U.S. patent application number 10/724380 was filed with the patent office on 2004-08-26 for sintering method for w-cu composite material without exuding of cu.
This patent application is currently assigned to AGENCY FOR DEFENSE DEVELOPMENT. Invention is credited to Hong, Moon-Hee, Kim, Dae-Gun, Kim, Eun-Pyo, Kim, Young-Do, Lee, Seoung, Lee, Sung-Ho, Noh, Joon-Woong.
Application Number | 20040166014 10/724380 |
Document ID | / |
Family ID | 32310872 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040166014 |
Kind Code |
A1 |
Kim, Eun-Pyo ; et
al. |
August 26, 2004 |
Sintering method for W-Cu composite material without exuding of
Cu
Abstract
Disclosed is a densification process of a W--Cu composite
material, and more particularly, a sintering method for a W--Cu
composite material without exuding of Cu. The sintering method
comprises the steps of: holding a W--Cu composite power compact for
a certain time at a Cu solid phase temperature or at a temperature
just above a melting point and thus inducing a nearly complete
densification; and sintering for a short time at a Cu liquidus
temperature.
Inventors: |
Kim, Eun-Pyo; (Daejeon,
KR) ; Hong, Moon-Hee; (Seoul, KR) ; Noh,
Joon-Woong; (Daejeon, KR) ; Lee, Seoung;
(Daejeon, KR) ; Lee, Sung-Ho; (Daejeon, KR)
; Kim, Young-Do; (Daejeon, KR) ; Kim, Dae-Gun;
(Seoul, KR) |
Correspondence
Address: |
SCULLY SCOTT MURPHY & PRESSER, PC
400 GARDEN CITY PLAZA
GARDEN CITY
NY
11530
|
Assignee: |
AGENCY FOR DEFENSE
DEVELOPMENT
DAEJEON
KR
|
Family ID: |
32310872 |
Appl. No.: |
10/724380 |
Filed: |
November 28, 2003 |
Current U.S.
Class: |
419/57 |
Current CPC
Class: |
B22F 2998/10 20130101;
C22C 1/045 20130101; C22C 27/04 20130101; H01H 1/025 20130101; B22F
1/0003 20130101; B22F 2999/00 20130101; B22F 9/22 20130101; B22F
2998/10 20130101; B22F 3/14 20130101; B22F 3/1035 20130101; B22F
3/1028 20130101; B22F 2998/10 20130101; B22F 1/0003 20130101; B22F
9/22 20130101; B22F 1/148 20220101; B22F 2999/00 20130101; C22C
1/045 20130101; B22F 9/22 20130101; B22F 1/0003 20130101; B22F
2999/00 20130101; B22F 1/148 20220101; B22F 1/0003 20130101; B22F
9/22 20130101; B22F 2998/10 20130101; B22F 1/0003 20130101; B22F
1/148 20220101; B22F 9/22 20130101; B22F 2999/00 20130101; B22F
1/0003 20130101; B22F 1/148 20220101; B22F 9/22 20130101 |
Class at
Publication: |
419/057 |
International
Class: |
B22F 003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2002 |
KR |
75678/2002 |
Claims
What is claimed is:
1. A sintering method for a W--Cu composite material without
exuding of Cu comprising the steps of: holding a W--Cu composite
material prepared by compacting a W--Cu composite powder for
0.5.about.10 hours at 800.about.1083.degree. C. (except
1083.degree. C.) which is a Cu solid phase temperature range under
a reduction atmosphere; and increasing temperature to
1200.about.1400.degree. C. and thereby cooling without a holding
time.
2. A sintering method for a W--Cu composite material without
exuding of Cu comprising the steps of holding a W--Cu composite
material prepared by compacting a W--Cu composite powder for
0.5.about.10 hours at 1083.about.1150.degree. C. which is just
above a Cu melting point under a reduction atmosphere; and
increasing temperature to 1200-1400.degree. C. and thereby cooling
without a holding time.
