U.S. patent application number 13/719772 was filed with the patent office on 2014-06-19 for components with near-surface cooling microchannels and methods for providing the same.
This patent application is currently assigned to General Electric Company. The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to John Wesley Harris, JR., Srikanth Chandrudu Kottilingam, Benjamin Paul Lacy, David Edward Schick.
Application Number | 20140170433 13/719772 |
Document ID | / |
Family ID | 49766919 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140170433 |
Kind Code |
A1 |
Schick; David Edward ; et
al. |
June 19, 2014 |
COMPONENTS WITH NEAR-SURFACE COOLING MICROCHANNELS AND METHODS FOR
PROVIDING THE SAME
Abstract
Methods for providing a near-surface cooling microchannel in a
component include forming a near-surface cooling microchannel in a
first surface of a pre-sintered preform, disposing the first
surface of the pre-sintered preform onto an outer surface of the
base article such that an opening of the outer surface of the base
article is aligned with the near-surface cooling microchannel in
the first surface of the pre-sintered preform, and, heating the
pre-sintered preform to bond it to the base article, wherein the
opening of the outer surface of the base article remains aligned
with the near-surface cooling microchannel in the first surface of
the pre-sintered preform.
Inventors: |
Schick; David Edward;
(Greenville, SC) ; Kottilingam; Srikanth Chandrudu;
(Simpsonville, SC) ; Lacy; Benjamin Paul; (Greer,
SC) ; Harris, JR.; John Wesley; (Taylors,
SC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenetady |
NY |
US |
|
|
Assignee: |
General Electric Company
Schenectady
NY
|
Family ID: |
49766919 |
Appl. No.: |
13/719772 |
Filed: |
December 19, 2012 |
Current U.S.
Class: |
428/548 ;
228/125; 228/174; 428/188 |
Current CPC
Class: |
B23P 2700/06 20130101;
Y10T 428/12028 20150115; Y10T 428/24744 20150115; B22F 5/10
20130101; F01D 5/187 20130101; Y02T 50/60 20130101; F05D 2260/204
20130101; B22F 7/08 20130101; B22F 5/009 20130101; Y02T 50/676
20130101; F05D 2230/22 20130101; C22C 1/0433 20130101; Y02T 50/671
20130101; B22F 5/04 20130101 |
Class at
Publication: |
428/548 ;
428/188; 228/174; 228/125 |
International
Class: |
B22F 7/08 20060101
B22F007/08 |
Claims
1. A method of providing a near-surface cooling microchannel in a
component, the component comprising an internal cooling passage
within a base article having an opening at an outer surface, the
method comprising: forming a near-surface cooling microchannel in a
first surface of a pre-sintered preform, wherein the pre-sintered
preform comprises a mixture comprising a base alloy and a second
alloy, the base alloy comprising about 30 weight percent to about
90 weight percent of the mixture and the second alloy comprising a
sufficient amount of a melting point depressant to have a lower
melting temperature than the base alloy; disposing the first
surface of the pre-sintered preform onto the outer surface of the
base article such that the opening of the outer surface of the base
article is aligned with the near-surface cooling microchannel in
the first surface of the pre-sintered preform; and, heating the
pre-sintered preform to bond it to the base article, wherein the
opening of the outer surface of the base article remains aligned
with the near-surface cooling microchannel in the first surface of
the pre-sintered preform.
2. The method of claim 1 further comprising forming a second
near-surface cooling microchannel in the first surface of the
pre-sintered preform, wherein when the pre-sintered preform is
disposed on the outer surface of the base article, the second
near-surface cooling microchannel aligns with a second opening in
the outer surface of the base article.
3. The method of claim 1, wherein the pre-sintered preform is
formed by combining base alloy particles and second alloy particles
with a binder to form a combined powder mixture, compacting the
combined powder mixture to form a compacted preform, and heating
the compacted preform to remove the binder and form the
pre-sintered preform.
4. The method of claim 3, wherein the near-surface cooling
microchannel is formed into the compacted preform prior to
heating.
5. The method of claim 1, wherein the pre-sintered preform has a
density of at least 90% of theoretical.
6. The method of claim 1, wherein the base alloy and second alloy
are mixed together at a weight ratio of about 30:70 to about 90:10,
respectively.
7. The method of claim 1, further comprising depositing a coating
on an exterior surface of the pre-sintered preform, wherein the
exterior surface is opposite the first surface.
