts are required to have a high density in most cases.
In order to produce high-density green compacts, it is inevitable
to form raw material powders by pressuring by high pressures.
Usually, however, the higher the compacting pressure is, the larger
the frictional force between the raw material powders and dies is.
As a result, when raw materials are formed by pressuring by large
pressures, it has become difficult to eject the resulting green
compacts from the dies. Moreover, galling and the like occur to
damage the dies when ejecting the green compacts, or the surface of
the green compacts is roughened.
[0005] It is possible, of course, to think of improving the
drawbacks by using lubricants in a large amount. However, such a
measure might eventually result in lowering the density of green
compacts. Moreover, the lubrication increases the working cost
because it is required to carry out a degreasing or dewaxing step
after the pressure compacting step.
[0006] Under the circumstances, there have been proposed a large
number of processes for efficiently producing high-density green
compacts. In the proposed processes, the type of lubricants, the
lubrication methods, the compacting temperatures are tried out
variously. For example, the following publications disclose the
relevant matters: Japanese Unexamined Patent Publication (KOKAI)
No. 62-109,902, Japanese Unexamined Patent Publication (KOKAI) No.
62-294,102, Japanese Unexamined Patent Publication (KOKAI) No.
5-271,709, Japanese Unexamined Patent Publication (KOKAI) No.
8-100,203, Japanese Unexamined Patent Publication (KOKAI) No.
9-104,902, Japanese Unexamined Patent Publication (KOKAI) No.
11-193,404, Japanese Unexamined Patent Publication (KOKAI) No.
11-100,602, Japanese Unexamined Patent Publication (KOKAI) No.
11-140,505, Japanese Unexamined Patent Publication (KOKAI) No.
2000-273,502, Japanese Unexamined Patent Publication (KOKAI) No.
2000-290,703, Japanese Unexamined Patent Publication (KOKAI) No.
2001-294,902, PCT International Laid-Open Publication No.
W098/41,347, U.S. Pat. No. 4,955,798, and a research paper
"INFLUENCE OF TEMPERATURE ON PROPERTIES OF LITHIUM STEARATE
LUBRICANT (Powder Metallurgy & Particulate Materials, vol. 1,
1997)." However, it is improper for all such proposals to produce
high-density green compacts at reduced cost.
[0007] Hence, the inventors of the present invention developed
first in the world a process for producing a high-density green
compact whose density is very close to the true density by
remarkably high compacting pressures which have not been available
conventionally while securing the longevity and the like of dies.
PCT International Laid-Open Publication No. WO01/43,900 discloses
the details.
[0008] However, when the aforementioned publications as well as the
descriptions of PCT International Laid-Open Publication No.
WO01/43,900 are examined, it is seen that the raw material powders
comprise iron powders or iron alloy powders in most of the
green-compact production processes proposed so far. Namely, no
actual proposals have been ever made on how to form raw material
powders whose major component is an active metallic element such as
Ti and Al into green compacts.
[0009] As far as the present inventors know at present, they have
not found out any processes at all in which raw materials are
formed by high pressures, not by means of internal or admixing
lubrication methods, but by means of die wall lubrication methods
at industrial or mass-production level at least.
[0010] The fact does not mean that demands are less for green
compacts whose raw material powder comprises Ti or Al. Demands for
such green compacts are rather high because it has been required
recently to make a diversity of component parts lightweight. In
particular, in the case of component parts made of pure titanium or
titanium alloys which are difficult to work, when a powder
compacting process is used, there arises a great merit in that it
is possible to reduce the cost by near-net or net shaping.
[0011] However, it has been the technical common knowledge that it
is impossible to form raw material powders comprising an active
metallic element such as Ti and Al by high pressures at industrial
level. This is because galling occurs on the inner surface of dies
instantaneously or the inner surface of dies is roughened when such
high-pressure compacting is carried out. Moreover, it is because
the resulting green compacts cannot be ejected from dies. In
addition, very expensive dies cannot be used even after one and
only high-pressure compacting operation so that a great loss might
arise.
[0012] Due to the circumstances, when raw material powders
comprising an active metallic element are formed by pressurizing,
it is not possible to heighten the compacting pressures.
Accordingly, the resulting green compacts naturally have a low
attainable density. For example, when green compacts comprise a Ti
powder, the green compacts have a density which is only 80% or less
of the true density.
[0013] Moreover, when Ti powders are formed conventionally by
pressuring by means of an internal lubrication method, a dewaxing
step is required additionally before the resulting green compacts
are sintered in vacuum. In addition, since the major components of
the lubricants used in this instance, such as hydrogen, nitrogen
and carbon, are likely solve in Ti, internal lubrication methods
are unpreferable.
[0014] In order to avoid using such lubricants, CIP (i.e., cold
isostatic press) forming and RIP (i.e., rubber isostatic press)
forming in which rubber molds are used. However, even when such
forming methods are employed, it is not possible to carry out
high-pressure compacting sufficiently. Moreover, the facilities are
very large and expensive. In addition, the resulting green compacts
exhibit low dimensional accuracy. Thus, net-shaped component parts,
the greatest characteristic of green compacts, have not been
produced yet actually.
[0015] The situations are the same for the case where Al powders
are used. Moreover, when Al powders are mixed with lubricants and
are formed thereafter, there arises another problem that it is
impossible to dewax sufficiently because the dewaxing temperature
of the lubricants is close to 500.degree. C. approximately, the
sintering temperature of the resulting green compacts.
SUMMARY OF THE INVENTION
[0016] The present invention has been developed in view of such
circumstances. It is therefore an object of the present invention
to provide a process for compacting a green compact with a raw
material powder whose major component is an active metallic element
such as Ti and Al, and which makes it possible to form the raw
material powder by high pressures at actual level, and to provide
high-density green compacts produced thereby.
[0017] Moreover, it is a further object of the present invention to
provide metallic sintered bodies which are made by sintering the
green compacts, and a process for producing the same.
[0018] In addition, not limited to the process for compacting a
green compact and the like, it is a furthermore object of the
present invention to provide a method of working a metallic
workpiece whose major component is an active metallic element, and
worked component parts produced thereby.
[0019] Hence, the present inventors studied wholeheartedly in order
to solve the problems, and repeated trials and errors. As a result,
they thought of applying warm compaction to raw material powders
whose major component is an active metallic element (hereinafter
simply referred to as an "active metallic powder" wherever
appropriate) by means of a die wall lubrication, and actually
confirmed advantages resulting therefrom. Thus, they arrived at
completing the present invention.
Process for Compacting Green Compact
[0020] A process for producing a green compact according to the
present invention comprises the steps of:
[0021] applying a higher fatty acid-based lubricant to an inner
surface of a die;
[0022] filling a raw material powder whose major component is an
active metallic element into the die;
[0023] compacting the raw material powder by warm pressurizing,
thereby making a green compact; and
[0024] ejecting the green compact from the die;
[0025] whereby the resulting green compact has a high density.
[0026] In accordance with the present compacting process, even when
active metallic powders are used, it is possible to produce
high-density green compacts by high-pressure compacting. In this
instance, no galling and the like occur on the inner surface of
dies substantially, and accordingly it is possible to produce green
compacts with favorable dimensional stability and superficial
roughness. Therefore, the longevity of dies is extended, the yield
of raw material powders is improved, and the working cost is
reduced by near net shaping. Thus, it is possible to sharply reduce
the cost of green compacts as well as sintered bodies made
therefrom.
[0027] Moreover, in accordance with the present compacting process,
it is possible to produce advantages satisfactorily, not by
lubricating raw materials internally, but by simply lubricating
dies. Accordingly, the using amount of lubricants is less. Further,
it is possible to highly densify green compacts, and it is
simultaneously possible to obviate dewaxing steps before green
compacts are sintered. Furthermore, it is possible to inhibit
lubricants from adversely affecting green compacts.
