U.S. patent application number 12/609168 was filed with the patent office on 2010-06-24 for method of producing nitride/tungsten nanocomposite powder and nitride/tungsten nanocomposite powder produced using the same.
Invention is credited to Soonhyung Hong, Dongju Lee, Kyongho Lee, Yoochul Shin.
Application Number | 20100154589 12/609168 |
Document ID | / |
Family ID | 41720638 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100154589 |
Kind Code |
A1 |
Hong; Soonhyung ; et
al. |
June 24, 2010 |
METHOD OF PRODUCING NITRIDE/TUNGSTEN NANOCOMPOSITE POWDER AND
NITRIDE/TUNGSTEN NANOCOMPOSITE POWDER PRODUCED USING THE SAME
Abstract
Provided is a method of producing a nitride/tungsten
nanocomposite powder. The method includes mixing nitride with
tungsten or a tungsten alloy, and mechanically alloying the mixture
in an inert atmosphere using a milling machine.
Inventors: |
Hong; Soonhyung;
(Yuseong-gu, KR) ; Lee; Kyongho; (Yuseong-gu,
KR) ; Shin; Yoochul; (Yuseong-gu, KR) ; Lee;
Dongju; (Yuseong-gu, KR) |
Correspondence
Address: |
SHERR & VAUGHN, PLLC
620 HERNDON PARKWAY, SUITE 320
HERNDON
VA
20170
US
|
Family ID: |
41720638 |
Appl. No.: |
12/609168 |
Filed: |
October 30, 2009 |
Current U.S.
Class: |
75/252 ;
75/352 |
Current CPC
Class: |
B22F 2009/041 20130101;
B22F 9/04 20130101; C22C 1/045 20130101; C22C 27/04 20130101 |
Class at
Publication: |
75/252 ;
75/352 |
International
Class: |
B22F 1/00 20060101
B22F001/00; B22F 9/02 20060101 B22F009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2008 |
KR |
10-2008-0131345 |
Claims
1-14. (canceled)
15. A method of producing a nitride/tungsten nanocomposite powder,
comprising: mixing a nitride with one of tungsten and a tungsten
alloy; and mechanically alloying the mixture in an inert atmosphere
using a milling machine.
16. The method according to claim 15, wherein the nitride comprises
at least one selected from the group consisting of ZrN, HfN, BN,
AlN, Si.sub.3N.sub.4, TiN, TaN, Ta.sub.2N, VN, CrN, Cr.sub.2N,
Mo.sub.2N, NbN, WN, and W.sub.2N.
17. The method according to claim 15, wherein the tungsten alloy
comprises tungsten and at least one element selected from the group
consisting of Nb, Tc, Ru, Hf, Os, Mo, Ta, Re and Ir.
18. The method according to claim 15, wherein the nitride and the
one of tungsten and a tungsten alloy are mixed at a volume ratio
(%) in a range of 0.1 to 95:5 to 99.9.
19. The method according to claim 15, wherein the inert atmosphere
comprises at least one selected from the group consisting of
vacuum, nitrogen gas, and argon gas.
20. The method according to claim 15, wherein the milling machine
comprises any one selected from the group consisting of a planetary
ball mill, an attritor, a stirred ball mill, and a vibration
mill.
21. The method according to claim 15, wherein the milling machine
uses ball-to-ball collision.
22. The method according to claim 15, wherein the milling machine
uses ball-to-jar collision.
23. The method according to claim 15, wherein a weight ratio of the
mixture to balls of the milling machine is in the range of 1:1 to
1:50.
24. The method according to claim 15, wherein a milling speed of
the milling machine is 1 rpm to 5000 rpm.
25. The method according to claim 15, wherein mechanically alloying
the mixture comprises mechanically milling the mixture and
producing a nanocomposite powder in which nitride nanoparticles are
uniformly dispersed at grain boundaries of the tungsten.
