U.S. patent application number 11/066228 was filed with the patent office on 2005-09-01 for method of producing target material of mo alloy.
This patent application is currently assigned to HITACHI METALS, LTD.. Invention is credited to Inoue, Keisuke, Iwasaki, Katsunori, Uemura, Norio.
Application Number | 20050191202 11/066228 |
Document ID | / |
Family ID | 34879772 |
Filed Date | 2005-09-01 |
United States Patent
Application |
20050191202 |
Kind Code |
A1 |
Iwasaki, Katsunori ; et
al. |
September 1, 2005 |
Method of producing target material of Mo alloy
Abstract
Disclosed is a method of producing a target material of a Mo
alloy, which includes the steps of (a) preparing a green compact by
compressing a raw material powder blend consisting of a Mo powder
having an average particle size of not more than 20 .mu.m and a
transition metal powder having an average particle size of not more
than 500 .mu.m; (b) pulverizing the green compact to produce a
secondary powder having an average particle size of from not less
than an average particle size of the raw material powder blend to
not more than 10 mm; (c) filling the secondary powder into a
container for pressurizing; and (d) subjecting the secondary powder
with the container for pressurizing to sintering under pressure
thereby obtaining a sintered body of the target material.
Inventors: |
Iwasaki, Katsunori; (Yasugi,
JP) ; Inoue, Keisuke; (Yasugi, JP) ; Uemura,
Norio; (Yonago, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
HITACHI METALS, LTD.
|
Family ID: |
34879772 |
Appl. No.: |
11/066228 |
Filed: |
February 25, 2005 |
Current U.S.
Class: |
419/28 ;
419/29 |
Current CPC
Class: |
B22F 3/162 20130101;
B22F 2003/248 20130101; B22F 2998/10 20130101; B22F 3/1208
20130101; B22F 2998/10 20130101; B22F 2998/00 20130101; B22F
2998/00 20130101; B22F 3/15 20130101; B22F 1/0096 20130101; B22F
3/162 20130101; B22F 1/0003 20130101; B22F 5/003 20130101; B22F
2998/00 20130101; C22C 1/045 20130101; C23C 14/3414 20130101 |
Class at
Publication: |
419/028 ;
419/029 |
International
Class: |
B22F 003/24 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2004 |
JP |
2004-055021 |
Claims
1. A method of producing a target material of a Mo alloy, which
comprises the steps of: (a) preparing a green compact by
compressing a raw material powder blend consisting of a Mo powder
having an average particle size of not more than 20 .mu.m and a
transition metal powder having an average particle size of not more
than 500 .mu.m; (b) pulverizing the green compact to produce a
secondary powder having an average particle size of from not less
than an average particle size of the raw material powder blend to
not more than 10 mm; (c) filling the secondary powder into a
container for pressurizing; and (d) subjecting the secondary powder
with the container for pressurizing to sintering under pressure
thereby obtaining a sintered body of the target material.
2. A method according to claim 1, wherein the transition metal is
any one selected from the group consisting of Ti, Zr, Hf, V, Nb,
Ta, Cr and W.
3. A method according to claim 1, wherein after the sintering
process (d), the sintered body being enveloped in the container is
subjected to hot plastic working.
4. A method according to claim 1, wherein the hot plastic working
is of plural times of plastic working under the conditions of a
reduction ratio of 2 to 50% and a temperature of 500 to
1500.degree. C.
5. A method according to claim 1, wherein after the step (d), the
sintered body being enveloped in the container is subjected to hot
plastic working followed by recrystallization heat treatment.
6. A method according to claim 5, wherein the hot plastic working
is of plural times of plastic working under the conditions of a
reduction ratio of 2 to 50% and a temperature of 500 to
1500.degree. C.
7. A method according to claim 6, wherein the recrystallization
heat treatment is carried out at a temperature of 1000 to
1500.degree. C.
8. A method according to claim 1, wherein the compression process
in the step (a) is carried out by cold isostatic pressing under a
pressure of not less than 100 MPa.
9. A method according to claim 1, wherein the sintering process in
the sintering process (d) is carried out by hot isostatic pressing
at a temperature of 1000 to 1500.degree. C. under a pressure of not
less than 100 MPa.
