U.S. patent application number 11/324458 was filed with the patent office on 2007-07-05 for nanostructured superalloy structural components and methods of making.
Invention is credited to Sundar Amancherla, Michael Francis Xavier Gigliotti, Luana Emiliana Iorio, Ramkumar Kashyap Oruganti, Suchismita Sanyal, Dheepa Srinivasan, Pazhayannur Ramanathan Subramanian, Craig Douglas Young.
Application Number | 20070151639 11/324458 |
Document ID | / |
Family ID | 38223131 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070151639 |
Kind Code |
A1 |
Oruganti; Ramkumar Kashyap ;
et al. |
July 5, 2007 |
Nanostructured superalloy structural components and methods of
making
Abstract
A superalloy-containing structural component includes a
superalloy matrix, and a plurality of hard phase nanoparticles
dispersed at grain boundaries within the superalloy matrix, wherein
the plurality of hard phase nanoparticles dispersed at the grain
boundaries comprise about 1 volume percent to about 30 volume
percent of the structural component, and wherein the superalloy
matrix and the plurality of hard phase nanoparticles dispersed at
the grain boundaries within the base superalloy matrix have been
thermo-mechanically processed to form the structural component. A
method for making a structural component includes introducing
dislocations into a superalloy particle matrix effective to form
new grain boundaries within a plurality of superalloy particles,
introducing hard phase dispersoid nanoparticles at a plurality of
grain boundaries of the superalloy particles effective to pin the
grain boundaries, and thermo-mechanically processing the superalloy
particles and hard phase dispersoid nanoparticles to form the
superalloy-containing structural component.
Inventors: |
Oruganti; Ramkumar Kashyap;
(Bangalore, IN) ; Subramanian; Pazhayannur
Ramanathan; (Niskayuna, NY) ; Gigliotti; Michael
Francis Xavier; (Scotia, NY) ; Iorio; Luana
Emiliana; (Clifton Park, NY) ; Young; Craig
Douglas; (Clifton Park, NY) ; Sanyal; Suchismita;
(Bangalore, IN) ; Srinivasan; Dheepa; (Bangalore,
IN) ; Amancherla; Sundar; (Bangalore, IN) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Family ID: |
38223131 |
Appl. No.: |
11/324458 |
Filed: |
January 3, 2006 |
Current U.S.
Class: |
148/677 ;
148/410 |
Current CPC
Class: |
B22F 2999/00 20130101;
B82Y 30/00 20130101; C22C 32/00 20130101; B22F 3/20 20130101; B22F
2009/041 20130101; C22C 1/0433 20130101; B22F 2999/00 20130101;
B22F 2003/248 20130101; B22F 2998/10 20130101; C22C 19/056
20130101; B22F 2998/10 20130101; C22F 1/10 20130101; B22F 3/02
20130101; B22F 9/04 20130101; B22F 3/15 20130101; B22F 9/04
20130101; B22F 2202/03 20130101; B22F 3/24 20130101; B22F 1/0003
20130101 |
Class at
Publication: |
148/677 ;
148/410 |
International
Class: |
C22C 19/05 20060101
C22C019/05; C22F 1/10 20060101 C22F001/10 |
Claims
1. A structural component formed from a superalloy, the structural
component comprising: a superalloy matrix; and a plurality of hard
phase nanoparticles dispersed at grain boundaries within the
superalloy matrix; wherein the plurality of hard phase
nanoparticles dispersed at the grain boundaries comprise about 1
volume percent to about 30 volume percent of the structural
component, and wherein the superalloy matrix and the plurality of
hard phase nanoparticles dispersed at the grain boundaries within
the base superalloy matrix have been thermo-mechanically processed
to form the structural component.
2. The structural component of claim 1, further comprising a gamma
prime phase.
3. The structural component of claim 1, further comprising a gamma
double prime phase.
4. The structural component of claim 1, wherein grains within the
superalloy matrix have an average longest dimension of about 10
nanometers to about 500 nanometers.
