U.S. patent application number 12/850343 was filed with the patent office on 2011-02-10 for techniques for depositing coating on ceramic substrate.
This patent application is currently assigned to Rolls-Royce Corporation. Invention is credited to Subhash K. Naik, Raymond J. Sinatra.
Application Number | 20110033630 12/850343 |
Document ID | / |
Family ID | 43003822 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110033630 |
Kind Code |
A1 |
Naik; Subhash K. ; et
al. |
February 10, 2011 |
TECHNIQUES FOR DEPOSITING COATING ON CERAMIC SUBSTRATE
Abstract
A method of coating a substrate, the method including depositing
mullite on the substrate during a first time period via thermal
spraying to form a first layer, the mullite comprising mullite
powder formed via at least one of a fused plus crush or sinter plus
crush process; and depositing a second material on the first layer
to form a second layer, wherein the substrate is at a temperature
less than approximately 50 degrees Celsius at approximately a
beginning of the first time period. In some embodiments, the method
may further include depositing silicon to form a silicon bond layer
between the substrate and mullite layer.
Inventors: |
Naik; Subhash K.; (Carmel,
IN) ; Sinatra; Raymond J.; (Indianapolis,
IN) |
Correspondence
Address: |
SHUMAKER & SIEFFERT, P. A.
1625 RADIO DRIVE, SUITE 300
WOODBURY
MN
55125
US
|
Assignee: |
Rolls-Royce Corporation
Indianapolis
IN
|
Family ID: |
43003822 |
Appl. No.: |
12/850343 |
Filed: |
August 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61231510 |
Aug 5, 2009 |
|
|
|
Current U.S.
Class: |
427/452 |
Current CPC
Class: |
C23C 28/00 20130101;
C23C 4/02 20130101; C23C 10/60 20130101; C04B 41/52 20130101; C04B
41/009 20130101; C04B 41/52 20130101; C04B 41/52 20130101; C04B
41/009 20130101; C04B 41/52 20130101; C23C 26/00 20130101; C04B
41/009 20130101; C23C 4/18 20130101; C04B 41/009 20130101; C23C
28/04 20130101; C04B 35/565 20130101; C04B 41/522 20130101; C04B
35/584 20130101; C04B 35/806 20130101; C04B 41/5096 20130101; C04B
41/5031 20130101; C04B 41/5037 20130101; C04B 41/5037 20130101;
C04B 35/806 20130101; C04B 41/4527 20130101; C04B 41/0072 20130101;
C04B 41/5024 20130101; C04B 41/4527 20130101; C04B 41/4527
20130101; C04B 41/4527 20130101; C04B 41/4527 20130101; C04B
41/5024 20130101; C04B 41/89 20130101; C04B 41/52 20130101; C04B
35/597 20130101; C04B 41/52 20130101 |
Class at
Publication: |
427/452 |
International
Class: |
C23C 4/10 20060101
C23C004/10; C23C 4/12 20060101 C23C004/12 |
Claims
1. A method of coating a substrate, the method comprising:
depositing mullite on the substrate during a first time period via
thermal spraying to form a first layer, the mullite comprising
mullite powder formed via at least one of a fused plus crush or
sinter plus crush process; and depositing a second material on the
first layer to form a second layer, wherein the substrate is at a
temperature less than approximately 50 degrees Celsius at
approximately a beginning of the first time period.
2. The method of claim 1, wherein the temperature of the substrate
is less than approximately 40 degrees Celsius at approximately the
beginning of the first time period.
3. The method of claim 1, further comprising maintaining the
substrate at a temperature less than approximately 200 Celsius
throughout the first time period.
4. The method of claim 1, wherein the first layer comprises
crystalline mullite substantially immediately following the
deposition of the mullite.
5. The method of claim 1, further comprising depositing silicon on
the substrate to form a silicon layer before depositing the mullite
on the substrate.
6. The method of claim 5, further comprising heat treating the
silicon layer prior to depositing the mullite.
7. The method of claim 6, wherein heat treating the silicon layer
comprises heat treating the silicon layer at a temperature of about
800 degrees Celsius to about 1250 degrees Celsius for about 0.2
hours to about 4 hours.
8. The method of claim 1, wherein the second layer comprises at
least one of barium strontium aluminum silicate (BSAS), ytterbium
mono-silicate or ytterbium di-silicate.
9. The method of claim 1, wherein the first layer has a thickness
of approximately 1 mil to approximately 6 mils.
10. The method of claim 1, wherein the second layer has a thickness
of approximately 2 mils to approximately 15 mils.
11. The method of claim 1, wherein the substrate is not heated via
a furnace during the deposition of the mullite in a manner that
substantially raises the substantially uniform temperature of the
substrate in conjunction with the deposition of the mullite.
12. The method of claim 1, wherein thermal spraying comprises
plasma spraying.
13. The method of claim 1, further comprising depositing silicon on
the substrate to form a silicon layer before depositing the mullite
on the substrate, wherein the silicon layer thickness is
approximately 0.5 mils to approximately 5 mils.
14. A method of coating a substrate, the method comprising:
depositing silicon on the substrate to form a silicon layer; heat
treating the silicon layer; and depositing mullite on the silicon
layer via thermal spraying to form a first layer subsequent to the
heat treatment of the silicon layer, the mullite comprising mullite
powder formed via at least one of a fused plus crush or sinter plus
crush process.
15. The method of claim 14, wherein the mullite is deposited on the
silicon layer during a first time period and the substrate is at a
temperature less than approximately 50 degrees Celsius at
approximately a beginning of the first time period.
16. The method of claim 14, wherein the heat treatment comprises
heat treating the silicon layer at a temperature of about 800
degrees Celsius to about 1250 degrees Celsius for about 0.2 hours
to about 4 hours.
17. The method of claim 14, further comprising depositing a second
material on the first layer to form a second layer, the second
layer comprising at least one of at least one of barium strontium
aluminum silicate (BSAS) or a rare-earth silicate.
18. The method of claim 14, further comprising: depositing a second
material on the first layer to form an intermediate layer; and
depositing a third material on the intermediate layer to form a
third layer.