10. A method according to claim 1, wherein the container filled
with the secondary powder is of a metal capsule having a
substantially rectangular parallelepiped form one of which face is
used as an inlet opening for filling the secondary powder, the face
being opposite to a bottom wall of the container forming the
maximum depth, and which inner space has a maximum length of not
less than 1000 mm.
11. A method according to claim 10, wherein the sintered body is
sliced to obtain a plurality of tabular targets so as to maintain a
maximum side length of the sintered body.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method of producing a
target material of a Mo alloy by a powder sintering method.
[0002] At present, a film of a refractory metal such as Mo having
low electric resistance is used for a thin film electrode, thin
film wiring and so on in a liquid crystal display (hereinafter
referred to as LCD), which thin metal film is generally formed from
a target material for sputtering. In recent years, there is a trend
toward larger size LCDs which accompany a demand for a larger size
of the target material, particularly, a long size article having a
length of not less than 1 m or a large size article having a
sputtering area of more than 1 m.sup.2.
[0003] Conventionally, in response to the trend toward a larger
size of the sputtering area, there have been proposed several ways
including a method of bonding a number of raw target material
sections to a backing plate. However, according to such a method of
using the number of bonded raw target material sections, there
arises a problem of particles contained in a deposited film due to
abnormal spatters of the material which are generated during
sputtering process because of a clearance existing between the
respective adjacent bonded raw target material sections. In order
to overcome such a problem, there has been a need for using an
integrated raw target material member.
[0004] Hitherto, while there has been used a powder sintering
process in order to produce a target material of a refractory metal
such as Mo, when producing such an integrated raw target material
member having a larger size, important is how to obtain a high
density and a larger size material. There are various types of the
powder sintering process, which include a hot isostatic pressing
method (herein below referred to as HIP). According to the HIP
method, it is possible to apply a high pressing pressure
three-dimensionally to a raw powder, whereby advantageously
enabling it to have a high and uniform density as compared with a
hot pressing method according to which the pressing pressure can be
applied to the raw powder only two-dimensionally.
[0005] In the HIP method, it is necessary to fill a raw powder to
be sintered into a container for pressurizing efficiently and
uniformly prior to pressurizing the raw powder. Thus, there has
been proposed some methods how to apply a pressurizing pressure to
the packed raw material powder, which can be seen JP-A-2002-167669
and JP-A-2003-342720, for example.
[0006] However, even by the method of producing a Mo or Mo alloy
target material disclosed in the above patent publications, when
producing the target material of a Mo alloy containing an additive
element(s), there arises a problem that a segregation of the
additive element(s) is liable to occur, which problem cannot be
solved by the above method. In addition, there arises also a
problem of an unfavorable shape-change of a pressurized and
sintered body.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a method of
producing a target material of a Mo alloy, according to which
method a packing density of a raw material powder in a container
for pressurizing is improved, an unfavorable shape-change of a
pressurized and sintered body is reduced, and a segregation of
material components is decreased.
[0008] The present inventors examined various methods of producing
the target material of the Mo alloy, and found that the above
problems can be solved by controlling a particle size of the raw
material powder blend which is filled into the container for
pressurizing whereby attaining the present invention.
[0009] According to one aspect of the invention, there is provided
a method of producing a target material of a Mo alloy, which
comprises the steps of (a) preparing a green compact by compressing
a raw material powder blend consisting of a Mo powder having an
average particle size of not more than 20 .mu.m and a transition
metal powder having an average particle size of not more than 500
.mu.m; (b) pulverizing the green compact to produce a secondary
powder having an average particle size of from not less than an
average particle size of the raw material powder blend to not more
than 10 mm; (c) filling the secondary powder into a container for
pressurizing; and (d) subjecting the secondary powder with the
container for pressurizing to sintering under pressure thereby
obtaining a sintered body of the target material.
[0010] According to one embodiment of the above method, the
transition metal is any one selected from the group consisting of
Ti, Zr, Hf, V, Nb, Ta, Cr and W.
[0011] According to another embodiment of the above method, after
the process (d), the sintered body being enveloped in the container
is subjected to hot plastic working.
[0012] According to still another embodiment of the above method,
after the step (d), the sintered body being enveloped with the
container is subjected to hot plastic working followed by
recrystallization heat treatment.
[0013] The raw material powder blend is preferably compressed by
cold isostatic pressing. More preferably the compression is
conducted under pressure of not less than 100 MPa.
