U.S. patent application number 13/402565 was filed with the patent office on 2012-06-14 for composition and method for a thermal coating system.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Jane Ann Murphy, Andrew Jay Skoog.
Application Number | 20120148834 13/402565 |
Document ID | / |
Family ID | 43302408 |
Filed Date | 2012-06-14 |
United States Patent
Application |
20120148834 |
Kind Code |
A1 |
Skoog; Andrew Jay ; et
al. |
June 14, 2012 |
COMPOSITION AND METHOD FOR A THERMAL COATING SYSTEM
Abstract
A thermal coating includes a substrate, a first coating layer,
and a second coating layer. The substrate is selected from the
group consisting of superalloys and ceramic matrix composites. The
first coating layer comprises an alumina powder, a silica binder,
and at least one additive selected from either a first group or a
second group. The second coating layer comprises at least one of
zinc titanate or cerium oxide. A method for applying a thermal
coating system includes spraying a bond coat mixture onto a
substrate using a liquid electrostatic sprayer. The bond coat
mixture comprises an alumina powder, a silica binder, and at least
one additive selected from either a first group or a second group.
The method further includes applying a top coat mixture onto the
bond coat mixture, wherein the top coat mixture comprises at least
one of zinc titanate or cerium oxide.
Inventors: |
Skoog; Andrew Jay; (West
Chester, OH) ; Murphy; Jane Ann; (Franklin,
OH) |
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
43302408 |
Appl. No.: |
13/402565 |
Filed: |
February 22, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12562527 |
Sep 18, 2009 |
8147922 |
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13402565 |
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Current U.S.
Class: |
428/334 ;
428/332; 428/448 |
Current CPC
Class: |
Y10T 428/264 20150115;
C23C 4/18 20130101; Y10T 428/263 20150115; Y10T 428/26 20150115;
C04B 41/52 20130101; C23C 24/00 20130101; C23C 4/12 20130101; Y02T
50/67 20130101; Y02T 50/60 20130101; B05B 5/043 20130101; C04B
41/89 20130101; Y10T 428/265 20150115; C04B 41/009 20130101; Y02T
50/6765 20180501; C04B 41/009 20130101; C04B 35/80 20130101; C04B
41/52 20130101; C04B 41/4543 20130101; C04B 41/4568 20130101; C04B
41/5031 20130101; C04B 41/5089 20130101; C04B 41/52 20130101; C04B
41/5041 20130101; C04B 2103/002 20130101; C04B 41/52 20130101; C04B
41/5045 20130101; C04B 41/522 20130101 |
Class at
Publication: |
428/334 ;
428/448; 428/332 |
International
Class: |
B32B 18/00 20060101
B32B018/00; B32B 33/00 20060101 B32B033/00; B32B 15/04 20060101
B32B015/04 |
Claims
1. A thermal coating system, comprising: a. a substrate selected
from the group consisting of superalloys and ceramic matrix
composites; b. a first coating layer applied to the substrate,
wherein the first coating layer comprises: i. an alumina powder;
ii. a silica binder; and iii. at least one additive selected from
either a first group or a second group, wherein 1. the first group
consists of toluene, xylene, cellosolve acetate, EE acetate, and
mineral spirits; and 2. the second group consists of methyl ethyl
ketone, methyl isobutyl ketone, lacquer thinner, and acetone; and
c. a second coating layer applied to the first coating layer,
wherein the second coating layer comprises at least one of zinc
titanate or cerium oxide.
2. The thermal coating system of claim 1, wherein the first coating
layer has a thickness of less than 0.004 inches.
3. The thermal coating system of claim 1, wherein the second
coating layer has a thickness of between 0.001 inches and 0.010
inches.
4. The thermal coating system of claim 1, wherein the first coating
layer is applied directly to the substrate.
5. The thermal coating system of claim 1, further including an
undercoat layer applied between the first coating layer and the
substrate, wherein the undercoat layer comprises an alumina powder
and a silica binder.
6. The thermal coating system of claim 5, wherein the undercoat
layer has a thickness of between 0.001 inches and 0.008 inches.
7-19. (canceled)
20. A thermal coating system, comprising: a. a substrate selected
from the group consisting of superalloys and ceramic matrix
composites; b. a first coating layer applied to the substrate,
wherein the first coating layer comprises an alumina powder, a
silica binder, and at least one additive selected from the group of
toluene, xylene, cellosolve acetate, EE acetate, and mineral
spirits; and c. a second coating layer applied to the first coating
layer, wherein the second coating layer comprises at least one of
zinc titanate or cerium oxide.
21. The thermal coating system of claim 20, wherein the first
coating layer has a thickness of less than 0.004 inches.
22. The thermal coating system of claim 20, wherein the second
coating layer has a thickness of between 0.001 inches and 0.010
inches.
23. The thermal coating system of claim 20, wherein the first
coating layer is applied directly to the substrate.
24. The thermal coating system of claim 20, further including an
undercoat layer applied between the first coating layer and the
substrate, wherein the undercoat layer comprises an alumina powder
and a silica binder.
25. The thermal coating system of claim 24, wherein the undercoat
layer has a thickness of between 0.001 inches and 0.008 inches.
26. A thermal coating system, comprising: a. a substrate selected
from the group consisting of superalloys and ceramic matrix
composites; b. a first coating layer applied to the substrate,
wherein the first coating layer comprises an alumina powder, a
silica binder, and at least one additive selected from the group of
methyl ethyl ketone, methyl isobutyl ketone, lacquer thinner, and
acetone; and c. a second coating layer applied to the first coating
layer, wherein the second coating layer comprises at least one of
zinc titanate or cerium oxide.
27. The thermal coating system of claim 26, wherein the first
coating layer has a thickness of less than 0.004 inches.
28. The thermal coating system of claim 26, wherein the second
coating layer has a thickness of between 0.001 inches and 0.010
inches.
29. The thermal coating system of claim 26, wherein the first
coating layer is applied directly to the substrate.
30. The thermal coating system of claim 26, further including an
undercoat layer applied between the first coating layer and the
substrate, wherein the undercoat layer comprises an alumina powder
and a silica binder.
31. The thermal coating system of claim 30, wherein the undercoat
layer has a thickness of between 0.001 inches and 0.008 inches.
Description
FIELD OF THE INVENTION
[0001] The present invention pertains to thermal barrier coatings
applied to protect components in high temperature environments. In
particular, the present invention describes a composition and
method for applying a thermal coating system.
BACKGROUND OF THE INVENTION
[0002] Systems located or operated in high temperature environments
often include thermal barrier coatings (TBCs) on components to
reflect heat and prevent the components from absorbing heat. For
example, jet engines and gas turbines include combustors and
turbines designed to operate in very demanding high temperature and
pressure environments. As a result, many components, such as
combustor liners, turbine blades, turbine casings, and rotors
routinely operate in high temperature environments that approach or
exceed the melting temperature of the constituent elements included
in the components. A TBC applied to the surface of these components
allows the components to operate at increasingly higher
temperatures and/or with increased intervals between maintenance
cycles.
[0003] The underlying components are typically designed to operate
for extended periods in the structurally demanding high temperature
and/or pressure environments. Superalloys such as Rene 80, Rene N4,
and other nickel-based superalloys are commonly used in the
underlying components. These superalloys may contain, by weight
percent, 10 to 80 percent nickel, 5 to 22 percent chromium, up to
10 percent molybdenum, up to 5.5 percent titanium, up to 6.5
percent aluminum, up to 3 percent columbium, up to 9 percent
tantalum, up to 15 percent tungsten, up to 2 percent hafnium, up to
1 percent rhenium, up to 1.5 percent vanadium, up to 40 percent
cobalt, and up to 6 percent iron.
[0004] Ceramic matrix composites (CMCs) may also be selected for
use in the underlying components. Examples of commonly used CMCs
include zirconia-based ceramics, alumina-based ceramics,
magnesia-based ceramics, and ceramic composites such as
alumina-silica (GE Gen 4), or a refractory material with, for
example, silicon carbide, silicon nitride, alumina, silica, and/or
calcia.
[0005] A suitable TBC applied to the underlying component should
include one or more of the following characteristics: low
emissivity or high reflectance for heat, particularly infrared heat
having a wavelength of 0.5 to 60 micrometers; a smooth finish; and
good adhesion to the underlying component. For example, thermal
bather coatings known in the art include metal oxides, such as
zirconia (ZrO.sub.2), partially or fully stabilized by yttria
(Y.sub.2O.sub.3), magnesia (MgO), or other noble metal oxides. The
selected TBC may be deposited by conventional methods using air
plasma spraying (APS), low pressure plasma spraying (LPPS), or a
physical vapor deposition (PVD) technique, such as electron beam
physical vapor deposition (EBPVD), which yields a strain-tolerant
columnar grain structure. The selected TBC may also be applied
using a combination of any of the preceding methods to form a tape
which is subsequently transferred for application to the underlying
substrate, as described, for example, in U.S. Pat. No. 6,165,600,
assigned to the same assignee as the present invention.
[0006] The thermal barrier coatings described above have
coefficients of thermal expansion that are significantly lower than
the coefficients of thermal expansion of the underlying components.
As a result, cyclic thermal stresses incident to repetitive heating
and cooling of the system components disrupts the adhesion between
the TBC and the underlying substrate, leading to .sub.Tailing of
the coating system.
[0007] A bond coat may be used between the TBC and the underlying
substrate to improve the adhesion between the TBC and the
underlying substrate. The bond coat may be formed from an
oxidation-resistant diffusion coating such as a diffusion aluminide
or platinum alumiminide, or an oxidation-resistant alloy such as
MCrAlY (where M is iron, cobalt and/or nickel). Aluminide coatings
are distinguished from MCrAlY coatings, in that the former are
intermetallics, while the latter are metallic solid solutions. U.S.
Pat. No. 6,210,791, assigned to the same assignee as the present
invention, describes one such bond coat applied between the TBC and
the underlying substrate that substantially improves adhesion
between the TBC and the underlying substrate. The bond described
therein is an alumina and silica mixture in an alcohol solvent.
[0008] The thermal barrier coatings, with our without a bond coat
to improve adhesion, typically require some type of
post-application drying or heating at 500 to 2000 degrees
Fahrenheit to sinter and/or stabilize the coating system. The
application and post-application curing produces volatile organic
compounds (VOCs) which may exceed current environmental, health,
and safety limits for VOC emissions. To reduce VOC emissions during
the application and post-application curing, the thickness of the
TBC and/or bond coat may be reduced. However, the thinner TBC
and/or bond coat results in a corresponding decrease in the thermal
reflection of the thermal barrier.
[0009] Therefore, the need exists for an improved thermal coating
system to protect system components from excessive heat. Ideally,
the thermal coating system will have low emissivity or high
reflectance for heat, particularly infrared heat having a
wavelength of 0.5 to 60 micrometers. In addition, the thermal
coating system should be able to be easily applied so as to produce
a smooth finish surface that adheres to the underlying substrate
component without producing excessive VOCs during the application
or post-application curing.
BRIEF DESCRIPTION OF THE INVENTION
[0010] Aspects and advantages of the invention are set forth below
in the following description, or may be obvious from the
description, or may be learned through practice of the
invention.
[0011] One embodiment of the present invention is a thermal coating
system. The thermal coating system includes a substrate, a first
coating layer applied to the substrate, and a second coating layer
applied to the first coating layer. The substrate is selected from
the group consisting of superalloys and ceramic matrix composites.
The first coating layer comprises an alumina powder, a silica
binder, and at least one additive selected from either a first
group or a second group. The first group consists of toluene,
xylene, cellosolve acetate, EE acetate, and mineral spirits. The
second group consists of methyl ethyl ketone, methyl isobutyl
ketone, lacquer thinner, and acetone. The second coating layer
comprises at least one of zinc titanate or cerium oxide.
[0012] Another embodiment of the present invention is a method for
applying a thermal coating system. The method includes applying a
first charge to a bond coat mixture, wherein the bond coat mixture
comprises an alumina powder, a silica binder, and at least one
additive selected from either a first group or a second group. The
first group consists of toluene, xylene, cellosolve acetate, EE
acetate, and mineral spirits. The second group consists of methyl
ethyl ketone, methyl isobutyl ketone, lacquer thinner, and acetone.
The method further includes applying a second charge to a
substrate, wherein the second charge has an opposite polarity of
the first charge, and spraying the bond coat mixture onto the
substrate. The method also includes applying a top coat mixture
onto the bond coat mixture, wherein the top coat mixture comprises
at least one of zinc titanate or cerium oxide.
[0013] A further embodiment of the present invention is a method
for applying a thermal coating system that includes spraying a bond
coat mixture onto a substrate using a liquid electrostatic sprayer.
The bond coat mixture comprises an alumina powder, a silica binder,
and at least one additive selected from either a first group or a
second group. The first group consists of toluene, xylene,
cellosolve acetate, EE acetate, and mineral spirits. The second
group consists of methyl ethyl ketone, methyl isobutyl ketone,
lacquer thinner, and acetone. The method further includes applying
a top coat mixture onto the bond coat mixture, wherein the top coat
mixture comprises at least one of zinc titanate or cerium
oxide.
[0014] Those of ordinary skill in the art will better appreciate
the features and aspects of such embodiments, and others, upon
review of the specification.
BRIEF DESCRIPTION OF TUE DRAWINGS
[0015] A full and enabling disclosure of the present invention,
including the best mode thereof to one skilled in the art, is set
forth more particularly in the remainder of the specification,
including reference to the accompanying figures, in which:
[0016] FIG. 1 provides a cross-sectional view of one embodiment of
a coating system within the scope of the present invention;
[0017] FIG. 2 illustrates liquid electrostatic spraying of a
coating system within the scope of the present invention; and
[0018] FIG. 3 is a graph of the reflective performance of one
embodiment of a thermal barrier coating system within the scope of
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Reference will now be made in detail to present embodiments
of the invention, one or more examples of which are illustrated in
the accompanying drawings. The detailed description uses numerical
and letter designations to refer to features in the drawings. Like
or similar designations in the drawings and description have been
used to refer to like or similar parts of the invention.
[0020] Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that modifications and
variations can be made in the present invention without departing
from the scope or spirit thereof. For instance, features
illustrated or described as part of one embodiment may be used on
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0021] FIG. 1 shows a cross-sectional view of a thermal coating
system 10 applied to a substrate 12 according to one embodiment of
the present invention. In this particular embodiment, the thermal
coating system 10 includes first and second coating layers referred
to respectively as a bond coat mixture 14 and a top coat mixture
16.
[0022] The substrate 12 may be any material composition suitable
for use in a high temperature environment. For example, superalloys
and ceramic matrix composites as previously described are
frequently selected for use in high temperature environments
because of their suitable strength, ductility, and other physical
characteristics.
[0023] The first layer or bond coat mixture 14 is applied to the
substrate 12 and provides tight adhesion between the substrate 12
and any additional layers. The bond coat mixture 14 may be a
modification of the bond coat described in U.S. Pat. No. 6,210,791,
the entirety of which is herein incorporated by reference for all
purposes. As described therein, the bond coat mixture 14 may be
metallic, non-metallic, or a combination thereof, depending on the
underlying substrate, and may include alumina powder, such as
aluminum oxide, with a silica binder. An evaporable solvent,
typically ethanol or isopropyl alcohol, is added to the bond coat
mixture 14 to achieve the desired consistency. A suitable thickness
for the bond coat mixture 14 may be approximately 0.5 to 8 mils
(0.0005-0.008 inches), depending on the method of application and
design needs.
[0024] To reduce the amount of VOCs generated during the
application and drying, the bond coat mixture 14 may be applied
using liquid electrostatic spraying (LES) techniques. In LES
applications, an electrical charge is applied to the material being
deposited, and a ground or opposite electrical charge is applied to
the substrate. The charged material is then sprayed onto the
substrate, and the polar attraction between the charged material
and the substrate results in an increased deposit efficiency of the
material onto the substrate with significantly less overspray and
waste. The increased deposit efficiency produces a more uniform
coverage, allowing the application of thinner layers of the
material to the substrate to provide the same or better
performance. As a result, LES applications provide significant cost
savings of materials compared to conventional application
techniques. In addition, the thinner application of the materials
results in lower VOC emissions during both the application and the
subsequent curing.
[0025] The electrical conductivity of the bond coat mixture 14 may
need to be adjusted to obtain a desired particle size that allows
the use of LES and improves the deposit efficiency. Additives such
as toluene, xylene, cellosolve acetate, EE acetate, and mineral
spirits may be added to the bond coat mixture 14 to make the
mixture less electrically conductive and prevent agglomeration of
the bond coat mixture 14 during spraying. Conversely, additives
such as methyl ethyl ketone (MIEK), methyl isobutyl ketone (MIBK),
lacquer thinner, and acetone may be added to the bond coat mixture
14 to make the mixture more electrically conductive.
[0026] FIG. 2 illustrates an application of the bond coat mixture
14 using LES. A powder spray gun 18, such as a Nordson Kinetix air
spray system sold by Nordson Corporation, Westlake, Ohio, includes
a nozzle 20 with an electrode 22. An opposite charge or ground 24
is applied to a substrate 26. As the spray gun 18 propels the bond
coat mixture 14 through the nozzle 20, the electrode 22 applies an
electrical charge to the bond coat mixture 14. The charged bond
coat mixture 14 flows to the oppositely charged or grounded
substrate 26 where the polar attraction between the charged bond
coat mixture 14 and substrate 26 deposits the bond coat mixture 14
uniformly on a surface 28 of the substrate 26. The magnitude of the
electrical potential between the charged bond coat mixture 14 and
the oppositely charged substrate 26 may be adjusted to increase or
decrease the deposition rate on the substrate surface 28, depending
on the desired thickness of the application.
[0027] The use of nano-sized particles as the constituent elements
in the bond coat mixture 14 further improves the benefits of LES.
For example, LES application of nano-sized particles having an
average diameter of less than approximately 500 nanometers may
readily achieve uniform thicknesses of the bond coat mixture 14 as
low as approximately 0.5 mils (0.0005 inches). A thinner
application of the bond coat mixture 14 produces several benefits.
For example, a thinner bond coat mixture 14 will have a
correspondingly smaller change in temperature across the bond coat
mixture 14, resulting in better adhesion to the substrate 26. In
addition, the nano-sized particles will produce a more tightly
packed and dense layer that increases the resistance of the bond
coat mixture 14 to erosion.
[0028] Referring back to FIG. 1, the thinner application of the
bond coat mixture 14 using LES may not adequately cover all
imperfections 30 in the surface 32 of the substrate 12. As a
result, an additional undercoat layer (not shown) may be included
between the bond coat mixture 14 and the substrate 12. The
undercoat layer may comprise the same bond coat as previously
described in U.S. Pat. No. 6,210,791. That is, the undercoat layer
may comprise an alcohol mixture of alumina powder, such as aluminum
oxide, with a silica binder. The undercoat layer may be applied
using conventional application techniques known in the art. For
example, the undercoat layer may be applied as a slurry spray,
using air plasma spraying (APS), low pressure plasma spraying
(LPPS), or physical vapor deposition (PVD) techniques such as
electron beam physical vapor deposition (EBPVD). If needed, the
undercoat layer is applied to a thickness of approximately 1 to 8
mils (0.001-0.008 inches) to fill in any imperfections 30 in the
surface 32 of the substrate 12. For applications in which the
substrate surface 32 is sufficiently smooth, the undercoat layer
may be reduced in thickness or omitted entirely.
[0029] The top coat mixture 16 is located on top of the bond coat
mixture 14. The combination of the bond coat mixture 14 and top
coat mixture 16 provides the desirable smooth, wear, and reflective
characteristics of the thermal coating system 10. Specifically, a
smooth outermost surface of the thermal coating system 10 promotes
improved aerodynamics across the surface which may be important in
various applications. The surface roughness of the top coat mixture
16 is preferably less than approximately 60 micrometers Ra and
potentially less than 20 micrometers Ra. In addition, the bond coat
mixture 14 tightly adheres the top coat mixture 16 to the substrate
12 to resist wear or spalling even after numerous thermal cycles.
Lastly, the top coat mixture 16 possesses the desired reflectance
characteristics, particularly for infrared heat having a wavelength
between 0.5 and 60 micrometers, to protect the substrate 12 from
heat in a high temperature environment.
[0030] The top coat mixture 16 may be comprised of zinc titanate or
cerium oxide to provide the desired heat reflectance
characteristics of the thermal coating system 10. Suitable
substitutes that may also provide the desired heat reflectance
characteristics include barium titanate, yttrium oxide, dysprosium
oxide, erbium oxide, europium, lanthanum oxide, lutetium oxide,
thorium oxide, tungsten oxide, barium stannate, and barium
tungstate, many of which may be supplied by Nano-Tek Technologies,
Ltd.
[0031] The top coat mixture 16 may be applied using conventional
application techniques known in the art. For example, the top coat
mixture 16 may be wetted and layered on top of the bond coat
mixture 14 as a slurry spray, using air plasma spraying (APS), low
pressure plasma spraying (LPPS), or physical vapor deposition (PVD)
techniques such as electron beam physical vapor deposition (EBPVD).
The thickness of the top coat mixture 16 depends on the desired
heat reflectance and application method and typically ranges from
approximately 1 to 10 mils (0.001-0.010 inches).
[0032] In particular embodiments of the present invention, the
thermal coating system 10 may be applied to the substrate 12 using
a tape process as described in U.S. Pat. No. 6,165,600 and assigned
to the same assignee as the present invention. In this process,
compositions of the bond coat mixture 14 and/or top coat mixture 16
and/or optional undercoat layer as described above may be cast on a
tetrafluoroethylene sheet. After the solvent evaporates from the
compositions, the dried compositions are removed from the
tetrafluoroethylene sheet and transferred to the substrate 12 to
form the thermal coating system 10. Pressure may then be applied to
the thermal coating system 10 to mechanically bond the thermal
coating system 10 to the substrate 12.
[0033] Regardless of the application method, whether directly onto
the substrate 12 or using the tape process as previously described,
the thermal coating system 10 may be heated or cured after
application to the substrate 12. An autoclave, oven, or similar
device may be used to heat the thermal coating system 10 at a
temperature of between 500 and 2,000 degrees Fahrenheit. The heat
removes the binders and remaining solvent and sinters the thermal
coating system layers 14, 16. The sintering forms both chemical and
mechanical bonds both in the thermal coating system layers 14, 16
and with the substrate 12. Alumina in the substrate 12 mixes with
the molten bond coat mixture 14 and raises the melting point of the
thermal coating system 10. The melting point of the resulting
thermal coating system 10 may thus be increased from approximately
1,500 degrees Fahrenheit to approximately 1,950 degrees Fahrenheit
or higher, depending upon the actual composition of the substrate
12. The increased melting point of the thermal coating system 10
allows the substrate to be exposed to higher temperatures, which,
for jet engine and gas turbine applications, typically produces
increased thermodynamic efficiency.
[0034] The duration of the heating varies from approximately 30
minutes to several hours, depending on the composition of the
substrate 12, bond coat mixture 14, and top coat mixture 16. For
example, FIG. 3 provides a graph of the reflective performance of
one embodiment of a thermal barrier thermal coating system within
the scope of the present invention. In this embodiment, the bond
coat mixture 14 was cast on a tetrafluoroethylene sheet and
transferred as a tape to the substrate 12. The top coat mixture 16
was then sprayed onto the bond coat mixture 14, and the combination
was then heated at 1,650 degrees Fahrenheit for approximately 1
hour. The graph provided in FIG. 3 shows the resulting reflectance
values for heat applied at various angles to the substrate.
[0035] It should be appreciated by those skilled in the art that
modifications and variations can be made to the embodiments of the
invention set forth herein without departing from the scope and
spirit of the invention as set forth in the appended claims and
their equivalents.
* * * * *