8. The method of claim 7, wherein the coating is deposited on the
pre-sintered preform before the pre-sintered preform is bonded to
the base article.
9. The method of claim 1 further comprising: disposing a filler
material in the internal cooling passage prior to heating the
pre-sintered preform; and, removing the filler material from the
internal cooling passage after heating the pre-sintered
preform.
10. The method of claim 1, wherein the pre-sintered preform is
bonded to the outer surface of the base article without filling the
opening.
11. A component comprising: a base article comprising an internal
cooling passage having an opening at an outer surface; and, a
pre-sintered preform having a first surface bonded to the outer
surface of the base article, wherein the pre-sintered preform
comprises a near-surface cooling microchannel in the first surface
aligned with the opening of the outer surface of the base article,
and wherein the pre-sintered preform comprises a mixture comprising
a base alloy and a second alloy, the base alloy comprising about 30
weight percent to about 90 weight percent of the mixture and the
second alloy comprising a sufficient amount of a melting point
depressant to have a lower melting temperature than the base
alloy.
12. The component of claim 11, wherein the base article comprises a
second opening at the outer surface, and wherein the pre-sintered
preform comprises a second near-surface cooling microchannel
aligned with the second opening.
13. The component of claim 11, wherein the pre-sintered preform is
formed by combining base alloy particles and second alloy particles
with a binder to form a combined powder mixture, compacting the
combined powder mixture to form a compacted preform, and heating
the compacted preform to remove the binder and form the
pre-sintered preform.
14. The component of claim 13, wherein the near-surface cooling
microchannel is formed into the compacted preform prior to
heating.
15. The component of claim 11, wherein the pre-sintered preform has
a density of at least 90% of theoretical.
16. The component of claim 11, wherein the base alloy and second
alloy are mixed together at a weight ratio of about 30:70 to about
90:10, respectively.
17. The component of claim 11 further comprising a coating on an
exterior surface of the pre-sintered preform, wherein the exterior
surface is opposite the first surface.
18. The component of claim 11, wherein the component comprises a
hot gas path component for a turbine.
19. The component of claim 11, wherein the near-surface cooling
microchannel is disposed in both the first surface of the
pre-sintered preform and the outer surface of the base article.
20. The component of claim 11, wherein the base alloy and the base
substrate share a common composition.
Description
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates to cooling
passages for components and, more specifically, to near-surface
cooling microchannels and methods for providing the same.
[0002] Turbine components, such as buckets (blades), nozzles
(vanes), and other hot gas path components of industrial and
aircraft gas turbine engines, are typically formed of nickel,
cobalt or iron-base superalloys with desirable mechanical and
environmental properties for turbine operating temperatures and
conditions. Because the efficiency of a turbomachine is dependent
on its operating temperatures, there is a demand for components
such as turbine buckets and nozzles to be capable of withstanding
increasingly higher temperatures. As the maximum local temperature
of a superalloy component approaches the melting temperature of the
superalloy, forced air cooling becomes necessary. For this reason,
airfoils of gas turbine buckets and nozzles often require complex
cooling schemes in which air, typically bleed air, is forced
through internal cooling passages within the airfoil and then
discharged through cooling holes at the airfoil surface to transfer
heat from the component. Cooling holes can also be configured so
that cooling air serves to film cool the surrounding surface of the
component.
[0003] Buckets and nozzles formed by casting processes require
cores to define the internal cooling passages. The cores and their
potential for shifting during the casting process limits the extent
to which a conventional casting process can locate a cooling
passage in proximity to an exterior surface of the component. As a
result, cooling passages are typically about 0.1 inch (about 2.5
millimeters) or more below a base metal surface of a cast turbine
bucket or nozzle. However, the heat transfer efficiency could be
significantly increased if the cooling passages could be placed
closer to the surface than is currently possible. While the cooling
passages may potentially be manufactured or machined into the
components, the components themselves may be difficult to machine
due to their high strength and thoroughness. Moreover, even if
channels are machined into the surface of the components, those
channels must be covered to form a near-surface cooling
microchannel which requires additional labor and resources.
[0004] Accordingly, alternative components with near-surface
cooling microchannels and methods for providing the same would be
welcome in the art.
