U.S. patent application number 14/103895 was filed with the patent office on 2015-06-18 for particulate strengthened alloy articles and methods of forming.
This patent application is currently assigned to General Electric Company. The applicant listed for this patent is General Electric Company. Invention is credited to Laura Cerully Dial, Richard DiDomizio.
Application Number | 20150167129 14/103895 |
Document ID | / |
Family ID | 52021075 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150167129 |
Kind Code |
A1 |
DiDomizio; Richard ; et
al. |
June 18, 2015 |
PARTICULATE STRENGTHENED ALLOY ARTICLES AND METHODS OF FORMING
Abstract
An article and a method for forming the article are presented.
The article includes a material comprising a metal matrix and a
first population of particulate phases disposed macroscopically
non-uniformly within the matrix. The particulate phases include an
oxide phase. Further embodiments include articles, such as
turbomachinery components, fasteners, and pipes, for example, and
methods for forming the articles.
Inventors: |
DiDomizio; Richard;
(Charlton, NY) ; Dial; Laura Cerully; (Clifton
Park, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
52021075 |
Appl. No.: |
14/103895 |
Filed: |
December 12, 2013 |
Current U.S.
Class: |
428/34.1 ;
419/62; 419/66; 419/67; 428/64.1; 75/232; 75/235; 75/236;
75/244 |
Current CPC
Class: |
B22F 7/06 20130101; B22F
3/15 20130101; B22F 5/106 20130101; C22C 33/02 20130101; B22F
1/0014 20130101; C22C 32/001 20130101; B22F 3/20 20130101; Y10T
428/13 20150115; C22C 32/0005 20130101; B22F 3/17 20130101; Y10T
428/21 20150115 |
International
Class: |
C22C 32/00 20060101
C22C032/00; B22F 1/00 20060101 B22F001/00; B22F 9/04 20060101
B22F009/04; B22F 3/02 20060101 B22F003/02; B22F 3/20 20060101
B22F003/20 |
Claims
1. An article, comprising: a material comprising a metal matrix and
a first population of particulate phases disposed macroscopically
non-uniformly within the matrix, the particulate phases comprising
an oxide phase.
2. The article of claim 1, wherein the matrix comprises nickel,
iron, chromium, aluminum, cobalt, titanium, or a combination
thereof.
3. The article of claim 1, wherein the matrix comprises iron and
chromium.
4. The article of claim 1, wherein the oxide phase comprises
aluminum, yttrium, magnesium, molybdenum, zirconium, silicon,
titanium, hafnium, tungsten, tantalum, or a combination
thereof.
5. The article of claim 1, wherein the oxide phase comprises
titanium and yttrium.
6. The article of claim 1, wherein the first population of
particulate phases has a median size less than about 20 nm.
7. The article of claim 1, wherein the first population of
particulate phases has a median size less than about 10
nanometers.
8. The article of claim 1, further comprising a second population
of particulate phases disposed within the matrix, wherein the
second population of particulate phases has a different size
distribution from the size distribution of the first population of
particulate phases.
9. The article of claim 8, wherein the second population of
particulate phases is distributed macroscopically non-uniformly
within the matrix.
10. The article of claim 8, wherein the second population of
particulate phases comprises an intermetallic compound.
11. The article of claim 8, wherein the second population of
particulate phases comprises an oxide, a boride, a carbide, a
nitride, or combinations thereof.
12. The article of claim 8, wherein the second population of
particulate phases has a median size in a range from about 25 nm to
about 10 microns.
13. The article of claim 1, wherein a first concentration of the
first population of the particulate phases in a first region of the
article is not equal to a second concentration of the first
population of the particulate phases in a second region of the
article, and wherein each of the first concentration and second
concentration is independently within a range from about 0.1 volume
percent to about 5 volume percent.
14. The article of claim 13, wherein at least one intermediate
region is disposed between the first region and the second region,
and wherein the concentration of the first population of the
particulate phases in the at least one intermediate region has a
value that is between the first concentration and the second
concentration.