[0014] Preferably the green compact has a relative density of not
less than 50%.
[0015] The sintering under pressure is preferably carried out by
the HIP method. Preferable conditions of the HIP method are of a
temperature of 1000 to 1500.degree. C. and a pressure of not less
than 100 MPa. Preferably the sintered body has a relative density
of not less than 98%.
[0016] Preferably the container filled with the secondary powder
has an inner space of which maximum length is not less than 1000
mm.
[0017] Preferably the container filled with the secondary powder is
of a metal capsule having a substantially rectangular
parallelepiped form one of which face is used as an inlet opening
for filling the secondary powder, the face being opposite to a
bottom wall of the container forming the maximum depth, and which
inner space has a maximum side length of not less than 1000 mm.
[0018] Preferably the hot plastic working is of plural times of
plastic working under the conditions of a reduction ratio of 2 to
50% and a temperature of 500 to 1500.degree. C.
[0019] The recrystallization heat treatment is carried out
preferably at a temperature of 1000 to 1500.degree. C.
[0020] Preferably the sintered body is sliced to obtain a plurality
of tabular targets so as to maintain a maximum side length of the
sintered body.
[0021] According to the present invention, it is possible to
achieve the above object that a packing density of a raw material
powder blend in a container for pressurizing is improved, an
unfavorable shape-change of a pressurized and sintered body is
reduced, and a segregation of material components is decreased.
BRIEF DESCRIPTION OF THE DRAWING
[0022] FIG. 1 shows schematically a longitudinal side view of a
sintered body in Example 1;
[0023] FIG. 2 is a photograph for evaluating a Nb region segregated
in a metal structure of Invention Specimen No. 2 target material in
Example 1;
[0024] FIG. 3 is a photograph for evaluating a Nb region segregated
in a metal structure of Comparative Specimen No. 9 target material
in Example 1;
[0025] FIG. 4 is a photograph of microstructure of Specimen No.
2-1-1 in Example 3, which was taken by an optical microscope with
magnification of 100; and
[0026] FIG. 5 is a photograph of microstructure of Specimen No.
2-1-3 in Example 3, which was taken by an optical microscope with
magnification of 100.
DETAILED DESCRIPTION OF THE INVENTION
[0027] A key aspect of the invention resides in the process of
obtaining the green compact by compressing the raw material powder
blend consisting of the Mo powder and the transition metal powder,
subsequently pulverizing the green compact to produce the secondary
powder having an average particle size of from not less than an
average particle size of the raw material powder blend to not more
than 10 mm, and filling the secondary powder into the container for
pressurizing, whereby improving a packing ratio of the secondary
powder in the container and decreasing a segregation of material
components.
[0028] In the case of producing a target material of a Mo alloy by
powder sintering with utilization of a container for pressurizing,
usually a fine Mo powder is used. However, when the Mo powder is
filled in the container, the distribution of powder components in
the container is liable to vary, because the Mo powder has high
liability of agglomeration and is inferior in fluidity.
[0029] In this regard, the present inventors found after full
consideration that it is possible to improve the packing ratio of
the raw material powder blend in the container by adjusting a
particle size of the raw material powder blend so as to be large in
some degree. On the other hand, in the case where the Mo powder and
the other transition metal powder are mixed, a segregation of
material components is liable to occur in connection with reasons
of the liability of agglomeration of the powder, the fluidity of
the powder and so on. Accordingly, the present inventors found also
that it is effective for solving the problem by obtaining the green
compact by compressing the raw material powder blend consisting of
the Mo powder and the transition metal powder, subsequently
pulverizing the green compact to produce the secondary powder, and
filling the secondary powder into the container for pressurizing,
whereby improving the segregation of the raw material powder blend
in the container for pressurizing and also the other segregation of
the material components of the sintered body in the container for
pressurizing.
[0030] Herein below, there will be provided details of the
invention method.
[0031] A common Mo powder has a fine particle size, which is of an
average particle size of not more than 20 .mu.m, because it is
produced chemically. On the other hand, transition metal powders of
Nb, Cr, Ti and so on have a comparatively large particle size,
which is of an average particle size of not more than 500 .mu.m,
because such powders are often produced by pulverizing a cast
ingot. In the present invention, the green compact is produced by
compressing the fine raw material powder blend, and subsequently
the green compact is subjected to pulverizing to obtain the
secondary powder, having an average particle size of from not less
than an average particle size of the raw material powder blend to
not more than 10 mm, is produced. The secondary powder is filled
into a container for pressurizing and subsequently subjected to
sintering under pressure, thereby obtaining the sintered body to be
used for a raw material of the target material.