BRIEF DESCRIPTION OF THE INVENTION
[0005] In one embodiment, a method is disclosed for providing a
near-surface cooling microchannel in a component. The component
includes an internal cooling passage within a base article having
an opening at an outer surface. The method includes forming a
near-surface cooling microchannel in a first surface of a
pre-sintered preform, wherein the pre-sintered preform comprises a
mixture comprising a base alloy and a second alloy, the base alloy
comprising about 30 weight percent to about 90 weight percent of
the mixture and the second alloy comprising a sufficient amount of
a melting point depressant to have a lower melting temperature than
the base alloy. The method further includes disposing the first
surface of the pre-sintered preform onto the outer surface of the
base article such that the opening of the outer surface of the base
article is aligned with the near-surface cooling microchannel in
the first surface of the pre-sintered preform, and, heating the
pre-sintered preform to bond it to the base article, wherein the
opening of the outer surface of the base article remains aligned
with the near-surface cooling microchannel in the first surface of
the pre-sintered preform.
[0006] In another embodiment, a component is disclosed including a
base article comprising an internal cooling passage having an
opening at an outer surface, and a pre-sintered preform having a
first surface bonded to the outer surface of the base article. The
pre-sintered preform has a near-surface cooling microchannel in the
first surface aligned with the opening of the outer surface of the
base article. Furthermore, the pre-sintered preform comprises a
mixture comprising a base alloy and a second alloy, the base alloy
comprising about 30 weight percent to about 90 weight percent of
the mixture and the second alloy comprising a sufficient amount of
a melting point depressant to have a lower melting temperature than
the base alloy.
[0007] These and additional features provided by the embodiments
discussed herein will be more fully understood in view of the
following detailed description, in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The embodiments set forth in the drawings are illustrative
and exemplary in nature and not intended to limit the inventions
defined by the claims. The following detailed description of the
illustrative embodiments can be understood when read in conjunction
with the following drawings, where like structure is indicated with
like reference numerals and in which:
[0009] FIG. 1 is a perspective view of an exemplary component
according to one or more embodiments shown or described herein;
[0010] FIG. 2 is an exploded perspective view of a component
according to one or more embodiments shown or described herein;
[0011] FIG. 3 is a cross-sectional view of a component according to
one or more embodiments shown or described herein; and,
[0012] FIG. 4 is an exemplary method according to one or more
embodiments shown or described herein.
DETAILED DESCRIPTION OF THE INVENTION
[0013] 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.
[0014] When introducing elements of various embodiments of the
present invention, the articles "a," "an," "the," and "said" 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.
[0015] The present disclosure is generally applicable to components
that operate within environments characterized by relatively high
temperatures, and particularly a component whose maximum surface
temperature approaches the melting temperature of the material from
which it is formed, necessitating the use of forced air cooling to
reduce the component surface temperature. Notable examples of such
components include the high and low pressure turbine buckets
(blades), nozzles (vanes), shrouds, and other hot gas path
components of a turbine, such as an industrial or aircraft gas
turbine engine.
[0016] Referring now to FIG. 1, an exemplary component 10 is
illustrated comprising a turbine bucket. The component 10 generally
includes an airfoil 12 against which hot combustion gases are
directed during operation of the gas turbine engine, and whose
surface is therefore subjected to very high temperatures. The
airfoil 12 is represented as configured to be anchored to a turbine
disk (not shown) with a dovetail 14 formed on a root section of the
component 10 that is separated from the airfoil 12 by a platform
16. The airfoil 12 includes internal cooling passages 18 (e.g.,
cooling holes) through which bleed air that enters the component 10
through its root section is forced to transfer heat from the
component 10. While the advantages of this invention will be
described with reference to the component 10 shown as a bucket in
FIG. 1, the teachings of this invention are generally applicable to
other hot gas path components of industrial and aircraft gas
turbine engines, as well as a variety of other components that are
subjected to extreme temperatures.
[0017] Referring now to FIG. 2, an exploded view of a component 10
is illustrated comprising a base article 20 and a pre-sintered
preform 30. The base article 20 generally comprises the internal
cooling passage 18 (e.g., cooling hole) that has an opening 24 at
an outer surface 26 of the base article 20. In some embodiments,
such as that illustrated in FIG. 2, the base article 20 may
comprise a single internal cooling passage 18 with a single opening
24 to supply coolant (e.g., cooling air) to the near-surface
cooling microchannel 32. In other embodiments, the base article 20
may comprise a plurality of internal cooling passages 18 connecting
to either a single opening(s) 24 or a plurality of openings 24.