26. The method according to claim 15, wherein mechanically alloying
the mixture comprises mechanically milling the mixture and
producing a nanocomposite powder in which nitride nanoparticles are
uniformly dispersed in grains of the tungsten.
27. The method according to claim 15, wherein mechanically alloying
the mixture comprises mechanically milling the mixture and
producing a nanocomposite powder in which nitride nanoparticles are
uniformly dispersed at grain boundaries of the tungsten alloy.
28. The method according to claim 15, wherein mechanically alloying
the mixture comprises mechanically milling the mixture and
producing a nanocomposite powder in which nitride nanoparticles are
uniformly dispersed in grains of the tungsten alloy.
29. A nitride/tungsten nanocomposite powder produced by the method
according to claim 15.
30. The nitride/tungsten nanocomposite powder according to claim
29, wherein nitride nanoparticles are uniformly dispersed at grain
boundaries of one of tungsten and a tungsten alloy.
31. The nitride/tungsten nanocomposite powder according to claim
29, wherein nitride nanoparticles are uniformly dispersed in grains
of the one of tungsten and tungsten alloy.
Description
TECHNICAL FIELD
[0001] The described technology relates generally to a method of
producing a nitride/tungsten nanocomposite powder in which nitride
is uniformly dispersed in tungsten, and a nitride/tungsten
nanocomposite powder produced using the method.
BACKGROUND
[0002] Tungsten is a heat-resistant metal having a high melting
point. Due to a low thermal expansion coefficient and excellent
high-temperature mechanical properties, tungsten is widely used in
various industrial fields. However, the strength of tungsten
steeply decreases at a high temperature of 1000.degree. C. or more.
For example, the strength of tungsten at 1000.degree. C. decreases
to 60 to 80% of the strength of tungsten at room temperature.
[0003] To overcome such a disadvantage of tungsten, a variety of
attempts are being made. For example, to improve the mechanical
properties of tungsten and tungsten alloys, fireproof carbide or
oxide such as TiC, ZrC, HfC, or ZrO.sub.2, which are stable at high
temperature, may be used as a dispersing agent. The carbide, etc.,
dispersed along a grain boundary of tungsten strengthens the grain
boundary or hinders the grain boundary from moving at high
temperature. Tungsten and tungsten composites whose above-mentioned
disadvantage is overcome have a high melting point, high thermal
shock resistivity, excellent ablation resistivity, etc., and can be
widely used in high-temperature environments. Thus, research for
improving the mechanical properties of tungsten and tungsten
composites is required.
SUMMARY
[0004] Embodiments provide a method of producing a nitride/tungsten
nanocomposite powder in which nitride is uniformly dispersed in
tungsten to improve mechanical properties of tungsten and a
nitride/tungsten nanocomposite powder produced using the
method.
[0005] In one embodiment, a method of producing a nitride/tungsten
nanocomposite powder is provided. The method includes: mixing
nitride with tungsten or a tungsten alloy; and alloying the mixture
in an inert atmosphere using a milling machine.
[0006] The Summary is provided to introduce a selection of concepts
in a simplified form that are further described below in the
Detailed Description. The Summary is not intended to identify key
features or essential features of the claimed subject matter, nor
is it intended to be used as an aid in determining the scope of the
claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The above and other features and advantages of the present
disclosure will become more apparent to those of ordinary skill in
the art by describing in detail example embodiments thereof with
reference to the attached drawings in which:
[0008] FIG. 1 is a scanning electron microscope (SEM) view showing
the structure of a nitride/tungsten composite powder produced
according to conventional art;
[0009] FIG. 2 is a schematic cross-sectional view of a milling
machine according to an embodiment of the present disclosure;
[0010] FIG. 3 shows X-ray diffraction (XRD) results of a
nitride/tungsten nanocomposite powder produced according to First
embodiment;
[0011] FIG. 4 shows results of measuring the tungsten crystallite
size of the nitride/tungsten nanocomposite powder produced
according to First embodiment;
[0012] FIG. 5 is a transmission electron microscopy (TEM)
photograph showing the structure of the nitride/tungsten
nanocomposite powder produced according to First embodiment;
[0013] FIG. 6A shows SEM photographs of a nitride/tungsten
nanocomposite powder obtained by performing a milling operation for
six hours according to Third embodiment, and FIG. 6B shows SEM
photographs of a nitride/tungsten nanocomposite powder obtained by
performing the milling operation for ten hours; and
[0014] FIGS. 7A and 7B show SEM photographs of a nitride/tungsten
mixture mixed according to the conventional method of First
comparative embodiment.
