U.S. patent application number 15/607775 was filed with the patent office on 2017-09-14 for precipitate strengthened nanostructured ferritic alloy and method of forming.
The applicant listed for this patent is General Electric Company. Invention is credited to Matthew Joseph Alinger, Laura Cerully Dial, Richard DiDomizio.
Application Number | 20170260609 15/607775 |
Document ID | / |
Family ID | 52115779 |
Filed Date | 2017-09-14 |
United States Patent
Application |
20170260609 |
Kind Code |
A1 |
DiDomizio; Richard ; et
al. |
September 14, 2017 |
PRECIPITATE STRENGTHENED NANOSTRUCTURED FERRITIC ALLOY AND METHOD
OF FORMING
Abstract
An alloy and method of forming the alloy are provided. The alloy
includes a matrix phase, and a population of particulate phases
dispersed within the matrix. The matrix includes iron and chromium;
and the population includes a first subpopulation of particulate
phases and a second subpopulation of particulate phases. The first
subpopulation of particulate phases include a complex oxide, having
a median size less than about 20 mu, and present in the alloy in a
concentration from about 0. 1 volume percent to about 5 volume
percent. The second subpopulation of particulate phases have a
median size in a range from about 30 nm to about 10 microns, and
present in the alloy in a concentration from about 1 volume percent
to about 15 volume percent.
Inventors: |
DiDomizio; Richard;
(Charlton, NY) ; Alinger; Matthew Joseph; (Delmar,
NY) ; Dial; Laura Cerully; (Clifton Park,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
52115779 |
Appl. No.: |
15/607775 |
Filed: |
May 30, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13931108 |
Jun 28, 2013 |
|
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15607775 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/183 20130101;
B22F 3/24 20130101; C22F 1/11 20130101; B22F 9/082 20130101; B22F
2003/248 20130101; C22C 32/0047 20130101; C22F 1/186 20130101; B22F
2998/10 20130101; B22F 9/08 20130101; C22C 33/0285 20130101; B22F
2998/10 20130101; B22F 2009/041 20130101; C22C 38/18 20130101; B22F
9/082 20130101; B22F 3/15 20130101; B22F 2003/248 20130101; B22F
3/17 20130101; C22C 38/00 20130101 |
International
Class: |
C22C 38/18 20060101
C22C038/18; C22C 32/00 20060101 C22C032/00; C22F 1/18 20060101
C22F001/18; B22F 3/24 20060101 B22F003/24; C22F 1/11 20060101
C22F001/11 |
Claims
1.-20. (canceled)
21. A method of forming an alloy, comprising: melting starting
materials comprising iron and chromium; atomizing the melt to form
an alloy powder; milling the alloy powder in the presence of an
oxide until the oxide is dissolved into the alloy powder, thus
forming a milled alloy powder; consolidating the milled alloy
powder at a first temperature; precipitating a first subpopulation
of particulate phases comprising a complex oxide having a median
size less than about 20 nm; and establishing a second subpopulation
of particulate phases having a median size in a range from about 30
nm to about 10 microns.
22. The method of claim 21, wherein a concentration of the first
subpopulation of particulate phases is in a range from about 0.1
volume percent to about 5 volume percent of the alloy.
23. The method of claim 21, wherein a concentration of the second
subpopulation of particulate phases is in a range from about 1
volume percent to about 15 volume percent of the alloy.
24. The method of claim 21, wherein the precipitated particulate
phases of the first subpopulation comprise at least two elements of
the following group: yttrium, titanium, aluminum, zirconium,
hafnium, and magnesium.
25. The method of claim 21, wherein establishing the second
subpopulation comprises an in-situ precipitation in the
consolidated, milled alloy powder.
26. The method of claim 25, wherein the particulate phases of the
second subpopulation comprise a Laves phase.
27. The method of claim 25, wherein the particulate phases of the
second subpopulation comprise a mu phase.
28. The method of claim 25, wherein the particulate phases of the
second subpopulation comprise a carbide, nitride, or carbonitride
phase.
29. The method of claim 25, wherein the particulate phases of the
second subpopulation comprise an intermetallic phase having a
Ni.sub.3M structure, wherein M comprises titanium, aluminum,
molybdenum, niobium, tantalum, or any combination of the
foregoing.
30. The method of claim 21, wherein establishing the second
subpopulation comprises an in-situ precipitation by heat-treating
the consolidated, milled alloy powder at a second temperature.
31. The method of claim 30, wherein the consolidated, milled alloy
powder is hot-worked before in-situ precipitation of the second
subpopulation by heat-treating.