[0032] The reason why the lower limit of the average particle size
of the secondary powder should be not less than the average
particle size of the raw material powder blend is that it will make
no sense to produce and pulverize the green compact in order to
obtain a secondary powder having an average particle size less than
the average particle size of the raw material powder blend. The
reason why the upper limit of the average particle size of the
secondary powder should be not more than 10 mm is that there will
be appeared clear lines of particle boundaries in the metal
structure of a sintered body produced from a secondary powder
having an average particle size exceeding 10 mm will have a clear
boundary line, which metal structure has a kind of patterned
appearance. Such a sintered body implies a risk of a locally high
oxygen amount because particle boundaries are in contact with the
atmosphere preferentially. Thus, the average particle size should
be not more than 10 mm in order to make the particle boundaries not
to be observed in appearance and also in order to make the particle
size of the secondary powder as uniform as possible.
[0033] In the present invention, while the Mo and the transition
metal powders are blended, important is to produce the green
compact and pulverize it, so as to have the average particle size
of not more than 10 mm, in order to restrain the segregation of the
transition metal powder blended with the Mo powder.
[0034] Herein, there is provided a definition that, in a particle
size distribution of the Mo powder, the transition metal powder,
the raw material powder blend, or the secondary powder, a size
(D.sub.50) of particles, of which number is 50% of a total number
of the particles, is referred to as the average particle (or grain)
size.
[0035] Preferably, the Mo powder to be compressed an average
particle size of not more than 10 .mu.m, and the secondary powder
obtained from the green compact by pulverizing has an average
particle size of not more than 5 mm.
[0036] The reason is that the smaller the particle size is, the
higher a relative density of the sintered body can be obtained
easily. From a viewpoint of improving the packing density of a
metal powder in the container for pressurizing, it is effective to
use a larger particle size of the secondary powder. However, from a
viewpoint of a sintering property, preferably the raw material
powder with a high density has a smaller particle size. Especially,
with regard to Mo which is a main component of the sintered body
produced by the invention method, since it is a refractory metal
and has generally a high diffusion temperature, preferably the raw
material powder blend in the container is processed at high
temperature while increasing contact areas of the particles of the
raw material. Thus, preferably the average particle size of the Mo
powder is not more than 10 .mu.m. The reason why the secondary
powder has preferably the average particle size of not more than 5
mm is that by such a particle size, it is possible to decrease
local concentration of the oxygen amount, and to enhance the
dispersion of an additive element(s) in Mo alloy. More preferably,
the average particle size of the secondary powder is not more than
0.5 to 3 mm.
[0037] Further, the reason why the transition metal powder blended
with the Mo powder has the average particle size of not more than
500 .mu.m is that, if the average particle size exceeds this value,
the segregation of component in the target material cannot be
reduced.
[0038] With regard to the green compact, preferably it is
compressed so as to have a relative density of not less than 50% in
order to maintain the particle size of the secondary powder to be
filled into the container for pressurizing.
[0039] The raw material, of which primary component is Mo, is
compressed preferably by a cold isostatic pressing method (herein
below referred to as CIP) in which preferably a pressure not less
than 100 MPa is applied to the raw material powder in order to
enhance the green compact to have relative density of not less than
50%.
[0040] Sintering of the raw material under pressure is preferably
carried out by the HIP method because it is possible to three
dimensionally apply a high pressure to the raw material during
sintering. Desirable conditions of the HIP method are a temperature
of 1000 to 1500.degree. C. and a pressure of not less than 100 MPa.
If the HIP method is carried out under a pressure of less than 100
MPa at a temperature of less than 1000.degree. C., it is hard to
produce the sintered body having a relative density of not less
than 98% which is required to the target material. On the other
hand, while it is preferable to conduct the sintering at a
temperature as high as possible in order to obtain the sintered
body of which primary component is Mo, the processing temperature
of the HIP method is restricted by a material type of the container
for pressurizing and an equipment. In a usual HIP apparatus, an
upper limit of the working temperature is approximately
1500.degree. C. A higher temperature than 1500.degree. C. will not
be practical.