Moreover, the internal cooling passages 18 and the openings 24 can
be disposed at any relative locations and comprise any
configuration that assists in cooling the base article 20 when in
operation. For example, in some embodiments, the internal cooling
passage 18 may comprise a serpentine configuration internal the
base article 20. In some embodiments, multiple internal cooling
passages 18 may be connected to each other in a variety of ways
such as a single internal cooling passage 18 with multiple internal
cooling passages 18 branching from it.
[0018] The base article 20 can comprise a variety of materials such
as one or more superalloys. In some embodiments, the base article
can comprise a nickel-, cobalt-, or iron-based superalloy. For
example, the base article 20 can comprise nickel-based superalloys
such as Rene N4, Rene N5, Rene 108, GTD-111.RTM., GTD-222.RTM.,
GTD-444.RTM., IN-738 and MarM 247 or cobalt-based superalloys such
as FSX-414. The base article 20 may be formed as an equiaxed,
directionally solidified (DS), or single crystal (SX) casting to
withstand the high temperatures and stresses to which it is
subjected such as within a gas turbine engine.
[0019] Referring to FIGS. 2 and 3, the component 10 further
comprises the pre-sintered preform 30. The pre-sintered preform 30
generally comprises a near-surface cooling microchannel 32 in a
first surface 36 of the pre-sintered preform 30. The near-surface
cooling microchannel 32 comprises any channel that can align with
the opening 24 in the outer surface 26 of the base article 20 so
that air can flow there between. The near-surface cooling
microchannel 32 in the pre-sintered preform 30 will serve as a
near-surface cooling microchannel 32 in the component 10 (as best
illustrated in FIG. 3) and may therefore have a sufficient
cross-sectional area to allow cooling air, such as compressor bleed
air when the component 10 comprises a bucket, to flow there
through. For example, in some embodiments, the near-surface cooling
microchannel 32 can comprise a width and depth (parallel and normal
to the first surface 36, respectively) of up to about 0.1 inch
(about 2.5 mm), with a typical range of about 0.01 to about 0.05
inch (about 0.25 to about 1.27 mm), though lesser and greater
widths and depths are possible. Furthermore, the near-surface
cooling microchannel 32 can have a cross-sectional area of up to
about 0.01 in.sup.2 (about 6.5 mm.sup.2), for example, about 0.0001
to about 0.0025 inch.sup.2 (about 0.065 to about 1.6 mm.sup.2).
[0020] Moreover, the near-surface cooling microchannel 32 can have
a variety of cross-sectional shapes and configurations. For
example, in some embodiments, such as that illustrated in FIGS. 2
and 3, the near-surface cooling microchannel 32 can comprise a
semi-circular tunnel. In other embodiments, the cross-sectional
shape of the near-surface cooling microchannel 32 can be
rectangular, circular, or any other geometrical or non-geometrical
shape or combinations thereof. Furthermore, the near-surface
cooling microchannel 32 can comprise a straight passage through the
pre-sintered preform 30, or can comprise a multi-directional
passage or passages such as a serpentine configuration. In some
embodiments, such as that illustrated in FIG. 2, the pre-sintered
preform 30 may comprise a single near-surface cooling microchannel
32. In other embodiments, such as that illustrated in FIG. 3, the
pre-sintered preform 30 may comprise multiple near-surface cooling
microchannels 32. In even other embodiments, multiple near-surface
cooling microchannels 32 may be connected to each other in a
variety of ways such as a single near-surface cooling microchannel
32 with multiple near-surface cooling microchannels 32 branching
from it.
[0021] In some embodiments, the near-surface cooling microchannels
32 may be formed through a plurality of other topographical
features in the pre-sintered preform 30 such that cooling air can
travel in a variety of directions such as when the passage is not a
discrete boundary. For example, the near-surface cooling
microchannel 32 may not be defined by a single set of walls, but
rather defined by the separation in the pre-sintered preform 30 and
the base article 20 via one or more topographical variations in the
first surface 36 of the pre-sintered preform 30.