32. The method of claim 30, wherein the second temperature is in a
range from about 550.degree. C. to about 850.degree. C.
33. The method of claim 21, wherein establishing the second
subpopulation comprises mechanically mixing the milled alloy powder
with an added particulate phase.
34. The method of claim 33, wherein the added particulate phase
comprises an oxide, boride, or a combination of oxide and
boride.
35. The method of claim 21, wherein establishing the second
subpopulation comprises a combination of in-situ precipitating of
the consolidated, milled alloy powder; and mechanically mixing an
added particulate phase to the milled alloy powder.
36. The method of claim 21, wherein establishing the starting
materials comprises a vacuum induction melting process.
37. A method of forming an alloy, comprising: melting starting
materials comprising iron and chromium through a vacuum induction
melting process; atomizing the melt to form an alloy powder;
milling the alloy powder in the presence of an oxide until the
oxide is dissolved into the alloy powder, thus forming a milled
alloy powder; consolidating the milled alloy powder at a first
temperature precipitating a first subpopulation of particulate
phases comprising a complex oxide comprising yttrium and titanium,
having a median size less than about 20 nm, in a concentration from
about 0. 1 volume percent to about 3 volume percent of the alloy;
hot-working the consolidated, milled alloy powder; and
heat-treating the hot-worked, consolidated, milled alloy powder at
a second temperature and establishing a second subpopulation of
particulate phases by an in-situ precipitation of a Laves phase
having a median size in a range from about 30 nm to about 10
microns, in a concentration from about 1 volume percent to about 4
volume percent of the alloy.
38. A method of forming an alloy, comprising: melting starting
materials comprising iron and chromium through a vacuum induction
melting process; atomizing the melt to form an alloy powder;
milling the alloy powder in the presence of an oxide until the
oxide is dissolved into the alloy powder, thus forming a milled
alloy powder; adding a particulate phase comprising an oxide,
boride, or a combination of an oxide and boride to the milled alloy
powder, and mixing; consolidating the milled and mixed alloy powder
at a first temperature precipitating a first subpopulation of
particulate phases comprising a complex oxide comprising yttrium
and titanium, having a median size less than about 20 nm, in a
concentration from about 0.1 volume percent to about 3 volume
percent of the alloy; and establishing a second subpopulation of
particulate phases resulting from the added particulate phase in
the consolidated, milled, and mixed alloy powder, wherein the
second subpopulation has a median size in a range from about 30 nm
to about 10 microns, and present in the alloy in a concentration
from about 1 volume percent to about 4 volume percent.
Description
BACKGROUND
[0001] The invention relates generally to a nanostructured ferritic
alloy. More particularly the invention relates to a nanostructured
ferritic alloy having dual scale dispersions.
[0002] Gas turbines operate in extreme environments, exposing the
turbine components, especially those in the turbine hot section, to
high operating temperatures and stresses. In order for the turbine
components to endure these conditions, they are manufactured from a
material capable of withstanding these severe conditions. As
material limits are reached, one of two approaches is
conventionally used in order to maintain the mechanical integrity
of hot section components. In one approach, cooling air is used to
reduce the part's effective temperature. In a second approach, the
component size is increased to reduce the stresses. However, these
approaches can reduce the efficiency of the turbine and increase
the cost.
[0003] In certain applications, super alloys have been used in
these demanding applications because they maintain their strength
at up to 90% of their melting temperature and have excellent
environmental resistance. Nickel-based super alloys, in particular,
have been used extensively throughout gas turbine engines, e.g., in
turbine blade, nozzle, wheel, spacer, disk, spool, blisk, and
shroud applications. In some lower temperature and stress
applications, steels may be used for turbine components. However,
conventional steels cannot currently be used in high temperature
and high stress applications because they do not meet the necessary
mechanical property requirements. Designs for improved gas turbine
performance require alloys that balance cost with higher
temperature capability.
[0004] Nickel-based super alloys used in heavy-duty turbine
components require specific elaborate processing steps in order to
achieve the desired mechanical properties, including three melting
operations: vacuum induction melting (VIM), electroslag remelting
(ESR), and vacuum arc remelting (VAR). Nanostructured ferritic
alloys (NFAs) are an emerging class of alloys that exhibit
exceptional high temperature properties, thought to be derived from
nanometer-sized oxide clusters that precipitate during hot
consolidation following a mechanical alloying step. These oxide
clusters are present at high temperatures, providing a strong and
stable microstructure during service. Unlike many nickel-based
super alloys, that require the cast and wrought (C&W) process
to be followed to obtain necessary properties, NFAs are
manufactured via a different processing route that requires fewer
melting steps.