[0041] With regard to a size of the container for pressurizing,
while there are problems that, when using a larger size container,
the packing density is hardly improved and the component
segregation is liable to occur, the invention method is suitable
for producing a large size target material which requires to use
the container for pressurizing which maximum length is not less
than 1000 mm. Regarding a way of filling the powder into the
container, in order to improve the packing density with utilization
of a specific gravity of the powder, it is more preferable to use
the container for pressurizing which has a substantially
rectangular parallelepiped form one of which face is used as an
inlet opening for filling the secondary powder, the face being
opposite to a bottom wall of the container forming the maximum
depth, and which inner space has a maximum length of not less than
1000 mm. After filling the powder into the container, it is
desirable to seal the container by means of a top lid while
pressing the top lid against the powder in the container. This is
because an extra space can be eliminated from a top region of the
powder in the container by such pressing the lid against the
powder, upon which region no effect by the specific gravity of the
powder is exerted, whereby attaining a uniform and dense packing
state of the powder in the container from the top region to the
bottom region.
[0042] According to one feature of the invention method, the
sintered body being enveloped in the container is subjected to hot
plastic working, since such working is suitable to make the
sintered body to have a much larger size.
[0043] One reason why the hot plastic working of the sintered body
is conducted together with the container is that, if the sintered
body is subjected to the working with its surface as exposed, there
is a risk of a surface contamination of the sintered body. From
another viewpoint, according to such a working way of the sintered
body with the container, it is possible to omit one process of
removing the container from the sintered body thereby enabling to
reduce the production cost.
[0044] Desirably the hot plastic working is conducted plural times
each with a reduction ratio of 2 to 50% while maintaining the
sintered body at a temperature of 500 to 1500.degree. C.
[0045] If the temperature is lower than 500.degree. C., a working
load applied to the sintered body must be increased due to lower
ductility thereof whereby arising a problem of the productivity. On
the other hand, if the temperature exceeds 1500.degree. C., there
are a risk that the container is melted and a problem that crystal
particles of the sintered body are coarsened. If the reduction
ratio of the hot plastic working exceeds 50%, there arise problems
that cracking and inner defects occur in the sintered body. If the
reduction ratio of the hot plastic working is lower than 2%, the
sintered body is hardly deformed thereby arising a waste production
cost problem. Further, in the case where a high reduction working
as a whole is required for the sintered body, plural times of
working under the above conditions of the temperature and the
reduction ratio are effective in order to avoid occurrence of
cracking or other defects.
[0046] According to another feature of the invention method, after
hot plastic working, the sintered body is subjected to
recrystallization heat treatment. The work as rolled has a fiber
metal structure, a degree of which structure differs every section
of the work, especially at a surface portion and a central portion
in the thickness direction of the work. Preferably the target
material should have a uniform crystal structure, since a
non-uniform crystal structure of the target material adversely
affect the uniformity of a film deposited by sputtering. Thus,
preferably the work as rolled is subjected to homogenization
treatment with utilization of the recrystallization phenomenon in
order to make its crystal structure uniform.
[0047] The recrystallization heat treatment is preferably conducted
at a temperature of 1000 to 1500.degree. C. If the temperature is
not higher than 1000.degree. C., there is a high possibility that
the fiber metal structure will remain after the heat treatment
because of properties of the chemical composition with a primary
component of Mo. If the temperature exceeds 1500.degree. C., there
will occur partially coarsening of crystal particles at a surface
region that has previously suffered high reduction working.
[0048] According to still another feature of the invention method,
the sintered bodies, which include those merely sintered, subjected
to hot plastic working and subjected to both of hot plastic working
and recrystallization heat treatment, are sliced to obtain a
plurality of tabular targets so as to maintain a maximum side
length of the respective sintered body. This method is advantageous
in the point that a number of target material are produced by only
one time pressurizing and sintering process in accordance with a
need for a large sized target material, whereby reducing the
production cost.
[0049] Desirably the raw powder material in the invention method
contains not less than 50 atomic % Mo. Taking into consideration
that the Mo powder, having high agglomeration property, is hard to
be filled uniformly into the container for pressurizing, it is very
effective to use the raw powder material in the invention method in
order to obtain a target material containing not less than 50
atomic % Mo.