[0028] In addition, in accordance with the present compacting
process, the ejection forces can be reduced sharply compared with
those in conventional compacting processes, though the compacting
pressures are enlarged remarkably. Accordingly, it is possible to
eject green compacts with ease. Consequently, it is possible to
greatly enhance the production efficiency of green compacts.
[0029] By the way, the present inventors are currently
investigating wholeheartedly the reasons why it is possible to form
active metallic powders by high pressures, which person having
ordinary skill in the art has been considering impossible. The
reasons can be believed as follows. A new metallic soap film, which
is different from the higher fatty acid-based lubricant used for
lubricating the die, is formed between the green compact and the
inner surface of the die to sharply reduce the friction coefficient
therebetween. Moreover, it is also possible to believe that the
higher fatty acid-based lubricant adsorbs to the surface of the
green compact to produce the Rebinder effect. In addition, it is
also possible to believe that it results from a super-lubricative
action which is beyond the conventional recognition so far.
However, according to the recent examinations and studies by the
present inventors, it is believed reasonable that it results from
the fact that the metallic soap film is formed newly on the surface
of the green compact in the compacting step. Namely, the compacting
step is believed to be a step in which a new metallic soap film,
which comprises the active metallic element and is different from
the higher fatty acid-based lubricant, is formed on the surface of
the green compact. For example, when the active metallic element is
Ti, the metallic soap film is believed to comprise Ti salts of
higher fatty acids. When the active metallic element is Al, the
metallic soap film is believed to comprise Al salts of higher fatty
acids.
[0030] It is apparent anyway that the frictional force between the
raw material powder or green compact and the die is reduced sharply
because the ejection force is very low. However, it is not directly
related to the fact that the friction coefficient is low
exceptionally. Depending on the types of the raw material powder,
there are green compacts whose expansion (or spring back magnitude)
is less after they are ejected from the die. In this instance, even
if the friction coefficient is not low exceptionally, the
frictional force is reduced when the green compact is ejected from
the die.
[0031] The active metallic element set forth in the present
specification can be Ti, Al, Mg, Zr, Na, and rare-earth elements
such as La and Ce. Ti, Al, Mg are important as actual metallic
materials. Namely, it is particularly important industrially when
the raw material powder comprises Ti, Al or Mg. The details will be
described later. Note that the "raw material powder whose major
component is an active metallic element" set forth in the present
specification means that the raw material powder comprises the
objective specific active element in an amount of 50 atomic % or
more when the entire raw material powder is taken as 100 atomic %.
The raw material powder can be not only metallic powders but also
ceramic powders. Therefore, the resulting green compact can be not
only formed metallic bodies but also formed ceramic bodies.
Green Compact
[0032] The present invention is not limited to the present
compacting process, and can be grasped as a green compact produced
as a result of the present production process.
[0033] For example, on the assumption that a green compact is
produced by the present compacting process, the present invention
can be adapted to a green compact wherein the active metallic
element is Ti; and a green density being an apparent density of the
green compact is 85% or more of a true density determined by a
composition of the raw material powder.
[0034] In this instance, the green density can be 88% or more, 90%
or more, 95% or more and even 98% or more of the true density by
controlling the compacting pressure. It is even possible to
approach the green density 100%, the upper limit, limitlessly.
[0035] Likewise, on the assumption that a green compact is produced
by the present compacting process, the present invention can be
adapted to a green compact wherein the active metallic element is
Al; and a green density being an apparent density of the green
compact is 90% or more of a true density determined by a
composition of the raw material powder.
[0036] In this instance as well, the green density can be 93% or
more, 95% or more and even 98% or more of the true density by
controlling the compacting pressure. It is even possible to
approach the green density 100%, the upper limit, limitlessly.
[0037] In the case of conventional green compacts comprising Ti
powders, the green density is about 80% of the true density at the
highest. In the case of conventional green compacts comprising Al
powders, the green density is about 85% of the true density at the
highest. Based on these facts, it is amazing precisely that the
present green compacts have such a high density. Of course, even
when such high-density green compacts are produced, in accordance
with the present compacting process, no galling and the like occur
to the die, the ejection force is low, and green compacts with
favorable dimensional accuracy and superficial roughness can be
obtained as described above.
Process for Producing Metallic Sintered Body
[0038] The present invention is not limited to the present
compacting process, and can be grasped as a process for producing a
metallic sintered body which is made by sintering the green compact
produced by the present compacting process.
[0039] The present invention can be adapted to a process for
producing a metallic sintered body comprising the steps of:
[0040] applying a higher fatty acid-based lubricant to an inner
surface of a die;
[0041] filling a raw material powder whose major component is an
active metallic element into the die;
[0042] compacting the raw material powder by warm pressurizing,
thereby making a green compact;
[0043] ejecting the green compact from the die; and
[0044] sintering the green compact by heating, thereby making a
metallic sintered body;
[0045] whereby the resulting metallic sintered body has a high
density.
[0046] In accordance with the present production process, it is
possible to produce high-density metallic sintered bodies with
ease. Moreover, since the amount of lubricants used in compacting
the green compact is extremely less, no dewaxing step is required
in the following sintering step so that the sintering step can be
simplified remarkably. As a result, the production cost can be
reduced accordingly so that it is possible to produce high-density
metallic sintered bodies at much lower cost.
Metallic Sintered Body
[0047] Moreover, the present can be grasped as a metallic sintered
body produced by the present production process.
[0048] For example, on the assumption that a metallic sintered body
is produced by the present production process, the present
invention can be adapted to a metallic sintered body wherein the
active metallic element is Ti; and a sintered-body density being an
apparent density of the metallic sintered body is 85% or more of a
true density determined by a composition of the raw material
powder.
[0049] In this instance, the greater the green density before
sintering is, the greater the sintered-body density is. The
sintered-body density can be 90% or more, 95% or more, 97% or more
and even 99% or more of the true density. Thus, the sintered-body
density approaches 100%, the upper limit, limitlessly more than the
green density does.
[0050] Likewise, on the assumption that a metallic sintered body is
produced by the present production process, the present invention
can be adapted to a metallic sintered body wherein the active
metallic element is Al; and a sintered-body density being an
apparent density of the metallic sintered body is 90% or more of a
true density determined by a composition of the raw material
powder.
[0051] In this instance as well, the greater the green density
before sintering is, the greater the sintered-body density is. The
sintered-body density can be 93% or more, 95% or more, 97% or more
and even 99% or more of the true density. Thus, the sintered-body
density approaches 100%, the upper limit, limitlessly more than the
green density does.
[0052] In either case, the present metallic sintered bodies suffer
less from dimensional variations such as dimensional contractions
after sintering, because the green density is large before
sintering. Accordingly, although they are sintered products
comprising the active metallic element, they can be formed as net
shapes. Consequently, it is possible to achieve reducing the cost
of Ti or Al products with ease.
Method of Working and Worked Component Member
[0053] In accordance with the present invention, it is possible to
form active metallic powders by high pressures. Based on the fact,
a variety of modes according to the present invention have been
described so far. However, it is believed that the present
invention can be fundamentally characterized in that the frictional
force acts remarkably less between the inner surface of the die and
the active metallic powder or the green compact produced by
pressurizing it. Therefore, the present invention is not limited to
the case where raw material powders are formed by pressuring, and
can be naturally applied to the case where physical metallic
workpieces are worked into desired shapes.
[0054] For example, the present invention can be grasped as a
method of working, comprising the steps of:
[0055] applying a higher fatty acid-based lubricant to at least one
surface selected from the group consisting of a surface of a
metallic workpiece whose major component is an active metallic
element and a working surface of a die; and
[0056] warm working the metallic workpiece with the die.
[0057] In accordance with the present working method, even metallic
workpieces comprising active metallic powders can be worked into
desired shapes not only efficiently and at reduced cost, but also
without causing galling and the like between them and the die, in
the same manner as the above-described present compacting
process.