3. The method of claim 1 or 2, wherein the WCu composite powder
prepared by a method disclosed in the Korean patent application No.
24857 in 2002 is prepared by mixing WO.sub.3/WO .sub.2.9 powder
with CuO/Cu.sub.2O milling, and performing a heat treatment for
reduction at a hydrogen atmosphere, and has a round shape of a
certain size that W powder surrounds Cu powder.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a densification process, of
W--Cu composite material, and more particularly, to a sintering
method for W--Cu composite material without exuding of Cu.
[0003] 2. Description of the Conventional Art
[0004] Generally, a W--Cu composite material has been spotlighted
as a material for high voltage electric contact or a material for
micro packaging, but it is difficult for the W--Cu composite
material to be used for a preparation of a composite material
having a dense structure.
[0005] A densification method of the W--Cu composite material is
divided into an infiltration and a sintering method. The
Infiltration method is for preliminarily sintering W to form a
skeleton having an open pore and infiltrating liquid phase Cu into
the open pore. According to the infiltration method, a complete
densification can be performed by permeating Cu by a capillary
force, but a composition range is limited due to a limitation of a
volume fraction of the open pore. Also, an isolated pore is formed
in the interior of a material. Besides, the W skeleton is collapsed
when a Cu melt is infiltrated into the W skeleton at high
temperature, thereby having a difficulty in forming a uniform
microstructure.
[0006] The sintering method is for mixing W with Cu metal powder
and then densifying at a temperature more than a Cu melting
temperature.
[0007] The densification of the W--Cu composite material according
to the conventional sintering method takes place only by a particle
rearrangement process due to no occurrence of solution
re-precipitation process and a high contact angle between W and Cu.
The particle rearrangement process means that Cu forms a liquid,
phase at a temperature more than a melting point 1083.degree. C.
and a W particle is re-arranged. In this case, the W--Cu composite
material experiences a drastic contraction and is densified. The
W--Cu composite material is densified up to a relative density of
approximately 90% by the particle rearrangement process, and then
has a relative density of approximately 95% by a densification due
to a grain growth process of the W. However, if the densification
process is not completed during the particle rearrangement process
and a densification by a W grain growth process is performed, a
phenomenon of an exuding of Cu is taken place. The phenomenon tends
to be accelerated towards a lower part of a sample. Also, the
higher a Cu composition is and the larger the sample is, the
phenomenon is more accelerated.
[0008] Due to the exuding of Cu, it was difficult to control a
desired Cu composition in the conventional sintering method for a
W--Cu composite material, and it was difficult to obtain a sample
with a uniform microstructure and to control a precise dimension
Furthermore, the phenomenon that Cu exudes troubles more in case
that a component shape has to be sophisticated and a composition
control has to be precisely performed.
[0009] Meanwhile, it has been reported that the densification of
W--Cu composite is increased with increasing degree of missing
between W and Cu and with decreasing particle size of W powder. To
this end, W and Cu oxides are mechanically mixed and milled, and
then reduced by a hydrogen gas, thereby facilitating a complete
densification.
SUMMARY OF THE INVENTION
[0010] Therefore, an object of the present invention is to provide
a sintering method for a W--Cu composite material without exuding
of Cu by a liquid phase sintering method.
[0011] To achieve these and other advantages and in accordance with
the purpose of the present invention, as embodied and broadly
described herein, there is provided a sintering method for a W--Cu
composite material without exuding of Cu comprising the steps of
holding a W--Cu composite power compact for a certain time at a Cu
solid phase temperature or at a temperature just above a melting
point and thus inducing a nearly complete densification; and
sintering for a short time at a Cu liquidus temperature, thereby
having a uniform microstructure and preventing Cu from being exuded
on a surface of a product.