DETAILED DESCRIPTION
[0015] It will be readily understood that the components of the
present disclosure, as generally described and illustrated in the
Figures herein, could be arranged and designed in a wide variety of
different configurations. Thus, the following more detailed
description of the embodiments of apparatus and methods in
accordance with the present disclosure, as represented in the
Figures, is not intended to limit the scope of the disclosure, as
claimed, but is merely representative of certain examples of
embodiments in accordance with the disclosure. The presently
described embodiments will be understood by reference to the
drawings, wherein like parts are designated by like numerals
throughout. Moreover, the drawings are not necessarily to scale,
and the size and relative sizes of layers and regions may have been
exaggerated for clarity.
[0016] The present disclosure provides a method of producing a
nitride/tungsten composite powder. The inventors of the present
disclosure have found that a nitride/tungsten composite formed by
dispersing nitride in a tungsten base can improve the strength of
tungsten at high temperature. For example, it has been found that
metal nitride having a similar melting point to tungsten whose
melting point is about 3410.degree. C., can maintain a stable state
at a high temperature of about 1000.degree. C. or more, effectively
hinders tungsten grains from moving when the metal nitride is
dispersed in a tungsten base, and improves the strength of tungsten
at high temperature. The present disclosure provides a method of
producing a nitride/tungsten nanocomposite powder that can be
applied to producing the above-mentioned nitride/tungsten
nanocomposite. In a nitride/tungsten nanocomposite powder produced
according to embodiments of the present disclosure, nitride
nanoparticles may be uniformly dispersed in the tungsten grains or
at tungsten grain boundaries. Thus, a nitride/tungsten
nanocomposite having improved strength at high temperature can be
obtained using a known sintering process. In this specification and
claims, a nitride/tungsten nanocomposite powder denotes a
nanocomposite powder including nitride and tungsten, and is not
limited to a nanocomposite consisting of nitride and tungsten. For
example, a nanocomposite powder including a nitride/tungsten alloy
may be referred to as a nitride/tungsten nanocomposite powder.
[0017] The method of producing a nitride/tungsten nanocomposite
powder includes mixing nitride with tungsten or a tungsten alloy,
and alloying the mixture in an inert atmosphere using a milling
machine. The nitride may include ZrN, HfN, BN, AlN,
Si.sub.3N.sub.4, TiN, TaN, Ta.sub.2N, VN, CrN, Cr.sub.2N,
Mo.sub.2N, NbN, WN, or W.sub.2N. However, the nitride is not
limited thereto, and may be any non-metal compound that is
generated by reaction between a metal element in the periodic table
and nitrogen and has high-temperature properties such as thermal
stability at a temperature of about 100.degree. C.
[0018] The tungsten alloy may include at least one element of Nb,
Tc, Ru, Hf, Os, Mo, Ta, Re and Ir. For example, the tungsten alloy
may be a tungsten-niobium (W--Nb) alloy, a tungsten-technetium
(W--Tc) alloy, a tungsten-ruthenium (W--Ru) alloy, a
tungsten-hafnium (W--Hf) alloy, a tungsten-osmium (W--Os) alloy, a
tungsten-molybdenum (W--Mo) alloy, a tungsten-tantalum (W--Ta)
alloy, a tungsten-rhenium (W--Re) alloy, a tungsten-iridium (W--Ir)
alloy, or a tungsten-molybdenum-tantalum-rhenium-iridium
(W--Mo--Ta--Re--Ir) alloy. However, the tungsten alloy is not
limited thereto, and may be any alloy containing tungsten.