[0058] The "metallic workpiece" set forth in the present
specification can not only be cast materials but also sintered
materials. The shape of the metallic workpiece is not limited in
particular, and accordingly can be ingots, plates and pipes. In
short, different from metallic powders, the metallic workpiece can
be those having macro contours. Moreover, the term, "working,"
means that the contour of macro physical workpieces is arranged to
desired shapes, specifically, the workpiece is worked into desired
shapes.
[0059] As for such working, there are forging, rolling, extruding,
drawing, component rolling, coining, sizing and re-compressing.
Depending on the types of working, different dies are used. For
example, the die can be forging molds, rolls and dies.
[0060] In order to carry out the working step in warm states, at
least one of the die and the metallic workpiece can be heated
before the working step, or can be heated simultaneously with the
working step.
[0061] Since the metallic workpiece has a contour, the higher fatty
acid-based lubricant can be applied to the metallic workpiece in
the applying step. Of course, the higher fatty acid-based lubricant
can be applied to the die in the same manner as the present
compacting process. For example, the applying step can be dipping
methods in which the workpiece, which is heated, is immersed into a
dispersion, in which the higher fatty acid-based lubricant is
dispersed, or spraying methods in which a dispersion, in which the
higher fatty acid-based lubricant is dispersed, is sprayed onto the
metallic workpiece or the die, which is heated. Note that it is
needless to say that the present invention can be grasped as a
worked component part produced by the present working method.
BRIEF DESCRIPTION OF THE DRAWINGS
[0062] A more complete appreciation of the present invention and
many of its advantages will be readily obtained as the same becomes
better understood by reference to the following detailed
description when considered in connection with the accompanying
drawings and detailed specification, all of which forms a part of
the disclosure:
[0063] FIG. 1 is a graph for illustrating the relationships between
the compacting pressures and the green densities (or relative
densities) when room-temperature and warm compaction were carried
out with a pure titanium powder;
[0064] FIG. 2 is a graph for illustrating the relationships between
the compacting pressures and the ejection forces in the compacting
operations;
[0065] FIG. 3 is a graph for illustrating the relationships between
the compacting pressures applied to the pure titanium powder and
the relative densities of the metallic sintered bodies produced by
sintering the resulting green compacts;
[0066] FIG. 4 is a graph for illustrating the relationships between
the compacting pressures applied to the pure titanium powder and
the dimensional changes after the green compacts were sintered;
[0067] FIG. 5 is a graph for illustrating the relationships between
the compacting pressures and the green-compact densities (or
relative densities) when warm compaction was carried out with
titanium alloy powders;
[0068] FIG. 6 is a graph for illustrating the relationships between
the compacting pressures and the ejection forces in the compacting
operation;
[0069] FIG. 7 is a graph for illustrating the relationships between
the compacting pressures applied to the titanium alloy powders and
the relative densities of the metallic sintered bodies produced by
sintering the resulting green compacts;
[0070] FIG. 8 is a graph for illustrating the relationships between
the compacting pressures and the green densities (or relative
densities) when room-temperature and warm compaction were carried
out with a pure aluminum powder;
[0071] FIG. 9 is a graph for illustrating the relationships between
the compacting pressures and the ejection forces in the compacting
operations;
[0072] FIG. 10 is a graph for illustrating the relationships
between the compacting pressures and the green-compact densities
(or relative densities) when room-temperature and warm compaction
were carried out with a pure aluminum powder and an aluminum alloy
powder;
[0073] FIG. 11 is a graph for illustrating the relationships
between the compacting pressures and the ejection forces in the
compacting operations;
[0074] FIG. 12 is a graph for illustrating the relationships
between the sintering time and the relative density exhibited by a
sintering-resistant material;
[0075] FIG. 13 is a graph for illustrating the relationships
between the sintering time and the dimensional change exhibited by
the sintering-resistant material;
[0076] FIG. 14 is a bar graph for comparing the differences of the
relative density, tensile strength and elongation between an
example and comparative examples when the production conditions
were changed;
[0077] FIG. 15 is a graph for comparing the differences of the
fatigue strength between an example and a comparative example when
the production conditions were changed;
[0078] FIG. 16 is a secondary ion image when a surface of a green
compact comprising a pure Ti powder was observed by TOF-SIMS (i.e.,
time of flight-secondary ion mass spectrometry); and
[0079] FIG. 17 is a secondary ion image when a surface of a green
compact comprising a pure Al powder was observed by TOF-SIMS.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0080] Having generally described the present invention, a further
understanding can be obtained by reference to the specific
preferred embodiments which are provided herein for the purpose of
illustration only and not intended to limit the scope of the
appended claims.
[0081] The present invention will be hereinafter described in more
detail with reference to specific preferred embodiments. Note that
the following descriptions are applicable appropriately to all of
the compacting process, green compacts, metallic sintered bodies,
process for producing the same, working method and worked component
part according to the present invention.
Raw Material Powder
[0082] As described above, the raw material powder comprises a
powder whose major component is an active metallic element.
Ti-based powders and Al-based powders are the representative
options.
[0083] When the active metallic element is Ti, the raw material
powder can comprise pure Ti powders, Ti alloy powders and Ti
compound powders, for example. The raw material powder can be
simple powders comprising one of the powders independently, or can
be mixture powders comprising two or more of the powders. In
addition to Ti, the raw material powder can further comprise at
least one element selected from the group consisting of Al, Zr, Hf,
V, Nb, Ta, Sc, Cr, Fe, Mo, Sn, W, Mn, Ni, Cu, Si, C, B, N and
O.
[0084] Representative Ti compound powders can be titanium boride
powders comprising TiB.sub.2, titanium carbide powders comprising
TiC, titanium nitride powders comprising TiN, and titanium oxide
powders comprising TiO.sub.2, for example.
[0085] The included form of the respective elements does not matter
at all. For example, the respective elements can be included in the
raw material powder as pure powders, alloy powders and compound
powders. The usage and characteristics of the green compacts, or
the sintered bodies resulting therefrom, and the cost of the
powders can determine which elements are included in the raw
material powder.
[0086] When the active metallic element is Al, the raw material
powder can comprise pure Al powders, Al alloy powders and Al
compound powders, for example. In addition to Al, the raw material
powder can further comprise at least one element selected from the
group consisting of Cu, Mn, Zr, Sr, Ni, Cr, Fe, Mo, Sn, Si, C, B, N
and O. Note that representative Al compound powders are aluminum
oxide powders comprising Al.sub.2O.sub.3.
[0087] Similarly to the raw material powder whose major component
is Ti, the raw material powder whose major component is Al can be
likewise simple powders comprising one of the powders
independently, or can be mixture powders comprising two or more of
the powders. The included form of the respective elements does not
matter at all.
[0088] The raw material powder can be mixture powders in which
hard-particle powders comprising borides, nirides, oxides or
carbides. In the mixture powders, two or more hard-particle powders
can be mixed. When hard particles comprise Ti or Al compounds, the
hard-particle powders make the above-described Ti compound powders
or Al compound powders.
[0089] When the raw material powder including a hard-particle
powder is subjected to powder compacting, it is possible to easily
produce a composite material in which the hard particles are
dispersed uniformly in the matrix composed of the active metallic
element, such as Ti and Al, and the alloys resulting therefrom.
Such a composite material is good in terms of the mechanical
characteristics, such as the strength, rigidity, heat-resistance
and wear-resistance. In particular, the metallic sintered bodies
made by sintering the green compacts effect the advantage
remarkably.
[0090] In addition to TiB.sub.2, TiB, TiC, TiN, TiO.sub.2 and
Al.sub.2O.sub.3 described above, the hard particles can comprise
SiC, Si.sub.2N.sub.4, B.sub.4C, CrN, Cr.sub.2N, MoB, CrB,
Y.sub.2O.sub.3, and ThO.sub.2.