5. The structural component of claim 1, wherein the plurality of
hard phase nanoparticles comprises an inorganic oxide, inorganic
carbide, inorganic nitride, inorganic carbonitride, inorganic
boride, inorganic oxycarbide, inorganic oxynitride, inorganic
silicide, inorganic aluminide, inorganic sulfide, inorganic
oxysulfide, or a combination comprising at least one of the
foregoing.
6. The structural component of claim 1, wherein the plurality of
hard phase nanoparticles have an average longest dimension of about
10 nanometers to about 500 nanometers.
7. The structural component of claim 1, wherein the structural
component comprises at least a portion of a hot gas path
assembly.
8. The structural component of claim 7, wherein the hot gas path
assembly is a steam turbine, gas turbine, or aircraft engine.
9. The structural component of claim 8, wherein the structural
component is a airfoil, disc, wheel, duct, frame, casing, bucket,
vane, or combustor.
10. The structural component of claim 1, wherein the superalloy
matrix comprises a Ni-base superalloy, Fe-base superalloy, Co-base
superalloy, or a combination comprising at least one of the
foregoing superalloys.
11. A structural component formed from a superalloy, the structural
component comprising: a superalloy matrix; a gamma prime phase,
wherein the gamma prime phase comprises about 10 weight percent to
about 60 weight percent of the nanostructured superalloy matrix;
and a plurality of hard phase nanoparticles dispersed at grain
boundaries within the superalloy matrix, wherein the plurality of
hard phase nanoparticles dispersed at the grain boundaries comprise
about 1 volume percent to about 30 volume percent of the structural
component, and wherein the superalloy matrix, gamma prime phase,
and the plurality of hard phase nanoparticles dispersed at the
grain boundaries within the superalloy matrix have been
thermo-mechanically processed to form the structural component.
12. The structural component of claim 11, wherein grains within the
superalloy matrix have an average longest dimension of about 10
nanometers to about 500 nanometers.
13. The structural component of claim 11, wherein the plurality of
hard phase nanoparticles comprises an inorganic oxide, inorganic
carbide, inorganic nitride, inorganic carbonitride, inorganic
boride, inorganic oxycarbide, inorganic oxynitride, inorganic
silicide, inorganic aluminide, inorganic sulfide, inorganic
oxysulfide, or a combination comprising at least one of the
foregoing.
14. The structural component of claim 11, wherein the plurality of
hard phase nanoparticles have an average longest dimension of about
10 nanometers to about 500 nanometers.
15. The structural component of claim 11, wherein the structural
component comprises at least a portion of a steam turbine, gas
turbine, or aircraft engine.
16. The structural component of claim 11, further comprising a
gamma double-prime phase.
17. A method for making a structural component comprising a
superalloy, the method comprising: introducing dislocations into a
superalloy particle matrix effective to form new grain boundaries
within a plurality of superalloy particles; introducing hard phase
dispersoid nanoparticles at a plurality of grain boundaries of the
superalloy particles effective to pin the grain boundaries; and
thermo-mechanically processing the superalloy particles and hard
phase dispersoid nanoparticles to form the superalloy-containing
structural component.
18. The method of claim 17, wherein introducing the dislocations
comprises cryomilling, high pressure torsion, equal channel angular
pressing, cyclic channel die compression, accumulative roll
bonding, repetitive corrugation and straightening, twist extrusion,
or a combination comprising at least one of the foregoing.
19. The method of claim 17, wherein introducing the hard phase
dispersoid nanoparticles comprises extrinsically combining the hard
phase dispersoid nanoparticles with the superalloy particle matrix
during and/or after introducing the dislocations into the
superalloy particle matrix.
20. The method of claim 17, wherein introducing the hard phase
dispersoid nanoparticles comprises creating the hard phase
dispersoid nanoparticles while introducing the dislocations into
the superalloy particle matrix.
21. The method of claim 17, wherein thermo-mechanically processing
the Ni-superalloy particles and hard phase dispersoid nanoparticles
to form the nanostructured Ni-superalloy-containing structural
component comprises forging, hot extrusion, hot rolling, or a
combination comprising at least one of the foregoing.
22. The method of claim 17, further comprising consolidating the
superalloy particle matrix and hard phase dispersoid nanoparticles
into a compact prior to the thermo-mechanically processing.