[0005] While NFAs yield enhanced tensile and creep properties
compared to conventional steels, additional benefits are sought. In
order for any material to be optimally useful in, e.g., large hot
section components of heavy duty turbo machinery, it may also
desirably exhibit a further increased creep resistance making it
useful for gas turbo-machinery applications. Any such alloy will
also desirably be capable of being manufactured into the desired
article utilizing a less energy intensive and/or time consuming
process, than the conventional cast and wrought process.
BRIEF DESCRIPTION
[0006] In one embodiment, an alloy is provided. The alloy includes
a matrix phase, and a population of particulate phases dispersed
within the matrix. The matrix includes iron and chromium; and the
population includes a first subpopulation of particulate phases and
a second subpopulation of particulate phases. The first
subpopulation of particulate phases include a complex oxide, having
a median size less than about 20 nm, and present in the alloy in a
concentration from about 0. 1 volume percent to about 5 volume
percent. The second subpopulation of particulate phases have a
median size in a range from about 30 nm to about 10 microns, and
present in the alloy in a concentration from about 1 volume percent
to about 15 volume percent.
[0007] In one embodiment, an alloy is provided. The alloy includes
a matrix phase, and a population of particulate phases dispersed
within the matrix. The matrix includes iron and chromium; and the
population includes a first subpopulation of particulate phases and
a second subpopulation of particulate phases. The first
subpopulation of particulate phases include a complex oxide having
yttrium and titanium, and having a median size less than about 10
nm, and present in the alloy in a concentration from about 0. 1
volume percent to about 3 volume percent. The second subpopulation
of particulate phases include precipitated Laves phase, have a
median size in a range from about 50 nm to about 3 microns, and
present in the alloy in a concentration from about 1 volume percent
to about 6 volume percent.
[0008] In one embodiment, a method of forming an alloy is provided.
The method includes melting starting materials comprising iron and
chromium; atomizing the melt to form an alloy powder; milling the
alloy powder in the presence of an oxide until the oxide is
dissolved into the alloy powder, thus forming a milled alloy
powder; consolidating the milled alloy powder at a first
temperature; precipitating a first subpopulation of particulate
phases comprising a complex oxide having a median size less than
about 20 nm; and establishing a second subpopulation of particulate
phases having a median size in a range from about 30 nm to about 10
microns.
[0009] In one embodiment, a method of forming an alloy is provided.
The method includes the steps of forming a milled alloy powder,
consolidating the milled alloy powder at a first temperature,
precipitating a first subpopulation of particulate phases including
a complex oxide comprising yttrium and titanium, and establishing a
second subpopulation of particulate phases by an in-situ
precipitation of a Laves phase. Forming a milled alloy powder
includes melting starting materials having iron and chromium
through a vacuum induction melting process; atomizing the melt to
form an alloy powder; and milling the alloy powder in the presence
of an oxide until the oxide is dissolved into the alloy powder. The
first subpopulation of particulate phases have a median size less
than about 20 nm, in a concentration from about 0.1 volume percent
to about 3 volume percent of the alloy. Establishing a second
subpopulation of particulate phases by an in-situ precipitation of
a Laves phase may include hot-working the consolidated, milled
alloy powder, and heat-treating the hot-worked, consolidated,
milled alloy powder at a second temperature. The Laves phase has a
median size in a range from about 30 nm to about 10 microns, in a
concentration from about 1 volume percent to about 4 volume percent
of the alloy.
[0010] In one embodiment, a method of forming an alloy is provided.
The method includes the steps of forming a milled alloy powder,
adding a particulate phase comprising an oxide, boride, or a
combination of an oxide and boride, mixing the added particulate
phase, consolidating the milled and mixed alloy powder at a first
temperature, precipitating a first subpopulation of particulate
phases including a complex oxide comprising yttrium and titanium,
and establishing a second subpopulation of particulate phases
resulting from the added particulate phases. Forming a milled alloy
powder includes melting starting materials having iron and chromium
through a vacuum induction melting process; atomizing the melt to
form an alloy powder; and milling the alloy powder in the presence
of an oxide until the oxide is dissolved into the alloy powder. The
first subpopulation of particulate phases have a median size less
than about 20 nm, in a concentration from about 0.1 volume percent
to about 3 volume percent of the alloy. The second subpopulation of
particulate phases have a median size in a range from about 30 nm
to about 10 microns, in a concentration from about 1 volume percent
to about 4 volume percent of the alloy.