[0012] The foregoing and other objects, features, aspects and
advantages of the, present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
[0014] In the drawings:
[0015] FIG. 1 is a graph showing a sintering method for a W--Cu
composite material according to the present invention;
[0016] FIG. 2 is a graph showing a variation of a relative density
according to a holding time of a W--Cu composite material having, a
composition of (a) W-25 wt % Cu, (b)W-35 wt % Cu, and (c)W45 wt % C
sintered according to the present invention;
[0017] FIG. 3 is a graph showing a sintering process for a W--Cu
composite material in accordance with the conventional art,
[0018] FIG. 4 is a graph showing a variation of a relative density
according to a is Cu composition of a W--Cu composite material
sintered by the conventional method;
[0019] FIG. 5A is an optical microscope picture of a W--CU
composite material sintered with 1 hour holding at 1200.degree. C.
accordance with the conventional art;
[0020] FIG. 5B is an optical microscope picture of a W--Cu
composite material sintered with 4 hour holding at 1100.degree. C.
and then sintered with 0 hour holding at 1200.degree. C. according
to the present invention;
[0021] FIG. 6A is a drawing showing a W45 wt % Cu W--Cu composite
material sintered with 1 hour holding at 1200.degree. C. in
accordance with the conventional art; and
[0022] FIG. 6B is' a drawing showing a microstructure of a W45 wt %
Cu W--Cu composite material sintered with 4 hour holding at
1100.degree. C. and then sintered with 0 hour holding at
1200.degree. C. according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings.
[0024] The present invention relates to a sintering method for a
W--Cu composite material without exuding of Cu comprising the steps
of: holding a W--Cu composite power compact for a certain time at a
Cu solid phase temperature or at a temperature just above a melting
point and thus inducing a nearly complete densification: and
sintering for a short time at a Cu liquidus temperature, thereby
having a uniform microstructure and preventing Cu from being exuded
on a surface of a product.
[0025] The process for holding the W--Cu composite powder compact
at a solid phase temperature for a certain time is performed by an
acceleration of a Cu solid phase sintering, and the reason is for
preventing an exuding of Cu by achieving a densification to some
degree and by finishing a particle rearrangement of W within a
faster time in a state that Cu is melted as a liquid phase.
[0026] The process for holding the W--Cu composite powder compact
at a temperature just above a Cu melting point for a certain time
is performed by an acceleration of a W particle rearrangement, and
the reason is for preventing an exuding of Cu by restraining a W
grain growth by accelerating a particle rearrangement and inducing
a densification at a region just above the Cu melting point where W
particle are initially rearranged and a grain growth is performed
to the minimum.
[0027] The sintering method for a W--Cu composite material without
an exuding of Cu according to the present invention comprises the
steps of: holding a W--Cu composite material prepared by compacting
a W--Cu composite powder at a reduction atmosphere for 0.5-10 hours
at a Cu solid phase temperature or at a temperature just above a
melting point corresponding to 800-1150.degree. C.: and cooling
without a holding time by increasing a temperature into
1200-1400.degree. C.
[0028] The reason why temperature and time are limited in the first
step will be explained. At a temperature below 800.degree. C.,
temperature is too low and thereby a solid phase sintering is not
briskly performed. Also, at a temperature above 1150.degree. C., a
grain growth of W is performed and thereby an exuding of Cu can be
taken place. When a sintering time is below 0.5 hour, a solid phase
sintering and a liquid phase sintering are not sufficiently
performed and a densification is not performed. Also, when a
holding time exceeds 10 hours, the sintering time becomes too long
thus not to have an economic efficiency.
[0029] The reason why temperature is limited as 1200-1400.degree.
C. in the second step is because a particle rearrangement is
briskly performed and an exuding of Cu is not taken place in the
temperature range. If the temperature rises above 1400.degree. C.,
the exuding of Cu is taken place.
[0030] The W--Cu composite powder prepared by a method disclosed in
the Korean patent application No. 24857 in 2002 is prepared by
mixing WO.sub.3/WO.sub.2.9 powder with CuO/Cu.sub.2O milling, and
performing a heat treatment for reduction at a hydrogen atmosphere.