23. The method of claim 17, further comprising introducing a gamma
prime phase into the superalloy particle matrix.
24. The method of claim 17, further comprising introducing a gamma
double-prime phase into the superalloy particle matrix.
Description
BACKGROUND
[0001] The present disclosure relates to superalloys, and more
particularly to structural components comprising nanostructured
superalloys.
[0002] Superalloys are metallic alloys that can be used at high
temperatures, often in excess of 0.7 of the absolute melting
temperature. Many structural components, such as those used in
aircraft engines or power generation devices, are formed from Fe-,
Co-, or Ni-base superalloys. There is a constant drive towards
improving the high temperature properties of these fatigue-limited
structural components in order to increase the strength or life of
the aircraft engine or power generation device.
[0003] Nanostructured materials often exhibit superior mechanical
properties (e.g., strength, hardness, ductility, and the like)
relative to their larger-scale counterparts. Moreover, the fatigue
initiation life of nanostructured materials is significantly higher
than that of larger-grained materials since dislocation activity
may be spread over a larger number of grains. Unfortunately,
nanostructured alloys, like their larger-scale counterparts,
undergo the processes of recovery, recrystallization, and/or grain
growth upon heating. In fact, owing to their non-equilibrium
nature, nanoscale grains are more susceptible to these processes
than are micrometer scale grains. Consequently, when
thermo-mechanically processing nanostructured alloys into a shaped
article, the nanostructure and, consequently, the superior
properties are often lost. Furthermore, during operation of the
structural components comprising the nanostructured alloys, new
opportunities for recovery, recrystallization, and/or grain growth
arise as the working temperatures increase.
[0004] One method of inhibiting recovery, recrystallization, and/or
grain growth (and therefore a method of strengthening alloys) is
through Orowan strengthening, in which a fine distribution of hard
phase particles is incorporated into the alloy composition matrix.
The strength of such hard phase particle-reinforced alloys is
inversely proportional to the spacing between the dispersoid
particles, which can be controlled by controlling the size of the
dispersoid particles. Thus, the use of nanoparticles as dispersoids
offers the potential of substantially enhancing alloy strength.
[0005] The introduction of hard phase dispersoid nanoparticles
during the processing of the alloys presents a major technical
challenge. Current processes to disperse particles include powder
metallurgy routes, such as mechanical alloying of micrometer-scale
particles, in combination with secondary processes, which include
hot-isostatic pressing and/or thermo-mechanical processing by
hot-forging or extrusion. In the mechanical alloying process,
nanoparticles are created by repeated fracture of the
micrometer-scale dispersoid particles during milling.
Unfortunately, these processes fail to produce a homogeneous
distribution of nanoparticles in the alloy matrix, especially for
large components. In addition, the loading of the hard phase
dispersoid particles in the alloy composites is frequently limited
to less than 2 volume percent. Thus, current processes are unable
to produce nanostructured alloys having a sufficiently high enough
loading of nanoparticle dispersoids to provide increased strength
to the alloy or article made therefrom.
[0006] There accordingly remains a need in the art for improved
methods of producing nanostructured alloys that have more stable
grain structures when exposed to heat. It would be particularly
advantageous if nanostructured superalloys could be produced by
such methods. It would be further advantageous if these
nanostructured superalloys could be used in fatigue-limited
structural components, resulting in increased lifetimes and/or
efficiencies of the devices making use of these structural
components.
BRIEF SUMMARY
[0007] A superalloy-containing structural component includes a
superalloy matrix, and a plurality of hard phase nanoparticles
dispersed at grain boundaries within the superalloy matrix, wherein
the plurality of hard phase nanoparticles dispersed at the grain
boundaries comprise about 1 volume percent to about 30 volume
percent of the structural component, and wherein the superalloy
matrix and the plurality of hard phase nanoparticles have been
thermo-mechanically processed to form the structural component.
[0008] In another aspect, a superalloy-containing structural
component includes a superalloy matrix; a gamma prime phase,
wherein the gamma prime phase comprises about 10 weight percent to
about 60 weight percent of the nanostructured superalloy matrix;
and a plurality of hard phase nanoparticles dispersed at grain
boundaries within the superalloy matrix; wherein the plurality of
hard phase nanoparticles dispersed at the grain boundaries comprise
about 1 volume percent to about 30 volume percent of the structural
component, and wherein the superalloy matrix, gamma prime phase,
and the plurality of hard phase nanoparticles dispersed at the
grain boundaries within the superalloy matrix have been
thermo-mechanically processed to form the structural component.
