U.S. patent application number 11/977330 was filed with the patent office on 2009-07-02 for coated silicon comprising material for protection against environmental corrosion.
This patent application is currently assigned to General Electric Company. Invention is credited to Brian Thomas Hazel.
Application Number | 20090169742 11/977330 |
Document ID | / |
Family ID | 37106910 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090169742 |
Kind Code |
A1 |
Hazel; Brian Thomas |
July 2, 2009 |
Coated silicon comprising material for protection against
environmental corrosion
Abstract
In accordance with an embodiment of the invention, an article is
disclosed. The article comprises a gas turbine engine component
substrate comprising a silicon material; and an environmental
barrier coating overlying the substrate, wherein the environmental
barrier coating comprises cerium oxide, and the cerium oxide
reduces formation of silicate glass on the substrate upon exposure
to corrodant sulfates.
Inventors: |
Hazel; Brian Thomas; (West
Chester, OH) |
Correspondence
Address: |
HARRINGTON & SMITH, PC
4 RESEARCH DRIVE, Suite 202
SHELTON
CT
06484-6212
US
|
Assignee: |
General Electric Company
|
Family ID: |
37106910 |
Appl. No.: |
11/977330 |
Filed: |
October 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11208245 |
Aug 19, 2005 |
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11977330 |
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Current U.S.
Class: |
427/255.7 ;
427/337 |
Current CPC
Class: |
C04B 41/89 20130101;
C04B 41/5045 20130101; C23C 28/322 20130101; C23C 28/345 20130101;
C04B 41/87 20130101; C23C 28/042 20130101; C04B 41/52 20130101;
C04B 41/009 20130101; C23C 28/3455 20130101; C04B 41/52 20130101;
C04B 41/4527 20130101; C04B 41/5096 20130101; C04B 41/52 20130101;
C04B 41/4527 20130101; C04B 41/5037 20130101; C04B 41/52 20130101;
C04B 41/4527 20130101; C04B 41/5024 20130101; C04B 41/52 20130101;
C04B 41/4527 20130101; C04B 41/5045 20130101; C04B 41/5045
20130101; C04B 41/4527 20130101; C04B 41/009 20130101; C04B 35/565
20130101; C04B 41/009 20130101; C04B 35/584 20130101; C04B 41/009
20130101; C04B 35/806 20130101 |
Class at
Publication: |
427/255.7 ;
427/337 |
International
Class: |
C23C 16/40 20060101
C23C016/40; C23C 16/42 20060101 C23C016/42 |
Goverment Interests
GOVERNMENT RIGHTS
[0001] The invention was made in part under contract number
NAS3-01135 awarded by the Government (NASA). Accordingly, the
Government has certain rights in this invention.
Claims
1-14. (canceled)
15. A method of reducing silicate glass formation on a gas turbine
engine component comprising: providing a substrate of the gas
turbine engine component, wherein the substrate comprises a silicon
material; and depositing cerium oxide directly on the substrate or
admixing cerium oxide with the silicon material of the substrate;
wherein the cerium oxide reduces formation of silicon glass on the
substrate upon exposure to corrodant sulfates.
16. A method of reducing silicate glass formation on a gas turbine
engine component comprising: providing a substrate of the gas
turbine engine component, wherein the substrate comprises a silicon
material; depositing a bond layer comprising a silicon material and
overlying the substrate; depositing a first layer comprising
mullite and overlying the bond layer; depositing a second layer
comprising barium strontium aluminosilicate overlying the first
layer; and depositing a layer consisting of cerium oxide overlying
second layer or admixing cerium oxide with the barium strontium
aluminosilicate; wherein the cerium oxide reduces formation of
silicon glass on the substrate upon exposure to corrodant
sulfates.
17. The method of claim 16, wherein each layer is deposited by a
method selected from the group consisting of: air plasma spray,
vacuum plasma spray, chemical vapor deposition and high velocity
oxy fuel.
Description
FIELD OF THE INVENTION
[0002] This invention relates to protecting materials comprising
silicon from environmental corrosion, such as that experienced in
the hostile thermal environment of a gas turbine engine. More
particularly, the invention relates to an environmental barrier
coating (EBC) system for use on silicon comprising substrates for
providing protection against environmental corrosion.
BACKGROUND OF THE INVENTION
[0003] Higher operating temperatures for gas turbine engines are
continuously sought in order to increase efficiency. However, as
operating temperatures increase, the high temperature durability of
the components within the engine must correspondingly increase. In
this regard, materials comprising silicon, particularly those with
silicon carbide (SiC) as a matrix material or a reinforcing
material, are considered useful for high temperature applications,
such as for combustor and other hot section components of gas
turbine engines.