[0022] Moreover, in some embodiments, such as that illustrated in
FIG. 2, the near-surface cooling microchannel 32 may be entirely
disposed in the pre-sintered preform 30. However, in some
embodiments, the near-surface cooling microchannel 32 may be
disposed in both the pre-sintered preform 30 and the base article
20. Specifically, both the first surface 36 of the pre-sintered
preform 30 and the outer surface 26 of the base article 20 can
comprise contours that, once aligned, combine to form the one or
more near-surface cooling microchannels 32. In such embodiments,
the contours in the outer surface 26 of the base article 20 may
align with the internal cooling passage 18 or be disposed separate
from the internal cooling passage 18. In even some embodiments, the
near-surface cooling microchannels 32 may transition back-and-forth
between the pre-sintered preform 30 and the base article 20.
[0023] The near-surface cooling microchannel 32 can further
comprise one or more exit holes or trenches to exhaust the flowing
air out of the pre-sintered preform 30. The exit holes or trenches
may comprise any configuration(s) and location(s) that would
otherwise be present if the near-surface cooling microchannel was
in the base article 20. For example, these exit holes or trenches
can comprise discrete holes or closed trenches that collect cooling
air from multiple near-surface cooling microchannels before
exhausting through a discrete hole. In some embodiments, one or
more near-surface cooling microchannels 32 may direct cooling air
into an open trench on an exterior surface of the pre-sintered
preform 30.
[0024] The pre-sintered preform 30 comprises a mixture of particles
comprising a base alloy and a second alloy that have been sintered
together at a temperature below their melting points to form an
agglomerate and somewhat porous mass. Suitable particle size ranges
for the powder particles include 150 mesh, or even 325 mesh or
smaller to promote rapid sintering of the particles and minimize
porosity in the pre-sintered preform 30 to about 10 volume percent
or less. In some embodiments, the density of the pre-sintered
preform 30 has a density of 90% or better. In even some
embodiments, the pre-sintered preform 30 has a density of 95% or
better. As discussed below, the sintered perform shell 120 can be
subjected to hot isostatic pressing (HIP) or vacuum/inert
atmosphere pressing to promote higher densities.
[0025] The base alloy of the pre-sintered preform 30 can comprise
any composition such as one similar to the base article 20 to
promote common physical properties between the pre-sintered preform
30 and the base article 20. For example, in some embodiments, the
base alloy and the base article share a common composition (i.e.,
they are the same type of material). In some embodiments, the base
alloy can comprise nickel-based superalloys such as Rene N4, Rene
N5, Rene 108, GTD-111.RTM., GTD-222.RTM., GTD-444.RTM., IN-738 and
MarM 247 or cobalt-based superalloys such as FSX-414 as discussed
above. In some embodiments, the properties for the base alloy
include chemical and metallurgical compatibility with the base
article 20, such as high fatigue strength, low tendency for
cracking, oxidation resistance and/or machinability.
[0026] In some embodiments, the base alloy may comprise a melting
point of within about 25.degree. C. of the melting temperature of
the base article 20. In some embodiments, the base alloy may
comprise a compositional range of, by weight, about 2.5 to 11%
cobalt, 7 to 9% chromium, 3.5 to 11% tungsten, 4.5 to 8% aluminum,
2.5 to 6% tantalum, 0.02 to 1.2% titanium, 0.1 to 1.8% hafnium, 0.1
to 0.8% molybdenum, 0.01 to 0.17% carbon, up to 0.08% zirconium, up
to 0.60 silicon, up to 2.0 rhenium, the balance nickel and
incidental impurities. In even some embodiments, the base alloy may
comprise a compositional range of, by weight, about 9 to 11%
cobalt, 8 to 8.8% chromium, 9.5 to 10.5% tungsten, 5.3 to 5.7%
aluminum, 2.8 to 2.3% tantalum, 0.9 to 1.2% titanium, 1.2 to 1.6%
hafnium, 0.5 to 0.8% molybdenum, 0.13 to 0.17% carbon, 0.03 to
0.08% zirconium, the balance nickel and incidental impurities. It
should be appreciated that while specific materials and
compositions have been listed herein for the composition of the
base alloy of the pre-sintered preform 30, these listed materials
and compositions are exemplary only and non-limiting and other
alloys may alternatively or additionally be used. Furthermore, it
should be appreciated that the particular composition of the base
alloy for the pre-sintered preform 30 may depend on the composition
of the base article 20.