19. The method of claim 18, wherein the intermediate layer
comprises approximately 20 to approximately 50 weight percent
mullite and at least one of ytterbium di-silicate and ytterbium
mono-silicate, and the third layer comprises one of ytterbium
di-silicate and ytterbium mono-silicate.
20. The method of claim 18, wherein the intermediate layer
comprises ytterbium di-silicate and the third layer comprises
ytterbium mono-silicate.
Description
[0001] This application claims priority from U.S. Provisional
Application Ser. No. 61/231,510 entitled "TECHNIQUES FOR DEPOSITING
COATING ON CERAMIC SUBSTRATE," filed Aug. 5, 2009, the entire
content of which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The disclosure relates to coatings for high-temperature
mechanical systems, such as gas turbine engines, and more
particularly to coatings including one or more mullite layers.
BACKGROUND
[0003] The components of high-temperature mechanical systems, such
as, for example, gas-turbine engines, must operate in severe
environments. For example, hot section components of gas turbine
engines, e.g., turbine blades and/or vanes, exposed to hot gases in
commercial aeronautical engines may experience surface temperatures
of greater than 1,000.degree. C. Furthermore, economic and
environmental concerns, e.g., the desire for improved efficiency
and reduced emissions, continue to drive the development of
advanced gas turbine engines with higher gas inlet temperatures. As
the turbine inlet temperature continues to increase, there is a
demand for components capable of operating at such high
temperatures.
[0004] Components of high-temperature mechanical systems may
include ceramic and/or superalloy substrates. Coatings for such
substrates continue to be developed to increase the operating
capabilities of such components and may include thermal barrier
coatings (TBC) and environmental barrier coatings (EBC). In some
examples, thermal barrier coatings (TBC) may be applied to
substrates to increase the temperature capability of a component,
e.g., by insulating a substrate from a hot external environment.
Further, environmental barrier coatings (EBC) may be applied to
ceramic substrates, e.g., silicon-based ceramics, to provide
environmental protection to the substrate. For example, an EBC may
be applied to a silicon-based ceramic or ceramic composite
substrate to protect against the recession of the ceramic substrate
resulting from operation in the presence of water vapor in a high
temperature combustion environment. In some cases, an EBC may also
function as a TBC based on low thermal conductivity values of the
EBC, although a separate compatible TBC may also be added to a
substrate in addition to an EBC to further increase the temperature
capability of a component.
SUMMARY
[0005] In general, the disclosure relates to techniques for
depositing one or more materials on a substrate to form layers that
make up a coating. Such techniques may be applicable to the
depositions of a coating on ceramic or ceramic composite
substrates, which in most cases may function as an environmental
barrier coating (EBC) e.g., when applied to ceramic components of
high temperature mechanical systems. In some cases, an EBC may
include a silicon bond layer, an intermediate layer containing
mullite (3Al.sub.2O.sub.3.2SiO2) and an outer layer. The
mullite-containing layer may be formed by depositing mullite powder
on the ceramic substrate. In some embodiments, mullite powder may
be deposited on a ceramic substrate via thermal spraying, e.g., air
plasma spraying, to form a layer including the deposited mullite.
The outer layer may be formed by depositing a second material on
the mullite-containing layer. In some embodiments, the second
material may include barium strontium aluminum silicate (BSAS) or
one or more rare-earth silicates, such as Yb-monosilicate or
Yb-disilicate.
[0006] According to some embodiments of the disclosure, mullite
powder may be deposited on a ceramic substrate via thermal spraying
to form a mullite-based layer of an EBC in a low temperature
environment. For example, a ceramic substrate may be at a
substantially uniform temperature of less than 50 degrees Celsius
at least at the beginning of the mullite deposition process. Such a
temperature limit may correspond to conditions achievable without
providing supplemental heat to a ceramic substrate, as may be the
case in a thermal spraying while the substrate is in a furnace
and/or the use of back side heating during the mullite deposition
process. Despite the low temperature environment in which the
thermal spraying of the mullite powder takes place, the mullite
layer formed from the deposition may perform substantially the same
or even better than mullite layers formed by depositing mullite via
thermal spraying in a higher temperature environment, e.g., those
associated with the use of furnace deposition and/or back-side
heating of the substrate.
[0007] As will be described in further detail below, mullite powder
that has been manufactured by a fused or sinter plus crush process,
e.g., rather than that manufactured by a spray granulation process,
may allow for the thermal spraying of mullite powder in a low
temperature environment to form a mullite layer that perform
substantially the same or even better than mullite layers formed
via thermal spraying of mullite powder in a higher temperature
environment. For example, mullite powder manufactured by a fused
plus crush or sinter plus crush process may be thermally sprayed on
ceramic substrates starting at a time when the substrate
temperatures is less than 50 degrees Celsius to form a
mullite-containing layer that performs adequately at high
temperatures without exhibiting substantial cracking or
delamination during thermal cycling, even without heat treating the
mullite layer after its formation.
[0008] Techniques for forming an EBC that includes a silicon bond
layer applied between a ceramic substrate and a mullite layer are
also described. Such a silicon bond layer may be formed by
depositing appropriate silicon material on a ceramic substrate
prior to the deposition of the mullite material via thermal
spraying. In some embodiments, the silicon bond layer may undergo a
high temperature heat treatment for a relatively short amount of
time, e.g., approximately 1 hour at about 1200 degrees Celsius,
prior to the deposition of the mullite material on the silicon bond
layer via thermal spraying. Such a technique may promote adhesion
between the silicon bond layer and the ceramic substrate to enhance
the adhesion of the EBC system to the ceramic substrate.
[0009] In one embodiment, the disclosure is directed to a method of
coating a substrate comprising depositing mullite on the substrate
during a first time period via thermal spraying to form a first
layer, the mullite comprising mullite powder formed via at least
one of a fused plus crush or sinter plus crush process; and
depositing a second material on the first layer to form a second
layer, wherein the substrate is at a temperature less than
approximately 50 degrees Celsius at approximately a beginning of
the first time period.