[0091] When such hard particles are dispersed in a large amount in
the raw material powder, even if the raw material powder is finely
pulverized, the formability and sinterability of the raw material
powder has been remarkably poor conventionally. On the contrarily,
in the case of the present invention, even when the hard particles
are included in a large amount in the raw material powder, it is
possible to produce high-density green compacts. Moreover, when the
resulting green compacts are sintered, it is possible to produce
high-density sintered bodies by heating the green compacts in a
short period of time. In addition, even when the heating time is
prolonged in the sintering step in order to sufficiently diffuse
the additive elements, the resulting sintered bodies exhibit the
dimensional change so less, and are accordingly stable
dimensionally.
[0092] Hence, when the present invention is used, it is possible to
produce high-density green compacts or sintered bodies even if the
upper limit proportion of the hard-particle powder in the raw
material powder is increased to 5% by mass, 10% by mass, 15% by
mass and 20% by mass. Note that the proportion of the hard-particle
powder is a proportion when the entire raw material powder after
mixing is taken as 100% by mass.
[0093] The alloys, compounds and hard particles included in the raw
material powder are not necessary required to keep the powdery
shape in the green compacts or the metallic sintered bodies
resulting therefrom. They can be turned into more stable states
when the raw material powders are made into the green compacts by
pressurizing or when the green compacts are made into the metallic
sintered bodies by heating. For example, in Ti-based sintered
bodies, there is a case where TiB.sub.2 particles are turned into
TiB which is more stable and harder.
[0094] The respective powders can be mechanically pulverized
powders, hydrogenated-dehydrogenated powders, and atomized powders.
Moreover, their production processes do not matter at all. In
addition, the raw material powder can be granulated powders. It is
not necessarily needed to specify the particle diameters of the raw
material powder. However, it is preferred that the average particle
diameter can fall in a range of from 1 to 100 .mu.m, for
example.
[0095] In the present invention, mixing the raw material powder
with lubricants is not excluded. When a lubricant is included in a
small amount in the raw material powder, it is possible to improve
the flowability of the raw material powder. If such is the case, it
is more preferable to use the higher fatty acid-based lubricant set
forth in the present specification. Note that the higher fatty
acid-based lubricant includes those dispersed in a dispersion.
However, when the raw material powder is mixed with a large amount
of lubricants, it is not preferable because the attainable density
of green compacts lowers as described above.
Higher Fatty Acid-based Lubricant
[0096] The higher fatty acid-based lubricant set forth in the
present specification means both lubricants, i.e., lubricants
comprising higher fatty acids and lubricants comprising metallic
salts of higher fatty acids. The higher fatty acid can be stearic
acid, palmitic acid, and oleic acid. The metallic salt of the
higher fatty acid can be lithium salts, calcium salts, and zinc
salts, for example. Specifically, the metallic salt of the higher
fatty acid can be lithium stearate, calcium stearate, zinc
stearate, barium stearate, lithium palmitate, lithium oleate,
calcium palmitate, and calcium oleate. Note that higher fatty
acid-based lubricants whose major component is at least one of the
compounds listed above can satisfactorily be the higher fatty
acid-based lubricant set forth in the present specification.
[0097] The higher fatty acid-based lubricant can preferably be
solid in a temperature range of from room temperature to warm
temperature. When the higher fatty acid-based lubricant is liquid,
it flows downward so that it is difficult to uniformly apply it to
the inner surface of the die.
[0098] In order to efficiently and uniformly apply the higher fatty
acid-based lubricant to the inner surface of the die, the higher
fatty acid-based lubricant can preferably be dispersed in a
dispersion. The dispersion can comprise water, alcohol-based
solvents, or mixture liquids of water and alcohol-based solvents.
When the higher fatty acid-based lubricant dispersed in such a
dispersion is sprayed onto the die, which is heated, the water
and/or the alcohol-based solvents evaporate instantaneously so that
it is possible to form a uniform lubricant film with ease. In
particular, when the dispersion is mixed with alcohol-based
solvents, the water and the like evaporate so quickly that it is
more likely to form a uniform and smooth lubricant film.
[0099] In the present invention, active metallic powders are used
which are very likely to be seized to dies inherently. Accordingly,
it is especially important to form a uniform lubricant film with
the higher fatty acid-based lubricant. The uniform lubricant film
prolongs the longevity of dies, and makes it possible to stably
produce high-density and quality green compacts.
[0100] When the die is heated, a suitable die temperature depends
on the dispresions. For example, when the dispersion comprises
water, the die temperature can preferably be controlled to
100.degree. C. or more. When the dispersion is mixed with
alcohol-based solvents, the die temperature can be low temperatures
of less than 100.degree. C. depending on the concentration of the
alcohol-based solvents. Indeed, it is further preferable to control
the die temperature to such temperatures that the compacting step
can be carried out in warm states. Anyway, the die temperature can
preferably be from the boiling point of the dispersion or more to
less than the melting point of the higher fatty acid-based
lubricant. The die temperature is controlled to less than the
melting point of the higher fatty acid-based lubricant in order to
inhibit the higher fatty acid-based lubricant from running
downward.
[0101] When mixture liquids in which water is mixed with
alcohol-based solvents are used as the dispersion, the dispersion
can preferably comprise alcohol-based solvents in an amount of from
1 to 50% by volume, further preferably from 5 to 25% by volume, and
the balance of water. When the proportion of alcohol-based solvents
is less than 1% by volume, the advantage of mixing alcohol-based
solvents is effected less. When the proportion of alcohol-based
solvents exceeds 50% by volume, the odors of alcohol-based solvents
degrade the working environments, and such a large amount of
alcohol-based solvents results in increasing costs involved.
[0102] As for such an alcohol-based solvent, it is possible to use
methyl alcohol, ethyl alcohol, and isopropyl alcohol. However, as
far as alcohol-based solvents exhibit a boiling point lower than
that of water, and as far as they are not harmful when they
evaporate, their types do not matter at all.
[0103] The higher fatty acid-based lubricant dispersed in the
dispersion can preferably be formed as powders comprising particles
whose maximum particle diameter is 30 .mu.m or less. When particles
whose maximum particle diameter exceeds 30 .mu.m are included, the
lubricant film formed on the inner surface of the die becomes
uneven. Moreover, the particles of the higher fatty acid-based
lubricant readily precipitate in the dispersion so that it is
difficult to uniformly apply the higher fatty acid-based lubricant
to the inner surface of the die.
[0104] Moreover, in order to uniformly disperse the higher fatty
acid-based lubricant in the dispersion such as water, it is
preferable to add a surfactant in the dispersion in advance.
[0105] The surfactant can be alkylphenol-based surfactants, 6-grade
polyoxyethylene nonyl phenyl ether (EO), 10-grade polyoxyethylene
nonyl phenol ether (EO), anionic surfactants, cationic surfactants,
amphoteric surfactants, nonionic surfactants and boric acid
ester-based emulbon "T-80" (trade name), for example.
[0106] One or more of the surfactants can be appropriately selected
to use depending on using higher fatty acid-based lubricants. For
example, when lithium stearate (hereinafter abbreviated to as
"LiSt") is used as the higher fatty acid-based lubricant, it is
preferable to simultaneously add three kinds of surfactants,
6-grade polyoxyethylene nonyl phenyl ether (EO), 10-grade
polyoxyethylene nonyl phenyl ether (EO) and boric acid ester
emulbon "T-80," to the dispersion at the same time.
[0107] The three surfactants are added to the dispersion, because
LiSt is less likely to disperse in water or the like when the boric
acid ester emulbon "T-80" is added to the dispersion independently.
On the other hand, LiSt disperses in water or the like, when the
6-grade polyoxyethylene nonyl phenyl ether (EO) and the 10-grade
polyoxyethylene nonyl phenyl ether (EO) are added to the dispersion
independently. However, when the resulting dispersions are diluted,
the higher fatty acid-based lubricant is less likely to disperse
uniformly. Therefore, when LiSt is used as the higher fatty
acid-based lubricant, it is preferable to compositely add the three
surfactants to the dispersion appropriately. The addition of the
surfactant can preferably fall in a range of from 1.5 to 15% by
volume when the entire dispersion involving the surfactant is taken
as 100% by volume. In this instance, note that it is preferable to
mix the three surfactants in a volumetric proportion of 1:1:1.