DETAILED DESCRIPTION
[0011] Embodiments of the invention described herein address the
noted shortcomings of the state of the art. One or more specific
embodiments of the present invention will be described below. In an
effort to provide a concise description of these embodiments, all
features of an actual implementation may not be described in the
specification. It should be appreciated that in the development of
any such actual implementation, as in any engineering or design
project, numerous implementation-specific decisions must be made to
achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which may vary
from one implementation to another. Moreover, it should be
appreciated that such a development effort might be complex and
time consuming, but would nevertheless be a routine undertaking of
design, fabrication, and manufacture for those of ordinary skill
having the benefit of this disclosure.
[0012] When introducing elements of various embodiments of the
present invention, the articles "a," "an," and "the," are intended
to mean that there are one or more of the elements. The terms
"comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements. Moreover, the use of "top," "bottom," "above,"
"below," and variations of these terms is made for convenience, but
does not require any particular orientation of the components
unless otherwise stated.
[0013] All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are combinable with each other. The terms
"first," "second," and the like as used herein do not denote any
order, quantity, or importance, but rather are used to distinguish
one element from another.
[0014] Approximating language, as used herein throughout the
specification and claims, may be applied to modify any quantitative
representation that could permissibly vary without resulting in a
change in the basic function to which it may be about related.
Accordingly, a value modified by a term such as "about" is not
limited to the precise value specified. In some instances, the
approximating language may correspond to the precision of an
instrument for measuring the value.
[0015] In one embodiment, a nanostructured ferritic alloy (NFA) is
provided. Typically a nanostructured ferritic alloy includes an
iron-containing alloy matrix that is strengthened by nanofeatures
disposed in the matrix. The concentration of iron in the alloy
matrix may be greater than about 50 wt %. In one embodiment, the
iron content in the alloy matrix is greater than about 70 wt %. In
one embodiment, the alloy matrix is in the form of the ferritic
body-centered cubic (BCC) phase. As used herein, the term
"nanofeatures" means particles of matter having a largest dimension
less than about 100 nanometers in size. The nanofeatures used
herein are typically in-situ formed. in NFA by the dissolution of
the initial added oxide and the precipitation of nanometer sized
clusters of a modified oxide that can serve to pin the alloy
structure, thus providing enhanced mechanical properties.
[0016] The nanofeatures of NFA may have any shape, including, for
example, spherical, cuboidal, lenticular, and other shapes. The
mechanical properties of the nanostructured ferritic alloys may be
controlled by controlling, for example, the density (meaning the
number density-number of particles per unit volume) of the
nanofeatures in the matrix, the composition of the nanofeatures,
and the processing used to form the article.
[0017] The alloy matrix of the NFA includes iron and chromium.
Chromium is important for both phase stability and corrosion
resistance, and may thus be included in the NFA in amounts of at
least about 5 wt %. Amounts of up to about 30 wt % may be included.
In one embodiment, chromium in the alloy matrix is in a range from
about 9 wt % to about 14 wt % of the alloy.
[0018] In one embodiment, the alloy may have titanium and yttrium.
The titanium and yttrium may be present in the metallic or alloy
form as a part of the matrix of the alloy, or may be present in the
dispersions as a part of the particulate phases of the alloy. In
some embodiments, the titanium is present in the alloy in a range
from about 0.1 weight percent to about 2 weight percent and yttrium
from about 0.1 weight percent to about 3 weight percent of the
alloy. In certain embodiments, the alloy matrix includes from about
0.1 weight percent titanium to about 1 weight percent titanium. In
addition to its presence in the matrix, titanium and yttrium may
play a role in the formation of the oxide nanofeatures, as
described hereinbelow.
[0019] Vanadium may also be present in the alloy matrix in certain
embodiments, where it may serve to strengthen the alloy through the
formation of precipitates or by altering phase stability. In some
embodiments, the vanadium is present in a range from about 0.1
weight percent to about 2 weight percent, and in particular
embodiments the range is from about 0.1 weight percent to about 1
weight percent.
[0020] In one embodiment, the alloy includes a population of
particulate phases dispersed within the matrix. As used herein,
"dispersed within the matrix" would include the dispersion of the
particulate phases in the grains and grain boundaries of the
matrix. In one embodiment, the particulate phases are substantially
dispersed in the grain boundaries of the iron and chromium
containing matrix.