[0009] A method of manufacturing a nanostructured
superalloy-containing structural component generally includes
introducing dislocations into a superalloy particle matrix
effective to form new grain boundaries within a plurality of
superalloy particles, wherein the grains are nanostructured;
introducing hard phase dispersoid nanoparticles at a plurality of
grain boundaries of the superalloy particles effective to pin the
grain boundaries; and thermo-mechanically processing the superalloy
particle matrix and hard phase dispersoid nanoparticles to form the
nanostructured superalloy-containing structural component.
[0010] The above described and other features are exemplified by
the following figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Referring now to the figures, which are exemplary
embodiments and wherein like elements are numbered alike:
[0012] FIG. 1 is a graphical representation comparing the tensile
strengths of a prior art alloy to an alloy made according to one
embodiment of the present disclosure;
[0013] FIG. 2 is a graphical representation of the high-cycle
fatigue properties of three different Ni--20Cr alloys;
[0014] FIG. 3 depicts representative scanning electron micrograph
images of a nanostructured Ni--20Cr alloy, which had dispersoid
nanoparticles introduced at the grain boundaries both ex-situ and
in-situ according to one embodiment of the present disclosure;
and
[0015] FIG. 4 is a graphical representation comparing the tensile
strengths of a prior art alloy to an alloy made according to
another embodiment of the present disclosure.
DETAILED DESCRIPTION
[0016] Nanostructured superalloy-containing structural components
and their methods of manufacture are described herein. In contrast
to the prior art, the methods and structural components disclosed
herein, owing to their nanoscale grain structure, allow for
increased stability in the superalloy when exposed to heat.
Consequently, fatigue limited structural components with increased
strength can be manufactured, resulting in increased lifetimes
and/or efficiencies of the devices making use of these structural
components. As used herein, the term "nanostructured" refers to
those materials having grains with an average longest dimension of
about 1 nanometer (nm) to about 500 nm.
[0017] Also, as used herein, the terms "first", "second", and the
like do not denote any order or importance, but rather are used to
distinguish one element from another, and the terms "the", "a", and
"an" do not denote a limitation of quantity, but rather denote the
presence of at least one of the referenced item. The modifier
"about" used in connection with a quantity is inclusive of the
stated value and has the meaning dictated by the context (e.g.,
includes the degree of error associated with measurement of the
particular quantity). Furthermore, all ranges disclosed herein are
inclusive of the endpoints and independently combinable.
[0018] The superalloy-containing structural component generally
comprises a superalloy matrix and a plurality of hard phase
nanoparticles dispersed at grain boundaries within the superalloy
matrix.
[0019] Any Fe-, Co-, or Ni-base superalloy composition may be used
to form the structural component. The most common solutes in Fe-,
Co-, or Ni-base superalloys are aluminum and/or titanium.
Generally, the aluminum and/or titanium concentrations are low
(e.g., less than or equal to about 15 weight percent (wt %) each).
Other optional components of Fe-, Co-, or Ni-base superalloys
include chromium, molybdenum, cobalt (in Fe- or Ni-base
superalloys), tungsten, nickel (in Fe- or Co-base superalloys),
rhenium, iron (in Co- or Ni-base superalloys), tantalum, vanadium,
hafnium, niobium, ruthenium, zirconium, boron, and carbon, each of
which may independently be present in an amount of less than or
equal to about 15 wt %.
[0020] An exemplary Ni-base superalloy composition, not including
the hard phase nanoparticle dispersoid composition, comprises about
12 to about 20 wt % Cr, less than or equal to about 22 wt % Co,
less than or equal to about 20 wt % Fe, about 2 to about 5 wt % Mo,
about 0.5 to about 5 wt % Ti, about 0.5 to about 4 wt % Al, less
than or equal to about 5 wt % W, less than or equal to about 3 wt %
Ta, less than or equal to about 3 wt % Re, less than or equal to
about 6 wt % Nb, less than or equal to about 3 wt % V, less than or
equal to about 2 wt % Hf, about 0.02 to 0.2 wt. % C, less than or
equal to about 0.03 wt. % B, less than or equal to about 0.1 wt. %
Zr, with the balance being essentially Ni. By "essentially Ni", it
is meant that the composition may include incidental or trace
levels of impurities.