The W--Cu composite powder has a round shape of a certain size that
W powder surrounds Cu powder, and has a very uniform mixed shape
and a very fine grain size thus to be able to obtain a relative
density more than 98% at the time of a sintering process.
[0031] A preparation method of the composite powder will be
explained in more detail. First, W and Cu are weighed for a certain
ratio with WO.sub.3/WO.sub.2.9 powder and CuO/Cu.sub.2O material,
and then uniformly mixed by using a turbular mixing or a ball
milling method. Next, the mixture is held for 1 min-5 hours at a
temperature of 200.degree. C..about.400.degree. C. at a reduction
atmosphere in the first step, then is held for 1 min-5 hours at a
temperature of 500.degree. C..about.700.degree. C. in the second
step, and then is reduced for 1 min-5 hours at a temperature of
750.degree. C..about.1080.degree. C. in the third step. The W--Cu
composite powder prepared by said method has a structure that W
surrounds Cu powder and has no intermediates generation and an
impurities contamination. The W--Cu composite powder has a proper
size and a round shape thus to have an excellent powder flow
characteristic, a molding, characteristic, and a powder injection
molding characteristic.
[0032] Preferred Embodiment
[0033] The preferred embodiment was performed by the sintering
process show in FIG. 1.
[0034] First, by an acceleration of a Cu solid phase sintering,
W--Cu composite powder having three compositions of W-25 wt % Cu,
W-35 wt % Cu, and W45 wt % C were respectively held for 1, 2, and 4
hours at 1000.degree. C., and then the temperature was increased up
to 1200.degree. C. thus to be cooled without a holding time,
thereby performing a densification process. According to this, a
phenomenon of Cu exuding was restrained, of which mechanism will be
explained as follows. Even in case of a large volume fraction due
to a high Cu composition in the W--Cu composite material, a
densification can be performed to some degree only with a Cu solid
phase sintering. Due to the densification in the solid phase step,
a rearrangement of W particles performed after Cu is melted into a
liquid phase is completed faster, thereby restraining the exuding
of Cu.
[0035] Second, by an acceleration of a W particle rearrangement,
W--Cu composite powder, the W--Cu composite powder was held for 1,
2, and 4 hours like the Cu solid phase acceleration method at
1100.degree. C. which is a temperature just above a Cu melting
point, and then the temperature was increased up to 1200.degree. C.
thus to be cooled without a holding time, thereby performing a
densification process. The process is for preventing an exuding of
Cu by restraining a W grain growth by accelerating a particle
rearrangement and inducing a densification at a region just above
the Cu melting point where W particles are initially rearranged and
a grain growth is performed to the minimum.
[0036] FIG. 2 is a graph showing a variation of a relative density
according to a holding time of the W--Cu composite material
prepared according to the present invention. As shown in FIG. 2A,
in case of 25 wt % where a Cu composition is relatively low, both
the Cu solid phase sintering acceleration method and the W particle
rearrangement acceleration method show a comparatively low relative
density. According to a holding time increase at each temperature,
the relative density is increased, but it is judged that a great
density increase can not be anticipated even if the holding time is
to be increased. However, it is observed that a relative density of
the sample prepared according to the present invention is the same
or higher than the sample shown in FIG. 4.
[0037] As shown in FIG. 2B, if the Cu composition is increased to
35 wt %, a relative density is considerably increased. It is
observed that a relative density held for 4 hours at 1000.degree.
C. or 1100.degree. C. according to the present invention is the
same or higher than that of FIG. 4. In case that the Cu composition
is the most increased to 45 wt %, the sample held for more than 2
hours at 1100.degree. C. and then increased to 1200.degree. C. thus
to be cooled as shown in FIG. 2C is almost densified. Also, in case
of the sample held at 1000.degree. C. and then treated with a
temperature increase thus to be cooled showed almost the same
relative density as the sample held at 1200.degree. C.