[0019] The nitride and the tungsten may be mixed at a volume ratio
(%) of 0.1 to 95:5 to 99.9. In another embodiment, the nitride and
the tungsten may be mixed at a volume ratio (%) of 1 to 50:50 to
99. In some embodiments, the nitride and the tungsten alloy may be
mixed at substantially the same volume ratio as those of the
nitride and the tungsten.
[0020] Alloying the mixture of the nitride with the tungsten or
tungsten alloy using a milling machine may be performed in an inert
atmosphere. The inert atmosphere may be a vacuum, nitrogen gas, or
argon gas atmosphere. To prevent tungsten from being oxidized, the
nitride/tungsten nanocomposite powder is produced in the inert
atmosphere. Tungsten, which is a polycrystalline material, includes
grains that are small crystals of microscopic size, and has grain
boundaries that are interfaces between the grains. In the inert
atmosphere, the nitride may be uniformly dispersed in the grains of
tungsten or at the grain boundaries. The conceptual diagram of such
a nitride/tungsten nanocomposite powder is shown in FIG. 1. In the
similar manner, in the inert atmosphere, the nitride may also be
uniformly dispersed in grains or grain boundaries of the tungsten
alloy.
[0021] The milling machine may be a planetary ball mill, an
attritor, a stirred ball mill, a vibration mill, and so on. In one
embodiment of the present disclosure, the milling machine mills the
mixture of the nitride with the tungsten or tungsten alloy, and
mechanical alloying (MA) of the nitride and the tungsten occurs
during the milling process. Here, MA of the nitride and the
tungsten denotes a process of mechanically milling nitride and
tungsten or nitride and a tungsten alloy to produce an alloy powder
having crystalline structures of nanoscale size. To enable such MA,
the milling machine may be a high-energy milling machine that can
perform a high-speed milling operation using high-strength balls.
The high-strength balls may be made of, for example, ZrO.sub.2,
Y.sub.2O.sub.3, Al.sub.2O.sub.3, WC--Co, high-strength steels
(HSS), etc. In one embodiment, the mixture of the nitride with the
tungsten or tungsten alloy may be provided in the form of a powder,
and the alloy powder produced by MA may be a nanocomposite powder
in which nitride nanoparticles are uniformly dispersed in tungsten
grains or at tungsten grain boundaries or a nanocomposite powder in
which nitride nanoparticles are uniformly dispersed in the grains
or at the grain boundaries of the tungsten alloy.
[0022] FIG. 2 is a schematic cross-sectional view of an
illustrative embodiment of a milling machine. Referring to FIG. 2,
a milling machine 200 may include a powder 210 to be milled, balls
220 colliding with the powder 210, and a jar 230 containing the
powder 210 and the balls 220.
[0023] The milling machine 200 mills the powder 210 by ball-to-ball
or ball-to-jar collision. When the ball-to-jar collision is used, a
ball filling ratio in the jar 230 that is a volume ratio (%) of the
jar 230 to the ball 220 may be set to 1 to 20:1. In one embodiment
of the present disclosure, a mixture of the nitride with the
tungsten or tungsten alloy is used as the powder 210.
[0024] In the milling machine 200, the weight ratio (%) of the
mixture of the nitride with the tungsten or the mixture of the
nitride with tungsten alloy to the balls 220 may be 1:1 to 50. The
milling machine 200 performs a rotary or back-and-forth motion at a
milling speed of 1 to 5000 rpm and mills the mixture, thereby
performing MA. As a result, a nanocomposite powder of
nitride/tungsten or nitride/tungsten alloy may be generated.
[0025] Embodiments of the present disclosure and Comparative
embodiment will be described in detail below. Embodiments and
Comparative embodiment regarding a nitride/tungsten nanocomposite
powder are suggested to aid in understanding the present
disclosure, and those of ordinary skill in the art will readily
appreciate that many modifications are possible in the embodiments
within the technological scope of the present disclosure. For
example, those of ordinary skill in the art can produce a
nanocomposite powder by mechanically alloying a nitride/tungsten
alloy. Therefore, it is to be understood that the appended claims
are not limited by Embodiments and Comparative embodiment.
First Embodiment
Alloying of Nitride and Tungsten
[0026] To produce a nitride/tungsten nanocomposite powder, a ZrN
powder having a purity of 99.9% and a particle size of 2 .mu.m and
a W powder having a purity of 99.9% and a particle size of 2.5
.mu.l were prepared. A mixture powder was obtained by mixing the
ZrN powder with the W powder at a volume ratio of 50:50.
[0027] After this, MA was performed using a planetary ball mill. In
the planetary ball mill, zirconia (ZrO.sub.2) balls and a jar
having a capacity of 600 cc were used. Also, the ball filling ratio
(%), that is the volume ratio of the jar to the balls, was 15:1.
Under these conditions, the prepared mixture powder was inserted
into the planetary ball mill so that the weight ratio of the
mixture powder to the balls could be 1:10. The milling speed was
set to 250 rpm, and the milling operation was performed for ten
hours.
[0028] X-ray diffraction (XRD) analysis was performed to examine
whether a material obtained through the process had been completely
alloyed, and the XRD analysis results of the present embodiment are
shown in FIG. 3. In FIG. 3, MA was not performed at all before the
milling machine was used (MA for 0 hr), and thus peaks indicating
ZrN and W elements are clearly distinguished from each other.
However, as a milling time increased, the intensities of the ZrN
and W peaks were reduced. When the milling operation was performed
for ten hours (MA for 10 hr), the intensities of the peaks were
remarkably reduced. In other words, it can be seen from the XRD
results that ZrN and W were not just simply mixed but mechanically
alloyed to be a nitride/tungsten nanocomposite powder.
Second Embodiment
Dispersion Scale of Nitride/Tungsten Nanocomposite Powder
[0029] To examine whether the nitride/tungsten nanocomposite powder
produced in First embodiment had a nanoscale size, the size of
tungsten grains was measured by the Scherrer formula using the XRD
results. When the size of tungsten grains was reduced through the
MA process, the dispersion scale of the nitride/tungsten
nanocomposite powder was also reduced as much as the size of
tungsten grains. To determine whether the dispersion scale of the
nitride/tungsten nanocomposite powder was reduced, the size of
tungsten grains was measured.
[0030] FIG. 4 shows results of measuring the size of tungsten
grains according to mechanical alloying time in the
nitride/tungsten nanocomposite powder of FIG. 3. Referring to FIG.
4, MA was not performed at all before the nitride/tungsten mixture
was milled using the milling machine (Mechanical Alloying Time: 0
hr), and thus the size of tungsten grains was 250 nm. However, as a
milling time increased, the size was reduced. When the milling
operation was performed for ten hours (Mechanical Alloying Time: 10
hr), the size of tungsten grains was 100 nm. In other words, it can
be seen from the results that the dispersion scale of the
nitride/tungsten nanocomposite powder is about 100 nm.
[0031] Also, to examine the sizes of nitride particles and tungsten
grains of the nitride/tungsten nanocomposite powder, the photograph
of the structure was obtained using a transmission electron
microscopy (TEM). The structure photograph is shown in FIG. 5, in
which it is possible to see that the nitride/tungsten nanocomposite
powder has a microstructure including nitride ceramic nanoparticles
of several to tens of nanometers and tungsten grains of tens to
hundreds of nanometers.
Third Embodiment
Degree of Dispersion of Nitride/Tungsten Nanocomposite Powder
[0032] Since the nitride/tungsten nanocomposite powder of the
present disclosure is intended to uniformly disperse nitride in
tungsten, the degree of dispersion of the nitride/tungsten
nanocomposite powder produced in First embodiment was confirmed
using a scanning electron microscope (SEM).