[0010] In another embodiment, the disclosure is directed to a
method of coating a substrate, the method comprising depositing
silicon on the substrate to form a silicon layer; heat treating the
silicon layer; depositing mullite on the silicon layer via thermal
spraying to form a first layer subsequent to the heat treatment of
the silicon layer, the mullite comprising mullite powder formed via
at least one of a fused plus crush or sinter plus crush process;
depositing a second material on the first layer to form an
intermediate layer; and depositing a third material on the
intermediate layer to form a third layer.
[0011] In another embodiment, the disclosure is directed to a
method of coating a substrate, the method comprising depositing
mullite on the substrate via thermal spraying to form a first
layer; and depositing a second material on the first layer via
thermal spraying to form a second layer, the second material
comprising at least one of barium strontium aluminum silicate
(BSAS) or a rare-earth silicate, wherein the substrate is at a
temperature of less than 150 degrees Celsius when the second
material is first deposited.
[0012] In another embodiment, the disclosure is directed to a
method of coating a substrate, the method comprising depositing
silicon on the substrate to form a silicon layer; heat treating the
silicon layer; and depositing mullite on the substrate during a
first time period via thermal spraying to form a first layer, the
mullite comprising mullite powder formed via at least one of a
fused plus crush or sinter plus crush process.
[0013] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a cross-sectional diagram illustrating an example
article including an example EBC on a substrate.
[0015] FIG. 2 is a flow chart illustrating an example technique for
applying layers of an EBC on a substrate to generate the example
article of FIG. 1.
[0016] FIG. 3 is a flow chart illustrating another example
technique for applying layers of an EBC on a substrate to generate
the example article of FIG. 1.
[0017] FIG. 4 is a cross-sectional diagram illustrating another
example article including an example EBC on a substrate.
[0018] FIGS. 5A and 5B are cross-sectional photographs of a portion
of example articles including example EBCs including layers that
were deposited at approximately 1200 degrees Celsius and
approximately 25 degrees Celsius, respectively.
[0019] FIGS. 6A and 6B are additional cross-sectional photographs
of the example articles of FIGS. 5A and 5B, respectively.
DETAILED DESCRIPTION
[0020] In general, embodiments of the disclosure relate to
techniques for applying coatings to a variety of substrates, such
as, e.g., ceramic substrates. In some embodiments, the applied
coatings may function as an EBC on ceramic substrates used for
components of high temperature mechanical system to increase the
operating capabilities of components of high temperature mechanical
systems and extend the components durability. For example, an EBC
may be applied to a silicon-based ceramic component to protect
against recession of the component caused by the volatilization of
silica scale by water vapor in the high temperature combustion
environment.
[0021] As will be described below, an EBC may be a multilayer
coating including an outer layer containing one or more rare-earth
silicates and/or barium strontium aluminum silicate (BSAS) that may
be bonded to the ceramic substrate via a mullite-containing layer,
which may be referred as the mullite layer. In some cases, the EBC
may include a silicon-based bond layer provided between the
substrate and mullite layer to adhere the mullite layer to the
substrate and to extend the life of the coating.
[0022] The mullite layer of an EBC may be formed by depositing
mullite in the form of mullite powder on the surface of a substrate
via a thermal spraying process, such as, e.g., plasma spraying. In
some examples, the mullite powder used may be manufactured using a
plasma spray granulation process. However, due to the relatively
high phase instability of mullite manufactured by a plasma spray
granulation process, the mullite layer formed via the thermal
spraying process may include non-homogenized mullite in both
amorphous and crystalline phases. If the mullite layer contains too
high a concentration of amorphous phase mullite, then the
environmental protection provided by the EBC to the substrate may
be reduced over the life of substrate. For example, the amorphous
non-homogenous mullite in a mullite layer may be prone to
crystalline phase transformations during thermal cycling that
induce volumetric changes within the mullite layer. In some cases,
the volumetric changes may cause cracking and/or delamination of
the mullite layer, which may reduce the extent of environmental
protection provided by the EBC to the ceramic component.
[0023] To reduce the amount of amorphous mullite in the mullite
layer, the thermal spraying process may include heating the ceramic
substrate to an elevated temperature within a closed environment
(e.g., by heating the substrate within a furnace room maintained at
approximately 1200 degrees Celsius or providing supplemental heat
towards one or more surfaces of the substrate) and maintaining the
substrate at the elevated temperature during the thermal spraying
of the mullite powder, which has been manufactured by plasma spray
granulation technique, to promote the deposition of crystalline
mullite rather than amorphous mullite. Similarly, the substrate may
also be maintained at an elevated temperature during the deposition
of the material used to form the outer layer, e.g., one or more
rare-earth silicates and/or BSAS, to provide for suitable
performance of the outer layer and/or bonding to the mullite
layer.
[0024] Additionally or alternatively, a substrate may be heat
treated, e.g., at a temperature greater than 1200 degrees Celsius
for greater than 10 hours, after one or more of these EBC layers
have been formed on the substrate to homogenize/stabilize the
crystalline phase mullite or transform amorphous mullite to
crystalline mullite in the EBC prior to exposing the substrate to
thermal cycling to increase the reliability of the EBC.
[0025] However, while the high temperature application and/or heat
treatment of one or more layers of the EBC can in some cases
address the phase instability issues, such a high temperature
process requirements can dramatically increase the cost and
relative complexity of applying an EBC to a ceramic component.
Furthermore, such process requirements can decrease the flexibility
of manufacturing and design of such components. For example, in
such cases, the overall size and/or shape of a component that the
EBC is being applied to may be limited by the relative dimensions
of the heat controlled environment, such as the size of the high
temperature furnace, required to maintain the component at an
appropriate elevated temperature during the application of one or
more EBC layers and/or heat treat a coated substrate.
[0026] As will be described in greater detail below, embodiments of
the disclosure may include techniques for forming one or more
layers of an EBC, including a mullite layer, on a substrate in a
low temperature environment by depositing the respective material
via thermal spraying without requiring extended high temperature
heat treatment of the mullite-coated substrate. Despite the low
temperature deposition of the materials that form the respective
layers of the EBC, the EBC may perform the same or similar to that
of an EBC with respective layer(s) that have been deposited via
thermal spraying on the substrate at elevated temperatures. In
particular, the mullite layer may be formed on a substrate by
depositing mullite powder manufactured via a fused or sinter plus
crush process, e.g., rather than a plasma spray granulation
process, via thermal spraying, such as, e.g., air plasma spraying,
even without substantially heating the substrate in conjunction
with the deposition and/or heat treating the mullite-coated
substrate. Despite the low temperature application, such a mullite
layer may not exhibit substantial cracking or delamination from the
substrate even after undergoing thermal cycling.
[0027] FIG. 1 is a cross-sectional diagram illustrating an example
article 10, which may be used in a high temperature mechanical
system. Article 10 includes EBC 14 applied on substrate 12. As
shown, EBC 14 is a multilayer coating that includes bond layer 16,
intermediate layer 18 and outer layer 20. In general, EBC 14 may
provide environmental protection to allow article 10 to operate in
severe environments, e.g., by preventing recession of substrate 12
in a high temperature combustion environment.
[0028] Substrate 12 may be a component of a high temperature
mechanical system, such as, e.g., a hot section component of a gas
turbine engine. Examples of such components may include, but are
not limited to, turbine blades, blade tracks, combustion liners,
and the like. Substrate 12 may include silicon-containing ceramics,
such as, e.g., silicon carbide (SiC), silicon nitride
(Si.sub.3N.sub.4), composites having a SiC or Si.sub.3N.sub.4
matrix, silicon oxynitride, and aluminum oxynitrides; an silicon
containing metal alloy, such as molybdenum-silicon alloys (e.g.,
MoSi.sub.2) and niobium-silicon alloys (e.g., NbSi.sub.2); and an
oxide-oxide ceramic.
[0029] Substrate 12 may include a matrix, such as, e.g., a ceramic
matrix composite (CMC), which may include any useful ceramic matrix
material, including, for example, silicon carbide, silicon nitride,
alumina, silica, and the like. The matrix may further include any
desired filler material, and the filler material may include a
continuous reinforcement or a discontinuous reinforcement. For
example, the matrix may be reinforced with ceramic fibers,
whiskers, platelets and chopped or continuous fibers.
[0030] The filler composition, shape, size, and the like may be
selected to provide the desired properties to the matrix. For
example, in some embodiments, the filler material may be chosen to
increase the toughness of a brittle ceramic matrix. In other
embodiments, the filler may be chosen to provide a desired property
to the matrix, such as thermal conductivity, electrical
conductivity, thermal expansion, hardness, or the like.
[0031] In some embodiments, the filler composition may be the same
as the matrix material. For example, a silicon carbide matrix may
surround silicon carbide whiskers. In other embodiments, the filler
material may include a different composition than the matrix, such
as mullite fibers in an alumina matrix, or the like. In one
embodiment, a CMC may include silicon carbide continuous fibers
embedded in a silicon carbide matrix.
[0032] EBC 14 may include bond layer 16, which in the example of
FIG. 1 is applied directly on substrate 12. Bond layer 16 may
include silicon, e.g., in the form of high purity, plasma sprayable
grade silicon powder, and may be formed by depositing the
appropriate silicon material on substrate 12 via one or more
suitable thermal spraying processes, such as, e.g., plasma
spraying. In some cases, bond layer 16 may optionally be included
in EBC 14 to promote adherence of intermediate layer 18 and/or
outer layer 20 to substrate 12. While EBC 14 is shown with bond
layer 16, in some embodiments, EBC 14 may not include bond layer
14. For example, intermediate layer 18 may be formed directly on
substrate 12 rather than being separated by bond layer 16.
[0033] Bond layer 16 may formed at any suitable thickness, such as
a thickness that allows EBC 14 to provide environmental protection
to article 10 as described herein. For example, in one embodiment,
bond layer 16 may have thickness in the range of approximately 0.2
mils to approximately 5 mils. In some embodiments, bond layer 16
may have thickness in the range of approximately 0.5 mils to
approximately 5 mils, such as approximately 2 mils to approximately
4 mils or approximately 1 mil to approximately 4 mils.
[0034] EBC 14 may also include intermediate layer 18, which may be
provided on top of bond layer 16 and/or substrate 12. Intermediate
layer 18 may include mullite manufactured by a fused or sinter plus
crushed technique, at least some of which is in the crystalline
phase, and may be formed by depositing mullite powder on substrate
12 via one or more suitable thermal spraying processes, including
plasma spraying. In some embodiments, intermediate layer 18 may
additionally include greater than approximately 50 percent by
weight crystalline mullite, such as, e.g., approximately 60 percent
by weight crystalline mullite or 80 percent by weight crystalline
mullite. In some examples, intermediate layer 18 may include
approximately 100 percent by weight crystalline mullite.
[0035] In some embodiments, the balance of intermediate layer 18
other than that of the mullite may include an amount of BSAS, e.g.,
in cases in which outer layer 20 includes BSAS. For example,
intermediate layer 18 may include up to approximately 80 percent by
weight BSAS, such as, e.g., approximately 40 percent by weight BSAS
or approximately 20 percent by weight BSAS. In other embodiments,
the balance of intermediate layer 18 may include an amount of
rare-earth silicate, e.g., in cases in which outer layer 20
includes rare-earth silicate. For example, intermediate layer 18
may include up to approximately 80 percent by weight rare-earth
silicate, such as, e.g., approximately 40 percent by weight
rare-earth silicate or approximately 20 percent by weight
rare-earth silicate.
[0036] The mullite material may be deposited on bond layer 16 and
substrate 12 via a thermal spraying process to form intermediate
layer 18 without maintaining or providing substrate 12 at an
elevated temperature relative the thermal spraying process and/or
heat treating intermediate layer 18 after the mullite has been
thermally sprayed. Despite the relatively low temperature
application, intermediate layer 18 may still perform the same or
similar to that of a mullite layer deposited at high temperature
and/or that has undergone heat treatment. In particular, the
mullite layer formed via the deposition of mullite powder
manufactured via a fused or sinter plus crush process may not
exhibit undesirable volumetric changes during thermal cycling that
may cause EBC 14 to fail, e.g., due to cracking or delamination,
even though the substrate was not maintained at an elevated
temperature during the thermally spraying process or heat treated
after intermediate layer 18 was formed. In some embodiments,
intermediate layer 18 may include greater than approximately 50
percent by weight crystalline mullite, such as, e.g., greater than
approximately 80 percent by weight crystalline mullite, even
without thermal spraying the mullite powder on substrate 12 via
thermal spraying or heat treating substrate 12 after the formation
of intermediate layer 18.
[0037] As previously mentioned, such a process may be enabled by
using a mullite powder for thermal spraying that has been generated
via a fused plus crush process and/or sinter plus crush process
rather than via a plasma spray granulation process, for example. In
some cases, mullite powder generated via a fused or sinter plus
crushed process may allow for deposition of the mullite powder via
thermal spraying at a relatively lower temperature than mullite
powder generated via spray granulation. Although not wishing to be
limited by theory, it is believed that mullite powder generated via
a fused or sinter plus crush process may contain relatively high
concentration of stoichiometric amorphous phase mullite in the
powder material. Conversely, mullite powder generated via spray
granulation may include a relatively high concentration of
non-stoichiometric or non-homogenous phase mullite powder. The
volumetric changes associated with conversion of stoichiometric
amorphous phase mullite to crystalline mullite in a high
temperature environment is less than the volumetric changes
associated with the phase conversion of non-stoichiometric
amorphous phase mullite due to increased homogenity. In some cases,
the volumetric changes associated with the conversion of
stoichiometric amorphous phase mullite may not be great enough to
cause delamination of an EBC due to the thermal expansion of the
mullite layer in high temperatures, while the volumetric changes
associated with the conversion of non-stoichiometric amorphous
phase mullite may be great enough to cause delamination of an EBC
due to the thermal expansion of the mullite layer in high
temperatures.
[0038] Intermediate layer 18 may be formed at any suitable
thickness, such as a thickness that allows EBC 14 to provide
environmental protection to article 10 as described herein. For
example, one embodiment, intermediate layer 18 may have thickness
in the range of approximately 1 mil to approximately 7 mils. In
still another embodiment, intermediate layer 18 may have thickness
in the range of approximately 4 mils to approximately 6 mils. In
some embodiments in which EBC 14 includes bond layer 16 and
intermediate layer 18, the ratio of layer thickness between bond
layer 16 and intermediate layer 18 may range from approximately 0.1
to approximately 1.5 such as, e.g., from approximately 0.2 to
approximately 1.0.
[0039] EBC 14 may also include outer layer 20. In the example of
FIG. 1, outer layer 20 has been formed directly on intermediate
layer 16 such that it is adhered to substrate 12 via intermediate
layer 18 and bond layer 16. Outer layer 20 may include one or more
components selected to provide environmental protection for
substrate 12 in combination with bond layer 16 and intermediate
layer 18 as described herein. In some embodiments, outer layer 20
may include one or more rare-earth silicates, such as, e.g.,
ytterbium mono-silicate or ytterbium di-silicate. Additionally or
alternatively, outer layer 20 may include BSAS, e.g., in situations
in which the operating temperature of the component is below
approximately 2400 degrees Fahrenheit.
[0040] The material selected for outer layer 20 may be deposited on
intermediate layer 18 via a thermal spraying process to form outer
layer 18. As will be described in further below with respect to
FIG. 2, in some embodiments, the outer layer material may be
thermally sprayed on intermediate layer 18 to form outer layer 20
while substrate 12 is maintained at substantially uniform
temperature that is less than 150 degrees Celsius, such as, e.g.,
less than 50 degrees Celsius. In some cases, this may include
depositing the outer layer material, e.g., BSAS or one or more
rare-earth silicates, via thermal spraying on substrate 12 while
the substrate is provided at a temperature that is approximately
the same as that of substrate 12 when the mullite material was
initially deposited via thermal spraying to form intermediate layer
18. Despite the relatively low deposition temperature, it may be
possible to form outer layer 20 including one or more rare earth
silicates or BSAS that is adequately bonded to intermediate layer
18 while still preventing coating delamination in outer layer 20.
In this manner, substrate 12 may be coated with intermediate layer
18 and outer layer 20 via thermal spraying without having to
provide additional heat to substrate 12 during the application
process of EBC 14.
[0041] Outer layer 20 may be formed at any suitable thickness, such
as a thickness that allows EBC 14 to provide environmental
protection and thermal barrier to article 10 as described herein.
For example, in one embodiment, outer layer 20 may have thickness
in the range of approximately 2 mils to approximately 15 mils. In
still another embodiment, outer layer 20 may have thickness in the
range of approximately 4 mils to approximately 12 mils.
[0042] FIG. 2 is a flow chart illustrating an example technique for
applying layers 16, 18, 20 of EBC 14 on substrate 12 to generate
article 10 of FIG. 1. As indicated in FIG. 2, uncoated substrate 12
may be provided at a temperature of less than approximately 50
degrees Celsius (22). In some cases, substrate 12 may be undergo
one or more preparation steps prior to the being coated with one or
more of the layers described herein. For example, substrate may be
grit blasted with a suitable material, e.g., aluminum oxide and the
like, to prepare the substrate surface for coating. In any case,
appropriate silicon material may be deposited of substrate 12 at
via any suitable process, including thermal spraying, to form bond
layer 16. In some embodiments, the deposition of the silicon
material may begin when substrate 12 is at a temperature of less
than 50 degrees Celsius (24).
[0043] After bond layer 16 has been formed on substrate 12, mullite
powder that has been manufactured via a fused plus crushed and/or
sinter plush crush process may be deposited on bond layer 16 via
thermal spraying to form intermediate layer 18(26). The deposition
of the mullite powder on the substrate may begin even when the
substrate is at a substantially uniform temperature of less than 50
degrees Celsius (26).
[0044] After intermediate layer 18 has been formed on substrate 12,
the outer layer material, e.g., one or more rare earth silicates or
BSAS, may be deposited on intermediate layer 18 via thermal
spraying to form outer layer 18. Such a deposition process may also
begin even when the substrate is at temperature of less than 50
degrees Celsius (28). In this manner, the respective layers 16, 18,
20 of EBC 14 may be applied to substrate 12 in a relatively low
temperature air environment while still forming a suitable coating
that provides environmental protection to substrate in a high
temperature combustion environment.
[0045] As illustrated by the example of FIG. 2, in some
embodiments, one or more layers of EBC 14 may be deposited on
substrate 12 via thermal spraying even when the temperature of
substrate 22 is at a relatively low, which may include temperatures
realized without purposefully elevating the temperature of the
substrate above that generally exhibited under normal conditions.
For example, in FIG. 2, each of bond layer 14, intermediate layer
18, and outer layer 20 may be formed on substrate via thermal
spraying when the substrate at a substantially uniform temperature
of less than approximately 50 degrees Celsius. Such a temperature
limit may generally correspond to the maximum temperature that may
be naturally exhibited in a space without providing substantial
supplemental heat to the space beyond that provided by conventional
device or systems that may be used to control the temperature of a
room, e.g., from a heating, ventilation and air conditioning (HVAC)
system. In particular, the low temperature process may be achieved
without requiring substrate to be heated in a furnace room or
purposefully providing supplemental heat directed to substrate 12
for purposes of heating all or portions of substrate 12 during the
deposition process.
[0046] Depending in part on the environment that the layer
deposition process is undertaken, e.g., the natural temperature of
the room at which the deposition process is undertaken, substrate
12 may be at a temperature less than approximately 50 degrees
Celsius at the beginning of the deposition of one or more of layer
16, 18, and 20, which includes the beginning of the deposition of
the mullite powder on the substrate (26), as previously described.
For example, substrate 12 may be at a temperature of less than
approximately 40 degrees Celsius at the beginning of the mullite
powder deposition, such as, e.g., between approximately 15 degrees
Celsius and approximately 35 degrees Celsius. In some embodiments,
substrate 12 is not be substantially heated above the temperature
of the surrounding space in which the thermal spraying of the layer
material is being performed, wherein the ambient temperature of the
surrounding space, e.g., the room in which the thermal spraying
process is performed, is less than approximately 50 degrees
Celsius. In some embodiments, the ambient temperature of the
surrounding space may be between approximately 10 degrees Celsius
and 40 degrees Celsius, such as, e.g., between approximately 15
degrees Celsius and 30 degrees Celsius.
[0047] Despite the relatively low temperatures of the substrate
during thermal spraying, intermediate layer 18 may contain a
concentration of stoichiometric and/or homogenous amorphous and
crystalline mullite phases such that cracking and/or delamination
of intermediate layer 18 is prevented during thermal cycling. In
this manner, one or more of layers 16, 18, 20 may be formed via
thermal spraying of mullite powder without having to provide
additional heat to substrate 12 to a temperature substantially
greater than that of the space
[0048] While substrate 12 may be at a temperature of less than 50
degrees Celsius at the beginning of the deposition of the materials
of layers 16, 18, and 20, it is recognized that the local
temperature of certain portions of substrate 12 may be increased
above approximately 50 degrees Celsius, including local temperature
greater than or equal to that of 50 degrees, at periods throughout
the overall deposition time of the respective layer material. For
example, during thermal spraying of mullite powder on substrate 12
to form intermediate layer 18, the deposition surface of substrate
22 may reach temperatures greater than or equal to 50 degrees
Celsius because of elevated temperature of the material being
deposited on the surface of substrate 22. However, while the
substrate temperature may increase above the temperature at the
beginning of the mullite deposition, it is as a result from the
heat provided by the thermal spraying process rather than by a
supplemental source, as would be the case in a furnace room or with
additional heat directed to substrate 12. Even with the additional
heat from the thermal spraying process, in some embodiments,
substrate 12 may be maintained at a temperature of less than 200
degrees Celsius, such as, for example, between approximately 15
degrees Celsius and approximately 200 degrees Celsius or between
approximately 20 degrees Celsius and approximately 150 degrees
Celsius, throughout the deposition of the mullite material via
thermal spraying.
[0049] The beginning temperature of substrate 12 relative the
deposition of one or more of the layer materials may be achieved
via any suitable method. Substrate 12 may be at a temperature of
less than approximately 50 degrees Celsius by simply allowing the
temperature of substrate 12 to be substantially equal to that of
the room temperature of the surrounding space, assuming that that
surrounding space is less than approximately 50 degrees Celsius.
This may allow EBC 12, and intermediate layer 18, in particular, to
be formed on substrate 12 via a thermal spraying process without
having to undertake any additional steps to heat substrate 12
during the deposition and/or heat treat substrate 12 after being
coated with EBC 14
[0050] FIG. 3 is a flow chart illustrating an example technique for
applying layer 16, 18, 20 of EBC 14 on substrate 12 to generate
article 10 of FIG. 1. The example of FIG. 3 includes a heat
treatment step after bond layer 16 has been formed on substrate 12
but before intermediate layer 18 has been deposited via thermal
spraying. As will be explained below, such an example technique may
be useful in situations in which the coefficient of thermal
expansion of two or more individual layers of coating 14 are not
approximately equal, e.g., differ by approximately 10 percent or
greater. However, the examples are not limited as such.
[0051] Similar to that of the example of FIG. 2, silicon material
may be deposited on uncoated substrate 12 to form bond layer 16 of
EBC 14 (32). The appropriate silicon material may then be deposited
at via any suitable process, including thermal spraying, to form
bond layer 16 and may be deposited in some cases when the substrate
is at a temperature of less than 50 degrees Celsius at the starting
of the bond layer deposition (30).
[0052] Unlike the example of FIG. 2, after bond layer 16 has been
formed, substrate 12 and bond layer 16 may undergo diffusion heat
treatment prior to the deposition of the mullite powder (34). Such
a heat treatment may include exposing substrate 12 and bond layer
16 to a relatively high heat environment, e.g., within a furnace,
for a relatively short amount of time. In some embodiments, the
heat treatment step may include placing substrate 12 and bond layer
16 in an environment at a temperature between approximately 800
degrees Celsius and approximately 1250 degrees Celsius for an
amount of time between approximately 0.2 hours and approximately 4
hours. For example, in some embodiments, heat treatment step may
include placing substrate 12 and bond layer 16 in an environment at
a temperature between approximately 1100 degrees Celsius and
approximately 1225 degrees Celsius for an amount of time between
approximately 0.5 hours and approximately 2 hours.
[0053] After undergoing diffusion heat treatment, mullite powder
may be deposited on bond layer 16 via thermal spraying to form
intermediate layer 18 (36) and outer layer material may be
deposited on intermediate layer 18 via thermal spraying to form
outer layer 20 (38), as described previously with respect to FIG.
2. Both intermediate layer 18 and outer layer 20 may be formed on
substrate 12 via plasma spraying without placing substrate 12 at a
high temperature environment, e.g., at a temperature greater than
50 degrees Celsius.
[0054] The inclusion of the diffusion heat treatment step may serve
to increase the adhesion of EBC 14 to substrate 12, especially in
cases in which the coefficient of thermal expansion of the layers
of EBC 14 are not the substantially the same. In some embodiment,
substrate 12 and bond layer 16 may undergo diffusion heat treatment
as described above when the coefficient of thermal expansions of
layers 16, 18, 20 differ by more than 5 percent, such as e.g., more
than 10 percent, to increase the adhesion of EBC 14 to substrate
12, even when intermediate layer 18 and outer layer 20 are formed
by deposition of the respective materials via thermal spraying
without maintaining substrate 12 at an elevated temperature, e.g.,
at a temperature greater than 50 degrees Celsius.
[0055] FIG. 4 is a cross-sectional diagram illustrating another
example article 39, which may be used in a high temperature
mechanical system. As shown, example article 39 includes substrate
40, which is substantially the same or similar to that of substrate
12 of FIG. 1, and EBC 42 applied on substrate 12. EBC 42 includes
bond layer 44, first intermediate layer 46, and outer layer 50,
which may be substantially the same or similar to that of bond
layer 16, intermediate layer 18 and outer layer 20, respectively,
of EBC 14 of FIG. 1.
[0056] Unlike the embodiment shown in FIG. 1, EBC 42 includes
second intermediate layer 48 provided between outer layer 50 and
first intermediate layer 46. Second intermediate layer 48 may
function to reduce the strain on the interface of outer layer 50
and first intermediate layer 46 during thermal cycling for cases in
which first intermediate layer 46 and outer layer 50 exhibit
different coefficients of thermal expansion. In some examples,
second intermediate layer 48 may provide chemical compatibility
and/or thermal expansion transition between first intermediate
layer 46 and outer layer 48.
[0057] The structure and composition of second intermediate layer
48 may vary, and may be selected based on one or more factors. With
reference to FIG. 4, second intermediate layer 46 may be a single
layer or include a plurality of sublayers. In some embodiments,
second intermediate layer 46 may have a substantially uniform
composition throughout, while in other embodiments second
intermediate layer 46 may be compositionally graded based on the
composition of the adjacent layers.
[0058] In some embodiments, second intermediate layer 48 may
include at least one of alumina and/or mullite. The composition of
second intermediate layer 48 may be selected based on the
composition of first intermediate layer 46 and/or outer layer 50.
For example, the composition of first intermediate layer 46 and
outer layer 50 may generally dictate the coefficient of thermal
expansion for the respective layers. Second intermediate layer 48
may include one or more components which allow for second
intermediate layer 48 to have a coefficient of thermal expansion
that is in between that of the coefficients of thermal expansion of
first intermediate layer 46 and outer layer 50. In some
embodiments, second intermediate layer 48 may have a coefficient of
thermal expansion that is within approximately 10 percent or less
than the coefficient of thermal expansion of first intermediate
layer 46 and/or outer layer 50.
[0059] In this manner, the difference in thermal expansion between
first intermediate layer 46 and outer layer 50 may be tempered by
the thermal expansion of second intermediate layer 48 when
configured as shown in FIG. 4. In some embodiments, alternately or
additionally, the composition of second intermediate layer 48 may
be selected to provide suitable adhesion between second
intermediate layer 48 and first intermediate layer 46, and also
between second intermediate layer 48 and outer layer 50.
[0060] In some embodiments, second intermediate layer 48 may
include one or more components of both first intermediate layer 46
and outer layer 50. For example, when first intermediate layer 46
includes mullite and outer layer 50 includes component ytterbium
di-silicate, second intermediate layer 48 may include a mixture of
mullite and component ytterbium di-silicate. The mixture may
include an approximately equal amount of the components of first
intermediate layer 46 and outer layer 50, or may include any other
desired mixture or proportion of components from first intermediate
layer 46 and outer layer 50.
[0061] Second intermediate layer 48 may be applied as a separate
layer from first intermediate layer 46 and outer layer 50. For
example, mullite powder may be deposited first via thermal spraying
to form first intermediate layer 46, as described herein. The
desired mixture of the first intermediate layer components, e.g.,
mullite, and the outer layer components may then be mixed and
deposited on first intermediate layer 46 via thermal spraying to
form second intermediate layer 48, followed by application of outer
layer 50 on second intermediate layer 48, as previously described.
Similar to that of outer layer 50 and first intermediate layer 46,
second intermediate layer 48 may be initially deposited on first
intermediate layer 46 when the temperature of substrate 40 is less
than approximately 50 degrees Celsius.
[0062] Additionally, second intermediate layer 48 may include more
than one sublayers (not shown). In some embodiments, a second
intermediate layer having one or more sublayers may allow for the
interface between first intermediate layer 46 and outer layer 50 to
be compositionally graded. Such compositional grading may reduce
the strain on the interface of outer layer 50 and first
intermediate layer 46 during thermal cycling for cases in which
first intermediate layer 46 and outer layer 50 exhibit different
coefficients of thermal expansion. For example, the inclusion of
second intermediate layer 48 having multiple sublayers that are
compositionally graded may reduce the coefficient of thermal
expansion gradient, or in other words, make the compositional
transition from the first intermediate layer 46 to outer layer 50
more gradual, thus making the change of coefficients of thermal
expansion more gradual. It may be understood that the more
sublayers included in the second intermediate layer, the lower the
interfacial stresses due to mismatches of coefficients of thermal
expansion. The number of sub-layers in the transitional layer need
not be limited, but may be chosen according to the desired
properties of the article and the time and expense involved in
producing the article.
[0063] Furthermore, a coating may also include a second
intermediate layer that is not divided into sub-layers, but which
includes a continuously graded composition. For example, the second
intermediate layer may be compositionally most similar to the first
intermediate layer at the first intermediate layer-transitional
layer interface, and most similar to the outer layer at the outer
layer-transitional layer interface, with a composition that
continuously transitions from the first intermediate layer
composition to the outer layer composition along the depth of the
transitional layer.
[0064] In some embodiments, intermediate layer 48 may be a
rare-earth silicate layer that transitions into another rare-earth
silicate layer. For example, intermediate layer 48 may include
Yb-disilicate while outer layer 50 may include Yb-monosilicate. The
respective layers may be deposited as discrete layers or as
functionally graded materials.
[0065] Some embodiments of the disclosure may relate to a method of
coating a substrate consisting essentially of depositing mullite on
the substrate via thermal spraying to form a first layer; and
depositing a second material on the first layer to form a second
layer, wherein the mullite comprises mullite powder formed via at
least one of a fused plus crush or sinter plus crush process.
[0066] Some embodiments of the disclosure may relate to a method of
coating a substrate consisting essentially of depositing silicon on
the substrate to form a silicon layer, depositing mullite on the
silicon layer via thermal spraying to form a first layer; and
depositing a second material on the first layer to form a second
layer, wherein the mullite comprises mullite powder formed via at
least one of a fused plus crush or sinter plus crush process. Such
a method may not include depositing the mullite layer at a
relatively high temperature and/or heat treating the mullite layer,
as previously described. In some examples, the method may further
consist essentially of heat treating the silicon layer and
substrate prior to depositing the mullite on the silicon layer.
Example
[0067] FIGS. 5A and 5B are cross-sectional photographs of
non-leading edge portions of example articles 52a and 52b,
respectively.
[0068] FIGS. 6A and 6B are cross-sectional photographs of a leading
edge portion of example articles 52a and 52b, respectively.
[0069] Referring to FIGS. 5A and 6A, article 52a included EBC 54a
provided on ceramic matrix composite substrate 56a. EBC 54a
included silicon bond layer 58a, intermediate layer 60a, and outer
layer 62a. Silicon bond layer 58a was formed by depositing silicon
directly on the surface of substrate 56a via plasma spraying.
Intermediate layer 60a was formed by depositing mullite powder that
was produced via a fused plus crush process via air plasma spraying
on silicon bond layer 58a. Outer layer 62a was formed by depositing
ytterbium di-silicate on intermediate layer 60a. Notably, each
layer 58a, 60a, 62a was formed by depositing the respective layer
material via air plasma spraying while the substrate was held in a
furnace at a temperature of approximately 1200 degrees Celsius.
Article 52a was not heat treated after EBC 54a was applied to
substrate 56a.
[0070] Referring to FIGS. 5B and 6B, article 52b included EBC 54b
provided on ceramic matrix composite substrate 56b. EBC 54b
included silicon bond layer 58b, intermediate layer 60b, and outer
layer 62b. Silicon bond layer 58b was formed by depositing silicon
directly on the surface of substrate 56b via plasma spraying. After
deposition, silicon bond layer 58b underwent diffusion heat
treatment at approximately 1225 degrees Celsius (+/-25 degrees) for
approximately 1 hour. Intermediate layer 60b was then formed by
depositing mullite powder that was produced via a fused plus crush
process via air plasma spraying on silicon bond layer 58b. Outer
layer 62b was formed by depositing ytterbium di-silicate on
intermediate layer 60b. Unlike article 52a of FIG. 5A, each layer
58b, 60b, 62b was formed by depositing the respective layer
material via air plasma spraying while substrate 56b was initially
at a temperature less than approximately 50 degrees Celsius. In
particular, the process of air plasma spraying of the layer
material on substrate 56b was initiated when substrate 56 was at
approximately 25 degrees Celsius, which was the ambient temperature
of the room in which the substrate was located in at the time the
process was carried out. Similar to that of article 52a, article
52b was not heat treated after EBC 54b was applied to substrate
56b.
[0071] Articles 52a and 52b were exposed to substantially the same
steam thermal cycling in an environment of greater than 1800
degrees Fahrenheit and greater than 60% humidity. The steam thermal
cycling involved exposing articles 52a and 52b to the described
environment for greater than 100 cycles for a total of amount of
time greater than 100 hours. Additionally, articles 52a and 52b
were exposed to laser heat flux through EBCs 54a and 54b,
respectively, above 1500 degrees Fahrenheit in conjunction with the
steam thermal cycling, for greater than 5 hours. Such testing of
articles 52a and 52b simulated engine operating conditions in a
high temperature combustion environment in the presence of water
vapor.
[0072] The cross-sectional photographs of FIGS. 5A, 5B, 6A and 6B
were taken after articles 52a and 52b, respectively, underwent the
above-described steam thermal cycling. As illustrated by the
photographs of FIGS. 5A and 5B and FIGS. 5A, 5B, 6A and 6B, article
52b exhibited equivalent durability to that of article 52a. In
particular, layers 58a, 60a, and 62a of EBC 54a, as well as layers
58b, 60b, and 62b of EBC 54b were substantially crack-free after
steam thermal cycling and maintained excellent adherence to
substrates 52a and 52b, respectively. Additionally, the oxidation
of substrates 52a and 52b was minimal, as evidenced by the lack of
oxide scale formed between EBC 54a, 54b and substrates 52a, 52b,
respectively, indicating that EBCs 54a, 54b provided excellent
environmental protection for articles 52a, 52b, respectively. It
was observed that that the room-temperature sprayed EBC (EBC 54b)
was more tolerant to mechanical strains than the furnace sprayed
EBC (EBC 54a), which likely may be due to the comparatively higher
porosity and microcracks in the room temperature sprayed EBC.
[0073] Various embodiments of the invention have been described.
These and other embodiments are within the scope of the following
claims.
* * * * *