U.S. patent application number 10/743237 was filed with the patent office on 2005-06-23 for metallic alloy nanocomposite for high-temperature structural components and methods of making.
This patent application is currently assigned to General Electric Company. Invention is credited to Amancherla, Sundar, Anand, Krishnamurthy, Angeliu, Thomas Martin, Corderman, Reed Roeder, Gray, Dennis Michael, Huang, Shyh-Chin, Marte, Judson Sloan, Oruganti, Ramkumar Kashyap, Srinivasan, Dheepa, Subramanian, Pazhayannur Ramanathan.
Application Number | 20050133121 10/743237 |
Document ID | / |
Family ID | 34552823 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050133121 |
Kind Code |
A1 |
Subramanian, Pazhayannur Ramanathan
; et al. |
June 23, 2005 |
Metallic alloy nanocomposite for high-temperature structural
components and methods of making
Abstract
A nanocomposite comprising a plurality of nanoparticles
dispersed in a metallic alloy matrix, and a structural component
formed from such a nanocomposite. The metallic matrix comprises at
least one of a nickel-based alloy and an iron-based alloy. The
nanocomposite contains a higher volume fraction of nanoparticle
dispersoids than those presently available. The structural
component include those used in hot gas path assemblies, such as
steam turbines, gas turbines, and aircraft turbine. A method of
making such nanocomposites is also disclosed.
Inventors: |
Subramanian, Pazhayannur
Ramanathan; (Niskayuna, NY) ; Angeliu, Thomas
Martin; (Clifton Park, NY) ; Corderman, Reed
Roeder; (Niskayuna, NY) ; Huang, Shyh-Chin;
(Latham, NY) ; Marte, Judson Sloan; (Wynantskill,
NY) ; Gray, Dennis Michael; (Delanson, NY) ;
Anand, Krishnamurthy; (Bangalore, IN) ; Srinivasan,
Dheepa; (Malleswaram, IN) ; Oruganti, Ramkumar
Kashyap; (Bangalore, IN) ; Amancherla, Sundar;
(Bangalore, IN) |
Correspondence
Address: |
General Electric Company
CRD Patent Docket Rm 4A59
Bldg. K-1
P.O. Box 8
Schenectady
NY
12301
US
|
Assignee: |
General Electric Company
|
Family ID: |
34552823 |
Appl. No.: |
10/743237 |
Filed: |
December 22, 2003 |
Current U.S.
Class: |
148/325 ;
148/427; 419/19 |
Current CPC
Class: |
B22F 2998/10 20130101;
B22F 2998/00 20130101; B22F 2999/00 20130101; C22C 1/05 20130101;
B22F 3/16 20130101; C22C 1/05 20130101; B22F 3/162 20130101; B22F
9/04 20130101; B22F 2009/041 20130101; B22F 3/162 20130101; B22F
2998/00 20130101; B22F 2999/00 20130101; B22F 1/0018 20130101; B22F
2998/10 20130101 |
Class at
Publication: |
148/325 ;
148/427; 419/019 |
International
Class: |
C22C 019/05; C22C
038/18 |
Claims
1. A structural component in a hot gas path assembly, said
structural component comprising a nanocomposite, wherein said
nanocomposite comprises: a) a metallic matrix; and b) a plurality
of nanoparticles dispersed throughout said metallic matrix, wherein
said plurality of nanoparticles comprises from about 4 volume
percent to about 30 volume percent of said nanocomposite.
2. The structural component according to claim 1, wherein said
metallic matrix comprises at least one of a nickel-based alloy, an
iron-based alloy, and combinations thereof.
3. The structural component according to claim 2, wherein said
nickel-based alloy is one of a Ni--Cr based alloy, a Ni--Cr--Al
based alloy, and combinations thereof.
4. The structural component according to claim 2, wherein said
iron-based alloy is one of a Fe--Cr based alloy, a Fe--Cr--Al based
alloy, and combinations thereof.
5. The structural component according to claim 2, wherein said hot
gas path assembly is a turbine assembly.
6. The structural component according to claim 5, wherein said
structural component is one of a combustor, a vane, a wheel, a
disc, and a casing.
7. The structural component according to claim 1, wherein each of
said plurality of nanoparticles comprises at least one of an
inorganic oxide, an inorganic carbide, an inorganic nitride, an
inorganic boride, an inorganic oxycarbide, an inorganic oxynitride,
an inorganic silicide, an inorganic aluminide, and combinations
thereof.