[0108] The more the addition of the surfactant is, the more the
higher fatty acid-based lubricant such as LiSt is dispersed in
water or the like. However, when the addition of the surfactant is
too much, the viscosity of the resulting dispersions heightens so
that it is difficult to finely pulverize the particles of the
higher fatty acid-based lubricant by a pulverizing treatment
described later.
[0109] Moreover, when an antifoaming agent is further added to the
dispersion in a small amount appropriately, a uniform lubricant
film is likely to form. The antifoaming agent can be silicone-based
antifoaming agents, for example. The addition of the antifoaming
agent can preferably fall in a range of from 0.1 to 1% by volume
approximately when the entire volume of the dispersion is taken as
100% by volume.
[0110] When a powdery higher fatty acid-based lubricant is
dispersed in the dispersion involving the surfactant, it is
preferable to carry out a ball-milling pulverizing treatment. For
example, the ball-milling pulverizing treatment can be carried out
in the following manner. 10 to 30 g LiSt is added to 100 cm.sup.3
dispersion, and is pulverized with steel balls covered with
polytetrafluorethylene. When the treatment is carried out for 50 to
100 hours approximately, LiSt which is pulverized to have the
maximum diameter of 30 .mu.m or less is dispersed to float in the
dispersion.
Applying Step
[0111] When the higher fatty acid-based lubricant is applied to the
inner surface of the die, it is preferable to properly dilute the
dispersion in which the higher fatty acid-based lubricant is
dispersed. Specifically, when the entire diluted dispersion is
taken as 100%by mass, the stock dispersion can preferably be
diluted so that the concentration of the higher fatty acid-based
lubricant such as LiSt is from 0.1 to 5% by mass, further from 0.5
to 2% by mass. When the stock dispersion is thus diluted, it is
possible to form thin and uniform lubricant films.
[0112] It is possible to uniformly apply the higher fatty
acid-based lubricant to the inner surface of the die by spraying
the diluted dispersion with spraying guns for coating operations,
for example. Moreover, the higher fatty acid-based lubricant can be
applied to the inner surface of the die with electrostatic coating
devices such as electrostatic guns. In addition, it is possible to
appropriately refer to the methods disclosed in FIG. 1 or FIG. 2 of
above-described PCT International Laid-Open Publication No.
WO01/43,900 for specific methods for uniformly applying the higher
fatty acid-based lubricant to the inner surface of the die.
Compacting Step
[0113] In the present compacting process, the compacting step is a
step in which the active metallic powder which is filled into the
die with the higher acid-based lubricant applied is formed by warm
pressurizing.
[0114] The term, "warm," set forth in the present specification
depends on using raw material powders and higher fatty acid-based
lubricants. It seems difficult to explicitly define the specific
temperatures. If the term, "warm," is defined daringly, it
specifies temperature ranges where the advantage of reducing
ejection forces are effected even when high-pressure compaction is
carried out. However, according to the experiences of the present
inventors, such a warm state can be defined by a temperature of an
area where at least the inner surface of the die contacts with the
raw material powder (hereinafter referred to as a "contact-area
temperature"), and the contact-area temperature can desirably fall
in a range of from 100 to 225.degree. C., further desirably from
100 to 180.degree. C. The contact-area temperature can be optimized
for every active metallic powder. For example, the contact-area
temperature can preferably fall in a range of from 130 to
160.degree. C. when the active metallic element is Ti, and can
preferably fall in a range of from 100 to 160.degree. C. when the
active metallic element is Al.
[0115] Such a warm state can be attained by heating at least one of
the die and the raw material powder. However, when both of them are
heated to an identical temperature substantially, it is possible to
produce a more stable warm state.
[0116] In the present compacting process, there is no upper limit
regarding the compacting pressure. If the range of the compacting
pressure is specified daringly, the compacting pressure falls in a
range where no dies or forming apparatuses are damaged or broken.
Therefore, it is possible to carry out forming powders without
problems even by such a high compacting pressure as 2,500 MPa
approximately, which has been unconceivable in forming active
metallic powders. However, there is a pressure range where not only
sufficiently high-density green compacts can be produced but also
the productivity can be improved, and the compacting pressure can
preferably fall in a range of from 392 to 2,000 MPa, further
preferably from 588 to 1,568 MPa. When the compacting pressure is
less than the lower limit, 392 MPa, no high-density green compacts
can be produced. Note that such compacting pressures do not
necessitate to use the present compacting process at all, and lie
at the level which even the conventional powder compacting
processes can reach. In the present compacting process, the lower
limit of the compacting pressure can preferably be 686 MPa or more,
further preferably be 784 MPa or more.
[0117] The compacting pressure can be optimized for every active
metallic powder. For example, the compacting pressure can
preferably fall in a range of from 500 to 2,500 MPa, further
preferably from 784 to 1,568 MPa, when the active metallic element
is Ti. Moreover, the compacting pressure can preferably fall in a
range of from 392 to 2,500 MPa, further preferably from 588 to
1,568 MPa, when the active metallic element is Al.
[0118] The relationship between the compacting pressures and the
ejection forces will be hereinafter described.
[0119] In usual powder compacting, the higher the compacting
pressure is, the higher the ejection force is required to eject
green compacts from dies. However, in the present compacting
process, although it is possible to achieve highly densifying green
compacts by enlarging the compacting pressure, the ejection force
is hardly changed or is increased slightly. In addition, in
accordance with the present compacting process, the ejection force
is reduced by a factor of about {fraction (1/10)} compared with the
case where the conventional powder compacting processes are used.
For example, the ejection force can be 10 MPa or less in the
ejecting step when the compacting pressure is 784 MPa or more in
the compacting step. The ejection force does not change even when
the compacting pressure is 980 MPa or more, further 1,176 MPa or
more, furthermore 1,372 MPa or more. To be more precise, the
ejection force can be 5 MPa or less, further 3 MPa or less.
[0120] Let us observe the ejection force for every active metallic
powder. When the active metallic element is Ti, the ejection force
can preferably be 10 MPa or less, further 3 MPa or less, when the
compacting pressure is 784 MPa or more. When the active metallic
element is Al, the ejection force can preferably be 5 MPa or less
when the compacting pressure is 392 MPa or more, and can further
preferably be 1 MPa or less when the compacting pressure is 588 MPa
or more.
[0121] In the present compacting process, when the pressure ratio,
the ratio of the ejection force with respect to the compacting
pressure, is examined, the pressure ratio can preferably show a
decreasing tendency when the compacting pressure increases.
Others
[0122] The die set forth in the present specification can be either
made of high-speed steel or high-speed tool steel, or can be made
of cemented carbide. The inner surface of the die can be subjected
to a TiN coating treatment. Note that the smaller the superficial
roughness of the die is, the more effectively the frictional force
between the die and the green compact is reduced. Accordingly, the
resulting green compact is improved in terms of the superficial
roughness and dimensional stability.
[0123] Since the present green compact and metallic sintered body
made by sintering it have a high density which is very close to the
true density, they are good in terms of the metallic
characteristics such as the strength. Therefore, they can be
applied not only to a variety of ordinary component parts but also
to structural component parts.
[0124] In particular, when the active metallic element is Ti, the
green compact and metallic sintered body resulting therefrom
according the present invention offer incredible effectiveness.
Conventionally, in the fields of aviation, space and military,
titanium alloys which are lightweight and exhibit high strength
(i.e., which are good in terms of the specific strength) have been
used in a large volume. However, titanium alloys haven been hardly
applied to consumer products which are mass-produced generally. In
particular, iron or steel materials have been often used in
mass-produced exclusive component parts. However, there has been no
example in which titanium alloys are applied to the mass-produced
exclusive component parts instead of the iron or steel materials.