[0027] As discussed above, the pre-sintered preform 30 further
comprises a second alloy. The second alloy may also have a
composition similar to the base article 20 but further contain a
melting point depressant to promote sintering of the base alloy and
the second alloy particles and enable bonding of the pre-sintered
preform 30 to the base article 20 at temperatures below the melting
point of the base article 20. For example, in some embodiments the
melting point depressant can comprise boron and/or silicon.
[0028] In some embodiments, the second alloy may comprise a melting
point of about 25.degree. C. to about 50.degree. C. below the grain
growth or incipient melting temperature of the base article 20.
Such embodiments may better preserve the desired microstructure of
the base article 20 during the heating process. In some
embodiments, the second alloy may comprise a compositional range
of, by weight, about 9 to 10% cobalt, 11 to 16% chromium, 3 to 4%
aluminum, 2.25 to 2.75% tantalum, 1.5 to 3.0% boron, up to 5%
silicon, up to 1.0% yttrium, the balance nickel and incidental
impurities. For example, in some embodiments the second alloy may
comprise commercially available Amdry DF4B nickel brazing alloy. It
should also be appreciated that while specific materials and
compositions have been listed herein for the composition of the
second alloy of the pre-sintered preform 30, these listed materials
and compositions are exemplary only and non-limiting and other
alloys may alternatively or additionally be used. Furthermore, it
should be appreciated that the particular composition of the second
alloy for the pre-sintered preform 30 may depend on the composition
of the base article 20.
[0029] The pre-sintered preform 30 can comprise any relative
amounts of the base alloy and the second alloy that are sufficient
to provide enough melting point depressant to ensure wetting and
bonding (e.g., diffusion/brazing bonding) of the particles of the
base alloy and the second alloy to each other and to the outer
surface 26 of the base article 20. For example, in some embodiments
the second alloy can comprise at least about 10 weight percent of
the pre-sintered preform 30. In some embodiments the second alloy
can comprise no more than 70 weight percent of the pre-sintered
preform 30. Such embodiments may provide a sufficient amount of
melting point depressant while limiting potential reduction of the
mechanical and environmental properties of the subsequent heating.
Furthermore, in these embodiments, the base alloy can comprise the
remainder of the pre-sintered preform 30 (e.g., between about 30
weight percent and about 70 weight percent of the pre-sintered
preform 30). In even some embodiments, the particles of the base
alloy can comprise about 40 weight percent to about 70 weight
percent of the pre-sintered preform 30 with the balance of the
composition comprising particles of the second alloy. It should be
appreciated that while specific relative ranges of the base alloy
and the second alloy have been presented herein, these ranges are
exemplary only and non-limiting and any other relative compositions
may also be realized such that a sufficient amount of melting point
depressant is provided as discussed above.
[0030] Aside from the particles of the base alloy and the second
alloy, no other constituents are required within the pre-sintered
preform 30. However, in some embodiments, a binder may be initially
blended with the particles of the base alloy and the second alloy
to form a cohesive mass that can be more readily shaped prior to
sintering. In such embodiments, the binder can include, for
example, a binder commercially available under the name NICROBRAZ-S
from the Wall Colmonoy Corporation. Other potentially suitable
binders include NICROBRAZ 320, VITTA GEL from Vitta Corporation,
and others including adhesives commercially available from
Cotronics Corporation, all of which may volatilize cleanly during
sintering.
[0031] The pre-sintered preform 30 may be formed by mixing the
powder particles of the base alloy (i.e., base alloy particles) and
the second alloy (i.e., second alloy particles) by any suitable
means such as stirring, shaking, rotating, folding or the like or
combinations thereof. After mixing, the mixture may be combined
with the binder (i.e., to form a combined powder mixture) and cast
into shapes (i.e., to form a compacted preform), during and/or
after which the binder can be burned off. The compacted preform may
then be placed in a non-oxidizing (vacuum or inert gas) atmosphere
furnace for the sintering operation, during which the powder
particles of the base alloy and the second alloy undergo sintering
to yield the pre-sintered preform 30 with good structural strength
and low porosity. Suitable sintering temperatures may at least in
part depend on the particular compositions of the particles of the
base alloy and the second alloy. For example, in some embodiments,
the sintering temperature may be in a range of about 1010.degree.
C. to about 1280.degree. C. In some embodiments, following
sintering, the pre-sintered preform 30 can be HIPed or vacuum
pressed to achieve densities greater than 95%.