[0050] Herein below, there will be provided a description of some
Examples with regard to the invention method.
EXAMPLE 1
[0051] There were prepared a Mo powder having an average particle
size of 12 .mu.m, a W (tungsten) powder having an average particle
size of 12 .mu.m, a Nb powder having an average particle size of
100 .mu.m, a Ti powder having an average particle size of 100
.mu.m, and a Zr powder having an average particle size of 100
.mu.m.
[0052] Specimen Nos. 1 to 6 target materials shown in Table 1 were
produced by the following process, which are of the present
invention.
[0053] (1) In order to produce each of the specimens, given amounts
in atomic % of the Mo powder and any one of the transition metal
powder were checkweighed.
[0054] (2) The checkweighed powders were blended for 10 minutes
with utilization of a V-type blender to obtain a raw material
powder.
[0055] (3) The raw material powder was compressed under pressure of
265 MPa by a CIP machine to form a green compact.
[0056] (4) The green compact was pulverized with utilization of a
jaw crusher and a disc mill to produce a secondary powder.
[0057] (5) The secondary powder was blended in a V-type blender for
10 minutes and subsequently filled into a container for
pressurizing, which is made of low carbon soft steel and has an
inner space dimension of a thickness of 100 mm, a width of 1000 mm
and a height of 1300 mm. After filling the secondary powder, a top
lid with a deaerating port was welded to the container in order to
close an inlet opening thereof.
[0058] (6) The container filled with the secondary powder was
subjected to a degassing process under vacuum at a temperature of
450.degree. C. and subsequently the deaerating port was sealed.
Thereafter, the secondary powder was sintered under pressure
together with the container by means of a HIP machine. Operational
conditions of the HIP machine were of a temperature of 1250.degree.
C., a pressure of 150 MPa and an operation time of 5 hours.
[0059] (7) The thus obtained sintered body was sliced and machined
to produce six tabular target materials each having a rectangular
parallelepiped shape of which dimension is of a thickness of 6 mm,
a width of 810 mm and a length of 950 mm.
[0060] (8) A packing density of the secondary powder in the
container was measured, which value is shown in Table 1.
[0061] (9) Specimens were taken from the green compact and the
sintered body to examine a relative density, respectively, by an
Archimedes method, which values are shown in Table 1.
[0062] Further, in order to produce Reference Specimen Nos. 7 and 8
target materials shown in Table 1, a Mo powder having an average
particle size of 6 .mu.m and a Nb powder having an average particle
size of 100 .mu.m were prepared, and processed to obtain sintered
bodies by the same manner as described above. Each of the thus
obtained sintered bodies was sliced and machined to produce six
tabular target materials each having a rectangular parallelepiped
shape of which dimension is of a thickness of 6 mm, a width of 810
mm and a length of 950 mm.
[0063] A packing density of the each secondary powder in the
container was measured, which value is shown in Table 1.
[0064] Specimens were taken from the green compact and the sintered
body to examine a relative density, respectively, by an Archimedes
method, which values are shown in Table 1.
[0065] In order to produce Comparative Specimen Nos. 9 and 10
target materials shown in Table 1, a Mo powder and a Nb powder were
prepared. Comparative Specimen Nos. 9 and 10 target materials were
produced by the following process.
[0066] (1) In order to produce Comparative Specimen Nos. 9 and 10,
given amounts in atomic % of the Mo powder and the Nb metal powder
were checkweighed, respectively.
[0067] (2) The checkweighed powders were blended for 10 minutes
with utilization of a V-type blender to obtain a raw material
powder for each of Comparative Specimen Nos. 9 and 10.
[0068] (3) The raw material powder for each of Comparative Specimen
Nos. 9 and 10 was filled into a container for pressurizing without
subjecting to the compression treatment, which is made of low
carbon steel.
[0069] (4) After filling the raw powder, a top lid with deaerating
port was welded to the container in order to close an inlet opening
thereof.