[0021] The population of particulate phases may include at least
two subpopulations. A first subpopulation of particulate phases may
be the above-described nanofeatures, providing enhanced tensile and
creep properties to the alloy. The nanofeatures of the first
subpopulation have a median size less than about 20 nanometers
(nm). In a particular embodiment, the particulate phases of the
first subpopulation have a median size less than about 10 nm.
[0022] The first subpopulation of particulate phases may include a
complex oxide. A "complex oxide" as used herein is an oxide phase
that includes more than one non-oxygen elements. The complex oxide
may be a single oxide phase having more than one non-oxygen
elements such as, for example, ABO; or may be a mixture of more
than one simple oxide phases (having one non-oxygen element) such
as, for example A.sub.xB.sub.yO.sub.z. The examples included here
are without accounting for any charge balance, hence will include
the oxides of elements of different valencies and deviations from
stoichiometry.
[0023] In one embodiment, an oxide phase may be added to the alloy
matrix, and processed to precipitate nanofeatures of the first
subpopulation. At least a part of the added oxide phase may be
dissolved in the alloy structure and precipitate as the
nanofeatures of same oxide or some other oxide phase. In one
embodiment, the new oxide in the NFA may include the transition
metals present in the starting materials and the metallic
element(s) of the initial oxide addition.
[0024] In one embodiment, the particulate phases of the first
subpopulation include at least two elements from the group of
yttrium, titanium, aluminum, zirconium, hafnium, and magnesium. The
particulate phases may include a combination of two or more simple
oxides; a combination of one or more simple oxide and one or more
complex oxides; or a combination of multiple different complex
oxides. In a particular embodiment, the particulate phases of the
first subpopulation includes a complex oxide with a single phase
including more than one non-oxygen elements, such as for example,
an yttrium titanium oxide; an yttrium titanium silicon oxide; an
aluminum titanium oxide; a magnesium titanium oxide; a zirconium
titanium oxide; hafnium titanium oxide; a magnesium zirconium
oxide; zirconium hafnium oxide; a yttrium zirconium oxide; a
yttrium magnesium oxide; a yttrium zirconium titanium oxide; or a
yttrium aluminum titanium oxide.
[0025] The nanofeatures of the first subpopulation of particulate
phases enhance the tensile and creep properties of the alloy.
However, further enhanced mechanical properties of the alloy are
desired for certain high temperature and harsh environment
applications. The mechanical properties of the alloy may be further
increased by an increment in the number density of the first
subpopulation of particulates; by an addition of hard second phases
of multiple length scales; or by a combination of the higher number
density and the second phase addition. However, increasing the
number density or adding the second phases may embrittle the alloy
thereby decreasing the ductile property of the alloy. It is known
in the art that as the volume fraction of the nanofeatures or the
hard second phases increases in the alloy, the ductility of the
material drops. Therefore, in the case of traditional oxide
dispersion strengthened alloys and in NFAs, the volume fraction of
any oxide features and any other hard, non-oxide second phase
particles are limited to a nominal amount so that the ductility of
the material does not drop to insufficient levels.
[0026] Traditionally, the total volume fraction of the dispersed
particles in an NFA is restricted to less than 2 volume percent of
the alloy. A volume fraction of the first subpopulation of
particulate phases in the current alloy may vary from about 0.1
volume percent to about 5 volume percent of the alloy. In a
particular embodiment, the volume percent of the first
subpopulation of particulate phases is in a range from about 1
volume percent to about 5 volume percent of the alloy.
[0027] In one embodiment of the current invention, an alloy having
a second subpopulation of particulate phases along with the
above-described first subpopulation of particulate phases is
presented without forgoing the ductility of the alloy. The alloy
has enhanced tensile and creep properties as compared to an NFA,
while maintaining a desirable level of ductility. The second
subpopulation of particulate phases may have a median particulate
size in a range from about 30 nm to about 10 microns. In one
embodiment, the second subpopulation of particulate phases has a
median size in a range from about 50 nm to about 3 microns. A
concentration of the second subpopulation of particulate phases in
the alloy may vary from about 1 volume percent of the alloy to
about 15 volume percent of the alloy. In one embodiment, the
concentration of the second subpopulation is in an amount from
about 1 volume percent to about 6 volume percent of the alloy. In a
particular embodiment, the population of particulate phases
(including both first subpopulation and second subpopulation) is in
a range from about 2 volume percent to about 6 volume percent of
the alloy.
[0028] The particulate phases of the second subpopulation may
include oxides or non-oxide phases. In one embodiment, the second
subpopulation includes an oxide phase, a boride phase, or a
combination of an oxide and boride phase. In one embodiment, the
concentration of total oxygen in the alloy is in a range from about
0.1 weight percent to about 0.6 weight percent of the alloy.