8. The structural component according to claim 7, wherein said
inorganic oxide is one of yttria, alumina, zirconia, hafnia, and
combinations thereof.
9. The structural component according to claim 7, wherein said
inorganic carbide is a carbide of at least one of hafnium,
tantalum, molybdenum, zirconium, niobium, chromium, titanium,
tungsten, and combinations thereof.
10. The structural component according to claim 1, wherein each of
said plurality of nanoparticles has at least one dimension, wherein
said at least one dimension that is in a range from about 10 nm to
about 500 nm.
11. The structural component according to claim 10, wherein said
dimension that is in a range from about 10 nm to about 30 nm.
12. The structural component according to claim 1, wherein said
plurality of said nanoparticles comprise from about 10 volume
percent to about 30 volume percent of said nanocomposite.
13. The structural component according to claim 1, wherein said
nanocomposite thermally stable up to about 1200.degree. C.
14. A nanocomposite, said nanocomposite comprising: a) a metallic
matrix; and b) a plurality of nanoparticles dispersed throughout
said metallic matrix, wherein said plurality of nanoparticles
comprises from about 4 volume percent to about 30 volume percent of
said nanocomposite, and wherein said nanocomposite is formed by
providing a nanocomposite powder, consolidating said nanocomposite
powder to form a green body, and thermomechanically processing said
green body to form said nanocomposite.
15. The nanocomposite according to claim 14, wherein said metallic
matrix comprises at least one of a nickel-based alloy, an
iron-based alloy, and combinations thereof.
16. The nanocomposite according to claim 15, wherein said
nickel-based alloy is one of a Ni--Cr based alloy, a Ni--Cr--Al
based alloy, and combinations thereof.
17. The nanocomposite according to claim 15, wherein said
iron-based alloy is one of a Fe--Cr based alloy, a Fe--Cr--Al based
alloy, and combinations thereof.
18. The nanocomposite according to claim 14, wherein each of said
plurality of nanoparticles comprises at least one of an inorganic
oxide, an inorganic carbide, an inorganic nitride, an inorganic
boride, an inorganic oxycarbide, an inorganic oxynitride, an
inorganic silicide, an inorganic aluminide, and combinations
thereof.
19. The nanocomposite according to claim 18, wherein said inorganic
oxide is one of yttria, alumina, zirconia, hafnia, and combinations
thereof.
20. The nanocomposite according to claim 18, wherein said inorganic
carbide is a carbide of at least one of hafnium, tantalum,
molybdenum, zirconium, niobium, chromium, titanium, tungsten, and
combinations thereof.
21. The nanocomposite according to claim 14, wherein each of said
plurality of nanoparticles has at least one dimension, wherein said
at least one dimension is a range from about 10 nm to about 500
nm.
22. The nanocomposite according to claim 21, wherein said dimension
is in a range from about 10 nm to about 30 nm.
23. The nanocomposite according to claim 14, wherein said plurality
of said nanoparticles comprise from about 10 volume percent to
about 30 volume percent of said nanocomposite.
24. The nanocomposite according to claim 14, wherein said
thermomechanical process is a cryogenic milling process.
25. The nanocomposite according to claim 24, wherein said cryogenic
milling process is one of a non-reactive milling process and a
reactive cryogenic milling process.
26. The nanocomposite according to claim 14, wherein said
thermomechanical process comprises at least one of extrusion,
forging, rolling, and swaging of said nanocomposite.
27. The nanocomposite according to claim 14, wherein said severe
plastic deformation comprises equiaxial channel angular processing
of said nanocomposite.
28. The nanocomposite according to claim 14, wherein said severe
plastic deformation comprises at least one of torsion extrusion and
twist extrusion of said nanocomposite.
29. A structural component in a hot gas path assembly comprising a
nanocomposite, wherein said nanocomposite comprises: a) a metallic
matrix, wherein said metallic matrix comprises at least one of a
nickel-based alloy, an iron-based alloy, and combinations thereof;
and b) a plurality of nanoparticles dispersed throughout said
metallic matrix, wherein said plurality of nanoparticles comprises
from about 4 volume percent to about 30 volume percent of said
nanocomposite, and wherein said nanocomposite is formed by a
thermomechanical process followed by severe plastic
deformation.