[0070] (5) The container filled with each of the raw powders was
subjected to a deaerating process under vacuum at a temperature of
450.degree. C. and the deaerating port was sealed. Thereafter, the
respective powder was sintered under pressure together with the
container by means of a HIP machine. Operational conditions of the
HIP machine were of a temperature of 1250.degree. C., a pressure of
150 MPa and an operation time of 5 hours.
[0071] (6) Each of the thus obtained sintered bodies was sliced and
machined to produce three tabular target materials each having a
rectangular parallelepiped shape of which dimension is of a
thickness of 6 mm, a width of 610 mm and a length of 710 mm.
[0072] (7) A packing density of each of the powders for Comparative
Specimen Nos. 9 and 10 in the container was measured, which value
is shown in Table 1.
[0073] (8) Specimens were taken from the respective sintered body
to examine a relative density by an Archimedes method, which value
is shown in Table 1.
[0074] With regard to all Specimen Nos. 1 to 10 target materials, a
form variation of the respective sintered body was evaluated, which
variation was occurred during sintering. FIG. 1 is provided in
order to describe a way how to conduct the evaluation. The drawing
shows schematically a longitudinal side view of a sintered body
model with a x-y coordinate, in which there is a reference point 3
at a longitudinal center 2 (on the y-axis) of the bottom surface of
the sintered body model 1. A left end of the sintered body model 1
is bent upwardly in the drawing so that a lowest point 4 of the
left side end of the sintered body model 1 deviates from the x-axis
by a distance 5 which exhibits a form variation degree. Evaluation
result of the form variation degree of the respective specimen is
shown in Table 1, wherein a character B means that the form
variation degree is of not less than 12 mm which has a problem, and
a character A means that the form variation degree is of less than
12 mm which is evaluated as good.
1 TABLE 1 Average particle size of Raw Powder Average particle
Dimension of Chemical Additive size of Container for Specimen
composition element Secondary Powder pressurizing No. (atomic %) Mo
(.mu.m) (.mu.m) (mm) (mm) 1 Mo 12 -- 1.4 100 .times. 1000 .times.
1300 2 95.0Mo--5.0Nb 12 100 1.1 100 .times. 1000 .times. 1300 3
95.5Mo--4.5Nb 12 100 1.2 100 .times. 1000 .times. 1300 4
70.0Mo--30.0Ti 12 100 1.3 100 .times. 1000 .times. 1300 5
65.0Mo--35.0W 12 12 1.2 100 .times. 1000 .times. 1300 6
91.6Mo--8.4Zr 12 100 1.5 100 .times. 1000 .times. 1300 7 Mo 6 --
0.8 100 .times. 1000 .times. 1300 8 95.0Mo--5.0Nb 6 100 0.8 100
.times. 1000 .times. 1300 9 95.0Mo--5.0Nb 12 100 -- 100 .times.
1000 .times. 1300 10 Mo 12 -- -- 100 .times. 1000 .times. 1300
Relative Packing density in Relative Evaluation density of
Container for Dimension of density of of form Specimen Green
compact pressurizing Sintered body Sintered body Variation No. (%)
(%) (mm) (%) degree Remarks 1 69.0 53.0 80 .times. 816 .times. 1054
98.2 A Reference specimen 2 71.0 54.0 81 .times. 817 .times. 1053
98.3 A Invention specimen 3 70.0 53.5 81 .times. 815 .times. 1052
98.4 A Invention specimen 4 69.5 53.0 80 .times. 813 .times. 1054
98.3 A Invention specimen 5 70.0 53.5 81 .times. 816 .times. 1054
98.1 A Invention specimen 6 69.0 52.5 80 .times. 812 .times. 1049
98.2 A Invention specimen 7 68.0 58.5 83 .times. 835 .times. 1088
99.6 A Reference specimen 8 69.0 60.0 84 .times. 844 .times. 1097
99.4 A Invention specimen 9 -- 39.5 73 .times. 735 .times. 955 98.3
B Comparative specimen 10 -- 38.5 72 .times. 729 .times. 945 98.1 B
Reference specimen
[0075] As shown in Table 1, in Invention and Reference Specimen
Nos. 1 to 8, since a secondary powder, having the average particle
size of not more than 10 mm, was produced by pulverizing a green
compact produced by compressing a raw material powder,
respectively, the packing densities of the secondary powders in
Specimen Nos. 1 to 8 are of not less than 52% which is
significantly high. From this, it is appreciated that the target
material can be produced with a satisfactory yield since degrees of
a dimensional contraction and a form variation of the sintered body
are reduced by virtue of a high packing density.