This is because the manufacturing cost has gone up sharply when
titanium alloys are used. Thus, titanium alloys are not adequately
applied to mass-produced component parts which are required to be
low cost. The biggest factor heightening the manufacturing cost is
that not only the material cost is expensive but also the secondary
working cost is extremely high when the workpieces are worked into
the respective component parts. This is because the workpiece
shapes of titanium alloys are limited.
[0125] On the other hand, when the present compacting process,
sintering process and working method are used, it is possible to
produce component parts made of titanium alloys, which are
lightweight and are good in terms of the strength, without
substantially generating the high secondary working cost.
Accordingly, it is possible to substitute a variety of
mass-produced component parts made of titanium alloys for those
conventional ones made of iron or steel materials.
[0126] As for such mass-produced component parts, there are
automotive component parts which require all sorts of strength, a
variety of sporting goods and tools, for example. More
specifically, the automotive component parts can be automotive
engine component parts such as engine valves, valve retainers,
valve lifters, piston pins, valve guides, connecting rods and
rocker arms. Moreover, the automotive component parts can be power
transmission component parts such as gears, driving shafts and
blocks for CVT (i.e., continuously variable transmission). The
sporting goods can representatively be golf clubs such as drivers,
irons and putters.
[0127] Moreover, when the present compacting process, sintering
process or working method is applied to conventional die-forming
designing, it is possible to form cylinder-shaped component parts,
such as billets for extrusion, piston pins, valve guides, valve
retainers, connecting rods, blocks for CVT, irons and putters.
[0128] In addition, when the present compacting process, sintering
process or working method is applied to advanced forming processes
such as CNC (i.e., computer numerically controlled) pressing, it is
possible to form engine valves, valve lifters, rocker arms, gears,
driving shafts and golf-club heads.
EXAMPLES
[0129] The present invention will be hereinafter describe in more
detail with reference to specific examples.
(1) Examples
Raw Material Powder
[0130] Before mixing a raw material powder, five powders were first
prepared as follows. A pure titanium powder, a pure aluminum
powder, an Al-6% Zn-2% Mg-1.5% Cu alloy powder, an Al.sub.3V powder
and a TiB.sub.2 powder were prepared. The pure titanium powder was
produced by WUYI Co., Ltd., and had an average particle diameter of
42 .mu.m. The pure aluminum powder was produced by FUKUDA KINZOKU
HAKUHUN Co., Ltd., and had an average particle diameter of 30
.mu.m. The alloy powder was produced by SUMITOMO KEIKINZOKU Co.,
Ltd., and had an average particle diameter of 35 .mu.m. Note that
the unit of the alloy composition is expressed by % by mass (being
the same hereinafter) The Al.sub.3V powder was produced by NIHON
DENKO Co., Ltd., and had an average particle diameter of 20 .mu.m.
The TiB.sub.2 powder was produced by NIHON SHINKINZOKU Co., Ltd.,
and had an average particle diameter of 3.5 .mu.m. Note that the
TiB.sub.2 powder corresponds to the hard-particle powder set forth
in the present specification.
[0131] Then, the powders were used independently, or were mixed
appropriately, thereby preparing active metallic powders having 5
compositions as set forth in Table 1.
Preparation of Die Wall Lubricant
[0132] As a surfactant, 6-grade polyoxyethylene nonyl phenyl ether
(EO), 10-grade polyoxyethylene nonyl phenyl ether (EO) and boric
acid ester-based emulbon "T-80" (trade name) were used. The three
sufactants were mixed in a ratio of 1:1:1 by volume, and the
resulting mixture surfactant was contained in a proportion of 1.5%
by volume in 100% by volume water (i.e., a dispersion). Moreover,
an antifoaming agent was added to the dispersion in a proportion of
0.1% by volume. In addition, a lithium stearate (hereinafter
abbreviated to as "LiSt") powder was dispersed in an amount of 25 g
with respect to the 100 cc water including the mixture surfactant.
The LiSt had a melting point of about 225.degree. C., and had an
average particle diameter of 20 .mu.m.
[0133] Then, the dispersion was subjected to a fine-pulverizing
treatment with a ball-milling pulverizing apparatus provided with
polytetrafluorethylene-coated steel balls for 100 hours. The
resulting stock solution immediately after the fine-pulverizing
treatment was diluted with water and an ethyl alcohol-based
solvent. In this instance, water was used in an amount of 14 parts
by volume, and the ethyl alcohol-based solvent was used in an
amount of 5 parts by volume, respectively, with respect to 1 parts
by volume of the stock solution. Hence, the ethyl alcohol-based
solvent was added in an amount of 25% by volume with respect to
100% by volume water. Thus, a die wall lubricant to be applied to
the inner surface of a die was prepared.
Die
[0134] A die was prepared. The die was made of cemented carbide,
and had a cylinder-shaped cavity whose size was .o
slashed.23.000.+-.0.005 mm.times.50 mm. Moreover, an upper punch
and a lower punch were prepared. The upper and lower punches were
made of high-speed steel. The inner surface of the die was
subjected to a TiN coating treatment in advance to exhibit a
superficial roughness of 0.4 Z. In addition, a band heater was
wound around the die so that the die could be heated whenever
appropriate.
Compacting
[0135] The die and the respective raw material powders were heated
to 150.degree. C. Note that the raw material powders were heated
with an oven (i.e., an electric furnace) in air.
[0136] To the inner surface of the die which was heated to
150.degree. C., the die wall lubricant was sprayed uniformly with a
spraying gun at a rate of 1 cm.sup.3/sec. approximately. Thus, a
lubricant film was formed on the inner surface of the die in a
thickness of about 1.5 .mu.m (i.e., an applying step).
[0137] Into the die, the heated raw material powders were filled,
respectively (i.e., a filling step). The raw materials were
compacted by warm pressurizing while changing the compacting
pressure in a range of from 392 to 1,568 MPa appropriately (i.e., a
compacting step). Table 1 also summarizes the compacting pressures
in the compacting step.
[0138] The upper and lower punches were actuated to eject the
formed green compacts from the die, respectively (i.e., an ejecting
step). The ejection forces in the ejecting step were also
measured.
[0139] Moreover, the green compacts comprising the Ti-based powders
were sintered in vacuum at 1,300.degree. C. for 4 hours (i.e., a
sintering step).
(2) Comparative Examples
[0140] As comparative examples, green compacts were produced with
the pure titanium alloy and pure aluminum alloy and by compacting
them at room temperature. In this instance, a commercially
available dry fluorine lubricant "YUNON-S" (trade name) was used as
a die wall lubricant, and was applied to the inner surface of the
die by spraying in the same manner as the examples. The compacting
pressure was controlled basically in such a range that the die was
not damaged by galling and the like. Table 1 also summarizes the
compacting pressures in the compacting operation.
Measurements
[0141] The green compacts produced in the examples and comparative
examples were examined for the green density and the ejection
force, respectively. Table 1 also summarizes the results of the
measurements. Moreover, Table 1 also summarizes the ratio (i.e.,
the relative density) of the green density with respect to the true
density. Note that the true density was found by examining cast
products, which had the same composition as those of the respective
raw material powders, for the density. The green density was
calculated from measured values which were obtained by measuring
the weight and dimensions of the respective green compacts.
[0142] The ejection force was determined in the following manner.
An ejecting load was measured with a load cell. The measured load
was divided by the lateral area of the respective green compacts to
determine the ejection force.
[0143] Moreover, regarding the metallic sintered bodies, the
dimensional change occurred in the sintering step was determined by
measuring the dimensions before and after the sintering step. The
sintered-body density of the respective sintered bodies was
measured by an Archimedes method.
Assessment
Examples Made of Titanium-based Raw Material Powder
Examples Made of Pure Titanium Powder
[0144] The lines of Table 1 designated with Sample Nos. 1-1 through
1-6 and Sample Nos. C1-1 though C1-3 as well as FIGS. 1 through 4
set forth the characteristics when the pure titanium powder was
compacted by a variety of compacting pressures.