30. The structural component according to claim 29, wherein said
nickel-based alloy is one of a Ni--Cr based alloy, a Ni--Cr--Al
based alloy, and combinations thereof.
31. The structural component according to claim 29, wherein said
iron-based alloy is one of a Fe--Cr based alloy, a Fe--Cr--Al bases
alloy, and combinations thereof.
32. The structural component according to claim 29, wherein said
hot gas path assembly is a turbine assembly.
33. The structural component according to claim 32, wherein said
structural component is one of a combustor, a vane, a wheel, a
disc, and a casing.
34. The structural component according to claim 29, wherein each of
said plurality of nanoparticles comprises at least one of an
inorganic oxide, an inorganic carbide, an inorganic nitride, an
inorganic boride, an inorganic oxycarbide, an inorganic oxynitride,
an inorganic silicide, an inorganic aluminide, and combinations
thereof.
35. The structural component according to claim 34, wherein said
inorganic oxide is one of yttria, alumina, zirconia, hafnia, and
combinations thereof.
36. The structural component according to claim 35, wherein said
inorganic carbide is a carbide of at least one of hafnium,
tantalum, molybdenum, zirconium, niobium, chromium, titanium,
tungsten, and combinations thereof.
37. The structural component according to claim 29, wherein each of
said plurality of nanoparticles has at least one dimension, wherein
said at least one dimension is a range from about 10 nm to about
500 nm.
38. The structural component according to claim 37, wherein said
dimension is in a range from about 10 nm to about 30 nm.
39. The structural component according to claim 29, wherein each of
said plurality of nanoparticles is substantially spherical.
40. The structural component according to claim 29, wherein each of
said plurality of nanoparticles has a substantially ellipsoidal
shape.
41. The structural component according to claim 29, wherein said
plurality of said nanoparticles comprise from about 10 volume
percent to about 30 volume percent of said nanocomposite.
42. The structural component according to claim 29, wherein said
nanocomposite thermally stable up to about 1200.degree. C.
43. The structural component according to claim 29, wherein said
thermomechanical process is a cryogenic milling process.
44. The structural component according to claim 29, wherein said
cryogenic milling process is one of a non-reactive milling process
and a reactive cryogenic milling process.
45. The structural component according to claim 29, wherein said
thermomechanical process comprises at least one of extrusion,
forging, rolling, and swaging of said nanocomposite.
46. The structural component according to claim 29, wherein said
severe plastic deformation comprises equiaxial channel angular
processing of said nanocomposite.
47. The structural component according to claim 29, wherein said
severe plastic deformation comprises at least one of torsion
extrusion and twist extrusion of said nanocomposite.
48. A method of making a bulk nanocomposite, wherein the
nanocomposite comprises a metallic matrix and a plurality of
nanoparticles dispersed throughout the metallic matrix, wherein the
metallic matrix comprises at least one of a nickel-based alloy, an
iron-based alloy, and combinations thereof, and wherein the
plurality of nanoparticles comprises from about 4 volume percent to
about 30 volume percent of the nanocomposite, the method comprising
the steps of: a) providing a nanocomposite powder, wherein the
nanocomposite powder comprises a plurality of nanoparticles and a
metallic matrix material; b) consolidating the nanocomposite
powder; and c) thermomechanically processing the nanocomposite
powder to form the bulk nanocomposite.
49. The method according to claim 48, wherein the step of providing
the nanocomposite powder comprises forming the plurality of
nanoparticles by at least one of mechanofusion, mechanical
alloying, cryomilling, and combinations thereof.
50. The method according to claim 49, wherein the step of forming
the plurality of nanoparticles comprises cryomilling the metallic
matrix material to form the plurality of nanoparticles.
51. The method according to claim 50, wherein the step of
cryomilling said metallic matrix material comprises cryomilling
said metallic matrix material in a reactive atmosphere.
52. The method according to claim 51, wherein the reactive
atmosphere comprises at least one of nitrogen and a
hydrocarbon.
53. The method according to claim 48, wherein the step of
consolidating the nanocomposite powder comprises pressing the
nanocomposite powder to form a compact.
54. The method according to claim 48, wherein the step of
thermomechanically processing the nanocomposite powder comprises at
least one of forging, hot-extruding, and hot-rolling, the
nanocomposite powder.
55. The method according to claim 48, wherein the step of
thermomechanically processing the nanocomposite powder comprises
subjecting the nanocomposite powder compact to severe plastic
deformation.
56. The method according to claim 55, wherein the step of
subjecting the nanocomposite powder compact to severe plastic
deformation comprises at least one of one of equiaxial channel
angular processing of the nanocomposite powder, torsion extruding
the nanocomposite powder, and twist extruding the nanocomposite
powder.
Description
BACKGROUND OF INVENTION
[0001] The invention relates to a nanocomposite comprising a
plurality of nanoparticles dispersed in a metallic alloy matrix and
structural components comprising such nanocomposites. More
particularly, the invention relates to method of making such
nanocomposites.
[0002] The continuing effort to design and build more powerful and
more efficient turbo-machinery, such as gas turbines, steam
turbines, and aircraft engines, requires the use of materials
having enhanced high temperature performance capabilities. Such
performance enhancements require state-of-the-art materials with
vastly improved mechanical properties such as strength and creep
resistance.
[0003] High temperature structural materials can be strengthened in
a number of ways such as, for example, grain refinement, solid
solution strengthening, precipitate strengthening, composite
strengthening, and dispersoid strengthening. One method of
strengthening alloys called Orowan strengthening incorporates a
fine distribution of hard particles into a metallic alloy matrix.
Orowan strengthening depends upon the formation of an array of
dispersoid particles that serve as obstacles for impeding
dislocation motion within the alloy matrix. The strength of these
particle-reinforced alloys is inversely proportional to the spacing
between these particles, which can be controlled in turn by
controlling the size of the dispersoid particles. Thus, the use of
nanoparticles as dispersoids offers the potential of substantially
enhancing alloy strength.
[0004] The introduction of hard dispersoid nanoparticles during the
processing of the nanodispersoid-reinforced alloys presents a
technical challenge. Current processes to disperse particles
include powder metallurgy routes, such as mechanical alloying of
micron-sized particles, in combination with secondary processes,
which include hot-isostatic pressing and thermomechanical
processing by hot-forging or extrusion. In the mechanical alloying
process, nanoparticles are created by repeated fracture of the
micron-size dispersoid particles during milling. While this is a
well-established process for oxide-dispersion strengthened (ODS)
alloys in iron- and nickel-based alloys (such as, for example,
Inconel MA alloys), the process fails to produce a homogeneous of
distribution of the particles in the alloy matrix, especially for
large components. In addition, the loading of the particles in the
alloy composites produced by this process is typically limited to
less than 2% by volume.
[0005] Current processes are unable to produce alloy nanocomposites
having sufficiently high loadings of nanoparticles. Therefore, what
is needed is an alloy nanocomposite in which dispersoid)
nanoparticles are homogeneously distributed throughout the metallic
alloy matrix. What is also needed is an alloy nanocomposite having
a sufficiently high loading of dispersoid nanoparticles having high
temperature performance capabilities that adequate for use in hot
gas path assemblies, such as turbine assemblies. What is further
needed is a method of making alloy nanocomposites having high
loadings of dispersoid nanoparticles, wherein the dispersoid
nanoparticles are homogeneously distributed throughout the alloy
nanocomposite.
BRIEF SUMMARY OF INVENTION
[0006] The present invention meets these and other needs by
providing a nanocomposite comprising a plurality of nanoparticles
dispersed in a metallic alloy matrix, and a structural component
formed from such a nanocomposite. The nanocomposite contains a
higher volume fraction of nanoparticle dispersoids than those
presently available. The nanocomposite may be used to fabricate
structural components, such as those used in hot gas path
assemblies, such as steam turbine, gas turbine, and aircraft
turbine. The present invention also discloses a method of making
such nanocomposites.
[0007] Accordingly, one aspect of the invention is to provide a
structural component used in a hot gas path assembly comprising a
nanocomposite. The nanocomposite comprises: a metallic matrix; and
a plurality of nanoparticles dispersed throughout the metallic
matrix, wherein the plurality of nanoparticles comprises from about
4 volume percent to about 30 volume percent of the
nanocomposite.
[0008] A second aspect of the invention is to provide a
nanocomposite. The nanocomposite comprises a metallic matrix and a
plurality of nanoparticles dispersed throughout the metallic
matrix. The plurality of nanoparticles comprises from about 4
volume percent to about 30 volume percent of the nanocomposite and
is formed by a thermomechanical process followed by severe plastic
deformation.