[0004] However, some silicon substrates may recede and lose mass as
a result of formation of volatile Si species, particularly
Si(OH).sub.x and SiO when exposed to high temperature, aqueous
environments, thus necessitating the use of a protective coating
thereon. Accordingly, methods such as described in U.S. Pat. Nos.
5,985,470, 6,444,335, 6,410,148 and 6,759,151, the contents of each
of which are incorporated by reference, have addressed shortcomings
concerning the use of such silicon substrates by providing an
environmental barrier coating (EBC) over the substrate. The EBCs
inhibit formation of volatile silicon species, Si(OH).sub.x and
SiO, thereby reducing recession and mass loss. A thermal barrier
coating (TBC) typically comprising yttria stabilized zirconia may
also be employed as an outer layer to the EBC depending upon the
operating conditions employed.
[0005] While the current state of the art EBCs, which are typically
multi-layer EBCs, may be effective in preventing water vapor
recession of the ceramic matrix composite (CMC) substrate, both
BSAS, SiC and some rare earth silicates such as some silicates
disclosed in U.S. Pat. No. 6,759,151 may be susceptible to silicate
glass formation when in contact with sulfate salt deposits as
operating conditions continue to increase.
[0006] Accordingly, there is a need to reduce the silicate glass
formation rate in materials comprising silicon, particularly in EBC
materials. Embodiments of the present invention satisfy this need
and others.
BRIEF DESCRIPTION OF THE INVENTION
[0007] In accordance with an embodiment of the invention, an
article is disclosed. The article comprises a gas turbine engine
component substrate comprising a silicon material; and an
environmental barrier coating overlying the substrate, wherein the
environmental barrier coating comprises cerium oxide, and the
cerium oxide reduces formation of silicate glass on the substrate
upon exposure to corrodant sulfates.
[0008] In accordance with another embodiment of the invention, an
article comprises a gas turbine engine component substrate
comprising a silicon material. The article further comprises a bond
layer comprising a silicon material and overlying the substrate; a
first layer comprising mullite and overlying the bond layer; a
second layer comprising an barium strontium aluminosilicate and
overlying the first layer; and a third layer consisting of cerium
oxide and overlying the second layer. The cerium oxide reduces
formation of silicate glass on the substrate upon exposure to
corrodant sulfates.
[0009] In accordance with another embodiment of the invention, a
gas turbine engine component is disclosed. The component comprises
a substrate comprising a silicon material; and at least one layer
on the substrate selected from the group consisting of: i) an
environmental barrier coating comprising cerium oxide, and ii) a
dual layer of barium strontium aluminosilicate and a layer
consisting of cerium oxide overlying the barium strontium
aluminosilicate; wherein the cerium oxide reduces formation of
silicate glass on the substrate.
[0010] In accordance with a further embodiment of the invention, a
gas turbine engine component comprises a substrate comprising a
silicon material. Cerium oxide is deposited directly on the
substrate or admixed with the silicon material of the substrate,
wherein the cerium oxide reduces formation of silicate glass on the
substrate upon exposure to corrodant sulfates.
[0011] In accordance with another embodiment, a method of reducing
silicate glass formation on a gas turbine engine component is
disclosed. The method comprises providing a substrate of the gas
turbine engine component, wherein the substrate comprises a silicon
material; and depositing cerium oxide directly on the substrate or
admixing cerium oxide with the silicon material of the substrate.
The cerium oxide reduces formation of silicon glass on the
substrate upon exposure to corrodant sulfates.
[0012] In accordance with another embodiment, a method of reducing
silicate glass formation on a gas turbine engine component
comprises providing a substrate of the gas turbine engine
component, wherein the substrate comprises a silicon material. The
method further comprises depositing a bond layer comprising a
silicon material and overlying the substrate; depositing a first
layer comprising mullite and overlying the bond layer; depositing a
second layer comprising an environmental barrier coating overlying
the first layer; and depositing a layer consisting of cerium oxide
overlying second layer or admixing cerium oxide with barium
strontium aluminosilicate. The cerium oxide reduces formation of
silicon glass on the substrate upon exposure to corrodant
sulfates.
[0013] Other features and advantages will be apparent from the
following more detailed description, taken in conjunction with the
accompanying drawing, which illustrate by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWING
[0014] FIG. 1 is a cross-sectional view of a gas turbine engine
component formed of a material comprising Si and having an
environmental barrier coating thereon, in accordance with an
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Applicant has determined through testing that silicon
comprising materials may adversely react with deposited sulfates.