[0033] The degree of dispersion varies according to a milling time.
Thus, SEM photographs of nitride/tungsten nanocomposite powders
obtained by performing the milling operation for six hours are
shown in FIG. 6A, and SEM photographs of nitride/tungsten
nanocomposite powders obtained by performing the milling operation
for ten hours are shown in FIG. 6B. Each of FIGS. 6A and 6B
includes two photographs. The right one of the two photographs is
an enlarged view of the left one obtained by analyzing the left one
in a backscattered electron (BSE) mode.
[0034] Referring to the enlarged view of FIG. 6A (that is, the
right one of the two photographs of FIG. 6A), nitride ceramic
nanoparticles (black portion) are partially mixed with and
dispersed in tungsten nanograins (white portion), but, referring to
the enlarged view of FIG. 6B (that is, the right one of the two
photographs of FIG. 6B), nitride ceramic nanoparticles (black
portion) are uniformly mixed with and dispersed in tungsten
nanograins (white portion). In other words, it can be confirmed in
the enlarged view of FIG. 6B that in the nitride/tungsten
nanocomposite powder obtained by performing the milling operation
for ten hours, nitride ceramic nanoparticles are mixed with and
dispersed in tungsten nanograins at a nanoscale of 100 nm or less
so that the colors of the nitride ceramic nanoparticles and the
tungsten nanograins cannot be distinguished.
First Comparative Embodiment
Degree of Dispersion
[0035] To confirm how uniformly nitride ceramic particles were
dispersed in tungsten particles in a nitride/tungsten nanocomposite
powder produced by the method according to the present disclosure,
the nitride/tungsten nanocomposite powder was compared with a
nitride/tungsten mixture mixed according to a conventional
method.
[0036] First, the nitride/tungsten mixture was prepared by the
conventional method. In the conventional method, a nitride powder
and a tungsten powder are simply mixed to produce a
nitride/tungsten mixture without a MA process. SEM photographs
showing the structure of the nitride/tungsten mixture are shown in
FIGS. 7A and 7B. In FIG. 7A, nitride ceramic particles condensed on
the surface of tungsten are shown. Also, in FIG. 7B, cross-sections
of condensed bodies of nitride ceramic particles non-uniformly
mixed with and dispersed in tungsten are shown.
[0037] On the other hand, the nitride/tungsten nanocomposite powder
according to the present disclosure is shown in FIGS. 5, 6A, and
6B. By comparing the results, it is possible to see that nitride is
remarkably uniformly dispersed in tungsten in the nitride/tungsten
nanocomposite powder produced by the method according to the
present disclosure in comparison with the conventional
nitride/tungsten mixture.
[0038] As described above, using a method according to the present
disclosure, it is possible to produce a nitride/tungsten
nanocomposite powder in which nitride is uniformly dispersed in
tungsten. The nitride/tungsten nanocomposite powder that may be
applied to a nitride/tungsten composite material is expected to
have excellent thermal shock resistivity, strength, and ablation
resistivity at high temperature, and can be used in various fields
such as parts used in the propulsion engines of airplanes or
rockets.
[0039] The foregoing is illustrative of the present disclosure and
is not to be construed as limiting thereof. Although numerous
embodiments of the present disclosure have been described, those
skilled in the art will readily appreciate that many modifications
are possible in the embodiments without materially departing from
the novel teachings and advantages of the present disclosure.
Accordingly, all such modifications are intended to be included
within the scope of the present disclosure as defined in the
claims. Therefore, it is to be understood that the foregoing is
illustrative of the present disclosure and is not to be construed
as limited to the specific embodiments disclosed, and that
modifications to the disclosed embodiments, as well as other
embodiments, are intended to be included within the scope of the
appended claims. The present disclosure is defined by the following
claims, with equivalents of the claims to be included therein.
* * * * *