[0009] A third aspect of the invention is to provide a structural
component comprising a nanocomposite. The nanocomposite comprises:
a metallic matrix, wherein the metallic matrix comprises at least
one of a nickel-based alloy, an iron-based alloy, and combinations
thereof; and a plurality of nanoparticles dispersed throughout the
metallic matrix. The plurality of nanoparticles comprises from
about 4 volume percent to about 30 volume percent of the
nanocomposite, and the nanocomposite is formed by a
thermomechanical process followed by severe plastic
deformation.
[0010] A fourth aspect of the invention is to provide a method of
making a nanocomposite. The nanocomposite comprises a metallic
matrix and a plurality of nanoparticles dispersed throughout the
metallic matrix, wherein the metallic matrix comprises at least one
of a nickel-based alloy, an iron-based alloy, and combinations
thereof, and wherein the plurality of nanoparticles comprises from
about 4 volume percent to about 30 volume percent of the
nanocomposite. The method comprises the steps of: providing a
nanocomposite powder, wherein the nanocomposite powder comprises a
plurality of nanoparticles and a metallic matrix material;
consolidating the nanocomposite powder; and thermomechanically
processing the nanocomposite powder to form the bulk
nanocomposite.
[0011] These and other aspects, advantages, and salient features of
the present invention will become apparent from the following
detailed description, the accompanying drawings, and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0012] FIG. 1 is a transmission electron microscopy (TEM) image of
a nanocomposite of the present invention;
[0013] FIG. 2 is a flow chart illustrating the method of making a
nanocomposite according to the present invention; and
[0014] FIG. 3 is a scanning electron microscopy (SEM) image of a
nickel-based alloy nanocomposite powder of the present invention
containing 5 volume percent yttrium oxide.
DETAILED DESCRIPTION
[0015] In the following description, like reference characters
designate like or corresponding parts throughout the several views
shown in the figures. It is also understood that terms such as
"top," "bottom," "outward," "inward," and the like are words of
convenience and are not to be construed as limiting terms.
[0016] Referring to the drawings in general and to FIG. 1 in
particular, it will be understood that the illustrations are for
the purpose of describing a preferred embodiment of the invention
and are not intended to limit the invention thereto. FIG. 1 is a
transmission electron microscopy (TEM) image of a nanocomposite 100
of the present invention. Nano composite 100 comprises a metallic
matrix 110 and a plurality of nanoparticles 120 dispersed
throughout the metallic matrix 110. The plurality of nanoparticles
120 comprises from about 4 volume percent to about 30 volume
percent of nanocomposite 100. In particular, FIG. 1 shows a
nanocomposite 100 in which metallic matrix 110 comprises a
nickel-based alloy and plurality of nanoparticles 120 comprises
yttrium oxide (Y.sub.2O.sub.3). In the sample shown in FIG. 1, the
yttrium oxide nanoparticles comprise about 5 volume percent of
nanocomposite 100.
[0017] Metallic matrix 110 comprises at least one of a nickel-based
alloy, an iron-based alloy, and combinations thereof. Non-limiting
examples of such nickel-based alloys that may be used to form
metallic matrix 110 include Ni--Cr based alloys, Ni--Cr--Al based
alloys, and combinations thereof. Iron-based alloys that may be
used to form metallic matrix 110 include, but are not limited to
Fe--Cr based alloys, Fe--Cr--Al based alloys, and combinations
thereof.
[0018] The plurality of nanoparticles 120 comprises at least one of
an inorganic oxide, an inorganic carbide, an inorganic nitride, an
inorganic boride, an inorganic oxycarbide, an inorganic oxynitride,
an inorganic silicide, an inorganic aluminide, and combinations
thereof. Inorganic oxides that may comprise the plurality of
nanoparticles 120 include, but are not limited to, yttria, alumina,
zirconia, hafnia, and combinations thereof. The inorganic carbides
that may comprise the plurality of nanoparticles 120 include, but
are not limited to, carbides of hafnium, tantalum, molybdenum,
zirconium, niobium, chromium, titanium, tungsten, and combinations
thereof.
[0019] In one embodiment, each of the plurality of nanoparticles
120 is substantially spherical in shape. In other embodiments of
the invention, each of the plurality of nanoparticles may be rods,
needles, spheroidal shapes, and the like. Alternatively, plurality
of nanoparticles 120 may comprise a mixture of nanoparticles having
a variety of such shapes. Each of the plurality of nanoparticles
has at least one dimension that is in a range from about 10 nm to
about 500 nm. In one embodiment, a dimension of each one of the
plurality of nanoparticles 120 is in a range from about 10 nm to
about 30 nm.
[0020] One method of strengthening of alloys is a mechanism known
as Orowan strengthening, in which a fine distribution of hard
particles is incorporated into an alloy. In this strengthening
mechanism, an array of such dispersoid particles impedes
dislocation motion. The strength of such particle-reinforced alloys
is inversely proportional to the spacing between the dispersoid
particles. Spacing of the dispersoid particles can, in turn, can be
controlled by controlling the size of the dispersoid particles. For
a given volume of dispersoid particles, using dispersoid particles
with sizes in the nanometer range can decrease spacing and thus
substantially enhance alloy strength.
[0021] Currently, powder metallurgy routes in combination with
secondary processes, such as mechanical alloying processes, are
used to disperse particles. In the mechanical alloying process,
nanoparticles are created by repeated fracture of micron-size
dispersoid particles during milling. Such processes fail to achieve
a homogeneous particles distribution within the alloy, particularly
for large components. In addition, the loading of the particles in
the alloys formed by such processes is typically limited to less
than 2% by volume.
[0022] Accordingly, the nanocomposite 100 provided by the present
invention overcomes the loading and dispersion limitations
encountered with current dispersoid strengthened alloys. The
invention provides a nanocomposite 100 with superior mechanical
properties achieved through dispersoid strengthening by a providing
a higher volume fraction of nanoparticle dispersoids than those
presently available. The plurality of nanoparticles 120 comprises
from about 4 volume percent to about 30 volume percent of
nanocomposite 100. In one embodiment, the plurality of
nanoparticles 120 comprises from about 10 volume percent to about
30 volume percent of nanocomposite 100.
[0023] The higher volume loadings of the plurality of nanoparticles
120 of the present invention provide nanocomposite 100 with
mechanical properties that are superior to those of current
state-of-the art materials. Nanocomposite 100 also exhibits greater
microstructural stability at elevated temperatures, allowing
strength and creep resistance to retained at much higher
temperatures than those provided by current oxide dispersion
strengthened (ODS) alloys. Nanocomposite 100 is thermally stable up
to about 1200.degree. C.
[0024] As described herein, the nanocomposite 100 of the present
invention may be formed into high-temperature structural components
for use in hot gas path assemblies, such as steam turbines, gas
turbines, and aircraft engines. Such components include, but are
not limited to: rotating components, such as turbine airfoils and
turbine disks; static components, such as ducts, frames, and
casings; combustors; and the like. Forming techniques, such as
powder metallurgy techniques, thermomechanical processing, and the
like, that are well known the art, can be used to form
nanocomposite 100 into the desired structural component.
[0025] In addition to nanocomposite 100 and a structural component
made from nanocomposite 100, the present invention also provides a
method of making nanocomposite 100. A flow chart illustrating the
method 200 of making nanocomposite 100 is shown in FIG. 2.
[0026] Referring to Step 210 in FIG. 2, a plurality of
nanoparticles 120 is first combined with a metallic matrix
material, such as, for example, an alloy powder, to form a
nanocomposite powder. In one embodiment, the nanocomposite powder
is produced by blending at least one metallic alloy powder with a
predetermined volume fraction of hard dispersoid nanoparticles.
Each of the dispersoid nanoparticles has at least one dimension
ranging from about 10 nm to about 500 nm. Techniques, such as,
mechanofusion, mechanical alloying, cryomilling, and the like, are
used separately or in combination with each other to form the
nanocomposite powder. Such methods, particularly mechanofusion and
cryomilling, act to coat and surround individual particles of the
metallic alloy powder with a plurality of dispersoid nanoparticles.
A SEM image of a nickel-based alloy nanocomposite powder,
containing 5 volume percent yttrium oxide, of the present invention
is shown in FIG. 3.
[0027] In one embodiment, the nanocomposite powder is produced by
in-situ formation of a plurality of nanoparticles 120 within an
alloyed metallic matrix 110. This is achieved by cryomilling
micron-sized particles of the metallic alloy matrix material in a
reactive atmosphere, comprising, for example, at least one of
nitrogen, and a hydrocarbon, such as, but not limited to, methane.
The gases present in the reactive atmosphere may additionally serve
as the coolant for cryomilling. Alternatively, cryomilling may be
performed in an inert atmosphere that comprises, for example, at
least one of argon and helium.