For example, this material may react with Na.sub.2SO.sub.4 at
temperatures such as about 1700.degree. F. (927.degree. C.) and
higher, and MgSO.sub.4/CaSO.sub.4 may react at temperatures such as
about 2200.degree. F. (1204.degree. C.) and higher. This reaction
causes corrosion and forms a silicate glass from the silicon
comprising material. Deep pitting and CO evolution can degrade the
performance of the silicon comprising material. Additionally, this
may prevent EBCs from acting as optimal water recession barriers
for silicon comprising substrates as silicate glass has a high
recession rate.
[0016] Embodiments of the present invention improve upon prior
coated silicon comprising materials, particularly EBC systems used
upon silicon comprising material substrates. These embodiments are
generally applicable to components that operate within environments
of relatively high temperatures, and are thus subjected to thermal
cycling, stresses, oxidation, and corrosion. Examples of such
components include, but are not limited to, combustor components,
blades, shrouds, flaps, seals, vanes, and other components of gas
turbine engines.
[0017] Referring to FIG. 1, an EBC system 10 of a first embodiment
is shown. The EBC system 10 includes an EBC 12, and a surface
region 16 or substrate of a component 18. The component 18, or at
least the surface region (substrate) 16 of the component 18, is
formed of a silicon comprising material (particularly those for
articles exposed to high temperatures), such as SiC/SiC ceramic
matrix composites (CMC). However, embodiments of the invention are
generally applicable to other materials comprising silicon.
Examples of silicon comprising materials include, but are not
limited to, those with a dispersion of silicon carbide, silicon
carbide and/or silicon particles as a reinforcement material in a
metallic or nonmetallic matrix. Also included are those having a
silicon carbide, silicon aluminum oxynitride, silicon nitride
and/or silicon comprising matrix, and particularly composite
materials that employ silicon carbide, silicon nitride and/or
silicon as both the reinforcement and matrix materials (e.g.,
SiC/SiC ceramic matrix composites (CMC)). Silicon comprising
materials further include metal silicides including, but not
limited to, molybdenum and niobium silicides. Thus, according to
embodiments of the invention, the silicon comprising substrate 16
may be a silicon comprising ceramic material as, for example,
silicon carbide, silicon nitride, silicon carbon nitride, silicon
oxynitride and silicon aluminum oxynitride. In accordance with one
embodiment, the silicon comprising substrate 16 comprises a silicon
comprising matrix with reinforcing fibers, particles and the like
and, more particularly, a fiber reinforced silicon based matrix.
Particularly suitable ceramic substrates are a silicon carbide
coated silicon carbide fiber-reinforced silicon carbide particle
and silicon matrix, a carbon fiber-reinforced silicon carbide
matrix and a silicon carbide fiber-reinforced silicon nitride
matrix. Particularly useful silicon-metal alloys for use as
substrates 16 for the article of embodiments of the invention
include molybdenum-silicon alloys, niobium-silicon alloys, and
other Si comprising alloys having a coefficient of thermal
expansion compatible with the other layer(s) described herein.
[0018] In accordance with one embodiment, the surface region or
substrate 16 of the component 18 is protected by the multilayer EBC
system 10 that includes the EBC 12 for providing environmental
protection to the component 18. Optionally, a top coat or
conventional thermal barrier coating (not shown), as well as
optional conventional intermediate layer(s) (not shown) may be
provided on top of the EBC 12 for providing further thermal
insulation to the underlying layers depending upon desired
operational temperatures.
[0019] The multi-layered EBC 12 of the embodiment shown in FIG. 1,
preferably has four layers, as shown therein. These four layers may
include a bond layer 22, a first layer 24, a second layer 26 and a
third layer 28. The bond layer 22 overlays the substrate 16 of the
component 18 and preferably comprises silicon, such as at least one
of silicon metal and silicon dioxide. This bond layer 22 is useful
to improve oxidation resistance of the surface region 16 and
enhance bonding between the first layer 24 and the surface region
16, particularly if the surface region 16 comprises silicon carbide
or silicon nitride. A suitable thickness for the bond layer 22 is
about 12.5 to about 250 micrometers. Suitable materials for bond
layer 22 also include those described in the afore-referenced U.S.
Pat. No. 6,410,148. For example, bond layer 22 can include a
silicon metal or a SiO.sub.2 layer.