[0021] In one embodiment, the superalloy matrix itself is
nanostructured. In one embodiment, the grains within the superalloy
matrix have an average longest dimension of about 10 nm to about
500 nm. In another embodiment, the grains within the superalloy
matrix have an average longest dimension of about 10 nm to about 30
nm.
[0022] The plurality of hard phase nanoparticles may comprise an
inorganic oxide, an inorganic carbide, an inorganic nitride, an
inorganic carbonitride, an inorganic boride, an inorganic
oxycarbide, an inorganic oxynitride, an inorganic silicide, an
inorganic aluminide, an inorganic sulfide, an inorganic oxysulfide,
or a combination comprising at least one of the foregoing.
Exemplary inorganic oxides include yttria, alumina, zirconia, or
hafnia. Exemplary inorganic carbides include carbides of hafnium,
tantalum, molybdenum, zirconium, niobium, chromium, titanium, or
tungsten. Exemplary inorganic sulfides and oxysulfides are cerium
sulfide and cerium oxysulfide, respectively.
[0023] In contrast to the prior art, the nanostructured
superalloy-containing structural components disclosed herein
overcome the loading and dispersion limitations encountered in
existing hard phase dispersoid strengthened alloys or superalloys.
In one embodiment, the superalloy-containing structural component
comprises about 1 to about 30 volume percent (vol %) hard phase
dispersoid nanoparticles. In another embodiment, the
superalloy-containing structural component comprises about 10 to
about 30 vol % hard phase dispersoid nanoparticles. This increased
loading of the hard phase dispersoid nanoparticles results in
greater grain boundary pinning and therefore greater strength in
the structural component.
[0024] The plurality of hard phase dispersoid nanoparticles may be
spherical, cubic, rod-like, needle-like, ellipsoidal, or like
shaped. It is not necessary that each of the plurality of hard
phase dispersoid nanoparticles have the same shape. In one
embodiment, the plurality of hard phase dispersoid nanoparticles
has an average longest dimension of about 10 nm to about 500 nm. In
another embodiment, each of the plurality of hard phase dispersoid
nanoparticles has an average longest dimension of about 10 nm to
about 30 nm.
[0025] The structural component may further comprise the so-called
"gamma prime" phase, which is an intermetallic compound generally
based on the formula Ni.sub.3(Al/Ti), and serves as an additional
strengthening mechanism. The gamma prime phase is particularly
resistant to thermal activation, caused by increased temperatures,
which can lead to recovery and therefore decreased strength.
Consequently, a structural component comprising an alloy with
nanostructured grains, hard phase dispersoid nanoparticles, and the
gamma prime phase can experience a substantial increase in its
fatigue life. Depending on the particular conditions to which the
structural component is exposed, the gamma prime phase may comprise
about 10 wt % to about 60 wt % of the nanostructured superalloy
matrix.
[0026] The structural component may further comprise the so-called
"gamma double-prime" phase, which is also an intermetallic compound
generally based on the formula Ni.sub.3Nb, and like the gamma prime
phase also serves as an additional strengthening phase. The gamma
double-prime, like the gamma prime phase increases in strength with
temperature up to about 1200 degrees Celsius (.degree. C.).
[0027] The method of manufacturing a nanostructured
superalloy-containing structural component generally includes
introducing dislocations into a superalloy powder particle matrix
effective to form new grain boundaries within a plurality of
superalloy grains, wherein the grains are nanostructured;
introducing hard phase dispersoid nanoparticles at the grain
boundaries effective to pin the grain boundaries; and
thermo-mechanically processing the superalloy powder particle
matrix and hard phase dispersoid nanoparticles to form the
nanostructured superalloy-containing structural component.