[0028] The cryomilling feedstock comprises at least one alloyed
metal powder that comprises at least one metallic element. The at
least one metallic element may be either reactive or refractory in
nature. Such metallic elements include, but are not limited to, Al,
Cr, Ti, Mo, Nb, Ta, W, B, Zr, Hf, Ta, combinations thereof, and the
like. The plurality of nanoparticles 120 comprising the metallic
elements is formed by cryomilling such metallic alloys. The
cryomilling action separates highly reactive nanosize particles
from the micron-size particles of metallic alloy matrix material.
When cryomilled in a reactive atmosphere, the metallic
nanoparticles react with the reactive gases to form hard dispersoid
nanoparticles, such as oxides, carbide, nitrides, combinations
thereof, and the like. The hard dispersoid nanoparticles surround
each of the micron-size particles of metallic alloy matrix material
to achieve the fine distribution incorporation that is needed for
Orowan strengthening.
[0029] The nanocomposite powder is then consolidated (Step 220) and
thermo-mechanically processed (Step 230) to form a bulk dispersoid
nanoparticle-reinforced metallic alloy nanocomposite 100.
Consolidation of the nanocomposite powder (Step 220) into a compact
is performed using techniques, such as cold pressing, hot pressing,
forging, extruding, canning, and the like, that are known in the
metallurgical arts. Step 230 is carried out using techniques such
as, but not limited to, forging, hot-extrusion, and hot-rolling,
either separately or in combination with each other. In another
embodiment, dispersoid nanoparticle-reinforced metallic alloy
nanocomposite 100 is formed from the consolidated nanocomposite
powder compact by subjecting the nanocomposite powder compact to
severe plastic deformation. Such severe plastic deformation may be
accomplished by one of equiaxial channel angular processing,
torsion extrusion, and twist extrusion of the nanocomposite
powder.
[0030] The following example illustrates the various features and
advantages offered by the present invention, and in no way is
intended to limit the invention thereto.
EXAMPLE 1
[0031] For the purpose of this example, the alloys Ni-20Cr and
Fe-12.5Cr were selected as the nickel-based and iron-based matrix
alloy materials, respectively, for the nanocomposite, and yttrium
oxide (Y.sub.2O.sub.3) was selected as the reinforcing dispersoid
nanoparticle.
[0032] Prototype nickel-based and iron-based metallic alloy
nanocomposites were fabricated by first forming nanocomposite
powders by blending -325 mesh (44 micron) of either nickel-based
(Ni-20 weight percent Cr) or iron-based (Fe-12.5 weight percent Cr)
alloy powder with various volume fractions (ranging from 5 to 10
volume percent) of size yttrium oxide nanopowders (particle sizes
ranging from 50-100 nm). The nanocomposite powders were formed
using mechanofusion, in which the yttrium oxide powder was
mechanically fused or embedded into the metal powder surface. As an
alternative to blending, other procedures, such as cryomilling or
mechanical alloying, can be employed to make the nanocomposite
powder. The nanocomposite powder was then consolidated by enclosing
the nanocomposite powder in a stainless steel can, evacuating, and
sealing the can, and extruding the can against a flat faced die at
a temperature of 1100.degree. C. The extruded can was re-machined
and hot extruded at a temperature of 1100.degree. C. using a 9:1
reduction ratio.
[0033] The resulting as-fabricated metallic alloy nanocomposites
were examined by transmission electron microscopy (TEM) and
scanning electron microscopy (SEM) to evaluate the respective grain
sizes of the matrix and the dispersoid nanoparticles, as well as
distribution of the dispersoid nanoparticles in the alloy matrix
and grain boundaries. A TEM image of an iron-based (Fe---12.5
weight percent Cr) alloy nanocomposite containing 5 volume percent
yttrium oxide is shown in FIG. 1. The microstructure of the
nanocomposite 100 comprises grains of metallic alloy matrix 110,
ranging from about 5 microns to about 10 microns in size, and
yttrium oxide nanoparticles 120, ranging from about 100 nm to about
500 nm in size.
[0034] While typical embodiments have been set forth for the
purpose of illustration, the foregoing description should not be
deemed to be a limitation on the scope of the invention.
Accordingly, various modifications, adaptations, and alternatives
may occur to one skilled in the art without departing from the
spirit and scope of the present invention.
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