[0029] The oxide or boride phases may be added to the alloy during
processing to further strengthen the alloy. One embodiment of the
present invention is a method of forming an alloy having a
precipitated first subpopulation of particulate phases and an added
second subpopulation of particulate phases. The process of fo ling
the alloy may start from melting starting materials such as, for
example, iron and chromium to form an initial melt. Melting may be
by any of the methods known in the art. A vacuum induction melting
process may be conveniently used to melt the starting material.
[0030] The melted material may be atomized to form an alloy powder
that can be milled along with the added oxide material to form a
milled alloy powder. The milled alloy powder may be consolidated at
a first temperature to precipitate the first subpopulation of
particulate phases having a complex oxide with a desired size in a
desired volume percent range. The majority, if not substantially
all, of the added oxide is dissolved into the alloy matrix during
powder attrition and participates in the formation of the
aforementioned nanofeatures when the powder is raised in
temperature during the consolidation process.
[0031] In one embodiment, the second subpopulation of particulate
phases is established by adding and mixing an oxide, boride, or a
combination of an oxide and boride particulate phase to the milled
alloy powder. The composition, size and volume ratio of the second
subpopulation of particulate phases may be similar to the added
phases.
[0032] In an alternate embodiment, an oxide, boride, or a
combination of an oxide and boride may be added before the
consolidation of the milled alloy powder. The added oxide, boride,
or a combination of an oxide and boride may partially react with
the matrix. with another added phase, or the first subpopulation of
particulate phase, and may remain or form a second subpopulation.
Based on the reactivity of the added phase with the other
constituents of the alloy-in the making, the composition, size, and
volume percent of the second subpopulation of particulate phases
may be the same or different from that of the added phases.
[0033] Depending on the elements that were added, and
thermodynamically favored compositions after certain subsequent
process steps to which different NFAs were subjected to, further
additional elements may be present in the alloy in order to form
oxide or boride particulate phases. The elemental concentration
ranges of two exemplary alloy compositions in the ranges of weight
% of the alloy are shown in Table 1 when borides or oxides are
present in the alloy.
TABLE-US-00001 TABLE 1 Oxide Borides Elements Range 1 Range 2 Range
1 Range 2 Cr 5-30 9-14 5-30 9-14 Ti 0.1-2 0.1-0.8 0.1-2 0.1-0.8 Y
0.1-1 0.2-0.6 0.1-1 0.2-0.6 O 0.1-0.6 0.1-0.2 0.1-0.6 0.1-0.2 Mo
0-5 0-3 0-5 0-3 W 0-5 0-4 0-5 0-4 Al 0-2 0-0.5 Zr 0-2 0-0.5 B 0-0.1
0-0.03
[0034] In one embodiment, the alloy includes an in-situ
precipitated second subpopulation of particulate phases along with
the precipitated first subpopulation of particulate phases. The
first subpopulation of particulate phases may be precipitated using
the aforementioned process methods. A temperature in a range from
about 500.degree. C. to about 1300.degree. C. may be used in the
consolidation process to precipitate out the particulate phases of
the first subpopulation. Transition metals, such as iron, chromium,
titanium, molybdenum, tungsten, manganese, silicon, niobium,
aluminum, niobium, or tantalum from the alloy matrix may also
participate in the creation of the nanofeatures.
[0035] The second subpopulation of particulate phases may be
in-situ precipitated in the NFA by varying the components of the
starting powder, or the additive phases, or by varying the steps of
the process of preparation of NFA. The precipitated second
subpopulation of particulate phases may include an oxide, boride,
carbide, nitride, carbonitride, or an intermetallic phase. The
in-situ precipitation of the particulate phases of the second
subpopulation may be formed by varying the process steps of
milling, consolidating, by changing the temperature, duration of
heating, or the heat-treatment cycles at different stages. For
example, a second subpopulation of particulate phases may be formed
by a prolonged milling or prolonged heat-treatment of the starting
materials and the added powders or by processing the milled alloy
powders in a second heat-treatment cycle. In another example, a
second subpopulation of particulate phases is formed by hot-working
the consolidated, milled alloy powder before subjecting them for a
second heat-treatment. Hot-working of the consolidated alloy powder
may be carried out by forging, hot extrusion, rolling, or any
combination of these methods.