[0020] The first layer 24 is located on the bond layer 22 and
comprises mullite. This mullite comprising first layer 24 serves to
adhere the second layer 26 to the surface region 16, while also
preventing interactions between the second layer 26 and the silicon
comprising surface region 16 at elevated temperatures. The first
layer 24 may also comprise BSAS for less demanding applications,
e.g. temperatures below about 1300.degree. C. The addition of BSAS
to the layer 24 is also relatively compatible with the silicon
comprising surface region 16 in terms of having a CTE of about 5.27
ppm/.degree. C., as compared to a CTE of about 4.9 ppm/.degree. C.
for SiC/SiC CMC. Preferably, first layer 24 comprises
mullite-barrium strontium aluminosilicate (BSAS) in an amount of
between about 40 to 80 wt. % mullite and between about 20 to 60 wt.
% BSAS. A suitable thickness range for the mullite comprising first
layer 24 is about 25 to about 250 micrometers.
[0021] The second layer 26 overlies the first mullite comprising
layer 24 and typically comprises BSAS and may consist essentially
of BSAS. This layer provides excellent environmental protection and
thermal barrier properties due to its low thermal conductivity.
Particularly, BSAS can serve as an environmental barrier to the
underlying mullite comprising layer 24, which would exhibit
significant silica activity and volatilization if exposed to water
vapor at high temperatures. Additionally, BSAS is physically
compliant with a SiC comprising substrate, such as that suitable
for surface region 16, and is relatively compatible with the
mullite comprising layer 24 and the silicon comprising surface
region 16 in terms of CTE. A suitable thickness range for layer 26
is about 25 to about 500 micrometers, depending upon the particular
application.
[0022] The second layer 26 may alternatively or additionally
comprise a rare earth silicate such as described in U.S. Pat. No.
6,759,151. For example, rare earth silicates, such as those
described in U.S. Pat. No. 6,759,151 may be employed as in place of
the BSAS described herein or admixed therewith. As a further
example, rare earth silicates include, but are not limited to,
RE.sub.2O.sub.3, SiO.sub.2, 2RE.sub.2O.sub.3.3SiO.sub.2,
RE.sub.2O.sub.3.2SiO.sub.2, and combinations thereof, where RE is a
rare earth element selected from the group consisting of Sc, Dy,
Ho, Er, Tm, Yb, Lu, Eu, Gd, Tb and combinations thereof.
[0023] In the embodiment shown in FIG. 1, the EBC 12 also comprises
a cerium oxide (CeO.sub.2) layer 28 (third layer 28) located on top
of the second layer 26. A suitable thickness range for this layer
is between about 5 to about 75 micrometers, also depending upon the
particular application. Alternatively, the cerium oxide may be
admixed with the second layer 26. For example, cerium oxide may be
admixed in any suitable amounts such as in a 50:50-weight
percentage with the constituents of the second layer 26.
[0024] In alternate embodiments of the invention, the EBC 12 may
comprise the second layer 26 deposited directly on the substrate
comprising silicon and the third layer 28 deposited on the second
layer 26. Alternatively, an admixed layer of the second layer and
the third layer 28 may be deposited on the substrate comprising
silicon. It should be noted that in these embodiments, bond layer
22 may also be employed and deposited directly on the substrate
comprising silicon with the additional layers deposited on the bond
layer 22. [0025] Thus, in accordance with embodiments of the
invention, a single layer, EBC of BSAS and CeO.sub.2 admixed
therewith, as described above, may be used to provide environmental
protection to the underlying silicon comprising material. This
embodiment is particularly useful for operating temperatures below
about 3000.degree. F. (1371.degree. C.), Alternatively, a CeO.sub.2
layer, as described above, may be deposited on top of the BSAS
layer.
[0026] The layers 22, 24, 26 and 28 can be individually deposited
by air and vacuum plasma spraying (APS and VPS, respectively),
though it is foreseeable that deposition could be performed by
other techniques, such as chemical vapor deposition (CVD) and high
velocity oxy fuel (HVOF). A heat treatment may also be performed
after deposition of the individual layers to relieve stresses
created during cooling from elevated deposition temperatures.
[0027] Accordingly, Applicant has advantageously determined that
deposition of this high melting point acidic compound, CeO.sub.2,
will result in dissolution into the basic corrosion melt and
increase the eutectic temperature and/or decrease the basicity of
the solution. This will advantageously slow and/or stop the
silicate glass formation on the surface of the silicon comprising
material by raising the melting point or decreasing the basicity of
the silicate glass of the corrodant mix.
[0028] While various embodiments are described herein, it will be
appreciated from the specification that various combinations of
elements, variations and improvements therein may be made by those
skilled in the art, and are within the scope of the invention.
* * * * *