[0028] Introducing the dislocations into the superalloy powder
particle matrix can be accomplished by cryomilling, high pressure
torsion (HPT), equal channel angular pressing (ECAP), cyclic
channel die compression (CCDC), accumulative roll bonding,
repetitive corrugation and straightening, twist extrusion, or a
similar severe plastic deformation technique, or a combination
comprising at least one of the foregoing techniques.
[0029] Introducing the hard phase dispersoid nanoparticles at the
grain boundaries can be done ex-situ and/or in-situ. By ex-situ
introduction of the hard phase dispersoid nanoparticles, it is
meant that the hard phase dispersoid nanoparticles are
intentionally physically added to the superalloy powder particle
matrix during and/or after the dislocation formation. By in-situ
introduction of the hard phase dispersoid nanoparticles, it is
meant that the hard phase dispersoid nanoparticles are created
(e.g., precipitated) within the superalloy powder particle matrix,
such as when cryomilling in a reactive atmosphere (e.g., in the
presence of liquid nitrogen, liquid hydrocarbons, oxygen, and the
like).
[0030] Thermo-mechanically processing the superalloy powder
particles to form the nanostructured superalloy-containing
structural component can be accomplished by forging, hot extrusion,
hot rolling, and/or like techniques.
[0031] Optionally, prior to the thermo-mechanical processing, the
superalloy powder particle matrix and the hard phase dispersoid
nanoparticles may be consolidated into a compact. Consolidation
into a compact may be performed by cold pressing, hot pressing, hot
isostatic pressing, forging, extruding, and/or like consolidating
techniques.
[0032] In one embodiment, a powder particle matrix of a superalloy
is cryomilled in liquid nitrogen for a time effective to reduce the
grain size within the powder particle matrix to the desired grain
size. During the cryomilling, dispersoid nanoparticles are formed
(e.g., precipitated) in-situ, for example by oxidizing (if any
oxygen is present) or nitriding a reactive metal component of the
superalloy composition. Additionally, if dispersoid nanoparticles
are extrinsically added before and/or during the cryomilling, then
they will be intimately mixed with the powder particle matrix such
that they serve as pinning agents as well. It should be recognized
that there will be a point after which no additional cold working
(cryomilling) will decrease the grain size of the particle powder
matrix, but instead will serve to provide an increased opportunity
for the in-situ formation of dispersoid nanoparticles. This may be
desirable depending on the specific properties targeted for the
final structural component. For example, in superalloys comprising
aluminum, it may be desirably to have a nitrogen content of less
than or equal to about 1.0 wt % in order to avoid the increased
brittleness that is accompanied by a higher nitrogen content. Once
the desired grain size reduction and nanoparticle dispersoid
addition has been achieved, the sample (i.e., the nanostructured
powder particle matrix and hard phase dispersoid nanoparticles) are
consolidated by hot isostatic pressing and subsequently forged to
form the desired shape.
[0033] The nanostructured superalloy-containing structural
components disclosed herein are suitable for use in at least a
portion of a hot gas path assembly, such as a steam turbine, gas
turbine, aircraft engine, and the like. These hot gas path
assemblies can have temperatures, to which the structural
components are exposed, of about 800.degree. C., specifically about
1000.degree. C., and more specifically about 1200.degree. C.
Exemplary structural components include rotating components (e.g.,
airfoils, discs, wheels, and the like), static components (e.g.,
ducts, frames, casings, buckets, vanes, and the like), combustors,
and the like.
[0034] Advantageously, the nanostructured superalloy-containing
structural components and methods of manufacture described herein
provide for increased stability in the base superalloy when exposed
to heat. Consequently, fatigue limited structural components with
increased strength can be manufactured, resulting in increased
lifetimes and/or efficiencies of the devices making use of these
structural components. For example, the finer grains and
dispersoids may make possible a doubling, or more, of tensile
strength and creep resistance. Alloying of the grain boundaries can
inhibit or eliminate loss in fatigue resistance from environmental
exposure.
[0035] The present disclosure is illustrated by the following
non-limiting examples.