[0038] Comparison Example
[0039] In order to compare with the present invention, a sintering
was performed by the conventional method using a W--Cu composite
powder W--Cu composite powder having three compositions of W-25 wt
% Cu, W-35 wt % Cu, and W45 wt % C prepared by mechanically
mixing/milling W--Cu oxide and then reducing by hydrogen was used
as an ingredient powder. The composite powder was molded with 100
MPa pressure in a cylindrical die, and sintered for 1 hour at
1200.degree. C. under a hydrogen atmosphere according to the
sintering process shown in FIG. 3. As the result, as shown in FIG.
4, the more the Cu composition was, the more increased the relative
density was, and a densification more than approximately 96% was
shown at 45 wt % Cu.
[0040] However, in case of densifying by the conventional sintering
method, a sufficient densification can not be obtained in a
particle rearrangement step, and a final densification is performed
in a pore removal step by a W grain growth. Also, a higher
sintering temperature is required in order to accelerate an
insufficient densification in the particle rearrangement step. The
W grain growth and the high sintering temperature accelerate a
phenomenon of exuding of Cu.
[0041] FIG. 5A is, an optical microscope picture of a W--Cu
composite material of 45 wt % in accordance with the conventional
art, and FIG. 5B is an optical microscope picture of a W--Cu
composite material of 45 wt % according to the present invention.
As shown, the phenomenon of exuding of Cu is restrained in the
sample prepared according to the present invention than the sample
prepared according to the conventional sintering method. Also, as
shown in FIG. 6, a microstructure of the W--Cu prepared by the
present invention has a uniform and smaller W grain size than that
prepared by a general sintering method, and the densification was
performed like a general sintering method.
[0042] That can be also certified by a W grain size measuring
result of a following table 1. From the table 1, it can be seen
that W grains by a particle rearrangement acceleration method are
finer than W grains by a general sintering method. This is because
exuding of Cu is restrained and a densification is increased by
accelerating a particle rearrangement and by decelerating a grain
growth.
[0043] The table 1 shows an average W grain size and a relative
density of samples sintered according to the present invention and
the conventional method by using an image analysis at W45 wt %
Cu
1TABLE 1 W-45 wt % Cu Feret diameter(.mu.m) Relative density(%)
1100.degree. C./4 h-1200.degree. C./0 h 0.764 97.5 (the present
invention) 1200.degree. C./1 h 0.859 96.7 (the conventional
method)
[0044] According to the densification method for a W--Cu composite
material of the present invention, the phenomenon of Cu exuding is
restrained and a W--Cu composite material having a uniform
microstructure can be provided. Especially, the present invention
can be applied to a preparation of W--Cu components having a minute
and sophisticated shape, thereby being able to be applied to a
powder injection molding (PIM) which is being spotlighted recently.
Also, the present invention can be applied to a preparation of a
large component since the phenomenon of exuding of Cu is more
generated at the time of preparing a relatively large component
[0045] Also, the phenomenon of exuding of Cu can be restrained to a
maximum and a densification can be performed by using a method that
a proper time is held at a Cu solid phase step and then temperature
is increased up to a periphery of a W rearrangement finishing
temperature thus to be cooled, or by using a method that a proper
time is held just above a Cu melting temperature and then
temperature is increased up to a periphery of a W rearrangement
finishing temperature thus to be cooled. This enables a precise
composition control of the W--Cu composite material, so that the
W--Cu composite material can have a constant characteristic.
According to this, a surface post-processing cost is reduced and a
component of a complicated shape required at a powder injection
molding can be easily prepared by a near net-shape forming.
[0046] As the present invention may be embodied in several forms
without departing from the spirit or essential characteristics
thereof, it should also be understood that the above-described
embodiments are not limited by any other details of the foregoing
description, unless otherwise specified, but rather should be
construed broadly within its spirit and scope as defined in the
appended claims, and therefore all changes and modifications that
fall within the metes and bounds of the claims, or equivalence of
such metes and bounds are therefore intended to be embraced by the
appended claims.
* * * * *