[0032] In some embodiments, the pre-sintered preform 30 may
actually comprise a plurality of layers, each being attached to
each other before or after being connected to the base article 20.
In such embodiments, the plurality of layers may combine to form
the near-surface cooling microchannel 32 or a single layer may
comprise the near-surface cooling microchannel 32 while additional
layers are present for additional protection of the base article
20. Such embodiments may also allow for specific thermal properties
in different zones of the pre-sintered preform 30 to be
individually tailored. In even some embodiments, the pre-sintered
preform 30 may be combined with one or more metal layers or
sections. For example, the pre-sintered preform 30 may form the
sides of the near-surface cooling microchannel 32 while a thin
metal film closes off the top of the near-surface microchannel 32.
In such embodiments, the metal film may be bonded prior to, after
or while the pre-sintered preform 30 is bonded to the base article
20. Or, in some embodiments, the pre-sintered preform 30 may bond
with the base article 20 via one or more additional metal
layers.
[0033] The near-surface cooling microchannel 32 can be formed into
the first surface 36 of the pre-sintered preform 30 using a variety
of methods and at a variety of times in the manufacturing of the
pre-sintered preform 30. For example, in some embodiments, the
pre-sintered preform 30 may be sintered into a base shape so that
the near-surface cooling microchannel 32 can be subsequently
machined into the base shape. Such machining (i.e., the removal of
some material from the pre-sintered preform 30) can occur via any
suitable material removal operation including, but not limited to,
milling, grinding, wire electrical discharge machining (EDM),
milled EDM, plunge EDM, electro-chemical machining (ECM), waterjet
trenching, laser trenching, or combinations thereof. In other
embodiments, the pre-sintered preform 30 may be cast such that the
near-surface cooling microchannel 32 is present when the
pre-sintered preform 30 is still in its pliable green state before
its initial sintering.
[0034] Referring specifically to FIG. 3, in some embodiments the
component 10 may have at least one additional coating 40 on an
exterior surface (opposite the first surface 36) of the
pre-sintered preform 30. The coating 40 can comprise any type of
coating that may be suitable for component 10 when in operation
such as those that assist in thermal, mechanical, or other
performance. For example, in some embodiments, such as when the
component 10 comprises a hot gas path component for a turbine, the
coating 40 can comprise a thermal barrier coating and/or an
environmental barrier coating. Exemplary, but non-limiting coatings
40 include one or more bond coats, transition or intermediate
layers, and/or topcoats. Non-limiting materials for the coatings 40
include ceramic materials, a notable example of which is zirconia
partially or fully stabilized with yttria (YSZ) or another oxide
such as magnesia, ceria, scandia and/or calcia, and optionally
other oxides to reduce thermal conductivity. Bond coat materials
used in thermal barrier coating systems include oxidation-resistant
overlay coatings such as MCrAlX (where M is iron, cobalt and/or
nickel, and X is yttrium, a rare-earth metal, and/or another
reactive metal), and oxidation-resistant diffusion coatings.
[0035] The coating 40 can be deposited to a thickness that is
sufficient to provide a desired level of thermal protection for the
underlying surface region such as, for example, on the order of
about 75 to about 300 micrometers, though lesser and greater
thicknesses are also possible. The coating 40 can be applied to the
pre-sintered preform 30 prior to bonding the pre-sintered preform
30 to the base article 20, after bonding the pre-sintered preform
30 to the base article 20, or combinations thereof.
[0036] Referring to FIGS. 2 and 3, the first surface 36 of the
pre-sintered preform 30 is disposed on the outer surface 26 of the
base article 20 such that the opening 24 of the outer surface 26 of
the base article is aligned with the near-surface cooling
microchannel 32 in the first surface 36 of the pre-sintered preform
30. The alignment between the near-surface cooling microchannel 32
and the opening 24 can allow cooling air to flow between the
internal cooling passage 18 and the near-surface cooling
microchannel 32.
[0037] The pre-sintered preform 30 is bonded to the base article 20
by heating the pre-sintered preform 30, such as within a
non-oxidizing (vacuum or inert gas) atmosphere, to a temperature
capable of melting the particles comprising the second alloy (i.e.,
the lower melting particles) of the pre-sintered preform 30, such
as within a range of about 2050.degree. F. to about 2336.degree. F.
(about 1120.degree. C. to about 1280.degree. C.) (depending on
composition) for a period of about 10 to about 60 minutes. The
second alloy particles can then melt and wet the particles of the
base alloy and the outer surface 26 of the base article 20 thereby
creating a two-phase mixture that alloys together. Additionally, by
using the combination of the base alloy and the second alloy, the
pre-sintered preform 30 may not significantly close, if at all,
either the opening 24 in the outer surface 26 of the base article,
or the near-surface cooling microchannel 32 in the first surface 36
of the pre-sintered preform 30, or any exit passage(s) out of the
near-surface cooling microchannel 32. It should also be appreciated
that any type of heating may be utilized such as, but not limited
to induction heating, torches, ovens or any other source to
sufficiently bond the materials. In even some embodiments, the
heating may be achieved through friction welding such that the
heating process is more localized to the surface regions.
[0038] In some embodiments, a small amount of additional low melt
constituent material can be placed between the pre-sintered preform
30 and the base article 20 to increase brazement quality.
Thereafter, the base article 20 and the pre-sintered preform 30 are
cooled below the solidus temperature of the pre-sintered preform 30
to solidify the mixture and form the superalloy brazement. The
brazement can then undergo a heat treatment at a temperature of
about 1975.degree. F. to about 2100.degree. F. (about 1080.degree.
C. to about 1150.degree. C.) for a duration of about thirty minutes
to about four hours to further interdiffuse the particles of the
base alloy and the second alloy as well as the alloy of the base
article 20. After heat treatment, any excess material in the
brazement can be removed by grinding or any other suitable
method.
[0039] In some embodiments, a filler material (not illustrated) may
temporarily be disposed in the internal cooling passage 18 prior to
bonding the pre-sintered preform 30 to the base article 20 to
ensure the internal cooling passage 18 does not clog. Such filler
material may be disposed through any suitable means and comprise
any suitable material for temporarily stopping-off the internal
cooling passage 18. For example, the filler material may comprise a
material that does not melt when the pre-sintered preform 30 is
bonded to the base article 20, but that can subsequently be removed
via additional heating at a higher temperature, the application of
select chemicals or any other suitable method. Such embodiments may
be particularly suitable for smaller internal cooling passages 18
such as those with a diameter of 0.03 inches (0.762 millimeters) or
less.
[0040] Referring now to FIGS. 2-4, an exemplary method 100 (FIG. 4)
is illustrated for providing a near-surface cooling microchannel 32
in a component 10. The method first comprises forming the
near-surface cooling microchannel 32 in the first surface 36 of the
pre-sintered preform 30 in step 110. As discussed above, the
near-surface cooling microchannel 32 can be machined into an
already sintered pre-sintered preform 30 or cast into the
pre-sintered preform 30 when it is still in its pliable green
state.
[0041] The method 100 further comprises disposing the first surface
36 of the pre-sintered preform 30 onto the outer surface 26 of the
base article 20 in step 120. Specifically, the pre-sintered preform
30 is disposed such that the opening 24 of the outer surface 26 of
the base article 20 is aligned with the near-surface cooling
microchannel 32 in the first surface 36 of the pre-sintered preform
30. Finally, the method comprises heating the pre-sintered preform
30 to bond it to the base article 20 in step 130. The bonding
occurs such that the opening 24 of the outer surface 26 of the base
article 20 remains aligned with the near-surface cooling
microchannel 32 in the first surface 36 of the pre-sintered preform
30. As discussed above, heating can occur for any temperature or
range of temperatures and for any time to sufficiently bond the
pre-sintered preform 30 to the base article 20. Furthermore,
bonding in step 130 can be achieved through any suitable means such
as heating the pre-sintered preform through induction heating,
friction welding or the like.
[0042] It should now be appreciated that a near-surface cooling
microchannel 32 can be formed into components by first
manufacturing them into a pre-sintered preform and then bonding the
pre-sintered preform to a base article. The internal cooling
passage of the base article can thereby connect to the near-surface
cooling microchannel to allow there passage of cooling air to flow
there between. By manufacturing the near-surface cooling
microchannel into the pre-sintered preform, the manufacturing
difficulty of machining such small channels into the tough
component material may be relieved. Moreover, by using pre-sintered
preforms, the bonding of the pre-sintered preform to the base
article will not significantly, if at all, close either the opening
of the near-surface cooling microchannel.
[0043] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
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