EXAMPLE 1
[0036] An alloy, comprising nickel and about 20 wt % Cr (Ni--20Cr),
was produced by melting and forging. The average grain diameter
after heat treatment of this prior-art material is approximately 64
micrometers (.mu.m). The same base alloy composition was produced
as a powder, cryomilled in liquid nitrogen, consolidated, and
heat-treated. The grain size after heat treatment of this novel
material was about 64 nm. Room temperature tensile tests were
conducted on both materials. FIG. 1 illustrates the tensile curves
for the two materials. The ultimate tensile strength of the prior
art micrometer-scale material was about 87 kilopounds per square
inch (ksi), or 600 MegaPascals (MPa), while the ultimate tensile
strength of the nanostructured alloy was about 162 ksi (1117 MPa).
This represented an 86% higher tensile strength in the alloy
produced by the methods disclosed herein.
EXAMPLE 2
[0037] A nanostructured Ni--20Cr sample was prepared as described
in Example 1, except that, in addition, a plurality of
Al.sub.2O.sub.3 dispersoid nanoparticles were introduced prior to
cryomilling. FIG. 3 presents representative scanning electron
microscope images of this superalloy composition.
[0038] The fatigue properties of 1) this nanostructured Ni--20Cr
superalloy, which had dispersoid nanoparticles introduced at the
grain boundaries both ex-situ and in-situ (designated
"nanostructured Ni--20Cr w/Al.sub.2O.sub.3"), 2) a nanostructured
Ni--20Cr superalloy prepared according to Example 1, which only had
dispersoid nanoparticles introduced at the grain boundaries in-situ
(designated "nanostructured Ni--20Cr"), and 3) a known Ni-20Cr
superalloy, obtained from Special Metals Corporation under the
trade designation INCONEL MA754 (designated "MA754") were studied.
FIG. 2 displays the results of the high-cycle fatigue properties of
these three samples. Data is presented for five samples of the
nanostructured Ni--20Cr w/Al.sub.2O.sub.3 superalloy, five samples
of the nanostructured Ni--20Cr superalloy, and two samples of the
MA754 superalloy. As evidenced in FIG. 2, each sample of both
nanostructured superalloys of the present disclosure were able to
withstand significantly greater stresses than the MA754 superalloy.
Furthermore, the nanostructured superalloys of the present
disclosure were also able to experience increased lifetimes before
failure owing to fatigue.
EXAMPLE 3
[0039] A Rene 104 alloy is a nickel-base superalloy having a
nominal composition (in weight percent): 0.05 carbon, 3.4 aluminum,
0.05 zirconium, 3.7 titanium, 0.025 boron, 2.4 tantalum, 3.8
molybdenum, 0.9 niobium, 2.4 tantalum, 13 chromium, 20.6 cobalt,
balance essentially nickel. The alloy was produced by consolidation
of atomized powder, forging, and heat treatment. One sample of the
powder was consolidated by hot isostatic pressing, extruded, and
heat-treated to yield a micrometer-scale product. Another sample of
the powder was cryomilled in liquid nitrogen and subsequently
thermo-mechanically processed by hot isostatic pressing, extrusion,
and heat treatment in a manner identical to the prior-art
micrometer-scale product.
[0040] The two samples were examined by electron microscopy; and
tensile tests were conducted. In the nanostructured Rene 104 alloy
of the present disclosure, there is a distribution of small
particles of zirconium and aluminum-rich oxides that also had been
present on the prior-art powder particle surface; additionally,
Ta-rich carbides and the gamma-prime phase were present. The grains
of the nanostructured Rene 104 alloy are much finer than what was
observed for the prior-art micrometer-scale product. In addition,
in the nanostructured Rene 104 alloy of the present disclosure,
there is a noteworthy distribution of fine titanium-rich particles
that are not present in the prior-art micrometer-scale product.
These titanium-rich particles appear to form by a reaction between
the milling fluid, (i.e., liquid nitrogen) and titanium from the
alloy. The titanium particles are associated with regions of much
finer grain size.
[0041] FIG. 4 illustrates the room temperature tensile curves for
the two samples. The nanostructured Rene 104 alloy has higher yield
(176 vs. 198 ksi) and ultimate (248 vs. 262 ksi) tensile
strengths.
[0042] While the disclosure has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
* * * * *