15. The article of claim 13, wherein the article is a
turbomachinery component, a fastener or a pipe.
16. The article of claim 15, wherein the article is a wheel or a
spacer.
17. The article of claim 16, wherein a first region comprises an
inner surface of the wheel or spacer, and a second region comprises
an outer surface of the wheel or spacer, and wherein a first
concentration of the first population of the particulate phases at
the inner surface is less than a second concentration of the first
population of the particulate phases at the outer surface.
18. The article of claim 17, wherein the first concentration is in
a range from about 0.1 volume percent to about 2 volume percent,
and the second concentration is in a range from about 0.7 volume
percent to about 3 volume percent.
19. A turbomachinery component, comprising: a radially symmetrical
body comprising an inner surface proximate to a center of the body
and an outer surface distal to the center of the body; wherein the
body comprises a material comprising a metal matrix, the matrix
comprising iron and chromium; a first population of particulates
having a median size less than about 20 nanometers, the particulate
phases comprising an oxide phase, the oxide phase comprising
titanium and yttrium, wherein a concentration of the first
population of the particulate phases at the inner surface is less
than a concentration of the first population of the particulate
phases at the outer surface, and wherein the concentration of the
particulate phases at the inner surface is in a range from about
0.1 volume percent to about 2 volume percent, and the concentration
of the particulate phases at the outer surface is in a range from
about 0.7 volume percent to about 3 volume percent.
20. A method comprising: joining a first composition comprising a
first oxygen concentration to a second composition having a second
oxygen concentration, the second oxygen concentration different
from the first oxygen concentration, to form a material comprising
a metal matrix and a first population of particulate phases
disposed macroscopically non-uniformly within the matrix, the
particulate phases comprising an oxide phase.
21. The method of claim 20, further comprising milling an alloy
powder comprising iron and chromium in the presence of a first
amount of an oxide until the oxide is at least partially dissolved
into the alloy powder, thus forming the first composition.
22. The method of claim 20, further comprising milling an alloy
powder comprising iron and chromium in the presence of a second
amount of an oxide until the oxide is at least partially dissolved
into the alloy powder, thus forming the second composition.
23. The method of claim 20, wherein the first composition, the
second composition, or both the first composition and the second
composition, are powder, and wherein joining further comprises
consolidating the powder.
24. The method of claim 23, wherein both the first composition and
the second composition are powder.
25. The method of claim 24, further comprising: disposing powder
comprising the first composition in a first region of a container;
disposing powder comprising the second composition in a second
region of the container; and consolidating the powders and thereby
joining the first and second compositions.
26. The method of claim 20, further comprising heating the first
composition, the second composition, or the material to form the
first population of particulate phases.
27. The method of claim 20, further comprising establishing a
second population of particulate phases within the matrix, the
second population of particulate phases having a median size in a
range from about 25 nm to about 10 microns.
28. The method of claim 20, wherein the first composition and the
second composition are solid feedstock, and wherein joining
comprises co-extruding, welding, solid-state joining, diffusion
bonding, shrink fitting, or a combination thereof.
29. The method of claim 23, wherein the first composition is a
solid feedstock and the second composition is a powder, and wherein
joining comprises consolidating the powder and bonding the first
composition to the second composition.
30. A method, comprising: milling a first powder comprising iron
and chromium in the presence of an oxide until the oxide is at
least partially dissolved into the alloy powder, thus forming a
first composition having a first oxygen concentration; milling a
second powder comprising iron and chromium in the presence of an
oxide until the oxide is at least partially dissolved into the
alloy powder, thus forming a second composition having a second
oxygen concentration that is greater than the first oxygen
concentration; disposing powder comprising the first composition in
a first region of a container; disposing powder comprising the
second composition in a second region of the container; and
consolidating the powders and thereby joining the first and second
compositions at a temperature to precipitate an oxide phase
comprising titanium and yttrium within a matrix comprising iron and
chromium; wherein the first region of the container and the second
region of the container respectively correspond to an inner surface
and an outer surface of a radially symmetrical body of a
turbomachinery component.