[0145] It is apparent from Table 1 and FIGS. 1 through 4 that, in
accordance with the present examples in which the pure titanium
powder was warm compacted, high-pressure compaction was realized in
which the pure titanium powder could be formed by a compacting
pressure beyond 1,500 MPa. Thus, it was possible to provide a
process for compacting an exceptionally high-density green
compact.
[0146] Specifically, the green relative density was well over 85%,
the conventional maximum level, and reached in a range of from 98
to 99%. Thus, green compacts were produced whose green density was
virtually equal to the true density.
[0147] Note that the relative density is employed as an index of
the green density in Table 1 as well as FIG. 1 and so on, because
the true density depends on the composition. Thus, the relative
density is employed in order to objectively assess the extent of
high densification by the present compacting process. The
discussion is similarly applicable to the sintered-body
density.
[0148] When observing FIG. 2, it is apparent that, in the examples,
the compacting pressure increased remarkably though the ejection
force hardly varied. Moreover, when the compacting pressure was
about to exceed 600 MPa, the ejection force decreased to such very
low values as 5 MPa or less. In addition, when the compacting
pressure exceeded 784 MPa, the ejection force was substantially
constant at such an extremely low value as about 2.5 MPa.
[0149] On the other hand, in room-temperature compacted
green-compacts of the comparative examples, galling occurred to the
die when the compacting pressure was no more than 588 MPa.
Moreover, the relative density of the produced green compacts did
not reach even 85% at best. In addition, when the pure titanium
powder was compacted at room temperature, the ejection force
enlarged sharply in proportion to the increment of the compacting
pressure substantially.
[0150] When observing FIG. 3, it is seen that the green density
increased as the compacting pressure increased, and that the
sintered-body density increased as the green density increased. In
particular, in the present examples, when the green compacts which
were compacted by the compacting pressure of 1,176 MPa or more were
sintered, the density of the resulting sintered body increased
virtually equal to the true density.
[0151] In addition, when observing FIG. 4, it is understood that
the dimensional change before and after sintering was very small in
the present examples so that it fell in a range of from about 1 to
3%. On the other hand, the comparative examples in which the pure
titanium powder was compacted at room temperature, the original
green compacts per se had a low density. Accordingly, the
dimensional change before and after sintering was considerably
large so that it fell in a range of from 4 to 10%.
Examples Made of Titanium Alloy Powder
[0152] The lines of Table 1 designated with Sample Nos. 2-1 through
2-3 and Sample Nos. 3-1 though 3-3 as well as FIGS. 5 through 7 set
forth the characteristics when the alloy mixture powder as well as
the alloy mixture powder with the TiB.sub.2 powder mixed were
compacted by a variety of compacting pressures. Note that the alloy
mixture powder was prepared by mixing the pure titanium powder with
the Al.sub.3V powder.
[0153] First, when the mixture powder whose alloy composition was
Ti-6Al-4V was warm compacted, green compacts and metallic sintered
bodies were produced whose green density and sintered body density
were exceptionally high. In particular, the sintered body density
stabilized at such a high value that the relative density was about
99.5% in all of Sample Nos. 2-1 through 2-3. Moreover, in Sample
Nos. 2-1 through 2-3, the ejection force stabilized at such a low
value that it was about 1 MPa or less.
[0154] Then, when the alloy mixture powder with the TiB.sub.2
powder mixed was compacted by warm pressurizing, the resulting
green compacts and metallic sintered bodies had a sufficiently
large green density and sintered body density, and were ejected
from the die by an adequately small ejection force. For example,
when the compacting pressure was 1,176 MPa, the relative density of
the green compact reached 94%, and the sintered-body density of the
metallic sintered body arrived even at 99%. In this instance, the
ejection force of the green compact was about 5 MPa or less in all
of Sample Nos. 3-1 through 3-3.
[0155] Moreover, when the TiB.sub.2 powder was mixed in an amount
of 6% by mass, it is understood from FIG. 6 that an unusual
phenomenon occurred that the ejection force decreased despite the
enlarging compacting pressure.
[0156] However, when Sample Nos. 3-1 through 3-3, in which the
TiB.sub.2 powder was mixed, were compared with Sample Nos. 2-1 and
2-3 free from the TiB.sub.2 powder, the densities were lower
slightly and the ejection forces were somewhat higher for identical
pressures. However, it seems that the density decrement and
ejection force increment depend on the mixing amount of the
TiB.sub.2 powder. It is needless to say that all of the density and
ejection-force values are remarkably good compared with the case
where the alloy mixture powder with the TiB.sub.2 powder mixed was
compacted at room temperature.
[0157] Moreover, it is understood from FIG. 7 that all of Sample
Nos. 2-1 through 2-3 and Sample Nos. 3-1 through 3-3 according to
the present examples had a higher density than comparative samples
did. Note that, in the comparative samples, the alloy mixture
powder with the TiB.sub.2 powder mixed was compacted by 392 MPa by
means of CIP.
Examples Made of Aluminum-based Raw Material Powder
Examples Made of Pure Aluminum Powder
[0158] The lines of Table 1 designated with Sample Nos. 4-1 through
4-7 and Sample Nos. C2-1 though C2-3 as well as FIGS. 8 and 9 set
forth the characteristics when the pure aluminum powder was
compacted by a variety of compacting pressures.
[0159] The overall tendency of the characteristics was similar to
Sample Nos. 1-1 through 1-6 in which the pure titanium powder was
warm compacted. The green compacts according to the present
examples had an extremely high density.
[0160] However, in Sample Nos. 4-1 through 4-7 according to the
present examples, the ejection force was so low as about 1 MPa or
less regardless of the compacting pressures. Namely, even when the
compacting pressure was low, for example, when it was 392 MPa in
Sample No. 4-1, the ejection force was low. When observing the
column of Table 1, "Outside Dia. after Ejection," it is understood
that the phenomenon seems to have resulted from the fact that the
outside diameter of the ejected green compacts was as large as or
slightly less than the inside diameter of the die. However, as can
be seen from Table 1 and FIG. 9, no such tendency was not observed
in Sample Nos. C2-1 through C2-3 in which the pure aluminum powder
was compacted at room temperature.
Examples Made of Aluminum Alloy Powder
[0161] The lines of Table 1 designated with Sample Nos. 5-1 through
5-3 as well as FIGS. 10 and 11 set forth the characteristics when
the one and only aluminum alloy powder whose alloy composition was
Al-6Zn-2Mg-1.5Cu was compacted by a variety of compacting
pressures. The overall tendency of the characteristics was similar
to Sample Nos. 4-1 through 4-7 in which the pure aluminum powder
was warm compacted.
[0162] However, compared with Sample Nos. 4-1 through 4-7 in which
the pure aluminum powder was warm compacted, the density of the
resulting green compacts was lower slightly and the ejection forces
were higher slightly for identical compacting pressures when the
aluminum alloy powder was warm compacted. It seems that this
phenomenon resulted from the fact that the aluminum alloy powder
comprised particles which exhibited higher strength than the pure
aluminum particles did so that the compressibility lowered.
Regardless of the phenomenon, the relative density of the green
compact reached 94% or more. Accordingly, it is understood that
fully high-density green compacts could be produced. It is needless
to say that all of the density and ejection-force values are
remarkably good compared with the case where the aluminum alloy
powder was compacted at room temperature.
Metallic-sintered Body Made of Raw Material Powder with Increased
Hard-particle Content
[0163] The larger the TiB.sub.2-powder content is, the resulting
metallic sintered bodies can exhibit higher rigidity and strength.
On the other hand, the larger the TiB.sub.2-powder content is, the
more the formability and sinterability of green compacts lowers in
general. Accordingly, in order to further assess the formability
and sinterability according to the present compacting process and
sintering process, a metallic sintered body was newly produced
whose TiB.sub.2-powder content was increased up to 12% by mass.
[0164] Except the TiB.sub.2-powder content, anew sample, another
example according to the present invention, was produced under the
same conditions as those of Sample No. 3-3. Specifically, the
titanium alloy mixture powder with the TiB.sub.2 powder mixed was
compacted with the die which was heated to 150.degree. C. by a
compacting pressure of 1,568 MPa, and thereafter the resulting
green compact was sintered at 1,300.degree. C. Moreover, a
comparative sample was produced in the following manner. A raw
material powder having the same composition as that of the new
sample was compacted by a compacting pressure of 588 MPa at room
temperature in the above-described manner, and thereafter the
resulting green compact was sintered at 1,300.degree. C.
[0165] FIGS. 12 and 13 illustrate how the relative density and
dimensional change of the present sample and comparative sample
changed when the sintering time was varied, respectively. Note that
the hard-particle content is expressed by 20% by volume TiB in the
drawings, because the 12% by mass TiB.sub.2 was turned into 20% by
volume TiB by sintering.
[0166] First, as can be seen from FIG. 12, in the present sample, a
sufficiently high-density green compacts were produced by sintering
the raw material powder in an extremely short period of time, and
the relative densities were close to 100%. On the other hand, in
the comparative sample, it took a longer time to sinter the raw
material powder in order to heighten the relative density of the
resulting metallic sintered bodies. Note that, even when the raw
material powder is pulverized to disperse a large amount of hard
particles in the raw material powder, the conventional process like
the comparative sample is considerably poor in terms of the powder
formability and sinterability, and accordingly cannot produce
metallic sintered bodies whose density is as high as those of the
metallic sintered bodies produced by the present sample.
[0167] Then, as can be understood from FIG. 13, in the present
sample, the dimensional change was very small, i.e., 2%
approximately, and stabilized thereat. On the other hand, in the
comparative sample, the dimensional change decreased greatly as the
sintering time prolonged, and did not stabilize at all.
[0168] Thus, in accordance with the present sample, it became
evident that metallic sintered bodies can be produced which have a
high density and are good in terms of the dimensional
stability.
Mechanical Characteristics of Metallic Sintered Body with Hard
Particles Dispersed
[0169] A raw material powder including a TiB.sub.2 powder was
compacted by pressuring, and was further sintered to produce a
metallic-sintered-body sample. The resulting sample was examined
for the tensile strength and fatigue strength.
[0170] The composition of the used raw material powder was the same
as that of Sample No. 3-3 recited in Table 1. The present sample
was produced in the same manner as Sample No. 3-3. However, the
present sample was formed as a shape of traverse test pieces whose
size was 10 mm.times.10 mm.times.55 mm. A comparative sample was
made by sintering a green compact, which was compacted as the
identical shape by 392 MPa by means of CIP, at 1,300.degree. C. The
comparative sample which was sintered for 4 hours was labeled as
Comparative Example No. 1. The comparative sample which was
sintered for 16 hours was labeled as Comparative Example No. 2. The
resulting samples were processed into a tensile-test test piece and
a rotating bending fatigue-test test piece. The respective test
pieces were examined for the mechanical characteristics. FIGS. 14
and 15 illustrate the result of the examinations. For reference,
the hard-particle content is expressed by 10% by volume TiB in the
drawings, because the 6% by mass TiB.sub.2 was turned into 10% by
volume TiB by sintering.
[0171] The following are apparent from FIGS. 14 and 15. The
metallic sintered bodies of the present sample had an exceptionally
higher sintered-body relative density than those of Comparative
Example Nos. 1 and 2. Moreover, it was verified that the metallic
sintered bodies of the present sample were remarkably better than
those of Comparative Example Nos. 1 and 2 in terms of all of the
tensile strength, elongation and fatigue strength
Results of Superficial Analysis on Green Compacts According to the
Present Invention
[0172] The surface of the green compacts of Sample Nos. 1-4 and 4-5
recited in Table 1 was analyzed by TOF-SIMS, respectively. Note
that the green compact of Sample No. 1-4 was made of the pure
titanium powder, and the green compact of Sample No. 4-5 was made
of the pure aluminum powder. FIGS. 16 and 17 illustrates secondary
ion images produced as a result of the analysis.
[0173] From the drawings, it was confirmed that, for both of Sample
Nos. 1-4 and 4-5, the distribution of stearic acid resembled the
distribution of Ti or Al rather than the distribution of Li. It
seems that the result suggests that a mechanochemical reaction
occurred to form a new metallic soap film, which are believed to be
titanium stearate or aluminum stearate, on the surface of the green
compacts in the compacting step according to the present
examples.
[0174] Having now fully described the present invention, it will be
apparent to one of ordinary skill in the art that many changes and
modifications can be made thereto without departing from the spirit
or scope of the present invention as set forth herein including the
appended claims.
1 TABLE 1 Green Compact Metallic Sintered Body Outside Dimension
Compac- Green- Dia. Sintered- Change be- Compo- tion Ejection
compact Relative after body Relative fore and after Sample sition
Pressure Force Density Density Ejection Density Density Sintering
No. (% by mass) (MPa) (MPa) (g/cm.sup.3) (%) (mm) (g/cm.sup.3) (%)
(%) Note Ex. 1-1 Pure Ti 588 3.5 4.025 89.2 23.059 4.325 95.9 -2.60
1-2 784 1.9 4.193 93.0 23.061 4.384 97.2 -1.59 1-3 980 2.4 4.292
95.2 23.065 4.451 98.7 1.37 1-4 1176 2.5 4.364 96.8 23.070 4.496
99.7 -1.11 1-5 1372 2.6 4.391 97.4 23.075 4.501 99.8 -0.87 1-6 1568
2.2 4.422 98.0 23.079 4.505 99.9 -0.60 2-1 Ti-- 784 0.9 3.991 91.1
23.065 4.403 99.3 -3.26 Mixture Powder of 2-2 6Al-- 1176 0.5 4.201
95.9 23.071 4.407 99.4 -1.61 Pure Ti Powder and 2-3 4V 1568 0.5
4.285 97.8 23.081 4.412 99.5 -0.96 Alloy Powder 3-1 Ti-- 784 5.1
3.956 90.2 23.072 4.332 97.4 -3.04 Mixture Powder of 3-2 6Al-- 1176
3.6 4.143 94.3 23.078 4.395 98.8 -2.06 said Mixture Powder 3-3 4V +
1568 2.7 4.234 96.5 23.083 4.412 99.2 -1.46 and Hard-particle
6TiB.sub.2 Powder TiB.sub.2: 6% by mass 4-1 Pure Al 392 0.3 2.613
96.8 22.997 -- -- -- 4-2 588 0.7 2.656 98.4 22.992 -- -- -- 4-3 784
0.7 2.672 99.0 22.994 -- -- -- 4-4 980 0.7 2.682 99.4 22.994 -- --
-- 4-5 1176 0.8 2.686 99.5 22.993 -- -- -- 4-6 1372 0.8 2.667 99.8
22.994 -- -- -- 4-7 1568 0.5 2.667 99.8 22.995 -- -- -- 5-1 Al--
588 1.3 2.616 93.4 23.014 -- -- -- Equivalent to 5-2 6Zn-- 980 1.1
2.741 97.9 23.029 -- -- -- JIS A7475 5-3 2Mg-- 1568 1.4 2.794 99.8
23.038 -- -- -- 1.5Cu Comp. Cl-1 Pure Ti 294 8.0 3.209 71.2 23.068
4.235 93.9 -9.58 Room-temp. Ex. Cl-2 441 16.3 3.521 78.1 23.075
4.290 95.1 -6.94 Compaction Cl-3 588 24.1 3.728 82.9 23.082 4.300
95.3 -4.95 C2-1 Pure Al 392 4.1 2.583 95.7 23.056 -- -- --
Room-temp C2-2 588 5.7 2.615 96.9 23.057 -- -- -- Compaction C2-3
784 6.5 2.640 97.8 23.059 -- -- --
* * * * *