[0036] Depending on the desired second subpopulation of particulate
phases, the starting materials for the formation of the alloy may
include more number or quantity of components than the elements
that are reflected as a matrix phase in the alloy. For example, the
starting materials may include iron, chromium, titanium,
molybdenum, tungsten, manganese, silicon, niobium, aluminum,
nickel, tantalum, yttrium, carbon, nitrogen. Some of these elements
may be present as a part of the matrix phase, as a part of the
first subpopulation of particulate phases, or as a part of the
second subpopulation of particulate phases in the alloy. The
quantity, composition, and percentage ratios of the elements of the
starting material may be different in different phases, and may
vary with the variation of process steps executed on the starting
materials.
[0037] In one embodiment, a part of the added oxide phase to the
starting materials may be dissolved in the alloy structure and
precipitate as the nanofeatures of same or some other nano-oxide
phase. Another part of the added oxide phase may remain as it is in
the alloy or may react with some other matrix or dispersion
elements and convert in to another oxide with a particulate size in
the size range of the second subpopulation of particulate
phases.
[0038] In one embodiment, one or more non-oxygen elements of the
added oxide phase may react with some other starting material or
dispersion elements and may precipitate into a different, non-oxide
particulate phase in the size range of the second subpopulation of
particulate phases.
[0039] In one embodiment, the non-oxygen elements of the starting
materials may partly form the matrix structure, and may partly
precipitate as a part of the second subpopulation of particulate
phases.
[0040] In one embodiment, the non-oxygen elements of the added
materials may partly form the matrix structure, and may partly
precipitate as a part of the second subpopulation of particulate
phases.
[0041] In one embodiment, the non-oxygen elements of the added
materials may completely precipitate as a part of the second
subpopulation of particulate phases. In one embodiment, a
substantial part of the starting materials may precipitate as a
part of the second subpopulation of particulate phases.
[0042] In one embodiment, depending on the variation in the process
steps, the elements to form particulate phases of the second
subpopulation may be present as a part of the matrix phase; or as a
part of the particulate phase of the first subpopulation at one
stage and may precipitate as the second subpopulation on further
processing, such as, for example, a second heat-treatment, a
heat-treatment at a little higher temperature than for the
precipitation of the particulate phases of the first subpopulation,
or a longer duration heat-treatment at a particular temperature. In
one embodiment, a second heat-treatment at a temperature range of
about 550.degree. C. to about 850.degree. C. is provided to the
formed NFA structure to precipitate the particulate phases of the
second subpopulation.
[0043] In one embodiment, a precipitated particulate phase of the
second subpopulation is an intermetallic phase. Non-limiting
examples of the intermetallic phase may include a Laves phase, a Mu
phase, a Z-phase, and a Ni.sub.3M structure. A Laves phase may have
an AB.sub.2 structure and may include magnesium, copper, zinc,
nickel, iron, tungsten etc. as the constituting elements. In one
particular embodiment, the precipitated Laves phase has a
composition having the elements selected from the group consisting
of molybdenum, niobium, magnesium, iron, zinc, nickel, copper, and
a combination thereof. A Laves phase may be formed by annealing the
NFA structure (with first subpopulation of particulate phases) at a
temperature below about 850.degree. C. In one embodiment, the NFA
is annealed at about 700.degree. C. for precipitating Laves phase
as the particulate phase of the second subpopulation at the size
ranges and volume fraction as mentioned hereinabove. Table 2
provides a list of non-limiting examples, crystal structure, and
additional elements of intermetallic phases that may be formed as a
particulate phase of the second subpopulation singularly or as a
combination with another phase.
TABLE-US-00002 TABLE 2 Additional elements Non-limiting that may
Phase Crystal Structure Examples be present Laves Cubic, Hexagonal
MgCu.sub.2, MgZn.sub.2, Mo, Nb MgNi.sub.2, Fe.sub.2W Mu (.mu.)
Rhombohedral, Fe.sub.7Mo.sub.6 W, Co Hexagonal MC/MN Cubic TiC,
NbC, CrN Ti, Nb, V, Ta, C, N, Ni.sub.3M Geometrically close M = V,
Mo, W, Nb, Ni, Ta, packed (D0.sub.22, D0.sub.a, Ti, Al Si, Co
D0.sub.24, L1.sub.2) Z-phase (CrMN) Distorted BCT or CrNbN Fe,
Cubic CrVN
[0044] While Table 2 lists some of the phases that were observed,
or thermodynamically favored structures by the process steps to
which different NFAs were subjected to, depending on the starting
materials, added elements, and process steps followed, further
additional elements may be present in the precipitated particulate
phase of the second subpopulation of the alloy in the ranges of
weight % of the alloy, as shown in Table 3.