Description
BACKGROUND
[0001] The invention relates generally to nano structured ferritic
alloys. More particularly, the invention relates to articles formed
of nanostructured ferritic alloys having non-uniformly distributed
dispersions, and methods of forming thereof.
[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, superalloys 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 superalloys, 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,
use of conventional steels is often limited in high temperature and
high stress applications because of not meeting the necessary
mechanical property requirements and/or design requirements.
[0004] Nanostructured ferritic alloys (NFA) are an emerging class
of alloys that are of considerable interest for the gas turbine
rotors. These alloys (NFAs) 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. Moreover, unlike many nickel-based superalloys, 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 for
rotor applications. It should be noted that for the heavy duty gas
turbine rotors, critical mechanical property requirements change
from the bore to the rim of a wheel. For example, the bore is
limited by burst strength, and hence would require a higher
ultimate tensile strength, and the rim is limited by a material's
creep life.
[0006] Accordingly, it is desirable to have a graded alloy article
that exhibits improved mechanical integrity over various regions
(locations) of the article with a proper balance of mechanical
properties.
BRIEF DESCRIPTION
[0007] In one embodiment, an article is provided. The article
includes a material comprising a metal matrix and a first
population of particulate phases disposed macroscopically
non-uniformly within the matrix. The particulate phases include an
oxide phase. Further embodiments include articles, such as
turbomachinery components, fasteners, and pipes, for example.
[0008] One embodiment is a turbomachinery component. The component
includes a radially symmetrical body having an inner surface
proximate to a center of the body and an outer surface distal to
the center of the body. The body includes a material comprising a
metal matrix and a first population of particulate phases. The
metal matrix includes iron and chromium. The first population of
particulate phases includes an oxide phase that includes titanium
and yttrium, and has a median size less than about 20 nanometers. A
concentration of the first population of the particulate phases at
the inner surface is less than a concentration of the first
population of the particulate phases at the outer surface. The
concentration of the first population of the particulate phases at
the inner surface is in a range from about 0.1 volume percent to
about 2 volume percent, and the concentration at the outer surface
is in a range from about 0.7 volume percent to about 3 volume
percent.
[0009] In one embodiment, a method includes joining a first
composition comprising a first oxygen concentration to a second
composition having a second oxygen concentration to form a
material. The second oxygen concentration is different from the
first oxygen concentration. The material includes a metal matrix
and a first population of particulate phases disposed
macroscopically non-uniformly within the matrix. The particulate
phases include an oxide phase. The material is processed to provide
an article.
[0010] In one embodiment, a method of forming a turbomachinery
component is provided. The method includes steps of milling a first
powder including iron and chromium in the presence of an oxide
until the oxide is at least partially dissolved into the alloy
powder, and thus forming a first composition having a first oxygen
concentration; and milling a second powder including iron and
chromium in the presence of an oxide until the oxide is at least
partially dissolved into the alloy powder, thus forming a second
composition having a second oxygen concentration that is greater
than the first oxygen concentration. The powder having the first
composition is disposed in a first region of a container, and the
powder having the second composition is disposed in a second region
of the container. These powders are consolidated to thereby join
the first and second compositions at a temperature to precipitate
an oxide phase comprising titanium and yttrium within a matrix
comprising iron and chromium. The first region of the container and
the second region of the container respectively correspond to an
inner surface and an outer surface of a radially symmetrical body
of the turbomachinery component.
DRAWINGS
[0011] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings.
[0012] FIG. 1 is a schematic representation of an article, in
accordance with one embodiment of the present invention;
[0013] FIG. 2 is a schematic representation of an article, in
accordance with one embodiment of the present invention;
[0014] FIG. 3 is a schematic representation of a top-down
cross-section of a turbomachinery component, in accordance with one
embodiment of the present invention;
[0015] FIG. 4 is a schematic representation of a top-down
cross-section of a turbomachinery component, in accordance with one
embodiment of the present invention;
[0016] FIG. 5 schematically represents a container for forming an
article, in accordance with one embodiment of the present
invention.
DETAILED DESCRIPTION
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] Embodiments of the invention provide an article including a
metal matrix and a first population of particulate phases that is
macroscopically non-uniformly disposed within the metal matrix. The
metal matrix may include nickel, iron, chromium, aluminum, cobalt,
titanium, or a combination thereof. In one embodiment, the metal
matrix includes an iron-containing alloy. The first population of
particulate phases includes an oxide phase.
[0022] As used herein, "macroscopically non-uniform disposition"
refers to heterogeneous dispersion of particulate phases over a
length scale of at least 0.5 centimeter of the metal matrix. That
is, a concentration of the particulate phases in a first portion of
the article varies from a concentration of the particulate phases
in a second portion, wherein the portions often extend over a
length scale of at least about 0.5 centimeter. In some embodiments,
the portions may extend to a length scale of up to about 200
centimeters. In certain embodiments, the portions may extend to a
length scale of up to about 100 centimeters. As used herein,
"disposed within the matrix" includes the dispersion of the
particulate phases in the grains and grain boundaries of the
matrix.
[0023] Some embodiments provide an article including a
nanostructured ferritic alloy (NFA). Typically a nano structured
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 weight percent. In one embodiment, the iron content in the alloy
matrix is greater than about 70 weight percent. 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 20
nanometers in size. The nanofeatures of an NFA may have any shape,
including, for example, spherical, cuboidal, lenticular, and other
shapes. The nanofeatures used herein are typically in-situ formed
in the NFA by the dissolution of at least a portion of the initial
added oxide and the precipitation of nanometer sized particles of a
modified oxide that can serve to pin the alloy structure, thus
providing enhanced mechanical properties.
[0024] FIG. 1 illustrates an article 10 in accordance with some
embodiments of the present invention. The article 10 includes a
nano structured ferritic alloy having a first population of
particulate phases macroscopically non-uniformally disposed within
the article, for example, from a first surface 12 to a second
surface 14. In some embodiments, the article 10 has graded
concentration of the first particulate phases from the first
surface 12 towards the second surface 14. The gradation may be
continuous or step wise.
[0025] In the illustrated embodiment, the article 10 includes a
first region 18 extending from the first surface 12 to a
predetermined surface 16, and a second region 20 extending from a
second surface 14 to the predetermined surface 16. The first region
18 includes a first concentration of the first particulate phases,
and the second region 20 includes a second concentration of the
first particulate phases, where the first concentration of the
first particulate phases in the first region 18 is not equal to the
second concentration of the first particulate phases in the second
region 20. In one embodiment, each of the first concentration in
the first region 18 and the second concentration in the second
region 20 is independently within a range from about 0.1 volume
percent to about 5 volume percent.
[0026] In some embodiments, the article 10 may have more than two
regions, wherein adjacent regions have different concentration of
the first particulate phases. For example, the article 10 may have
at least three regions, as illustrated in FIG. 2, with an
intermediate region 22 extending from the predetermined surface 16
to another predetermined surface 26. The intermediate region 22 is
disposed between the first region 18 and the second region 20. The
concentration of the first particulate phases in the intermediate
region 22 may be different from the first concentration of the
first particulate phases in the first region 18 and the second
concentration of the first particulate phases in the second region
20. In some embodiments, the concentration of the first particulate
phases in the intermediate region 22 has a value between the first
concentration and the second concentration. The article 10 may have
a number of intermediate regions between the first region 18 and
the second region 20. In one embodiment, the concentration of the
first particulate phases in each intermediate region is between the
concentrations of the particulate phases in adjacent regions. The
concentrations of the first particulate phases may increase or
decrease from the first region 18 towards the second region 20. In
some embodiments, the alternate regions may have a same
concentration of the first particulate phases. It should be noted
herein that although the below material details are discussed with
reference to FIGS. 1 and 2, the details are also equally applicable
to the embodiment of FIGS. 3 and 4.
[0027] A metal matrix (may also be referred to as alloy matrix) of
the NFA includes iron and chromium. Chromium is important for both
phase stability and oxidation and/or corrosion resistance, and may
thus be included in the NFA in amounts of at least about 5 weight
percent. Amounts of up to about 30 weight percent may be included.
In one embodiment, chromium is present in a range from about 9
weight percent to about 14 weight percent of the alloy. In some
embodiments, 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 particulate
phases of the alloy. They may play a role in the formation of the
oxide nanofeatures, as described herein. In some embodiments, the
titanium is present 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 addition, the alloy may
include one or more of vanadium, molybdenum, manganese, tungsten,
niobium, silicon or tantalum.
[0028] The first population of particulate phases may be the
above-described nanofeatures, providing enhanced tensile and creep
properties to the alloy. The nanofeatures of the first population
have a median size less than about 20 nanometers (nm). In some
embodiments, the particulate phases of the first population have a
median size less than about 15 nm. In certain embodiments, the
median size of the particulate phases is less than about 10 nm. In
some embodiments, the first population 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 (where A, B signify
non-oxygen elements); or may be a mixture of multiple simple oxide
phases (having one non-oxygen element) such as, for example
A.sub.xB.sub.yO.sub.z, where x, y, z denote the relative molar
ratios of the elements in the mixture. The examples included here
do not account for charge balance, and hence will include the
oxides of elements of different valencies and deviations from
stoichiometry.
[0029] In one embodiment, an oxide material may be added to the
alloy matrix, and processed to precipitate nanofeatures of the
first population. At least a part of the added oxide phase may be
dissolved in the alloy structure and precipitated as the
nanofeatures. In one embodiment, the precipitated oxide in the NFA
may include transition metals (for example, titanium and yttrium)
present in the starting materials and the metallic element(s) of
the initial oxide addition.
[0030] In one embodiment, the particulate phases of the first
population include at least two elements from the group of yttrium,
titanium, aluminum, zirconium, molybdenum, silicon, hafnium,
magnesium, tungsten, and tantalum. 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 population include
a complex oxide with a single phase including more than one
non-oxygen element, such as for example, a yttrium titanium oxide;
a 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.
[0031] It should be noted here that the use of the plural term
"phases" in this context does not necessitate that multiple phase
compositions are present within a population; rather, "phases" is
used to denote the presence of a plurality of particles in the
matrix, which may or may not be of homogeneous composition.
[0032] In some embodiments, the article 10 (FIGS. 1 and 2) further
includes a second population of particulate phases within the alloy
matrix. The addition of the second particulate phases may enhance
the tensile and creep properties of the NFA, while maintaining a
desirable level of ductility. The second population of particulate
phases may have a different particle size distribution than that of
the first population of the particulate phases. The second
population of the particulate phases may have a median particulate
size in a range from about 25 nm to about 10 microns. In one
embodiment, the second population of particulate phases has a
median size in a range from about 50 nm to about 3 microns.
[0033] The second population of the particulate phases may be
distributed uniformly or non-uniformly within the article 10. In
one embodiment, the second population of the particulate phases is
disposed macroscopically non-uniformly within the alloy matrix. For
example, as discussed with respect to the first population of
particulate phases in previous embodiments, a concentration of the
second particulate phases in each intermediate region is between
the concentrations of the particulate phases in adjacent regions
(FIG. 2). The concentrations of the particulate phases may increase
or decrease from the first region 18 towards the second region 20.
The concentrations of the second population of particulate phases
in each region of the article may independently be within a range
from about 1 volume percent to about 15 volume percent, and more
particularly, from about 1 volume percent to about 6 volume percent
of the alloy. In a particular embodiment, the concentration the
population of particulate phases (including both first population
and second population) in each region of the article is in a range
from about 2 volume percent to about 6 volume percent in the
alloy.
[0034] In some embodiments, the second population may include an
oxide, a boride, a carbide, a nitride, or a combination thereof. An
oxide may be added to the alloy during processing to further
strengthen the alloy. 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. In some embodiments, a
precipitated particulate phase of the second population 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. Various features and methods of forming an
alloy having a precipitated first population of particulate phases
and an added second population of particulate phases are described
in details in previously filed patent application Ser. Nos.
13/931,108 and 14/074,768.
[0035] Referring to FIGS. 1 and 2 again, the article 10 may be a
turbomachinery component, in some embodiments. In other
embodiments, the article 10 may also be applicable for any other
applications involving operation at a high temperature, such as a
fastener, a pipe etc, as well as a low temperature, such as pipes
and disks for transporting oils and gases. In one embodiment, the
article 10 is a turbine wheel. In another embodiment, the article
10 is a turbine spacer.
[0036] As discussed previously, critical mechanical properties
change from the bore to the rim of a turbine wheel. For example,
the bore is limited by burst strength, and hence would require a
higher ultimate tensile strength, and the rim is limited by a
material's creep life. Generally, increasing the concentration of
the oxide nanofeatures results in improved tensile properties as
required for the wheel's bore and improved creep properties for the
wheel's rim. However, the concentration of the oxide nanofeatures
is limited to a nominal amount because of a reduction in the
ductility of the material, which is a larger concern at the bore
than the rim.
[0037] Some embodiments of the present invention provide a
turbomachinery component having macroscopically non-uniform
dispersion of a first population of the particulate phases that
includes an oxide phase, to provide required mechanical properties
in particular locations or regions, for example at a bore and a rim
of the turbomachinery component. FIG. 3 illustrates a top-down
cross-section of a turbomachinery component 30 having a radially
symmetrical body, for example a wheel or a spacer. The center of
the radially symmetric component 30 is located at 31. The component
30 includes a nanostructured ferritic alloy (NFA) as described
herein. In the illustrated embodiment, the turbomachinery component
30 includes an inner surface 32 (bore) proximate to a center 31 of
the radially symmetrical body of the component 30, and an outer
surface 36 (rim) distal to the center 31 of the component 30. The
inner surface 32 of the component 30 defines a hole concentric with
the radially symmetrical body. In one embodiment, a first
concentration of the first particulate phases in the alloy at the
inner surface 32 is less than a second concentration of the first
particulate phases at the outer surface 36 of the wheel. In one
embodiment, the wheel 30 includes a nanostructured ferritic alloy
having a graded concentration of the first particulate phases from
the inner surface 32 to the outer surface 36.
[0038] In some embodiments as illustrated in FIG. 4, the
turbomachinery component 30 has a first region 38 extending from
the inner surface 32 to a predetermined surface 34, and a second
region 40 extending from the outer surface 36 to the predetermined
surface 34. In one embodiment, the first region 38 and the second
region 40 include the same composition of the NFA matrix and the
concentration of the first particulate phases in the alloy varies.
A first concentration of the first particulate phases in the first
region 38 is less than the second concentration of the first
particulate phases in the second region 40 of the component 30.
[0039] In some embodiments, the first concentration of the first
particulate phases in the first region 38 is in a range from about
0.1 volume percent to about 2 volume percent of the alloy, and the
second concentration of the first particulate phases in the second
region 40 is in a range from about 0.7 volume percent to about 3
volume percent of the alloy. In some embodiments, the component 30
may have a number of intermediate regions disposed between the
first region 38 and the second region 40, as discussed in previous
embodiments. In certain embodiments, the component 30 may include a
graded nanostructured ferritic alloy i.e. a nanostructured ferritic
alloy having a gradually increasing concentration of the first
particulate phases from the inner surface 32 to the outer surface
36 (FIG. 3).
[0040] By tailoring the concentration of the first particulate
phases (that includes an oxide phase) in the alloy matrix, desired
mechanical properties in specific locations of a component can be
achieved. For example, a wheel may have a low concentration of an
oxide phase near the bore region to provide good ultimate tensile
strength and ductility to resist burst, and a high concentration of
the oxide phase near the rim region to enhance creep resistance.
Typically, these location specific properties can be achieved by
using multiple alloys. However, use of these multiple dissimilar
chemistry alloys results in inter-diffusion at the joining surface.
This inter-diffusion may adversely affect mechanical properties
during the service of the component, and thus reduce service life.
Use of a consistent alloy matrix throughout the wheel with varying
concentration of an oxide phase enables location specific
properties to be achieved while maintaining the same matrix to
eliminate diffusion issues and property changes with time.
[0041] Some embodiments provide a method of forming an article. The
method includes joining a first composition and a second
composition to form an article. The first composition and the
second composition may be joined through one or more than one
intermediate composition disposed between them. In one embodiment,
a number of compositions may be joined by joining one composition
with an adjacent composition. The first composition may have a
first oxygen concentration and the second composition may have a
second oxygen concentration that is different from the first oxygen
concentration. The resulting article includes a metal matrix and a
first population of particulate phases disposed macroscopically
non-uniformly within the article. The first population of
particulate phases includes an oxide phase. In certain embodiments,
the resulting material includes a NFA.
[0042] Oxygen concentration, as used herein, refers to a total
oxygen concentration of a composition, which may include dissolved
oxygen and any other oxygen that is present in the form of an oxide
or in other phases present in the NFA.
[0043] The method of forming a composition of NFA may include
forming an alloy powder and consolidating the powder. The alloy
powder may be formed by any of the methods known in the art. A
process of forming the alloy powder may start from melting starting
materials such as, for example, iron and chromium to form an
initial melt. A vacuum induction melting process may be
conveniently used to melt the starting material. The melted
material may be atomized to form the alloy powder that can be
milled along with an added oxide material to form a milled alloy
powder. In one embodiment, the oxide material includes yttria,
zirconia, hafnia, alumina, silica, magnesia, or a combination
thereof. Usually, the milled alloy powder may be processed by
consolidating at a temperature to precipitate a desired
concentration of the first population of the particulate phases
having an oxide phase with a desired size. Suitable processing
techniques may include isothermal forging, hot isostatic pressing
(HIP), extrusion, or a combination thereof. In one embodiment, the
processing of the milled alloy powder includes hot isostatic
pressing (HIP). At least some of the added oxide is dissolved into
the alloy matrix during powder attrition, and precipitates in the
formation of the aforementioned nanofeatures when the powder is
raised to a temperature during the consolidation process. In any
given instance of this method, the amount of added oxide that
dissolves can be less than a majority, or substantially all of the
added oxide, depending on processing parameters and materials
selected. In one embodiment, the first particulate phases of
complex oxides may precipitate during the consolidation step. In
one embodiment, a second population of particulate phases may be
established by adding and mixing an oxide to the milled alloy
powder as described in patent application Ser. Nos. 13/931,108 and
14/074,768.
[0044] An article, for example the turbomachinery component 30
(FIG. 4) may be manufactured using several techniques. The first
region 38 includes the first composition, and the second region 40
includes the second composition. The first composition and the
second composition may be formed by the process as discussed above.
The formation of the first composition includes milling an alloy
powder in presence of a first amount of an oxide, and the formation
of the second composition includes milling the alloy powder in
presence of a second amount of the oxide. The alloy powders are
milled until the oxide is at least partially dissolved into the
alloy powder. In any given instance of this method, the amount of
added oxide that dissolves can be less than the majority, or a
majority, or substantially all of the added oxide, depending on
processing parameters and materials selected.
[0045] In some embodiments, the first composition and the second
composition are present in milled alloy powder form. Referring to
FIG. 5, the method includes steps of disposing the first
composition in a first region 52 of a container 50 (for example,
HIP can), and disposing a second composition in a second region 54
of the container 50. The container 50 is cylindrical about an axis
60. The first region 52 of the container 50 proximate to the axis
60, is defined by a first surface 56 that may correspond to the
predetermined surface 34 of the component 30 of FIG. 4. Further, a
portion of the first region 52 of the container 50 may correspond
to the first region 38 of the component 30. A second surface 58 of
the container 50 may correspond to the second surface 36 (FIG. 4),
i.e. the second region 54 of the container 50 may correspond to the
second region 40 of the component 30 (FIG. 4). The two alloy
powders may be separated by a metallic sheet (for example, baffle)
at the time of disposing the compositions in the container 50. The
method further includes simultaneously consolidating the milled
alloy powders of the first composition and the second composition,
and thereby joining the two consolidated compositions to form a
solid feedstock (defined below) having a first portion and a second
portion corresponding to the first and second regions 52 and 54 of
the container 50. The metallic sheet can be removed from the
container before the consolidation step to allow the two
compositions to join during the HIP process. In certain
embodiments, the two alloy powders are consolidated by HIP followed
by forging or extrusion. The consolidation process may be performed
at a temperature to precipitate a first concentration and a second
concentration of an oxide phase including titanium and yttrium in
the first region 52 and the second region 54 of the container,
respectively. In certain embodiments, the first concentration of
the oxide phase in the first region 52 is less than the second
concentration of the oxide phase in the second region 54.
[0046] The container 50 used to consolidate the NFA alloy, may not
have a bore hole as shown in FIGS. 3 and 4 defined by the inner
surface 32 of the radially symmetrical body of the component 30.
The bore hole can be machined in a first portion of the resulting
solid feedstock after completion of the processing of the NFA. As
used herein, the first portion of the solid feedstock corresponds
to the first composition that forms the inner surface 32 of the
first region 38 of the component 30 after the bore hole is
machined.
[0047] In some embodiments, the first composition and the second
composition are present in form of solid feedstock. Solid feedstock
refers to a solid continuous structure that does not include a
powder form. The milled alloy powders of first composition and the
second composition are separately consolidated in desired shapes to
form solid feedstocks. For example, referring to FIG. 5, a first
(i.e., inner) feedstock corresponding to the first region 52
including the first composition and a second feedstock
corresponding to the second region 54 including the second
composition are manufactured beforehand, and then joined. As
discussed, a bore hole can be machined in the first feedstock
including the first composition. In these embodiments, joining may
be performed by welding, co-extruding, solid state joining,
diffusion bonding, shrink fitting, or a combination thereof.
[0048] In some embodiments, at least one of the first composition
or the second composition is in form of solid feedstock, and the
other composition is in powder form. In one example, the first
composition may be a solid feedstock that can be placed in the
first region 52 of the container 50, and the second composition may
be a powder that can be disposed in the second region 54 (i.e.
around the solid feedstock of the first composition) of the
container 50. In another example, the second composition may be a
solid feedstock of having a hollow space substantially in the
middle, which can be placed in the second region 54 of the
container 50. The first composition may be a powder that can be
disposed in the first region 52 (i.e., the hollow space of the
solid feedstock). In these embodiments, the method further includes
consolidating the powder of the second composition and thereby
bonding the second composition to the first composition. In some
embodiments, the first and the second compositions are processed by
HIP followed by forging. In some embodiments, the first composition
and the second compositions are processed by HIP and extrusion.
Examples of other suitable bonding techniques include co-extrusion,
and spray techniques such as cold spray, thermal spray, and plasma
spray.
[0049] 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.
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