[0076] Seeing Invention Specimen No. 8 in Table 1, it is
appreciated that with utilization of a raw material powder blend
having an average particle size of not more than 10 .mu.m, and a
secondary powder having an average particle size of not more than 1
mm, the packing density and the relative density are significantly
increased.
[0077] On the other hand, with regard to Comparative Specimen No. 9
in which the raw material powder blend was filled directly without
compression into the container for pressurizing and subjected to
sintering under pressure, an yield is inferior when producing the
target material because of a low packing density of not more than
40%, and because a dimensional contraction and a form variation of
the sintered body are large. Further, even if a container with the
same size as the other cases is used, there is a risk that a target
material with an expected size can not be produced because of a
large dimensional contraction and a large form variation of the
sintered body.
[0078] FIGS. 2 and 3 show photographs for evaluating Nb regions
segregated in metal structures of Invention Specimen No. 2 and
Comparative Specimen No. 9, respectively. In the case of
Comparative Specimen No. 9 shown in FIG. 3 in which no secondary
powder is produced, there exists a Nb region having a major axis of
not less than 20 mm at a center of the photograph. From this, it is
appreciated that a segregation of Nb occurs. On the other hand, in
the case of Invention Specimen No. 2 shown in FIG. 2, the Nb
regions are dispersed in a Mo matrix, so that no clear segregation
of Nb exists.
EXAMPLE 2
[0079] A sintered body, having the same chemical composition and
the same size as those of Invention Specimen No. 2 shown in Example
1, was produced by the same manner as the case of Invention
Specimen No. 2, and after the HIP process it is subjected to hot
rolling thrice together with a container for pressurizing under
conditions of a temperature of 1150.degree. C. and a reduction
ratio of not more than 50%. An expected size of a target material
is of a width of 1500 mm and a length of 1800 mm. A result of
rolling of the sintered body is shown in Table 2.
2TABLE 2 Dimension of Objective Heating First time Second time
Third time Chemical Sintered dimension temper- Total rolling
rolling rolling rolling Specimen composition body in rolling ature
reduction reduction reduction reduction No. (atomic %) (mm) (mm)
(.degree. C.) (%) (%) (%) (%) Result 2-1 95.0Mo-- 81 .times. 812
.times. 25.7 .times. 1500 .times. 1150 68 20 30 43.5 No cracking
5.0Nb 1053 1800
[0080] As will be seen from Table 2, by carrying out the rolling
under conditions of a heating temperature of 500 to 1500.degree. C.
and a reduction ratio of 2 to 50%, a large size target raw material
can be produced without occurrence of cracking.
[0081] It should be noted that while a sintered body was subjected
to rolling at a temperature of 450.degree. C., ductility of the
sintered body cannot be maintained due to a low heating
temperature, disadvantageously resulting in that rolling of a
reduction ratio of a few percent had to be conducted
cyclically.
EXAMPLE 3
[0082] The target material as hot-rolled in Example 2 was subjected
to a recrystallization heat treatment in vacuum at temperatures of
900.degree. C., 1150.degree. C. and 1300.degree. C., respectively.
After the work is heated up to a heat treatment temperature, the
temperature is held for one hour, and thereafter the work is
cooled. Specimen Nos. 2-1-1 , 2-1-2 and 2-1-3 were taken from the
three type works, respectively. Microstructures of the specimens
were compared with one another with utilization an optical
microscope with magnification of 100. The observation result is
shown in Table 3. With regard to the specimens subjected to a
recrystallization heat treatment at temperatures of 900.degree. C.
and 1300.degree. C., respectively, there are provided photographs
showing microstructures of the specimens with utilization of an
optical microscope with magnification of 100 in FIGS. 4 and 5,
respectively.
3TABLE 3 Recrystallization Chemical heat treatment Specimen
composition temperature No. (atomic %) (.degree. C.) Microstructure
2-1-1 95.0Mo--5.0Nb 900 Fiber metal- structure is remained 2-1-2
95.0Mo--5.0Nb 1150 Isotropic structure 2-1-3 95.0Mo--5.0Nb 1300
Isotropic structure
[0083] From Table 3, FIGS. 4 and 5, it can be seen that when a
recrystallization heat treatment temperature is lower than
1000.degree. C., there is a possibility that a fiber structure
remains.
* * * * *