TABLE-US-00003 TABLE 3 Laves and Mu MC/MN Ni.sub.3M Z-phase
Elements Range 1 Range 2 Range 1 Range 2 Range 1 Range 2 Range 1
Range 2 Cr 5-30 9-14 5-30 9-14 5-30 9-14 5-30 9-14 Ti 0.1-2 0.1-0.8
0.1-2 0.1-0.8 0.1-2 0.1-0.8 0.1-2 0.1-0.8 Y 0.1-1 0.2-0.6 0.1-1
0.2-0.6 0.1-1 0.2-0.6 0.1-1 0.2-0.6 O 0.1-0.6 0.1-0.2 0.1-0.6
0.1-0.2 0.1-0.6 0.1-0.2 0.1-0.6 0.1-0.2 Mo 0-5 0.5-3 0-5 0-3 0-5
0-3 0-5 0-3 W 0-6 1-5 0-5 0-4 0-5 0-4 0-5 0-4 Nb 0-2 0-0.5 0-2
0-0.5 0-2 0-0.5 0-2 0-0.5 V 0-1 0-0.3 0-1 0-0.3 0-1 0-0.3 Al 0-2
0-0.5 Ni 0-8 0-2 0-8 0-2 Ta 0-2 0-0.5 0-2 0-0.5 C 0.01-0.5 0.01-0.1
N 0.01-0.5 0.01-0.1 0.01-0.5 0.01-0.1
[0045] The particulate phase of the second subpopulation may have a
combination of added dispersion phases and in-situ precipitated
phases. For example, the particulate phases of the second
subpopulation may have a precipitated Laves phase, mu phase, a
precipitated carbide, nitride, carbonitride, or an intermetallic
phase having a Ni.sub.3M structure; along with a non-precipitated
oxide or boride phase. The non-precipitated (added) dispersion
phases may be added to the NFA structure before the precipitation
of the particulate phases of the first subpopulation; before the
precipitation of the particulate phases of the second subpopulation
and processed to have both the precipitated and added particulate
phases of the second subpopulation.
EXAMPLES
[0046] The following example illustrates methods, materials and
results, in accordance with a specific embodiment, and as such
should not be construed as imposing limitations upon the
claims.
[0047] A vacuum induction melting furnace was charged with the
following composition: Fe-14Cr-0.4Ti-3W-0.5Mn-0.5Si (wt %). Once
the alloy was molten and well mixed, it was atomized via argon gas.
The powder was sieved to a final cut size of about +325/-100 and
sealed in a container. The powder was then transferred to an
attrition vessel. In addition to the atomized powder, 0.25 wt % of
yttrium oxide and 5 mm diameter steel balls were added to the
attrition vessel. The balls were added such that the ball to powder
ratio was 10:1 by mass. The powders were then milled for
approximately 20 hours or until the yttrium oxide was dissolved in
the metal matrix. The powder was separated from the steel balls
during unloading of the vessel, while under inert gas. The powder
was then loaded into a container (can) for hot isostatic pressing
(HIP). The can was then evacuated at room temperature until a
leak-back rate of about 15 microns/hour or better was reached. Once
evacuated and sealed, the HIP can was subjected to HIP at about 30
ksi for 4 hrs at a temperature of about 1000.degree. C. During this
consolidation step, the first dispersion of complex oxides was
precipitated.
[0048] Following HIP, the material in the HIP can was heated in a
furnace with flowing argon to a temperature of about 1000.degree.
C. The can was then transferred to an open die forging press and
the height was reduced by about 60% at a strain rate of about 0.6
min.sup.-1. The forged material was then allowed to cool.
[0049] After forging, the transmission electron microscopy (TEM)
analysis of the microstructure of the material shows a first
dispersion of nm-size complex oxides. The volume fraction of the
dispersion, as measured through small angle xray scattering (SAXS)
was about 0.8-1 vol %. The size of the particles of the first
dispersion, also measured through SAXS, is between about 2-5 nm. A
second dispersion of larger particles was not evident here in the
post-forging stage.
[0050] The forged material was once again heated in a furnace for
about 5 hrs at a temperature of about 700.degree. C., to force the
precipitation of a second dispersion of particles. TEM analysis of
this sample was carried out and a Fe,W based Laves phase was found
to be present in the microstructure. The concentration of this
second dispersion of particles was measured using image analysis
software and was found to be approximately about 2 vol % in this
example. The average size of the Laves phase was measured to be
between about 100 nm and 500 nm.
[0051] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *